Handbook of Detergents, Part D: Formulation (Surfactant Science)

Author: Michael Showell

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HANDBOOK OF DETERGENTS Part D: Formulation

© 2006 by Taylor & Francis Group, LLC

SURFACTANT SCIENCE SERIES

FOUNDING EDITOR

MARTIN J. SCHICK 1918–1998 SERIES EDITOR

ARTHUR T. HUBBARD Santa Barbara Science Project Santa Barbara, California

ADVISORY BOARD

DANIEL BLANKSCHTEIN Department of Chemical Engineering Massachusetts Institute of Technology Cambridge, Massachusetts

ERIC W. KALER Department of Chemical Engineering University of Delaware Newark, Delaware

S. KARABORNI Shell International Petroleum Company Limited London, England

CLARENCE MILLER Department of Chemical Engineering Rice University Houston, Texas

LISA B. QUENCER The Dow Chemical Company Midland, Michigan

DON RUBINGH The Procter & Gamble Company Cincinnati, Ohio

JOHN F. SCAMEHORN Institute for Applied Surfactant Research University of Oklahoma Norman, Oklahoma

BEREND SMIT Shell International Oil Products B.V. Amsterdam, The Netherlands

P. SOMASUNDARAN Henry Krumb School of Mines Columbia University New York, New York

© 2006 by Taylor & Francis Group, LLC

JOHN TEXTER Strider Research Corporation Rochester, New York

1. Nonionic Surfactants, edited by Martin J. Schick (see also Volumes 19, 23, and 60) 2. Solvent Properties of Surfactant Solutions, edited by Kozo Shinoda (see Volume 55) 3. Surfactant Biodegradation, R. D. Swisher (see Volume 18) 4. Cationic Surfactants, edited by Eric Jungermann (see also Volumes 34, 37, and 53) 5. Detergency: Theory and Test Methods (in three parts), edited by W. G. Cutler and R. C. Davis (see also Volume 20) 6. Emulsions and Emulsion Technology (in three parts), edited by Kenneth J. Lissant 7. Anionic Surfactants (in two parts), edited by Warner M. Linfield (see Volume 56) 8. Anionic Surfactants: Chemical Analysis, edited by John Cross 9. Stabilization of Colloidal Dispersions by Polymer Adsorption, Tatsuo Sato and Richard Ruch 10. Anionic Surfactants: Biochemistry, Toxicology, Dermatology, edited by Christian Gloxhuber (see Volume 43) 11. Anionic Surfactants: Physical Chemistry of Surfactant Action, edited by E. H. Lucassen-Reynders 12. Amphoteric Surfactants, edited by B. R. Bluestein and Clifford L. Hilton (see Volume 59) 13. Demulsification: Industrial Applications, Kenneth J. Lissant 14. Surfactants in Textile Processing, Arved Datyner 15. Electrical Phenomena at Interfaces: Fundamentals, Measurements, and Applications, edited by Ayao Kitahara and Akira Watanabe 16. Surfactants in Cosmetics, edited by Martin M. Rieger (see Volume 68) 17. Interfacial Phenomena: Equilibrium and Dynamic Effects, Clarence A. Miller and P. Neogi 18. Surfactant Biodegradation: Second Edition, Revised and Expanded, R. D. Swisher 19. Nonionic Surfactants: Chemical Analysis, edited by John Cross 20. Detergency: Theory and Technology, edited by W. Gale Cutler and Erik Kissa 21. Interfacial Phenomena in Apolar Media, edited by Hans-Friedrich Eicke and Geoffrey D. Parfitt 22. Surfactant Solutions: New Methods of Investigation, edited by Raoul Zana 23. Nonionic Surfactants: Physical Chemistry, edited by Martin J. Schick 24. Microemulsion Systems, edited by Henri L. Rosano and Marc Clausse

© 2006 by Taylor & Francis Group, LLC

25. Biosurfactants and Biotechnology, edited by Naim Kosaric, W. L. Cairns, and Neil C. C. Gray 26. Surfactants in Emerging Technologies, edited by Milton J. Rosen 27. Reagents in Mineral Technology, edited by P. Somasundaran and Brij M. Moudgil 28. Surfactants in Chemical/Process Engineering, edited by Darsh T. Wasan, Martin E. Ginn, and Dinesh O. Shah 29. Thin Liquid Films, edited by I. B. Ivanov 30. Microemulsions and Related Systems: Formulation, Solvency, and Physical Properties, edited by Maurice Bourrel and Robert S. Schechter 31. Crystallization and Polymorphism of Fats and Fatty Acids, edited by Nissim Garti and Kiyotaka Sato 32. Interfacial Phenomena in Coal Technology, edited by Gregory D. Botsaris and Yuli M. Glazman 33. Surfactant-Based Separation Processes, edited by John F. Scamehorn and Jeffrey H. Harwell 34. Cationic Surfactants: Organic Chemistry, edited by James M. Richmond 35. Alkylene Oxides and Their Polymers, F. E. Bailey, Jr., and Joseph V. Koleske 36. Interfacial Phenomena in Petroleum Recovery, edited by Norman R. Morrow 37. Cationic Surfactants: Physical Chemistry, edited by Donn N. Rubingh and Paul M. Holland 38. Kinetics and Catalysis in Microheterogeneous Systems, edited by M. Grätzel and K. Kalyanasundaram 39. Interfacial Phenomena in Biological Systems, edited by Max Bender 40. Analysis of Surfactants, Thomas M. Schmitt (see Volume 96) 41. Light Scattering by Liquid Surfaces and Complementary Techniques, edited by Dominique Langevin 42. Polymeric Surfactants, Irja Piirma 43. Anionic Surfactants: Biochemistry, Toxicology, Dermatology. Second Edition, Revised and Expanded, edited by Christian Gloxhuber and Klaus Künstler 44. Organized Solutions: Surfactants in Science and Technology, edited by Stig E. Friberg and Björn Lindman 45. Defoaming: Theory and Industrial Applications, edited by P. R. Garrett 46. Mixed Surfactant Systems, edited by Keizo Ogino and Masahiko Abe 47. Coagulation and Flocculation: Theory and Applications, edited by Bohuslav Dobiás

© 2006 by Taylor & Francis Group, LLC

48. Biosurfactants: Production Properties Applications, edited by Naim Kosaric 49. Wettability, edited by John C. Berg 50. Fluorinated Surfactants: Synthesis Properties Applications, Erik Kissa 51. Surface and Colloid Chemistry in Advanced Ceramics Processing, edited by Robert J. Pugh and Lennart Bergström 52. Technological Applications of Dispersions, edited by Robert B. McKay 53. Cationic Surfactants: Analytical and Biological Evaluation, edited by John Cross and Edward J. Singer 54. Surfactants in Agrochemicals, Tharwat F. Tadros 55. Solubilization in Surfactant Aggregates, edited by Sherril D. Christian and John F. Scamehorn 56. Anionic Surfactants: Organic Chemistry, edited by Helmut W. Stache 57. Foams: Theory, Measurements, and Applications, edited by Robert K. Prud’homme and Saad A. Khan 58. The Preparation of Dispersions in Liquids, H. N. Stein 59. Amphoteric Surfactants: Second Edition, edited by Eric G. Lomax 60. Nonionic Surfactants: Polyoxyalkylene Block Copolymers, edited by Vaughn M. Nace 61. Emulsions and Emulsion Stability, edited by Johan Sjöblom 62. Vesicles, edited by Morton Rosoff 63. Applied Surface Thermodynamics, edited by A. W. Neumann and Jan K. Spelt 64. Surfactants in Solution, edited by Arun K. Chattopadhyay and K. L. Mittal 65. Detergents in the Environment, edited by Milan Johann Schwuger 66. Industrial Applications of Microemulsions, edited by Conxita Solans and Hironobu Kunieda 67. Liquid Detergents, edited by Kuo-Yann Lai 68. Surfactants in Cosmetics: Second Edition, Revised and Expanded, edited by Martin M. Rieger and Linda D. Rhein 69. Enzymes in Detergency, edited by Jan H. van Ee, Onno Misset, and Erik J. Baas 70. Structure-Performance Relationships in Surfactants, edited by Kunio Esumi and Minoru Ueno 71. Powdered Detergents, edited by Michael S. Showell 72. Nonionic Surfactants: Organic Chemistry, edited by Nico M. van Os 73. Anionic Surfactants: Analytical Chemistry, Second Edition, Revised and Expanded, edited by John Cross

© 2006 by Taylor & Francis Group, LLC

74. Novel Surfactants: Preparation, Applications, and Biodegradability, edited by Krister Holmberg 75. Biopolymers at Interfaces, edited by Martin Malmsten 76. Electrical Phenomena at Interfaces: Fundamentals, Measurements, and Applications, Second Edition, Revised and Expanded, edited by Hiroyuki Ohshima and Kunio Furusawa 77. Polymer-Surfactant Systems, edited by Jan C. T. Kwak 78. Surfaces of Nanoparticles and Porous Materials, edited by James A. Schwarz and Cristian I. Contescu 79. Surface Chemistry and Electrochemistry of Membranes, edited by Torben Smith Sørensen 80. Interfacial Phenomena in Chromatography, edited by Emile Pefferkorn 81. Solid–Liquid Dispersions, Bohuslav Dobiás, Xueping Qiu, and Wolfgang von Rybinski 82. Handbook of Detergents, editor in chief: Uri Zoller Part A: Properties, edited by Guy Broze 83. Modern Characterization Methods of Surfactant Systems, edited by Bernard P. Binks 84. Dispersions: Characterization, Testing, and Measurement, Erik Kissa 85. Interfacial Forces and Fields: Theory and Applications, edited by Jyh-Ping Hsu 86. Silicone Surfactants, edited by Randal M. Hill 87. Surface Characterization Methods: Principles, Techniques, and Applications, edited by Andrew J. Milling 88. Interfacial Dynamics, edited by Nikola Kallay 89. Computational Methods in Surface and Colloid Science, edited by Malgorzata Borówko 90. Adsorption on Silica Surfaces, edited by Eugène Papirer 91. Nonionic Surfactants: Alkyl Polyglucosides, edited by Dieter Balzer and Harald Lüders 92. Fine Particles: Synthesis, Characterization, and Mechanisms of Growth, edited by Tadao Sugimoto 93. Thermal Behavior of Dispersed Systems, edited by Nissim Garti 94. Surface Characteristics of Fibers and Textiles, edited by Christopher M. Pastore and Paul Kiekens 95. Liquid Interfaces in Chemical, Biological, and Pharmaceutical Applications, edited by Alexander G. Volkov 96. Analysis of Surfactants: Second Edition, Revised and Expanded, Thomas M. Schmitt 97. Fluorinated Surfactants and Repellents: Second Edition, Revised and Expanded, Erik Kissa 98. Detergency of Specialty Surfactants, edited by Floyd E. Friedli

© 2006 by Taylor & Francis Group, LLC

99. Physical Chemistry of Polyelectrolytes, edited by Tsetska Radeva 100. Reactions and Synthesis in Surfactant Systems, edited by John Texter 101. Protein-Based Surfactants: Synthesis, Physicochemical Properties, and Applications, edited by Ifendu A. Nnanna and Jiding Xia 102. Chemical Properties of Material Surfaces, Marek Kosmulski 103. Oxide Surfaces, edited by James A. Wingrave 104. Polymers in Particulate Systems: Properties and Applications, edited by Vincent A. Hackley, P. Somasundaran, and Jennifer A. Lewis 105. Colloid and Surface Properties of Clays and Related Minerals, Rossman F. Giese and Carel J. van Oss 106. Interfacial Electrokinetics and Electrophoresis, edited by Ángel V. Delgado 107. Adsorption: Theory, Modeling, and Analysis, edited by József Tóth 108. Interfacial Applications in Environmental Engineering, edited by Mark A. Keane 109. Adsorption and Aggregation of Surfactants in Solution, edited by K. L. Mittal and Dinesh O. Shah 110. Biopolymers at Interfaces: Second Edition, Revised and Expanded, edited by Martin Malmsten 111. Biomolecular Films: Design, Function, and Applications, edited by James F. Rusling 112. Structure–Performance Relationships in Surfactants: Second Edition, Revised and Expanded, edited by Kunio Esumi and Minoru Ueno 113. Liquid Interfacial Systems: Oscillations and Instability, Rudolph V. Birikh,Vladimir A. Briskman, Manuel G. Velarde, and Jean-Claude Legros 114. Novel Surfactants: Preparation, Applications, and Biodegradability: Second Edition, Revised and Expanded, edited by Krister Holmberg 115. Colloidal Polymers: Synthesis and Characterization, edited by Abdelhamid Elaissari 116. Colloidal Biomolecules, Biomaterials, and Biomedical Applications, edited by Abdelhamid Elaissari 117. Gemini Surfactants: Synthesis, Interfacial and Solution-Phase Behavior, and Applications, edited by Raoul Zana and Jiding Xia 118. Colloidal Science of Flotation, Anh V. Nguyen and Hans Joachim Schulze 119. Surface and Interfacial Tension: Measurement, Theory, and Applications, edited by Stanley Hartland

© 2006 by Taylor & Francis Group, LLC

120. Microporous Media: Synthesis, Properties, and Modeling, Freddy Romm 121. Handbook of Detergents, editor in chief: Uri Zoller Part B: Environmental Impact, edited by Uri Zoller 122. Luminous Chemical Vapor Deposition and Interface Engineering, HirotsuguYasuda 123. Handbook of Detergents, editor in chief: Uri Zoller Part C: Analysis, edited by Heinrich Waldhoff and Rüdiger Spilker 124. Mixed Surfactant Systems: Second Edition, Revised and Expanded, edited by Masahiko Abe and John F. Scamehorn 125. Dynamics of Surfactant Self-Assemblies: Micelles, Microemulsions, Vesicles and Lyotropic Phases, edited by Raoul Zana 126. Coagulation and Flocculation: Second Edition, edited by Hansjoachim Stechemesser and Bohulav Dobiás 127. Bicontinuous Liquid Crystals, edited by Matthew L. Lynch and Patrick T. Spicer 128. Handbook of Detergents, editor in chief: Uri Zoller Part D: Formulation, edited by Michael S. Showell

© 2006 by Taylor & Francis Group, LLC

HANDBOOK OF DETERGENTS Part D: Formulation

Edited by Michael S. Showell Procter & Gamble Company Cincinnati, Ohio, U.S.A.

Boca Raton London New York Singapore

A CRC title, part of the Taylor & Francis imprint, a member of the Taylor & Francis Group, the academic division of T&F Informa plc.

© 2006 by Taylor & Francis Group, LLC

Published in 2006 by CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 © 2006 by Taylor & Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group No claim to original U.S. Government works Printed in the United States of America on acid-free paper 10 9 8 7 6 5 4 3 2 1 International Standard Book Number-10: 0-8247-0350-2 (Hardcover) International Standard Book Number-13: 978-0-8247-0350-9 (Hardcover) This book contains information obtained from authentic and highly regarded sources. Reprinted material is quoted with permission, and sources are indicated. A wide variety of references are listed. Reasonable efforts have been made to publish reliable data and information, but the author and the publisher cannot assume responsibility for the validity of all materials or for the consequences of their use. No part of this book may be reprinted, reproduced, transmitted, or utilized in any form by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying, microfilming, and recording, or in any information storage or retrieval system, without written permission from the publishers. For permission to photocopy or use material electronically from this work, please access www.copyright.com (http://www.copyright.com/) or contact the Copyright Clearance Center, Inc. (CCC) 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400. CCC is a not-for-profit organization that provides licenses and registration for a variety of users. For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged. Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe. Library of Congress Cataloging-in-Publication Data Catalog record is available from the Library of Congress

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© 2006 by Taylor & Francis Group, LLC

and the CRC Press Web site at http://www.crcpress.com

Preface We are all familiar with the most common form of detergent formulations—household cleaners, laundry detergents, dishwashing detergents, shampoos, body washes, bar soaps, toothpastes, etc. While pervasive in developed markets in a variety of forms for a variety of uses, even developing markets offer an array of such products for consumer use. However, detergents, a term applied to any material which either aids in the removal of foreign matter from surfaces or promotes the dispersion and stabilization of one or more ingredients in a bulk matrix, are widely used in a number of applications and industries not generally familiar to the public (the reader is referred to Volume C of this series: Applications). These include additives to lubricants to aid the removal of deposits from internal surfaces of engines, formulations to aid in the cleanup of, or to enhance the biodegradation of, oil spills and other environmental contaminants, paper and textile processing aids, and as components in the formulation of paints, inks, and colorants. The purpose of this volume, Part D in the Handbook of Detergents series, is to provide an overview of the full range of detergent formulations used today, from common household products to the more esoteric specialty applications. Detergents, although thousands of years old, continue to evolve, providing the end user with an array of beneﬁts and services. In their most common form, as aids in household cleaning and personal care, detergents generally offer not only a basic cleaning beneﬁt but also a range of ancillary beneﬁts intended to better meet the needs of the consumer. For example, today’s laundry detergents provide good general cleaning of fabrics while delivering additional beneﬁts like increased fabric wear, color rejuvenation, and longlasting fresh scent. The increasing complexity of detergent formulations, which combine surface-active agents, builders, sequestering agents, bleaches, enzymes, and other components, places a high demand for creativity and innovation on the part of the detergent formulator. Furthermore, economic constraints and an increasing expectation that detergent formulations meet the ever-increasing demands of sustainability place even more demand on, and require more responsibility from, the formulator. This, in turn, requires that the formulator be knowledgeable of the conditions under which the product will be used, stored, and shipped as well as the end user’s needs and constraints so that formulations are designed which are shelf stable, have acceptable consumer aesthetics, and provide the intended beneﬁt with each particular use. In addition, the increasing volume of detergents and their use across a range of product segments, categories, and industries increases the load on the environment to which they are eventually released. This makes it necessary for the detergent formulator to consider the use of environmentally friendly, and ultimately biodegradable, raw materials whenever possible, creating additional formulation challenges.

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© 2006 by Taylor & Francis Group, LLC

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Preface

This volume of the Handbook of Detergents series provides a review of the process and chemical technologies involved in producing various detergent formulations. Attention is given to formulations in the consumer products area—laundry detergents, dishwashing products, and household cleaning formulations (Chapters 3–7) as well as a number of specialty areas like Auto Care and Industrial/Institutional Products (Chapter 8), Textile Processing (Chapter 9), Separation Science (Chapter 10), Oil Recovery (Chapter 11), Environmental Cleanup (Chapter 12), Paints and Colorants (Chapter 13), Polymerization Processes (Chapter 14), and Lubricants (Chapter 15). Formulations based on N-alkyl amide sulfates are covered in Chapter 16. A major aim of this book is to provide the reader with some general guidance on formulation approaches. To that end, Chapter 2 provides an overview of the use of statistical mixture design in detergent formulations. This book should serve as a useful reference for scientists, engineers, technicians, managers, policymakers, and students having an interest in detergents and emerging technology trends and formulations that will sustain the industry for years to come. I would like to thank the contributing authors for their time in preparing the highly authoritative individual chapters for this volume, Dr. Uri Zoller for his helpful suggestions and guidance, and Helena Redshaw for her patience, encouragement, and support. Michael S. Showell

© 2006 by Taylor & Francis Group, LLC

About the Editor Michael S. Showell joined Procter & Gamble in 1984 in the Packaged Soap Division and has had various assignments with increasing responsibilities within P&G’s laundry and cleaning product research and development community. He currently is associate director of R&D in the Fabric & Home Care Technology Division at P&G’s Miami Valley Innovation Center in Cincinnati, Ohio. His research interests include: enzymes and their application in laundry and cleaning products, enzyme/detergent interactions, protein engineering to improve enzymes for use in consumer product applications, enzymatic synthesis of detergent ingredients, bioremediation, bioprocessing, and detergents. He is author or coauthor of a number of articles, book chapters, and presentations on the use of enzymes in laundry and cleaning products. In 1999 he was one of the recipients of the American Chemical Society award for Team Innovation. Mike received a B.S. in chemistry from Willamette University in 1978, and M.S. and Ph.D. degrees in physical chemistry from Purdue University in 1980 and 1983, respectively.

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© 2006 by Taylor & Francis Group, LLC

Contributors Thanaa Abdel-Moghny, tute, Cairo, Egypt Achim Ansmann, Shoaib Arif,

Application Department, Egyptian Petroleum Research Insti-

Cognis Deutschland GmbH & Co. KG, Düsseldorf, Germany

Noveon, Inc., Cleveland, Ohio

Samir S. Ashrawi, Surface Sciences Division, The Austin Laboratories, Huntsman Corporation, Austin, Texas Alessandra Bianco Prevot, Torino, Italy

Dipartimento di Chimica Analitica. Università di Torino,

Jean-François Bodet, Brussels Technical Center, Procter & Gamble Eurocor NV, Strombeek-Bever, Belgium Peter Busch,

Cognis Deutschland GmbH & Co. KG, Düsseldorf, Germany

Jeffrey H. Harwell, School of Chemical Engineering and Materials Science and The Institute for Applied Surfactant Research, The University of Oklahoma, Norman, Oklahoma and Surbec-ART Environmental, LLC, Norman, Oklahoma Hermann Hensen, Karlheinz Hill,

Cognis Deutschland GmbH & Co. KG, Düsseldorf, Germany

Cognis Deutschland GmbH & Co. KG, Monheim, Germany

Krister Holmberg, Department of Applied Surface Chemistry, School of Chemical and Biological Engineering, Chalmers University of Technology, Göteborg, Sweden Tze-Chi Jao, Research & Development Department, Afton Chemical Corporation, Richmond, Virginia Glenn T. Jordan, Fabric & Home Care Technology Division, Miami Valley Innovation Center, The Procter & Gamble Company, Cincinnati, Ohio Robert C. Knox, School of Chemical Engineering and Materials Science and The Institute for Applied Surfactant Research, The University of Oklahoma, Norman, Oklahoma and Surbec-ART Environmental, LLC, Norman, Oklahoma Hans-Udo Krächter,

Cognis Deutschland GmbH & Co. KG, Düsseldorf, Germany

Hiromoto Mizushima, Wakayama, Japan Felix Mueller, Michael Müller,

Material Development Research Laboratories, Kao Corporation,

Degussa AG Goldschmidt Home Care, Essen, Germany Cognis Deutschland GmbH & Co. KG, Düsseldorf, Germany vii

© 2006 by Taylor & Francis Group, LLC

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Contributors

Charles A. Passut, Research & Development Department, Afton Chemical Corporation, Richmond, Virginia Jörg Peggau,

Degussa AG Goldschmidt Home Care, Essen, Germany

Gianmarco Polotti,

Lamberti SpA, Albizzate, Italy

Edmondo Pramauro, Italy

Dipartimento di Chimica Analitica, Università di Torino,Torino,

Kenneth N. Price, Global Household Care Technology Division, Miami Valley Innovation Center, The Procter & Gamble Company, Cincinnati, Ohio David A. Sabatini, School of Civil Engineering and Environmental Science, and School of Chemical Engineering and Materials Science, and The Institute for Applied Surfactant Research, The University of Oklahoma, Norman, Oklahoma and Surbec-ART Environmental, LLC, Norman, Oklahoma William M. Scheper, Fabric & Home Care Technology Division, Miami Valley Innovation Center, The Procter & Gamble Company, Cincinnati, Ohio Stefano Scialla, Pescara, Italy

Italia SpA, Pescara Technical Center, The Procter & Gamble Company,

Jichun Shi, Fabric & Home Care Technology Division, Miami Valley Innovation Center, The Procter & Gamble Company, Cincinnati, Ohio Ben Shiau,

Surbec-ART Environmental, LLC, Norman, Oklahoma

Michael S. Showell, Fabric & Home Care Technology Division, Miami Valley Innovation Center, The Procter & Gamble Company, Cincinnati, Ohio Mark R. Sivik, Fabric & Home Care Technology Division, Miami Valley Innovation Center, The Procter & Gamble Company, Cincinnati, Ohio George A. Smith, Surface Sciences Division, The Austin Laboratories, Huntsman Corporation, Austin, Texas Brian X. Song, Home Care Product Development, Ivorydale Innovation Center, The Procter & Gamble Company, Cincinnati, Ohio Oreste Todini, Household Care, Bruxelles Innovation Center, The Procter & Gamble Company, Bruxelles, Belgium Jiping Wang, Fabric & Home Care Technology Division, The Procter & Gamble Company, Cincinnati, Ohio Randall A. Watson, Beijing, P.R. China

Beijing Technical Center, The Procter & Gamble Company,

Yong Zhu, Fabric & Home Care Technology Division, The Procter & Gamble Company, Cincinnati, Ohio

© 2006 by Taylor & Francis Group, LLC

Table of Contents 1.

Introduction to Detergents Michael S. Showell

1

2.

Statistical Mixture Design for Optimization of Detergent Formulations Samir S. Ashrawi and George A. Smith

27

3.

Laundry Detergent Formulations Randall A. Watson

51

4.

Dishwashing Detergents for Household Applications Jichun Shi, William M. Scheper, Mark R. Sivik, Glenn T. Jordan, Jean-François Bodet, and Brian X. Song

105

5.

The Formulation of Liquid Household Cleaners Stefano Scialla

153

6.

Liquid Bleach Formulations Stefano Scialla and Oreste Todini

179

7.

Personal Care Formulations Achim Ansmann, Peter Busch, Hermann Hensen, Karlheinz Hill, Hans-Udo Krächter, and Michael Müller

207

8.

Special Purpose Cleaning Formulations: Auto Care and Industrial/Institutional Products Felix Mueller, Jörg Peggau, and Shoaib Arif

261

9.

Surfactant Applications in Textile Processing Jiping Wang and Yong Zhu

279

10.

Detergent Formulations in Separation Science Edmondo Pramauro and Alessandra Bianco Prevot

305

11.

Surfactant Formulations in Enhanced Oil Recovery Thanaa Abdel-Moghny

325

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© 2006 by Taylor & Francis Group, LLC

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Table of Contents

12.

Surfactant-Based Systems for Environmental Remediation David A. Sabatini, Robert C. Knox, Jeffrey H. Harwell, and Ben Shiau

347

13.

Paints and Printing Inks Krister Holmberg

369

14.

Surfactant Formulations in Polymerization Gianmarco Polotti

387

15.

Detergent Formulations in Lubricants Tze-Chi Jao and Charles A. Passut

437

16.

N-Alkyl Amide Sulfates Hiromoto Mizushima

473

17.

Future Outlook for Detergent Formulations Kenneth N. Price

483

© 2006 by Taylor & Francis Group, LLC

1 Introduction to Detergents Michael S. Showell

CONTENTS I. II.

Introduction ............................................................................................................... 2 Common Detergent Ingredients ................................................................................ 4 A. Surfactants ..................................................................................................... 4 B. Dispersing Polymers ..................................................................................... 4 C. Builders and Chelants ................................................................................... 8 D. Bleaching Systems ........................................................................................ 9 E. Solvents ....................................................................................................... 10 F. Performance Enhancing Minor Ingredients................................................ 11 III. Representative Detergent Formulations ................................................................. 13 A. Laundry Detergent Formulations ................................................................ 13 B. Dishwash Detergent Formulations.............................................................. 13 C. Hard Surface Cleaning Formulations ......................................................... 13 D Personal Care Detergent Formulations ....................................................... 13 E Oral Care Detergent Formulations.............................................................. 13 F. Agricultural Detergent Formulations .......................................................... 13 G. Automobile Detergent Formulations........................................................... 13 H. Detergent Formulations for Cleaning Food Processing Equipment .......... 14 I. Detergent Formulations for Metal Component Cleaning........................... 15 IV. Detergency Theory and Mechanisms...................................................................... 15 A. Removal Mechanisms ................................................................................. 19 B. Suspension Mechanisms ............................................................................. 23 Acknowledgments............................................................................................................. 24 References ......................................................................................................................... 25

1

© 2006 by Taylor & Francis Group, LLC

2

Showell

I. INTRODUCTION Generally, the term “detergents” is applied to materials and/or products that provide the following functions: 1. 2.

Promote removal of material from a surface, e.g., soil from a fabric, food from a dish, or soap scum from a hard surface; Disperse and stabilize materials in a bulk matrix, e.g., suspension of oil droplets in a mobile phase like water.

The ability of a detergent to perform either of these functions depends on the composition of the formulation, the conditions of use, the nature of the surfaces being treated, the nature of the substance to be removed and/or dispersed, and the nature of the bulk phase. Accordingly, detergent formulation is a complex process driven by the speciﬁc needs of the end user, economics, environmental considerations, and the availability of speciﬁc “actives” that can provide the required functionality. By far the most common and familiar detergents are those used in household cleaning and personal care. These products can be grouped into four general categories: 1.

2.

3.

Laundry detergents and laundry aids. These comprise mainframe laundry detergents in powder, liquid, tablet, gel, and bar form, fabric conditioner products typically in liquid or sheet form, and an array of specialty products like pretreaters (as sticks, gels, sprays, bars), presoaks (liquids, powders), and bleaches (liquids, powders). Typical laundry detergents are formulated to provide general cleaning, which includes removal of soils and stains as well as the ability to maintain whiteness and brightness. In addition, many premium laundry detergents offer additional beneﬁts like fabric softening, dye lock, ﬁber protection, and disinfectancy. Dishwashing products. These include detergents for hand and machine dishwashing and are typically provided in liquid, gel, powder, or tablet form. Hand dish wash products are formulated to remove and suspend food soils from a variety of surfaces. They also must deliver long-lasting suds, even at high soil loads, and they must be mild to skin. Products designed for automatic dishwashing must provide soil removal and suspension, control of water hardness and sheeting of water off dish surfaces in order to achieve a spot- and ﬁlm-free ﬁnish, and produce little or no suds that would otherwise interfere with the operation of the machine. Rinse aids are specialty detergent formulations for automatic dishwashing designed to promote drainage of water from surfaces via lowering of surface tension. This helps minimize spotting and ﬁlming during drying. Household cleaning products. Because no single product can provide the range of cleaning required on the various surfaces found in the home a broad range of household cleaning products are currently marketed. These are typically formulated either in liquid or powder form although gel, solid, sheet, and pad products are also available. So-called “all-purpose” cleaners are designed to penetrate and loosen soil, control water hardness, and prevent soil from redepositing onto clean surfaces. Many of these products also contain low levels of antibacterial actives like Triclosan to sustain disinfectancy claims. Powdered abrasive cleaners remove heavy accumulations of soil via the use of mineral or metallic abrasive particles. Some of these products may also bleach and disinfect through the incorporation of a bleach precursor like sodium perborate, sodium percabonate, or sodium dichloroisocyanurate.

© 2006 by Taylor & Francis Group, LLC

Introduction to Detergents

4.

3

Personal cleansing products. These include products for hand and body washing as well as shampoos, conditioners, and toothpastes. They are marketed primarily in bar, gel, and liquid forms. A major consideration in formulation of such products is the desired consumer aesthetic such as lather, skin feel, rinsability, smell, and taste. Formulations designed for cleaning may also provide moisturizing beneﬁts, disinfectancy, conditioning, and styling effects.

Within each of these categories products are formulated with speciﬁc ingredients selected on the basis of their ability to perform the desired function and deliver “consumer preferred” aesthetics while meeting speciﬁc cost constraints, environmental regulations, and human safety guidelines. In addition to these familiar consumer products, detergent formulations are used in a number of other applications and industries. These include: 1.

Environmental remediation. Surfactant systems have been developed to aid in the clean up of contaminated groundwater supplies [1]. 2. Enhanced oil recovery. Micellar and surfactant “ﬂoods” are among the most successful methods of enhancing recovery of oil from depleted reservoirs [2]. 3. Nanoegineering. Researchers have used the phase behavior of surfactants to generate self-assembling nanosystems [3]. 4. Formulation of paints and printing inks. Paints and inks comprise formulations wherein a pigment is dispersed into a liquid phase. The dispersion is typically achieved with surfactants and/or dispersing polymers [4]. 5. Preparation and application of synthetic polymers. Emulsion polymerization and the preparation of latexes represent one of the largest uses for surfactants outside the cleaning arena [5]. 6. Industrial/metal parts cleaning. Detergent compositions based on a CO2 bulk phase have application in the cleaning of microelectronic components [1]. 7. Medical applications. Mimics of human lung surfactants have been developed to treat respiratory distress syndrome in premature infants [1]. 8. Lubricants. While highly diverse, lubricant formulations utilize the same basic additives: surfactants, dispersants, antiwear actives, antioxidants, corrosion inhibitors, and viscosity modiﬁers. 9. Textile processing. Detergent formulations are used to clean ﬁbers prior to manufacture into ﬁnished textiles as well as lubricate the ﬁbers during spinning and weaving. 10. Agricultural preparations. Pesticide and herbicide preparations are often formulated as aqueous dispersions with speciﬁc functional actives to promote even distribution of the active during application and fast penetration of the active upon contact with plants [6]. This diversity of application of detergents presents a rather formidable challenge when compiling a volume such as this on detergent formulations. Accordingly, rather than try to cover authoritatively all aspects of detergent formulations—a monumental task in its own right— I have elected instead in this chapter to provide some general background on detergency, the common ingredients used in detergent formulations, and general approaches to detergent processing or manufacture. This should provide a solid framework for the more in-depth discussions found in later chapters of this book. In addition, there are several good reference books available on the topic of detergent formulations [7– 9].

© 2006 by Taylor & Francis Group, LLC

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II. COMMON DETERGENT INGREDIENTS Modern detergents can comprise 20 or more ingredients depending on what beneﬁts the detergent is meant to deliver. It is not within the scope of this chapter to provide an extensive review of the myriad ingredients used in detergent formulations. Rather, the intent of this section is to provide a general overview of the more common elements— surfactants, dispersing polymers, builders and chelants, bleaching systems, solvents, and performance enhancing minors — in order to familiarize the reader with the general chemistry of detergent formulation. Subsequent chapters will provide signiﬁcantly more detail on many of these ingredients and there are several reference books available on the topic [6–12]. A. Surfactants Surfactants are arguably the most common ingredient of the detergent formulations described in this book. Their primary function is to modify the interface between two or more phases in order to promote the dispersion of one phase into another. In cleaning formulations, for example, surfactants serve to wet surfaces and reduce the interfacial tension between soil and water such that the soil is removed from the surface to be cleaned and dispersed in the aqueous phase. The ability of surfactants to concentrate at interfaces derives from their amphiphilic character—the combination of hydrophilic and hydrophobic moieties within the same molecule. Generally, surfactants are classiﬁed according to their hydrophilic component as nonionic, anionic, cationic, or amphoteric. The nonionic surfactants have a hydrophilic component that is not ionized. Typical nonionic groups consist of polyoxyethylene, polyoxypropylene, alkanolamides, or sugar esters. As the name implies, the hydrophilic component of anionic surfactants comprises an anionic group, typically a sulfate, sulfonate, or carboxylate moiety. Likewise, the cationic surfactants comprise molecules containing a positively charged group such as a quaternary amine. The amphoteric surfactants are perhaps the most unique in that they comprise a hydrophilic group containing both anionic and cationic character such as the amino acids. Typical hydrophobes for surfactants are the alkyl chains between C10 and C20. However, in some specialty surfactants the hydrophobe may consist of polysiloxane or perﬂuorocarbon backbones. Examples of common surfactants are shown in Table 1. Until the 1940s detergents were formulated principally with the sodium or potassium salts of C12–C18 chain length fatty acids. The synthesis of surfactants from petroleum feed stocks in the late 1940s spurred the development of soap-free synthetic detergents that proved much more effective for cleaning in cooler wash temperatures and in hard water. Today, the linear alkyl benzene sulfonates, alkyl sulfates, alkyl ethoxy sulfates, and alkyl ether ethoxylates are the workhorse surfactants for most detergent formulations. Alkyl polyglucosides, alkyl glucosamides, and methyl ester sulfonates are also widely used [13]. Recent attention has been given to the use of internal methyl branched alkyl chains as the hydrophobe for certain anionic surfactants [14]. Such branching promotes improved solubility, particularly in cold, hard water. For systems where water is not the continuous phase a variety of specialty surfactants are used. Examples include the polydimethylsiloxane-based surfactants for use in highly hydrophobic media and the acrylate-polystyrene co-polymers designed by DiSimone and colleagues for applications in cleaning systems utilizing condensed phase CO2 [15]. B. Dispersing Polymers The suspension of solids or liquids in a continuous phase is a critical aspect in the formulation of paints, inks, coatings, and agricultural products such as herbicides. Suspension of soil after removal from a surface is important in cleaning applications to

© 2006 by Taylor & Francis Group, LLC

Introduction to Detergents Table 1

5

Common Surfactants Used in Detergent Formulations

Type

Structure

Anionic

CH3-(CH2)n-CH-(CH2)m-CH3

Linear Alkyl Benzene Sulfonate

SO3Na CH3-(CH2)n-CH-(CH2)m-CH3

Paraffinsulfonate

SO3Na Alkyl Ether Sulfate

CH3-(CH2)n-O-(CH2-CH2-O)xSO3Na

Fatty Acid Soap

O CH3-(CH2)nCONa

Methyl ester sulfonate

O CH3-CH2-(CH2)nCO-CH3 SO3Na

Cationic Quaternary monoalkylammonium chloride

CH3-(CH2)n-N+(CH3)3Cl-

Nonionic

CH3-(CH2)n-O-(CH2-CH2O)nH

Fatty alcohol ethoxylate

CH3-(CH2)n-N(CH3)2

Amine oxide

O

CH3-(CH2)n-C-NH-CH2-CH2OH

Alkyl monoethanolamide

O N-methylglucosamide

OH OH CH3-(CH2)n-C-N-CH2-CH-CH-CH-CH-CH2OH O CH3 OH OH

Amphoteric

CH3-(CH2)n-C-NH-(CH2)3-N+(CH3)2-CH2-C-OAmidopropyl betaine

Alkyl sulfobetaine

O

O

CH3-(CH2)n-N+(CH3)2-CH2-CH-CH2-SO3OH

avoid redeposition of the soil back onto the cleaned surface. Generally speaking, the particles to be suspended are sufﬁciently large that deﬁnite surfaces of separation exist between the dispersed phase and the dispersion medium [16]. In order to keep the dispersed phase stable it is important to adsorb functional actives at these surfaces to prevent aggregation. This is one of the critical functions of surfactants. However, another class of detergent actives has been developed to assist in particle suspension—the polymeric dispersants.

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In general two types of polymeric dispersants are used in detergent formulations—polymers comprising ionically charged groups and nonionic polymers. Typical of the ionic dispersing polymers are the homopolymers of acrylic acid and copolymers of acrylic and maleic acids which are widely used in laundry detergent formulations:

H

H

C

C

Z

COOH

n

where Z is either hydrogen, in the case of homopolymers of acrylic acid, or a carboxyl group in the case where the monomer unit is maleic acid. Polymers of this type are commonly found in powdered laundry detergent formulations where they assist in cleaning by acting as a dispersant for soil and inorganic salts, provide alkalinity control, and serve as crystal growth inhibitors [17]. Anionic dispersing polymers comprising carboxyl and sulfonate groups in the same backbone have been developed for use in water treatment where they act to prevent formation of inorganic scale. The polymers are generally of the following hybrid type:

A Sulfonated monomer(s)

B

C

D

Carboxylate monomer(s)

Optional neutral monomer(s)

Optional charged monomer(s)

The key features are A and B. A, the sulfonated monomers, include the following groups:

H

R1

N

R

SO3H

O

O

O R2

SO3H

(OR)nSO3H (OR)qSO3H

n

SO3H

O

(CH2)nSO3H

H SO3H

N

q

SO3H

O SMS

AMPS SSS

SO3H

OH O AHPS

SO3H

HO3S

O

OH R

SPMS

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Introduction to Detergents

7

B usually comprises maleic, acrylic, or methacrylic acid. C and D are optional but can include acrylamide, vinyl acetate (alcohol), acrylate esters, cationics, or phosphonates [18]. Carboxymethylcellulose is another example of an anionic dispersing polymer widely used in laundry detergent applications

CH2OCH2COO− O

O OH O OH n

Considerable attention has been paid over the years to the preparation of biodegradable dispersants [19–21]. Examples include polyamino acid polymers such as polyaspartate prepared from the catalytic condensation of polyaspartic acid [22] and functionalized polysaccharides such as oxidized starches [23]. Recently, a novel process was reported for the preparation of functionalized polyaspartic acid polymers that expands the utility of these materials as dispersants for a variety of applications [24]. Cationic dispersants are less commonly used although some amphiphilic structures have been described as effective dispersants in high salt content media [25]:

[CH2-CH]n

CH]m

[CH O

C

C

O

N CH2 H3C

N+ CH3 Cl− CH3

Amphoteric dispersing polymers of the types shown below have also been reported to be good clay and particulate dispersants in certain laundry detergent formulations [26]:

(CH2CH2O)24SO3Na NaO3S-(OCH2CH2)24N +

N-(CH2CH2O)24SO3Na

Cl−

(CH2CH2O)24SO3Na

CH3

(CH2CH2O)20SO3Na NaO3S(OCH2CH2)20-N + Cl−

© 2006 by Taylor & Francis Group, LLC

CH3 + Cl−

(CH2CH2O)20SO3Na N + Cl−

(CH2CH2O)20SO3Na + Cl−

N-(CH2CH2O)20SO3Na

8

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Nonionic polymers include polyethylene glycol, polyvinyl alcohol, and random and block ethoxy propoxy copolymers. Graft copolymers of polyalkylene oxide and vinyl acetate are reported to be effective antiredeposition agents for hydrophobic surfaces like polyester fabric [27]. C. Builders and Chelants Metal ion control is a common need in many detergent formulations. For example, in aqueous cleaning applications the presence of Ca2+ in the water can lead to the precipitation of anionic surfactant reducing the effective concentration available for cleaning. Fatty acids can precipitate as calcium soaps resulting in the formation of soap scum on hard surfaces, and many soils, especially inorganic clays, will precipitate with calcium leading to redeposition of the soil onto the surface being cleaned. Builders—a generic term used to refer to any number of materials whose primary function is the removal of Ca2+ and Mg2+ ions from aqueous solutions—and chelants are widely used in the formulation of various detergents. Sodium tripolyphosphate (STPP) is among the best known and widely used detergent builder. In laundry detergent formulations it serves not only as an extremely effective calcium control agent but also provides dispersion, suspension, and anti-encrustation beneﬁts. However, environmental concerns associated with large-scale release of phosphates into the environment lead to the development of a number of substitutes. Citric acid and sodium nitrilotriacetate are representative of soluble detergent builders

CH2COONa

CH2COOH

HO

C

COOH

CH2COOH Citric Acid

N

CH2COONa CH2COONa

Sodium nitrilotriacetate

Sodium carbonates and noncrystalline sodium silicate form sparingly soluble precipitates with calcium and are frequently used in powdered detergent formulations where they also provide a source of alkalinity. However, to avoid encrustation of the calcium carbonate/silicate onto surfaces these building agents generally are co-formulated with a dispersing polymer like the polyacrylate/maleic acid copolymers described above and crystal growth inhibitors like HEDP (1-hydroxyethane diphosphonic acid). Insoluble builders include the zeolites and layered silicates, which bind calcium via an ion exchange mechanism [28]. Zeolite A, Na12(AlO2)12(SiO2)12∑27H2O, is the principal alternative to phosphate as a detergent builder. The Na+ ions are exchangeable for Ca2+ while the larger hydration shell around Mg2+ tends to impede exchange. Citric acid is also an excellent chelant for metal ions other than calcium and can be employed where the removal of transition metals such as copper, zinc, and iron is important. Other commonly used detergent chelants include ethylenediaminetetraacetate (EDTA)

© 2006 by Taylor & Francis Group, LLC

Introduction to Detergents NaOOCCH2

9

CH2COONa N-CH2CH2-N CH2COONa

NaOOCCH2

and diethylenetriaminepentaacetate (DTPA)

NaOOCCH2

CH2COONa N-CH2CH2-N-CH2CH2-N

NaOOCCH2

CH2COONa

CH2COONa

D. Bleaching Systems Bleaches are common components of laundry, automatic dish wash, and hard surface cleaning detergent formulations where they act to destroy chromophoric groups responsible for color in soils via oxidative attack. Four basic technology approaches have been taken to deliver bleaching in these products—chlorine-based bleaches, peroxide-based bleaches, activated peroxide systems, and metal catalysts. Chlorine-based systems are common in some powdered abrasive hard surface cleaners and automatic dishwashing products. Typically, hypochlorite bleach is delivered via precursor like sodium dichloroisocyanurate according to the reaction:

Na

Na N

O C

C

N

N

O

H2O

Cl

Cl

2HClO

+

N

O C

C

N

N

O

H

H O

O

Peroxide-based bleaches either use hydrogen peroxide directly or appropriate precursors like perborate monohydrate, which generate peroxide according to the reaction: (NaBO2H2O2)2 Æ H2O2NaBO2 + 2H2O2 + H2O Activated peroxide systems rely on perhydrolysis of a precursor molecule (generally referred to as an “activator” to generate a peracid bleach in situ: RCO2H + H2O2 Æ RCO3H + H2O The two most common activators used in laundry detergents are N¢N≤-tetraacetyl ethylene diamine (TAED) and nonanoyloxybenzene sulfonate (NOBS). In an aqueous environment TAED undergoes perhydrolysis with the perhydroxyl anion from peroxide to

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generate peracetic acid. NOBS reacts in much the same way but generates the more hydrophobic pernonanoic acid. A frequently studied approach to bleaching involves the use of transition metal catalysts [29]. Complexes of metals like Mn, Fe, Cu, and Co with certain organic ligands can react with peroxygen compounds to form reactive intermediates, which can potentially result in powerful bleaching action. Typical of these systems are the structures shown below:

H3N

Co

Cl

N

N

NH3

2+

Me

Me

NH3

O Me

N Me

MnIV O MnIV

N

NH3

(PF6−)2

O NH3

From US Patent 5, 798, 326

N

N

Me

Me

From US Patent 5, 246, 612

E. Solvents The selection of solvents for use in detergent formulation depends on the nature of the actives being formulated, the intended application of the detergent, and economics. Water is the dominant solvent in most household and industrial cleaning formulations. Generally speaking, water-based detergents are less toxic, more environmentally friendly, cheaper, more surface compatible, and easier to handle than petroleum-based solvents. However, many common detergent actives have limited solubility in water requiring formulation of a co-solvent and/or hydrotrope. Typical co-solvents used in household cleaning formulations include ethanol, glycerol, and 1,2-propanediol. A hydrotrope, also called a “coupling agent,” is an organic compound that increases the ability of water to dissolve other molecules. Hydrotropes are commonly used in aqueous-based detergent formulations containing high concentrations of surfactant in order to achieve a shelf-stable, clear, isotropic ﬂuid. Common hydrotropes are sodium xylene sulfonate, sodium toluene sulfonate, and sodium cumene sulfonate. A typical liquid dishwashing formulation, shown below in Table 2, is a good example of a surfactant-rich aqueous-based detergent system comprising both a co-solvent (in this case ethanol) and a hydrotrope (sodium cumene sulfonate): Of course there are applications where water must be avoided. Perhaps the most recognizable of these is in the dry cleaning of ﬁne textiles like silk and wool. Historically, this process has used volatile organic solvents like perchloroethylene as the bulk cleaning ﬂuid. Concerns that such solvents may represent human and environmental safety hazards has recently lead to the development of alternative processes utilizing condensed phase CO2 [30] and certain silicone oils like cyclic decamethylpentasiloxane, D5 [31]. Detergent formulations for use in such systems will typically comprise a solvent compatible with the bulk phase (e.g., polydimethylsiloxane in the case of the D5 system) and capable of solublizing the cleaning actives to be introduced into the bulk phase.

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Introduction to Detergents Table 2

11

Typical Hand Dishwash Formulation Ingredient

C12-C13 Alkyl ethoxy (E1.4) sulfate C12-C14 Polyhydroxy fatty acid amide C14 Amine oxide C11 Alcohol ethoxylate E9 MgCl2 Calcium citrate Polymeric suds booster Ethanol Sodium cumene sulfonate Minors and water

Weight % 33 4 5 1 0.7 0.4 0.5 1 0.5 Balance

Other areas where water is not a suitable solvent include the cleaning of certain metal parts and electronic circuit boards. Here chlorinated hydrocarbons like perchloroethylene or methylene chloride, or volatile organics like methyl ethyl ketone have historically been used but regulatory pressure has resulted in a shift to more environmentally friendly solvents like terpenes and dibasic esters. F. Performance Enhancing Minor Ingredients Depending upon the end use of the detergent formulation and the beneﬁts to be delivered a number of performance enhancing minor ingredients may be used. These include: 1.

2.

3.

Enzymes. Used primarily in cleaning formulations enzymes promote soil removal by the catalytic breakdown of speciﬁc soil components. Proteases (enzymes that degrade protein) are the most common of all the detergent enzymes but amylases (starch degrading), lipases (lipid degrading), and cellulases (cellulase degrading) are also used [32]. Brighteners/fabric whitening actives. These materials enhance the visual appearance of white surfaces, typically cotton fabrics, by absorbing ultraviolet (UV) radiation and emitting via ﬂuorescence in the visible portion of the spectrum. Typical whitening actives are built from direct linkage or ethylenic bridging of aromatic or heteroaromatic moieties. Among the most commonly used whiteners in laundry detergents are the derivatives of 4,4-diaminostilbene-2,2-disulfonic acid. Foam boosters. In some applications, most notably hand dishwashing and shampoos; it is desirable for the detergent formulation to generate a large-volume, stable foam. While most surfactants are capable of generating and sustaining foam in the absence of soil, these foams rapidly collapse in the presence of soil, especially particulate and fatty soils. In applications where foam must be maintained throughout the course of detergent use, speciﬁc boosters may be added. Proteins have been shown to promote foaming in certain systems [33] especially in food and beverage applications [34]. Alkanolamides, particularly mono- and diethanolamides, are effective foam stabilizers used in dishwashing liquids and

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shampoos [7]. Polymeric foam boosters of the type shown below have also proved effective in hand dish wash applications [35]:

n

N O

4.

5.

6.

O

Antifoam agents. In many applications it is desirable to minimize foam generation. For example, in automatic dishwashing foam generation can interfere with rotation of the spray arm leading to degradation in the performance of the dishwasher. Antifoam agents act to reduce or eliminate foams. They either prevent formation of the foam or accelerate its collapse. Alkyl ethoxylate nonionic surfactants are commonly used as foam control agents in detergents where application temperatures exceed the cloud point of the surfactant—the temperature at which the surfactant becomes insoluble. The insoluble nonionic-rich surfactant phase acts to break foam lamella promoting foam collapse. Hydrophobic particulate antifoam agents physically break foams by lodging in the foam ﬁlm promoting rapid localized draining in the region of the ﬁlm in contact with the particles. The calcium soaps of long-chain fatty acids are effective at foam control as are hydrophobic silica particles. Particularly effective antifoams are comprised of colloidal hydrophobic silica particles suspended in a silicone oil like polydimethyl siloxane. The hydrophobic oil promotes spreading of the particles at the air-water interface thereby ensuring entrapment in the foam ﬁlm and subsequent foam disruption [7]. Thickeners. It is often desirable to modify the rheology of a detergent formulation to ﬁt a particular application. For example, gel-type automatic dishwashing detergents are thickened to help suspend phosphate and other solids that would otherwise separate out from the liquid phase. Thickening can be achieved through the use of inorganic electrolytes, e.g., NaCl; clays, such as laponite or hectorite; or a high-molecular-weight polymer like carboxymethylcellulose, guar, or xanthan gum. The Carbopol“ series of polymers from Noveon, homoand copolymers of acrylic acid cross linked with polyalkenyl polyether, are particularly effective thickeners for household cleaning detergent formulations. Soil release polymers. Soil release refers to the enhanced removal of soil from a surface as a result of modiﬁcation of that surface with a speciﬁc agent, typically a polymer that alters surface polarity thereby decreasing adherence of soil. Used primarily in laundry detergent formulations soil release polymers provide signiﬁcant changes in surface energy, which in turn can lead to dramatic improvements in the removal of soils. Carboxymethyl cellulose (CMC) is the archetypical soil release polymer. CMC absorbs onto cotton fabric owing to the similarity in structure between the cellulose backbone of CMC and the cellulose polymer of cotton ﬁbers. Once absorbed, the carboxyl moiety creates a high net negative charge on the fabric surface effectively repelling negatively charged soils, especially clays [7].

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Introduction to Detergents

13

Other soil release polymers used in detergents are derivatives of polyester-polyether block copolymers that are capped with nonionic (ethoxylates), anionic (typically sulfonates), or cationic (typically quaternary amines) groups to achieve deposition and release from speciﬁc formulations [36].

III. REPRESENTATIVE DETERGENT FORMULATIONS This section provides examples of detergent formulations comprising the ingredients discussed in Section II. This is by no means an exhaustive compilation. Rather, the intent is to illustrate the variety of detergent formulations and how the composition of the formulation varies depending on the intended use. Subsequent chapters of this book will provide more detail on detergent formulations for speciﬁc applications. A. Laundry Detergent Formulations Examples of granular laundry detergent formulations are shown in Table 3. Table 4 illustrates typical liquid laundry detergent formulations. B. Dishwash Detergent Formulations Examples of typical liquid hand dishwash formulations are provided in Table 5. Examples of granular detergent formulations for use in automatic dishwashing applications are illustrated in Table 6. C. Hard Surface Cleaning Formulations Examples of liquid hard surface cleaning formulations are illustrated in Table 7. D. Personal Care Detergent Formulations Table 8 provides examples of typical shampoo formulations. Examples of body washes are provided in Table 9. E. Oral Care Detergent Formulations An oral mouthwash formulation is illustrated in Table 10. Examples of Toothpaste formulations are provided in Table 11. In the toothpaste formulations illustrated in Table 11 note the use of silica as an abrasive cleaning agent. F. Agricultural Detergent Formulations Herbicidal compositions typically comprise an aqueous emulsion of the active with appropriate surfactants to insure effective spreading and penetration of the herbicide into plants. Typical compositions comprising the well-known herbicidal active glyphosphate are illustrated in Table 12. G. Automobile Detergent Formulations A variety of detergent compositions are used in the care and maintenance of automobiles. Chapter 8 provides an extensive review of the components used in such formulations. The composition in Table 13 illustrates a formulation designed to clean and provide a waxed ﬁnish to the exterior of automobiles. A formulation designed to remove grease from automobile engines and engine compartments is illustrated in Table 14.

© 2006 by Taylor & Francis Group, LLC

14 Table 3

Showell Representative Granular Laundry Detergent Formulations Weight %

Ingredients Examples

A

B

C

C11-C13 Linear alkyl benzene sulfonate C12-C16 Alkyl ethoxy (E2) sulfate C14-C16 Secondary alkyl sulfate C14-C15 Alkyl sulfate C16-C18 Alkyl sulfate C14-C15 Alkyl ethoxy (E2) sulfate C12-C15 Alcohol ethoxylate E7 C14-C15 Alcohol ethoxylate E7 STPP Zeolite A Carbonate Silicate Sodium sulfate Na perborate tetrahydrate Na perborate monohydrate TAED NOBS HEDP DTPA Proteasea Amylasea Lipasea Cellulasea Acrylic/maleic copolymer CMC Polyester-based soil release polymer Minors

8 — 2 — 2 — 3.4 — — 18 13 1.4 26 9 — 1.5 — 0.3 — 0.8 0.8 0.2 0.15 0.3 0.2 0.2 Balance

10 — — 7 — 1 — 1 — 22 19 1 10 — 1 — 4 — 0.4 0.3 0.1 — — 1 — 0.4 Balance

— 5.3 — — — — — 3.3 10.7 10.7 6 7 40 5 — 0.5 — — — 0.3 0.1 0.2 0.3 0.8 0.2 — Balance

a

Enzymes are added in granulated form where typical enzyme level in the granulate ranges from 1 to about 8% by weight of the granulate formulation. Source: From U.S. Patents 6,326,348 B1 and 6,376,445 B1.

H. Detergent Formulations for Cleaning Food Processing Equipment Processing of food contaminates surfaces with lipids, carbohydrates, and proteins. A variety of detergent formulations have been developed speciﬁcally for cleaning food processing and preparation equipment. Table 15 provides an example of one such detergent utilizing high alkalinity as the major detersive component: More user friendly and environmentally compatible formulations can be built around enzyme technology to facilitate the removal of protein bound to surfaces. Examples are illustrated in Table 16.

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Introduction to Detergents Table 4

15

Representative Liquid Laundry Detergent Formulations

Ingredients Examples C11-C13 Linear alkyl benzene sulfonate C12-C15 Alkyl sulfate C14-C15 Alkyl sulfate C14-C15 Alkyl ethoxy (E2.5) sulfate C12-C13 Alcohol ethoxylate (E7) C11-C13 Alcohol ethoxylate (E8) C16-C18 Alkyl N-methyl glucamide C12-C14 Fatty acids Oleic acid Citric acid Sodium cumene sulfonate NaOH Ethanol 1,2 propanediol Monoethanolamine Proteasea Amylasea Lipasea Cellulasea Polyester-based soil release polymer Water + minors

Weight % A

B

C

12 — — 12 3 — — 2

— 18 — 2 4 — 8 11 — 5 — — 3 10 9 0.8 0.3 0.1 0.1 0.2 Balance

28 — 14 — — 3 2 — 3.4 5.4 — 0.4 7 6 17 1 — — — — Balance

3 4 6 — 3 3 0.8 — — — 0.2 Balance

a

Enzymes are added from liquid stocks where typical enzyme levels in the stock ranges from 1 to about 8% by weight of the liquid stock formulation. Source: From U.S. Patent 6,376,445 B1.

I. Detergent Formulations for Metal Component Cleaning Industries involved in repair and replacement of mechanical parts often require that those parts be cleaned prior to inspections, repair, or replacement. Generally, mechanical parts have been exposed to a wide variety of contaminants including dirt, oil, ink, and grease that must be removed for effective repair or service. A variety of metal cleaners have been developed to clean such surfaces. For example, solvent-based cleaners containing either halogenated or nonhalogenated hydrocarbons are common. However, the use of these cleaners carries certain environmental and worker safety issues. Where appropriate, aqueous-based cleaners are preferred for cost, safety, and environmental concerns. Table 17 provides example formulations of aqueous-based metal cleaning formulations:

IV. DETERGENCY THEORY AND MECHANISMS As noted in the introduction the two major functions of detergents are to remove materials from surfaces and keep materials suspended in a bulk phase. Each function requires work

© 2006 by Taylor & Francis Group, LLC

16 Table 5

Showell Representative Liquid Hand Dishwash Detergent Formulations Weight %

Ingredients Examples

A

B

C

C12-C13 Alkyl ethoxy (E3.5) carboxylate C11-C17 Alkyl ethoxy (E2.5) sulfate C12-C13 Alcohol ethoxylate (E3.5) Polyhydroxy fatty acid amide C12-C13 Alkyl sulfate C12-C14 Amidopropyl diemethyl betaine C14 Amine oxide MgCl2 Mg(OH)2 Methyldiethanol amine Ethanol Xylene sulfonate Water + minors

22 — 1.3 — 6 3 3 0.6 — 10 9 — Balance

— 29 — — — 0.9 3 3.3 — — 4 2 Balance

— 34 — 7 — 2 3 — 2 — 9 2 Balance

Source: From U.S. Patents 5,376,310 and 6,376,445 B1.

Table 6 Representative Granular Automatic Dishwashing Detergent Compositions

Ingredients Examples STPP Carbonate Silicate Sodium perborate monohydrate Alcohol ethoxylate Metal bleach catalyst TAED Proteasea Amylasea Sulfate Minors a

Weight % A

B

54 14 15 8 2 0.01 — 2 0.3 5 Balance

30 31 7.4 4.4 1.2 — 1 2.5 0.5 23.4 Balance

Enzymes are added in granulated form where typical enzyme level in the granulate ranges from 1 to about 8% by weight of the granulate formulation. Source: From U.S. Patent 6,376,445 B1.

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Introduction to Detergents Table 7

17

Representative Liquid Hard Surface Cleaning Compositions

Ingredients Examples Hydrogen peroxide C10 Alkyl sulfate Na octyl sulfate Na dodecyl sulfate C12-C13 Alcohol ethoxylate (E3) C9-C11 Alcohol ethoxylate (E10) Betaine Butyl octanol Butyl carbitol Isopropanol Butoxypropanol Sodium hydroxide Silicate Monoethanolamine Quaternary ammonium disinfectant Tartaric acid Water + minors

Weight % A

B

C

7 2 — — 2 2 — 0.5 — — — — — — — — Balance

— — 2 4 — — — — 4 — — 0.8 0.04 — — — Balance

— — — — — — 0.8 — — 30 15 — — 2.5 0.5 0.1 Balance

Source: From U.S. Patents 6,277,805 and 6,376,445.

Table 8

Representative Shampoo Formulations Weight %

Ingredients Examples

A

B

C

D

Ammonium lauryl sulfate Isostearamidopropyl morpholine lactate Cocoamidopropylbetaine Sodium cocosulfate Polyquaternium-10 Trimethylolpropane caprylate caprate Cocamide MEA Cetyl alcohol Stearyl alcohol Glycerol stearate Ethylene glycol distearate Dimethicone EDTA Water + minors

14 — 2.7 — 0.3 0.3 0.8 — — — 1.5 1 — Balance

12.5 — 4.2 — 0.3 0.3 — 0.4 0.2 — 1.5 1 — Balance

48 3 — 4 — — — — — 1.5 — — — Balance

50 6 — 3 — — — — — 1.5 — — 0.4 Balance

Source: From U.S. Patent 6,007,802 and HAPPI, February 2001.

© 2006 by Taylor & Francis Group, LLC

18

Showell

Table 9

Representative Body Wash Formulations Weight %

Ingredients Examples

A

B

Sodium cocoamphoacetate Cocaminopropyl betaine Disodium lauryl sulfosuccinate Disodium oleamido MEA sulfosuccinate Disodium laureth sulfosuccinate Sodium laureth sulfate Isostearamidopropyl morpholine lactate Hydrolyzed wheat protein derivative Polyquaternium–7 Glycol distearate Sodium chloride Water + minors

5 10 — 5 5 17 2 1 2 — — Balance

14 10 30 — — — 6 — 3 3.5 3 Balance

Source: Courtesy of T. Schoenberg, The McIntyre Group Ltd.

Table 10

Oral Mouthwash Formulation

Ingredients tb Glycerine Betaine Ethanol Propylene glycol Flavoring Triclosan Water

Weight % 10 10 1.4 10 7 0.2 0.06 Balance

Source: From U.S. Patent 5,681,548.

(W) to be done on the system. In the case of removal that work, deﬁned here as WR, is a measure of the energy required to move a substance from a surface into the bulk phase. In general, surface-active agents like surfactants promote removal from surfaces by lowering the interfacial energy between the substrate and the bulk phase. In the case of suspension, the work, WS, to suspend in the bulk phase is a measure of the energy required to keep materials from aggregating, ﬂocculating, or adhering to a surface. Generally, suspension is achieved either by electrostatic repulsive effects or steric stabilization. Subsequent chapters of this book provide extensive detail on how to remove and suspend materials via chemical means. The purpose of this section is to provide a general thermodynamic underpinning to the phenomena of soil removal and particulate suspension so that the reader can better understand the mechanisms by which detergent chemicals function.

© 2006 by Taylor & Francis Group, LLC

Introduction to Detergents Table 11

19

Representative Toothpaste Formulations Weight %

Ingredients Examples

A

B

C

Glycerin Polyethylene glycol Xanthan gum CMC Water Sodium saccharin Sodium ﬂuoride Xylitol Poloxamer Sodium alkyl sulfate Cocamidopropyl betaine Flavoring Sodium carbonate Titanium dioxide Silica Sodium bicarbonate Propylene glycol Tetrasodium pyrophosphate Calcium peroxide

27 2 0.3 0.2 5 0.5 0.2 10 2 6 — 1.1 2.6 1 20 1.5 15 5 0.5

29 1 0.4 0.2 7 0.4 0.2 10 3 4 — 1 3 1 20 1 11 7 1

29 3 0.3 0.2 5 0.5 0.2 10 — 4 2 1 3 1 20 1 12 7 1

Source: From U.S. Patent 5,849,269.

Table 12

Representative Herbicidal Formulations Weight %

Ingredients Examples

A

B

C

Butyl stearate Span 80 Tween 20 C12-15 Alcohol ethoxylate (E20) Glyphosphate (as g a.e./liter) Water

18 3 5 — 100 Balance

1 — — 10 163 Balance

7.5 3 5 — 160 Balance

Note: a.e. = active ether Source: From U.S. Patent 6,479,434.

A. Removal Mechanisms For simplicity, in the following discussion, materials to be removed from a surface will be generically referred to as soils. The basic concept illustrated here will be for surfactant-

© 2006 by Taylor & Francis Group, LLC

20 Table 13

Showell Detergent Formulation for Cleaning and Care of Automobile Exteriors Ingredients

Weight %

Micronized polymer wax Amino functional silicone Polydimethylsiloxane Parafﬁnic hydrocarbon solvent Alkyl alcohol ethoxylate Fluoroamide polymer Water

6 3 1 15 0.5 0.2 Balance

Source: From U.S. Patent 5,782,962.

Table 14

Automobile Engine Cleaner Ingredients

Dodecyl oxydibenzene disulfonate Nonylphenol-9 ethoxylate Sodium orthosilicate Tetra potassium pyrophosphate C18 tall oil Heavy aromatic naphtha Water

Weight % 6 1.2 1.2 8 9.5 14 Balance

Source: From U..S Patent 3,717,590.

Table 15

Detergents for Cleaning Food Processing Equipment

Examples Sodium hydroxide Sodium polyacrylate 1,2,4 Tricarboxylic acid 1-Hydroxyethylidene-1,1-disphosphonic acid Sodium hypochlorite Water Source: From U.S. Patent 4,935,065 to Ecolab Inc.

© 2006 by Taylor & Francis Group, LLC

A 15 2.7 0.8 — 2 Balance

B 15 2.7 — 0.3 3 Balance

C 15 2.7 — 0.8 3 Balance

Introduction to Detergents Table 16

21

Enzymatic Based Detergents for Cleaning Food Processing Equipment

Ingredients Examples Triethanolamine Sodium metabisulﬁte Propylene glycol Sodium xylene sulfonate Ethoxylated propoxylated nonionic Protease Water

Weight % A

B

2 1 12 20 25 6.3 Balance

2 1 12 20 25 6.3 Balance

C 2 1 15 20 25 3.1 Balance

D 2 1 15 20 25 3.1 Balance

Source: From U.S. Patent 6,197,739 B1 to Ecolab Inc.

Table 17

Representative Aqueous-Based Metal Cleaning Detergents

Ingredients Examples Sodium carbonate Borax N-octylpyrrolidone 1,2,3-Benzotriazole C9-C11 Alcohol ethoxylate (E2.5) C9-C11 Alcohol ethoxylate (E6) C12-C15 Alcohol ethoxylate (E9) C14-C15 Alcohol ethoxylate (E7) Acrylic acid polymer NaOH Sodium silicate Sodium nonanoate Water

Weight % A

B

3 0.3 — 0.3 2 2 — — 0.5 0.5 2 6.5 Balance

3 0.3 — 0.3 — — 4 — 0.5 0.5 2 6.5 Balance

C 3 0.3 — 0.3 — — — 4 0.5 0.5 2 6.5 Balance

D 3 0.3 2 0.3 2 2 — — 0.5 0.5 2 6.5 Balance

Source: From U.S. Patent 6,124,253 to Church & Dwight Co.

mediated removal of soil from a surface. Soil removal mechanisms can be considered to comprise several steps: 1.

2.

Surfactant transport to an interface. This can occur with the surfactant in the monomeric form, in which case kinetics of transport are fairly rapid (10–5 cm2/sec), or with the surfactant in aggregated or micellar form in which case the kinetics of transport are relatively slow (10–7 cm2/sec). The kinetics of surfactant transport and adsorption at the interface can be measured via dynamic interfacial tensiometry [37–41]. Adsorption of surfactant at the solution/soil interface, solution/atmosphere interface, and surface/solution interface. This step results in lowering of the interfa-

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3.

4.

5.

6.

cial energies at each of these interfaces. Adsorption is driven by the surfactant packing parameter (P = V/aoI) where V is the volume described by the hydrophobic portion (alkyl chain) of the surfactant, ao is the mean cross-sectional area of the surfactant head group, and l is the all trans alkyl chain length of the hydrophobe (alkyl chain) [42]. Surfactants with 0 < P < 1/3 form micelles in aqueous solution. Surfactants with 1/3 < P < 1/2 form wormlike micelles and surfactants with 1/2 < P < 1 display vesicle formation. Controlling the surfactant packing parameter close to 1 (ﬂat surfactant ﬁlm) promotes strong adsorption and delivers very low-soil/bulk phase equilibrium interfacial tensions. Formation of a surfactant:soil complex. This typically is represented as surfactant coating the soil to be removed either in a monolayer, or, at high enough surfactant concentrations with bilayer structures. During this step surfactant can promote solid soil softening and liquifaction. This is a critical step to promote roll-up or emulsiﬁcation that takes place only with liquid soils. Desorption of the surfactant:soil complex. For oily soils this occurs either via the classical roll-up mechanism or by solubilization of the oil into micellar surfactant aggregates. In the case of liquid soil, the energy required to remove the soil can be expressed as gow (1+cosq) where gow is the soil/solution interfacial tension and q is the soil/substrate contact angle. For large contact angle (180o) roll-up of the soil occurs. For small contact angles emulsiﬁcation via low gow is the major mechanism of soil removal. Transport of the surfactant:soil complex away from the surface. In the case of greasy soils that have lower density than the bulk solution, the soil simply ﬂoats to the surface. In other cases, mechanical energy or agitation is critical to move the surfactant:soil complex away from the interface. Stabilization of the dispersed soil to prevent redeposition (see Section IV B).

The work, WR, to move soil (o) from the surface (s) to the bulk phase (w) can be directly related to the interfacial tensions of the various interfaces through the following [7]: WR = gsw + gow - gos

(1)

where gsw is the interfacial tension between the surface and bulk phase, gow is the interfacial tension between the soil and the bulk phase, and gos is the interfacial tension between the soil and the surface. From this equation it can be seen that the work required to remove soil from a surface is reduced when the interfacial tensions between the surface and bulk phase and soil and bulk phase are minimized and the interfacial tension of the soil-surface is increased. This is exactly the effect that surfactants have. By adsorbing at the surface, bulk-phase, and soil interfaces surfactant lowers interfacial energies, decreasing the free energy associated with moving the soil from the surface into the bulk phase. Surfactant adsorption causes the surface/bulk phase (gsw ) and soil/bulk phase (gow) interfacial tensions to drop while the interfacial tension between soil and surface (gos) increases thereby facilitating movement of the soil into the bulk phase. One aspect of the above that is often ignored is step one, transport of surfactant to the various interfaces. The presence of monomeric surfactant is critical to rapid transport of surfactant to the interface and rapid lowering of the interfacial tensions (IFT). However, solubilization is dependent on the presence of micelles. As surfactant concentration in solution is raised aggregates (micelles) form and at a certain concentration (critical micelle concentration, CMC) the monomer concentration of surfactant remains constant and addi-

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Introduction to Detergents

23

tional surfactant resides in micelles. The formation of micelles reduces the capacity of the surfactant to adsorb at the interface and reduce IFT that is critical in step 2. Therefore, there is an optimum CMC that must be achieved in order to optimize steps 1 and 2 above while still allowing efﬁcient solubilization. This optimum is dependent on the nature of the soil being removed, the substrate (hydrophobicity), and the surfactant system used. The mechanism outlined above is generally applicable for oily soils. For particulate soils consideration of the electrostatic and van der Waals forces of attraction between the particle and the surface need to be considered because most particulate dirt and most surfaces tend to be charged due to the presence of surface exposed silicic acid, hydroxyl, or carboxyl groups [43]. . Again, the process can be described in a series of steps [44]. In the ﬁrst step a soil particle, P, adhering to a surface, S, is removed a distance d with no penetration of liquid between the soil and the surface. The process requires work input, w1, to overcome the van der Waals attraction between P and S. Then detergent solution penetrates the space between P and S, allowing surfactant to adsorb at the solution-particle interface and the surface-solution interface, and a net sum of work, w2 , is obtained. The total work done in this ﬁrst step is: W1 = w1 - w2

(2)

In the second step the particle is removed from the surface to a distance large enough that there are effectively no forces of interaction between P and S. The work for this second step, W2, is composed of contributions from van der Waals attractions and the electrostatic repulsions between P and S, and is equal to the total potential energy of the system at the distance d such that W2 = -jd and the work done for the total process of removing an adhering particle, P, from surface S is equal to the sum of W1 and W2 or: SW = W1 + W2 = w1 - w2 - jd

(3)

The work, w2, created when surfactant adsorbs onto the particle and the surface can, in the ﬁrst approximation, be described as the sum of various interfacial energies, similar to Eq. (1): w2 = gsp - gsw - gpw

(4)

where gpw is the interfacial tension between the particle and the solution phase. According to Eq. (3) the removal of particulate soil becomes easier as the total work to remove the particle, SW, becomes smaller. The addition of surfactant reduces both gsw and gpw such that w2 increases, which helps to lower the total work of removal. In addition, the total potential energy of the system jd is the sum of the attractive van der Waals interactions, jd,A, and the repulsive interactions, jd,R, due to surface charges. The adsorption of surfactant, especially anionic surfactant, at the surface-solution and particle-solution interfaces serves to decrease the attractive force and increase the repulsive force thereby promoting removal to a distance where there are no longer any attractive forces between particle and surface. B. Suspension Mechanisms Once material is removed from a surface it must be suspended in the bulk phase to avoid redeposition. For hydrophobic liquid soils in aqueous media, suspension is typically accomplished by entrapment of the soil within the surfactant micelle or vesicle. For particulate soils suspension is often best achieved by adsorption of a charged polymer onto the surface of the particle thereby increasing electrostatic repulsion between particle-

© 2006 by Taylor & Francis Group, LLC

24

Showell

particle and particle-surface interactions. There are two general mechanisms for suspending soil in solution— electrostatic repulsion and steric stabilization. In polar media, most substances will acquire a surface electric charge as a result of ionization of surface chemical groups, ion adsorption, and ion dissolution [16]. In aqueous solutions most surfaces and most soil particles are negatively charged. As a result both soil and surface possess an electrical double layer. The electrical double layer is comprised of a compact layer of ions of opposite charge to the surface and a more diffuse double layer comprised of counter- and co-ions distributed in a diffuse manner in the polar medium. As described in Section IV A, the total potential energy for a system comprised of a particle at some distance, d, from a surface is the sum of the attractive force, jd,A, and the repulsive force jd,R. When two particles of the same net surface charge approach one another, or when a particle approaches a charged surface, they repel each other as their double layers start to overlap. The particles have to overcome this electrical barrier in order to get close enough for van der Waals attraction to take over. When the potential energy barrier jd,R is high particles tend to stay dispersed in the bulk phase. However, if the electrical double layer is compressed by high ionic strength or shielded by adsorption of an organic layer coalescence and aggregation can occur resulting in redeposition of soil particles back onto the surface. Electrostatic repulsion is best achieved in low ionic strength media where the electrical double layer on particles and surfaces is diffuse. An alternative strategy is to adsorb a charged polymer, such as the acrylic acid polymers described in Section II B, or a charged surfactant onto the surface. When particles having adsorbed layers (polymer or surfactant) collide, their adsorbed layers may be compressed without penetrating. This results in reduced conﬁgurations available to the adsorbed layer. In thermodynamic terms the reduction in potential conﬁgurations is expressed as a decrease in entropy for the system or an increase in free energy. This increased free energy of stabilization results from the “elastic” effect of colliding adsorbed layers and is referred to as steric stabilization. The positive free energy change is related to both the enthalpy and entropy change by DG = DH – TDS. Stabilization can therefore come either as a result of a positive change in enthalpy or a decrease in entropy. A positive DH reﬂects the release of bound solvent from the polymer chains as they interact and a negative DS results from the loss of conﬁgurational freedom of the polymer [16]. Steric stabilizers are usually block copolymers that make up a hydrophobic part (e.g., polyethyleneterepthalate) which attaches to the particle surface and a hydrophilic part (e.g., polyethylene glycol) which trails out into the bulk solution. Effective detergency results when the detergent formulation is designed to maximize four basic properties; penetration, wetting, dispersion, and emulsiﬁcation. These four factors combined determine the ultimate effectiveness of the detergent formulation. Subsequent chapters of this book provide signiﬁcantly more detail on how to design effective detergents for a variety of speciﬁc applications.

ACKNOWLEDGMENTS I thank each of the authors of the individual chapters in this work for their effort and dedication in bringing the vision to life. Thanks to all of my friends and colleagues at Procter & Gamble who contributed their time and expertise to review and critique of the contributions.

© 2006 by Taylor & Francis Group, LLC

Introduction to Detergents

25

REFERENCES 1. 2. 3. 4.

5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18.

19. 20. 21. 22. 23. 24. 25. 26. 27.

INFORM, Vol. 13, pp. 682–695 (September 2002). J. W. B. Gogarty, Petroleum Techn., pp. 1475–1483 (1976). X. Zheng, Y. Xie, L. Zhu, X. Jiang, and A. Yan, Ultrasonics Sonochem., 9(6):311 (2002). R. W. Bassemir, A. Bean, O. Wasilewski, D. Kline, W. Hills, C. Su, I.R. Steel, and W. E. Rusterholz, in: Kirk-Othmer, Encyclopedia of Chemical Technology, Vol. 14, 4th ed., New York, Wiley, pp. 482–503 (1995). H. Hendricks and C. Nootens, J. Eur. Coat., 6:710 (2003). T. F. Tadros, Surfactants in Agrochemicals, Vol. 54, Marcel Dekker Surfactant Science Series, New York (1995). L. H. Tan Tai, Formulating Detergents and Personal Care Products, AOCS Press, Champaign, Illinois (2000). Liquid Detergents, Vol. 67, ed. K-Y. Lai, Marcel-Dekker Surfactant Science Series, New York (1997). Powdered Detergents, Vol. 71, ed. M. S. Showell, Marcel-Dekker Surfactant Science Series, New York (1998). Nonionic Surfactants, Vols. 1(1967) and 23 (1987), ed. M. J. Schick, Marcel Dekker Surfactant Science Series, New York. Anionic Surfactants: Organic Chemistry, ed. H. W. Stache, Vol. 56, Marcel Dekker Surfactant Science Series, New York (1995 ). Novel Surfactants: Preparation, Applications, and Biodegradability, ed. K. Holmberg, Vol 74, Marcel Dekker Surfactant Science Series (1998). Detergency of Specialty Surfactants, ed. F. E. Friedli, Vol. 98, Marcel Dekker Surfactant Science Series, New York (2001). P. K. Vinson, P. R. Foley, T. A. Cripe, D. S. Connor, and K. W. Willman, U.S. Patent 6,326,348 to The Procter & Gamble Co. (2001). J. B. McClain, D. E. Betts, D. A. Canelas, E. T. Samulski, J. M. DeSimone, J. D. Londono, H. D. Cochran, G. D. Wignall, D. Chillura-Martino, and R. Triolo, Science, 274:2049 (1996). D. J. Shaw, Introduction to Colloid and Surface Chemistry, 3rd ed., Butterworth & Co. Ltd., London (1980). G. Swift in Powdered Detergents, Vol. 71, ed. M. S. Showell, Marcel Dekker Surfactant Science Series, New York (1998). (a) A. M. B. Austin, A. M. Carrier, and M. L. Standish, U.S. Patent 5547612 to National Starch and Chemical Investment Holding Corp. (1996); (b) A. M. B. Austin, A. M. Carrier, and M. L. Standish, U.S. Patent 5,698,512 to National Starch and Chemical Investment Holding Corp. (1997); (c) E. Penzel, G. Franzmann, A. Maximilian, J. Pakusch, and B. Schuler, U.S. Patent 5604272 to BASF Aktiengesellschaft (1997); (d) W. Denzinger, A. Kisternmadner, J. Perner, A. Funhoff, B. Potthoff-Karl, and H-J. Raubenheimer, U.S. Patent 5,658,993 to BASF Aktiengesellschaft (1997). A. duVosel, F. Francalanci, and P. Maggiorotti, Eur. Patent Application 454,126-A1 to Montedipe S.r.l. (1991). T. Cassata, U.S. Patent 5,219,986 to Cygnus Corporation (1993). M. Kroner, G. Schornick, W. Denzinger, R. Baur, K. Alexander, B. Potthoff-Karl, V. Schwendemann, German Patent Application DE 4,308,426-A to BASF AG (1993). M. B. Freeman, Am. Oil Chemists Soc. Annual Meeting, San Antonio, Texas (1995). S. W. Heinzman and S. J. Dupont, Eur. Patent 542,496-B1 to The Procter & Gamble Company (1998). S. C. Sikes, L. Ringsdorf, and G. Swift, U.S. Patent 6,495,658 to Folia, Inc. (2002). D. T. Nzudie and C. Collette, U.S. Patent 6,221,957 to Elf Atochem S. A. (2001). (a) K. N. Price, U.S. Patent 6,444,633 B2 to The Procter & Gamble Company (2002); (b) K. N. Price U.S. Patent 6,479,451 B2 to The Procter & Gamble Company (2002). J. V. Boskamp, Eur. Patent Apps. 0358473-A2 and 0358472-A2 to Unilever NV (1990).

© 2006 by Taylor & Francis Group, LLC

26

Showell 28. H.-P. Rieck in Powdered Detergents, Vol. 71, ed. M. S. Showell, Marcel Dekker Surfactant Science Series, New York (1998). 29. See, e.g., U.S. Patents 5,132,431; 5,208,340; 5,246,612; 5,279,757; 5,310,934; 5,391,324; 5,415,796; 5,466,825; 5,798,326. 30. C. Wu, Science News Online, August 16, 1997. www.sciencenews.org/pages/sn—arc97 /8—16—97/bob1.htm 31. D. Halvorsen, Minnesota Star Tribune, July 6, 2001. www.greenearthcleaning.com/newsarticles.asp 32. Enzymes in Detergency, Vol. 69, ed. J. H. van Ee, O. Misset, and E. J. Baas, Marcel-Dekker Surfactant Science Series (1997). 33. A. Prins, F. J. G. Boerboom, and H. K. A. I. Vankalsbeeck, in Colloids and Surfaces A: Physiochemical and Engineering Aspects, Vol. 143, Issues 2–3:395 (1998). 34. (a) W. P. Hsu, T. W. Foley, and H. J Haller in U.S. Patent 5,387,425 to Rhone-Poulenc Specialty Chemicals Co. (1995), (b) Y. Ishibashi, T. Kakui, K. Nakatani, and Y. Terano in U.S. Patent 6,080,405 to Suntory Ltd. (2000). 35. C. Kasturi, M. G. Schafer, M. R. Sivik, W. B. Kluesner, and M. W. Scheper in PCT WO9927058 to the Procter & Gamble Co. (1999). 36. E. Gosselink in Powdered Detergents, Vol. 71, ed. M. S. Showell, Marcel Dekker Surfactant Science Series, New York (1998). 37. J. Chatterjee, J. Colloids and Surfaces, A:Physiochemical and Engineering Aspects, 204(1–3) (2002). 38. J. R. Campanelli and X. Wang, and J. Coll., Int. Sci., 213:340 (1999). 39. A. Bonﬁllon, F. Sicoli, and D. Langevin, J. Coll. Int. Sci. 168:497 (1994). 40. Nasr-El-Din, A. Hisham, K. C. Taylor, Colloids and Surfaces, 66(1):23 (1992). 41. A. W. Adamson and A. P. Gast in Physical Chemistry of Surfaces, Wiley-Interscience, p. 33, New York (1997). 42. D. J. Mitchell and B. W. Ninham, J. Chem. Soc. Faraday Trans., 2, 77:601 (1981). 43. H. Schott in Detergency Part I, Vol. 5, eds. W. G. Cutler and R. C. Davis, Marcel Dekker Surfactant Science Series, New York (1972). 44. H. Lange in Detergency Part I, Vol. 5, eds. W. G. Cutler and R. C. Davis, Marcel Dekker Surfactant Science Series, New York (1972).

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2 Statistical Mixture Design for Optimization of Detergent Formulations Samir S. Ashrawi and George A. Smith

CONTENTS I. II. III.

Introduction ............................................................................................................ Mixture Design Experiments ................................................................................. Examples of Mixture Design Experiments............................................................ A. Heavy Duty Liquid Detergent Optimization ............................................. B. Light Duty Liquid Detergent Optimization ............................................... C. Detergent Concentrate Robustness Study.................................................. IV. Conclusions ............................................................................................................ References ........................................................................................................................

27 29 31 32 39 45 49 49

I. INTRODUCTION Development of new cleaning formulations can be a very arduous and time-consuming task. The formulator must choose from literally hundreds of raw materials. The individual ingredients must be combined in the proper ratio to obtain the best cost performance while satisfying a myriad of physical property and stability criteria. The formulation must also be robust enough to be produced on a commercial scale with little or no rework required to meet product specifications. Traditionally, formulators of cleaning products have used a trial-and-error approach to arrive at cost-effective, robust formulations. The formulator selects ingredients based on experience, availability, and cost in order to develop an initial starting formulation. The starting formulation is tested against competitive products and the results are analyzed to determine which physical and performance properties need improvement. The formulation is then modified and the process repeated in an iterative fashion until acceptable performance is obtained. It is common to optimize the formulation components one at a time to avoid confounding the response with other variables. 27

© 2006 by Taylor & Francis Group, LLC

28

Ashrawi and Smith

In the trial-and-error approach, component variations are usually fairly small, which limits the composition space that is investigated to small perturbations around the starting formulation. Because responses are optimized one at a time, one is never quite sure that all properties and performance responses have been optimized. Furthermore, one is not sure if the observed optimum is local within the small composition space that was investigated, or global within a much larger composition space. Finally, since this approach does not yield maps of performance over the composition space, it is not possible to predict the behavior of new formulations without continuous tweaking. An alternative, and more informative, approach is the use of statistical experimental design to optimize formulations. We have used various types of statistically designed experiments in our laboratories to help develop and optimize formulations for different applications [1,2]. Factorial screening designs are extremely helpful in identifying the vital factors or components that affect the desired product. Response surface designs are useful in locating the ideal criteria or process settings that yield optimum performance. And finally, mixture designs yield performance maps over a defined composition space, enabling us to discover the optimum formulation and to predict performance in other regions of the defined composition space. Figure 1 describes the framework of our statistical experimental approach to formulation development. Beginning with a well-defined goal of achieving certain performance criteria, physical properties, and cost, we conduct screening experiments to determine the components that would be vital to achieving our goal. Once the trial mixtures are prepared and the desired property or performance response is measured, the results can be analyzed

Goal Definition

Screening Design

Properties

Mixture Design

Performance

Data Analysis

Optimization

Figure 1

Model Generation & Validation

Scenario Analysis

Framework for formulation development using statistical experimental design.

© 2006 by Taylor & Francis Group, LLC

Statistical Mixture Design for Optimization of Detergent Formulations

29

to determine how each component affects a particular response as the amount of that component is changed. Next, we use the components that most affect the measured response to develop a suitable mixture design. The mixture design trial formulations are prepared and the physical properties and performance responses are measured and recorded. A model that best fits the data is then generated and validated by exploring its statistical significance. With a good-fit model, one can then proceed to optimization of the composition to meet the required performance criteria. The authors have used mixture design experiments to optimize different types of cleaning formulations. Examples include laundry liquids, dishwashing liquids, and hard surface cleaners. Many times the results indicate that improvements in one property come at the expense of another. By measuring multiple responses it is possible to optimize the formulation to get the best overall performance for a wide variety of performance factors. Mixture design experiments can also be used to optimize formulation robustness. This allows us to obtain a product that can be easily manufactured on a commercial scale.

II. MIXTURE DESIGN EXPERIMENTS It is not the purpose of this chapter to delve into all the mathematical details of mixture design experiments. Our intent is to present only the major salient points to better understand the basic assumptions behind the technique. For a more complete discussion of statistics as applied to mixture designs, the reader is invited to peruse the pertinent literature [3–5]. In a mixture design experiment, two or more individual ingredients are blended together to produce a final product or formulation. Measurements of the physical properties and the performance for several different trial blends are made and the results used to find the best overall result. The measured properties depend only on the relative proportions of the individual ingredients and not on the total amount present. The defining feature of a mixture design is that the proportions of the ingredients sum to unity. In mathematical terms, if the number of ingredients in the system is given by q, and the proportion of the ith component is given by xi For xi ≥ 0 and i = 1, 2,..., q

(1)

q

∑χ = χ + χ i

1

2

+ ..... + χq = 1

(2)

i =1

Because of the restrictions imposed by Eqs. (1) and (2), the experimental region of interest is a (q-1) dimensional space. For q = 2, the dimensional space is a straight line and can be represented on a conventional x-y plot. For q = 3, the dimensional space is an equilateral triangle and can be represented in triangular coordinates. For q = 4, the dimensional space is a tetrahedron. Since the proportions sum to unity, the xi are constrained variables; varying the proportion of one component will change the proportion of at least one other component in the mixture. In mixture design experiments, the experimental data are defined in a quantitative fashion, the purpose of which is to model the mixture behavior using some form of a mathematical equation. This allows for predictions of the response for any combination of ingredients and allows for a measure of the influence for each component or combination of components on the measured response.

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The data from a mixture design experiment are modeled in the following fashion. Assuming that the response factor η depends only on the proportions of the individual components: η = f (χ1, χ2 ,.....χq )

(3)

We assume that the function is continuous for all χi, and can be represented by a first- or second-order polynomial. Only on rare occasions is a third-degree (cubic) polynomial necessary to represent the data. In actual practice, it is convenient to use a canonical form for the polynomial fitting equation. This acts to reduce the number of fitting parameters compared to a standard power series polynomial expression. Canonical polynomial expressions were developed by Henri Scheffé in the early 1950s specifically for mixture design experiments [6,7]. The Scheffé quadratic polynomial for two components is given by q

η=

∑ i

βi χi +

q

q

i

j

∑∑β χ χ ij

i

j

(4)

The Scheffé form of the fitting equation is also easy to interpret. The coefficients for the main effects βi are responses for the pure components. The coefficients for the mixed terms βij give a measure of positive or negative deviation from the response predicted for ideal mixing of the individual components. Up until this point, we have not discussed the experimental error associated with the measured responses. Experimental error can arise from various sources including sample preparation, analytical methodology, mechanical noise, and equipment problems. In an experimental program consisting of N trials, the observed value of the response in the uth trial is given by yu and is assumed to vary about the mean of η with a common variance σ2. The observed response value contains experimental error εu

( )

( )

yu = η + ε u 1 ≤ u ≤ N

(5)

where the errors are assumed to be independent with a common variance. The Scheffé expression for two components becomes yu = β1χ1 + β2 χ2 + εu

(6)

With N ≥ 2 observations collected on yu, we can obtain the estimates b1 and b2 of the parameters β1 and β2 , respectively. The parameters of Eq. (6) can be replaced by their respective estimates to give the approximating equation yˆ ( x ) = b1χ1 + b2 χ2

(7)

where yˆ ( x ) is the predicted value of η for given values of x1 and x2. The estimated parameters contain the main effects plus any error associated with measurement of the response variables. In practice, the magnitude of error associated with the measured responses can be determined by replicating some of the trial blends. Differences in the response values of the replicate samples are taken as a measure of the experimental error. Lack of fit tests

© 2006 by Taylor & Francis Group, LLC

Statistical Mixture Design for Optimization of Detergent Formulations

31

can be used to make certain that the level of noise arising from the experimental error is not greater than the effect one is trying to measure. After the experiments are performed and the data collected, the best-fit parameters given in Eq. (7) are determined using least squares analysis. Initially the fitting parameters are estimated to give a predicted response, which is compared to the measured response. The parameters are then optimized to minimize the sum of squares between the measured and predicted response values. q

Sum of squares =

∑ (y − yˆ ) i

2

(8)

i

1

A variety of optimization methods have been developed for determining the best-fit parameters. For simple, well-defined mixture designs, the fitting parameters can be calculated in closed form. For more complicated designs, multivariable optimization techniques are required. Many of these techniques are based on matrix inversion algorithms. A complete discussion of multivariable optimization methods is beyond the scope of this chapter. For a more complete discussion, the reader is invited to peruse the pertinent literature [8]. In the early days of design of experiments (DOE), determination of the best-fit parameters was a tedious and labor-intensive task. With the advent of the personal computer, the calculations involved in determining the best-fit parameter values for the fitting equation became relatively easy. There are several software packages available for running mixture design experiments, some of which are listed in Table 1. Many of these programs will perform screening designs, response surface designs and mixture designs. The reader is invited to contact the software manufacturers for more details.

III. EXAMPLES OF MIXTURE DESIGN EXPERIMENTS In the last few years, there have been a number of published works using design of experiments to study and optimize detergent formulations. Response surface designs have been used to model the critical micelle concentration (CMC) of ternary surfactant mixtures. Results agree with those obtained using thermodynamic modeling [9]. Mixture design has

Table 1 Commercially Available Design of Experiments (DOE) Software Software Design Expert 6 DoE Fusion JMP 4 Minitab 13 MultiSimplex 2.1 Sirius Stratgrapics Plus

© 2006 by Taylor & Francis Group, LLC

Company Stat-Ease S-Matrix Corp. SAS Institute Inc. Minitab Inc. MultiSimplex AB PRS Manugistics, Inc.

URL www.statease.com www.s-matrix.com www-jmpdiscovery.com www.minitab.com www.multisimplex.com www.prs.no www.statgraphics.com

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Ashrawi and Smith

been used to optimize the ratio of amphoteric, nonionic, and anionic surfactants in a shampoo formulation. The authors report that the methodology offered the maximum return in terms of information about the interplay of multiple factors at the minimum investment [10]. Mixture design experiments have been used to optimize surfactant blend ratio to obtain low foaming and good detergency at high and low use levels [11]. Mixture design experiments have been used to solve solubilization problems in light-duty liquid detergents [12]. Factorial and mixture design methods have been used to develop solid esterquats and ensure compatibility with other formulation components [13]. A.

Heavy Duty Liquid Detergent Optimization

Mixture designs have been used extensively in our laboratory to help develop and optimize formulations for different cleaning applications. This technique can be used to solve a variety of problems. In some cases, the goal is to optimize the ratio of different formulation components to get the best performance at the lowest formulation cost. In other cases, the goal is to understand the role of different ingredients in a formulation and to identify any interactions or synergies between the components. There are also cases where we are interested in establishing product specifications based on the accuracy to which the manufacturing plant can charge the individual raw materials. Formulation optimization always starts with the goal clearly defined. Key information includes performance criteria, physical property requirements, and finished formulation costs. To illustrate the mixture design approach, we will examine the development of an economical laundry detergent formulation with performance comparable to a leading national brand. Product requirements include performance at a given dose level and finished formulation costs. In developing the formulation, a combination of different surfactants was used, based on single-surfactant screening experiments. Figure 2 shows a schematic factorial screening design using two components, A and B. In this design, one prepares at least five mixtures (dark shaded points) that include the apexes of the composition space and a centroid point. The centroid is duplicated to get a measure of the variation in the measurement. Four more points (light shaded) can be added to determine any curvature in the response of the performance criteria.

Component A

High

Centroid

Low Low

Figure 2

Component B

High

Schematic of a two-component factorial screening design.

© 2006 by Taylor & Francis Group, LLC

Statistical Mixture Design for Optimization of Detergent Formulations

33

Once the mixtures are prepared and the desired property or performance response is measured, the results can be plotted in a manner that demonstrates how each component affects that particular response as the amount of that component is changed away from its level at the centroid. This is schematically shown for a four-component screening design, with a response Y, in Fig. 3, where it can be seen that components A and B have opposing effects, while component C has no effect on response Y. For the purpose of our working example, we conducted three screening experiments, each comprising six surfactants. These surfactants included various salts of linear alkylbenzene sulfonate, and a host of nonionic surfactants including different types of amine ethoxylates. All told, we screened 18 surfactants in four families, and selected three components for our next step, the mixture design. These surfactants were a linear alkylbenzene sulfonate (LAS), linear alcohol ethoxylate (LAE), and a polyetheramine ethoxylate (PEA). Linear alkylbenzene sulfonate (LAS) was used because of its relatively low price, good detergency for oily soils and because it provides the formulator the ability to adjust formulation viscosity through the salt effect (14,15). In this study, high 2-phenyl, lowdialkyl tetralin LAS with an average alkyl chain length of 12 was used. The free acid was neutralized with caustic to give the sodium salt (NaLAS). Typically, the high 2-phenyl grades of LAS are used in liquid formulations due to solubility and stability issues [16–18]. An alcohol ethoxylate (AE) was used because it is reasonably inexpensive and shows good performance on greasy soils [19,20]. The properties of AE depend primarily on the alcohol source and the degree of ethoxylation. Oxo alcohols contain both even and odd carbon chain lengths and have 10 to 20% branching in the hydrophobe. Natural and Ziegler alcohols contain only even carbon chain lengths and are relatively linear. In this study, a C12–14 Ziegler alcohol was reacted with 7 Mol of ethylene oxide using a base catalyst (L24–7). Polyetheramine ethoxylates (PEA), a relatively new type of nonionic surfactant, show excellent detergency for dust sebum and help prevent dye transfer in the laundry process [21]. In this study, a C12–14 Ziegler alcohol was reacted with 2 moles of propylene oxide using a base catalyst. The alcohol propoxylate was then reacted with ammonia using

120

D

A

60

C

Response Y

90

30 B 0 −10

−5

0

5

10

Deviation from centroid

Figure 3

Schematic results for a four-component screening design.

© 2006 by Taylor & Francis Group, LLC

34

Ashrawi and Smith

a heterogeneous catalyst to form the primary amine. The amine was reacted with 10 Mol of ethylene oxide. The nominal structure of the resulting material is C 12–14 –2PO–N–10EO(PEA210). To understand the effect of each surfactant on the overall performance and to identify regions of optimum performance, a three-component mixture design was developed. The concentration of each surfactant was varied from 0 to 100%, holding the surfactant actives in the formulation constant at 20%. Each trial blend contained 1% monoethanolamine (MEA) to increase alkalinity and avoid variations in formulation pH as a function of surfactant blend ratio. No dyes, fragrance, or optical brighteners were added to the formulation since we were mainly concerned with the effect of surfactant blend ratio on the cleaning performance. To model the system, an augmented simplex lattice design was used. The dimensional space and the mixture design points covered in this example are shown in Fig. 4. To express the composition of the design points, a ternary diagram is used. The diagram is normalized so that any point on the surface represents 100% surfactant actives. The apices of the triangle correspond to single surfactants, the sides represent binary surfactant mixtures and the interior points correspond to mixtures of all three surfactants. Sufficient mixture points were used to model any interactions between the surfactants. Several of the design points were replicated to determine the experimental uncertainty in the measured response factors. Cleaning performance was determined by washing standard soil swatches in a sixpot Tergtometer (Model 7243ES, Instrument Marketing Services, Inc., Fairfield, New Jersey) under carefully controlled conditions. The wash temperature and water hardness were held constant at 100oF and 150 ppm (Ca+2/Mg+2 = 2/1). This corresponds to standard warm-water wash and average water hardness conditions in the United States [22]. The wash cycle and agitation rate were held constant at 15/5 minutes (wash/rinse) and 100 RPM, respectively. The detergent was charged to each Terg pot by weight. The amount of detergent corresponds to a 1/2 -cup formulation in a conventional top-loading, verticalaxis washing machine

NaLAS (100/0/0)

(50/50/0)

(50/0/50)

(33/33/33)

(0/0/100)

(0/100/0)

L24-7

Figure 4

(0/50/50)

PEA

Heavy duty liquid detergent mixture design space.

© 2006 by Taylor & Francis Group, LLC

Statistical Mixture Design for Optimization of Detergent Formulations

35

Cleaning performance was determined for different soil types and fabrics. Soils of interest included dirty motor oil (DMO), dust sebum (synthetic sebum/air conditioner filtrate), EMPA 101 and 104 (olive oil/carbon black, Eldgenossiche Materials Prufings Anstalt, St. Gall, Switzerland) and clay on both cotton and polyester/cotton fabrics. Dust sebum and clay soil swatches were obtained from Testfabrics (Testfabrics, Inc., West Pittston, Pennsylvania). DMO swatches were prepared using spent 10W40 motor oil. Each soil/fabric type combination was run in triplicate and the results were averaged to obtain the measured response data. Soil redeposition was assessed by including clean cotton and polyester/cotton swatches along with the standard soil swatches in the wash. Redeposition swatches were washed three times to determine the effect of multiple wash cycles. The optical reflectance of each soil swatch was measured before and after cleaning using a HunterLab Labscan XE reflectometer (HunterLab, Reston, Virginia). A 1-in.-diameter view port was used to average the reflectance over a wider area of fabric. An in-line ultraviolet (UV) filter was used to suppress any fluorescence effects, which could affect the measured reflectance. The reflectance was measured using the tristimulus L a b scale. The change in measured reflectance was used as a measure of the cleaning performance. For soil detergency, greater differences in reflectance indicate greater amount of soil removed from the fabric. Similarly, for soil redeposition, smaller changes in reflectance indicate smaller amounts of soil deposited on the clean fabric during the washing process. The actual mixture design and cleaning performance data are shown in Table 2. The design consisted of 12 trial formulations, which were run in standard order. The composition of each trial formulation is given as a percentage of the total surfactant in the formulation. The pH and viscosity averaged 11.5 and 27 cP, respectively. No attempt was made to adjust formulation viscosity because all of the detergency samples were charged by weight. The change in reflectance is the average of three different experiments. The raw detergency data was analyzed using Design-Expert 6 software (DesignExpert is a registered trademark of Stat-Ease, Inc., Minneapolis, Minnesota). The program analyzes the raw data using several different statistical models and data transformations to determine the empirical best fit for the data. The empirical best-fit model can be used to determine how each response factor changes as a function of surfactant composition either numerically or graphically. Graphical results can be viewed as a perturbation plot, a contour plot or a three-dimensional response surface. The contour plots generated by the Design-Expert software are shown in Fig. 5. The detergency results for cotton and polyester/cotton blends have been combined to obtain the total cleaning performance. Also included is the formulation cost given in dollars per pound of the finished detergent. For each response variable, a contour plot has been superimposed on the surface of the design space. Three of the responses are best represented using a linear model indicating little interaction between the individual components. The other three responses show interactions between the components and are best represented using a quadratic model. We can now examine each of the responses, one at a time. For dirty motor oil (DMO), cleaning performance on cotton is much better than on polyester/cotton. This is somewhat expected since motor oil is a hydrophobic material which would adhere more strongly to a hydrophobic substrate. A linear model gives the best fit of the experimental data. The cleaning performance increases with increasing concentration of nonionic surfactant and decreases with increasing concentration of NaLAS. L24-7 and PEA210 give about the same level of cleaning performance. For the ubiquitous ground-in clay, the cleaning performance is about the same on either cotton or polyester/cotton. A linear model gives the best representation of the experimental data. Clay detergency increases with increasing concentration of L24-7 in the formulation and decreases with increasing concentration of PEA210. Under alkaline

© 2006 by Taylor & Francis Group, LLC

36

Table 2 Heavy Duty Liquid (HDL) Detergent Mixture Design and Performance Data

RUN ORDER

1 2 3 4 5 6 7 8 9 10 11 12

NaLAS (%)

0.0 100.0 50.0 16.7 66.7 33.3 0.0 50.0 100.0 0.0 16.7 0.0

L24-7 (%)

0.0 0.0 0.0 16.7 16.7 33.3 50.0 50.0 0.0 100.0 66.7 0.0

PEA (%)

VISCOSITY (cps)

pH (as is)

COSTS ($/LB)

REDEP

DUST SEBUM

DMO

OLIVE OIL

CLAY

C

PC

C

PC

C

PC

C

PC

C

PC

100.0 0.0 50.0 66.7 16.7 33.3 50.0 0.0 0.0 0.0 16.7 100.0

8.6 19.0 9.0 6,4 36.8 10.8 10.0 112.0 19.0 68.0 24.6 4.4

11.3 11.9 11.7 11.7 11.8 11.7 11.0 11.8 11.8 10.8 11.4 10.9

0.20 0.09 0.15 0.17 0.12 0.14 0.16 0.10 0.09 0.11 0.13 0.20

-2.0 -1.4 -2.2 -2.2 -1.8 -1.8 -1.9 -1.5 -1.1 -2.2 -2.1 -2.0

-1.1 -15.7 -1.9 -1.3 -1.8 -1.3 -1.2 -1.6 -16.1 -1.0 -1.1 -0.9

25.0 25.2 25.5 25.4 25.6 26.0 26.1 26.6 24.8 26.0 26.2 25.3

9.0 2.0 6.0 7.3 6.2 7.6 9.4 6.0 1.9 7.3 7.4 10.0

15.1 11.0 14.0 14.1 13.8 13.7 15.0 13.9 11.5 14.1 14.4 14.2

15.6 3.4 12.4 13.7 9.8 11.3 14.2 9.8 2.9 11.6 12.3 15.3

15.9 15.9 13.8 15.0 14.1 13.8 16.2 14.0 14.2 14.5 14.2 16.6

24.7 19.6 18.2 21.3 18.7 19.6 22.1 18.7 19.8 21.4 19.5 23.1

12.1 13.9 13.6 12.5 14.1 14.0 13.0 13.4 14.1 14.2 13.2 13.2

13.6 14.5 15.7 15.6 16.4 15.9 15.6 16.0 17.0 20.9 21.5 21.7

AVE STDEV

27.4 32.0

11.5 0.4

0.1 0.0

-1.8 0.3

-3.7 5.7

25.6 0.5

6.7 2.5

13.7 1.3

11.0 4.1

14.9 1.0

20.6 2.0

13.4 0.7

17.0 2.8

Ashrawi and Smith

© 2006 by Taylor & Francis Group, LLC

Statistical Mixture Design for Optimization of Detergent Formulations NaLAS

NaLAS

37

NaLAS

29 0.11 30

Dirty Motor Oil

31

Formulation Costs ($/LB)

Clay 30

33 34 34

L24-7

0.17 0.19 PEA

L24-7

NaLAS

NaLAS −11.6 −9.0

19.8

33.3 32.7 32.5

−4.0 −3.2

Dust Sebum

Olive Oil

24.9 26.6

−1.9

−2.2

27.5

Figure 5

PEA

L24-7

32.7 33.3 34.7

28.9

36.1

−3.2 L24-7

PEA NaLAS

22.4

−6.5 Redeposition

0.15 27

33 PEA

L24-7

0.13

29

32

PEA

L24-7

37.4

38.8 PEA

Heavy duty liquid detergent response contour plots.

conditions, the clay particles carry a negative charge. It appears that the nitrogen atom in the PEA head group acts to neutralize some of this charge, thus reducing the amount of soil removed from the fabric. The concentration of anionic surfactant has little effect on the cleaning performance. There is no interaction observed between the surfactants. For dust sebum detergency, a quadratic model gives the best empirical fit of the experimental data. The cleaning performance on cotton is about the same as on polyester/cotton except at the higher levels of NaLAS, where it is much lower. Overall, cleaning performance increases with increasing concentration of PEA210 in the formulation. We hypothesize that the amine in the surfactant head group forms salts with the fatty acid in the soil, thus improving detergency. The model shows a slight synergy between the anionic (NaLAS) and the nonionic surfactants (L24-7 and PEA210) so that combination of the two gives better performance than either of the two pure surfactants. No interaction is observed between the two nonionic surfactants. For olive oil detergency, a quadratic model gives the best fit of the experimental data. Cleaning performance on polyester/cotton is higher than on cotton. Olive oil detergency increases with increasing concentration of PEA in the formulation. The model shows an antagonism between the anionic (NaLAS) and the nonionics (L24-7 and PEA210). Anionic to nonionic surfactant ratios of 3:1 give the worst cleaning performance. Considering soil redeposition, we find that a quadratic model provides the best fit of the experimental data. Redeposition on polyester/cotton is slightly higher on average than on cotton. Redeposition increases with increasing concentration of NaLAS in the formulation especially on polyester/cotton fabric. This result indicates that NaLAS is relatively poor at keeping soil suspended in the wash liquor after it has been removed form the fabric. There is a significant interaction between NaLAS and the two nonionic surfactants. A nonionic to anionic surfactant ratio of 3 to 1 gives the lowest amount of soil redeposition. © 2006 by Taylor & Francis Group, LLC

38

Ashrawi and Smith

For the cost ($/lb) of the finished formulation, a linear model gives an exact representation of the data. Formulation cost is a calculated value based on the price of the individual components, so it will always be a linear function. The formulation cost increases with increasing concentration of PEA210 since it has the highest raw material cost. The results from the various contour plots illustrate a common difficulty in detergent formulation work. Different types of surfactants are required to clean different types of soils. One of the most difficult tasks facing the formulator is determining the optimum surfactant ratio to achieve the best performance for a variety of different soil types. One of the features of mixture design experiments is the ability to simultaneously optimize each response to find compositions that give the best overall performance. Alternatively, a formulator could choose to favor particular performance criteria in order to support a desired marketing claim. The Design-Expert software provides both numerical and graphical optimization options where the user specifies the response factors and the performance criteria and the program identifies compositions that meet a defined level of performance. Results from a graphical optimization treatment are shown in Fig. 6. In the overlay plot, the darkly shaded area represents compositions that satisfy the defined performance criteria. The results from the optimization show that the best overall cleaning performance is obtained with mixtures that are rich in L24-7. The optimum ratio of L24-7 to PEA 210 is around 3:1. The model shows that only a small amount of LAS is needed to get the overall best performance. The size of the optimized region gives an indication of product robustness. In general, the larger the size of the optimized region, the more robust the formulation will be to small changes in product composition. While only a small amount of NaLAS was needed to optimize cleaning performance, the amount of NaLAS, in actual practice, needs to be at least 10% in order to provide viscosity building through the salt effect. This could have been demonstrated by including salt as a component in the mixture design experiments.

NaLAS

DMO REDEP Dust Sebum Clay $/LB Olive Oil

L24-7

PEA Overlay Plot

Figure 6

Heavy duty liquid detergent graphical optimization plot.

© 2006 by Taylor & Francis Group, LLC

Statistical Mixture Design for Optimization of Detergent Formulations

39

The optimization procedure is completely general. An unlimited number of response factors can be optimized. We can combine different types of response factors including performance, physical properties, and cost to arrive at the optimum formulation. Often several iterations of mixture designs are used. A broad design is used to identify the general composition; a second design then focuses on this region to elucidate the fine details of the optimized region. To help validate the model and compare performance to a commercial laundry detergent, a dose-response experiment was performed on the optimized HDL formulation. In this experiment, the ratio of surfactants was held constant and the total actives was varied from 5 to 30%. The cleaning performance as a function of surfactant actives was determined in the Terg pot along with a commercial HDL formulation of known surfactant actives. The total detergency for each sample was determined by summing the change in reflectance over each soil and fabric type. The dose-response curve is shown in Fig. 7. The solid points represent the total detergency scores for the optimized HDL formulation at five different actives levels. The star represents the performance of the commercial HDL. Because the commercial HDL gives lower performance than the optimized HDL, it is possible to get better performance at equal surfactant actives. Alternatively, it is possible to get equal cleaning performance at lower surfactant actives, which results in a raw material cost savings. B. Light Duty Liquid Detergent Optimization Another example of the usefulness of mixture design techniques is the formulation of a light duty liquid detergent (LDL). Our goal is to develop a high-active, premium liquid dish product with the lowest formulation cost possible. In this example, we look at using a combination of alkyl ether sulfate (AES), linear alkylbenzene sulfonate (LAS), linear alcohol ethoxylate (LAE), and fatty acid monoethanolamide (FAMA). Performance factors of interest include the total amount of foam, the persistence of the foam under a soil load, soil emulsification, and the formulation cost. Before we discuss the mixture design, we need to say a few words about surfactant selection. In this work, the sodium salt of a 3-mole ether sulfate based on C12–14 Ziegler fatty alcohol was used. The 30% active grade was used to avoid handling issues associated with the high-viscosity paste. In general, AES surfactants show good detergency, generate a large amount of foam and are relatively mild to the skin [23]. The latter is especially true when the ether sulfate is partially neutralized with magnesium. The magnesium salt is also more surface active than the sodium salt which results in better soil emulsification and cleaning performance [24].

Total Detergency

120 110 L24-7 = 70% PEA = 20% NaLAS = 10%

100 90 0%

10%

20%

30%

Surfactant Actives

Figure 7

Optimized heavy duty liquid detergent dose-response curve.

© 2006 by Taylor & Francis Group, LLC

40

Ashrawi and Smith

Linear alkylbenzene sulfonate (LAS) was used because it is inexpensive, is a moderate foamer and shows good detergency for oily types of soils. For this study, the triethanolamine (TEA) salt of a low 2-phenyl, low-tetralin LAS was used. While low 2phenyl LAS is not commonly used in liquid formulations, addition of a hydrotrope will increase its solubility. Propylene glycol and denatured alcohol are commonly used as hydrotropes in LDL formulations. LAS will also interact with calcium or magnesium ions to increase mildness and surface activity [25]. Linear alcohol ethoxylate (LAE) was used because it is inexpensive and shows good cleaning performance for greasy soils commonly encountered in hand dishwashing. In this work, a C12–14 Ziegler fatty alcohol was reacted with 7 Mol of ethylene oxide using a base catalyst. The structure of the material was confirmed using hydroxyl number titration and supercritical fluid chromatography. Fatty acid monoethanolamide (FAMA) was used as a foam booster. Foam boosters are known to improve the performance of LDL formulations by increasing foam volume and stabilizing the foam in the presence of food soils [26]. In this work, the C12–14 coconut fatty acid was reacted with monoethanolamine under dehydrating conditions. To reduce the melting point of the MEA amide and improve its handling characteristics, the reaction product was dissolved in an aqueous solution of sodium xylene sulfonate (SXS) to give a low-melting, 40%-active mixture. Until recently, it was common to use diethanolamine (DEA) amides in this type of formulation. DEA amides are liquid products whereas the MEA amides are hard waxy solids at room temperature. Concerns with nitrosamine formation in the DEA amides have largely limited their use in applications that require human contact [27]. Foam is one of the main performance criteria for an LDL formulation. Consumers equate foam and foam persistence with cleaning performance. So, more is always better. To produce large amounts of persistent foam, the formulation should be rich in anionic surfactant. Rather than look at the entire dimensional mixture space as we did in the case of the HDL, we concentrate on anionic-rich compositions and constrain the variables as shown in Table 3. AES and LAS were varied from 0 to 100% of the surfactant actives while the nonionics were limited from 0 to 20%. Because some of the components are constrained, a d-optimal mixture design was used. Each of the 16 trial formulations was prepared holding the total surfactant actives constant at 30%. To increase the solubility of the LAS and FAMA, 5% SD3A alcohol was added to each of the formulations. The amount of TEA in each formulation varied with the amount of LAS. In general, each formulation was prepared with sufficient TEA to give a pH in the range of 6 to 7. The amount of water in each formulation was varied to give 30%-active surfactant. The trial formulations were run in the standard order as randomized by the software. Several of the formulations were replicated to assess the degree of experimental error associated with measurement of the response factors. A number of response factors were examined including initial foam, foam under soil load, soil emulsification, and formulation costs. The initial foam was determined by diluting the concentrated samples to 0.2% surfactant active in 150 ppm hard water (Ca+2/Mg+2 = 2/1) and mixing the solution in a commercial Waring blender for 10 sec. Under the resulting high-shear conditions, a large amount of foam was generated. The contents of the Waring blender were then transferred to a 1000-ml graduated cylinder and the foam height measured. Since we are working with four formulation variables, it is not possible to view the entire response surface. The analyzed results for the mixture design model are most easily visualized using a perturbation plot. The perturbation plot in Fig. 8 shows how the initial foam changes as the concentration of each surfactant moves from the chosen reference

© 2006 by Taylor & Francis Group, LLC

Light Duty Liquid (LDL) Detergent Mixture Design and Performance Data

RUN ORDER

AES (%)

LAS (%)

LAE (%)

FAMA (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

0 0 20 0 45 0 30 0 70 60 80 100 0 20 50 45

80 80 60 60 45 80 30 80 0 20 0 0 100 50 20 45

10 0 15 20 10 0 20 20 20 5 0 0 0 15 15 0

10 20 5 20 0 20 20 0 10 15 20 0 0 15 15 10 AVE STDEV

TERGE (GMS SOIL0

INITIAL FOAM (ML)

FOAM WIHT SOIL (ML)

COSTS $/LB

30 35 30 39 30 25 34 18 28 39 30 30 16 35 37 30

400 425 425 320 500 460 375 420 475 500 575 600 500 425 450 450

225 225 240 230 275 225 240 240 300 275 310 340 290 250 240 280

0.173 0.191 0.182 0.186 0.198 0.191 0.213 0.156 0.234 0.236 0.263 0.250 0.160 0.198 0.225 0.216

30.3 6.5

456.3 70.0

261.6 35.1

0.2 0.0

Statistical Mixture Design for Optimization of Detergent Formulations

Table 3

41

© 2006 by Taylor & Francis Group, LLC

42

Ashrawi and Smith

A

600

530

B

Initial Foam

D

B

460

390

C

A

320 −0.417

−0.167

0.083

0.333

0.583

Deviation from Reference Blend Actual Components A: AES = 41.67 C: LAE = 8.33 B: LAS = 41.67 D: FAMA = 8.33

Figure 8

Liquid duty liquid detergent initial foam height perturbation plot.

point, while holding all other factors constant. By default, the software sets the reference point at the center of the design space but it is possible to view the results from any reference point within the design space. This is useful in determining the robustness of a formulation if the reference point is set at the optimized composition. Taking AES as an example, as we change the concentration of AES in the reference blend, the foam height varies from 400 to 600 ml. Overall, increasing the concentration of AES increases the foam height. This is the major effect in the model. As we change the concentration of LAS from the reference point, there is little change in the foam height. Increasing the concentration of either LAE or FAMA decreases the initial foam height. Using the perturbation plot as a tool to determine which components have the most effect on the measured response, it is possible to construct contour plots for slices of the response surface. Contour plots for a number of different response factors are shown in Fig. 9. The initial foam height ranges from 325 to 600 ml. A quadratic model best represents the initial foam data. The initial foam increases with increasing concentration of AES and decreases with increasing concentration of LAS. There is a slight antagonism between the foam booster and the anionic surfactants. Intermediate levels of FAMA give slightly lower foam heights. For perception reasons, a light duty liquid detergent must maintain foam in the presence of food soils. To study the effectiveness of different surfactants in the formulation, we examined foam in the presence of an artificial soil using a 0.2%-active solution prepared in 150 ppm hard water (Ca+2/Mg+2 = 2/1). Two grams of an artificial soil consisting of 12.5% egg powder, 37.5% vegetable shortening, and 50% 150 ppm hard water were added

© 2006 by Taylor & Francis Group, LLC

Statistical Mixture Design for Optimization of Detergent Formulations

43

AES

AES

306

527 492

Foam under Soil Load

Initial Foam

291

457 275 260 431 245

LAS

FAMA

FAMA

LAS

AES

AES 34

Formulation Costs ($/lb)

32

Soil Emulsification

0.2407 0.2262

29 0.2117

26

0.1972 23

LAS

Figure 9

0.1828

FAMA

LAS

FAMA

Light duty liquid detergent response contour plots.

to each solution and mixed for 10 sec in the Waring blender. With the addition of soil, the foam height was reduced to about half of the initial value. Foam height increased with increasing AES and decreased with increasing concentration of LAS. The foam height in the presence of soil decreased slightly with increasing concentration of FAMA. We also examined soil emulsification using the six-pot Tergtometer holding the temperature and water hardness constant at 110oF and 150 ppm (Ca+2/Mg+2 = 2/1). In the soil emulsification test, we determine the amount of soil required to dissipate a known volume of foam. Each of the trial formulations is diluted to 0.2% active surfactant, charged to a Terg pot, and suds are generated using a paddle impeller. To each Terg pot is pipetted 1 gram of artificial soil, every minute, until the suds dissipate. The grams of soil required to completely break the foam are recorded. The soil emulsification response shows a different trend than that observed for foam height. The amount of soil emulsified increased with increasing concentration of FAMA. The increase is greater for mixtures that are rich in AES. These results are quite informative. They help us understand the role of different surfactants in the formulation. The foam test measures the total volume of foam while the soil emulsification test measures the amount of soil required to completely break the foam. Anionic surfactants are responsible for producing large amounts of foam. AES produces more foam than LAS and the foam is more persistent under soil load. Nonionic surfactants are responsible for emulsifying soil and stabilizing the foam produced by the anionic surfactants in the formulation. FAMA is more effective than LAE at stabilizing the foam. To complete the mixture optimization, we examined the relative formulation costs. The cost of each formulation was calculated using surfactant raw material costs and the

© 2006 by Taylor & Francis Group, LLC

44

Ashrawi and Smith AES Initial Foam

Foam with Soil

Terge

Initial Foam

LAS

FAMA Overlay Plot LAE = 0

Figure 10

Light duty liquid detergent graphical optimization plot.

concentration in each trial formulation. The formulation costs increase most with increasing concentration of AES. This is not surprising since AES is the most expensive surfactant in the formulation. Formulation costs decrease with increasing concentration of LAS. LAE and FAMA do not have a large effect on the overall formulation cost since both surfactants were used at relatively low levels in the mixture. These results are similar to those observed for the HDL formulation. Performance increases with increasing concentration of AES but so do the formulation costs. To obtain the best cost performance, the response models can be optimized simultaneously as before. Results for this treatment are shown in Fig. 10. The optimization treatment shows LAE does little to increase performance. The results also indicate that it is not possible to obtain the optimum performance at the minimum formulation costs. Using performance as the main criteria, the optimum formulation is obtained for compositions rich in AES using FAMA as a foam stabilizer. To determine the amount of LAS which could be added before performance decreases dramatically and to validate the optimized formulation, experiments were performed varying the concentration of AES and LAS, holding the amount of FAMA constant. Results are given in Fig. 11. The initial foam decreases with increasing concentration of LAS in the formulation. At low levels of LAS, the foam height decreases only slightly. Above 40% LAS, the foam height decreases rapidly with increasing concentration. The inflection point represents the highest level of LAS, and the lowest formulation cost, before performance starts to fall off rapidly.

© 2006 by Taylor & Francis Group, LLC

Statistical Mixture Design for Optimization of Detergent Formulations

LAS + AES = 90% FAMA = 10% LAE = 0%

500

Foam Height (ml)

45

400

300

200

0

20

40

60

80

100

Percent LAS (LAS + AES = 100)

Figure 11

Optimized light duty liquid detergent initial foam plot.

C. Detergent Concentrate Robustness Study One last example involves the manufacture of a concentrated detergent blend developed for use in a heavy duty liquid (HDL) detergent. By preblending the ingredients, the customer avoids having to inventory and store separate components. Preblending also results in shorter production times since only one component must be charged versus many. To avoid shipping water, the concentration of the blend should be as high as possible. In this case, the blend contained 20% water to prevent the product from stratifying in the customer’s storage tanks. The composition of the blend was optimized using mixture design experiments as shown in previous examples. In order to manufacture the blend consistently, we must determine how small changes in the composition affect the physical properties. This information allows us to determine the amount of variability we can expect in the finished product and provides information on how best to correct production batches to meet product specifications. The blend is composed of the six components given in Table 4. Nonylphenol ethoxylate with 9.5 Mol of ethylene oxide (N-95) is the main component of the blend. In general, nonylphenol ethoxylates are excellent detergents due to their low cost, ease of handling, and good cleaning performance [28]. Linear alkylbenzene sulfonate (LAS) is used as the main anionic surfactant. Again we used a low 2-phenyl, low-tetralin grade with an average carbon chain length of 13. Tallowamine ethoxylate with 15 Mol of ethylene oxide (T-15) is used as a secondary nonionic surfactant. T-15 has properties similar to the polyetheramine surfactant described previously [29]. Because the nitrogen atom in the surfactant head group is basic, T-15 acts to neutralize some of the LAS in the formulation. On a molar basis, the amount of T-15 is insufficient to neutralize all of the LAS so MEA is used to fully neutralize the LAS in the formulation. Polyethylene glycol with a molecular weight of 300 (PEG 300) is added to reduce formulation viscosity and to prevent gel phase formation when the blend is diluted down to use concentration. Water is added to reduce blend viscosity and prevent stratification of the blend in storage. Because we are interested in how changes in the blend ratio affect the physical properties, all of the component ranges were constrained. The blend has six components,

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Table 4

Concentrated Detergent Blend Mixture Design and Physical Properties MEA (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27

15.4 15.4 17.2 15.4 19.4 15.4 19.4 19.4 19.4 17.2 19.4 19.4 17.4 19.4 15.4 15.4 19.4 15.4 15.4 15.4 19.4 19.4 17.4 15.4 18.5 19.4 17.6

2.2 2.2 2.6 2.6 2.2 2.2 2.2 2.4 2.6 2.6 2.6 2.2 2.4 2.2 2.6 2.2 2.2 2.6 2.2 2.2 2.4 2.4 2.4 2.6 2.2 2.6 2.2

PEG 300 (%)

T-15 (%)

N-9.5 (%)

WATER (%)

ACIDITY (meq/gm)

pH (1%)

SOLIDS (%)

8.1 10.0 10.0 10.0 8.2 10.0 6.0 8.0 7.9 10.0 6.0 6.0 6.0 8.1 6.0 8.2 6.0 7.8 6.0 10.0 10.0 6.0 8.0 7.8 10.0 7.8 6.0

17.5 19.4 15.4 15.4 19.4 17.6 17.5 15.4 15.4 19.4 19.4 17.6 15.4 17.5 17.2 15.4 15.4 19.4 19.4 19.4 17.4 19.4 17.4 19.4 15.4 15.4 19.4

36.8 35.0 36.8 34.6 32.8 32.8 34.9 36.8 34.7 32.8 34.6 32.8 36.8 34.9 36.8 36.8 36.8 32.8 35.0 35.0 32.8 32.8 34.8 36.8 32.8 32.8 36.8

20.1 18.0 18.0 22.0 18.0 22.0 20.1 18.0 19.9 18.0 18.0 22.0 22.0 18.0 22.0 22.0 20,2 22.0 22.0 18.0 18.0 20.0 20.0 18.0 21.1 22.0 18.0

0.48 0.49 0.55 0.49 0.62 0.49 0.62 0.62 1.32 0.55 0.61 0.62 0.55 0.62 0.49 0.49 0.61 0.49 0.49 0.49 0.62 0.62 0.55 0.49 0.58 0.62 0.56

8.9 8.9 8.6 9.0 3.5 8.7 3.4 3.5 4.0 8.9 8.0 3.5 7.9 3.4 9.0 8.5 3.3 9.1 8.8 8.8 3.5 4.2 8.4 9.1 3.5 4.1 7.5

78.0 82.0 82.0 78.0 82.0 78.0 80.0 82.0 80.0 82.0 82.0 78.0 78.0 81.0 78.0 78.0 79.0 77.0 78.0 82.0 82.0 80.0 80.0 82.0 79.0 78.0 82.0

AVE STDEV

© 2006 by Taylor & Francis Group, LLC

0.58 0.2

6.6 2.5

79.9 1.8

VISCOSITY (gm/ml)

577 497 460 428 550 526 11300 589 577 442 561 12900 3860 580 515 538 10760 578 563 504 532 10900 579 532 580 5880 548

2475 4013

DENSITY (gm/ml)

COLOR (GARDNER)

1.0646 1.0668 1.0678 1.0663 1.0665 1.0660 1.0650 1.0668 1.0658 1.0663 1.0650 1.0609 1.0642 1.0648 1.0630 1.0654 1.0663 1.0628 1.0629 1.0669 1.0679 1.0634 1.0658 1.0610 1.0593 1.0612 1.0630

5 5 4 4 4 4 3 3 3 5 5 3 4 3 4 4 3 5 5 5 3 4 5 5 3 4 5

1.065 0.002

4.1 0.8

Ashrawi and Smith

LAS (%)

46

RUN ORDER

Statistical Mixture Design for Optimization of Detergent Formulations

47

which requires 27 trial formulations using a d-optimal mixture design. In general, the constraints are based on the accuracy to which the plant can charge individual components. For N-95 LAS, PEG 300, T-15, and water, the constraint is ±2 weight percent using load cells to charge the mixing vessel. For MEA, the constraint was ±0.2 weight percent using a micro-motion flow controller. Each of the 27 trial formulations was prepared and the physical properties measured. Physical property responses included acidity, pH, nonvolatiles, viscosity, and color. Because we have six components it is impossible to view the response surface for this design. To determine which variables are important, we use perturbation plots. For pH of the blend, the main factors are LAS, MEA, and T-15. Since LAS is a strong acid, whereas MEA and T-15 are weak bases, this is not unexpected. The contour plot for pH with respect to the three main components is given in Fig. 12. The pH varies from 3.5 to 9 depending on the ratio of the three components. MEA is more effective at increasing pH than T-15 since it has a lower molecular weight and is a stronger base. Formulation nonvolatiles were measured using a moisture balance (Denver Instruments, Arvada, CO) at 140oC. Solids varied from 77 to 82% depending to a large extent on the amount of water in the formulation. Surprisingly, the ratio of MEA to LAS also has a small effect. Formation of the MEA/LAS salt reduces the volatility of MEA and increases the measured solids. The color of each trial formulation was measured with a HunterLab ColorQUEST II spectrophotometer (HunterLab, Reston, Virginia) using the Gardner scale. The color of the blend varies from 3 to 5 depending on the amount of LAS, MEA, and T-15 in the mixture. The color increases most with the amount of T-15 in the mixture, in general,

LAS Acid

LAS Acid 4.9

81.6

Solids pH (1%)

79.8

6.8

Color (gardner) LAS Acid = 19.6

7.8

PEG 300 = 8 N-9.5 = 34.8 WATER = 20 MEA

79.3

3.3

8.7

T-15

PEG 300 = 8 T-15 = 17.4 N-9.5 = 34.8

3.7 3.9

LAS Acid

78.7

MEA

4.1

Water LAS Acid

Viscosity (cps)

MEA = 2.4 T-15 = 17.4 N-9.5 = 34.8

80.9

5.9

4.3

PEG 300 = 8 N-9.5 = 34.8 Water = 20

7531 5854 4178 2502

Acidity (meq/gm)

4.5 4.9

0.67 0.63 0.59

MEA = 6.4

T-15 = 19.6

826 0.55 826

PEG 300 = 8 N-9.5 = 34.8 Water = 20

2502

Water

PEG 300 MEA

Figure 12

Concentrated detergent blend response contour plots.

© 2006 by Taylor & Francis Group, LLC

0.52

T-15

48

Ashrawi and Smith

Table 5 Optimized Concentrated Detergent Product Specifications Specifications pH, 1% SOLUTION SOLIDS (%) VISCOSITY (cps @ RT) LVT#2 @ 30 RPM ---COMPOSITION, WT%

C C C

LOADING MEASURE

Min

Max

Target

7.5 77 1

9.5 82 1000

8.5 80 575

Min

Max

Typical 0–1 3–7

C

LAS ACID MEA POGOL 300 SURFONIC T-15 SURFONIC N-95 WATER TYPI

Additional Information: ACID VALUE (meq/gm) COLOR, GARDNER, PT-CO APPEARANCE

CLEAR, AMBER LIQUID

tallowamine ethoxylates tend to be amber in color so this is not too surprising. The color decreases with increasing concentration of LAS but also depends on the amount of MEA in the mixture. It appears that the color of the LAS increases with increasing level of neutralization. The viscosity of each trial formulation was measured with a Brookfield LVT viscometer using a #2 LVT spindle (Brookfield Engineering Laboratories, Middleboro, MA) at 25oC. The viscosity varies from 440 to 13,000 cP depending primarily on the amount of LAS, water, and PEG 300 in the mixture. In general, viscosity increases with increasing concentration of LAS and decreases with increasing concentration of water and PEG 300 in the mixture. PEG 300 is more effective at reducing the viscosity than water. There is a slight interaction between LAS and PEG 300, which acts to further reduce viscosity at intermediate levels of both components. Acidity was determined by titration of each trial formulation with a strong base. The acidity of the blend provides a consistency check that the acidic (LAS) and basic (T15 and MEA) components of the blend are present in the correct ratio. Acidity increases with increasing concentration of LAS and decreases with increasing concentration of MEA and T-15. This response is very nearly the same as pH. MEA is more effective at decreasing acidity that T-15 because of its lower molecular weight. The results for each of the models are used to set product specification ranges. These must be wide enough to account for small changes in the ratio of the different components. In addition, the model provides a tool for manufacturing personnel to use in adjusting production batches to meet specifications. The proposed manufacturing specifications are given in Table 5. The pH, solids and viscosity are all primary product specifications along

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Statistical Mixture Design for Optimization of Detergent Formulations

49

with the loading measure for each component. All of these properties appear on the certificate of analysis. Additional tests which are measured but not reported include acidity, color and appearance of the blend. The specification range for each property was set wide enough to cover the variability seen in the mixture design.

IV. CONCLUSIONS Experimental mixture design can be used to optimize detergent cleaning formulations. The method is simple, fast, and greatly reduces the amount of work required to optimize detergent formulations. The results can be used to predict behavior for mixtures within the design space. Mixture design experiments can also be used to determine the robustness of a formulation prior to scale-up and manufacture. Setting appropriate specification ranges to cover the variability observed from small changes in the mixture ratios can reduce cycle times in the manufacturing of the product. The information from the robustness study can also be used to adjust batches as needed to meet the product specifications.

REFERENCES 1. SS Ashrawi, GA Smith. Use of experimental mixture design to optimize cleaning formulations. Proceeding of the 5th World Surfactants Congress, Florence, Italy, 2000, pp. 1253–1261. 2. SS Ashrawi, CM Elsik, HM Stridde, GA Smith. Strategies for agricultural formulations: a statistical design approach. In: Pesticide Formulations and Application Systems: A New Century for Agicultural Formulations, Vol. 21, ASTM STP 1414, JC Mueninghoff, AK Viets, and RA Downer, Eds., American Society for Testing and Materials, West Conshohocken, PA, 2001. 3. J Cornell. In: S. Ghosh, Ed. Statistical Design and Analysis of Industrial Experiments. New York: Marcel Dekker, 1990, pp. 175–209. 4. J Cornell. Experiments with Mixtures: Designs, Models, and the Analysis of Mixture Data. New York: John Wiley & Sons, 1981. 5. GEP Box, WG Hunter, JS Hunter. Statistics for Experimenters. New York: John Wiley & Sons, 1978. 6. H Scheffé. J Royal Statist Soc B 20:344–360, 1958. 7. H Scheffé. J Royal Statist Soc B 25:235–263, 1963. 8. PR Adby, MAH Dempster. Introduction to Optimization Methods. London: Chapman and Hall, 1974. 9. J Coret, A Shiloach, P Berger, D Blankschtein. J Surfactants Deterg 2(1): pp 51–58, 1999. 10. G Marti-Mestres, F Nielloud, R Marti, H Maillols. Drug Dev Ind Pharm 23(10): 993–998, 1997. 11. C Verite. Utilization of the simplex experimental design for optimization of a low foaming household detergent. Phys Chem Snwendungstech Grenzflaechenaktiven Stoffe Int Kongr, 1973, pp 203–212. 12. JP Narcy, J Renaud. J Am Chem Soc 49:598–608, 1972. 13. R Pi. Comun Horn Com Esp Deterg 25: pp 267-279, 1994. 14. JC Drozd, W Gorman. J Am Oil Chem Soc 65: 398–404, 1988. 15. KL Matheson, TP Matson. J Am Oil Chem Soc 69: 1693–1609, 1983. 16. DL Smith. J Am Oil Chem Soc 74: 837–845, 1997. 17. L Cohen, R Vergara, A Moreno, JL Berna. J Am Oil Chem Soc 72: 115–122, 1995. 18. MF Cox, DL Smith. Inform 8: 19–24, 1997.

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Ashrawi and Smith 19. MJ Schick. In: MJ Schick, ed. Nonionic Surfactants: Physical Chemistry. New York: Marcel Dekker, 1987, pp. 753–833. 20. MF Cox. J Am Chem Soc 66: 367–371, 1989. 21. E Garcia, R Smadi, GA Smith. Physical chemical characterization of ethoxylated polyetheramine surfactants. Proceedings of the 5th World Surfactant Congress, Florence, Italy, 2000, pp. 1341–1348. 22. ASTM D-459, West Conshohocken, Pennsylvania. 23. MF Cox. J Am Oil Chem Soc 66: 1637–1646, 1989. 24. MJ Schwuger. J Am Chem Soc 59: 265, 1982. 25. L Cohen, A Moreno, JL Berna. Tenside Surf Det 35: 265–269, 1998. 26. FE Friedli. In: JM Richmond, Ed. Cationic Surfactants: Organic Chemistry. New York: Marcel Dekker, 1990, pp. 51–99. 27. HM Fishman. HAPPI 45, April 2001. 28. KW Dillan, ED Goddard, DA McKenzie. J Am Chem Soc 57: 230–237, 1980. 29. A Shoaib. HAPPI 67–72, February 1997.

© 2006 by Taylor & Francis Group, LLC

3 Laundry Detergent Formulations Randall A. Watson

CONTENTS I.

II. III.

IV.

V.

Introduction ............................................................................................................. 52 A. Scope of Chapter......................................................................................... 52 B. Why Different Forms? ................................................................................ 52 Unifying Formulation Concepts.............................................................................. 54 Typical Laundry Detergent Ingredients .................................................................. 56 A. Surfactants ................................................................................................... 56 1. Anionic Surfactants ............................................................................... 56 2. Nonionic Surfactants ............................................................................. 56 3. Cationic Surfactants............................................................................... 58 4. Others..................................................................................................... 58 B. Builders........................................................................................................ 58 C. Polymers ...................................................................................................... 59 D. Enzymes ...................................................................................................... 61 E. Bleach .......................................................................................................... 62 F. Chelating Agents ......................................................................................... 63 G. Perfumes ...................................................................................................... 63 H. “Minors” ...................................................................................................... 65 Heavy Duty Granules.............................................................................................. 66 A. Phosphate vs. Nil-Phosphate....................................................................... 67 B. Low Density vs. High Density ................................................................... 69 C. Machine Wash vs. Handwash ..................................................................... 70 Heavy Duty Liquids ................................................................................................ 71 A. Isotropic Liquids ......................................................................................... 71 B. Structured Liquids ....................................................................................... 76 C. Bleach-Containing Liquids ......................................................................... 79 D. Dual-Bottle Liquids..................................................................................... 81

51

© 2006 by Taylor & Francis Group, LLC

52

Watson

VI.

Unit Dose Detergents............................................................................................. 82 A. Tablets.......................................................................................................... 82 B. Liqui-Tabs.................................................................................................... 87 C. Sheets........................................................................................................... 89 VII. Laundry Bars ........................................................................................................... 90 VIII. Specialty Detergents................................................................................................ 93 A. Care Formulas ............................................................................................. 94 B. 2-in-1 Detergents......................................................................................... 96 IX. Summary.................................................................................................................. 99 Acknowledgments........................................................................................................... 100 References ....................................................................................................................... 100

I. INTRODUCTION A. Scope of Chapter A chapter on laundry detergent formulations would have been significantly shorter and less complex a few decades ago. It wasn’t so long ago that the same basic detergent was used for clothes, dishes, floors, and even the body! In the search for ever better cleaning and value, and larger market shares, there has been an incredible multiplication of laundry detergents. Not all of the forms and formulations are available or relevant in every market. Nonetheless, today in most markets the choices presented to consumers in the laundry detergent section of their local store is nothing short of bewildering. Likewise, the number of choices and demands faced by the detergent formulator continues to grow. This chapter is designed to first present the logic behind the plethora of laundry detergent forms and formulations. Despite the growing diversity of forms and formulas, the underlying chemistry and general concepts remain essentially unchanged. A brief discussion of the key unifying formulation concepts is therefore presented, along with a brief description of the key ingredients used in these formulations. The bulk of this chapter is devoted to discussion and examples of each of the key laundry detergent forms available today. Some general conclusions and discussion of future trends closes the chapter. The reader will appreciate that each of the topics covered in this chapter could be, and in many cases are, the subject of entire chapters or books in and of themselves. As such, it is not the aim of this chapter to provide an exhaustive discussion of each topic. Rather, it is intended to provide an overview of the many different products and product forms that fall generally under the heading of “home laundry detergent.” For those looking for still more details, the references will direct them to more in-depth reviews. B. Why Different Forms? The number of different laundry products and types available today is nothing short of remarkable. So is the level of effort from the large number of different formulators in different companies around the world. On one level the reason for this is clear. Consumers have become more demanding and more discriminating in their purchases of all types of consumer goods. They are also looking for more and more customization. “One size fits all” no longer works in much of the world. These trends are also reflected in laundry products. As companies have responded to these new consumer demands they have also realized that the company who best meets their needs can reap rich rewards. Why there should be so many different formulas and forms is perhaps less obvious, though for most there are equally clear answers. These answers are usually related to differences in con-

© 2006 by Taylor & Francis Group, LLC

Laundry Detergent Formulations

53

sumer habits and wash conditions, differences in the targeted benefits, and differences in consumer preferences. Different laundry habits and conditions are the most obvious reasons for different laundry formulations. Wash conditions range in concentration from several thousand ppm of detergent in the typical European front-loading washing machine, to only a few hundred ppm in Japanese machines. These same two countries also illustrate the extremes in wash temperatures. Though the average washing temperature is falling everywhere in the world due to energy and environmental concerns, the typical front loading machine still includes a boil-wash cycle. On the other hand, in Japan and several others countries consumers often use ambient wash-water temperatures, meaning that in the winter the wash can be as low as 2°C. Add onto these variations the differences in wash/rinse times—where in a U.S. top-loading machine it can be as short as 12 minutes and in a European front loader as long as almost 2 hours—and one can easily see the challenge. Of course many consumers in the world don’t even use washing machines. When considering the various ways that handwash laundry is executed around the world the variables multiply even more. One of the more interesting variables the formulator encounters in handwash laundry is the reuse of the laundry liquor for more than one load. This is done both to conserve often-precious water supplies, and to stretch the value of their detergent purchase. In this situation consumers often start with a load of whites and then reuse the wash solution for one or more loads of their colored or more delicate items. Providing good performance throughout this habit is extremely challenging. Also, hand washers can spend several hours each week with their hands immersed in laundry liquors. Hand skin mildness is therefore another concern largely absent from machine wash geographies. Even within a given laundry habit, a single detergent formulation that can work for all clothes under all conditions remains unobtainable. The same formulation that delivers superior dingy cleaning and whiteness can result in unacceptable fading of colored garments. In a similar vein, formulas containing protease enzymes provide superior stain removal, but can prove disastrous when used to wash fine wool or silk garments. For formulas that deliver through-the-wash softening via clay, the challenge is to provide acceptable base cleaning while still depositing enough softening clay for a benefit. These are just a few of the many dichotomous challenges faced by the formulator. The result is a number of detergents formulated specifically against targets such as softness, delicate care items, brightly colored items, etc.

Table 1

Average Global Machine Wash Conditions

Wash water volume (L) Washing Time (min) –Total wash cycle –Main wash duration Ave. wash temp. (˚C) Water Hardness Detergent Concentration (ppm)

© 2006 by Taylor & Francis Group, LLC

Europe

North America

Japan

13

64

49

115a 75a aLong cycle 40–90 2.5 mmol 5000–7500

35 12

na 10

10–45 1.0 mmol 1200–2000

4–20 0.5 mmol 600–1000

54

Watson

Table 2 Representative Global Handwash Conditions

Wash water volume (L) Washing time (min) - Soak - Wash Duration Avg. wash temp. (˚C) Water hardness Detergent concentration (ppm)

Russia

Brazil

China

India

24

20

5

4.5

— 24 40 2.5 mmol 8300

22 n/a 22 0.3 mmol 4000

10 10 25 1.4 mmol 4800

30 n/a 25 0.5–3.4mmol 5555

Note: n/a, not applicable.

A final driver for multiple laundry formulations is consumers’ preferences themselves. Some prefer granular detergents and others liquids. Still others, at least in the handwash world, prefer bars or pastes. Some want to be able to adjust their dosage freely and others prefer the simplicity of predetermined doses as found in laundry tablets or liquitabs. But perhaps the best example is odor. There are those consumers who want as much perfume odor on their clothes as possible, as well as those who will go to great lengths to avoid perfume altogether. Likewise, not every scent pleases every consumer, so often you can find the exact same cleaning formula sold under the same brand name, but in multiple scent variations. There are also consumers who have real or perceived skin sensitivity to perfumes, dyes or enzymes, and for these consumers “free” products are available that contain none of these items.

II. UNIFYING FORMULATION CONCEPTS The key, unifying concept of all the different forms and formulations is that consumers expect their laundry detergent to clean their clothes. As such, the underlying chemistry of detergents is, not unexpectedly, quite similar. With a few exceptions that have been touched on above and will be discussed later, their primary job is the same—clean clothes. Briefly, following the laundry mechanism laid out by Venegas [1], all detergents in one way or another need to: (1) hydrate the soil, (2) remove the soil from the fabric, (3) fragment the soil to aid suspension, (4) prevent the redeposition of said soils, (5) bleach any residual soils to lessen their visual impact, and (6) provide any final modification to the fabric as desired (e.g., deposit perfume, brighteners, etc.). The general approach to meeting these needs looks quite similar in all detergents. In all cases one or more surfactants provide the primary wetting and soil removal power (excluding the very large impact of water via machine or hand agitation alone). Surfactants provide the basis and bulwark of the cleaning power as illustrated in Figure 1 [2]. Builders of one sort or another are included to protect anionic surfactant from precipitation as calcium salts, aid in removal of calcium sensitive soils like clay and particulate soils, and depending on the builder, aid in peptization and suspension of soils. Very few if any detergents exist that lack one or the other of these two actives.

© 2006 by Taylor & Francis Group, LLC

Laundry Detergent Formulations

55

Performance Contribution to Detergency 40

% Contribution

35 30 25 20 15 10 5 0 Surfactant

Figure 1

Bleach

Polymer

Builder

Enzyme

Relative Contribution of Actives to the Cleaning Process.

The actual selection of surfactant(s) and builder and their relative ratios can vary widely however. The level of cleaning and overall price desired largely determines the presence and level of additional actives besides surfactant and builder. In less expensive, more basic detergents there may be nothing additional besides a buffer system to maintain pH and some level of perfume. In top-tier, flagship detergents, typically one or more enzymes, soil suspension polymers, and/or bleaching agents are also added. There are a number of variants of each available to the formulator (see below). The exact choice and number is often dictated by questions of availability of proprietary materials, mutual compatibility with other actives present in the detergent, and the particular role the detergent is designed for. Technologies that work very well in one habit or in one form may not work at all in another. An obvious example is heavy duty granules (HDG) vs. heavy duty liquids (HDL), where there is a big difference in the actual wash pH. While both commonly use a protease enzyme, they must use different strains of the enzyme to obtain maximum activity at wash pH. The kinetics can also be vastly different between habits. In the short, cool wash cycles of Japan or North America, only technologies that work very quickly are useful. In the longer, warmer, European wash cycle the kinetics are still important, though not to the same degree. This difference can often be observed in the chain length of surfactants used, and also accounts for the relative efficiency of some builders in each habit. Regardless of the form, for a detergent whose focus is primarily cleaning you can expect to see surfactant and builder at the core, with one or more cleaning adjuncts added to boost the performance further and some level of perfume. The exception to this is those detergents that are designed to deliver a different primary benefit, plus a base level of cleaning. Examples of this include 2-in-1 detergents, which seek to soften clothes as they clean, and color-care or fabric-care detergents that strive to maintain the look and feel of clothing as close to the original, store-bought, appearance as possible. In these cases the formulator is often forced to make tradeoffs in absolute cleaning (either for cost or chemical reasons) to facilitate delivering these benefits. More will be said about this in the section on specialty detergents (Section VIII).

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III. TYPICAL LAUNDRY DETERGENT INGREDIENTS A. Surfactants A number of excellent reference works are available covering every aspect of surfactant chemistry and use [3]. Today’s formulator has an extensive pallet of surfactants to choose from. What surfactant is chosen, and what level is used in product, is determined by a number of different factors. These include cost and supply availability of course. Additional requirements are often dictated by machine type and wash conditions, compatibility with the rest of the formulation, concerns with mildness where handwash is involved, and existing local regulations regarding biodegradability, to name a few. 1. Anionic Surfactants Anionic surfactants, especially the sulfates and sulfonates, dominate laundry detergent formulations. Their ready supply, generally low cost, and excellent performance make them a clear choice [4]. Linear alkylbenzene sulfonate (LAS) remains the most important of the anionic surfactants. When used as the sole surfactant it suffers due to its hardness sensitivity and generally poor surface activity. As a result LAS is usually formulated along with a lower level of cosurfactant to ameliorate these weaknesses. A recent interesting development involves introducing a mono-methyl substitution in the alkyl chain and increasing the percentage of terminal-phenyl isomers to nearly 100%. [5] This has the effect of improving the overall surface activity and eliminating the internal phenyl isomers that are most responsible for the hardness sensitivity of LAS. The alcohol sulfates and alcohol ether sulfates account for most of the remaining anionic surfactants in common detergent usage. The ether sulfates in particular are useful for boosting the hardness tolerance of LAS containing systems. They also have the benefit (or issue, depending on your point of view) of being high foaming. Other sulfates and sulfonates such as secondary alkane sulfonates, and sulfo fatty acid esters (e.g., MES) [6], are also known, but are currently less widely used. Methyl substituted versions of AS and AES, similar to the methyl-substituted LAS discussed above, have also been developed [7]. There are several other anionic surfactants known (e.g., phosphate esters, sulfosuccinates, taurates, isethionates, carboxylates), but aside from the simplest of the carboxylates—soap—they are seldom widely used. Soap is sensitive to low pH, and to polyvalent cations such as calcium, and hence is not used much as the primary surfactant in laundry detergents. Having said that, in situations where these factors can be controlled, soap provides excellent cleaning properties. In Japan, for instance, soap bars represent the gold standard for collar and cuff soil removal. Figure 2 presents exemplary structures of common surfactants in detergents. 2. Nonionic Surfactants Almost by definition nonionic surfactants [8] are insensitive to hardness ions. As such they can make excellent cosurfactants with anionics as discussed above. They also have the advantage of being relatively mild toward dyes and delicate fabrics, making them good candidates for color-care or delicate garment formulations. Nonionics are generally kinetically slower than anionics though, sometimes limiting their cleaning contribution in shortwash cycle, cold water conditions. Alcohol ethoxylates are by far the most important of the nonionic surfactants. By proper balance of the alkyl chain length with the number of ethoxy groups a wide range of surfactants with varying properties is possible. As a result, interaction and compatibility

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Linear Alkylbenzene Sulfonate (LAS) (CH2)x

H3C

CH

(CH2)y

CH3

SO3Na Alcohol ether sulfate (AES) O(CH2CH2O)xSO3Na Alcohol sulfate (AS) OSO3Na Alcohol ethoxylated (AE) O(CH2CH2O)xH Alkyl N-methyl glucose amide O R

OH

OH OH

N CH3

OH

OH

Alkyl dimethyl hydroxyethyl ammonium chloride CH3Cl− R

N+

(CH2CH2)OH

CH3 Alkyl dimethyl amine oxide

CH3 N

O

CH3

Figure 2

Exemplary Structures of Common Surfactants in Detergents

with other surfactants and detergent actives, overall performance for a given wash condition, and stain removal performance on various soils, can be accurately optimized. Versions using an alkyl phenol instead of a simple alcohol are known to provide even better performance, but environmental concerns have limited their use in household products. There are other important nonionics as well, though their significantly higher cost and lower supply availability limit the actual volumes used. Included here are amine oxides, alkanolamides, EO/PO block copolymers, and various surfactants made from polysaccharides. Amine oxides are often used as suds boosters, and can sometimes play a similar role in surfactancy as cationic surfactants.

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3. Cationic Surfactants Cationic surfactants [9] present a series of different opportunities and challenges to the formulator. Since most fabric surfaces and many soils are negatively charged at wash pH, cationic surfactants have a natural affinity and can build up in significant amounts. This can be a positive or a negative depending on the desired outcome. Likewise, the interaction of cationics with anionic surfactants is important (formulating a laundry detergent with all cationic surfactants is not done). When used at the right ratio cationics can significantly boost the cleaning power of an anionic surfactant like LAS. Use at too high a level results in precipitation and loss of both. The most common cationic surfactants are quaternized ammonium compounds. These can be as simple as a single alkyl chain of typical detergent length, along with three methyl groups on the nitrogen. Others incorporate various levels of ethoxylation on the nitrogen along with methyl groups. These quaternary compounds are often referred to as “true quats.” Regardless of the pH of the wash solution they remain cationic. A “pseudoquat” then, is a surfactant like an alkyl amine, which becomes protonated below it’s pKa and behaves as a quat. Above its pKa it is a neutral surfactant. Materials like this can be important, for example, in heavy duty liquids where formulating a true quat along with anionic surfactant can pose significant formula stability issues. 4. Others The simple classification of anionic, cationic, and nonionic above easily captures the lion’s share of surfactants actually used in laundry detergent formulations today. There are also amphoteric surfactants [10] like the betaines and sultaines that are also used occasionally. There are some specialty surfactants like the chelating surfactant N-acyl ED3A marketed by Hampshire Chemical (Nashua, NH) [11], and short-chain surfactants that are more often used as hydrotropes, though they can provide good cleaning benefits if present in high enough concentration as in a specialty pretreater. Research continues as well on Gemini, twin-tail surfactants, on polymeric surfactants, and others. To date none of these new developments offers a suitable cost/performance value to be used extensively in laundry detergents. B. Builders The primary role of builders in a laundry detergent is sequestering calcium and magnesium ions. All other considerations are secondary. There are numerous reasons why this is important, not the least of which is that calcium and magnesium lead to precipitation of anionic surfactants, or help form multilamellar vesicles, both situations leading to significant loss of performance. Both the rate of sequestration and the absolute capacity for sequestration are important considerations in the choice of builder. Beyond removal of hardness ions, builders can also play a variety of additional roles. Depending on the builder they can also provide dispersancy and peptization of soils, can serve as a source of alkalinity, and in granular and tablet detergents can be important carriers of other organic actives in the formula. The number of practically important builders for laundry detergents remains relatively small [12]. Sodium tripolyphosphate (STPP) is the standard by which all other builders are measured. It delivers rapid sequestration of hardness ions while also serving as an excellent peptization and soil suspension agent. It is also inexpensive, readily available and easy to formulate in a granular product (isotropic liquid products are a different matter as discussed later in this chapter). Today it is largely limited in use to handwash countries due to concerns over its role in eutrophication of waterways. As a result of these concerns, the development and use of a variety of substitutes has ensued.

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Zeolites, primarily Zeolite A and Zeolite MAP, are the primary replacement for STPP in granular detergents today. Like STPP, Zeolite A is readily available and relatively cheap, and it has high capacity for calcium ions. The primary drawback of zeolite builders is that they are kinetically slower in the uptake of calcium (something that becomes more and more important as wash temperatures and wash times decrease), and are relatively ineffective in removal of magnesium. Also, because they are insoluble, concerns with deposition and buildup on fabrics is also always present. Recent work [13] has looked at reducing the primary particle size of the zeolite in an attempt to increase the rate of calcium ion exchange, but as of this writing it is not yet commercially common. Builders based on carboxylic acids become more important for liquid detergents than granular ones, but they are used in both. The simplest form of this type of builder is soap. In liquid detergents, fatty acids sometimes represent the only builder present in the formula. Citric acid is also an effective carboxylate builder, used most often in liquid detergents. Polycarboxylate polymers are effective dispersants that also deliver some building power. Use is largely limited to granules due to formulatability concerns in liquids. Amino carboxylic acids, like nitrilo triacetic acid (NTA), are excellent builders, though their use is limited by toxicological concerns. Other builders include amorphous silicates, materials common in granular detergents as a source of alkalinity and as anticorrosion aids. Layered silicates are a more recent development used in some markets. Calcium carbonate is ubiquitous in granular detergents and tablets, and its role as a builder is sometimes overlooked. By forming insoluble calcium carbonate it efficiently removes calcium from solution, but brings with it the concern of inorganic encrustation of fabrics. As often as not, this trait of carbonate is viewed more as a liability in detergents than as a positive. C. Polymers The use of polymers has increased as detergent formulations have evolved. Initially, as phosphate use was curtailed, the focus was on polyacrylate-type polymers with the goal of replacing some of the lost building and dispersancy power of STPP. Carboxymethyl cellulose is another of the oldest polymers and represents one of earlier attempts at soil release. From these successful beginnings, a large number of polymers for a variety of purposes have emerged [14]. Several new dispersants have been commercialized, as have polymers for dye transfer inhibition, soil release and soil repulsion, for structuring liquid detergents and for aiding dissolution of tablets. For every new polymer actually commercialized there are myriad additional ones patented, attesting to the level of interest in the area. Dispersancy and soil removal remains the primary role of polymers today [15]. The choice of dispersant is governed by a number of factors. The formulator must first be clear on what it is they want to disperse and where. Is it clay-type soils in the wash, solids in the crutcher of their spray-tower, dyes in the rinse, hydrophobic soils in the wash, etc.? Poly(acrylic acid) or poly(acrylic/maleic) copolymers are the most popular dispersants for granules, but their use in liquids is limited due to solubility concerns and limited efficacy at the lower pH. For HDLs, smaller polymers, such as ethoxylated polyamines are more common. Recently, more specialized (and more expensive) polymers have been developed to broaden the spectrum of soils against which they work. These include a variety of ethoxylated polyamines, and zwitterionic polymers [16]. Figure 3 presents exemplary structures of common polymers in detergents. Soil release polymers are another important class [17]. In simple terms, these are polymers deposited on fabrics through the wash cycle (this discussion excludes polymers applied in the mill for similar benefits) such that they form a “protective layer” between the fabric and subsequently encountered soil. In it’s most common application the polymer

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Poly(acrylic)/Poly(maleic) acid (PAA/PMA) H2 C

H C

x

CO2H

H C

H C

CO2H

CO2H

y

Ethoxylated tetraethylene pentaimine EO15

EO15

N

N

EO15

EO15 N

N

N

EO15

EO15

EO15

Ethoxylated Polyethyleneimine EO20

EO20 N EO20

EO20 N N EO20 N

EO20

N

N

EO20 N

N

EO20

EO20 EO20

N

N EO20 EO20

N

N

N

N EO 20

EO20

EO20

EO20

Soil Release Polymers O NaO3S(CH2CH2O)2 C

O

O CO

O

O

CH2CHO C

CH2CHO C

C O

O CH2CH2OCH2CH2SO3Na

C O

R

R

y

x SO3Na

O CH3O(CH2CH2O)x

O

O

O (OCH2CH2)yOCH3

OCHCH2O CH3 z

PVNO n

N O

Figure 3

Exemplary Structures of Common Polymers in Detergents

is based on a terephthalate polyester backbone and builds up primarily on synthetic fabrics over multiple cycles. This buildup makes the otherwise hydrophobic (and therefore hard to wet and clean) fabric more hydrophilic thereby aiding in soil removal. CMC has also been claimed to provide some soil release benefits on cotton, though the size of benefits are rather limited. The last main class of polymers currently in use are dye transfer inhibition polymers. These polymers are included to trap fugitive dyes released from fabrics and prevent them

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from depositing on other fabrics. The fugitive dyes can be released due to the nature of dye used on a new garment initially, or due to the action of the detergent itself. Whatever the primary cause of dye release, these polymers work by complexing with the dyes, usually via dipole-dipole interactions, and keeping them well solubilized. The most common DTI polymers are based on poly(vinylpyridine) and related derivatives. New developments in nondispersant polymers are focused on delivering totally new “fabric-care” benefits. The ultimate goal is to repair damaged fibers and/or prevent damage in the first place to keep clothes looking like new. Work in this area is still in the early stages, but some materials have already been introduced into the market. Recent developments in this area are covered in Section IXA—Care Detergents. D. Enzymes Enzymes offer a great deal to the detergent formulator. By definition they work catalytically and hence take up little formulation space. They are also biodegradable, making them a good choice for today’s increasingly environmentally conscious consumer. Enzymes have also proven beneficial in keeping performance high as wash temperatures have fallen. Some have predicted that enzymes will become the single most important detergent component as environmental pressures continue to mount on other actives. While this may still be some time away, detergents containing as many as four or five different enzymes are already on the market. Several different enzymes are commercially available today for detergents and research continues apace to discover and develop new ones [18]. In choosing an enzyme the formulator needs to consider what the target soil or benefit is. The answer to this question determines what enzymatic activity is required. The formulator also needs to consider the wash pH and wash temperature. All enzymes have a pH and temperature window in which activity is maximized. Moving too far out of this window can make the enzyme so inefficient that it becomes cost prohibitive, or perhaps even impossible, to formulate an efficacious amount. Finally, the formulator needs to consider the mutual compatibility of the enzyme and other detergent actives. By far the most common enzyme in use today is protease. Not coincidentally it was also the first enzyme to be successfully commercialized in detergents. Protease works by cleaving peptide chains found in proteins, producing smaller, more soluble or easy to disperse fragments. Since proteins are found in some of the most common and important consumer stains (e.g., grass, blood, skin cells, sweat, many foods) it is a natural fit in most detergents. Protease presents a unique challenge for formulators (especially of liquid detergents) since it can also undergo autolysis and degrades other enzymes that are present in the formula. This is a well-understood phenomenon and solutions generally take the form of a reversible inhibitor that releases the protease on dilution into the wash. Amylases, more specifically alpha-amylases, are the second most commonly used enzyme in detergents. By hydrolyzing glycosidic bonds in starch, amylase can deliver significant stain removal benefits on food stains such as chocolate, gravy, and spaghetti, as well as body soil removal benefits. Also, amylase can sometimes deliver multicycle whiteness benefits by removing starch that could otherwise serve as a “glue” to attract other soils to the garment. Because amylases require calcium ions to maintain their threedimensional structure, care must be given to how they are formulated, with liquid detergents again providing the largest challenge. Lipases offer great potential in principle, though their actual impact in detergents thus far has been limited. Lipases work by hydrolyzing triglycerides and fatty esters to the corresponding fatty acids. The fats and oils that are susceptible to hydrolysis by lipase are often difficult to remove by surfactants alone, especially in colder water. Hydrolyzing

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them to fatty acid and glycerol makes removal by surfactants much easier. The issue has been that today’s lipases require multiple cycles to provide benefits. Also, lipases generally require the presence of calcium ions for maximum activity, and these same calcium ions can form a hard soap layer over the oily stain, blocking further action. Cellulase rounds out the roll call of today’s commonly used enzymes. It is different from those listed above in that it does not work directly on any stains, but rather directly on the fabric itself. By hydrolyzing the glycosidic β-1,4 bonds of cellulose, cellulase can remove the topmost layer of microfibers from cotton garments. The result can include stain removal by loosening the cloth “fingers” that help trap soils, but the focus has generally been on depilling, color restoration and softness. The obvious challenge with cellulases is balancing the benefits obtained with damage to the strength of the cotton garment itself over several cycles. As mentioned above, there is a great deal of ongoing work by enzyme suppliers, academics, and detergent makers themselves to discover and develop new enzymes. This work involves screening of natural isolates and “evolution” of existing enzymes, with the goal of both improving on existing activities (where improving can mean higher activity, greater stability, wider temperature and pH applicability, etc.) and developing new ones. One recent example of a newly commercialized enzyme activity for detergents is mannanase [19]. Mannanase hydrolyzes the mannan backbone of galactomannans and glucomannans. Because these materials are common rheology modifiers in a variety of foods and consumer care products, they can form a gluey film on fabrics. By removing this film, mannanase helps prevent fabric dinginess. E. Bleach Bleach contributes to stain removal by either oxidatively modifying the stain such that it becomes more water soluble and easier to remove, or by decolorizing the stain such that it is no longer visible. In some cases the oxidative bleach can also provide antibacterial benefits. There are also reductive bleaches available, but generally speaking they are not popular in laundry detergents for a variety of reasons. There are several oxidative bleaches available to the formulator today, though like most actives discussed in this chapter, a relative few dominate commercially [20]. The simplest and most common bleach is hydrogen peroxide. The ability of peroxide to decolorize and help remove hydrophilic stains like tea, coffee, and wine has been known for a very long time. It has been used in granular detergents for over 100 years. Of course hydrogen peroxide itself cannot be formulated in a granular detergent, so it is usually formulated as the stable perborate salt. Also available is percarbonate, which is actually carbonate with the hydrogen peroxide trapped in the crystal lattice. Just which material is used is based on a number of factors. Stability, dissolution rates, environmental legislation all comes into play. Whichever form one chooses, the performance of the resulting peroxide is most powerful at high temperature and long wash times. In all other situations, an additional bleaching agent is needed for strong performance. This “additional bleaching agent” takes the form of a bleach activator. A bleach activator is a peracid precursor that reacts with peroxide in the wash solution to form a peracid. They have the advantage being more reactive and therefore more effective than peroxide. Also, because they are hydrophobic, they offer better performance on body soils and hydrophobic stains. The combined bleaching profile of hydrogen peroxide and peracid gives a much broader performance profile, both in terms of stains affected and conditions in which good performance is observed. By far the two most common bleach activators are tetraacetylethylenediamine (TAED) that generates two equivalents of peracid, and nonanoyloxybenzenesulfonate (NOBS) that generates one [21].

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Preformed peracids are also known. They offer a weight efficiency advantage since no hydrogen peroxide is required and there is no “wasted” leaving group. The main issue with preformed peracids is stability—both of the raw material itself and in finished product. Phthalimidoperoxycaproic acid (PAP) is probably the best known. Metal bleach catalysts also offer great promise of weight efficiency. Bleach catalysts are transition metal compounds, typically Mn, Fe, Cu, or Co, with various chelating organic ligands. They react with appropriate oxygen sources to form high valent metal oxides that are potent oxidizing agents. Most are designed for use with hydrogen peroxide, but the obvious goal is to develop a catalyst that works with molecular oxygen. To date there is no successful commercial example, but the search continues within many academic and corporate labs. In some regards photobleaches (normally metal phthalocyanines) could be considered as bleach catalysts. They generate singlet oxygen, a powerful bleaching species, on exposure to light and air. Because of the need for sunlight, and because the bleach is only really effective while the clothing is still wet, the utility of photobleach is greatest in areas where consumers air dry their laundry outside. Figure 4 presents the exemplary structure of common bleaches and chelants. F. Chelating Agents Chelants are often formulated in detergents because metal ions in the wash are almost always a detriment to end performance. Many highly colored stains incorporate metals. Removal of the metal can often decolorize the stain and/or make it easier to remove by destabilizing its structure. Examples include porphyrins found in blood and tannins in tea. Metal ions can also catalytically decompose bleach in a formulation, leading to significantly reduced performance. Finally, metals often find their way onto fabric surfaces, either as insoluble salts as with calcium or magnesium fatty acids, or as metal oxides. Both lead to a multicycle dinginess and fabric feel issues. What chelant is used depends largely on local environmental regulations. Diethylene triamine pentaacetic acid (DTPA) is commonly used in North America. It’s an analog of the more well-known ethylenediaminetetraacetate (EDTA), but has a better environmental profile. In Europe, however, DTPA is banned due to concerns with aquatic toxicity. As a result, European formulations rely more on phosphonate-based chelants such as diethylene triamine penta(methylene phosphonic) acid (DTPMP) or ethylene diamine tetra(methylene phosphonic) acid (DDTMP). In an interesting twist, these materials cannot be used in North America due to bans on phosphorous in laundry detergents. In environmental terms, ethylene diamine disuccinic acid (EDDS) represents the best achievement thus far. The molecule has two chiral centers and only the S,S-isomer is fully biodegradable. This makes it a more expensive chelant than the phosphonate chelants mentioned previously. It is used in some European granules today. HEDP, 1hydroxyethyidene-1,1-diphosphonic acid, is not truly a chelant in the sense of the materials mentioned above, but because it also helps control deposition of metals on fabrics it deserves mention in the same section. HEDP works more by inhibiting crystal growth. G. Perfumes In a technical sense perfumes add no cleaning power to a detergent. However, from a consumer point of view perfumes have a major impact on the overall impression of how well a detergent works. Even a perfectly clean garment can be judged substandard due to lack of a “fresh and clean” odor. Odor has been proven to be an important driver for consumer acceptance, and thus should be carefully considered when formulating a product. As a result, as much effort is put into formulating different perfumes [22] as goes into formulating the rest of the laundry product, it’s just done by a different set of people—perfumers. Perfumers

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PB1 2

HO

2Na+

O

O

O

O

B HO

B

OH OH

NOBS O SO3Na

O

C8 TAED

O

CH3

O N

N

H3C H3C

CH3 O

O

PAP O O

N OOH O Photobleach SO3Na

N NaO3S

N N

N

N

Mn

N

N

N

SO3Na

SO3Na

Figure 4A Exemplary Structure of Common Bleaches and Chelants.

are highly trained technologists skilled in the science and art of creating unique winning perfumes with odor performance profiles meeting consumer needs. Perfumes are complex mixtures of organic compounds. For example, a detergent perfume may be composed of 30, 50, or even over 100 different organic materials. Given this nature, perfumes can have complex interactions with detergent actives that affect both the perfume character and possibly the actives’ performance. In addition, detergent actives often have odor properties themselves, and these “base odors” should also be considered

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DTPA Ac Ac

Ac N

N

Ac

N Ac DDTMP

O−

O

O−

P

O−

−O

P N

O N

O P −O

−

P

O

O−

O

−O

EDDS CH2 CH2 COOH

CH COOH

NH

CH2 NH

CH

CH2

COOH COOH

Figure 4B

when formulating detergents since they can impact the final product odor profile. The detergent formulator should work in partnership with the perfumer to ensure the final product odor profile best meets consumer’s needs. Most of the perfume formulated in laundry detergent ends up being washed down the drain. Deposition onto fabric is inefficient. To further complicate things, what perfume does deposit on a fabric is relatively short lived. As a result, there has been a great deal of research in recent years to aid in delivery and sustained release of perfumes. The result is a number of additional technologies available to the formulator, including those that aid in deposition of traditional perfumes, those that extend the longevity (usually via delayed release) of perfume on fabrics, and even those that only generate perfume after some triggering event such as heat, sun, or moisture exposure. All of these new developments are beyond the scope of this chapter to describe. H. “Minors” Whether a detergent ingredient is a “minor” or not is all in the eye of the beholder. In this section, “minor” simply refers to actives that are included at a relatively low level in detergent, or have no direct cleaning benefit (these items are sometimes referred to as “fillers”). “Minor” should not be taken as statement of the importance of these actives, as their absence will generally result in overall poorer performance. Discussion here is limited and the list should not be considered as exhaustive. Fluorescent whitening agents (FWA) are included at some level in most detergents today [23]. The primary benefit of FWAs is observed over multiple cycles as white

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garments begin to become dingy. By absorbing ultraviolet (UV) light and emitting it in the violet-blue visible region, FWAs increase the apparent whiteness of a garment. FWAs are also added at the mill as garments are made, but these FWAs are removed with multiple washes and need to be replenished. FWAs additionally have a benefit in solid detergents by making the granule appear whiter, and hence more attractive to consumers. The watch out, especially in liquid detergents that are often used for pretreating fabrics, is that when applied in excess to light-colored clothing, the fluorescence in the violet-blue region can appear as a light-colored stain. By careful selection of the right FWA this issue is easily avoided in most situations. In liquid detergents there is often a need for solvents or hydrotropes to ensure formula stability across the wide range of temperatures it will experience from plant to the consumer’s home. Typical solvents and hydrotropes include ethanol, propanediol, toluene sulfonate, or xylene sulfonate. The effect of solvents and hydrotropes on liquid stability and physical properties (e.g., viscosity) is not always straightforward. Effects can reverse depending on the formulation, and stability issues may not materialize for many months. Optimization of the solvent system for a product is therefore an involved process involving many samples and various rapid aging techniques. Liquid detergents, especially the more dilute ones where water makes up a greater fraction of the total product, also often contain an antibacterial agent of some sort to protect against microbial growth over the lifetime of the product [24]. Liquids are also the biggest users of dyes, pigments, or colorants [25]. In all detergents, maintaining the optimum pH for performance is crucial. As such, most contain a buffering system of some sort. This is much easier in a granular detergent than a liquid where solubility of common buffering salts is problematic. In granules this is accomplished with carbonate, silicate, and STPP. In liquids there is essentially no buffering capacity in the real sense of the word. What pH control exists comes from the degree of neutralization of acid surfactants and fatty acid, as well as the nature of the neutralizing agent itself. Suds control [26] is important as consumers make many judgments relating to the performance of their detergent based on the suds profile. Unfortunately not all consumers want the same suds profile, so knowing the consumer preference is key. It’s not just important from a consumer preference point of view, but in machine wash it is often necessary for correct machine performance. For example, a typical handwash or North American detergent will result in suds flowing out of a European machine, at best making a mess and at worst locking-up the machine such that it shuts down. Some degree of suds control is possible via careful selection of surfactant type and level, but often a separate suds control material is required. The most important type of suds suppressor is based on organic silicone compounds, though metallic soaps of carboxylic acids, insoluble nitrogenous compounds, and branched alcohols are also used.

IV. HEAVY DUTY GRANULES Heavy duty granules (HDG) were the first mass marketed consumer laundry detergents. They remain the dominant laundry form in most markets today, with a few notable exceptions such as in North America where heavy duty liquids have overtaken them in volume sold. Even in markets such as North America, however, HDGs remain a very important and dominant form. The range of different formulations on the market around the world today is quite wide. Extremely basic formulas that contain little more than carbonate, some LAS, and a bit of sulfate that are simply made by stirring them all together are sold very cheaply in some developing markets. Somewhat more complex (but devel-

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opmentally still very simple) formulas made by spray-drying LAS, STPP, carbonate and fillers are found widely around the world in handwash geographies. In developed machine wash countries one can find very complex products with mixed surfactant systems, mixed builder systems, multiple enzymes, and polymers, and made via agglomeration techniques. As the formulas gain in complexity they also gain in cleaning power, benefits delivered, and cost. In general the HDG form leverages high pH and high builder levels, both made possible by the relative ease of formulating solid buffer like carbonate and solid builders such as STPP or zeolite. Surfactant levels and types are determined in part by cost considerations of course, but manufacturing and flowability concerns have a significant impact as well. As will be seen, these considerations generally limit total surfactant levels to under 25%, and nonionic surfactant to less than 5%. Additional performance is provided by bleach, and a wide variety of enzymes and polymers. Most recent patent art is focused on new developments in these areas versus the fundamental formulation. Processes for making granules also dominate the patent art. In an attempt to bring some clarity, discussion of HDG formulations in this chapter is focused on the basic formulation and is grouped according to three key questions. First, does the desired formulation contain phosphate (usually as STPP) or not? In many markets today the use of phosphate builder is banned or severely limited. Whether or not phosphate is present can have major implications on the remainder of the formulation. Second, is this a low-density (aka “fluffy”) product or a high-density (aka “compact”) product? All markets used to be made up of fluffy products, with a density of around 350–– 500 g/L. In the late 1980s there was a significant shift to compacts with a density of around 600 to 900 g/L [27]. Finally, is this a product intended for use in washing machines or for use in handwashing of clothes? The delineation provided by these questions is somewhat arbitrary as the answers can be combined in many different ways. There are both highdensity and low-density phosphate containing formulas for machine wash for example. Likewise, there are both phosphate and nil-phosphate low-density formulas for handwash, and so on. Examples of all these formulations abound in the patent literature. The discussion below is illustrative of the more common approaches. A. Phosphate vs. Nil-Phosphate Phosphate, typically STPP, has been the preferred builder of formulators for many years. STPP readily sequesters hardness, acts as a soil peptizer and dispersant, provides some buffering capacity and helps carry the organic load in granules. It is still the preferred builder in many parts of the world today. In others, such as North America, the use of phosphate in laundry detergents has been banned and so alternative such as zeolite A are used. Zeolite A replaces the builder function and organic carrying function of STPP, but other actives are required for buffering, soil peptization, and soil suspension. Also, since the calcium binding kinetics and capacity of zeolite is not as high as STPP, more hardness tolerant surfactant systems are often used in nil-P products. Hence, to get equal performance from a nil-P product can mean additional formulation cost to pay for the chemistry needed to offset the loss of STPP. Table 3 illustrates a high-end, phosphate built detergent [28]. Compared to the nilP detergent in Table 4 [29], the biggest apparent difference in the core formula (aside from replacing STPP with zeolite A) is the presence in the nil-P formula of a polyacrylic/maleic acid copolymer and of the soda ash/silicate co-granulate sold commercially by Rhodia under the name Nabion 15. These extra actives help compensate for the dispersancy power lost when STPP is removed. Even with such additions, it is very difficult to achieve the same level of clay stain removal from a nil-P product at equal cost to a P product without

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Table 3 Example of Phosphate Built HDG Ingredient

Percent

Sodium C11-13 alkylbenzene sulfonate Sodium C14-15 alcohol sulfate Sodium C14-15 alcohol ethoxylate (0.5) sulfate Sodium C14-15 alcohol ethoxylate (6.5) STPP Sodium carbonate Sodium silicate (1:6 ratio NaO/SiO2) (46%) Sodium sulfate PEG 4000 (50%) Dispersant polymer Soil release polymer Suds suppressor Water and minors

13.7 4.0 2.0 0.5 41.0 12.4 6.4 10.9 0.4 0.76 0.10 0.60 Balance

Table 4 Example of Nil-Phosphate HDG Ingredient

Percent

C9-13 Alkylbenzene sulfonate C12-18 Alcohol sulfate C12-18 Alcohol ethoxylate (5) C12-18 Fatty acid PEG 400 Zeolite A Nabion 15 (Rhodia) Acrylic/maleic copolymer Silicate PB1 Chelant Dusting agent EDTA Protease Suds suppressor Water, misc.

13.6 3.9 3.6 0.7 1.5 17.6 12.0 3.5 1.5 17.4 0.5 1.5 7.0 1.6 3.6 10.3

Note: EDTA, ethylenediaminetetraacetate.

compromising in other areas (e.g., surfactancy). Mixed STPP and zeolite products are also known as illustrated in Table 5 [30]. This complex formula also illustrates the trend to using a mix of agglomerated and/or spray dried particles of varying composition to form the total formulation. This approach provides increased flexibility over a single spraydried or agglomerated particle.

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Table 5 Example of Mixed Builder HDG Ingredient

Percent

Base Powder STPP Sodium LAS Sodium silicate Sodium sulfate Moisture, minors

51.2 28.3 27.8 11.0 21.0 11.8

LAS Granule Sodium LAS Zeolite 4A Zeolite MAP Moisture, etc.

11.1 70.0 20.0 5.0 5.0

Nonionic granule Sodium carbonate Citric acid AE3 Water

12.0 62.8 8.1 20.9 8.2

Admixes Dense sodium carbonate Sodium sulfate Savinase Lipase Perfume

10.7 13.86 0.754 0.166 0.22

Relying on the building capacity of carbonate is another, less common, approach to nil-P formulas. Whereas STPP is a soluble builder that remains soluble when complexed with calcium, and zeolite is an insoluble builder from the start, carbonate is a precipitating builder. That is to say, it remains soluble until it interacts with calcium. As such it has the additional challenge of controlling the growth of calcium carbonate crystals and the fabric incrustation that can result when too large crystals are formed. Table 6 illustrates one approach that relies on polyacrylic acid and a maleic acid/olefin copolymer to limit encrustation [31]. Another approach to carbonate builders involves the use of very small calcite particles that act as seeds for calcium carbonate growth, resulting in more controlled and smaller crystal sizes [32]. Many other nil-P builders are known: soluble, precipitating, and zeolitic. However, they all come with significant additional cost and are used far less commonly. B. Low Density vs. High Density The choice between high- and low-density products is primarily market driven. In most of the developed world today consumers prefer high-density products. The products take up less shelf space in their homes, have less packaging waste, lower dosages, and are seen as better for the environment and as a better value. Not long ago in these same markets

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Table 6 Example of Carbonate Built HDG Ingredient

Percent

Nonionic EO5 Sodium carbonate Sodium bicarbonate Acusol 445ND (polyacrylic acid) Acusol 460ND (maleic acid/olefin copolymer) PB1 Sodium silicate Sodium sulfate

4.0 25.6 4.0 3.4 0.9 4.0 9.6 48.5

consumers looked for large boxes at low prices, and in much of the handwash world this is still the case. The formulation strategy for high- and low-density products is essentially the same. However, because of limitations in the end density that can be provided with different processes, some changes are required. Most low-density products are made via spray-drying. The products contain large amounts of carbonate and sulfate, and the surfactant system is limited somewhat by what can safely and stably go through the spray-drying tower. Additional surfactant and other organics can be sprayed onto the surface of the tower made granule, but only at low levels. Otherwise the granule can become “wet” and sticky, resulting in poor flowability and poor aesthetics. “Dusting” the finished particle with zeolite or other flow-aids is commonly done to prevent stickiness. High-density products are typically made via agglomeration processes, though postspray-tower densification processes are also used. Low-efficiency actives such as sulfate and carbonate are significantly reduced in high-density products relative to their lowdensity counterparts. Within the practical limits of marketed detergents there is not a large difference in the overall formulation beyond this. There is a great deal of patent art related to the challenges of making agglomerated powders that flow and dissolve as readily as low-density, tower-made granules [33]. C. Machine Wash vs. Handwash Much of the world today still does laundry by hand. In most cases handwash consumers use the presence of suds as a signal that sufficient detergent is present in the wash. To meet the cleaning and sudsing needs of handwash consumers, formulators have added high levels of anionic surfactants such as LAS. However, many anionic surfactants can be harsh to skin at high concentrations, especially when the skin is repeatedly exposed for relatively long periods of time as in handwashing. As a result, the formulator needs to be aware and adjust accordingly. In addition, the handwash consumer often has a much higher soil load, either due to environmental reasons or due to a lower overall frequency of garment washing. This results in increased demand on the detergent actives, including enzymes and bleach. A handwash detergent could use the same formulation as a machine wash detergent minus the suds suppressor in the simplest situation. More often though, handwash formulations include higher levels of builder and dispersants, and special care is taken to limit the level of protease and other actives that can be harsh to skin under certain conditions.

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Table 7 Example of a Simple Handwash HDG Ingredient Sodium LAS STPP CMC Polyacrylic acid Protease Carbonate Silicate Sulfate FWA Perfume Water

Percent 15.0 17.0 0.1 0.1 0.1 12.0 8.0 38.0 0.1 0.2 Balance

Because the handwash habit is predominately found in lower income markets, many handwash formulas are relatively simple, as shown in Table 7. With lower priced formulations consumers frequently “titrate” the dosage and the amount of time scrubbing to get the end benefit they desire. Top performing handwash detergents, however, contain a mixed enzyme system, bleach, chelant and other performance boosting actives. The increased performance allows consumers to dose less and spend less time scrubbing while still obtaining the desired end result. Combined with a surfactant system designed to maximize cleaning while still being mild to hands results in a very mild formulation. Table 8 illustrates this approach [34].

V. HEAVY DUTY LIQUIDS The first heavy duty liquids (HDL) were introduced as early as the 1950s, though it wasn’t until the early eighties that the form really took hold in the United States and Europe. Formulators of HDLs generally fall into two different schools of thought. The first focuses on the intrinsic benefits of the liquid form, allowing for the incorporation of surfactants at high levels and for pretreatment (i.e., direct application of the HDL to the stain prior to addition to the washing machine). This route leads to low viscosity, isotropic liquids and has been the preferred route for Procter & Gamble and Henkel for example. The second school of thought is to make the HDG into a liquid form. This route leads to structured liquid detergents containing high levels of suspended builders such as STPP or zeolites, a route championed by Unilever. These two schools remain dominant today, roughly 50 years after the introduction of the first HDLs [35]. Recently, however, new concepts have emerged including “liquigels” or “liquitabs,” essentially an HDL in a soluble pouch (a form covered in the section on Unit Dose Detergents), and HDLs packaged in dual compartment bottles. A. Isotropic Liquids Isotropic liquids are by far the largest in terms of market share and number of formulations on the market. In many markets in North America in particular, isotropic HDLs have

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Table 8 Example of Handwash HDG Designed for Mildness Ingredient C16-18 N-methyl glucose amide C12-14 Dimethyl amine oxide C12-15 Alkyl ethoxylated (EO = 5) C14-15 Alkyl ethoxy (EO = 1) sulfate STPP Sodium polyacrylate (MW = 4500) DTPA CMC Protease Cellulase Amylase Sodium silicate Soil release polymer PB1 NOBS bleach FWA 15 FWA 49 Misc. (sulfate, water, perfume, etc.)

Percent 2.3 1.9 7.3 14.0 15.0 15.0 1.6 0.4 1.0 0.15 0.15 7.0 0.3 2.0 3.2 0.15 0.05 15.1

become the leading seller, surpassing HDGs. HDLs offer a number of intrinsic advantages over HDGs. The form itself makes the pretreatment of stains easy and effective, allowing levels of stain removal not otherwise possible. The advent of dosing cups with built-in rollerballs or pour spouts makes this even easier. Rapid and complete dissolution is another inherent advantage of isotropic liquids. As wash cycles become shorter and temperatures cooler this takes on increasing importance. Liquids also offer the opportunity to formulate much higher levels of surfactant than is possible in a granule, resulting in much better greasy stain removal. Ease of dosing and less mess are also advantages noticed by consumers. The key disadvantage liquids have faced versus powders is poorer cleaning due to lack of bleach. This is the origin for much research in liquids as will be discussed below. The biggest challenge for the formulator of an isotropic liquid is stability—both physical and chemical. These considerations are the primary driving force behind what today’s isotropic liquid formulations look like. Stability must be maintained across a wide range of conditions and for a considerable period of time. From the time product is made and stored in bulk at the manufacturing plant, through bottling and warehouse storage, on to retail outlets and finally into consumer’s homes, the HDL can experience wide swings in storage conditions. Temperatures ranging from below freezing to over 40°C are not unheard of. In well-developed markets where product is made on demand, the time gap between manufacturing and use can be relatively short. In less developed markets, where perhaps product is imported from a manufacturing site in another country, the time gap can stretch to several months. Water is the primary solvent in HDLs, though various cosolvents such as propanediol, and hydrotropes like toluene- or xylen-sulfonate, are also used at low levels.

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Maintaining solubility of all actives, especially as formulas become more compact (i.e., more concentrated so lower volume doses are needed for each wash), is the main challenge. Surfactants with high Krafft temperatures are particularly troublesome, and longer-chain length hydrophobes are strictly limited. Surfactants that tie up large amounts of water, such as highly ethoxylated nonionics are also troublesome, as can be some of the more commonly used polymers in HDGs. The problem becomes further aggravated as other actives are included and as the ionic strength increases. Several “tricks” can be used such as using monoethanolamine (MEA) or triethanolamine (TEA) neutralized surfactants. Because they have lower hydration demand, these counterions have been key in the development of concentrated HDL formulas. Using potassium instead of sodium as the counterion is also done, but this has limited effect for the increased cost. These solubility issues are a main reason why most HDLs in the market today have a pH of around 7 to 9. It is impractical to try to formulate the amount of buffer that would be required to raise the pH to 10 or higher that is common for HDGs. The lower pH and lack of in-wash buffering is not a major issue though, provided the formulator keeps it in mind when selecting actives such as enzymes. In fact, this lower pH can often have a beneficial effect in reducing dye bleeding and damage to fabrics. Delivering the HDL with the right viscosity is also important. If the viscosity is too low consumers view the product as being dilute and therefore poor cleaning. If the viscosity is too high the rate of dissolution under stressed conditions (e.g., low temperature, short wash cycle, low agitation) can be negatively impacted. Most isotropic HDLs in the market today have a viscosity of between 100 and 400 centipoise (cps), though examples are available outside of this at either extreme. In simple HDLs with high water levels the issue is increasing viscosity without adding expensive thickening chemicals. In top-end HDLs with numerous cleaning actives the issue is often keeping the viscosity from becoming too high. Careful balance of solvent and hydrotrope types and levels, often determined by laborious trial and error, is usually sufficient. Maintaining chemical stability, that is preventing or limiting interactions among the various actives included in an HDL, is also a challenge. The challenge is much higher in isotropic HDLs than in other detergent forms since all actives are dissolved in solution and free to interact with everything else in solution. The most commonly encountered chemical stability issues are reactivity and stability of enzymes, formulation of oppositely charged actives, hydrolysis of actives, and microbial growth. The formulation of bleach also falls into this category, but because there are no isotropic HDLs containing bleach this will be covered in the section on bleach containing liquids (Section V.C.). The issue of autoproteolysis in protease containing HDLs was mentioned briefly in the section on laundry detergent ingredients (Section III). If formulated without a stabilizing system, protease will rapidly consume itself and other enzymes the formulator may have added. A number of different strategies have been examined to overcome this issue. A reversible inhibitor of protease is the most common solution employed. In the relatively concentrated neat formula the inhibitor binds to the active site of the protease, preventing any unwanted reactivity. Once dosed into the wash solution the detergent is diluted and the inhibitor releases, freeing the protease active site. Boric acid and boronic acids are the most commonly used reversible inhibitors. These are added in the form of borate or boric acid and propylene glycol, which form the active stabilizer species in situ. Novozymes has recently begun offering “prestabilized” proteases for sale, which include 4-formyl phenyl boronic acid as the enzyme stabilizer already mixed into the enzyme solution [36]. Other enzymes have additional stability concerns. Amylase for example, requires low levels of free calcium to stabilize their tertiary structure. Without the calcium they

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Table 9 Example of Dilute Isotropic HDL Ingredient AES AS AE Citric acid (50%) Protease Propylene glycol Monoethanol amine Borax (38%) NaOH (50%) Na formate (36%) Suds suppressor Dye Perfume w/benzyl salicylate FWA Water

Percent 5.0 5.0 1.0 0.75 0.24 0.28 0.32 0.6 1.4 1.25 0.02 0.016 0.30 0.10 Balance

essentially denature and become inactive. Low levels of calcium are often formulated for this reason. The challenge comes when chelating agents, fatty acids, citric acid, etc. are also formulated. These materials can all effectively bind calcium. Careful consideration and balance are required to include all these actives. The formulation of oppositely charged actives can also present difficulties. Interactions between anionic and cationic surfactants, resulting in the precipitation of their large uncharged complex are an obvious example. Most HDLs today do not include cationic surfactants, but there are examples that have been marketed in the past, where low levels of cationic surfactant were successfully formulated. Pseudoquats, namely tertiary amines that are not fully protonated at the pH of the formulation, are also used. Less obvious are problems that can arise from FWAs, which are also anionic species. The formula shown in Table 9 is illustrative of one way to formulate a “low-cost” dilute HDL while maintaining suitable aesthetics [37]. The challenge in a formula with over 80% water and around 10% surfactant is getting an acceptable viscosity. In this particular case the formulators found that certain perfume raw materials had an added benefit of thickening to greater than 160 cps. Finding actives that can play a dual role such as this is always a challenge. Adding a thickening polymer is also a possible solution. However, since most thickening polymers add nothing in terms of cleaning or odor, this represents an extra cost that is usually avoided. At the other extreme are formulas containing 20 to 30% surfactant, soil release polymer and/or dispersant, chelant, and multiple enzymes. Table 10 illustrates such a detergent that contains a pseudoquat amine surfactant [38]. Compared to the simple formula of Table 9, the increased use of solvent is apparent. There are numerous variations existing between these two formulas with variations on surfactant system, enzyme stabilization system (e.g., see Table 11 where sucrose is added [39]), solvents, and perfume. In all cases the underlying formulation strategy and challenges remain basically the same.

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Table 10 Example of “Fully Loaded” Isotropic HDL Ingredient LAS C8-10 Propyldimethyl amine C12-14 Alkyl ethoxylated C12-18 Fatty acid Citric acid DTPA Monoethanol amine NaOH Propane diol Ethanol Amylase enzyme Lipase enzyme Protease enzyme Endo-A glucanase enzyme Carezyme Terepthalate polymer Boric acid Suds suppressor Water/various

Percent 18.0 2.0 12.0 11.0 5.0 1.0 11.0 1.0 12.7 1.8 0.1 0.15 0.5 0.05 0.09 0.5 2.4 1.0 balance

Table 11 Example of Isotropic HDL with Sucrose Ingredient NaLAS NaAES AE7 Na borate Sucrose Na citrate Propylene glycol Monoethanol amine Coconut fatty acid Protease enzyme Lipase enzyme NaOH Water

Percent 7.0 11.6 7.0 2.0 3.2 5 3.42 0.24 0.85 0.3 0.4 to pH 8.0 Balance

Both batch and continuous processes are used in the manufacturing of isotropic liquids. The manufacturing process is relatively straightforward and does not normally add additional constraints to the formulator. The primary concern is that the order of

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addition is defined to avoid formation of highly viscous phases or generate insoluble precipitates. Since neutralization of acid surfactants can generate considerable heat, care must also be taken to add heat sensitive materials only after the batch has been sufficiently cooled. This usually means items like enzymes and perfumes are added very late in the making process. B. Structured Liquids Those formulators who prefer to formulate the liquid more along the lines of an HDG favor structured liquids. The key difference in structured liquids is the opportunity to suspend solids and possibly to formulate a higher concentration of cleaning actives without stability issues. This makes it possible to include actives that would otherwise not be soluble in an isotropic liquid, and to add actives that might otherwise be too reactive in their dissolved form. The resulting liquids are typically opaque and highly viscous, hence offering an entirely different aesthetic appearance to the consumer as well as a different performance profile. The higher viscosity of typically 500 to 9000 cps can also result in lower pretreat performance since the liquid does not penetrate the fabric as well as an isotropic liquid. The most common structured liquids are based on liquid crystalline surfactant phases. The structure comes from the dispersion of surfactant vesicles in the aqueous phase. The advantage of this method of structuring is that the structurant is also a cleaning agent and does not add extra cost. The surfactant (including fatty acid for purposes of this discussion) concentration is increased, and/or the electrolyte concentration is increased to push the system to form enough of these vesicles to become space filling. In practice this occurs when the vesicles have a solution volume fraction of above around 0.6 [40]. As the volume fraction of vesicles increases, the viscosity increases, as does the stability. Because the viscosity must be low enough to make the product easily pourable from the product bottle, there is a compromise that must be made between stability and pourability. The other common issue is flocculation of the vesicles that can result in significantly increased product viscosity due to the formation of networks, or can result in the destabilization of the structure due to a decrease in the total number of vesicles. Overcoming the viscosity/stability compromise and the flocculation issue is where most recent patent art is focused. Deflocculating or decoupling polymers are the most commonly used solution. These polymers are typically comb-type polymers with a hydrophilic backbone and hydrophobic teeth and there are numerous examples in the patent art. They are thought to perform two functions. First, they stabilize against flocculation by providing a barrier between individual vesicles in solution. Second, by inserting the hydrophobic teeth into the lamellar sheets that make up the vesicle walls, they can increase the size of individual vesicles, thereby increasing stability. The hydrophilic backbone is often a polyacrylate derivative and the hydrophobic teeth a long alkyl chain. Table 12 shows an example of a phosphate containing HDL [41] made in this way. Adding even a fraction of this level of STPP in an isotropic HDL would not be possible. A similar, nil-phosphate version is illustrated in Table 13 [42]. There are alternatives to structuring via surfactant phase. These alternatives typically involve creating a network throughout the solution that reduces the tendency of other materials in solution to coalesce or phase-split. This network can be established via some soluble polymers [43], though this approach is typically very expensive and is not always sheer-thinning, thus making pouring difficult. A more common means of creating this network involves the use of insoluble or sparingly soluble solids. The use of organically modified clay particles to create a “house-of-cards” structure in a liquid is well known and will be discussed briefly in the section on 2-in-1 detergents. A more recent example

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Table 12 Example of a Phosphate Containing Structured HDL Ingredient NaLAS K Laurate K Oleate AE7 Glycerol Boric acid KOH STPP Gasil 200 Silicon oil FWA NaCMC Dequest 2060S Protease enzyme Perfume Deflocculating polymer Water

Table 13

Percent 6.3 3.8 5.5 10.0 5.0 2.28 1.0 19.0 2.0 0.25 0.1 0.3 0.4 0.5 0.3 0.75 Balance

Example of Nil-Phosphate Structured HDL Ingredient

LAS AES AE Na citrate Borax Glycerine Protease enzyme Deflocculating polymer FWA Colorant Preservative Fragrance Water

Percent 20.0 5.5 10.0 10.0 2.0 4.0 1.5 1.0 0.4 0.75 0.05 0.4 Balance

involves the controlled crystallization of hydroxyl-modified oils to create a fibrous or entangled thread-like network in situ [44]. One such example is trihydroxystearin, sold under the trade name Thixcin by Rheox, Inc. It is possible to generate a stable structured gel without the use of decoupling polymers or other external structurants. An example is shown in Table 14 [45]. In this

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Watson Example of Structured Gel HDL without Deflocculating Polymer Ingredient

C25E1.8S C12 LAS C23 E9 C10 Amidopropylamine Citric acid DTPA C12-16 FA Rapeseed FA Protease enzyme Amylase enzyme Cellulase enzyme FWA Soil suspending polymer Ethanol Propane diol Monoethanol amine NaOH Na sulfate Borax Suds suppressor Perfume Dye Water

Percent 23.5 3.0 2.0 1.5 2.5 0.5 5.0 6.5 0.88 0.1 0.05 0.15 1.2 0.5 4.0 0.48 7.0 1.75 2.5 0.06 0.5 0.02 balance

example the careful balancing of electrolyte levels via citric acid and sodium sulfate is used to move the surfactant into a planar lamellar phase. The result is a shear thinning gel that remains transparent. Gels of this type can be sensitive to fluctuations in raw material quality and process variations that affect electrolyte levels. Otherwise they offer an interesting alternative to the more traditional opaque structured liquids. Transparent gels packaged in transparent bottles open the possibility of delivering unique aesthetics via the suspension of visible particles of various sizes and compositions. Robust, clear gels based on lamellar phase droplets dispersed in an isotropic aqueous phase have been reported [46]. The key is to reduce the size of the lamellar phase droplets via either very high sheer rate during processing, and/or by use of deflocculating polymers. Careful matching of refractive index between the droplets and the continuous phase via addition of sugars can also help. An interesting new issue of such a clear product in a clear product is the effect of UV light on the actives. Degradation of actives such as enzymes or dyes when exposed to normal daylight is well know and must be avoided. Addition of fluorescent dyes, UV absorbers, and antioxidants are all shown to aid stability [47]. Encapsulation of actives in polymers or other protective shells can also work [48]. The production of structured liquids is more problematic than that of isotropic liquids. Depending on the structuring method used the process required can vary dramatically. Also, some systems need to “age” before their full structuring capability is realized. In systems where solids will be suspended this is an important consideration. In a typical

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batch mixer with blade agitation, large amounts of air can be incorporated into the product. This needs to be removed before the structuring step or it can become entrapped in the liquid. As it slowly deaerates an undesirable foam layer can form on top of the liquid, and the process of deaerating can destabilize suspended solids. C. Bleach-Containing Liquids As mentioned above, one of the largest challenges in liquid detergents is the inclusion of bleach. There are two primary reasons for this, and two primary avenues used to overcome them. First, most of the nonchlorine oxidizing bleaches are unstable as the aqueous solution. Second, even if the bleach is stable, the other actives in the formula are typically not stable toward the bleach. In both cases, by the time the detergent reaches the consumer’s home there is little bleaching power remaining, and often little of anything else. Conceptually the solutions are straightforward—keep the bleach separate from the rest of the detergent and/or make the detergent nonaqueous. Executionally things are less straightforward. One way to keep the bleach separated from the rest of the detergent is to use a bleach that is either insoluble or only very slightly soluble in the detergent matrix. Provided the insoluble bleach is present in small enough (i.e., submicron) particle size it can be suspended directly in a non-structured liquid. More commonly, a structured liquid is utilized. If totally insoluble, such a bleach could theoretically be added into any structured HDL with appropriate suspending power. The bleach is typically an organic peroxy acid, examples of which include: N,N′-terephthaloyl-di-(6-aminopercarboxycaproic acid) (TPCAP); 1,12-diperoxydodecenoic acid (DPDA); and N,N-pthaloylaminoperoxycaproic acid (PAP). The reality is that these bleaches do have limited water solubility—enough to be of concern. Hence thought has to be given to their chemical stability as well. The stability of these peracids is much higher at low pH (i.e., pH 3–6), but for good performance of the detergent the wash pH needs to be higher (i.e., pH 7–9). So formulators have developed “pH-jump” systems. In a pH-jump system the neat product pH remains low, but on dilution in the wash jumps to a suitably high pH of 7 to 8. This is commonly accomplished by formulating borax and a polyol. The polyol complexes the borate in the concentrated neat liquid, keeping the pH low. On dilution they dissociate, releasing borate into solution and thereby raising the pH. Table 15 illustrates a bleach containing HDL formulated around this concept [49]. Another potential problem area for bleach stability is the presence of trace transition metals in the formulation. Even with careful attention to water sources and raw material quality, the presence of trace transition metals in the formulation is all but unavoidable. Transition metals decompose the peracid bleaches via a radical mechanism. To shut down the decomposition pathway the formulator can either add a chelant to sequester the transition metals, or add a radical scavenger such as an amine-oxide or an antioxidant like BHT. An example of a formulation with the later is shown in Table 16 [50]. Suspending the bleach in an anhydrous liquid detergent is another possibility. This also opens the possibility to formulate a bleach activator such as TAED or NOBS for better performance. The challenge in this case is insuring there is no free water to begin decomposition of the bleach, and ensuring the liquid remains stable at a pourable viscosity. These two items are often related since decomposition of activators such as NOBS leads to formation of colloidal fatty acid derivatives that leads to irreversible thickening upon aging. Stable products are obtained by the careful choice of organic solvent and liquid raw materials (such as some nonionic surfactants). The rest of the raw materials are added as fine powders. Table 17 illustrates a formula where butoxy-propoxy-propanol is the primary solvent, and NOBS/percarbonate makes up the bleach system [51]. Processing of

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Table 15 Example of pH-Jump with Bleach HDL Ingredient

Percent

DPDA LAS C25 E9 Na borate 10H2O sorbital Na sulfate Na polyacrylate Decoupling polymer Chelant Minors Water

2.0 16.1 6.9 5.0 20.0 0–5 0 – 0.20 0.5 – 1.0 0.30 0.5 Balance

Table 16 Example of Stabilized HDL with Bleach Ingredient HLAS Sorbitol (70%) DI H2O AE9 Na citrate NaOH (50%) Decoupling polymer Sodium borate BHT TPCAP

Percent 29.5 16.1 15.2 12.9 9.7 7.4 1.8 3.7 0.84 3000 ppm AvO

anhydrous formulas such as this is much more complex than for isotropic liquids or even for most structured liquids described above. Bleach catalysts offer perhaps the most promising approach to an HDL with bleach, though to date none have appeared on the market. The reasons for this are tied to the design and performance of the bleach catalyst more than to the HDL itself [52]. As already discussed in the section on raw materials, catalysts react with appropriate oxygen sources to form high valent metal oxides that are potent oxidizing agents. These metal oxides provide enhanced performance at lower temperatures and in shorter time. More importantly for HDLs they take up far less formulation space since they are catalytic. The ultimate goal for an HDL is to have a catalyst that forms the metal oxide bleaching species using molecular oxygen or the low levels of peroxides that preexist in stains. Such a catalyst would remove the challenge of formulating either peroxide sources or preformed peracids in the HDL.

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Table 17 Example of Anhydrous with Bleach HDL Ingredient

Percent

NaLAS C11E5 BPP Na citrate NOBS Soil suspension polymer EDDS Na carbonate Acrylate polymer Protease enzyme prills Amylase enzyme prills Cellulase enzyme prills Na percarbonate Suds suppressor Perfume TiO2 FWA Thixatrol ST Speckles Misc.

16.0 21.0 19.0 4.0 6.0 1.2 1.0 7.0 3.0 0.4 0.8 0.5 16.0 1.5 0.5 0.5 0.14 0.1 0.4 to 100%

D. Dual-Bottle Liquids One of the goals mentioned above for structured and anhydrous liquids is to keep reactive or incompatible ingredients separate. The same goal can be accomplished in a chemically simpler way by keeping the different actives physically separated via the packaging. That is to say, the bottle is made up of two (or more) separate compartments such that their contents mix only on dosing. This opens up several degrees of freedom to the formulator, but adds packaging complexity and cost. With such a packaging system in hand a number of possibilities emerge. The utility of the dual-bottle approach is currently limited by packaging and production constraints much more so than formulation constraints. Formulating for a dual-bottle approach is not as straightforward as putting a normal HDL in one bottle and a solution of the incompatible active in the other. Unless the dosage volume is doubled, the result would be to dilute the HDL with the second bottle. Where possible then, the main cleaning actives are often formulated into both bottles, with the main incompatible actives formulated more concentrated in separate bottles. In this way, deliver of sufficient actives can be balanced against dosage volume. The degree to which this is an issue depends on the volume ratio delivered by the two bottles on dosing and on how concentrated the particular formula can be. Matching the viscosity between the two liquids is also an important challenge to maintain optimum pouring and mixing properties. An example of a dual-bottle approach delivering softening benefits is shown in Table 18 [53]. In this case the second compartment contains a quaternary softening active that

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Table 18 Example of Dual-bottle HDL with Softener Active Ingredient AE Alkyl amine oxide Citric acid Ethoxylated alkyl amine Chelant N,N-dimethyl N,Ndi(tallowacyloxyethyl) ammonium chloride Protease enzyme Amylase enzyme Boric acid Ethanol Propanediol Sodium cumene sulfonate NaOH Monoethanolamine Perfume/minors Water

Percent A

Percent B

15.0 5.0 — 1.0 0.4 —

5.0 — 10.0 — — 15.0

0.10 0.22 2.0 — 10.0 2.0 — to pH 7.5 1.5 Balance

— — — 5.0 — 2.0 to pH 3.0 — 1.5 Balance

would otherwise precipitate with the anionic surfactant in a single bottle HDL. Note that the dual-bottle approach also allows for formulating at the optimum pH for chemical stability of the softener active on the one hand, and the detergent enzymes on the other. Incorporation of a bleach such as PAP in the second bottle is also of key interest [54]. Another interesting possibility disclosed in the same patent application is delivery of “signals” that reinforce to consumers that the detergent is working as intended. Examples could include release of a specific consumer appreciated fragrance, or production of a color that indicates mixing is complete. Table 19 illustrates a formula where the signal is effervescent foaming created by the reaction of catalase enzyme with hydrogen peroxide. The foam is created as the gas generated from the decomposition of peroxide bubbles through the concentrated surfactant solution of the HDL.

VI. UNIT DOSE DETERGENTS A. Tablets Laundry tablets are small “briquettes” of solid laundry detergent. Shapes vary, but the typical tablet contains roughly 40 G of detergent making the normal dose two per wash load. The primary advantage of tablets comes in ease of dosing—aside from deciding how many tablets to add to the wash there is no measuring. Given their highly compact nature, tablets also offer some economy in shipping and storage, but this is secondary. The basic idea of laundry tablets has been around since the 1960s. Initial launches failed due to poor solubility and poor consumer acceptance. Tablets were relaunched in Europe in the late 1990s, where they have taken a firm place in the market. Improvements in

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Table 19 Example of Dual-bottle Effervescent HDL Ingredient

Percent

Bottle A

MEA C10 APA Na C25 AE1.8S Propylene glycol Neodol 23-9 FWA Na toluene sulfonate NaOH N-cocoyl N-methyl glucamine Citric acid C12–16 real soap Borax Ethanol Ca formate Ethoxylated polyethyleneimine Ethoxylated tetraethylene pentaimine Na formate Fumed silica Soil release polymer Water Dye Protease enzyme Cellulase enzyme Amylase enzyme Silicone Perfume DTPA Catalase enzyme

1.1 0.5 19.35 7.5 0.63 0.15 2.25 2.79 2.5 3.0 2.0 2.5 3.25 0.09 1.3 0.6 0.115 0.0015 0.08 46.08 0.016 1.24 0.043 0.15 0.119 0.35 0.3 0.15

Bottle B

NaOH Hydrogen peroxide Water Titanium dioxide Xanthan gum

3.46 4.0 72.69 2.5 0.45

tablet design and changes in consumer habits and preferences have contributed to the new success. Tablets are the same as HDGs in terms of actual cleaning chemistry delivered to the wash process. The basic cleaning chemistry is reapplied from HDG developments, described previously in this chapter. Most developments in the field of tablets are targeted at overcoming the manufacturing and dosing/dissolution constraints inherent in the form. The first step of manufacturing tablets often involves making a traditional laundry granule

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via either spray-drying or agglomeration. These granules are then combined with other actives, a binder of some kind (e.g., polyethylene glycol, water soluble polyacrylates, etc.), and the combination is then “pressed” with high pressures into the tablet form. Due to the force used to compact the tablets, they dissolve slower in the wash compared to the same actives in granule form. If less force is used a more porous, faster dissolving tablet results. Unfortunately such tablets are usually not physically robust enough to withstand the packaging and shipping operations. Developing a tablet with good handling characteristics and good dissolution profile at the same time is the primary challenge. A number of approaches have been developed against this challenge, many of them learned from the pharmaceutical industry that faces related challenges in medicinal tablets. Some solutions do not affect the tablet per se, but rather how the tablet is physically added to the wash. These range from hard plastic devices to simple mesh bags [55]. In all cases the idea is to insert the tablet into the device to help break-up the tablet and to prevent large chunks from becoming lodged in nonproductive places in the washing machine. Once broken into small enough pieces the same dynamics affect dissolution as in HDGs. Approaches that affect the tablet itself usually rely on an added swelling agent, hydrotropes, or disintegrant to help the tablet break apart rapidly and completely in the presence of water. This is the preferred approach for tablets of uniform density and hardness. There are also approaches that involve more complex processing of the tablet to include layers of different hardness, or coatings to protect softer interiors. Combinations of all these approaches are also known. In phosphate-containing tablets it is possible to use materials high in Phase I STPP to aid in rapid disintegration [56]. Phase I STPP, available commercially for example as Rhodiaphos HPA 3.5, is the high temperature stable version of crystalline anhydrous STPP. It hydrates and dissolves more rapidly than phase II material and has been shown to aid dissolution of granules. Additional dissolution aides can also be used at the same time as shown in the example in Table 20, which includes an effervescent system. This example also highlights another common feature of tablet design, the use of multiple layers to separate actives (e.g., the phase I STPP is best separated from other hydrated species), or to provide additional mechanical stability. Table 21 illustrates the use of phase I STPP in a zeolite-containing tablet [57]. In nil-P products a different approach is required. In this case, the use of other higher water-soluble salts is found to be beneficial [58]. Sodium acetate trihydrate is claimed for use in this role [59]. Another approach is to use swellable polymers, which on wetting serve as an “explosive agent” to aid disintegration of the tablet. Henkel, for example, use a form of compacted cellulose sold as “Arbocell” by Rettenmaier, for this purpose [60]. A wide variety of other disintegrants are known from the pharmaceutical industry, including starches, and gums [61]. Generating a tablet with a softer, more readily dispersed and dissolved interior, coated with a harder protective “shell” is another approach to the problem. The shell coating is designed to provide mechanical stability during manufacturing, shipping, and handling, and also to provide some level of moisture protection. The coating should be easily broken in the washing machine, via mechanical action and via interaction with water, to release the softer contents rapidly. The coating can be applied over the already formed tablet interior either in the molten form, or as an aqueous solution. Dicarboxylic acids, such as adipic acid, are the preferred coatings in many applications [62]. The coating can also include a disintegrant as discussed above to aid the breakup of the coating. Likewise, reinforcing fibers (e.g., 100 to 400 µm synthetic or natural fibers) can also be included to help avoid premature cracking of the coating during handling. It should be noted that tablets using a coating such as this generally require a flow wrap of some sort for moisture protection to prevent premature swelling and cracking.

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Table 20 Example of Tablet with Phase I STPP and Effervescent System Ingredient Base powder Na-LAS Nonionic surfactant Soap AA/MA copolymer (70:30) STPP (builder) Na silicate Na carboxymethyl cellulose Moisture Total

Percent

23.55 10.42 0.72 3.22 40.63 8.63 0.67 12.15 100.0

Tablet Thick Layer Base powder Na percarbonate TAED granules (83%) Rhodiaphos HPA 3.5 Citric acid Na bicarbonate Minors + moisture Total

39.00 — 4.40 49.00 — — 7.60 100.00

Thin Layer 22.00 49.00 — — 9.62 19.30 0.08 100.00

Overall 35.60 9.80 3.52 39.20 1.92 3.96 6.10 100.00

An interesting possibility being explored recently is development of tablets with controlled release of actives. Increased performance and/or delivery of additional benefits can be obtained by controlling the order and timing in which various actives enter the wash process. Tablets offer some additional avenues by which to do this. For example, by changing the pressure used to compress different layers of a tablet, different dissolution rates can be obtained. Generally speaking the higher the compression force used the slower the dissolution. The addition of different binding agents at different levels can complement this effect. Likewise, by using different coating or even the same coating with varying thickness the dissolution rate of different layers of the tablet can be retarded by varying amounts of time. Finally, disintegrants can be added to selected layers to help them dissolve more rapidly. An example of this approach is illustrated in Table 22 [63]. This particular example is a four-phase tablet wherein the surfactants and nonprotease enzymes are released almost immediately in the wash, followed 5 to 10 min later by protease enzyme, builder, and alkali. Bleach follows closely in the third phase, and finally a fabric softener active is added in the final rinse. The advantage to this approach is the separation of actives that normally interfere with each other. The nonprotease enzymes have time to function before protease is added and begins degrading them. All of the enzymes have time to function before bleach is added, and the cationic fabric softener is well separated from the anionic surfactants, thereby preserving the function of both.

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Table 21 Example of Tablet with Mixed Zeolite/STPP System Ingredient

Percent

Base Powder

Na-LAS Nonionic surfactant Soap Zeolite 4A Na carbonate STPP (fully hydrated) Moisture/minors Total

22 5 3 35 20 10 5 100%

Tablet

Base powder Rhodiaphos HPA 3.5 Blue speckles Sequestrant, enzymes, perfume Total

Table 22

66 31 1.5 3.5 100%

Example of Tablet Utilizing Controlled Release of Actives

Ingredient C12-18 Alkylbenzene sulfonate C12-18 Alkyl sulfate C12-18 Alkyl ethoxylate EO7 Zeolite A Sodium carbonate Water glass Polycarboxylate polymer Sodium percarbonate TAED Protease Amylase Lipase Cellulase Auxiliary materials (antifoam, perfume) Water Sodium sulfate Esterquat softener

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Amount (G/Wash Load) 9.75 1.95 2.93 14.63 7.31 2.91 2.44 11.25 4.5 0.75 0.23 0.75 0.23 3.75 6.5 to 100 7

Phase I

Phase II

Phase III

Phase IV

x x x x x x x x x x x x x x x x x

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B. Liqui-Tabs Liqui-tabs, i.e., a single dose of liquid detergent contained in a water-soluble pouch, are a relative newcomer in the market. The first versions for laundry began appearing in Europe less than 5 years ago. The main benefit of liqui-tabs, like tablets, is primarily convenience—there is no need to measure the dose or come into contact with the enclosed liquid. The cleaning chemistry is the same as in conventional HDLs, and the water-soluble pouch is typically made of polyvinylalvohol (PVA) or some derivative thereof. The pouches are typically filled and sealed using either vertical form-fill-seal (VFFS) or horizontal form-fill seal (HFFS) processes. In the vertical processes the pouch is formed into a rectangular shape without stretching the film material. In the horizontal processes one sheet of film is drawn into a mould with thermo- and/or vacuum-forming techniques, filled with the liquid and sealed with another (not-stretched) sheet of film. The advantage of the horizontal processes is the higher production speed (translating into a lower production cost) and the possibility to give the pouch a shape that will be more attractive to consumers. Research development in liqui-tabs are primarily addressed at overcoming challenges that come from the water-soluble film itself, and from the need to keep pouches stable during shipping and handling. The major differences between an HDL formulation and a liquitab formulation are driven by these challenges. The most obvious challenge is how to put a formula that normally contains up to 50% or more water into a water-soluble pouch. The obvious answer is to remove the water, though as discussed in the HDL section this is not as easy as it sounds. This is especially true if you do not want to invest a lot of money into expensive nonaqueous solvents. In practice, formulas with <5% water and 15 to 25% solvent are utilized. The challenge is to keep the formulation clear and stable (of course structured liquids could also be used). Inexpensive solvents such as propanediol and glycerol play an even more important role in liqui-tab formulations as a result. Also, organic neutralization (e.g., monoethanolamine) is used instead of inorganic neutralization (e.g., Na, K). Maintaining a relatively low ionic strength also helps, and on dissolution can help to avoid formation of PVA gels. A simple example of the resulting formula is shown in Tables 23 [64] and 24 [65]. A quick comparison of Table 23 or Table 24 with Table 10, for example, highlights the changes vs. a conventional HDL. Interaction of the PVA film with soils and with actives in the detergent formulation can be a source of several challenges for the formulator. PVA, for example, can interact with clay, serving to crosslink clay platelets making them much harder to remove from fabrics [66]. The use of classical dispersing polymers has proven limited in overcoming this issue; so new polymers are being developed. One example is a highly ethoxylated tallow alcohol and related materials [67]. Also, normal HDLs rely heavily on borate/polyol enzyme stabilization systems. Borate, however, is an excellent crosslinker of PVA, resulting in solubility and hardening issues of the pouch. These solubility and hardening issues can translate into large consumer negatives. Hence there has been considerable effort to find a suitable, inexpensive, enzyme stabilization system that eliminates or minimizes borate. The best solution to date involves the use of short-chain carboxylic acids and a careful balancing of calcium and magnesium to provide enzyme stability. Table 25 illustrates a formulation using this approach [68]. There are several other known interactions. High concentrations of any inorganic salt are known to cause precipitation for example. Other compounds that are of relevance to the laundry formulator that can insolubilize or precipitate PVA films include polyphosphates, perborates, some silicates, and di- or polycarboxylic acids [69]. The result of any of these interactions includes poorly dissolving liqui-tabs, the appearance of globs of

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Table 23 Premix I

II III

IV

Example of Simple Liqui-tab Formulation Ingredient Soft water DTPA MEA Soft water Citric acid Soft water Propylene glycol FWA C11.8 HLAS C12-14 fatty acid AE Ethoxylated tetraethylene pentaimine pH trim (MEA) Perfume

Percent 4.76 0.75 10.71 5.95 3.48 3.57 16.37 0.21 31.0 9.77 6.94 2.17

4.0 0.3

Table 24 Example of Liqui-tab Formulation Ingredient Nonionic (Neodol C11.5EO) HLAS Priolene 6907 fatty acid Glycerol Perfume Enzyme + polymer Monopropylene glycol MEA Water

Percent 26 20 13 20 1 2 7 7.6 Balance

incompletely dissolved PVA on clothing or washing machine parts, and cleaning negatives. In addition to formulation changes of the HDL there is a great body of work on modification of the PVA film itself to address these issues. Incorporation of co-monomers in the PVA film is the most common solution. These co-monomers include carboxylic acids and esters, amides, imides, and sulfonates [70]. Unfortunately, it is beyond the scope of this chapter to cover the work on modification of PVA film to any meaningful extent. It would be wrong to suggest that all research on this form is directed only against the challenges above. There is also thought and work looking at how best to exploit the form. In other words, what does the form allow you to do that otherwise would be impossible or cost prohibitive? The patent literature has many examples, though as of the writing date none have appeared on the market. One common theme is the separation of

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Liqui-tab Formulation with Alternative Enzyme Stabilization System Ingredient

Percent

LAS C8-10 APA C12-14 AE9 Citric acid C12-18 FA Protease Amylase Mannanase Ethanoic acid MgCl2 CaCl2 Ethoxylated tetraethylene Pentaimine Ethoxylated polyethylenimine DTPA FWA 1,2-propanediol MEA Perfume Dye/misc.

21.0 1.8 18.0 1.5 16.0 1.0 0.2 0.1 1.0 0.1 0.2 1.5 1.5 0.8 0.3 15.0 11.0 1.5 to 100%

the pouch into two compartments. One compartment is typically set aside for a liquid component that can be opened for pretreatment [71], while the second contains a liquid or granular product for the mainwash [72]. Such an arrangement capitalizes on the relative strengths available from each detergent form. One example that leverages the ability to formulate high levels of surfactant in the liquid portion for pretreatment and stain removal, while formulating bleach and enzyme in the solid portion is shown in Table 26 [72a]. C. Sheets Forming detergent into sheets that can be easily added to the wash is another approach that has been heavily researched. The idea is to make available a roll, or stack, of sheets that can be added one at a time to the wash. Detergent sheets using both insoluble and soluble carriers are known. Insoluble carriers include paper, woven and nonwoven cloth, the actual selection of material based on cost, absorptive capacity, compatibility, etc. The detergent actives are loaded onto the carrier substrate. The amount and nature of detergent actives that can be loaded is relatively limited. Small particle size silicas or clays are often added to control bleeding of active off of sheets and to impart a dry-hand to the detergent impregnated fabric [73]. While test markets of these types of sheet detergents have occurred in the past, they are not widely marketed today. More recently Kao has introduced a sheet detergent in Japan with a doughlike detergent sandwiched between water-soluble polymer sheets. As a result, these sheets are much thicker than those discussed above, ranging from 0.1 to 0.5 cm thick. They have the advantage of easier incorporation of a wide range of detergent actives, with the final formulas looking more like a granule or tablet than a liquid product as shown in Table 27

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Table 26

Example of Dual-pouch/Dual-form Product Ingredient

Percent

Solid Component

Zeolite Bleach Chelating agent Enzyme Suds suppressor Sodium carbonate Brightener Minors

64 16 2 10 1 4 1 to 100%

Liquid Component

Nonionic surfactant Solvent Perfume Water Bleach activator Minors

Table 27

69 9 10 3 8 to 100%

Example of Soluble Sheet Detergent Ingredient

Nonionic surfactant Anionic surfactant Carbonate Zeolite Sulfite Polycarboxylate PEG Water Misc. (enzyme, perfume, FWA)

Percent 15–40 6–15 15–30 18–36 0–1 3–5 0–3 0–3 Balance

[74]. As with other forms of unit dose, much research is currently focused on overcoming limitations of the delivery method as opposed to new formulation approaches.

VII. LAUNDRY BARS A laundry detergent bar used directly on stains for handwashing of fabrics is one of the oldest versions of laundry detergent and is still very prevalent in developing countries. The earliest versions of laundry bars were made of soap. Since the late 1960s synthetic detergent bars started replacing the traditional soap bars. In Philippines, India, and other

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Far East countries, synthetic detergent bars are the dominant form. In Latin America, Africa, and China soap bars are still the major form of bars used. Recently a trend toward soap-syndet combo bars is gaining ground in some markets. In all regions of the world, however, conversion to granules and powders is taking place at a steady pace. The basic bar making process involves neutralization of LAS sulfonic acid (in the case of LAS containing bars) using sodium carbonate and mixing with all other ingredients in a particular sequence followed by extrusion of the mixed mass through an extrusion die. The bars coming out of the extruders are cut to the desired size and stamped with the logo and cooled in trays or on a belt in a cooling tunnel prior to packing. During processing the actives are exposed to relatively high moisture, high temperatures, and high shear stress. An alternative process is to compression mould the mixed mass. This process is more compatible with many actives such as bleach and enzyme due to the relatively lower temperature processing. These processing conditions, and the need to maintain chemical and physical stability of the bar through repeated wetting/drying cycles (as the bar is used over multiple days) represent key challenges to the formulator. Synthetic detergent bars deliver much of the same chemistry to the wash as heavy duty granules. The primary cleaning power comes from anionic surfactants, along with phosphate builders like STPP and TSPP. In India, Latin America, and Africa LAS is used as the main surfactant while in the Philippines a combination of alcohol sulfates (preferably coconut based) and LAS is used as the surfactant system. In premium bars STPP is the preferred builder as it offers, in addition to excellent hardness binding capacity, very good processability, and control of in-use physical properties like bar wear rate, sogginess or mushiness etc. In low-priced bars, a small amount of STPP is sometimes used for processability reasons. Performance enhancing actives, like chelants, polymers, FWA, and more recently enzymes and bleach are often included as well, as are sodium carbonate, sodium sulfate, inorganic fillers like calcite, talc, clay, etc. Carbonate and some times sodium silicate provide the necessary alkalinity while the inorganic fillers give “body” to the bar and also act as process aids. Surfactant level varies from 10 to 15% in low priced bars to 20 to 30% in premium bars. Where a combination of surfactants is used, as in the Philippines, typically a mixture of alcohol sulfate and LAS is used in a ratio of 50:50 to 85:15. Bars containing only AS as the surfactant are very brittle and need a high amount of humectants like glycerine or addition of hydrotropes to reduce the brittleness. STPP/TSPP level ranges from 0 to 3% in low-priced bars to 15-30% in premium bars. The moisture level in the bars varies from 3 to 12%. The level of carbonate is typically 10 to 25% and fillers like calcite, talc, and clay fill the balance of the formulation. Table 28 [75] and Table 29 [76] show two examples of bars with mixed surfactant systems. Because the presence of free water in the bars can lead to mushiness as made or during use, a variety of desiccants and/or adsorbent materials have also been added to bars to control the moisture. Examples include phosphorous pentoxide, sulfuric acid, boric acid, and calcium oxide [77], as well as a variety of clays [78]. In situ structuring of the bar is another approach taken to control physical properties of bars. Due to the noncrystalline nature of the surfactant, bars high in LAS are particularly difficult to process and the bars tend to remain soft for a long period of time. In situ structuring is an elegant technique used to overcome this problem. A complex is formed between sodium silicate and divalent or trivalent inorganic salts like aluminum sulfate, magnesium sulfate, etc. The in situ formation of these complexes in the bar making process makes the LAS-based bars more easily processable, and also controls in-use physical properties like bar wear rate and sogginess [79]. Typically 2 to 5% sodium silicate and 2 to 5% aluminum sulfate or magnesium sulfate is used to form these complexes. Table 30 illustrates bars using this approach.

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Table 28 Example of Laundry Bar with Mixed Surfactant System Ingredienta C9-18 Alkyl benzene sulfonate Magnesium sulfate (25% soln) Sodium carbonate Tetrasodium pyrophosphate Calcium carbonate Coco fatty alcohol sulfate paste (70%) Calcium carbonate Opacifiers, coloring agent, perfume Minor amount of water

Percent 25.5 2.9 14.4 9.6 17.3 9.2 19.1 1.7

a

Mixed in order shown.

Table 29 Example of Laundry Bar with Mixed Surfactant System Ingredient Tallow soap (Na) Coconut soap (Na) Coconut alkyl sulfate (Na) C12-14 alkyl N-methyl glucamide Na tripolyphosphate Bentonite Talc Sodium carbonate Water Titanium dioxide Optical brightener NaCl (salt) Misc. Total

Percent 16.00 16.00 12.00 4.00 5.00 6.00 17.00 4.00 15.00 1.00 0.03 2.00 1.97 100.00

Incorporation of enzymes and bleaches in bars is a challenge. Bar processing involves relatively high temperatures (50 to 75˚C) and very high shear stress in the extrusion process (which can shear protective enzyme granules, for example) and these conditions, coupled with water content of 3 to 12% in the formulation, result in instability of enzymes and bleaches. In addition, bars are used for more than one wash load, and the bars are often left standing wet until the next wash load. The bar may or may not have sufficient time to dry between washes. Also, the wash water often introduces other destabilizing materials like heavy metal ions and reducing agents. This means there is ample time for even relatively slow reaction chemistry to take place, thereby destroying enzyme and/or bleach activity.

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Table 30 Example of Laundry Bar with In Situ Structuring System Ingredient Linear alkyl benzene sulfonate Soda ash Sodium tripolyphosphate Calcium carbonate Sodium sulfate Calcium sulfate Powdered sodium silicate (78% solids) Calcium hydroxide Talc Anyhydrous magnesium sulfate FWA Perfume Moisture (final comp.) Polyvinyl alcohol Sodium borate Other conventional ingredients

Percent 21.0 12.0 20.0 3.7 3.0 5.0 3.46 3.45 10.0 3.0 0.225 0.35 4.75 0.6 1.5 Balance

Controlling order of addition, and paying careful attention to metal contaminants in raw materials during the manufacturing process can manage a portion of the problem. Gently adding enzymes and bleaches only after the bar mixture has sufficiently cooled is standard. Metal chelating agents are also added to control the inevitable presence of trace metal ions introduced as contaminants in raw materials and the higher levels introduced in the wash water itself. It has also been found that addition of hydrating inorganic materials such as aluminum or magnesium salts, sodium sulfate, etc. can have a stabilizing effect, presumably via formation of a complex with the peroxygen bleach [80]. Table 31 illustrates a bar containing enzyme and bleach. Soap/syndet combo bars have mixture of soap and synthetic surfactants and a very low level of builders, if any. Soap is the primary surfactant and presence of synthetic surfactants makes the surfactant system more efficient. These bars, however, require some “structuring” to control the in-use physical properties. For example, addition of starch to the combo bar reduces the mushiness of bars in-use significantly. Also, manipulation of the soap phase via electrolyte level is required both from process and physical properties points of view. Table 32 illustrates a typical soap/syndet bar formula [81].

VIII. SPECIALTY DETERGENTS “Specialty detergents” in the context of this chapter refers to laundry detergents of any form whose primary benefit is no longer delivering the best cleaning (i.e., stain removal and whitening) possible. The reasons consumers will willingly trade-off cleaning for other benefits are varied. In many regions of the world much of the clothing that is laundered each day is not visibly soiled. Consumers wash them nonetheless, often with the goal of “freshening” or “disinfecting,” or merely out of force of habit. For these consumers, trading

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Table 31 Example of Laundry Bar with Enzyme and Bleach Ingredient

Percent

Linear alkyl benzene sulfonate Soda ash Sodium tripolyphosphate Calcium carbonate Zeolite Perborate monohydrate FWA Enzyme Perfume Total moisture content (final bar) Diethylenetriamine pentaacetate Calcium sulfate 1/2 H2O Other conventional ingredients

22.0 15.0 20.0 20.0 1.0 6.0 0.2 0.1 0.35 4.75 0.9 10.0 Balance

Table 32 Example of Soap/Syndet Laundry Bar Ingredient

Percent

LAS Soap STPP Starch Sodium carbonate (calculated residual) Sodium bicarbonate (added) FWA Perfume Sodium sulfate Titanium dioxide Bentonite clay Water Sodium chloride (from soap stock) Misc.

12.00 44.00 5.00 3.00 8.00 2.00 0.03 0.45 3.29 1.00 1.39 19.00 0.42 0.42

away some stain removal performance for other benefits is not a tough choice. Consumers who wear brightly colored clothing are often more interested in keeping their bright colors than they are in the occasional stain. In other cases consumers more reluctantly trade off some cleaning benefits to get more softness, or to avoid the use of enzymes or perfumes. This section describes some of the resulting formulas. A. Care Formulas It is well known that fabrics and garments “wear out” over time. Mechanical action (both from in-use stress and from wash cycle stress) dislodges short fibers from woven and knit

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fabrics. This creates lint, fuzz, and “pills” on the fabric surface and leads to dulling of colors and an overall poor appearance. Likewise, multiple washes, even in nil-bleach products, can result in removal of fabric dyes resulting in a faded, worn-out appearance. Color intensity is diminished and sometimes the hue can even change significantly. Fabrics thin, wrinkle, shrink, lose their overall shape, and generally become “worn.” There is an understandable desire among consumers to slow, stop, and even reverse this process to keep their clothes looking “new” longer. Detergent formulators are responding with ever more sophisticated chemistry and formulas in an attempt to meet this need. The first “care” formulas were focused on maintaining colors. The simplest approaches are based on reducing the harm done by “regular” formulas. That is to say, those actives most responsible for dye fading, bleaching, bleeding, etc. are reduced or removed. In those countries where chlorine is routinely added to the municipal water supply, chlorine scavengers are added to the wash to prevent damage to colors. These scavengers include a variety of amines, including polyamines and simple inorganic ammonium salts, reducing agents such as sulfite, and peroxide bleach sources such as perborate [82]. These chlorine scavengers can typically be added without difficulty into the detergent formula. The level is set high enough to destroy residual chlorine from the water supply, but low enough that it will not affect hypochlorite bleach that may be added by consumers. Another commonly encountered consumer problem is the transfer of dye from one garment to another in the wash. This is particularly acute when white garments are included in the same wash load with colored ones, or where a single garment has both white and colored portions (e.g., a striped shirt). Dye transfer inhibition polymers are added to formulas to combat this issue. The most commonly used polymers are polyvinlypyrrolidone (PVP), polyvinylimidazole (PVI), copolymers of PVP-PVI [83], polyvinylpyridine N-oxide (PVNO) [84], and more recently poly(vinylpyridine betaine) [85]. Again, addition of these technologies does not require significant reformulation, though their benefits can be maximized via proper optimization of the surfactant system. Work continues to develop new DTI polymers to broaden the effectiveness against a wider range of dyes, and to increase the efficiency. Another approach for DTI that has not seen broad commercial activity is the use of oxidative enzyme systems [86] or bleach catalysts [87] to decolorize fugitive dyes before they deposit on fabrics. This approach tends to be more expensive and difficult to formulate, and also has concerns regarding dye safety on garments. Preventing dyes from escaping from the fabric surface is another approach to limiting dye transfer. A number of “dye fixatives” are used commercially in the fabric milling and dyeing process, but few of these are applicable through-the-wash as they are typically highly cationic species that interfere with cleaning. One example of a dye fixative material that appears to overcome this is a copolymer of epichlorohydrin and a cyclic amine monomer such as piperadine [88]. These relatively small polymers contain a limited number of positive charges and are shown to effectively fix dyes through-the-wash, while minimizing negative interactions with other anionic actives. There is rapidly growing interest in formulas and technologies that move well beyond “simple” color care. The careful use of cellulase enzyme is one approach that has been used successfully. Originally cellulase was proposed as a technology for reducing fabric harshness [89]. By removing the pills from the surface of cotton fabrics a softer fabric feel is obtained and the entrapment of harshness causing inorganic residues is also reduced. The removal of pills also delivers color “rejuvenation” benefits and an overall better fabric appearance. The key, of course, is in balancing the benefits of pill removal with weakening and damage of fabric that can occur with too high levels of cellulase. The current focus for care is primarily on fabric substantive polymers that can deliver antiabrasion benefits, dye fixation, antiwrinkle or ease of ironing benefits, and general

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improvements in overall appearance and maintenance. There are too many different polymers being patented and developed to review in much depth here. Examples of polymers used for antiabrasion and dye fixation benefits include polyamide-polyamine polymers [90] such as Kymene (e.g., Hercules) or Cartaretin (e.g., Sandoz); commercial dye-fixative polymers that are normally used in the milling process, but can be made to work well in consumer washing machines by complexing with fatty acids [91]; and cellulosic derivatives such as hydrophobically modified carboxymethylcellulose [92]. The use of modified silicone polymers (e.g., organisilicones, cationic silicones, reactive silicones, etc.) for antiabrasion, dye fixation, antiwrinkle, and general appearance benefits is also rapidly expanding [93]. While the primary focus of recent research is apparently development of care actives themselves, formulating them into products in such a way that care benefits and cleaning are both maximized is also a challenge. Many of the materials briefly mentioned above are cationic in nature and can interact strongly with anionic surfactants and anionic soils. One approach around this has been to remove or minimize the anionics in the detergent while keeping cleaning strong, and then adding in the care technology. Table 33 illustrates an HDL following this approach [93b]. B. 2-in-1 Detergents Traditionally, rinse added fabric softeners have deposited long-chain hydrocarbons in the form of dialkyl quats to lubricate fibers and provide a softness benefit. These rinse added actives cannot be delivered through the wash as they complex with anionic surfactant resulting in very poor cleaning and softening. The challenge of 2-in-1 detergents is to deliver both a softness benefit and cleaning from the same dose as the name implies. This requires a softening active that is compatible with the remainder of the detergent matrix. By far the most common active used today is clay, though ion-pairs and various silicone

Table 33 Example of Fabric Care HDL Ingredient

Percent

C13-15 EO7 Ethoxylated surfactant C12-14 Amine oxide surfactant Citric acid Diethylene triamine pentamethylene phosphonic acid Hydroxyethanedimethylenephosphonic acid Ethoxylated polyethyleneimine, MW 1600 Boric Acid Calcium chloride Propanediol Ethanol Monoethanolamine Protease Amylase Cellulase Cationic silicone polymer Water

20.0 5.0 6.0 0.4 0.45 2.65 2.0 0.02 18.0 1.0 to pH 8.5 0.77 0.06 0.16 1.0 to 100%

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polymers are also used and a variety of other actives appear in the patent literature. Likewise, the use of cellulase to remove fibrils on cotton fibers (discussed elsewhere in this chapter) can provide modest softness benefits. A thin layer of clay platelets deposited evenly on fabric can deliver good softness benefits by providing a slippery or soft feel and by breaking up interfiber hydrogen bonding. Negative interactions with other detergent actives can be minimized with proper formulation. The challenge to the formulator is primarily ensuring efficient and even deposition of the clay on fabrics, minimizing the visual impact of the deposited clay, and for liquid detergents, formulating the clay in physically stable form. This is assuming, of course, that the proper clay has already been selected. In almost all cases smectite-type clay is used for softening. This includes, e.g., montmorillonite, hectorite, bentonite, and saponite. Physical characteristics such as level of nonsmectite impurities, particle size, color, and ion exchange capacity are carefully defined for maximum benefit, maximum formulatability, and minimum negatives [94]. As mentioned above, obtaining an even coating of the clay on fabric is a requirement for optimum softness benefit. Good efficiency of deposition is also desired to get the maximum benefit from the minimum amount of clay. Conventional builders and polymers retard or inhibit deposition of clay however. Some reduction of builders and polymers can help with clay deposition, but at an obvious cost to overall cleaning. As a result, formulators have begun adding very low levels of deposition aids specific for the softening clay. The most commonly used material is poly(ethyleneglycol) with a molecular weight of anywhere from 300,000 to 5,000,000. The HDL formulation in Table 35 includes 0.03% PEG with a molecular weight of 4,000,000. Other examples in the patent literature use higher levels of lower molecular weight PEG to the same effect. In HDL formulations, maintaining the clay in a physically stable form can be a significant challenge. Many clays will self-stabilize in high water environments by swelling and formation of various “house-of-cards” structures. In low water content systems, which would characterize many HDL formulations, another means is required to stabilize the clay. In structured liquids (see Section V.B in this chapter) this is accomplished by thoroughly mixing the clay into the HDL prior to formation of the structure. The challenge here is to avoid unwanted increase in viscosity due to swelling of the clay. The presence of high levels of electrolyte in the form of STPP often helps as it reduces the swelling capacity of many clays. Table 34 shows an example of a simple structured 2-in-1 HDL [95]. Another approach is to use a low level of a clay that is capable of swelling and forming a structure even in low water. Organically modified clays, created by ion exchange of the clay inorganic cations with an organic cation containing a hydrocarbon chain of around ten carbons, can swell in certain organic liquids [96]. When used at a relatively low level the commercially available organically modified clays provide the needed suspending power to stabilize the suspended softening clay. The HDL formula in Table 35 illustrates this approach [97]. Maintaining the particle size of the longest dimension of the softening clay to less than1 µm, ensuring that both the softening and the structuring clay are well dispersed in the matrix, and ensuring that the structuring clay is “activated” (i.e., that the structure is formed) are all important in maintaining good physical stability. This is usually achieved via high-shear mixing. Formulating clay in heavy duty granules is easier since it can be simply admixed into a base granule or in the cructher. Adding the clay directly can be done, though issues of segregation can occur due to particle size differences between the clay and the base granule. More often an agglomerated clay particle of some kind is used. The clay can be agglomerated with just about anything that allows for rapid dispersion in the wash solution. More often, a binder that provides an actual benefit is used. Table 36 shows a granular 2-

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Table 34 Example of a Structured 2-in-1 HDL Ingredient

Percent

Sodium C12-alkyl benzene sulfonate Soap Alcohol ethoxylate 7EO Clay Sodium carboxymethyl cellulose Sodium tripolyphosphate Sodium silicate Fluorescent agent Glycerol Borax Silicone Perfume Proteolytic enzyme Water

6.5 1.0 2.5 5.0 0.1 22.8 1.0 0.1 4.85 3.1 0.16 0.29 0.80 balance

Table 35 Example of a 2-in-1 HDL Ingredient

Percent

Dodecyl benzene sulfonate TEA coconut sulfate C14-15 alcohol ethoxylate EO7 Ethanol Propylene glycol Triethanolamine Coconut fatty acid Oleic acid Citric acid Calcium bentonite M-P-A 14 antisettling clay (NL Industries) Polyethylene oxide (MW 4,000,000) Water Misc.

9.0 4.0 11.0 6.0 2.0 7.0 9.0 3.0 1.0 5.0 0.8 0.03 33.0 Balance

in-1 where the clay is admixed as an agglomerate with nonionic and pentaerythritol compounds [98], though other polyols are also used. There is also interest in using polysiloxane polymers as softening agents in 2-in-1 detergents. In granular applications the silicones are often used in combination with clay [99]. This provides both a convenient delivery method, and allows for synergistic combinations of the softening benefits of both clay and silicone polymer. In HDLs the key is stabilizing silicone emulsions in the product. Smaller droplets are more stable, but larger droplets have been demonstrated to provide better softening performance [100]. The use

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Table 36 Example of a 2-in-1 HDG Ingredient

Percent

Spray-Dried Components

Sodium linear C10-13 alkybenzene sulfonate Zeolite 4A (hydrated) Sodium silicate (Na2O:SiO2 = 1:2) Sodium maleate methacrylate copolymer Ethylene diamine tetra(methylene phosphonate) sodium salt Sodium carboxymethyl cellulose Stilbene fluorescent brightener Sodium sulfate, anhydrous

6.0 19.0 3.5 1.1 0.5 0.4 0.2 13.54

Clay Agglomerate

Calcium bentonite Pentaerythritol distearate, technical Nonionic surfactant (C12-15 EO7)

18.0 4.25 6.0

Other Admixes

Sodium carbonate, anhydrous Sodium perborate, monohydrate Tetraacetyl ethylene diamine Hydroxylamine sulfate Enzyme blend Sodium aluminosilicate Perfume Water

10.0 9.0 1.8 0.5 0.36 0.4 0.55 4.9

of ion pairs, similar to rinse added fabric softeners is less common for the reasons mentioned in the beginning of this section. One example of an ion-pair softener in an HDL is shown in Table 37 [101]. In this particular example the ion-pair softening complex is added as an insoluble prill, a stable suspension being created via structuring with organically modified clay.

IX. SUMMARY Future developments in laundry formulations will be driven by a number of different factors. Consumer preferences and habits will continue to be first and foremost of course. This includes both consumers’ concerns and desires regarding the end result on their fabrics, but also the growing consumer concerns about chemicals in the environment. This chapter has not attempted to cover changing demographics or consumer trends, nor the immense economic pressure driving detergent costs lower. Both of these factors are also impacting new formulation development. Governmental regulations, such as the spreading limits on phosphate containing detergents worldwide, can also introduce new challenges and opportunities that would not otherwise arise. The impact of other developments, such as the emergence of new fibers and fabrics that claim improved resistance to soils, odors, wrinkles, etc., and the development of new washing machines that claim to need less or

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Table 37 Example of a 2-in-1 HDL Using Ion-pair Technology Ingredient Sodium C12-14 alkylethoxy (1) sulfate C12-13 alcohol polyethoxylate (6.5) Sodium cumene sulfonate Prills Hydrogenated ditallow amine (HDTA):cumene sulfonate (1:1 molar) (5.0%) (HDTA)2 sulfate (2:1 M) Clay (organically modified) (2.1%) Ethanol Sodium formate Calcium formate DTPA antiredeposition polymer Protease enzyme Amylase enzyme Blue dye Perfume Water

Percent 4.7 10.75 1.33 7.10 70% 30% 1.5 3.1 1.6 0.1 0.2 1.5 0.88 0.15 0.004 0.5 66.5

no detergent for cleaning, remains to be seen, but most certainly they cannot be ignored by the formulator. The bottom line, however, is that after years of research and “new and improved” detergents, there remains a surprising level of opportunity and challenge for development of new laundry actives and new laundry formulations. The simple fact is that consumers on the whole are still not totally satisfied with the level of cleaning they get day-to-day with today’s detergents. In addition, consumers are demanding an increasing number of additional benefits beyond cleaning. The result is a great deal of innovative work under way in the labs of both detergent manufacturers and raw material suppliers. Research in laundry detergent formulations remains a remarkably fertile area.

ACKNOWLEDGMENTS The author gratefully acknowledges the generous help of several of his colleagues throughout Procter & Gamble. In particular, Robin Hall, Jeanpol Boutique, Regine Labeque, Peter Forth, Kevin Kott, Raj Panandiker, Ramanan Ramanan, and Kenji Shindo all provided detailed comments and references for their particular areas of expertise. Without their help, and the help of many others not listed, this chapter could not have been written. Any errors and omissions are strictly due to the author.

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2. G. Baillely et al., The Changing Paradigm in the Surfactants Hydrophobe Structure, 5th World Conference on Detergents, Montreux, Switzerland, October 2002. 3. For a good start, see: (a) L.O. de Guertechin in Surfactant Sci. Ser., Vol. 82, Handbook of Detergents Part A: Properties (G. Broze, Ed.), New York: Marcel Dekker, 1999, 7–46. (b) J. Falbe, Surfactants in Consumer Products. Theory, Technology and Application, Berlin: Springer-Verlag, 1987. (c) M.F. Cox in Detergents and Cleaners: A Handbook for Formulators, (K.R. Lange, Ed.), Munich: Hansen, 1994, 43–90. (d) M. Ash, I. Ash Eds., Handbook of Industrial Surfactants, New York, Endicott, 2000. (e) M.R. Porter, Handbook of Surfactants, London: Blackie Academic, 1994. 4. H. Stache, Ed., Surfactant Sci. Ser., Vol. 56, Anionic Surfactants, New York: Dekker, 1995. 5. (a) J.J. Scheibel et al., PCT International Patent Application WO9905242 to Procter & Gamble (1999). (b) J.J. Scheibel et al., PCT International Patent Application WO9905243 to Procter & Gamble (1999). (c) J.J. Scheibel et al., PCT International Patent Application WO9905244 to Procter & Gamble (1999). 6. T. Germain in Surfactant Sci. Ser., Vol. 98, Detergency of Specialty Surfactants (F.E. Friedli, Ed.), New York: Marcel Dekker, 2001, 117–143. 7. (a) T.A. Cripe et al., U.S. Patent 6,008,181 to Procter & Gamble (2000). (b) T.A. Cripe et al., U.S. Patent 6,020,303 to Procter & Gamble (2000). (c) T.A. Cripe et al., U.S. Patent 6,060,443 to Procter & Gamble (2000). 8. (a) N.M. VanOs, Ed., Surfactant Sci. Ser., Vol. 79, Nonionic Surfactants: Organic Chemistry, New York: Marcel Dekker, 1997. (b) M.J. Schick, Ed., Surfactant Sci. Ser., Vol. 23, Nonionic Surfactants: Physical Chemistry, New York: Marcel Dekker, 1987. 9. D.N. Rubingh, P.M. Holland, Surfactant Sci. Ser., Vol. 37, Cationic Surfactants, New York: Marcel Dekker, 1990. 10. E. Lomax, Ed., Surfactant Sci. Ser., Vol. 59, Amphoteric Surfactants, New York: Marcel Dekker, 1996. 11. J. Crudden in Surfactant Sci. Ser., Vol. 98, Detergency of Specialty Surfactants (F.E. Friedli, Ed.), New York: Marcel Dekker, 2001, 195–219. 12. (a) H.P. Rieck in Surfactant Sci. Ser., Vol. 71, Powdered Detergents (M. Showell, Ed.), New York: Marcel Dekker, 1998, 43–108. (b) D. Joubert, R. Gresser, J.P Cuif, in Surfactant Sci. Ser., Vol. 82, Handbook of Detergents Part A: Properties (G. Broze, Ed.), New York: Marcel Dekker, 1999, 511–558. 13. (a) D.J. Micco, et al., PCT International Patent Application WO 0170629 to PQ Holding, Inc. (2001). (b) S.M. Kuznicki, et al., PCT International Patent Application WO 0170630 to Engelhard Corporation (2001). 14. P. Zini in Surfactant Sci. Ser., Vol. 82, Handbook of Detergents Part A: Properties, (G. Broze, Ed.), New York: Marcel Dekker, 1999, 559–595. 15. (a) G. Swift in Surfactant Sci. Ser., Vol. 71, Powdered Detergents, (M. Showell, Ed.), New York: Marcel Dekker, 1998, 109–135. (b) W. Bertleff, P. Neumann, R. Baur, D. Kiessling, Journal of Surfactants and Detergents, 1(3), 419–424, 1998. 16. For example see: (a) R.A. Watson et al., U.S. Patent 5,565,145 to Procter & Gamble (1996); (b) R.A. Watson et al., U.S. Patent 6,291,415 to Procter & Gamble (2001). 17. (a) E.P. Gosselink in Surfactant Sci. Ser., Vol. 71, Powdered Detergents, (M. Showell, Ed.), New York: Marcel Dekker, 1998, 205–239. (b) A.J. O’Lenick, Journal of Surfactants and Detergents, 2(4), 553–557, 1999. 18. (a) J.H. Van Ee, O. Misset, E.J. Baas, Eds., Surfactant Sci. Ser., Vol. 69, Enzymes in Detergency, New York: Marcel Dekker, 1997. (b) E. Gormsen, E. Marcussen, T. Damhus in Surfactant Sci. Ser., Vol. 71, Powdered Detergents, (M. Showell, Ed.), New York: Marcel Dekker, 1998, 137–163. (c) A. Crutzen, M.L. Douglass, in Surfactant Sci. Ser., Vol. 82, Handbook of Detergents Part A: Properties, (G. Broze, Ed.), New York: Marcel Dekker, 1999, 639–690. (d) H.S. Olsen, P. Falholt, Journal of Surfactants and Detergents, 1(4), 555–567, 1998.

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19. (a) J-L.P. Bettiol et al., U.S. Patent 6,440,911 to Procter & Gamble (2002); (b) J-L.P. Bettiol 20.

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47. (a) M. Bae-Lee et al., Patent Application WO 0036062 to Unilever (2000); (b) M. Bae-Lee et al., PCT International Patent Application WO 0036068 to Unilever (2000); (c) D.S. Murphy et al., PCT International Patent Application WO 0036074 to Unilever (2000). 48. F.T. Van de Scheur et al., PCT International Patent Application WO 0036067 to Unilever (2000). 49. J.L. Coope et al., European Patent Application 564,250 to Unilever (1993). 50. C. N. Knowlton et al., U.S. Patent 5,712,239 to Lever Brothers (1998). 51. J.P. Boutique et al., PCT International Patent Application WO 9900482 to Procter & Gamble (1999). 52. There are numerous bleach catalysts in the patent art. For some leading references old and new see: (a) G. Schlingloff et al., PCT International Patent Application WO 02088289 to Ciba (2002); (b) D. Cong-Yun et al., U.S. Patent 6,432,901 to Unilever (2002); (c) T.L.F. Favre et al., U.S. Patent 5,246,621 to Unilever (1993); (d) T.L.F. Favre et al., U.S. Patent 5,244,594 to Unilever (1993). 53. F. de Buzzacarini et al., PCT International Patent Application WO 0222772 to Procter & Gamble (2002). 54. F. de Buzzacarini et al., PCT International Patent Application WO 0100765 to Procter & Gamble (2001). 55. For some examples see G.T. Dawson, UK Patent Application 2,323,606 to Unilever (1998) and references therein. 56. For example see (a) P. Ferlin et al., PCT International Patent Application WO 0022090 to Rhodia Chimie (2000), (b) P.W. Appel et al., PCT International Patent Application WO 0138478 to Unilever (2001), (c) P.W. Appel et al., PCT International Patent Application WO 0138479 to Unilever (2001). 57. O.C. Beers et al., PCT International Patent Application WO 0242398 to Unilever (2002). 58. H. Kruse et al., PCT International Patent Application WO 9002165 to Henkel (1990). 59. R.J. Jannsen, PCT International Patent Application WO 002289 to Hindustan Lever (2000). 60. (a) S. Herzog, PCT International Patent Application WO 9840462 to Rettenmaier (1998); (b) G. Blasey et al., PCT International Patent Application WO 9840463 to Henkel (1998). 61. Handbook of Pharmaceutical Excipients, ed 2 (A.H. Kibbe, Ed.), Washington, D.C., American Pharmaceutical Association. 62. L.B.M. Genix, et al., European Patent Application EP 1026227 to Procter & Gamble (1999). 63. T.O. Gassenmeier et al., PCT International Patent Application WO 02070641 to Henkel (2002). 64. S.P. Kennedy, U.S. Patent 4,973, 416 to Procter & Gamble (1990). 65. M. Hewitt, PCT International Patent Application WO 0179416 to Unilever (2001). 66. K. Toyoshima in Polyvinyl Alcohol Properties and Applications (C.A. Finch, Ed.), New York: John Wiley & Sons, 1973, 331–338. 67. B.T. Ingram et al, UK Patent Application GB 2,361,689 to Procter & Gamble (2001) 68. P.J. Forth, PCT International Patent Application WO 02074893 to Procter & Gamble (2002). 69. For good general information on PVA films see (a) C.A. Finch, Polyvinyl Alcohol Properties and Applications, New York: John Wiley & Sons, 1973. (b) J.G. Pritchard, Poly(Vinyl Alcohol) Basic Properties and Uses, New York: Gordon and Breach, 1970. 70. C. Yang et al., U.S. Patent 4,885,105 to Clorox (1989). 71. B.M. Dasque et al., UK Patent Application GB 2,367,557 to Procter & Gamble (2000). 72. For example see (a) N.P.S. Roberts et al., UK Patent Application GB 2,361,707 to Procter & Gamble (2000); (b) E.J. Giblin et al., PCT International Patent Application WO 02053696 to Unilever (2002). 73. For example see (a) C.M. Cambre, U.S. Patent 4,199,464 to Procter & Gamble (1980); (b) S.M. Gillette, U.S. Patent 6,130,193 to Precision Fabrics Group (2000). 74. See (a) H. Hiromitsu et al., Japan Patent Application 11-021594 to Kao (1997); (b) S. Hiroyuki et al., Japan Patent Application 2000-026899 to Kao (1998); (c) H. Hirohiko et al., Japan Patent Application 2000-096095 to Kao (1999). 75. D.P. Joshi et al., U.S. Patent 5,069,825 to Colgate-Palmolive (1991).

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76. J.J. Tee et al., PCT International Patent Application WO 9805752 to Procter & Gamble (1998). 77. D.R. Eyres et al., Philippine Patent 18128 to Unilever (1982). 78. For example see I. R. Kenyon et al., Philippine Patent 23689 to Unilever (1987). 79. (a) P.J. Powers, UK Patent GB 2,099,013 to Unilever (1982); (b) P.J. Powers, UK Patent GB 2,235,205 to Unilever (1989); (c) G.V. Ramanan et al., PCT International Patent Application WO 9838269 to Procter & Gamble (1998). 80. N.V. Shenai et al., PCT International Patent Application WO 9920731 to Procter & Gamble (1999). 81. R.M. Wise et al., U.S. Patent 5,952,289 to Procter & Gamble (1999). 82. M.P. Siklosi et al., PCT International Patent Application WO 9117234 to Procter & Gamble (1991). 83. J. Detering et al., PCT International Patent Application WO 9410281 to BASF (1992). 84. A. Fredj et al, U.S. Patent 5,458,809 to Proctor & Gamble (1995). 85. B. Srinivas et al., U.S. Patent 6,482,790 to ISP (2002). 86. For example see: (a) D.K.K. Liu et al. U.S. Patent 5,451,337 to Procter & Gamble (1995); (b) T. Damhus et al., U.S. Patent 5,855,621 to Novo Nordisk (1999); (c) D. Convents et al., PCT International Patent Application WO 9949010 to Unilever (1999). 87. For example see (a) A. Fredj et al., European Patent Application EP 0596184 to Procter & Gamble (1998); (b) R. Labeque et al., U.S. Patent 5,908,821 to Procter & Gamble (1999). 88. (a) R.K. Panandiker et al., PCT International Patent Application WO 0022077 to Procter & Gamble (2000); (b) R.K. Panandiker et al., PCT International Patent Application WO 0022078 to Procter & Gamble (2000); (c) H. Baba et al., PCT International Patent Application WO 0159054 to Procter & Gamble (2001). 89. (a) P.O. Barbesgaard et al., U.S. Patent 4,435,307 to Novo (1984); (b) C.P. Barrat et al., European Patent EP 0269169 to Procter & Gamble (1992). 90. (a) S.L. Randall et al., U.S. Patent 6,140,292 to Procter & Gamble (2000); (b) P. Griffiths et al., PCT International Patent Application WO 0015747 to Hindustan Lever (2000); (c) W. Mooney et al., PCT International Patent Application WO 0179406 to Unilever (2001). 91. M. Concannon, European Patent Application EP 462,806 to Unilever (1991). 92. (a) J.A. Leupin et al., U.S. Patent 6,384,011 to Procter & Gamble (2002); (b) M. Lahteenmaki et al., PCT International Patent Application WO 9961479 to Metsa Specialty Chemicals (1999). 93. For example see (a) C. Popoff et al., U.S. Patent 6,040,288 to Rhodia (2000); (b) A. Masschelein et al., PCT International Patent Application WO 0218528 to Procter & Gamble (2001); (c) D.S. Murphy et al., PCT International Patent Application WO 0024857 to Unilever (2000); (d) T.W. Coffindaffer et al., U.S. Patent 4,800,026 to Procter & Gamble (1989). 94. For more detailed information on clay properties see, H. van Olphen, Clay Colloid Chemistry, 2nd ed., Malabar, Florida: Krieger Publishing (1991). 95. Y.J. Nedonchelle, PCT International Patent Application WO 8703297 to Unilever (1987). 96. For example see C.M. Finlayson et al., U.S. Patent 4,287,086 to NL Industries (1981). 97. R. Mermelstein et al., European Patent Application EP 328,182 to Procter & Gamble (1989). 98. J.R.P. Doms et al., European Patent Application EP 0,570,237 to Colgate-Palmolive (1993). 99. For example see C.A.A. Marteleur et al., European Patent Application EP 0,483,411 to Procter & Gamble (1992). 100. For example see (a) L.M. Madore et al., U.S. Patent 5,091,105 to Dow Corning (1992); (b) Y. Zhen et al., U.S. Patent 5,759,208 to Procter & Gamble (1998). 101. R. Mermelstein et al., European Patent Application EP 0,328,183 to Procter & Gamble (1989).

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4 Dishwashing Detergents for Household Applications Jichun Shi, William M. Scheper, Mark R. Sivik, Glenn T. Jordan, Jean-François Bodet, and Brian X. Song

CONTENTS I. II.

III.

Summary................................................................................................................ 106 Introduction ........................................................................................................... 106 A. Market Penetration of Residential Automatic Dishwashers..................... 107 B. Smaller Households................................................................................... 108 C. Busier Consumer Lifestyles ...................................................................... 108 Hand Dishwashing Detergents.............................................................................. 109 A. Chemistry of Hand Dishwashing.............................................................. 109 1. Hand Dishwashing Process........................................................ 109 2. Methods of Hand Dish Washing ............................................... 110 3. Mechanisms of Cleaning by Hand Dishwashing Detergents ... 111 B. Basic Building Blocks of Hand Dishwashing Detergents........................ 112 1. Surfactants.................................................................................. 112 2. Foam or Suds Stabilizers ........................................................... 113 3. Hydrotropes and Dissolution Aids ............................................ 115 C. Recent Developments in Key Hand Dishwashing Technologies ............. 115 1. Surfactants.................................................................................. 115 2. Low-IFT Grease Cleaning Technologies................................... 116 3. Suds Boosting Polymers............................................................ 118 4. Product Dissolution Aids ........................................................... 120 5. Enzymes ..................................................................................... 121 6. Bleaches ..................................................................................... 121 D. New Product Forms................................................................................... 121 1. Dish Wipes ................................................................................. 121 2. Hand Dishwashing Implement .................................................. 122 105

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E. Summary of Recent Patents for Hand Dishwashing Detergents ............. 122 Automatic Dishwashing Detergents...................................................................... 122 A. Chemistry of Automatic Dishwashing...................................................... 122 1. Automatic Dishwashing Process............................................................... 122 2. New Product Forms for Automatic Dishwashing Detergents... 132 3. Key Consumer Benefits of Automatic Dishwashing Detergents .................................................................................. 133 4. Major Ingredients in Automatic Dishwashing Detergents........ 133 B. Bleach Catalyst Technologies for Automatic Dishwashing ..................... 135 1. Bleach Metal Catalyst Technology Design ............................... 135 2. Product Performance of the Cobalt (III) Bleach Catalyst ........ 138 C. Bleach Technologies for Hydrophobic Stains .......................................... 138 D. Low-Foaming Nonionic Surfactants ......................................................... 139 E. Glass Surface Care Technologies.............................................................. 141 1. Anticorrosion Glass Care........................................................... 142 2. Antifilming Surface Care........................................................... 142 F. Summary of Recent Patents for Automatic Dishwashing Detergents ..... 143 V. Concluding Remarks ............................................................................................. 143 References ....................................................................................................................... 150 IV.

I.

SUMMARY

Dishwashing detergents play an essential role in consumers’ everyday lives. Both hand and automatic dishwashing detergents help consumers clean and care for a wide range of kitchenware, including dishes, pots, pans, and utensils. Over the years, dishwashing detergent manufacturers and suppliers have conducted extensive research and development activities to improve product performance in order to satisfy consumers’ needs better. New technologies and new product forms have emerged in recent years, fueling the dynamic growth of hand and automatic dishwashing detergents in the global marketplace. This chapter reviews the key new technologies and new product forms for both hand and automatic dishwashing detergents over the last 10 to 15 years. Significant progress has been made since the earlier reviews on hand dishwashing detergents by Lai et al. (1997), on liquid automatic dishwashing detergents by Gorlin et al. (1997), and on general automatic dishwashing detergents by Heitland and Marsen (1987). For hand dishwashing detergents, this review covers key new cleaning technologies such as new surfactants, low interfacial tension (IFT) technologies based on divalent cations, suds boosting polymers, dissolution aids, enzymes, and bleaches. For automatic dishwashing detergents, we review new product forms such as gels and tablets and new cleaning technologies such as bleach catalysts, low-foaming non-ionic surfactants and glass surface care technologies. Summaries will also be provided on the key patent activities in both hand and automatic dishwashing detergents.

II. INTRODUCTION Dishwashing detergents play an essential role in the consumer’s everyday life. The primary purpose of dishwashing is to remove soils, mainly food material residues, from kitchenware surfaces, including dishes, pots, pans, utensils, and a wide range of other items. Although

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dishwashing detergents can be traced to ancient times, the first modern-day liquid hand dishwashing detergent was developed in the 1940s (Lai et al., 1997; Mizuno, 1975). The mechanical dishwasher was invented in the early 1900s, and this mechanization of the dishwashing process significantly simplifies the consumers’ lives. However, even in the twenty-first century after many innovations in the electronics and control systems of the dishwasher, it still does not fully replace hand dishwashing. Instead, machine and hand dishwashing coexist in many consumer’s homes, addressing the wide variety of consumers’ everyday dish care needs. The efficiency and efficacy of the dishwashing process is determined by several key factors. First, the efficacy of the detergents is crucial to dishwashing. These detergents are generally designed to facilitate soil removal and make the dishwashing job easier and more enjoyable for the consumer. Second, the amount of mechanical action is highly variable in the dishwashing process. For difficult to remove soils, consumers generally apply a large amount of mechanical action by scrubbing, often with the help of an implement. With the automatic dishwasher, the amount of mechanical action is in general much higher than dishwashing by hand. Third, soil removal efficacy is highly influenced by wash temperature. For greasy soils, higher wash temperatures help to melt the grease particles, making them easier to remove with detergent solutions. High-performance dishwashing detergents are generally carefully formulated to work with all the key factors or variables in the dishwashing process. For example, given the large amount of mechanical action and high wash temperatures involved in the automatic dishwasher, the composition of an automatic dishwashing detergent is very different from that of a hand dish detergent. To ensure that high performance detergents truly meet the needs of the consumer, detergent formulators have devoted considerable resources to the study and monitoring of consumer habits and practices for both hand and automatic dishwashing. Over the last 20 years or so, society has been undergoing fundamental changes on a global basis, and these changes are profoundly impacting consumers’ dish care habits and practices. Leading dish detergent formulators monitor these relevant consumer trends closely to aid their product development efforts. Several key consumer trends are summarized briefly below. A. Market Penetration of Residential Automatic Dishwashers Since the early to mid-1900s, ownership of residential dishwashers has been steadily increasing, similar to other major household appliances. Today dishwasher ownership is one of the major measures of consumer living standard around the globe (Bauman, 2003). In recent years, the household penetration rates of dishwashers continue to increase in many countries, as shown in Fig. 1. However, an equally important take-away from this figure is that the market penetration rate of residential dishwashers is still quite low when compared to other major appliances. This is the case even in major industrialized countries such as the United Kingdom, Spain, and Italy, where dishwasher market penetration remains below 40% (AEA Technology, 2001). Despite the increasing trends in dishwasher penetration rates, hand and automatic dishwashing detergents are expected to remain equally important to consumers in the foreseeable future. A majority of dishwasher owners often wash some of their kitchenware items by hand. This is especially the case for large, difficult-to-clean items such as those with cooked-on and baked-on greasy soils and for items such as fine crystal stemware and silver flatware. Furthermore, as the size of consumer household decreases (see discussions later in this section), consumer’s dishwashing loads are expected to become smaller and

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70

60

50

40

30

20

10

Spain

UK

Italy

US

Japan

Germany

0 1998

Figure 1

1999

2000

2001

2002

2003

Dishwasher market penetration rates in key global markets

smaller. Many consumers find it more convenient to wash smaller dish loads by hand, instead of using dishwashers. B. Smaller Households The size of an average consumer household has decreased steadily in many industrialized countries over the last half a century. For example, the average household size in the United States has fallen from 3.32 in 1965, to 2.69 in 1985, and to 2.58 in 2002 (U.S. Census Bureau, 2002). Similar trends can be found in many industrialized countries. In the European Union, the average household size has decreased from 2.82 in 1980, to 2.68 in 1985 and 2.49 in 1995 (OECD, 1998). The size of consumer household significantly impacts the habits and practices of dishwashing detergent users. As the size of the household decreases, the number of dirty dishes also decreases on average. This could lead to smaller, but more frequent, dishwashing jobs. As the dishwasher is generally more suited for larger dishwashing jobs, a smaller consumer household may do more hand dishwashing, or at least experience less frequent use of automatic dishwashing machines. C. Busier Consumer Lifestyles Several important factors contribute to consumers’ increasingly busier lifestyles. First, more and more women have joined the labor force. For example, in the United States, women’s share of the labor force was 28.8% in 1967. This share increased to 40.7% in 1997 (U.S. Census Bureau, 1998). Similar trends exist in other industrialized countries. Second, many consumers have busier activity schedules, such as children’s after-school activities. Consumers’ busier lifestyles often lead to less frequent formal meals at home and more income spent on eating outside the house. The consumer and market trends as discussed above have significant implications for the formulation of hand and automatic dishwashing detergents. The busier consumer lifestyles lead the demand for faster and simpler dishwashing jobs, with reduced efforts.

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At the same time, many consumers still want the reassurance and emotional satisfaction that their dishwashing jobs are accomplished to personal satisfaction and their families are well taken care of.

III. HAND DISHWASHING DETERGENTS Hand dishwashing detergents are primarily used by consumers to wash dishes, pots, pans, flatware, and other kitchenware items. They are also often used to wash delicate fabrics and to a lesser extent for general household cleaning and washing automobiles. The first hand dish detergent was developed in the 1940s. Like other liquid detergents, hand dishwashing detergents offer the advantage of convenience and are well accepted by consumers in both the developed and developing countries. As discussed above, many consumers use hand and automatic dishwashing detergents together to meet their various dish care needs in the kitchen. Two major articles have been devoted specifically to manual dishwashing detergents, one by Heitland and Marsen (1987) and the other by Lai et al. (1997). Since then, there have been significant advances in both cleaning technologies and product forms, as documented in the patent literature. This section provides a detailed review on these cleaning technology advancements and novel product forms in the market place. A.

Chemistry of Hand Dishwashing

1. Hand Dishwashing Process In simple terms, dishwashing by hand is a process in which soils are removed from dish surfaces through various washing methods that combine the mechanical action of stirring and/or scrubbing with chemical action afforded by the cleaning ingredients of a detergent. As illustrated by Lai et al. (1997), the effectiveness of the hand dishwashing process is ultimately impacted by four key parameters: the soil type, the mechanical action, the type of dish surfaces and detergent composition, in additional to other parameters such as quality of the wash water (e.g., hardness). In a typical consumer’s home, the principal types of soils involved in dishwashing are oily soil, including various types of animal fats (e.g. chicken, pork, and beef fats) and vegetable oils, proteins, carbohydrates, and particulate soils. Baked-on or cooked fatty soils require vigorous treatment actions, either mechanical or chemical. This also includes soaking to allow soil rehydration and removal by the detergent formulation. The oily soils are almost exclusively triglycerides, which contain predominantly C10-C18 saturated and unsaturated alkyl carbon chains. These triglycerides are considerably more polar and have higher molecular weights than hydrocarbon soils encountered in other cleaning processes such as fabric laundry. As a result, the chemistry of manual dishwashing presents unique and interesting challenges for product formulators and raw material suppliers. Mechanical action is another very important factor in hand dishwashing. When consumers wash dishes, they actively stir the wash water or rub the dish surface. A wash implement (e.g., sponge, wash cloth, etc) is often used to aid the process. Mechanical action serves two distinct purposes. First, it helps to soften the soils. As discussed by Lai et al.. (1997) and Heitland and Marsen (1987), mechanical action alone can remove a significant amount of soils, especially for particulate soils encountered around the kitchen. The second purpose of mechanical action is to mix the cleaning ingredients with soils, especially difficult-to-remove soils, enhancing the cleaning efficacy.

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The amount of mechanical action employed in hand dishwashing is extremely variable, from consumer to consumer and from one cleaning job to another. For example, difficult-to-clean dish items may be soaked in a wash solution in which very little mechanical action is applied. Under such conditions, the surface chemistry actions of cleaning ingredients are critical. After soaking, consumers may apply a large amount of mechanical action by scrubbing the still difficult-to-clean soils off dish surfaces. Every consumer has his or her favorite dishwashing techniques and preferred mechanical activities for dishwashing. Nevertheless, detergents are generally designed to increase the efficiency of the consumer’s mechanical actions, and as a result to reduce the amount of mechanical actions needed for difficult-to-clean soils. In essence, dish detergents make the consumer’s dishwashing jobs easier and more enjoyable. The type of dish surface is also a key consideration for hand dishwashing. Typical consumer kitchenware materials include metals (aluminum, stainless steel, carbon steel, cast iron, silver, and tin), glass and ceramics, and various plastics (polypropylene, polyethylene terephthalate [PET], etc.). These materials have a wide range of hydrophobicity or hydrophilicity. For example, surfaces of new metal, glass and ceramic items are typically hydrophilic, while those of plastic items are highly hydrophobic. Oily soils are especially difficult to clean off plastic items, primarily due to the tight bonding of greasy soils to the hydrophobic surfaces. 2. Methods of Hand Dishwashing As discussed above, consumers typically have their own favorite method for hand dishwashing. These methods can be broadly classified into three categories: the full sink (FS) method, the direct application (DA) method, and the concentrated minisolution (CMS) method. a. Full Sink (FS) Method. In this method, the consumer first fills the sink with hot or warm water and then applies an appropriate amount of detergent to make a dilute wash solution. Soiled dishes and other kitchenware are placed in the sink for soaking and washing. An implement (e.g., sponge) is often used to aid the cleaning action. The washed items may be rinsed one by one to remove detergent suds. Detergent concentration used by the consumer varies widely, typically ranging from 0.05 to 0.5% in the full sink method (Lai, et al., 1997). b. Direct Application (DA) Method. The consumer typically applies an appropriate amount of detergent on the implement (e.g., sponge), which is then squeezed to generate suds and applied to dish surfaces for the cleaning action. Rinse water is often applied to remove soils and detergent suds after cleaning action is complete. Detergent concentration in the direct application method is typically much higher than the dilute wash solution used in the full sink method, ranging from 0.5 to 5% (Lai et al., 1997). c. Concentrated Minisolution (CMS) Method. The consumer typically prepares a small amount of concentrated wash solution in a container by the side of the wash sink. An implement/sponge is then used to pick up the concentrated mini-solution and apply to soiled dish surfaces for washing. The dishes are often rinsed one by one at the end of the wash process. Detergent concentration in the CMS method is typically lower than the DA method, but much higher than in the dilute wash solutions used in the full sink method. The consumer’s hand dishwashing methods are typically a combination of the three methods as discussed above. Typical hand dishwashing methods are summarized in Table 1 for several representative countries, based on unpublished data from Westfield and RuizPardo (2004). As is evident from Table 1, the consumer’s hand dishwashing methods are highly variable from country to country.

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Typical Consumer Hand Dishwashing Methods in Selected Countries

Countries

Full Sink (FS)a

Direct Application (DA)a

Concentrated Minisolution (CMS)*

United States United Kingdom Germany France Spain Japan Mexico

72 82 93 51 35 3 1

27 14 7 38 50 90 15

1 4 — 11 15 7 83

a

Data are percentages (%) of dish wash loads by consumers.

3.

Mechanisms of Cleaning by Hand Dishwashing Detergents

Detailed discussions have been presented by Lai et al. (1997) on the various cleaning mechanisms of hand dishwashing detergents. A brief summary is presented below. a. Emulsification. Like many other detergents, emulsification is the primary cleaning mechanism for greasy soils in hand dishwashing. In this mechanism, surfactants partition onto the soil-water interface, and reduce the interfacial tension (IFT). This enables the soils to form an emulsion of small particles in the wash water (Neiditch, 1975). These emulsion particles are <0.5 µm in size and thermodynamically unstable. However, given the relatively short wash time, this thermodynamic instability does not significantly impact the soil cleaning efficiency. The key driver for the emulsification mechanism is the low IFT between greasy soils and wash water. Over the last 10 to 15 years, low-IFT technologies (e.g., Mg2+ and organic diamines) have played a critical role in improving the cleaning performance of hand dishwashing detergents. b. Grease “Roll-Up”. For greasy soils on highly hydrophobic surfaces (e.g., plastics), the emulsification mechanism is generally not effective. To improve cleaning, wetting agents and/or surfactants with strong surface wetting capabilities are typically needed to increase the contact angle and binding strength between the greasy soil and the hydrophobic surface. When the contact angle increases to between 90˚ and 180˚, the greasy soil can effectively “roll-off” from the surface with small mechanical agitation. The “roll-off” mechanism is illustrated in Fig. 2. The theory of surface wetting has been discussed extensively by Clint (1992) and by Holmberg et al. (2003). Most surfactants have some ability to induce wetting on hydrophobic surfaces. However, the wetting ability of surfactants varies widely depending on their amphophilic structures. c. Solubilization. In detergency, the solubilization mechanism refers surfactantaided dissolution of insoluble soils in wash water. This dissolution is achieved when soils partition inside the core of or around the surfactant micelles (Lai et al. 1997; Neiditch, 1972). The solubilization mechanism differs from emulsification in that the solubilized soil particles are thermodynamically stable in water. The size of these particles are generally similar to surfactant micelles, i.e., 5 to 100 nm in diameter. The efficiency of the

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θ

θ

Figure 2 Schematic of the “roll-up” mechanism. With poor surface wetting, the contact angle θ is <90˚ and removal is difficult. When θ increases to >90˚, soil “roll-up” becomes possible, with easier removal by low mechanical agitation.

solubilization mechanism depends on a complex set of surfactant parameters such as the micelle structure and the critical micelle concentration (CMC). More detailed discussions about this mechanism can be found in the work by Dunaway et al. (1995). d. Formation of Surfactant-Rich Intermediate Phases. A review by Miller and Raney (1993) discussed a novel cleaning mechanism in which a surfactant-rich intermediate phase is formed between the soil and wash water. Such intermediate phases may be a microemulsion or liquid crystal and can improve dish soil cleaning as they grow to large sizes such that small mechanical agitation can break them off the surface. The intermediate phase mechanism is efficient for many hydrocarbon soils with nonionic surfactant systems, but relatively high temperatures (>65˚C) are typically required. This mechanism is much less efficient with triglyceride soils and anionic surfactant systems that are typical of hand dishwashing detergents. B. Basic Building Blocks of Hand Dishwashing Detergents A typical hand dishwashing detergent in today’s market place contains ingredients for cleaning, foaming, product dissolution, and other minor functions (preservation, color, fragrance, anti-irritation, etc.). Some products also contain antibacterial agent(s). The typical physical properties and composition of hand dishwashing detergents are summarized in the Table 2 (see Modler et al., 2002). 1. Surfactants Surfactants are the primary cleaning ingredients in hand dishwashing detergents to provide cleaning performance. They are also the primary drivers for suds or foams, which are important sensory signals for consumers on the cleaning power of hand dishwashing detergents. Beyond cleaning and suds performance, mildness to human skin is another key requirement for surfactants in hand dishwashing detergents. Mildness is an increasingly important consideration for hand dish detergent consumers across all market segments around the globe. Three main classes of surfactants have found widespread applications in hand dishwashing detergents: anionic, nonionic and amphoteric surfactants. The most commonly used surfactants are summarized in Table 3, based on recent surveys by Lai et al. (1997) and Modler et al. (2002). Cationic surfactants as a class have not been widely used in hand dishwashing detergents, primarily due to their generally detrimental impact on detergent suds. Anionic surfactants are the workhorses for grease cleaning performance of hand dishwashing detergents. They help to reduce the interfacial tension (IFT) between greasy soils and wash water to achieve effective cleaning. In most hand dishwashing detergents, anionic surfactants are often used in combination with nonionic or amphoteric surfactants such as amine oxides and alkyl polyglucosides (APGs). As discussed by Holmberg, et al. © 2006 by Taylor & Francis Group, LLC

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Table 2 Typical Properties and Ingredients of Hand Dishwashing Detergents Ingredients or Properties Viscosity (cps) Product pH (10% solution) Cloud point (˚C) Surfactants Foam/suds stabilizers Hydrotropes and dissolution aids Salts Preservatives Fragrance Dyes Other additives Water

Typical Values 100–1,200 6–10 <5 10–50% 0–5% 0–10% <3% <0.1% 0.1–1% <0.1% 0–5% Balance

(2003) and Holland and Rubingh (1992), these mixed surfactant systems help to achieve very low IFT between greasy soils and wash water and thus significantly improve the detergent’s cleaning efficiency. Amphoteric surfactants typically exhibit both good cleaning for greasy soils and foaming/sudsing properties. More importantly, they offer excellent mildness for human skin (Holmberg et al., 2003). In recent years, these surfactants have found more widespread applications in hand dishwashing detergents due to increasing consumer need for product mildness. As shown in Table 3, the most widely used amphoterics are betaines, which are generally more expensive than other surfactants. This has prevented them from being used more widely. 2. Foam or Suds Stabilizers Detergent foam (or suds) is an important sensory signal that consumers often use to judge the performance of hand dishwashing detergents. They typically use the amount of initial foam to determine the amount of detergent to use for a specific dishwashing job. Suds longevity or mileage is also used as an indicator of the cleaning power of the product. Because of the great importance that consumers attach to suds, formulators and suppliers of hand dishwashing detergents have conducted extensive research to improve the detergent’s initial foam generation and the foam’s longevity or mileage in the wash process. Most hand dishwashing detergents marketed today utilize several unique highfoaming surfactants to “boost” suds formation. The surfactants below are often referred to as “suds boosting” surfactants. • Amine oxides: With unique combinations with anionic surfactants, amine oxides have been proven to be very effective in boosting suds performance of hand dishwashing detergents. The mostly widely used are C10-C16 dimethyl amine oxides, which are commercially available from several manufacturers (see Modler, et al. [2002] for more details). • Fatty alkanol amides: Similar to amine oxides, fatty alkanol amides are good foam boosters with unique values to hand dishwashing detergents. As pointed

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Table 3

Major Surfactants Used in Hand Dishwashing Detergents

Surfactant Description

Chemical Structures

Anionic Surfactants

Linear alkylbenzene sulfonate (LAS) SO3− Na+

R

Alkylethoxy sulfate (AES) [OCH2CH2]nOSO3− Na+

R

Alkyl sulfate (AS) OSO3− Na+

R

Sodium paraffin sulfonate SO3− Na+ R2

R1

α-Olefin sulfonate R1

SO3− Na+

(CH2)n

Nonionic surfactants

Alcohol ethoxylate (AE) R

[OCH2CH2]nOH

Alkyl polyglucoside (APG) HO

O O

HO OH HO

O OR

HO

OH

Fatty acid glucamide CH3

OH

OH

N R

OH

C OH

OH

O

Amine oxide CH3 R

N O CH3

Amphoteric surfactants

Alkyl dimethyl betaine O R

N +

O− Na+

Alkyl dimethyl amidopropyl betaine O O R

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NH

N +

O− Na+

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out by Modler et al. (2002), theses amide surfactants are typically used in conjunction with LAS-based formulations (likely due to the unique foaming properties of this surfactant combination). Most commonly used are lauric/myristic and coco mono- or di-ethanol amides. In recent years, detergent formulators have developed polymeric technologies to increase or “boost” the suds mileage or longevity of hand dishwashing detergents. More discussion will be provided on this subject later in this chapter. 3. Hydrotropes and Dissolution Aids Hydrotropes play a crucial role in the performance of hand dishwashing detergents, which are typically designed to be used in diluted form, but are often sold to the consumer as thickened compositions to facilitate product dispensing and to achieve product aesthetic benefits. It is therefore necessary that the detergent composition dissolves quickly and efficiently in water. The dissolution functions of hydrotropes in liquid detergents have been discussed extensively in the past by Friberg and Brancewicz (1997). The most commonly used and cost effective hydrotropes include sodium cumene sulfonate (SCS), sodium xylene sulfonate (SXS), and sodium toluene sulfonate (STS). Several solvent hydrotropes have also found application in hand dishwashing detergents, including ethanol, isopropanol, propylene glycol, and polyethylene glycol ethers. C.

Recent Developments in Key Hand Dishwashing Technologies

1. Surfactants As discussed by Lai et al. (1997), most hand dishwashing detergents utilize unique surfactant mixtures to achieve their performance objectives. These surfactant systems often contain a broad mixture of alkyl chain lengths in the surfactant hydrophobes, because micelles with mixed hydrophobe chain lengths are energetically favored in general when compared to those with the same hydrophobe chain lengths (see Schambil and Schwuger, 1987). Over the last 5 to 10 years, there has been a large amount of patent activity on novel combinations of existing main frame surfactants as discussed in the previous section (see Section III.E for a detailed summary of the patent activities for hand dishwashing detergents since 1995 ). Key new developments have focused on improving surfactant water solubility and co-surfactant development. Drivers for these co-surfactants included (1) additional surfactant functionality (e.g., chelating surfactants) to improve grease cleaning and (2) improvement in the mildness of surfactants to human skin. a. High-Solubility Anionic Surfactants. Mid-branched anionic surfactants in cleaning applications have been the recent focus of a large amount of patent activity and scientific literature. The key innovative feature of these anionic surfactants is the introduction of a limited amount of alkyl branching (e.g., methyl) in the middle of the hydrophobic alkyl chain. An example of such surfactant structures is shown in Fig. 3. The limited alkyl branching on the hydrophobe increases the water solubility of the anionic surfactants dramatically, while maintaining the ready biodegradability of these surfactants (Connor et al, 2001; Schmidt et al., 2000; Shi et al., 2000). Applications of these high-solubility anionic surfactants in dishwashing detergents have been described in detail in the patent literature (see, e.g., Connor et al., 2001). Due

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n

H

Figure 3

An example structure of high-solubility mid-branched anionic surfactants.

to high water solubility, these mid-branched anionic surfactants are highly available in the wash solution for grease removal. b. Chelating Surfactants. Anionic surfactants with additional functionality have attracted attention for application in hand dishwashing detergents in recent years. Examples for such surfactants are acyl ethylene diamine triacetate (e.g., LED3A) and alkyl ethoxy caboxylates (AECs). Both of these surfactants have head groups (ethylene diamine triacetate (ED3A) and carboxylate, respectively) that exhibit significant chelating capacities. Applications of AECs in hand dishwashing detergents have been described in detail by Wise and Cripe (1993). Similarly, D’Ambrogio and Connors (2001) have described applications of LED3A in hand dishwashing detergent compositions for excellent grease cleaning and skin mildness. Despite the unique functionalities of these chelating surfactants, their commercial applications in current dishwashing detergents are rather limited, primarily due to relatively high costs when compared to other workhorse anionic surfactants. The strong grease cutting ability of chelating surfactants is believed to be related to their ability to pack tightly at the grease/water interface. This leads to low interfacial tension (IFT) and thus good removal of grease by the emulsion mechanism described in Section III.A.3. For typical greasy soils encountered in dishware, fatty acids are present at significant levels (see Institute of Shortening and Edible Oils, 1999). These fatty acids are known to partition at the grease/water interface due to their amphiphilic properties. In the presence of hardness ions (Ca2+ and Mg2+), the fatty acids turn into a thin layer of soap, preventing the tight packing of anionic surfactants at the grease/water interface. The chelating surfactants can disrupt this thin soap layer at the grease/water interface, thus yielding low IFT for the mixture surfactant system and excellent grease cleaning. c. New Amphoteric Surfactants. Amphoteric surfactants are believed to be superior suds boosters and exceptionally mild to human skin (Lai et al., 1997). Efforts continue over the last several years to explore the applications of such surfactants in hand dishwashing detergents. Beyond the traditional amphoteric betaines, cocoamidopropyl dimethyl hydroxyl sultaine has also been explored by Arvanitidou et al. (2001) in hand dishwashing detergents. Good suds profiles and grease cutting were observed in detergents formulated with sultaine in conjunction with other relevant surfactants. 2. Low-IFT Grease Cleaning Technologies Historically, anionic surfactants have been the predominant surfactants for hand dishwashing detergents. This is largely a result of their availability and economics. The anionic surfactants commonly used are alkyl ethoxy sulfate (AES), linear alky benzene sulfonate (LAS) and sodium paraffin sulfonate (SPS). However, these surfactants by themselves have critical micelle concentrations (CMCs) typically higher than 1000 ppm (Swisher, 1987), which are too high for effective partition to the grease/water interface and effective grease cleaning under typical dilute wash conditions. To improve the grease cleaning and sudsing performance of traditional anionic systems, dishwashing detergent formulators have over the years developed several key low-IFT technologies. The best-known such technologies are amine oxide co-surfactant © 2006 by Taylor & Francis Group, LLC

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Impact of Amine Oxide (AO) on the CMC of AE1S Surfactant Mixturesa

Surfactant Mixture AE1S Amine oxide AE1S/AO (1.8:1 Mol ratio) AE1S/AO (0.7:1 Mol ratio) AE1S/AO (0.28:1 Mol ratio)

Critical Micellar Concentration (CMC, molal) 1.2 2.1 4.0 4.3 3.1

10–3 10–4 10–5 10–5 10–5

a

Wash water conditions: 0 gpg water hardness and 46˚C water temperature.

and divalent cations such as Mg2+. The impact of amine oxide (AO) on the surfactant mixture CMC is illustrated in Table 4. The addition of amine oxide (AO) to AE1S reduces strongly the CMC of the surfactant system. The surfactant synergism of AES with amine oxide has been discussed in detail by Holland and Rubingh (1992) and Holmberg et al. (2003). Mg2+ divalent ion also helps reduce grease-water IFT and improves significantly the grease removal of hand dishwashing detergents, as discussed by Lai et al. (1997). It is generally believed that divalent ions improve grease cleaning by improving surfactant packing at the grease-water interface to achieve low IFT and to some extent by changing the micelle structures of the surfactant mixture in solution. The impact of Mg2+ on the anionic with amine oxide surfactant system can be explained below. • In absence of Mg2+ divalent ion, the amine oxide monomer available in solution is very low, primarily due to the strong interactions between the anionic surfactant and protonated amine oxide in the micelles. Thus only AES anionic surfactant is free in solution and available to partition onto the grease-water interface. The grease removal performance is thus relatively poor without Mg2+. • With Mg2+ divalent ion added to the surfactant mixture, it weakens the interaction between AES and protonated amine oxide inside the surfactant micelles. The level of free amine oxide monomers in solution is thus increased dramatically. Both the anionic surfactant and amine oxide monomer are then available to partition onto grease-water interfaces, resulting in lower IFT and dramatically increased grease removal. Despite the impact of Mg2+ divalent ion on grease removal, it does have a significant drawback. Hand dishwashing detergents with >0.5% Mg2+ can have significant storage stability issues under conditions experienced in some countries (e.g., the storage temperature can reach below 0˚C in Japan in the winter). To solve this problem, organic diamines have been developed in recent years to replace Mg2+ and avoid the low-T storage stability issues (see, e.g., Castro et al., 2000). Organic diamines work similarly to Mg2+ for improving grease cleaning of hand dishwashing detergents. At the pH of the wash solution, the diamines are typically protonated into small organic cations, which weakens the micellar interactions between anionic surfactants and protonated amine oxide. Therefore, organic diamines help to reduce greasewater IFT and improve grease cleaning. Applications of the organic diamines in hand dishwashing detergents have been described extensively in the patent literature over the last 10 years (see patent summary table in Section III.E). © 2006 by Taylor & Francis Group, LLC

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3.

Suds Boosting Polymers

a. Background. Previous efforts to evaluate suds boosting polymers in hand dishwashing detergents have focused on polymers that could enhance the bulk/film viscosities (e.g., celluloses, guars, acrylamides, polysaccharides, etc) (Lai and Dixit, 1995). Broadbased polymer screening programs (varying backbone, charge, hydrophobicity, etc.) demonstrated the suds boosting benefits of polymers such as hydroxypropyl cellulose, but most of these polymers had several significant compatibility issues with liquid hand dishwashing detergents: (1) no significant benefits under high dilution product usage conditions (typically 0.004 to 0.1% in use), (2) materials are difficult to formulate into product matrix, and (3) poor product dissolution in wash water. Based on the above findings, technology developers turned their attention to another mechanism of polymer suds stabilization, i.e., using macromolecules to prevent the antifoam effects of greasy soils. This mechanism led to the development of several key suds stabilizing polymers that include weakly charged cationic polymers. b. Optimization of Cationic Suds Boosting Polymers. A wide range of cationic hydrophobic polymers have been tested for suds stabilization benefits in hand dishwashing detergents (Sivik et al., 2004). The test method used in this evaluation was similar to the foam stability tests described by Lai et al. (1997). Typical test results are shown in Fig. 4. Notice that the cationic polymer did not significantly affect the initial suds volume of the detergent, but suds longevity was significantly extended by using weakly charged hydrophobic polymers. The suds longevity benefit of the cationic hydrophobic polymers is highly influenced by the charge density on the polymer chain, as discussed by Sivik et al. (2004). This is illustrated by Fig. 5. If the charge density is too high, the cationic hydrophobic polymers would lead to undesirable interactions with anionic surfactants in the product formulation. Based on these data, Bodet et al. (2003) and Sivik et al. (2004) found that the optimum charge density was about 0.15, as shown in Fig. 5. Over the last 10 years, several key cationic polymeric structures have been reported for optimum suds boosting performance in hand dishwashing detergents. Two of these structures are shown in Table 5. At the pHs of typical dishwashing solutions, the amine

4.0

Suds Height (in)

3.5

LDL with Polymer

3.0 2.5 2.0

LDL

1.5 1.0 0.5 0.0 0

5

10

15

20

25

Soil Additions

Figure 4 Detergent suds boosting benefits of cationic hydrophobic polymers (LDL is the control detergent formulation).

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119

120

Suds Performance

115

HEA-DMAM HPA-DMAM PVP-DMAM

110 105 100 95 90 85 80 0.0

0.1

0.2

0.3

0.4

0.5

0.6

Charge Density

Figure 5 Impact of polymer charge density on suds boosting performance.

Table 5

Key Structures for Cationic Hydrophobic Suds Boosting Hydrophobic Polymers

Poly(dimethylaminoethyl Methacrylate)

Poly(hydroxypropyl acrylate-co-dimethylaminoethyl Methacrylate)

∗

∗

n

O

O

N

∗

∗ O

O

∗

∗

2n

n

OH O

O

N

groups on the polymers protonate to introduce cationic charges along the polymer chains. This yields the charge density desired for suds boosting polymers. Applications of these cationic hydrophobic polymers in hand dishwashing detergents have been discussed extensively in existing patent art over the last 5 to 10 years. See, e.g., Kasturi et al. (2003), Bodet et al. (2003), and Sivik et al. (2003). c. Polymer Suds Stabilization Mechanism. The interactions between cationic hydrophobic suds boosting polymers and grease particles have been discussed by Sivik et al. (2004). There are broadly two types of interactions, as illustrated in Fig. 6. The first type of interaction is electrostatic in nature. Greasy soil particles in a wash solution typically contain fatty acids, which often partition to the interface between greasy soil and water. Under consumer wash conditions, the fatty acids deprotonate, introducing negatives charges at the grease-water interface. These negatively charged fatty acids interact with positive charges on the suds boosting polymer. This results in a tight interaction between the grease particle and the polymer.

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+grease grease

-+

grease

+ Hydrophobic

Electrostatic

Figure 6 Illustration of interactions of cationic hydrophobic polymers with grease particles.

The second type of grease-polymer interaction is hydrophobic in nature. A large part of the polymer structure is hydrophobic. They can interact with the bulk surface of grease particles via van der Waals forces. This is illustrated in Fig. 6. To further elucidate the mechanism of polymeric suds boosting, Kasturi and Schafer (1999) examined the impact of Poly(DiMethylAminoethyl Methacrylate), or PolyDMAM, on the grease-water interface and the surface tension of the wash solution. The results are summarized in Fig. 7. Key indication is that PolyDMAM reduces the grease/water IFT significantly at low concentrations (20 ppm in wash solution), but its impact on wash solution surface tension is not significant. This suggests that PolyDMAM has a unique ability to partition onto the grease-water interface, consistent with the grease-polymer interactions illustrated in Fig. 6. 4. Product Dissolution Aids As discussed above, hand dishwashing detergents are typically sold to consumers as a thick and viscous paste to facilitate product dispensing and to achieve product aesthetic benefits. The key requirement for these products is fast dissolution in the wash solution. This is typically achieved by the use of traditional hydrotropes (e.g., sodium cumene sulfonate), as discussed in detail by Lai et al. (1997). Over the last 10 years, a wide range of hydrophobic polymers have been reported as good dissolution aids in hand dishwashing detergents. For example, Brumbaugh (1999) described using solvent hydrotropes such as alkoxylated glycerides to improve detergent

80 Surface Tension, mN/m

LDL3 LDL 3 + 20 ppm PolyDMAM

20 16 12 8

/

Interfacial Tension, mN/m (sunflower oil)

24

4 0 0.001

0.01

0.1

Concentration LDL3, g/l

1

10

70

LDL-3

60

LDL 3 + 20 ppm PolyDMAM

50 40 30 20 0.001

0.01 0.1 1 Concentration LDL3, g/l

10

Figure 7 Impact of PolyDMAM on grease-water IFT and wash solution surface tension. The IFT was measured with sunflower oil, and LDL3 was a control product.

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121

dissolution. Clarke et al (2000) described using polymeric glycols of certain molecular weight to improve dissolution of concentrated liquid dishwashing detergents. Similarly, Borgonjon et al. (2002) reported using a broad range of alkylene oxide polymers as dissolution aids in hand dishwashing detergents. These hydrophobic polymers can reduce or eliminate the formation of surfactant liquid crystals in the concentrated detergent product. 5. Enzymes Enzymes have been widely used in detergents and cleaning products (Axelsen et al, 1999). Applications of enzymes in hand dishwashing detergents occurred more recently. Because of their versatile properties, enzymes can be designed to clean a wide range of difficultto-clean soils, especially starches and baked-on greasy soils. For example, amylolytic enzymes, or amylases, can catalyze the hydrolysis of starch soils. Proteolytic enzymes, or proteases, can catalyze the hydrolysis of peptide bonds in proteins. Lipolytic enzymes, or lipases, can catalyze the hydrolysis of fats or oils. In addition to cleaning, enzymes can also help provide hand care benefits for dishwashing detergents when formulated appropriately. There are many descriptions in the patent literature on using enzymes in hand dishwashing detergents. Foley (1998) described using lipolytic enzyme in combination with amylolytic enzyme for hand dishwashing applications. This combination is especially useful for the removal of baked-on or burnt-on starch and greasy soils in dishwashing. Such soils are known to be particularly difficult to remove in a hand dishwashing process. Mao et al. (1999) described that proteases, when used in a liquid or gel hand dishwashing detergent composition, improve the mildness of the composition and reduce skin dryness experienced by consumers. Kasturi et al. (2004) described using an amylase enzyme additive to soften soils on hard surfaces to improve cleaning. 6. Bleaches Like many other liquid detergents, it’s difficult to stabilize traditional bleaches in liquid hand dishwashing detergents. In the last several years, formulators have been able to stabilize hydrogen peroxide in a hand dishwashing detergent context (see Arvanitidou et al., 2003). However, the pH of these products is typically kept at 3 to 4. Products of this low pH are typically poor in grease cleaning. Transition metal bleach catalyst is another class of bleaching agents that has been discussed for potential applications in hand dishwashing detergents. For reference, see, e.g., Perkins et al. (2003). Significant technology development is still needed for these bleach catalysts to become practical for hand dishwashing detergents. D. New Product Forms Over the last 5 to 10 years, several new product forms have been introduced into the market to aid the consumer’s hand dishwashing jobs. These include dish wipes and cleaning implements. No detailed discussions will be provided here as the major detergent ingredients in these new product forms are largely similar to traditional products. 1. Dish Wipes Major hand dishwashing detergent manufacturers have recently introduced dish wipes to consumers. These wipe products can simplify the consumer’s dishwashing jobs by combining the detergent and sponge or dish cloth into one. Cleaning ingredients are typically loaded into an inside layer of the dish wipe. Given that the ingredients are loaded on a

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solid substrate, there may be additional flexibility in using ingredients like bleaches in the dish wipes. 2. Hand Dishwashing Implement A battery-powered dishwashing brush implement has recently been introduced to consumers (please refer to http://www.homemadesimple.com/dawn/dish_brush.shtml for more details on this dish brush implement). This brush implement is designed to reduce the amount of effort for the consumers to wash dishes by hand, especially to remove difficultto-clean soils. A detergent is still needed for cleaning with this new implement. The major future impact of this new product is expected to be on how dishwashing detergents would be tested for their cleaning efficacy in the future. E. Summary of Recent Patents for Hand Dishwashing Detergents An extensive patent summary had been provided previously by Lai et al (1997) for 1979 to 1995. The present summary covers only hand dishwashing detergent patent activities since 1995. Table P-1 covers hand dishwashing patents related to grease cleaning, and Table P-2 covers those related to suds, dissolution and other product aesthetics.

IV. AUTOMATIC DISHWASHING DETERGENTS As discussed earlier in Section II, the modern-day dishwasher was introduced early in the twentieth century and significantly simplified the dishwashing process for many consumers. Today, “smart” dishwashers based on advanced microelectronics are more userfriendly than ever. In many industrialized countries, the residential dishwasher is a key household appliance and often a measure of the consumer’s standard of living (Bauman, 2003). In addition to residential applications, automatic dishwashers are also widely used in institutional applications (e.g., restaurants, hospitals, hotels, etc.). However, these dishwashing machines are designed quite differently from residential ones and are not the focus of discussion here. The chemistry of automatic dishwashing detergents has been reviewed in the past by Mizuno (1975) and Heitland and Marsen (1987). Gorlin et al. (1997) also reviewed liquid automatic dishwashing detergents. In this section, we briefly review the chemistry of automatic dishwashing detergents and focus on the key developments in detergent technologies and product forms over the last 10 to 15 years. A. Chemistry of Automatic Dishwashing 1. Automatic Dishwashing Process Residential automatic dishwashing is typically divided into four distinct steps: prewash, main wash, rinsing, and drying, with the total wash time ranging from about 50 to 90 minutes. In the prewash step, easy-to-remove food residues and highly foaming soils are typically washed away from dish surfaces. In the main wash step, detergents are added to aid the mechanical cleaning action. The temperature in the main wash step can reach as high as 65˚C to ensure good removal of difficult-to-remove soils and stains. In the rinsing step, the wash temperature is typically reduced to about 40 to 50˚C, and a rinse aid is often added to aid residue removal and to avoid formation of water spots on dishware surfaces, especially glasses. In the final drying step, the dishwasher is heated to as high as 60˚C to dry out the wash water completely.

© 2006 by Taylor & Francis Group, LLC

Summary of Hand Dishwashing Detergent Patents on Grease Cleaning (1995–2004)

Inventor(s)

Patent Number and Date

Key Technologies

Stated Benefits

Kasturi et al. Procter & Gamble [P&G])

U.S. Patent 6727212 (2004)

Amylase enzymes as soil softening additive

Softening soil on hard surfaces without needing excess scrubbing

Giesen et al. (Henkel)

DE 10106712 (2002)

Surfactants and enzymes include carbohydrate

Carbohydrate stabilizes the enzymes, especially amylases

Foley et al. (P&G)

WO 2000063336 (2000)

Enhance enzyme stability in light-duty liquid

Foley et al. (P&G)

WO 2000046335 (2000)

Enzyme-containing core material, with acidic barrier layer and a physical barrier layer coated sequentially on core material. Amylase enzyme + suds booster at pH >8

Vinson et al. (P&G)

U.S. Patent 6589926 (2003)

Organic diamines

Improved grease removal and suds benefits

Castro et al. (P&G)

WO 2001019947 (2001)

Organic diamine + olefin derived amine oxide + alkylene aminomethylene phosphoric acid salt.

Improved food soil cleaning, handling, and suds characteristics and improved color stability

Clarke et al. (P&G)

WO 2000046331 (2000)

Castro et al. (P&G)

U.S. Patent 6362147 (2002)

Low-MW organic diamine + anionic surfactant + amphoteric surfactant + diol and/or polymeric glycol Low-MW organic diamine with pK1 and pK2 of 8–1.5. Free of Mg and Ca.

Muller et al. (Henkel)

DE 10060095 (2002)

Improved dissolution and rheological behavior, plus food soil cleaning, handling, grease cutting and enzyme stability Improved grease removal with improved antibacterial properties and suds. Low-T stability. Process eliminates need for two separate containers for premixes of both phases 123

© 2006 by Taylor & Francis Group, LLC

Upper and lower aqueous phases of detergent can be temporarily converted into an emulsion or dispersion by shaking

Excellent greasy and starch-based soil removal. Enzyme stability.

Dishwashing Detergents for Household Applications

Table P-1

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Table P-1

Summary of Hand Dishwashing Detergent Patents on Grease Cleaning (1995–2004) (continued)

Inventor(s)

Patent Number and Date

Key Technologies

Stated Benefits

WO 2001030958 (2001)

Organic solvent with lower and upper aqueous phases to temporarily form emulsion by shaking

Highly effective cleaning

Erilli et al. (ColgatePalmolive)

U.S. Patent 6156717 (2000)

Water insoluble organic compound + ethoxylated methyl ester

High foaming, mildness on human skin and improved cleaning performance

Drapier et al. (ColgatePalmolive)

U.S. Patent 6046151 (2000) U.S. Patent 5874393 (1999)

Clear microemulsion with Alkyl ether sulfate (AES) + Alkyl polyglycoside (APG)

Desirable high foaming and cleaning, but is mild to human skin

Drapier (ColgatePalmolive)

U.S. Patent 5912223 (1999)

Clear microemulsion with surfactants and waterinsoluble heterocyclic compound

High foaming and good cleaning, but mild to the skin

Kacher (P&G)

U.S. Patent 5891836 (1999)

Oil-in-water microemulsion has desirable greasy soil removal and suds performance

Excellent greasy soil removing and suds

Bala et al. (ColgatePalmolive)

U.S. Patent 5616548 (1997)

Light duty liquid cleaning microemulsion with dlimonene

Superior grease removal

Bodet et al. (P&G)

U.S. Patent 6710023 (2004)

Organic polyamines containing at least three protonatable nitrogen atoms

Improved grease removal and suds benefits in soft water

Broze et al (ColgatePalmolive)

U.S. Patent 6380150 (2002) U.S. Patent 6339058 (2002)

Polyacrylate polymeric thickener to suspend oilcomprising gelatin beads

Boeckh et al. (BASF)

U.S. Patent 6156720 (2000)

Alkoxylated polyalkyleneimine soil dispersant compounds

High foaming and high cleaning properties; mild to human skin. Polyacrylate thickener leads to viscoelastic properties, with acceptable flowability. Hydrophobic dispersants with enhanced bleach compatibility and enhanced dispersancy

© 2006 by Taylor & Francis Group, LLC

Shi et al.

Giesen et al.. (Henkel)

Arvanitido et al. (ColgatePalmolive)

U.S. Patent 6387860 (2002) U.S. Patent 6197735 (2001)

C12-20 paraffin sulfonate + alpha -olefin sulfonate + amine oxide + Mg

Arvanitidou (ColgatePalmolive)

U.S. Patent 6187734 (2001) U.S. Patent 6165958 (2000)

Arvanitidou et al. (ColgatePalmolive)

U.S. Patent 6258763 (2001) U.S. Patent 6268331 (2001)

Kott et al. (P&G)

U.S. Patent 6506717 (2003)

C10-20 paraffin sulfonate + alpha olefin sulfonate + sultaine surfactant + poly(oxyethylene) diamine + magnesium C10-20 paraffin sulfonate + alpha -olefin sulfonate + Mg + sultaine surfactant + hydroxy containing organic acid, with pH of 3––5.5 Mid-chain branched surfactants

Detergent is high foaming. Magnesium salt improves cleaning performance in dilute usage, particularly in soft water areas. High foaming, good storage stability

Connor et al. (P&G)

U.S. Patent 6281181 (2001)

Mid-chain branched surfactants

Connors et al. (ColgatePalmolive)

U.S. Patent 6331516 (2001)

Lauryol ethylene diamine triacetate with other surfactants

Broze et al. (ColgatePalmolive)

U.S. Patent 6187735 (2001)

Arvanitidou et al. (ColgatePalmolive)

U.S. Patent 6184194 (2001)

C14–18 trimethyl ammonium chloride + disinfecting agent + amine oxide + C12-14 fatty acid monoalkanol amide Alpha olefin sulfonate + proton donating agent

U.S. Patent 5552089 (1996)

Berta et al. (ColgatePalmolive)

High foaming, good grease-cutting, and colorstability

Metal salt or oxide provides improved grease cleaning even in diluted form, particularly in soft water Improved detergency and better removal of greasy or particulate soils Increased resistance to water hardness, greater efficacy, and improved removal of greasy or particulate soils High foaming and good grease cutting properties

Dishwashing Detergents for Household Applications

Grease release agent decreases anchoring of greasy soil on surfaces to prevent buildup

U.S. Patent 6326347 (2001)

Grease release agent (fatty acid soap, nonionic, anionic, zwitterionic, or alkyl polysaccharide surfactant, or mixtures) Sodium bisulfite

Erilli, et al. (ColgatePalmolive)

Excellent grease cutting and mildness to human skin High foaming and good grease cutting properties; good mildness and excellent disinfecting properties 125

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Summary of Hand Dishwashing Detergent Patents on Grease Cleaning (1995–2004) (continued)

Inventor(s)

Stated Benefits

Patent Number and Date

Key Technologies

Arvanitidou (ColgatePalmolive)

U.S. Patent 6172022 (2001)

High foaming and good grease cutting; excellent disinfectancy

Lazarowitz (Cognis)

U.S. Patent 6248792 (2001)

Na or Mg LAS + AES + APG + poly(oxyethylene) diamine + amine oxides and/or C12-14 fatty acid monoalkanol amides Anionic surfactant + carboxylated alkyl polyglycoside

Burckett-St. Laurent et al. (P&G)

WO 2000043478 (2000)

Modified alkylbenzene sulfonate surfactant + cosurfactant

Superior cleaning, hardness tolerance and satisfactory biodegradability

Burckett-St. Laurent et al. (P&G)

WO 2000043476 (2000)

Alkylarylsulfonate mixture of crystallinitydisrupted mixtures

Smadi et al (Huntsman)

WO 2000042140 (2000)

Ethoxylated amine or ethoxylated ether amines

Superior cold-water solubility, superior hardness tolerance, excellent detergency, improved removal of lipid or greasy soils Improved triglyceride detergency for cooking oils and fats

Frazer et al. (Cognis)

WO 2000011123 (2000)

Enhanced foam stability and cleaning

Abbas et al. (ColgatePalmolive)

U.S Patent 5939378 (1999)

Alpha -olefin sulfonate + sugar surfactant + foam stabilizer, with alpha -olefin sulfonate and sugar surfactant at weight ratio of 1:2–2:1 Amine oxide and formic acid

Bala et al. (ColgatePalmolive)

U.S. Patent 5912222 (1999)

Microemulsion with improved cleaning

Bell et al. (Rhodia)

U.S. Patent 5906972 (1999)

Mg LAS + AES + APG + alkyl monoalkanol amide + water insoluble hydrocarbon + water soluble glycol ether Imidazoline derived amphoacetate surfactant

Good foaming and detersive property

Improved foam stability and grease cutting

Shi et al.

© 2006 by Taylor & Francis Group, LLC

Improved foaming

WO 9856496 (1998)

Sugar surfactant (polyhydroxy fatty acid amide and/or APG) + amphoacetate

Excellent cleaning performance with enhanced foam stability

Broze, G. et al. (ColgatePalmolive)

U.S. Patent 5770554 (1998)

Good grease soil removal

Biermann et al. (Henkel)

WO 9614374 (1996)

Analephotropic negatively charged complex comprising an anionic surfactant and a zwitterionic surfactant, amide oxide surfactant. or alkylene carbonate Novel surfactant compositions containing sugar surfactant solubilizers

Ofosu-Asante (P&G)

U.S. Patent 5698505 (1997)

Enhanced grease and oil removal

Ilardi et al. (Unilever)

U.S. Patent 5393466 (1995)

Spontaneous grease emulsifying surfactant systems with polyhydroxy fatty acid amides and amine oxide Esters of alkoxylated isethionate compounds

Richter (Reckitt & Colman)

U.S. Patent 5728667 (1998)

Alkyl ether carboxylate surfactant

Good detersive action and foaming characteristics

Ofosu-Asante (P&G)

U.S. Patent 5378409 (1995)

Alkyl ethoxy carboxylates

Improved grease cleaning and mildness

Cripe et al. (P&G)

U.S. Patent 5230823 (1993)

Alkyl ethoxy carboxylates

Superior grease cleaning and skin mildness

Desai (Henkel)

U.S. Patent 5451342 (1995)

Excellent detersive activity vs. wide range of food soils

Lazarowitz et al. (Cognis)

U.S Patent 5686400 (1997)

Na, K, or NH4 salts of C10-18 AES (1-3EO) with C10-18 mono- or di-ethanolamide or isopropanolamide AS + ammonium quat. surfactant + APG + trialkyl betaine

Garrett et al. (Unilever)

U.S. Patent 5352387 (1994)

N-alkylglyceramide derivatives

Markedly higher solubilizing power than conventional aromatic hydrotropes

Superior in mildness and cleaning performance and much more hardness tolerant

Dishwashing Detergents for Household Applications

Frazer et al. (Henkel)

Superior foaming and detergency properties. Trialkyl betaine has synergistic to resist the defoaming effect of grease soil. Grease cleaning benefits and skin mildness 127

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Summary of Hand Dishwashing Detergent Patents on Grease Cleaning (1995–2004) (continued)

Inventor(s)

Patent Number and Date

Key Technologies

Stated Benefits

Ofosu-Asante (P&G)

U.S. Patent 5716922 (1998)

Polyhydroxy fatty acid amide

Good grease removal and suds benefits

Auet al. (Unilever)

U.S. Patent 5389279 (1995)

Aldobionamide surfactant (amide of an aldobionic acid or aldobionalactone)

Superior grease cleaning and good foaming

Gomes et al. (Colgate Palmolive)

U.S. Patent 5866529 (1999) U.S. Patent 5629279 (1997)

High-level nonionic surfactants

High foam and detersive qualities. Nonirritating to human skin.

Dahanayake et al. (RhonePoulenc)

U.S. Patent 6204297 (2001)

Nonionic Gemini surfactants

High emulsifying power and detergency at very low concentrations

Erilli, R. (ColgatePalmolive)

U.S. Patent 5561106 (1996)

Nonionic surfactant based system

Desirable cleansing and mild to the skin

DeGuchi et al. (Kao)

U.S. Patent 5230835 (1993)

APG and polyhydric alcohol-polyalkylene oxide adduct with MW = 300–4000 at specific ratios

Grease cleaning and skin mildness

Shi et al.

© 2006 by Taylor & Francis Group, LLC

Summary of Hand Dishwashing Detergent Patents on Suds Boosting, Dissolution and Other Aesthetics (1995-–2004)

Inventor(s)

Patent Number and Date

Key Technologies

Stated Benefits

Sivik et al. (P&G)

U.S. Patent 6656900 (2003)

Amine oxide monomer-containing polymeric suds enhancer

Increased suds/foam volume and retention

Sivi, et al. (P&G)

U.S. Patent 6645925 (2003)

Quaternary nitrogen-containing or zwitterionic unitcontaining polymeric suds enhancer

Suds enhancer and volume extender. Increased grease re-deposition prevention

Sivik et al. (P&G)

U.S. Patent 6573234 (2003)

Polymeric suds stabilizer

Suds enhancer and volume extender. Increased grease re-deposition prevention

Bodet et al. (P&G)

U.S. Patent 6528476 (2003)

Block polymeric suds stabilizer

Suds enhancer and volume extender. Increased grease re-deposition prevention

Kasturi et al. (P&G)

U.S. Patent 6528477 (2003) U.S. Patent 6372708 (2002)

Polymeric suds stabilizer

Suds enhancer and a volume extender

Borgonjon et al. (P&G)

EP 1221475 (2002) JP 2002309292 (2002)

Quaternary nitrogen-containing or zwitterionic unitcontaining polymeric suds enhancer

Enduring suds with effective grease cutting properties

Liu et al. (Rhodia)

U.S. Patent 6376631 (2002)

Process reduces initiator consumption and produces low residual monomer polymers

Bergeron et al. (P&G)

WO 2000071660 (2000)

Suds boosting polymers with tertiary aminocontaining monomer separate from vinyl-functional monomer prior to copolymerizing. Block polymeric suds stabilizer, at pH of 4 to 12 in 10% solution

Bergeron et al. (P&G)

WO 2000071659 (2000)

Block polymeric suds stabilizer

Increased suds volume and suds retention. Good grease cutting and anti-redeposition.

Hutton et al. (P&G)

WO 2000071658 (2000)

Polymeric suds stabilizer

Suds longevity and improved skin feel or mildness

Increased suds volume and suds retention

129

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Table P-2

Summary of Hand Dishwashing Detergent Patents on Suds Boosting, Dissolution and Other Aesthetics (1995-–2004) (continued)

Inventor(s)

Patent Number and Date

Key Technologies

Stated Benefits

WO 02077143 (2002)

Hydrophobic polymer with MW >500 and containing butylene oxide moieties.

Increased viscosity and better dissolution.

Kasturi et al. (P&G)

WO 02077144 (2002)

Hydrophobic polymer with MW > 500 and containing alkylene oxide moieties, in addition to a solvatrope

Increased viscosity and better dissolution.

Bodet et al. (P&G)

U.S. Patent 2001016565 (2001)

Mixture of linear and branched AS/AES.

Improved viscosity and low-T stability vs. purely linear or purely branched surfactants

Brumbaugh (Amway)

U.S. Patent 5998355 (1999)

Alkoxylated glyceride, glycerine, or fatty acids

Increased viscosity and better dissolution

Bodet et al. (P&G)

WO 9700930 (1997)

Polyhydroxy fatty acid amide

Improved suds and rinsing performance

Connors et al. (ColgatePalmolive)

U.S. Patent 6617296 (2003)

Lauryol ethylene di-amine triacetate and zinc inorganic salt

Antibacterial efficacy and grease cleaning

Arvanitiodou et al. (Colgate-Palmolive)

U.S. Patent 6586014 (2003)

Hydrogen peroxide at specific pH ranges

Antibacterial and grease cleaning

Boucher et al. (P&G)

U.S. Patent 6387856 (2002)

Complexed iodine ions with amphoteric surfactant, at pH = 7–10

Exceptional antimicrobial protection against a broad array of microorganisms

Aszman et al. (ColgatePalmolive)

U.S. Patent 2002058603 (2002)

Amine oxide + disinfecting agent + nonionic surfactant + polymeric viscosity modifier

Disinfection. Detergent with improved ecotoxocity and remains clear and stable at 2–50º C.

Shi et al.

Borgonjon et al. (P&G)

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Table P-2

U.S. Patent 6369013 (2002)

Trimethyl cationic ammonium chloride and disinfecting agent

Disinfectancy + grease cutting and skin mildness to human skin

Frazee et al. (P&G)

WO 2001051096 (2001)

Ozone

Kills and/or renders inactive pathogens better than ozone alone

Bermejo et al. (Kao)

U.S. Patent 6265373 (2001)

Mixture of alkoxylated mono-, di- and tri-glycerides, and glycerine.

High viscosity, good foam stability, and skin mildness

Mao et al. (P&G)

U.S. Patent 5599400 (1997) US 5952278 (1999)

Improved mildness and dryness of skin

Lazarowitz et al. (Cognis)

WO 2002092738 (2002)

Active protease selected from serine proteolytic enzymes from Bacillus subtilis and/or Bacillus licheniformis. APG and co-surfactant from betaine, amphoacetate, and primary alkyl amine

Feldbruegge et al. (Henkel)

WO 2000034426 (2000)

Effervescent system

Foams readily on contact with water; providing good cleaning power

Burckhardt et al. (P&G)

WO 2001023516 (2001)

Anionic surfactant, a solvent and fragrance materials. Fragrance material with complexing agent.

Excellent cleaning and effective malodor suppression

High foaming and enhanced mildness to human skin

Dishwashing Detergents for Household Applications

Broze et al. (ColgatePalmolive)

131

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132

Shi et al.

The soils encountered in automatic dishwashing are similar to those in hand dishwashing as discussed in Section III. The principal soils include oily soil, mainly comprising various animal fats and vegetable oils, proteins, carbohydrates, and particulate soils. Oily soils can be easily removed if the wash temperature in the dishwasher is above the melting point of these soils. However they can be the hardest to remove if the wash temperature is too low, because automatic dish detergents normally do not contain high foaming cleaning surfactants that are effective in removing greasy soils. Proteins and carbohydrates are harder to remove, especially those dried or burnt-on soils. Examples include burnt-on starch soils and egg soils. However, the introduction of enzymes in the last 10 years has significantly improved the cleaning performance for these types of soils. The high temperature, high alkalinity, and high mechanical actions involved in the main wash step are especially helpful in removing these soils. For very hard to remove soils, consumers often wash them using a hand dishwashing detergent and by soaking and scrubbing. 2. New Product Forms for Automatic Dishwashing Detergents Traditionally, automatic dishwashing detergents are powders or granules. This product form is especially well suited to incorporate bleaches, strong builders for water hardness control and alkalinity building agents. In recent years, however, liquid or gel products and tablets have gained wide consumer acceptance. In North America, these new product forms now account for more than 50% share of the automatic dishwashing detergent market, as shown in Fig. 8. Tablets alone are now approaching 20% market share. In Western Europe, the dominant form of automatic dishwashing detergent is tablets that accounts for more than 70% of the total detergent market. Fluffy or compact powders account for the remaining market shares. Gel or liquid products are only a very small part of the automatic dishwashing detergent market in Western Europe. The popularity of the gel and tablet products with global consumers is probably related to their ease of handling and convenience. Consumers often complain about the messiness in product dosing with many traditional powdered detergents. This consumer trend away from the traditional powders has been experienced by other powdered deter-

80

Volume Share (%)

70 60 50 Powders

40 30

Liquids

20

Tablets

10 0 95/96 96/97 97/98 98/99 99/00 00/01 01/02 02/03 03/04 Year

Figure 8 America.

Recent trends in automatic dishwashing detergents by their market shares in North

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gents as well, e.g., laundry detergents. Traditional powdered laundry detergents now account for less than 50% of the market share in North America (Carpenter, 1999). As discussed above, there are significant differences in product form for automatic dishwashing detergents between North America and Western Europe. Take tablets as an example. They are relatively new in North America, while the Western Europe markets have gone through several generations of automatic dishwashing tablets. Tablet forms such as 2-in-1 product (detergent plus rinse aid) is an old story there, and 3-in-1 products (detergent, rinse aid, and salt) are now the standard. In North America, however, 2-in-1 tablets are just starting to gain popularity with consumers, especially water soluble pouches of liquid and liquid/powder combinations. These water soluble pouches are even more convenient to use than the tablets, as they can be directly put into the dispenser cup, without the need of unwrapping the product. Another important recent trend in automatic dishwashing is driven by the design of the dishwasher. This is related to the smaller dispenser cups in many newer dishwasher models. Some of these dishwashers even eliminated the prewash cup all together. This could negatively affect the wash performance of many traditional detergents such as powders. Product reformulation to more concentrated dishwashing products may be necessary in the future. 3. Key Consumer Benefits of Automatic Dishwashing Detergents Similar to hand dishwashing detergents, automatic dishwashing detergents are designed to facilitate the cleaning actions inside the dishwasher and make the whole dishwashing process more effective and the end results more satisfactory to consumers. The key consumer benefits of an automatic dishwashing detergent are summarized in Table 6. The relevant ingredients that are important for these detergent benefits are also summarized. Some of these ingredients are dosed into the dishwasher in the main wash step, while others in the rinsing step. 4. Major Ingredients in Automatic Dishwashing Detergents Given the extensive mechanical actions inside the dishwasher, there is one key consideration for all ingredients in automatic dishwashing detergents—their ability to foam under vigorous mechanical actions. For example, most surfactants that are effective in cleaning

Table 6 Summary of the Key Product Benefits of Automatic Dishwashing Detergents Desired Detergent Benefits Soil cleaning

Stain removal Dishware antispotting Dishware surface care and shine

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Key Ingredients • Alkalinity builders • Enzymes • Soil suspension agents • Bleaches, activators, and bleach catalysts • Builder, dispersants, and crystal growth inhibitors • Surface wetting agents • Silicates • Metal ions

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greasy soils are also high-foaming, thus their applications in automatic dishwashing detergents are rather limited. In this section, we briefly summarize the key ingredients being used in automatic dishwashing detergents and the typical formulations for major detergent forms. a. Builders. A key need for automatic dishwashing detergents is the management of hardness ions in the wash water. Hardness ions (Ca2+ and Mg2+) not only negatively impact the removal of greasy soils or stains, they can cause lime build-up and surface damage on dishware as well, especially glass items. These damages reduce the surface shine of many glass or ceramic items. Builders used in powdered automatic dishwashing detergents are similar to those in other powder detergents (for a more detailed discussion on detergent builders, please refer to Rieck [2001]). Three types of builders are widely used in automatic dishwashing, as listed below. • Sodium tripolyphosphate (STPP) • Sodium silicate • Sodium citrate The choice of the right builder for automatic dishwashing detergents is determined by the product form and compatibility with other desired ingredients in the product. b. Enzymes. Two types of enzymes are used in automatic dishwashing detergents. Proteases are used to breakdown protein soils such as eggs, while amylases are used to help remove tough-to-clean soils such as rice and spaghetti. Choosing the right enzymes or combinations for the specific product form depends on their compatibility with other ingredients in the products. In many applications, especially in liquid or gel products, enzyme stabilization systems are employed to improve their shelf stability. Applications of enzyme stabilization systems are widely described in the patent art. For example, Aquino et al. (2002) described an enzyme stabilization system for powders and tablet formulations. Boric acid and diol-based systems can be used to stabilize enzymes in liquid or gel products. c. Bleaches. Bleaching agents are widely used in automatic dishwashing detergents. The key performance benefits include (1) improved removal of food and/or beverage stains (e.g., tea and coffee) and (2) prevention of redeposition of hydrophobic soils on dish surfaces, which leads to spot formation. Two types of bleaching agents are often used. The first is chlorine-based bleach such as sodium hypochlorite, which is predominately in high pH gel or liquid automatic dishwashing detergents. The downside for chlorinebased bleach relates to its incompatibility with most enzymes in automatic dishwashing detergents. The second type of bleaches includes a broad range of oxygen bleaches such as perborate, which are used predominantly in powders and tablets. d. Polymer Dispersants. One of the utilities of polymeric dispersants in automatic dishwashing detergents is to minimize deposition of inorganic materials on glass surfaces. This often helps to prevent or reduce spotting and filming on glass surfaces. This polymer dispersancy is often achieved by two mechanisms: (1) suspension of inorganic materials in solution, and (2) inhibition of crystal growth for inorganic materials on glass surfaces. These dispersants are usually homopolymers or copolymers of acrylic, maleic, and methacrylic acids. The carboxylate groups in these polymers are especially effective in preventing the deposition of CaCO3 on glass surfaces.

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e. Nonionic Surfactants. Due to their generally low foaming potential, nonionic surfactants are widely used in automatic dishwashing detergents and rinse aids. A key performance requirement is their ability to “wet” hydrophobic surfaces or certain hydrophobic areas of dishware to reduce surface spotting on glasses, and in some cases to improve soil removal. Another performance need for nonionic surfactants is their ability to suppress foam or suds that often develop from food soil materials due to the vigorous mechanical actions involved in automatic dishwashing. A key balance that needs to be maintained for nonionic surfactants is surfactant foaming vs. surface wetting properties. As discussed by Heitland and Marsen (1987), nonionic surfactants with low cloud points often have low foaming potential. At temperatures above the cloud point, phase separation occurs with nonionic surfactants, which greatly reduces their foaming potential. However, low cloud point non-ionic surfactants often are not effective as surface wetting agents. As will be discussed later in this section, a key technology innovation is to optimize the nonionic surfactant structure in order to achieve both low foaming potential and good surface wetting capability to prevent surface spotting. The above ingredients have seen wide applications in automatic dishwashing detergents and rinse aids. Typical formulations of detergent powders, tablets, gels, and rinse aids are summarized in Table 7(a), (b), and (c). B. Bleach Catalyst Technologies for Automatic Dishwashing Bleaches and enzymes are two key technologies to improve the performance of automatic dishwashing detergents, especially for difficult-to-clean soils and stains. However, many cleaning enzymes are not stable in the presence of bleaches in the automatic dishwashing detergent matrix. This is especially the case with chlorine bleach (e.g., sodium dichloroisocyanurate [NaDCC]), which is a very effective bleach at low cost. Chlorine bleaches also develop an unpleasant smell in the course of dish washing and have environmental safety concerns (Scheper et al, 1998). In recent years, a new generation of bleach boosting catalysts have been developed by Scheper et al. (1998) and successfully formulated into automatic dishwashing detergents. Unlike chlorine bleaches, these bleach boosting catalysts are both effective in removing bleachable stains and compatible with key enzyme technologies. We provide here a summary of this bleach metal catalyst technology. 1. Bleach Metal Catalyst Technology Design The key objective of the bleach boosting catalyst is to match the stain removal efficacy of chlorine bleach with good enzyme compatibility. Many attempts have been made in the past to develop similar technologies, as indicated by the patent art that includes more than a thousand patent publications covering bleach boosters (activators and catalysts) and cleaning compositions to improve the bleaching efficacy of hydrogen peroxide. However, the bleach activator approach using perborate or percarbonate plus tetraacetylethylenediamine (TAED) has several significant issues in the context of automatic dishwashing detergents: • The performance of bleach activator systems, while an improvement over peroxide alone, does not match that of the chlorine bleaches; • High levels of bleach activators are often needed as they work in a stoichiometric manner with peroxide, i.e. one mole of bleach activator reacts with one mole of peroxide. The bleach activator approach was not mass efficient. It was not only expensive, but it was also limited by product formula space as well; • Many of the more aggressive bleach activators also negatively impact the enzyme system stability and performance via enzyme oxidation and/or degradation.

© 2006 by Taylor & Francis Group, LLC

136 Table 7

Shi et al. Typical Formulations for Automatic Dishwashing Detergents and Rinse Aids

(a) Powders and Tablets

Ingredients

Usage

Functions or Benefits

STPP

20–30%

Dispersant polymers Low-foaming nonionic surfactant(s) Sodium carbonate Silicates

0–4% 1–2% 20–30% 2–8%

Enzymes Bleach and catalyst

1–2% 1–5%

Perfumes

<0.1%

Builder, soil cleaning and suspension, and stain removal Antifilming and antispotting Antispotting and suds suppressor Alkalinity and builder Alkalinity, surface care agent, and processing aid Tough soil cleaning and antispotting Color stain removal and soil antiredeposition Aesthetics

(b) Gels or Liquids

Ingredients

Usage

Functions or Benefits

STPP Low-foaming nonionic surfactant(s) Silicates

15–25% 0–2% 0–8%

Enzymes Enzyme stabilization Bleach

0–2% 0-4% 0–3%

Thickener Perfumes

1–2% <0.1%

Builder and soil cleaning and suspension Antispotting and suds suppressor Alkalinity, surface care agent, and processing aid Tough soil cleaning and antispotting Enzyme stabilization system Color stain removal and soil antiredeposition Thickener for solid suspension in product Aesthetics

(c) Rinse Aids

Ingredients

Usage

Low-foaming nononic surfactant(s)

20–40%

Hydrotropes (e.g., SCS) Ethanol Perfumes Water and adjuncts

2–4% 4–6% <0.1% Balance

Functions or Benefits Surface wetting and water sheeting; antispotting; drying aid Phase stabilizer Phase stabilizer, preservative Aesthetics

With the bleach catalyst approach, Scheper et al. (1998) successfully introduced a transition metal bleach catalyst into automatic dishwashing detergents in recent years. This catalyst is PentaAmmineAcetatocobalt(III) Nitrate (PAAN), whose molecular structure is depicted in Fig. 9. As discussed by Scheper et al. (1998), the PAAN colbalt (III) bleach catalyst is easy to make in high purity and has several key advantages:

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Dishwashing Detergents for Household Applications 2+

NH3 H3N

137

NH3

Co

2 NO3−

NH3

H3N

CH3

O O

Figure 9

Molecular structure of PentaAmmineAcetatocobalt(III) Nitrate (PANN)

% Protease Activity

100

0.004% PAAN 80

60 2% TAED 2% NaDCC

40 0

10

20

30

40

50

60

Time, Minutes

Figure 10 Compatibility of PAAN colbalt (III) catalyst as measured by protease activities under wash conditions in automatic dishwasher tests.

• This PAAN catalyst is stable in an aqueous and alkaline product matrix. Co3+ is stable to ligand substitution due to its electronic configuration. Its stability has been tested with the presence of all of the “intentionally added” ingredients in typical automatic dishwashing detergents, as well as the “unintentionally added” materials present in the consumer dishwashing process such as food soils, hardness ions, and chlorine from drinking water treatment; • This catalyst achieves high mass efficiency in soil and stain removal under typical automatic dishwashing conditions due to its large number of catalytic turnovers. The ammonia ligand is very effective at hydrogen bonding with soils and dish substrates, improving the efficiency of soil removal. Since ammonia is a noncharged ligand, PAAN is also designed to carry a cationic charge, which allows the catalyst to react more rapidly with peroxide anions and to interact more strongly with the glass and ceramic surfaces on which most stains and soils reside; • The PAAN catalyst is compatible with key enzyme systems in automatic dishwashing detergents, as shown in Fig. 10. The stability of protease in the presence of PAAN is significantly better under through-the-wash conditions than with TAED and of course than with chlorine bleach.

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138

2.

Shi et al.

Product Performance of the Cobalt (III) Bleach Catalyst

a. Beverage Stain Removal. As shown in Fig. 11, the PAAN catalyst provides outstanding removal of tea stains in automatic dishwasher tests. This catalyst has been found to be effective at levels as low as 200 ppb in the wash, provided that an adequate amount of peroxide is present. Under typical cleaning test conditions, the tea stain removal benefits of the PAAN catalyst has been found to be equivalent to those obtained from chlorine bleach (NaDCC). Also, PAAN’s bleaching performance is considerably better vs. TAED. b. Cleaning Mechanisms. The bleaching and stain removal mechanism of the PAAN catalyst has been investigated extensively by Scheper et al (1998). As is generally known, mechanistic elucidation of bleach catalytic systems is often difficult due to the short lifetimes of the reactive intermediates and transition states. However, Scheper, et al. (1998) reported that the most likely bleach catalysis mechanism of PAAN involves an outer-sphere complex formed between PAAN and peroxide anion HOO–, as shown in Fig. 12. The reactive intermediate complex then oxidizes hydrophilic stains upon contact with dish surfaces, achieving the cleaning benefits observed for hydrophilic stains such as tea and coffee. Furthermore, this oxidative reaction helps to cycle the intermediate complex back to the starting catalyst, continuing the catalytic chain reaction and achieving good mass efficiency of the bleach catalyst system. C. Bleach Technologies for Hydrophobic Stains Red tomato stain is a high visibility and difficult-to-remove stain for many consumers, especially for automatic dishwasher users. Tomato stains are highly hydrophobic and

Perborate∗ Base Matrix ∗2.2% AvO as H2O2

Perborate∗ Base Matrix + 2.2% TAED

Perborate∗ Base Matrix + 0.008% PAAN

Figure 11 Tea stain performance of PAAN vs. TAED and chlorine bleach.

Proposed Performance Mechanism

Sub

HOO−

[Co(NH3)5OAc]2+ (HOO)−

pH Sensitive Reaction Propose HOO− is only Reactant

Outer-Sphere Complex - Ionic/H-Bonding Bleaching Species

[Co(NH3)5OAc]2+

+

Subox [Co(NH3)5OAc]2+ Catalyst Recycled

Technical Performance Model [Co(NH3)5OAc]2+ (HOO)− Ionic Interaction with Stain/Surface Tea Stained Surface

Activated Peroxide Bleaches Stain

Catalyst/Stain Interaction

Cleaned Surface

Figure 12 Bleaching and stain removal mechanism of PAAN cobalt (III) catalyst.

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139

adsorb easily onto plastic surfaces. Under the high-temperature wash conditions of automatic dishwashers, tomato stains are often driven deeply into the surface layer of plastic items, making them even more difficult to remove. In recent years, bleach technologies have been developed to remove tomato stains from hard plastic surfaces. For example, Ofosu-Asante and Hutton (2002) described a detergent composition containing diacyl peroxide as the bleaching agent that is especially effective in removing tomato stains. An example of diacyl peroxides is benzoyl peroxide. Under the high wash temperatures of automatic dishwashing, benzoyl peroxide thermally dissociates to generate reactive radicals to react with lycopene pigments in tomato stains. Despite its effectiveness in bleaching tomato stains, diacyl peroxide has been found to be incompatible with ingredients in a typical automatic dishwashing detergent, such as enzymes. Benzoyl peroxide itself is also not stable in a high alkalinity product matrix that is typical for automatic dishwashing detergents. As a result, the benzoyl peroxide stain removal technology has only been applied to stand-alone additive products over the last several years. D. Low-Foaming Nonionic Surfactants Low-foaming nonionic surfactants have been widely used in automatic dishwashing detergents. They perform two crucial functions: (1) surface wetting to prevent spot and film formation and (2) suds control. Selected nonionic surfactants are not only low foaming themselves; they have antifoaming properties as well. In rinse aid formulas, these nonionic surfactants are often used to prevent spot and film formation. In the main wash step, nonionic surfactants can help improve the water sheeting action and prevent soil residues from re-depositing onto dish surfaces (e.g., food, detergent, CaCO3, etc.). Suds control is essential for automatic dishwashing detergents given the rigorous mechanical actions inside the automatic dishwasher. Suds or foam generated by either food proteins or detergent ingredients can reduce the dishwasher’s spray arm velocity and disrupt water recirculation inside the machine. This has a direct effect on the overall cleaning performance. Suds control is also crucial to prevent water leakage out of the dishwasher. Historical experience has shown that water leakage is far more damaging to a product’s consumer acceptance than any cleaning failures. Low-foaming nonionic surfactants do not provide traditional grease cleaning benefits such as those delivered by traditional hand dishwashing detergents, which include soluble work-horse surfactant systems (e.g. amine oxide, anionics and soluble nonionics) for grease cleaning. Truly soluble ‘cleaning’ surfactants are not usually used in automatic dishwashing detergents because of the difficulty in suds control. In recent years more emphasis has been placed on no prerinsing/pretreating of dishes, and automatic dishwashing detergents are increasingly required to deliver better grease cleaning performance. This need has driven the development of better suds suppressing materials that are capable of controlling suds, but allow the traditional work-horse surfactant (e.g. amine oxide) to be effective at removing greasy soils from dishware. Despite the wide applications of traditional nonionic surfactants, there is still a broad opportunity to optimize the balance between their low-foaming properties and spot prevention performance. In recent years, several alkyl capped nonionic (ACNI) surfactants have been developed for applications in automatic dishwashing detergents. The molecular structure of ACNI surfactants are depicted in Fig. 13. The alkyl end cap can be designed to improve both suds control and surface spot/film prevention. More detailed discussion about these ACNI wetting agents can be found in Jordan et al. (2004).

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140

R1

Shi et al.

O

O

x

O

R2

Figure 13 General molecular structure of alkyl capped nonionic (ACNI) surfactants.

10

Cleaning Grade (1–10; 10 = Clean)

9

R R

O O O

C C9/11 9/ 11

8

88

7 6 5 4 3 2 1 0 R = C5 (branched)

C5 (linear)

C8

C10

C12

Figure 14 Cleaning performance (lipstick removal) as a function of alkyl capping group.

To optimize the suds suppressing properties and cleaning compatibility of ACNI surfactants, a wide range of R2 alkyl end caps have been investigated. Cleaning measurements were made based on the amount of lipstick soil removal with C16 amine oxide as the traditional grease cleaning surfactant and in combination with the ACNI surfactant series derived from C9-11(EO)8 varying the length of the capping group. The test conditions were those typically found in an automatic dishwashing process, with 120˚F wash temperature and 0 gpg of water hardness. As can be concluded from Fig. 14, the size of the alkyl end cap group has a large impact on ACNI cleaning performance. Short-chain C5 cap group had the best cleaning performance in combination with C16 amine oxide. This loss in cleaning performance with longer-chain end cap groups may suggest that they lead to undesirable interactions between the ACNI surfactant and other ingredients in the base product matrix. The suds control performance of several ACNI surfactants has also been tested by measuring the suds height in both the main wash and rinse steps. The suds data are summarized in Table 8. It’s clear from this table that the size of the end cap group again has a clear impact on the level of suds generated in both the main wash and the rinse steps. ACNI surfactants with C3 to C4 end cap groups are significantly less effective in suds control when compared with those with alkyl end cap groups of >C5. Combining the cleaning performance and suds control data together, it appears that the optimum alkyl end cap group is C6-C8 for the C9-11(EO)8 nonionic surfactant backbone.

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Dishwashing Detergents for Household Applications Table 8.

141

Suds Control Data of Selected ACNI Surfactants in Automatic Dishwashing Suds Height (Inches) ACNI Compound

O

C9/11

C9/11

C9/11

C9/11

O

O

O

O

O

O C9/11O

C9/11

O

O

O

O 8

0.9

1.0

Pyranyl (C5)

0.2

0.7

Pyranyl (C5)

0.05

0.4

Amyl (C5)

0.1

0.2

Cyclohexyl acetal (C6)

0.15

0.01

2-Ethylhexyl acetal (C8)

0.05

<0.01

Butylene oxide

0.05

0.05

8

8

O C9/11O

t-Butyl (C4)

O

8

O

Rinse 2 (36 min)

O

6

O

Main Wash (20 min)

8

8

O

Capping Group

O

H

3

This optimum alkyl end cap size range for the ACNI surfactant has been discussed by Sivik et al. (2001) and Jordan et al. (2003). E. Glass Surface Care Technologies Corrosion of glass surfaces in automatic dishwashers is a well known phenomenon. As early as 1971, Joubert and van Daele (1971) discussed the etching of glassware surfaces in mechanical dishwashing. More recently, Sharma et al. (2003) discussed the roles of silicate on the corrosion of soda-lime-silicate glassware in automatic dishwashing. Glass corrosion and filming have been discussed extensively in the patent art over the last 10 to 20 years.

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142

Shi et al. (A) Glass Etching (10 K)

(B) Cloudy Glass Surface (100 K)

Figure 15 Scanning electron microscope (SEM) images of (A) etched glass surface and (B) deposits on cloudy glass surface.

The glassware corrosion or filming problem actually consists of two separate phenomena. The first relates to glass corrosion or etching caused by the leaching of minerals in the glass itself and/or hydrolysis of the silicate network. The glass surface etching or defect phenomenon is illustrated in Fig. 15A. This surface etching process is highly influenced by two factors in the dishwasher: high alkalinity (pH > 9.5) and high builder concentration. The second phenomenon relates to the deposition of inorganic materials such as carbonate, phosphate, and silicate onto glass surfaces. Such deposits are illustrated in Fig. 15B. Both surface phenomena lead to cloudy appearance of glassware after repeated washes in an automatic dishwasher, which often manifests itself as an iridescent film in the early wash stages and then becomes progressively more opaque with repeated washing. Glass care technologies have been successfully applied in automatic dishwashing products in recent years. In North America, major manufacturers have incorporated glass care technologies into both the dishwashing detergents and rinse aids. In Western Europe, most major automatic dishwashing detergents now offer glass care benefits in 3-in-1 tablets. 1. Anticorrosion Glass Care One approach to reduce glassware corrosion is to add silicate materials into automatic dishwashing detergent. Such silicates include mixtures of disilicate and metasilicate, copolymer of an organomineral and siliconate, and silicate with calcium, magnesium, strontium, or cerium counter-ions. However, these silicate materials are not stable under lower alkalinity conditions, as discussed recently by Waits and Brooker (2004). A cost-effective and simple approach to reduce glassware corrosion is to add soluble or slightly soluble inorganic metal salts or oxides of zinc, titanium and aluminum (refer to Caravajal and Hatfield [1997]) and Ahmed and Buck (1992) for more details]. The key drawback for these inorganic salts is that they cause lumping in gel products. To overcome this, Waits and Brooker (2004) have recently developed encapsulation technologies for these anticorrosion glass care actives. 2. Antifilming Surface Care Dishware surface filming typically relates to the formation of scale deposits such as carbonate and phosphate scales, which are formed in the presence of high hardness ions (Ca2+ and Mg2+). Two typical antifilming technologies have been described in the patent literature.

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• Polycarboxylates (e.g., polyacrylates, polymethyacrylates, etc.) • Sulfonate/carboxylate copolymers (e.g., Alcosperse® 240 and Acusol® 586) High cost has limited the broad applications of polycarboxylates and sulfonate/carboxylate copolymers in automatic dishwashing detergents. Recently, Price et al. (2004) reported the discovery of cost-effective sulfonate/carboxylate materials for antiscaling, antifilming, and antispotting benefits. F. Summary of Recent Patents for Automatic Dishwashing Detergents An extensive patent summary had been provided previously by Gorlin et al. (1997) for liquid automatic dishwashing detergents for the period up to about 1995. The present summary covers the patent activities for all forms of automatic dishwashing detergents (powders, liquids and tablets) from ~1990 to 2004. Table P-3 covers automatic dishwashing patents related to cleaning, and Table P-4 covers those related to glass antietching and dish surface care.

V. CONCLUDING REMARKS Hand and automatic dishwashing detergents play an essential role in consumers’ everyday lives. They help consumers clean and care for a wide range of kitchenware, including dishes, pots, pans, and utensils. Over the last 10 to 15 years, dishwashing detergent manufacturers and suppliers have conducted extensive research and development activities to improve product performance in order to satisfy consumers’ needs better. New technologies and new product forms have emerged in recent years, fueling the dynamic growth of hand and automatic dishwashing detergents in the global marketplace. New technology development in dishwashing detergents has focused on both cleaning and dish surface care. For hand dishwashing, key new cleaning technologies include new surfactants, low interfacial tension (IFT) technologies based on divalent ions, suds boosting polymers, dissolution aids, enzymes, and bleaches. For automatic dishwashing, new product forms such as liquid gels and tablets have gained considerable consumer acceptance and significant market shares. Key new cleaning technologies include metal bleach catalysts and low-foaming nonionic surfactants. Dish surface care technologies include glass antietching and antifilming technologies. Many of these new technologies have been well accepted by consumers and are expected to fuel the continued dynamic growth of dishwashing detergent products in the global marketplace.

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Table P-3 Summary of Automatic Dishwashing Patents on Cleaning (1990–2004)

Inventor(s)

Patent Number and Date

Key Technologies

Bennie et al. (P&G)

U.S. Patent 6740628 (2004)

Removal of cooked-, baked-, or burnt-on food soils from cookware and tableware

Clare (P&G)

U.S. Patent 6723687 (2004)

Organic solvent with volatile organic content of <50%. Dishwashing detergent composition from multi-compartment containers. Diacyl peroxide bleach and blooming perfume

Busch et al. (P&G)

U.S. Patent 6608015 (2003)

Transition-metal bleach catalyst with crossbridged macropolycyclic ligand

Enhanced cleaning/bleaching benefits

Patel (P&G)

U.S. Patent 6602837 (2003)

Alkaline liquid detergent containing diacyl peroxide, solvent, and chelant

Effective in removing carotenoid stains from plastics

Jordan et al. (P&G)

U.S. Patent 6593287 (2003)

Ether-capped poly(oxyalkylated) alcohol surfactants

Superior grease cleaning and improved spotting/filming benefits

Aquino et al. (P&G)

U.S. Patent 6432902 (2002)

Improved cleaning for tough soils

Perkins et al. (P&G)

U.S. Patent 6399557 (2002)

Detersive protease enzymes composite particle with water soluble carboxylate barrier layer Transition-metal bleach activator and/or organic percarboxylic acid

Busch et al. (P&G)

U.S. Patent 6387862 (2002)

Transition-metal bleach activator + oxygen bleach

Enhanced cleaning/bleaching benefits

Chatterjee et al. (P&G)

U.S. Patent 6326341 (2001)

Low cloud point nonionic surfactant

Spot prevention and suds control

Removal of tough-to-clean soils

Enhanced cleaning/bleaching benefits

Shi et al.

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Stated Benefits

U.S. Patent 6119705 (2000)

Cobalt chelated catalysts are provided

Enhanced cleaning/bleaching benefits for tea stain removal

Scheper et al. (P&G)

U.S. Patent 6034044 (2000)

Mixture of low cloud point and high cloud point nonionic surfactants

Spot prevention and suds control

Baillely et al. (P&G)

U.S. Patent 6017867 (2000)

Percarbonate bleach with particle size of 250900 µm

Bleaching benefits

Moss et al. (P&G)

U.S. Patent 5972040 (1999)

Percarbonate and amylase enzyme

Bleaching benefits and tough soil cleaning

Chatterjee et al. (P&G)

U.S. Patent 5967157 (1999)

Ether-cappe nonionic surfactant

Spot prevention and suds control

Haeggberg et al. (P&G)

U.S. Patent 5968881 (1999)

Manganese catalyst and/or cobalt/ammonia catalysts

Enhanced bleaching performance

Scheper et al. (P&G)

U.S. Patent 5962386 (1999)

Cobalt catalysts

Enhanced cleaning/bleaching benefits for tea stains removal

Chatterjee et al. (P&G)

U.S. Patent 5912218 (1999)

Low cloud point nonionic surfactant

Spot prevention and suds control

Rai et al. (P&G)

U.S. Patent 5904161 (1999)

Stability-enhanced amylase and bleachimproving materials

Enhanced cleaning/bleaching benefits

Painter (P&G)

U.S. Patent 5902781 (1999)

Cobalt (III) or manganese (III) bleach catalyst combined with protease or amylase enzymes

Enhanced cleaning/bleaching benefits

Scheper et al. (P&G)

U.S. Patent 5804542 (1998)

Certain cobalt catalysts

Enhanced cleaning/bleaching benefits for tea stains removal

Perkins et al. (P&G)

U.S. Patent 5703030 (1997)

Carboxylate-containing cobalt catalysts

Enhanced cleaning/bleaching benefits for tea stains removal

Dishwashing Detergents for Household Applications

Getty et al. (P&G)

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Table P-3 Summary of Automatic Dishwashing Patents on Cleaning (1990–2004) (continued)

Inventor(s)

Patent Number and Date

St. Laurent et al. (P&G)

U.S. Patent 5698046 (1997)

C12-14 N-(3-methoxypropyl) glucamide.

Improved cleaning and filming and spotting performance

Goldstein (P&G)

U.S. Patent 5663133 (1997)

Diacyl peroxide particle

Effective removal of carotenoid stains from plastics and tea stains from china

Taylor et al. (P&G)

U.S. Patent 5654421 (1997)

Enhanced cleaning/bleaching benefits

Miracle et al. (P&G)

U.S. Patent 5616546 (1997)

Quaternary-substituted bleach activators, such as with caprolactam or valerolactam leaving groups Bleach activators with monoquaternary substituted bis(peroxycarbonic) acids

Hartman et al. (P&G)

U.S. Patent 5559089 (1996)

Good cleaning of tableware

Willey et al. (P&G)

U.S. Patent 5405412 (1995)

Monopersulfate bleach with protease or amylase enzymes and acrylate organic dispersants. Bleach activators of N-acyl caprolactams and nonanoyloxybenzene sulfonate

Painter, et al. (P&G)

U.S. Patent 5292446 (1994)

Nil-P builder system with polyacrylate dispersant

Nil-P automatic dishwashing detergent

Prince et al. (P&G)

U.S. Patent 5130043 (1992)

Enhanced stability and cohesiveness

Kinstedt et al. (P&G)

U.S. Patent 4988452 (1991)

Aqueous automatic dishwashing detergent comprising polycarboxylates and phosphate esters Capped polyalkylene oxide block copolymer nonionic surfactants

Stated Benefits

Enhanced cleaning/bleaching benefits

Stronger performance on hydrophobic and hydrophilic stains

Spot prevention and suds control

Shi et al.

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Key Technologies

U.S. Patent 6605578 (2003)

Gorlin et al. (ColgatePalmolive)

U.S. Patent 5698507 (1997)

Ahmed et al. (ColgatePalmolive)

U.S. Patent 5423997 (1995)

Krishnan (ColgatePalmolive)

U.S. Patent 5318715 (1994)

Ahmed (ColgatePalmolive)

U.S. Patent 5229027 (1993)

Water-soluble iodide/iodine mixture as hypochlorite bleach stabilizer

Better bleach stability and better cleaning

Tartakovsky et al. (Unilever)

U.S. Patent 6345633 (2002)

Water soluble cationic surfactants

Reduce spotting, filming, and damage on plastic articles

Angevaare et al. (Unilever)

U.S. Patent 5705465 (1998)

Improved cleaning of tough soils

Bahary et al. (Unilever)

U.S. Patent 5336430 (1994)

C12-22 unsaturated fatty acid + >C25 ketone at weight ratio of 1:4 to 1:2, plus proteolytic enzyme Microbial polysaccharide, in combination with wax encapsulated chlorine bleach

Romeo et al. (Unilever)

U.S. Patent 5281351 (1994)

Antiscalant agents with acidic functionalities in zero-P or low P powder detergents

Prevent scale buildup and improve detergent solubility

Elliott et al. (Unilever)

U.S. Patent 5135675 (1992)

Stable thixotropic liquid automatic dishwashing composition.

Solid particle suspension and hypochlorite stability

Phosphate-free ultraconcentrated powder, containing a mixture of protease and amylase enzymes Liquid compositions with binary mixture of Maxacal enzyme and Maxamyl enzyme

Removal of protein and carbohydrate soils from dishware Effective dishware cleaning

Removal of protein and carbohydrate soils

Dishwashing Detergents for Household Applications

Aqueous liquid automatic dishwashing composition disposed in a water soluble package Mixture of acid resistant protease enzyme and acid resistant amylase enzyme

Convenient delivery system

Fleckenstein et al. (Colgate-Palmolive)

Improved cleaning

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Table P-4 Summary of Automatic Dishwashing Patents on Glass Anti-Etching and Dish Surface Care (1990–2004)

Inventor(s)

Patent Number & Date

Key Technologies

Stated Benefits

WO04046299 (2004)

Encapsulated glass care actives

Cleaning and protecting glassware in automatic dishwashing

Pric et al. (P&G)

U.S. Patent 20040121928 (2004)

Cost-effective sulfonate carboxylate functional polymers

Preventing glass filming due to carbonate and phosphate scale formation

Ghosh et al. (P&G)

U.S. Patent 6693071 (2004)

Rinse aid with nanoparticle system

Sadlowski (P&G)

U.S. Patent 5786315 (1998)

Polymer dispersant and silicate

Longlasting or semipermanent multiuse benefits— surface wetting and sheeting, uniform drying, anti-spotting, antistaining, antifilming, self-cleaning or durability Enhanced antifilming performance

Caravajal et al. (P&G)

U.S. Patent 5703027 (1997)

Metasilicate with other silicate (polymeric) components

Surface antifilming

Sadlowski (P&G)

U.S. Patent 5597789 (1997)

Silicate and low-molecular-weight polyacrylate copolymer

Enhanced hard water filming performance

Wise; R.M.

U.S. Patent 5384061 (1995)

Cross-linked polycarboxylate polymer

Glass antifilming

Cilley et al. (P&G)

U.S. Patent 4933101 (1990)

Insoluble inorganic zinc salt

Inhibition of glassware corrosion

Caravajal et al. (P&G)

U.S. Patent 4908148 (1990)

Insoluble inorganic zinc salt

Inhibition of glassware corrosion

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Shi et al.

Waits et al. (P&G)

U.S. Patent 6191088 (2001)

Polymer containing sulfonic acid groups

Reduced filming on dishware

Gorlin et al. (ColgatePalmolive)

U.S. Patent 6162777 (2000)

Crosslinked polyacrylic acid polymer

Reduced filming on dishware

Ahmed et al. (ColgatePalmolive)

U.S. Patent 5089161 (1992)

Alumina or titanium dioxide

Reduced filming on dishware, particularly in hard water

Dixit (ColgatePalmolive)

U.S. Patent 4971717 (1990)

Aluminosilicate zeolite as antifilming and antispotting agent

Reduced filming on dishware, particularly in hard water

Ahmed et al. (ColgatePalmolive)

U.S. Patent 968445 (1990)

Silica antifilming agent

Reduced filming on dishware, particularly in hard water

Ahmed et al. (ColgatePalmolive)

U.S. Patent 4968446 (1990)

Alumina or titanium dioxide antifilming agent and polyacrylate polymer antispotting agent

Reduced filming on dishware, particularly in hard water

Tartakovsky et al. (Unilever)

U.S. Patent 6334452 (2002)

Water-soluble cationic surfactants

Reduce glass decor fading without composing tea stain removal

Tartakovsky et al. (Unilever)

U.S. Patent 6281180 (2001), U.S. Patent 5981456 (1999)

Water-soluble cationic or amphoteric polymer + phosphate or nonphosphate builder

Prevent fading or corrosion of dishware

Tartakovsky et al. (Unilever)

U.S. Patent 6239091 (2001)

Water-soluble cationic or amphoteric polymer

Reduce spotting and filming on glassware

Gary et al. (Unilever)

U.S. Patent 5480576 (1996)

1,3-N azole compound with pKa < wash pH

Prevent tarnishing of silver and silver-plated articles

Hahn (ReckittBenckiser)

U.S. Patent 6622736 (2003)

Water soluble glass in detergent or rinse aid

Corrosion protection for glassware

Dishwashing Detergents for Household Applications

Binstock et al. (Colgate-Palmolive)

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5 The Formulation of Liquid Household Cleaners Stefano Scialla

CONTENTS I.

II.

Introduction ........................................................................................................... 154 A. Background................................................................................................ 154 B. Classification of Household Soils ............................................................. 154 C. Classification of Household Surfaces ....................................................... 156 D. Test Methods ............................................................................................. 157 1. Encrusted grease and soap scum removal................................. 157 2. Limescale removal ..................................................................... 158 3. Shine performance ..................................................................... 158 4. Foaming profile.......................................................................... 158 Surface Cleaner Formulations............................................................................... 159 A. All-Purpose Cleaners................................................................................. 159 1. Suds and Other Aesthetic Parameters ....................................... 159 2. Performance Profile ................................................................... 159 3. Technology ................................................................................. 160 B. Bathroom Cleaners.................................................................................... 164 1. Suds and aesthetics .................................................................... 164 2. Technology ................................................................................. 165 C. Toilet Bowl Cleaners................................................................................. 167 D. Bleach Cleaners......................................................................................... 169 E. Cream Cleansers........................................................................................ 170 F. Glass Cleaners ........................................................................................... 171 G. Carpet Cleaners ......................................................................................... 172 1. Spotters and High Traffic Cleaners ........................................... 172 2. Shampoos ................................................................................... 173

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3. Spray Extraction Formulations .................................................. 173 III. Future Trends......................................................................................................... 174 Acknowledgments........................................................................................................... 175 References ....................................................................................................................... 175

I. INTRODUCTION A. Background In this discussion we will define household surface cleaners as products used to clean hard or soft surfaces in the home, with the exclusion of dishes and laundry items. The above definition gives an idea of the vastness of the field in terms of soil and surface types to deal with. Just to provide a few examples, soils can go from generic dust to clay, oil, greasy encrustations, soap scum, limescale, water marks, urine, mold, and mildew. Surfaces can vary from wood to ceramic, enamel, porcelain, glass, marble, stainless steel, various metals, linoleum, carpets, and several plastics. This variety of soils and surfaces causes a significant complexity for the formulator, who needs to make sure products are effective against virtually any type of soil without damaging the substrate to be cleaned. An additional difficulty stems from the fact that hard surface cleaners are mostly used at room temperature, where reaction kinetics is relatively slow, and contact time between product and surface is usually quite short. Also, the user can have a big and to a large extent unpredictable influence on the cleaning end result, for instance by using different application methods (e.g., sponge or wipe or kitchen paper), applying different degrees of pressure/rubbing, or adopting different levels of dilution with tap water. Thus the household surface cleaning process has a much higher degree of variability than the laundry cleaning process, which typically occurs inside a washing machine and therefore is more reproducible. Due to this high degree of complexity, it is useful to adopt a classification of soils and surfaces that allows us to make reference to them in a simplified manner. B. Classification of Household Soils A possible approach is to divide household soils into greasy, encrusted greasy, bleachable, particulate, soapy, and pH sensitive. Greasy soils are probably the most common ones and can be found on all surfaces in every part of the household. From a physical standpoint they are essentially liquid or waxy fluids. Typical examples are cooking oils, sauces, fingerprints, cosmetic products (e.g., lipstick), and shoe polish. Cooking oils in particular are ubiquitous because the vapors produced during the frying process spread around the house and deposit on all surfaces. Also, once even a very thin layer of oil has deposited on a surface, this catalyzes the deposition of more soil, such as dust, by acting as a glue between the surface and the new soil. Thus greasy soils are very relevant to consumers both because they are so common and because they can have a significant impact on surface appearance. Encrusted greasy soil is the most typical example of stubborn soil found in the kitchen, particularly near the cooking area or inside ovens. Its specific composition can vary significantly, however in most cases it derives from a complex series of reactions oils undergo when exposed to high temperature or upon aging. The main reactions occurring during a frying process, for instance, include formation of conjugated dienes, formation and decomposition of hydroperoxides, formation of low-molecular-weight carbonyl compounds, hydrolysis of triglycerides, and polymerization via complex free

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radical processes at elevated temperatures around 180˚C [1]. Particularly important with respect to the formation of encrusted greasy soil is the latter phenomenon, which concerns triglyceride molecules containing unsaturated fatty acids with one, two, or three double bonds (oleic, linoleic, and linolenic acid, respectively). These react with atmospheric oxygen forming hydroperoxides (autooxidation), which then combine together leading to three-dimensional cross-linked polymeric structures responsible for soil hardening [2]. Bleachable soils include all those surface contaminants that carry oxidizable—usually colored—groups. Examples are beverages such as tea, coffee, wine, or body fluids/excrements such as urine and feces. Beverages are relatively common soils on carpets and upholstery, whereas urine and feces can be found in or around toilet bowls. Other important and difficult to remove bleachable soils are molds and mildews, which can cause black spots on walls, wallpaper, shower curtains, and grout. Obviously the distinction between bleachable and greasy soils is not at all clear-cut and there can be many soils having at the same time bleachable and greasy character. For instance, encrusted grease usually has a strong sensitivity to bleaching agents because its polymeric chains can be partly oxidized, which results in increased solubility and removability. Particulate soils are very common especially on horizontal surfaces such as floors and furniture. Their particle size distribution and composition can vary significantly depending on the location of the house and on the season [3]. Various attempts to determine the average composition of particulate soil for technical testing purposes have been made, an example is reported in Table 1. Soapy soils can be found particularly in the bathroom, for instance on sinks, bathtubs, or in the shower area. The so-called “soap scum” is essentially soap that has been precipitated by Ca and Mg ions and is usually mixed with insoluble carbonates, skin flakes, fabric fibers and dust [5]. Upon aging, soap scum can undergo some of the processes described above for encrusted grease, which obviously increase its hardness and adhesion to the surface making it much more difficult to remove. The most important pH sensitive soil is limescale. This can be easily found in kitchens and bathrooms, particularly around taps, inside sinks, bathtubs, and showers. Thick limescale encrustations can also form inside toilet bowls, particularly at the bottom or just below the rim. Limescale is a mix of Ca/Mg carbonates and oxides, which

Table 1

Analysis of Vacuum Cleaner Dust [4] Composition

Sand, clay, quartz, feldspar Animal fibers Cellulosic materials Resins, gums, starches Fat, oils, rubber, tar Gypsum, apatite Limestone, dolomite Moisture Undetermined

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Weight % 45 12 12 10 6 5 5 3 2

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originate from repeated water evaporation on the same surface. Once a layer of limescale is formed, this can attract not only more limescale but also soils of different nature, for instance rust or organic material. This is typically what happens in toilet bowls. Water marks are a pH sensitive soil very similar to limescale encrustations, since they are essentially salt deposits left on a surface by evaporation of water droplets. However, they are perhaps even more relevant to consumers because they are extremely common and visible. C. Classification of Household Surfaces As for surfaces, a possible classification is to divide them into glassy, wood, plastic, metal, and fiber surfaces. Glassy surfaces are a vast category including glass itself, ceramic, porcelain, and enamel. Although different from a structural standpoint, we may include in this category also stones, hard floors in general, and marble. Glassy surfaces are characterized by high surface energy, which essentially derives from the high concentration of oxides they contain. This means that their tendency to be wetted by soil and to form bonds with it is relatively high, due to the possibility of strong polar interactions. In particular, soils that are able to form hydrogen bonds or have cationic or polar groups, such as limescale, can adhere very tenaciously to these surfaces. Glassy surfaces have an excellent resistance to chemicals including surfactants, solvents and bleaching agents. They also have a good compatibility with acids, with the exception of enamel (compatible with mild acids) and marble. Wood is probably the most delicate surface encountered in household cleaning. Its properties depend to a large extent on the specific treatment originally applied on the surface. Lacquering is obviously the type of treatment that offers better resistance to soil and makes the surface easier to clean. Wood can only be treated with mild surfactants/ solvents and is not usually compatible with bleaching agents, strong acids, or strong alkalis. Plastic surfaces include a large variety of materials, which tend to be characterized by a relatively low surface energy and high hydrophobicity. Thus adhesion between plastic surfaces and soil is usually lower than in the case of glassy materials. Plastic surfaces have a tendency to accumulate electrostatic charges and to attract dust. From a compatibility standpoint the most critical cleaning agents for plastics are solvents, some of which may damage some plastic surfaces due to partial solubilization of the material. Metals have high surface energy like glassy materials. The ability of encrusted grease to adhere to a stainless steel surface is well known to most consumers and is often used in advertising as a “torture test” to show the effectiveness of a cleaner. Metal surfaces have excellent compatibility with surfactants and solvents but in some cases might be damaged by acids and bleaches. Stainless steel has good resistance to acids and bleaching agents provided that pH conditions and active concentrations are not too extreme. Carpeted floors are by far the largest fiber surface of the household. Carpets are typically made of nylon (predominant in the United States), polypropylene, wool, or wool/nylon mixes. The surface properties of carpets—especially the synthetic ones—are determined to a large extent by soil and stain repellent treatments applied on fibers during carpet manufacturing [6]. Static electricity has been mentioned as an important factor determining the pickup of particulate soil and dust from carpets, particularly for nylon carpets and in North America [7]. Carpets have a good compatibility with sur-

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Wet abrasion scrub tester. (Courtesy of BYK Gardner.)

factants, solvents, mild bleaching agents, and mildly acidic or mildly alkaline pH conditions. D. Test Methods A huge variety of test methods have been and can be developed in surface cleaning, to measure product effectiveness on different soils and surfaces. Therefore we will limit our discussion to the most important and commonly used test methods, which concern encrusted grease removal, soap scum removal, limescale removal, shine performance, and sudsing profile. 1.

Encrusted grease and soap scum removal

A standard apparatus present in most performance evaluation laboratories to run various kinds of soil removal tests, is the Gardner abrasion scrub tester shown in Fig. 1. This machine can be used to simulate cleaning of a surface by a consumer in a reproducible way, allowing quantitative performance measures. The machine has an electric motor that moves back and forth with constant frequency a metal brace carrying two holders for cleaning implements, usually sponges. The brace moves parallel to a platform that can host two “tiles” of the surface to be cleaned. It is possible to vary the pressure exerted by the sponges on the surface tiles, thus modulating the effect of mechanical vs. chemical action. Some models are equipped with peristaltic pumps that deliver the test products on the surface tiles, allowing precise dosage and simultaneous product application on the two sides. Alternatively, one can manually pour a given amount of test product on either sponge before putting them in their holders. After positioning the artificially soiled tiles on the platform and loading the sponges with the two test products, one can start the machine. There are two ways to evaluate results: (1) by counting the number of strokes required to achieve complete soil removal on either tile; or (2) by running the machine for a fixed number of strokes and comparing the degree of cleaning obtained on the two tiles (this can be done visually or instrumentally, e.g., by a reflectometer). The most common use of Gardner scrub testers is to assess the removal of the two most relevant soil types: encrusted greasy soil and soap scum. In both cases, an artificial soil simulating as closely as possible the chemical composition and physical characteristics of real soils found in consumers’ homes, is applied on tiles of various materials, for instance stainless steel or white enamel [8]. Soil application can be

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performed by a brush, roller, or spray. The soil can be aged at room or high temperature (e.g., above 100˚C) to accelerate hydrolysis and polymerization processes thus increasing its adhesion on the surface. The “recipes” to make artificial greasy soil and soap scum can vary significantly due to the high variability of soil composition in real life. Thus the formulator should identify the soil types that are most relevant to target consumers, and develop artificial soils able to approximate as closely as possible the chemical-physical characteristics of real soils. In doing this it is key to elaborate a fully reproducible making procedure for artificial soils, in order to ensure a constant soil quality and therefore a good reproducibility of cleaning test results. Artificial soils that simulate encrusted grease are usually obtained by mixing different types of cooking oils or fats with particulates, for instance carbon black or dust [5]. Artificial soap scum can be produced by mixtures of calcium stearate with commercially available artificial body soils. As mentioned above, artificial soils can be baked on test tiles to increase their tenacity and make the test more stressed. 2.

Limescale removal

This is an important parameter in the development of all acidic cleaners, for instance bathroom or toilet bowl cleaners. A simple test consists in soaking a small marble block into the neat or diluted product. Marble is chemically speaking similar to limescale, i.e., it is essentially made of calcium carbonate. The marble block is weighed before and after the soaking, and the performance is expressed in grams of marble dissolved over time. As an alternative to gravimetric determination, one can evaluate limescale removal performance also by measuring the release of CO2 from the marble block, which occurs upon hydrolysis of calcium carbonate [8]. The marble block test is widely used due to its simplicity but has limitations as it does not take into account: (1) the impact of surface inclination and (2) the effect of additional soils, which are usually mixed with limescale under realistic conditions. 3.

Shine performance

Although there are instruments designed to measure the shine/gloss of a surface, visual grading remains the best method for an overall evaluation of this parameter. The test is usually performed by applying the product on a clean or slightly soiled tile made of stainless steel or ceramic. The surface is wiped, rinsed with tap water, and left to dry. It can be important to observe not only the final result obtained after complete surface drying, but also the way water spreads on the treated surface during the evaporation phase. A good shine performance results from a good product/water spreading over the surface and, as a consequence, reduced formation of water marks after product/water evaporation. Test surfaces can be visually compared either vs. tiles treated with other products used as a reference, or vs. clean untreated tiles. 4.

Foaming profile

It is very important to be able to characterize in a quantitative fashion the level of suds generated by a surface cleaner and the time required for it to collapse. The most common method used to achieve this goal is the so-called “cylinder test.” According to this method, a fixed amount of the household cleaner is poured into a graduated glass or plastic cylinder. The cylinder is inverted or rotated a certain number of times, then the

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height reached by the suds on the cylinder graduation is recorded. This first reading is a measure of the maximum sudsing ability of the product. Additional readings are taken at fixed time intervals in order to monitor the progressive suds collapse. As it can be easily imagined, the rapidity of collapse is equally—if not more—important than the maximum suds height, since it has a strong impact on product rinseability. The cylinder test is usually performed with both neat and diluted product.

II. SURFACE CLEANER FORMULATIONS A. All-Purpose Cleaners We will focus our discussion on the technology of liquid all-purpose cleaners, which today dominate the most important markets leaving little room for powder products. All-purpose cleaners are usually transparent products that can be used either neat or in dilute form. Neat application is recommended to clean relatively small surfaces with a high soil load, whereas dilution with tap water (in the range of 1:20 up to 1:100) can be used to treat larger surfaces such as floors. 1.

Suds and Other Aesthetic Parameters

The fact that these cleaners can be used in both neat and dilute form creates a challenge for the formulator to carefully control their suds level. An excessive suds level upon neat application can greatly affect the ease of product rinsing, with an obvious negative impact on consumer satisfaction. The same is true also in the case of dilute application on large surfaces such as floors, where uncontrolled suds can generate even more serious problems. Other important “aesthetic” parameters are rheology and fragrance. Rheology plays a role in neat usage, where an optimized viscosity can help apply the product more conveniently on vertical or inclined surfaces. However, rheology seems less important for all-purpose cleaners than for other categories of cleaners (e.g., bathroom cleaners), given that many all-purpose cleaners continue not to be viscous. On the other hand, fragrance is often considered to be one of the most important drivers of product acceptance by consumers, particularly for this category of cleaners where application on large surfaces is a significant source of consumption. From a technology standpoint, the incorporation of a fragrance into a formula can represent a challenge because its ingredients may be difficult to solubilize or unstable, due to pH or presence of other reactive ingredients. A well-known approach to facilitate fragrance solubilization is to premix it with either a surfactant or a solvent (or a combination of the two), before adding the mix to the rest of the formula. 2.

Performance Profile

Upon neat usage, all-purpose cleaners are expected by consumers to deliver good performance especially on greasy and encrusted greasy soils, since the kitchen is a primary household area for their application. This calls for relatively high levels of surfactants (anionic and nonionic) and solvents, combined with a pH in the neutral to alkaline range. Under dilute usage conditions they should maintain good grease cleaning, which is needed for instance to clean hard floors in the kitchen, and at the same time they should deliver a good shine performance. The latter requirement implies a low level of inorganic salts, which would otherwise tend to form crystalline residues

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resulting in visible streaks. Thus the level of inorganic builders used in older formulations has been substantially decreased and compensated for through surfactant systems with lower sensitivity to water hardness and/or through the addition of organic hardness chelators. However, the consumer need for shine performance is so strong that formulators had to go beyond the simple elimination of a negative, such as the decrease of inorganic salts. Some modern all-purpose cleaners contain polymers whose specific function is to deliver a shine performance sometimes approaching that of waxes, with the big advantage that buffing is not required. Disinfectancy is another important benefit more and more cleaners tend to deliver. Some products make precise claims on efficacy against bacteria and viruses, while others talk more generically about hygiene or removal of germs. This is a response to the increasing need from consumers to be reassured on product efficacy beyond what they are able to judge visually. The need stems both from the increasing consumer awareness of potential health effects caused by germs growing in the domestic environment, and from the improved aesthetics of modern cleaners which tend to appear and feel more and more “gentle” unlike the visibly harsh products of the past. 3.

Technology

As mentioned above, surfactants and solvents constitute the backbone of a typical allpurpose cleaner formulation. The most recent tendency has been to move from the traditional workhorse surfactant of all detergent products—linear alkylbenzene sulfonate (LAS)—to other anionic surfactants such as paraffin sulfonates (PS), alkyl sulfates (AS) and alkyl ethoxy sulfates (AES). This process has occurred for the following main reasons: 1.

2.

3.

4.

AS and particularly AES have a lower sensitivity than LAS to water hardness, because their Ca and Mg salts are relatively water soluble [8a]. This allows the formulator to deliver good cleaning performance even under dilute conditions and in the presence of low levels of builders, which as seen before means advantages in terms of shine. With AES-based surfactant systems in particular, one can observe good cleaning advantages in the absence of builders or in underbuilt [9]. PS, AS, and especially AES exhibit Krafft temperatures [8a, 9a] that are significantly lower than the one of LAS. This allows to achieve better performance in cold water, which is now the standard in household cleaning, and improves the physical stability of liquid products thus offering more formulation flexibility. The latter is an important benefit in today’s products, which tend to become more and more concentrated following the “ultra” trend started with laundry detergents. The critical micelle concentration (cmc) of the above anionics is usually lower than that of LAS. Again this implies the possibility to deliver good cleaning performance even under highly dilute conditions [8a]. AES in particular shows increased skin mildness vs. LAS [9].

On the downside, PS, AS, and AES are more expensive than LAS and have a higher foaming tendency, so they require more effort from the formulator to get the right suds profile. An interesting subclass of anionics emerged over the past few years and, typical of household cleaning applications, is that of short chain anionic surfactants. These are

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most often PS and AS surfactants with a chain length in between C6 and C10, which are claimed to improve cleaning performance on greasy and encrusted greasy soil [10,11]. In parallel to the shift from LAS to other anionics, there has been an increase in the use of nonionic surfactants—especially polyethoxylated alcohols—combined with anionics. This is driven by the following key factors: 1.

2.

3.

The development of more efficient ethoxylation processes by suppliers has made the cost of polyethoxylated alcohols more affordable than in the past, and competitive with that of anionic surfactants. A large variety of nonionics with different degrees of ethoxylation and alkyl chain lengths have become available to formulators. This offers the flexibility to vary the hydrophobicity of the surfactant system depending on the types of soil one wants to attack [9]. The combination of anionic and nonionic surfactants allows the formulator to create self-thickening systems and to modulate product rheology in a very fine manner, including the possibility to make highly pseudoplastic or shear thinning liquids [12].

Solvents represent the second most important formulation block of all-purpose cleaners. They have a strong impact on grease cleaning upon neat application, while they do not significantly influence performance under dilute conditions. This is because their effect is essentially related to the ability to change the polarity of the neat liquid product rather than to interfacial phenomena. Upon dilution this effect is lost since it strongly depends on concentration. Another important performance contribution of solvents concerns their microbiocidal potential [5]. From this standpoint they may represent an interesting alternative to cationic surfactants, especially when the latter are not a practicable option due to incompatibility with anionic surfactants or other ingredients. The most popular solvents used in all-purpose cleaners are alcohols such as ethanol, isopropanol (often referred to as IPA), butanol, pentanol, hexanol [13], tertiary alcohols [14], benzyl alcohol [15]; glycols and glycol ethers such as ethylene, propylene and butylene glycol, propylene glycol n-propyl ether, ethylene glycol butyl ether or butoxyethanol [16]; terpenes such as limonene (see Fig. 2) and pine oil [17]; alkanes such as paraffins and isoparaffins [18]. The choice of a specific solvent or combination of solvents often depends on the type of soil one wants to attack preferentially. As a general rule, the strongest grease-cutting performance is delivered by solvents with relatively high hydrophobicity [19]. There are four main constraints that limit the choice of solvents: human and environmental toxicity, impact on product odor, surface safety, and formulatability. The toxicity of ethylene glycol butyl ether and other ethers has been the subject of several studies, often making reference to exposure conditions related to their use in cleaning agents [20]. Solvent impact on product odor is an unavoidable consequence, as virtually all solvents that exhibit cleaning performance do have a distinct odor. The most effective solution available to the formulator is the careful adjustment of solvent concentration and the selection of perfuming agents that are able to mask the base odor caused by solvents. As for surface safety, plastics are usually the most sensitive materials and extensive testing should be performed especially in the case of high-solvent formulations to determine potential compatibility issues. Formulatability can be an issue particularly

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Scialla CH3 limonene

H3C

C

CH2

Figure 2

Chemical structure of limonene.

-OOC

CH2 N CH2

-OOC

CH2 CH2

CH2

COO-

CH2

COO-

N

EDTA Anion

COOH2C CH2

NTA Anion

HO

N -OOC

CH2

Figure 3

CH2

COO-

C H2C

COOCOO- Citrate COO-

Most common organic builders.

with highly hydrophobic solvents, such as alkanes or terpenes. In these cases the formulator needs to achieve an emulsification or microemulsification of the hydrophobic solvent, usually through an increase of surfactant concentration and the combination with more hydrophilic solvents (e.g., alcohols or ethers) [21]. Builders constitute the third most important formulation block related to cleaning performance. Like in the laundry cleaning process, builders are essential to control water hardness and to avoid surfactant precipitation. In addition, builders often perform the function of controlling pH under both neat and dilute usage conditions. For most allpurpose cleaners, the best pH is in the range between 7 and 11. This is because alkalinity can to some extent hydrolyze triglycerides and polymerized grease, thus helping the surfactant/solvent system in the removal of encrusted greasy soil. The most recent tendency, however, is to use pH values not too far from neutrality, thus improving surface compatibility and increasing the skin mildness of formulations. Also, excessive levels of builders/buffers may result in the formation of visible salt residues on the treated surface after drying, which can obviously have a negative impact on shine. The most commonly used builders are (see Fig. 3) citrates, various chelants (e.g., ethylene diamino tetraacetic acid [EDTA], or nitrilo triacetic acid [NTA]), silicates, carbonates, phosphates, N-diethylene glycol-N,N-diacetic acid [22]. Hydrotropes are widely used in liquid cleaner formulations. As is well known, these ingredients can enhance the water solubility of organic species that would otherwise be insoluble or scarcely soluble. Thus hydrotropes are often essential to stably formulate surfactants under conditions of relatively high ionic strength, which can occur when using builders or self-thickening surfactant systems based on the addition of

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Typical All-Purpose Cleaner Formulations

Ingredient Class Anionic surfactant Nonionic surfactant

Typical Examples LAS, alkyl sulfates, alkyl ethoxy sulfates, paraffin sulfonates Polyethoxylated alcohols

Solvent

IPA, benzyl alcohol, glycol ethers, limonene, pine oil

Builder

Citrates, silicates, carbonates, EDTA/NTA, phosphates

Polymer Alkaline or acidic agents

Polyacrylates, PVP Sodium hydroxide, ammonia, ethanol amine, hydrochloric acid Cumene sulfonate, xylene sulfonate, p-toluene sulfonate

Hydrotrope

Fragrance, color Water

Function

Typical Levels (%)

Greasy soil removal, surface wetting, selfthickening Greasy soil removal, surface wetting, selfthickening Greasy soil removal (neat application), shine, disinfection Improved surfactancy, pH control, selfthickening Shine pH adjustment

2–40

Improved formulatability and physical stability Aesthetics

0–5

0–30

1–30

0–15

0–5 0–5

0.1–2 Balance

Source: From Wisniewski, K.L., Liquid Detergents, Marcel Dekker, New York (1997) pp. 463–512.

electrolytes. Most common hydrotropes are p-toluene sulfonate, xylene sulfonate, and cumene sulfonate, usually in the form of their sodium salts [22,23]. The true novelty of the last decade in the area of all-purpose cleaners was the introduction of film-forming polymers to deliver shine. This was a response to various emerging consumer needs: 1.

2.

Consumer expectations in regard to household cleaners have continued to increase. After a product has delivered against the objective of removing soil from a surface as thoroughly as possible, shine is the next parameter to judge how good the product is. The continued improvement of living standards implies an increasing penetration of precious surfaces (e.g., parquet) around the house. These surfaces are usually kept quite clean and shiny as a consequence of their value.

The most commonly used film-forming polymers are polyacrylates, or nonionic polymers such as polyethylene glycols (PEG), methyl hydroxy propyl cellulose, and polyvinyl pyrrolidone (PVP) [24]. In order to obtain the formation of a transparent film and a good scratch resistance, the glass transition temperature of the polymer

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should be chosen not to be too high. Some of these polymers can introduce not only a change in surface appearance due to their refractive index, but also a modification of the surface hydrophilicity. Since the surface is made more hydrophilic, it is more uniformly wetted by the product or by water used for rinsing so the likelihood of water marks formation upon surface drying is decreased [25]. In addition, polymers left on the surface after product application can deliver a next-time cleaning benefit, preventing strong adhesion of soil and making its removal significantly easier in subsequent cleaning operations [26]. As mentioned above, another frequent added benefit in all-purpose cleaners is disinfection. Disinfection can be delivered through a number of active ingredients belonging to very diverse chemical classes, which can be used individually or in synergistic combinations [27,28]. Examples mentioned in some compositions are: 1.

2. 3. 4. 5.

6.

Quaternary ammonium compounds (quats), such as alkyl trimethyl ammonium chlorides, alkylpyridinium chlorides, alkylisoquinolyl chlorides, and alkyl dimethyl benzyl ammonium chloride. Alcohols and phenolic compounds, such as o-phenyl phenol, o-benzyl(p-chlorophenol), and 4-tertamyl phenol. Aldehydes, such as glutaraldehyde, formaldehyde, and glyoxal. Parabens, such as ethyl paraben, propyl paraben, and methyl paraben. Essential oils with antimicrobial properties, such as those extracted from thyme, lemongrass, citrus, anise, clove, pine, cinnamon, geranium, citronella, eucalyptus, peppermint, camphor, etc. These oils contain active molecules with antimicrobial properties that include thymol (in thyme), eugenol (in clove and cinnamon), menthol (in peppermint), geraniol (in geranium and citronella), eucalyptol and pinocarvone (in eucalyptus), and limonene (in lemongrass). Oxidizing agents, such as hydrogen peroxide or organic peroxides.

Combinations of different antimicrobial agents often lead to synergies and increased efficacy. B.

Bathroom Cleaners

1. Suds and aesthetics The same considerations made for all-purpose cleaners on the importance of suds level and fragrance apply to bathroom cleaners as well. An element of differentiation between the two product segments is that bathroom cleaner fragrances tend to be of sharper character and more intense than the ones used in all-purpose cleaners. But the most important aesthetic difference concerns the rheological profile, which is by far more relevant for bathroom cleaners. This is because of the presence of many vertical surfaces in the bathroom that need to be thoroughly cleaned. The formulator needs to make sure that consumers are able to conveniently apply the product on these surfaces, and that its residence time is sufficient for the cleaning ingredients to perform their function. This is achieved by providing the product with a viscosity typically in the range of 80 to 300 cps as measured by a Brookfield viscometer. However, the importance of rheology is such for this product segment that formulators usually go well beyond the measurement of Newtonian viscosity. Most products have a shear-thinning or pseudoplastic rheological profile, i.e., they are thicker when they are static while they become thinner when they flow. This allows to maximize the “cling” effect (see Fig. 4) on vertical or

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Figure 4 “Cling” effect of a bathroom cleaner applied on a vertical surface.

inclined surfaces, without affecting the ease of pouring for the consumer. Advanced rheometers are used to fully characterize and optimize the rheological behavior of nonNewtonian formulations. 2.

Technology

While all-purpose cleaners are usually in the mildly alkaline pH range, modern bathroom cleaners tend to be acidic. This is because most soils present in the bathroom are sensitive to acidic pH, particularly soap scum and limescale/water marks. The removal of soap scum is facilitated by acidic pH because the insoluble fatty acid salts (typically Ca and Mg salts) are reverted to the corresponding free acids. Limescale encrustations and water marks are pH-sensitive soils par excellence and require acidity to be removed. Organic acids are often preferred over the inorganic ones, since weak but wellbuffered acidity is almost equally effective against soil than strong acidity [29]. Suitable organic acids are, for instance, citric, maleic, lactic, glycolic, succinic, glutaric, and adipic [30,31]. In addition to the removal of pH-sensitive soil, acids in bathroom cleaners often perform a second function by providing the formulation with ionic strength. The combination of ionic strength with anionic or anionic/nonionic surfactant systems can be used to obtain self-thickening formulations that do not require the addition of specific thickeners to achieve the desired rheological profile [12]. The types of surfactants used in bathroom cleaners do not differ significantly from those found in all-purpose cleaners. The absolute surfactant levels tend to be slightly

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Scialla Typical Bathroom Cleaner Formulations

Ingredient Class

Typical Examples

Anionic surfactant

LAS, alkyl sulfates, alkyl ethoxy sulfates, paraffin sulfonates Polyethoxylated alcohols Ethanol, IPA, butoxyethanol Citrate, EDTA, NTA, phosphonates Citric, glutaric, succinic, hydrochloric, sulfuric, phosphoric

Nonionic surfactant Solvent Builder/chelant Acid

Fragrance, color Water

Function

Typical Levels (%)

Soap scum removal, surface wetting, self-thickening

2–10

Soap scum removal, surface wetting, self-thickening Soil removal, shine, disinfection Improved surfactancy, pH control, self-thickening Soap scum and limescale removal, pH adjustment, selfthickening

0–8

Aesthetics

1–10 0–5 0–10

0.1–2 Balance

Source: From Wisniewski, K.L., Liquid Detergents, Marcel Dekker, New York (1997) pp. 463–512.

lower and are often determined not only on the basis of cleaning performance but also to optimize viscosity. Solvents may or may not be present in bathroom cleaner formulations. Their concentration is usually lower than in all-purpose cleaners. This is a consequence of the fact that encrusted grease is not an important soil component in the bathroom. Still, solvents may assist surfactants in the removal of soap scum so they are used in some formulations. The solvents that best serve this purpose are those with relatively high hydrophilicity and water solubility, such as low-molecular-weight alcohols, glycols and— most often—glycol ethers [32]. Because of the great importance of viscosity in bathroom cleaners, some formulations may contain specific rheological modifiers, such as cross-linked polyacrylates or other polymeric thickeners. However, in most products viscosity is obtained by appropriate combinations of surfactants and acids or salts. Thickening is not the only possible function of polymers in bathroom cleaners. Similarly to what happened in allpurpose cleaners with film-forming polymers to deliver shine, recent years have seen the market introduction of bathroom products that claim protection of surfaces against resoiling thanks to surface modification by appropriate polymers. The mechanistic model usually invoked for the observed antisoiling effect of these polymers, is that by depositing on the surface they increase its hydrophilicity thus preventing tenacious adhesion of soap scum or other encrustations, which is favored by soil dehydration at the interface [33]. Bathroom cleaners may contain antimicrobial agents, whose activity can be enhanced by the combination with acidic pH. Examples include chlorhexidine, acid stable quaternary ammonium compounds, betaines, glutaraldehyde, and formaldehyde [31].

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C. Toilet Bowl Cleaners Since the main soil type these products have to deal with is limescale, most toilet bowl cleaners are strongly acidic, often with a pH below 3. Although modern formulations are evolving toward less and less harsh products, strong acids are still often used in toilet bowl cleaners due to the need for a very low pH and a high acidity reservoir. The most commonly used inorganic acids are sulfuric, phosphoric, hydrochloric, sulfamic [34]. Quite often organic acids are used as well, for instance acetic, citric, lactic, tartaric, glycolic, which allow to make formulations with a lower degree of corrosiveness vs. those based on inorganic acids [35]. Organic acids belonging to the series of linear dicarboxylic acids, for instance oxalic, maleic, malic, malonic, succinic, glutaric, adipic, are also frequently used [34]. Aryl sulfonic acids are claimed to offer advantages due to their limescale removal efficacy combined with storage stability under strongly acidic conditions, even in the presence of oxidizing agents [36]. Similar to bathroom cleaners, the acid(s) contributes to the ionic strength of the formulation and usually plays a role in determining the rheological profile. The latter is even more important in toilet bowl cleaners than in bathroom cleaners, since toilet bowl cleaners are applied on an inclined surface by definition. The way the product spreads on toilet bowl walls and achieves uniform coverage has a fundamental impact not only on consumer perception, but also on the objective limescale removal performance, since an adequate contact time on vertical surfaces and below the rim is essential to effectively remove encrustations. At the same time, the product needs to eventually reach the water line and dissolve, in order to attack limescale encrustations and soil that are present on the bottom of the toilet bowl. Finally, it must be easy to squirt or pour the product out of the bottle, which normally has an inclined neck with a narrow hole. All of the above requirements call for a sophisticated, usually shear-thinning rheological profile. An optimized product should have a viscosity of 450 to 550 cps at 12 rpm, and of 150 to 250 cps at 60 rpm, as measured by a Brookfield viscometer [37]. This level of rheological control is more difficult to achieve in toilet bowl than in bathroom cleaner formulations due to the more limited choice of ingredients, which have to be stable in a strongly acidic environment. Besides the combination of acid(s) with surfactants, inorganic salts such as NaCl can be added to toilet bowl cleaner formulations to increase ionic strength and build up viscosity [38]. Specific thickeners can also be used such as clays, for instance montmorillonite type clays, and various polymers, e.g., xanthan or jaguar gum, carboxy methyl cellulose [38]. However, some of these additives may have issues of solubility or hydrolytic stability at low pH [34], so the approach of combining anionic/nonionic surfactants with acids and salts to generate self-thickening systems is the one most frequently adopted. Surfactants used in toilet bowl cleaners are similar to those of bathroom cleaners, with the important additional constraint that they have to be hydrolytically stable at very low pH. Thus specific surfactant choices will depend, among various factors, on the specific formulation pH. Among anionic surfactants, alkyl sulfonates, alkyl ether sulfates, LAS and alkyl sulfates are commonly used. Among nonionic surfactants ethoxylated alcohols are as usual a very frequent choice. Amine oxides are relatively frequent too since they have excellent storage stability at low pH and are also compatible with oxidizing agents that may be present in some toilet bowl products. Quaternary ammonium surfactants are used sometimes to deliver disinfection, which is an important added benefit in toilet bowl cleaning [36]. Bleaching agents are optional ingredients in acidic toilet bowl cleaners. Their function is to attack the bleachable soil present in toilet bowls, constituted by residues of urine/feces and their pigments. In addition they can exert a strong germicidal action,

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Scialla Typical Acidic Toilet Bowl Cleaner Formulations

Ingredient Class Anionic surfactant Nonionic surfactant Acid Bleaching agent

Typical Examples

Function

Alkyl sulfonates, LAS, alkyl ethoxy sulfates Polyethoxylated alcohols

Soil removal, surface wetting, self-thickening Soil removal, surface wetting, self-thickening Limescale removal, selfthickening Chemical degradation of bilirubine/ urobiline, disinfection Aesthetics

Phosphoric, hydrochloric, aryl sulfonic, citric, oxalic Monopersulfate, peracetic acid, hydrogen peroxide

Fragrance, color Water

Typical Levels (%) 2–10 0–10 2–30 0–15

0.1–2 Balance

Source: From Wisniewski, K.L., Liquid Detergents, Marcel Dekker, New York (1997) pp. 463–512.

which is enhanced by the combination with acidity. Peroxides are the most suitable bleaching agents for this application due to their relatively good stability at low pH. The patent art mentions hydrogen peroxide but also inorganic and organic peracids, such as monopersulfate and peracetic acid, as the most suitable peroxides [36]. Monopersulfate is of particular interest because it is odorless and can be stabilized in the formulation at a pH value in the range from 0 to 2. When the product reaches the water line in the toilet bowl, it gets diluted and pH increases by 1 or 2 units. This “pH jump” effect works as a trigger for the bleaching activity of monopersulfate, which in general has a faster oxidation kinetics at higher pH [39]. The stability of monopersulfate can be significantly improved by the addition of chelants and radical scavengers [40]. Color and fragrance have a great importance for toilet bowl cleaners, if possible even greater than for other classes of household cleaners. Color helps the user to make sure that the product has been uniformly applied, to appreciate its rheological behavior, and to follow its flow toward the bottom of the toilet bowl. Thus most toilet bowl cleaners are intensely colored. Fragrance is obviously very important too and should persist in the toilet bowl even after several flushes, thus providing reassurance that a thorough cleaning has been performed and a long-lasting antimicrobial action is being delivered. Stably incorporating a dye/pigment and a fragrance in a toilet bowl cleaner can be a major technical challenge, especially in the case of formulations containing bleaching agents. While most recently introduced products tend to be acidic, the traditional segment of alkaline toilet bowl cleaners containing hypochlorite bleach continues to exist. These formulations contain a level of hypochlorite usually below 5% and are highly alkaline to maximize storage stability (pH between 10 and 13). Combinations of anionic surfactants and electrolytes are the most frequent approach to build up viscosity, due to the low compatibility of polymeric thickeners with hypochlorite. Among anionic surfactants, alkyl sulfates are one of the most common choices. Among nonionic surfactants, amine oxides are compatible with hypochlorite whereas ethoxylated alcohols can be oxidized and are usually not suitable (see also the following Section II.D on bleach cleaners).

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Typical Bleach Cleaner Formulations

Ingredient Class

Typical Levels (%)

Typical Examples

Function Soil removal, surface wetting, self-thickening

2–10

Nonionic surfactant

Alkyl sulfates, alkyl ether sulfates, alkyl phenol ether sulfates, LAS Amine oxides

0–10

Bleaching agent

Hypochlorite

Builder

Carbonates, silicates

Alkali Hydrotrope

Sodium hydroxide Xylene sulfonate, cumene sulfonate

Soil removal, selfthickening Chemical degradation of soil, disinfection Improved surfactancy, pH buffering, self-thickening pH adjustment Improved physical stability Aesthetics

Anionic surfactant

Fragrance, color Water

0–15 0–15 0–5 0–5 0.1–2 Balance

These toilet bowl cleaners rely on the outstanding bleaching, whitening and germicidal performance of hypochlorite, which is well known to consumers. However, they are ineffective against limescale and may even contribute to its deposition, by creating strongly alkaline conditions in the toilet bowl water. D. Bleach Cleaners Bleach all-purpose cleaners have similar compositions to alkaline toilet bowl cleaners, however they are usually less viscous. They deliver removal of bleachable soil/stains and disinfection, thanks to the strong oxidizing action of hypochlorite. They are also quite effective against encrusted grease, which is sensitive to both alkalinity and strong bleaching agents. In general, these products are the best solution available whenever there are very difficult soils to be removed, a typical example being mold. Their main disadvantage is harshness both on surfaces and for the user, although most recent products have been rendered significantly milder than in the past. Surfactants used in bleach cleaners have to be stable in strongly alkaline and oxidizing conditions, thus the most common choices are amine oxides [41], alkyl sulfates, alkyl ether sulfates, and fatty acids [42]. Chemical stability of hypochlorite formulations can be improved by the addition of radical scavengers and/or chelants [43]. Physical stability is often increased by the addition of hydrotropes [44]. These can be relatively more important in bleach cleaners to avoid phase separation of surfactants, which can be favored by the high ionic strength. Bleach cleaners usually don’t contain solvents, since most of them would not be stable either chemically or physically, plus they would not add much to the already powerful performance of hypochlorite combined with alkalinity. Bleach cleaners do contain inorganic builders (typically carbonates or silicates), which also perform the function of high-pH buffering agents and contribute to the ionic strength of the formulation.

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The most typical aesthetic characteristic of bleach cleaners is their pungent “bleach odor,” which is due to hypochlorite itself as well as other components of the formulation such as hypochlorous acid and molecular chlorine [45]. The latter is often present when the product pH is decreased, for instance by contact with acidic materials that may be present on the surface to be cleaned. Paradoxically, odor is at the same time a strength and a weakness of bleach cleaners. Many consumers, especially in Southern Europe, feel greatly reassured about hygiene when a bathroom or a kitchen has a distinct bleach odor. For other consumers this is the primary reason why they would never buy a hypochlorite-based cleaner. Obviously there are intermediate positions too, such as those who would like to be able to smell some hypochlorite, but not too much and perhaps partly covered with a fragrance. The importance of these factors for consumers has generated a significant amount of research and development (R&D) work and patent activity on how to control the odor impact of hypochlorite. Viscosity can help controlling bleach odor by decreasing the volatility of the formulation and its tendency to generate misting, which can occur upon dispensing. Also, the diffusion rate of molecular chlorine through the liquid is slower in thickened formulations. These benefits are maximized in the case of a shear-thinning rheological profile, which as discussed above also offers the best ‘clinging’ effect on surfaces [41, 45]. This type of rheology can be obtained in bleach cleaners by a self-thickening surfactant system containing an amine oxide in combination with other surfactants and/or various counterions [45]. However, some formulators claim that cross-linked polyacrylates are able to generate an even better rheological behavior and that the resulting formulations have a good chemical and physical stability [46]. In addition to physical methods of reducing bleach odor through product thickening, some chemical technologies have been developed. These utilize inorganic or organic –NH2 compounds, such as sulfamic acid, sulfamide, p-toluene sulfonamide, etc., which are able to control the activity of free halogen in the formulation, thus limiting its tendency to react with skin proteins. The latter reaction is responsible for the typical odor left on hands by bleach cleaners [47, 48]. An additional benefit of the –NH2 technology is a significantly reduced skin harshness [49]. Obviously, the development of a fragrance with good ability to cover bleach odor is an approach that can be used in combination with any of the above technologies. This is a major technical challenge, due to the extremely harsh formulation environment that makes several perfume ingredients unstable, and to the difficulty of covering such a pungent and easily perceivable odor. Equally challenging can be the stable incorporation of a colorant. Suspended pigments are usually preferred to dyes, in order to avoid the oxidative attack of hypochlorite on chromophoric groups [50]. E. Cream Cleansers Since bleach cleaners are by definition heavy duty products, some versions include a suspended abrasive to deliver an even stronger performance on encrusted soil. These products are usually referred to as cream cleansers (or scouring creams). The main challenge for the formulator is to achieve the stable suspension of abrasive particles avoiding their syneresis. Particle syneresis is an issue for the physical stability of the formulation, given that bigger particles than the original ones will tend to segregate, potentially forming big solid blocks inside the bottle. Obviously this is perceived by consumers as a signal of poor quality and can make it impossible to dispense the product due to the occlusion of the bottle orifice. Thus most of the patent art deals with thickening systems able to produce suspensions that avoid particle syneresis and are physically and chemically stable. The thick-

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ening systems more often used are based on polymers [51–53], clays [54], or colloidal alumina particles [55,56]. These systems are always combined with surfactants, which are essentially the same we mentioned in the section on Bleach Cleaners, above. In the case of cleansers without hypochlorite bleach there is more freedom in the choice of surfactants, which may include for instance ethoxylated alcohols as nonionics [57]. The abrasive is usually represented by calcium carbonate particles (calcite) with an average diameter that can range from 10 to 20 to a few hundred microns. Other abrasives mentioned in the art are perlite, silica sand, quartz, pumice, feldspar, tripoli, and calcium phosphate [57]. However, calcite is by far the most commonly used material because it is cheap and its hardness allows to get a good balance between scouring performance and surface safety. The concentration of calcite particles in most formulations ranges from 10 to 40% by weight. F. Glass Cleaners Glass cleaners have the most dilute formulations among all household cleaners. This is because these products should leave the least possible residue on the treated surface, in order to minimize the occurrence of streaks/spots that are particularly visible on glass, mirrors, or other vitreous materials. Since glass cleaners have to deal with relatively light soil (e.g., dust, fingerprints, water spots from rain), the requirement for low level of actives—particularly surfactants—is not incompatible with a satisfactory cleaning performance. Unlike other household cleaners, which depend mainly on surfactants to deliver their grease-cutting performance, glass cleaners utilize solvents as primary ingredients. Solvents present the advantage with respect to surfactants that they can completely evaporate leaving no solid residue. Preferred solvents are the ones with low molecular weight, typically alcohols (e.g., ethanol, isopropanol) or glycol ethers [58]. The reason for privileging light molecules is that they have a faster evaporation rate. By increasing the evaporation rate of the cleaner, the formulator can decrease the likelihood of droplet formation on the surface, which may result in visible spots after drying. Therefore the solvent not only performs a cleaning and grease-cutting function, but also has the fundamental role of increasing the evaporation rate of the glass cleaner formulation. Surfactants are used in glass cleaners at the minimum concentration required to achieve sufficient surface wetting and some grease emulsification. In addition they have the function of helping perfume solubilization in the formula. Not only the level but also the choice of surfactants can be different from other household cleaners. For instance, while the most common anionics such as LAS, alkyl sulfates, alkyl ethoxy sulfates and alkyl sulfonates are used in several glass cleaning products, some formulators found that amphoteric and zwitterionic surfactants offer advantages in terms of reduced streaking [59,60]. Ammonia or monoethanol amine are often used as buffering agents / surfactant counterions [61]. Unlike metal hydroxides, they have the advantage of evaporating upon product drying so they do not contribute to the formation of solid residues. Builders are either not used at all or only at very low levels, in order to avoid the formation of residues through their salts. Polymers can be present at very low levels in glass cleaners with various functions. The most important ones are shine/antistreaking and antifogging. The shine effect is usually achieved by depositing polymers able to make the surface more hydrophilic, for instance polyacrylates, polyvinyl alcohols (PVA), polysaccharides [62]. The antifogging effect is mentioned in the art to be achievable by two opposite approaches: one consists

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Scialla

Table 6

Typical Glass Cleaner Formulations

Ingredient Class

Typical Examples

Solvent

Ethanol, IPA, glycol ethers

Anionic surfactant

LAS, alkyl sulfates, alkyl ethoxy sulfates, alkyl sulfonates Polyethoxylated alcohols

Nonionic surfactant Builder/buffer

Polymer

Silicates, carbonates, ammonia, monoethanol amine Polyacrylates, PVA, PEG

Fragrance, color Water

Function Grease removal, shine, fast evaporation Grease removal, surface wetting

Typical Levels (%) 3–20 0–5

Soil removal, selfthickening Improved surfactancy

0–5

Shine, antistreaking, antifogging Aesthetics

0–5

0–1

0.01–1 Balance

Source: From Wisniewski, K.L., Liquid Detergents, Marcel Dekker, New York (1997) pp. 463–512.

in making the surface more hydrophilic and therefore relies on the same polymers used for soil prevention and shine [63,64]. The other approach is to make the surface more hydrophobic by silicones, for instance triethoxy silane compounds, or by fluoropolymers [65,66]. G. Carpet Cleaners Carpet cleaners are products in between laundry detergents and household cleaners. They have some affinity with laundry detergents and laundry additives because their purpose is to remove soil and stains from fibers. However, the fact that carpets cannot be moved, immersed in a washing liquor and rinsed, makes the carpet cleaning process closer to a household cleaning than to a laundry task. Carpet cleaners can be divided into spotters, high traffic cleaners, shampoos, and spray extraction products. Deodorizing or cleaning powders are outside the scope of the present chapter, which is focused on liquid cleaners only. 1.

Spotters and High Traffic Cleaners

These products are used to remove stains and localized soil. Spotters make most of their claims around stain removal (usually beverages or food), whereas high traffic cleaners are more focused on removing the mix of particulate and greasy soil that tends to accumulate near doors or in hallways. Most spotters are in trigger spray form, although aerosol cans and foams are also rather frequent. Foam is a particularly common form for high traffic cleaners. Both spotters and high traffic cleaners are used neat, often in conjunction with scrubbing tools such as brushes. The formulations of spotters and high traffic cleaners are rather similar, although spotters are usually more concentrated. They typically include anionic surfactants, solvents, and builders as the main ingredients. They may also contain polymers for soil suspension, such as polyacrylates [67]. Since

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it is practically impossible in carpet cleaning to achieve complete product rinsing, it is key that the residues left behind on the carpet by the cleaner are as much as possible “crystalline” and nonsticky. This is because sticky residues may promote carpet resoiling, a well-known issue. Surfactants mentioned in the literature to help getting crystalline product residues are, for instance, alkyl sulfates, sarcosinates, and sulfosuccinates [68]. Also, vinyl or styrene-acrylate copolymers can be added to carpet cleaning formulations with the main objective of rendering product residues less sticky [68]. Some degree of alkalinity is useful to effectively deal with greasy soil, however most formulators have moved away from high pH due to the associated risk of color damage. Thus the pH of most products falls in the range between 7 and 10. In order to further reduce the risk of resoiling, some of these products contain fluorochemicals able to decrease the surface energy of carpet fibers making them hydrophobic and lipophobic at the same time, thus soil and stain repellent. However, the use of fluorochemicals is more common in shampoos and spray extraction products, which are designed to treat the whole carpet. 2.

Shampoos

These products are designed for use in rotary or cylindrical brush machines. They are usually high foaming and need to be diluted with water in the range of 1:20 up to 1:40. Ingredients used for shampoo formulations are essentially the same seen in previous paragraph for spotters, with the addition of some actives whose utilization is justified only in the case of whole carpet treatment. The latter are, e.g., fluorochemicals, optical brighteners, antistatic compounds, and mold/mildew inhibitors. Fluorochemicals are most often fluorosurfactants or fluoropolymers, which typically have a pendant perfluoroalkyl group of C6 to C8 chain length. Fluorinated acrylates and urethanes are the polymer types most commonly used. In order to achieve an even stronger soil and stain repellency, fluorinated polymers can be combined with the so-called “stain blockers.” These are species able to occupy active dye sites on the fiber surface, making them unavailable for stain attack [68,69]. Examples of compounds used for this purpose are phenol-formaldehyde polymers, styrene-maleic acid copolymers, and polymethacrylic acid copolymers [69]. Optical brighteners are sometimes used to increase the reflectance of the carpet and make it look cleaner and shinier, similarly to the effect delivered on clothes by brighteners contained in laundry detergents [70]. However, carpets are washed much less frequently than clothes and it has been observed that some brighteners deposited on carpets can decompose due to ultraviolet (UV) light exposure, forming colored by-products which may result in carpet staining. Thus brighteners used in carpet cleaning products must be carefully checked for UV light stability and nature of their degradation products. Hydrophilic compounds can be added to shampoo formulations in order to decrease the carpet tendency to develop electrostatic charges, which may attract dust and accelerate soiling. Examples of compounds reported to have antistatic properties are amines, betaines [71], quats, and sulfonic acids [72,73]. Mold/mildew inhibitors—for instance phenols—may also be present in carpet shampoos to control the formation of mildew, which can be favored by the natural humidity of the household but also, to some degree, by the significant dampness left on the carpet at the end of the shampooing process. 3.

Spray Extraction Formulations

These products are completely analogous to shampoos, with the only important difference of a much lower sudsing profile. Spray extraction machines (see Fig. 5) work by

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Figure 5 Modern spray extraction machines.

spraying the cleaning solution (which is usually heated) on the carpet and sucking it back through a vacuum cleaning system able to handle fluids [74]. The dirty solution is collected into a waste tank that becomes progressively full. Thus excessive suds can fill up the piping and waste tank of the spray extraction machine, preventing correct operation or even damaging the machine. Consequently defoamers—usually silicones—are standard ingredients in spray extraction liquids, while they are not used in shampoos.

III. FUTURE TRENDS Given the wide and increasing variety of household products available in the market, it is quite difficult to identify common trends across different segments. However, from the above discussion it should appear that there is a general tendency to: 1.

2. 3.

Make household cleaners more gentle for the user and for surfaces but equally effective against target soils, by using more sophisticated and selective chemistry; increase the aesthetic appeal of products through a multiplication of perfume variants and a continued improvement of rheology; and maximize benefits that go beyond plain soil removal. From a technology standpoint this translates into strong activity in the area of polymers.

The pace of technology innovation required by this market is continuing to grow: 583 U.S. patents related to hard surface cleaning were published in 2000, vs. 364 in 1995, 231 in 1990, and 112 in 1985. We expect this trend to continue, making hard

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surface cleaning an ever more exciting category for technologists and formulators to work on.

ACKNOWLEDGMENTS Many colleagues have contributed to the work reported in this chapter and it would be impossible to mention all of them. Just to name a few, I am particularly grateful to M. Evers, M. Morini, N. Gordon, and A. Sherry for the work done on all-purpose cleaners; to P. Iakovides and S. Cardola for their work on bleach cleaners; and to G. Sirianni, V. Tomarchio, G. Bianchetti, O. Todini, and R. Scoccianti for their work on specialty cleaners.

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176 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 48. 49. 50. 51. 52. 53. 54. 55. 56. 57. 58. 59. 60. 61. 62. 63. 64. 65. 66. 67. 68. 69. 70.

Scialla H.R. Baker, E.S. Thrower, and D.C. Simpson, U.S. Patent 4690779 (1987) S. Cardola, P. Iakovides, L. Orlandini, and M.R. Rescio, EP 957156 (1999) N.J. Gordon and M.F.T. Evers, EP 859044 (1998) G. Sirianni and M. Trani, EP 966883 (1999) G. Serego Allighieri, G. Sirianni, V. Tomarchio, and M. Trani, EP 948892 (1999) S.B. Kong and R.L. Blum, EP 606712 (1994) S. Cardola, P. Iakovides, L. Orlandini, and M.R. Rescio, EP 957156 (1999) W.J. Cook, N.S Dixit, K.L. Wisniewski, and N.S. Rao, EP 379256 (1990) I. Takumi, Y. Shu, I. Naoki, S. Masami, and T. Kazunori, United Kingdom Patent (GB) 2279362 (1995) K.L. Wisniewski, N.S. Dixit, and N.S. Rao, EP 467472 (1992) F.J. Miskiel and Y. Solanki, WO 9746656 (1997) C.L. Stamm, WO 9945088 (1999) G.O. Bianchetti, S. Cardola, and S. Scialla, U.S. Patent 5686399 (1997) S. Scialla, S. Cardola, and G. Bianchetti, WO 9411474 (1994) C.D. Hager, Riv. Ital. Sostanze Grasse 68 (1991) 267–271 G. Bianchetti, S. Campestrini, S. Scialla, and F. Di Furia, EP 598694 (1994) G. Bianchetti, S. Campestrini, S. Scialla, and F. Di Furia, EP 672748 (1995) C.K. Choy and B.P. Argo, WO 9710320 (1997) C. Fontana and L. Novita, WO 9964553 (1999) O. Todini, A. Agostini, and G. Grande, EP 905225 (1999) C. Steiner and G. Pochard, WO 9006682 (1990) C.K. Choy and P.F. Reboa, EP 594314 (1994) C.K. Choy and A. Garabedian, EP 606707 (1994) H.C. Na, P.A. Rodriguez, and M. Petri, WO 9627651 (1996) H.C. Na, M.C. Frazee, J.C. Burckett St. Laurent, K.D. Jones, and M. Petri, WO 9743392 (1997) G. Sirianni, EP 834549 (1998) G. Grande and O. Todini, EP 931829 (1999) A. Luciani, B. Antelme, S. Fauvet, V. Manget, and J. Loste, WO 9711147 (1997) T. Weibel, WO 9635771 (1996) C.K. Choy, B.P. Argo, K.J. Brodbeck, and L.M. Hearn, WO 9508619 (1995) J.M. Brierly and M. Scott, U.S. Patent 4530775 (1985) B.P. Argo and C.K. Choy, U.S. Patent 5279755 (1994) B.P. Argo and C.K. Choy, U.S. Patent 5346641 (1994) C.K. Choy, B.P. Argo, K.J. Brodbeck, and L.M. Hearn, WO 9508619 (1995) S.M. Maile and A.E. Sherry, WO 9909135 (1999) R.A. Masters, M.S. Maile, and T.C. Roetker, WO 9513345 (1995) T. Trinh, D.R. Bacon, P.A. Blondin, A.H. Chung, M.S. Maile, and R.A. Masters, U.S. Patent 6194362 (2001) R.A. Masters and M.S. Maile, U.S. Patent 5534198 (1996) M.A. Deleo, R.L. Blum, M.G. Ochomogo, P.A. Pappalardo, and E. Swayne, WO 0138480 (2001) J.F. Karls and J.A. Sramek, WO 0053692 (2000) K. Ikemori, K. Ohtaka, H. Ukuda, T. Yamamoto, S. Yoshida, and H. Ikari, EP 908500 (1999) M. Tanomura, H. Yamagishi, T. Hori, and T. Okubo, Japanese Patent (JP) and p. 66 21031995 (2001) Y. Luan, Chinese Patent (CN) 1183450 (1998) S. Scialla and F. Raso, WO 9615308 (1996) E.M. Brown, Fundamentals of Carpet Maintenance, p. 43 and p. 66, Cleaning Research International Ltd., Otley, UK (1995) N.S. Rao and B. E. Baker, in Organofluorine Chemistry (R.E. Banks, B.E. Smart, and J.C. Tatlow, eds.), pp. 321–338, Plenum Press, New York (1994) P.A. Dresco, F. Lumino, and S. Scialla, EP 1118656 (2001)

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71. M. Kawashima, JP 61066781 (1986) 72. L.E. Walp, in Kirk-Othmer Encyclopedia of Chemical Technology, 4th ed., Vol. 3, p. 553, John Wiley & Sons, New York (1992) 73. J.A. Rosie and J. Watkins, Comun. Jorn. Com. Esp. Deterg. 30 (2000) 129–138 74. E,M. Brown, An Introduction to Carpet Cleaning, Cleaning Research International Ltd., Otley, UK (1998)

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6 Liquid Bleach Formulations Stefano Scialla and Oreste Todini

CONTENTS I.

The Formulation of Liquid Bleaches.................................................................... 180 A. Introduction ............................................................................................... 180 B. Evaluation of the Performance of Liquid Bleaches ................................. 180 1. Washing Procedure .................................................................... 180 2. Stain Removal Test .................................................................... 180 3. Fabric Oxidation ........................................................................ 181 II. The Formulation of Liquid Chlorine Bleaches .................................................... 182 A. Introduction ............................................................................................... 182 B. Stability of Hypochlorite Liquid Bleach Formulations............................ 183 C. Fabric Safety Profile of Hypochlorite Bleaches ....................................... 187 III. The Formulation of Liquid Hydrogen Peroxide Bleaches ................................... 191 A. Introduction ............................................................................................... 191 B. Stability of Liquid Hydrogen Peroxide .................................................... 192 C. Boosting the Performance of Liquid Hydrogen Peroxide........................ 198 1. Activation by Peracid Precursors .............................................. 198 2. Peracids in Equilibrium with Hydrogen Peroxide .................... 199 3. Activation by Alkaline pH......................................................... 200 D. Color and Fabric Safety ............................................................................ 201 IV Future Trends ....................................................................................................... 202 Acknowledgments........................................................................................................... 203 References ....................................................................................................................... 203

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I. THE FORMULATION OF LIQUID BLEACHES A. Introduction The removal of tough stains from laundry is the main benefit delivered by liquid bleaches. Although there are significant differences in usage habits across different geographies, a common element is that liquid bleaches are used as detergent boosters, i.e., to improve the stain removal performance of laundry detergents. Depending on the type of bleach and the geography, this is done by combining the bleach with the detergent either in the same or in a separate washing step. Despite continuous improvements in the technology of laundry detergents, which more and more often tend to incorporate a built-in bleach system, the consumer need for separate bleach products has not diminished. Part of the reason may be the fact that a separate bleach product allows consumers to have more control on the laundry process, since they can tune the ratio between the detergent and the bleach in a continuous manner, based on their own perception of how dirty and stained their laundry is. A second key benefit delivered by liquid bleaches is hygiene and disinfection. This benefit is very important for consumers both in laundry and in hard surface cleaning applications of bleach products. For many consumers, particularly in Southern Europe, the odor left on surfaces by hypochlorite bleach is an unequivocal signal of indepth cleaning and disinfection. Our discussion in this chapter will be focused on laundry applications of liquid bleaches and on the two most important product types in this category: hypochlorite and hydrogen peroxide bleaches. B.

Evaluation of the Performance of Liquid Bleaches

1. Washing Procedure The performance assessment of a bleaching formulation can be done either via realistic or technical washing tests. The former reproduces the machine or the hand wash procedure followed by consumers and generally includes the use of a clean or soiled ballast to simulate a typical load and a statistically significant number of fabric tracers for the evaluation of the bleach performance. Product dilution, water hardness, use and type of co-detergents, temperature, cycle, and washing machine type and model are chosen to simulate the most representative conditions of a specific country or consumer segment. The test conditions will therefore vary significantly from geographic region to region. Technical tests are aimed to compare under controlled and reproducible conditions the performance of a specific product vs. a reference. In this context, several washing devices, that allow the accurate monitoring of the key chemical and physical parameters of the wash, such as temperature and pH, and the mixing conditions have been developed. 2. Stain Removal Test Stains are generally classified into four groups: bleachable, greasy, enzymatic, and particulate. Bleachable stains are characterized by the presence of one or more chromophors that can be oxidized by a bleaching agent. Most beverages, such as coffee, tea, and wine belong to this category. For example, tea contains several components, such as cinnamic acid, flavonols, and leucoanthocyanine among the polyphenols. as well as chatechins and coumarines, which are sensitive to bleaching.

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Greasy stains are characterized by the presence of fatty components. For example, oil, makeup, and lipstick belong to this group. These stains are typically insensitive to the action of bleach and they require the presence in the formulation of surfactants and/or solvents to be removed. Enzymatic stains are sensitive to the action of the enzymes present in powder and liquid detergents. Belong to this class of stains egg, mayonnaise, blood, and to some extent also tomato or meat sauce. Enzymatic stains also show a certain sensitivity to bleaching agents, and some, such as blood for instance, are effectively removed by both chlorine and oxygen bleaches. Particulate stains, like clay for instance, are also insensitive to the action of bleach. Stain removal tests for the evaluation of the bleach performance are done on technical stain sets or realistically soiled garments. The former can be produced in-house or purchased from specialized suppliers (e.g., WFK, Germany; E-Quest, UK) and are produced by fixing on a support textile the staining ingredient and drying it under controlled conditions. In the case of realistically stained items, the textile swatch is generally cut in two halves to perform a pair comparison evaluation of the performance of two products or to evaluate the absolute stain removal efficacy by comparing the bleached half with the untreated one. The evaluation of the stain removal performance can be done visually or instrumentally. In the latter case, either colorimeters that measure the color intensity of the stain or image acquisition/elaboration software (image analysis) can be used. The latter offers over the visual assessment the advantage of an absolute measurement of the stain removal on a continuous scale. Image analysis is also more accurate and reproducible than the colorimetric analysis, especially if the washed stain is not very homogenous in color. 3. Fabric Oxidation The repeated bleaching of a textile leads to a certain degree of fabric damage. Fabric oxidation is generally assessed under multicycle conditions (10 to 40 bleaching cycles) because the fiber damage after one single treatment is generally too low to be determined. Scanning electron microscopy (SEM) can be used for the qualitative determination of the fiber damage [1,2]. SEM can also offer important insight on the structure of the fiber [3]. Among the quantitative techniques, tensile strength measurement of standard textile swatches or yarns is probably the most common technique to evaluate the damage due to bleaching [4]. Generally, the results are expressed as tenacity in mN/tex or gf/tex, where 1 tex is equal to 1 g/km and gf refers to grams force or grams weight and represents the force necessary to give 1 g mass an acceleration of 980 cm/sec2 [5]. The tenacity end result depends on the specific method conditions, such as humidity and temperature. Cotton is the only significant textile fiber whose strength increases with humidity, while most others are weakened by increased moisture [5]. Increased temperature reduces the tenacity [5]. A more accurate technique to measure the fabric damage is the determination of the degree of polymerization (DP) of the fabric by dissolving the fibers in an appropriate solvent and by determining the viscosity of the resulting solution by a capillary viscometer [6,7]. Specific solvents are used for different fabric types, e.g., cupryethilendiamine for cotton and formic acid for nylon. DP and tenacity results are generally in good agreement, even though some deviation from the linearity can be observed at low DP values [8] and nonlinear correlations have been reported [9].

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In addition to the quantification of the fabric damage, a number of analytical techniques are available to assess the type of fabric modification induced by bleaching. Of particular interest is the assessment of the carboxylic, ketone, and aldhehyde groups formed on cotton fibers as a consequence of bleaching. Lewin [10] reports that a direct assessment of the carboxylic functionalities on the cotton fibers without the need of fabric pretreatment can be done via the estimation of the methylene blue cations absorbed on the carboxyl groups of the cellulose from a solution of the hydrochloride buffered at pH 8.4 with veronal. The determination of the aldehyde groups can be done with the same method after converting the aldehyde groups to carboxylic ones with sodium chlorite. Because sodium chlorite is not capable of the oxidation of ketone groups, the net increase in carboxylic groups after the treatment with chlorite is a measure of the aldehyde groups present on the fiber. The copper number is a semiquantitative method to determine the total carbonyl groups present on the fiber. The method is based on the capability of the carboxylic group to reduce copper solutions [10]. FTIR can be more advantageously used to assess the increase in the carbonyl content (C=O stretching band at 1740 cm-1) due to fabric damage [1]. The thermal analysis of the fiber can also provide insight on the fiber degradation process [11].

II. THE FORMULATION OF LIQUID CHLORINE BLEACHES A. Introduction In 1792 hypochlorite bleach became commercially available in France as “eau de Javel.” It was produced according to Berthollet’s method by absorbing chlorine on a weak KOH solution. In 1820, Labarraque proposed the use of the cheaper NaOH in replacement of KOH [10,12]. Since then, the most important source of chlorine in chlorine bleaches has been sodium hypochlorite. Today, sodium hypochlorite is still produced by the reaction between chlorine gas and caustic soda according to reaction (1). Cl2 + 2 NaOH → NaOCl + NaCl + H2O

(1)

Both chlorine and caustic soda are produced by the electrolysis of NaCl. The final concentration of hypochlorite ranges between 5 and 15% w/w available chlorine.1 A slight excess of caustic soda (generally less than 5% w/w in the final hypochlorite solution) facilitates the process control and maintains the pH above 11, to minimize the decomposition of NaOCl and buffer the adsorption of atmospheric CO2. NaCl is generally present at a concentration slightly above the stoichiometric one, because of some NaOCl decomposition to chloride and chlorate during manufacturing and storage.

1

Available chlorine (AvCl2) is the most frequently used unit to define the strength of a chlorine bleach solution. The conversion from AvCl2 to NaOCl can be done by multiplying the AvCl2 concentration by the ratio of the molecular weights of NaOCl and Cl2, e.g., % w/w NaOCl =

Mw NaOCl Mw Cl2

⋅ %w / w AvCl2 =1.05 % w/w AvCl2.

The analysis of AvCl2 is commonly performed by redox titration according to [12] or the DPD method as reported by Nowell and Hoigné [28].)

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Typical hypochlorite bleaches have a concentration of 3 to 6% AvCl2, typically, 5.25% w/w in the United States and 3 or 5% w/w in Europe. In some countries, e.g., France, also concentrated hypochlorite pouches (12% AvCl2) are commercially available. Usually they are diluted with water to about 3.5% AvCl2 prior to use. With few exceptions among premium price brands, regular hypochlorite bleaches usually do not contain any other ingredient. Perfumed variants are also commercially available and more recently thick and colored formulations with a higher performance profile have been introduced in the United States and Europe. In laundry, hypochlorite bleaches provide whiteness and stain and dinginess removal. Dyes oxidation prevents the use of hypochlorite bleaches on colored garments. Cotton is the most commonly bleached fabric, even though the large progresses made on the fabric safety profile of chlorine bleaches have considerably extended the use of these products also to synthetics, such as nylon. The usage conditions can vary significantly from country to country. However, a general division can be made between North America and Europe. In the United States, hypochlorite bleach is normally used in combination with the detergent even if usually washing machines can also run a short prebleaching cycle prior to the addition of the detergent. Product dilution is often higher in the United States than in Europe because of the larger volume of washing machines. In Europe bleach usage is most popular in southern countries, such as Spain, Italy, and France for instance. Bleach is usually added in the bleach dispenser that automatically releases the bleach during the second rinse. As a consequence the bleaching cycle is performed in cold water and it is rather short (about 5 minutes). Also prewash is occasionally recommended in case of difficult stains or heavily soiled loads. Because of their relatively low price and high germ killing power, hypochlorite bleaches are also extensively used for household cleaning (especially on floors and toilets). B. Stability of Hypochlorite Liquid Bleach Formulations Hypochlorous acid is a weak acid with a Ka of 2.63·10–8 at 20˚C [12]: HOCl + OH–

T ClO– + H2O

(2)

Therefore only at pH above 11, hypochlorous acid concentration can be considered negligible (Fig. 1). Below pH 4, chlorine gas starts to develop [12,13]. For this reason, hypochlorite bleaches should not be mixed or used in combination with acidic products (e.g., limescale removal formulations) [14,15]. The decomposition rate of hypochlorite solutions is strongly dependent on the pH. At pH above 11, hypochlorite is rather stable and the decomposition proceeds according to reactions (3) and (4) [12]: 2 NaOCl

→ NaClO2 + NaCl

NaClO2 + NaOCl

→ NaClO3 + NaCl

(3) (4)

At pH below 11, i.e., in the presence of HClO, the competing acid production reaction (5) is also reported to occur [16,17]: NaOCl + 2 HOCl

→ NaClO3 + 2 HCl

(5)

Reaction (5) is self-accelerated, because HCl reduces the pH and increases the concentration of HClO in solution [16]. Adam and co-workers [18] report a maximum of

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NaOCl

% moles

80 HOCl 60 40 20 0 6

Figure 1

8

10 pH

12

14

Composition of hypochlorite solutions in the pH range 5-13.5.

the hypochlorite/hypochlorous acid decomposition rate at pH 6.89. The mechanism pro⋅ 2O and ClO2- as intermediates. To posed by Adam involves the formation of Cl2O⋅H minimize the occurrence of reaction (5), hypochlorite bleaches have generally a pH ranging between 12 and 13.5 obtained mainly by the addition of NaOH to the finished product. In the presence of heavy metal impurities oxygen evolution and bottle bulging is observed [12,19,20]: 2 NaOCl → O2 + 2 NaCl

(6)

The relative impact of heavy metal ions on the stability of hypochlorite solutions is difficult to predict because synergistic effects are often encountered. For example, iron is considered a weak catalyst when present alone, but strongly enhances the activity of nickel and copper [12,19]. Additionally, heterogenous catalysis by insoluble heavy metals and metal combinations is complex and poorly reproducible [12]. The common practice is to minimize the contamination of heavy metal impurities during hypochlorite production and bleach making. Few chelants stable to hypochlorite are reported in the patent literature and their main effect is on performance rather than on stability. Among them, polyacrylates [21], phosphonates [22] and phosphates [23], alkali heptonate, or boroheptonates [24]. Additional key factors that enhance the kinetics of hypochlorite decomposition are the increase of the hypochlorite concentration, ionic strength and temperature [12,16,17,18,19,20,25]. According to reactions (2) to (6), concentrated hypochlorite solutions decompose much more rapidly than diluted ones. Additionally the rate constants of these reactions are increasing functions of the ionic strength [12], which increases with the bleach strength. The kinetics of hypochlorite decomposition exponentially increases with the temperature. Photochemical decomposition can also occur and for this reason hypochlorite bleaches are generally stored in opaque containers. Light, especially at a wavelength below 500 nm, is reported to break down the hypochlorite molecule to chlorite and oxygen [18]. The photolysis of hypochlorite/hypochlorous acid is also reported to lead to the formation of OH and Cl radicals [26,27,28]. Under these conditions, the oxidation of model organic compounds (ethanol, n-butanol, and benzoic acid) by aqueous hypochlorous acid proceeds mainly via a radical pathway [26]. The stability of formulated products is also affected by the compatibility of hypochlorite with the other co-ingredients present in the formulation. Hypochlorite/hypochlorus acid can act both as an oxygen donor, such as in reaction (7) or as a chlorination agent such as in reaction (8):

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Liquid Bleach Formulations

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.. S..

δ+ Cl

185

H O

Cl −Cl−, −H+

δ− OH

Cl C+

O

S. .

H2O

O

HOCl

O O

S O

Cl

H2O

(7)

Cl

+

H

H2O+ CH3

HO

CH3

Chloroidrin

(8)

In addition to this, hypochlorite/hypochlorous acid solutions are also reported to lead to radical formation in the presence of metal catalysts [29,30,31]. Minisci [32] describes the chlorination of alkanes and alkylbenzenes with hypochlorous acid in a twophase system to occur by a noncatalyzed radical chain chlorination mechanism (alkane and benzylic substitution, addition to benzene) that operates in competition with electrophilic chlorination, whenever this last is structurally possible. Cl2O is assumed to be involved in the initiation step and OH radicals to be responsible for the chain propagation. Among surfactants, alcohol ethoxylates are generally unstable to hypochlorite and lead to a fast loss of AvCl2. Nonylphenol ethoxylates have been found more stable than linear alcohol ethoxylates in 4.5% AvCl2 bleach solutions at 37˚C [33]. Alkyl sulfates are among the most stable anionic surfactants, even at nonoptimal pH of the bleach composition (11.3) [33,34]. The mass spectrometry (MS) analysis of linear sodium dodecyl sulfate aged for 10 days at 50˚C in a 3% AvCl2 solution at pH 13, confirms the good stability of this surfactant, showing little variation of the peak at 265. Only monoand to a much lower extent di-chlorination of the surfactant appears to occur (Fig. 2). A drawback associated to the use of alkyl sulfate is the relatively poor water solubility at the high ionic strength of hypochlorite bleaches and at room temperature. This prevents the use of alkyl chain lengths equal or above 12 carbon atoms for AvCl2 concentrations above 1.5 to 2% w/w. Alcohol ether sulfates are much more soluble in hypochlorite bleach solutions, especially if they contain two or more ether groups, but their stability to hypochlorite is poorer than that of the corresponding alkyl sulfate [33]. In line with this, the MS analysis of pure cut sodium dodecyl ether(4) sulfate aged for 10 days at 50˚C in a 3% AvCl2 solution at pH 13 shows a significant reduction of the intensity of the peak at 441 as a consequence of the cleavage of the surfactant molecule and chlorination (Fig. 3). Linear alkyl sulfonates are less soluble and less stable to hypochlorite than the corresponding sulfates [33]. The stability of linear alkyl sulfonates appear to decrease with the pH of the hypochlorite bleach [34]. Trautman [35] found that blends of secondary alkane sulfonates with aminoxide are more stable than the single surfactants. Linear alkyl benzene sulfonate, alkyl aryl sulfonate and alkyl naphthalene sulfonate are also reported to negatively affect hypochlorite stability, whereas alkyldiphenyl oxide disulfonate are quite stable to hypochlorite, even when used at high concentrations [33,34]. A good compatibility with hypochlorite bleach is also shown by phosphate esters [33,36]. Cationic surfactants can affect the reactivity of sodium hypochlorite by acting as phase transfer catalysts. Under these conditions the oxidation chemistry of hypochlorite appears to follow a radical pathway [37–39].

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100

Mono-chlorination 299

%

0

301 di-chlorination 266 333 267 302 335 263 281 532 553 117 141 153 185 197 223 225 367369371 405 417439449469 323 474 499 550 554 587589

265

100

%

0

266 267 348 231 261 141 489 593 595 149 201 133 268 293 306 327347 385 387 407 429 441469 209 223 150 508 511 531 553 554 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 420 440 460 480 500 520 540 560 580 600

Figure 2 Negative ion mass spectrum of sodium dodecyl sulfate in a 3% AvCl2 bleach solution (pH 13), fresh (bottom spectrum) and aged for 10 days at 50˚C (top spectrum).

Among amphoteric surfactants, aminoxides are generally stable and highly soluble in hypochlorite matrices for a carbon chain length up to C15 to C16. Betaines generally show a poor stability to hypochlorite. Surfactants have also been used for the thickening of hypochlorite bleaches. For example, thickening systems comprising alcohol ether sulfate stabilized via the use of radical scavengers are reported in the patent literature [40]. Alternative thickening systems are based on cross-linked polyacrylates [41], possibly stabilized against oxidative decomposition [42]. Since the 1960s, formulators have tried to combine the “whitening” action of hypochlorite bleach to that of optical brighteners and molecules with a relatively good stability to hypochlorite have been developed [43,44,]. However, because they are highly unsaturated, brighteners are intrinsically unstable to hypochlorite and their complete decomposition in relatively diluted bleaches (2.5 to 3% AvCl2) typically varies from few hours at room temperature, such as for 4,4'-bis(2-sulfostyryl)biphenyl disodium salt (Tinopal CBS), to few days at 50˚C, such as for Tinopal PLC. Transition metals present in the wash solution are also reported to affect the stability of stilbene type of brighteners [45]. The most common approach to overcome the chemical incompatibility between hypochlorite and brighteners in the finished product has been to segregate the brightener in surfactant and/or polymer matrices or by the formation of insoluble complexes [46–54]. Recently, also the use of radical scavengers has been proposed for the stabilization of brighteners in hypochlorite [55]. Because brighteners are used at low concentrations, even their complete degradation leads to a low loss of AvCl2.

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141

187

C12E4S cleavage 273 185 199

229 C12E4S 441

%

Mono-chlorination 475

213

215

124

243

153 183

267 259

274

117

di-chlorination 287 442 477 509 305 443 341 375 511 543 478 387 397411 307 331 544 577579 499 541 431 457

0 1512983 320 (5.900) Cm (310:343-(366:400+253:305) × 2.000)

100

C12E4S

441

%

442

0

135

265 149 150 276 209 223 231 268

300 305

345

387 397398 439

443 444 482495 523 585 459 524 549 567 586

100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 420 440 460 480 500 520 540 560 580 600

Figure 3

Negative ion mass spectrum of sodium dodecyl ether (4) sulfate in a 3% AvCl2 bleach solution (pH 13), fresh (bottom spectrum) and aged for 10 days at 50˚C (top spectrum).

Pigments and dyes are also generally unstable to hypochlorite. Among the few exceptions reported in the patent literature are phtalocyanines [56], ultramarine blue, chlorinated hydantrone, and cobalt aluminate [54,57]. Silicate is also reported to stabilize ultramarine blue against hypochlorite attack [58]. The water insolubility of most typical perfume ingredients and their incorporation in the bleach matrix by the use of surfactants provide a partial protection against hypochlorite attack. The selection of saturated molecules, possibly not bearing readily oxidizable groups, is a common strategy in the selection of perfume ingredients for a hypochlorite bleach formulation. C. Fabric Safety Profile of Hypochlorite Bleaches Similarly to stability, the fabric safety of hypochlorite bleaches decreases with the pH. The maximum decomposition rate of cotton is reported to occur at about the pK of hypochlorous acid, i.e., at about pH 7 [10]. As an example, Fig. 4 reports the effect of the initial pH of the wash solution on the repeated bleaching of cotton and nylon 6,6 fibers as DP vs. machine washes. Gel permeation chromatography (GPC) can also be used to determine the molecular weight of fibers [59–64]. The GPC analysis of fabrics bleached under washing conditions similar to those reported in Fig. 4, confirm that the reduction of DP is due to a depolymerization phenomenon (Fig. 5). The extent of depolymerization can vary with the type of cotton and fabric. As shown in Fig. 5a, single yarns that are more easily accessible to hypochlorite during the wash are those that show the most remarkable decrease in molec-

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Scialla and Todini

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pH 8.8 pH 9.4

1600

1200

800

400 0

20

40

60

80

Degree of polymerization of nylon 6.6 fibers

Degree of polymerization of cotton fibers

188

70

pH 8.4

60

pH 9 50 40 30 20 10

Machine washes

0

10 20 30 Machine washes

40

Figure 4 Effect of bleaching with hypochlorite on the degree of polymerization (DP) of cotton and nylon 6,6 fibers at two initial pH of the wash solution. Test conditions: Bleach dilution: 5 ml/l, initial AvCl2 in the wash solution: 250 ppm, washing time: 20 minutes per washing cycle followed by three rinsing steps of about 5 minutes each, cold water, S. Giorgio washing machines. Fabrics: WFK 11A cotton (WFK, Germany); Polyamide:Lycra 80:20 (Italpack, Italy).

1E+5 9E+5

Cotton yarn (Standard fabrics)

Mn Mw

8E+4

8E+5

Mw

7E+5 6E+5

Mz Cotton 11a (WFK) Cotton jeans (WFK)

Cotton sponge (WFK)

6E+4

Mp Polydispersity

4E+4 2E+4

5E+5 0E+0 Virgin Bleached Bleached fiber at pH 9 at pH 8.4

4E+5 (a)

(b)

Figure 5 Gel permeation chromatography of bleached fabrics. (a) Variation of the molecular weight (MW) of cotton fibers after 20 bleaching cycles. (b) Effect the initial pH of the wash solution on the variation of molecular weight of nylon 6,6 fibers after 20 bleaching cycles. Bleaching procedure as for Fig. 4.

ular weight. In the case of nylon 6,6 (Fig. 5b), a lower initial pH of the wash solution enhances the depolymerization phenomenon. Three-dimensional (3D) images of bleached cotton 11a (WFK) acquired via confocal laser microscopy [65,66] show that the reduction of the DP and molecular weight of cotton fibers can translate into a thinning of the fabric. The phenomenon is more pronounced at the lowest initial pH of the wash solution. In this case, also pinholing of the fabric can be observed (Fig. 6). The pH of the bleaching solution can vary significantly depending on the product usage conditions and the chemical-physical characteristics of the water used for the bleach dilution. When hypochlorite is used alone in tap water, the pH of the wash solution

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Figure 6 Confocal laser microscopy of cotton swatches (WFK 11A, WFK Germany) new and after 20 bleaching cycles according to condition reported in Fig. 4. The circles indicate the areas where pinholing occurred.

Scialla and Todini Demineralized water Tap water (30 f)

12

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11 10 9 8

0

4

8

12

16

20

10.5 10.0 9.5 9.0

Bleach alkalinity (mmoles NaOH) 14.5 32.5 42.5

8.5 8.0 0

Hypochlorite bleach dilution (g bleach/l water)

4

8

12

16

20

Hypochlorite bleach dilution (g bleach/l water)

Figure 7 Effect of (a) water hardness and (b) hypochlorite bleach alkalinity on the initial pH of the bleach wash solution as a function of product dilution. Temperature 20˚C. (a) bleach alkalinity measured by titration to pH7: 14.5 mmol NaOH; (b) water hardness measured with aqua Merck total hardness test (Merck): 30 French degrees (f).

generally ranges between about 8 and 9.5 depending on the alkalinity of the hypochlorite bleach, the dilution factor, and the water hardness (Fig. 7). To maintain as high as possible the pH of the wash solution caustic soda, sodium carbonate and silicate are proposed as a source of alkalinity for bleach formulations [25,67]. The maximum level of alkalis that can be added to a hypochlorite bleach formulation is generally limited by the safety profile of the resulting composition. In fact, local legislations can limit the concentration of alkalis present in a chlorine bleach formulation of a certain strength. Independently from the initial pH of the wash solution, CaCO3 precipitation can lead to a rapid decrease of the pH during the wash (Fig. 8). The phenomenon is enhanced by the presence of sodium carbonate in the hypochlorite bleach and, especially under handwash conditions, by the adsorption of atmospheric CO2.

pH of the wash solution

9.4 9.2 9.0 8.8 8.6 8.4 0

10

20

30

Time (minutes)

Figure 8 Decrease of the wash solution pH as a function of soaking time. Temperature 20˚C, water hardness 30 f, bleach alkalinity: 42.5 mmol NaOH, bleach dilution 5 ml/l.

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When hypochlorite bleaches are used in combination with powder or liquid detergents, the buffer power of the detergent often prevails and the pH of the corresponding wash solution shows very little deviation from that of a wash solution constituted by the detergent only. Powder detergents not containing a source of oxygen bleach represents an exception, because they do not require the presence of a strong buffer to facilitate the hydrolysis of percarbonate or perborate. In this case, the hypochlorite bleach alkalinity tends to slightly increase the natural pH of the detergent wash solution (generally from about 8 to 9, depending on the dilution factor). Dyes for cellulose and synthetic fibers are generally oxidized by hypochlorite leading to complete discoloration or color change. In the case of metallized dyes, common for example for dark colors, the metal ions can also initiate the metal-catalzsed decomposition of hypochlorite. This prevents the use of hypochlorite bleach on colored cloths. Similarly to dyes, most brighteners are sensitive to the oxidative action of hypochlorite bleaches and repeated bleaching in the absence of any brightener replenishment from the detergent wash solution can lead to fabric yellowing. Transition metals, such as Fe and Mn for instance, are reported to induce the yellowing of white fabrics upon bleaching with hypochlorite and chelants can be used to prevent or mitigate this phenomenon [21]. Radical scavengers are also reported to reduce the fiber damage due to bleaching. For example, Hinojosa and co-workers [68] report that in the treatment of cotton and chemically modified cotton with hypochlorite bleach in the pH range 9 to 11, the presence of chlorine dioxide free radicals has been observed via ESR. This radical is stabilized in benzoylated and benzylated yarns, indicating that these functionalities can offer protection against the oxidative attack of cellulose by chlorine dioxide radicals. Also compounds that are able to interact with cotton fiber sites are reported to reduce the oxidative damage of fabrics and the yellowing of white garments [69,70].

III. THE FORMULATION OF LIQUID HYDROGEN PEROXIDE BLEACHES A. Introduction A key limitation of hypochlorite bleach is the lack of color safety. Although the technology of hypochlorite has made tremendous progress so this ingredient can now be used with a high degree of safety on white fabrics, current best formulations are still far from being usable on colored items. This generates the consumer need for a liquid bleach that qualitatively delivers the same kind of performance as hypochlorite, i.e., removal of hydrophilic colored stains, but has a broader spectrum of applicability. In relatively recent times formulators have identified liquid hydrogen peroxide as the best bleaching agent to match these performance objectives. This ingredient offers the advantage vs. hypochlorite of being intrinsically safer on colors, odorless and more compatible with other detergent actives. Liquid hydrogen peroxide has been present for decades in almost any U.S. or European household, in the form of a 3% solution stored in a dark brown bottle, for occasional uses such as wound disinfection [85]. It was only in the early 1990s that liquid bleaches based on hydrogen peroxide started to appear on supermarket shelves and became a significant segment of the bleach market. This was due not only to an increasing consumer need for colorsafe products—which perhaps was already there before—but also to the progress made in the technology of hydrogen peroxide stabilization. In addition, new peroxide-stable detergent ingredients became available to formulators. This progress made it possible to move from the plain 3% solution stored in

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brown bottles, to fully formulated products containing surfactants, solvents, fragrance, optical brighteners, etc. Hydrogen peroxide bleaches are mostly used in two ways: (1) in combination with a laundry detergent, i.e., mixed with a detergent in the same washing liquor; (2) through direct application of the neat product on stains (pretreatment) prior to a machine or hand wash. The combination with a laundry detergent is a common practice under U.S. washing conditions also with hypochlorite bleach, whereas in Europe most detergents contain their own peroxide-based bleaching system, which is incompatible with hypochlorite. Instead, hydrogen peroxide bleaches can be mixed with European laundry detergents without compatibility issues. Unfortunately, while liquid hydrogen peroxide has a much better color safety profile than hypochlorite and, therefore, a broader applicability, the other side of the coin is that, quantitatively, hydrogen peroxide delivers a poorer stain removal performance than hypochlorite. Thus a lot of the technology work in this area has been devoted to the development of new systems to boost the stain removal of hydrogen peroxide. This needs to be achieved under two key constraints: (1) maintaining a good storage stability of the final formulation, and (2) not losing the advantages in terms of color and fabric safety. B. Stability of Liquid Hydrogen Peroxide From a thermodynamic standpoint, hydrogen peroxide is a highly unstable material that tends to decompose according to the following net reaction: 2 H2O2 → 2 H2O + O2 which formally implies a disproportionation of hydrogen peroxide. Since the decomposition leads to the production of gaseous oxygen, it can be dangerous especially if it takes place quickly. As we will see, there are various possible mechanistic pathways leading to this net reaction, often not yet completely understood [71]. What is very important from a practical standpoint is that the decomposition kinetics is extremely slow in the absence of catalysts or other accelerating factors. Thus it is possible to have even highly concentrated2 (e.g., 50% or 70%) hydrogen peroxide solutions that exhibit activity losses below 1% after 1 year of storage. In a different fashion from hypochlorite, the relative stability of hydrogen peroxide solutions does not decrease upon increasing peroxide concentrations. The decomposition mechanisms of hydrogen peroxide can be divided into two types: (1) polar or bimolecular and (2) radical. Polar decomposition (sometimes also called “spontaneous” decomposition) can be postulated to occur through the nucleophilic attack of a perhydroxyl anion HOO– on a neutral hydrogen peroxide molecule [71,77]. The perhydroxyl anion is formed from the hydrogen peroxide dissociation equilibrium:

2

The activity of hydrogen peroxide solutions is most often expressed as % w/w. However, other units are also relatively common, such as “active oxygen” or AvO. The AvO of a hydrogen peroxide solution having a weight percent concentration C can be calculated from the following formula: AvO =

MwO ⋅ C = 16/34 C = 0.47 C Mw H 2O 2

A detailed discussion of concentration units and analytical methods for hydrogen peroxide determination can be found in [72].

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2 H2O2 → 2 H2O + O2 Its nucleophilic attack on H2O2 can be expected to lead to the following transition state: -

H O O

O O H

H This mechanism, which involves an attack of oxygen on oxygen and is similar to the one proposed for Caro’s acid [73,74], is obviously pH dependent. The fastest reaction kinetics is reached at a pH equal to the pKa of hydrogen peroxide, i.e., pH = 11.75. This is because when pH = pKa the expression vdecomp = k [HOO–] [H2O2] which represents the rate of the bimolecular polar decomposition reaction [75], reaches its maximum value. If the polar one previously described were the only decomposition mechanism to be taken into account, we should expect to observe that the more we move away from pH = pKa, the more stable hydrogen peroxide solutions become. However this is true only to some extent, because there are other mechanisms that in parallel contribute to determining the overall stability. One of them is a second type of polar decomposition catalyzed by strong acidity. It has been postulated [73,77] that at very low pH hydrogen peroxide may become protonated forming perhydroxonium ions: H 2 O 2 + H 3O + T H 3O +2 + H 2 O Under these conditions unprotonated hydrogen peroxide can be thought to perform a nucleophilic attack on perhydroxonium ions, thus originating a transition state and decomposition pathway analogous to the one occurring at high pH.

H H O O

H

+

O O H

H The other big contribution to hydrogen peroxide decomposition comes from radical chain processes. In this case the initiating step consists in the formation of the hydroxyl radical OH•. This may be favored typically by transition metal ion impurities or by electromagnetic radiation. In the most common and well-known case of catalysis by iron impurities (Fenton system), the sequence of initiation and propagation steps is as follows [71,76]: Fe2+ + H2O2 T FeOH2+ + OH OH . + H2O2 T H2O + HO2

.

.

HO2 . + H2O2 → H2O + O2 + OH

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(1) (2) .

(3)

Fe3+ + H2O2 T Fe2+ + HO2 . + H+

(4)

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Fe3+ + HO2. → Fe2+ + O2 + H+

(5)

Fe2+ + OH. → FeOH2+

(6)

where (1) and (4) are initiation, (2) and (3) propagation, and (5) and (6) are termination steps. Equation (4), being an equilibrium, shows that the initial oxidation state of iron is irrelevant. Several other transition metals can promote analogous radical decomposition processes, for instance copper, manganese, chromium, cobalt, etc. A comprehensive list of catalytic elements and of their relative catalytic strength is provided in [77]. Reactions (2) and (3) also constitute the propagation steps in the decomposition induced by electromagnetic radiation. In this case the initiation step is represented by the following homolysis: H2O2 → 2 OH hv

.

This reaction is caused by UV radiation in the broad wavelength range between 380 and 200 nm [77]. As a consequence of the above discussion, there are essentially four ways for the formulator of liquid hydrogen peroxide to improve product stability (excluding for the time being the choice of ingredients, which will be discussed below): 1. 2. 3. 4.

pH control Transition metal ion control and chelation Use of radical scavengers Protection against UV radiation

As for pH control, it turns out experimentally that the minimum decomposition rate, thus the maximum stability, is usually achieved in a pH range between 2 and 5 for most hydrogen peroxide solutions or formulations. This stems from the sum of various decomposition contributions which have different types of pH dependence, i.e., the polar mechanism based on perhydroxyl anion; the polar mechanism based on peroxonium; and the metal catalysis which can change as a function of pH due to changes in the solubility and coordination sphere of catalytic ions. The desired pH value can be achieved either by mineral acids (e.g. sulfuric, hydrochloric), or by carboxylic acids (e.g., citric) when some buffering is required. Transition metal ion control is of great importance due to the substantial decomposition that can be caused by even trace amounts of metal ions. Metals like iron, copper, and manganese are strongly catalytic already at concentrations of one ppm or even less [78]. Metal ion control should be obtained first of all by a careful selection of the grades of all raw materials used besides hydrogen peroxide, e.g., deionized water, surfactants, solvents, etc. After having minimized all the potential sources of catalytic metal ions in the product, the formulator can control the remaining impurities by appropriate chelants. The chelants reported to be most effective are aminopolycarboxylates such as ethylenediaminetetraacetate (EDTA), polyphosphates, aminopolyphosphonates, and polyphosphonates [79,80]. Aminophosphonates are often preferred to aminocarboxylic acids because, according to some authors [79], the oxidation of their amino groups to the corresponding amine oxides (by hydrogen peroxide) does not affect their chelating ability. This is not the case for EDTA and similar compounds, whose chelating ability is diminished by partial oxidation. Commonly used aminophosphonates are those available under the tradename Dequest® from Monsanto.

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Radical scavengers work against the same type of decomposition process as chelants, i.e. radical decomposition, but they do it through a different mechanism. Chelants try to occupy active sites in the coordination sphere of transition metals, thus making them unavailable for interaction with hydrogen peroxide and preventing the formation of OH. radicals. Instead radical scavengers perform the function of stopping OH. radicals once they have been formed. Typical radical scavengers are molecules that can donate a hydrogen atom to a reactive radical, such as OH., thus transforming it into a nonradical species with lower reactivity. The radical scavenger molecule, after donating its hydrogen atom, becomes itself a radical, however, the new radical formed is a more stable one with low reactivity, so the original radical chain reaction is terminated or significantly slowed down. Usually the stable radical obtained from the scavenger is an oxygen-centered radical derived from a phenolic structure. The phenolic structure allows to delocalize the unpaired electron on the aromatic ring, which results in lower energy, higher stability and lower reactivity of the radical molecule (see Fig. 9). Well-known examples of radical scavengers are butylated hydroxy toluene (BHT), mono-tert-butyl hydroquinone (MTBHQ) [81,82], and other phenolic compounds. Primary or secondary aryl amines have also been proposed as effective radical scavengers [83]. According to some authors, the amine oxide functionality may perform a radical scavenging action too. Thus the effectiveness of amino phosphonates as stabilizers may be related not only to their chelating ability, but also to the formation of amine oxide functionalities upon oxidation of their tertiary amine sites [79]. The possibility of synergisms between different stabilizers combined together in the same formulation has been highlighted by several authors [84]. The most frequently exploited combination is the one between a chelant and a radical scavenger [81–83], however, the combination of chelants with other classes of compounds, e.g., polyacrylates, has also been mentioned as synergistic [80]. Hydrogen peroxide solutions are not significantly affected by exposure to visible light, while they are decomposed by radiation in the ultraviolet region, particularly between 380 and 200 nm as mentioned above. The rate of decomposition is directly proportional to the concentration of hydrogen peroxide and to the square root of radiation intensity. Unfortunately, the reproducibility of UV light-induced decomposition experiments is low and strongly dependent on the particular grade of hydrogen peroxide used, so specific decomposition data as a function of UV frequency and intensity are not very reliable. However, what’s most important for the formulator from a practical standpoint is that ordinary plastic bottles usually provide a sufficient light barrier for storage on indoor shelves. It may be required to add to the plastic a charge of a UV absorber, if the product needs to be sold in countries where storage conditions are such that prolonged exposure to direct sunlight is likely to occur.

O.

OH R

R

- H.

R

O R R

O

O R R

.

R R

.

R

. Figure 9 Stabilization of oxygen-centered radical through delocalization of the unpaired electron on the aromatic ring, in a typical radical scavenger with phenolic structure.

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Although not directly controllable by the formulator, temperature is another very important factor determining the stability of liquid hydrogen peroxide products. In the range between 10 and 70˚C, the decomposition rate of hydrogen peroxide in solution follows the Arrhenius’s law, i.e., a temperature increase of 10˚C accelerates the decomposition rate by a factor of about 2. The presence of stabilizers decreases the absolute decomposition values but has a negligible effect on the above temperature dependence factor. This makes temperature a very critical parameter in warm countries, where the stability properties of hydrogen peroxide products need to be checked even more carefully. On the other hand, the strong temperature dependence of hydrogen peroxide decomposition rate can be used advantageously by formulators to run rapid ageing tests of their products, usually at temperatures around 40˚C or 100˚F. Our discussion so far has been focused on the key chemical-physical factors influencing the stability of hydrogen peroxide solutions, regardless of whether additional ingredients beyond peroxide are present or not. In other words, the above factors apply to formulated products as well as solutions of plain hydrogen peroxide. The rest of the discussion in this section will concern the additional considerations that come into play when hydrogen peroxide is formulated together with other ingredients, which is obviously the case in liquid bleaches. As it should be apparent from the above discussion, the first requirement for any material to be a suitable ingredient for liquid hydrogen peroxide formulations, is that it should contain the lowest possible level of transition metal ion impurities. Even if chelants can be used to “neutralize” the catalytic effect of metal ions, it is very important in the first place to limit as much as possible their presence. Typical sources of transition metal ions are salts, or ingredients that require the use of metal catalysts in their manufacturing process. In the industrial production of liquid peroxide bleaches, the presence of metal ion impurities may be due also to accidental contamination. This introduces the need for a constant quality control on raw materials and finished products in terms of their heavy metal ion content [85]. Among surfactants used in liquid peroxide bleaches, the ones most commonly mentioned in the literature are anionic and nonionic surfactants. Anionic surfactants that exhibit good compatibility with hydrogen peroxide are LAS, alkyl sulfates, alkyl ethoxy sulfates, alkane sulfonates, and fatty acid salts. Most often used nonionics are ethoxylated alcohols and amine oxides. Some formulators [82] mention that a surfactant system based on ethoxylated alcohols only (without anionics) is preferred to a mixed surfactant system. Others [86] found good stability with formulations containing specific classes of nonionic surfactants mixed with anionics. Mixtures of various nonionics with different values of hydrophilic-lipophilic balance (HLB) have also been investigated [87]. Hydrogen peroxide bleaches are relatively often viscous. Viscosity can be achieved either by self-thickening systems based on combinations of surfactants and ionic strength [89], or by specific thickening or gelling agents. These are typically polyacrylates or maleic acid/acrylic acid copolymers [89], cross-linked polyacrylates [90], or polyoxyethylene/ polyoxypropylene block copolymers [91]. Optical brighteners can be incorporated in peroxide bleaches but need to be carefully chosen. For instance, the older diaminostilbene-type brighteners—still broadly used in laundry detergents—are usually incompatible with hydrogen peroxide due to the oxidation of various nitrogen sites (see Fig. 10), which results in bond cleavage and consequent loss of fluorescent properties. One of the brighteners most often used in liquid hydrogen peroxide products is Tinopal® CBS-X ex Ciba Specialty Chemicals. This has a distyryl biphenyl structure (DSBP) carrying two sulfonic groups. In this molecule the only possible sites of attack for hydrogen peroxide are the two double bonds, which can undergo a

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Oxidative Degradation

DSBP NaO3S

SO3Na

Hydroxylation

DAS1 O N Hydroxylation

NaO3S

N

N

NH

N NH N-Oxidation

HN N HN

N N

SO3Na

N O

Figure 10 Reproduced by permission from Ciba Specialty Chemicals Holding Inc., Tinopal—The Absolute White, CD-ROM, Basel, Switzerland (1998).

hydroxylation (see Fig. 10). However, because of the strong conjugation of the double bonds with aromatic rings, this reaction occurs at a negligible rate in properly formulated peroxide bleaches. Color is an important aesthetic parameter in liquid peroxide bleaches, since it should help communicate the better mildness of these products vs. hypochlorite and their suitability for colored laundry items. The color should not fade significantly upon product ageing, which would otherwise connote poor quality to the consumer. There are a number of pigments and dyes having good stability in liquid hydrogen peroxide, for instance, color index vat blue 4 or color index vat red 23 among pigments, and color index acid blue 229 or color index acid blue 112 among dyestuffs [80]. Fragrance is very important as well from an aesthetic standpoint and is a further element of differentiation vs. hypochlorite bleach. Specifically there are two important advantages: (1) the range of perfume ingredients that can be used with hydrogen peroxide is significantly broader than with hypochlorite; and (2) hydrogen peroxide causes virtually no base odor, whereas hypochlorite has a well-known, strong odor that needs to be covered by whatever fragrance one wants to use. Still, formulating a fragrance compatible with hydrogen peroxide is a difficult task since several common perfume ingredients, for instance aldehydes, can be unstable. Formulating a hydrogen peroxide bleach with good stability is important from a practical standpoint not only for the loss of cleaning performance and aesthetic properties that can be caused by product decomposition, but also because of the undesired production of significant amounts of gaseous oxygen. If we take a formulation containing 4% hydrogen peroxide, for instance, it is easy to calculate that a change of hydrogen peroxide concentration down to 3.8%, i.e., a relatively small decomposition, would already cause the production of more than a liter of gaseous oxygen per liter of bleach, under standard temperature and pressure conditions. Considering that the headspace available in common bottles is rather limited, such an amount of gas would significantly increase the internal pressure, potentially causing bulging of bottles unless appropriate valves are used.

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C. Boosting the Performance of Liquid Hydrogen Peroxide In principle there are a lot of ways to enhance the stain removal performance of liquid hydrogen peroxide formulations. However, looking at the patent literature, we can identify essentially three main approaches that have been and continue to be investigated: (1) activation by peracid precursors; (2) peracids in equilibrium with hydrogen peroxide; and (3) stabilization at alkaline pH. 1. Activation by Peracid Precursors This approach is widely used in powder detergents, where the most common peracid precursors are tetra acetyl ethylene diamine (TAED) (in European detergents) and nonanoyl oxy benzene sulphonate (NOBS) (in U.S. detergents) [92]. Peracid precursors are usually esters (like NOBS) or N-substituted amides or imides (like TAED), which react with hydrogen peroxide and the hydroperoxide anion forming a percarboxylic acid through a reaction called perhydrolysis. HOO

O R

C

-

R

+

L

L-

O C

+

OOH

H2O2

LH

O L = OR', NHR', NR'R", NR'

C R"

The hydroperoxide anion comes from the deprotonation equilibrium of hydrogen peroxide (see section on stability of liquid hydrogen peroxide, Section III.B), which in powder detergents is generated from the dissolution in water of salts such as perborates or percarbonates. The peracid thus formed is kinetically more reactive than hydrogen peroxide and can deliver a good bleaching action already at low washing temperatures, where hydrogen peroxide alone is less effective due to the high activation energy of most of its oxidation reactions. The peracid is more reactive toward stains but is also much more unstable than hydrogen peroxide. This is why the peracid precursor approach has been so successful in powder detergents, as it allows to generate the peracid in situ thus avoiding the problem of stabilizing a preformed peracid in the formula. This in general is a challenge not only in a liquid matrix but also in powder products. As shown above, the perhydrolysis is due to a nucleophilic attack of hydrogen peroxide or the hydroperoxide anion on the carbonyl group of the peracid precursor. However, the perhydrolysis rate is significantly higher for the hydroperoxide anion than for hydrogen peroxide. Therefore the overall peracid conversion rate of the precursor is strongly pH dependent and increases dramatically at alkaline pH values, where the deprotonation equilibrium of hydrogen peroxide becomes more shifted to the right. This is one of the reasons why the wash solution pH of most powder detergents is in the range between 9 and 10. The storage stability of peracid precursors in powder detergents is usually quite good, i.e., they do not show a strong tendency to hydrolyze or perhydrolyze inside the product. The perhydrolysis starts only upon contact with water and consequent dissolution of the various ingredients. Only in powder formulations containing very high levels of bleach and in compact products, the stabilization of peracid precursors may present some difficulty. The situation is very different in liquid hydrogen peroxide bleaches, where stably incorporating the peracid precursor is a major challenge. Formulators can play with essen-

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tially three parameters: reactivity of the precursor, formulation pH, and water solubility of the precursor. Given the difficulty of obtaining a formulation with good storage stability, the peracid precursor should not be chosen among those with the highest reactivity. Probably esters are the class of precursors most often mentioned in the literature for this kind of application. For the same reason, an acidic pH in the range from 2 to 6 is compulsory in order to minimize the concentration of hydroperoxide anion in the product. Precursor solubility is the third key parameter to help controlling stability. A precursor with low solubility in the formulation environment will have less chances to interact with hydrogen peroxide and to undergo perhydrolysis. Some formulators claim to have achieved good stability by using precursors that have a pH-dependent solubility. The precursor is insoluble at the acidic pH of the formulation but becomes soluble when pH increases, which is what happens in the wash solution. A typical functional group able to impart insolubility at low pH and solubility at alkaline pH is –COOH. This approach requires a thickener to keep the precursor suspended in its insoluble form at acidic pH [93,94]. Other formulators have used hydrophobic liquid precursors that are emulsified by a surfactant system based mainly on nonionics. Stability is achieved by keeping the hydrophobic liquid precursor separate from hydrogen peroxide through emulsification or microemulsification, and by a pH in the acidic range. An example of such liquid precursors is acetyl triethyl citrate (ATC) [95,96,97]. Enol esters have also been claimed to be suitable as activators in emulsions containing hydrogen peroxide [98,99]. A microemulsification approach utilizing activators that carry quaternary ammonium functionalities is described in [100]. 2. Peracids in Equilibrium with Hydrogen Peroxide Unlike the previous peracid precursor approach, which is used in both powder and liquid products, the equilibrium peracid approach is typical of liquid hydrogen peroxide formulations only. It is based on a well-known equilibrium reaction catalyzed by acidic pH: R-COOH + H2O2 T RCOOOH + H2O This equilibrium is usually shifted to the left, so the corresponding formulations contain an excess of hydrogen peroxide/carboxylic acid and a relatively small concentration of peracid [101]. The acids most commonly used in this approach are short chain, water-soluble carboxylic acids, typically acetic or propionic acid. In order to obtain formulations with a lower odor impact, short chain dicarboxylic acids such as glutaric, succinic, or adipic and their monomethyl esters are also used [79]. The storage stability of equilibrium peracid solutions can be made acceptable for some practical applications. Similarly to plain hydrogen peroxide, the addition of chelants and radical scavengers is essential to control the catalytic action of heavy metal ions and free radical processes [102]. Similarly to plain hydrogen peroxide, pH is crucial, but needs to be kept at even lower values in order to achieve good stability. This is because the polar decomposition mechanism of peracids in solution, which occurs through a nucleophilic attack of the peracid anion on the undissociated peracid [73]:

-

O H3C

O

O

C

H O

O O

C CH3

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is even more pH-dependent. Similarly to what happens with plain hydrogen peroxide, the expression vdecomp = k [R-COOO-] [R-COOOH] which represents the rate of the bimolecular polar decomposition reaction, reaches its maximum value when pH = pKa. So the more we move away from pH = pKa, the more stable the equilibrium peracid solution becomes. But the pKa of most organic peracids is around 8.0 to 8.5, whereas the pKa of hydrogen peroxide is 11.75. Therefore most equilibrium peracid solutions need to be kept below pH 3 in order to achieve acceptable stability. Even under optimal conditions, however, the stability of equilibrium peracid solutions is significantly lower than that of plain acidic hydrogen peroxide and—probably—of various formulations based on the peracid precursor approach. The challenge of achieving good stability increases dramatically upon addition of other ingredients such as surfactants, perfume, etc., due to the high reactivity of the free percarboxylic acid. Some authors [79] found that peracid recoveries for a fully formulated product (pH 2) based on the equilibrium peracid approach, can be as high as about 90% after 6 months at 25˚C. 3. Activation by Alkaline pH The alkaline pH approach is based on the fact that, although acidic H2O2 has a higher thermodynamic oxidation potential than alkaline H2O2, the hydroperoxide anion HOO– is kinetically more reactive and is the species of interest in most practical applications. Accordingly hydrogen peroxide formulations deliver a stronger bleaching performance at alkaline vs. acidic pH. The other side of the coin is that alkaline hydrogen peroxide formulations, being more reactive, are more difficult to formulate and stabilize. Thus most of the literature on alkaline hydrogen peroxide deals with the challenge of increasing the shelf life of the corresponding formulations. The technologies used to achieve stabilization at alkaline pH are not substantially different from those already reviewed in previous paragraphs. Therefore the key ingredients involved are chelants and radical scavengers. However, the literature related to alkaline hydrogen peroxide focuses on specific chelants (usually phosphonates) or combinations of chelants that would be particularly effective in controlling decomposition at high pH. For example, some formulators claim the combination of a borate buffer with CDTMPA chelant (cyclohexane-1,2-diaminotetrakis phosphonic acid) to be particularly effective for the stabilization of hydrogen peroxide at a pH around 8.5 [103]. Others found the class of aminophosphonate chelants with the general structure

CH2(PO3H2)

(PO3H2)CH2 N-CH2-CH2-(N-CH2-CH2)n-N (PO3H2)CH2

CH2(PO3H2)

CH2(PO3H2)

where n = 1 to 4, to be the most effective at alkaline pH [104]. Recently the role of cobalt in catalyzing H2O2 decomposition at alkaline pH has been emphasized [105,106]. According to these studies, most commonly used phosphonate chelants are not as effective against Co2+ as they are against other catalytic ions (e.g., Fe3+, Mn2+, Cu2+). Consequently, unless appropriate precautions are taken, formulations stabilized by “standard” chelant systems would contain a relatively large concentration of free or only partly complexed Co ions, which are able to trigger a significant catalytic decomposition. A better stability can be

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obtained by the combination of a chelant having specific activity against Co ions, such as dipyridylamine or triazacyclononane, with a “standard” phosphonate chelant. Despite the appearance in the marketplace of a few products based on alkaline hydrogen peroxide, this approach continues to be less preferred than the ones utilizing an acidic pH. This is because the stability of alkaline formulations continues to have limitations with respect to acidic products and, as a consequence, there are more constraints around the choice of compatible ingredients. Also, in laundry applications hydrogen peroxide bleaches are typically used on top of a detergent, which provides the wash solution with an alkaline buffer. Thus there is no performance difference between an alkaline and a nonactivated acidic hydrogen peroxide bleach, when they are used in combination with a laundry detergent that determines the same wash solution pH for both. The built-in alkalinity may offer an advantage in terms of stain removal when the peroxide bleach is used on its own, for instance upon pretreatment. D. Color and Fabric Safety As stated at the beginning of this chapter, liquid hydrogen peroxide bleaches offer the key advantage vs. hypochlorite of being safer on colored items and less aggressive in general toward fabrics. While this is true without any doubt, it is essential for the formulator to recognize that the risk of damage still exists with these milder products as well. The risk is related particularly to the case in which the peroxide bleach is used to pretreat a stain prior to a machine or hand wash. In this situation there are two key factors that may play a role favoring the occurrence of color or fabric damage: 1.

2.

The presence of transition metal ion impurities, such as copper, chromium, iron, and manganese, on the fabric surface. These may come from dyes present on the fabric, for instance metal-azo dyes, or from stains and soil. The time interval between product application on fabrics and main wash. The longer this time interval, the higher the likelihood of damage due to water evaporation, which causes an increase of hydrogen peroxide concentration in contact with the fabric.

The combination of the above factors may favor the start of radical decomposition processes on the fabric surface, which can result in color fading or even fabric damage. Starting from the assumption that the damage risk is essentially related to the formation of free radicals on the fabric surface, some formulators have proposed the use of radical scavengers to decrease it [107]. In model experiments they found that white cotton swatches artificially contaminated with 50 ppm of copper ions, had a significant tensile strength loss (TSL) when pretreated for 24 hours by a hydrogen peroxide bleach without radical scavengers, whereas the TSL was as low as 2%, i.e., within the experimental error, when pretreatment was done by formulations containing combinations of radical scavengers such as BHT and MTBHQ. Benefits were observed also in terms of reduced color fading on cotton swatches dyed with Direct Blue 1 and Reactive Purple. In order to specifically control factor (1), above, i.e., transition metals, other formulators found some specific chelants and their combinations to be particularly effective in reducing the damage risk. Examples of these chelants are alkyl polyamines such as 1,4butyl diamine, propylene diamine, and ethylene diamine [108]. An important criterion for the selection of chelants or radical scavengers to control damage, is their ability to migrate through the fabric fibers as the product is applied and progressively spreads, wetting different fabric areas. During this wetting process, partitioning equilibria are established for each ingredient between the solution and the fibers

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similarly to what happens in chromatography. Thus ingredients with a high mobility on cellulose (in the case of cotton fabrics) will move together with the hydrogen peroxide fluid, while ingredients with a high affinity for cellulose, and therefore low mobility, will tend to separate from the fluid. Chelants and radical scavengers with a high mobility on cellulose deliver the best protection against color and fabric damage [109], because they are able to be present in every point of the fabric that is reached by hydrogen peroxide. Mobility can be measured by running a thin-layer chromatography of a solution containing the ingredients of interest on a chromatographic plate made of cellulose (or other materials depending on the fabric of interest). Examples of fabric protection agents with a high mobility on cellulose are glycine, salicylic acid, aspartic acid, glutamic acid, and malonic acid. In order to specifically mitigate the effects of factor (2), above, i.e., water evaporation and subsequent concentration of hydrogen peroxide in contact with the fabric, one can also try to decrease the product evaporation rate. This can be achieved by introducing suitable polymers into the formulation, typically cross-linked polyacrylates or copolymers of acrylic acid and other comonomers. By retaining at least part of the water originally present in the formulation, these polymers can prevent or delay complete product drying, thus decreasing the risk of damage [110].

IV FUTURE TRENDS In the past decade, the innovation in chlorine bleach design has seen a strong focus on the improvement of the fabric safety profile and it is likely that this will be maintained in the future. More recently technologists have also started to look at the aesthetic aspects and simplicity of use of chlorine bleaches and thick and colored products have been introduced in the market. The intrinsic limitation on the use of hypochlorite bleach on colored garments represents a strong barrier to expand the use of this powerful stain remover and germ killing agent, and it is foreseeable that in the long term oxygen bleaches rather than chlorine bleaches will be the theater of the most important technology developments in the liquid bleach market. As far as laundry detergency is concerned, the focus of technology innovation in peroxide bleach will probably continue to be on developing products that have an increased color and fabric safety but are equally (or more) effective against stains. This would be consistent with the consumer trend of an increasing number of delicate and precious laundry items, for which the requirement of safety is as important as that of stain removal performance. In addition, the effort to improve stain removal performance through new activation technologies will continue to be significant. However, it is likely that the most important trend for liquid hydrogen peroxide products will be their expansion into new market segments. After evolving from the old 3% disinfectant solution to fully formulated colorsafe bleaches, liquid hydrogen peroxide products have recently started to appear also among household cleaners. The versatility, formulatability, environmental compatibility and low toxicity of liquid hydrogen peroxide are so relevant today, that we may soon see it exploited in several other consumer product categories besides laundry and household detergency. Although the technologies for hydrogen peroxide stabilization and activation discussed above are universally valid and reapplicable in different contexts, it is reasonable to expect that the expansion of liquid hydrogen peroxide into new product categories, and the growth of the already existing segments, will create great opportunities for formulators to solve new challenges and develop completely new technologies in the coming years.

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ACKNOWLEDGMENTS Many colleagues have contributed to the work reported in this chapter. We are particularly grateful to A. Briatore and G. Grande for the work done on hypochlorite bleach formulation; to V. Del Duca and G. Bianchetti for the work done on hydrogen peroxide formulation; and to R. Scoccianti and J. Stonehouse for the analytical support.

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66. 67. 68.

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7 Personal Care Formulations Achim Ansmann, Peter Busch, Hermann Hensen, Karlheinz Hill, Hans-Udo Krächter, and Michael Müller

CONTENTS I.

II.

III.

Introduction ........................................................................................................... 208 A. Trends for Cosmetic Cleansing Formulations .......................................... 208 1. Evolution of Cleaning................................................................ 208 2. Future Cleansing Concepts ........................................................ 210 3. Psychological Trends ................................................................. 211 B. Testing Strategy To Evaluate the Dermatological Properties of Surfactants ................................................................................................. 214 Formulation Techniques ........................................................................................ 216 A. Emulsions .................................................................................................. 216 1. Physicochemical Stability.......................................................... 218 2. Liquid Crystals and Gel Phases................................................. 220 3. Nanoemulsions........................................................................... 221 4. Multiple Emulsions.................................................................... 225 5. Gel Emulsions (High Internal Phase Emulsions)...................... 227 B. Microemulsions and PIER ........................................................................ 227 C. Surfactant Concentrates............................................................................. 230 D. Encapsulated Systems ............................................................................... 231 Formulations—Examples and Concepts............................................................... 233 A. Shampoos Based on Alkyl Polyglycosides............................................... 234 B. Shower Gels .............................................................................................. 235 C. Peeling Preparations.................................................................................. 236 D. Microemulsions as Bath Oils.................................................................... 236 E. Facial Cleansers......................................................................................... 236 F. Hair Conditioners ...................................................................................... 236 G. Styling and Permanent Wave Products ..................................................... 237 H. Creams and Lotions for Sensitive Skin .................................................... 238 207

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I. Sun Protective Lotions .............................................................................. 240 J. Active Face Creams .................................................................................. 241 IV. Performance Properties ......................................................................................... 241 A. Testing Methods for the Hair.................................................................... 242 1. Wet Combing ............................................................................. 242 2. Dry Combing ............................................................................. 242 3. Tensile Strength ......................................................................... 243 4. Hair Thickness ........................................................................... 244 5. Shadow-Image Analysis of Tresses of Hair .............................. 245 6. Atomic Force Microscopy ......................................................... 245 7. Oscillation Properties of Hair.................................................... 246 8. Hair Gloss .................................................................................. 247 B. Foam .......................................................................................................... 247 C. Cleansing Effects....................................................................................... 248 D. Testing Methods for the Skin.................................................................... 249 1. Skin Surface Properties.............................................................. 249 2. Spreading Behavior of Cosmetics ............................................. 251 3. Mechanical Properties................................................................ 253 4. Sensory Properties/Sensory Assessment ................................... 254 5. Skin Moisture............................................................................. 255 6. Skin Surface Lipids.................................................................... 256 7. Skin Surface pH......................................................................... 256 V. Trademarks ............................................................................................................ 257 References ....................................................................................................................... 257

I. INTRODUCTION A.

Trends for Cosmetic Cleansing Formulations

1.

Evolution of Cleaning a. Basic Cleansing. The process of cleansing is most probably one of the oldest humankind has integrated into its lifestyle. It has been documented that all ancient cultures have used products like soap for this purpose. This development was not only driven by the desire to increase one’s own beauty; hygienic aspects most likely contributed to this use as well. The aspect of ritual cleansing in different religions is another possible factor contributing to the regular use of these remedies [1–3]. The history of cleansing started with the ﬁrst natural soaps that could be easily produced from animal fat through alkaline reactions. These soaps were used for cleansing the body as well as for all other purposes that required water-based cleaning. However, it was soon discovered that all-purpose soaps had their limitations. Water hardness as well as the composition of the object to be cleansed implicated that better results could be obtained if substances other than soaps were used for cleaning. Skin-cleansing soaps have been used for a very long time in human history because they produced the desired results and could be altered by many different kinds of additives. Although the skin compatibility is often an issue, basic soaps are still used in signiﬁcant amounts for personal hygiene around the world today. However, humankind’s progress in understanding chemistry and molecular structures allowed further developments to be made with respect to the cleansing performance of

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the molecules used. This progress achieved by the development of chemistry and an increased number of new chemical substances allowed improved cleansing conditions in the working environment [4]. b. Improved Cleansing Conditions. More powerful cleaning molecules were discovered to improve cleansing performance. A typical representative of this development is sodium lauryl ether sulfate (SLES), for example. The diversiﬁcation in molecules led to molecules that behaved in speciﬁc ways, which could then be used for various purposes. These molecules were not limited to use in anionic surfactants. Chemical classes such as cationic, nonionic, and amphoteric surfactants were developed. These allowed the cleansing process to be tailored speciﬁcally to the intended purpose. The utilization of these chemical components made it possible to pursue the goal of optimized cleansing. Through the combination of different surfactants, desired results like “foam improvement” and “more specialized cleansing” could be achieved [5–7]. The next step in the development of cleansing processes brought attention to the aspect of product safety. c. Safety for the User and the Environment. This aspect became more important with the increasing use of cleansing products worldwide and a basic consciousness regarding product safety. It is one of the major criteria for the use of surfactants today. The evaluation includes the environmental safety of the base materials as well as the production process of the surfactants. Even the overall eco-balance of a cleansing molecule is considered by many users and producers of cosmetic products. For users of cleansing products, the aspect of safety to the body is crucial. This aspect is taken into consideration from the very start of personal cleansing material development. Strict criteria applied in this process have led to safer materials and to this end the cost aspect was given lower priority [8–13]. The next trend in the development of chemistry for skin cleansing was deﬁnitely the trend to mildness. d. Mildness. Being aware of the skin’s sensitivity to cleansing products, it is obvious that users tend to look for products based on mild surfactants. Since the discovery of the natural moisture factor on the surface of the skin and the subtile structure of lipid, the bilayers that seal the outer layers of the stratum corneum, it has become clear that this fragile equilibrium could be easily disturbed by products that interfere with these. The nature of cleansing-speciﬁc chemistry implicates that disturbances of this “homeostasis” are likely to be caused by the use of cleansers on the skin. Mild surfactants must incorporate the other beneﬁts achieved with modern cleansing molecules regarding performance and safety. The well-documented aggressiveness of soaps and other cleaning molecules toward the skin throughout history was deﬁnitely the driving force behind the mildness trend. A typical example for this can be seen in alkyl polyglycosides, which combine all the desired properties of a state-of-the-art surfactant for skin cleansing [14]. Because skin types as well as usage habits for skin cleansing products differ, it is necessary to deﬁne mildness with regard to speciﬁc requirements. Developments that consider the speciﬁc needs of the skin to recover after the cleansing process can be determined by a set of tests that can identify the right surfactant or surfactant combination for each purpose. Choosing mildness and performance in favor of a low cost option is a common outcome of this testing strategy. Synergistic surfactant systems, in which combinations of different surfactants are generally preferable to single surfactant solutions, can be identiﬁed by following a deﬁned test path. Animal testing is fundamentally avoided for this purpose [8–12]. The development of a dermatological test strategy is covered in more detail in Section I.B.

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The mildness concept was not the ﬁnal development in the production of cleansers. This trend was followed by an increased effort to develop formulations with additional beneﬁts. e. Additional Beneﬁts. The addition of nonsurfactant molecules to cleansers for the purpose of enhancing cosmetic beneﬁts can be seen as the next step in this evolution. Products were designed as part of a cosmetic skin care series and partly included the same active ingredients. Skin type-speciﬁc cleansing was introduced (e.g. for young, old, or acne-prone skin). The incorporation of oil replenishing ingredients was developed and perfected by adding molecules that restore oil to the skin while maintaining the same cleansing performance. This principle is based on chemistry which naturally takes place on the skin’s surface. As a result, the skin stays close to its natural, undisturbed status after cleaning (homeostasis). Not only the skin barrier was restrengthened, though. The “bonding” of cleansing with performing active substances (a-hydroxy acids, ceramides, vitamins, moisturizers, 2 in 1 concepts, etc.) led to a cleansing process followed by a treatment that actively improves the skin. Another aspect can be seen in the development of cleansers and cleanser foams which exhibit exceptional sensory properties. The optimization of formulation with respect to “instant gratiﬁcation” (sensory sensation) for the user can also be seen as a major trend in cleansers today. 2. Future Cleansing Concepts Future cleansing concepts will continue to build on existing ones and provide additional beneﬁts. As the boundary between dermatology and cosmetology diminishes, new scientiﬁc concepts will be regularly incorporated into cleansing products. The focus will be set on ensuring the least skin irritation possible while integrating future cosmetic active substances in the cleansing process. Tailor-made molecules for selective cleansing and distinguished absorption behavior will be developed and used in cosmetic cleansers. Biomimetic products, which copy the natural chemistry of the skin to prevent irritation during the cleansing process, will be used more frequently. Products are also used to achieve a change in appearance as a result of the cleansing process (i.e., skin becomes more or less shiny). Future cleansers more frequently claim to provide such desired results. Cleansing will also be designed according to sociological differences and the idea of skin type-speciﬁc cleansing (age, gender, season, skin type, demands) will be optimized [13]. It seems obvious that new cleansers and applications will follow the developing trends of wellness and comfort. “Mainstream” expectations will not only affect our leisure time and our work environment, but will also deﬁne the role that cosmetic products play in our world. It is obvious that the most important tools to meet the challenging requirements of cleansing innovation, as outlined in Fig. 1, are: • • • •

More detailed information from dermatological research Market trend research Sociological studies Testing strategy that includes new scientiﬁc measuring methods in addition to the aspects mentioned above

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Needs of the Body

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Figure 1

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Requirements for cleansing innovation.

3. Psychological Trends The psychological trends leading us to more easily adapt to lifestyle changes and which also lead to a change in our use of cosmetic products are described below. a. Our Changing World. The societies of the Western world, especially in developed countries, experience a constant, rapid and thorough change of their daily lives, value systems, and technical possibilities. These changes also strongly impact the ﬁeld of cosmetics. b. Tendency Toward Narcissism and Introversion. Modern men and women are characterized by a degree of narcissism. In many cases, physical features play the most important role, with thoughts and desires concentrated on the ideal slim, youthful, and strong body. On the other hand, there is a distinct shift to introspective experiences, perhaps because the fast-moving technological world cannot satisfy holistic desires, i.e., it does not encompass both the body and mind of the contemporary-day person. Successful cosmetics try to fulﬁll narcissistic desires and contribute to emotional needs by offering special products and concepts. Though the main focus in this chapter is on cosmetics with cleansing power, care aspects cannot be neglected. In addition to other special beneﬁts, modern cosmetics always contribute to the care of the different parts of the body. c. Convenient Products Help Save Time. Completing multiple tasks at once emphasizes the maxim: Don’t lose time, instead structure your life as conveniently as possible by doing several jobs simultaneously. One of the best known ideas in this concept is the two-in-one shampoo which cleanses and conditions the hair [15]. The concept is still valid although it has been reﬁned in many aspects. The shampoo should moisturize [16] the hair to keep it ﬂexible, rather than brittle, and should keep it free from split ends [17]. This can be achieved (at least to a certain degree) by incorporating protein hydrolysates, peptides, or amino acids. A volumizing shampoo should add body and make styling easier. A repair shampoo should protect the hair from damage from UV light, abrasion or chemical processes. Therefore, a shampoo is no longer a combination of anionic, nonionic, or amphoteric surfactants. It is rather a carefully balanced blend with added cationics, polymers, fruit extracts (in order to avoid heat damage from blow drying), antioxidants, substances with softening power (mostly emollients [18], or silicones [19]). The two-in-one, three-in-one or more-in-one concept was successfully applied to many other product categories, e.g., in the home care sector, oral, or skin care cosmetics. Thus, a typical facial cleanser may contain substances with wrinkle-reducing, moisturizing,

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and exfoliating effects. The motto is: Get as much as possible out of one single treatment in order to gain free time. d. Advanced Cosmetic Knowledge and Novel Application Systems. Advanced technical possibilities are best reﬂected in the development of galenic preparations, our understanding of the ﬁne structure of skin, hair [20], mucous membranes, and teeth and their interaction with different products. Our capability to determine and quantify effects using highly developed and digitalized instrumentation is yet another example. There is an abundance of galenic preparations for all kinds of applications. The bestsuited formulation is selected by the technical purpose, e.g., should the product penetrate into the skin or hair or should it stay on the surface, should the product interact with the substrate within a certain time frame, should it apply to a large or small surface area. Not less important is the sensory expectation when applying the product: A clear lotion is associated with purity and sincerity, a mousse or paste suggests fun and adventure. Foam can be gentle and protective; it signals warmth and protection [21]. Although the skin is a most effective barrier to water and other (very often harmful) substances, it demonstrates a certain permeability. Cosmetic substances can traverse the skin primarily either through the pores of the hair follicles, sweat gland ducts or by passing through the protein/lipid domains of the stratum corneum. It is known that the permeability of a molecule is related to its lipo/hydrophilicity and its size. The transportation of molecules into deeper regions of the skin is of great interest. This approach makes it possible to enhance the attractiveness of the skin. For example, moisturizing systems can be developed which cause the dermis to swell, introducing free radical scavengers (such as tocopherols) which can prevent the cross-linking of collagen ﬁbers (which cause the skin to develop permanent wrinkles) or inﬁltrate hair growth promoters which interact with the alpha-reductase and inhibit premature hair loss. The efforts can be intensiﬁed by using the most suitable vehicle. Liposomes are among the most popular cosmetic systems. Liposomes store water-soluble substances in their interiors. In their lipophilic walls they can carry various liquid contents. Lipid nanoparticles are vesicles formed by lecithin encapsulated in an oil core and thus ideal carriers for lipophilic substances. Multiple emulsions are ideal three-compartment systems; i.e. an emulsion dispersed in a third phase. There are two types: o/w/o (water/oil/water) = o/w emulsion in oil phase and w/o/w = w/o emulsion in a water phase. They have many distinctive attributes, especially the compartmentalization of active substances in the three phases, the controlled and sustained release of active substances and w/o hydrating performance with o/w skin feel. They also provide longer lasting moisturizing effects comparable to a conventional emulsion. Microemulsions [22] and nanoemulsions are relatively new systems with droplet sizes in the submicron range (typically 100 to 200 nm). The small droplets facilitate the effective transport of the active substance to the skin. Another very sophisticated technology, microencapsulation, uses collagen, glycosaminoglycans such as chondroitin sulfate or polysaccharide of plant (soy and wheat) or marine origin (shells of crustaceans). The active compound is wrapped in a thin, natural, tough membrane. The membrane will be broken down under the enzymatic action of amylases or proteases, slowly releasing the contents of the capsule (see Section II). Cleansing and caring wipes provide a much more straightforward approach [23]. Wipes have two distinctive advantages: They are convenient to use, e.g., for cleaning parts of the body, and they require less water. One should not forget that the conservation of the most valuable raw material—water—will be a key issue in near future. e. The Consumer as an Emotional Being. There is no doubt about the fact that science, especially bioscience, is highly regarded, primarily because as a result of suc-

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cessful research efforts in the ﬁelds of genomics or proteomics, the hope remains that the problem of ageing will be reduced and thus growing older becomes less frightening. Nevertheless, the main impact of cosmetics is currently directed more toward the emotions [24] of the consumer. The consumer experiences his surroundings through his senses. Of particular importance currently is the tactile feel [25]. Tactile feel suggests personal closeness and intimacy, erotic seduction, the impression of being safe and snug. Cosmetic products can assure a positive tactile experience for numerous aspects. The skin can be gentle, ﬂexible, youthfully ﬁrm, without oily or greasy residues, hair may be soft, full, shiny, bouncy. The haptic and visual impressions can be described precisely in sensory assessment. Since our sensory experience is linked to our verbal abilities, a thorough linguistic analysis must be the ﬁrst step to understand what we see, taste, smell, hear, or feel. If this is done properly, the sensory assessment will reveal numerous insights of the consumer’s likes and dislikes. The sensory assessment can be applied to skin, hair, teeth, the oral cavity, and to the cosmetic product itself, e.g., the feel of the shampoo or rinse in the palm. The research dealing with sensory experience is fast-moving and adopts much from psychology, psychophysics and other psycho-oriented disciplines. An old saying in the cosmetic ﬁeld tells us: A cosmetic effect is only valuable if it can be perceived by the senses of the consumer. Such a statement may appear trivial, but because our sensory experiences are always connected with inner psychological interpretations, it is not. A perfume without a seductive connotation is just a scent without any excitement. When selling products, it is essential to provide them with the appropriate context [26]. Only if the consumer is surrounded by a pleasant ﬁeld of associations will he or she experience the beneﬁt of the product offer. f. The New Age of Health and Well-Being. Our society’s extreme interest in bodily features is associated with our passion for health issues. Cosmetics must enhance our health, not endanger it. Thus, substances derived from plants are preferably considered as raw materials for the development of cosmetic products. The inclination to use botanicals as natural sources is one of the most important issues in the cosmetic ﬁeld. There is an abundance of botanicals for personal care. Aloe vera, for example, is believed to relieve rashes and burns and also hydrates the skin without the use of oil. Green tea is reputed to have antioxidant properties and like sesame oil, also provides protection against ultraviolet (UV) damage. The extent of the list of botanicals used in cosmetic formulations is beyond the scope of this chapter. Consumers are looking to achieve balance, improve their quality of life, and feel better both inside and out. Health is one of the key issues in Western society. Natural products are viewed as one way to achieve these goals. Well-being is even more important with respect to cosmetics. Well-being implies more than just health. Health means to be free from diseases. In addition to being healthy, well-being means feeling the vigor and vitality of youth, being able to rely on the full capacity of our sensory organs, being ﬂexible and active and being admired in our personal domain because of an attractive appearance and agile movements. This leads to a positive view of life. It is exactly this positive consciousness, the feeling to be alive or even to be a new person, that modern cosmetics tries to provide. This effort is based on the knowledge that well-being always affects three basic components: body, spirit, and mind. Thus, no one is surprised that the spa movement has become one of the leading marketing concepts. There is a heightened interest among both men and women in spoiling themselves. At-home spa products are an easy and affordable alternative to actually going to the spa. Some examples of spa products are: cleansing products such as face washes, sea sponges, milk body bars, exfoliation masks, or bathing lotions. Most important are

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products associated with the word “nature,” e.g., Chinese herbs, minerals, or vitamins. Best-selling products are spa-inspired body scrubs, e.g., peeling salt or ginger scrubs which remove dead cells from the skin surface, render it smooth, and make it ready for a treatment with a dihydroxy aceton-based ﬂash toner, for example. Effective spa treatments offer advice and education encompassing the mind and spirit as well. g. Global-Reach and Individually Customized Cosmetics. Our present time is characterized by surpassing limits which were valid for centuries. Our world is no longer the world of our home where we were brought up or where we live. We have become more and more cosmopolitan. Cosmetics are globally-oriented. Nowadays, the cosmetic industry can have a global impact at the click of a mouse: by taking advantage of virtual trading places in the e-community. While extending our limits all over the world, we still discover how surprisingly unique we are. We continue to learn that each person needs his and her personalized cosmetic treatment and products. Until now, the fulﬁllment of such a wish seemed to be impossible. But today, in the age of the Internet, each personal and anatomical peculiarity can be detected, consulted and treated properly. We are moving toward a customized cosmetic market with new challenges of how to address the mature consumer and to manufacture highly-differentiated products which no longer serve an impersonal mass market, but are tailor-made for our individual needs [27,28]. B.

Testing Strategy To Evaluate the Dermatological Properties of Surfactants A new modern surfactant used in body-cleansing formulations must be perfectly compatible with the skin and mucous membranes. Dermatological and toxicological tests are essential for the risk assessment of a new surfactant and are designed above all to determine any possible irritation of living cells in the basal layer of the epidermis (primary irritation). In the past, this was the basis for such claims as the “mildness” of a surfactant. Nowadays, the meaning of mildness has changed considerably. Today, mildness is understood to be the all-round compatibility of a surfactant with the physiology and function of the human skin, more precisely: the epidermis. The physiological effects of surfactants on the skin are investigated by various dermatological and biophysical methods starting with the surface of the skin and progressing through the horny layer and its barrier function to the deeper layer of the basal cells. At the same time, subjective sensations, such as the feeling on the skin, are recorded through the expression of tactile sense and experience. The strategy of setting up a dermatological evaluation scheme can be demonstrated by using the example of alkyl polyglycosides. Alkyl polyglycosides with C8 to C16 alkyl chains belong to the group of very mild surfactants used in body-cleansing formulations. In a detailed study, the compatibility of alkyl polyglycosides was described as a function of the pure alkyl chain and the degree of polymerization [29]. In the modiﬁed Duhring Chamber Test, C12 alkyl polyglycoside shows a relative maximum within the range of mild irritation effects whereas C8, C10 and C14, C16 alkyl polyglycoside produce lower irritation scores. This corresponds to observations with other classes of surfactants. In addition, irritation decreases slightly with the increasing degree of polymerization (from DP = 1.2 to DP = 1.65). On the other hand, mucous membrane compatibility, as determined by the in vitro test on the chorionallantois membrane of fertilized hens' eggs (HET-CAM or CAM test) [30] as an alternative to Draize's mucous membrane compatibility test, shows a monotonic decrease from C8 to C14 alkyl polyglycoside within the range of mild irritation. The DP causes only a slight and non-signiﬁcant differentiation of compatibility in this case. Commercial APG products (Plantacare® 1200, Plantacare® 2000, Plantacare® 818—

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INCI: Lauryl Glucoside, Decyl Glucoside, Coco-Glucoside) with mixed alkyl chain lengths have the best overall compatibility with relatively high proportions of long-chain (C12/14) alkyl polyglycosides. They join the very mild group of highly ethoxylated alkyl ether sulfates, amphoglycinates, or amphodiacetates and the extremely mild protein fatty acid condensates based on collagen or wheat protein hydrolyzates. Comparative tests have been carried out [31,32]. Another in vitro test (RBC, red blood cell test) investigates the haemolysis of erythrocytes under the inﬂuence of surfactants. A so-called “mean index of ocular irritation” (MIOI) has been derived, which correlates sufﬁciently with the Draize test. The MIOI lies at very low values for alkyl polyglycosides as with other very mild surfactants [33,34]. Similarly, alkyl polyglycosides produce a very mild skin reaction in the modiﬁed Duhring Chamber Test [9,32,35,]. In mixed formulations with standard alkyl ether sulfate (sodium laureth sulfate, SLES), the score for erythema decreases with increasing levels of alkyl polyglycoside without a synergistic effect being observed (Fig. 2). A complete study of skin compatibility investigates surface conditions, the inﬂuence on the transepidermal water loss through the horny layer, dermatological parameters, and subjective sensorial effects after surfactant application. This compilation test system also enables combination effects to be studied so that the most compatible formulations can be gradually built up from basic surfactants, additives and special ingredients [9]. A suitable test procedure is the arm ﬂex wash test [36] which simulates the daily use of a product by open repeated application under accelerated conditions [9,32, 38]. The condition of the skin surface can be best documented using a ﬂexible microscope (Fig.3). Proﬁlometry offers a more detailed evaluation of the skin surface following the application of alkyl polyglycoside. The various statistical parameters which deﬁne the roughness of the skin describe a skin-softening effect for alkyl polyglycosides [9,33,38]. The standardized mean swelling values (Q according to Zeidler) [39] of the horny layer, as determined on isolated pig epidermis, lie within the swelling-inhibiting range. Q values of -6% to -9% (±7% with 95% conﬁdence) were measured at pH 5.6 for C12/14 alkyl polyglycoside. The lower swelling level of the epidermis caused by an alkyl polyglycoside solution as compared with water is a sign of the functional compatibility of alkyl polyglycosides and contributes by way of compensation to limiting irritation mechanisms of other components in the formulation. In addition, the loss of moisture content in the horny layer is reduced by 30 to 40% under the effect of alkyl polyglycoside as compared with standard ether sulfate based on corneometer measurements [35]. This corresponds to the effect of the very mild zwitterionic amphodiacetates. The inﬂuence of surfactants on the barrier function of the epidermis, either by deteriorating the functional structure or by eluting components (horny layer, lipids, natural moisturizing factor), is characterized by evaporimeter measurements as a change in the natural transepidermal water loss (TEWL). Investigations in connection with the arm ﬂex wash test show that changes in relation to the normal state of the skin barrier caused by standard surfactants are reduced in the presence of alkyl polyglycosides. This effect can be enhanced in the systematic composition of formulations by incorporating additional additives, such as protein derivatives [9,32]. Dermatological ﬁndings in the arm ﬂex wash test show the same ranking as in the modiﬁed Duhring Chamber Test where mixed systems of standard alkyl ether sulfate and alkyl polyglycosides or amphoteric co-surfactants are investigated. However, the arm ﬂex wash test allows the effects to be better differentiated. The formation of erythema and squamation can be reduced by 20 to 30% if about 25% of SLES is replaced by alkyl polyglycoside (Fig. 4). The recording of the volunteers’ subjective feelings (itching,

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Skin effects in the arm ﬂex dermatological wash test/assessment

stinging etc.), which indicates a reduction of about 60%, is of greater importance. Protein derivatives or amphoterics [9] can be added to achieve the optimal formulation. The dermatological testing strategy is outlined in Fig. 5.

II. FORMULATION TECHNIQUES A. Emulsions Theoretical considerations regarding the preparation of emulsions focus primarily on either mechanical methods or physicochemical concepts. Of course, the properties of ordinary emulsion, like other thermodynamically unstable systems, depend on both the speciﬁc interactions of the included molecules and the mechanical impact. Knowing the physicochemical properties of the dispersed ingredients leads thus to a deeper understanding of emulsion-forming processes. When two mutually nonsoluble liquids (oil and water) are mixed without an emulsiﬁer, these liquids separate spontaneously. The driving force of the phase separation from a thermodynamic perspective is the high amount of free interfacial energy that results from the increased interface between inner and outer phases after dispersing. The change in free interfacial energy ∆F is proportional to the change in interface ∆A and interfacial

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Treated

Untreated

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Figure 4 Four-arm ﬂex test: Inﬂuence of C8-14 alkyl polyglycoside (APG) and sodium lauryl ether sulfate (SLES) on skin roughness (duration 14 days, inspection by ﬂexible microscope, magniﬁcation 50x).

Market Observation

Use Test Application Test Patch Test Short Term Application In Vitro Tests Toxicology

Figure 5

Dermatological testing strategy (from basic investigations to use conditions).

tension (Eq. [1]). The coalescence of droplets reduces the free interfacial energy again. Two droplets hitting each other merge to a larger one with a reduced interface as compared to the interfaces of the two smaller ones added together. The droplets will rise or fall due to gravity depending on whether the inner phase is of higher or lower density. Adding amphiphilic molecules such as emulsiﬁers to the system changes the situation dramatically as the interfacial tension and therefore the free energy of the system are decreased. Such amphiphilics consist of a hydrophilic (polar) and a hydrophobic (nonpolar) portion and are incorporated into the oil/water interface with the hydrophilic portion facing the water phase and the hydrophobic portion facing the oil phase. The interfacial tension is lowered by an order of magnitude depending on the nature of the emulsiﬁer and often on parameters like temperature, pH value, and salinity. Therefore, the use of emulsiﬁers is a presuppo-

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sition for dispersing two mutually non- or only slightly soluble liquids in order to obtain an emulsion that does not immediately separate into two phases. ∆F = γ ⋅ ∆A

(1)

The nature of the emulsiﬁer and its physicochemical properties determine the performance of the emulsion with regard to droplet size and long-term stability as mentioned above. Emulsiﬁers can be divided up into three classes regarding their polar groups. Ionic surfactants have either an anionic (e.g., carboxylates, alkyl sulfates, alkyl ether sulfates) or a cationic group (e.g. alkylimidazolines, esterquarts). Amphoterics or zwitterionics (e.g., acyl ethylenediamines, imino diacids) exhibit negative charge as well as positive charges within one molecule. Nonionic emulsiﬁers (e.g., ethoxylated alcohols, alkyl polyglycosides, glycol esters) are the third group. A special class of nonionics is represented by the polyoxyethylene and poloxypropylene alcohols. This kind of polymeric emulsiﬁer consists of chains of polyethylenglycol and polypropylenglycol. Emphasis must be placed on the class of ethoxylated alcohols, not only because they represent the most widely used nonionics but also because of their well-understood physicochemical behavior. As a series of homologues can be synthesized through the ethoxylation of different linear alcohols, this class of surfactants is suitable for designing molecules with a deﬁned hydrophilic–lipophilic ratio. The entire emulsiﬁer exhibits a more hydrophilic or lipophilic character depending on the carbon number of the lipophilic alkyl chain and the number of hydrophilic ethoxy groups. In other words, the emulsiﬁers tend to form oil in water emulsions or water in oil emulsion depending on their character. To give this observation a more quantitative character, Grifﬁn [40,41] introduced the semiempirical hydrophilic-lipophilic balance (HLB) concept. This expresses the hydrophobic/hydrophilic characters of emulsiﬁers containing ethoxy and/or polyol groups as shown in Eq. (2), N HLB =

E+P 5

(2)

with NHLB being the HLB number and E and P being the weight percentage of the ethoxy and the polyol groups in the entire molecule, respectively. The theoretical limits of this scale are 0 for totally hydrophobic and 20 for totally hydrophilic. In general an all-purpose o/w emulsiﬁer has a HLB number in the range of 13 to 15. Grifﬁn also derived an equation for fatty esters that calculates NHLB from the saponiﬁcation index of the ester and the acid index of the free acid. A survey of HLB numbers for different emulsiﬁers was provided by Shinoda and Kunieda [42]. Davies [43] proposed another way to calculate the HLB number including ionic surfactants. He gave numbers to speciﬁc groups (positive for hydrophilic and negative for hydrophobic groups) which have to be added to seven to yield the HLB number. The listed group numbers enable one to calculate the HLB number for every hydrophilic/hydrophobic combination. Since the hydrophilic properties of an ethoxylated alcohol are not only a function of the HLB number but are also inﬂuenced by temperature, the HLB concept has to be expanded to consider the effect of temperature and the nature of the oil. Oils used in cosmetic products differ in their molecular structure, their molecular weight, and in viscosity. They have to satisfy different performance criteria, i.e., spreading properties and the oil replenishing/moisturizing of the skin. 1. Physicochemical Stability The kinetic stability of emulsions is not only governed by the mechanical conditions during formation and the resulting droplet size but can also be achieved by preventing the

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conditions required for the breakdown of the emulsion. However, one must be familiar with the mechanisms that lead to emulsion breakdown and storage instability. Some of the most important mechanisms and their physicochemical background are discussed in this section. Positively curved interfaces produce an additional pressure (Laplace pressure) inside the oil droplet, which increases the chemical potential of the oil [44]. The Laplace 2γ pressure ∆p equals with representing the interfacial tension and r the radius of r causes an increased solubility of the oil in the continuous water the droplet. This pressure phase as compared to an oil droplet bounded by an interface with a hypothetical curvature of zero. As a result, oil molecules, especially those of lower molecular mass, are transported from small droplets to bigger ones. The phenomenon of the disappearance of small aggregates accompanied by the growth of the larger ones due to differences in curvature is called Ostwald ripening. Because of the interfacial tension dependence of the Laplace pressure, Ostwald ripening can be reduced by lowering interfacial tension. This emphasizes again the importance of using well-balanced emulsiﬁers or combinations of them. Adding a component to the dispersed phase in which solubility in the outer phase is less than that of the other components can also inhibit the disappearance of small droplets [45,46]. Adding a component to the dispersed phase which solubility in the small droplets generates an osmotic pressure that induces back-diffusion. In practice, this means mixing oils with different solubility (e.g., caused by different molecular weight or polarity) if the outer phase is aqueous or adding salt to the water if the continuous phase is oil. Another way of reducing Ostwald ripening is to create a yield stress in the continuous phase, preventing the droplets from swelling. Because of the different densities of the continuous and dispersed phase, particles or droplets either move upward (creaming) or downward (sedimentation) in a viscous continuum. According to Stokes’ law (Eq. [3]): υ=

2 g ⋅ ∆ρ ⋅ r 2 ⋅ 9 η

(3)

the velocity of an emulsion droplet is proportional to r 2 and ηη−1 . This clearly demonstrates the inﬂuence of the droplet radius and the viscosity of the outer phase on the long-term stability of emulsions. Consider the example of two emulsions: One with a droplet size of r = 15 µm and a viscosity of 1 mPas for the outer phase and another one with r = 0.15 µm (e.g., phase inversion temperature [PIT] emulsion) and = 10 mPas. The creaming rate is increased by a factor of 104 by the different radii alone and by an additional factor of 10 due to the difference in viscosity. In real systems, of course, parameters that antagonize a straight creaming/sedimentation process as expressed by Stokes’ law must be taken into account. For example, temperature ﬂuctuations that induce convection currents or deviations from Newtonian behavior have to be considered. Emulsion droplets have to be protected from coalescence by special mechanisms. Otherwise, every single encounter of two droplets would lead to the disappearance of one droplet. A proper mechanism can be the buildup of an electrostatic double layer using ionic surfactants. The charges on the interface of the emulsion droplet that are needed to create the electric double layer can be generated by replacing nonionic by ionic emulsiﬁers. The interaction of two droplets can be described quantitatively by the DLVO theory [47–49] in a ﬁrst approximation. The DLVO theory (named after Derjaguin, Landau, Verwey, and Overbeek) includes the attractive (van der Waals) interaction forces and repulsive electric forces arising from the double layer. A superposition of the two inter-

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action energies can create an energy barrier that has to be overcome before the two droplets come into contact. The dimension of the electric double layer and therefore the repulsive interaction is reduced by an additional electrolyte. This explains the sensitivity of some emulsions to salt content in practice. Emulsions can be stabilized by polymers that are adsorbed at the interface and cause steric repulsion [50]. The ﬂexibility of the hydrophilic (hydrophobic) polymer chains exposed to the outer water (oil) phase is restricted when the adsorbed layers overlap, causing a loss in entropy. Osmotic pressure also increases as close contact leads to a local increase in polymer chain concentration. Polymers should be used with caution, however. If nonadsorbing polymers remain free in the continuous phase, polymer coils can be excluded from interparticle regions smaller than the dimension of the coil [51]. The increasing polymer concentration gradient induces an osmotic pressure that forces solvent molecules to diffuse from the polymer-poor regions to the polymer-rich regions. The arising phase separation is called depletion ﬂocculation [52]. 2. Liquid Crystals and Gel Phases Liquid crystals and gel phases play an important role in emulsion formulation technology, not only as viscosity regulators, but also as protecting shields for the droplets. One possibility to avoid coalescence is to take advantage of crystalline or liquid crystalline structures surrounding the emulsion droplets. Bragg reﬂections and melting points obtained by small angle x-ray scattering (SAXS) and differential scanning calorimetry (DSC) measurements proved the existence of liquid lamellar or crystalline lamellar structures for several systems [53,54]. Saturated monoglycerides represent one class of crystal builders. Studying the temperature and concentration dependent phase behavior of monoglycerides has revealed lamellar phases of both liquid and crystalline states [55]. When a liquid lamellar phase of the considered type is cooled, a phase transition from liquid to crystalline can take place. The crystalline lamellar phase is sometimes also referred to as the gel phase. The lamellar phase (liquid or crystalline) forms multilayer shells around the oil droplet and generates interfacial properties that are totally different from a normal monolayer interface. The barrier for two droplets to coalesce is increased signiﬁcantly, especially in the case of the crystalline lamellae. The ability to form crystalline lamellar structures is not restricted to monoglycerides, though. Figure 6 illustrates an emulsion protected from coalescence by crystalline lamellar structures consisting of fatty alcohol. The image shows

Figure 6 Image through a polarizing microscope of an emulsion stabilized by crystalline lamellae showing “Maltese crosses.” The emulsion consists of a combination of alkyl polyglycosides and cetylstearyl alcohol (Emulgade“ PL 68/50) as emulsiﬁer/coemulsiﬁer and capric acid triglyceride (Myritol“ 312) as the oil component.

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Figure 7 DSC measurements from an emulsion containing crystalline structures. The two heating curves, one from the fresh emulsion and the other from the same emulsion after 3 months’ storage, clearly exhibit two endothermic peaks between 60 and 70˚C.

droplets of an emulsion containing alkyl polyglycoside as emulsiﬁer and cetylstearyl alcohol as coemulsiﬁer under a polarizing microscope. The visible “Maltese crosses” arise from the anisotropic optical properties of the multilayer structures that cover the oil droplets. Repulsion and therefore interlamellar spacing can be adjusted by the incorporation of charged emulsiﬁers into the lamellae. The electrostatic stabilized structure displays a pronounced sensitiveness to electrolyte. Figure 7 conﬁrms the crystalline structure of the droplet shell of the system mentioned above by DSC measurements. 3. Nanoemulsions Emulsions can be considered as nanoemulsions when their overall particle size is below 500 nm in diameter. Thus, thermodynamically stable microemulsions (ME) can also be regarded as nanoemulsions under this deﬁnition because the droplet size in Winsor I and II ME phases [56] falls within the range of 10 to 100 nm and the domain size of bicontinuous structures is typically about 10 nm [57]. The name microemulsion for transparent, isotropic surfactant solutions containing a remarkable amount of oil has historical origins. The term microemulsion was originally introduced by Schulman [58] in 1959 although the ﬁrst descriptions of the systems date back to the 1940s. Schulman and his co-workers titrated short-chain alcohols into coarse (macro) emulsions and obtained transparent solutions with low viscosity. The word “miniemulsion” covers all thermodynamically unstable emulsions with “small” droplets irrespective of the way they are produced. In some reports, emulsions are denoted mini when the size range is as high as 10 µm, others reveal diameters of about 0.1 µm [46], which is the range of PIT or HPH (high-pressure homogenization) emulsions. The proper selection of emulsiﬁers and coemulsiﬁers to achieve droplet sizes of about 1 µm seems to be an alternative method to mechanical agitation. Möhle [59] reported about a formulation that is able to form ﬁne sprayable emulsions without the use of special mechanical equipment. The composition is placed between the microemulsion and a twophase milky emulsion region in the phase diagram. The closeness to the microemulsion

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Droplet size (µm)

Oil 1 Bluish white

0.2 10−1

10−2

Oil

PIT Emulsion Miniemulsion Nanoemulsion Microemulsion

Oil Translucent

Micellar solutions Transparent Molecular solutions 10−3

Figure 8 Typical size scales of different kinds of emulsions. The appearance of an emulsion is primarily determined by the size of the particles.

phase with its low interfacial tension seems to be crucial for obtaining ﬁne droplets. Among other parameters, droplet size and concentration of the dispersed phase determine the rheological and optical properties of the emulsion. Figure 8 provides an overview of different particle sizes occurring in emulsion and microemulsion systems. a. High-Pressure Homogenization (HPH). High-pressure homogenization (HPH) [60–62] is one mechanical method of obtaining emulsion droplets in the submicron range. In this technique, a primary coarse emulsion is compressed up to 1000 bar and forced through a homogenizing valve. In this so-called microﬂuidizer‚ technology, the ﬂow of products is divided up in several spray streams that are recombined in a special mixing chamber. The extreme shear force exerted in the mixing chamber creates very small droplet sizes which can even be decreased if this procedure is repeated several times. This method enables the production of ﬁne-sprayable emulsions with ingredients that would lead to coarse emulsion if conventional production methods were used. HPH has been used successfully to disperse several kinds of cosmetic oils, fragrances, UV ﬁlters, and vitamins with phospholipids acting as emulsiﬁers [63]. Besides HPH, several other mechanical methods for producing ﬁne emulsion droplets deserve mention, including colloid mills and ultrasonic homogenizing [64,65]. b. Phase Inversion Temperature. Because the real phase behavior of a ternary water /oil/ethoxylated alcohol system cannot be reﬂected by the HLB concept, the PIT method [66,67] has been developed to satisfy the requirements of more advanced emulsion formulation techniques. For cosmetic applications, oil in water emulsions often have to fulﬁll special requirements regarding their stability and performance. In addition to having long-term stability, emulsions sometimes have to exhibit low viscosity and appear translucent. Mixing oil and water with an emulsiﬁer or a blend of emulsiﬁers/coemulsiﬁers at moderate temperature

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160

100

120

80 70

80

60

T (°C)

Conductivity (µS/cm)

90 Temperature

50 Conductivity 40

40 30

0

20 0

5

10

15

20

25

30

35

40

45

50

t (min)

Figure 9 (PIT).

Temperature dependency of the electric conductivity at the phase inversion temperature

usually produces coarse, white emulsions with an increased viscosity. The PIT method, which is based on the fundamental work of Shinoda [68], utilizes the reversible temperature-induced phase inversion exhibited by emulsions that contain ethoxylated alcohols as emulsiﬁers. The actual hydrophilic–hydrophobic ratio of ethoxylated alcohols not only depends on their molecular structure but also on the temperature, e.g. demonstrated by the existence of the cloud point. The origins of these phenomena can be explained by the destruction of the hydrogen bonding between water and the ethoxy groups when thermal energy is increased. Another theoretical description makes conformational changes of ethoxy chains responsible for the decreased water solubility. In a ternary system of oil/water/ethoxylated alcohol, the change in the hydrophilic/hydrophobic ratio of the emulsiﬁer leads to an inversion from an o/w to a w/o emulsion. The inversion of outer and inner phases is accompanied by an inversion of the curvature of the interfacial layer. The system changes from a positive curvature (o/w emulsion) to a negative curvature (w/o emulsion) by passing through a region with zero curvature. The hydrophilic- hydrophobic properties of the emulsiﬁers are balanced at zero curvature. That means the emulsiﬁer has no clear preference neither to the water nor to the oil phase. The zero curvature produces structures with high interfacial areas between the oil and the water phases, like bicontinuous (spongelike) [69,70] or lamellar phases. Such a high interfacial area is only possible if the interfacial tension is very low (compare Eq. 1). Indeed, the minimum interfacial tension is located at exactly the same temperature at which the phase inversion occurs. One method of exploring the phase inversion is to prepare the temperature-dependent phase diagram and determine the inversion temperature by measuring the interfacial tension. Another less time-consuming process is to measure the temperature-dependent electric conductivity while heating and cooling an emulsion. Figure 9 illustrates schematically the temperature dependency of the conductivity of an o/w emulsion passing through a PIT. The water-soluble electrolytes (from impurities of the components) are trapped in the newly created inner water phase when the system begins to invert. When the PIT is exceeded (T > 70˚C) the conductivity falls to zero as all of the outer phase consists of the oil phase. In practice, the PIT procedure can be carried out in a one-step emulsiﬁcation as mentioned above or in a two-step emulsiﬁcation. In a two-step emulsiﬁcation, the oil/emul-

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Temperature (°C)

W/O

Microemulsion/Phase inversion W/O

O/W

O/W

Oil

Water 80:20

Figure 10

50:50

20:80

Principal phase behavior in a two-step PIT emulsiﬁcation process.

siﬁer phase and the water phase are heated, mixed separately and cooled (hot-hot process). Using the hot-cold process, an oil-enriched phase is heated above the PIT and the inverted emulsion is then reinverted by diluting with cold water, which leads to a temperature decrease below the PIT. Figure 10 is a schematic illustration of the hot-cold process. The emulsion concentrate shown in Fig. 10 contains all of the emulsiﬁer and oil/water at a ratio of about 60:40 and represents an o/w emulsion below the PIT. When heated, the emulsion inverts to a w/o emulsion in the temperature range 80 to 85˚C. Adding cold water to the hot w/o emulsion causes a phase inversion because of cooling effect and shifts the emulsion composition to the desired one (oil/water ratio 30:70). The advantages of this hot-cold two step procedure are obvious. Heating only a part of the ﬁnal formulation saves energy and the quick cooling process is less time-consuming as compared to either the one-step or hot-hot processes. In general, phase inversions at low temperatures should be avoided because coalescence is increased when the storage temperature is in the same range as the PIT [68]. Real emulsion systems are, of course, restricted regarding the starting and end points of the process. Phase inversion cannot take place at the very left or right side of the phase diagram (Fig. 10) because of geometric considerations for extremely high or low oil contents. c. CAPICO. As mentioned previously, the PIT is not only inﬂuenced by the HLB number but also depends on the nature of the oil selected. Early physicochemical works [71] that clearly demonstrated the inﬂuence of the oil on the phase inversion temperature provided the basis for the calculation of phase inversion in concentrates (CAPICO) system [72,73]. CAPICO can be considered an expanded equivalent alkane carbon number (EACN) concept. The central statement of the EACN concept is the approximately linear dependence of the PIT over the length of a linear alkyl chain at a given emulsiﬁer [74]. If the linear dependence of an emulsiﬁer is known, an equivalent alkane carbon number can be determined for an unknown oil provided that the PIT can be measured. CAPICO modiﬁed this concept regarding the use of mixed emulsiﬁers and mixed oil components. As both the mixing of emulsiﬁers and the mixing of oils do not include terms of higher order, the mixing dependence of PIT and alkyl carbon number ACN mix can be expressed by simple linear equations (Eqs. [4] and [5]).

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PITmix =

∑ X ⋅ (SF ⋅ ACN + PIT j

j

0, j

)

(4)

j

ACN mix =

∑ X ⋅ ACN i

i

(5)

i

with X j ( Xi ) representing the weight percentage of type j (i) in an emulsiﬁer (oil) mixture. SF is the slope of the equation and PIT0 the interception at ACN = 0 . Even if a single emulsiﬁer shows no PIT with hydrocarbons in an attainable temperature range, speciﬁc SF and PIT0 values can be calculated when a mixture with another emulsiﬁer (with known parameters) exhibits a PIT. The same applies to oils that reveal no PIT. Therefore CAPICO allows for a classiﬁcation even if the emulsiﬁer is not an ethoxylated alcohol. Mixed emulsiﬁer systems should be preferred to single emulsiﬁers. Single emulsiﬁer systems do not exhibit the same long-term stability as compared to mixed systems [75]. CAPICO proved to be a powerful tool in selecting the right emulsiﬁer mixture when an oil is deﬁned and a desired PIT is to be reached, and vice versa. Selected formulations, which produce emulsions that exhibit low viscosity, long-term stability and a translucent bluish appearance (e.g., a sprayable hair conditioner), are listed in Section III of this chapter. The long-term stability of PIT emulsions can be increased further by the use of coemulsiﬁers like glyceryl monostearate. Added to a PIT formulation, glyceryl monostearate provided a constant small particle size and dramatically increased long-term stability. This observation can be attributed to a lamellar phase generated by the glyceryl monostearate preventing the droplets from coalescing [54]. 4. Multiple Emulsions Multiple emulsions provide good examples for demonstrating that the properties of emulsions do not only depend on the type of ingredients used but often on the preparation technique. Multiple emulsions (sometimes described as double emulsions) exhibit droplets that contain a second phase themselves. If the outer phase is aqueous, the oil droplets contain small water droplets (Æ w/o/w) and vice versa. This kind of emulsion attracted attention because of its capability to act as a controlled release system. Consider water droplets trapped in a larger oil droplet that is dispersed in an aqueous phase. The two aqueous phases are separated by a hydrophobic barrier, which can hardly be overcome by a hydrophilic material dissolved in the innermost water phase. Multiple emulsions can be prepared using two methods. In the two-step process, a primary emulsion is prepared by standard means (add water to an oil phase containing a hydrophobic emulsiﬁer and homogenize it). The resulting w/o emulsion is then added to an aqueous solution of a hydrophilic emulsiﬁer. In contrast to the homogenization of the primary emulsion, where small particles are to be obtained, the homogenization of the resulting emulsion should yield relatively large droplets. It is obvious that the oil droplets act as a container for the water droplets and should therefore differ in size from the water droplets. In practice one would use a high shear mixer to produce the small droplets in the ﬁrst emulsiﬁcation process and an ordinary stirrer for the ﬁnal emulsiﬁcation. Typical sizes for the small “inner” droplets are about 1 µm or less and about 10 µm for the “outer” droplets. In the second method, water is added to an oil phase that contains hydrophilic emulsiﬁer. Due to geometric considerations, this leads to a w/o emulsion for small amounts of water. On increasing the water content, the w/o emulsion begins to invert because of

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the emulsiﬁer‘s tendency to build o/w emulsions. During the change of continuous and discontinuous phases intermediate aggregates arise in which the former inner phases (water in our example) are embedded. This inversion method can be applied both to o/w and to w/o emulsions as the starting point. The inversion itself can be triggered either by a change in composition or by a temperature change when the emulsiﬁer is an ethoxylated alcohol. Gohla and Nielsen [76] described an inversion method that leads to long-term stable multiple emulsions. They initially placed a hydrophilic emulsiﬁer (polyethoxylated fatty acids) in polar oil phases with high water solubilizing capacities (e.g., castor oil, rape seed oil) and then heated the mixture until the phase inversion temperature was reached (ª80˚C). The hot oil phase was then combined with a water phase that was heated to PIT separately under constant stirring. A second homogenization takes place after cooling to medium temperature (35˚C). All water-soluble components, including hydrophilic gelifying agents and a remarkable amount of salt (sodium chloride and magnesium chloride), were dissolved in the aqueous phase. Because of the incomplete phase inversion and the high water-solubilizing capacity of the used oil, Gohla and Nielsen denoted the method as partial phase solu-inversion technology (PPSIT). The added electrolyte induces salt out of the emulsiﬁer during the inversion process. The ions affect the structure of the water and therefore the interaction of water with the ethoxy groups. This reduction of the emulsiﬁer’s hydrophilic character seems to be essential in the PPSIT process to stabilize the intermediate multiple emulsion droplets. A multilamellar gel network surrounding the water and the oil droplets provides further stability. Another beneﬁt is the increased stability toward electrolytes. The consistency of a multiple emulsion can be described qualitatively and quantitatively by light microscopy. Another more simple way to check the amount of water that is entrapped in the oil droplets is to measure the electric conductivity. Besides conductivity, the yield of preparation can also be determined by ﬂuorescent measurement [77], microanalysis [78], or nuclear magnetic resonance spectroscopy (NMR) [79]. When salt is added to the mixture in the ﬁrst emulsiﬁcation step of a two-step emulsiﬁcation process, the resulting w/o emulsion displays no conductivity. If all of the salt-containing water remains in the new oil droplets during the last emulsiﬁcation step, the ﬁnal multiple emulsion should exhibit low conductivity. In practice, of course, the conductivity of the w/o/w multiple emulsion type is increased as compared to pure water, because not 100% of the primary water remains entrapped during the second emulsiﬁcation. The conductivity of such an emulsion increases with time as the emulsion will break down and release salty water. A further reason why the multiple character of such an emulsion is destroyed, besides normal mechanisms like coalescence and aggregation, is the high osmotic pressure inside the inner water droplets. Water will diffuse from the external phase inside the oil droplets to dilute the water droplets and to match the differences in pressure of the two water phases. The permeability of the oil phase in a w/o/w emulsion for hydrophilic material is a characteristic parameter that inﬂuences the longterm stability of the emulsion and its potential as a delivery system. If the oil phase exhibits good barrier properties for water and water-soluble active substances, the multiple character opens a wide range of advanced formulation techniques: • The two water phases can be loaded with different additives that are incompatible in one phase (e.g., different salts that would precipitate, surfactants that increase viscosity)

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• Hydrophobic ingredients that compensate each other’s activity can be separated in a multiple o/w/o emulsion. • Time-delayed release systems can be designed. The oil barrier inhibits a fast deposition of water-soluble components when they are entrapped in the water droplets of a w/o/w emulsion. The oil droplets ﬁrst have to be destroyed by mechanical agitation ﬁrst before the inner water phase can be released. The method of preparation, the nature of the oil and the HLB number of the emulsiﬁers used in the single steps determine the type of emulsion. The viscosity of the oil and the droplet size of the primary emulsion seem to be the factors that most effect the long-term stability in w/o/w emulsions. It has been demonstrated that increasing the viscosity of the oil phase stabilizes the emulsion as the rate of transfer through the oil phase is reduced [80]. 5. Gel Emulsions (High Internal Phase Emulsions) Gel emulsions with a high content of internal phase can be achieved for systems exhibiting two-phase regions of the type Winsor I and Winsor II in the phase diagrams of the system ethoxylated alcohol/oil/water. When water is gradually added to a mixture of emulsiﬁer/oil above the phase inversion temperature (PIT) while stirring, the system changes from an isotropic micellar solution to a turbid two-phase system (Winsor II). The turbid dispersion changes into a transparent stiff gel phase with sufﬁcient water content. If the temperature is below the PIT, the whole procedure can be carried out in the opposite direction. Below the PIT, the emulsiﬁer is soluble in the water phase and oil is added under continuous stirring until the turbid mixture (Winsor I phase) changes into a clear gel rich in oil. A water/polyol mixture [81] can also be used instead of a pure aqueous phase to produce oil-rich gel emulsions. Investigations regarding the internal structure of the gel phases demonstrated that the phase is formed by an inner oil (water) phase and a continuous phase consisting of the water (or oil)/emulsiﬁer mixture. Because of the temperaturesensitive character of ethoxylated alcohols, gel phases can also be prepared by a rapid temperature change in o/w microemulsions. Micrographs [82,83] provided images of polyhedral-shaped oil droplets of about 1 µm diameter surrounded by a three-dimensional network of thin layers. The transparent appearance of the phase derives from the matched refractive indices of the inner and outer phases. Because the mismatching of refractive indices is a premise for light scattering, the gel phase reduces the intensity of scattered light to a minimum. This type of emulsiﬁcation process is sometimes referred to as D-phase emulsiﬁcation because the starting point is an isotropic micellar solution. One has to keep in mind that the produced emulsions are not stable from a thermodynamic point of view. Therefore, exact phase boundaries for the gel depend on preparation parameters like the extent of stirring and number of mixing steps. B. Microemulsions and PIER Microemulsions are multicomponent ﬂuids consisting of oil, water, and a properly selected surfactant or surfactant/cosurfactant mixture. One characteristic feature of microemulsions is that they are thermodynamically stable. This means that one macroscopic phase does not change its characteristic physical parameters at a ﬁxed temperature and pressure. Density, refractive index, and the phase composition do not change as a function of time. Their optical appearance (transparent), rheological properties (low viscosity) and interfa-

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cial tension (extremely low) make them interesting for several applications, including cleansing products. Ternary systems of water, oil, and ethoxylated nonionic surfactants attracted much attention because of their capability to incorporate oil at distinguished compositions. The appearance of microemulsion phases as a consequence of temperature and concentration is a main feature of these systems and the inﬂuence of temperature on the solubility of oil in particular has been documented [84,85]. However, the existence of microemulsion is not restricted to systems with ethoxylated alcohols. Thermodynamically stable formulations with a remarkable oil content can be achieved by using suitable emulsiﬁers and coemulsiﬁers. The hydrophilic-lipophilic properties of non-EO type surfactants have to be balanced with other parameters, such as hydrophobic coemulsiﬁers and/or salinity, for example. Adding a certain coemulsiﬁer to the basic emulsiﬁer has the same effect on the hydrophilic-lipophilic ratio as increased temperature for ethoxylated alcohols; the balance is shifted to the lipohilic side. The changed hydrophilicity causes a phase inversion from water to oil as outer phase. Microemulsions that are inverted by the ratio of properly selected emulsiﬁers are considered phase inversion by emulsiﬁer ratio (PIER) microemulsions. The advantage of this method for formulation concepts as compared to the temperature method is obvious. The temperature dependency of conventional microemulsions balanced by ethoxylated emulsiﬁers implies a critical long-term stability if the temperature is changed, since the maximum of solubilized oil is a function of temperature. The emulsifying capacity of PIER emulsions remains practically unaffected by temperature, whereby PIER microemulsions open a broad ﬁeld of formulating temperaturestable microemulsions. PIER is explained for two cases of emulsiﬁer/coemulsiﬁer mixtures in the following examples. Figure 11 demonstrates the PIER effect for the emulsiﬁer alkyl polyglycoside (APG) and the coemulsiﬁer sorbitan monolaurate (SML) [86]. Mixing APG with water/dodecane at a ratio of 1:1 leads to an o/w emulsion with excess oil in the concentration range from 0 to 8 wt% APG. If about 40% of the APG is replaced by SML, a three-phase region occurs. This multiphase region contains a microemulsion. Increased SML content leads to an inversion of the system. The outer phase is now represented by the oil phase and the inner phase by water. The inversion is accompanied by a signiﬁcant decrease in the interfacial tension between oil and aqueous solution (Fig. 11). The value of the minimum (ª10-3 mN/m) is about three orders of magnitude lower than the interfacial tension in a normal o/w or w/o emulsion. When the total emulsiﬁer concentration is increased at a constant APG/SML ratio of 1:1 a single-phase microemulsion is achieved (denoted as D in Fig. 11). The similarity between the behavior of APG/coemulsiﬁer and the temperature-induced phase behavior of ethoxylated alcohols is clearly visible in the ﬁsh shape of the phase borderlines in Fig. 11. The so-called Kahlweit ﬁsh is a typical feature of balanced surfactant systems. SML molecules with their small head group size are incorporated in the interfacial APG ﬁlm and cause a small average in head group size, leading to high interfacial activity. In contrast to ethoxylated alcohols, the temperature effect on the APG/coemulsiﬁer mixture can be ignored [87]. The temperature-insensitive emulsifying capacities of APG/coemulsiﬁer mixtures open a wide ﬁeld for basic cosmetic applications. The appearance of APG-based microemulsions is not restricted to the use of sorbitan monolaurate as a coemulsiﬁer as demonstrated by the pseudoternary phase diagram in Fig. 12. The surfactant component is represented by a mixture of C8–14 APG/SLES (5:3), the oil consists of dicaprylyl ether/octyl dodecanol (3:1), glyceryl oleate (GMO) was taken

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cSML cAPG + cSML

γ (mN/m)

SML 1.0

1 w+D+o

w+o

0.8

0.1

0.6 w+D+o

D

0.4

APG

0.01

o+w

0.2 0 0

2

4

6

8

0.001

10

0

Concentrationsurf.(wt.-%)

0.2

0.4

APG

0.6

0.8

cSML cAPG + cSML

(a)

1.0 SML

(b)

(a) Phase behavior of the system dodecane/water in a ratio of 1:1, C12/14 APG, sorbitan monolaurate in dependence upon the ratio of APG to SML as a function of the total surfactant concentration; (b) Interfacial tension of the system dodecane/water in a ratio of 1:1 C12/14 APG, sorbitan monolaurate in dependence upon the ratio of APG to SML for a total surfactant concentration of 15%

Figure 11 Kahlweit ﬁsh (left) and interfacial tension as a function of the emulsiﬁer/coemulsiﬁer ratio (right) of the system SML/C12/14 APG. The interfacial tension against dodecane has a minimum at a ratio of about 55% SML in the C12/14 APG/SML mixture.

80

40

no l=

w/o

20

3/1

SL

ME

C

Lα + o

HIα

(c)

ca

80

ME

de

(b)

60

Do

8-1

4

tyl

AP

60

Oc

G/

o/w

40

er/

Eth

ES

yl

ryl

=5

20

ap

Dic

/3

Dicaprylyl Ether/Octyl Dodecanol = 3/1 100

HIIα + o

Lα

C+w

100 C8-14 APG/ SLES = 5/3

20 (a)

40

60

80

100

GMO

GMO

Figure 12 Pseudoternary phase diagram of C8–14 APG/SLES (5:3), dicaprylyl ether/octyl dodecanol (3:1), and glyceryl oleate.

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as a coemulsiﬁer [87]. The water content is kept constant for all mixtures at 60%. Because of their good foaming behavior, APG/SLES mixtures make up the basic formulations of many body-cleansing formulations. The phase diagram displays two distinct microemulsion regions that differ in oil content. One microemulsion phase with a low to medium oil content is situated along the surfactant/oil line of the phase triangle. Point (b) of the GMO-poor microemulsion consists of 12% oil, 24% surfactants, and 4% coemulsiﬁer and exhibits a viscosity of 1.6 Pa s at a shear rate of 1 sec–1. The region of the second oil-rich microemulsion is shifted to higher concentrations of glyceryl oleate and reveals a gel-like appearance. The composition of point (c) is 20% oil, 12% surfactant, and 8% coemulsiﬁer glyceryl oleate. An intense dilution of the microemulsion while keeping the other ratios constant causes a release of oil. This effect can be utilized to formulate products with both cleansing and oil replenishing properties. Combining the good cleansing and foaming performance of the APG/SLES surfactants mixture with the moisturizing skin care properties of the microemulsion leads to a moisturizing foam bath oil. C. Surfactant Concentrates Cosmetic raw materials and core concentrates for the production of cosmetic formulations often consist of concentrated blends of different surfactants with water. But even the simplest formulations of a few components open up a wide range of possibilities regarding viscosity, foaming properties, and cleansing. The formulations have to be a compromise between easy handling, processing properties and, of course, economic requirements. Due to their tendency toward self-aggregation, surfactants show more or less ordered structures in aqueous media [88]. The type of structure depends on parameters like molecular structure [89], surfactant concentration and temperature. The actual form of aggregation is affected by all of these parameters. Understanding the general phase behavior of surfactants is very helpful in balancing the desired parameters in the right way. Figure 13 demonstrates the inﬂuence of concen-

Viscosity (Pa × s)

100

10

1 H2O

L1

L1 Gel

0 0

5

10

15

T = 25°C Viscosity at 30/s

20

25

Hexagonal

30 35 40 45 50 55 wt-% Surfactant in water

Lamellar 60

65

70

75

80

FAES FAES : C12/14-APG 2:1

Figure 13 Phase behavior and viscosity for sodium laureth sulfate (SLES) and a 2:1 mixture of SLES with C12/14 APG.

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tration and aggregation form on the viscosity for sodium laureth sulfate (SLES) and a 2:1 mixture of SLES with APG [90]. Above its critical micellar concentration (cmc), sodium laureth sulfate (SLES) forms globular micelles (denoted as L1) that do not inﬂuence the ﬂow properties in a signiﬁcant way. The situation is different when the concentration is increased by about over 20% of its weight. The aggregation form changes from globular micelles to rod-like micelles that inﬂuence ﬂow properties because of their anisotropic shape and their tendency to form entanglements at a sufﬁciently high concentration [91]. The appearance is now gel-like due to the arising elastic properties. When the surfactant content is increased further, the rodlike micelles are forced into a structure of higher order, resulting in an hexagonal array. This causes a stiff gel phase. The densely-packed cylinders inhibit ﬂow almost completely which is caused by the dramatic increase in viscosity. It is obvious that this form of SLES concentrate is hardly suitable for pipe ﬂow or for further mixing with other ingredients. Moving on from the hexagonal phase (35-55%) in the phase diagram by further increasing the concentration exhibits an astonishing effect. The viscosity decreases about one order of magnitude despite the higher concentration. The reason for this viscosity progress is based on another transformation. This time, the packing of surfactants changes from cylindrical to lamellar. In contrast to the hexagonal arrangement, planar lamellas are capable of sliding and can therefore react more ﬂexibly to external pressure. Replacing SLES partially by C12/14 APG causes a disruption of the ordered hexagonal phase, therefore reducing viscosity. On the other hand, the crystallization of C12/14 APG is inhibited by the SLES. This viscosity dependency demonstrates nicely that it is not possible to adjust the rheology of a system without knowing the types of phases and their regions in the diagram. The phase sequel L1 (micellar solution) Æ hexagonal phase Æ lamellar phase is frequently observed at the considered concentration range of aqueous surfactant solutions [92,93]. Other lyotropic liquid crystalline phases that occur in binary or ternary surfactant/water systems and increase viscosity are cubic and inverse hexagonal phases, for example. D. Encapsulated Systems Modern cosmetic formulations often have to exhibit a degree of functionality that exceeds basic cosmetic requirements like cleansing and moisturizing. Therefore, more advanced methods such as encapsulation techniques have been developed. The general task of capsules is to store, deliver, and control the release of active compounds, a process which cannot be fulﬁlled by conventional formulation techniques. Encapsulation techniques provide the possibility of combining effects in one product that would not be possible without encapsulation. For example, it is known that high amounts of oil reduce the foaming power of aqueous formulations. If the oil is separated from the aqueous solution in a microscopic range, the foaming properties can be maintained until the walls of the capsules break down due to external pressure and the oil is released. Therefore, the design of the capsule wall must always incorporate a compromise between increased impermeability during storage on the one hand and easy breakdown during application on the other. Depending on the wall material used, the destruction of the protective layer can also be triggered by a change in temperature, pH value, and salinity as well as by mechanical impact. The methods used to encapsulate materials can be distinguished with regard to the process and the material used to form the capsule. The molecules of some materials are connected by covalent bonds (e.g., through polymerization) and others by noncovalent forces like ionic interactions and molecular interactions arising in self-assembling systems.

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Widely used self-assembling molecules for encapsulations are phospholipids that are able to form liposomes in aqueous media. Usually external forces like shearing or ultrasonication [94] have to be applied in the process. Liposomes are vesicles made of lipids. Vesicles are globular particles that consist of at least one (lipid) bilayer forming closed spherical bodies. The capability of forming this kind of hollow sphere is not restricted to phospholipids, though. Several single-tailed amphiphilics, both ionic and nonionic are able to create vesicles [95–97], some of which are suggested to be thermodynamically stable. Vesicles differ in the number of bilayers and in their diameter. Small unilamellar vesicles (SUV) exhibit diameters in the range of 30 to 100 nm [97,98] whereas large unilamellar or multilamellar vesicles (LUV and MLV, respectively) have diameters up to 0.5 µm. Lasic [99] clearly describes the different ways of preparing liposomes and the physicochemical properties that determine the applications. Liposomes can encapsulate watersoluble ingredients in their interior or lipophilic material in their lipid membrane. Adsorption on the bilayer surface is another way of delivering molecules. Simonnet [100] reported on nonionic surfactant vesicles (NSV) that stabilize oil droplets (even silicon oils) in aqueous medium by covering the emulsion droplet’s surface. The breaking of the vesicle’s bilayer structure and the release of the entrapped substances can be triggered by a change in the pH value, temperature or the composition of the solution (e.g., electrolyte content, surfactants). Several possibilities for encapsulating diverse active molecules for skin treatment have been developed with varying degrees of success [101]. An interesting option for cosmetic application is the option of producing alcohol-free solutions that contain fragrances [102]. Ghyzcy [103] documented a method of preparing aqueous dispersions of liposomes that contain water-insoluble fragrances. Liposomes are also used as enzyme carriers, e.g., for DNA repair [104]. Liposomes are also applied without any added substances. Because phospholipids are a part of the human cell membrane, the liposome alone is supposed to improve skin conditions. It has been demonstrated that phospholipids are able to enhance skin moisture [105] and are likely to decrease skin roughness [106]. The controversial issue of whether liposomes are able to penetrate the stratum corneum as intact particles to deeper layers of the human skin is still under discussion [107–109]. Another method of entrapping material is to utilize coacervate phases as insoluble particle layers. If negatively charged polymers are added to a solution of positively-charged polymers (e.g., gelatin) the attractive polymer interactions dominate the repulsive electrostatic interactions. The repulsive electrostatic interactions vanish as negative and positive charges compensate each other. This attractive interaction induces a new polymer-rich phase called the coacervate phase. Carboxymethyl cellulose or polyacryl acid can be used as a negatively charged polymer. Ionic strength, pH value, and the relative concentration of the oppositely charged polymers can adjust the yield of the coacervate and its properties. Magdassi [110,111] demonstrated that oppositely charged surfactants can also lead to insoluble complexes which are suitable for encapsulation. If oil droplets or hydrophobic particles are present in the water phase the hydrophobic coacervate phase covers them with a water-insoluble viscous shell. The coacervation process is illustrated schematically in Fig. 14. The resulting emulsion can be used directly or can be treated in a further step with cross linkers if the polymers or surfactants have the suitable chemical structure. The covalent bonding between the polymer molecules increases the compactness and stability of the particle shell. Emulsions or dispersions that contain core material covered with such rigid layers can be dried to obtain the capsules. The polymer can be modiﬁed in order to reinforce the coacervate phase. Chitosan glycolate as positively charged and carboxymethyl cellulose as charged molecules have been successfully used to stabilize vitamin A by entrapping it in a coacervate process. The tendency

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o/w

+

Coacervation I

II

Polymerization

III

Dry

Figure 14

Different steps in a coacervation process (schematically).

of polyvinyl alcohol coacervate to build crystalline structures has also been utilized to achieve highly-impermeable wall material [112]. The wall material can also be produced directly in polymerization. Among others, polyurea, polyphenylester and epoxy resins have been reported to form polymeric coatings by in situ interfacial polymerization [113]. These capsules represent small slow-release containers in which the polymer matrix that surrounds the core hinders diffusion of the inner material to the outside. When the size of the capsule obtained using this method lies within the range of a few micrometers, the capsules are denoted as microcapsules. If the droplet size can be reduced further in the emulsiﬁcation process even nanocapsules can be achieved. The sizelimiting crux is not the formation of the shell, but the minimal droplet size that can be obtained in the primary emulsion process. One has to keep in mind that a decrease in capsule size introduces some disadvantages. The ratio of wall material to core material is shifted toward wall material as a reduction in particle size increases the interfacial area.

III. FORMULATIONS—EXAMPLES AND CONCEPTS To exploit the full spectrum of modern formulations and possibilities for skin and hair products, comprehensive examples and concepts have been investigated for the beneﬁt of

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manufacturers and customers. In recent raw material development, alkyl polyglycosides are a class of products that represent a new concept in compatibility and performance in personal care formulations. They are multifunctional raw materials which are becoming highly signiﬁcant for modern formulation techniques. By virtue of their physicochemical and performance proﬁles, alkyl polyglycosides may be combined with additional ingredients and active substances to allow new types of formulations to be developed. These are discussed in the following sections [90]. A. Shampoos Based on Alkyl Polyglycosides It is an established fact that combinations of betaine and quaternary active substances only provide conditioning effects in the presence of anionic surfactants. However, in combination with cationic substances, alkyl polyglycosides signiﬁcantly reduce wet combability with or without the addition of betaines (formulations 1 and 2, Table 1). To provide formulations containing alkyl polyglycoside with conditioning properties, any of the usual cationic materials may be used, including cationic proteins, cationic cellulose and guar derivatives, cationic polymers (polyquaternium types), etc. Formulations 3 and 4 (Table 2) show exciting, alternative shampoos based on alkyl polyglycosides.

TABLE 1

Shampoos

No. INCI declaration Decyl glucoside Cocamidopropyl betaine Polyquaternium-10 Water, preservative pH value Residual wet combability (%)

TABLE 2

1 AS (%) 55 30

2 (wt.-%)

24.0 — 0.3 ad 100 5.5 47

24.0 10.0 0.3 ad 100 5.5 57

Shampoos

No. INCI declaration Lauryl glucoside Cocamidopropyl betaine Hydrolyzed almond protein Xanthan gum Disodium laureth sulfosuccinate Laureth-2 Polyquaternium-10 Water, preservative pH value

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3 AS (%) 50 30 22 40

4 (wt%)

8.0 27.0 2.0 1.0 — — — ad 100 5.5

12.0 7.0 — — 8.0 1.5 0.2 ad 100 5.5

Personal Care Formulations TABLE 3

235

Shower Gels No. INCI declaration

Sodium laureth sulfate Sudium laureth sulfate (and) lauryl glucoside Decyl glucoside Cocamidopropyl betaine Lauryldimonium hydroxypropyl hydrolyzed wheat protein Polyquaternium-10 Guar hydroxypropyl trimonium chloride PEG-7 Glyceryl cocoate

30 60 55 30 35

Glycol distearate (and) laureth-4 (and) cocamidopropyl betaine Laureth-2 Laureth-6 Sodium laureth sulfate (and) lauryl glucoside Water, preservative pH value

45

TABLE 4

5

6 (wt%)

7

— 12.0 — 14.0 3.0

25.0 — 6.0 10.0 2.0

— — — 10.0 2.0

0.5 1.0

— 2.0

3.0

—

1.0 — — ad 100 5.5

— — 20.0 ad 100 5.5

AS (%)

0.1 —

— 3.0 60 ad 100 5.5

Shower Gels

No. INCI declaration Sodium laureth sufate Lauryl glucoside Polyglyceryl-2-PEG-4 stearate Octyl dodecanol Ceteareth-20 Sodium chloride Water, preservative pH value Rel. TEWL Rel. TEWL (standard)

AS (%) 30 50

8 (wt.-%) 22.0 16.0 4.0 3.0 1.0 0.4 ad 100 5.5 1.1 g/m2h 1.75 g/m2h

B. Shower Gels The feeling of shower and bath gels on the skin is an important factor for consumer acceptance. A pleasant feeling can be achieved using the same conditioning agents described for shampoos. Formulations 5 to 7 (Table 3) represent examples of such products. They were evaluated in a test against a market standard involving eight volunteers. The sensation on both wet and dry skin was assessed on a scale from 1 to 6 (from pleasant to

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236 TABLE 5

Ansmann et al. Peeling Preparations No. INCI declaration

Decylglucoside Texapon ASV (Cognis) Sodium laureth sulfate Flora Beads Jojoba 40/60 Gypsyrose (Rovi) Xanthan Gum Water, preservative pH value

AS (%) 55 30 30 2

9 (wt%) 20.0 — 7.2 1.0 50.0 ad 100 5.5

dry). The market product achieved an average score of 2.8 while formulations 6 and 7 achieved an average score of 2.1. An interesting concept for “shower and lotion” products is the incorporation of oilcontaining emulsions in a surfactant base. The skin-care effect of such formulations can be evaluated by determining the transepidermal water loss (TEWL), for example. A market product and formulation 8 (Table 4) were applied to the inside of the right and left forearms of 10 volunteers. One hour after the treatment, the TEWL was measured using an evaporimeter. The TEWL value of formulation 8 is better than that of the market product. The two products differ from one another with a statistical signiﬁcance of 95%. C. Peeling Preparations Formulations with peeling properties, a modern market trend, incorporate soft abrasive particles, such as hardened jojoba wax, walnut bark, cellulose granules, apricot kernels, etc., to remove scales and to achieve a particular feeling. In addition, the abrasive particles promote circulation through a gentle massaging effect on the skin. The exfoliating effects provided by active substances like alpha-hydroxic acids (AHA) and their derivatives must be carefully adapted to the type of skin and the speciﬁc consumer group and can best be evaluated by a panel test. The forearm is washed and foaming properties, exfoliating effects, and the appearance of the products are assessed. Formulation 9 (Table 5). D. Microemulsions as Bath Oils Good foaming and moisturizing performance characterize an alkyl polyglycoside microemulsion that is mild to the skin (Table 6, formulation 10) and that is broken down by dilution during application. E. Facial Cleansers Facial cleansers are specialty formulations. The dermatological properties of alkyl polyglycosides and their beneﬁcial deep pore cleansing effects renders them most suitable for use in many types of clear formulations, for formulations 11 to 13 (Table 7). New products like biphase face cleansers have been developed and have shown effective cleansing capabilities. One example is formulation 14 (Table 8). F. Hair Conditioners Alkyl polyglycosides can be formulated as the basis of rinses and conditioners for the same reasons and by virtue of their positive influence on combability, coupled with

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Personal Care Formulations TABLE 6

Microemulsions as Bath Oils

No. INCI declaration Lauryl glucoside Decyl glucoside Glyceryl oleate Dicaprylyl ether Octyl dodecanol Citric acid Water, preservative pH value

TABLE 7

237

10 (wt%)

AS (%) 50 55

23.2 15.1 6.0 28.0 7.0 0.8 ad 100 5-6

Facial Cleansers

No. INCI declaration Lauryl glucoside Sodium laureth sulfate Cocoamphodiacetate Carbomer Aloe vera Hydrolyzed wheat protein Panthenol Allantoin Polyquaternium-10 Sodium chloride PEG-7 glyceryl cocoate Glycerol Cetearyl alcohol Cetearyl glucoside Water, preservative

11

12 (wt%)

13

10.0 3.6 — — — 0.5 0.2 0.2 — 1.0 — — — — ad 100

12.0 2.0 1.5 0.8 0.2 — — 0.2 0.1 — — — — — ad 100

10.0 — — — — — — — — — 5.0 3.0 7.5 7.5 ad 100

AS (%) 50 30 30

40 50

86

the fact that they may readily be combined with cationic compounds. Formulation 15 (Table 9) is one example of such a product. In combination with an esterquat as a conditioner, alkyl polyglycosides can be used to develop rinses based on vegetable materials. G. Styling and Permanent Wave Products The effects of alkyl polyglycosides in styling formulations are based on their substantivity to hair. Formulation 16 (Table 10) is an example of a styling gel, while formulation 17 represents a styling mousse (Table 11). In permanent wave formulations, the use of alkyl polyglycosides provides an improved permanent wave effect while simultaneously

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TABLE 8

Facial Cleansers

No. INCI declaration

AS (%)

Dicaprylyl carbonate Diethylhexyl cyclohexane Hexylenglykol Di Potassium hydrogenphosphate Potassium dihydrogenphosphate Sodium chloride Benzylalkohol Lauryl glucoside EDTA Water, preservative pH value

TABLE 9

14 (wt%) 20.0 20.0 1.0 0.2 0.1

50

0.9 0.5 0.2 0.1 57.0 5–6

Hair Conditioners

No. INCI declaration Lauryl lucoside Dipalmitoyl hydroxyethylmonium Methosulfate (and) cetearyl alcohol Cetearyl alcohol Glyceryl stearate Octyl dodecanol Water, preservative pH value

AS (%) 50

15 (wt%) 2.0 3.5 0.5 0.5 1.0 ad 100 3.5

reducing hair damage. Formulations 18 and 19 (Table 12) are examples of such products. H. Creams and Lotions for Sensitive Skin A long-chain alkyl polyglycoside compound provides a valuable solution for vegetable based products, especially for sensitive skin (Table 13, formulations 20 to 22). In addition to mildness aspects, sensory considerations play an important part in the development of creams and lotions. The oil mixtures follow the concept of the spreading properties of emollients [114,115] for a smooth and pleasant feeling of the skin.

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Personal Care Formulations TABLE 10

239

Styling Gels

No. INCI declaration Lauryl glucoside Hydrolyzed collagen Carbomer Propylene glycol PEG-40 hydrogenated castor oil Sodium hydroxide Tetrasodium EDTA Water, preservative pH value

TABLE 11

50 50 2

4.0 1.5 60.0 3.0 2.0 3.0 0.2 ad 100 5.6

10 40

Styling Mousse Products

No. INCI declaration

17 (wt%)

AS (%)

Chitosan Glycolic acid Cetrimonium chloride Hydrolyzed wheat gluten Water, preservative pH value

TABLE 12

16 (wt%)

AS (%)

1.0 0.4 1.0 3.0 94.6 4-5

Permanent Wave Products

No. INCI declaration Thioglycolic acid Ammonia Etidronic acid Ammonium carbonate Decyl glucoside Hydrogen peroxide Xanthan gum Water, preservative pH value

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18 AS (%) 98 25 60 55 35 2

19 (wt%)

8.0 10.0 0.3 3.0 1.0 — — ad 100 8.5

— — 0.3 — 1.0 7.5 15.0 ad 100 3.5

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TABLE 13

Creams and Lotions for Sensitive Skin

No. INCI declaration

20

Cetearyl alcohol Cetearyl glucoside Dicaprylyl ether Decyl oleate Caprylic/capric triglyceride Oleyl erucate Dimethicone a-Tocopherol Glycerol Water, preservative Viscosity 23˚C [mPas] (Brookﬁeld)

TABLE 14

21 (wt%)

AS (%)

87

6.0 1.5 2.0 4.0 4.0 3.0 0.5 1.0 3.0 75.0 75,000

3.6 0.9 2.0 2.0 4.0 3.0 0.5 1.0 3.0 80.0 6,000

22

2.3 3.6 2.0 4.0 4.0 3.0 0.5 1.0 3.0 76.6 10,000

Lotions for Sun Care

No. INCI declaration Lauryl glucoside, polyglyceryl-2Dipolyhydroxystearate, glycerin Sodium-cetearyl sulfate Dicaprylyl carbonate Dibutyl adipate Cocoglycerides Hexyldecyl stearate Tocopherol Ethylhexyl methoxycinnamate Octocrylene Bisabolol Zinc oxide Titanium dioxide, alumina, simethicone Magnesium aluminium silicate Xanthan gum Glycerin Water, preservative

AS (%)

23 24 (wt%) 4.0

4.0

1.0 6.0 4.0 12.0 10.0 1.0 — — 0.5 7.0 5.0 1.5 0.5 3.0 44.5

1.0 — 10.0 12.0 — — 7.5 9.0 0.5 5.0 — 1.5 0.5 3.0 46.0

I. Sun Protective Lotions Examples for sun care formulations are found in Table 14 (formulations 23 and 24). The formulations use micronized inorganic active substances that are easily dispersed by a liquid alkyl polyglycoside compound. A similar alkyl polyglycoside compound to the o/w emulsiﬁer also allows for the formulation of sun protection products with organic UV absorbing material.

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Personal Care Formulations TABLE 15

241

Facial Care Creams No. INCI declaration

Cetearyl glucoside, cetearyl alcohol Potassium cetyl phosphate Glyceryl stearate Dicaprylyl carbonate Caprylic/capric triglyceride Olus Ethylhexyl stearate Golden palm oil Tocopherol Dimethicone Titanium dioxide Glycerin Butylene glycol Panthenol Prunus amygdalus dulcis protein and glycerin Polyacrylamide, C13-14 isoparafﬁn, laureth-7 Water, preservative pH value Viscosity 23˚C [mPas] (Brookﬁeld)

25 AS (%)

26 (wt%)

5.0 0.5 2.0 5.0 — 3.0 4.0 2.0 1.0 0.5 — 2.0 2.0 — — — 73.0 5.5 162,500

4.0 0.2 — 5.0 3.0 — 5.0 — 0.5 0.5 1.5 5.0 — 0.5 4.0 2.8 68.0 5.5 125,000

J. Active Face Creams The two active facial care creams in Table 15 (formulations 25 and 26) demonstrate the abilities of alkyl polyglycoside based o/w emulsions to produce mild creams that are most suitable for sensitive skin and thus appropriate for this type of facial care product. The viscosity and consistency of creams [116] are adjusted by the concentration of the C16/18 alkyl polyglycoside cream base (see Table 15, formulations 25 and 26).

IV. PERFORMANCE PROPERTIES Important criteria for successful products are product safety (for environment and user), product economy (for manufacturer and customer), and product performance. The product performance is described by claims in the advertising and on packaging. All these claims must be objectively measurable or subjectively perceivable. In the European Union, the production and marketing of cosmetic products is regulated by Council Directive 76/768/EEC (1976). The latest approved amendments to this directive introduced several new points. Among these, banning the use of animals in the safety testing of cosmetic ingredients was one important issue. In addition, proof of efﬁcacy of the cosmetic claims are required, too. This product performance evaluation can be done using objective and subjective testing methods. A multitude of testing possibilities exist for the various cosmetic applications. Only a small selection of these will be discussed [117].

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A. Testing Methods for the Hair To test the inﬂuence of cosmetics on hair performance, salon tests such as the half-head test or so-called objective testing methods using cut hair can be utilized. 1. Wet Combing A very practice-oriented test is the determination of the inﬂuence of products on the wet combability of the hair [118]. All cosmetic formulations applied to wet hair like shampoos, conditioners, bleaching agents, perms, and hair dyes should have a positive inﬂuence on wet combability. The consumer especially expects that wet hair will be much easier to comb after applying treatments like rinse-off and leave-on conditioners. The formulater of hair conditioners has to elaborate a well-tuned balance between the sufﬁcient conditioning effect and undesired build-up, i.e., an accumulation of the conditioning agent, which overloads the hair. So-called 2-in-1 shampoos have maintained a strong market position for years. Twoin-one shampoos combine cleansing properties with conditioning effects that are almost comparable to classic hair rinses. Automatic equipment should be used to determine wet combability. This allows for a high output of sample results for achieving representative statistics. The objective measurement of the wet combability of cut hair makes it possible to utilize hair of different origins, e.g., Asian and Caucasian hair or hair with notable levels of predamage. In this way, one can ensure that the test results will correlate with consumer test results. 2. Dry Combing In principle, the determination of the dry combability is comparable to that of the wet combability [118,119]. There are two important differences, however: The measurement has to be done under controlled climate conditions. The dry combing work values depend greatly on the environmental humidity. Therefore, the measurement should be done in an air-conditioned area. Electrostatic charging of the hair is an issue to be considered when testing dry combing. Therefore, the dry combing measurement is best carried out in a Faraday cage. The dry combing values provide a great deal of information with respect to the interaction of hair ﬁbers. Especially for thin hair, high values are desired at the beginning and in the middle section of the measurement, whereas at the end of the measurement, low values should be achieved. Such values show that the hairs interact—which is a prerequisite for achieving hair volume and manageability. The peak at the end of the dry combing process strongly corresponds with the tangling of the ends of the hair ﬁbers and should be as low as possible (Fig. 15). By adding special cosmetic ingredients to consumer products, the dry combing values at the beginning, middle, and end of the combing process can be reduced. That means that the use of normal hair rinses decreases the interaction of the hair ﬁbers, therefore a detangling of the hair occurs. On the other hand, these ingredients do not contribute in a positive manner to manageability and body. However, this negative effect of conditioning agents can be counteracted in readymade formulations by adding polymers or special surfactants like alkyl polyglycosides (Fig. 16).

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Personal Care Formulations

243

(mN) 2500 a 2000 b

1500

1000

c

500

0 0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

(s)

Figure 15 Dry combing curves: (a) untreated hair, (b) hair treated with manageability-improving agents, and (c) hair treated with strong conditioning agents.

Residual combing work (%) 140 120 122 100 80 83 60 40 20 0

1

2

1: Sodium Laureth Sulfate 2: Sodium Laureth Sulfate/Lauryl Glucoside (3:1)

Figure 16 value: 6.5.

Inﬂuence of lauryl glucoside on dry combability; test concentration: 12 % AS, pH

3. Tensile Strength The most studied physical properties within the hair are the mechanical properties. Mechanical properties provide information about ﬁber integrity. Tensile properties are primarily determined to evaluate hair integrity [117–119]. The test can be run either on single hair ﬁbers or on a tress of hair. The common procedure for evaluating the stretching properties of human hair is by using load-elongation (stress-strain) methods: A ﬁber of known length and diameter is stretched at a ﬁxed rate in water, in a buffer or at ﬁxed relative humidity near room temperature on an automated instrument.

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Ansmann et al. C

A

B

100% RH

A

Load

C

65% RH

B Yield region

Hookean region

Post-yield region

Strain A = elasticity limit B = Plasticity limit C = break point

Figure 17

Stress/strain curves of hair at different relative humidities.

Tensile properties are obviously whole-ﬁber properties whereas it has been suggested that they are cortical properties, practically unrelated to the cuticle. Factors inﬂuencing tensile strength properties are relative humidity and moisture content, ﬁber diameter, bleaching, permanent waving, cosmetic formulations, light radiation, and other environmental factors. Figure 17 shows the stress-strain curves of hair at different relative humidities. During the stress-strain experiment, three different regions are evaluated that characterize hair quality: • The elastic Hookean region (below 5% elongation) • The plastic region (up to approx. 25% elongation) • The nonplastic region; breaking point (characterized by a strong increase of the force values up to the breaking point of the ﬁber) Because of the different ﬁrmness of the cortex of the hair as well as of the individual hair thickness, the measured values are widely scattered. For this reason, an accurate statistical evaluation of the elaborated values must be carried out. A minimum of 50 single hair ﬁbers have to be treated and tested. 4. Hair Thickness The characterization of the dimensions of the hair ﬁber, e.g., thickness and shape (round or elliptical) is particularly important in determining mechanical properties of the hair, such as tensile strength, torsion, elasticity, and swelling behavior. The diameter of the hair ﬁber can be measured using a laser device [118]. During the measurement, the hair ﬁber is placed in a laser beam. The diameter and the ellipticity of the hair can be determined from the resulting shadow.

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Personal Care Formulations

245

60 µm

95 µm

Figure 18

163 µm

110 µm

(a)

(b)

Asian (A) and Caucasian (B) hair.

Both values/parameters depend on the age of the person and on the ethnic culture: The hair of a baby is much thinner than that of an adult; Asian hair is rounder and thicker than Caucasian hair (Fig. 18). The hair diameter has a strong impact on the body, combability, manageability, and permeability of the hair. 5. Shadow-Image Analysis of Tresses of Hair The volume of the tresses of hair expands with increasing humidity. Rotating movements of the hair ﬁbers as a result of humidity changes and internal stress are thought to be the reason for this effect. This strongly depends on the degree of the damage to the hair and the substances are put onto the hair. The hair volume can be easily assessed by means of shadow-imaging analysis. In shadow-image analysis a tress of hair illuminated by a spotlight casts a shadow onto a surface. The shadow area can be determined planimetrically or by image analysis [118] (Fig. 19). The volume of hair increases characteristically with increasing humidity. On the other hand, oily tresses of hair stick to each other and consequently produce a smaller shadow than clean hair. Using shadow-imaging analysis, one can determine the performance properties of hair cosmetics for greasy hair, for example. 6. Atomic Force Microscopy The atomic force microscopic (AFM) technique is a new method available for researching hair cosmetics. In addition to conventional techniques (light microscopy, scanning electron microscopy, transmission electron microscopy, x-ray, photoelectron spectroscopy, etc.) which determine the morphology, particle size and element composition of the hair surface, other

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Screen

Camera

Loose strand

Light source

Shadow image of the strands Fatty strand

Figure 19

Shadow-image analysis.

physical properties can be evaluated. The quantitative determination using AFM allows for a differentiation of hair conditioning agents with respect to hair combing forces and hair gloss. In AFM a sharp silicon or silicon nitride crystal tip is mounted onto a cantilever and moves mechanically over the sample. The deﬂection of the tip is measured by a laser system [120]. AFM is a technique used to investigate surfaces treated with different hair care products like hair rinses, for example. Using this technique, conditioning formulations containing, e.g., waxes, glycerides, or silicones can be differentiated in their surface inﬂuencing properties. 7. Oscillation Properties of Hair The appearance and the bounce of hair is determined by oscillation processes [118]. The causative physical phenomena for oscillation are highly sophisticated and are based on several aspects, such as • • • •

Bounce of separate areas of hair Bending and torsion processes Dynamic-rhythmic behavior of hair style Alteration of the hair style by humidity

An exact objective description of such complex terms using physical parameters is almost impossible. Simple models can quantify aspects of these complex terms. One possibility is to ﬁx a curl at the measuring head of a tensile strength device. A beam moves along the curl and creates an attenuated oscillation of the curl. It is possible to determine the following physical parameters using computerized testing equipment: elongation work, O-amplitude, frequency, and attenuation. These parameters depend on selected conditions such as humidity, type of hair, and the size of the curl and are sensitive to hair treatments. For example, cold wave formulations have a decisive inﬂuence on the oscillating behavior of the hair.

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Personal Care Formulations

247

8. Hair Gloss Hair gloss or shine is considered to be a desired property of hair, as it implies health and beauty. The optical reﬂection occurs when a beam of light falls on the surface [119,121]. The beam may be either reﬂected, absorbed, scattered, or combined. The correlation of objective hair gloss measurement with the subjective observations of the consumer is very often problematic because gloss is a complex term, of a holistic nature for the consumer. The hair ﬁber or tress of hair is illuminated under the deﬁned angle (between 20˚ and 85˚). The reﬂected light is detected by the photodetector. The detection angle may be ﬁxed (adjusted by diaphragm) or it may vary between –90˚ and +90˚. Light polarization enables a better distinction between the specular and diffuse reﬂection. The gloss increases with increasing specular reﬂection and decreases with increased diffuse scattering. B. Foam In many areas of application where surfactant-based products are marketed, the precise adjustment of a required foam characteristic during application is extremely important. Especially in the ﬁelds of skin and hair care products, the foaming performance of the product is tailored to achieve a positive sensory perception by the consumer. A multitude of publications focus on parameters like foam volume and foam stability. Based on profound knowledge from both theory and experiments, foam volumes and foam stabilities can be adjusted to meet the actual requirements of the products. In addition to the foam beating method according to DIN 53902 and the Ross-Miles method, there are further possibilities for examining foam. The Rotor-Foam test has been especially designed for a quick and reliable assessment of the foam kinetics of test solutions [122]. The solution is thermostated in a cylindrical 2-l vessel with a water jacket. A stirrer with a rotating disk at the bottom end of the stirring rod is immersed. The disk is modiﬁed in order to maximize the amount of foam generated. The revolutions per minute (rpm) of the stirrer can be set precisely and controlled via an optical display. With this commercially available equipment (Company: Sita), a maximum of about 1200 ml of foam can be produced. In addition to these objective foam methods, subjective test methods are also available. The so-called sensory assessment has been developed for the subjective evaluation of surfactant-based products. This involves parameters that can be perceived by tactile and visual means [123] (Fig. 20). The data obtained can be correlated to objective measurements or evaluations from the so-called half-head test. During the sensory assessment of the ﬂash foam, both hands are wet with warm water (38˚C) before the test. A total of 0.5 g of the product is placed in the palm of the hand together with 2.5 g water. The test candidate is asked to start washing by moving the other hand lightly over the area where the product has been applied at a frequency of two movements/sec for 10 seconds. After that, 2.5 g of water is applied and the procedure is repeated for another 10 seconds. The speed of foam formation is evaluated in comparison to the benchmark product. The foam can also be evaluated according to bubble size, stability, ﬂuidity, etc.

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Distribution Flash Foam Foam Bubble Size Foam Stability Smoothness of the Skin Slipperiness Amount of Foam Creaminess Foam Cushion Skin Dryness

Figure 20

Sensory assessment parameters for surfactant-based cleansing products.

The half-head test is a common foam test for shampoo applications. It is a one-toone comparison of a newly developed shampoo with a reference product under normal conditions. The two products are applied on either one of the two sides of the head of a test person respectively. Standard parameters such as foam kinetics (ﬂash foam), the feel of the foam as well as the feel of the wet and dry hair, the visual appearance and the rinsing characteristics of the foam are evaluated by a group of experts. C. Cleansing Effects Cleansing power is generally important for surfactant-based cleansing products and particularly for special cosmetic formulations, such as facial wash formulas or makeup removers. One factor that contributes to cleansing performance is the strong solubilizing effect of a surfactant combination.

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γ (mN/m) 12 10 8

C8G1 C12G1

C10G1

6 4 2 0.1

1

10

40

Concentration (mmol/l)

Figure 21 Inﬂuence of alkyl polyglycosides (CnG1) on decane/water interfacial tension. Equilibrium values of the interfacial tension as a function of the initial concentration of the surfactant in the water phase.

This can be achieved by using surfactant systems which demonstrate low interfacial tension. The interfacial tension of surfactant solutions with respect to oils can be measured using various methods. If the values are very low, a spinning drop tensiometer is normally used. The interfacial tensions between various alkyl polyglycosides and decane at 60˚C depending on the surfactant concentration is illustrated in Fig. 21. As expected, the C12 alkyl polyglycosides exhibited the lowest interfacial tension in this example. The C12 alkyl polyglycoside possesses the strongest emulsifying power in this product series. A more practice-oriented test for determining the cleansing power of surfactants can be done using isolated pig epidermis as a substrate. A combination of microscopy and digital image analysis can be used to demonstrate the deep pore cleansing power of alkyl polyglycosides in comparison to standard fatty alcohol ether sulfate (Fig. 22). D. Testing Methods for the Skin Several methods are available for achieving a quantitative determination of the different functions of the skin, consistently with the skin’s multifunctional task. Some of these methods are widely used in dermatology, whereas others are especially adapted for evaluating cosmetic effects. 1. Skin Surface Properties One of the major properties of a cosmetic formulation, in addition to its moisturizing effect, undoubtedly lies in the formulation’s ability to have a positive effect on the surface structure of the skin. Topometric tests are often based on the replica technique. A replica of the skin is ﬁrst prepared using a self-aging silicone compound. The resulting skin replica is then measured using mechanical-electronical devices. A diamond, which is mounted on a cantilever, moves along the replica. The resulting upstroke of the diamond tip is converted into electrical voltage via inductive measuring equipment [124]. The measured amplitudes are proportional to the ups and downs of the replica. Using this technique, it is possible to determine 20 different parameters, such as the medium skin surface roughness, the maximum skin surface roughness, the depth of the lines, and the number of peaks depending on the section of measurements.

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Treated with soil

Washed with SLES 3% active

Figure 22

Washed with water

Washed with Lauryl Glucoside 3% active

Cleansing properties of alkyl polyglycosides on the skin.

500 µm (A)

Figure 23

500 µm (B)

Topographies of young (A) and old (B) skin.

Laser beam–assisted systems can be used instead of mechanical sensors. Special devices used in conjunction with advanced software can provide three-dimensional illustrations of the skin topography. This technique makes it possible to visualize skin performance depending on age (Fig. 23). Young skin shows a strong network of ﬁne skin lines. With increasing age the amount of ﬁne lines reduces and deeper skin wrinkles appear with a parallel orientation to each other. The most widespread of these methods are deﬁnitely image analysis, mechanical scanning of replicas, and digitization by means of touch-free laser proﬁlometry as mentioned above.

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Difference (% from starting conditions)

3 Shower bath without lipid layer enhancer

2 1

Area untreated

0 −1

Shower bath with 3% Lamesoft PO 65

−2 pre-conditioning

day 1 Measurement 4 h

Figure 24

day 21

day 22

24 h After the last treatment

FOITS/skin surface structure [Rz]; washing of forearms, 30 persons.

What all these methods have in common is that topometric analysis is divided into two parts—a replica phase and a time-consuming analysis phase. The fast optical in vivo topometry of human skin (FOITS) technique provides a new approach to measuring the skin surface. This touch-free technique allows three-dimensional information to be gathered from the surface of the skin in an extremely short time (less than one second) [125]. The new touch and replica-free FOITS technique enables extensive new test designs to be conceived that accompany conventional use-tests involving measurements before the ﬁrst and after the last application of a product. The positive inﬂuence of a lipid layer enhancer (e.g., Lamesoft® PO 65)—as a component of a shower gel—on the skin surface structure is shown in Fig. 24. In addition to this mathematical analysis, FOITS also enables video images to be linked directly to the mathematical information. 2. Spreading Behavior of Cosmetics An important feature of cosmetics is the spreading behavior of products like oils, alone or as part of an emulsion, on the skin. The spreading characteristics of the oily ingredients determine the distribution properties of the cosmetic formulation. An eye creme should not run to avoid eye irritation. A body lotion should possess a high spreadability to achieve a homogeneous distribution of the cosmetic onto the skin. The rate of spreading depends on the interfacial tension between the oil and the skin on the one hand, and on the molecular structure, the viscosities and relative molecular weight of the oils on the other. A further decisive factor is the constitution of the skin, e.g., the surface texture. This is one reason why individual cosmetic formulations are developed for different skin types. In the laboratory, the spreading rate of cosmetic oil can be determined precisely using an impression method. A small amount of the oil is placed on the inside of the forearm according to a standardized procedure. After an application time of 10 minutes, an impression is taken from the area of application using a transparent paper [126]. The area of application imprint on the transparent paper is then measured by image analysis (Fig. 25).

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Reference oil (V) Test substance (T)

S* = FV*

FT FV

Spreading area (F)

(mm2)

Figure 25 Determination of spreading values S* of oily components (V = reference oil, T = test substance, V* = mean value of V, F = spreading area).

Smoothness

Quick

Slow Time

Figure 26

Inﬂuence of quick- and slow-spreading oils on smoothness.

The spreadability of an emollient or emollient system is often decisive for the consumer acceptance of a product. It has been demonstrated that fast-spreading emollients, those with high spreading values, result in a distinct initial feeling of lubricity which quickly diminishes. Conversely, slow-spreading emollients, those with low spreading values, exhibit a much lower lubricity. However, this lubricous feeling lasts much longer. The fast-spreading emollient initially delivers great lubricity, but wears off rapidly leaving only the sensation of the slow-spreading emollient. This can be seen in Fig. 26. This sharp gradient in lubricity is perceived as an unﬁnished nonelegant product. The cascading emollient effect and gradual lubricity gradient are produced by combining fast-, medium-, and slow-spreading emollients. Very often, several medium-spreading emollients with different spreading values are combined to produce a perfect gradient (see Fig. 27). When emollients are combined in this manner, the lubricity of the fast-spreading emollient is experienced ﬁrst [127]. Then, there is a gradual transition toward the sensation

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Smoothness Quick

Medium

Slow

Time

Figure 27

Spreading cascade of oils.

of medium-spreading emollients, and ﬁnally, the transition to the long-lasting effect of the slow-spreading emollients. The overall sensation of this cascading effect is one of completeness. 3. Mechanical Properties Cosmetics are used by consumers among other things as a way of keeping their skin young and elastic. Skin elasticity is equated with resilience, youthfulness and vitality. These rather subjective judgments are difﬁcult to assess objectively, but some aspects of elasticity can nevertheless be quantiﬁed. The levarometric method (cutometer) uses a vacuum to raise a few millimeters of the outer skin and then allows it to return to its original state [128]. The force needed to extend the skin together with its hysteresis characteristics are directly related to the skin cell turgor. Young, ﬁrm skin, in which the epidermis and dermis are still tightly interlaced, offers high resistance to the vacuum. Its elasticity, that is, the ability of the raised skin to return to its original state, is very high. Another method, ballistometry, assesses the skin’s elasticity by means of a suspended diamond hemisphere. The diamond is attached to the end of a thin pendulum. On being released from its resting position, the diamond swings toward the skin, penetrating a certain distance on contact. The diamond will rebound to a greater or lesser extent depending on the elasticity of the skin. At the one extreme, if the skin is completely inelastic, the diamond will immediately come to a complete stop. If the skin is as taut as a drum, the diamond will rebound virtually undisturbed. Both of these methods displace several layers of skin and the effect of the extremely thin stratum corneum hardly comes into play at all. The torsion method is useful for investigating this layer alone [129]. This method has become a generally-accepted practice in skin cosmetology and dermatology [130,131]. The method consists of twisting the skin to a certain extent and then allowing it return to its initial state. The required torsional force (torque), angular displacement and elapsed time are used to quantify the elasticity of the outer skin layers, in which the stratum corneum plays an important role.

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The outer skin surface is ﬁrmly attached to the torsion-measuring device by dots of adhesive—in this way, only the twisting of the outermost skin layers is assessed. If direct adhesion is dispensed with, torsional angles—although only small ones—can be still be recorded via frictional adhesion; furthermore, the transition from adhesion to the point of release can also quantiﬁed by means of a sensor. The inﬂuence of lipid layer enhancers (e.g., Lamesoft® PO 65) applied in surfactant systems on skin smoothness can be demonstrated using this methodology. As seen in Fig. 28, lipid layer enhancers reduce or counteract the skin-hardening effect of surfactants. 4. Sensory Properties/Sensory Assessment Cosmetics are intended to care for, clean, and beautify the exterior of the human body. The interactions of the cosmetic product with the body can be measured in many cases using physical or physicochemical instruments. In compliance with the limiting factors, the results are precise and can be easily communicated between different people. The problem with many physical or physicochemical results is the fact that they lack relevance in practice. For example, transepidermal water loss (TEWL) values may be very exact. The consumer, however, is not able to experience the impact of those results immediately. There is no sensory organ that directly tells about the barrier properties of the upper layer of the skin. Another possibility of gaining insight into cosmetic effects are subjective experiences or by running a sensory assessment [123]. The subjective assessment is based on psychological and linguistic aspects. As a ﬁrst step, descriptive terms must be generated. They are clustered and arranged using appropriate generic terms. The 10 most important parameters for the evaluation of skin care products are pickup, consistency, peaking, cushion, distribution, adsorption, smoothness, thickness, oiliness, and waxiness. These parameters can be quantiﬁed by special comparison tests whereby a test kit allows the products to be sorted in ranking order. The sensory assessment is economical, practice-relevant, and surprisingly precise and reproducible for a subjective test device. It is possible to draw sensory proﬁles using this technique. The sensory assessment is a useful tool for product and concept development and for describing and evaluating the performance proﬁles of cosmetics.

Angle of torsion %-change (treated-untreated/untreated)

Significance: 95%

0 (b) −10

−20

−30

(a)

Figure 28 Inﬂuence of lipid layer enhancers on skin smoothness; 10% active substance of sodium laureth sulfate without lipid layer enhancer (A) and with 5% of lipid layer enhancer (Lamesoft ® PO 65) (B). Torque measurements are carried out by using an in vitro skin model.

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Skin Moisture a. Transepidermal Water Loss / Skin Barrier. The most important task of the skin is to function as a barrier for the body to avoid the penetration and the loss of substances [124]. The efﬁcacy of the barrier function can be checked by the determination of the TEWL. This refers to the evaporation of water from the interior of the body, not including the water lost through perspiration. The evaporimeter, a convenient measuring device for determining the TEWL, has been available since 1977. The probe head of the evaporimeter consists of a Teﬂon tube with two temperature and humidity sensors, which are positioned a short distance apart from each other. The microclimate above the skin remains practically undisturbed by the measuring probe head because this tube is open at the top and is therefore an open system. Both pairs of sensors determine the gradient of vapor pressure of the skin within the diffusion region between the pair of sensors. Water loss (in grams) can be calculated per square meter and time (in hours) on the basis of the values measured. The determination of TEWL values is extremely valuable for the diagnosis of cracked and chapped skin, for the evaluation of the skin compatibility of surfactants with different chemical structures and for the determination of the occlusivity of, e.g., Vaseline® and night cremes. The TEWL value of dark-skinned humans is higher than that of humans with fair skin. The increased evaporation is advantageous for regulating body temperature. The TEWL values are almost the same for females and males and do not change greatly with age. b. Corneometer/Magnetic Resonance Imaging. The moisture content of the thin stratum corneum is of great importance for the appearance and the well-being of the skin. The skin moisture can be positively inﬂuenced to a small extent if moisturizing regulators are applied. Skin hydration is normally measured using the capacitance method with a corneometer [132]. The corneometer consists of a plastic casing and a sensor, also referred to as the measuring head. On the display panel of the casing, the measured value is represented as a max. three-digit ﬁgure. The measuring head has a cylindrical shape. The measuring principle requires an even positioning of the front face under a constant pressure level. The inner movable part – the active front face – is pressed against the skin using a spring. The mode of operation of the corneometer is based on changes in electrical capacitance that are caused by the differences in water content in the volume to be measured. The front face of the measuring head is a ﬂat capacitor in the volume to be measured, against which the skin surface is placed. Measuring results can be inﬂuenced by the following factors: Uneven positioning, measurement during or directly after emotional stress or physical strain, presence of conducting substances on the skin or measurement in a room of high humidity. Nowadays, the more sophisticated method of magnetic resonance imaging (MRI) is used to determine skin moisture. The MRI is an in vivo measurement, which can be carried out on the forearm of the test candidate. This method allows for a quantitative measurement of the skin moisture. An increase in the epidermis relaxation time, T2, corresponds to the skin hydration [133]. At present, it is not possible to differentiate between the moisture content of the corneocytes and the intercellular regions. Furthermore, the signiﬁcance of free water is

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not well established. Water is very tightly linked, and there is also water which is almost free. It is not clear how the water composition changes with increasing age. Little is known about the water content of the dermis and how it can be determined exactly. It is known that the dermis of an elderly person contains strongly cross-linked collagen ﬁbers which do not link with water as well as the dermis of a young person. 6. Skin Surface Lipids Skin lipids are divided into two categories. Internal lipids play an important role for the efﬁcacy of the barrier function of the epidermis [134]. Skin surface lipids primarily consist of a mixture of lipids produced by the sebaceous glands, water, and eliminated corneocytes. As a result, skin surface lipids are not a uniformly-composed substance. Their composition varies from person to person and the amount of skin surface lipids is different for each part of the body. Skin surface lipids can be determined using various methods. One is the Sebumeter method. The Sebumeter measures the normal/average lipid level on the skin by adsorbing it into a turbid plastic ﬁlm and measuring its transparency with a photometer. The transparency is proportional to the lipid quantity. The operation procedure is simple and is widely used in practice. Sebum production is low during childhood, increases during puberty and decreases again in later years. The sebum production of the glands is strongly dependent on the sex. An additional method for the evaluation of the sebum production is the so-called Sebutape method. Sebutape is a special adhesive tape containing several small cavities. When the tape is applied to the skin, the sebum is collected in these micropores and can be evaluated using image analysis. The Sebutape method is more accurate than the Sebumeter method and can be used on different areas of the face—e.g., on the nose, chin, or forehead. Therefore, it is possible to differentiate between normal, oily, and mixed skin using this method. 7. Skin Surface pH Numerous studies have conﬁrmed the acidic nature of the human skin surface. The normal distribution of skin surface pH on the foreheads and cheeks of adults was recently described by Zlotogorski in an extensive study of men and women [135]. No difference was found between men and women regarding forehead and cheek pH distribution. The normal pHrange for the population is 4.0 to 5.5 on the forehead and 4.2 to 5.9 on the cheek. The pH values become more alkaline for people over 80. Any commercial portable pH meter can be used for this assessment. A planar electrode, which combines glass and reference electrodes in one single probe, is connected to the meter. It is necessary to use a planar electrode in order to maintain good contact with the skin. An accurate measurement can be assured if the following guidelines are followed. Place one or two drops of distilled water on the planar surface of the electrode and dry the surface with a ﬁlter paper. The electrode is attached to the skin for at least 10s until the reading has stabilized. The electrode should always remain wet. The preferred storage solution is a pH 4.0 buffer with 1/100 parts of saturated potassium chloride. The pH meter is calibrated daily before use with standard solutions of pH 4.0 and 7.0. Sweat can inﬂuence the reading, so measurements are only performed below 23˚C and at a relative humidity below 65%. Any cosmetics applied to the skin can also change the results. Readings should be taken at least 12 hours after cosmetic products have been applied [136].

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Until now no disease has been associated with an increase or decrease in skin surface pH. However, several observations support the need to maintain the skin surface pH within the normal representative range. Elderly people around the age of 80 possess a skin with a more alkaline pH. Alkaline skin exhibits an increased propionibacterial count and an increased severity of irritant dermatitis [137]. Lactic acid seems to be the most reasonable source of the acidic pH value of the human skin, but this remains to be conﬁrmed.

V. TRADEMARKS APG®, Emulgade®, Lamesoft®, Myritol®, Plantacare® are registered trademarks of Cognis.

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105. Garcia-Anton, A Nieto, A Del Pozo. Plurilamellar Multivesicular Liposomes: Methodology and Cosmetic Application. In: Fact and Illusions in Cosmetics, IFSCC Congress, Montreaux, 1995, pp. 249–255. 106. K Stanzl. In: S Magdassi, E Touitou, eds. Novel Cosmetic Delivery Systems. New York: Marcel Dekker, 1999, pp. 252–253. 107. MG Ganesan, ND Weiner, GL Flynn, HFH Ho. Int J Pharm 20:139–154, 1984. 108. VM Knepp, FC Szika, RH Guy. J Control Rel 12:25–30, 1990. 109. M Mezei. Life Sci 26:1473–1477, 1980. 110. S Magdassi, Y Vinetsky. J Microencaps 12:537, 1995. 111. Y Vinetsky, S Magdassi. Colloid Surface A 122:227, 1997. 112. K Kiyama, H Yamamoto, H Nakano, A Kiyomiya. J Soc Cosmet Chem Jpn 29:258, 1995. 113. Y Watanabe, M Hayashi. In: JR Nixon, ed. Microencapsulation, Vol. 3. New York: Marcel Dekker, 1978, pp. 14. 114. U Zeidler. Fette, Seifen, Anstrichm 87:403, 1985. 115. A Ansmann, R Kawa, E Prat, A Wadle. SÖFW-Journal 120:158, 1994. 116. M Weuthen, R Kawa, K Hill, A Ansmann. Fat Sci Technol 97:209, 1995. 117. CR Robbins. Chemical and Physical Behavior of Human Hair. New York: Van Nostrand Reinhold Company, 1978. 118. P Busch. Ärzt. Kosmetol 19:270315, 1989. 119. G Pauly. Nancy: Laboratoires Sérobiologiques, personal communication, 2000. 120. L Kintrup, H Hensen, W Seipel, HJ Schwark, H Waschipky, Proceedings, XXI IFSCC International Congress 2000, Berlin, Poster 28. 121. T Maeda, M Okada, T Hara. Cosm Toil 107:53–59, 1992. 122. Th Engels, H Hensen, J Kahre, H Tesmann, W v. Rybinsky. SÖFW-Journal 126 (3):19–23, 2000. 123. P Busch, T Gassenmeier. Parfümerie und Kosmetik 78:16-21, 1997. 124. W Umbach. Kosmetik. Georg Thieme Verlag, Stuttgart, New York, 1995. 125. M Rohr, K Schrader. SÖFW-Journal (Sonderdruck) 3–8, 1998. 126. U Zeidler. Fette Seifen Anstrichmittel 87:403–408, 1985. 127. A Ansmann, R Kawa, E Prat, A Wadle. SÖFW-Journal 120 (4):158–161, 1994. 128. I Serup. Handbook of Non-Invasive Methods and the Skin. CRC Press, 335–340, 1995. 129. W Both, P Busch. SÖFW-Journal 124 (4):182–195, 1998. 130. DC Vlasblohm. Skin elasticity. Thesis, Utrecht, 1967. 131. DC Salter. J Cosm Sci 15:200–218, 1993. 132. R Bimczok, A Ansmann, S Bielfeldt, D Billek, H Diller, G Feiskorn, et al. J Soc Cosmet Chem 45:1-19, 1994. 133. F Franconi, S Akoka, Y Guesnet, JM Baret, D Dersigny, B Breda, C Muller, P Beau. Br J Dermatol 132:913–917, 1995. 134. M Nazzaro-Porro, S Passi, L Boniforti, F Belisto. J Invest Dermatol 73:112–117, 1979. 135. A Zlotogorski. Arch Dermatol Res 279:398–401, 1987. 136. R Bechor, A Zlotogorski, S Dikstein. J Appl Cosmetol 6:123–128, 1988. 137. HCh Korting, K Hübner, K Greiner, G Hamm, O Braun Falco. Acta Derm Venereol 70:429–457, 1990.

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8 Special Purpose Cleaning Formulations: Auto Care and Industrial/Institutional Products Felix Mueller, Jörg Peggau, and Shoaib Arif

CONTENTS I. II.

Introduction ........................................................................................................... 262 Auto Care .............................................................................................................. 262 A. Manual Car Wash ...................................................................................... 262 B. Automatic Prewash/Main Wash ................................................................ 262 1. Main Car Wash (Brush Wash or Touchless) ............................. 263 C. Rinse/Drying Aids ..................................................................................... 265 D. Exterior Car Care Agents/Polishes ........................................................... 267 E. Interior Car Care/Leather Care ................................................................. 268 F. Rim/Tire Care............................................................................................ 269 G. Glass/Windshield Cleansing...................................................................... 269 III. Industrial and Institutional Products for Special Purposes ................................. 270 A. Gel Cleansing Products............................................................................. 270 B. Quick Dry Floor Cleansers ....................................................................... 271 C. Nanostructured Floor Tile Cleansing........................................................ 272 D. Odor Control Products .............................................................................. 272 E. Water-Based Steel Cleaner........................................................................ 273 F. Glass Cleaning........................................................................................... 275 G. Sugar-Based Surfactants for CIP .............................................................. 275 H. Cleaning with Natural Raw Materials ...................................................... 276 IV. Conclusion............................................................................................................. 276 References ....................................................................................................................... 277

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I. INTRODUCTION The number of formulations used for specialty cleaners has been growing in the last decade for several reasons. New materials demanded new cleaning solutions; the pressure to fulfill a cleaning job in the minimum amount of time increased dramatically; and many general purpose formulas were phased out and replaced with a variety of dedicated products. In addition there was a new demand for problem solving in areas like odor control, and a desire to have products with an acceptable ecological profile. Whereas the basic principles of cleaning are not affected by this, thus keeping the dominance of anionic and nonionic surfactants in standard main cleanser products, the special effects demanded now are only to be solved by specialized products which are often tailor made and in their use complex and sometimes restrictive [1–4]. The need for a formulation strategy is evident. In this chapter we examine in depth the topic of car care, showing formulations and recommendations for this highly specialized area. We describe specialized cleaning systems for industrial and institutional applications, which are examples of the possibilities of modern special surfactants, and additives, which can be used for a lot of problem solving. As part of this, formulations based on modern ecologically acceptable raw materials are discussed, because they have attracted more attention now.

II. AUTO CARE In auto care, the complex system of the “car” creates the need for a lot of specialty cleaning systems and care agents which depend on automatic or manual use, and also on the national legislation and use practices of the countries. Here we can give only a small overview, for a current review on the situation in the United States, see [5]. A. Manual Car Wash Liquid manual car wash products are a blend of surfactants, builders, and solvents dissolved in water. The economical versions of car wash soaps are made with anionic and nonionic surfactants and some contain carbonates and/or chelating agents dissolved in water. The cleaning performance of the main anionics linear alkyl benzene sulfonate (LAS), sodium lauryl ether sulfate (SLES), and sodium alkyl sulfate (SAS) can be enhanced by adding co-surfactants. Typical, easy-to-use, co-surfactants are cocamidopropyl betaines, amine oxides, hydroxysultaines, and amphopropionates. Mostly they reduce the irritation level on the skin of the most aggressive anionics. These co-surfactants also minimize the influence of water hardeners. The depicted formulations (Table 1) are based on anionic surfactants, which are enhanced by co-surfactants ratio in the range of 15% of the active material. The various builder systems depend on each locality’s different legal requirements. Phosphates showed the best results, but have some environmental disadvantages. The amphoterics in the formulations stabilize the foam and enhance the corrosion inhibition of the formulation. They will be cost effective formulations, when prices per weight are calculated. B. Automatic Prewash/Main Wash Automatic car wash is divided into two categories. • Portal car wash • Tunnel car wash

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Special Purpose Cleaning Formulations Table 1

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Manual Car Shampoos

Car Shampoo with EDTA Sodium alkylbenzene sulfonate, 40% Sodium lauryl ether sulfate, 28% Cocamidopropyl hydroxysultaine, 50% Sodium carbonate Sodium metasilicate EDTA, 87% Water to 100%

20.0% 10.0% 5.0% 2.0% 3.0% 1.0%

Car Shampoo with Phosphates Sodium alkylbenzene sulfonate, 40% Sodium lauryl ether sulfate, 28% Disodium coco amphopropionate, 40% Potassium tripolyphosphate, 50% Sodium metasilicate Water to 100%

20.0% 10.0% 5.0% 2.0% 3.0%

Note: EDTA = ethylenediaminetetraacetate.

Generally speaking, the cleaning process uses the same chemistry and the same steps of technology: Presoaker—Car Shampoo—Rim and Underfloor cleaning—Blower drying. Presoaks are most often used by detailers in general. A good presoak will loosen the dirt, grease and traffic film from the car surface and make the car ready for the car washing soap. The presoak is applied to the car and allowed to work for a short time. It may or may not be rinsed before applying the car wash soap to remove the traffic film prior to the remainder of the cleaning process. A standard presoak formula will contain good builders, surfactants with excellent wetting and penetrating properties and perhaps some solvents like glycol ethers. The pH value is adjusted at pH 9 to 12. Most presoak formulas are high pH and contain fair amounts of electrolytes such as phosphates, carbonates, silicates etc. The surfactants suitable for this application must meet two important requirements. They must be stable at high pH values as well as in high electrolyte environments. Most amphoterics are good in alkali stability. In fact, amphoterics are stable in alkaline as well as acidic solutions. Ethoxylated amines, amine oxides, or hydroxy sultaines are also good examples of the surfactants that can be used in the presence of electrolytes as well as in high and low pH applications (Table 2). 1. Main Car Wash (Brush Wash or Touchless) Car wash soaps are designed for : • • • • • •

High initial foam, reduced foam after usage Cutting through the traffic film on the car Removing dirt, grease, and grime Easy rinseability No damage to paint or car surface Biodegradable components

Car wash soaps can be formulated as powders or liquids. Powders are a mixture of builders like phosphates, carbonates, silicates, etc. blended in a ribbon blender, and surfactants like dodecyl benzenesulfonic acid (DDBSA) and nonylphenol ethoxylate 9EO (NP-9) adsorbed onto the powder. Liquid car wash soaps are a blend of surfactants, builders and solvents

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Table 2

Presoaker Formulations

Presoaker, Active Foam Sodium laurylsuccinate, 40% Cocamidopropylbetaine, 47% NTA, 92% Sodium hydroxide, 50% Water to 100%

Presoaker, Cost Effective 0.6% 12.0% 10.0% 4.0%

Disodium cocoampho propionate, 40% NTA, 92% Sodium carbonate 2-Butoxylethanol Sodium metasilicate Water to 100%

3.0% 3.0% 2.0% 4.0% 2.0%

Presoaker, concentrated Propylene glycol Monoethanolamine Sodium ethyl hexyl sulfate, 40% Ethylene diamine triacetate cocosalkyl acetamide, 40% Sodium caprylampho propionate, 50% Water to 100%

5.0% 15.0% 15.0% 5.0% 15.0%

dissolved in water. If a creamy, dense foam is desired then amphoterics like cocamidopropyl betaine can be added. For foam stability and viscosity building an amide or amine oxide can be used. Low foaming surfactants derived from short-alkyl chain materials of the above listed products have shown interesting results. These low foaming surfactant systems show a high initial foam which will be reduced after a few seconds. The cleaning effect on the car is comparable to common systems while decreasing the foam formation after usage making rinsing easier [6–8]. The bulk of the surfactant system used in a car wash soap is anionic, due mainly to its lower cost. The most commonly used surfactant systems are a combination of LAS and SLES. The following surfactants are used to enhance the cleaning effectiveness of this basic surfactant system and other anionic systems: Amphoterics • Betaines • Glycinates • Sultaines Nonionics • Amine oxides • Amides Depicted formulas (Table 3) are for use in an automatic car wash. Moderate foam and high dirt carrying capacity have led us to select these formulas. All selected raw materials will not interfere with the later drying aids. The nonuse of anionic surfactants prevents

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Special Purpose Cleaning Formulations Table 3

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Car Shampoos for Automatic Use

Car Shampoo NTA, 92% Capryl/capramidopropyl betaine, 38% Decaminoxide, 30% Decylethoxylate/butoxylate Water to 100%

Car Shampoo 8.0% 19.7% 12.5% 3.8%

NTA, 92% Laureth-10 Capryl/capramidopropyl betaine, 38% Water to 100%

8.0% 10.0% 11.5%

Note: NTA = nitrile triacetate

building of bacteria smell in the recycling waste water systems. A high dosage of chelating agents is used to remove the remaining traffic film. C. Rinse/Drying Aids The mode of action of drying aids is that they form a thin, almost invisible, layer of quat and mineral seal oil or ester oil on the car surface. The quat molecules have the tendency to attach themselves to the surface and they take the mineral seal oil with them. Together they form an efficient hydrophobic layer. When water comes in contact with this layer, it immediately gets repelled and forced to stick together rather than sticking to the car surface. That is what makes water bead off. Nonionic surfactants are sometimes used along with the quat to form a microemulsion. Nonionic surfactants like nonylphenol ethoxylates or alcohol ethoxylates can be used, but the disadvantage is that they can reduce the beading effect. Nonionics like ethoxylated amines are more compatible with quats due to a pseudo positive charge on the nitrogen in ethoxylated amines. All of our test results point to the fact that ethoxylated amines work much better than other nonionics in this application (Table 4). The use of a cationic surfactant after an anionic cleaning process is standard through the whole spectrum of the car care industry. For very quick processes, where the rinse aid has to work within a few seconds, this is a major problem. This fact leads to the application of cationic surfactants as a rinse aid and additive in car cleaning. We have depicted various formulations which are used in different areas around the world. Different regulations create the basis of the rinse aid formulations.

Table 4

Hydrophilic Rinse Aids Rinse Aid

Decylethoxylate/butoxylate Sodium ethyl hexyl sulfate, 40% Propylene glycol Water to 100%

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Rinse Aid 20.0% 2.0% 2.0%

Decylethoxylate/butoxylate Propylene glycol Decaminoxide, 30% Citric acid monohydrate Water to 100%

10.0% 2.0% 10.0% 5.0%

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Typical formulations for the European Union (EU) market are ester oil or glycol based systems. Here esterquats and imidazolinium compounds are used to enhance in the first step of activity the penetration onto the surface. Additional beading and sheeting can be enhanced by usage of amides, silicones, or waxes (Table 5). On large surfaces found on vans, buses or trains, blowers are usually not used to speed drying. A drying aid for these surfaces could be a hydrophile or hydrophobe. Both effects can be used to shorten the drying time on vehicles. The hydrophilic effect uses the good spreading ability of surfactants. Only a thin layer of water will be left on the surface that dries very fast, leaving a nonstreaky surface. This prevents formation of stains caused by the drying of the drops from the last rinse water. The hydrophobe effect uses the same system that is used in the blower drying operation. When the vehicle is moved, the airstream will dry the vehicle automatically. This procedure creates more gloss than the hydrophilic system. If the remaining water dries unevenly on the surface, it could create white visible spots. Therefore exacting formulation work has to be carried out to avoid this. Acidic systems are easier to rinse than neutral systems. In the United States, rinse aids are based on dicocoquats. The dicocoquat forms a crystal clear microemulsion of the mineral seal oil in water. For the ester oil based systems esterquats or imidazolinium quats are used. Both form microemulsions which can be diluted indefinitely without losing the clarity. Transparency of the product is a very important property, not only in appealing to the eye, but also in relation to the performance of the product. In order for the product to work its best, the microemulsion must have a certain particle size. If the product is hazy or cloudy, the particle size is not optimum and thus the performance will not be the best. If a mixture of coconut and soya or other product

Table 5

Rinse/Drying Aids

Rinse/Drying Aid, Acidic Dioleic acid isopropylester dimethyl ammonium methosulfate 1-Hydroxyethyl-2-heptadecenyl imidazoline Laureth-3 Butyl diglycol Isopropanol Acetic acid Water to 100%

Rinse/Drying Aid, Acidic

7.5% 10.0% 1.5% 4.0% 10.0% 3.0%

Rinse/Drying Aid, neutral (U.S. type) Dicoco quat PEG-5-cocoamine 2-Butoxyethanol Methyl soyate Water to 100%

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20.0% 5.0% 6.0% 25.0%

Dioleic acid isopropylester dimethyl ammonium methosulfate 1-Methyl-2-noroleyl-3oleic acid aminoethyl imidazolinium methosulfate, 90% Ethylhexyl palmitate PEG-30 Glyceryl cocoate butyl diglycol Dipropylenglycol methyl ether Isopropanol Water to 100%

5.0%

10.0% 5.0% 15.0% 11.0% 2.0%

Special Purpose Cleaning Formulations

267

with higher alkyl chain is used, when making the quat, the performance will not be optimum. Most rinse aids are formulated at slightly acidic pH values, therefore noncorrosive materials or corrosion inhibitors should be used. With the imidazolines we can enhance the rinsing properties and the corrosion inhibition on the surfaces and equipment used in automatic car washes. If better shine and more protection are required, addition of real wax could help to enhance this effect. To meet different environmental requirements, more and more European formulations that are based on ester- and imidazolinequats in combination with glycols and esteroils are being introduced. These kinds of formulations show excellent performance which can be further improved by using special silicones and silicone derivatives. For more sheeting and beading, the use of cationic silicone compounds like silicone quats enhance the effectiveness and create more gloss after drying. One to three percent of the siliconequat can be added to the standard formulation. [9,10] D. Exterior Car Care Agents/Polishes Silicone oils, especially polydimethylsiloxanes and aminosiloxanes, have been in use in all kinds of polishes for decades. They are common ingredients in car, furniture, and shoe polish for use in household and industrial applications. Despite this, the use of silicone surfactants is still not as well established in polish product formulations and not nearly as well in cleaning systems. Silicone surfactants in this context are silicones modified with polar groups such as polyethers, quaternary, anionic or amphoteric groups, as well as silicone emulsifiers with hydrophilic polyether and hydrophobic alkyl chain moiety. As silicones and aminosiloxanes are not directly water soluble or dispersible, they have to be emulsified to cope with users’ needs in aqueous systems. The derivation of silicones with functional groups like polyethers is leading to silicone surfactants. These can be incorporated into water or work as emulsifiers and solubilizers on their own. The most important silicone surfactant is the polyether siloxane. In a good car polish, for achieving a longlasting gloss, which is detergent resistant for several washings, it is recommended to use an aminosiloxane. This is usually formulated as oil in water emulsion with emulsifier, thickener, and abrasive and other ingredients (Table 6). For the convenience of the production as well as for the improvement of product performance the use of a self-emulsifying aminosiloxane is interesting. It is a clear

Table 6

Rinse/Drying Aids with Silicone Quat

Rinse/Drying Aid, Premium Silicone quat Coco DEA Oleic acid DEA Cyclomethicone Dimethicone copolyol Propylene glycol Water to 100%

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Rinse/Drying Aid, Premium U.S. type 3.0% 3.0% 3.0% 6.0% 3.0% 27.0%

Silicone quat Dicoco quat PEG-5-Cocamine Mineral seal oil 2-Butoxylethanol Water to 100%

3.0% 18.0% 2.0% 25.0% 5.0%

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Table 7

Car Polish

Car Polish o/w, solvent free Aminosiloxane PEG-30 Glyceryl stearate Glyceryl stearate Silicone oil, 350 mPas Wax Sodium chloride Water, abrasive to 100% Car Polish w/o Carnauba wax White spirit Aminosiloxane, self-emulsifying Silicone oil, 350 mPas Water, abrasive to 100%

Car Polish o/w, convenient 3.0% 3.6% 1.8% 5.0% 60% 0.2%

Aminosiloxane emulsion Silicone oil emulsion Carbomer Wax emulsion, 12% Water, abrasive to 100%

7.6% 8.6% 0.2% 33.0%

2.0% 15.0% 10.0% 5.0%

aminosiloxane which forms an emulsion with water of water/oil (w/o) type without any further emulsifiers or additives [10,11]. For formulations, see Table 7. For all surfaces where stress cracks can come up, like polymethylmethacrylate or polycarbonate, special silicone emulsions free from nonionic surfactants have to be used. Here the emulsifier system is based on anionic materials that are nonethoxylated and therefore prevent stress cracking. E. Interior Car Care/Leather Care The market offers a broad range of special interior cleansers for all kind of surfaces, e.g., plastics, leather, wood, and fine metal finishes. Antistatic and ultraviolet (UV) protection are market claims for these product groups. The interior cleanser should not interact with plastic materials and should protect materials as well. It should remove greasy spots and create an antistatic effect without visible residues on hard surfaces. The formulation (Table 8) could be with or without alcohol and slightly acidic when the antistatic effect is the main criterion. On the other hand it could be slightly alkaline for more grease removing capacity with a low antistatic effect. The refractive index of a silicone emulsifier is quite high and compared to organic emulsifiers it is nearly as crystal clear as other silicone compounds. This effect is already used in the cosmetic industry for the creation of clear gels as antiperspirants and for other applications. A transparent gel system is achieved only when both of the emulsion phases have the same refractive index. In the water phase, by correct selection of polyalcohols like glycerol, polyglycerol, or propylene glycol the refractive index can be adapted very easy. Therefore, the continuous phase, the oil phase, is blended first and the water phase is then made up and added. In cosmetics, skin feel can be improved by these gels, using high amounts of volatile silicone oils. For leather polishes, the use of volatile silicone oils is suitable due to the fact that the cleaning effect of these oils is excellent. In addition a silicone wax which stays on the leather surface for a prolonged period, is more important [9,10].

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Special Purpose Cleaning Formulations Table 8

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Car Interior Formulations Plastic Cleanser

Cocamidopropyl amine oxide, 35% PEG-5 Cocomonium methosulfate Citric acid monohydrate Isopropanol Water to 100%

Leather Care Gel

1.3% 0.5% 1.2% 10.0%

Stearyl dimethicone Cetyl dimethicone copolyol Cyclomethicone Isopropylmyristate Silicone oil, 350 mPas Glycerol Sodium chloride Water to 100%

1.8% 1.6% 7.2% 3.6% 1.8% 48.4% 2.5%

F. Rim/Tire Care Tire cleaners are formulated to remove the tough road film, grease, grime, and dirt from the tire. They are heavy in caustic and builders. The surfactants used in this application must be stable to high pH and presence of electrolytes. Amphoteric surfactants that can provide performance advantages in this application include sulfobetaines or amphopropionates. Nonionics like amine oxides or alkyl polyglucosides are also used because of their good cleaning ability in alkaline conditions. This process is accomplished using the same raw materials with different concentrations of builder systems and a different pH range. Chemicals are used in higher concentrations than the car wash soaps with different brushes and pickup systems. G. Glass/Windshield Cleansing Windshield washers are designed to remove greasy soil and dust from the glass. Since the greasy soil is comparatively light and the substrate glass is a hard, nonporous surface, it is easier to clean. Here the important requirement is that the surfactant should not leave spots and streaks. Most formulators use alcohol, generally isopropyl alcohol (IPA), to prevent the formula from freezing. Glycol ethers like dipropylene glycol monomethyl ether are used as solvents to dissolve any oil or grease and grime. Ammonia or other suitable alkalies are used to give alkalinity to the formula and enhance the grease removing capacity as can be seen in Table 9. Surfactants are used in low amounts of 0.2 to 1.0% to provide the wetting and penetrating action to the formula.

Table 9 Rim Cleanser Formulations Rim Cleanser, Alkaline Disodium cocoampho propionate, 40% Potassium tripoly phosphate, 50% Potassium hydroxide, 45% Water to 100%

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Rim Cleanser, Active

8.0% 12.0% 13.0%

Sodium lauryl sulfate, 30% Myristylaminoxide, 30% Sodium carbonate Water to 100%

2.5% 6.3% 0.3%

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Binary blends of low foaming surfactants also have interesting properties, especially when looking at the blend of capryl/capramidopropyl betaine and decaminoxide on glass or car windshields [8]. The very low wetting effect, i.e., slightly hydrophobic effect created by water soluble ingredients of the blend, can be of use in glass cleaners for car windshields, as the dilution required to use the product is very easily removed by the wiper. Due to the increasing use of polyacrylate and polycarbonate in car headlights, and the problem of stress cracking, use of nonionics should no longer be recommended. The formula for a summer product is developed with the objective that the windshield is clear after only one or two strikes of the wiper. A similar formulation for winter is possible with antifreeze agents. As a consequence, an all-season concept does not interfere with the spray jets (Table 10).

III. INDUSTRIAL AND INSTITUTIONAL PRODUCTS FOR SPECIAL PURPOSES In this section we would like to focus on specialty cleansers which can be used in a variety of industrial and institutional (I&I) applications. From food, pharmaceutical, and cosmetic industry plant cleaning via big kitchens, hotels, hospitals, and public buildings, many needs, e.g., for floor care or vertical surface cleaning, are going in the same directions. With the help of modern specialty additives, many solutions are at hand which are shown in the following sections. A. Gel Cleansing Products The cleaning of production areas in the food, pharmaceuticals, and cosmetics industry with gel cleansers plays an ever-increasing role [12]. As cleansers should also be as easy to handle as possible, the aim is to formulate systems that—as concentrate—are of very

Table 10

Windshield/Glass Cleanser Formulations

Windshield Cleanser, Summer Sodium lauryl sulfate, 30% Decaminoxide, 30% Ammonia, 25% Sodium iminodisuccinate, 30% Water to 100%

Windshield Cleanser, Winter

4.5% 25.0% 0.5% 5.0%

Glass Cleanser, Trigger Spray Disodium caprylampho diacetate, 35% Ammonia, 25% Dipropylene glycol methyl ether Ethylene glycol Water to 100%

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0.5% 0.5% 4.0% 6.0%

Decaminoxide, 30% Capryl/capramidopropyl betaine, 38% Isopropanol Ethylene glycol Water to 100%

0.5% 0.1% 70.0% 10.0%

Special Purpose Cleaning Formulations Table 11

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Gel Cleanser Formulations

Acid Gel Cleanser, pH 3 Laurylaminoxide, 30% Myristylaminoxide, 30% Sodium nitrate Phosphoric acid, 85% Propylene glycol Water to 100%

2.0% 15.0% 3.0% 3.0% 3.0%

Alkaline Gel Cleanser, pH 14 Oleic acid Myristylaminoxide, 30% PEG-20-Glyceryl oleo ricinoleate Sodium butylmonoglycol sulfate, 50% Sodium hydroxide, 50% Gluconic acid, 50% Water to 100%

2.0% 16.0% 2.0% 20.0% 20.0% 4.0%

low viscosity, but that undergo a considerable viscosity increase upon dilution with water to a use concentration of 5 to 10%. This dilution adheres to a surface in a gel-like manner so that soil is effectively attacked. Such low-viscosity concentrates can be easily sucked up with common foam lances and then injection-sprayed after mixing with water [13]. (See Table 11.) Thickening effects in cleansers may also be achieved with polymeric thickeners or with surfactant blends of different kinds. The use of polymeric thickeners (e.g., on the basis of cellulose), however, is problematic as industrial cleansers are often highly acidic or alkaline. In practical application preference is therefore given to thickening effects caused by the interaction of surfactants. A new approach concerning the preparation of gel forming cleansers, focuses on the use of an emulsifier with solubilizing properties similar to those of alcohol, which controls the viscosity and in addition improves the dirt removal capacity of the cleanser from the boundary between molecular solutions and (macro)emulsions [14–16]. In practical applications the cleanser concentrate can be applied with the usual foam lance dosing systems or with high pressure cleaning systems. As it does not contain any alcohol, effective cleaning is also possible in problem areas of production. The cleanser concentrate is applied like conventional alkaline foam cleansers. It forms a foam that runs down the surface leaving a coherent film which ensures a long contact time. Foam cleansers usually run down more quickly. B. Quick Dry Floor Cleansers Especially when cleaning public areas, e.g. in airports, a quick-drying floor is essential. An acceptable drying time is below 10 minutes, depending on ambient temperature and humidity. For a substantial reduction of this, the use of silicone quat is described below. A silicone quat, already described above in the auto care chapter, is, due to its insensitivity to anionics and its improving of spread on polyvinyl chloride (PVC) and other floors, an excellent tool for this [17]. The formula shown in Table 12 provides an example of how drying under standard conditions can be reduced to 4 1/2 minutes under standard conditions. The dosage of the cleaner was 0.6% in 40˚C water. Other aspects of the cleaner, like cleaning performance or foam generation, are not influenced.

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272 Table 12

Mueller, Peggau and Arif Quick-Dry Effect Quick-Dry Floor Cleaner

Silicone quat C12–18- alcohol-1,2-propoxylate-6,4-ethoxylate Sodium laureth-2-sulfate, 28% Coconut fatty acid Capryl/capric polyglucoside, 50% Sodium hydrogen carbonate Sodium hydroxide, 50% Sodium gluconate Water, fragrance, dye to 100%

1.00% 2.00% 1.00% 0.55% 5.00% 0.42% 2.20% 1.87%

C. Nanostructured Floor Tile Cleansing The use of floor tiles has increased in the last few years, both in private homes and in newly constructed public buildings, especially in the northern part of Europe. Whereas, in Mediterranean areas, the floor tile already had a good reputation due to the warmer climate where cool stone materials are more attractive than carpets. The technology of tile production has changed in the last years from classic glazed or open porous structures to new tiles which have no glaze but a very dense and still structured top layer, making these tiles very slip resistant. These floor tiles do not need a surface glaze or a sealer as the material is virtually non-porous. Cleaning of these materials is usually done with ordinary floor cleaners used as well for PVC and other floor types. Especially in the public area, in some public buildings with a lot of traffic of people passing every day, the contract cleaning companies noticed after some years an increase in the cleaning time needed for an acceptable treatment of the tiles. Whereas an experienced cleaner can clean 100 m2 of PVC floor in 30 minutes, for 100 m2 of nanostructured floor tiles 75 minutes was required. Therefore a need for more efficient floor cleaners seemed to be evident. In trials we could show that the addition of cationic surfactants lead to an improvement in spreading across the tile. As the cleaners are formulated with anionic surfactants, a quat with anionic compatibility was needed. Therefore, coco pentaethoxy methylammonium methosulfate was used [18,19] . The products were tested in two frame formulations for I & I floor cleaners and a commercial product. The formulations are shown in Table 13. The first formulation is an alkaline high active cleaner with a low foaming ternary blend of an ethoxylate, an aminoxide and sodium ethyl hexyl sulfate as surfactants and imino disuccinate as complexing agent. The use dilution is 0.3%. The second formulation is a typical standard cleaner with ethyl hexyl sulfate and sodium diisooctyl sulfosuccinate as actives, which is used at 1.2%. With both formulations, an increase of 80% in spreading and speeding the cleaning process was observed. D. Odor Control Products Odor elimination is an ever-growing problem: from cooking smells at home, smoke remains in rental cars, to big emitters as compost plants, the problems with malodors are ubiquitous.

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Special Purpose Cleaning Formulations Table 13

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Cleaners for Nanostructured Tiles

High-Performance Cleaner Decylethoxylate/butoxylate Sodium ethylhexyl sulfate, 40% Sodium stearate Decylaminoxide, 30% Triethanolamine IDS PEG-5-Cocomonium methosulfate Water to 100%

10.00% 9.00% 1.20% 4.35% 2.00% 0.9%

Standard Cleaner Sodium ethylhexyl / sulfate, 40% Sodium diethylhexyl sulfosuccinate, 75% Sodium phosphonate PEG-5-Cocomonium methosulfate Water to 100%

4.80% 0.90% 0.32% 1.00%

1.00%

Actually, cyclodextrin is used in large scale to control odors by absorbing in the helical starch structure, a system which lacks in selectivity and efficiency for I & I and is therefore mainly used in households [20]. A new approach to malodor is done with zinc ricinoleate. Zinc ricinoleate has been common for 30 years in personal care deodorants. Although this material was successful in reducing human odor, its mode of action was not really understood. New investigations revealed the special properties of zinc ricinoleate in water as the zinc is not only ready for being attacked but is in an activated environment, as the organic molecules around it form a kind of pocket where there is a way for the zinc to complex in a pronounced way [21–24]. Zinc ricinoleate is a complex metallorganic system which is especially efficient in absorbing nucleophile compounds. As most of the malodors are in fact good nucleophiles as amines or thio derivatives, it is an excellent base for high performance odor absorbing products in households as well as industry. With its activity zinc ricinoleate is an excellent starting material for homes as well as for industrial and institutional applications. For formulation reference, see Table 14. The pure zinc ricinoleate is a waxy material that is difficult to incorporate into formulations. Therefore, a blend of zinc ricinoleate (50%) with solubilizers is used. E. Water-Based Steel Cleaner The removal of fatty or oily residues often requires solvent-based cleaners. For environmental reasons as well as the dangers connected with flammables, interest is growing in cleaners that have solvent performance without these problems. A solution is depicted in Table 15 [9,10]. A 10% portion of solvent naphtha with a high boiling point (>150˚C) is emulsified with an amount of 3% silicone emulsifier and as balance 86.5% of water phase and a small amount of sodium chloride for stabilization. A stable w/o emulsion results that has no flash point, only a small amount of solvent, but still the cleaning properties of a solventbased cleaner. As it is a w/o emulsion, residues are water resistant but detergent soluble. In addition to the emulsifying properties, the silicone emulsifier works as a silicone polish in the system. Thus cleaning with this kind of water-filled oil bubbles is very easy. Typical applications are tar removers for car care, cleaners for machinery in food and cosmetic

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Table 14

Odor Absorber Formulas

Odor Absorber, Aqueous

Trigger Spray, Aqueous

Zinc ricinoleate blend Sodium laureth sulfosuccinate, 40% Phosphonate (DTPMP), 32% Triethanolamine Lactic acid, 88% Water, fragrance to 100% Alcoholic Room Spray

1.0% 6.0% 2.5% 0.6% 0.6%

1.0% 6.0% 0.6% 0.6%

All-purpose Cleanser

Zinc ricinoleate blend Ethanol Polysorbate 80 Triethanolamine Lactic acid, 88% Water, fragrance to 100%

Table 15

Zinc ricinoleate blend C8-10 amidopropylbetaine Triethanolamine Lactic acid, 88% Water, fragrance to 100%

2.2% 33.0% 3.3% 0.5% 1.0%

Zinc ricinoleate blend Cocamidopropylbetaine, 47% Sodium laureth sulfosuccinate, 40% Sodium laureth sulfate, 28% Triethanolamine Phosphonate (DTPMP), 32% Lactic acid, 88% Water, fragrance to 100%

1.0% 4.0% 8.0% 15.0% 0.6% 2.5% 0.6%

Metal Cleansing Pastes

Cleaning Polish without Abrasive Cetyl dimethicone copolyol 3.0% White spirit 10.0% Sodium chloride 0.5% Water to 100% Cleaning Polish with Wax Cetyl dimethicone copolyol Silicone oil, 100 mPas White spirit Beeswax Water to 100%

Cleaning Polish with Abrasive Cetyl dimethicone copolyol White spirit Silica (abrasive) Water to 100%

2.0% 10.0% 8.0%

3.0% 5.0% 25.0% 2.0%

industry, and others. It can be used for industrial hand cleaners as well. With some cosmetic additives to enhance the skin feeling, an elegant formula is at hand. Abrasives of different kinds, from silica to polyurethane (PUR) powder can be incorporated easily, as shown above. The production is possible with standard medium-speed stirrers and at ambient temperature. Incorporation of waxes is possible as well. The formulations show the great possibilities with silicone emulsifiers for cleaning and polish applications. Again, it has

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Special Purpose Cleaning Formulations Table 16

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Glass Cleaners Glass Spray Cleanser with Antifogging

Glass Spray Cleanser Capryl/capramidopropyl betaine, 38% Decaminoxide, 30% Trisodium NTA, 40% Isopropanol Ammonia, 25% Water to 100% Glass Coat Aminosiloxane Ethylene glycol Tryglycol Isopropanol

Effect

0.1% 0.5 % 0.3% 30.0% 0.3%

Decaminoxide, 30% Trisiloxane Trisodium NTA, 40% Isopropanol Citric acid monohydrate Water to 100%

0.5% 1.0% 0.26% 15.0% 0.04%

2.2% 6.8% 2.0% 89.0%

to be mentioned that beside the surfactant properties the emulsifiers demonstrate their silicone properties as it improves polish and cleaning properties. F. Glass Cleaning The cleaning of glass surfaces has seen some improvements in recent years. Antifogging and glass coat effects have been established. The surfactant used in small quantities was usually a simple nonionic. In a recent study, the synergistic behavior of low foaming surfactants was investigated. Especially surprising was the effect of capryl/capramidopropyl betaine with decaminoxide with regard to the contact angle on glass. It did not give a lower contact angle as could be expected but a rise above that of pure water [7,8]. Due to the solubilizing properties, the system could remove dirt, but was then especially easy to remove from the glass. Formulations are shown in Table 16. With the addition of a trisiloxane, an antifogging effect can be achieved. With the use of an aminosiloxane, a very hydrophobic glass coat can be formulated that leads to an improved blow-away effect of water on the glass. G. Sugar-Based Surfactants for CIP Alkyl polyglucosides have been discussed for a long time as surfactants for personal care and dishwashing, as they are mild products at neutral pH, reasonably good foamers, and have, due to their raw material sources, an ecological image. More recently, their high alkaline stability and the good hydrotroping properties have come into focus for use in industrial areas. Ethylhexyl polyglucoside with high polymerization degree of the glucose (dp = 2) can be incorporated directly into high active caustic or potassium hydroxide [25]. This is especially interesting for Cleaning In Place (CIP) products for milk, beverage, and brewing industries. Based on hexylpolyglucoside, high-pressure cleaners can formulated that are essentially nonfoaming but still have a good degreasing property. For plastic cleaners as well, alkylpolyglucosides may provide a good choice [26,27] as shown in Table 17.

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Table 17

Alkyl Polyglucoside Formulations CIP-Cleanser

Ethylhexylpolyglucoside, 50% Gluconic acid, 50% Sodium hydroxide, 50%

High-Pressure Cleanser 10.0% 10.0% 80.0%

Hexylpolyglucoside/ethoxylate blend, 70% Gluconic acid, 50% Sodium hydroxide, 50% Water to 100%

2.0% 3.0% 30.0%

Plastic Cleanser Ethylhexylpolyglucoside, 50% Decaminoxide, 30% Monoethanol amine Phosphonate (DTPMP), 32% Gluconic acid, 50% Water to 100%

0.2% 0.3% 5.0% 2.0% 3.0%

H. Cleaning with Natural Raw Materials The use of natural raw materials like D-limonene or lactic acid or synthetic materials like glycolic acid in cleaning formulations is increasing [28]. They are usually low in toxicity and readily biodegradable. They present many additional benefits. D-Limonene is an excellent solvent and gives a fresh citrus smell to the formulation. L(+)-Lactic acid has excellent descaling properties with some microbiocidal effects and can be used especially for tile and appliance cleaning in bathrooms, etc. [29]. Formulas are depicted in Table 18. Glycolic acid is an excellent chelating agent and is useful for metal cleaning and polish formulations.

IV. CONCLUSION The formulations described in this chapter show the growth of possibilities by sophisticated addition of cleaning products. The approach of new materials for car production and new technological and ecological demands in the car care industry are reasons for a continuous improvement of formulations. As new trends in the professional cleaning industry are emerging, formulators are in need of additives and specialized surfactants. In the near future this will be more and more influenced by computerized work [30,31]. With newly available computer performance it is already possible to calculate meso-scale effects at high precision. The phase behavior of surfactants could be calculated successfully. The possibilities arising with this technology are broad. Formulation design on the computer may be an option in the future, as well as an improved understanding of the raw materials used.

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Special Purpose Cleaning Formulations Table 18

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Cleaning with Natural Raw Materials Cleaner Concentrate

Cleaning Emulsion

D-Limonene Butylenglycol PEG-5-Sorbitanmonooleate Cetylalcohol-5 EO Water to 100% Toilet Bowl Cleaner

47.0% 3.0% 3.0% 2.0%

D-Limonene PEG-20-glyceryltrioleate PEG-20-Glyceryl oleo dicinoleate Water to 100% Bathroom Cleaner

L(+)-Lactic acid, 80% Sulfamic acid Decylpolyglucoside, 64% Isotridecanol-10 EO Xanthan gum Water to 100% Aluminum Cleanser

10.0% 3.0% 2.0% 1.0% 0.5%

L(+)-Lactic acid, 80% Ether carboxylic acid, 30% KOH Water to 100%

Glycolic acid, 70% Citric acid Butyl cellosolve solvent Isotridecanol 10 EO Water to 100%

70.0% 1.0% 9.0%

4.0% 3.0% to pH = 3

Copper and Brass Polish 5.0% 3.6% 5.0% 2.0%

Glycolic acid, 70% Sodium chloride Silica flour Water to 100%

10.0% 7.0% 40.0%

REFERENCES 1. CD Hager, Surface Active Cleaners for the Food and Non-Food Industry, Tens Surf Det 36: 1999, 334–339. 2. G Bognolo, Industrial Applications of Surface Active Agents, CESIO 2000, Florence, Italy, Proceedings, Vol. 2, pp. 866–872. 3. J Henning, W Hilmes, F Müller, J Peggau, H Schramm, Cleaning and Care Additives for Innovative Consumer Products, CESIO 2000, Florence, Proceedings, Vol. 2, 1036–1044. 4. S Arif, FE Friedli, Nitrogen-Containing Specialty Surfactants. In Detergency of Specialty Surfactants, ed. FE Friedly, Marcel Dekker, New York 2001, pp. 71–115. 5. S Arif, Formulating Car Care Products, HAPPI 2001: 3, 60–70. 6. F Müller, J Peggau, Low-foaming Surfactants in Ternary Blends, Jorn Com Esp Deterg 28:1998, 127–136. 7. F Müller, J Peggau, Ternary Surfactants in Synergistic Blends, 4th World Conference on Detergents, Montreux 1998, Proceedings of the 4th World Conference on Detergents, A. Cahn ed., Champaign, 1999, pp. 234–237. 8. F Müller, J Peggau, Low-Foaming Surfactants in Synergistic Ternary Blends, SÖFW-Journal 125: 1999 5, 2–10. 9. J Henning, F Müller, J Peggau, Novel Applications of Silicone Surfactants in Cleaners and Polishes, Jorn Com Esp Deterg 29:1999, 235–246. 10. J Henning, F Müller, J Peggau, Novel Applications of Silicone Surfactants in Cleaners and Polishes, SÖFW-Journal 127: 2001 1–2, 38–43.

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11. I Eissmann, J Henning, F Müller, S Stadtmüller, W/O-Emulsionen, enthaltend aminofunktionelle Organopolysiloxane, German Patent Application (DE) 198 56 930.0, 1998. 12. D Ouzounis TFC setzt Maßstäbe bei der Oberflächenhygiene, ZFL 4: 1996, 10, 14–16. 13. TB Neil, DJ Wilson Thickening Gels, European Patent Application (EP) 0314232, 1988. 14. F Müller, J Peggau, Niedrigviskose alkalische Reinigeremulsion, DE 197 15 599.5, 1997. 15. F Müller, J Peggau, Thickening by Thinning: New Approaches for Gel Cleansers SÖFWJournal 123: 1997, 746–753. 16. M Pflaumbaum, F Müller, J Peggau, W Goertz, B Grüning, Rheological Properties of Acid Gel Cleansers, J Polym Coll Sci, 183–185:2001, 777–784. 17. A Ditze, M Halfmann, R Hamacher, G Meine, F Müller, Allzweckreiniger mit diquaternärem Polysiloxan, DE 198 53 720.4, 1998. 18. H Armstrong, F Müller, J Peggau, Wässrige Reinigungsmittelkonzentrate für raue, insbesondere profilierte Fliesen, DE 100 38198.7, 2000. 19. J Henning, F Müller, J Peggau, Cationic and Anionic Surfactants—Compatibilities and New Effects on Hard Surfaces, SÖFW 127:2001, 6, 30–35. 20. GR Whalley, Cyclodextrins: Their Production and Application, HAPPI 12:1998, 60–65. 21. F Müller, J Peggau, H Kuhn, Investigations on Odour Absorber TEGO® Sorb with Molecular Dynamics Calculations, Household Ingredients, Paris, 1999, Abstract Book pp. 74-81. 22. H Kuhn, F Müller, J Peggau, R Zekorn, The Mechanism of the Odour-Absorption Effect of Zinc Ricinoleate. A Molecular Dynamics Computer Simulation, J Surf Det 3: 2000, 335–343. 23. F Müller, J Peggau, H Kuhn, Investigations on Odor Absorber Zinc Ricinoleate, Jor. Com Esp Deterg 30: 2000, 83–92. 24. F Müller, J Peggau, H Kuhn, TEGO SORB, Detergents & Cosmetics (China) 23(2): 2000,12–16. 25. W Berkels, B Grüning, F Müller, J Peggau, Alkylpolyglucosid mit hohem Oligomerisierungsgrad, DE 100 10 420.7, 2000. 26. G Karlsson, I Johansson, The New Generation of Alkyl Glucoside Based, Liquid Alkaline Cleaning Systems, Household Ingredients, Paris, 1999, Abstract Book pp. 101–111. 27. I Johansson, C. Strandberg, B Karlsson, B Gustavsson, Structure-Property Relationship for some Alkyl Polyglucosides, 4th World Surfactant Congress, Barcelona, 1996, Abstract, Vol. 2, pp. 283–298. 28. B Ziolkowsky, Jahrbuch für den Praktiker, Augsburg, 1999, pp. 81–105. 29. PKE Houtman. L(+)Lactic Acid in Acidic Cleaning Formulations, SÖFW 126:2000, 10, 120-125. 30. H Kuhn, H Rehage, Ber Bunsenges Phy Chem 101:1997, 1485–1492. 31. E Rykina, H Kuhn, F Müller, J Peggau, H Rehage Moleküldynamik-Computersimulation des Phasenverhaltens nichtionischer Tenside, Angew Chem, (Int. Ed.) 41:2002, 983–986.

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9 Surfactant Applications in Textile Processing Jiping Wang and Yong Zhu

CONTENTS I.

II.

III.

Introduction ........................................................................................................... 280 A. Textile Fiber Consumption........................................................................ 280 B. Textile Processes ....................................................................................... 281 C. Uniqueness of Textile Chemicals.............................................................. 282 D. Surfactant’s Role in Textile Processing .................................................... 283 E. Surfactant’s Market in Textile Chemicals................................................. 283 Surfactants in Textile Preparation ......................................................................... 284 A. Naturally Occurring Impurities on Textile Fibers .................................... 284 1. Impurities on Raw Cotton ........................................................ 284 2. Impurities on Raw Wool ........................................................... 284 3. Impurities on Raw Silk ............................................................. 285 B. Process-Added Impurities on Textile Fibers............................................. 285 1. Sizing Agents ............................................................................. 285 2. Yarn Lubricants.......................................................................... 286 C. Desizing Agents......................................................................................... 286 D. Scouring Agents ........................................................................................ 287 E. Bleaching Assistants.................................................................................. 288 Surfactant Applications in Textile Dyeing............................................................ 289 A. Leveling Agents......................................................................................... 290 1. Cellulose Dyeing........................................................................ 290 2. Polyester Dyeing........................................................................ 291 3. Wool Dyeing .............................................................................. 292 4. Acrylic Fiber Dyeing ................................................................. 292 B. Dispersing Agents ..................................................................................... 294

279

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C. Wetting and Penetrating Agents................................................................ 294 D. Foaming and Defoaming........................................................................... 295 E. Aftertreatment Applications ...................................................................... 296 IV. Surfactant Applications in Textile Printing........................................................... 297 V. Surfactant Applications in Textile Finishing ........................................................ 298 A. Softeners .................................................................................................... 298 B. Antistatics .................................................................................................. 300 C. Other Finish Applications ......................................................................... 301 1. Antimicrobial Finishing. ............................................................ 301 2. Water/Oil Repelling and Soil-Release Finishing. ..................... 301 3. Optical Finishing........................................................................ 302 References ....................................................................................................................... 302

I. INTRODUCTION From textile fibers to consumer garments, many textile processes are needed to meet consumers’ demands on fabric aesthetic and functional properties. Except for spinning and weaving, most textile processes involve fiber/yarn/fabric/garment treatments in aqueous solutions and surfactants play an important role in practically every wet processing. In 1998, global surfactant consumption in the textile industry was about $2 billion which accounted for about 25% of the total textile chemicals excluding textile dyes [1]. This surfactant market share is relatively higher in developing countries such as China, etc. because the industry there is very strong on textile preparation and dyeing which heavily use surfactants as processing assistants. On the other hand, developed countries such as United States and Western Europe have lower surfactant market shares due to their strong business in textile finishes and coatings that normally do not need large amount of surfactants in these processes. A. Textile Fiber Consumption Fiber type is one of the most important factors to determine surfactant selections for textile processes. Different fibers often require different surfactants for wetting, detergency, and other process functions. Natural fibers need strong textile chemicals to remove their naturally occurring or process added impurities. For example, cotton fabrics often have more than 10% noncellulose materials which need to be removed in the wet process. Natural protein fibers such as wool and silk have even more impurities than cotton fibers. On the other hand, artificial fibers such as polyester and rayon are much cleaner than natural fiber so only small amount of surfactants are needed for detergency, etc. Textile fibers are commonly classified as natural fibers and artificial fibers. In consumer garments, fibers may present as either pure state such as 100% cotton, 100% polyester, and 100% wool or as blends such as 50/50 poly/cotton and 65/35 poly/rayon. Textile chemical treatments for these blends often require different surfactants for different types of fibers. Commonly used textile fibers are classified in Figure 1. In 2002, about 20.7 billion kg of cotton was consumed in the global textile industry. China, India, and South Asia were the top three cotton consumers in terms of textile mill consumption, accounting for about 60% of total global consumption (Figure 2). For wool mill consumption, China was the top consumer with a share of 25% in 2002, followed by Western Europe with a share of about 23% (Figure 3). On the other hand, China, North America, and Western Europe were the top three artificial fiber consumers with more than

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Textile Fibers

Natural Cellulose Cotton

Flax

Man-made Regenerated

Protein Wool

Synthetic

Silk Rayon Lyocell Acetate

Polyester

Nylon

Spandex

Acrylic

Polyolefins Carbon

Figure 1 Classification of commonly used textile fibers.

NA 8%

Other 16%

LA 8% W. Europe 5% E. Europe 5%

China 28%

S. Asia 16% India 14%

Figure 2 Market share of 20.7 billion kg global cotton consumption in 2002.

Japan 3%

Africa/ME NA LA 1% 4% 9%

Other 14%

China 25%

India 7%

W. Europe 23%

S. Asia 5%

E. Europe 9%

Figure 3 Market share of 1.3 billion kg global wool consumption in 2002.

half the global mill consumption [2] (Figure 4). China was the clear leader in the manmade fiber mill consumption with a 34% share in 2002. B. Textile Processes In order to meet consumer demand in textile appearance, aesthetic, and functional properties, most textiles are dyed with different colors and finished mechanically or chemically with varieties of functional agents. Before dyeing and finishing, the gray fibers and fabrics

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Other 16%

Japan 3%

NA 14%

LA 4% W. Europe 11%

China 34%

India 6%

S. Asia 10%

E. Europe 2%

Figure 4 Market share of 34.0 billion kg man-made fiber consumption in 2002.

must be prepared to assure complete wetting, good water absorbency/penetration, and uniform application of dyes and finishing agents. The preparation includes desizing to remove sizing agents from woven and warp knitted fabric, scouring to remove naturally occurring and process added impurities, and bleaching to destroy naturally occurring colors or yellowness in textile fibers for bright color and appearance of end-use products. The table below listed some common textile processes and their functions. Process Singeing Desizing Scouring Bleaching Mercerization Dyeing Printing Finishing

Major Functions To remove protruding fiber by burning for smooth and uniform fabric surface To remove sizing agents added onto warp yarns before weaving for effective dyeing and finishing To remove impurities from all natural or synthetic fibers for better water absorbency To oxidize or reduce colored materials for bright fabric appearance To improve the moisture sorption, dye pick-up and fabric strength on cellulose fabrics. To impart color on textiles for aesthetic purposes To impart colored patterns or designs on textiles for desirable appearance To improve specific functional properties on textile such easy care (durable press), antimicrobial, flame retardency, softness, etc.

C. Uniqueness of Textile Chemicals A household detergent is a complicated multifunctional mixture including surfactants, builders, alkali suppliers, enzymes, suds control agents, optical brighteners, fragrances, dye transfer inhibitors, etc. Some detergents even contain bleaches, fabric softeners and other fabric care components. All functions such as wetting, emulsification, chelating, antifoaming, and fabric care, etc. are included in household detergents. However, textile chemicals are often formulated to focus on individual functions such as wetting agents, detergents, lubricants, fabric softeners, dyeing assistants, and different finishing agents. Because different fiber/fabric types, different process equipment, different end-use applications need different textile chemicals, the textile mills must have enough freedom to select and combine formulations together to optimize the textile processes. Therefore, most of textile detergents cannot formulate too many functions together in one product. The pH range used in textile processes is very broad. The pH could be as low as 1 to 2 in some acid dyeing and as high as 13 in the textile scouring and mercerization. The

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process pH is one of the major factors to determine textile chemical formulations and surfactant selections [3]. D. Surfactant’s Role in Textile Processing Almost all textile processes use water as a process medium. In order to conduct these processes, the textile substrate must be totally wet out. Surfactants are necessary to lower the surface tension of process solutions for uniform application. How fast and uniformly aqueous solutions wet textile substrates often impacts processing performance. It is a common practice to use surfactants in almost all textile processes to help increase wettability, often referred to as wetting agents. In fiber manufacture of synthetic/regenerated fibers and yarn spinning of cotton, wool, and their blends, surfactants are often sprayed on the fiber and yarn surface to reduce fiber-fiber and fiber-metal friction, referred to as yarn lubricants. In desizing and scouring of natural textile fibers and theirs blends, surfactants are often used as detergents and emulsifiers to help remove impurities that are originated from natural fibers or added in the early processes such as spinning and weaving. In textile dyeing, surfactants are broadly used as dispersants and leveling agents to help uniform dying and better dye penetration. Dye fixatives and dye carriers are also surface active although they are not as common as other dyeing assistants. In textile finishes, surfactants are often used as fabric softeners to improve fabric hand or feel and used as antistatic agents to control static electricity built up on the surface of textile fibers, particularly on synthetic fiber due to their low moisture contents. Surfactants are also useful to control foam formation during textile processes, referred as antifoaming agents, particularly in dyeing and other processes with high-speed padding. E. Surfactant’s Market in Textile Chemicals With $8 billion of global textile chemicals in 2000, about $2 billion was total surfactant consumption. As shown in Figure 5, Western Europe, United States and China are the top three value-based surfactant consumers in total textile applications [1]. In the past few years, the surfactant consumptions in developed countries such as United States, Western Europe, and Japan remained stable. The most increases of surfactant consumption were from developing countries such as China, India and South Asia because of the booming textile industry. Surfactant consumption in textile application is expected to increase 3 to 5% globally in the next few years. Most of them will come from Asia and Latin America. Global market share of the surfactant applications in the total textile chemicals is about 25%, value-based (Figure 6). In different countries and regions, many factors, including cost, influence this market share. However, activities in different industrial areas

US 15%

Other 28%

WE 26%

India 8% China 13%

Japan 10%

Figure 5 Surfactant market in global textile application.

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35 30

% Share

25 20 15 10 5

W or ld w id e

In di a

C hi na

Ja pa n

W E

U S

0

Figure 6 Surfactant market share in total textile chemicals.

also play a key role. In the United States, the surfactant share is relatively small in total textile chemicals because textile coating and finishing are very strong in the U.S. textile industry. On the other hand, preparation and dyeing which need large amount of surfactant applications are not as important as textile coating and finishing.

II. SURFACTANTS IN TEXTILE PREPARATION A. Naturally Occurring Impurities on Textile Fibers Natural cellulose fibers such as cotton and protein fibers such as wool and silk contain impurities which have to be removed to ensure uniform bleaching, dyeing, and finishing as well as to enhance other end-use properties such as wettability and absorbency. The types and amount of these impurities often determine the surfactant selection and detergent formulation to scour them. 1. Impurities on Raw Cotton [4a] On average, cotton may contain about 5 to 7% by weight impurities in the form of waxes, proteins, pectins, inorganic salts, hemicelluloses, pigments, etc. The hydrophobic nature of the waxes make their removal difficult relative to the removal of other impurities. The composition of cotton wax consists mainly of a variety of long chain (C15 to C33) alcohols, acids, and hydrocarbons as well as some sterols and polyterpenes. The pectins are primarily methyl ester of poly-D-galacturonic acid. Effective removal of impurities in cotton, particularly waxes, is achieved commonly by sodium hydroxide solutions at high temperature. The proper choice of textile auxiliaries in the alkaline bath is essential for good scouring. Chelating agents are needed to ensure effective use of surfactants which serve as a detergent, dispersing agent and emulsifying agent, etc. 2. Impurities on Raw Wool [4b] Wool scouring is much more complex and difficult than cotton fibers because raw wool may contains 40% or more by weight of impurities in the form of waxes, suint, cellulosic

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material such as straw and dried grass, dirt, and proteinaceous materials. Various scouring processes are used to remove waxes, suint, and noncellulosic compounds. The wool is then carbonized with sulfuric or other strong acids to remove cellulosic materials. Wool waxes are comprised of a variety of monocarboxylic, dicarboxylic, and hydroxycarboxylic acids as well as steroidal alcohols such as cholesterol and lanosterol. The wool waxes are often recovered from the grease during scouring. Suint is usually considered to be a variable composition of water soluble materials which are readily removed by scouring. The dirt with wool fibers consists of both inorganic and organic materials. The proteinaceous material consists of skin flakes from the sheep and soluble peptides. 3. Impurities on Raw Silk [4c] The main impurity to be removed from silk is the protein sericin, also known as gum, so scouring of the silk fibers is also known as degumming. A raw silk contains normally 20 to 25% of the sericin. Soap and alkali are often used to remove sericin from silk fibers. Enzymatic degumming is gaining interest recently. B.

Process-Added Impurities on Textile Fibers [1,3,5,9]

1. Sizing Agents Most warp cotton and synthetic fiber staple yarns used on woven fabrics are sized prior to weaving with various natural and/or synthetic polymers. The sizing increases yarn’s abrasion resistance which is critical for maintaining modern high processing speeds. It is essential to prevent weaving damage that could subsequently lead to a nonuniform fabric for dyeing and finishing. Natural sizing agents are primarily starches, modified starches, natural gums, and cellulose derivatives. Starch and starch derivatives used for sizing include most types of native starches, the amylose and amylopectin fractions of starch, and starch derivatives such as dialdehyde starch, hydroxyethylated and acetylated starches. Carboxymethylcellulose (CMC) is the most frequently used cellulose derivative for sizing. Poly(vinyl alcohol) (PVA) and a variety of acrylic homopolymers and copolymers are frequently used as sizing agents. To a lesser extent partially hydrolyzed poly(vinyl acetate), polyester dispersions, polyurethanes and styrene are also used as sizing agents. Although requirements for polymers used for sizing vary from one type of fiber to another, the polymer should have properties such as a good film-former with appropriate surface hardness, good adhesive, tensile strength, abrasion resistance, flexibility, and compatible with other ingredients in the formulation. A typical add-on for yarn sizing is as little as 3% to over 20% of sizing agents. Antifoaming agents, lubricants such as waxes and surfactants may also be present in the sizing formulations. A biocide is also added to the formulation to prevent mildew formation during storage such as zinc chloride, phenol or salicylaldehyde. The ethoxylated, gelatinized, and acrylated starches dominate the cotton spun yarn sizing agents markets in the United States and Western Europe. This is primarily because starch is a very inexpensive and good film-forming material. In Japan, blends containing polyvinyl alcohol, polyacrylate and starch are commonly used as sizing agents. Polyesterrich yarns are often sized with synthetic formulations, as the natural sizing agents do not have enough adhering properties on these materials.

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2. Yarn Lubricants Lubricants are broadly used in the yarn and fiber production stages to reduce friction and fiber/yarn damage during weaving and knitting. They are often classified as yarn lubricants. Cotton and wool mills use yarn lubricants while their fibers are being spun into yarn. They could be used together with sizing agents. In the synthetic fiber industry, they are applied when the fibers are being produced. After weaving and knitting, these yarn lubricants need to be removed in the fabric scouring to ensure uniform dyeing and finishing. The amount of lubricant added generally varies, but is of the order of 1% for synthetic fibers and 1.5% for natural fibers, based on the total weight of the fibers. Lubricating oils of vegetable and animal mixed with several types of ingredients are sprayed onto the fibers at the blending stage or padded onto yarns. Although the exact composition of these oils are often proprietary, they contain mineral oils, fatty acid esters or ethoxylates, other hydrocarbons, polyalkylene glycols, silicones, etc. Other ingredients are antistatic agents, biocides, emulsifiers, etc. Fatty acid esters account for about 50% of all lubricants in fiber and yarn production. C. Desizing Agents [1,3,9,15,17] Sizing agents stay on warp yarn surface and penetrate between the fibers of the yarn. These discontinuous spot-welded yarn protection or continuous polymer films hinder the subsequent dyeing, printing and finishing processes. For example, the presence of starch hinders the penetration of the dye into the fibers during dyeing. Therefore, they have to be removed to ensure the uniform fabric treatment. Synthetic polymers such as polyvinyl alcohol (PVA) or modified natural sizing agents such as carboxymethyl cellulose (CMC) may simply be removed in water containing a surfactant. On the other hand, starch, the most frequently used material in large volumes must first be degraded by enzymes and/or oxidizing agents. Amylases are common enzymes used in enzymatic desizing process. In addition to amylases, detergents and nonionic wetting agents are added to improve the penetration of the enzyme into the sizing agents. Very small amounts of metal salts such as sodium chloride, calcium chloride, sulfate, or acetate, and a chelating agent that provides some heat protection to the enzyme may also be added. Emulsifiers may be needed to help remove the wax component of the size. After size degradation to water soluble products, they are washed away in the rinsing or in the following scouring process. Since anionic surfactant may deactivate the enzyme activity, nonionic wetting agent are often used in enzymatic desizing. As an alternative to enzymatic desizing, ammonium persulfate or peroxide compounds may be used to degrade starch, called oxidative desizing. Here are few actual examples used in textile mills to desize cotton greige goods. • The cotton greige good in rope form is padded with a solution containing 0.5 to 1.0 g/l of the enzyme, 0.5 to 1.0 g/l of sodium chloride, and 0.25 g/l of a nonionic surfactant at 50 to 55°C, stored overnight, and washed. • Alternatively, the temperature may be raised to 70 to 75°C and the desizing can be done in 4 to 6 hours. The desizing activity of most amylases is destroyed above 75°C although some recently developed high temperature enzymes may remain active above 90°C. • A general oxidative desizing formulation containing 5.0 to 7.5% H2O2, 1.5 to 2.5% NaOH, 1.5 to 2.5% sodium silicate, 0.3 to 0.5% emulsifier, and 0.1 to 0.2% wetting agent is suitable for continuous pad-steam desizing.

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Good wetting agents are essential for desizing. In enzymatic desizing, ethoxylated surfactants are good choice. Alkylphenol ethoxylates, phosphated alcohol ethoxylates, and linear alcohol ethoxylates are commonly used with amylases together. In alkali or oxidative desizing, anionic surfactants could be selected as wetting agents. Alkyl sulfates, alkyl sulfonates, and alkylbenzene sulfonates are some good examples. D. Scouring Agents [1,3,9,15,17] Sections 2.1 and 2.2 described the impurities present in greige goods. The main purpose of textile scouring is to remove these impurities which can be observed as 5 to 10% of fabric weight loss for cotton fibers, up to 40% of the weight loss for wool fibers, and 20 to 25% of the weight loss for silk fiber during the process. For cotton fabrics, the weight loss results from degradation and dissolution of the hemicelluloses, pectins, proteins, lignins, waxes, etc. These impurities could be emulsified by the soaps formed by fatty acids and fatty ester reacted with caustic soda during saponification. For effective scouring, high temperature (90 to 120°C) and high pH are often needed to secure enough melting of the fatty alcohols and hydrocarbon waxes. In order to prevent the redeposition of the impurities from the scouring liquor to fabrics, a hot wash is very important to a good textile scouring. The fabric absorbency not only depends on scouring formulations and conditions, but also largely relies on how to wash scoured fabrics. For wool scouring, the conditions are milder than the scouring used on cellulose fibers. A typical soap alkali wool scouring utilizes less than 0.5% sodium carbonate with a process temperature below 50°C. Nonionic detergents such as condensates of nonyl phenol and ethylene oxide could be used to replace soap to scour wool, but the scouring temperatures are usually higher than those employed in soap-alkali scouring. The use of organic solvents produces cleaner wool, but solvent disposal, flammability, and toxicity are issues associated with the solvent scouring. It is common to recover wool waxes from the grease during scouring. These waxes are comprised of a variety of carboxylic acids as well as steroidal alcohols, etc. Almost all textile scouring agents contain a surfactant or surfactant mixture as major ingredients. For cotton and cotton blends, high levels of caustic are used in the scouring. Therefore, an excellent compatibility with alkali is critical for surfactant selections. In addition, the surfactants should have a strong capability for emulsifying and detergency along with good wetting power. Alkyl naphthalene sulfonic acids are good wetting agents, but not good scouring agents due to lack of emulsifying and detergency. Fatty alcohol sulfate and fatty acid amides have been used successfully for a long time as kier boiling assistant. Nonionic alkylphenol ethoxylates are broadly used in the scouring of cotton and synthetic fabrics for better fabric absorbency. Alkyl alcohol ethoxylates are also important. Good anionic scouring agents include the phosphate esters of ethoxylated alcohols and ethoxylated alkylphenol, alcohol sulfates, and sulfated fatty acids. Nonionic and anionic blends are also good choices for some of cotton and synthetic fabric scourings. For wool fabrics, alkylphenol ethoxylates dominate the scouring market. For silk fabrics, synthetic surfactants are not good choices because they cause harsh hand on scoured silk fabrics. Soap solutions are broadly used for natural silk. The market of scouring agents in the United States in 1998 is estimated to be about 25,000 metric tons. The market value for scouring agents is in the range of $125 million which account for about 40% of total surfactant applications in the textile industry. In Western Europe, the consumption of scouring agents is around 45,000 metric tons which is higher than in the United States. However, the market value is very similar to that of the United States with about $120 million because of lower average price. In Japan, the demand for scouring agents is around 20,000 metric tons per year, valued at about $50 million. For developed countries such as the United States, Western Europe, and Japan,

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the market size for scouring agents remained stable in the past decade. On the other hand, the consumption of scouting agents is increasing in countries in China, South America, and South Asia due to strong activities in the textile industry. The selection of scouring formulations depends on many factors such as fiber contents, fabric types, equipment types and processing conditions. Examples of scouring formulations commonly used for different equipments in the textile industry are summarized in the tables below. For continuous processing, a common wet pickup is in the range of 80 to 120%.

Scouring Formulations and Conditions in Batch Processing [9,15] Jet or Winch Wetting Agent (g/l) Detergent (g/l) 50% NaOH (g/l) Liquor/fabric ratio Temperature (oC) Time (hours)

0.3–1.0 1.0–3.0 4.0–15.0 8–15 90–98 0.5–1.0

Jig 0.5–1.0 2.0–4.0 5.0–20.0 2–5 90–98 0.5–1.5

Kier 0.5–1.0 2.0–4.0 4.0–15.0 3–5 120–130 3.0–6.0

Beam 0.5–1.0 2.0–4.0 20.0–35.0 5–10 100–130 3.0–5.0

Scouring Formulations and Conditions in Continuous Processing [9,15] Steamer Types Wetting agent (g/l) Detergent (g/l) 50% NaOH (g/l) Temperature (oC) Time (min)

J-Box 1.0–5.0 4.0–10.0 20–50 95–100 30–90

Open-width 1.0–5.0 5.0–12.0 25–60 95–100 10–30

Pressure 1.0–5.0 4.0–12.0 30–80 120–140 1–2

E. Bleaching Assistants [1,3,15] There are many bleaching assistants used to optimize the release of active oxygen, whether in long-term cold pad-batch or short-term hot batch and continuous processes. They are bleaching stabilizers, chelating agents, activators and even fiber protectors. The major function of surfactants in textile bleaching is to facilitate the even penetration of the bleaching liquor into the substrate, i.e., wetting agents. The major surfactant types include fatty alcohol ethoxylates, sulfonates, alkyl phosphates, etc. In the United States, the estimated surfactant market share in the total bleaching assistants is about 10%. The surfactant value in textile bleaching is only about 2% of the total surfactant value used as textile chemicals. In Western Europe, the surfactants used as bleaching assistants consist of about 20% of the bleaching assistant market and 5% of the total textile chemical market. These numbers are significantly higher in Western Europe than in the United States.

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Table I Estimated Surfactant Consumptions in 1998 Textile Markets of Three Major Geographies (volume in millions of dollars) Textile Surfactants

United States

Western Europe

Japan

Triad

%

Scouring agent Dyeing auxiliary Softening agent Antistatic agent Bleach formulation Printing assistant Total surfactant

125.0 88.0 42.0 18.2 6.0 15.0 294.2

118.3 225.0 124.0 28.6 24.0 2.6 522.5

52.8 61.6 64.8 6.0 13.8 0.2 199.2

296.1 374.6 230.8 52.8 43.8 17.8 1015.9

29.1 36.9 22.7 5.2 4.3 1.8 100

Source: World Markets for Textile Chemicals [1].

In a typical bleaching formulation, about 0.5 to 1.0% of surfactant based on weight of fabrics are used with bleaching agents such as hydrogen peroxide, alkaline such as caustic and other bleaching assistants. The actual amount depends on fabric types, process equipment and conditions, types of bleaching agents, and different fabric end uses.

III. SURFACTANT APPLICATIONS IN TEXTILE DYEING Surfactants have broad application in the textile industry, primarily in textile wet processing, mostly in aqueous media, that includes wetting, scouring or detergencing, bleaching or whitening, dyeing, printing, softening, and functional or specialty finishing, Dyeing assistance is one of the most important applications of the textile surfactants in wet processing. As reported in World Markets for Textile Chemicals [1], surfactants for dyeing were ranked as the number one in the global surfactant market, account for about 37% of total textile surfactant consumption (Table 1). In the European market, the dyeing assistant is predominant in the total consumption of the textile surfactants (about 43%). In the U.S. and Japanese markets, the dyeing assistants are the second most important among the textile surfactants, next to scouring agents and softening agents, respectively. Surfactants as dyeing assistants, can be classified in four major groups: • • • •

Leveling and retarding agents Dispersing and solubilizing agents Wetting, rewetting and penetrating agents Stripping agents and postwashing detergents.

There are other textile chemicals with surface activity that are widely used as dyeing auxiliaries for broader applications. These applications include: • • • •

Dye carriers Dye-fixing agents Migrating agents Defoaming and foaming agents

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• Emulsifiers and stabilizing agents • Lubricants The dyeing assistants provide high quality dyeing results, such as improving dye leveling, promoting fiber wetting and dye penetration, enhancing color fastness, and/or increasing dye exhaustion (as well color yields). The surfactants as dyeing assistants can be nonionic, anionic, cationic, and amphoteric. Most of these surfactants improve dye solubility in the daybath. Nonionic surfactants are usually more effective than ionic surfactants in solubilizing dyes [6]. However, dyeing yields may be reduced due to the increased dye solubility by high levels of surfactants. As a general rule, minimum amounts of the surfactants should be used to maximize dyeing quality, efficiency, and cost benefits. In this chapter, only the four major groups of the dyeing surfactants above are discussed with brief coverage of some other surface-active chemicals. Non-surfactant dyeing detergents or auxiliaries, in a broad definition, (such as chealators, bleaches, solvents, hydrotropes, polymers, enzymes, electrolytes, acids/bases) are not included in this review. A. Leveling Agents Leveling agent is the major category of surfactants as dyeing auxiliary [1]. The leveling agents promote uniform and reproducible dyeing of textile fibers, yarns, and fabrics, via even dye uptake of fibers from a dye bath and balanced dye transfer within fibers. This can be achieved with surfactants via two major mechanisms. First, the leveling surfactants retard dye adsorption and/or balance dye desorption-readsorption to the fiber surfaces, which facilitates uniform dye uptake. Second, the surfactants enhance dye migration and penetration between and within the fibers, which corrects the unevenness and improves the thoroughness of the shade. The leveling agents are normally selected based on the class of dyes, dyeing process (bathwise or continuous), dyeing equipment, dyeing conditions (such as pH, temperature, liquor ratio, and flow rate), fiber materials, color strength, cost, and environmental impact. There are two basic types of leveling agents, dye-substantive and fiber-substantive [3] that influence the thermodynamic and kinetic behaviors of the dyeing process. The dye-substantive leveling agents have a relatively stronger binding force with soluble dyes that leads to formation of stable dye-surfactant complexes and/or micellized dyes at the beginning of a dyeing process, in competing with fibers to slow down the dye adsorption. The complexes and micelles, as free dye reservoirs, release dye molecules gradually during the equilibrium-driven dyeing process, so that fast deposition of dyes in the dye bath is well prevented and uneven adsorption is significantly reduced. In addition, the leveling agents may also interact with heavily deposited dyes to promote dye migration from the deeper shaded areas to lighter or less dyed areas, resulting in an even shade distribution. The fiber-substantive leveling agents, on the other hand, have kinetically favored binding force to fibers than to dyes, due to their unique amphipathic structures and smaller molecular weights. This leads to preferred surfactant interactions with the fiber sorption sites. The surfactants on the binding sites of the fibers are then slowly replaced by dyes from the dyebath, since the affinity of the dyes to the fibers is thermodynamically much stronger than that of the leveling surfactants. The competition of surfactants with dyes for the active sites of fibers retards dye adsorption and therefore leads to uniform dyeing. 1. Cellulose Dyeing Cotton and other cellulosic fibers (e.g., viscose rayon, linen, hemp, jute, flax, and ramie) are generally dyed with direct, reactive, sulfur, vat, and azoic dyes, and occasionally with

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basic or mordant dyes [8,9a]. All of these dyes can be applied with exhaustion or bathwise method, or a continuous method, depending on dye substantivity, color depth, and volume of fibers to be dyed. Salts (e.g., Glauber’s salt, and common salt) are often added to promote exhaustion of the direct dyes. The total amount of salt is usually in a range of 5 to 25% [10]. Anionic (fiber-substantive), nonionic (dye-substantive), or a combination of the surfactants are also used in the dyeing process to improve wetting and leveling. The nonionic surfactants, such as polyoxyalkylenes usually have no fiber substantivity and form water-soluble complexes with anionic dyes or their leuco forms (in case of vat and sulfur dyes) to retard the dye adsorption to the fibers. Typical nonionic polyoxyalkylene surfactants include ethoxylated (EO) alkyl phenols, EO alcohols, EO/propoxylated (PO) alcohols, EO/PO copolymers, as well EO alkylmercaptans. Most of these polyoxylalkylenes are derivatives of fatty alcohols/alkylphenol ethers, fatty acid esters, and fatty amines and amides [10a]. Sucrose esters have also found applications in dye leveling. On the other hand, the anionic surfactants compete for fiber active sites to reduce dye sorption, and/or promote dye migration and redistribution between and within fibers. Typical anionic surfactants include alkylaryl sulfonates (e.g., linear alkylbenzene sulfonate, or LAS), alkyl sulfates (e.g., sulfates of fatty alcohols and esters), alkyl sulfosuccinates (e.g., dioctyl sodium sulfosuccinate, and phosphate ester (e.g., nonyl phenol or alcohol phosphate esters) [11]. Ethoxylation is sometimes introduced to modify the hydrophilicity of the alkyl chains. Higher doses of surfactants usually lead to lighter shades and lower yields. In most dyeing processes, surfactant dose of 0.5 to 3% owf (on weight of fiber) is recommended [1]. For direct dyeing, more leveling agents are required, since direct dyes usually have higher substantivity in order to minimize the problems of low wet-fastness. A typical formulation of direct dyebath includes dyes, salts (e.g., Na2SO4 or NaCl), surfactants, and other chemicals [12a]. Leveling is particularly important in vat dyeing. The substantivity of leuco dyes is higher than that of most direct dyes and reactive dyes. Fast deposition of the leuco molecules results in uneven dye distribution that cannot be easily corrected by surfactant-assisted dye migration or redistribution as soon as the leuco dyes are re-oxidized. In vat dyeing, nonionic surfactants are often used to reduce exhaustion rates of the leuco dyes. The surfactant dose is normally higher in vat dyeing (e.g., 0.2 to 2 g/l) than in basic dyeing (e.g., 0.05 to 0.3 g/l). To prevent heavy metal (such as Ca++, Mg++, Fe++, Fe+++) induced dye precipitation, sequestering agents are commonly used. Leveling is also a key in continuous dyeing to reduce uneven shades (e.g., tailing) and increase fastness (e.g., wet-fastness with direct dyes). These leveling agents are also often used to remove unfixed and/or faulty dyes in post-scouring or stripping processes [10b]. 2. Polyester Dyeing Polyesters (polyethylene terephthalate) and their physically or chemically modified polymers/copolymers, along with cotton, are the most abundant fibers in the textile markets [1]. Disperse dyeing is the most important dyeing method for polyester and other hydrophobic synthetics. Other dyes occasionally used for polyester and other hydrophobic fibers are azoic, vat, basic dyes, and pigments [5a] that are mostly used for blend or for specific shades. Polyester fibers are tightly packed (essentially free of voids) with high crystalline structures that are not easily accessible to all types of dye molecules. Accordingly, polyester dyeing is often conducted at high temperature (under high pressure), with dye carriers (assistant by solvents), or via pad-dry heat to facilitate dye uptake. A typical high temperature (e.g., 250 to 275 ºF) dyeing bath includes about 0.5 to 2% anionic surfactant,

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∼∼1% low-foam nonionic surfactant, ∼ ∼0.25% chelant (e.g., ethylenediaminetetraacetate [EDTA], hydroxyethylethylenediaminetriacetate [HEDTA], or diethylenetriaminepentaacetate [DTPA]), 0 to 3% carrier (for uniform dye distribution and dyeing acceleration), antifoam agent (if needed), and acetic acid (to adjust pH to 4.5 to 5.0), in addition to disperse dyes or dye mixtures [6, 8]. The anionic surfactants as disperse dyeing assistants have functions of dye dispersing, leveling, and fiber lubricating. The nonionic surfactants, such as polyethylene-glycol esters, enhance greatly dye penetration and migration via solubilization, which leads to improved leveling and exhaustion yields [7]. The nonionic surfactants also enhance fiber wetting and emulsification of residual oils and waxes. However, precipitation of nonionic surfactants and formation of insoluble complexes with dyes at or above cloud points during high temperature dyeing causes severe uneven shades and staining. In the dyeing practice, anionic surfactants are often added to increase the cloud points and stabilize the nonionic surfactants. In many cases, a combination of nonionic and anionic surfactants is recommended. In some cases, sequestering agents are added to prevent precipitation of heavy metal–sensitive dyes. The same leveling principle of the exhaust dyeing can be applied to the continuous and semicontinuous dyeing processes. The leveling surfactants can also be applied to the disperse dyeing processes of other hydrophobic fibers, such acetates, triacetates, Nylons, olefins, acrylics, aramids, modacrylics, and saran. 3. Wool Dyeing Wool and other protein-based fibers, such as silk, fur, and leather, are typically dyed under acidic conditions with acidic dyes, a major group of anionic dyes. Other dyes, such as metal-complex, mordant, vat, basic, and reactive, as well as azoic dyes are also used for dyeing of the protein fibers [9a]. Leveling is particularly important to wool dyeing, because of the “tip frosting” problem—uneven shades between fiber tips and roots. The unevenness can be partially reduced by temperature and pH control, and with addition of electrolytes, such as Glauber’s salt (Na2SO4•10H2O), common salt, and ammonium sulfate, that neutralizes the positively charged surface to reduce electrostatic interactions [8]. With surfactants, the leveling effect is more effective in wool dyeing. Anionic surfactants (e.g., LAS, or alkylsulfosuccinates) as well as other anionic surface-active aromatics (e.g. condensates of naphthalene-sulfonate or naphthalene-phenol with formaldehyde, or sulfonated phenol complexes) are effective fiber-substantive leveling agents that reduce dramatically striking rates of acidic dyes. Nonionic (mostly polyalkyloxylated) surfactants [1] help solubilizing dye molecules in the dyebath, which leads to reduced exhaustion rates and improved dye migration. Amphoteric surfactants are also used for wool dyeing, often under well-controlled pH conditions. The amphoteric surfactants may interact with cationic fiber sites or with anionic dyes differentially, depending on pH of the dyeing solutions. These surfactants can be used alone, but often applied in a combination of two or three, to enhance leveling effects. The concentration of the total surfactants is usually less than 2 g/l in the dyebath. The same leveling agent systems can also be used for synthetic polyamides (such as Nylon and modified acrylic fibers) under acidic conditions. In addition, cationic surfactants have been used as a key leveling agent for nylon dyeing. Very often, the cationic surfactants are used in a combination with nonionic and/or anionic surfactants [7]. 4. Acrylic Fiber Dyeing Acrylic fibers are synthesized by addition polymerization of acrylnitrile that is different from the poly-condensation process of polyester and polyamide fibers. The acrylic polymer

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is less packed than polyester fibers, and often contains anionic functional groups (such as sulfonic, carboxylic, and/or phosphoric), mostly at the chain terminals. Therefore, the acidic-modified acrylic fibers are dyeable to basic or cationic dyes. Same as acidic dyeing, the main driving force for dye uptake of fibers is electrostatic. The striking rate at initial dyeing is very fast. Therefore, leveling is important for basic dyeing. Cationic surfactants, such as trimethylalkylammonium halides are important leveling agents for acrylic dyeing. A surfactant with a longer chain usually provides better leveling ability. The cationic surfactants with chain length of C12 to C18 (e.g., dodecyltrimethyl ammonium bromide) are often used for leveling in basic dyeing. Benzyl trimethyl ammonium chloride (BTMAC) is another commonly used leveling agent for basic dyes. An aromatic ring in a cationic surfactant facilitates delocalization of the positive charge further reducing the binding strength of the surfactant with fibers. Therefore, basic dyes can easily replace these surfactants, which leads to uniform dyeing with a high exhaustion yield. The surfactants compete with the basic dyes for the acidic sites of the fibers, therefore, reduce the dye sorption and exhaustion yields. All these leveling surfactants should be selected with lower affinity to the acrylic fibers than the basic dyes to avoid permanent blocking of the anionic sites of the fibers [10c]. Polymers with multiple cationic functional groups may also provide leveling effects. These polycationics form a protective layer on the fiber surfaces to reduce dye uptake and diffusion rates. Anionic surfactants, as dye-substantive leveling agents, reduce availability of the basic dyes. To inhibit potential precipitations of the complex of basic dyes and anionic surfactants (via charge neutralization), nonionic surfactants are often added in combinations with the anionic surfactants [10c]. The nonionic surfactants solubilize dye-surfactant complexes that have no or little substantivity to the acrylic fibers. As a result, dye molecules are slowly released from the soluble complexes in the dyebath and give uniform adsorption and distribution in the fibers. The functions of a typical formulation of dyeing auxiliaries for acidic acrylic fibers [8] are shown in the Table 2.

Table 2

Chemicals Used in Basic Dyeing

Ingredient

% owf

Chelating agent (e.g., EDTA) Neutral electrolyte (e.g., Na2SO4)

∼0.25

Leveling agent

1.0–3.0

Nonionic surfactant Acid (e.g. acetic acid)

0.3–0.5

5–10

0.5–1.0

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Function Sequester heavy metals, prevent precipitation, and reduce uneven shades Slow down dye uptake, and promote dye transfer. As a mild leveling agent, not sufficient to compete with highly substantive dyes. Need surfactants for best leveling results. Promote uniform dye distribution. As fiber-substantive retarders, cationic surfactants are predominant, including surface-active aromatics. Some cationic surfactants also provide softening benefits to enhance feel characteristic of the fibers. Solubilize and stabilize dyes and dye complexes Adjust pH of dyebath for desirable dye exhaustion and leveling control (e.g., pH 4.5–5.0).

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In addition to the basic dyes, acrylic fiber can be dyed with disperse dyes and pigments, similar to the disperse dyeing of polyester fibers. Small size dyes are often selected for acrylic dyeing, due to the limited solubility of the disperse dyes in the acrylic dyebath. Therefore, dye diffusion is usually more effective in the acrylic dyeing. As a result, less leveling surfactants are required for disperse dyeing of the acrylic fibers. In addition to the anionic modification with acids, the acrylic fibers can be modified with esters or bases. Copolymers of the acrylic and esters have reduced fiber glasstransition temperature (Tg) and improved diffusability to dyes. With basic co-monomers, such as amines or pyrimidines, the acrylic copolymers are dyeable to anionic dyes. With such modified acrylic copolymers, the leveling surfactants are used in a similar way to that in an anionic dyeing process. B. Dispersing Agents Dispersing agents are able to provide fine, stable and uniform suspensions of waterinsoluble dyes, particularly disperse dyes. They are widely used both in dye preparations (as commercial blends of disperse dyes and dispersants) and in dyeing processes (as additives in disperse dyeing). The commercial disperse dye powders contain high percentage of dispersing agents (commonly about 60% or more, by weight) [9]. The dispersing agents have two key functions to assist dyeing. First, they reduce and prevent dye aggregation and precipitation, to reduce high initial dye striking and provide uniform dyeing. Secondly, they solubilize and micellize dyes, to enhance dye transfer and penetrate (thermo-migration) in hydrophobic fibers mono-molecularly. The dispersing agents include surfactants and some surface-active polyelectrolytes or polymers. Surfactants in disperse dyeing may provide functions of wetting, penetrating, leveling, softening, lubrication, and emulsifying, in addition to dispersing and solubilizing. In commercial disperse dye products, anionic polyelectrolytes are often incorporated [13]. The most common dispersing polyelectrolytes include lignin sulfonates and oligocondensed naphthalene sulfonates with formaldehyde. In dyeing applications, anionic surfactants are often added, in combination with nonionic surfactants and/or polymeric dispersants. In general, anionic surfactants promote wettability of dye particles and stabilize dye suspension, while nonionic surfactants promote solubility and dispensability of the dyes. The anionic surfactants adsorbed on the dye particles wet and induce negative charges on the dye surfaces. The resulting zeta potential of the double layer leads to strong repulsion of the charged dye particles that compensates the strong cohesive attraction driven by unbalanced high surface energy of the small dye particles. The main anionic surfactants include petroleum sulfonates, olefin-sulfonates, sulfonated fatty alcohols, and glycerol esters. The nonionic surfactants facilitate uniform uptake of the disperse dyes either via sufficient dye micellization or via enhanced solubilization in a continuous aqueous phase [14]. The most often used nonionic surfactants include alcohol ethoxylates and alkylphenol ethoxylates. The nonionic surfactants as dispersants usually have higher cloud point to avoid dye aggregation during the disperse dyeing process. A combination of anionic and nonionic surfactants usually provides better dispersing functions to enhance dye migration and prevent precipitation. Dispersing agents are critical in dyeing with disperse and vat dyes. Typically, a dose of 0.75 to 1.0 g/l dispersants provides satisfactory dispersing effects. However, with lower fiber load or for higher color depth, the dispersant concentration can be up to 2 g/l [9]. C. Wetting and Penetrating Agents Quick and thorough wetting is vital for quality dyeing that facilitates complete adsorption and penetration of dyes and dye auxiliaries to the fibers, particularly in the continuous

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dyeing process [12b,15]. In an immersive dyeing process, air bubbles are often trapped in the fibers that have to be completely removed for ultimate spreading of the fibers by dye liquors. Fibers have different wettability in dyebath, due to variations of surface property/morphology, textures, structures, and compositions/contaminations. Synthetic fibers, such as polyesters or polyamides, are more hydrophobic. They are very difficult to wet due to significantly low surface energy. Natural fibers, such as cotton or wool, are more hydrophilic with relatively higher surface energy. However, the native fibers are very heterogeneous structurally, depending on geometry, climate, nutrients, treatment conditions and other factors that often cause difficulty for uniform wetting. Effective wetting and deaeration can be accomplished by wetting agents, primarily surfactants. Surfactant induced interfacial interactions lead to reduced surface tension of dye solutions and lower contact angle of the fiber surfaces that promotes surface sorption and dye penetration throughout fibers. Fast and thorough spreading over the fiber surfaces by dye solutions is critical at the beginning of most dyeing processes to achieve uniform dyeing. Depending on fiber, dye, and dyeing process, the surfactants used for wetting can be anionic, nonionic, or combinations. Alkylbenzenesulfonates, naphthalenesulfonates, olefinsulfonates, alkyl succinates and sulfosuccinates, alkyl sulfates, sulfonated alkyl ethoxylates, sulfonated alkyl phenol ethoxylates, sulfated fatty acid esters and amides, sulfated natural oils, and alkyl phosphate esters are main commercial anionic surfactants, while alcohol exothylates, alkylphenol ethoxylates, ethoxylate/propoxylate copolymers, polyethylene glycol fatty acid esters, and fatty acid alkyl amides are typical nonionic surfactants [16]. Anionic surfactants usually have better wetting performance. Ethoxylated nonionic surfactants normally have better deaeration properties. In a practical application, surfactants with hydrophile-lipophile balance (HLB) in a range of 7 to 9 usually have best wetting effects. Synergistic wetting effects can be attained with a combination of anionic and nonionic surfactants, such as a blend of phosphalated alcohols and alcohol ethoxylates. Most of these wetting surfactants also play roles in dyeing process as penetrants to facilitate dye diffusion into the fibers, which is a rate-determining step in almost all the single dyeing and some printing processes [17]. Sufficient dye diffusion leads to enhanced color depth and fastness (such as wet, rubbing, and light fastness). Cationic surfactants are rarely used in the dyeing process for fiber wetting. D. Foaming and Defoaming Surfactants have important applications in foaming as well defoaming applications. Foam dyeing, printing and finishing have advantages in saving energy and water, and reducing effluents. Surfactants, particularly anionic and some nonionic, promote foaming. Typical textile foaming surfactants include alkyl sulfates, dialkyl sulfosuccinates, polyoxyalkylene fatty alcohols, and their blends. However, the foaming technologies in textile dyeing and finishing processes are largely limited, due to the poor evenness and reproducibility. Defoaming, on the other hand, is very important in many textile applications for uniform and high quality results, particularly in a high-speed or high-agitation process. Silicone based emulsions, containing silica (often chemically modified to enhance surface hydrophobicity) or other inorganic fillers, are the most effective and widely used defoaming systems. Some organic based emulsions are also frequently used in textile defoaming that contain surface active materials, such as fatty acids and ester derivatives, higher alcohols, polyglycols, and alkyl phosphoric acid esters [10b]. These emulsified hydrophobic materials are able to penetrate the lamellar walls and insert to the liquid/air interfaces of the dense foams, leading to rupture of the foam bubbles. In addition to the emulsion systems, some surfactants are also used for defoaming. The surfactants, mainly the ones with lower surface tensions, tend to spread over the surface of the intercellular films, which is

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especially effective to destabilize the light foams [10b]. In most defoaming applications, surfactants alone are often insufficient. They are often used in combinations with defoaming emulsions to improve the system stability and facilitate dispersing efficiency of the hydrophobic defoaming particles. A combination of low and high HLB surfactants, such as glycerol or sorbitan monostearate with polyethyleneglycol monostearate, is a most common surfactant system used in the textile defoaming emulsion systems [10b]. E. Aftertreatment Applications After dyeing, textiles often undergo further postdyeing treatment to enhance dyeing quality judged by dye fastness. Surfactants play roles in some of these aftertreatment processes. Post-scouring is essential to remove unfixed and loosely bound dyes and auxiliaries remaining on the fiber surfaces. This leads to improved fastness properties, such as wet, rubbing, and sometime light fastness. Anionic and nonionic surfactants are often used to assist the post-scouring process, usually in a dose range of 0.5 to 3 g/l [8, 18]. Most scouring processes are conducted under alkaline conditions (such as alkaline reduction) with or without surfactants. The scouring can also be applied under acidic conditions for wool-containing fabrics. Salts are often added in the scouring process to accelerate dye removal. Particularly for reactive (such as hydrolyzed), sulfur and vat (before and after oxidation stage), azoic, basic, and disperse dyes, post-scouring is very important [8,15,18]. Stripping is applied to remove dyes when faulty dyeing occurs. Stripping is often conducted under much stronger conditions than post-scouring. Different types of surfactant systems are selected for different dyes and auxiliaries. To strip vat dyes, cationic surfactants (such as cetyl trimethylammonium bromide) are commonly used, while nonionic surfactants are typically used for disperse dyes [1]. Anionic surfactants can be used to remove cationic fixing agents for direct dyes [6]. These surfactants may be used in a mixture with disperse polymers, such as polyvinyl pyrrolidone (PVP), that form a complex with anionic dyes (such as direct, luco form of vat, and sulfur dyes), to prevent dye redeposition onto the fibers. Very often, to remove deeply trapped dye residues, bleaches (reductive or oxidative, under alkaline or acidic conditions), sequestering agents, solvents and/or carriers are added in stripping process. In addition to stripping, leveling and over-dyeing are also helpful in correction of faulty dyeing, such as in vat dyeing [15]. Fixing is used to improve wet fastness of water-soluble dyes, such as direct, or sulfur dyes for cotton fibers, and acidic, or basic dyes for wool fibers. The prime surfactants in this application are cationic, typically quaternary ammonium salts, such as alkyl trimethyl ammonium. The cationic fixing agents interact with anionic dyes to form insoluble complexes on the fiber surfaces. Typically, 1 to 2% owf cationic surfactant is used at pH 5-6 (usually adjusted by acetic acid) to fix direct dyes on a 1% dyed fiber surface [6]. Other cationic surfactants include alkyl or pyridiniums, amide-formaldehyde condensates, fatty amides, polyamine derivatives of polyethylene diamines, and cationic polymers. Some cationic dye fixing surfactants contain two or more quaternary ammonium groups, and some contain different cationic centers, such as phosphonium, sulfonium, arsonium, or iodonium that, however, are not commonly used in the industry. The cationic fixing agents can also be applied to reactive dyes, particularly in printing, to reduce contamination of hydrolyzed dyes and improve color value. The post-treatment with a cationic surfactant, however, may lead to shade changes and reduced dye fastness (e.g. light fastness) in some cases [10b]. Other fixing methods include bridging dyes and fibers with metals (such as complexation with cupper), chemical reactions (such as diazotization), polyfunctional cross-linking (such as formaldehyde treatment), and surface protection (e.g., resin treatment) [18]. In these processes, surfactants may not be needed.

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IV. SURFACTANT APPLICATIONS IN TEXTILE PRINTING Printing is often described as local dyeing. The principles of dyeing, therefore, can be applied essentially to printing, except that the printing has very restricted boundary conditions [1,9]. In a printing process, highly concentrated dyes and pigments are applied to very confined fabric areas by dye/pigment pastes, inks, or dispersions, containing thickeners and pigment binders [19]. The dyes used in textile printing are fundamentally the same as those used in dyeing for different fabrics, in terms of dye selection, application, and mechanism [9]. Pigments, which are less frequently used in dyeing on the other hand, have a broad application to printing, due mainly to the low cost, easy processing, universal applicability (to almost all classes of fabrics, with all types of methods and styles), wide range of pigment colors, and superiority in some fastness (e.g., light fastness). As estimated, pigment printing accounts for 80 to 85% total printing market in the United States, and about 50% globally [19]. In textile printing industries, surfactants are extensively used to assist pigment/dye emulsification in both manufacturing and applications, with functions of leveling, dispersing and wetting, similar to the applications in textile dyeing. The printing surfactants have a $15 million market in the United States (Table 1) that accounts for about 5% of total surfactant market in the U.S. textile industry. These surfactants improve stability of printing pastes and promote uniform printing for quality color (e.g., fuller shades and higher fastness). As estimated, the levels of the surfactants used in printing pastes are about 2% in the United States, and 2.5% in Western Europe [1]. Surfactants also play an important role in washing and detergent scouring processes to remove excess amounts of dyes/pigments and thickeners, after printing. In screen printing, which is a predominant printing process in the industry (about 80% worldwide) [15], the surfactant emulsifiers are extensively used to reduce screen clogging and staining/contaminations, assist cleaning of printing equipment (screens, pipes), and improve color quality and printing effectiveness. As emulsifiers and dispersants, the surfactant usage is about 0.1 to 1.0% [19]. As wetting agents, the surfactants promote fast and uniform color spreading and penetration. The typical use level of the wetting agents are in a range of 0.1 to 1.0% [19]. The wetting agents in the printing process should always be kept to a minimum. With extensive shearing force in the printing process, foam is easily formed that may cause uneven color transfer and loss in color value. Surfactants and/or solvents are added in some printing process to defoam. The typical defoamer usage is in a range of 0.5 to 1.0% [19]. The surfactants are also used in gasoline printing, conservations, and antimigration applications [1]. Like those used in dyeing, the surfactants for textile printing and pigment preparation/ suspension include nonionic, anionic, and amphoteric, as well as cationic surfactants. The nonionic surfactants, which have low foaming tendency, are particularly effective to promote fast wetting, leveling printing, and brushability, and prevent feathering or bleeding. Combinations of nonionic and anionic surfactants are also frequently used in printing. The surfactants for dispersing, wetting, and scouring are essentially the same as those used in dyeing. The typical surfactants for printing emulsification include ethoxylated fatty esters, amides and alcohol, polyglycol ethers, alkylaryl sulfonates, and alkyl sulfates. The common surfactants for thickener removal include alkylaryl acids, alcohol ethoxylates, fatty acids, polyglycol ether, alkyl phosphonates, and quaternary ammoniums [1]. The defoamer surfactants are usually very hydrophobic, with HLB in a range of 1.5 to 3.0. Specifically, sulfated sperm oil and pine oil were used as antifoaming agents, but silicone oils or mineral oils are often selected. Polydimethylsiloxane (PDMS) and derivatives incorporated to inorganic particles (e.g., silica, zeolites, aluminum or titanium oxides, and

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zinc or aluminum chlorides) are the most frequently used antifoaming agents in the textile industry [1].

V. SURFACTANT APPLICATIONS IN TEXTILE FINISHING Surfactants play important roles in textile finishing, primarily wet finishing or chemical finishing processes. The textile finishing include, in a broad sense, both textile preparation or purification (such as sizing and desizing, scouring/carbonizing, bleaching, mercerizing) and final finishing for aesthetic and functional property improvement. The preparation finishing with surfactants has been introduced in Section II of this chapter. Only the final finishing applications of surfactants will be discussed here. The textile finishing in a narrow sense refers all the final finish processes after dyeing that includes aesthetic and functional finishing to improve softening, hand building, backcoating, wrinkle/crease resistance, shrink proofing, durable press, water repelling, soil release/stain repelling, flame retardency, adsorbency/hydrophilicity, comfort, antistatic, antimicrobial, pilling resistant, abrasion/wear resistant, light or heat resistant, and other properties [9b]. In a chemical finish process, chemical agents are applied to the textile. Complete wetting of the fiber surface, and fast and even spreading of the finish agents are the critical first step of a wet process for a desired result. The surfactants, in principle, can be used as wetting/spreading and dispersing/emulsifying agents in all wet finishing processes. A. Softeners Softening and antistatic finishing are the most important applications of surfactants in textile finishing, that account for about 14% and 6% of the total textile surfactant consumption in the United States, respectively (Table 1). The consumption of the softening surfactants is even higher in Western Europe (about 24%) [1]. The softeners improve textile softness, smoothness, hand feel, and also fiber lubricity, flexibility, elasticity, fullness, and processibility [20]. The textile softeners typically include mainly surfactants and polymers, and easily applied via a padding or exhaustion process. As estimated [1], there are about 35 to 40% cationic, 40 to 45% nonionic, 8 to 10% anionic, and a small portion of amphoteric surfactants in the textile softener market. In general, surfactant softeners are not wash fast. Most of the surfactants are washed off from the fibers by detergent solutions. In general, surfactant softeners are relatively poor in wash fastness. Most of them can be washed out by regular detergent solutions. Cationic surfactants have high substantivity to most fibers, particularly the natural fibers, such as cotton. They are more effective than other surfactants in terms of exhaustion yields, low-dose softening efficiency, and relative wash fastness. In addition, the cationic softeners often provide antistatic and water-repelling properties, antimicrobial properties, sewability, and corrosion resistance [1, 21]. They are more compatible with most resin finishes. However, they are not effective for hydrophobic fibers, due to the poor substantivity. The main disadvantages of the cationic softeners include incompatibility to anionic auxiliaries, yellowing fabrics, affecting dye shades and fastness, and soiling fabrics. A cationic surfactant softener typically contains a positively charged nitrogen and at least one hydrophobic chain, typically two alkyl chains at each molecule. The alkyl substitutes contain usually C12 to C22 carbon-chains, derived from fatty acids or alcohols, such as coconut or tallow. The fatty chains (such as tallow) are often hydrogenated for desired softening and hydrophilic properties. Some fatty chains may be further ethoxylated/propoxylated, and/or esterified or aminated for different finishing, formulation, and

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solubility properties. Substituted quaternary ammoniums salts are the most extensively used cationic softeners, such as disterayl dimethyl ammonium chloride (DSDMAC) [21] that deliver desired silky, pliable handle at a low concentration (e.g., 0.07 to 0.1% owf). Imidazolinium surfactants are probably the second most extensively used softeners, but some other nitrogen-heterocyclic surfactants, such as pyridinium, pyrimidinium, quinolinium, morpholinium, piperidinium, and piperazinium derivatives, are also used as textile softeners. Other important surfactants used in textile softening include neutralized longchain fatty amines, fatty amides, alkanolamides, polyethylene imines, aminoesters, amidoamines (such as amide derivatives of ethanol-ethylenediamine), diquaternary amines or ammoniums (such as tallow ethanol substituted and fatty acid-ethyoxylester substituted propylenediamines, bisimidazoliniums), and polyammoniums or polyamines [21]. Very often, these surfactants are used in blends, particularly in combinations with quaternary ammonium and/or imidazolinium softeners. The typical anionic counterion is chloride, and sometimes bromide, methyl sulfate, ethyl sulfate, or acetate. An exhaustion finishing process at a neutral to slightly acidic pH is often preferred for a uniform distribution of the cationic surfactants on the fibers, due to their high adsorption efficiency to the negatively charged fiber surfaces. Nonionic surfactants also provide good softness with lubricating and antistatic benefits. They are more resistant to yellowing, more compatible to most textile auxiliaries, and do not affect dye shades [1]. However, the nonionic surfactants have poor wash fastness due to the low substantivity to most fibers. Higher concentrations of a nonionic surfactant (such as 0.5 to 2.0% wof) are required to deliver desired softening properties. The most common nonionic surfactants for textile softening are polyoxyalkylene derivatives (such as polyethyleneglycol esters or amides of fatty acids) and condensates of fatty alcohols or acids (such as glycol stearates). Nonionic surfactants are rarely used alone. They are often used in combinations with cationic softeners and/or other textile auxiliaries. Anionic surfactants are more stable with good yellowing resistant, which are also good rewetting agents without interference to foam finishes. They are often used in starchbased temporary finishes. The anionic surfactants promote penetration of starch materials, and therefore, improve size retention. They also increase fiber elasticity, flexibility, and weaving efficiency. However, the softening applications of the anionic surfactants are limited in the textile industry, due mainly to their low substantivity (poor wash fastness) and incompatibility with resin finishes and cationic auxiliaries. To produce desired softening benefits, higher surfactants doses are often required due to the low adsorption to the fibers or poor exhaustion yields. In general, the anionic surfactants produce inferior softening properties to cationic and nonionic softeners. Typical anionic surfactants as textile softeners include soaps, fatty alcohol sulfates, sulfated or sulfonated oils and tallows, fatty acid condensates, and some oils, fats, and wax emulsions [20]. Particularly, sulfonated monoglyerides and alkyl sulfonates are often used [1]. Polymer softeners include mainly silicone and polyethylene emulsions that lubricate the surface of individual fibers, with better fastness than surfactant softeners. Silicones are the most extensively used polymer softeners that account for 20-25% of the textile softener marked [1]. The silicones have superior softening properties (slick, silly handle) with good wash fastness, stability (thermal and oxidative), and wrinkle resistant properties. They also improve tear, abrasion and wear strength, sewability, water repellent, foam depressing, and processibility of the fibers/fabrics. The main disadvantage of the silicone softeners is the cost that limits their extensive application in textile treatment. Silicones are often applied in emulsions with nonionic surfactants, such as polyethoxylated lauryl alcohol, or as additives with other softeners for cotton and synthetics or blends. Dimethyl

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silicones (such as PDMS) and organo-modified derivatives (such as amino-functional silicones) are often used as textile softeners and lubricants. Polyethylene wax emulsions are often used for toweling [1]. Nonionic or anionic surfactants are typically added as dispersing or emulsifying agents to stabilize the polymer emulsions. The polymer softeners are usually stable and more compatible with most cationic, anionic and nonionic softeners. They also provide improved fabric tear and abrasion strength [1]. Reactive surfactant softeners are developed to enhance wash fastness or durability. They contain a reaction group at the end of a softening group (such as fatty alkyl chains) to react with fiber active sites (such as OH groups of cotton). Some examples of the reactive softeners include stearyl aminomethyl pyridinium chloride (restricted due to toxic pyridine release), methyl steramide, octacdecylethylene urea, and fatty acid derivatives of melamines, triazones and carbonates [1]. B. Antistatics Antistatic finishing becomes more important with introduction of synthetic fibers. Electrostatics may be generated by simply rubbing, contacting, and many other ways, which causes often problems in textile manufacturing and end uses. Static electricity leads to repelling fibers (therefore difficulties in fiber carding, drawing, weaving, knitting, roving, spinning, extruding, and fabric folding), attracting dirts and dusts, soiling/ staining, cling to the body and undergarments, and creating electric discharge/shocks or sparks that could cause fires and even explosions [1,22]. Natural fibers, such as cotton and wool, are more hygroscopic (hydrogen-bonding with water molecules) that adsorb moisture and quickly disperse electric charges. Synthetic fibers, on the contrast, are hydrophobic with very low moisture adsorption, and therefore, have poor electric conductivity. To avoid buildup and/or facilitate rapid dissipation of the static charges on the hydrophobic fibers, antistatic finishes are developed. Many surfactants have antistatic properties, particularly cationic and nonionic surfactants that form condensed hygroscopic layers on fiber surfaces to increase moisture contents and/or electric conductivity. Cationic surfactants are the most important antistatic finishes. Alkyl quaternary ammonium salts, polyethoxylated fatty ammonium salts, fatty ammonium esters, alkyl imidazoliniums, perquaternized alkyldiamine derivatives, alkylamides of polyethylene derivatives, alkyl betains, long-chain ammine-oxides, and fatty acid polyamine condensates are typical examples of the cationic antistatic surfactants [20]. Alkyl quaternary ammonium salts, containing usually C8 to C18 carbon chains, such as dihydrogenated tallow or coconut dimethyl ammonium chloride, are probably the most widely used temporary antistatics, with superior static properties at very low application level (e.g., 0.25% wof) [22]. Most cationic softeners for synthetic fibers, as described in the previous section, offer good antistatic benefit. For example, long-chain heterocyclic amines (imidazolinium, pyridinium, piperidinium, and morpholinium) have been extensively used as antistatics. Nonionic surfactants are usually more effective with initial antistatic, but lose the function quickly in the wash due to the low substantivity to the fibers. Polyethoxylated paraffins and alkylphenols, polyethylene/propylene glycol esters, polyethylene glycols and alkylphenyls are examples of the nonionic antistatic surfactants [1]. The surfactants and surfactant combinations can be used either alone or in a finishing formulation (such as with some softeners, lubricants, and hand building agents) for temporary (such as spin finishes) or durable (such as crosslink curing) antistatic finishing. For temporary finishing, surfactants, predominantly cationic and nonionic surfactants, are frequently used in aqueous emulsions containing lubricants, such as vegetable

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or mineral oils, waxes, hydrogenated tallow, and alkylesters [1]. Anionic surfactants are as well used, such as alkyl sulfates, sulfonates, or phosphates, and fatty acids, that have some antistatic properties but are mainly used as emulsifiers to improve formulation stability and uniform adsorption and penetration. The antistatic emulsions may also include some humectants, such as glycerols, amines, and inorganic salts [22]. A durable finish is primarily achieved by a polymeric surface modification of hydrophobic fibers via, such as in situ crosslinking. The resulting polymer network may contain ionic groups that are highly attractive to antistatic agents (such as electrostatic interactions between cationic surfactants and acidic functional groups of the polymers), and/or hygroscopic groups, that promote electric conductivity (such as polyethylene/polyamine glycol coatings, quaternized prepolymer modifications) [22]. Incorporation of electrically conductive elements, such as metal particles (copper, silver, cobalt, gold, nickel, aluminum, stainless steel) and carbon fibers into the synthetic fibers, particularly nonwoven, is an alternative way to improve antistatic properties. These durable finishes usually provide high antistatic efficiency under dry conditions and superior fastness to laundry and wear or other end uses. C. Other Finish Applications Surfactants are extensively used in chemical finishing processes as wetting agents, emulsifiers, dispersing agents, and play important roles in textile softening and antistatics. In addition, surfactants have some minor applications in other wet finishing processes. 1. Antimicrobial Finishing Quaternary amine surfactants have a broad spectrum of activities that have been widely used in antimicrobial treatment as nondurable finishes. The antimicrobial finishes have functions to prevent against contamination by bacteria (both gram positive and negative), fungi, yeast, protozoa, virus, and other microorganisms, and against attack of insects and other pests. These surfactants are mainly used as bactericides and mildewcides in textile antimicrobial finishes. Examples of the cationic surfactants used as textile biocide finishes include chloride salts of cetyl benzyl dimethyl ammonium, tertiary octylphenoxyethoxylethyl benzyl dimethyl ammonium, tridecyl hydroxyethtyl benzyl imidazolinium, lauryl pyridinium, and some phenyl mercuric ammoniums. In the industrial material finishing, dimethyl benzyl ammonium phosphate is often used as rot-proofing finish [23]. Nonionic and anionic surfactants are much less effective than cationic in the antimicrobial application. They are occasionally used with a role of bacterial removal and/or inactivation. 2. Water/Oil Repelling and Soil-Release Finishing Some surfactants provide textile with water or oil repelling function, and/or soil-release or antisoiling benefits via fiber surface modification. The surfactants modify surface hydrophilicity/hydrophobicity of the fibers or fabrics, reduce surface energy, and facilitate water/oil repelling and soil release. The surface modification depends on types and structures of fibers (such as hydrophobicity, texture). Therefore, there are many types of repelling agents for different fibers. Fluoroalkyl chemicals, including surfactants and polymers, are most effective finishes in water and oil repelling, and soil release for both synthetic and natural fibers that are often used in combinations with other repelling agents and auxiliaries. Silicone emulsions are the most important water repelling finishes with excellent softening properties [1]. Soap and fatty acid salts, such as aluminum, titanium, zinc, zirconium soap, and pyridinium salts of fatty acids or amides are some earliest nondurable water repellents in textile industries [24]. Emulsions of paraffin waxes – metal salts are also old and economical water repelling agents that are still used in textile

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finishing. Fatty acid derivatives and fatty alcohols, ethoxylated alkylphenols, quaternary alkyl amines, and other surfactants are an important type of repelling agent, often used to improve soil release and anti-soiling properties of textiles. Quaternary ammoniums are the most commonly used soil release surfactant. Reactive quaternary surfactants, such as octadecyloxylmethyl pyridinium, stearaminomethyl pyridinium, offer durable water repelling properties. However, most other surfactants have low wash fastness that are normally used as temporary finishes. The surfactant repelling agents are usually used in combinations with other finishes, such as anticrease and durable press agents. 3. Optical Finishing Surfactants are often used with emulsified waxes, polyolefins, glycols, fats, oils as lustering agents, and also with dispersed pigments and binders as delustering agents [1]. Surfactants have extended applications in many different fabric-finishing processes to facilitate operation, and improve process uniformity, efficiency, and quality control. In general, anionic and nonionic surfactants are more extensively applied in the textile wet process. Cationic surfactants have relatively limited applications, due to restricted compatibility and cost-effectiveness. Amphoteric surfactants are only a very small portion of the total textile surfactants. Anionic and nonionic surfactants are widely used in textile preparation/purification, dyeing, and finishing/posttreatment, as wetting and spreading, leveling, emulsifying, dispersing, solubilizing, detergencing/scouring, and/or foaming agents. They also serve, with a minor role, as softening, lubrication, and antistatic agents. Nonionic surfactants have some advantages in pH stability, hardness tolerance, compatibility with both anionic and cationic auxiliaries, and are relatively less deactivating to enzymes. Cationic surfactants are mostly used in finishing processes, as softening or lubricating, antistatic, antimicrobial, water/oil-repelling, antisoiling agents, and also used in dyeing as dye-fixing, and dye-leveling (such as acrylic dyeing) agents.

REFERENCES 1. World Markets for Textile Chemicals 1999–2009, a Report from Hewin International, Chapters 1 and 2, pp. 1–154, 2001, John Willey & Sons, Inc., New York, ISBN: 0-471-36351-0. 2. Textile Pipeline, A Quarterly Review of Textile and Fiber Demand, Quarter 3 2005, PCI – Fibers & Raw Materials, West Sussex, England. 3. Handbook of Fiber Science and Technology, Vols. 1 and 2: Chemical Processing of Fibers and Fabrics, edited by M. Lewin and S. B. Sello, 1984, Marcel Dekker, New York. 4. Handbook of Fiber Science and Technology, Volume 7: Fiber Chemistry, edited by M. Lewin and E. M. Pearce, 1985, Marcel Dekker, New York. 4(a) Chapter 10: Cotton Fibers, p. 809. 4(b) Chapter 6: Wool Fibers, p. 589. 4(c) Chapter 7: Silk: Composition, Structure and Properties, p. 647. 5. Wellington Sears Handbook of Industrial Textiles, edited by S. Adanur, 1995, Technomic Publishing Company, Lancaster, Pennsylvania. 6. J. Rivlin, The Dyeing of Textile Fibers – Theory and Practice, 1992, ISBN: 0-9633133-0-4 7. E. I. Valko, Textile Auxiliaries in dyeing – Review of Progress in Coloration, Vol. 3, 1972, pp. 50–62. 8. AATCC, Dyeing Primer, 1981, Am. Assoc. Text. Chem. Color., Raleigh, North Carolina 9. T. L. Vigo, Textile Processing and Properties – Preparation, Dyeing, Finishing and Performance, Textile Science and Technology, Vol. 11, Elsevier, New York, ISBN: 0-444-882243. 9(a) Chapter 3: Method of Applying Dyes to Textiles, pp. 112–192. 9(b) Chapter 4: Fabrics with Improved Aesthetic and Functional Properties, pp. 193–291.

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10. T. M. Baldwinson, in Colorants and Auxiliaries, ed. J. Shore, Vol. 2, 1990, Society of Dyes and Colourists. 10(a) Chapter 8: Functions and Properties of Dyeing and Printing Auxiliaries, pp. 373–397. 10(b) Chapter 10: Classification of Dyeing and Printing Auxiliaries by Function, pp. 398– 469. 10(c) Chapter 12: Auxiliaries Associated with Main Dye Classes, pp. 512–567. 11. H. D. Pratt, Jr. How to Use Anionic Surfactants in Textile Wet Processing, American Dyestuff Report, 1990, June, pp. 38N51. 12. A. Datyner, Surfactant in Textile Processing, Surfactant Science Series, Vol. 14, 1983, Marcel Dekker, Inc., New York, ISBN 0-8247-1812-. 12(a) Chapter 5: Dyeing, pp. 66–112. 12(b) Chapter 10: Wetting, pp. 22–32. 13. A. Datyner, Rev. Prog. Coloration, Vol. 23, 1993, pp. 40–50. 14. F. Jones, JSDC, 1984, Vol. 100, pp. 66–72. 15. J. Shore in Cellulosics Dyeing, ed. J. Shore, 1995, Society of Dyers and Colourists, pp. 367–375, ISBN 0-90195668-6. 16. Kirk-Othmer, Encyclopedia of Chemical Technology, 4th ed., 1997, Vol. 23, John Wiley & Sons, New York. 17. E. I. Valko, Textile Research Journal, August 1969, pp. 759–773. 18. S. M. Burkinshwa, Applications of Dyes, Chapter 7 in The Chemistry and Application of Dyes – Topics in Applied Chemistry, ed. D. R. Waring, G. Hallas, 1990, Plenum Press, New York, ISBN 0-306-43278-1. 19. AATCC Committee RA80, Pigment Printing Handbook, pp. 1–112, 1995, AATCC, Research Triangle Park, North Carolina. 20. H. H. Mosher, Chapter 5, in Textile Chemical and Auxiliaries, ed. H. C. Speel and E. W. K. Schwarz, 2nd ed., 1957, pp. 110–141, Reinhold Publishing Corporation, New York 21. R. Puchta, JAOCS, 61 (2), 1984, pp. 367–376. 22. S. B. Sello, C. V. Stevens, Antistatic Treatment, Chapter 4, in Chemical Processing of Fibers and Fabrics—Functional Finishes, Part B, Handbook of Fiber Science and Technology: Volume II, ed. M. Lewin, S. B. Sello, pp. 291–316, Marcel Dekker, New York, ISBN 08247-7118-4. 23. R. S. Mahomed, Antibacterial and Antifungal Finishes, Chapter IX, in Chemical Aftertreatment of Textiles, ed. H. Mark, N. S. Wooding, S. M. Atlas, 1970, pp. 507–552, WileyInterscience, New York. 24. H. L. Needles, Finishes and Finishing, Chapter 18, in Textile Fibers, Dyes, Finishes, and Process, 1986, pp. 193–223, Noyes Publications, New Jersey, ISBN 0-8155-1076-4.

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10 Detergent Formulations in Separation Science Edmondo Pramauro and Alessandra Bianco Prevot

CONTENTS I.

Introduction ........................................................................................................... 305 A. Micellar Solubilization.............................................................................. 306 1. Experimental Determination of Binding Constants ............................. 307 2. Indirect Evaluation of KB...................................................................... 308 B. Micelle-Mediated Separation/Preconcentration Techniques..................... 308 1. Micellar Extraction of Sparingly Soluble Compounds from Solid Matrices ............................................................................ 308 2. Preconcentration/Extraction Based on Thermal Phase Separation (Cloud-Point Extraction)............................................................ 309 3. Micellar Ultrafiltration .......................................................................... 313 C. Micellar Liquid Chromatography ............................................................. 316 D. Micellar Electrokinetic Capillary Chromatography (MECC) .................. 318 Acknowledgments........................................................................................................... 320 References ....................................................................................................................... 320

I. INTRODUCTION For several years now surfactant molecules and their aggregates have been applied in various domains of separation science exploiting the peculiar properties of these microheterogeneous systems and the practical advantages that they can offer as alternative solvent systems. Surfactant-based separations play a significant role in important areas including analytical chemistry, industrial chemistry, biotechnology, and environmental remediation processes, where micellar solutions are at the basis of recent successful procedures applied to clean polluted water, soils, and sediments. 305

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In particular, the usefulness of surfactant systems in analytical separations has been evidenced in a large number of reports dealing on their applications in various techniques including liquid chromatography, electrophoresis, ultrafiltration, liquid–liquid extraction, and solid–liquid extraction. The development of separation schemes which are not viable in homogeneous solutions allowed to improve the performances of several established methods and to propose completely new protocols, examined in detail in various reviews and books appeared since 1978 [1–11]. Most reported applications concerned the use of aqueous micellar solutions, although other amphiphilic aggregates, such as reverse micelles and water-in-oil microemulsions, have been also employed, especially for biomolecules recovery. In the following sections the applications of aqueous micellar solutions are examined taking into account the existing relationships between the solute/micelle interactions and the performances of the proposed procedures, with particular attention focused on the use of micellar systems as alternative cheap and safe solvents suitable for extraction/preconcentration of a variety of chemical species. Three main applications are discussed: (1) solubilization of target compounds (initially present in complex solid samples) in micellar aggregates without inducing phase changes; (2) application of the cloud-point extraction approach, based on the solute’s enrichment in a thermally generated new liquid phase; (3) concentration of micelles and their guest solutes by ultrafiltration. The development of aggregates exhibiting complexing capabilities toward metal ions, particularly useful for selective metals separation and recovery in methods (2) and (3), is also examined. Finally, the more recent applications of micellar liquid chromatography and micellar capillary electrophoresis in current analytical work and the actual trends of such techniques are briefly discussed and reviewed. A. Micellar Solubilization Aqueous micellar solutions can be used to dissolve a variety of compounds that are sparingly soluble in water through their incorporation in different regions of the microaggregates. In general, the solubilizing capacity toward solutes located in the inner part of micellar aggregates roughly follows the order: nonionics > cationics > anionics, for surfactants having the same hydrocarbon-chain length [12]. Incorporation of guest molecules tends to swell the micelles and can further favor the solubilization of other solutes. Interactions between solutes and micelles are usually described in terms of a binding process [13] involving the solutes, initially present in the aqueous phase, and the aggregates: S w + M ↔ MS

(1)

where S is a solute molecule, M is a micellar aggregate, and MS represents the solute bound to the micelle. The corresponding binding constants (KB), determined using different experimental techniques, are defined as follows: KB =

[S]m [S]w CD

(2)

The subscripts m and w indicate the micellar phase and the bulk aqueous phase, respectively; CD is the concentration of micellized surfactant defined as: CD = CT – cmc (CT is the analytical surfactant concentration). In dilute surfactant solutions quantitative association to micelles is observed when KB is higher than ca. 1000 M–1.

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Detergent Formulations in Separation Science Table 1

307

Experimental Methods for KB Evaluation Method

pKa variation: Absorbance variation: Micellar HPLC:

Equation Applied

Ref.

Ka(m)/Ka(w) = 1 + KB(HA)CD (A – Aw)–1 = (Am – Aw)–1 + (Am – Aw)–1(KBCD)–1 CF = (PSW) –1 + KB (PSW)–1 CD

14 15 16

Note: Aw, Am, and A: absorbances in water, in micellar phase (solute fully bound), and at a given surfactant concentration, respectively. CF = Vs/(Ve – Vm), where Vs and Vm are the volumes of stationary and mobile phases, respectively, and Ve is the elution volume. PSW: partition coefficient of solutes between stationary phase and bulk aqueous phase.

1. Experimental Determination of Binding Constants Among the various experimental techniques suitable for the determination of KB, those listed in Table 1 are the most widely reported: a. 1.1.1. Measurement of KB Using MECC. More recently, the introduction of micellar electrokinetic capillary chromatography (MECC) has offered a new choice for a rapid and cheap evaluation of KB. In this technique the migration times of the analytes (tR) are limited between the migration time of the bulk solution (to), due to the electroosmotic flow, and that of the micelles (tmic) and depend on the distribution coefficients of solutes between aqueous and micellar phase (PMW). The relationship between PMW and the capacity factor, k’ is described by the following equation Eq. [17]: k’ ≅ PMW V

m

(Ctot cmc)

(3)

where V m corresponds to the partial molar volume of the micelle. The capacity factor, k’, can be readily calculated from the retention times: k’ = (tR – to) / to (1 – tR/tMC)

(4)

where to corresponds to the migration time of a neutral solute totally excluded from the micelles (usually methanol) and tMC corresponds to the migration time of analytes strongly bound to the aggregates. Usually methanol and the lipophilic dye Sudan III are introduced as suitable markers for estimating to and tmc, respectively. From the linear relationship obtained when plotting k’ versus Ctot, PMW can be estimated from the slope. The partition coefficients are in turn related to KB through the Berezin’s equation [14]: KB = (KMW-1) V m

(5)

The intercept (extrapolated to k' = 0) in Eq. (3) should correspond to the cmc under the operating conditions. Concerning this additional type of information the proper choice of the tMC marker has been demonstrated to be of fundamental importance. In fact, recent studies on partitioning between hydrophobic preservants used in cosmetics and SDS micelles [18], clearly showed that lipophilic markers with a tunable alkyl chain (such as some amphiphilic alkyl derivatives of 1-(2-pyridylazo)-2-naphthol, PAN-Cn ) which exhibit longer retention times than Sudan III, allow to obtain a more accurate evaluation of the

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k′

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30 25 20 15 10 5 0 0.01

0.03

0.05

0.07

0.09

(SDS) mM

Figure 1 Determination of partitioning coefficient for ethylparaben () and propylparaben (▫) using Sudan III (solid symbols) or PAN-C4 (open symbols) as tMC marker. (From T.L. Chester, et al. Anal Chem 66:106R–130R, 1994.)

tMC, thus resulting not only in more suitable KB measurements but also in a good estimation of cmc value. The different results obtained by using either Sudan III or PAN-C4 are shown in Figure 1. With both the markers a good linear correlation between k’ and Ctot is achieved, but the value of the intersection on the x-axis is negative when using Sudan III, thus resulting in a negative meaningless cmc value. On the contrary, when using PAN-C4 as tMC marker, the intersection falls on the positive x-axis side and the calculated cmc value is in good agreement with that obtained by independent tensiometric measurements. The MECC technique was used to estimate the hydrophobicity of many analytes [19], with an extension also to anionic and cationic solutes [20,21]; moreover this approach was applied to estimate n-octanol/water partition coefficients [22]. The determination of binding constants higher than those usually measured by applying the other techniques has been performed in these MECC experiments. 2. Indirect Evaluation of KB It is important to note that all the experimental methods fail when highly hydrophobic solutes are examined, being difficult the evaluation of binding constants higher than ca. 2000 to 3000 M–1. In these cases, a rough but useful estimation of KB can be obtained using indirect methods based on the additivity of hydrophobic contributions arising from different parts of the solute molecule [23–25]. B.

Micelle-Mediated Separation/Preconcentration Techniques

1. Micellar Extraction of Sparingly Soluble Compounds from Solid Matrices The extraction of hydrophobic species from complex solid samples is usually achieved by using traditional extraction methods involving organic solvents, such as Soxhlet extraction. However these methods have some recognized drawbacks, being in particular timeconsuming and requiring the handling of relatively large amounts of more or less toxic, hazardous, and expensive solvents. To overcome most of the above problems microwaveassisted solvent extraction (MAE) [26], accelerated solvent extraction (ASE) [27], supercritical fluid extraction (SFE) [28] have been developed in recent years and proposed as suitable new procedures for the extraction of solid matrices. Very recently, the combination of the MAE approach with the use of aqueous surfactant solutions as extracting phase was proposed by some research groups as an effective new extraction approach. The term microwave-assisted micellar extraction (MAME) was suggested to indicate this peculiar procedure [29]. Recovery efficiencies

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Detergent Formulations in Separation Science Table 2 Analytes PAHs PAHs PAHs PCBs

a

309

Examples of Microwave-Assisted Micellar Extractions Extracting System 2.9 x 10–2 M SDS, focused microwaves, (40 min) 2.0 x 10–2 M Brij 35, microwaves, T ≈ 90˚C, 15 min 0.02 M C12E10, microwaves, T ≈ 90˚C, 15 min 0.02 M Genapol X-080, microwaves (3 steps, 45 min)

Recoveries

Sample

Ref.

98–100%

Soila

30

80–100%

Marine sedimenta

29

85–94%

River sediment

31

81–95%

Marine sediment

32

Verified on certified samples.

comparable to those obtained using classical extraction methods, but with a neat reduction of the extraction times and better reproducibilities, are reported. Table 2 summarizes the results obtained by applying MAME extractions to the analysis of some organic pollutants present in complex environmental samples. 2.

Preconcentration/Extraction Based on Thermal Phase Separation (CloudPoint Extraction) Turbidity is often observed when aqueous micellar solutions of various nonionic and zwitterionic surfactants are heated or cooled, due to the formation of two isotropic liquid phases. This phenomenon, which is still subject of debate, seems to depend on the removal of hydration water from the hydrophilic region upon heating [33]. The reduced solubility of the amphiphile in water and the neat increase of the aggregation number are also claimed to play an important role [34]. The temperature at which the transition is observed, called cloud-point (CP) temperature, depends on the surfactant structure and concentration and a minimum (or maximum) in the corresponding phase diagram is usually noted. Table 3 lists the measured cloud-point temperatures of aqueous solutions of some selected nonionic surfactants, largely used in many reported extractions [35]. The presence of additives (salts, hydrophobic solutes) can significantly alter these values. Since the first example of extraction exploiting the cloud point of nonionic surfactants, proposed by Watanabe [36] to concentrate metal ions as hydrophobic chelates, most of the successively reported data concerned the use of aqueous solutions of this class of surfactants. Figure 2 shows a typical phase diagram of these systems. At temperatures below the CP the surfactant solution of composition Co is isotropic and transparent, whereas it becomes turbid after heating at the working temperature Tw. A low-volume liquid phase of composition C1 is dispersed in an aqueous phase where the surfactant concentration is in the cmc range (C2). The micelle-bound solutes accumulate in the surfactant-rich layer. The phase separation occurs spontaneously at a rate depending on the density of the two liquids; centrifugation is usually used in laboratory practice to speed up the process. Addition of inert salts increases the density of the aqueous phase, allowing the accumulation of the extracted species in the upper phase (see inset in Figure 2), thus facilitating

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Table 3 Cloud-point Temperatures of Selected Nonionic Surfactant Surfactanta

Usual name

C8E4 C8E8 C12E4 C12E8 C12E10 C12E23 C16E10 C13E8 p-t-octylphenol-E7-8 p-t-octylphenol-E9-10 p-nonylphenyl-E7-8

Brij 30 POLE Brij 35 Brij 56 Genapol X-80 Triton X-114 Triton X-100 PONPE 7.5

Cloud-point (˚C) 40 96 4 71–78 77 100 64 42 23–25 65 1-4

a

Surfactant concentration chosen: 1% w/v. In alkylpolyoxyethylene surfactants Cn indicates an aliphatic hydrocarbon chain of n carbon atoms and Em represents a polyoxyethylene chain having m (O-CH2-CH2) units. Source: Data taken from Hinze, W.L. and Pramauro, E. Crit Rev Anal Chem 24:133–177, 1993, and references cited therein.

50 45 40

T (°C)

35 30

TW

25 20 15 10 5

C1

0 0

30 Co

C2 60

90

Surfactant (% wt)

Figure 2 Schematic phase diagram for a nonionic surfactant and typical test tubes used in some reported CP experiments.

the sampling. The choice of suitable pure surfactants or surfactant mixtures and the presence of additives allow to perform extractions under mild conditions, at or near room temperature, allowing to handle thermally labile solutes. The CP extraction yield can be evaluated, as in usual liquid-liquid extractions, by measuring the solute distribution ratio. The volume ratio Vs/Vw (Vs and Vw are the volumes of the surfactant-rich phase and of the aqueous phase, respectively) defines the attainable concentration factor, it varies with surfactant concentration and is largely dependent on the phase behavior. For example, in solutions containing 1% w/v of surfactant, the mea-

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sured Vs values after phase separation are ca. 2.6% of the total volume for Brij 30, ca. 11% for Brij 97 (polyoxyethylen(12)oleyl ether), and ca.6% for the mixture C12E8/C12E4.2 (1:1, w/w), respectively. Most of the reported concentration factors lie in the range 10 to 200, comparable with those obtained using traditional liquid–liquid extraction. a. Cloud-Point Extraction/Preconcentration of Organic Compounds. E ff e c tive CP extractions have been reported for preconcentration and removal of a variety of organic solutes present in aqueous samples, including various pollutants (pesticides, aliphatic and aromatic hydrocarbons, aromatic amines, polychlorinated biphenyls [PCB’s], chlorinated dibenzofurans, dioxins, phenols, etc.), biochemical molecules (such as proteins, enzymes, vitamins), and other compounds. In some cases sensitized determinations of the concentrated analytes (i.e., fluorimetric, phosphorimetric, electrochemical, etc.) can be directly performed on the surfactant-rich extract. Cloud-point preconcentration can be also coupled with microwave-assisted micellar extraction, as recently reported [50]. Table 4 lists some examples of CP extractions of organic molecules of environmental concern. A threshold value of KB around 103 M–1 has found to be a necessary condition in order to obtain the quantitative extraction of the target solutes under usual experimental conditions [42]. As expected, the influence of pH is relevant when the solute exhibit acid or base properties (e.g., aromatic amines, phenols, carboxylic acids, etc.), being the charged forms only partially extracted. The effect of pH on analytes recovery is almost negligible for neutral compounds. Cloud-point extractions using zwitterionic amphiphiles were also reported in the literature, especially for separation and recovery of biomolecules [35,51,52]. The corresponding consolution curves exhibit a maximum. It is possible to obtain a phase separation also working with ionic surfactants, even if they do not undergo the cloud point phenomenon. In these cases the phase separation is mainly due to salting-out effects. The extraction of selected chlorophenols in river water using a mixture of different alkyltrymethylammonium bromides and 1-octanol as cosurfactant [53] and the extraction of polar PAHs from liquid and solid samples exploiting the acid-induced phase separation of sulfate and sulfonate surfactants [54] are examples of such separations. Another interesting application of CP extraction is the possible on-line incorporation of this step in flow injection analysis. The determination of porphyrin derivatives in urine samples via FIA using Triton X 100 and ammonium sulfate, is an example of such an approach [55]. b. Cloud-point Extraction/preconcentration of Metal Ions. Several metal ions (Ni(II), Zn(II), Cd(II), Cu(II), Au(III), Fe(III), U(VI), Al(III), etc.) were extracted and preconcentrated as hydrophobic metal chelates in the surfactant-rich phase of nonionic surfactant solutions after clouding. Various commercial ligands were used, including 1(2-pyridylazo)-2-naphthol (PAN), 1-(2-thiazolylazo)-2-naphthol (TAN), 2-(2-thiazoylazo)-4-methylphenol (TAC), oxine (8-hydroxyquinoline) and others [35,56-59]. Extraction yields in the range 80-100% have been reported for metals present in concentrations up to ca. 0.1 mg/ml, after addition of 0.2 to 2% w/v of solubilizing surfactant and 0.1 to 1 mg/ml of ligand. The ligand hydrophobicity is a crucial factor since, due to the more polar nature of the hydrated extracting surfactant phase, the partition coefficients of usual ligands (and of their corresponding metal complexes) are lower than those measured in traditional organic solvent/water systems [35]. The use of chelating micelles containing amphiphilic ligands having a tunable lipophilic moiety has been proposed in order to improve the selective metals recovery [60]; this approach, which was applied in few cases for CP extraction, was more extensively applied in micellar ultrafiltration and will be examined in detail in the corresponding section.

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Table 4 Recoveries of Some Organic Pollutants after Cloud-Point Extraction Analytes Preconcentrated Aromatic hydrocarbons and PAHs: Benzene, toluene, xylenes Biphenyl Fluorene, fluoranthene, pyrene, benzopyrenes Fluoranthene, benzopyrenes, Fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene Phenanthrene, pyrene Naphthalene PCBs, PCDDs PCDFs: 3-chlorobiphenyl, 3,3′-dichlorobiphenyl 1,4,7,8-TCDD, 1,2,3,4-TCDD, 1,2,4,6,9-PCDD DBF, 4-CDBF, 2,8-DCDBF 2,4,8-TCDBF, 2,3,7,8-TCDBF Phenols: Phenol, 4-chlorophenol, 3,5-dichlorophenol, 2,4,5-trichlorophenol, 2,3,4,5-tetra- chlorophenol, pentachlorophenol Phenol 4-t-butylphenol 4-t-butylphenol Pesticides: Methylparathion, ethylparathion Paraoxon Folpet Endrin, DDT, lindane, aldrin, chloropyrifos, methoxychlor, BHC 2,4-D, 2,4,5-T Chlorinated aliphatic solvents: 1,2-dichloroethane, 1,1,1-trichloroethane, 1,1,1,2-tetrachloroethane

Nonionic Surfactant

%E

Ref.

C8E3 Brij 30, Brij 97c,e Igepal CO-630 Triton X-114a,e Genapol X-80b

50–99 95 ≈100 98–99 79–100

35 37 38 39 40

Tergitol 15-S-7e + 0.5 M Na2SO4

>80 96

41

C12E8/C12E4.2 Triton X-100f

100 98–100

42 43

Genapol X-80 Brij 56c

98–100 92–96

44 ”

C12E8/C12E4.2

72–100

42

C8E3 C12E5 Igepal CA-520

35–40 79 97

45 ” 46

Triton X-114 Triton X-114d PONPE-7.5

100 63–77c 76–98 100

47 ” 48 38

C12E8/C12E4.2

84.5-98

42

Igepal CA 620g, 50˚C

79-87

49

Surfactant concentration (w/v): 1% if not indicated otherwise: a0.5%, b0.2%, c2%, d0.25%, e3%, f 2%; g50 mM. Undissociated solutes are considered.

Examples of recent applications of CP extractions of metals using commercial ligands include: use of Triton X-114 to preconcentrate U(VI) as PAN complex prior to the flow injection analysis [61]; preconcentration of Ni(II) and Zn(II) as PAN chelates in micellar Triton X-114 prior to the flame atomic absorption analysis [62]; determination via FIA of Al(III) present at trace levels in parenteral solutions, preconcentrated as Chrome Azurol S (CAS) chelate in the presence of cationic surfactants and nonionic PONPE 7,5 [63]; preconcentration of gadolinium present in urine after reaction with the ligand 2-(3,5dichloro-2-pyridilazo)-5-dimethylaminophenol and CP extraction with: PONPE 7.5 [64].

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Cloud-point extraction of metals can also exploit the complexing ability of the surfactant oxyethylene units, without the introduction of auxiliary ligands [65]. 3. Micellar Ultrafiltration Micellar-enhanced ultrafiltration (MEUF) is a separation method proposed by Scamehorn and coworkers [66] which combines the good selectivity performances of reverse osmosis with the higher flux rate of ultrafiltration, allowing the separation of dissolved solutes bound to carrier micellar aggregates. The removal of micelles from the bulk solution is performed provided the UF membrane pore-size is small enough to reject micelles (and their guest solutes), leaving them in the retentate phase. Since the mean weight of usual aggregates is in the range 10 to 100 kDa, membranes having pore diameters between 20 and 100 Å are normally suitable, with corresponding acceptable fluxes of the solution to be treated. In most reported frontal ultrafiltration experiments, membranes with MWCO in the range 55 kDa were successfully employed. Various types of hydrophilic (largely cellulose-based) and hydrophobic membranes can be applied under different conditions [67]. Most laboratory ultrafiltration experiments were performed in cylindrical stirred cells, where the feed solution is forced to permeate under the pressure exerted by an inert gas (see Figure 3). Efficient stirring just above the membrane surface reduces the formation of a solute concentration gradient, referred to as concentration polarization, which decreases the flux rate. A surfactant concentration limit exists above which the flux drops to zero (gel point). The use of centrifuge tubes having an incorporated suitable membrane allows to obtain a faster filtration (see Figure 3) The efficiency of micellar ultrafiltration is measured by the rejection coefficient (or rejection factor), defined as: R = 1 – Cp/Co

(6)

where Cp and Co are the solute concentrations in the permeate and in the initial (feed) solution, respectively. Since micelles are completely rejected by the membranes, they accumulate in the retentate phase and the permeate contains only low concentrations (near the cmc) of the amphiphile. a. Preconcentration of Organic Solutes via Micellar Ultrafiltration. Irrespective of the micellar system used and of the substrate structure, complete rejection of solutes in the retentate is achieved when they are completely bound to the aggregates (as for quantitative cloud-point extractions, KB must be higher than ca. 1000 M–1). Several highly hydrophobic compounds satisfy the above requirement, but for more hydrophilic solutes permeation becomes relevant and changes in the operating conditions are necessary in

Inert gas

Permeate

Figure 3

Laboratory ultrafiltration devices: centrifuge tube and stirred cell.

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100 90

4

80

2

%R

70

4

5 3

5

5

6

6

2

60 50 40

HTAB SDS

1

30 20 0

300

600

900

1200

KB

Figure 4 %R vs. KB (M–1) in MEUF experiments performed with ionic micelles. (1) aniline; (2) 4-ethylaniline; (3) 4-tert-buthylaniline; (4) phenol; (5) 4-chlorophenol; (6) 2,4-dichlorophenoxyacetic acid. (From Pramauro, E. Ann Chim (Rome) 80:101–109, 1990 and Pramauro, E. et al. Analyst 118:23–27, 1993.)

order to increase KB. Figure 4 shows the separation performances of various aromatic solutes as a function of KB in ultrafiltrations performed with ionic micelles. Amphiphiles having longer hydrocarbon chains are generally preferred since increased rejection and decreased cmc values are obtained. However, when ionic surfactants are used, the risk of phase separation exists because the Krafft temperature of these compounds rapidly increases with the alkyl chain length [12]. The effect of surfactant concentration on rejection is relevant for partitioned solutes, whereas no significant changes in the bound fraction is observed for highly hydrophobic compounds. For example, the permeation of 4-chlorophenol present in aqueous acidic wastes passes from ca. 40% to ca. 15% of the initial feed concentration (0.1 mM) increasing the SDS concentration from 20 to 80 mM. Under the same conditions, permeation of 3,5dichlorophenol decreases from ca. 3% to ca. 2% [42]. Changes of pH alter the rejection of ionic solutes either in the presence of ionic or nonionic micelles; for ionic aggregates, in particular, the role exerted by electrostatic repulsions or attractions is very important. For example, the preconcentration of aniline from aqueous samples can be achieved with good yields (R > 0.95) using SDS micelles at a working pH at which the analyte is fully protonated [68]. Under these conditions, the loss of hydrophobicity due to protonation is largely compensated by the electrostatic attraction exerted by the anionic aggregates. On the contrary, electrostatic repulsion reduces the rejection factor when HTAB aggregates are used to remove the same compounds from acid solutions (R < 0.10). In Figure 5 the effect of pH variation on rejection is showed for 4ethylaniline and 2,4,5-trichlorophenoxyacetic acid, in presence either of HTAB or SDS micelles. Ionic strength plays an important role when ionic solutes are extracted using oppositely charged ionic aggregates. Shielding effects are observed in these cases, with a corresponding decrease of the rejection coefficients; on the other hand, no significant changes due to ionic-strength have been reported for ultrafiltration of neutral solutes in the presence of nonionic aggregates. b. Ultrafiltration of Inorganic Ions using Micelles Bearing Opposite Charge. M u l ticharged ions can be efficiently removed via micellar ultrafiltration using oppositely charged aggregates, but the system is not selective and is highly sensitive to the ionic strength. Rejection coefficients higher than 99% have been reported, under the same

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Detergent Formulations in Separation Science

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Solute rejected (%)

100 80 60 40 20 0 2

3

4

1SDS

5 pH 1HTAB

6

2SDS

7

8

2HTAB

Figure 5 Effect of pH variation on R values for 4-ethylaniline (1) and 2,4,5-trichlorophenoxyacetic acid (2), in presence either of HTAB or SDS micelles. (From Pramauro, E. Ann Chim (Rome) 80:101–109, 1990 and Pramauro, E. et al. Analyst 118:23–27, 1993.)

experimental conditions, for divalent cations (Co2+, Zn2+, Cu2+, Cd2+) using SDS micelles and similar rejection values were measured for divalent anions in the presence of cationic micelles [69]. The effective removal of Sr2+ present in nuclear wastes is a recent example of these applications [70]. c. Use of Chelating Micelles. The combined use of ligand micelles and UF can be effective either for preconcentration or separation of metals present in complex aqueous mixtures [60,71-77]. Cationic surfactants are in principle the best candidates to form the mixed chelating micelles since uncomplexed cations should be repelled from the aggregates, but partial rejection of the free cations was observed in some cases [78]. Nonionic polyoxyethylene-type amphiphiles do not show these undesirable effects, although they exhibit some complexing ability toward metal ions. Rejections of divalent cations up to ca. 55% were, in fact, observed in blank ultrafiltration runs performed with Triton X-100 aggregates [74]. The increase of ligand hydrophobicity increases the bound chelate fraction, thus improving the metal rejection. For example, the rejection of Cu(II) (present at the trace level in aqueous acidic wastes) passes from less than 10% using mixed micelles of HTAB and the ligand C4-NHMePyr to more than 99% working with C16-NHMePyr [72]. Similarly, the rejection of Fe(III) at pH 3.5, in the presence of host C12E8 micelles, was 84% using Y-PAS-C4 and nearly 100% using Y-PAS-C8, respectively [78]. The structures of some lipophilic ligands used in micellar ultrafiltration work are shown in Figure 6. The stoichiometry of the complexes formed in micellar media is usually different from that observed in homogeneous solutions and tends to 1:1 for hydrophobic ligands. For example, the ligand PAN reacts with Ni(II) in Triton X-100 micelles forming a 2:1 chelate (as in homogeneous water-dioxane solutions) whereas a 1:1 complex is formed when the more hydrophobic derivative PAN-C4 is used [79]. Higher complex stabilities are preferred because the ligand excess can be minimized, thus reducing the costs. PAR, PAN, 8-hydroxyquinoline, etc. (and their lipophilic derivatives) are particularly suitable. The complex formation kinetics also changes dramatically depending on the reaction site (aqueous vs. micellar phase) and is very sensitive to electrostatic repulsion or attraction between the metal ions and the chelating ligands [73,80,81]. In some cases the kinetic effects can be exploited for separation purposes. For example, mixtures of Co2+ and Ni2+

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Pramauro and Prevot CH3

OH N

CH2CH3

CnH2n+1O

CHCH2CH2CHC4H9

C11-HQ

N

COOH

Cn-PIC: 5-alkoxypicolinic acid

CnH2n+1

COOH OH

N

N HO

NHCOCnH2n+1 Cn-PAS: 4-alkylamido-2-hydroxybenzoic acid

Cn-PAN

CH2COOH HOH2C

CnH2n+1NHCH3

CH3(CH2)11 N CH2COOH

N CnNHMePyr: 6-[(alkylamino)methyl]-2(hydroxymethyl) pyridine

DIDA: dodecyliminodiacetic acid

Figure 6 Molecular structure of some amphiphilic ligands used to form ligand micelles.

(in the ppm range) can be separated using the ligand C11-HQ solubilized in HTAB/butanol microemulsions. The complex formation takes few minutes for Co2+ and hours for Ni2+ at pH ca.6, thus allowing their separation via micellar ultrafiltration [82]. As expected on the basis of chelate formation from ionizable ligands, the ultrafiltration performances are pH-dependent and the corresponding R vs. pH curves are similar to the typical liquid–liquid extraction profiles [72,74,75]. The performances of micellar UF are in many cases comparable with those obtained using usual extraction methods [83]. Figure 7(a) shows the variation of rejection for three different metal ions in the pH range 3 to 7.5, measured after treating the feed with ligand micelles of Triton X-100 and C4-PAN. Quantitative or nearly quantitative recovery of Co(II) is possible by ultrafiltration in the reported pH range. On the contrary, very low retention has been observed for Ca(II), whereas quantitative recovery of Zn(II) is achievable only in the pH range 5 to 7.5. Selective separation and purification of Co(II) from mixtures containing Zn(II) and Ca(II) can be achieved at pH 3, by applying a multistep ultrafiltration (see Figure 7b). C. Micellar Liquid Chromatography In reverse-phase micellar liquid chromatography (RP-MLC) aqueous micellar solutions, usually containing some proper additives such as alcohols or acetonitrile, are used as mobile phases instead of usual hydroorganic mixtures. The peculiar features of micellar eluents and the retention models describing the solutes behavior have been analyzed in detail in some comprehensive reviews [2-4,7,9] and books [10,84]. The micellar HPLC

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1 Co(II) Zn(II) Ca(II)

0.8 0.6 R 0.4 0.2 0 2.0

4.0

6.0

8.0

pH (a)

0.5

0.5

0.5

0.5

CR

0.4

Co (II) Zn (II)

0.3 0.2

0.14

0.1

0.03

0.01

0 I stage

II stage

III stage

(b)

Figure 7 a. Effect of pH on R values for different metal cations. b. CR (metal ion concentration in the retentate) vs. consecutive MEUF stages. Initial metal concentration: 0.5 mg/l–1. (From Pramauro, E. et al. Talanta 41:1261–1267, 1994.)

equation reported in Table 1 describes the basic Armstrong-Nome retention model, valid for solutes attracted by the micelles. Several advantages related to the use of micellar eluents have been evidenced: enhanced selectivities, lower costs, more safety, specific detection modes, possibility of direct injection of biological samples, and fast gradient elution capabilities. The main inconvenient of RP-MLC is the low efficiency, but this drawback has been at least in part compensated by adding adequate organic modifiers to the eluent. The direct injection of biological fluids samples in RP-MLC is particularly interesting since the development of sensitive methods for HPLC analysis of metabolites and drugs in such matrices requires a careful elimination of proteins to avoid column clogging and interference effects. Protein extraction (or precipitation) preliminary steps increase the analysis time and the possibility of error; these pretreatments can be avoided using micellar eluents due to the solubilization of the proteins through surfactant coating. Several reports appeared during the last 5 to 6 years were focused on both applicative and mechanistic studies on RP-MLC. Contributions to the knowledge and prediction of the MLC performances include: analysis of band broadening [85] and peak shape [86]; examination of the effect of organic modifiers on retention [87,88]; introduction of ionexchange stationary phases for separation of dansylated amino acids [89]; characterization of retention in MLC [90]; retention prediction and modelling studies for pyridine derivatives [91], peptides [92], catecholamines [93], anesthetics [94], metal-dithiocarbamate complexes [95]; prediction of ecotoxicity of various organic pollutants [96,97] from MLC partition data; studies on pharmacokinetics and pharmacodynamics of antihistamines via MLC [98], etc. A systematic optimization of micellar eluents for improved MLC separations has also been examined on chemometric bases [99].

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Table 5 MLC Analysis of Complex Samples Analyzed compounds

Chromatographic Eluent

Samples

Ref.

Pentobarbital Synthetic antioxidants Derivatized amino acids

0.02M CTAB + 15% 1-propanol 0.05-0.15 M SDS + (1–9)% 1-propanol 0.05 M SDS + 1.2% 1-propanol

100 101 102

Parabens

0.1 M SDS + 2.5% 2-propanol, pH 3 (phosphate) 0.05 M SDS + 10-15% 1-propanol, (after derivatization) pH 3 0.01 M HTAB + 20% acetonitrile, pH 6.3 (phosphate) 0.05–0.15 M SDS + 15% 1-propanol +1% triethylamine, pH 3

Plasma, urine Dairy products Aqueous samples Cosmetics Urine

104

River waters

105

Urine

106

Pharmaceutical formulations Pharmaceutical formulations

107

Thiazide diuretics Thiram (fungicide) Antagonists (acebutolol, atenolol, nadolol, metoprolol, celiprolol, etc.) Antihistamines Caffeine

0.15 M SDS + 6% 1-pentanol 0.05 M SDS + 1.5 % 1-propanol, pH 7

103

108

Chromatographic columns: RP-C18.

Table 5 summarizes some recent examples of MLC determinations. D. Micellar Electrokinetic Capillary Chromatography (MECC) This powerful surfactant-based separation technique, introduced by Terabe and coworkers [17] can be considered as a combination of MLC and capillary zone electrophoresis (CZE). In MECC a surfactant is dissolved in the background electrolyte solution at a concentration higher than its cmc; both ionic and non ionic surfactants can be used. Anionic micelles (i.e., SDS) have an electrophoretic mobility and a migration direction opposite to that of the electroosmotic flow (EOF). Being this last usually faster than the aggregates migration velocity, the direction of flow of all the components is the same, but micelles migrate slowly. In these conditions, a chromatographic like system is operative in which two distinct phases, the aqueous (mobile) and micellar (pseudostationary), are present within the capillary column and migrate at different velocities toward the electrode with the same charge as the micelles. Solutes partitioned between these two phases will move more or less slowly depending on their binding constants to the micelles, whereas, if charged analytes are present, they will in addition undergo electrophoretic migration either in the opposite direction of the electroosmotic flow (micelle-like charged analytes) or in the flow direction if they act as micelle counterions. In presence of cationic aggregates (i.e., HTAB) the direction of the electroosmotic flow will be reversed due to the formation of double layer or surfactant hemimicelles at the capillary wall surface. Compared to micellar liquid chromatography (MLC), MECC has the advantages related to the absence of a stationary phase: faster preconditioning and cleaning of the system, higher reproducibility and decreased error caused by intercolumn variability [109];

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moreover this technique is faster than MLC, needs only few µl of sample and few milliliters of buffer. The present state of the technique has been recently discussed [110–112]. The papers published about MECC can be divided in two main groups: those improving the knowledge on the separation principles and the effect of different surfactants, buffer modifiers, and pH changes on the separation performances, and those devoted to the application of the technique to real samples analysis. Hereafter we will report essentially on the second kind of research. Concerning the surfactant type relevance many studies describe the effect of different surfactants on the retention behavior and chemical selectivity [113–115]. In particular was the use of mixed micelles formed from similar charged surfactant [116], charged and nonionic or zwitterionic surfactants [117], and oppositely charged surfactants was investigated [118]. Considering the applications, many efforts have been done to overcome the principal limit of MECC: the low sensitivity when absorption spectrometry detection is used (most cases). Good results have been obtained by applying on-line preconcertration technique and in particular the sample stacking with reverse migrating micelles [119 and refs. therein]. On the other hand efforts have been done to improve the detection sensitivity, by employing different cells with longer pathlength; in this case the drawback is the loss in separation efficiency. Otherwise more sensitive detector were used, such as fluorescence, in particular laser-induced, because of the importance of having a light source with beams that could be focused on a small volume. For electroactive analytes amperometric detection gave good results. The coupling with mass spectrometry would be able to render this technique very powerful, but, the problem of the introduction of a nonvolatile buffer into the interface is still to be solved. Despite to its limits, MECC is a powerful technique, especially for real samples; due to the absence of the stationary phase, often no sample pretreatment is required, contrary to what HPLC needs. Some examples of recent MECC determinations performed on biological and environmental samples are illustrated in Table 6.

Table 6

Examples of MECC Separations Analytes

Creatinine, uric acid, and antipyrine Heroin, opium alkaloids, amphetamines, benzodiazepine Ibuprofen, codeine phosphate and degradation products Essential and branched-chain amino acids 28 Biogenic amines Postharvest fungicides Explosives and transformations products Herbicides 22 aromatic sulfonate derivatives Tropane alkaloid Sesquiterpene lactone

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Sample Type

Ref.

Human plasma and urine Human biological fluids

120 121–123

Commercial tablets

124

Nutraceutical products

125

Red wines Grape, lettuce, orange, and tomato Soil and groundwaters

126 127 128

Lake sediments Industrial effluents Plant extracts Magnolia grandiflora

129 130 131 132

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ACKNOWLEDGMENTS Financial support from Ministero dell’Istruzione, dell’Universitá e della Ricerca (MIUR) (Rome), Programmi di Ricerca di Rilevante Interesse Nazionale (PRIN) 2000 is gratefully acknowledged.

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11 Surfactant Formulations in Enhanced Oil Recovery Thanaa Abdel-Moghny

CONTENTS I.

II.

Scope ..................................................................................................................... 326 A. Primary Recovery...................................................................................... 326 B. Secondary Recovery.................................................................................. 326 C. Tertiary Oil Recovery................................................................................ 326 Introduction ........................................................................................................... 327 A. Enhanced Oil Recovery............................................................................. 327 B. Chemical Flooding .................................................................................... 327 1. Development of Chemical Flooding ......................................... 327 C. Chemical Surfactant .................................................................................. 329 1. Surfactants.................................................................................. 329 2. Cation Exchange ........................................................................ 332 3. Stability ...................................................................................... 332 D. Surfactant Flooding ................................................................................... 332 1. Mechanism of Surfactant at Reservoir Rocks........................... 333 E. Surfactant Mixture..................................................................................... 333 1. Ideal Mixtures ............................................................................ 334 2. Application of Ideal Mixing ...................................................... 334 3. Nonideal Mixtures ..................................................................... 334 F. Polymer Flooding...................................................................................... 335 G. Alkaline Water Flooding ........................................................................... 336 H. Traditional Surfactant/Polymer Flooding ................................................. 336 I. Surfactant-Polymer Interaction in Solution .............................................. 337 J. Relation between the Interfacial Tension and Residual Oil Saturation ... 338 K. Phase Behavior in EOR ............................................................................ 339 L. Application of Surfactants in Enhanced Oil Recovery ............................ 339 325

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1.

Interaction between Surfactant and Polymer at Reservoir Rock ........................................................................................... 340 2. Displacement of Oil by Spontaneous Imbibition of Aqueous Surfactant Solution..................................................................... 340 3. Adsorption of Different Surfactants on Kaolinite..................... 341 4. Acidified Oil/Surfactant Enhanced Alkaline System ................ 341 5. Dual Surfactants—System for Enhanced Oil Recovery at High Salinity .......................................................................... 341 6. Ultralow IFT Using Neutralized Oxidized Hydrocarbon Surfactant ................................................................................... 342 7. Mixed Micelles .......................................................................... 342 8. Biosurfactants as New Surfactant.............................................. 342 Acknowledgments........................................................................................................... 342 References ....................................................................................................................... 343

I. SCOPE A. Primary Recovery A traditional step for increasing oil recovery is to inject gas or water into an oil reservoir for the purpose of delaying the pressure decline during oil production; a technique called pressure maintenance. A well-executed pressure maintenance program can substantially increase the amount of economically recoverable oil over that to be expected with no pressure maintenance. Without either fluid injection or an active natural water drive, oil recovery falls to where further production is no longer economically feasible. In the early days of the petroleum industry, reservoirs were allowed to produce naturally until a certain stage of depletion had been reached, generally when the production rates had become uneconomic. This was known as the primary production phase. B. Secondary Recovery To produce more oil, the pressure in the reservoir must be maintained by injecting another fluid. This second stage of production is called secondary oil recovery. The injection of fluids into the reservoir actually has two closely linked objectives: to maintain the pressure in the reservoir, and to push forward the oil contained in the reservoir toward the producing wells. Several types of fluid injection are used according to the reservoir fluid and rock characteristics. For oil field, the pressure may effectively be maintained by injecting water into the zone at the periphery of the reservoir, or gas into gas cap at the center of the reservoir. C. Tertiary Oil Recovery The major tertiary recovery method falls into two basic categories thermal methods and miscible method. Thermal methods aimed to reducing the viscosity of the oil by heating. The most widely used thermal techniques are in situ combustion, continuous injection of hot fluids such as steam, water, or gases, and cyclic operations such as steam soaking. The chemical method involves the injection of a fluid into the oil-bearing strata for the purpose of overcoming the deficiencies of conventional secondary techniques. The fluids are designed so that they will alter the capillary forces trapping the oil and reduce the tendency of bypassing the oil in the less permeable portions of the reservoir.

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II. INTRODUCTION A. Enhanced Oil Recovery After a successful water or gas injection project as much as 50% of the initial oil in place remains entrapped in the pores of the reservoir rock. This remaining oil needs a very high pressure gradient to be mobilized due to the capillary forces needed to drive the isolated oil bubbles through the narrow necks of the porous medium. To recover this residual oil under the usually applied field pressure gradients, the interfacial tension between the oil and the displacing fluid must be either greatly reduced or completely eliminated. This can be done either thermally by vaporizing the oil and water into a single vapor phase or chemically by injecting solutions completely or partially miscible in both oil and water phase. Recovery methods that are used to recover some or all of the residual oil are termed as enhanced oil recovery (EOR) methods. They may be divided into (1) thermal methods (hot water flooding, steam flooding and in situ combustion), (2) chemical methods (polymer flooding, surfactant flooding, and alkaline flooding), and (3) gas injection methods (hydrocarbon miscible flooding, and carbon dioxide flooding). B. Chemical Flooding Chemical flooding of oil reservoirs is one of the most successful methods to enhance oil recovery from depleted reservoirs at low pressure. Initially, the objective of chemical flooding was to recover additional oil after a waterflood, and it is therefore described as a tertiary oil recovery process. A lot of papers and reviews, both laboratory work and field tests, have been published on this subject since the first work by Marathon Oil Company in the early 1960s [1]. The research declined drastically during the 1990s, but still some research groups were active trying to improve the technique by: (1) simplifying the flooding process, (2) improving the efficiency of surfactants, and (3) developing new chemicals (surfactants). Chemical flooding processes is meant to include the “water-based” processes such as micellar and surfactant floods, alkaline water-floods and polymer floods. These processes are all sensitive to certain environmental elements or factors that are commonly present in oil reservoirs. These are the in-place oil and water, the mineralogy, the geology/ lithology and the temperature. These can influence the process selection and the composition of the chemical slugs [2]. 1.

Development of Chemical Flooding a. In the Laboratory. Essentially, two different methods have developed for using surfactants to enhance oil recovery. One uses a large pore volume (PV) of a low-concentration surfactant solution. The other uses a small pore volume of a high-concentration surfactant solution. Laboratory results reported in the literature indicate that, with low concentration surfactant injection, oil production is sustained at a lower level for a longer period of time than with high-concentration surfactant injection. The two different processes including; (i) displacement, (ii) adsorption, (iii) mobility control, and (iv) scaling. i. Displacement with Surfactant Systems. The displacement results come from different laboratories are reported by [3–5], and are presented in Table 1. All floods took place in Berea cores and petroleum sulfonate as the surfactant. The recoveries indicate that both types of surfactant processes are capable of recovering significant quantities of tertiary oil. Process efficiency can be related to the ratio of oil recovered divided by the amount of surfactant injected.

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328 Table 1

Flood Gale 3 Hill 4 Davis 5

Abdel-Moghny Laboratory Displacement with Surfactant Surf. Concs. % 2 1.3 10.4

PV Injected %

CD (in) x Length (ft)

R/P

TOR %

Efficiency Ratio

50 25 2

2x3 2x16 2x4

3 psi 1.4ft/D 44ft/D

70 85 85

0.70 2.62 4.09

Abbreviations: Surf. Concs.= Surfactant concentrations %, PV = pore volume injected %, CD = core dimension diameter (in) x length (ft), R/P = rate/pressure, TOR = tertiary oil recovery, and efficiency ratio = (oil recovery:surfactant injected)

ii. Adsorption. Various methods have been suggested for reducing surfactant loss in low-tension flooding: these methods include the use of different salts and mixtures of petroleum sulfonate with broad equivalent weight distributions. Such broad equivalent weight distribution is reported to increase recovery because the critical portions of the distribution act as sacrificial adsorbates. This adsorption minimizes the loss of the high equivalent weight fraction that is most efficient in lowering the interfacial tension. iii. MC = Mobility Control. Mobility control is necessary for enhanced oil recovery using both high and low-concentration surfactant-flooding processes. With low-concentration surfactant injection, mobility control of the surfactant slug is accomplished by dissolving polymer in the surfactant solution. The mobility of the high-concentration surfactant slug is fixed by adjusting the composition of such micellar components as the co-surfactant and electrolyte. iv. Scaling. Scaling of laboratory results to the field is a difficult problem with any recovery process. The displacement mechanism, associated adsorption, and mobility control with surfactant systems make scaling particularly difficult. b. Field Testing. Field results indicate that higher recovery values are obtained with high- concentration–surfactant, low-pore volume systems than with low-concentration, high-pore-volume systems. In terms of efficient surfactant use, the amount of oil recovered needs to be related to the amount of surfactant injected within the pattern from where the oil is displaced. c. Commercial Application. The key factors in any economic projections for enhanced oil recovery processes using surfactant are investment requirements including chemical and development costs, oil recovered, the time required to obtain that oil, oil price, and tax load. The historical developments of chemical flooding, are reported elsewhere [6–9]. A review by Austad et al. [10] focus on the recent laboratory developments in chemical flooding of oil reservoirs within: (1) traditional chemical flooding of sandstone reservoirs, and (2) imbibition of aqueous surfactant solution into low-permeable chalk. Other reviews reported that the uses of surfactant in flooding oil reservoirs are: (1) alkaline/surfactant/polymer flooding (ASP) is hoped to be a low-cost improvement over micellar /polymer flooding [11]; (2) surfactants based mobility control, i.e., foam generation during gas injection; and (3) partial or complete blocking of high-permeable regions, forcing injected displacing fluid into low-permeability areas of high oil content [12].

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329

Chemical Surfactant

1. Surfactants Surfactants are classified by the polar head group. It is common practice to divide surfactants into the classes anionics, nonionics, cationics, and zwitterionics (Fig. 1). • Anionic. Carboxylate, sulfate, sulfonate, and phosphate are the polar group found in anionic surfactants. • Nonionic. Ethoxylated alcohols, ethoxylated alkylphenols, ethoxylated acids, fatty acid alkanolamides, ethoxylated alkanolamides, ethoxylated amine, ester of polyhydroxy compounds, i.e., sorbitan distearate, ethoxylated esters, i.e., ethoxylated sorbitan monostearate, ethylene oxide/propylene oxide block copolymers, amine oxides. • Cationic. Fatty quaternary ammonium salts, benzylalkyldimethylammonium salts. • Zwitterionic. Amino acids. These amphoteric surfactants are generally prepared by reaction of a fatty primary amine with an α-unsaturated methyl ester, followed by hydrolysis of the ester. De Groot [13,14] reported that the polycyclic sulfonic body and wood sulfite liquor could be used as water-soluble surfactants for oil recovery. Other water soluble compounds have been suggested by Holbrook [15] for surfactant flooding; these compounds include organic perfluoro compounds, fatty acids soaps, polyglycol ether, salts of fatty or sulfonic acids, and polyoxyalkylene compounds. Laboratory results were presented showing that these solutions reduced interfacial tension and enhanced oil recovery. Publications since then have stressed coupling different salts with surfactants to reduce the interfacial tension to a minimum value and to prevent the adsorption of surfactants within the reservoir. These techniques have given rise to the low-tension surfactant flooding processes. In low-tension floods, much of the reservoir pore volume (PV) is filled with surfactant solution of a relatively low concentration. For example, a 30% PV slug containing less than 2% surfactant might be used [16]. To reduce surfactant adsorption in water wet formation a 0.1 to 3% surfactant dissolved in low-viscosity hydrocarbon solvent was injected [17]. For the soluble-oil flooding process a mixture of an anhydrous soluble oil and a nonaqueous solvent containing up to about 12% surfactant was injected [18]. The injection of microemulsion into production wells to remove objectionable waxy solids was described by Blair et al [19]. The interfacial surface between oil and water must covered by at least a monolayer of surfactants. High surface coverage is needed in order to obtain low enough IFT. Thus, the surfactant molecules must have strong lateral intermolecular association without forming liquid crystal and gels. Furthermore, the surfactant must also grade smoothly from being oil-to water-soluble over a sufficient length of the molecule. In this way it will be a smooth transition from oil- to waterlike fluid along the interphase. A lot of papers have shown it is possible to synthesize anionic surfactants with these properties that tolerate high concentrations of multivalent cations [20–23]. Anionic surfactants containing multiple units of ethylene oxide and propylene oxide (EO and PO) in their middle section were found to satisfy many of the desired conditions. Examples are:

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330

Abdel-Moghny O

O

OCH2COO− Alkyl ethercarboxylate

O

OSO−3

O O O Alkyl ethersulfate

Alkyl sulfate

OSO−3

O

SO−3 Alkylbenzene sulfonate

SO−3

O-C

Dialkyl sulfosuccinate

O-C O

OPO32−

O O O Alkyl etherphosphate

Alkyl phosphate

OPO32−

(a)

O

O

O

O

O

O

O

O

O

O CONH

O

O

O O

O

OH

O

COO

OH

O

O

Fatty alcohol ethoxylate

Alkylphenol ethoxylate O

OH Fatty acid ethoxylate

O

OH Fatty amide ethoxylate

OH

O

N O

O

O

O

Fatty amine ethoxylate

OH

CH2OH OH OH OH O

Alkyl glucoside

O C

O

CH2

OH CH O OH

Sorbitan alkanoate

OH O C

O

O n

O

O CH CH2

m

OH

O

O

m

O

O

OH

Ethoxylated sorbitan alkanoate

OH m

(b)

Figure 1 (a) and (b) Classification of surfactant types. (From Jonsson, Lindman, Holmberg, and Kronberg. Surfactants and Polymers Interfacial Tension Aqueous Solution. John Wiley & Sons, 1998.)

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NH+3

Fatty amine salt

NH+2

Fatty diamine salt

NH+3

O2C

O

N+

N+

N+ O2C O

Alkyl ‘quat’

Ester ‘quat’

Dialkyl ‘quat’

(c)

N+ –CH2COO

Betaine

N+ –CH2COO−

CONH O

Amidobetaine

CH2CH2OH

CNH–CH2CH2NH

Imidazoline

CH2COO− N

O

Amine oxide

(d)

Figure 1 (c) and (d).

R- (PO) Y– (EO) X–SO3– (alkyl propoxy-ethoxy-sulfonate) R- (PO) Y– (EO) X–OSO3– (alkyl propoxy-ethoxy-sulfate) R- Ph- (PO) Y– (EO) X-SO3– (alkylarylpropoxy-ethoxy-sulfonate) Where y = 0, 1, 2, 3, …., x = 1,2,3,… R 12 -15-O- (CH (CH3) CH2O) 7-(CH2CH2O) 2-(CH2CH (OH) CH2)-SO3–Na+ Pure and highly substituted benzene sulfonates, n-C 12-o-xylene-SO3–, have similar properties regarding low IFT in the two-phase region without using alcohol [24].

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The PO/EO sulfonate showed an IFT value close to 10–2 mN/m toward n-heptane in seawater. Also showed a remarkable performance in the presence of high concentration of Ca2+ and Ma2+ ions. This mean that calcium and magnesium salts of these surfactants have a limited solubility in oil, which will reduce possible trapping of surfactant at low concentration in the residual oil phase. Austad et al. [25] found that the small change in IFT is observed by doubling the salinity of seawater. 2. Cation Exchange The most common anionic surfactants (petroleum, alpha-olefin, and alkylaryl sulfonates) have great potential for extracting adsorbed multivalent cations, Mg2+, Ca2+, etc., into the micellar slug, with the consequence of a drastic change in phase properties. Therefore, a preflush of water containing monovalent cations is often performed to obtain a cation exchange. In order to compensate for reservoir parameters, which disturb the phase behavior of the surfactant slug during the process, an imposed phase gradient is normally used. If the phase gradient does not behave properly, a great loss of surfactants may take place due to phase trapping; i.e., the surfactant is trapped in the oil or in the middle phase [10]. 3. Stability Ethoxylated anionic sulfonates are fairly stable regarding desulfonation by breakage of the C-S bond at ordinary reservoir conditions [26]. Water solvolysis, H+ catalyzed hydrolysis, and nucleophilic (HS– and Cl–) displacement reactions have, however, been observed. Each and every one of these reactions can dominate the decomposition rate under different conditions. Even though oil reservoirs have a reducing environment, air or oxygen is usually not excluded from solutions in surfactant flood experiments, and it is therefore important to be sure that the loss of surfactant is not due to chemical decomposition during the experimental period. Under aerobic conditions, oxygen is important in the decomposition of the EO-groups. The main mechanism is believed to be cleavage of the ether bonds in the same way as in the decomposition of polyethylene oxide [27]. The ether bonds are broken by formation of hydroperoxides as intermediates. The peroxides are then decomposed by a radical mechanism, which may initiate chain scission reactions. The decomposition may also be catalyzed by metal ion [28]. The EO-sulfates are cheaper than the corresponding EO-sulfonates, but they are hydrolyzed at high temperatures and low pH. The pH of injected seawater is normally changed from about 8 to 4-6 due to solubilization of CO2 and ion exchange between water and the reservoir rock. At 60°C, the half-life time for EO-sulfates is estimated to be about 7 and 30 years at pH ≈ 5 and pH ≈ 8, respectively [29]. D. Surfactant Flooding Surfactant is characterized by its tendency to adsorb at a surface. The driving force for a surfactant to adsorb at an interface is to lower the free energy of that phase boundary. The interfacial free energy per unit area represents the amount of work required to expand the interface. The term interfacial tension is often used instead of interfacial free energy per unit area. Surfactant flooding process are referred to detergent floods, sulfonate floods, microemulsion floods, emulsion floods, micellar floods, and soluble oil floods (Figure 2a). In this process a slug of surface-active material is injected into reservoir to mobilized the residual oil which can be displaced and produced. The surfactant slug, representing only a fraction of the total pore volume, is driven through the reservoir by a subsequent slug

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Surfactant Formulations in Enhanced Oil Recovery Injection Drive

↓

Figure 2a

Water Mobility buffer

333 Production

Slug

Oil Water

↑

Surfactant flood.

of thickened water (polymer solution), which is in turn displaced by water or brine. The mobility’s of each these slugs are adjusted to minimize by–passing and channeling and to improve the volumetric coverage of the process. Ideally, the displacement by surfactant flooding approaches a miscible displacement. It is important that integrity of the slugs be maintained for as long as possible. They are sensitive to certain elements of the reservoir, and these factors can contribute to early attenuation [2]. The goal of the research on surfactant flooding during the 1990s was to develop surfactants that can recover additional oil in a cost-effective manner during a normal water flood using produced brine (due to environmental aspects) or seawater as injection fluid. In order to avoid many of the problems associated with complicated chemical slugs with high concentration of surfactants and cosurfactants/alcohols, the following criteria should apply: (1) The only chemicals used are surfactants and polymers, (2) low chemical concentration (surfactant 0.1 to 0.5 wt%, polymer < 500 ppm), (3) no imposed salinity gradient or other phase gradients, (4) these chemicals should be insensitive to multivalent cations, and (5) the flooding conditions should be a two-phase flood with the surfactant and polymer present in the aqueous phase, forming an oil-in-water microemulsion [10]. Surfactant loss due to phase trapping is minimized if only oil and water phases are present at all times during the flood. Surfactant loss is only related to adsorption onto the mineral surface provided that the surfactant tolerates multivalent cations, i.e., no precipitation [10]. 1. Mechanism of Surfactant at Reservoir Rocks Fluid/rock interactions that affect surfactant flooding are adsorption, cation exchange, precipitation dissolution phenomena, capillary phenomena, and dispersion. All of these directly or indirectly affect the retention of surfactant. Adsorption at the solid liquid interface should be at minimum and be the only retention mechanism for a type oil-in-water microemulsion phase behavior. In case of brines of high hardness, the surfactants will partition in the oil/or in the upper-phase microemulsion formed under these conditions, rather than precipitate. Phase trapping are caused by microscopic capillary forces in the pores of the rock [30]. E. Surfactant Mixture Most practical application of surfactants makes use of mixture of surfactants [31,32]. There are two reasons for this (1) technical–grade surfactants are themselves mixtures of chain lengths/isomers and (2) mixture of different types of surfactants often perform better than individual components. Surfactants in solution undergo two physical processes, which must be understood by the technologist: (1) they adsorbs onto surfaces thereby modifying surface energy, (2) they self-aggregate to form micelles or larger structures such as vesicles and liquid crystalline phase.

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Micelle formation is actually an equilibrium process in which micelles are in equilibrium with unassociated surfactant molecules (called monomers). The monomer concentration increases up to the CMC and then becomes essentially constant. Thus, the monomer concentration is always less than or equal to the CMC. This relationship between the monomer concentration and the CMC is one reason why the CMC is such an important measurement for understanding the behavior of surfactants and surfactant mixtures. The interaction which favors micelle formation generally favors also adsorption. Adsorption is a key link between surface activity and many applications because it controls such properties as particle-substrate adhesion, wetting, soil roll-up, emulsification, and particle suspending efficiency. Such a linkage between performance and micellar mixing behavior is supported by data presented by Schambil and Schwuger [31] showing that the mixture composition which corresponds to the minimum CMC also gives the best wetting, highest contact angle, lowest dynamic surface tension (best foam), and best emulsification. In the air–water interface, the hydrocarbon tails interact only weakly with the air molecules, whereas in an oil–water interface, for example, interactions with oil molecules are strong and can be very specific. Such work should be based on adsorption and phase diagram data, and oil-water interfacial tension rather than surface tension. The properties of mixtures of surfactants have been studied in recent years [31–33]. Surfactants are classified according to the nature of their hydrophobic and hydrophilic groups. Typical hydrophobic groups include hydrocarbons, polypropylene oxide, fluorocarbons, and siloxanes, whereas hydrophilic groups consists of polar nonionic species such as polyethylene oxide (POE), anionic groups such as sulfate, or cationic groups such as quaternary ammonium salts. Zwitterionic surfactants contain both an anionic and a cationic group. 1. Ideal Mixtures Mixtures of surfactants that belong to the same hydrophope and hydrophile class, such as a pair of homologous alkyl ethoxylates, have properties, which are simply predictable from the individual components [32,33]. This is done by treating of the micelle as a condensed “phase” in equilibrium with its “vapor”the unassociated monomers (the water in which this equilibrium with takes place is ignored). The CMC is treated as analogous to a vapor pressure. This is referred to as the pseudophase model. 2. Application of Ideal Mixing The addition of a small proportion of a long chain alkyl sulfate to a shorter chain alkyl sulfate improves the brine and water hardness tolerance of the mixture, even though the longer-chain material by itself is much more sensitive to water hardness than the other component [33,34]. The longer-chain surfactant lowers the mixed CMC and, therefore, the monomer concentration, but itself partitions almost entirely into the micelle. This leads to improved detergency over a range of water hardness conditions. 3. Nonideal Mixtures Mixtures of surfactants drawn from different hydrophope or hydrophile classes, such as a mixture of an ionic hydrocarbon surfactant and a nonionic hydrocarbon surfactant, usually show some deviation from ideal behavior. In the case of ionic-nonionic mixtures, the physical origin of the nonideality is a combination of reduction of electrostatic energy and complex formation [32,33].

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4. Application of Nonideal Mixing. One of the largest potential applications of surfactant mixtures is enhanced oil recovery. This is a vast field with an extensive literature [2,35–39] dealing with the physical and interfacial properties of temperature, pressure, and salinity. Cox et al. [40] investigated the effects of interactions between linear alkyl sulfate (LAS) and several nonionic surfactants on CMC, surface tension, water hardness sensitivity, and detergency performance. They found that nonionic surfactants lowered the CMC of the LAS, promoted micelle formation, and improved hard water detergency. In a related series of studies of studies, Cox and co-workers systematically investigated interactions between water hardness ions and LAS [41–43]. They report precipitation boundary diagrams and detergency results for LAS and mixtures of LAS with other surfactants, which act to promote micelle formation. They found that lowering the CMC led to improved cleaning in hard water. There are many papers and patents, which report synergistic performance of mixtures of alkyl ethoxylate nonionic surfactants with commonly used anionic surfactants such as LAS and sodium dodecyl sulfate (SDS) [31,32]. These systems show strong negative deviation from ideality, and the monomer concentrations above the CMC can be very much lower than either surfactant alone. As for ideal mixing, the composition of the micellar and monomer phases may be quite different. These effects are exploited, as mentioned above, to prevent calcium sensitive anionic surfactants from precipitating in hard water [44]. Nonionics are generally more effective in this regard than the insoluble anionics referred to above because they are more effective at lowering the monomer concentration and they are not susceptible to precipitation themselves. These principles have also been applied to formulating detergents, enhanced oil recovery, ore flotation, and ag-adjuvants [44]. The adsorption of a dual surfactant system of the type nonylphenol-6-ethoxy-sulfonate (6EOS) and dodecyl-benzene-sulfonate (DDBS) in the mole ratio of 1:1 has been studied by: (1) static adsorption onto kaolinite, (2) nonequilibrium long-term dynamic adsorption on a reservoir core, and (3) dynamic slug injection in a Berea core. The studies were conducted at 70°C using artificial seawater. The core floods were performed at residual oil saturation. The static adsorption of the mixture showed that DDBS adsorbed more strongly than 6EOS at surfactant concentration below the CMC. The plateau adsorption appeared to be quite similar, but significantly higher than for pure 6EOS. The logterm dynamic study was conducted by circulating the dual surfactant solution through the core for 16 weeks, and injecting 0.5 PV of the surfactant mixture followed performed the slug injection by a xanthan solution. In both cases it appeared to be a selective adsorption until the surfactant mixture, forming the most stable micelles, was obtained. Further adsorption at surfactant concentration above the CMC seems to be governed by a linear relationship between the two surfactants. Possible impacts on surfactant flooding, using dual surfactant mixtures of this type are discussed [45]. F. Polymer Flooding As mentioned above, in a surfactant flood the polymer solution is injected to aid in obtaining a good volumetric sweep of the reservoir by the process. A polymer solution may also be used in conjunction with a water flood to achieve the same purpose. This is illustrated in Figure 2b. it is if we are looking at only the portion of the surfactant flood with no mobilization of residual oil downstream of the polymer solution. The intent is to reduce the mobility of the water, thus forcing the water to flow through more flow channels in the rock than would be the case with water injection alone [2]. The polymer must be water soluble and of low flexibility to give high viscosity at low polymer concentration and high salinities. The two biopolymers, xanthan and sclero-

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Abdel-Moghny Injection

Drive

↓ Water

Production Oil

Polymer Solution

↑

Water

Figure 2b

Polymer flood.

Injection ↓

Production Oil Bank

Residual Oil Drive Water

Figure 2c

Buffer slug

NaOH solution

Initial Oil Preflush

↑

Connate Water

NaOH waterflood.

glucan, are good candidates. Xanthan acts as a negatively charged double helix in saline solution, while scleroglucan acts as an unchanged triple helix in solution. Polymers forming a helix usually hide their hydrophobic sections in the interior of the helix, minimizing surfactant–polymer complex formation. Both of the polymers tolerate high salinity and can be in seawater. Hydrolyzed polyacrylamide, HPA, is a good alternative at low salinities, but is not recommended to be used in hard water at high salinities. Copolymers containing sulfonate groups (acrylamide and sodium 2-acrylamido-2-methylpropane sulfonate from Floerger) are designed to tolerate high temperatures and seawater salinities [10]. G. Alkaline Water Flooding In the alkaline waterflood, a slug of water containing caustic is injected into the reservoir and followed by water or brine Figure 2c. The slug might contain up 5% sodium hydroxide and approximate about 15% of the pore volume. The caustic effects an increase in oil recovery by one or more of the following mechanisms (1) a favorable change in the wettability of the rock, (2) a low tension displacement, and (3) improved sweep [2]. H.

Traditional Surfactant /Polymer Flooding Surfactants and polymers are the principal components used in chemical flooding. The surfactants lowers the interfacial tension (IFT) between the reservoir oil and the injected water, while the polymer will create favorable viscosity conditions and good mobility control for the surfactant slug. The viscous forces acting on the oil then displace the oil by the flowing water. For this reason, chemical flooding is also denoted as: (1) micellar/polymer flooding, (2) surfactant /polymer flooding, and (3) microemulsion flooding. In general terms, Fig. 3 illustrates the various regions of immiscible flow during a typical displacement of oil by a surfactant solution. Provided that a water flood was performed prior to the chemical flood, the various zones are described as: Region 1: waterflooded residual oils saturation, only water is flowing. Region 2: an oil bank is formed, both oil and water are flowing. Region 3: surfactant slug forming the low IFT region, two-or three- phase flow of oil, brine, and microemulsion depending on the actual phase behavior. Region 4: polymer solution for mobility control, single-phase flow of water [10].

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Flow direction

Region 4 polymer

Figure 3

Region 3 surfactant

Region 2 oil bank

Region 1 wros

Phase position in a typical chemical flood.

I. Surfactant-Polymer Interaction in Solution In the traditional way of micellar flooding the surfactant is present most of the time in the microemulsion phase, i.e., the middle phase, and the polymer is present in the excess water phase. Due to the negative salinity gradient usually applied, a high concentration of surfactant is also present in the oil-in-water phase, at the back of surfactant slug. A rather high concentration of polymer must initially be injected to obtain mobility control of the surfactant slug. Thus, at the rear of the surfactant slug, both surfactant and polymer are present in the oil-in-water phase in significant concentration (5 to 10 wt% surfactant and more than 1000 ppm of polymer). It is well documented in the petroleum and chemical literature that mixtures of anionic surfactants and different water soluble polymer tend to phase separate in saline aqueous solutions [46–47]. The incompatibility phenomena can be chemically explained by considering the micelle–polymer system as a colloidal system according to the DLVO theory for the stability of colloids [48–49]. Therefore, the micellar–polymer systems usually contain alcohol in order to obtain gel-free microemulsions and to improve the compatibility of the surfactant–polymer solution. High salinities require larger concentrations of alcohol to prevent phase separation. Piculell and Lindman [50] recently discussed the phase separation of aqueous mixtures of polymer/polymer and polymer/surfactant solutions in terms of association and segregation. When one of the phases is concentrated with both of the components, the phase separation is termed associative, and when the separating phases contain components of comparable total concentrations it is called a segregative phase separation. Mixtures of nonionic polymer and ionic surfactant mainly show an associative phase separation. However, this may be due to the fact that most studies performed in the chemical literature have been specifically concerned with systems where P-S association has been important. Systematic experiments on P-S systems where both are negatively charged are reported to show a segregative phase separation. Taugbøl et al. reported that it is possible to recover more than 50% of water flooded residual oil by performing a low tension polymer water flood (LTPWF), i.e., no complicated phase gradients are used. Core flood experiments in Berea and Bentheim sandstone cores are conducted using a surfactant of the type alkylpropoxy-ethoxy sulfate, xanthan as polymer, model oil (n-heptane), and synthetic seawater. The floods are performed in the two-phase state with the surfactant and the polymer dissolved in the aqueous phase using different polymer concentrations and a low surfactant concentration, 0.5 wt%. In the presence of a polymer, the oil recovery was improved and the retention of surfactant was decreased. The results are discussed in relation to dissociative surfactant polymer interaction in solution and the effect of polymer on the flow performance of the surfactant in the porous media. Depending on the porous media, an important criteria for success is that the surfactant system must be able to decrease the interfacial tension by a factor of about 103 [22].

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The presence of polymer and surfactant in injection water will improve the oil recovery during a water flood. The flooding method is termed low-tension polymer water flood. During the flooding process both chemicals are present in the aqueous microemulsion phase. Core flood experiments were conducted using an alkyl xylene sulfonate, xanthan, model oil (n-heptane), NaCl brine, and Berea sandstone cores in the two-phase ° Surprisingly, at low surfactant concentration, the flooding behaviour of region at 50°C. the surfactant is influenced by the presence of polymer in a negative way regarding oil recovery, even though a dissociative surfactant–polymer interaction is observed in static experiments. The polymer appears to have a negative effect of the flow performance of the surfactant in the porous media possibly owing to very large micellar aggregates [51]. It is, however, very important that no association between surfactant and polymer takes place in solution. In the presence of excess polymer, the surfactant monomer concentration will then become lower than the CMC. The monomolecular packing of surfactants at the interface decreases, and the IFT will increase drastically. It is important to note that the association between ethoxylated sulfonates [52] and sulfates [53] and nonionic polymer decreases as the ethoxylation degree increases. Practically no interaction was observed with EO-groups higher than 3-4. This means that the free energy for normal micelle formation is more favorable than for forming micellar aggregates on the polymer. J.

Relation between the Interfacial Tension and Residual Oil Saturation At the end of primary recovery and/or secondary recovery (water flooding), the residual oil trapped in the pore structure due to capillary forces. The displacement of residual phases is strongly influenced by the competition between two forces, viscous and capillary. Viscous force is known to be a driving force to mobilize the residual oil droplet while capillary force is defined as a resistant force to entrap this residual oil drop. Therefore, the trapped drop does not flow until the viscous forces of the displacing fluid exceeds the capillary forces, usually quantitatively presented by the capillary number Nc. The basic correlation between the Nc and the level of the residual oil had been remodified by Tabor [54] in the form equation (1). Nc = µν /σφ

(1)

where Nc capillary number. µ viscosity of the displacing fluid, dyne. Sec/cm2. ν velocity the displacing fluid, cm/sec. σ is the interfacial tension, dyne/cm. φ the porosity. The value of the capillary number is around 10-6 after water flooding and should be increased by 3 to 4 orders for enhanced oil recovery processes [55]. So the interfacial tension between oil and brine, which is usually around 30 mNm, must be reduced by a factor of 103 or 104. This was shown with gas/liquid mixtures without any additives and confirmed with surfactant containing system in the early 1970s. The waterflooded residual oil saturation may be in the range of 30 to 40%. It must be noticed that these data are mainly based on model cores (Berea and other outcrop sandstone cores) which have never been in contact with reservoir crude oil. Much lower

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values are, however, observed under mixed wet condition [56]. This implies that it is about 10 times more difficult to remobilize capillary-trapped discontinuous oil, compared to continuous oil. In order to be able to mobilize a significant amount of the waterflooded residual oil, it is expected that the capillary number must be increased by a factor of 103 to 104. The only practical way to do this is to reduce the IFT between the reservoir oil and the injected water by the same factor using surfactants, which normally means that the IFT should be between about 0.01 and 0.001 mN/m. K. Phase Behavior in EOR A pseudoternary diagram including surfactants, brine, and oil, respectively, often represents the phase behavior of EOR systems. Possible combinations of oil, water/salt, and surfactant/co-surfactant/alcohol will give different phase behavior depending on actual conditions. The liquid phase containing the surfactant is a thermodynamically stable phase usually termed a microemulsion. In the pseudophase model, microemulsion phases formed from oil/brine/surfactant/alcohol mixtures consist of three microemulsions. Generally, their three phase terminology for microemulsion phases in EOR are divided as follows: (1) Oil in water microemulsion phase that exhibits equilibrium with excess oil is called type II (-). (2) The micromulsion phase which exhibits equilibrium with excess oil and water is called type III. (3) Water in oil microemulsion phase that exhibits equilibrium with excess water is called type II (+) [10]. In general, the phase behavior conditions for oil-water-surfactant system without alcohol present is very sensitive to the oil composition. Polar components in the crude oil may act as cosurfactants, so, a model oils like n-alkane can be used. The Exxon surfactant product termed RL-3011 (dodecyl-o-xylene sulfonate) illustrates the importance of oil composition on the phase behavior regarding changes in reservoir parameters like temperature, pressure, and salinity [57–60]. Forming a thermodynamically stable microemulsion phase between the oil and the water developed complicated formulations of injected flooding. At equal solubilization of oil and water into this middle phase, the IFT between the microemulsion phase and the two excess phases, oil and water, is ultralow and equal, fulfilling the conditions for displacing most waterflooded residual oil. A variety of chemicals, mixtures of surfactants and low molecular weight alcohols, were needed to design a gel-free chemical formulation. The amount of polymer needed for maintaining mobility control must be high because the middle phase microemulsion is normally rather viscous. Because of the complexity of the chemical formulation, the slug is affected by mass transfer and changes in phase behavior as the fluids propagate through the reservoir. The process is sensitive to many parameters including: (1) rock type, (2) mineral content, (3) interstitial brine salinity and composition, (4) pH, (5) injection rate, (6) slug composition, (7) polymer concentration and type, (8) oil viscosity and composition, (9) pressure, (10) temperature, and (11) heterogeneities of the formation [10]. Sanz and Pope [61] have screened combinations of ethoxylated sulfonates and alkylaryl sulfonates for alcohol-free chemical flooding purposes. They observed difficulties in obtaining clean or gel-free, liquid crystals, macroemulsions, and precipitates along the compositional path during a chemical flood if cosurfactants/alcohols are not part of the chemical formulation. Phase trapping and blockage of the porous medium must be avoided. L. Application of Surfactants in Enhanced Oil Recovery Enhanced oil recovery is the additional recovery of oil from a petroleum reservoir over that which can be economically recovered by conventional primary and secondary methods [30].

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1. Interaction between Surfactant and Polymer at Reservoir Rock During flooding process such interaction is also affected by chromatographic separation between the chemicals due to size exclusion phenomena, relative diffusion rate between surfactant monomers and polymers and between polymers of different molecular weight, and the access to the surface area. The polymer will move ahead of the surfactant when the chemicals are injected into a porous medium. Mixtures of xanthan, acrylamide, sodium 2-acrylamido-2-methylpropane sulfonate (AN125), crude oil, and synthetic seawater were circulated through clay-containing reservoir cores for several weeks. They injected at constant slug concentration at different slug size, through model sandstone cores. Various adsorption regimes of the surfactant were detected at different contact times between the reservoir core material and the circulated chemical solution, and it was observed that xanthan behaves as a sacrificial adsorbate towards the surfactant by decreasing the surfactant adsorption. In the slug experiments, using model cores, xanthan appeared to decrease the surfactant adsorption when using small surfactant slug sizes, but no measurable effect of xanthan or AN 125 on surfactant adsorption was observed for large slug sizes. A dynamic reversible adsorption model appeared to predict the propagation of the surfactant slug through the porous medium, but the adsorption level was not fitted. Thus, the polymer may decrease the adsorption of surfactant in reservoir rock of high clay content, approximately 20 wt%. In cores of low clay content, approximately 5 wt%, the polymer will probably have negligible effect on the surfactant adsorption onto the rock [25] 2.

Displacement of Oil by Spontaneous Imbibition of Aqueous Surfactant Solution Imbibition of water is a physical process caused by adsorption of water to hydrophilic ion- groups forming a hydrophilic surface. A porous reservoir medium, consisting of a hydrophilic surface, may contain lipophilic liquid such as oil. When such an oil-filled reservoir rock is exposed to water, the water may spontaneously be sucked into the pores and displace the oil. Spontaneous imbibition of water into low-permeable fractured chalk is an wellaccepted method to improve the oil recovery from water to mixed wet rock material [62]. Normally, this process is driven by capillary forces, and it may seem a little strange to lower the capillary forces by adding surfactants to the injected water. In the same way as the viscous forces will mobilize capillary trapped water flooded oil, the gravity forces may be active in displacing the oil by spontaneous imbibition at low IFT [63]. Spontaneous imbibition experiments in nearly oil-wet, low-permeable chalk material saturated with oil are performed at ambient conditions with and without the cationic surfactant dodecyltrimethylammonium bromide present in the aqueous solution. Without surfactant present in the water, the rate of imbibition is, as expected, very small, and only approximately equals 13% of the oil was expelled from the core within 90 days. After that time, a sudden increase in the oil production was observed by exchanging the water with a 1.0 wt% surfactant solution. If the surfactant is present from the beginning, an oil production plateau of approximately equals 65% recovery was obtained within 90 days. The imbibition mechanism at low interfacial tension is discussed in terms of the phase behavior of the oilbrine surfactant system, and the ability of the surfactant to enhance the water wettability [64]. The improved spontaneous imbibition of water into oil saturated, fractured, low permeable (2 to 3 mD) chalk material of the Ekofisk type by means of surfactants was studied. The experiments were performed at room temperature, using long (55 cm) and

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short (5.0 cm) core samples of different wettabilities, i.e., water-wet, mixed-wet, and nearly oil-wet. For the two former systems, anionic surfactant of the alkyl-propoxy-ethyl sulfate type was used. A cationic surfactant, dodecyltrimethylammonium bromide, was used for the oil-wet condition. The imbibition mechanism in the water and mixed wet system at high IFT was found to be a countercurrent flow governed by capillary forces. At low IFT, the fluid flow appeared to be countercurrent at the start. Later, the oil expulsion was very slow and governed by gravity forces. Surprisingly, spontaneous oil expulsion from the nearly oil-wet core took place in the presence of the cationic surfactants by a countercurrent flow mechanism. The mechanism is discussed in terms of reversed micelle formation turning the chalk more water wet just across the water/oil interface [65). 3. Adsorption of Different Surfactants on Kaolinite The adsorption of anionic, cationic, and nonionic surfactants on kaolinite has been investigated. Anionic surfactants are widely used in enhanced oil recovery. The lower the adsorptions on the oil-bearing rock the higher the advantage of the surfactant to be used. Whilst the adsorption of anionic and nonionic surfactants are negligible, that of cationic surfactants is relatively high. For this reason, the use of cationic reagents in the enhanced oil recovery is not recommended. The adsorption of cationic surfactants was found to follow an ion-exchange mechanism, while that of anionic and nonionic surfactants proceed through electrostatic attraction and precipitation [66]. 4. Acidified Oil/Surfactant Enhanced Alkaline System A model acidic oil has been used to examine the effects of various alkali and added surfactant concentrations on dynamic interfacial tension. Experimental results revealed the existence of a characteristic behavior exhibited by the acidified oil against aqueous solutions. The dynamic interfacial tension is a function of acid concentration, alkali concentration, and added surfactant concentration. It has been found that there exists an optimum concentration with respect to both alkali and added surfactant, at which the interfacial tension is the lowest. The optimum concentration has been found to be dependent on acid concentration. The results suggest that the unionized acid contributed to the lowering of the dynamic interfacial tension between the model acidic oil and alkali and added surfactant solutions. The results also suggest that the unionized acid, ionized acid added surfactant adsorbed simultaneously onto the interface, resulting in low dynamic interfacial tension [67]. 5. Dual Surfactants—System for Enhanced Oil Recovery at High Salinity Surfactants for the enhanced oil recovery of crude oil were studied with a model oil by means of phase experiments and core floods. As single surfactants, alkylphenol ether sulfonates have only a limited potential for enhanced oil recovery at high salinities. If the surfactant is made hydrophilic enough to dissolve in brine it is no longer able to form a microemulsion with the hydrocarbon. This problem may solve by using dual surfactant systems consisting of alkane sulfonate and ether sulfonate. At high salinities these surfactant combinations dissolve in brine to form a homogeneous dispersion. Such mixtures are also cheaper than the ether sulfonate alone. Core floods with model oil demonstrate the efficiency of these surfactant mixtures and their compatibility with a modified polyacrylamide polymer specially developed for high salinity reservoir [68].

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6. Ultralow IFT Using Neutralized Oxidized Hydrocarbon Surfactant Surfactants that may be suitable for application in enhanced oil recovery have been produced from C22 and C26 paraffinic and naphthenic petroleum fractions by a two-step process. The hydrocarbon feed stocks were first oxidized in the vapor phase, followed by neutralization of the oxidized products with aqueous alkali. As a result, dilute solutions of organic acid salts were produced that achieved ultralow (less than 10–2 dyne/cm) interfacial tensions against a synthetic oil. Surfactant solutions that exhibited the lowest interfacial tensions (IFTs) were prepared from neutralizations that used low concentrations of sodium hydroxide rather than sodium silicate, sodium tripolyphosphate, or sodium carbonate. Neutralizations that used sodium silicate or sodium carbonate resulted in surfactant solutions having IFT profiles that were less sensitive to the electrolyte concentration. When sodium hydroxide was combined with either sodium silicate or sodium tripolyphosphate in the neutralizations, solutions having intermediate IFT properties were produced [69]. 7. Mixed Micelles Micelles composed of mixed surfactants with different structures (mixed micelles) are of great theoretical and industrial interest. Abdel-Moghny et al. maximize the reduction of the interfacial tension by blending four types of fatty acid amides based on lauric, myristic, palmetic and stearic acid with dodecyl benzene sulfonic acid at molar ratio 4:1 and designated as A1, A2, A3, and A4, respectively. The IFT was measured for each blend against different concentrations using Badri crude oil. The most potent formula (A4) was evaluated for using in enhanced oil recovery (EOR). The IFT was tested in the presence of a different electrolyte concentration with different crude oils at different temperatures. Finally, several runs were devoted to study the displacement of Badri crude oil by A4 surfactant solution using different slug sizes, 10, 20 and 40% of pore volume (PV). The study revealed that, Badri crude oil gave ultra low IFT at lowest surfactant concentration and 0.5% of NaCl. The recovery factor at slug size of 20% PV was 83% of original oil in place (OOIP) compared with 59% in case of conventional water flood [70]. 8. Biosurfactants as New Surfactant Surfactants are widely used for various purposes in industry, but for many years were mainly chemically synthesized. It has only been in the past few decades that biological surface active compounds (biosurfactants) have been described. Biosurfactants are gaining prominence due to their advantages of biodegradability, production on renewable resources and functionality under extreme conditions; particularly those pertaining during tertiary crude oil recovery. However, caution is frequently exercised with respect to their use because of possible subsequent microbial contamination of either underground oil reservoirs or products. The limited successes and applications for biosurfactants production, recovery, use in oil pollution control, oil storage tank clean up and enhanced oil recovery were reviewed from technological points of view [71].

ACKNOWLEDGMENTS I express my thanks to the staff of the Egyptian Petroleum Research Institute (EPRI) particularly, Prof. Dr. Ahmed Kadry Aboul-Gheit, professor of process development, who devoted time and effort to review this text. I am very grateful for his continuous encour-

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agement. Without his support this entire subject would not have been possible. In addition Prof. Dr. Abdel-Fattah Badawi, professor of petrochemicals, contributed many valuable suggestions. Also, many thanks to Dr. Mahmoud Ramzi, in the production department, for his help and final montage.

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12 Surfactant-Based Systems for Environmental Remediation David A. Sabatini, Robert C. Knox, Jeffrey H. Harwell, and Ben Shiau

CONTENTS I. II. III. IV.

Summary................................................................................................................ 347 The Problem .......................................................................................................... 348 The Approach ........................................................................................................ 350 Surfactant Fundamentals ....................................................................................... 351 A. Key Economic/Technical Factors.............................................................. 353 1. Minimizing Surfactant Losses ................................................... 354 2. Maximizing Contaminant Extraction ........................................ 354 3. Surfactant Regeneration/Reuse .................................................. 355 4. Mitigating Vertical Migration Concerns.................................... 356 B. Field Results.............................................................................................. 358 1. Hill Air Force Base (AFB)—Maximizing Contaminant Extraction ................................................................................... 358 2. Tinker AFB—Surfactant Decontamination for Reinjection...... 361 3. Alameda Point NAS—Mitigating Vertical Migration (Supersolubilization) .................................................................. 362 C. Future Advances/Applications .................................................................. 364 Acknowledgments........................................................................................................... 366 References ....................................................................................................................... 366

I.

SUMMARY

Widespread use of petroleum hydrocarbons and chlorinated solvents has resulted in their contamination of valuable ground water supplies. This chapter summarizes key technical and economic issues for surfactant-enhanced remediation of such contamination episodes. 347

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The major issues considered include: maximizing the amount of contaminant extracted by surfactant injection, minimizing the surfactant losses in the subsurface, mitigating concerns of vertical contaminant migration, and decontaminating and recycling the surfactant solutions. Both laboratory and field results are presented to demonstrate how we address each of these issues. Finally, we will discuss recent innovations in surfactant systems to further improve the economics of subsurface remediation efforts, and describe how these systems may be useful in other applications (e.g., detergency, solvent replacement).

II. THE PROBLEM Widespread use of petroleum hydrocarbons and chlorinated solvents has resulted in contamination of valuable ground water resources. Figure 1 is a schematic illustration of an oil spill that occurs at the land surface and migrates downward due to gravity forces. The oil first moves through the unsaturated zone and eventually reaches a depth where the porous media (soil) is saturated with water, known as the water table. In this illustration (Fig. 1) the oil phase continues to migrate downward through the saturated zone, indicating that this oil is denser than water. Finally, the oil reaches a confining layer that it cannot penetrate, and begins to pool at this depth. In the environmental literature these oil phases are referred to as nonaqueous phase liquids, or NAPLs. In Fig. 1 the oil is denser than water, and is thus referred to as a dense nonaqueous phase liquid (DNAPL). Chlorinated hydrocarbons are typical examples of a DNAPL. If the oil is less dense than water, as true for petroleum hydrocarbons, they are known as “light” nonaqueous phase liquids, or LNAPLs. These oil phases are immiscible with water because of the interfacial tension that exists between the phases. Capillary forces cause oil droplets to be trapped in the porous media as the oil phase migrates through the porous media—as illustrated on a macroscopic scale in Fig. 1 and at a mesoscale in Fig. 2. The trapped oil (residual saturation) is held against gravity forces for dense chlorinated solvents and against buoyancy forces for petroleum hydrocarbons; the latter can become trapped in the saturated zone due to a rising water table. The water solubility of

Injection well

Extraction well Treat

Pump Unsaturated zone Water table

Trapped (residual) oil A

Saturated zone

Confining layer

Figure 1 Schematic cross-section of trapped (residual) oil in subsurface and flushing based remediation—Box A is enlarged in Fig. 2.

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Trapped oil

Porous media

Fluid flow

Dissolved oil Ground water flow

Figure 2 Trapped oil (residual NAPL) in a porous medium and the resulting aqueous solubility during ground water flow/pump-and-treat flushing.

these trapped oil phases is both too high and too low. The high water solubility of these oils causes their ground water concentrations to exceed treatment goals (health standards). At the same time, their low water solubility renders water-based flushing of the contamination highly inefficient (much as washing dirty clothes in water alone is highly inefficient). Nevertheless, water-based flushing, as depicted in Figs. 1 and 2, has been the traditional approach for addressing these contamination scenarios. In water-based flushing, water is injected into the subsurface and flushed through the zone containing the trapped oil. However, the water immiscibility and low solubility of these compounds severely limits the effectiveness of water-based flushing. At the same time, large dissolved contaminant plumes can emanate from these trapped oil “source” zones, as depicted in Fig. 3. For example, a source zone of relatively small size (acres or less) can produce dissolved plumes that are miles in length. While traditional pump-and-treat remediation (water-based flushing) is generally effective for treating dissolved contaminant plumes (Fig. 3), as discussed above it is very inefficient for trapped oil phases (the source zone in Fig. 3). And if the dissolved plume is addressed without removing the source zone, the plume reappears when additional ground water flows through the source zone. For this reason, innovative methods have been developed to significantly enhance the extraction of residual oil saturation. Chemical

Ground Water Flow

Source Zone

Dissolved Contaminant

Figure 3 Top view of trapped oil/source zone which acts as a source to create a dissolved contaminant plume.

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additives have been widely evaluated for this purpose, with surfactants being a prime candidate [1,2]. This is analogous to adding surfactants to a washing bath in an effort to improve contaminant “extraction” from the clothes. Both surfactants and alcohols can increase the apparent water solubility of the oil phase, and, when these systems are properly designed, can dramatically reduce the interfacial tension responsible for trapping the oil phase. Since the surfactant has little or no impact on treating the dissolved plume, it will be targeted at the trapped oil phase. In this chapter we discuss key technical and economic considerations for successful application of surfactant enhanced aquifer remediation. We then share laboratory and field results from our group that illustrate each of these issues and show how they can be addressed. We conclude by presenting recent advances that are still in the developmental stages. But first, we will provide a brief overview of the surfactant enhanced subsurface remediation technology in the next section, and an introduction to fundamental surfactant concepts critical to this technology in the following section.

III. THE APPROACH

As mentioned above, surfactant enhanced aquifer remediation seeks to overcome the limitations of water-based pump-and-treat remediation. In our approach, a surfactant or surfactant mixture is added to the injection side of the system in Fig. 1 in an effort to significantly increase the contaminant extraction efficiency. This can be accomplished in one of two ways; by increasing the contaminant solubility without significantly reducing the interfacial tension (“solubilization”), or by significantly reducing the interfacial tension and mobilizing the trapped oil phase (“mobilization”). Relative advantages and disadvantages of these two approaches are discussed later. For a chlorinated solvent (e.g., tetrachloroethylene or PCE), water-based flushing of the trapped oil may require 1000 flushing cycles (pore volumes) to dissolve the trapped oil. In contrast, by increasing the PCE solubility 50-fold in surfactant micelles, surfactantenhanced solubilization will accomplish the same level of remediation in 20 pore volumes. In this case the oil remains trapped (as in Fig. 2), but the surfactant solution flowing through the pores achieves significantly higher extraction concentrations. Conversely, by virtually eliminating the interfacial tension causing the oil to be trapped in the first place, surfactant enhanced mobilization will accomplish the same level of removal in several pore volumes. In this case, the oil trapped in Fig. 2 is largely or totally released from the trapped stage. Thus, in the example above the relative efficiencies of water, solubilization and mobilization are 1000:20:2, respectively. While the exact numbers and ratios are system specific, these values give an idea of the relative efficiencies of each system. Using this example, and given that a full-scale remediation system may require months to flush a single pore volume, surfactant enhanced aquifer remediation could reduce the remediation times from hundreds of years for water alone to 5 years for solubilization to less than a year for mobilization. The potential advantages of surfactant enhanced subsurface remediation are therefore obvious. But beyond technical viability, this technology must also be economically viable. Because of the surfactants costs, the surfactant solution is designed to maximize the amount of contaminant extracted per mass of surfactant injected. We must also seek to minimize surfactant losses due to sorption and precipitation in the subsurface. When using multiple flushing cycles, it may be more economical to regenerate (decontaminate) the surfactant solution for recyling (reinjection). Finally, reducing the surfactant concentration necessary

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to achieve a given solubility enhancement is desirable. But implicit to all this is the basic question: How clean is clean enough? How much of the “oil stain” (residual saturation) must be removed to be successful? Before discussing these points in further detail, we will first discuss surfactant fundamentals critical to this technology.

IV. SURFACTANT FUNDAMENTALS Surfactants (surface active agents) are unique because of their amphiphilic nature, which makes them surface active and causes them to accumulate at interfaces. Thus, when placed in water-oil or water-air systems, surfactants accumulate at the interface with their waterlike moiety in the polar water phase and the oil-like moiety in the nonpolar oil or less polar air phase. In this way, both surfactant moieties are in a preferred phase and the free energy of the system is minimized [3]. By definition, alcohols could be considered as surfactants since they also accumulate at interfaces. However, a unique characteristic of surfactants differentiates them from alcohols. When the aqueous surfactant concentration exceeds a certain level, the surfactant molecules (monomers) self-aggregate into spherical aggregates known as micelles. In contrast, alcohols do not form such micellar aggregates. Surfactant micelles form when increasing surfactant concentrations first exceed the critical micelle concentration (CMC). Surfactant micelles have polar exteriors and nonpolar interiors. The polar exterior makes micelles highly soluble in water, while the nonpolar interior provides a hydrophobic sink for organic compounds, which effectively increases the compound’s solubility. Thus, by adding surfactant well above the CMC, we significantly increase the micelle concentration and thus the contaminant’s apparent solubility. In contrast, adding surfactant near or only slightly above the CMC will have minimal effect on contaminant solubility and extraction efficiency. We therefore desire to be well above the CMC (e.g., 10 to 20 times the CMC) to maximize contaminant solubility and extraction efficiency. Surfactants are capable of producing other structured phases. Some of these phases are undesirable for subsurface remediation (e.g., liquid crystals, gels). In contrast, middle phase microemulsions can be desirable for subsurface remediation. In particular, middle phase microemulsion systems produce ultra-low oil-water interfacial tensions and ultrahigh contaminant solubilization (supersolubilization). Since it is the oil–water interfacial tension that originally trapped the oil in porous media, virtually eliminating the interfacial tension will mobilize the trapped oil phase (i.e., cause the oil to come out as a bulk phase rather than simply increasing its water solubility). While micelles form spontaneously above the CMC, forming middle phase microemulsions is not so simple. The surfactant system must be carefully tailored to each specific contaminant phase. Before describing a middle phase microemulsion we will first discuss two other surfactant systems; micelles, which we have described above, and inverse micelles. While micelles form when water-soluble surfactants are added to an aqueous phase, inverse micelles occur when oil-soluble surfactants are added to an oil phase. For oil-soluble surfactants, the hydrophilic surfactant moiety (head) accumulates in the interior of the aggregate and the hydrophobic moiety (tail) orients toward the oil phase. The inverse micelle thus has a hydrophobic exterior, which makes it oil soluble, and a hydrophilic interior, which acts as a sink to “solubilize” water. For the descriptions of micelles and inverse micelles we considered surfactants in a single phase system (oil or water). If both oil and water phases coexist, as is true with residual oil in a ground water system, the surfactant will partition between the two phases in accordance with the surfactant’s relative hydrophilicity. The hydrophilic-lipophilic balance (HLB)

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O/S interface

W/S interface

Optimum formulation

I

III

Oil solubilization, %V/V

Interfacial tension, mN/m

is a surfactant property that approximates this partitioning. Surfactants with relatively high HLB values (e.g., 20) are water soluble, while relatively low HLB values (e.g., 5) indicate surfactants that are oil soluble. As the HLB of a surfactant, or surfactant mixture, varies between these extreme values it transitions from being water soluble (micelles) to oil soluble (inverse micelles); this transition occurs at intermediate HLB values (approximately 8 to 12, depending on the oil). By varying system conditions we can force water-soluble surfactants to partition into the oil phase. For example, by increasing the salt concentration we can reduce the HLB of ionic surfactant systems. When the salt concentration is increased sufficiently ionic surfactants will eventually partition into the oil phase. This is illustrated in Fig. 4, which shows aqueous micelles at lower salt concentrations and oil-phase inverse micelles at higher salt concentrations. Increasing the system temperature will likewise decrease the system HLB for nonionic surfactant systems. Middle phase microemulsion systems form when the surfactant system HLB (or effective HLB, as a function of salinity or temperature) is adjusted such that the surfactant is just ready to leave the water phase, but is not yet ready to go into the oil phase. At this point the surfactant system dislikes both the water and oil phases and would prefer to accumulate at the interface. In simple terms, since all the surfactant cannot fit at the oil–water interface, a new phase forms. This new phase, which we call a middle phase microemulsion, combines virtually all of the surfactant with portions of both the oil and water phases, and exists in equilibrium with surfactant-free oil and water phases. Middle phase microemulsions appear at intermediate salt concentrations in Fig. 4. Unlike an oilwater emulsion, which breaks given sufficient time, a middle phase microemulsion system is thermodynamically stable and thus does not break with time. Winsor referred to this new phase as a Type III microemulsion, as opposed to Type I (micelles) and Type II (inverse micelles) microemulsions [3,4].

II

Increase Salinity, Decrease temperature or increase long chain alcohol content

Figure 4 Surfactant scan showing transition from micelles to middle phase microemulsions to inverse micelles. Note that the oil (PCE) is the lower phase in the vials.

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The middle phase microemulsion occurs over a limited HLB range as the system transitions from a Type I to a Type II system. When salinity is used to adjust the system HLB, this middle phase range is known as the salinity window. Within the salinity window, as the HLB decreases the middle phase system transitions from being under-optimum (more water than oil in the middle phase) to optimum (equal volumes of water and oil) to over-optimum (more oil than water). Optimum here refers to the lowest interfacial tension within the middle phase regime, which experience teaches us occurs when equal volumes of oil and water coexist in the middle phase microemulsion. Recalling that ultralow interfacial tension and superhigh solubilization are two desirable characteristics of middle phase microemulsion systems, we now know that the lowest possible interfacial tension occurs in middle phase microemulsions with equal volumes of oil and water. An obvious question is; When is the supersolubilization potential at its maximum? This question can be answered by considering the Chun-Huh relationship [5], as shown below. S=

C IFT

where S = solubilization ratio (vol/mass) C = constant IFT = interfacial tension (mN/m) The Chun-Huh relationship demonstrates that solubilization potential is inversely proportional to the square root of the interfacial tension. Since interfacial tension continuously decreases as we move towards a middle phase microemulsion system, the ChunHuh relationship demonstrates that the solubilization potential also continuously increases, within both the Winsor Type I and Type III regions (see Fig. 4). We refer to this increased solubilization within the Type I region as supersolubilization [6]. But why operate in a supersolubilization region instead of in the optimum middle phase microemulsion region? Because the supersolubilization system can mitigate vertical migration of released DNAPL droplets. If the interfacial tension is reduced to the point that DNAPL droplets are released in bulk, then gravity forces will cause these released droplets to migrate downward, potentially allowing them to enter zones previously inaccessible to the oil. By operating in a supersolubilization region, the system HLB is adjusted such that the lower interfacial tension does not release the trapped oil but does maximize the solubility enhancement. A. KEY ECONOMIC/TECHNICAL FACTORS Having discussed surfactant fundamentals pertinent to environmental remediation, we now identify key technical and economic issues relative to successful implementation of this technology. In many respects this technology is an outgrowth of surfactant enhanced oil recovery in petroleum reservoirs; Pope and Wade [5] do an excellent job of identifying similarities and differences between these two applications. After discussing economic factors below, we will then summarize our previous laboratory and field results that illustrate successful implementation of this technology relative to each of the key economic factors.

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Full-scale application of surfactant enhanced subsurface remediation requires that this approach be economically competitive with other methods. Krebbs-Yuill et al. [7] demonstrated that surfactant enhanced subsurface remediation is economically competitive when surfactant losses are minimized, surfactant extraction efficiency is maximized and surfactant regeneration and reuse are implemented. These factors reflect the fact that surfactant capital costs can, and initially were, the single largest expense for these systems. In addition, we will further describe an approach for mitigating vertical migration concerns, a problem introduced above. Another simple alternative for improving the overall system economics is to spatially divide the residual zone into compartments and march the surfactant remediation through the compartments one at a time, thereby reducing the capital expenditure for surfactant. While having the potential to decrease the capital costs, this approach will extend the time necessary to clean up the site, which may have negative repercussions. 1. Minimizing Surfactant Losses Surfactant losses in the subsurface negatively impact system performance and economics, and can potentially result in system failure. Careful surfactant selection can minimize surfactant precipitation and sorption losses. For example, we have demonstrated that disulfonated vs. monosulfonated surfactants [8] and ethoxylated vs. nonethoxylated alkylsulfate surfactants [9] reduce surfactant sorption and precipitation losses, while maintaining good solubilization potential. We have used the disulfonated surfactant Dowfax 8390 in several field demonstrations [10–12]; its robustness and conservative nature have validated its ability to minimize surfactant losses (> 95% recovery of injected surfactant in the above tests). 2. Maximizing Contaminant Extraction Maximizing contaminant extraction is also important to overall system performance. As discussed above, the greatest possible extraction enhancement occurs with middle phase microemulsion systems. In their work with chlorinated solvents, Shiau et al. [13] focused on the use of direct food additive surfactants for both solubilization and mobilization (via middle phase microemulsions). Shiau et al. [13] demonstrated that surfactant selection was much more critical when forming middle phase microemulsions. While initial surfactant scans transitioned from micellar phases (Winsor Type I) to reverse micelles (Winsor Type II), undesirable phases occurred in the transition region (e.g., liquid crystals) instead of the target middle phase microemulsions. Only when the branched surfactant Aerosol OT (AOT) was used did middle phase microemulsion systems occur; the branched AOT surfactant sterically hinders liquid crystal formation and thus promotes formation of middle phase microemulsions. Shiau et al. [13] also demonstrated that middle phase microemulsion formation is temperature and hardness sensitive, especially when using nonionic and anionic surfactants, respectively. Shiau et al. studied PCE, TCE, and 1, 2-DCE individually [13] and in binary and ternary mixtures [14]. Using regular solution theory it was possible to predict ternary and binary system behavior based on binary and single-component system results, respectively. Using column studies, Shiau et al. [15] demonstrated that mobilization was significantly more effective than solubilization (>97% of PCE was extracted in 3 pore volumes with mobilization, while <90% was extracted in 30 pore volumes using solubilization). Shiau et al. [15] showed that even when the surfactant system deviated from ideal middle phase composition into the Type I region, system performance was still quite good. This follows from the fact that the interfacial tension is still significantly reduced and solubilization is

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still super-high even as we approach the Type I to Type III transition (i.e., the supersolubilization region). This robustness is quite encouraging given that this technology will be implemented in an inherently heterogeneous subsurface environment. In addition, a variation of this concept is proposed below to help minimize the vertical migration potential of chlorinated solvents. Thus, by simply adjusting the HLB of a surfactant system we can greatly improve the contaminant extraction efficiency, while maintaining the total amount of surfactant (and thus the overall cost) virtually constant. This approach has been successfully implemented in the field, as will be presented in the field demonstration section. In addition, ongoing research is looking to reduce the amount of surfactant from 3 to 6 wt%, as commonly evaluated in field tests to date, to <1 wt%, and to replacing a fraction of the costly surfactant molecules with cheaper linker molecules. These efforts, described in the last section in this chapter, can thus further improve the cost efficiency of surfactant systems, and decrease the surfactant costs to a smaller fraction of the overall costs. 3. Surfactant Regeneration/Reuse In general, if more than five or six pore volumes of surfactant flushing are required, and if surfactant concentrations are several weight percent or more, economic considerations mandate that the extracted surfactant solution should be regenerated and the surfactant reused. Surfactant reinjection requires decontamination of the extracted solution; the level of decontamination will be based on regulatory requirements and economic considerations. Regulators we have visited with indicate that 95% contaminant removal will be sufficient to permit surfactant reinjection. This is good news, as the costs of going from 95 to 99% removal may be equal to the costs of achieving 95% removal. A key to selecting the unit process for surfactant–contaminant separation is the contaminant volatility. Numerous systems can be used for volatile contaminants; however, fewer alternatives exist for nonvolatiles. Air stripping (encouraging the volatile compound to move from liquid to gaseous phases) is the most promising technology for volatile compounds, while liquid-liquid extraction is most promising for semi- to nonvolatile compounds. The strong affinity of both the surfactant and contaminant for activated carbon limits the utility of carbon adsorption as a separation process. While ion exchange resins will preferentially adsorb oppositely charged ionic surfactants, contaminant solubilization into adsorbed surfactant bilayers, or adsolubilization [16], will reduce process effectiveness [17,18]. Air stripping processes encourage aqueous-gaseous phase transfer by maximizing the interfacial area and driving force for mass transfer. Most commonly this is done by flowing water into the top of a packed column (a cylinder filled with a high-porosity/highsurface-area media) while forcing air up through the bottom of the column. The packing medium helps to maximize the air-water interface, while the flowing air maximizes the contaminant concentration gradient across the air-water interface, both of which promote mass transfer of the contaminant from the water to the air. Surfactants will impact air stripping (and liquid-liquid extraction) in several ways. Lipe et al. (19] demonstrated that air stripping efficiency declines with increasing surfactant concentration above the CMC. Contaminant partitioning between aqueous and micellar phases reduces the aqueous phase contaminant activity [extramicellar concentration). The aqueous phase activity drives Henry’s law-based stripping, and since the aqueous phase activity decreases with increasing micelle concentration (increased competitive partitioning), the results of Lipe et al. [19] are as expected. Lipe et al. [19] rederived the air stripper design equations to account for this competitive partitioning and found excellent agreement between model predictions

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and laboratory data. Hasegawa et al. [20] did likewise for liquid–liquid extraction and also found good agreement between model predictions and experimental results. In liquid–liquid extraction, the extracting oil will be chosen to minimize water solubility, improve environmental acceptance, and maximize the contaminant extraction efficiency. Surfactants can also impact air stripping and liquid–liquid extraction performance due to foam and emulsion formation, respectively. Air strippers are designed to maximize the air–water interfacial area for mass transfer. This is most commonly accomplished by countercurrent flow of water and air through a packed-tower. These conditions are also optimal for foam generation; the same is true for liquid–liquid extraction and emulsion formation. Lipe et al. [19] demonstrated that reducing the liquid loading rate, and corresponding turbulence, could reduce the foaming potential. Lipe et al. [19] and Hasegawa et al. [20] demonstrated that air stripping and liquid–liquid extraction in hollow-fiber membranes can also mitigate foam and emulsion formation, respectively. Due to the surfactant-decreased surface or interfacial tension, it may be necessary to apply a backpressure in these systems to prevent fluid penetration across the membrane. In addition, experience has shown that minimizing turbulent zones in these reactors (e.g., freefall) also helps mitigate foam/emulsion formation. For cases where surfactant reconcentration is necessary prior to reinjection, ultrafiltration (UF) membranes can be used. The UF process will retain surfactant micelles while allowing monomers to pass through. For example, using a filter with a 10,000 molecular weight cutoff (MWCO) will retain micelles while the monomers flow through the membrane. Lipe et al. [19] achieved 93 to 99% retention of surfactants using a 10,000 MWCO membrane. While the UF process effectively retains surfactant micelles, monomeric concentrations will pass through with the permeate. If economics dictate, smaller filters may be used to capture this additional surfactant for reuse. 4. Mitigating Vertical Migration Concerns The use of middle phase microemulsions is more complicated when addressing DNAPLs such as chlorinated solvents. Because chlorinated solvents are denser than water (e.g., tetrachloroethylene has a specific gravity of PCE is 1.6), the release of trapped oil can result in downward migration due to gravity forces. If this vertical migration is into previously uncontaminated zones, or worse yet through lower confining layers protecting another aquifer system, then the problem may be amplified. In contrast, vertical migration is much less of a concern for oils lighter than water (LNAPLs) because they will rise to the water table due to buoyancy forces [6,11]. It was vertical migration concerns that caused early researchers to focus on surfactants that maintained relatively high interfacial tensions at the CMC rather than middle phase microemulsions. As discussed above, minimal reductions in interfacial tension result in only minor solubilization enhancements. Because of this, other researchers have recognized the advantages of increasing the solubilization potential, and have proposed operating with more efficient micellar systems, but still well away from middle phase microemulsion systems. While this approach is much more efficient than using simple micelles, it still compromises the extraction efficiency possible with middle phase microemulsion systems. By identifying the threshold of mobilization one can increase the solubilization as much as possible (supersolubilization) without mobilizing trapped oil. To further explain this concept, we will make use of the capillary curve, which is a plot of residual oil saturation vs. the capillary number (Fig. 5). Residual oil saturation is the volume of trapped oil normalized by the total pore volume, or the fraction of the pore volume filled with trapped oil. The capillary number is a dimensionless number that quantifies the

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Residual saturation (Sn)

0.13 0.12 012x005

0.11

IFT = 3.92 dynes/cm 0.1 0.09 0.08

IFT = 0.095 dynes/cm

0.07 0.06 −7

−6

−5

−4

−3

−2

log (Capillary No.) Mobilization (free phase + middle phase PCE)

Figure 5 Capillary number curve showing residual saturation (trapped oil) vs. log capillary number for a PCE/Dover AFB soil system. (Adapted from Sabatini et al., Contam. Hydrol. 45(1–2):99–121, 2000.)

ratio of forces trying to displace trapped oil vs. those forces resisting this displacement. In our flowing system (see Figs. 1 and 2), the displacement forces result from a combination of groundwater velocity and fluid viscosity, and the resistance forces are a result of the oil–water interfacial tension. Thus, an increasing capillary number indicates that the groundwater velocity or viscosity has increased, or that the interfacial tension has decreased. Conversely, a decrease in residual oil saturation indicates that the capillary forces (e.g., interfacial tension) have decreased and the amount of trapped oil has decreased. Figure 5 shows such a capillary curve for tetrachloroethylene (PCE) and a subsurface media from Dover Air Force Base [6]. From Fig. 5, we see that we can increase the capillary number to ~5 x 10–6 without mobilizing PCE (since the residual saturation level remains constant, no free phase PCE has been released from residual saturation). This capillary number corresponds to an interfacial tension of ~ 4 dyn/cm. Thus, designing a surfactant system with an interfacial tension of 4 dyn/cm will maximize the supersolubilization potential, while still mitigating vertical migration concerns. However, if the interfacial tension is further decreased the capillary number increases and the residual saturation level decrease—the magnitude of the residual saturation decrease reflects the amount of trapped oil released, as illustrated below. To demonstrate the importance of interfacial tension, let’s see what happens if we start out with a system having an interfacial tension below 4 dyn/cm (Fig. 5). A 2% Isalchem (ISA) 145-4PO, 1% Dowfax 8390, 0.6% CaCl2 system has an interfacial tension of 0.095 dyn/cm [6]. From Fig. 5 we would expect the residual oil to decrease from 0.12 to 0.065, or roughly 45% of the residual phase PCE would be released. Figure 6 shows the results of a column study using this surfactant system. Out of an initial amount of residual oil of 2.5 ml almost 1.0 ml is mobilized, with the majority of this occurring within the first pore volume and all occurring within the first two pore volumes (Sabatini et al., 2000). Thus, 40% of the residual oil was released by this surfactant system; this agrees well with the 45% predicted from the capillary number curve, and illustrates the danger of “overshooting” when enhancing the extraction efficiency via supersolubilization. In a separate column run, an interfacial tension of 4.0 dyn/cm was used and no visible PCE was mobilized, again in agreement with the capillary number curve in Fig. 5 [6].

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Accumulated PCE (ml)

1.4 1.2 1 0.8 0.6

Mobilized PCE

0.4 0.2

Total PCE Removal: 96.9%

0 0

1

2

3

4

5

6

Pore volumes

Figure 6 Plot showing accumulated PCE vs. pore volumes from column illustrating amount initially mobilized vs. amount eventually solubilized. (Adapted from Sabatini et al., Contam. Hydrol. 45(1–2):99–121, 2000).

We have now discussed various factors critical to the economic success of surfactant enhanced aquifer remediation. In this section we have focused on research conducted by our group to address these factors and advance this technology. Other researchers have also conducted timely and important research to advance this technology. Space does not allow us to document all these efforts, but the interested reader is directed to the following references [21–40]. B. FIELD RESULTS One of the critical steps in developing innovative technologies is to pilot test and validate the technology. In surfactant enhanced aquifer remediation, the technology is pilot tested by conducting in situ field studies, which encompass all the heterogeneities inherent in environmental systems. These field studies provide not only technical validation of the technology but also proof of concept to encourage early adopters of the technology. To date, we have conducted successful field studies and site remediations in a wide range of contaminant types, geological conditions, and scales, all of which indicate the viability and robustness of this technology. Below we will discuss results from several of these sites to demonstrate our solutions to the technical and economic issues discussed above. 1. Hill Air Force Base (AFB)—Maximizing Contaminant Extraction Laboratory work has thus demonstrated that middle phase microemulsion systems are much more efficient than solubilization systems for extracting trapped oil phases [13,15]. This conclusion is corroborated by field results from Hill AFB, Utah, as reported in Knox et al. [11]. Solubilization and mobilization studies were conducted in two separate field demonstrations at Hill Air Force Base, UT. A jet fuel (JP-4) leak had occurred in the vicinity of a chemical disposal pit, thereby solubilizing lubricating oils and chlorinated organics (such as pesticides and polychlorinated biphenyls). Over several decades the jet fuel had become highly weathered due to volatilization, dissolution and degradation processes. These processes dramatically changed the mixture from its original composition, which significantly impacted the design of the middle phase microemulsion system. Since the weathered NAPL was still lighter than water, we did not need to be concerned about vertical migration of released oil.

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4.62 m

IW1

MLS12 MLS13 MLS14

EW1

MLS11 IW2

MLS22 MLS21

3.33 m

MLS23

MLS24

EW2 2.67 m

IW3 MLS31

MLS32

MLS34

EW3

MLS33 IW4

5.26 m Sheetpiling

MLS′s

Injection/extraction

Figure 7 Top view of treatment cell formed by driving corrugated sheet piling into a lower clay layer at Hill AFB, Utah. (Adapted from Knox et al., ACS Symposium Series 725, American Chemical Society, Washington, D.C., 1999.)

Two test cells were constructed by driving sheet piling down into an underlying clay layer, creating a treatment zone that is isolated from the adjacent material. The sheet piling is installed as the outside of a “box” (“bathtub”) with grout installed in the joints to make the sides of the box watertight. By driving the sheet piling into the clay layer, not only are the sides watertight but the bottom of the cell is also watertight. The resulting zone (treatment cell) is hydraulically isolated from the rest of the subsurface, which mitigates any potential impacts on the adjacent material. Regulatory personnel at times required this level of precaution when conducting such studies, especially during early tests of the technology. Figure 7 provides a top view of the resulting test cell, showing the sheet piling as the outside of the cell and indicating the location of the four injection wells, the three extraction wells, and the 12 multilevel samplers, which were installed to monitor the spatial and temporal progress of the remediation experiment. The cells were 3 m x 5 m in cross section and up to 10 m in depth. Figure 8 shows the contaminant levels in the soil before (pre) and after (post) the remediation efforts. The data show that while the contaminant concentrations decreased significantly during both tests, they decreased more dramatically for the mobilization than the solubilization test. During the field studies, ten pore volumes of 4.3 wt% Dowfax 8390 solubilized between 40 and 50% of the contaminants (the range represents values based on soil coring, partitioning interwell tracer tests (PITTs), and mass extracted). By comparison, 6.6 pore volumes of 2.2 wt% AOT, 2.1 wt% Tween 80, and 0.43 wt% CaCl2 achieved 85 to 90% contaminant removal. Water alone would have extracted less than 1 percent of the contaminant during this same flushing period. The mobilization system thus outperformed the solubilization system without requiring additional surfactant (4.3 wt% surfactant total in both cases), although the mobilization system did require a unique and somewhat elusive surfactant mixture. In addition, while the surfactant flood did release free phase oil, middle phase microemulsions were not observed during field sampling,

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800.000

120.000

Mass before (g)

700.000

100.000

600.000 80.000

500.000

60.000

400.000 300.000

40.000

200.000 20.000

100.000

0.000 p na

un

tm

de

b/ 10 d/ 10 0 dc b

yl c/ 10

l xy

_x m

o_

eb

nz *1 tc 0 e* 10 to l

be

tc a

0.000

Mass after (g) & % Remove

Cell 5 Average Removal = 97.2%

Contaminant Cell 5 (before)

Cell 5 (after)

Percent Removals

(a) Cell 6 Average Removal = 58.2%

80

80.000

70

70.000

60

Mass (g)

60.000

50

50.000 40 40.000 30

30.000

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90.000

20

20.000

10

10.000

0

0.000 tol*10

eb

o_xyl m_p_xyl tmb/10

dcb

ap/10

Contaminant Cell 6 (after)

Cell 6 (before)

Percent Removals

(b)

Figure 8 Before and after treatment soil contaminant concentrations for mobilization (cell#5, -A-) and solubilization (cell#6, -B) test cells at Hill AFB, Utah. (Adapted from Knox et al., ACS Symposium Series 725, American Chemical Society, Washington, D.C., 1999.)

likely due to field heterogeneities in oil distribution/composition and/or mixing during sample collection. Thus, as demonstrated in the laboratory column studies, middle phase systems are much more efficient and excellent system performance can be maintained in the field even when ideal middle phase systems are not achieved. At the same time, the middle phase flood viscosity showed a six-fold increase during the remediation test. While this viscosity increase was workable in our system, and was reversed when we switched back to water, these results do show the need to carefully design the surfactant chemistry of these systems.

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Table 1 Tinker AFB, Oklahoma: Unit Processes and Dimensions Used for Surfactant Decontamination with Goal of Reinjection Unit Air stripper— packed tower Air stripper—hollow fiber Ultrafiltration membrane (spiral wound)

Dimensions 0.66 ft ID 8.0 ft tall 0.33 ft ID 2.5 ft tall 2.0 ft long 05 ft ID

Media 1-in. polyethylene flexirings Celgar X 30 membrane; 0.24-mm fibers (ID) with 30-nm pores 10,000 molecular weight cutoff

Abbreviations: ID = inside diameter.

2. Tinker AFB—Surfactant Decontamination for Reinjection A field demonstration was conducted at Tinker AFB, OK to evaluate decontamination of surfactant solutions for reinjection. This field study did not seek to remediate a treatment zone, but rather the goal was to flush surfactant through the subsurface in order to “load” the surfactant with contaminant and then process the contaminant-laden surfactant stream using one of several treatment processes. The treatment processes evaluated were air stripping, in both packed tower and hollow fiber systems, and ultrafiltration, as summarized in Table 1. The contamination at Tinker AFB was an LNAPL consisting largely of toluene, and the formation was a silty material. Eight pore volumes of 4 wt% Dowfax 8390 (C16 DPDS) were injected at a rate of 0.2 gallons per minute (gpm), while the extraction wells operated at a combined 0.8 gpm. More water was extracted than injected to make sure that the surfactant injected was recovered (captured) in the extraction wells in this open system (sheet piling was not used at this site). This overpumping causes the surfactant solution to be diluted in the extraction wells, thus requiring use of ultrafilters to reconcentrate the surfactant prior to reinjection. As mentioned previously, surfactant micelles reduce the air stripping efficiency by effectively reducing the Henry’s constant of the contaminants. Thus, an air stripper designed for treating water in the absence of surfactant will perform less efficiently in the presence of the surfactant. In this field study we wanted to validate the modified air stripper design equations derived by Lipe et al. [19] and demonstrate our ability to operate packedtower and hollow-fiber strippers without foam formation [12]. Results from the field study are summarized in Table 2. The stripper was under-designed so that surfactant impacts on system performance would be readily apparent. This explains why removal efficiencies without surfactant were in the 85 to 93% range (see Table 2), instead of the 98 to 99% range (where impacts would have been harder to see). The modified design equations predicted a 20% reduction in system performance due to the presence of the surfactant. In actuality, the field results demonstrated a 17 to 23% reduction in efficiency (Table 2). These results thus provide field corroboration of the modified design equations, and indicate that we can use these design equations to properly size air strippers to achieve desired removal efficiencies (say 95 to 99%) while accounting for surfactant impacts on the system. In addition, both the packed-tower and hollow-fiber air strippers operated flawlessly during the field demonstration, without foam formation or other operating problems [12]. And finally, the ultra-

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Table 2 Tinker AFB, Oklahoma: Air Stripper Removal Efficiencies in the Presence and in the Absence of Surfactant and the Difference Between the Two, Which Indicates the Level of Surfactant Impact on System Performance

Removal Efficiency Unit Process

Packed column Hollow fiber unit 1 Hollow fiber unit 2

With Surfactant %

Without Surfactant %

Difference %

63 70 74

85 93 91

22 23 17

filtration system effectively reconcentrated the surfactant solution so that it was ready for reinjection. 3. Alameda Point NAS—Mitigating Vertical Migration (Supersolubilization) This study, which was our first opportunity to apply the supersolubilization concept in the field, was conducted at the former Alameda Point Naval Air Station (NAS), California. As you recall, the supersolubilization system operates near the Winsor Type I to Type III boundary in an effort to maximize solubility enhancement while minimizing the potential for vertical migration. The contaminant at this site was a DNAPL comprised mainly of tricholorethane (TCA), trichloroethylene (TCE) with lesser fractions of other chlorinated solvents (e.g., dichloroethylene [DCE] and dichloroethane [DCA]). Since the NAPL at this site is denser than water, it was a good candidate for a surfactant supersolubilization system. Geological studies at the site indicated that two distinct hydrogeological units were present. The upper unit (0 ft to 19 ft) consisted of back-filled sandy material with 1 to 5 ft/d of hydraulic conductivity. The lower section consisted of bay mud (19 ft to 30 ft) with a hydraulic conductivity four orders of magnitude less than the upper fill material. Based on the ground water modeling results, a line drive well configuration was selected; i.e., two surfactant injection wells feeding into four recovery wells, with two hydraulic control wells installed to insure recovery of all the injected solution (this configuration helps to create a hydraulic “bathtub” similar to the physical bathtub created with the sheet piling at Hill AFB, UT). The goal of this study was to achieve greater than 95% removal of the DNAPL in the test zone. Eight anionic surfactants or mixtures were investigated for their potential use at this site. Based on the screening batch and one-dimensional column tests, the following surfactant system was selected: disodium hexadecyldiphenyloxide disulfonate (Dowfax 8390) (5 wt%), sodium dihexyl sulfosuccinate (AMA-80I) (2 wt%), NaCl (3 wt%), and CaCl2 (1 wt%) [41]. Based on the flow rates and concentrations in the recovery wells, the total mass of TCA and TCE recovered was 320 kg (see Fig. 9) or 65 gal, while the total NAPL recovered (including DCE and DCA) was approximately 80 gal. The mass recovery trend in Fig. 9 is a steep linear relationship through day ten (four pore volumes), followed by a significant reduction in slope. This is consistent with the depletion of DNAPL as the project proceeds. After ten days of surfactant injection, an intermittent injection/recovery approach was used to evaluate the possibility of rebound in contaminant concentrations. After the system was

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shut down for 12 hours the surfactant injection resumed. No concentration rebound was observed as a result of this intermittent injection (see Fig. 9). The study was run for a total of 6 pore volumes, which for this highly conductive formation and small test site were flushed in 18 days. Results from two different methods, soil corings and partitioning interwell tracer tests (PITTs), suggest that 98 and 99% of the DNAPL was removed during the test, and in only six pore volumes (vs. 100s or 1000s that would be required with water alone). These removal values exceed the 95% removal goal established for the test. These high removal efficiencies indicate that the DNAPL was solubilized rather than released for downward migration, as was corroborated by the lack of DNAPL in sampling wells located in the lower portion of the aquifer. In addition, the groundwater concentrations decreased by 56 to 80% after the study vs. the pre-study concentrations. These results demonstrate the ability of surfactant enhanced aquifer remediation to remove trapped oil phases and thereby decrease ground water concentrations of these compounds. Surfactant decontamination and reinjection was implemented during this study using a liquid–liquid extraction system. Hasegawa et al. [20] demonstrated that liquid-liquid extraction could be highly efficient even for volatile compounds because of their high partitioning coefficients into the extracting solvent. The liquid–liquid system used in this study was a macroporous polymer (MPP) system from Akzo Nobel. In this system a macroporous polymer is impregnated with a proprietary extracting solvent and used as a resin in a column. As the surfactant solution flows through the column, the contaminant partitions out of the solution into the extracting solvent within the MPP. As expected, MPP removal of TCA and TCE was less effective while surfactant concentrations were highest, during the surfactant injection stage. On average, the MPP removed 80% (during peak surfactant concentrations) to 95% (lower surfactant concentrations) of the contaminant from the waste stream. Overall, the MPP system provided an effective, trouble free process for decontaminating the surfactant solution and allowed it to be reinjected, thereby improving system economics. Having earlier presented various factors critical to the economic success of surfactant enhanced aquifer remediation, in this section we have reported on several of our field studies that illustrate our ability to address these economic factors. Due to space limitations

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we have not presented results from all of our field studies, nor from the field studies of others [25,30,31,40]. C. FUTURE ADVANCES/APPLICATIONS We will close this chapter by briefly mentioning several ongoing activities to further improve the economics of surfactant enhanced aquifer remediation. We will also describe how innovations in surfactant enhanced aquifer remediation may be useful in other applications (e.g., detergency, solvent replacements). In most studies to date, surfactant formulations have been based on surfactant concentrations between 3 to 8 wt%. Since the main purpose of earlier efforts was to demonstrate significant oil removal from the source area, these higher surfactant concentrations were likely warranted, even if conservative. However, with an increased emphasis on improving system economics, and as light oils (LNAPLs) are receiving more attention, we have begun to look at lower and lower surfactant concentrations. Achieving ultra-low interfacial tensions with low surfactant concentrations can maximize the amount of oil mobilized and minimize the effort necessary to remove oil from the solubilized state, which is especially attractive for LNAPLs. We’ll briefly describe two recent efforts where we are developing such low surfactant systems. For the Tinker North Tank Area site, located at Tinker Air Force Base, Oklahoma, the main contaminant is No. 2 heating oil. Based on screening tests, we concluded that the following surfactant system was the best candidate to mobilize the NAPL for this test: a combination of anionic surfactant mixture, AOT (sodium dioctyl sulfosuccinate, 0.5%)/Lubrizol-132225 (alkylamine sodium sulfonate, 0.5%)/NaCl (3.25%) followed by a polymer drive (BetzDearborn AP-1120 at 120 mg/l). Laboratory studies illustrated that this system can recover a significant amount of the Tinker NAPL from soil column studies in one to two pore volumes. For the Golden UST site, located in Golden, Oklahoma, the main contaminant is gasoline fuel from a service station. Surfactant screening identified the following low surfactant approach using the mobilization mechanism: AOT (0.75%), Calfax (diphenyl sulfonate derivative, 0.186%), and NaCl (1.2%). Again, this system demonstrated excellent results in column studies. It should be noted that both of these formulations used 1.0 wt% or less of surfactant. Based on this developmental work, field scale demonstration studies have/are being implemented at both sites. Results to date corroborate that, when properly designed, lower surfactant concentrations (1.0 wt% or less) can efficiently remediate these sites. Thus, future work will continue to focus on formulating surfactant systems with low surfactant concentrations in an effort to further improve system economics. In addition to lowering the overall surfactant concentration, we are also looking at ways to couple surfactants with other molecules to reduce the amount of surfactant in the formulation. One approach to achieve this goal is by using lipophilic and hydrophilic linker molecules. The use of lipophilic linkers was first proposed by Graciaa et al. [42,43], while Uchiyama et al. [44] first proposed the use of hydrophilic linkers along with lipophilic linkers (i.e., combined linkers). A typical example of a lipophilic linker is a long chain alcohol (e.g., dodecanol) while the hydrophilic linker could be a short chain alcohol or a hydrotrope (e.g., sodium mono- and di-methyl naphthalene sulfonate [SMDNS]). Figure 10 shows a schematic of an oil–water interface along with surfactants, lipophilic linkers and hydrophilic linkers. The surfactant bridges the interface, while the linkers favor either the oil or water side of the interface, as discussed above. When the hydrophilic and lipophilic linkers occur together, one can imagine that they would line up in the resulting cavity between surfactant molecules, and could take on a surfactant-like property themselves. Thus, the advantage of lipophilic linkers is that they extend the surfactantacy effect

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further into the oil phase, improving system [44,45]. Conversely, combined linkers have the potential to substitute less expensive molecules for surfactant molecules, improving system economics (as discussed further below). Research has demonstrated that it is not possible to totally replace the surfactant with linker molecules, but that combined linkers can be substituted for a certain amount of the surfactant molecules [46]. Using combined linkers has three distinct advantages: (1) it allows us to achieve success where middle phase microemulsions are otherwise difficult to achieve, (2) it improves system economics over using surfactants alone, and (3) it allows us to use a single surfactant system over a wide range of oils. Figure 11 illustrates these two points by looking at the use of aerosol MA for super-solubilizing/ mobilizing a range of oils (from TCE to octadecene). This covers a wide range of oils, as described by their relative equivalent alkane carbon numbers (EACN). Hexane, decane, tetradecane, and octadecene have EACN values of 6, 10, 14, and 18, respectively. Trichloroethylene (TCE) and tetrachloroethylene (PCE) have EACN values of minus two (–2) and plus 3, respectively, indicating that they are much more hydrophilic than the other

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oils. These oils thus cover an EACN range of 20, which is very large. Using AMA alone was only able to achieve middle phase microemulsions for the more hydrophilic oils (TCE, PCE and hexane); the AMA phase separated when using more hydrophobic oils. However, when using combined linkers with AMA, we were able to achieve middle phases for even octadecene. And we were able to use the same system for oils from TCE to octadecene, representing an EACN range of 20 units. And finally, and most importantly, when comparing the system costs for surfactant alone and surfactants with combined linkers, the surfactants with combined linkers were more economical, and became increasingly more economical as the oil became more hydrophobic (higher EACN). Thus, based on these preliminary laboratory studies, these systems show great promise for developing more robust and economical surfactant systems. Our work on improving surfactant system efficiency has been largely motivated by our desire to further improve the surfactant enhanced aquifer remediation technology. However, these advances also have potential use in other applications. For example, more cost effective systems for minimizing oil-water interfacial tension and maximizing solubility enhancement have potential applications in the detergency arena. Developing aqueous-based surfactant systems capable of solubilizing octadecene has potential applications for hydrophobic trioleins with similar to slightly higher EACN values. Developing aqueous based systems that are virtually miscible with oil phases has the potential to develop waterbased alternatives to oil-based solvents. And these are just few examples of how our environmental formulation approach can be useful to nonenvironmental applications, as is the subject of ongoing research.

ACKNOWLEDGMENTS The work described in this chapter has been made possible through the collaborative efforts of numerous colleagues and funding from numerous sources. This work is an outgrowth of collaborative research in the Institute for Applied Surfactant Research (IASR) at the University of Oklahoma—we would like to acknowledge our colleague and IASR director Professor John Scamehorn. We would also like to acknowledge current and former students at the University of Oklahoma and colleagues at Surbec-ART Environmental, LLC (Jeff Childs, Edgar Acosta, Joe Rouse, Erika Szekeres, Marshall Brackin, Mark Hasegawa, Jeff Brammer, Tracee Carter, and Micah Goodspeed). This research has been funded in part by the U.S. Environmental Protection Agency (USEPA), U.S. Department of Defense (USDOD), and the U.S. Department of Energy (USDOE), Oklahoma Center for Advancement of Science and Technology, and industrial sponsors of IASR (Akzo Nobel Chemicals Inc., Church & Dwight, Clorox Company, Colgate, ConocoPhillips Corporation, Dial Corporation, Ecolab, Oxiteno, Procter and Gamble, Shell Chemical Company, and Unilever Inc.). And finally, we would especially like to thank Mr. Edgar Acosta and Ms. Phuong Mai Do for all their help in putting together the figures and references for this chapter.

REFERENCES 1. D. A. Sabatini, R. C. Knox, and J. H. Harwell, eds. Surfactant-Enhanced Subsurface Remediation: Emerging Technologies. ACS Symposium Series 594, American Chemical Society, Washington, D.C., 1995.

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2. C. D. Palmer and W. Fish. “Chemical Enhancements to Pump and Treat Remediation.” USEPA, EPA/540/S-92/001, 1992, 20 pp. 3. M. J. Rosen. Surfactants and Interfacial Phenomena, 2nd ed., John Wiley & Sons, Inc., New York, NY, 1989. 4. M. Bourrel and R. Schechter. Microemulsions and Related Systems. Surfactant Science Series, Vol. 30, Marcel Dekker, Inc., New York, 1988. 5. G. Pope and W. Wade. In: D. A. Sabatini, R. C. Knox, and J. H. Harwell, eds. SurfactantEnhanced Subsurface Remediation: Emerging Technologies. ACS Symposium Series 594, American Chemical Society, Washington, D.C., 1995, pp. 142–160. 6. D. A. Sabatini, R. C. Knox, J. H. Harwell, B. Wu. J. Contam. Hydrol. 45(1–2): 99–121, 2000. 7. B. Krebbs-Yuill, J. H. Harwell, D. A. Sabatini, and R. C. Knox. In: D. A. Sabatini, R. C. Knox, and J. H. Harwell, eds. Surfactant-Enhanced Subsurface Remediation: Emerging Technologies. ACS Symposium Series 594, American Chemical Society, Washington, D.C., 1995, pp 265-278. 8. J. D. Rouse, D. A. Sabatini, and J. H. Harwell. Environmental Science and Technology 27(10): 2072-2078, 1993. 9. J. D. Rouse, D. A. Sabatini, R. E. Brown, and J. H. Harwell. Water Environment Research 68(2): 162–168, 1996. 10. R. C. Knox, D. A. Sabatini, J. H. Harwell, R. E. Brown, C. C. West, F. Blaha, and S. Griffin. Ground Water 35(6): 948–953, 1997. 11. R. C. Knox, B. J. Shiau, D. A. Sabatini, and J. H. Harwell. In: M. L. Brusseau, D. A. Sabatini, J. S. Gierke, and M. D. Annable, eds. Innovative Subsurface Remediation: Field Testing of Physical, Chemical and Characterization Technologies. ACS Symposium Series 725, American Chemical Society, Washington, D.C., 1999, pp 49–63. 12. D. A. Sabatini, J. H. Harwell, M. Hasegawa, and R. C. Knox. Journal of Membrane Science 151(1): 89–100, 1998. 13. B. J. Shiau, D. A. Sabatini, and J. H. Harwell. Ground Water 32(4): 561–569, 1994. 14. B. J. Shiau, D. A. Sabatini, J. H. Harwell and D. Vu. Environmental Science and Technology 30(1): 97–103, 1996. 15. B. J. Shiau, D. A. Sabatini, and J. H. Harwell. Journal of Environmental Engineering Division—ASCE 126(7): 611–621, 2000. 16. S. P. Nayyar, D. A. Sabatini, and J. H. Harwell. Environmental Science and Technology 28(11): 1874–1881, 1994. 17. H. Cheng and D. A. Sabatini. Separation and Purification Technology 24(3): 437–449, 2001. 18. H. Cheng and D. A. Sabatini. Water Research 36: 2062–2076, 2002. 19. M. Lipe, D. A. Sabatini, M. Hasegawa, and J. H. Harwell. Ground Water Monitoring and Remediation 16(1): 85–92, 1996. 20. M. Hasegawa, D.A. Sabatini, and J. H. Harwell. Journal of Environmental Engineering Division—ASCE 23(7): 691–697, 1997. 21. A. S. Abdul, T. L.Gibson, C. C. Ang, J. C. Smith, and R. E. Sobczynski. Ground Water 30(2): 219–231, 1992. 22. L.M. Abriola, T.J. Dekker, and K.D. Pennell. Environmental Science and Technology 27(12): 2341–2351, 1993. 23. J.R. Baran, G. A. Pope, W. H. Wade, V. Weerasooriyaa, and A. Yapa. Environmental Science and Technology 28(7): 1361–1366, 1994. 24. R. C. Borden, and C. M. Kao. Water Environment Research 64(1): 28–36, 1992. 25. C. L. Brown, M. Delshad, V. Dwarakanath, R. E. Jackson, J. T. Londergan, H. W. Meinardus, D. C. McKinney, T. Oolman, G. A. Pope, and W. H. Wade. In M. L. Brusseau, D. A. Sabatini, J. S. Gierke, and M. D. Annable, eds. Innovative Subsurface Remediation: Field Testing of Physical, Chemical, and Characterization Technologies. ACS Symposium Series 725, American Chemical Society, Washington, D.C., 1999, pp. 64–85. 26. V. Dwarakanath, K. Kostarelos, G. A. Pope, G. A., D. Shots, W.H. Wade. Journal of Contaminant Hydrology 38 (4): 465–488, 1999.

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27. V. Dwarakanath and G. A. Pope, G. A. Environmental Science and Technology 34(22): 4842–4848, 2000. 28. D.A. Edwards, R. G. Luthy, and Z. Liu. Environmental Science and Technology 25(1): 127–133, 1991. 29. W.D. Ellis, J. R. Payne, and G. D. McNabb. Treatment of Contaminated Soil with Aqueous Surfactants. EPA/600/2-85/129, U.S. Environmental Protection Agency, Cincinnati, Ohio, 1985. 30. J. C. Fountain, R. C. Starr, T. Middleton, M. Beikirch, C. Taylor, and D. Hodge. Ground Water 34(5): 910–916, 1996. 31. J. Fountain, C. Waddell-Sheets, A. Lagowski, C. Taylor, D. Frazier, and M. Byrne. In: D. A. Sabatini, R. C. Knox, and J. H. Harwell, eds. Surfactant-Enhanced Subsurface Remediation: Emerging Technologies. ACS Symposium Series 594, American Chemical Society, Washington, D.C., 1995, pp. 177–190. 32. J. W. Jawitz, M. Annable, P.S.C. Rao, and R. D. Rhue. Environmental Science and Technology 32(4): 523–530, 1998. 33. M. Jin, M. Delshad, V. Dwarakanth, D. C. McKinney, G. A. Pope, K. Sepehrnoori, C. Tilburg, and R. E. Jackson. Water Resources Research 31(5): 1201–1211, 1995. 34. R. Martel, P. J. Gelinas. J. Contaminant Hydrology 29(4): 317, 1998 35. R. Martel, L. Rene, P.J. Gelinas. J. Contaminant Hydrology 30(1–2): 1, 1998. 36. M. Oostrom, C. Hofstee, R. C. Walker, and J. H. Dane. Journal of Contaminant Hydrology 37 (1–2): 179–197, 1999. 37. K. D. Pennell, L. M. Abriola, and W. J. Weber Jr. Environmental Science and Technology 27(12): 2332–2340, 1993. 38. K. D. Pennell, M. Jin, L.M. Abriola, and G. A. Pope. Journal of Contaminant Hydrology 16: 35–53, 1994. 39. K. D. Pennell, G. A. Pope, and L. M. Abriola. Environmental Science and Technology, 30(4): 1328–1335, 1996. 40. V. Weerasooriya, S. L. Yeh, and G. A. Pope. In: J. F. Scamehorn and J. H. Harwell eds. Surfactant-Based Separations: Recent Advances, ACS Symposium Series 740, 1999, pp. 23–34. 41. B. J. Shiau, M. A. Hasegawa, J. M. Brammer, T. Carter, M. Goodspeed, J. H. Harwell, D. A. Sabatini, R. C. Knox, and E. Szekeres, “Field Demonstration of Surfactant-Enhanced DNAPL Remediation: Two Case Studies.” In Innovative Strategies for the Remediation of Chlorinated Solvents and DNAPLs in the Subsurface, Henry, S. M. ed. ACS Symposium Series, American Chemical Society, Washington, D.C., 2003, pp. 51–72. 42. A. Graciaa, J. Lachaise, C. Cucuphat, M. Bourrel, and J. L. Salager. Langmuir 9(3): 669, 1993. 43. A. Graciaa, J. Lachaise, C. Cucuphat, M. Bourrel, and J. L. Salager. Langmuir 9(12): 3371, 1993. 44. H. Uchiyama, E. Acosta, D. A. Sabatini, and J. H. Harwell. Ind. Eng. Chem. Res. 39(8): 2704, 2000. 45. E. Acosta, H. Uchiyama, D.A. Sabatini, and J. H. Harwell. Journal of Surfactants and Detergents 5(2), 2002, 151–157. 46. E. Acosta, S. Tran, H. Uchiyama, D.A. Sabatini, and J. H. Harwell. Environmental Science and Technology 36(21), 2002, 4618–4624.

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13 Paints and Printing Inks Krister Holmberg

CONTENTS I.

Introduction ........................................................................................................... 369 A. Paints ......................................................................................................... 370 B. Printing Inks .............................................................................................. 371 II. Surfactants for Stabilization of the Binder Dispersion ............................................. 371 A. Lattices ...................................................................................................... 371 B. Postemulsified Binders.............................................................................. 374 III. Surfactants for Pigment Dispersion ...................................................................... 377 A. Dispersants for Waterborne Formulations ................................................ 379 B. Dispersants for Solventborne Formulations ............................................. 383 IV. Wetting Agents ...................................................................................................... 383 V. Speciality Surfactants for Paints ........................................................................... 384 VI. Surfactants for Fountain Solutions ....................................................................... 384 References ....................................................................................................................... 385

I. INTRODUCTION Paints and printing inks have much in common. Their most basic constituent is a pigment and a binder is needed to glue the pigment to the underlying surface. A solvent is usually required in order to achieve proper application viscosity and good wetting of the substrate. The solvent may be water, which is advantageous from an environmental point of view, or an organic liquid, which is usually better in terms of performance; the choice of solvent is the classical compromise issue in the coatings area. Apart from the three main components, i.e., pigment, binder, and solvent, paints and printing inks invariably contain a number of additives [1,2]. Surfactants are one important additive with a variety of uses. In the formulations they are often not referred to as surfactants; instead, they are named after their intended function: dispersants, emulsifiers, 369

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wetting agents, antifoaming agents, etc. In reality, a dispersant, an emulsifier, etc. may have very similar structure and when mixed in a formulation they will interact with each other and with all available surfaces. Competitive adsorption of different surfactants, as well as amphiphilic polymers, is a well-known phenomenon in these systems. Thus, paints and printing inks formulations can be extremely complex from a surface chemistry point of view. Waterborne coatings are often used as a textbook example of applied surface and colloid chemistry. The formulation may at the same time be a suspension of the pigment and an emulsion of the binder. The rheology of the formulation is carefully controlled by an amphiphilic polymer, a so-called associative thickener. Extra surfactant may be added as wetting agent and for spray-gun applications a surfactant is usually added to suppress foaming [3]. Surfactants are less important in paints and printing inks based on organic solvents because the binder is usually in the form of a solution, not a dispersion. (However, socalled nonaqueous dispersions also exist.) Wetting of the substrate is normally not a problem in nonaqueous formulations because good wetting follows the low surface tension of most organic solvents and for the same reason foaming is also less of a problem. However, surfactants are needed as pigment dispersants also in nonaqueous formulations. In the following, emphasis will be put on the use of surfactants in waterborne paints and printing inks formulations. A. Paints Traditionally, paints have been formulated from organic solvents. Waterborne paints, which were introduced in the 1950s, provided the technological basis for electrodeposition paints in which charged paint particles are deposited from an aqueous solution onto a conductive substrate by application of an electrical field. Electrodeposition remains an important technique but today the main driving force behind water-based formulations is environmental and health concern rather than technical aspects. From a technical point of view water is not an ideal solvent for coatings. The high cohesive energy density of water is responsible for two unfavourable characteristics, a high heat of evaporation and a high surface tension. Control of solvent evaporation is necessary in order to achieve good film formation. This is a difficult issue if one is restricted to only water as solvent. It has therefore become common practice to incorporate smaller amounts of water miscible solvents, in particular glycols and glycol ethers, into the aqueous formulation. These help in the film formation process but addition of organic solvents is clearly unwanted from an environmental point of view. The other unfavorable characteristics with water as a paint solvent, that of high surface tension, is less of a problem. Addition of a surfactant reduces the surface tension to the same level as that of most organic solvents. Surface chemistry issues are important in all stages of the lifetime of a paint. In the preparation of the paint surfactants are needed to disperse the pigment and to stabilize the binder if the latter is in the form of a dispersion. In the application step rheological aspects are extremely important and intermolecular associations govern rheology. In waterborne formulations the dominating rheological control agents are surface active polymers. Foaming may be a problem, particularly in spray-gun applications, and is controlled by special surfactants. In the film forming step surface defects can appear and a number of additives are used to prevent these. So-called craters are formed if the surface to be coated is locally contaminated with substances such as oils and fats with very low surface free energy. The surface tension of the paint may then not be low enough to wet these areas. Surface tension differences may also develop within the paint film itself as an effect of uneven solvent evaporation. Surface tension differences lead to material transport within the wet film from

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the region of lower surface tension to that of higher surface tension, an example of the Marangoni effect. This movement may lead to the formation of Bénard cells, which may result in visible surface defects such as orange peel [4]. Speciality surfactants, in particular silicone surfactants and fluoro surfactants, are added to minimize surface tension differences. B. Printing Inks Printing inks are similar to paints from a composition point of view. Some kind of colorants, i.e., pigments, toners, dyes, or combinations of these, are dispersed or dissolved in a bindersolvent mixture. The types of binders used resemble those in paints and, similar to paints, there is a choice between organic solvent based and waterborne formulations. When organic solvents are used highly volatile liquids, such as isopropanol, are often employed in order to speed up the drying process. This is particularly important for letterpress inks that dry by solvent evaporation. Other inks, such as newspaper inks, dry primarily by penetration or absorption into the pores of the printed stock. Such ink formulations are usually based on mineral oil as solvent and a small amount of resin or other binder that assist in the wetting of the pigment. As with paints, drying can also involve the formation of chemical bonds, either through radiation curing (in particular ultraviolet and electron beam curing) or by autoxidation (through crosslinking of unsaturated fatty acyl chains). Printing inks are applied in much thinner films than normal paints. Whereas the thickness of a paint film is usually 20 to 50 µm, an ink film is in the range 2 to 10 µm thick. A typical ink has a pigment concentration of 10 to 20%. It is common practice to make concentrates of dispersed pigments and to use such concentrates in a variety of ink formulations. For instance, the flushed color concentrates used in offset inks may contain pigment concentrations as high as 50 %. Such concentrates are highly viscous pastes or even solids. In the final formulation the concentrate is dissolved in a suitable solvent. As for paints, surfactants play a larger role in waterborne printing inks formulations than in formulations based on organic solvents. In the former systems, surfactants are employed to stabilize the binder dispersion, which may be a latex or a postemulsified binder, such as an alkyd. Surfactants are also needed to disperse the pigments, just as in paints formulations. Contrary to pigments, dyes are soluble in the solvent–binder mixture and, therefore need no dispersants.

II. SURFACTANTS FOR STABILIZATION OF THE BINDER DISPERSION A. Lattices Latex paints are aqueous dispersions of water-insoluble polymers made by emulsion polymerization using free radical initiators. In the majority of cases the polymers are based on combinations of monomers, often with a high content of water-insoluble entities such as methyl methacrylate, butyl acrylate, and styrene and a much smaller fraction of watersoluble monomers such as acrylic and methacrylic acid. The water-soluble monomers give oligomeric acid segments at the latex particle surface, which improves the colloidal stability of the formulation and adhesion and curing characteristics of the film. Most lattices for paints have an average particle diameter in the range 100 to 500 nm [5,6]. The emulsifier used in latex preparation is often a combination of nonionic and anionic surfactants. The nonionic surfactant has traditionally been an alkylphenol ethoxylate, but environmental concern has caused a change over to other ethoxylated surfactants, such as fatty alcohol ethoxylate or fatty acid monoethanolamide ethoxylate. The ethoxylate is the surfactant mainly responsible for dispersion stabilization. The steric stabilization provided by surfactants with relatively long polyoxyethylene chains (>10 EO) is needed

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n

A mixed monolayer of nonionic and anionic surfactant usually stabilizes latex droplets.

in order to retain stability at high solids content in the presence of electrolytes. Steric stabilization also gives proper shear stability to the latex. The presence of anionic surfactant, usually an alkyl sulfate or an alkylaryl sulfonate, during the latex synthesis is needed to compensate for the reverse temperature dependence of ethoxylated surfactants. For nonionics an increase in temperature leads to a decrease in water solubility and an increase in oil solubility. During the course of the emulsion polymerization there is an increase in temperature, which would lead to formation of a water-in-oil emulsion if nonionic surfactants were the sole emulsifier. Upon depletion of the monomer phase, i.e., at high conversion, there would be a phase inversion into an oil-in-water emulsion. Such a phase inversion leads to a very broad particle size distribution since particle nucleation, as well as reaction kinetics, will be out of control. A way to circumvent the problem is to use a semicontinuous polymerization process with the monomer being slowly fed into the reactor during the polymerization. Figure 1 shows a typical surfactant monolayer at the surface of latex droplets. It is important to realize that the surfactants are not permanently adsorbed at the surface but subject to a continuous adsorption-desorption process. As was discussed above, the driving force for adsorption at a hydrophobic latex surface is stronger for nonionic surfactants than for anionics, unless the electrolyte concentration is very high. This leads to a higher ratio of nonionic to anionic surfactant at the surface than in the bulk solution. Anionic surfactants provide electrostatic stabilization and such lattices exhibit good storage stability in formulations containing low or moderate salt concentration. However, lattices made with only anionic emulsifier are not stable at high electrolyte concentration. Evaporation of water during the drying process leads to a continuous raise in ionic strength of the formulation. Often the stability limit is exceeded at a relatively early stage, leading to particle coagulation and consequent loss in film gloss. Steric and electrostatic stabilization of dispersions is further discussed below. In recent years there has been a considerable interest in the use of polymerizable surfactants for lattices [7,8]. Such surfactants contain a polymerizable group, which may be an acrylate, a methacrylate, an allyl ether or a maleate double bond. Both anionic and

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nonionic reactive surfactants are commercially available. The polymerizable surfactant is usually added from the beginning, in essence serving as a comonomer in the emulsion polymerization. The reactive surfactant may also be added at the end of the polymerization process, in which case conventional surfactants are needed to prepare the latex. By using surfactants that become covalently bonded to the latex particle, many of the problems encountered with conventional surfactants can be avoided or at least minimized. Positive effects are often obtained both on the dispersion itself and on the dried film. The surfactant-related problems in lattices, as well as in many other dispersions, arise from the fact that surfactants physically adsorbed on the particle surface may desorb into the bulk aqueous phase and that the equilibrium between surface and bulk surfactant concentration is governed by factors such as particle concentration, temperature, ionic strength and pH, all of which may be changed during storage, paint application and film formation. Since a certain surface concentration of surfactant is needed to give proper latex stabilization, a change in the adsorption-desorption equilibrium may severely affect rheology and stability of the dispersed system. Formulations containing a latex in combination with another dispersion, such as a pigment slurry, constitute a particular problem from a stability point of view. The physically adsorbed latex surfactant may have higher affinity for the pigment than for the latex, a situation that often leads to latex instability. The surfactants used as pigment dispersants are usually different from those used as emulsifier in the emulsion polymerization process. Hence, the different surfactants will compete for both surfaces, the latex and the pigment, and the surface composition and coverage obtained in the equilibrium situation may be very different from that of the two components before mixing. This type of competitive adsorption may drastically affect rheology and stability of a formulation. The presence of surfactant in the dried latex film may also impair film properties. During drying the surfactant is adsorbed on the latex particles. As the particles coalesce during the annealing process, the surfactant migrates out of the bulk phase and concentrates at the interface. It has been shown that surfactant molecules preferably go to the film-air interface, where they align with their hydrophobic tails pointing toward the air. Calculations from electron spectroscopy for chemical analysis (ESCA) spectra show that a lacquer film containing 1% surfactant may have an average surface surfactant concentration of around 50%. Such a high concentration of a non-chemically incorporated, water-soluble component at the film surface will adversely affect adhesion properties and create problems in terms of repaintability. It may also impair the water resistance of the film. Studies using atomic force microscopy (AFM) have demonstrated that during the film forming process many conventional surfactants phase separate from the binder. When the surfactant has phase separated, the water flux may carry it to the film surface. Alternatively, it may accumulate in the interstices between the particles from where it will migrate to the film–air or film–substrate interface through a long-term exudation process. Eventually the surfactant will be present in aggregates of considerable size, seen by AFM as “hills.” After treatment with water, the surfactant aggregates are washed away and distinct “valleys” replace the hills. The rough surface will give rise to poor gloss. It has been shown that many of the surfactant-related problems in latex paints can be minimized by the use of a polymerizable surfactant as emulsifier in the emulsion polymerization process. Several types of reactive surfactants are used for this purpose, some of which are shown in Fig. 2. Block copolymers of ethylene oxide and propylene or butylene oxide with a polymerizable group at far end of the hydrophobic segment (Compounds I and II) have become popular, partly due to ease of preparation. Of particular interest from performance point of view are surfactants that preferably undergo copolymerization rather than homopolymerization. A good example of such surfactants is maleate

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374

Holmberg O

I

O

H3CO

O

O

O

C

n m

II

O

O O

O

OH

x

x=

n

SO3−Na+

m

III

Figure 2

O

OSO3−Na+

O

O

C

C

O

SO3Na

Examples of polymerizable surfactants for lattices.

half esters of fatty alcohols, such as Compound III of Fig. 2. However, even surfactants based on highly reactive groups such as maleate do not become quantitatively copolymerised during the emulsion polymerization [9]. The polymerizable emulsifiers are sometimes referred to as “surfmers.” Surface active polymerization initiators, “inisurfs,” and surface active chain transfer agents, “transurfs,” have also been developed [10]. B. Postemulsified Binders Another common approach to water-based coating formulations is post-emulsification of a polymer in water. Several condensation polymers, such as alkyds, i.e., fatty acid modified polyesters, polyurethanes, and epoxy resins, have been made into dispersions by use of a suitable emulsifier and application of high shear. For instance, long oil alkyd resins of the type used in white spirit-based formulations have been successfully emulsified using nonionic surfactants such as fatty alcohol ethoxylates, alkylphenol ethoxylates, or fatty acid monoethanolamide ethoxylates. Neutralization of alkyd carboxylic groups helps in producing small emulsion droplets and with the proper choice of surfactant droplet diameters of less than 1 µm can be obtained. Such dispersions are sufficiently stable for most applications. Figure 3 illustrates the important fact that whereas a nonionic surfactant needs to be added in an amount sufficient to give close packing of the emulsifier on the surface in order to give sufficiently small droplets, an anionic surfactant gives small droplets already at concentrations that give very low packing density [11]. This is consistent with the different mechanisms by which nonionic and anionic surfactants exert stabilization, as discussed above. Figure 4 shows that there is good correlation between droplet size and mechanical stability, the smaller the droplet, the higher the shear rate needed for coalescence. As for latex dispersions, alkyd emulsions stabilized with only anionic surfactants are highly sensitive to electrolytes. The main drawback of waterborne alkyd paints is slow drying. This is partly due to the comparatively low evaporation rate of water but there is also strong evidence that catalysis of autoxidation does not work properly in waterborne systems. The distribution of the drier, in particular cobalt alkanoate, between the alkyd and water phases is believed to influence the early stages of drying of alkyd emulsions.

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Droplet size (µm)

10

DoBS

1

C16/C18-E02-S

C16-S .1

0

2

4

6

8

12

10

Emulsifier concentration (% of alkyd)

Droplet size (µm)

100

10 C12/C13-E015 1 NP-E020 LA 13 .1

0

2

4

6

8

10

12

Emulsifier concentration (% of alkyd)

Figure 3 Effect on initial droplet size of concentrations of top: the anionic surfactants sodium dodecylbenzene sulfonate (DoBS), sulfated hexadecylalcohol (C16-S), and sulfated hexadecyl/octadecylalcohol ethoxylate (2 EO) (C16/C18-EO2-S); bottom: the nonionic surfactants dodecyl/tridecylalcohol ethoxylate (15 EO) (C12/C13-EO15), nonylphenol ethoxylate (20 EO) (NP-EO20, and linseed oil fatty acid monoethanolamide ethoxylate (13 EO) (LA 13). (From A.-C. Hellgren et al., Progr. Org. Coatings, 903:1, 1999.)

Surfactants capable of participating in autoxidative drying are of interest for the post-emulsification of alkyd resins [12]. Ethoxylated monoethanolamides of unsaturated fatty acids are one such type of surfactant that can be chemically incorporated into the network during drying of an alkyd based coating film. The general structure of this surfactant type is given below: R-CONH-(CH2CH2O)n-H where R-CO is an unsaturated acyl group, derived from an unsaturated triglyceride such as soybean oil, linseed oil, sunflower oil, or tall oil. (There must be more than one double bond in the acyl chain; oleoyl is not reactive enough.) Figure 5 illustrates the difference in surface composition with respect to the surfactant for a polymerizable amide ethoxylate and a conventional nonionic surfactant of similar hydrophilic-lipophilic balance. Surfactant concentrations at the film–air interface were measured by ESCA. As can be seen, both the conventional surfactant, a nonylphenol ethoxylate, and the amide ethoxylate accumulate at the surface and the concentration increases with time. Whereas the concentration vs. time curve is almost linear for the nonylphenol ethoxylate, it levels off for the amide ethoxylate. For the latter species, the distribution of surfactant in the film seems to be established within 3 days of drying.

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Holmberg

Droplet size (µm)

10 8 6 4

3 µm 1.4 µm

2

<0.6 µm 0 0

10000

20000

30000

Shear rate (1/S) (a)

Droplet size (µm)

40 30 7 µm 20 2 µm

10

<0.6 µm 0 0

10000

20000

30000

Shear rate (1/S) (b)

Figure 4 Mechanical stability of emulsions stabilized by top: the anionic surfactant sodium dodecylbenzene sulfonate; bottom: the nonionic surfactant linseed oil fatty acid monoethanolamide ethoxylate (13 EO). The initial droplet sizes are given in the figures. Increase in droplet size on shearing is a sign of coalescence. The decrease in droplet size for the 7-µm droplets of the bottom figure reflects shear-induced disintegration of the large aggregates formed. (From G. Östberg et al., Progr. Org. Coatings, 24:281, 1994.)

The difference in behavior between the nonylphenol ethoxylate and the amide ethoxylate is probably due to the fact that the latter surfactant becomes immobilized through coupling to binder molecules during the drying process. Once covalently incorporated into the network, the migration process will cease. Another contributing factor for the low degree of migration of the amide ethoxylate could be that this surfactant is likely to be very compatible with the binder, a long oil alkyd resin. Surfactant-polymer compatibility is often decisive for the distribution of surfactants in films. Surfactants are carried towards the surface by the flux of water during film drying and this process is particularly effective when there is poor compatibility between surfactant and polymer. The effect on surface composition of soaking the dried film in water is also shown in Fig. 5. Whereas more than half of the nonylphenol ethoxylate disappears from the outermost surface layer (the analysis depth is approximately 5 nm), the effect on the amide ethoxylate is small, in spite of the fact that both surfactants have about equal water solubility. This is a further indication of the amide ethoxylate being immobilized during the drying process, although one must keep in mind that the evidence shown in Fig. 5 is

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15

(Surfactant at surface) (Surfactant in bulk)

NP ethoxylate 10 Soaking in water (2 × 2 h)

5 Amide ethoxylate

5

10

Drying time (d)

Figure 5 Relative surface concentration of surfactant as a function of drying time as determined by ESCA. The NP ethoxylate is nonylphenol ethoxylate (12 EO) and the amide ethoxylate is linseed oil fatty acid monoethanolamide ethoxylate (14 EO). (Redrawn from K. Holmberg, Progr. Colloid Polym. Sci., 101:69, 1996.)

only indirect. The sensitivity of ESCA is not sufficient for monitoring disappearance of carbon–carbon double bonds, which would have been the most direct way of studying surfactant polymerization. However, studies on cobalt initiated autoxidation of ethyl esters of unsaturated fatty acids have shown that oleate ester does not polymerize over 110 days, whereas linoleate ester polymerises almost completely over three days [13]. These findings support the view that amide ethoxylates based on fatty acids with a high degree of unsaturation become covalently incorporated in the dried film. Post-emulsification is simplified if the polymer itself is surface active. This can be achieved by using polymers of high acid values or by using polymers with uncharged, hydrophilic segments such as polyoxyethylene chains. Such polymers can often be emulsified with considerably less surfactant, but the trade-off is water and chemical resistance of the paint film. If the polymer is sufficiently polar, no emulsifier at all is needed. However, such binders need to be crosslinked during curing in order to give acceptable film properties.

III. SURFACTANTS FOR PIGMENT DISPERSION Pigments are used in paints to give desired color, hiding and other optical properties to the coating. In addition, pigments often impart mechanical strength and protective properties to the paint. Anti-corrosion pigments are a well-known example of pigments whose prime role is to confer a specific technical property rather than color or hiding to the paint film.

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In order to effectively obliterate the underlying substrate (which may be a paint film of different color), the pigments used must prevent light from passing through the film to the substrate and back to the eye of the observer. The pigments do this by absorbing and by scattering the incoming light. The hiding power of a pigment is a function of the refractive index of the pigment and the pigment particle size. (Also pigment shape influences hiding power because the shape of the particles affects their packing in the film.) The hiding power of the pigment is high if the refractive index of the pigment is much higher than that of the binder used in the paint formulation. Most pigments have a refractive index above 2.0 while most binder resins have a refractive index of 1.4 to 1.6. The very common white pigment, titania (titanium dioxide) has an unusually high refractive index, 2.55 for the anatase crystallographic form, and 2.76 for the rutile form. The perfect particle size for maximum scattering of light is equal to the wavelength of the light within the particle, which roughly corresponds to half the wavelength of light in air, i.e., 0.2 to 0.4 µm. Some pigments are far below this value, e.g., iron blue with a typical particle size range of 0.01 to 0.2 µm, some are in this range, e.g., rutile titanium dioxide which is usually 0.2 to 0.3 µm in size, and some are far above, e.g., micaceous iron oxide with a particle size in the range 5 to 100 µm. The right particle size in combination with the high refractive index is the main reason for the excellent hiding power of titania. Inorganic pigments with low refractive indices (below 1.65) and with concomitant poor hiding power are usually referred to as extenders or fillers. They are employed in paint formulations to control rheological properties (thickening agents, antisag agents), to reduce gloss (flattening agents), to improve mechanical properties (reinforcing agents) or to improve barrier properties of the film. Silica, barium and calcium sulfates, calcium carbonates, and silicates such as china clay, talk, mica, and bentonite are the most common types of extenders. The average particle size of extenders is often large. Pigments need to be finely dispersed in the paint in order to retain good hiding power. Pigment dispersion has therefore been a key process in paint making throughout the long history of paints and it remains an important issue today. The pigment is usually supplied as a powder with the primary particles clustered into agglomerates. The agglomerates must be broken and the primary particles obtained dispersed throughout the coating formulation. In this way a colloidal dispersion of the pigment is produced, with either water or an organic solvent (or more often solvent mixture) as the continuous phase. The dispersion is performed in some kind of grinding process with an input of high shear. Various types of mills have been developed for the purpose, such as high speed dispersers, ball mills (with the cylinder partly filled with steel or porcelain balls), and bead mills (with glass beads or course sand as the grinding medium). In order to economize the grinding process, only a part of the total paint formulation is charged into the mill. Together with all the pigment and pigment dispersants a fraction of the binder is added together with enough solvent to reduce the viscosity to an acceptable level. After milling, a rather stiff paste is obtained to which the remaining amounts of binder and solvent are added together with the various types of additives used in the specific formulation. The primary function of pigment dispersants is to surround the suspended pigment particles with a barrier envelope that by either ionic repulsion, or steric hindrance, or both prevents random contact with other pigments [4,14]. In waterborne paints electrostatic repulsion is usually the most important stabilizing mechanism and the well-known DeryaginLandau-Verwey-Overbeek (DLVO) theory that accounts for the balance of attractive van der Waals forces and repulsive electrostatic forces in suspensions can be used as a tool to understand the stability characteristics of the system. In media of low dielectric constant,

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Paints and Printing Inks

(a)

Figure 6.

379

(b)

(c)

Electrostatic (left), steric (middle), and electrosteric (right) stabilization of a dispersion.

such as white spirit or xylene, steric repulsion is the dominating force. Steric repulsion is achieved by polymers with an anchoring group attached to the particle surface and a segment with high compatibility with the continuous phase extending away from the particle. Steric repulsion can be explained as a loss of entropy when the polymer chains attached to two different pigment particles are forced to penetrate into each other. In order to maximize this loss in entropy, i.e., to achieve maximum stabilization, the density of polymer chains on the particle surface must be high. Sometimes a stabilizing system is used that provides both electrostatic and steric stabilization; this is referred to as electrosteric stabilization. Figure 6 illustrates electrostatic, steric, and electrosteric stabilization. (Electrosteric stabilization is very common for lattices and Fig. 1 shows latex particles stabilized by this mechanism.) Most inorganic pigments are oxides. These exhibit a surface charge in aqueous systems that is characteristic of the oxide and the pH of the water. Each pigment has an isoelectric point, which corresponds to the pH at which the positive and negative charges on the oxide surface are balanced. By moving away from this pH a net charge, positive or negative, starts to develop that leads to pigment particle repulsion. Since the introduction of an ionic dispersant onto the oxide surface alters the balance of charges on the surface, it also acts to alter the isoelectric point of the pigment particle, as shown in Figure 7. For any given pH, adding an ionic dispersant may improve or reduce dispersion stability depending on whether the charge will increase or decrease. In principle, electrostatic stabilization can be achieved by either anionic or cationic pigment dispersants. In order to be compatible with the other components of a paint formulation, in particular the latex that is almost always negatively charged, anionic dispersants are usually employed. A good dispersant for inorganic pigments for waterborne paints should (1) give a low isoelectric point of the coated particle, i.e. should be the salt of a relatively strong acid, (2) have a strong affinity for the pigment surface. A. Dispersants for Waterborne Formulations The most common type of dispersants for inorganic pigments for use in waterborne paints is polyelectrolytes. These may be inorganic, e.g., various types of polymeric phosphates, or organic, such as polyacrylates or styrene–maleate copolymers. Organic polyelectrolyte dispersants are polymers of relatively low molecular weight. For instance, polyacrylate dispersants usually give best performance when composed of between 12 and 18 monomer units. The optimum in length probably reflects the balance between proper anchoring at the particle surface, which is favored by high molecular weight, and rate of adsorption at the surface, which is faster for species of lower molecular weight. In evaluating the dispersion efficiency of added dispersants one must also take into account the wettingdispersing properties of the binder used in the formulation. Alkyd resins, in particular,

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Holmberg +60 Increasing acidity

Zeta potential, ζ (mV)

+40

Increasing alkalinity

+20 0 Phosphate dispersant

−20

No dispersant

−40 −60

2

3

4

5

6

7 pH

8

9

10

11

12

Figure 7 Plot of z-potential of aqueous dispersions of kaolin pigments particles as a function of pH with and without a phosphate dispersant present. (From T.C. Patton, Paint Flow and Pigment Dispersion, 2nd ed. Wiley, New York, 1979, p. 292.)

have good wetting properties, and often contribute considerably to the dispersing power of the total coating formulation. Polyphosphates are versatile inorganic polyelectrolytes that at relatively low concentrations disperse a variety of inorganic pigments. Table 1 shows some common polyphosphates used as pigment dispersants. Polyphosphates are suitable as pigment dispersants on two accounts. First, the polyphosphoric acids are relatively strong acids, i.e., the first pKas are low; thus, the polyphosphate coated particles become strongly negatively charged at all relevant pH values. Secondly, the phosphates bind remarkably strongly to many inorganic surfaces. The anchoring can occur by either of two mechanisms, acid–base interactions or chemisorption. Acid–base interactions usually occur with oxide or hydroxide pigments and the polyphosphate molecule with its regular pattern of P–O–, P=O, and P–OH can act both as the base, being an electron donor, or acid, being an electron acceptor, in the interaction with the pigment surface. Chemisorption may occur at the surface of pigments such as CaCO3, BaSO4, and ZnO since phosphates form insoluble precipitates with calcium, barium, and zinc ions (as well as with many other metal ions). Regardless of the mechanism of anchoring, polyphosphates binding to an inorganic pigment can often be regarded as irreversible. For this reason polyphosphates are very efficient dispersants for many inorganic pigments in water-based formulations.

Table 1

Examples of Alkali Phosphate Dispersing Agents

Common Name Orthophosphate Pyrophosphate Tripolyphosphate Metaphosphate a

Ratio of Basic Oxide to Acidic Oxidea 3 2 1.67 1

Basic oxide: Na2O, K2O; acidic oxide: P2O5.

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Number of P Atoms 1 2 3 n

Representative Formula K3PO4 K4P2O7 K5P3O10 Nan(PO3)n

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A number of problems are associated with the use of polyphosphates, however. They contribute to eutrophication leading to an acceleration of the metabolism and reproduction of some fungi on paint films and at runoff areas. Polyphosphates may also give rise to blooming, although this occurs much less with potassium than with sodium salts and less with polymeric phosphates than with monomeric species. The bloom is a frosty, crystalline deposit that may appear on the surface of aged paint films. The blooming problem is the reason why the more expensive potassium polyphosphates are preferred to the corresponding sodium salts. Furthermore, polyphosphates may degrade by hydrolysis, particularly when the paints are kept at an alkaline pH (and most latex paints are formulated at a pH of 8 to 9) or when certain transition metals that form strong complexes with phosphates are present. The degradation may lead to unexpected rheological changes of the formulation. Also organic dispersants are used with inorganic pigments for waterborne coatings. For instance, polyamines impart excellent dispersion properties to many inorganic pigments. In order to achieve optimum properties the spacer length between the amino groups must be such that it matches the distance between adsorption sites on the pigment surface. As an example, 1,3-propylene diamine, with three carbons between the amino nitrogen atoms, is a better dispersant for clay particles than either ethylene diamine (with a twocarbon spacer) or 1,4-butylene diamine (with a four-carbon spacer). Various types of amino alcohols are excellent dispersants for some inorganic pigments used in water-based formulations. The amino group anchors the molecule to the pigment surface and the hydrophilic hydroxyl group extends out into the aqueous phase. Amino diols are often preferred to simple amino alcohols. Organic pigments for waterborne paints are often more hydrophobic in character than the inorganic pigments. Inorganic polyelectrolytes often do not bind strongly to the surface of these hydrophobic particles. Instead, surfactants of various types are commonly used. Anionic surfactants may be employed to provide electrostatic stabilization, nonionics to give steric stabilization or a mixture of the two to impart electrosteric stabilization, as discussed above and illustrated in Fig. 6. Alkylbenzene sulfonates is the most commonly used anionic surfactant for the purpose and alkylphenol ethoxylates with relatively long polyoxyethylene chains, typically 20 to 30 oxyethylene units, have been the nonionic surfactant of choice. For environmental reasons the slowly biodegradable alkylphenol ethoxylates are gradually being replaced by fatty alcohol ethoxylates of similar hydrophliclipophilic-balance (HLB) value. The switch away from alkylphenol ethoxylates is not without problems, however. Anchoring of the fatty alcohol chain to the pigment surface is often not as good as for alkylphenol. It is probable that alkylphenol derivatives can form electron donor-acceptor (EDA) complexes with pigment surfaces that contain electrondeficient groups, as is illustrated in Fig. 8. Such EDA complexes may also form with alkylbenzene sulfonates. No such contribution is, of course, possible in the case of alcohol ethoxylates, which are always based on saturated alkyl chains. Monoethanolamide ethoxylates of polyunsaturated fatty acids that were discussed above are an interesting class of surfactants in this context. This type of nonionic surfactant seems to work well as pigment dispersant and it is likely that these compounds which contain π-electrons in the acyl chain can form EDA complexes with some organic pigment surfaces, although these complexes may not be as strong as for alkylphenol ethoxylates. Figure 9 shows the structure of an alkylbenzene sulfonate, an alkylphenol ethoxylate, an alcohol ethoxylate, and a monoethanolamide ethoxylate of a diunsaturated fatty acid, linoleic acid. Linoleic acid is the main fatty acid in common drying oils such as soy been oil and sunflower oil. Figure 9 also shows the structure of lecithin, a zwitterionic surfactant that has a long tradition as dispersant of organic pigments for paints.

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Holmberg Pigment

O e−

O

O

x

O

O

O O

O O

O O

O O

O O O

O

Figure 8. Schematic illustration of an electron donor-acceptor complex between an alkylphenol ethoxylate and unsaturated moieties on a pigmented surface.

(a) SO−3

(b)

O

O

O

O

OH

O

(c) O (d)

O

O

O

OH

O

O C

O

N

O

O

O

OH

H (e)

O C–O–CH2 C–O–CH

O

O H2C – O–P–O–CH2–CH2–N(CH3)+3 O−

Figure 9. Structure of (from top to bottom) dodecylbenzene sulfonate, nonylphenol ethoxylate, dodecyl alcohol ethoxylate, monoethanolamide ethoxylate of linoleic acid, lecithin (phosphatidylcholine).

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B. Dispersants for Solventborne Formulations Pigment dispersion in organic solvent formulations are based on steric stabilization since electrostatic interactions in media of low dielectric constant are weak. In order to give proper stabilization, the lyophilic part of the dispersant molecule, i.e., the part that stretches out into the continuous liquid phase, must be relatively large; thus, pigment dispersants for solvent-borne paints are polymeric in nature. Pigment dispersants have for a long time been the most important application for polymeric surfactants and both graft and block copolymers are used for the purpose. Graft copolymers, often referred to as comb polymers, are more frequently used than block copolymers. It is important that the segments that extend away from the pigment surface are very compatible with the binder–solvent mixture, or, expressed in other words, that the binder–solvent mixture is a very good solvent for those segments. Only then do the dispersants keep the particles well separated, which is a necessary condition in order to achieve low viscosity with minimal amount of solvent in the formulation. Different lyophilic segments, with different solubility characteristics, are needed for different types of binder–solvent mixtures. One approach to this problem has been to use the solubility parameter concept of Hildebrand [15,16]. Maximum dispersion efficiency is obtained when the solubility parameters of the binder–solvent mixture match the solubility parameters of the polymer segments that stretch out in solution. The polymeric dispersants need to contain groups that provide strong anchoring of the molecule to the pigment surface. As was discussed above for dispersants for pigments in waterborne paints, the choice of anchoring group depends on the type of pigment used in the formulation. The anchoring mechanism is usually based on acid–base interaction, with the pigment surface constituting either the acid or the base moiety. For instance, acidic pigments are properly dispersed by graft copolymers with a poly(alkylene imine) backbone that forms a multiple of acid–base interactions with the pigment surface. Pigments with a basic character, on the other hand, may be dispersed by copolymers containing pendant carboxylic acid groups. Poly(12-hydroxystearic acid) is a well-known example of such a polymeric dispersant. Hydrogen bonding should be regarded as one example, and indeed a very important example, of acid–base interactions, and anchoring of dispersant to pigments in solvent-based paints can often be viewed as hydrogen bonding interactions. For instance, phthalimine groups, which are typical hydrogen bond acceptors, can be used as anchoring groups of polymeric dispersants to hydroxyl-containing pigments.

IV. WETTING AGENTS Proper wetting of the substrate is a necessary requirement in order to achieve good film properties and surfactants are sometimes added to the formulation with the specific purpose to improve the wetting. Extra addition of wetting agents is likely to be more important as the use of polymerizable surfactants as latex stabilizer increases. Surfactants covalently bound to the surface of latex droplets will not act as wetting agents. The concept of critical surface tension of a solid is useful for many practical applications, e.g., surface coatings [17,18]. In order for a coating to spread on a substrate, the surface tension of the liquid coating must be lower than the critical surface tension of the substrate. (In addition, since a liquid is easier to break up and atomise when the surface tension is low, lower surface tension means better sprayability of the coating.) The wellknown coatings defect, “cratering,” is also surface tension related. Contaminants on the surface, such as fingerprints and oil spots, usually have lower critical surface tension than

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the surrounding areas, thus putting extra demand on the coating with regard to low surface tension. The polymer and the solvent largely determine the surface tension of the coating. The polymers usually have relatively high surface tensions, values between 35 and 45 mN/m being typical. The organic solvents have surface tension values between 20 and 30 mN/m. In general, when comparing solvents within the same solvent class it has been found that faster evaporating solvents usually have lower surface tension values than the slower evaporating counterparts. Furthermore, increased branching of the solvent molecule leads to a lowering of the surface tension. Isopropyl alcohol, which fulfils the two above-mentioned requirements, has an extremely low surface tension, 21.4 mN/m. Evidently, the higher the solvent content of the coating, the lower the surface tension. Conventional coatings normally lie in the range of 25 to 32 mN/m. This is low enough to give proper wetting on most surfaces, i.e., to get below the values of the critical surface tension of the substrates. As the resin becomes the major component of the coating, problems related to surface tension are frequently encountered. So-called high solids coatings are, therefore, extremely sensitive to dirt and fingerprints (the surface tension of which is around 24 mN/m). Paint defects, such as “cratering” and “picture framing” occur more frequently with high solids than with conventional systems [4]. Water is a liquid of high surface tension and obviously not suitable for wetting of surfaces. Use of waterborne paints would have been very limited had it not been possible to use surfactants in the formulation. A good surfactant reduces the surface tension of water down to 28 to 30 mN/m, i.e., to the same range as that of the organic solvents used in paints and lacquers.

V. SPECIALITY SURFACTANTS FOR PAINTS The majority of surfactants used in coatings formulations are standard anionic and nonionic amphiphiles, such as fatty alcohol sulfates, alkylaryl sulfonates, and alcohol ethoxylates. Cationic and amphoteric surfactants are rarely used. A few types of speciality surfactants have found specific niches. Fluorosurfactants and silicone surfactants reduce surface tension to extremely low values. They are used in paint formulations to eliminate surface tension gradients that can form due to faster evaporation of the solvent from the coating edges than from the center. Silicone surfactants are used as defoamers (antifoamers) for both solvent-based and waterborne coatings. A defoamer formulation is in itself quite complex, often consisting of a mixture of hydrophobic particles, a silicone surfactant and mineral oil, all of which have defoaming properties. Acetylenic glycols, characterized by having two short, bulky hydrocarbon chains surrounding the polar group, are another type of niche surfactant widely used as antifoaming agent in coatings. These non-micelleforming surfactants form expanded films on water surfaces, which can withstand high surface pressures.

VI. SURFACTANTS FOR FOUNTAIN SOLUTIONS In offset printing the ink is transferred from the printing plate to an intermediate cylinder covered with a rubber blanket. The rubber blanket, in turn, transfers the ink to the paper substrate. On the printing plate, the image and nonimage areas are on the same plane but

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Non-image area Fountain solution Image area Ink

Figure 10. Schematic picture of an offset press. The nonimage areas are wetted by the fountain solution while the image areas are not.

differ in their compatibility with ink and water. The image areas are hydrophobic while the nonimage areas are hydrophilic. The nonimage areas must be prevented from picking up ink. Water serves this purpose by wetting the hydrophilic areas. Surfactants are added to the water in order to facilitate spreading of the water on these areas. This aqueous solution is referred to as fountain solution. The fountain solution normally also contains gum arabic, a pH buffer, and a preservative [19]. Figure 10 shows an offset press. The fountain solution is applied on the printing plate where it wets the nonimage areas. A small amount of fountain solution is emulsified into the ink that covers the image areas. Fountain solution from the nonimage areas and ink from the image areas are transferred to the rubber blanket and then on to the paper surface (not shown in the figure). Thus, the fountain solution surfactant has two roles: it improves the speed of wetting of the nonimage areas and it emulsifies water droplets into the ink. Relatively hydrophobic nonionic surfactants are suitable for the purpose. Addition of a small amount of a water-miscible organic solvent, such as isopropanol, is an alternative way to reduce the ink–water interfacial tension necessary to obtain a fine emulsion of water in ink.

REFERENCES 1. D.R. Karsa. Additives for Water-Based Coatings. Royal Society of Chemistry, Cambridge, UK, 1990. 2. R.W. Bassemir, A. Bean, O. Wasilewski, D. Kline, W. Hillis, C. Su, I.R. Steel, W.E. Rusterholz. In: Kirk-Othmer, Encyclopedia of Chemical Technology, 4th ed.,Vol. 14. New York: Wiley, 1995, pp. 482–503. 3. D.S. Stoye, W. Freitag. Paints, Coatings and Solvents, 2nd ed. Weinheim, Germany: WileyVCH, 1998. 4. T.P. Patton. Paint Flow and Pigment Dispersion, 2nd ed. New York: Wiley, 1979. 5. S. Paul. Surface Coatings, Science & Technology, 2nd ed. New York: Wiley, 1996. 6. K. Tauer. In: K. Holmberg, ed. Handbook of Applied Surface and Colloid Chemistry. Chichester, UK: Wiley, 2001, pp. 2002, pp. 175–200.

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7. K. Holmberg, B. Jönsson, B. Kronberg, B. Lindman. Surfactants and Polymers in Aqueous Solution, 2nd ed. Chichester, UK: Wiley, 2003, Chap. 11. 8. A. Guyot, K. Tauer. In: J. Texter, ed. Reactions and Synthesis in Surfactant Systems. New York: Marcel Dekker, 2001, pp. 547–573. 9. M.J. Unzué, H.A.S. Schoonbrood, J.M. Asua, A. Montoya Goni, D.C. Sherrington, K. Stähler, K.-H. Goebel, K. Tauer, M. Sjöberg, K. Holmberg. J Appl Polymer Sci 66:1803–1811, 1997. 10. A. Guyot, K. Tauer. Adv Polym Sci 111:45–65, 1994. 11. G. Östberg, M. Huldén, B. Bergenståhl, K. Holmberg. Progr Org Coatings 24:281–297, 1994. 12. K. Holmberg. Surface Coatings Int 76:481–489, 1993. 13. W.J. Muizebelt, J.C. Hubert, R.A.M. Venderbosch. Progr Org Coatings 24:263–269, 1994. 14. J.D. Schofield. In: L.J. Calbo, ed. Handbook of Coatings Additives. New York: Marcel Dekker, 1992. 15. J.H. Hildebrand, R.L. Scott. Regular Solutions. Englewood Cliffs, New Jersey: PrenticeHall, 1962. 16. C. Hansen, A. Beerbower. In: Kirk-Othmer, Encyclopedia of Chemical Technology, 2nd ed., Suppl. Vol. New York: Wiley, 1971, pp. 889–910. 17. N.L.Jarvis, W.A. Zisman. In: Kirk-Othmer, Encyclopedia of Chemical Technology, 2nd ed., Vol. 9. New York: Wiley, 1966, pp. 686–738. 18. K. Holmberg, B. Jönsson, B. Kronberg, B. Lindman. Surfactants and Polymers in Aqueous Solution, 2nd ed. Chichester, UK: Wiley, 2003, Chap. 18. 19. G.B. Burdall, D. Owen, R. Paradine. In: The Printing Ink Manual, 5th ed. London: Blueprint, 1993, pp. 342–452.

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14 Surfactant Formulations in Polymerization Gianmarco Polotti

CONTENTS I.

Role of Surfactant ................................................................................................. 388 A. Advantages and Disadvantages................................................................. 388 B. Alternatives to Their Use .......................................................................... 391 II. Emulsion Polymerization ...................................................................................... 392 A. Micellar Nucleation Mechanism............................................................... 393 B. Homogeneous Nucleation Mechanism ..................................................... 396 C. Latex Stabilization..................................................................................... 398 D. Choice of the Surfactant ........................................................................... 400 1. Anionic Surfactants.................................................................... 401 2. Nonionic Surfactants.................................................................. 402 3. Anionic/Nonionic Surfactant Mixtures...................................... 405 4. Cationic Surfactants ................................................................... 419 III. Suspension Polymerization ................................................................................... 419 IV. Miniemulsion Polymerization ............................................................................... 421 V. Inverse Emulsion Polymerization ......................................................................... 426 References ....................................................................................................................... 433

Surfactants are very extensively used in both the preparation and the application of synthetic polymeric materials. Possibly, the largest use for surfactants in this field is the emulsion polymerization and the preparation of latexes both of elastomeric and plastic polymers. There are, however, many other important applications in the polymer industry. Among these are suspension, miniemulsion, inverse emulsion polymerizations, dispersing of prepolymerized materials in water and other liquid media, creaming of natural latex, formation of plastic foams, bonding of polymers to fabrics and other materials, and dispersion of fillers and pigments into polymers.

387

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Table 1 Overall Resin Product in United States in the Year 2000 Polymer

Thousands of metric tonsa

Polystyrene Styrene/Acrylonitrile copolymer Acrylonitrile/Butadiene/Styrene & Styrene copolymer Polyvinyl Chloride and copolymers Acrylics

2.968 0.056 1.415 6.464 0.152

a

C&EN / June 25 : 42-81 2001

The choice of the proper emulsifier in polymer synthesis is very complicated, since it greatly affects not only the reaction itself but also the physicochemical and technological properties of the final product. Latex technology began around World War II in an effort to commercialize a process for the replacement of natural rubber with synthetic materials. In the following decades, latex or emulsion polymerization technology rapidly expanded to include vinyl acetate, vinyl chloride, acrylics, acrylonitrile, and ethylene in addition to the established monomers of styrene, butadiene, and isoprene. Commercial thermoplastics that are prepared using emulsion polymerization include acrylonitrile-butadiene-styrene (ABS), high-impact polystyrene (HIPS), and styrene-acrylonitrile (SAN). A large family of impact modifiers for a variety of thermoplastics, as well as heat distortion, temperature modifiers for polyvinyl chloride are also made by emulsion polymerization. Emulsion polymers are produced on a multimillion metric ton scale annually. Table 1 summarizes the annual production of the above-mentioned polymers in United States.

I.

ROLE OF SURFACTANT

A. Advantages and Disadvantages Several surfactant compositions have been proposed in the literature to be used in small proportion for improvement of polymer production or polymer products. The increased demand for polymers produced or commercialized in clean solvent is also stimulating research toward a greater use of surfactants in water solvent [1]. While a decade ago it was common practice to minimize the amount of volatiles in polymer dispersions, nowadays environmental issues mandate that volatile organic content (VOC) be virtually diminished to zero. While the elimination of VOC is an important goal, the consequences resulting from higher water content generate a spectrum of new problems [2]. The use of selected surfactants brings about the following improvements: 1.

2.

During Polymerization. Surfactants permit controlled conversion of the monomers into polymers by broadly stabilizing the reaction locus. This effect is very much dependent on the polymerization process. We will see extensively these effects for the main polymerization methods. Following Polymerization. Surfactants maintain the stability of the final emulsion by preventing agglomeration of polymer particles together or with pigments

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or fillers subsequently added. The amount of surfactants employed must be carefully controlled, since their hydrophilic nature can lead to products displaying water sensitivity. Hence, the type and amount of surfactants used depend on the properties required during the reaction and on the final product specifications, e.g., particle size, latex stability, etc. Usually, a selected surfactant will have several different effects in the process of polymer production and, while some of these effects may be advantageous, it is very often the case that some others are unwanted. Surfactants are often described as a necessary “evil” in polymer production processes: necessary for the reasons listed above, but evil as they have been shown to influence the glass transition temperature [3] of the fully coalesced polymer film. This will ultimately affect film formation, its water sensitivity and all its macroscopic properties. The main cause for defects in the dry polymer film, related to the presence of surfactants, is phase separation of the surfactant from the polymer matrix during film formation. Hence, the chemical structure of the surfactants becomes a significant factor in determining parameters such as, transition temperature, hydrolytic stability and optical properties. Surfactants migrate through the film surface from the substrate/polymer interface or aggregate to form hydrophilic microdomains in the bulk of the film [4]. A series of studies on latex films indicated that the mobility of low-molecular-weight species, surfactants in particular, may be affected by the glass transition temperature of the polymer which is inherently related to the free volume of the polymer matrix [5], surface tension at the film–air and film–substrate interface [6], compatibility of individual components [7], and coalescence time [8]. Study on surface composition by FTIR spectroscopy [9] provided evidence of essudation of anionic surfactants in neutralized ethylacrylate/methacrylic acid latex films, but not in acidic latex film. The inhibited exudation of anionic surfactants is attributed to the increased compatibility of surfactant with polymers resulting from surfactant penetration into the swollen latex particles. This is followed by the formation of solubilized polymer–surfactant complexes through the adsorption of the surfactant onto the hydrophobic polymer segments. The effect of neutralization of carboxylic acid groups on the exudation of anionic surfactants suggests the formation of hydrophobic interactions that overwhelm surface tension effect and prevents surfactant enrichment at either surface. On the other hand, nonionic surfactants do not exhibit enrichment at the film interface. In the effort to determine the relationship of surfactant compatibility and exudation behavior, Vanderhoff [10] analyzed a series of styrene–butadiene latexes by electron microscopy. The compatibility of nonylphenol ethoxylate surfactants with the nonpolar copolymer was shown to decrease with increasing hydrophilicity of the surfactant. In contrast, adsorption studies [11] on the more polar polyvinylacetate butylacrylate latexes, stabilized by the same nonionic surfactants, indicated an increased surfactant adsorption with increasing hydrophilicity. In all cases, mechanical elongation of the latex films enhances surfactant exudation to the surface due to the increased surface, energy of the film forcing surfactants to the latex surface. These compatibility problems can occur even in simple practical operations such as the blending of two latexes. Latex polymer blends are quite common in industry, because a combination of soft and hard particles provides a number of additional useful properties. A practical example is given by Y. Zhao [12] for the blending of polystyrene/poly nbutylacrylate blend with the expulsion of sodium dioctylsulfosuccinate from the film. Surfactant rich sites will always affect the performance of the polymer in its final appli-

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cation and inevitably cause high water uptake and blooming, poor barrier properties, poor blocking, and gloss, together with adhesion. Film defects are, in turn, the main cause of water rebound in the film, which is detrimental to protection of the substrate against corrosion. To overcome the migration problems related to the presence of surfactant, studies [13] were carried out aimed at transforming the surfactant from an additive in polymer production to a standard ingredient with the function of plasticizer. Several nonylphenol ethoxylate surfactants are miscible with polybutylmethacrylate latex film at 90˚C [14] and act as a plasticizers to accelerate polymer diffusion rates in the films. However, nonylphenol ethoxylate EO20 has only a limited (ca. 2 wt%) miscibility with high molecular weightpolymers if blended at room temperature. Another case when surfactants may be seen as real ingredients, instead of simple additives, is formulations based on hydrophobically associating polymers [15]. They form a class of commercial products present in many industrial applications and mainly used as thickeners and as rheology modifiers. These polymers are composed of hydrophilic backbone with a small number of hydrophobic substituents, in the form of pendant side chains or terminal groups. Their peculiar linear and nonlinear rheological behavior is due to the formation of an intermolecular hydrophobic association network with the nonionic surfactant micelles. The type of surfactant significantly modifies the rheological properties of hydrophobically associating polymers in the semidilute and concentrate regime, where the hydrophobic interaction network exists. In this case, the surfactant becomes a useful and necessary solvent for the commercialization of the polymer. Aside from forming the micelles which serve as polymerization loci, the surfactant can often play a secondary and unwanted role in accelerating or retarding polymerization by virtue of its chemical structure. In industrial practice, it is normal to use surfactants of technical grades without any prior purification. It is not uncommon for surfactants of technical grades to be bleached in order to improve color. Residues of bleaching products and catalysts used in manufacturing can have an undesired or unpredictable effect on the polymerization process. In some cases, surfactants may themselves react with monomers and initiators, or form degraded by-products that are more reactive. For example, surfactants that form peroxides (e.g., octylphenolethoxylate [16]) can act as initiators of polymerization reactions, quite independently of their surface activity. Other kinetic studies indicate that the rate of decomposition of potassium persulfate increases with the ethylene oxide content of the surfactant used in the same recipe. Another side effect of surfactantpolymer interaction is the chain transfer agent capability that some surfactant structures have. By this effect the molecular weight of the polymer can be reduced by an order of magnitude, as shown by Piirma [18]. In addition, surfactants may desorb from the latex, for example if applied at high speed or shearing and cause destabilization. The phenomenon is also very common in commercial latexes and causes severe problems during their packaging and transportation. Finally, if mixed with pigments the surfactant may migrate onto the pigments and also destabilize the latex particles. In the process of polymer recovery via coagulation, the surfactants are wastewater pollutants and have a negative effect on the chemical oxygen demand (COD) and on the biological oxygen demand (BOD) [19] by increasing both. Finally, we would like to point out that surfactants, especially nonionic, are supplied for industrial use as complex mixtures, very often characterized by the simple name usually assigned by the supplier. This is particularly true for ethoxylated alcohols and sorbitol/sorbitan ester series which are multicomponent mixtures. However, it is possible and even

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probable that the emulsification process benefits from the use of these mixtures rather than from the use of a single component [20]. B. Alternatives to Their Use Studies on the production of polymer latexes that avoid the use of surfactants, have been carried out for the past 30 years. A few industrial processes are currently in use [21,22], so-called surfactant-free, but they generally do not represent standard for polymer production, because surfactant-free emulsions have limited stability. Variations include, for example, emulsifier free recipes in which the surfactants are created in situ. This is realized by copolymerization of a hydrophobic co-monomer by a hydrophilic, generally ionic, initiator fragment. The use of copolymerizable surfactants has also been studied, representing a compromise between a classical and an emulsifier-free emulsion polymerization. The relevance of these systems derives mainly from the intrinsic immobilization of the surfactant on the latex particles. Hindered desorption of the emulsifier from the latex should improve latex stability and facilitate “core-shell” procedures (namely polymer particles having an internal part made of one type of polymer and an outer shell made of a different one). This technique should prevent the migration and the accumulation of the emulsifier after filming of the latex.This class of molecules, i.e., co-polymerizable surfactants, are referred to as surfmers and have the advantage that their incorporation into the polymer chains does not necessarily affect the molecular weight or the rate of polymerization. For an overview on surfmers see references [23–25]. Being monomers rather than surfactants, surfmers find increasing difficulties in their incorporation into the polymer chain [26]. In systems such as traditional acrylic copolymers it was found that the reactivity ratio was the most important variable controlling the incorporation of surfmer. Surfmer conversion also depends on particle size: the larger the particle size, the lower the surfmer conversion. However, a drawback for achieving high conversion rate is that a significant part of the surfmer is buried in the particle interior, leading to unstable latexes. Surfmers can also be used to form miniemulsions [27]. As an alternative to covalent binding of the emulsifier onto the latex particles by copolymerization, strong adsorption of polymeric surfactant may be considered [28]. These polymeric materials have been referred to in various publications as polymeric surfactants, protective colloids, polymer supports, support resins, polymer seeds, or polymeric stabilizers, and are typically lower molecular weight (between 4,000 and 20,000 dalton) macromolecules. The polymeric materials’ functionality yields a polymer that is either water soluble or soluble upon addition of a base (known as alkali soluble resin, which contains carboxylic or sulfonic acid) or upon addition of an acid (known as acid soluble nitrogencontaining resin). The polymeric surfactants serve the same purpose of conventional surfactants and add additional performance characteristics such as gloss development, flow and leveling control, and dry time control. Polymeric stabilizers are preferably prepared using weak acids such as carboxylic acid instead of sulfonic acids, and utilize a fugitive amine, for example triethyl amine or ammonia, which ultimately results in a noncharged stabilizing component in the film.The presence of large amounts of ionic species in the final polymer can decrease performance characteristics such as water resistance. Systems containing polymeric stabilizers exhibit improved resistance properties including water resistance, when compared to conventional stabilizers. Some reviews are available on this topic [29,30]. Amphiphilic block copolymers can be viewed as oversized surfactants as they preserve the bipolar structure of traditional lowmolecular-weight surfactants. Hydrophobic aggregation typically occurs intermolecularly and the large block allows electrostatic beside steric stabilization, if the hydrophilic block

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is charged. In contrast, amphiphilic graft copolymers tend to aggregate intramolecularly, due to the possibility of minimizing hydrophobic contact within the macromolecules. Therefore, the emulsifier is believed to produce a thin protective coating layer on the latex surfaces. Polymeric surfactants are mainly used in inverse polymerization, but several examples have been shown in emulsion polymerization as well [31].

II. EMULSION POLYMERIZATION Emulsion polymerization is a major route by which polymers are prepared. The advantages of emulsion polymerization are obvious from the practical point of view, e.g., the cheapness and nonflammable property of the medium, and its function as a controlling factor of the heat developed by the reaction. Polymer emulsions can be used straight in many applications, but the disadvantages include the presence of a relatively high quantity of stabilizers, which is sometimes undesirable, especially when the film is required to have electrical insulation properties, or extreme resistance to water. Emulsion resins are produced by the controlled addition of several chemical components and are obtained as dispersions of discrete particles (0.05 to 1.0 µm) in water. The problem in emulsion polymerization is to have to perform a chemical reaction on droplet, while maintaining the mechanical stability of the system. This problem is complicated by the considerable exothermicity of the process, about 14 to 22 kcal/Mol of monomer. Technically, it is desirable to complete the reaction in the shortest possible time, hence in a large plant efficient cooling is essential, as well as that the reaction goes to virtual completion (Fig. 1). Indeed, at least 99.5% of the starting monomer should be completely polymerized, so that the residual monomer is below 0.1%. Experience has shown that each monomer has its own specific features in emulsion polymerization and requires a specific approach: to a certain extent this is also true of other components in the reaction system, e.g., the emulsifier. Attempt to fit various emulsion reaction systems into one physicochemical model or theoretical scheme have therefore failed. Nevertheless, several features that are common to all polymerization colloidal systems have been established. In the polymerization recipes surfactants are about 1 to 4%, if anionic, or 2 to 6%, if nonionic (% amount based on monomer content). Other key ingredients are the monomers, the water and the initiator, the latter sometimes improperly called a catalyst. Further common components, although not necessarily essential, are: buffers, protective colloids, cross-linkers and chain transfer agents. The process of emulsion polymerization consists essentially of forming an emulsion of a monomer, or a mixture of co-monomers, in an aqueous medium and causing the monomers to polymerize. The end product is a stable latex or a suspension of finely divided polymer particles. The starting emulsion contains not only the monomers and the emulsifying agent but also polymerization initiator and regulators to control the course of the polymerization and the molecular weight in the final polymer. The emulsifying agent in true emulsion polymerization is invariably a water-soluble surfactant or a mixture of surfactants. The first function of the surfactant, but likely its least important one, is to emulsify the monomer or the mixture of co-monomers. Monomer droplets of 1 to 10 µm diameter are formed. It has long been accepted that the main phase for initiation of emulsion polymerization is the aqueous phase because the initiator is a water-soluble compound as well. However two alternative mechanisms have been proposed (Fig. 2):

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SURFACTANT SURFACTANT BLENDING

STEAM FILTER ROTAMETER

WATER

SAFETY HEAD VENT

INITIATOR MONOMER STORAGE

~

M

MONOMER FEED

BLENDING HIGH-TEMPERATURE SHUTOFF

TEMPERATURE CRT CONTROLLER LM

REACTOR

MONOMER BLENDING

AIR PRESSURE

FI ROTAMETER WATER

MONOMER STORAGE

STEAM FILTER FINISHED EMULSION STORAGE STEAM

Figure 1

1.

2.

Typical plant for emulsion polymerization by batch and semibatch process.

Radicals generated in the aqueous phase enter monomer-swollen micelles of emulsifier and rapidly polymerize the solubilized monomer, forming a monomer swollen polymer particle (micellar nucleation); Radicals generated in the aqueous phase add solute monomer molecules to form an oligomeric radical which precipitates out of solution at a critical chain length to form a stable primary latex particle or to coagulate with a previously formed polymer particle (homogeneous nucleation).

A. Micellar Nucleation Mechanism According to the theory developed by Harking [32] the emulsified droplets of monomer serve simply as reservoir from which molecules of monomer may rapidly diffuse into the solution and into the micelles of the surfactant where they become solubilized. The role of the surfactant micelles (with a rather small diameter of ca. 5 nm diameter) in solubilizing the monomer molecules is of vital importance in the polymerization mechanism.The emulsifier is located in the monomer-swollen micelles, adsorbed on the droplet surface,

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Surfactant Molecules 1–10 nm 1023 units/liter

Mag

nific

ation

× 10 00

Monomer Droplets 10000–100000 nm 106 units/liter

Surfactant Micelles 10–20 nm 1019 –1021units/liter

Homogeneous Nucleation Radical Aggregation

Micellar Nucleation Radical Diffusion in Micelles

Polymer Radicals 10−8–10−11 mol/liter

Polymer Radicals 10−8–10−11 mol/liter

Particle Growth

Polymer Particle 100–500 nm 1016–1018 units/liter

Figure 2

Drop Shrinking

Emulsion polymerization: micellar and homogeneous particle nucleation mechanism.

and dissolved in the aqueous phase as in a traditional three-phase thermodynamic equilibrium. This is particularly true in the case of monomers, which are insoluble or only slightly soluble in water, but it is for this type of monomer that the emulsion polymerization is

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most effective and widely used. The free radicals in these systems are formed by the initiating catalysts in the aqueous solution phase. These radicals cannot readily migrate into the relatively large emulsified droplets of insoluble monomer molecule and conversely the concentration of the monomer molecules in the aqueous phase is quite low. The initiating free radicals can however migrate to the interior of a surfactant micelle, where they contact and react with solubilized molecules of monomer. In this manner, the polymerization reaction is initiated in the interior of the micelles and can proceed rapidly because of the relatively high concentration of solubilized monomer, which is available to the free radicals. As the polymerization proceeds and new monomer molecules continue to be imbibed into the micelle, where they react with and add onto the growing polymer chain, the latter very soon grows to a size that makes further retention within the micelle impossible. This is easily understood when it is considered that an average surfactant micelle may contain about 100 surfactant molecules, whereas a typical polymer molecule consists of several hundred or more monomer units. When the growing polymer chain becomes too large for its micelle, it emerges, and the particle retains surfactant molecules adsorbed on its surface. The emergent polymer particle can react with other monomers, which may continue to diffuse from the droplets of emulsified monomer. In this way, the polymer particle once initiated within the micelle, continues to grow and act as a nucleus for further addition of monomer molecules even after emerging from the micellar surface. Accordingly, it would be expected that the initial concentration of a surfactant would have a profound effect on both the particle count and the particle size in the final latex, since these parameters depend on the number of micelles present in the solution at the time the polymerization reaction begun. At a certain stage of the polymerization reaction, the concentration of surfactant micelles in the solution becomes vanishingly small, since all the surfactant originally present as micelles is now adsorbed on the surface of polymer particles. Particle size should also be influenced by the concentration and the specific micelle forming properties of the surfactant as well as by the presence or absence of inorganic electrolytes in the solution. The rate of emulsion polymerization is influenced by the concentration of the surfactant in a rather complex way, which can, nevertheless, be qualitatively predicted. Thus, the rate of polymerization increases with increasing surfactant concentration up to a certain point, above which it remains fairly constant or may even decrease. The mechanism proposed by the Harkins theory is supported by the argument that the final particle diameter (200 to 500 nm) is much smaller than the droplet diameter and that the corresponding number of latex particles is much greater than the number of emulsion droplets present at the beginning of the process [33]. A quantitative study of the theory was developed by Smith and Ewart [34]. They showed that the polymerization rate (Rp) is linearly dependent on particle number (Np) and it is related to surfactant concentration (Ce ) to the 0.6 power and to initiator concentration (Ci ) to the 0.4 power. Rp ∝ Np ∝ Ci

0.4 •

Ce

0.6

(1)

Thus, the importance of the emulsifier is greater in systems in which the monomer is least soluble and lesser in those systems in which the free radicals can contact the monomer molecules either in the aqueous phase or in the oil phase. Generally, the course of a batch emulsion polymerization is subdivided into three intervals. Particle formation takes place during Interval I and, depending on the water solubility of the monomer, normally ends at ca. 1 to 5% conversion. Interval II is characterized by the growth of the primary particles and ends when the separate monomer phase

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Table 2 Critical Micelle Concentration of Commonly Used Surfactants

Surfactant typea Sodium Sodium Sodium Sodium Sodium

/ Potassium alkyl satured fatty acid alkyl sulfate alkyl sulfonate alkyl benzene sulfonate di-n-alkyl sulfosuccinate

Potassium n-alkyl malonate

Log Critical Micelle Concentration (Mole/l)b 1.96-0.296 n 1.43-0.290 n 1.53-0.290 n 0.084-0.253 n 2.08-0.681 n 1.30-0.219 n

Sodium lauryl ether alcohol sulfate Sodium myristic ether alcohol sulfate

-2.12-0.198 m -2.61-0.200 m

Sodium cetyl ether alcohol sulfate

-3.42-0.219 m

Sodium oleyl ether alcohol sulfate

-3.78-0.165 m

Polyoxyethylene nonyl phenyl ethers

-4.54+0.014 m

Sodium lauryl sulfate

8 10 –3

a

J. Brandrup, E H Immergut, Polymer Handbook, Second Edition, John Wiley & Sons, NY, 1975

b

n = number of carbon in alkyl part; m = number of ethoxylate groups

disappears. In Interval III, the particle volume decreases, i.e., the monomer concentration into the particle decreases with a corresponding increase in polymer viscosity. Experimental work has proven the application of the Harkins theory to the relatively water insoluble monomers below a particle concentration of 3 x 1014 particles/ml. The micellar nucleation theory was developed with early polymerization systems in mind (e.g., artificial rubber), where insoluble monomers were often utilized, together with surfactants of low critical micelle concentration (CMC) (Table 2). B. Homogeneous Nucleation Mechanism The micellar nucleation mechanism has several drawbacks. The most important are: • Particles are formed even if no micelles are present. • Predicted particle number is twice what found experimentally. • Partially water-soluble monomers (e.g., those with water solubility > 0.05%) deviate from the predicted kinetic model. There is considerable evidence to support an alternative theory: the homogeneous nucleation theory that was first formulated by Fitch [35] and has become known as the HUFT (Hansen-Ugelstad-Fitch-Tsai) theory [36]. Homogeneous nucleation occurs instead of micellar adsorption when the water-soluble free radicals cannot be adsorbed into the

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Table 3 Water Solubility of Some Commercially Important Monomers Monomer

Temperature (°C)

Styrene Butyl acrylate Butadiene Vinylidene chloride Vinyl chloride Ethylene Methyl methacrylate Ethylacrylate Vinyl acetate Methyl acrylate Acrylonitrile Methyl acrylate t-Butyl acrylate 2-Ethylhexyl acrylate Lauryl acrylate n-Butyl methacrylate

20 25 50 50 20 20 30 25 20 25 25 25 25 25 25 25

Solubility g/100 g water 0.0125 0.16 0.19 0.63 0.06 0.8–1.6 1.5 1.8 2.5 5.2 7.4 5.2 0.15 0.04 <0.001 0.08

hydrophobic interior of a micelle, but will start particle growth in the aqueous phase. After propagation in the water phase and when the radical chains reach a critical degree of polymerization that makes them insoluble, they start to coalesce in a self-nucleation mechanism.The growing radicals will then adsorb surfactant and thus become new stable particles. This coagulate-nucleation model is independent of micelles, except insofar as they serve as surfactant reservoirs. Because particles are formed without micelles it is quite obvious that homogeneous mechanism must be active below the CMC. It is now generally accepted that homogeneous nucleation must be operative at low surfactant concentrations, where there are no micelles present. At surfactant concentrations near and above the critical micelle concentration we shall show that, while data are readily found which are consistent with either models, it has so far proved impossible to find data in the literature which are widely accepted as proof against one or the other model. A combination of theories of micellar nucleation and homogeneous nucleation can be combined in a single view where both mechanisms are present. Even the role of surfactant micelles is still being debated. The main argument in favor of micellar theory is that micelles are so numerous above the CMC that they must be the locus for nucleation (1019 to 1021 dm–1). But the possibility for limited coagulation above the CMC not necessarily excludes the possibility of micelles as nucleation loci. Monomers such as styrene do not show a very steep change in particle numbers around the CMC, while more watersoluble monomers (e.g., methyl methacrylate, vinyl acetate, and vinyl chloride and others in Table 3) do not show such behavior. For the more water-soluble monomers, interaction between the surfactant and the oligomer may be more complex. If the oligomer is long, its interaction with micelles may be gradual; micelles may form around the oligomer as easily as absorption of oligomers in micelles because the diffusion constant of the surfactant becomes comparable to that of the oligomer. Oligomers may also associate with monomers in the aqueous solution, leading to the formation of particles (Fig. 2). These

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phenomena, together with a lower absorption efficiency in new particles because of its higher water solubility and lower number of active radicals in the particles may be the reason why we do not see any reduction in the particle number at the CMC for these monomers. Recently, Chern [37] proved by the use of a water-insoluble dye that the homogeneous nucleation mechanism is dominant in the semibatch polymerization of methylmethacrylate. Based on the number of latex particles per unit of volume of water and the weight percentage of the dye ultimately incorporated into latex particles, the mixed model of particle nucleation (micellar and homogeneous) is supposed when the concentration of the surfactant is above its CMC. Nevertheless, the fraction of latex particles originating from micellar nucleation is much smaller (ca. 16%) than the fraction of latex particles originating from homogeneous nucleation. This result strongly suggests that a homogeneous process is predominant not only in absence of micelles but also when they are present. However, monomer droplet nucleation cannot be ruled out because an appreciable amount of dye can be detected in the resultant latex particles (ca. <1%). C. Latex Stabilization A last function of a surfactant in emulsion polymerization is to stabilize the latex, which is the end product of the polymerization. Such latexes are essentially suspensions of solid polymer particles containing an adsorbed surface layer of surfactant. The stability of the suspension depends on how effectively the surfactant originally added to the system prevents agglomeration of the polymer. It is frequently observed that certain surfactants, at concentrations suitable for the polymerization reaction, are not at all suitable for stabilizing the resulting latex. It is customary in many instances to add an excess of an appropriate stabilizing surfactant to the system as the polymerization is reaching completion. Emulsion polymers are generally considered to be metastable systems. The large surface represented by the particles is thermodynamically unstable and any perturbation affecting the balancing forces results in a change of the kinetics of particle agglomeration. The main forces that affect stability are: 1. a repulsive force which results from the interactions of similarly charged particle surfaces; 2. entropic repulsive forces that are generated by steric reduction of solvation; and 3. attractive forces of the London–van der Waals dispersion type. The balance of these forces determines the stability of the polymer colloid. The parameters that can perturb these forces are: electrolyte addition, mechanical agitation, thermal effects (freeze-thaw), and organic solvent addition. In some cases these are also the methods by which the polymer is recovered by coagulation in case of production of elastomers and plastics. In other cases, when the latex is the desired product, a premature coagulation is undesirable and, therefore, the goal is to preserve stability under potentially perturbing conditions, which are in many instances an integral part of the process. Anionic surfactants can cause the product latex to be susceptible to other ionic components or impurities and to foam formation. The adsorption of ionic surfactants on polymer surface at saturation adsorption depends on several variable as shown for sodium alkyl sulfate and potassium oleate by Piirma [38].The adsorption and the consequent latex stability are function of (1) temperature, (2) electrolyte concentration of the medium, (3) alkyl chain length of the surfactant, (4) particle size of the latex, (5) composition and nature of the polymer.

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Surfactant Formulations in Polymerization

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All these effects can be explained in term of: (1) adsorption equilibrium, (2) orientation of the surfactant molecule on the surface, (3) affinity of the surfactant molecules with the surface [39], (4) penetration effect of the surfactant. For instance, the hydration of the surfactant molecules and the electrostatic repulsion between its polar heads may be critically reduced in the presence of a electrolyte [40]. More surfactant molecules can be adsorbed and packed close together on polymer surface with less energy. The addition of an electrolyte therefore results in a smaller molecular area of saturation adsorption. Following the same line of reasoning the CMC of the solution decreases as the electrolyte concentration increases. No general conclusions can be drawn only considering the surfactant alone, since the molecular area at adsorption equilibrium varies with the chemical composition of the surface, i.e., of the polymer. Specific combinations of surfactant and polymer must therefore be studied together. For a nonpolar polymer such as polystyrene, the adsorption force of the hydrophobic portion on the polymer molecule is comparable to the association force of the hydrophobic tails, so that the surfactant is tightly packed on the surface like in a micelle. As the polarity of the surface is increased by change in the composition of the polymer, the affinity between the surfactant and the particle surface is not as great as the affinity between the surfactant molecules themselves. The stronger the polarity of the polymer, the smaller the surface area that is covered at saturation and the smaller becomes the stability of the latex. Other effects may be present with polar polymers, as shown by Edelhauser in the case of sodium dodecyl sulfate in latex of polyvinyl acetate [41]. The experimental data indicate a twofold mechanism that destabilizes particles: a surfactant can penetrate into the interior of the polymer particles carrying water along with it and causing swelling to the point of particle disintegration. In parallel polymer chains from the outer part of the particles become detached and solubilized. It is concluded that for polyvinylacetate latex only a comparatively small portion of the anionic surfactant are on the particle surface, a relatively large part being in the aqueous phase and in the particle interior. All of this may account for sodium dodecyl sulfate being a poor stabilizer in vinyl acetate emulsion polymerization at high solid content. Nonionic surfactants are surely less efficient in providing latex stability than anionics. Grainy products can result from their use as primary surfactants for polymerization. However, the product latex is less sensitive to other ionic components and to freezing. The addition of nonionic surfactants and their adsorption on the particle interface results in a steric stabilization which is not overly sensitive to electrolyte concentration; in such a case it is important that the particles be fully covered. Vice versa, increasing surface coverage of ionized surface groups and adsorbed surfactants yield greater stability to mechanical agitation. The surface ionized groups, belonging to anionic/cationic surfactants, are more efficient than steric stabilization. Mixed steric stabilization gives excellent results [42]. Mixed surfactants of anionic surfactant and long-chain fatty alcohol lead to a broad droplet size distribution for styrene and give bimodal particle size distributions in the final latex [43]. Freeze-thaw stability is important for shipping and storing of latexes. Generally, the freezing of drums that contain latex is slow and is an equilibrium process. In the aqueous phase and as the temperature decreases, some anionic surfactants tend to fall out of the solution with a resultant desorption of surfactant and a consequent reduction in particle stability. With further lowering of the temperature, ice tends to separate and the latex becomes more concentrated. This effect of squeezing the particles together may be compensated by the repulsion between charged particles. If the repulsion is small, then eventually the van der Waals attractive forces take over and coagulation occurs. In sterically

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stabilized systems, ice formation or cooling may not be necessary for coagulation. Sterically stabilized lattices, which are dependent on the chemical nature of the stabilizing moiety, can have an enthalpy or entropic contribution to stabilization. Entropic stabilization yields coagulation upon cooling, e.g., polyacrylic or polyacrylamide stabilized latexes flocculate upon cooling. Enthalpically stabilized latexes, e.g., using polyethylene oxide or polyvinyl alcohol stabilizers flocculate upon heating. The combined enthalpic-entropic stabilization in principle gives systems that do not flocculate as result of either cooling or heating. Much of the limitation in latex stabilization comes from a poor knowledge of particle morphology and control [44]. Particle morphology can be determined either by thermodynamic equilibrium conditions or by non-equilibrium conditions, i.e., kinetically controlled, as in latex agglomeration. Significant advantages have been made in predicting equilibrium structures, even when cross-linking is involved. The role of surfactant is not always clear and there is a great need for basic knowledge and the development of reliable experimental measurements of interfacial energies at the internal and external phase boundaries of the structured particle. Non-equilibrium morphology development is not at all well understood, but many experimental studies have been reported and, qualitatively predictive models have been proposed. Lastly, the analytical determination of the actual structure of the particles can be completely determined by a single technique, although transmission electron microscopy (TEM) is most often used. Two or more complementary techniques (e.g., nuclear magnetic resonance [NMR] + TEM) are likely to provide more complete evidence of latex morphology. While basic knowledge is improving, experiments run on latex stabilization with a sort of “trial and error” methodology help find a quick and easy solution to the problem. For instance, it was found that the use of sodium (α-alkyl-ω-aryl) polyethoxyethanol sulfate in conjunction with sodium di-hexyl sulfosuccinate and octylphenol-ethylene oxide condensate results in carboxylated styrene latex [45] stable to freeze-thaw cycles. For a butadiene styrene latex, freeze-thaw stability is achieved with the use of an alkyl aryl polyethylene oxide alcohol [46]. Latex instability at elevated temperatures is observed when sulfated anionic surfactants are used, since these undergo hydrolysis. Several poststabilizers for polyvinylacetate latexes have been suggested, including polyethylene glycol nonylphenyl ether. A surfactant which was proven successful in stabilization of polyvinyl alcohol latexes is tetrasodium N-(1,2-dicarboxyethyl)-N-octadecylsulfosuccinate. It is also possible to obtain a solubilized polymer of vinyl acetate by polymerizing vinylacetate (2.58% by w/v) in 0.06 M sodium lauryl sulfate. There are several cases with polymer latexes where the coagulation process can occur at the liquid–air interface under conditions of electrolyte concentration that are far removed from those required to produce coagulation in the bulk solution. The effect has appropriately been named “surface coagulation” by Heller who studied it intensively [47,48]. The mechanism appears to be related to de-wetting of the particle at the water air interface either as a consequence of desorption of stabilizing surfactant or of nonhomogeneity of the particle surface. Polytetrafluoroethylene lattices are particularly prone to surface coagulation and this may be partially due to their nonspherical shape. The latter is a consequence of crystallinity and polymer chain folding, which may mean that the ionic surface groups at the chain ends are concentrated on some areas of the surface, whereas other areas are devoid of stabilizing entities. One practical method of preventing surface coagulation is to store the latex in containers without a water–air interface. D. Choice of the Surfactant A large number of surfactants have been found suitable for emulsion polymerization. Selection of the most suitable surfactant as emulsifier for use in any emulsion polymer-

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Surfactant Formulations in Polymerization

401

ization latex will depend upon the favorable modifications that are wanted and, equally important, upon the absence of any undesirable side effects. 1. Anionic Surfactants Anionics are the most frequently used emulsifiers. About 1 to 4% of anionics on monomers are normally added to provide stable emulsions and fine particle size. Certain alkyl sulfate [49] arylalkylsulfonates and phosphates have been recommended as the most effective class as primary emulsifiers for many years [50]. Phosphate surfactants are very effective as primary emulsifiers and the resulting emulsion products are reported to be noncorrosive to metal substrate and to form films of high clarity, but they tend to become insoluble in acid solutions and should not be used below pH 5. Many anionic surfactants have low CMC and are quite active in reducing the surface and interfacial tension. Their kinetic mechanism very often follows the classical micellar nucleation mechanism which is related to the solubility of the monomer that has to be emulsified. Zuikov [51] studied the polymerization of styrene, butylmethacrylate, methylmethacrylate, and methylacrylate, i.e., of a series of monomers with increasing polarity and water solubility, initiated by ammonium persulfate in presence of sodium dodecylsulfate. Since in all the experiments the emulsifier concentration was below CMC, particle generation was lower for styrene and higher for methylmethacrylate and methylacrylate. Accordingly, a smaller number of large particles is formed showing that nucleation particle generation was the dominant mechanism and it follows the intrinsic water solubility of any given monomer. The critical size of polymer radicals, i.e., the maximum size of water polymer radical prior to coagulation, increases with the solubility of monomer in water: 8 units for styrene and 65 for methylmethacrylate. There is evidence in the literature that the rate of emulsion polymerization increases by a large factor as the alkyl chain length of a homologous series of surfactants [52] increases. It is easily explained from the ratio between the amount of the surfactant used and its CMC [53]. There is a large increase in the number of polymer latex particles formed and consequently in the rate of polymerization as the surfactant concentration is increased above the CMC. The large increase of particle number is explained because the lower members of the homologous series of surfactants are below their CMC but the higher members are above. When a equal concentration is chosen that is above CMC for all the anionic surfactants, only a relatively small increase in latex particle number and rate of emulsion polymerization with alkyl chain length of the surfactant is observed. Moreover, the area occupied by the anionic surfactant in a saturated monolayer at the polymer/water interface is independent of chain length for alkyl sulfates. Relatively small amounts may be therefore used to provide emulsions with very fine particle size [54].The viscosity and storage stability of finished emulsions stabilized by anionic surfactants may vary with time. This variation is thought to be related to the ionic charge imparted by the emulsion to the surface of the polymer particle; the charge distribution may vary with the structure of emulsifier. The stabilization efficiency of such surfactants is dependent of many parameters such as the ionic strength and pH, and this is the major drawback in terms of stability of the latex. Because of this charge, anionically stabilized emulsions are inherently sensitive in varying degrees to electrolytes, to freeze-thaw cycles, and to emulsifiers contained in other non-anionic latexes. The conventional anionic emulsifiers, e.g., sodium dodecyl sulfate, are much less strongly adsorbed by polar polymers, e.g., polyvinylacetate, than they are by hydrocarbon polymer such as styrene. This type of latex also tends to form large amount of stable foam that is troublesome in transfer and formulation. Mixtures of anionic surfactants of different structures have been recom-

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mended in order to overcome some of the shortcomings observed in storage stability and in foaming. 2. Nonionic Surfactants Nonionic surfactants of the type of the polyoxyethylene condensates and the ethylene oxide–propylene oxide condensate are often included in formulations, usually more often with an anionic emulsifier than alone. Proportions of nonionic surfactants may be quite high, as much as 6 to 7% on weight monomer basis if used alone, though their tendency to precipitate at elevated temperature may interfere with their stabilizing action. It is well known that the average particle size of latexes produced using a nonionic emulsifier alone are much larger than those produced using comparable concentrations of ionic emulsifiers although they are smaller than latexes produced by surfactant-free emulsion polymerization. Moreover, such latexes are generally monodisperse. Although the micelles of nonionic emulsifiers are much larger in size and fewer in number than those of ionic emulsifiers and will have relative low rates of dilatation when they polymerize, nonionic emulsifiers also have lower diffusion coefficients and much lower critical micelle concentration than ionic emulsifiers. Consequently, their rates of absorption are relatively low compared to their dilation rate, allowing for more extensive coalescence to occur and to produce the larger average particle sizes observed. Moreover, these systems were reported to deviate from the micellar model [55] and very often to present homogeneous nucleation. The micellar structure is the key parameter for the polymerization kinetic and it is the reason for the different behavior found with the use of nonionic surfactant alone. In the case of polymerization of vinylacetate with polyethylene oxide dodecylether, Okamura [56] found that the rate of polymerization decreased with increasing emulsifier concentration, whereas for the homopolymerization of styrene he found an increase proportional to power of 0.6 of emulsifier concentration in agreement with a pure micellar theory. But this is not always the case since even with styrene nonionic surfactants show homogeneous nucleation depending on their structure and aggregation properties in micelles. Piirma [57] studied the emulsion polymerization of styrene with tridecyloxypolyethyleneoxy ethanol EO15 and observed two nucleation regions. Bimodality in the particle size distribution started at 40% conversion. The particles generated in the second nucleation stage were much greater in number and smaller in size than those generated in the first stage. The second nucleation period was reported to be dependent on the temperature and the concentration of the organic phase. The explanation may be that the first generation is related to a micellar mechanism and the second to a mixed micelle formation between oligomers and surfactant molecules. Emelie [58] extended the study to monomers with high polarity (butylacrylate, ethylacrylate, methylmethacrylate) and found approximately the same behavior with two nucleation periods. More recently Ozdeger [59] proved that the partitioning of the surfactant between the phases play the major role in determining the nucleation mechanism. Although the total concentration of the emulsifier may be at a level above the CMC based on the weight of water phase, the portion of the surfactant initially present in the aqueous phase may be below the CMC due to partitioning. Under these conditions, he proposed that the first of the two nucleation periods be attributed to homogeneous nucleation, while the second to a micellar nucleation. In any case, both mechanisms seems to be present with the use of nonionic surfactants alone. The partition of the surfactant among monomer drops, micelle, and water phase also explain the inverse relation between the number of particles and rate of polymerization observed in the synthesis of polybutylacrylate [60] and the kinetic behavior of the copolymer styrene-butylacrylate [61] with octylphenoxypolyethoxyethanol EO40. In the latter

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Surfactant Formulations in Polymerization

403

case, the kinetic varies widely depending on emulsifier concentration. Unimodal particle size distributions were produced at low and at high levels of emulsifier while at intermediate levels bimodal distribution were produced. Consequences of this behavior were practically seen in a semibatch reaction process where all the surfactant was initially present in the aqueous phase and too many particles were nucleated, leading to massive coagulation due to insufficient surfactant to stabilize particles. The only general theory on polymerization kinetic that takes into account the effect of nonionic surfactant structure was developed by Yeliseyeva [62]. It does not follow from Eq. (1) that the polymerization rate, being a function of emulsifier concentration, also depends on the emulsifier activity. The emulsifier activity at the water organic interface is determined by the structure of the emulsifier molecule and the polarity of the organic phase. Hence the use of the emulsifier concentration value in the rate equation without taking into account its activity is inadequate. Therefore, in order to extend the applicability of Eq. (1) to monomers of various polarity in the presence of emulsifier of various structures, a parameter characterizing the emulsifier activity in any given system should be introduced. Whereas this parameter may be neglected when considering polymerization of some hydrophobic monomers, it must be taken into account in the case of polymerization of highly polar monomers where the colloidal behavior of the system, and consequently the polymerization kinetics, depends on emulsifier activity. The proposed kinetic equation may be written Rp ∝ Np ∝ Ci x • Ce

0.6

(2)

where x is the reaction order with respect to emulsifier which varies 0.4 for oxyethylated cetyl alcohol EO30, 0.25 for octadecyl oxyethylated sulfate EO10, and 0.21 for sodium dodecyl sulfate. Such dependence must be associated with the energy of adsorption of the latter at the interface. Since the reactivity of the system seems to be strictly related to the behavior of the surfactant in solution, it is important to consider all together the parameters that affect the phenomenon. First of all, there is a strong temperature effect on the solubilization of an oil in the aqueous solution of a surfactant which results from a change in the hydrophilic-lipophilic balance (HLB) of the surfactant. With a rise in temperature a point is reached where phase inversion occurs. At the phase inversion temperature (PIT), the oil in water emulsion inverts to a water in oil emulsion. The PIT for emulsion is a unique function of the HLB. Emulsification of monomer droplets can be defined by the two parameters HLB and PIT. These parameters are an indication of monomer surfactant interaction. Accordingly, reaction rate, viscosity and particle size are related to this interaction. Greth and Wilson [63] first applied the HLB theory to emulsion polymerization. Following the usual procedure that applies when the HLB method is used to solve emulsification problems, the most important properties of emulsion polymerization, i.e., latex stability, particle size, emulsion viscosity, and conversion rate, have to be plotted against the HLB number of emulsifiers used. Usually curves are obtained with maximum or minimum values falling within a fairly narrow HLB range, peculiar for each kind of monomer (Table 4). The variation between different types of emulsifiers and the length of the oligomer chain relative to the micelle size have not been considered in detail. Different factors may be due to the effects of surfactant type and the effect of oligomer or monomer type. The variation between surfactants results in differences in micellar size and stability, differences between the diffusion constant into micelles, and differences between where in the micelle the monomer is solubilized. The type of monomer that makes up the oligomer causes differences in solubility of the oligomer in the micelle, in the diffusion constant of the

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Table 4 Optimal HLB Range of the Surfactant System for the Emulsion Polymerization

Monomer Styrene Vinyl acetate Methylmetacrylate Ethylacrylate Acrylonitrile 50% Methylmethacrylate 50% Ethylacrylate Vinyl Chloride

Optimal HLB Range of the Surfactant System 14–15 16–17.5 12.1–13.7 11.8–12.4 13.3–13.7 11.95–13.05 30–40

oligomer, in the size of the oligomer relative to the micelle, and in surface activity (possibility for mixed micelle formation). This becomes even more complicated with copolymers. For polymethylmethacrylate, acrylonitrile methacrylate copolymer, and acrylonitrile-styrene copolymer it was found that the particle diameter increases with an increase in the amount of nonionic surfactant in the surfactant mixture; the diameter also depends on the HLB value of the nonionic surfactant used. The values of critical coagulation concentration, i.e., the amount of electrolyte needed to bring about coagulation, increase with increasing proportion of nonionic [64]. Chao [65] investigated the emulsion polymerization of styrene at 50˚C using different nonionic surfactants of the polyoxyethylene type. His results showed that the HLB of the surfactant has important effects on the polymerization kinetic and latex particle size distribution. The monomer/surfactant ratio was also shown to be an important variable in these studies. The unusual behavior of bimodality was attributed to the high solubility of the nonionic surfactant in monomer droplets and to a possible phase change from oil/water (o/w) to water/oil (w/o) emulsion. The work of Schomacker [66] involved the study of the phase behavior of the initial monomer emulsion and how it was related to the polymerization rate and final latex particle size distribution for the polymerization of different monomers with various nonionic emulsifiers. It was seen that above the PIT the surfactant type and concentration did not have any significant influence on the kinetic. Problems occur when the reaction temperature goes beyond the PIT, because the final latex particle size and particle size distributions are affected by the difference between the reaction temperature and the PIT itself. In this situation, it may happen that the kinetic rate Rp goes through a maximum if conducted at a temperature slightly below the PIT and decreases if conducted at higher temperature. To understand many of the effects found in the kinetic of nonionic surfactants, the key is to know the thermodynamic behavior of the three component system (surfactant/monomer/water) and how it changes with the temperature [67]. It is quite general that the domain of water-in-oil emulsion, approaching the PIT from lower temperatures, grows and reaches a maximum at the PIT. A further rise in temperature (with phase inversion at the PIT) leads to a diminution of the domain. Due to this fact, the number of micelles varies quite significantly and drops after the PIT point. This influences the kinetic of polymerization and justifies the maximum vs. the reaction temperature that cannot be explained by any Arrhenius-type kinetic mechanism.

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3. Anionic/Nonionic Surfactant Mixtures Nonionic or polymeric surfactants provide steric stabilization and this is the main reason for their inclusion in emulsion polymerization recipes. Actually, the steric stabilization effect provided by a pure emulsifier is not enough to prevent the interactive polymer particle to flocculate. The repulsion among particles is provided by the thermodynamically favored steric repulsion of the adsorbed materials. It is therefore practical to use mixtures of anionic and nonionic surfactants in emulsion polymerization to combine their different stabilization properties. Mixtures of anionic and nonionic surfactants have been found to produce monodisperse latexes with up to 50% solid content [68]. Mixed emulsifiers containing low concentrations (below the CMC) of a ionic emulsifier in addition to the nonionic emulsifier may be used to reduce the average particle size obtained. In a mixture of ionic and nonionic micelles, the final particle number is not directly related to the number of micelles. The following experimental evidence appears to be highly significant when dealing with mixture of ionic and nonionic emulsifiers: 1.

2. 3.

uniform particle latexes are obtained when both ionic and nonionic surfactants are used, but polydisperse latexes are formed when a comparable amount of either surfactant type is used separately; the effect of increased ionic surfactant content is to decrease the latex particle size; an increase in nonionic surfactant content causes an increase in latex particle size.

Most industrial emulsion polymerization processes use a mixture of surfactants, but little work has been published on the use of mixtures of surfactants in reactive system. The kinetic of polymerization can be very different in these reactions because the CMC of the surfactant system changes and also the micelle composition, dimension and number are quite different (Table 5). Chen [69] determined the CMC of sodium lauryl sulfate/octylphenoxypolyethoxyethanol EO40 system and found values lower than expected on the basis of the individual CMCs of the two surfactants. This greatly modifies the conversion of styrene as a function of time: a kinetic profile following the micellar mechanism was shown only when the nonionic surfactant content was below 30%. From 30% to 50%, the homogeneous nucleation mechanism probably becomes dominant so that data on conversion and number of particles in the latex do not deviate significantly from a pure micellar mechanism. Homogeneous nucleation is present above 80% of nonionic surfactant content. Also, the rate of polymerization displays a maximum when 80% of the surfactant is nonionic and the latex stability is high as well [70]. Using the nonionic surfactant alone makes the kinetic very slow since the number of particles greatly decreases. Further studies on the same system based on thermocalorimetry [71] showed that most of the octylphenoxypolyethoxyethanol initially partitions into the monomer droplets and is later released into the aqueous phase when monomer droplets disappear. Consequently, the micelles of nonionic surfactant do not participate in the nucleation mechanism simply because they are not present at this reaction step. Above the CMC, no constant rate period was observed. The rate of polymerization and the number of particles increase even after disappearance of micelles, which may be attributed to homogeneous nucleation. Below the CMC, a short homogeneous nucleation is observed, followed by an extended constant rate period. At a low ratio of anionic/nonionic surfactant, most of the nonionic surfactant is associated with the oil phase, and no micelle is present in the system.

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Table 5 Emulsion Polymerization Composition

Surfactant [1] 1°

2°

3°

% w Surfactant 4°

1°

2°

3°

Monomer[2] 4°

1°

2°

3°

% w Monomer 4°

5°

1°

2°

Temp.

Polym

(°C)

%

3° 4° 5°

Part. Process Size

Initiator %

(3)

A12E12

2

2EHMA

100

30–65

20

PP

SA12BS

0.9–2.6

AN

100

70–80

10

None

SA12S

6.7

BA

100

50

33

PP

0.67

SB/SE

0.6-2.4

NNP-40 SA4NS

SS18

A12E12

0.37

2

OPE-40 TSO

0.19 4.5

SO

0.32

0.1

0.15

(4)

Ref

(nm)

B

Pag

(5)

1

B

2 88

3

BA

100

70

30

PP

0.12

B

4

BMA

100

80

25

BP

0.19

B

5

c-HMA

100

30–65

20

PP

0.15

B

1

DEAEMA

100

50–70

50

SP

0.15

SC

EA

100

85

34

HP

0.3

B

38

100

6

219

5

100

ABES

1.41

EA

100

90

43

AP

1.41

SB

5

110

NNP-35

1.5

EA

100

60

26

AP/SH

0.04/0.04

SB

5

914

ABES

1.1

EA

100

75

41

HP

3.2

SB

7

ABES

1.3

EA

100

85–90

43

AP

0.08

SB

8

ABES

1.1

EA

100

89

34

AP/SM

0.16/0.16

SB

8

ABES

1.4

EA

100

70

43

AP/SM

0.21/0.21

2SB

8

SB

0.6

DEA12SA OSSA

NNP-12

3.6

1.8

EA

100

70

43

AP/SH

0.05/0.05

LA

100

70

20

SH

0.15

SB

0.5-0.75

B

9

SA12S

0.5–0.75

MAN

100

50

25

PP

SA12BS

0.23

MMA

100

80

8

None

B

10 10

SA12BS

0.23

MMA

100

80

8

None

B

SA12S

0.23

MMA

100

80

8

None

B

10

SO

0.23

MMA

100

80

8

None

B

10

NNP-8

0.23

MMA

100

80

8

None

B

10

A12E

0.23

MMA

100

80

8

None

B

10

MMA

100

50

19

PP

B

11

SA12S

A13E18

0–0.45

0–2.25

0.1

ABES

1.1

MMA

100

75

41

HP

3.2

SB

7

ABES

1.1

MMA

100

68.5

34

AP/SM

0.16/0.16

SB

8

MMA

100

60

10

PP/SB

0.05/0.01

B

SA12S

1

MMA

100

50

30

AP/SB

1/0.1

B

SA12S

0.01–0.4

MMA

100

80

20

SP

0.12

SB

SA12S

A18E6

0.002–0.02

0–0.02

78–126

12

17–211

14

13

294

225

2

n-BMA

100

30–65

20

PP

0.15

B

1

2

n-HMA

100

30–65

20

PP

0.15

B

1

SDDS

0.70

S

100

75

46

PP

0.3

SB

5

112

CFA

2.80

S

100

85

37

PP

0.33

SB

5

867

© 2006 by Taylor & Francis Group, LLC

Polotti

A12E12 A12E12

11

S

100

50

PP

0.35

B

6

29

SA12S

0.60

S

100

50

50–62

PP

0.1

B

6

52

SA12S

.001–0.02

S

100

50

20

AIBM

0.036

B

6

60

SA12BS

0.9–2.6

S

100

80

10

None

B

2

S

100

46

10

DABP

0.2

B

15

SA12S

OPE-40

0.02–0.1

0–1

S

100

70

22

PP

0.1

B

16

SA12S

NNP-40

0–0.128

0–0.128

S

100

80

15

SP

0.13

B

17

S

100

70

30

PP

0.12

B

18

0.5

DMHEDAB

0.6–12

NNP-40 OPE-9

SA12S

1

0.5

S

100

50/60

36

PP

0.1

B

19

A13E8-14

SA12S

2–5

0.5

S

100

50/60

36

PP

0.1

B

19

PO

SA12S

0.5–5

0.5

S

100

50/60

36

PP

0.1

B

19

OPE-9

SA12BS

0–1.57

0.03–0.1 5

S

100

65–70

53

PP

0.27

B

120–580 20

OPE-9

SA12BS

1.69

0.3–0.7

S

100

65–70

50

SPO

0.05

B

170–330 20

OPE-9

SA12BS

1.87

0.3–0.7

S

100

65–70

50

SPO

0.05

B

180–350 20

20

10

AP/ST

0.07/0.07

B

58–60

25

PP

0.123

B

22

40

PP/SB

0.15/0.06

B

23

E20A12S

4.5-9

S

100

SA12S

0.868

S

100

S

100

SS

A18E

1–4.75

1–4.75

50

SA12S

0.03

S

100

70

30

PP

0.02

B

OPE-40

4.5

TBAEM

100

50–70

50

SP

0.15

SC

OSSA

0.15

VAC

100

82

53

HP

0.02

OSSA

0.15

VAC

100

82

53

HP

SABS

0.20

VAC

100

82

53

21

13

16

6

219

SB

5

380

0.02

SB

5

380

PP

0.2

SB

5

380

76

EPBC

SS

3.48

0.23

VAC

100

70

48.4

PP

0.62

SB

5

104

EPBC

SS

3.43

0.23

VAC

100

70

50.5

PP

0.62

SB

5

104

VAC

100

80

56.2

PP

0.147

SB

5

108

VAC

100

60

40

PP

C

24

CSP SA12S

0.20 DEHSS

0–0.8

0–1.33

SA12S

0.868

VAC

100

25

PP

0.123

B

SA12S

0.13

VC

100

50

46

SP

0.03

SB

SS-18

0.61

VC

100

18

45

AP

0.61

AP/SB 90

33

AP

22 850

5

114

B

5

116

0.5/0.2

B

13

397

0.17

B

13

451

0.2

SB

SA12S

1

VC

100

SSWO

3.12

VDC

100

SA12BS

0.95

AN

BA

20

80

70

31

AP

SA4NS

5

AN

BD

25

75

50–60

42

None

B

13

286

SA4NS

0.16

AN

MA

90

10

70

34

BP

0.24

B

5

100

SS-18

0.42

AN

MA

75

25

70

16

PP

0.04

B

13

285

0.05/0.01

B

62–102

12 12

A18E6

.002–0.02

0-0.02

AN

MMA

62

38

60

10

PP/SB

SA12S

A18E6

0.02

0.02

AN

S

34

66

60

10

PP/SB

0.05/0.01

B

116

SA12S

NNP-10

0.02

0.02

AN

S

34

66

60

10

PP/SB

0.05/0.01

B

103

12

SA12S

E30A18S

0.02

0.02

AN

S

34

66

60

10

PP/SB

0.05/0.01

B

82

12

BA

AA

98

2

70

43

AP/SM

0.15/0.22

SB

© 2006 by Taylor & Francis Group, LLC

0.48

407

SA12S

SA12BS

Surfactant Formulations in Polymerization

DHSSA

408

Table 5 Emulsion Polymerization Composition (continued)

Surfactant [1] 1°

2°

3°

% w Surfactant 4°

SA12S AE15

1°

2°

0.33 BMF

2.50

1.5

0.6–2.4

NNP-40

3°

Monomer[2] 4°

1°

2°

3°

% w Monomer 4°

5°

1°

BA

MA

BA

S

62.5

43

BA

S

50

2°

Temp.

Polym

(°C)

%

3° 4° 5°

Part. Process Size

Initiator %

(3)

(4)

Ref

(nm)

Pag

(5)

57

25

50

PP

0.03

SB

25

37.5

45

38

PP

0.15

B

5

50

70

30

PP

0.12

B/SB

26

40

35

PP

0.16

B

5

838

34

AIBM

0.1

SB

6

258

718

SS

1.30

BD

AN

60

40

SA12S

0.55

BD

AN

65

35

PM

1.7

BD

S

75

25

50

35

PP

0.3

B

27

PL

1.7

BD

S

75

25

50

35

PP

0.3

B

27

SC

1.7

BD

S

75

25

50

35

PP

0.3

B

27

SR

1.7

BD

S

75

25

50

35

PP

0.3

B

27

ASSA

1.7

BD

S

75

25

50

35

PP

0.3

B

27

DOSSA

1.7

BD

S

75

25

50

35

PP

0.3

B

27

SS

1.7

BD

S

75

25

50

35

PP

0.3

B

27

SS

1.7

BD

S

75

25

50

35

PP

0.3

B

27

SS

1.7

BD

S

75

25

50

35

PP

0.3

B

OPE-40

4.5

DEAEMA

EMA

10

90

50–70

50

SP

0.15

SC

44

6

OPE-40

4.5

DEAEMA

EMA

25

75

50–70

50

SP

0.15

SC

44

6

219

OPE-40

4.5

DEAEMA

i-BMA

25

75

50–70

50

SP

0.15

SC

44

6

219

OPE-40

4.5

DEAEMA

MMA

25

75

50–70

50

SP

0.15

SC

24

6

219

HESSA

0.8

EA

AA

95

5

70

40

AP

0.22

SB

70

27 219

EA

AN

90

10

42

AP/SM

0.07/0.09

SB

SA12S

0.50

EA

GMA

97

3

31

AIBM

0.02

SB

5

597

SA12S

0.50

EA

GMA

94

6

31

AIBM

0.02

SB

5

597

SA12S

0.48

EA

GMA

97

3

31

AIBM

0.01

5

597

DEA12SA

0.82

EA

IA

96

4

70

34

AP/SM

0.12/0.04

OSSA

2.3

EA

MAA

95.8

4.2

70

46.6

AP

0.26

SB

224

28

SA12S

2.3

EA

MAA

95.8

4.2

70

46.6

AP

0.26

SB

97

28

SA12BS

2.3

EA

MAA

95.8

4.2

70

46.6

AP

0.26

SB

122

28

ABES

2.3

EA

MAA

95.8

4.2

70

46.6

AP

0.26

SB

116

28

NNP-40

2.3

EA

MAA

95.8

4.2

70

46.6

AP

0.26

SB

122

28

SB

NNP-40

SA12ES

2.5

MAA

75

25

70

39

HP/AA

0.3/0.1

EA

MAA

93

7

70

20

HP/AA

0.18/0.6

SB

SA12ES

0.43

EA

MAA

59

41

70

29

AP

0.02

SB

ABES

1.41

EA

MMA

50

50

90

43

AP

1.41

SB

© 2006 by Taylor & Francis Group, LLC

5

110

Polotti

EA

2

DENPSA

0.18

SB

DENPSA

HESSA

1.22

0.03

1.3

EA

MMA

50

50

85–90

43

AP

0.08

SB

8

1.1

EA

MMA

50

50

79

34

AP/SM

0.16/0.16

SB

8

EA

NMA

92.5

7.5

41

AP/SM

0.07/0.03

EA

NMA

95

5

60

50

AP

0.2

SB

EA

VAC

35

65

80

56

PP

0.16

SB

MA

S

71

29

92

7.8

PP

0.231

SB

SA12S

NNP-30

0.28

ABES

NNP-10

NNP-4

0.21

1.7

0.21

0.42

SA12S

0.94

SS 16 SA12BS

1.53

3

HESSA

0.06

NNP-40

0.1

5

602

29 7 17

30

MMA

n-BMA

85

15

52

33

AP

0.33

B

13

225

MMA

S

50

50

80

60

AIBM

0.2

SB

6

238

60

112

SDDS

1.00

S

2EHA

30

SA12S

0.16

S

AA

90–100 0–10

82

35

AP/SM

0.16/0.16

SB

5

70

10

SP

0.2

SB/SE

31

NPES-25

RSSA

0.89

0.45

S

BA

80

20

80

38

SP

0.48

SB

205

32

DEA12SA

DHSSA

NNP-9.5

2.35

0.61

0.48

S

BA

60

40

72

50

AP

0.19

SB

70

33

DEA12SA

DHSSA

NNP-9.5

1.18

0.62

0.48

S

BA

60

40

72

50

AP

0.19

SB

78

33

DEA12SA

DHSSA

NNP-9.5

1.06

0.55

0.43

S

BA

60

40

65

50

AP/SM

0.17/0.07

SB

69

33

HESSA

DEA12SA

1.45

1.58

S

BA

70

30

72

50

AP

0.2

SB

84

33

HESSA

DEA12SA

1.30

1.41

S

BA

70

30

65

45

AP/SM

0.17/0.07

SB

59

33

SA12S

2.5

S

BA

50

50

15–40

10–35

U

B

34

SA12S

0.33

S

BA

30

70

50

50

PP

0.03

SB

25

S

BD

65

35

50

60

PP

0.27

SB

5

117

S

BD

33

67

60

50

HP

B

13

87

S

BD

25

75

30

PP

B

13

87

0.16

B

13

94 95

DHSSA

SDDS

SINE

1.84

1.84

5

SO SM

0.80

S

BD

25

75

50

44

PP

SM

2.1

S

BD

25

75

30

28

PCC

0.14

B

13

SR

1.80

S

BD

25

75

50

36

PP

0.1

B

13

98

SO

0.18

S

BD

25

75

30

36

TBH

0.18

B

13

103

SA12S

2.5

S

EA

50

50

15–40

10–35

U

B

34

SA12S

2.5

S

MA

50

50

15–40

10–35

U

B

34

SA12S

0.33

S

MA

39

61

50

50

PP

0.03

SB

25

OPE-40

4.5

TBAEM

EMA

10

90

50–70

50

SP

0.15

SC

28

6

219

OPE-40

4.5

TBAEM

EMA

25

75

50–70

50

SP

0.15

SC

18–24

6

219

OPE-40

4.5

TBAEM

EMA

50

50

50–70

50

SP

0.15

SC

30

6

219

OPE-40

4.5

TBAEM

i-BMA

25

75

50–70

50

SP

0.15

SC

27–86

6

219

OPE-40

4.5

TBAEM

i-BMA

50

50

50–70

50

SP

0.15

SC

36

6

219

OPE-40

4.5

TBAEM

i-BMA

25

75

60

50

SP

0.15

B

28

6

219

OPE-9

4.5

TBAEM

i-BMA

25

75

60

50

SP

0.15

SC

142

6

226

4.5

OPE-70 OPE-40

SA12S

2.2

2.2

TBAEM

i-BMA

25

75

60

50

SP

0.15

SC

51

6

226

TBAEM

i-BMA

25

75

60

50

SP

0.15

SC

50

6

226

32

DE50ASA

1.64

VAC

2EHA

85

15

70

63

PP

0.19

SB

190

OSSA

1.58

VAC

2EHA

85

25

75

53

PP

0.11

SB

750

105

DHSSA

0.79

76

VAC

2EHA

85

25

75

53

PP

0.11

SB

750

5

105

DHSSA

TOSSA

0.79

76

VAC

2EHA

85

25

75

53

PP

0.11

SB

750

5

105

OPE-16

OPE-30

0.8

0.8

VAC

2EHA

80

20

75–80

48.5

PP/SM

0.06/0.13

SB

© 2006 by Taylor & Francis Group, LLC

7

409

5

OSSA

Surfactant Formulations in Polymerization

ABES ABES

410

Table 5 Emulsion Polymerization Composition (continued)

Surfactant [1] 1°

2°

3°

% w Surfactant 4°

1°

2°

3°

Monomer[2] 4°

1°

2°

3°

% w Monomer 4°

5°

1°

2°

Temp.

Polym

(°C)

%

3° 4° 5°

Part. Process Size

Initiator %

(3)

(4)

Ref

(nm)

Pag

(5)

DPOS

NNP-20

0.26

0.85

VAC

BA

80

20

60

53

PP

0.2

SB

238

SDPODS

NNP-20

0.4

1.3

VAC

BA

80

20

60

53

PP

0.2

SB

241

33

VAC

BA

85

15

80

40

AP

0.25

SB

307

6

118

VAC

BA

0–100

100–0

60

SB

115–161 6

164 204

0.1

SA12S DHSSA

OSSA

AP

33

AP-25/40

SS

3.8

0.1

VAC

BA

57.4

42.6

70

50

TBH/SFS

0.2/0.2

SB

6

OSSA

DHSSA

0.4

0.4

VAC

BA

0–100

0–100

75

30

AP

0.00

B/SB

35

VAC

BA

80

20

50

SB

36

A16E16

0.13

0.54

VAC

CA

95

5

76

56

PP/SP

0.16/0.16

SB

5

VAC

DOM

60–80

20–40

50

SB

36

SA12S SA12BS SA12S

SP SP

NNP-20

NNP-9

1.16

0.58

VAC

E

81

19

50

48

PP/SFS

0.04/0.1

SB

NNP-20

NNP-9

0.55

0.38

VAC

E

82

18

50

53

PP

0.05

SB

OSSA

NNP-20

0.21

0.62

VAC

IBM

70

30

65

54

PP

0.17

SB

SS-2

SA12S

0.22

0.06

200

5

107

5

107

420

33

145

33

DENPSA

NNP-20

0.5

0.99

VAC

IBM

70

30

60

52

PP

0.2

SB

DEA12SA

NNP-20

0.71

0.98

VAC

IBM

70

30

60

52

PP

0.2

SB

DEA12SA

DHSSA

0.49

0.5

VAC

IBM

80

20

60

52

PP

0.2

SB

VAC

MMA

0–100

0–100

40–75

20

PP

0.06

B

37

VAC

NMA

96

4

65

45

PP

0.24

SB

33

VAC

NMA

98

2

65

55

PP/SM

0.22/0.09

SB

5

VAC

NMA

95

5

50

SB

36

OSSA DENPSA

0.1 1.2

NNP-30

1.33

0.79

DEA12SA SA12S

SP

109

33 33

601

AP-25/40

SS

3.8

0.1

VAC

VEH

70–90

10–30

70

50

TBH/SFS

0.2/0.2

SB

6

204

AP-25/40

SS

3.8

0.1

VAC

VEH

50.3

49.7

70

50

TBH/SFS

0.2/0.2

SB

6

204

DEA12SA

NNP-20

0.74

1

VAC

VEOVA10

80

20

60

52

PP

0.2

SB

33

DENPSA

NNP-20

0.5

0.98

VAC

VEOVA10

71

29

60

52

PP

0.2

SB

DEA12SA

NNP-20

0.73

0.98

VAC

VEOVA10

71

29

60

52

PP

0.2

SB

OSSA

NNP-20

0.2

0.62

VAC

VEOVA10

70

30

65

54

PP

0.2

SB

DENPSA

NNP-20

0.48

1.13

VAC

VEOVA10

71

29

60

54

PP

0.2

SB

33 199

33

150

33

33

DENPSA

NNP-20

DTSSA

0.48

1.13

0.25

VAC

VEOVA10

71

29

60

54

PP

0.2

SB

161

33

DENPSA

NNP-20

DTSSA

0.49

0.98

0.26

VAC

VEOVA10

71

29

60

53

PP

0.2

SB

135

33

A16E15

ALEP

0.52

0.26

VAC

VEOVA10

75

25

80

54

SP

0.15

SB

5

561

A16E15

ALEP

0.52

0.26

VAC

VEOVA10

75

25

80

54

AP/SM

0.005/0.005

SB

5

561

SS

3.8

0.1

VAC

VND

46.5

53.5

70

50

TBH/SFS

0.2/0.2

SB

6

204

SS

3.8

0.1

VAC

VNN

48.3

51.7

70

50

TBH/SFS

0.2/0.2

SB

6

204

AP-25/40

SS

3.8

0.1

204

VAC

VNP

57.4

42.6

70

50

TBH/SFS

0.2/0.2

SB

6

SS-18

0.67

VC

DEF

78

22

33

45

AP

0.14

B

5

116

SSSO

4

VDC

VC

60

40

30

22

AP/ST

0.67/0.33

B

13

456

ABES

1.1

MMA

BA

45

45

67

33

AP/SFS

0.16/0.1

SB

8

© 2006 by Taylor & Francis Group, LLC

2HEMA

10

Polotti

AP-25/40 AP-25/40

IBMA

2HEMA

95

3

2

53

TBH

0.15

SB

0.53

BA

AN

2HEMA

40

40

20

35

AP

0.035

SB

5

605

OSSA

0.53

BA

S

2HEMA

30

40

30

35

AP

0.035

SB

5

605

5

605

NNP-20

0.72

0.97

60

260

33

BA

S

2HEMA

50

30

20

35

AP

0.035

SB

DE50ASA

A13E20

1.16

1.19

EA

MMA

AA

69

30

1

70

46

PP

0.2

SB

300

32

DE50ASA

NNP-30

0.24

1.02

VAC

VEOVA10

AA

70

29

1

80

48

PP

0.05

SB

100

32

AN

BA

AA

21

75

4

70

39

AP

0.22

SB 67

33

OSSA

0.53

1.2

DEA12SA DOSSA

2.48

DCHSS

0.52

1.15

HESSA

S

BA

AA

47

50

3

65

45

PP/SM

0.22/0.12

SB

AN

BA

AA

68

26

6

70

40

AP

0.22

SB SB

AN

BA

AA

20

75

5

70

40

AP

0.25

HESSA

1.46

BA

MMA

AA

59

40

1

60

50

AP/SM

0.48/0.1

SB

168

33

HESSA

1.46

BA

MMA

AA

59

40

1

60

50

AP/SM

0.48/0.1

SB

155

33

140

38

HESSA

DEA12SA

0.2

2.40

NNP NNP-20

0.08

SA12S

0.27

0.8

VAC

2EHA

AA

19

80

1

75

46

AP/SM

0.01/0.01

B

MMA

BA

AA

54

44

2

80

44.2

SP

0.32

SB

5

NPES-10

1.22

S

BA

AA

65

33

2

70

42

SP

0.19

SB

70

32

NPES-10

1.22

S

BA

AA

65

33

2

70

42

SP

0.19

SB

100

32

150

32

NPES-25

2.18

EA

MMA

AA

70

29

1

75

45

PP

0.18

SB

NPS-4

0.12

BA

MMA

AA

55

43

2

80

34

PP

0.2

SB/SE

39

OPE-40

2.1

EA

MMA

AA

62

37

1

70

45

AP/SH

0.05/0.07

2SB

8

SS

NNP-40

0.50

1

VAC

VEOVA10

AA

56

43

1

70

50

PP

0.25

SB

DENPSA

NNP-9.5

1.38

0.84

S

2EHA

ACM

59

39

2

55

48

AP/SM

0.22/0.11

SB

131

33

5 38

311

403

SA12S

0.03

MMA

BA

AMPS

54

45

1

80

43.8

SP

0.33

SB

220

SA12S

0.026

S

BA

AMPS

52

47

1

80

49.8

SP

0.3

SB

280

38

SA12S

0.95

VAC

BA

AMPS

79

20

1

80

50.87

PP

0.21

SB

132

38

50

AP

0.2

SB

29

AP/SFS

0.06/0.12

B

13

457

58

PP

0.1

SB

5

674

24

AP

0.02

SB 109

HESSA

3

EA

NMA

AN

87

3

10

60

SS 14-16

0.24

VDC

VC

AN

85

13

2

30

OSSA

0.60

VAC

AA

BA

80

10

10

SA12ES

0.36

EA

MAA

DAF

59

40.5

0.5

70

SA12BS

A16E16

0.05

1.6

VAC

AA

DBF

81.3

3.7

15

76

56

PP

0.16

SB

5

SA12BS

A16E16

0.05

1.6

VAC

AA

DBM

81.3

3.7

15

76

56

PP

0.16

SB

5

109

MA

MMA

DEAEMA

14

61

25

90

33

AP

0.13

SB

5

873 874

9.80

AP-30/50 AE

SA12ES

0.55

1.86

MMA

EA

DMAEMA

45

42

13

84

35

AP

0.12

SB

5

SA12S

NNP

0.62

0.8

BA

2HEMA

GMA

90

8

2

45

44.4

AP

0.5

SB

5

606

AAES

SAES

0.33

0.45

EA

S

IA

58

38

4

75

50

AP/SM

0.18/0.91

SB

5

115

SB

NNP

0.68

DEA12SA

0.01

EA

MMA

IA

86

10

4

70

44

AP/SM

0.06/0.08

HESSA

3

EA

NMA

IA

95

3

2

60

50

AP

0.2

SB

29

NNP-35

2.00

EA

AA

IA

92

5

3

60

30

AP/SH

0.03/0.04

SB

5

914

SA12S

0.36

VDC

MA

IA

52.5

46.5

1

63

34

AP/SP

0.21/0.21

B

5

116

MMA

IA

87

10.5

2.5

48

AP

0.1

B

5

314

OSSA

0.92

0.23

EA

VAC

IBMA

68

30

2

80.5

46.5

PP

0.2

SB

5

315

HESSA

DENPSA

2.46

0.76

BA

MMA

IBMA

48.5

48.5

3

60

51

TBH/FO/CS

0.1/0.1/0.04

SB

33

TNP-30

2.90

© 2006 by Taylor & Francis Group, LLC

411

EA

AE

Surfactant Formulations in Polymerization

VAC

OSSA

DEA12SA

412

Table 5 Emulsion Polymerization Composition (continued)

Surfactant [1] 1°

2°

3°

% w Surfactant 4°

1°

2°

3°

Monomer[2] 4°

1°

2°

3°

% w Monomer 4°

5°

1°

2°

Temp.

Polym

(°C)

%

3° 4° 5°

Part. Process Size

Initiator %

(3)

(4)

Ref

(nm)

HESSA

DENPSA

2.44

0.75

BA

MMA

IBMA

58

39

3

65

51

PP/IC

0.13/0.001

SB

84

33

HESSA

DENPSA

3.00

0.93

BA

MMA

IBMA

59

39

2

65

50

PP

0.23

SB

135

33

HESSA

DENPSA

2.44

0.75

BA

MMA

IBMA

58

39

3

65

51

PP

0.19

SB

145

33

HESSA

DENPSA

2.45

0.75

BA

MMA

IBMA

58

39

3

65

51

PP

0.19

SB

124

33

HESSA

DHSSA

2.29

0.33

BA

MMA

IBMA

55

35

10

60

50

AP/SM

0.48/0.15

SB

113

33

HESSA

DHSSA

2.29

0.33

BA

MMA

IBMA

55

35

10

60

50

AP/SM

0.48/0.15

SB

128

33

HESSA

DHSSA

NNP-20

1.55

0.23

0.4

BA

MMA

IBMA

27

58

10

60

32

AP/SM

0.48/0.15

SB

122

33

DENPSA

NNP-20

DTSSA

0.5

0.4

0.26

VAC

VEOVA10

i-BMA

69

28

3

60

54

PP

0.2

SB

HESSA

DENPSA

1.1

0.23

VAC

BA

i-BMA

84

13

3

65

44

PP

0.2

SB

132

33

1.1

0.23

VAC

BA

i-BMA

84

13

3

65

44

PP

0.2

SB

131

33

BA

MMA

MAA

49

50

1

50

51

AP/SM

0.19/0.1

SB

89

33

HESSA

DENPSA

OIPA

DEA12SA MEMNP10

HESSA 1.31

0.78

0.23

0.98

5

33

ABES

1.41

EA

MMA

MAA

59

40

1

90

43

AP

1.41

SB

5

ABES

1.3

EA

MMA

MAA

59

40

1

85-90

43

AP

0.08

SB

8 8

ABES

1.1

EA

MMA

MAA

60

39

1

81

33

AP/SB

0.16/0.16

SB

ABES

1.3

EA

MMA

MAA

65

33

2

73

45

AP/SH

0.1/0.1

2SB

BA

MMA

MAA

49

50

1

72

51

AP

0.19

SB

82

33 33

OIPA

DEA12SA NNP-9.5 HESSA 1.31

0.78

0.19

0.98

3.15

EA

MMA

MAA

65

25

10

68

50

PP

0.24

SB

108

DENPSA

2.02

BA

MMA

MAA

22

65

13

85

36

AP

0.17

SB

84

33

DPOS

NNP-9.5

1.10

0.20

MMA

BA

MAA

49.5

49.5

1

72

51

AP

0.2

SB

146

33

DPOS

NNP-9.5

1.23

0.22

S

BA

MAA

49.5

49.5

1

72

51

AP

0.22

SB

112

33

DPOS

NNP-20

1.12

0.63

S

BA

MAA

49.5

49.5

1

72

51

AP

0.2

SB

99

33

HESSA

1.40

BA

MMA

MAA

22

65

13

85

36

AP

0.17

SB

85

33

HESSA

1.46

BA

MMA

MAA

48

50

2

60

50

AP/SM

0.48/0.1

SB

125

33

HESSA

1.46

BA

MMA

MAA

48

50

2

60

50

AP/SM

0.48/0.1

SB

113

33

BA

MMA

MAA

65

33

2

75

46

PP

0.25

SB

148

33

2.21

HESSA

NNP-9.5

HESSA

DHSSA

1.89

0.29

BA

MMA

MAA

59

39

2

75

31

AP

0.18

SB

64

33

HESSA

DENPSA

1.88

0.69

BA

MMA

MAA

59

39

2

75

31

AP

0.18

SB

59

33

EA

MMA

MAA

48

50

2

60

50

AP

0.2

SB SB

124

33

3

HESSA

29

NNP-20

1.00

0.63

S

BA

MAA

49.5

49.5

1

72

51

AP

0.2

HESSA

NNP-9.5

1.00

0.2

S

BA

MAA

49.5

49.5

1

72

51

AP

0.2

SB

152

33

HESSA

DENPSA

1.42

1.4

S

BA

MAA

47.5

47.5

5

72

51

AP

0.19

SB

84

33

HESSA

DENPSA

1.18

1.33

S

BA

MAA

47.5

47.5

5

65

51

AP/SM

0.20/0.07

SB

80

33

Polotti

HESSA

© 2006 by Taylor & Francis Group, LLC

110

8

DEA12SA

0.89

Pag

(5)

A8E35

2.00

0.4

2.3

NNP-40

2

NNP-40

EA

MMA

MAA

66

32.7

1.3

EA

MAA

MAA

71

27

2

27 70

42

SB AP/SM

0.05/0.07

SB

EA

MMA

MAA

70

27

3

70

39

AP

0.05

SB

S

2EHA

MAA

58

40

2

60

45

AP

0.2

5

SB

100

32

NPES-4

2.29

BA

MMA

MAA

22

65

13

85

36

AP

0.17

SB

89

33

OPE-30

2.36

EA

MMA

MAA

59

40

1

65

46

AP

0.06

SB

5

OPE-30

2.3

EA

MMA

MAA

60

49

1

65

46

AP/SH

0.05/0.07

2SB

8

NPES-10

1.53

NNP-9

0.9

PH

0.7

EA

MMA

MAA

49

49

2

77

36

AP/SFS

0.16/0.1

SB

8

PH

1.3

EA

MMA

MAA

49

49

2

65

46

AP/SH

0.3/0.22

SB

8

PH1

0.9

EA

MMA

MAA

49

49

2

72

35

AP/SFS

0.16/0.1

SB

SA12ES

0.25

EA

S

MAA

59.7

35.8

4.5

82

50

PP

0.2

SB

SA12S

1.00

EA

S

MAA

65

25

10

83

39

PP/SP

0.1/0.02

SB

SA12S

0.52

MMA

EA

MAA

66

29

5

84

43

AP

0.1

SB

SA12S

0.026

S

BA

MAA

52

47

1

80

49.7

SP

0.3

SB

MMA

BA

MAA

49.5

49.5

1

72

51

AP

0.2

SB

EA

MMA

MAA

87

3

10

48

AP

0.1

B

5 7

SDPODS

0.50

NNP-9.5

0.20

2.90

TNP-30 TOSSA

NNP-9

1.3

0.45

EA

S

MAA

60

33

7

85-90

38

PP

0.1

SB

TOSSA

SA3NS

0.70

0.7

S

BD

MAA

48

48

4

48

60

PP

0.23

SB

VAC

BA

MAGME

85

11

3

65

50

AP

0.5

SB

1

DEA12SA

5

501

5

591

90–220

5

1009

281

38

168

33

5 353

DENPSA

2.45

0.75

BA

MMA

MAGME

58

39

3

65

50

PP

0:13

SB

33

DENPSA

2.47

0.76

BA

MMA

MAGME

47

47

3

60

50

TBH/FO/CS

0.1/0.1/0.04

SB

33

29

SP

0.15

C

60

45

PP

0.2

SB

BA

MMA

11

57

32

0.21

VAC

VEOVA10

NBMA

69

28

3

EA

MMA

NMA

79

18

3

60

50

AP

0.2

SB

29

0.22

0.11

0.44

VAC

IA

NMA

93

3

4

65

45

PP/SM

0.22/0.09

SB

5

0.48

0.95

1.33

VAC

VEOVA10

NMA

68

28

3

60

53

PP

0.2

SB

33

0.4

0.8

0.21

VAC

VEOVA10

NMA

69

28

3

60

43

PP

0.2

SB

AN

BA

NMA

20

76

4

70

40

AP

0.2

SB

DTSSA

0.4

DEA12SA

OSSA

NNP-9.5

DENPSA

NNP-20

DENPSA

NNP-20

3

HESSA

DTSSA

0.84

HESSA

110

33

105

33

HESSA

DENPSA

1

0.12

AN

BA

NMA

19

75

6

70

51

AP

0.26

SB

HESSA

DENPSA

0.82

1.21

BA

MMA

NMA

58

39

3

65

50

PP

0.1

SB

HESSA

DENPSA

1.2

0.25

BA

MMA

NMA

47

47

3

60

49

TBH

0.1

SB

137

33

145

33

HESSA

1.44

BA

MMA

NMA

59

38

3

60

50

AP/SM

0.48/0.1

SB

HESSA

0.84

EA

MAA

NMA

86

6

8

70

41

AP

0.2

SB

EA

MAA

NMA

94

3

3

70

50

PP

0.34

SB

EA

MMA

NMA

66

31

3

60

50

AP

0.2

SB

31

AP/SM

0.05/0.03

HESSA

DENPSA

1.24

0.12

3

HESSA

601

33

29 602

SB

5

601

0.42/0.08

SB

5

601

0.22/0.08

SB

5

601

AP/SM

0.22/0.01

SB

66

33

53

PP

0.2

SB

209

33

53

PP

0.2

SB

207

33

NNP-30

0.30

1

EA

MMA

NMA

80

20

TOSSA

DEA12SA

0.53

0.26

EA

MMA

NMA

70

28

2

65

45

AP/SM

0.5/0.1

TOSSA

DHSSA

0.42

0.53

EA

MMA

NMA

93

5

2

65

55

AP/SM

TOSSA

DEA12SA

0.42

0.42

EA

S

NMA

33

65

2

65

45

PP/SM

TOSSA

DEA12SA

1.23

2.47

S

BA

NMA

65

33

2

65

45

DENPSA

NNP-20

0.26

0.84

VAC

BA

PE

79.5

20

0.5

60

DENPSA

NNP-20

0.26

0.84

VAC

BA

PE

79

20

1

60

413

5

SA12S

© 2006 by Taylor & Francis Group, LLC

117

40

VAC 0.8

0.32 NNP-20

314

33

HESSA SA12S

111

8 1000

HESSA

DENPSA

693

Surfactant Formulations in Polymerization

NNP-35

414

Table 5 Emulsion Polymerization Composition (continued)

Surfactant [1] 1°

% w Surfactant

2°

3°

4°

NNP-30

SAES

SABS

1°

2°

3°

Monomer[2] 4°

1°

2°

3°

% w Monomer 4°

5°

1°

2°

VAC

EA

PMA

65

34

1

0.50

BA

NMA

S

50

4

46

SA12S

0.95

VAC

BA

SVS

79

20

1

0.32

1

0.2

0.2

Polym

(°C)

%

3° 4° 5°

AE25

SS

Temp.

82

53

Part. Process Size

Initiator %

(3)

AP

0.16

(4)

SB

40 80

50.87

Ref

(nm)

Pag

(5)

5

497

5

716

PP

0.21

SB

147

38

130

33

DENPSA

NNP-30

0.81

0.9

VAC

NMA

TAC

96

4

0.2

65

43

PP

0.16

SB

AE

SA12ES

0.55

1.86

2EHA

S

TBAEM

24

60

16

84

35

AP

0.12

SB

5

874

AE

SA12ES

0.55

1.86

MMA

EA

TBAEM

45

42

13

84

35

AP

0.12

SB

5

874

EA

MMA

TBAEM

60

30

10

SB

5

874

0.1

VAC

2EHA

VEH

70

6–30

0–24

70

50

TBH/SFS

0.2/0.2

SB

6

204 204

0.90

SA12S AP-25/40

3.8

SS

32

AP-25/40

SS

3.8

0.1

VAC

BA

VEH

70

6–30

0–24

70

50

TBH/SFS

0.2/0.2

SB

6

AP-25/40

SS

3.8

0.1

VAC

BA

VND

41.7

10.3

48

70

50

TBH/SFS

0.2/0.2

SB

6

204

AP-25/40

SS

3.8

0.1

VAC

VEH

VND

31.8

31.5

36.7

70

50

TBH/SFS

0.2/0.2

SB

6

204 204

AP-25/40

SS

3.8

0.1

VAC

BA

VNN

43.1

10.7

46.2

70

50

TBH/SFS

0.2/0.2

SB

6

AP-25/40

SS

3.8

0.1

VAC

VEH

VNN

32.7

32.3

35

70

50

TBH/SFS

0.2/0.2

SB

6

204

AP-25/40

SS

3.8

0.1

VAC

BA

VNP

50.2

12.5

37.4

70

50

TBH/SFS

0.2/0.2

SB

6

204

AP-25/40

SS

3.8

0.1

VAC

VEH

VNP

36.6

36.2

27.2

70

50

TBH/SFS

0.2/0.2

SB

6

204

EA

MMA

MAA

65

25

10

70

10

AP/SM

0.04/0.04

SB

2.26

NNP-20

674

41

A13E20

2.26

EA

MMA

MAA

65

25

10

70

10

AP/SM

0.04/0.04

SB

554

41

A10-11E20

2.26

EA

MMA

MAA

65

25

10

70

10

AP/SM

0.04/0.04

SB

515

41 41

A12-13E20

2.26

EA

MMA

MAA

65

25

10

70

10

AP/SM

0.04/0.04

SB

537

A12-16E20

2.26

EA

MMA

MAA

65

25

10

70

10

AP/SM

0.04/0.04

SB

587

41

NNP-40

2.26

EA

MMA

MAA

65

25

10

70

10

AP/SM

0.04/0.04

SB

512

41

A13E40

2.26

EA

MMA

MAA

65

25

10

70

10

AP/SM

0.04/0.04

SB

617

41

A10-11E40

2.26

EA

MMA

MAA

65

25

10

70

10

AP/SM

0.04/0.04

SB

547

41

A12-13E40

2.26

EA

MMA

MAA

65

25

10

70

10

AP/SM

0.04/0.04

SB

511

41

A12-16E40

2.26

EA

MMA

MAA

65

25

10

70

10

AP/SM

0.04/0.04

SB

516

41

PP

0.19

SB

219

33

5

A12E

SA12BS

1.16

1.16

DBF

BBF

i-B

MAA

70

5

25

DEA12SA

NNP-20

0.69

0.933

VAC

IBM

NMA

2FOEM A

66

28

2

BA

MMA

MAGME

2HEMA

47

47

3

3

70

47

AP

0.34

SB

DEA12SA

OSSA

3.51

0.57

S

BA

IBMA

2HEMA

40

42

10

8

65

45

AP

0.2

SB

64

33

DEA12SA

OSSA

3.21

0.52

3.64

DEA12SA

55 4

55

54

33

BA

IBMA

2HEMA

40

42

10

8

65

45

AP/SM

0.2/0.03

SB

67

33

1

VAC

BA

MAGME

2HEMA

83

12

3

2

65

51

AP

0.5

SB

277

33

DEA12SA

1

VAC

BA

MAGME

2HEMA

79

11

6

4

65

52

AP

0.5

SB

238

33

© 2006 by Taylor & Francis Group, LLC

0.49

Polotti

S

DEA12SA

NNP-20

796

1

VAC

BA

NMA

2HEMA

84

12

2

2

65

50

AP

0.5

SB

244

DEA12SA

1

VAC

BA

NMA

2HEMA

81

11

4

4

65

50

AP

0.5

SB

241

BA

MMA

IBMA

2HEMA

56

38

3

3

65

50

PP

0.13

SB

HESSA

2.41

DENPSA

0.74

33 33 33

HESSA

DENPSA

2.43

0.75

BA

MMA

IBMA

2HEMA

47

47

3

3

60

51

TBH/FO/CS

0.1/0.1/0.04

SB

HESSA

DENPSA

2.44

0.75

BA

MMA

IBMA

2HEMA

56

38

3

3

65

51

PP/IC

0.13/0.001

SB

84

33

33 129

33

HESSA

DENPSA

2.41

0.74

BA

MMA

IBMA

2HEMA

56

38

3

3

65

52

PP

0.18

SB

HESSA

DENPSA

2.42

0.74

BA

MMA

MAGME

2HEMA

57

38

3

3

65

51

PP

0.13

SB

33

HESSA

DENPSA

2.43

0.75

BA

MMA

MAGME

2HEMA

47

47

3

3

60

50

TBH/FO/CS

0.1/0.1/0.04

SB

33

1.2

0.25

BA

MMA

NMA

2HEMA

57

38

3

3

65

51

PP

0.2

SB

DENPSA

0.81

0.25

BA

MMA

NMA

2HEMA

47

47

3

3

60

50

TBH

0.1

SB

HESSA HESSA

33 153

33

SA12BS

EPBC

1.00

2.85

2EHA

MA

MAA

2HPMA

84

10

3

3

82

51.2

PP

0.19

SB

DEA12SA

OSSA

3.51

0.57

S

BA

IBMA

AA

40

47

10

3

65

45

AP

0.2

SB

71

33

5 259

33

361

33

316

DEA12SA

0.7

VAC

BA

NMA

AA

63

32

3

2

60

49

AP

0.5

SB

HESSA

3

EA

MMA

IBMA

AA

58

29

12

1

60

50

AP

0.2

SB

HESSA

0.7

VAC

BA

NMA

AA

63

32

3

2

60

49

AP

0.5

SB

40

PP/SM

0.2/0.2

SB

5

597

70

40

PP

0.2

SB

5

613

0.80

NNP-35 OSSA

0.80

NNP

0.8

EA

S

GA

AA

86

10

2

2

S

BA

GMA

AA

58

30

4

8

29

MMA

BA

2HEMA

AA

42

42

15

1

45

34

AP/SFS

0.16/0.05

SB

OIPA

DEA12SA NNP-9.5 HESSA 1.31

0.78

0.19

0.98

BA

MMA

MAA

ACM

48

50

1

1

72

51

AP

0.19

SB

84

33

OIPA

DEA12SA MEMNP10

0.78

0.23

0.98

BA

MMA

MAA

ACM

48.5

50

1

0.5

50

51

AP/SM

0.19/0.1

SB

90

33

1.3

PH

HESSA 1.31

HESSA

NNP-9.5

1.40

DEA12SA

0.4

NPES-4 NNP-30

BA

MMA

MAA

ACM

47

47

1

5

74

51

AP

0.19

SB

223

33

0.2

BA

MMA

MAA

ACM

47

47

1

5

74

51

AP

0.19

SB

265

33

BA

MMA

MAA

ACM

47

47

1

5

74

51

AP

0.19

SB

196

33

1

AN

EA

IA

ACR

11

87

1

1

70

35

HP/AA

0.3/0.1

SB 138

33

1.40

HESSA

8

1.26

SA12BS

0.42

AN

EA

AA

ACR

11

87

1

1

70

35

AP/SM

0.07/0.04

SB

HESSA

1.46

BA

MMA

MAA

AN

70

25

2

3

60

50

AP/SM

0.48/0.1

SB

HESSA

3

EA

MMA

NMA

AN

70

25

2

3

60

50

AP

0.2

SB

45

PP

0.28

SB

5

434

100-400 5

872

5

716

OPE-9

SAES

0.23

1.25

2EHA

S

MAA

AN

39

48.5

6.5

6

SA12BS

NNP

1.25

0.6

S

2EHA

MAA

AN

53

31

13

3

85

40

SP

0.2

SB

70

20

AP/SM

0.18/0.05

SB

51

AP

0.19

SB

SA12BS

0.94

AN

MMA

MAA

BA

8

22

15

55

NPS-20

0.50

BA

AN

NMA

BD

44

20

6

30

BA

MMA

MAA

DOM

41

43

15

1

OIPA

DEA12SA NNP-9.5 HESSA 1.31

0.78

0.19

0.98

29

40 72

HESSA

3

VAC

DBM

MAA

GMA

70

26

0.2

3.8

55

PP

0.22

SB

DEA12SA

1.1

AN

ACR

EA

IA

15

2

71

2

70

35

HP

0.3/0.07

SB

80

33 42

HESSA

3

EA

MMA

NMA

IA

58

37

3

2

60

50

AP

0.2

SB

HESSA

3

EA

VAC

NMA

IA

32

63

3

2

60

50

AP

0.2

SB

29

S

BA

AA

IBMA

49

47

1

3

65

46

PP/SM

0.2/0.1

SB

33

0.7

0.47

VAC

BA

i-BMA

MAA

83

13

3

1

60

48

PP

0.2

SB

270

33

0.28

0.33

0.33

VAC

BA

NMA

MAA

83

13

3

1

60

47

PP

0.2

SB

276

33

0.47

1.4

VAC

BA

NMA

MAA

83

13

1

3

70

47

AP

0.17

SB

246

33

DEA12SA

DHSSA

DEA12SA

OSSA

NNP-9.5

DEA12SA

NNP-9

NNP-30

0.37

415

1.08

DHSSA

© 2006 by Taylor & Francis Group, LLC

29

2.47

TOSSA

Surfactant Formulations in Polymerization

DEA12SA

416

Table 5 Emulsion Polymerization Composition (continued)

Surfactant [1] 1°

2°

3°

% w Surfactant 4°

1°

2°

3°

Monomer[2] 4°

1°

2°

3°

% w Monomer 4°

5°

1°

2°

Temp.

Polym

(°C)

%

3° 4° 5°

Part. Process Size

Initiator %

(3)

(4)

Ref

(nm)

DEA12SA

DHSSA

1

0.65

VAC

BA

NMA

MAA

87

9

3

1

60

47

PP

0.3

SB

409

33

DENPSA

NNP-30

0.51

0.2

VAC

BA

NMA

MAA

87

9

3

1

70

47

AP/TBH

0.2

SB

203

33

DENPSA

DEA12SA NNP-30

0.28

0.51

VAC

BA

NMA

MAA

87

9

3

1

65

47

AP

0.2

SB

156

33

HESSA

NNP-9.5

1

0.39

VAC

BA

2EHA

MAA

20

48

28

4

80

50

PP

0.4

SB

200

33

NNP-40/50

ABES

2.6

0.65

EA

2EHA

AA

MAA

69

22

5

4

70

36

AP

0.25

SB

0.94

SA12S

0.16

BA

AN

GMA

MAA

27

63

5

5

33

PP/SM

0.03/0.01

SB

SA12BS

0.77

AN

BA

MAA

MMA

10

79

1.5

9.5

70

38

AP

0.15

SB

SA12ES

0.71

EA

AA

NMA

MMA

49

3

6

42

70

42

AP

0.25

SB

SA12ES

0.6

EA

MAA

NMA

MMA

83

1

1

15

70

33

AP/SH

0.08/0.05

SB

5

BA

MMA

AN

NMA

67

28

3

2

60

50

AP/SM

0.48/0.1

SB

171

33

HESSA

NNP-9.5

0.97

0.2

BA

MMA

MAA

NMA

48

48

1

3

72

51

AP

0.19

SB

263

33

HESSA

DENPSA

1.22

0.12

EA

BA

MAA

NMA

65

27

3

5

70

51

AP/SH

0.33/0.1

SB

BA

MMA

AN

NMA

66

10

20

4

132

33

1.46

HESSA

0.50

NPS-10

5

40

DENPSA

NNP-30

DEA12S A

0.28

0.92

0.5

VAC

BA

NMA

MAA

2FOE 84 MA

8

3

1

4

65

48

AP

0.2

SB

TOSSA

DHSSA

NNP-20

2.43

1.06

0.42

S

BA

AA

IBMA

2HEM 48 A

45

1

3

3

65

46

PP/SM

0.2/0.1

SB

1.5

70

35

AP/SM

0.07/0.04

SB

34

AP/SH

0.2/0.2

SB

SA12BS

0.43

AN

EA

AA

MAA

ACR

11

77

1.5

9

SA12S

0.10

AN

BA

NMA

ACM

BDM 58 A

28

2

1.5 10.5

SA12BS

0.34

AN

S

BA

MAA

MAA 19.5

0.5

43

15 22

70

20

AP/SM

0.18/0.05

SB

SA12BS

0.28

AN

S

BA

MAA

MAA 8

0.5

53.5 14 20

70

20

AP/SM

0.17/0.05

SB

BA

MMA

MAA

DOM

TAC

42.8

15

72

51

AP

0.19

SB

OIPA

DEA12SA NNP-9.5 HESSA 1.31

0.78

0.19

0.98

41

1

0.2

Pag

(5)

597

716

33

5

78

619

33

Polotti

© 2006 by Taylor & Francis Group, LLC

[2] EA, ethylacrylate; MMA, Methylmetacrylate; NMA, N-methylolacrylamide; AN, Acrylonitrile; IA, itaconic acid; MAA, Methacrylic acid; VAC, Vinylacetate; IBMA, N-(isobutoxymethyl)acrylamide; AA, acrylic acid; MA , methylacrylate; BA, Butylacrylate; S, Styrene; BMA, Butylmethacrylate; 2EHA, 2,ethylhexyl acrylate; ACM, Acrylamide; 2HEMA, 2-hydroxyproylmetacrylate; 2HPMA, 2-hydroxyethylmetacrylate; BD, Butadiene; VC, Vinyl chloride; CA, Crotonic Acid; VDC, vinylidene chloride; 2FOEMA, 2-(n-fluoro-octyl)ethylmethacrylate; IBM , di-isobutylmaleate; i-BMA, isobutylmetacrylate; n-BMA, nbutylmethacrylate; t-BMA, tertbutylmethacrylate; TAC, Triallylcyanurate; VEOVA10, vinyl ester of Versatic 10 (Shell); MAGME, methylacrylamidoglycolate methylether; DOM, dioctylmaleate; EMA, ethylmethacrylate; MAN, methacrylonitrile; DEAEM, diethylaminoethyl methacrylate; DMAEMA, dimethylaminoethyl methacrylate; TBAEM, t-butylaminoethyl methacrylate; E, ethylene; DBM, dibutylmaleate; DBF, dibutylfumarate; DEF, diethylfumarate; GMA, glycidyl methacrylate; GA, glycidyl acrylate; BDMA, butylene dimethacrylate; VEH, vinyl 2-ethylhexanoate; VNP, vinyl neopentanoate; VNN, vinyl neononanoate; VND, vinyl neodecanoate; PMA, phenylmercuric acrylate; PE, polyester E9064; BBF, 1,3-butylene glycol bisbutyl fumarate; i-B , isobutylene; ACR, acroleine; LA, laurylacrylate; DAF, Diallyphthalate; AMPS, 2-acrylamido-2-methyl propane sulfonic acid ; SVS, Sodium vinyl sulfonate; c-HMA, Cyclohexylmethacrylate; n-HMA, n-Hexylmethacrylate [3] AP Ammonum persulfate; PP Potassium persulfate; SP Sodium persulfate; TBH t-butylhydroperoxide; SM Sodium metabisulfite; SH Sodium hydrosulfite; SB Sodoium bisulfite; ST Sodium thiosulfate; SPO Sodium perborate; HP Hydrogen Peroxide 130 vol; SFS sodium formaldehyde sulfoxylate; AA Ascorbic Acid; FO Formasol; IC Iron Chloride; CS Cupper sulfate; BP Benzoylperoxide; AIBM Azo-di-iso-butyramidine dihydrochloride; PCC Potassium cobaltic cyanide; DABP 2,2'Dimethyl-2,2'-azo-N-benzylpropionamidine hydrochloride; U Ultrasonic [4] SB Semibatch; SE Seeded; B Batch; nB n consecutive batch; SC Semicontinous; C Continous [5] 1, R.Schomacker P Muller In DECHEMA Monographs vol 131 VCH Verlagsgsgesellschaft 1995; 2, T Asahara M Seno S Shiraishi Y Arita Bull of the Chem Soc of Japan 46:249-252 1973; 3, S Sajadi J of Polym Sci: Part A: Polym Chem, 38:3612-3630 2000; 4, E Ozdeger E D Sudol M S EL-Aasser A Klein J Polym Sci Polym:Part A: Polym Chem 35:3827-3835 1997; 5, H.Warson The Applications of Symthetic Resin Emulsions Ernest Benn Limited London 1972; 6, E S Daniels E D Sudol M S El-Asser Polymer Latexes Preparation, Characterization and Applications ACS Symposium Series 492 1992; 7, Acrylates Amcel Corporation litterature 1959; 8, Rhom & Haas Corporation literature 1970s; 9, C E Schildknecht Vinyl and Related Polymers John Wiley & Sons Inc New York 2nd ed 1959; 10, T Asahara M Seno S Shiraishi Y Arita Bull of the Chem Soc of Japan 43:3895-3898 1970; 11, W Hein-Herng C Hou-Hesein Polym Bull 24:297-214 1990; 12, H Oso E Jidai A Fujii The J of Phys Chem 79:2020-2024 1975; 13, C E Schildknecht Vinyl and Related Polymers John Wiley & Sons Inc New York 2nd ed 1959; 14, C S Chern C H Lin Polymer 41:4473-4481 2000; 15, D. Cochin A Laschewsky F Nallet Macromoleculs 30:2278-2287 1997; 16, D Colombee E D Sudol M S El-Aasser Macromolecules 33:7283-7291 2000; 17, C S Chern S Y Lin L Chen S C Wu Polymer 38:1977-1984 1997; 18, E Ozdeger E D Sudol M S EL-Aasser A Klein J Polym Sci Polym:Part A: Polym Chem 35:3813-3825 1997; 19, I Piirma V R Kamath M Morton J of Polym Sci Polym Chem Ed 13:2087-2102 1975; 20, M F Woods J S Dodge I M Krieger P E Pierce J Paint Tech,40:541-548 1968; 21, I Capek J Chudei Polym Bull 43,417-424 1999; 22, H A Edelhauser J Polym Sci: Part C 27:291-309 1969; 23, G G Greth J E Wilson J of Appl Polym Sci 5:135-138 1961; 24, C H Lee R G Mallinson J Appl Polym Sci 39:2205-2218 1990; 25, G H J Doremaele in Model prediction, exerimental determination and control of emulsion copolymer microstructure, PhD Thesis 1990; 26, E Ozdeger E D Sudol M S EL-Aasser A Klein J Polym Sci Polym:Part A: Polym Chem 35:3837-3846 1997; 27, C W Carr, I M Kolthoff, E J Meehan, D E Williams J of polym Sci,5:201-206 1950; 28, K W Evason M W Urban J Appl Polym Sci 42:2287-2296 1991; 29, USP 3947400 1976; 30, G H J Doremaele H A S Schoonerood J Kurja A L German J of Appl Polym Sci 45:957966 1992; 31, M Slawinski J Meuldijk A M van Herk A L German J of Appl Polym Sci 78:875-885 2000; 32, Emulsifiers for Polymer Dispersions Goldschmidt Essen Germany 7/2000; 33, E.Saly Recipe Handbook for Surfactants Cytec Rotterda-Botlek KA - USA 1991; 34, L Jiang C Keqiang L Zili Polym J, 32:103-106 2000; 35, M S El-Aasser T Makgawinata J W Vanderhoff J of Polym Sci: Polym Chem Ed 21:2363-2382 1983; 36, X Q Wu F J Shork Ind Eng Chem Res 39:2855-2865 2000; 37, A M Santos G Fevotte N Othman S Othman T F Mckenna J Appl Polym Sci 75:1667-1683 2000; 38, G P Marks A C Clark Cap 5. In Speciality Monomers and Polymers Synthesis, Properties and Applications, K O Havelka C L McCormick ACS Symposium Series 755 ACS Washington DC; 39, C Sayer E L Lima J C Pinto G Arzamendi J M Asua J of Polym Sci: Part A Polym Chem 38:1100-1109 2000; 40, I Saez de Buruaga J R Leiza J M Asua Polym Reaction Eng 8:39-75 2000; 41, G Polotti T Pellizzon T Verzotti M Pellizzon 5th World Surfactants Congress Cesio 2000 May 29 – June 2 Proceedings 2:889-898 Firenze 2000; 42, H Warson Polymers Paint Colours J., 180,473-475 1990

Surfactant Formulations in Polymerization

[1] HESSA, Solfosuccinic acid half esters; ASSA, Sodium diamyl sulfosuccinate; OSSA, Sodium dioctyl sulfosuccinate; DHSSA, Sodium dihexyl sulfosuccinate; DTSSA, Sodium ditridecylsulfosuccinate; RSSA, Sodium ricinoleic monoethanol amido sulfosuccinate; DOSSA, Disodium -N-octadecyl-sulfosuccinamate; DCHSS, Sodium dicyclohexylsulfosuccinate; DEHSS, Sodium di(2-ethylhesyl)sulfosuccinate; TOSSA, Tetrasodium N-(1,2-dicarboxy-ethyl)-N-octadecyl sulfosuccinamate; DEA12SA, Disodium ethoxylated alcohol (C10-12) half ester of succinic acid; DEnASA, Disodium ethoxylated (nEO) alcohol half ester of succinic acid; DENPSA, Disodium ethoxilated nonyl phenol half ester of sulfosuccinic acid; DPOS, Disodium mono and didodecyl diphenyl oxide disulfonate; EnA12S, Polyoxyethylene sorbitan monolaurate (nEO); NPES-n, Sodium salt of sulfated nonylphenoxy poly(ethyleneoxy) ethanol (nEO); SAnS, Sodium alkyl(Cn)sulfate; SAnES, Sodium alkyl(Cn) ethoxy (1-3EO) sulfate; AAnES, Ammonium alkyl(Cn) ethoxy (1-3EO) sulfate; OPE-n, Polyoxyethylene (nEO) isooctylphenylether; ABES, Alkyl benzene ethoxysulfonate 2EO; SAnBS, Sodium alkyl(Cn)benzene sulfonate; SAnNS, Sodium alkyl(Cn)naphthalene sulfonate; AmPn, Alkyl (Cm) phenol ethoxylate alcohol (nEO); NNPn, n-nonylphenol ethoxylated alcohol (nEO); TNPn, tert-nonylphenol ethoxylated alcohol (nEO); NPSn, n-Nonylphenol ethoxysulfate (nEO); EPBC, Ethylene/propylene block copolymer 80/6 molar; CSP, γ-stearylaminopropyl-dimethyl-β-hydroxyethylammonium dihydrogen phosphate; SSn, Sodium alkyl/aryl sulfonate (Cn); AmEn, Alcohol (Cn) Ethoxylated (nEO); DMHEDAB, N,N-Dimethyl-N-(2-hydroxyethyl)-N-Dodecylammonium bromide; SDDS, Sodium dodecyldiphenyl ether disulphonate; SO, Sodium Oleate; TSO, Triethanolamine monooleate ester ; ALEP, Ammonium lauryl ether phosphates; PH, Phosphate surfactant in free acid form (Triton QS44); PH1, Phosphate surfactant in free acid form (Triton QS10); SDPODS, Sodium dodecyl diphenyloxide disulfonate; CFA, Coconut fatty acid; SSSO, Sodium sulfonate sperm oil alcohols; BMF, Nbutyltaurine,methacrylamide, formalin condensate; OIPA, Aerosol OIPA ; PO, Potassium oleate; SSWO, Sodium sulfonate white oil; PM, Potassium myristate; PL, Potassium Laurate; SC, Sodium caprate; SR, Sodium rosinate; SM, Sodium myristrate; SO, Oleic / linoleic sodium salt; MEM-NP10, Aerosol MEM-NP10; SINE, Saponine

417

© 2006 by Taylor & Francis Group, LLC

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The nucleation is homogeneous and the nonionic surfactant repartitions into the aqueous phase to adsorp onto the surface of the particle. The initial number of particles formed in the system is enhanced (as compared to an anionic surfactant used alone at the same concentration or to a nonionic surfactant used alone), but the surfactant is not sufficient to prevent some limited aggregation from taking place as the reaction proceeds. When a mixed emulsifier system is used, the relative high surface area available for adsorption on the particle combined with cooperative adsorption of the two surfactants prevents the occurrence of a secondary nucleation at the disappearance of the monomer droplets (as opposed to the case when the nonionic surfactant is used as the sole emulsifier). Athigh anionic/nonionic surfactant ratio, the initial partitioning of the nonionic surfactant into the oil phase was reduced and the amount present in the aqueous phase allows the formation of mixed anionic/nonionic micelles. The kinetic of the reaction is fast. No secondary nucleation is observed either. Again, the high surface area of the particles prevents the occurrence of a second nucleation when the monomer droplets disappear. In this case, the stability of the system is preserved during the whole course of the polymerization. Results are very much dependent on the specific polymer and conclusion may vary. The same study run on a semibatch polymerization of acrylic monomers using sodium dodecyl sulfate/onylphenoxypolyethoxyethanol EO40 [72] showed that the concentration of the anionic surfactant in the initial reactor charge is the most important parameter in determining particle size and kinetic of reaction. On the other hand, the nonionic surfactant is less effective in nucleating and stabilizing the polymer particles and it only acts as an auxiliary surfactant. In the polymerization of methylmethacrylate with sodium dodecyl sulfate/alkyl ethoxylate alcohol EO18 [73], the aqueous phase polymerization becomes relatively important because of the much higher water solubility of the monomer. Consideration should also be given to the paste formation which occurs during polymerization that creates sticky state network among particles with obvious problems related to latex stabilization. Considerably larger particles are found if the nonionic surfactant is used alone. For the mixed surfactant system, the general trend shows that particle size decreases with the increase in concentration of either anionic or nonionic surfactants and the particle size distribution has a very low index of polydispersity. As we have seen with styrene, the particle number varies with conversion depending whether or not a surfactant is available. Changes in particle number can reveal information about the stability of the latex and the increased water solubility of the monomer does not change the result that the number of particles depends on conversion. Only coagulation may modify the particle number and an increase in the level of surfactant always reduces oscillations. In the case of methyl methacrylate, it seems there is a dynamic equilibrium among particle nucleation, particle growth and particle coagulation that is evident when anionic surfactant or mixed surfactant are used. Interesting results were found in the choice of the optimal surfactant mixture for the synthesis of polyvinylacetate with the sodium dodecyl sulfate / sodium bis(2-ethylhexyl) sulfosuccinate in a continuous process [74]. There was a significant difference in the kinetic mechanism for the mixed and nonmixed surfactant systems. The total number of particles calculated in the mixed systems was three times larger compared to the number of sodium dodecyl sulfate alone, also the average number of active radicals per particle and the desorption rate constant varied. Unpredictably, the molecular weights showed that the branched long-chain nonionic surfactant probably acted as a chain transfer site during polymerization. Strong evidence for this conclusion was drawn when the alkyl sulfosuccinate was part of the surfactant system. Furthermore, the terminal double bond reaction

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and radical transfer to polymer chain were shown to cause especially large polydispersity index on molecular weight distribution. 4. Cationic Surfactants For a number of applications, such as coating of negatively charged surfaces, cationic latexes are required. In the literature, few cases of synthesis of cationic latexes by conventional emulsion polymerization are reported, but usually large latexes are obtained and rather large amounts of surfactant are required [75]. On the other hand, it is known that cationic latexes can be easily produced in a microemulsion based process. The most important class of cationic surfactants is the quaternary ammonium salts substituted with at least one long organic tail, normally a long alkyl chain or alkyl aryl group. Another important class of cationic surfactant is based on one or more heterocyclic ionic moieties, among which pyridinium salts are the most representative. The emulsification properties of these amphiphiles depend strongly on their ionic part and to some extent on the structure and size of the nonionic radical, which can modify the performance of the surfactant. Conventional cationic surfactants do not undergo modification in decomposition kinetics when initiators of opposite charge are used. Instead, cationic polymerizable surfactants and polysoaps are very sensitive to the initiator used [76], although they confer a better latex stabilization by improving its surface tension. Cationic polymer emulsions are well known, even if only manufactured in fairly small quantities. Indeed cationic surfactants can occasionally create some difficulty in production due to the reactive amine or reactive imine groups causing inhibition of polymerization. This is particularly true in polymerizing vinyl acetate or other monomers which hydrolyze readily forming acetaldehyde. The latter tends to react with the amines producing nitrogen derivatives which form stable radicals and inhibit polymerization. They may also react with the initiators, usually a peroxide, thus causing decomposition of amines to the corresponding fatty acid, or oxidation of imines to products with little cationic surfactant properties.When a latex with a positive charge is considered, it is prepared by charge reversal. A negatively charged emulsion is first prepared, or sometimes even an entirely nonionic-type emulsion and the charge is then reversed by carefully adding a cationic surfactant as a solution or a gel, stirring vigorously until the charge is reversed and the product restabilized. Research on new types of cationic surfactants that can improve latex stability without interfering with polymerization are currently under way. New structures having three distinct parts in the following sequence were reported to work in the polymerization of styrene [77]: a positively charged pyridinium ring associated with a negatively charged counter ion, a flexible aliphatic chain, and rigid methoxybiphenyl groups.

III. SUSPENSION POLYMERIZATION Suspension polymerization, otherwise known as granular, bead, or pearl polymerization, is sharply different from emulsion polymerization in several respects. This technique involves the suspension of monomer droplets in an aqueous solution and subsequent polymerization using soluble monomer initiator to give polymer beads. The particle size of the final polymer is very much larger in suspension polymers than it is in emulsion polymers. The potential of this technique to generate high-molecular-weight resins along with the wide choice of solvents available for subsequent formulations has led to its use

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particularly in the manufacturing of solvent-based inks. In some cases, since a true latex is not formed, the suspension polymers can be separated from water by simple filtration and washing. One of the disadvantages of emulsion polymerization is the difficulty in precipitating and separating the polymer from the latex. Very fine precipitates are often obtained which are difficult to be filtered, making the removal of coagulating salts, such as alum and catalyst residues slow, expensive and incomplete. Suspension polymerization is consequently designed to overcome some of these difficulties and to give directly a granular product. The preparation of stable polymer suspensions or dry polymer beads has become very important in the case of vinylacetate and vinylchloride, but also other polymers are manufactured using this technique: methylmethacrylate and copolymers of acrylic and methacrylic acid, styrene, and vinyliden chloride copolymers. Suspension polymerization closely resembles polymerization in bulk, each suspended droplet acting simply as a small homogeneous bulk polymerization system. It is evident that micelle-forming surfactants would not give a true suspension system even if they happened to be poor emulsifying agents. If they can solubilize the monomer, the resulting system would be of the emulsion polymerization type. It is, therefore, not surprising that the micelle-forming surfactants, even though they might aid the stability of the suspension, are not used as the suspending agents in these systems. The preferred suspending agents fall into two classes. These are: 1. 2.

The hydrophilic–organic colloids, such as polyvinyl alcohol, the vegetable gums, the water soluble cellulose derivatives The inorganic suspending agents such as clays, bentonites, and various other finely divided solids

However, traditional surfactants are sometimes added in formulation to provide further stabilization to the suspension of the polymer beads, but their level is very low and commonly below their CMC. For instance, the ethylene oxide-propylene oxide emulsifiers, molecular weight 2500 to 3500, in conjunction with polyvinyl alcohol, increase stability and reduce foaming in polyvinylacetate latexes [78]. Sodium dodecyl sulfate [79] is used as stabilizer together with polyvinylalcohol in the preparation of microspheres of styrene/methylmethacrylate. The need for polymeric microspheres of controlled size with a narrow size distribution via suspension polymerization has grown steadily because they are used in scientific and industrial applications such as chromatographic packing materials, dry and liquid toner for electrophotography, and support for medicines. A typical process for carrying out suspension polymerization is as follows [80]: 1.

2. 3.

The monomer phase, consisting of monomers, initiator and chain transfer agent are suspended in the aqueous phase consisting of water, dispersing agents (such as polyvinyl alcohol, polyacrylate salts, cellulose derivatives or gelatin, etc.) and various salts (e.g., buffer and compounds that stabilize the monomer droplets). The chain transfer agent is added to control molecular weight and its efficiency is dependent on type and amount. The amount of initiator also influences the resin’s final molecular weight. Vigorous controlled stirring of the reaction mixture takes place. Agitation is important to maintain the resin beads in suspension and to determine their size. The reaction is allowed to proceed at temperatures generally around 60 to 85˚ C. Initiation is carried out using a soluble monomer but a water insoluble initiator

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421

with a suitable half-life at the temperature employed. Typical initiators employed include organic peroxides, such as percarbonates, perpivalates, peroctanoates, etc., and azo compounds such as AIBN (2,2'-azo-bis-isobutyronitrile). Agitation is generally increased around the peak exotherm to prevent agglomeration. Following completion of polymerization, stirring is continued while the product is transferred into a holding vessel. Separation, washing, and drying of the beads is then carried out.

IV. MINIEMULSION POLYMERIZATION Since emulsion polymerization is an important process which produces a wide variety of polymer colloids or latexes for direct industrial applications, the interest for one possible use of the similar miniemulsion polymerization has grown considerably. Miniemulsion polymerization has also attracted considerable interest for the versatile nature of miniemulsion itself (Table 6). They are isotropic, optically transparent, or translucent, and, above all, thermodynamically stable. Freshly prepared emulsion may be stabilized but show a slow and progressive growth, whereas a miniemulsion in equilibrium generates constant particle size on a longer time scale. Polymerizations have been carried out mainly in oil-in-water, but also in water-in-oil and bicontinuous emulsion systems [81]. The latter is especially interesting for the production of unpolar monomers in the absence of water. Such a procedure is needed when latexes are to be made from water sensitive monomers (e.g., epoxides, acid chlorides) or the polymerization temperature exceeds 100˚C. In this instance, monomers are miniemulsified in highly polar, organic media and the system becomes the dispersion of an organic monomer in an immiscible organic fluid. High solid content offers numerous advantages for most commercial applications, e.g., low shipping costs and no need to remove water. In practice, the solid content of a latex is limited by its viscosity. For a monodisperse latex the viscosity approaches infinity as the volume fraction of the polymer fraction reaches 0.62. Vice versa, polydisperse latexes show a lower viscosity, because small particles fit within the voids in the array of larger particles. Polydispersity is associated with long nucleation periods that are typical of miniemulsion polymerization. Masa [82] showed that a styrene/2-hexylethylacrylate/ methacrylic acid 34/60/6 at 55% solid content has 4.5 Pas viscosity if produced by conventional emulsion and only 0.7 Pas if made by miniemulsion. This suggest that highly concentrated latexes can be obtained through miniemulsion polymerization. Miniemulsions are relatively stable sub-µm (30 to 500 nm) dispersion of monomer in water prepared by shearing a system containing oil, water, surfactant, and additionally, a “co-surfactant” or hydrophobe. The principle behind the making of a stable miniemulsion is the introduction of a low-molecular-weight and relatively insoluble compound, the hydrophobe, inside the monomer droplets. Fatty alcohols and long-chain alkanes have commonly been used to stabilize miniemulsion. At high emulsifier concentration, the dissociation of the emulsifier ion-pairs is depressed. The presence of nonionized amphiphilic molecules separates the emulsifier ion pairs sufficiently to prevent the repulsion between them that would otherwise occur, and converts the repulsion in the mono layers to an attraction by forming complexes with the emulsifier. A direct microdroplet (a monomer swollen emulsifier/coemulsifier micelle) consists of a spherical organic core surrounded by a monomolecular shell of amphiphilic molecules, whose polar groups are in contact with the continuous aqueous phase. The alkyl groups of emulsifier and cosurfactant are in contact with monomer in the micelle core. Moreover, the presence of the

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Table 6 Miniemulsion Composition Monomer

Surfactant

Co-Surfactant

Emulsion

Sodium lauryl sulfate

Cetyl alcohol

o/w

Styrene

Sodium lauryl sulfate

1-pentanol

o/w

Styrene

Hexadecane

o/w

Vinyl acetate / butyl acrylate

Sodium dodecyl benzene sulfonate Sodium hexadecyl sulfate

Hexadecane

o/w

Methyl methacrylate / styrene

Sodium lauryl sulfate

Cetyl alcohol and Hexadecane

o/w

Styrene / 2-Hydroxyethyl methacrylate Styrene/ 2-Hydroxypropyl methacrylate Vinyl acetate

Sodium dodecyl sulfate

Lauryl methacrylate or Stearyl methacrylate

o/w

Sodium dodecyl sulfate

Hexadecane

o/w

Vinyl acetate

Arkpal N230 / ammonium 8[4(n-nonyl)phenoxy]-(6,3)dioxa-n-octylsulfate

Polyvinylacetate

o/w

© 2006 by Taylor & Francis Group, LLC

J Ugelstad M S El-Aasser J W Vanderhoff Polym Letters Ed 11:503-513 1973 Y T Choi, M S El-Aasser, E D Sudol, J W Vanderhoff, J Polym Sci Polym Chem Ed, 23:2973 1985 K Suzuki A Goto M akayama A Muramatsu M Nomura Macromol Symp 155:199-212 2000 P J MacLeod R Barber P G Odell B Keoshkerin M K Georges Macromol Symp 155:31-38 2000 J Delgado Miniemulsion Copolymerization of Vinyl Acetate and n-Butyl Acrylate Ph.D. Dissertation, Lehigh University 1986 V S Rodriguez, M S El-Aasser, J M Asua, C A Silebi J Polym Sci Polym Chem Ed, 27:3659 1989 C Chorng-Shyan, S Jih-Cheang J Polym Sci: Part A: Polym Chem, 38:3188-3199 2000

I Aizpurua, M J Barandiaran Polymer 40:41054115 1999 I Aizpurua J Amalvy M J Barandiaran J C de la Cal J M Asua Macromol Symp 111:121-131 1996

Polotti

Styrene

Reference

Styrene Acrylamide Butyl acrylate

Sodium dodecyl sulfate

The polymer oligomers after the first reaction step.

o/w

I Capek, V. Juranicova, J Barton, J M Asua K Ito, Polym Int 43.1-7 1997

Sodium dodecyl sulfate Alkyl (C16H33) Alcohol ethoxylated (50 EO) Styrene block copolymer (Sty)10/30 – block – (EO)50/68 Sodium dodecyl sulfate

Oligo-epoxide themselves

o/w

K Landfester F Tiarks, H P Hentze M Antonietti Macromol Chem. Phys 201:1-5 2000

1-butanol

o/w , w/o

J Hao Colloid Polym Sci, 278:150-154 2000

Polystyrene Polymethylmethacr ylate Polybutylacrylate Polyvinylpyridone 4-stearoyloxy2,2,6,6-tetramethyl piperidine-1-oxyl 4-hydroxy-2,2,6,6tetramethyl piperidine-1-oxyl hexanol

o/w

I Capek Polymer J 32:670-675 2000

o/w

I Capek V Juranicova Polym J 32:91-96 2000

o/w

hexadecane

o/w

S S Atik J K Thomas J Am Chem Soc 103:4279 1981 K Landfester N Bechthold F Tiarks M Antonietti Macromolecules 32:2679-2683 1999

Sodium dodecyl sulfate

Sodium dodecyl sulfate

Styrene

Cetyltrimethylammonium bromide Cetyltrimethylammonium Bromide/Terephtalate/Tartrat e Polyethylene oxide (C16C18/EO50)

Styrene

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Butyl acrylate

Surfactant Formulations in Polymerization

Methyl acrylate Ethyl acrylate Butyl acrylate Hexyl acrylate 2-Ethylhexyl acrylate Oligo-epoxide and diammine or dimercaptanes or bisphenols (*)

424

Table 6 Miniemulsion Composition (continued) Monomer Styrene

Hydroxyethylmethacrylate Acrylamide Acrylic Acid Methylmethacrylate/Butylacrylate/ Vinylacetate (35/50/15 molar)

Surfactant

Co-Surfactant

Emulsion

Reference

Sodium Dodecyl Sulfate / Cetyl alcohol pentadecanethoxylate sorbitan monooleate / poly(ethylene-co-butylene)b-polyethylene oxide (Mw = 6600 dalton, 44 wt% EO) ammonium 8-[4(nnonyl)phenoxy]-(6,3)-dioxan-octylsulfate / C16H31-O-(C2H4O)18

formamide / glycol

o/hexadeca ne

K Landfester M Willert M Antonietti Macromol 33:2370-2376 2000

water

w/cyclohex ane

K Landfester M Willert M Antonietti Macromol 33:2370-2376 2000

hexadecane

o/w

M J Unzue J M Asua J Appl Polym Sci 49:81-86 1993

(*) Polyaddition reactions

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co-surfactant substantially delays the diffusion of monomer out of the monomer droplets. The hydrophobe suppresses the mass exchange between the different oil droplets by osmotic forces (the Ostwald ripening effect [83], namely, the diffusion of the oil phase from small to large droplets to minimize the interfacial free energy of the emulsion), but immediately after miniemulsification the dispersion is only critically stabilized in terms of collisions, and the droplets can still increase in size by collision and fusion. A fully stable miniemulsion system can be obtained by collisional growth until the surface tension induced Laplace pressure and the osmotic pressure counterbalance one another. Alternatively, stable systems can be achieved by post stabilization of the primary droplets directly after miniemulsification with an adequate second charge of surfactant. Due to the fact that the polymerization is usually faster than the growth of the droplets by collisions, the polymerization in carefully prepared miniemulsions results in latex particles which have about the same size as the initial droplets. In conventional emulsion polymerization, the principal locus of particle nucleation is the aqueous phase of the monomer swollen micelles depending on the degree of water solubility of the monomers and the amount of surfactant used. However, in miniemulsion polymerization the small size of the monomer droplets enable them to become the principal locus of particle nucleation. The extremely large oil–water interfacial area associated with these droplets requires adsorption of surfactant on the droplet surface to prevent coalescence among the interactive droplets. Furthermore, the size distribution of the homogenized droplets is quite broad and diffusion of monomer from small droplets to large ones may take place to a significant extent. In other words: the appropriate formulation of a miniemulsion suppresses coalescence of droplets and Ostwald ripening, and a situation very close to a 1:1 copying procedure of droplets to particles can be obtained. Recently, Capek [84] used a different definition of the miniemulsion polymerization: transparent and semitransparent emulsions with droplet size between 10 and 60 nm are called microemulsions, whereas sub-µm dispersion with droplet size 100 to 300 nm are called miniemulsions. The distinction is justified by the fact that there are clear difference in the kinetic of the two cases, though in either case the principal locus of particle nucleation is the emulsified monomer droplet. In the former case (microemulsion) the dependence of the rate vs. conversion is described by a curve with a maximum at ca. 20 to 40% conversion and nucleation proceeds to the final conversion. In the latter case (miniemulsion) particle nucleation is somewhat decreased to ca. 30 to 50% and the dependence of the rate vs. conversion is described by a curve with two maxima. Microand miniemulsions exhibit large interface between oil and water and there is no apparent constant rate period in thermally initiated polymerizations. In the formulation of miniemulsions a wide variety of anionic, cationic, and nonionic surfactants can be used in order to get stable polymer dispersions of different size ranges. Up to now, polymerization in miniemulsion processes are exclusively based on water as the dispersion medium. The conventional hydrophobic component such as hexadecane or cetyl alcohol incorporated in the colloidal system, delays the diffusional degradation of the droplets, but this effect may be achieved also with preformed polymers (seeded polymerization) or oleophylic initiators and transfer agents. There is also evidence that the miniemulsion polymerization can be a good strategy to eliminate the oscillatory behavior of continuous stirred tank reactors, even under very unfavorable conditions. In spite of the many advantages of continuous processes, complex dynamics, essentially oscillation mechanisms and multiple steady states, have restricted their practical use. Oscillations produce heterogeneous polymers and make product control difficult. An increase in polymer concentration can cause an increase in molecular weight,

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branching of the polymer and create problems during processing. Furthermore, the sudden decrease in surfactant concentration can produce coagulation of the latex. In addition, the new nucleations create a large number of small particles, thus increasing the viscosity of the system that can reduce stirring and raising heat transfer problems. The oscillatory behavior in classical emulsion polymerization arise as a result of the role of the surfactant in particle nucleation. At the beginning of the process, a large number of small particles are formed, their number being controlled by the amount of the emulsifier available in the system. As the polymer particle grows by polymerization, the free emulsifier concentration falls, depleting the aqueous phase of the emulsifier, as a result of additional surfactant being adsorbed onto the new polymer surface. Therefore, new particles are not formed and, as particles are continuously washed out of the reactor, the number of the particles decreases. After some time, this process counterreacts the increase in size of the particles and the amount of emulsifier increases allowing nucleation of new particles. The cycle then repeats itself. The oscillatory behavior can be avoided by modifying the nucleation mechanism. As was described before, miniemulsion has a different nucleation mechanism than conventional emulsion polymerization. The main difference is that in miniemulsion polymerization, particle nucleation occurs in sub-µm monomer droplets, unlike emulsion polymerization where most of the polymerization takes part in the micelles. Barnette [85] described miniemulsion polymerization of methylmethacrylate that did not exhibit oscillation as does the conventional emulsion process. The same was reported by Aizpurua [86] for the miniemulsion polymerization of vinyl acetate. A drawback of miniemulsion polymerization is that the water-insoluble hydrophobe remains in the polymer particles after polymerization and may have a deleterious effect on the properties of the polymer. However there are already techniques that overcome this problem as in [87]. Hydrophobes are low-molecular-weight compounds that remain in the particles after polymerization, plasticizing the polymer and hence affecting its properties. This effect may be reduced if the hydrophobe becomes covalently bonded to the polymer during polymerization or if a preformed polymer is used as hydrophobe. This may be achieved by using water insoluble macromonomers, initiators or chain transfer agents. Aldicin [88] studied the ability of a series of initiators with different solubilities (lauroyl, benzoyl peroxide, etc.) in the miniemulsion of styrene, obtaining good results only with lauroyl peroxide but with an overall reduction of molecular weight.

V. INVERSE EMULSION POLYMERIZATION Inverse emulsion polymerization is utilized for water-miscible monomers, e.g., sodium pvinylbenzenesulfonate, 2-sulfoethylmetacrylate, acrylamide, cross-linked polyacrylic and methacrylic acids, 2-methacryloyl oxyethyl trimethyl ammonium chloride, etc. Polyacrylamide and its copolymers are the main synthetic water soluble polymers (more than half a million tons per year) and are used in waste and potable water treatment applications as flocculants, as pushing fluids in enhanced oil recovery, and as drag reduction agents in drilling fluids. The inverse emulsion polymerization method provides a versatile route to manufacture and, for the above application, a convenient form for transport and use without the need of dispersing solid polymers in water (Table 7). An additional advantage of inverse emulsion polymerization compared with solution polymerization is that the lower viscosity of emulsion facilitates easier and safer handling of the exotherm. The heat of polymerization of water soluble monomers is very high (20 kcal/Mol of monomer). In addition, the solutions of the polymer in water are very viscous. These features make the solution polymerization process unattractive. Industrial synthesis

© 2006 by Taylor & Francis Group, LLC

Monomer

Surfactat

Solvent

Reference

Acrylamide

Sorbitan monostearate

Benzene

Acrylamide

Sorbitan monostearate or Cetyl or stearyl hydrogen phthalates Sorbitan monooleate or sorbitan monostearate Sorbitan esters

Xylene or perchoroethylene n-hexane Isoparaffine (Isopar M)

US Pat 4,010,131 ; US Pat 4,021,399

Sorbitan monoleate

Isoparaffine (Isopar M)

US Pat 4,070,321

Sorbitan esters, ethoxylated alkanolamides anionic surfactants Fatty alkanolamides /dialkanolamides

Benzene, toluene, xylene

US Pat 3,278,506

Benzene, toluene, isoparaffine; xylene Jet A1 (aviation kerosene) Hydrocarbon

US Pat 5,298,555; US Pat 4,024,097; US Pat 4,672,090

Acrylamide Quaternary modified monomers Acrylamide/vinyl carboxylic acid Acrylamide Acrylamide Acrylamide Acrylamide/N-vinyl lactam/vinyl sulfonic monomers Acrylamide

Glycerol monooleate/ester of diacetyl tartaric acid with mono and diglycerides Sorbitan ester / Sorbitan ester ethoxylated / ABA block copolymer (A=poly 12 hydrostearic acid B= Poly oxyethylene)

© 2006 by Taylor & Francis Group, LLC

US Pat 4,078,133

M T McKechnie Emulsion Polymers 1-3/12 16-17 June Institute of Electrical Engineers London 1982 US Pat 4,906,701; US Pat 5,290,479

EP Pat 854,154

Benzene, toluene, isoparaffine, xylene

US Pat 854,154 427

Acrylamide / 3methacrylamidopropyl trimethylammonium chloride / Octylacrylamide

Sorbitan monoleate 20EO ethoxylate/Sorbitan ester Sorbitan ester/sorbitan ester ethoxylated or sorbitol ethoxylated ester

J W Vanderhoff E B Bradford H L Tarkowski J B Shaffer R M Wiley ACS 34:32-51 1962 US Pat 3,284,393

Surfactant Formulations in Polymerization

Table 7 Inverse Emulsion Composition

428

Table 7 Inverse Emulsion Composition (continued) Monomer

Surfactat Behenyl methacrylate

Solvent

Reference

Vinylbenzene sulfonate

Sorbitan monostearate

Isoparaffine (Isopar M), mineral spirit Benzene

Acrylamide/p-Styrene sulfonic acid Acrylamide

Sorbitan monostearate

Toluene

Polyethoxylated sorbitan sesquioleate/polyethoxylated mono and dialkyl phenols Sorbitan monooleate

Toluene

n-alkane C14-C18

D Benda J Snuparek V Cermark Eur Polym J 33:1345-1352 1987

Ethoxylated/propoxylated ethylene diamine Sorbitan monoleate or ABA block copolymer (A=poly 12 hydrostearic acid B= Poly oxyethylene) ABA block copolymer (A=poly 12 hydrostearic acid B= Poly oxyethylene)/Sorbitan trioleate 20EO/Sorbitan sesquioleate Sorbitan monoleate or ABA block copolymer (A=poly 12 hydrostearic acid B= Poly oxyethylene)

o-Xylene

J W Vanderhoff F V DiStefano MS El-Asser R O’Leary O M Shaffer D L Visioli J of Disper Sci and Tech 5:323-363 1984 J Hernandez-Barajas D J Hunkeler Polymer 38:449-458 1997

Acrylamide/ Ammonium Acrylate Acrylamide Acrylamide

Acrylamide

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V F Kurenkov A S Verizhnikova E V Kuznetsov V A Myagchenkov Int Polym Sci and Tech 9:7 T/65 1982 V F Kurenkov M N TrivonovaV A Myagchenkov Eur Polym J 23:685-688 1987

P Becher N K Clifton J of Colloid Sci 14:519-524 1959

A Renken D Hunkeler Polymer 40:3545-3554 1999

Isoparaffine (Isopar M)

J Hernandez-Barajas D J Hunkeler Polymer 38:449-458 1997

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Acrylamide/trimethylm ethacryloxyethyl ammonium chloride/trimethylacryl oxyethyl ammonium chloride

US Pat 5,721,313

Z Liu B W Brooks J Appl Polym Sci 66:2192-2197 1997

Toluene or n-heptane

Acrylamide

Cetyl trimethyl ammonium bromide

Toluene

Acrylamide/methylene bisacrylamide Acrylamide/Sodium Acrylate Acrylamide/Acrylolylo xyethyl trimethylammonium chloride Acrylamide

Sodium bis(2-ethylhexyl) sulfosuccinate/lauryl 4EO ethoxylated Sorbitan sesquioleate/hexaoleate sorbitol 20EO ethoxylated

n-hexane

Sodium bis(2-ethylhexyl) sulfosuccinate

Toluene

F Candau Y S Leong G Pouyet S Candau J. of Colloid and Interface Sci 101:167-183 1984

Acrylamide

Hexadecanol 2EO ethoxylate/dodecanol 4EO ethoxylate Sorbitan monoleate

Ethane/Propane

Sorbitan monoleate / Alkanolamide /Polyoxyethylene 5 sorbitan monooleate

Mineral oil

E J Beckman J I Fulton D W Matson R D Smith ACS 406:184206 1989 C Mayoux J Dandurand A Ricard C Lacabanne J of Appl Polym Sci 77:2621-2630 2000 EU Pat 1059305

Span 60

Cyclohexane

G Wang M Li X Chen J of Appl Polym Sci 65:789-794 1997

Sodium acrylate N,Ndimethylacrylamide / 2-acrylamido-2-methyl propane sulfonic acid Sodium acrylate © 2006 by Taylor & Francis Group, LLC

Toluene

L W Chen B Z Yang M L Wu Progress in Organic Coatings 31:393-399 1997 A Pross K Platkowski K H Reichert Polym Int 45:22-26 1998 M Lezovic K Ogino H Sato I Capek J Barton Polym Int 46:269274 1998 F Yang C Zheng X Zhai D Zhao J Appl Polym Sci 67:747-754 1998 US Pat 4,021,364 R S Farinato L A Jackson Polymeric Materials, 79:432-433 1983

Heptane

429

Sorbitan sesquioleate/polyethoxylated sorbitan trioleate Monomyristrate ester of pentaerythritol Sodium bis(2-ethylhexyl) sulfosuccinate

Surfactant Formulations in Polymerization

N,N-bis(hydroxyethyl) tall oil amide

Ammonium acrylate/methylene bisacrylamide Acrylamide/methylene bisacrylamide Acrylamide Acrylamide

430

Table 7 Inverse Emulsion Composition (continued) Monomer

Surfactat

Solvent

Acrylic acid/acrylamide

Sorbitan monoleate

n-Hexane

Sodium acrylate / 2acrylamido-2-methyl propane sulfonic acid Acrylamide

Sorbitan monoleate

Iso-Hexadecane

Poly(methyl methacrylate) graft polyoxyethylene (PMMA-g-PEO)

Toluene

Reference S.Kiatkamjornwong P Phunchareon J of Appl Polym Sci 72:1349-1366 1999 EU Pat 1055451

X Zushun Y Changfeng C Shiyuan F Linxian J Appl Polym Sci 79:528-534 2001

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in inverse emulsion typically involves emulsification of an aqueous monomer solution in a nontoxic aliphatic oil, using an emulsifier system with average an HLB between 4 and 7 at 2 to 4% weight of the whole formulation. The ratio of monomer to oil is in the range of 2 to 4:1 with an active polymer content between 25% and 45%. As in traditional polymerization, the reactivity is related to the solubility of the monomer in w/o dispersion. For instance, the oil-soluble monomer styrene in the continuous oil phase in the acrylamide/styrene copolymerization in inverse emulsion points to an effective competition between the monomers in oil phase (where styrene is more abundant) and monomers in the water pools of inverse micelles (enriched in acrylamide). One of the essential problem in the preparation of an inverse emulsion as a medium for the free radical polymerization is the stability of the reacting emulsion before and during polymerization. The mechanism for stabilization is different than in oil-in-water emulsion polymerization since the external medium in not as polar as water. In the conventional oil-in-water polymerization, the electric double layer arising from the use of ionic surfactants provides good protection from coalescence and separation. In water-in-oil emulsion there is no possibility to form an electrical repulsion and the nonionic surfactants used provide only steric stabilization. A method proposed by Barton [89] uses a stepwise addition of water to the macroscopically inverse emulsion toluene/sodium bis(2-ethylhexyl) sulfosuccinate/water/acrylamide to perform preliminary studies of the phase space of stability. In the specific case after several dilution steps we observe the formation of a two phase o/w and w/o emulsions. Obviously, the polymerization in a double phase system can be very dangerous in terms of heat exchange and flowability. The same preliminary study is recommended for for the styrene/acrylamide copolymerization with the same surfactant–oil couple. The choice of the initiator system is one of the key decision concerning the ultimate quality and properties of the polymer since it influences the kinetic mechanism of polymerization. Either water- or oil-soluble initiators can be used. The latter ones are less used but generally form high molecular weight polymers. Suzuki [90] proved that the same polymer can be obtained with a miniemulsion of styrene using either an oil-soluble or a water-soluble initiator. The mechanism of polymerization in inverse emulsions is still insufficiently studied and few quantitative studies have yet been reported [91]. Detailed knowledge of the kinetics of the inverse emulsion polymerization is important for optimal performance of the polymerization as well as for optimal properties of the polymer.When water-soluble monomers are polymerized using oil-soluble initiators and an aromatic solvent as the organic phase, the kinetic profile resembles that of an emulsion polymerization process with the locus of initiation occurring in inverse micelles [92]. However, when the monomers are polymerized in the presence of oil-soluble initiator in the aliphatic oil phase, the kinetic behavior resembles that of a suspension polymerization with the locus of reaction in the monomer droplets. In inverse emulsion polymerization, literature data show kinetic orders for initiator and emulsifier very much dependent of the chemical structure of the species involved: Rp ∝ Np ∝ Ci

0.5-1 •

Ce

0-0.2

(3)

where the lower couple 0.5/0 were found for water-soluble initiators [93] and 1.0/0.2 for the oil-soluble ones [94]. Most studies published have used sorbitan esters of fatty acids, such as sorbitan monoleate, which display a degradative chain transfer resulting in a higher molecular weight and lower polymerization rate. In addition, contrary to many conventional emulsions that remain stable indefinitely, inverse emulsions with these surfactants flocculate quite rapidly and their stability is

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generally poor. Many tests were done using emulsifiers with low and medium HLB depending on the hydrophilic character of the monomer in order to obtain stable w/o emulsions. Usual levels are between 0.5 and 10% by weight and include: sorbitan monooleate [95], ethylene oxide condensates of fatty acid amides [96], hexadecyl sodium phthalate, sorbitan monostearate, cetyl and stearyl sodium phthalate and metal soaps [97], oil-soluble alkanolamide together with unesterified dialkanol fatty amides, quaternized ammonium salts of fatty tertiary amines, salts of fatty tertiary amines, alkaline metal salts of fatty acids and alkyl or alkylaryl sulfates or sulfonates [98], oil-soluble alkanolamide together with a polyoxyethylene derivative of sorbitan ester (e.g., polyoxyethylene sorbitan monooleate), and sorbitan monoleate or monostearate [99]. Currently the best category of surfactants remains the sorbitan family [100]: sorbitan monoleate is widely used due to its good balance between technical performance and price; sorbitan sequioleate is used in few cases, e.g., with some cationic monomers due to better technical performance; sorbitan monolaurate and sorbitan stearate can also be used. In some applications of inverse emulsions polymers, used as thickeners in coloring paste for textile printing or in cosmetic creams, the emulsion needs to be inverted by dilution in water, i.e., it must be transformed from a w/o to an o/w emulsion. To speed up this process and make it as easy and fast as possible some additional surfactants are used in post-addition at the end of the reaction. These surfactants called “inverting agents” are usually common nonionic surfactants with an HLB above 12 such as sorbitan monoleate ethoxylated with 20 ethoxy groups, ricinoleic alcohol ethoxylated with 40 ethoxy groups, sorbitan monolaurate ethoxylated with 20 ethoxy groups, lauryl alcohol ethoxylated with 7 ethoxy groups, alkyl polyglucosides [101], and the nonylphenol ethoxylated. The first step in the inversion process is the swelling of the internal aqueous polymer gel as result of the osmotic pressure gradient between this phase and the bulk water phase to which the inverse emulsion has been added. Finally, when the oil phase can no longer contain the swollen polymer droplets, the polymer is released into the external aqueous phase. Kumar [102] showed a multistage mechanism which proceeds from the water-inoil emulsion through a water-in-oil-in-water particle, to free particles of polymer gel and finally to polymer solution. In the early 1980s, the market introduction of crosslinked polyacrylic acid with superadsorbent properties used in the manufacturing of baby diapers raised the interest for this kind of polymerization. This type of chemicals is particularly attractive for industrial applications, especially as thickeners of coloring paste for textile printing with pigments or reactive dyes [103]. The best control of the reaction kinetics in polymer synthesis is necessary. Parameters such as temperature, cross-linking ratio, stirring speed, pH, and above all the surfactant system need to be under control. The choice of surfactant is indeed crucial to reach the proper conditions under which the inverse suspension is stable. However, the literature does not describe a general reaction and each author presents his own recipe with different alternative solutions [104–107]. Block and graft copolymers are generally found to be the best steric stabilizers. Their amphipathic nature provides an opportunity to construct them in such a way that part of the molecule exhibits affinity for the dispersed phase, while the other part is soluble in the dispersion medium. Maximum stabilizing effectiveness in colloidal dispersions is achieved when the hydrophobic group or anchoring moiety is highly soluble in the continuous phase. A number of researchers have synthesized a variety of interesting polymeric surfactants that can be used as stabilizers in aqueous and organic dispersions [108–111].

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Also for polyacrylamide and its copolymers, higher polymerization rates, higher molecular weights, and superior stability are obtained using polymeric surfactant in comparison with sorbitan esters of fatty acids such as sorbitan monoleate. Industrially the concentration normally used is between 5 and 10% of the oil phase, and 2 to 4% of the overall mixture. Therefore, the use of polymeric surfactants provides higher productivity and superior quality [112] in industrial processes. The combined interest for inverse emulsion polymerization and microemulsion is an obvious breakthrough of recent research in the field. Landfester[113] described the possibility of inverse microemulsion with polar monomer hydroxyethylmethacrylate, acrylamide, or acrylic acid in cyclohexane or hexadecane as the unpolar continuous phase. It was shown that during high shear dispersion a steady state of droplet size is reached and the addition of strong lipophobe is required to stabilize the resulting miniemulsion for sufficient length of the time. With surface tension measurements, the coverage of the particles with surfactant was determined to be incomplete. For these examples the surfactants used were: sorbitan monooleate and a poly(ethylene-co-butylene)-b-polyethylene oxide (Mw = 6600 dalton, 44 wt% EO).

REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25.

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15 Detergent Formulations in Lubricants Tze-Chi Jao and Charles A. Passut

CONTENTS I. II. III.

IV.

V.

Introduction ........................................................................................................... 438 Chemistries of Detergents and Dispersants .......................................................... 439 Types of Metallic Detergents ................................................................................ 439 A. Sulfonates .................................................................................................. 439 B. Phenates..................................................................................................... 442 C. Salicylates.................................................................................................. 442 D. Phosphonates and Thiophosphonates........................................................ 443 E. Other Detergents ....................................................................................... 444 Types of Ashless Dispersants................................................................................ 445 A. Succinimides.............................................................................................. 445 B. Esters ......................................................................................................... 446 C. Oxazolines ................................................................................................. 447 D. Mannich Condensates ............................................................................... 448 E. Graft Ethylene–Propylene Copolymers .................................................... 449 F. Thiophosphonates...................................................................................... 450 G. Other Dispersants ...................................................................................... 450 Solution Behavior of Detergents and Dispersants in Oils ................................... 451 A. Micellar Properties of Sulfonate Detergents in Hydrocarbon Solvents ..................................................................................................... 451 B. Counter Ion Effect on Sulfonate Detergent Micellar Stability ................ 452 C. Thermodynamic Energetics of Micellar Formation Process .................... 452 D. Micellar Properties of Other Metallic Detergents in Hydrocarbon Solvents ..................................................................................................... 453 E. Micellar Properties of Ashless Dispersants .............................................. 453 F. Rigidity of Metallic Detergent Micelles................................................... 454 G. Effect of Overbasing on Micellar Structures............................................ 454 H. Overbasing Mechanism............................................................................. 455 437

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VI.

Action Mechanisms of Metallic Detergents and Ashless Dispersants................. 455 A. Acid–Base Neutralization Mechanisms in Lubricating Oils.................... 455 B. Rate of Alkalinity Depletion in Oils......................................................... 456 C. Peptization Mechanisms to Keep Insoluble Particles in Suspension....... 457 D. Prevention of Varnish and Lacquer Deposition Formation ...................... 458 E. As Friction and Wear Reduction Agents .................................................. 458 F. Solubilization of Polar Species ................................................................. 458 VII. Additive–Additive Interactions ............................................................................. 459 A. Strength and Type of Additive–Additive Interactions .............................. 459 B. Effect of Additive–Additive Interactions on Oxidation Stability............. 460 C. Effect of Additive–Additive Interactions on Antiwear and Anti-EP Performance............................................................................................... 460 D. Effect of Additive–Additive Interactions on High-Temperature Deposit Formation .................................................................................................. 461 VIII. General Formulations Utilizing Detergents and Dispersants in Lubricants ........ 462 A. Use of Detergents and Dispersants in Engine Oil Formulations ............. 462 B. Use of Detergents and Dispersants in Automatic Transmission Fluids and Gear Oils ................................................................................. 464 References ....................................................................................................................... 465

I.

INTRODUCTION

There are a large number of different lubricants in the market. Lubricants today have found their applications in two major areas—automotive and industrial. Major automotive lubricants include engine oils (commonly called crankcase oils), transmission fluids (automatic or manual), hydraulic fluids, and gear oils. Engine oils can be further classified into gasoline engine oils, light-duty and heavy-duty diesel engine oils, railroad diesel engine oils, marine diesel engine oils, natural gas engine oils, aircraft engine oils, and two-cycle engine oils. For industrial applications, in addition to hydraulic fluids and gear oils, the products include metalworking fluids, process oils, turbine oils, circulation oils, compressor oils, and greases. Depending on the application, lubricant formulations can be radically different from one type of lubricant to another. Even within the same lubricant type, the formulations can be quite distinct. For example, gasoline engine oil formulations are significantly different from those of diesel engine oils. The designs for these two types of engines are based on different combustion principles. Gasoline engines are equipped with spark plugs, which initiate combustion while diesel engines are designed to trigger self-ignition with high compression pressure and temperature. These two engines have radically different appetites for fuel. These differences result in different combustion temperatures, pressures, and byproducts. The differences in combustion reaction, power output, and duty cycle for these two classes of engines, requires a different styles of engine oil formulation to provide adequate lubrication. While lubricant formulation compositions can be extremely diverse, they are usually composed from the same set of additive components. They are detergents, dispersants, antiwear agents, antioxidants, extreme pressure additives, rust and corrosion inhibitors, friction modifiers, antifoam agents, demulsifiers, viscosity modifiers, and others. The largest applications of detergents and dispersants are in automotive engine oils.These two

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additives are also used in considerable quantities in transmission fluids, gear oils, and hydraulic fluids.The discussion of detergent formulations in lubricants in this chapter will focus on the uses of detergents and dispersants in automotive applications. In engine oils, both metallic detergents and ashless dispersants are used to keep engine parts clean and thus both are considered detergents in the conventional chemical sense.The different terminology used for these two classes of lubricant additives is for a practical purpose. Metallic detergents are salts of metal soaps, while ashless dispersants are polymeric compounds made without any metal. Like household and cosmetic detergents, they are also surface-active materials, but they are different from the household detergents in one major aspect — they must be oil-soluble. It is estimated that total annual combined global usage of these two detergents alone is approximately 1.5 to 1.8 million metric tons, having a value of 1.5 to 2.0 billion U.S. dollars [1]. Metallic detergents and ashless dispersants are also important additive components in automatic transmission fluids, gear oils, and hydraulic fluids. However, their roles in lubrication are quite different from those in engine oils, because the main oil contaminants are not the same. It is noteworthy that the use of metallic detergents and ashless dispersants in these non-crankcase fluids historically, and even to some extent today, were discovered by extrapolating their use from engine oils.

II. CHEMISTRIES OF DETERGENTS AND DISPERSANTS Like the water-soluble surfactant molecules, the metallic detergent molecule is composed of two parts—a polar head group and a hydrocarbon tail.The polar head group usually consists of an anionic functional group attached by an alkaline earth metal ion, which can be magnesium, calcium, or barium. At present, the most commonly employed alkaline earth metal ion is calcium. Alkaline metal ions, such as sodium, are also used though their applications are limited in crankcase lubricants because of cost/performance factors.The most commonly used functional groups are sulfonates, phenates, salicylates, and phosphonates. The use of barium detergents has been curtailed greatly due to potential toxicity and higher ash content.The hydrocarbon tail, or the oleophilic group, acts as the solubilizer to ensure that the detergent is fully compatible and soluble in base oil.The ashless dispersant, as the name implies, is a non-metallic or ashless cleaning agent. Ashless dispersants like their metallic detergent counterparts, in general, can be considered to have a polar head group and an oleophilic hydrocarbon tail. Besides being nonmetallic, the polar head group of an ashless dispersant is most often made of nitrogen and oxygen atoms.The hydrocarbon tail has a much higher molecular weight than its metallic detergent counterpart.

III. TYPES OF METALLIC DETERGENTS A. Sulfonates There are two types of sulfonates used as lubricant additives. One type is known as natural or petroleum sulfonates and the other is known as synthetic sulfonates.The subject has been extensively reviewed by Colyer and Gergel [2] and SRI International Reports [1]. The petroleum sulfonates are obtained as by-products from the manufacture of white oil. White oil is made by treating mineral oil with oleum or SO3. The reaction

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products contain the white oil and a mixture of sulfonic acids, which are known as mahogany acids because of their reddish color. To separate sulfonic acids from oil, they are converted to sodium salts followed by extraction of the salts with a low molecular weight alcohol solvent, such as methanol, ethanol, or isopropanol. Sodium sulfonates were the starting material for the original petroleum sulfonate lubricating additives [2]. The structure of petroleum sulfonates is quite complex and not well defined [3]. The great majority of petroleum sulfonates used as lubricant additives are alkaline earth metal salts.These salts can be made by either converting sodium sulfonates through a metathesis reaction with a suitable metal chloride or direct neutralization of the mahogany acids with the appropriate metal hydroxide. The general reaction sequence for the conversion of mineral oil to petroleum sulfonic acid is shown below [2]:

Mineral oil

+

Sulfuric acid

→

White oil

+

Sulfonic acid mixture

Sulfonic acid mixture

+

Sodium hydoxide

→

Mahogany acid soaps (oil soluble)

+

Green acid soaps (water soluble)

The source and type of base oils, from which sulfonate detergents are obtained, have an important impact on the performance characteristics of the sulfonates in lubricants. In general, paraffinic base oils are preferred over naphthenic base oils as the source of sulfonic acids [4]. Sulfonates made from naphthenic base stocks were found to be more corrosive to copper–lead bearings and less resistant to oxidation compared with those derived from paraffinic base stocks. Synthetic sulfonates are made from long chain alkyl substituted benzenes. Initially, they were obtained as the by-products from the manufacture of household detergents. Because of the performance advantage, there is a trend toward the use of synthetic sulfonates. Though some petroleum sulfonates are still used today, most of the sulfonate detergents used in lubricants are made from a synthetic route. Many synthetic sulfonates were specifically made from synthesized benzene alkylates. Alkylates can be derived from polymers of ethylene, propylene, and butylene. It is generally considered that at least twelve carbon atoms in at least one of the alkyl groups of a polyalkylated benzene are necessary to make the sulfonate oil soluble. The process of making oil-soluble sulfonic acid from alkylates is considerably different from that of making petroleum sulfonic acid. Both batch and thin film processes have been used to manufacture synthetic sulfonic acids. An efficient batch process was first developed by Anderson and McDonald [5].

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A generalized reaction sequence for the manufacture of synthetic sulfonic acid is shown below [6]:

H

H

H

H Catalyst

Cl + H

R

H H

Alkyl Chloride

R

H + HCl

H

Alkyl Hydrogen Benzene Chloride

Benzene H

H

H

H

H

H O

H + SO3

R H

R

SOH O

H

H

Alkyl Benzene

Sulfur Trioxide

H

Synthetic Sulfonic Acid

R is an aliphatic hydrocarbon radical with 15–30 carbon atoms

Neutral metal petroleum sulfonates were first used commercially during World War II [7,8]. By 1950, techniques had been developed for making basic sulfonates, which contained twice as much metal and which had superior detergency and neutralizing properties. In the early 1950s, it was discovered that substantially more metal could be incorporated into the products in the form of colloidal dispersions of salts, such as carbonates and hydroxides, with corresponding increases in detergency and neutralizing power [9,10]. By the mid-1960s, highly overbased sulfonates incorporating over 10 equivalent bases per equivalent of sulfonic acid had been successfully made [11,12]. These products are known as “overbased,” “hyperbasic,” or “superbasic” and they can be made from petroleum or synthetic sulfonates. The general reaction scheme for the overbasing process of sulfonate is given below [2]:

RSO3H

+

MO or MOH

Sulfonic acid

+

Metal oxide Metal hydoxide

RSO3M

+

xMOH

Neutral sulfonate

Metal hydroxide

 →

Promoter CO2

 →

RSO3M

+

H2O

Neutral sulfonate

+

Water

RSO3M-xMCO3

+

H2O

Overbased sulfonate

Where x of metal hydroxide (M–OH) can vary from 1 to 30.

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B. Phenates Phenate detergents are metal salts of alkyl phenols and substituted alkyl phenols. The alkyl group contains an aliphatic hydrocarbon chain with a carbon atom number between 8 and 30.The substitution can be either methylene or sulfur. The commonly used metal is calcium but magnesium and barium are also used. The use of barium is decreasing because of its potential toxicity and higher ash content. Being a weak acid, alkyl phenol cannot be readily converted into a salt by direct acid-base neutralization. It requires a very reactive basic material, such as calcium carbide [13], elementary alkali metals in finely divided form, or an alcoholate [14]. This is especially true if the molecular weight of the alkyl group is high. The reactivity of alkyl phenol can be enhanced by substitution with methylene or sulfur, which increases its acidity. The methylene substituted phenates can be formed by a condensation reaction between alkyl phenol and formaldehyde [15]. Sulfurized phenates can be obtained by any of the three sulfurization methods using sulfur monochloride, sulfur dichloride, and elemental sulfur. The chemical structures of a generalized alkyl phenol and substituted alkyl phenol are shown below:

OH

OH

OH

H

H

H

CH2

H

H

H

H

H Sy

R

H

R

R x

Alkyl Phenol

Methylene Substituted Alkyl Phenol

Sulfur Substituted Alkyl Phenol

Overbased phenates can be prepared by a similar overbasing process to overbased sulfonates. For example, overbased calcium phenate can be obtained by mixing a neutral calcium phenate with calcium hydroxide in a low viscosity hydrocarbon solvent. CO2 is blown into the heated reaction mixture for a certain period of time using methanol as the promoter. However, commercial processes often prepare overbased phenates using alkyl phenol as the starting material. This is the case for some overbased calcium sulfurized phenates, prepared by blowing CO2 into the heated reaction mixture containing alkyl phenol, elemental sulfur, ethylene glycol, and calcium hydroxide. C. Salicylates Salicylates were developed during the same time phenates were introduced as lubricant detergents. The early salicylates included the zinc salt of di-isopropyl salicylic acid [16] and alkaline earth metal salts of “wax”-substituted hydroxyl-aromatic carboxylic acids [17]. Though the solubility of the zinc salt of di-isopropyl salicylic acid in oils was relatively low because of its short alkyl chains, it became the first known commercial salicylate product used as a lubricant detergent additive. This salicylate has higher thermal

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stability than its longer chain analogs. Due to cost performance consideration this product was eventually replaced by longer chain salicylates. Alkaline earth metal salts of alkylsubstituted salicylic acids are the most commonly used salicylate lubricant detergents. The generalized chemical structure is given below:

OH

O C

O

Ca

R 2

Calcium Alkyl Salicylate (Calcium can be replaced by magnesium or barium.)

Since the carboxylic acid moiety has a stronger acidity than the hydroxyl group in a phenol, it will be converted to the salt preferentially over the hydroxyl group. Salicylates are typically produced by a Kolbe reaction, in which an alkaline salt of alkyl phenol is carboxylated usually under high pressures at elevated temperatures [17,18]. The products can be made by a continuous process [19]. Highly basic salicylates can also be made by an overbasing process [20,21]. Sulfurized salicylates can be made by the Kolbe reaction from sulfurized alkyl phenol or by sulfurization of salicylic acids or their metal salts [22–24]. It has been claimed that sulfurization by sulfur halide is a preferred process over the use of elemental sulfur [23–25]. D. Phosphonates and Thiophosphonates Phosphonates and thiophosphonates were introduced as lubricant detergent additives in 1943 by Loane and others in Standard Oil Company of Indiana [26–29]. Both phosphonates and thiophosphonates are the reaction products of liquid polyolefins such as polyisobutene with phosphorus pentasulfide. The reaction products were found to consist of a mixture of phosphonate, thiophosphonate, and thiopyrophosphonate [30]. The commercial products are generally called either phosphonates or thiophosphonates depending on the extent to which sulfur has been remove by steam treatment and the length of hydrolysis. When the detergent was first introduced into the market, it was supplied as a normal potassium salt. Later, it was changed to a barium salt [31].

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The chemical structures of normal phosphonate, thiophosphonate, and thiopyrophosphonate are shown below:

O

O

O O R

R

P

S

P

O

M

O

O Phosphonate

Thiopyrophosphonate

O

S S

R

R

M

P

P

O M

O

R

M

P O

Thiophosphonates R = polyolefin group

R has a molecular weight (MW) ranging from 500 to 2000. Typically, the alkyl group is a Friedel-Crafts reaction product of isobutylene. Overbased metal salts have been prepared using the same overbasing process for the other detergents such as sulfonates, phenates, and salicylates. The processes developed for production of overbased phosphonates or thiophosphonates include the use of methanol [32] and phenol [33] as the promoter. An overbasing ratio of at least 4:1 has been reported [34]. E. Other Detergents It is noteworthy to mention that normal neutral and overbased detergent, such as calcium sulfonate and overbased calcium sulfonate, is usually derived from one type of organic acid. The inorganic base responsible for the “alkalinity reserve” is usually hydroxide or carbonate of alkaline earth metals. Detergents derived from a mixture of organic acids have recently been reported. Overbased detergents of mixed phenate/sulfonate have been prepared by carbonating phenate in the presence of 5 to 50% sulfonate [35–37]. Incorporating various amounts of sulfonate in the mixed overbased detergents was shown to improve solubility of highly overbased phenate in viscous oils. A small amount of sulfonate was claimed to reduce the tendency of the product to form a skin on exposure to air. Likewise, overbased detergents of mixed phenate/carboxylate with carboxylate as the minor component have also been reported [38]. The incorporation of carboxylate with a hydrocarbon chain of C10 to C24 was claimed to improve the stability of the oil, particularly when the oil was formulated with overbased sulfonates. It also improved foaming tendency. Neutral metal salts of polyalkenylsuccinic acid or anhydride reacted with a polyhydric alcohol or aminoalcohol have been shown to be useful lubricant detergents [39]. The metals used in these detergents include zinc, zirconium, cobalt, and copper. Improved detergency with these detergents has been shown in fully formulated oils containing calcium sulfonate, calcium phenate, zinc dithiophosphate and an acrylic viscosity index improver. Neutral and overbased ortho-carboxyl phenylphenones have been developed [40]. The ortho-carboxyl phenylphenones were obtained by reacting an alkylbenzene, with sufficiently long side chains to give oil solubility, with phthalic anhydride. The acid products were neutralized to form alkaline earth metal salts. A process was also developed to convert the products to highly basic materials.

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Some overbased detergents are made with mixed alkalinity bases. Alkaline earth borate can be incorporated into overbased sulfonate by post-treating overbased sulfonate with boric acid [41-43]. The post treatment with boric acid has been claimed to create a coating of borate anion over the carbonate core [41]. A completely borated overbased sulfonate and salicylate can also be prepared in a one-step reaction [44,45]. Incorporating borate into overbased detergents was claimed to provide antioxidant, antirust, improved frictional characteristics, and extreme pressure qualities to the lubricating oil. It was also claimed to offer better hydrolytic stability than the carbonated overbased counterparts.

IV. TYPES OF ASHLESS DISPERSANTS A. Succinimides Succinimide dipsersants are the most commonly used ashless dispersants in engine oil formulations. The development of the succinimide type of ashless dispersants started in the early 1950s when serious engine sludge lubrication problems were observed. In the early stage of succinimide dispersant development, several groups worked independently and almost simultaneously on similar chemistries. This includes Le Suer and his coworkers [46,47], and Stuart and his coworkers [48]. The basic form of succinimide dispersants is made first by the preparation of a polyisobutenyl succinic anhydride (commonly called as PIBSA) followed by reacting the PIBSA with a polyamine. PIBSA can be made by reacting a chlorinated polyisobutylene with a maleic anhydride or reacting polyisobutylene directly with a maleic anhydride at high temperatures. The generalized structure of succinimide dispersants is given below:

CH3 CH3

C CH3

CH3

CH3 CH2

CH

C CH3

x

C

O CH2

CH

C

CH2

C

N O

CH2CH2NH

H y

It is generally recognized that the useful range of molecular weights for the polyisobutylenes is between 750 and 4000, implying that the number of carbon atoms should be greater than 50. The size of the hydrocarbon group affects both the additive’s oil solubility and its effectiveness as a dispersant. Though higher molecular weight has been shown to be capable of providing significant antifriction and antiwear characteristics in addition to dispersancy [49], too high a molecular weight has produced excessive viscosity thickening in oils. To take advantage of the higher molecular weight benefits and at the same time to minimize the viscosity problem, it has been suggested that a narrow molecular weight distribution, which asymmetrically leans towards higher molecular weights, is preferred [50]. Meinhardt showed that improved dispersancy can be achieved by incorporating at least 1.3 succinic groups for each equivalent weight of the substituent group [51]. Instead of using a dicarboxylic acid as the linkage, monocarboxylic acids, such as acrylic acid, have also been used to link a polyamine with a polyisobutene to create a dispersant of ammonium carboxylate salt [52]. Since the introduction of the succinimide ashless dispersants, modifications have been made to the basic chemistry of succinimides. Le Suer and his coworkers made several

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modifications of succinimides. One modification was to posttreat succinimides with boron compounds to reduce bearing wear and improve dispersancy [53]. Another modification was to react succinimides with carbon disulfide to form either an amide-dithiocarbamic acid:amine salt or an amide-thiourea for applications in diesel engine oils, gear oils, and automatic transmission fluids [54,55]. A third modification was to react succinimides with pentaerithritol or other polyhydric alcohols [56]. Ratner and Bergstrom made the modification to improve antiwear and anticorrosion characteristics of the dispersant by neutralizing succinimides with an organic sulfonic acid to form salts [57]. Similar reactions were employed by Wisotsky to post-treat either succinimide dispersants or borated succinimide dispersants with an oil-soluble strong acid, such as alkaryl sulfonic acid or a dialkyl monoacid phosphate, to improve diesel disperancy [58]. It is believed that the acid reacts with unreacted amino moieties to form an amide. Buckley showed that borated succinimides can be modified by substituting one or more of the nitrogens of the polyamino moiety with a hydrocarbyloxydicarbonyl group or a hydroxyhydrocarbyldicarbonyl group to form some kind of amide ester [59]. Similarly, Wollenberg and his coworkers modified succinimides by reacting one or more of nitrogens of the polyamino moiety with an ethylene carbonate or other carbonates including mono and polycarbonates to create carbamate functionalities [60]. Erdman indicated that the high temperature detergency of succinimides can be improved by reacting with SO2 to form an amido-sulfurous salt [61]. Barbic offered a method to modify succinimide dispersants by reacting with a thiourea or carbon disulfide in the presence of aqueous ammonia or aqueous potassium hydroxide to improve bearing corrosion resistance, dispersancy, oxidative stability, and diesel detergency [62]. Karol showed that modification can be made by post-treating with 1,3,6-hexane tricarboxylic acid or other organic polycarboxylic acid to improve corrosion resistance and dispersancy [63]. Karol further showed that when the nitrogens of the polyamino moiety are capped with glycolic acid or other hydroxyalkylene carboxylic acids the modified succinimide dispersants can inhibit the deterioration of flouro-elastomerengine seals [64]. B. Esters Esters formed from the reaction products of PIBSA and polyols were first shown to be effective as ashless dispersants for engine oils, gear oils, and automatic transmission fluids by Le Suer [65] and Krukziener [66]. They showed that for the ester dispersants to be effective at least three hydroxyl groups per polyol are needed. In applications, pentaerithritol is one of the most commonly used polyols to prepare the ester dispersant. A generalized ester dispersant derived from pentaerithritol is given below:

CH3 CH3

C CH3

CH3

CH3 CH2

CH

C CH3

x

C

O CH2

CH

C

OCH

CH2

C

OCH

O Succinate Dispersant

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C CH2OH C CH2OH

3

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Both ester dispersants and succinimide dispersants are known to promote emulsification in the presence of water. Meinhardt showed that demulsification characteristics can be incorporated into the dispersants by reacting PIBSA with pentaerithritol, polyoxypropylene diamine, and tetraethylene pentamine [67]. Other polyols, polyoxyalkylenes, and polyamines can also be used. Miller indicated that similar demulsification characteristics can also be incorporated into the ester or succinimide dispersants by mixing a certain amount of polyoxyalkylene triol demulsifier during the reaction to make either dispersant [68]. In this example, the polyoxyalkylene triol has an average molecular weight of about 4800 and can be prepared by first reacting propylene oxide with glycerol and then reacting the product with ethylene oxide so that the ethylene oxide is about 18% by weight. Brois and Gutierrez showed that improved oxidative stability and dispersancy can be achieved by first reacting PIBSA with sulfur halide, thiol, or thiolacid to form a thio-bis-(polyalkyl lactone acid) or other thio-bis-(hydrocarbyl substituted diacid materials) and reacting with pentaerithritol or other polyols [69]. C. Oxazolines In addition to the two classes of PIBSA-derived dispersants, succinimides and esters, oxazoline dispersants can also be derived from PIBSAs. Ryer and his coworkers showed that useful dispersants, which have some diesel detergency, can be made by reacting PIBSA with tris-hydroxymethylaminomethane (THAM) at one-to-one mole ratio to form a monooxazoline followed by reaction with either a tetraethylene pentamine or a pentaerithritol [70]. O’Halloran showed that bis-oxazoline, which is the reaction product of PIBSA and tris-(hydroxymethyl)-aminomethane, itself is a dispersant and its oxidative stability can be improved by post-treating with carbon disulfide or sulfide of phosphorus [71]. Oxazoline dispersants resistant to oxidation can also be made by reacting thio-bis-(hydrocarbyl lactone carboxylic acid), which is a product of PIBSA and sulfur halides,with tris(hydroxymethyl)-aminomethane [72]. A thio oxazoline dipsersant has the following structure:

O C CH

O

CH2

HC

CH2

N C

C

CH2OH

O

CHR

CH2OH

CH2 R = C15H3

S CHR HC

CH2

O

CH C

O

CH2 CH2OH

C CH2

C N

CH2OH

O

(Taken from Example 42 in U.S. Patent 4,174,322)

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D. Mannich Condensates This type of dispersant is not based on PIBSA chemistry but is Mannich condensation products of alkyl-substituted phenol with amines. It is believed that the first Mannichbased ashless dispersant used in crankcase motor oils was developed by Verdol [73]. He used p-tert-octylphenol as the alkylphenol to make the Mannich condensation product with tetraethylene pentamine. The dispersant was not effective because the molecular weight of the alkyl group was too low. Like PIBSA based ashless dispersants, in order for the Mannich products to be effective as ashless dispersants, the molecular weights of the alkyl groups must be higher. This was demonstrated by Piasek and his coworkers in the mid-1960s and early 1970s [74–78]. In addition to higher molecular weights for the alkyl groups, suitable amines for the Mannich condensation products must have at least 4 nitrogen atoms per amine molecule. This class of dispersants are commonly called Mannich dispersants. A typical amine used in Mannich dispersants is tetraethylene pentamine. The alkyl groups used are often derived from polypropylene. Boron can also be incorporated into the product as an interaction product with any or all of the polar groups, which include phenolic hydroxy, the secondary amino and primary amino groups. A minimum boron to nitrogen ratio of 0.1 is required to obtain the complete benefits of boration. Mannich dispersant products are likely to be a mixture of tail-to-tail and tail-tohead couplings as illustrated below:

Tail - to - Tail OH

OH CH2

N

A

N CH2 N x

H

H

A

N

x

H

CH2

H

R

R Tail - to - Head

OH

OH CH2

N H

A

N CH2

CH2

x

H

R

N

A

N H n

H

H

R

(Taken from page 9 of U.S. Patent 3,697,574)

Hanson showed that improved high temperature deposit control and diesel detergency can be achieved by modifying the Mannich dispersants using ditertiary alkyl phenol in the Mannich condensation reaction [79]. One potential difference from the unmodified

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Mannich dispersants is that the product could consist of a mixture of molecular formulas given below:

OH

OH CH2

NH

CH2

2

N

CH2

CH2 R

R R

R OH OH R

R

CH2

OH CH2

N

OH CH2

2

R

NH

CH2

R

(Taken from page 6 of U.S. Patent 4,242,212.)

Serres created a different kind of Mannich dispersant using olefin polymer, which has a carbonyl function group, instead of alkyl phenol [80]. The Mannich condensation reaction was believed to be effected through the active acidic protons on carbon atoms alpha to the carbonyl functions in the polymer. It has been shown that dispersants can be made from a phenolic compound without going through a Mannich condensation reaction. An example is provided by Byrant, who showed that a polyamine or a polyol can be incorporated into a phenolic compound through an alpha-beta olefinic carboxylic acid group formed by reacting maleic anhydride with an alpha hydroxyalkyl phenolic compound [81]. E. Graft Ethylene–Propylene Copolymers Ashless dispersants were developed from grafted ethylene-propylene copolymers in the 1970s. Dorer showed that a polyamine can be incorporated into ethylene-propylene copolymers through grafted maleic anhydride [82]. Because of its low graft level, the product was not cost effective. More efficient grafting reactions were later developed by two different groups, Engel and Gardiner [83] and Stambaugh and Galluccio [84], so that a sufficient level of either polyamines or polyols could be incorporated to make the products effective as dispersants. Since ethylene-propylene copolymer can be readily polymerized, dispersants derived from this type of copolymer can have a wide range of molecular weights. This means that the products can be tailor-made as a 5,000 to 15,000 lowmolecular-weight dispersant component or a 30,000 to 100,000 molecular weight multifunctional viscosity modifier. For example, Migdal et al showed that effective dispersant

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additives possessing antioxidant properties with a number average molecular weight between 7,000 and 15,000 can be made from grafted ethylene–propylene copolymers [85]. Likewise, Nalesnik showed that viscosity modifiers incorporated with dispersant and antioxidant functionalities can be made from ethylene–propylene copolymers by a similar process [86]. Both are known as dispersant-antioxidant olefin copolymers (DAOCP). The generalized structure of a DAOCP is given below:

X

X = functional group Functionalized OCP (DAOCP structure)

F. Thiophosphonates This class of ashless dispersants can be prepared by reacting polyisobutene with phosphorus pentasulfide and treated with steam followed by reacting with alkylene oxide (e.g., propylene oxide) in the presence of a catalyst [87]. The reactions are illustrated below:

S PIB + P2S5

Water Treatment

PIB

P

OH

OH

S PIB

P

CH3

S OH + 2PrO

PIB

P

OCH2

CH

OH 2

OH

(Use the reactions shown on page 76 in Colyer and Gergel [2].)

G. Other Dispersants There are several other ways to introduce dispersant functional groups, such as polyamines and polyols, onto polyisobutene polymers other than through PIBSA created from maleic anhydride. A few examples are: Brois used a dimeric thionophosphine sulfide to react with an olefin polymer followed by reaction with a polyamine [88]. Spence showed that polyamines can be incorporated by reacting with a sulfurized polyisobutylene [89]. Lee reacted an olefin polymer with an acetonitrile and chlorine in the presence of iodine as a catalyst, followed by reaction with a polyamine [90]. Miller prepared a dispersant by reacting a polyamine with a halogenated polybutene followed by reaction with propylene oxide [91].

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With the trend toward the use of environmentally-friendly dispersants, several methods have been developed to produce low chlorine dispersants. A low-chlorine dispersant can be made by reacting an olefinic compound with a glyoxylic acid and a basic compound containing a primary or secondary amine group [92]. A chlorine-free polyalkylene succinimide has been made from the reaction of polyisobutenyl succinic anhydride, polymaleic anhydride, and a polyamine [93]. Also, a chlorine-free polymeric amide dispersant can be made by reacting an esterified ethylene-butene-1 copolymer with a polyamine [94]; the copolymer is made by a metallocene chemistry while its ester functionalization employs a Koch reaction involving carbon monoxide and 2,4-dichlorophenol.

V. SOLUTION BEHAVIOR OF DETERGENTS AND DISPERSANTS IN OILS A.

Micellar Properties of Sulfonate Detergents in Hydrocarbon Solvents Metallic detergents are known to form micelles in hydrocarbon media. Micelle formation behavior by metallic sulfonate lubricant detergents in hydrocarbons has been extensively studied by Singleterry and his coworkers at the Naval Research Laboratories [95,96]. The critical micelle concentrations of these lubricant detergents were found to be between 10–7 and 10–6 molar. The aggregation numbers of sodium dinonylnaphthalene sulfonate and barium dinonylnaphthalene sulfonate were determined to be 12 and 7 molecules per micelle, respectively. The aggregation number for barium petroleum sulfonate was found to be 35. They attributed the micelle sizes observed to the balance required between the driving energy provided by the interaction of polar heads through a generalized dipole attraction and/or the formation of specific atom-to-atom coordination and the geometric factor governing the packing of the associated hydrocarbon chains. Peri came to the same conclusion from his investigation of calcium petroleum sulfonate and lead alkylbenzene sulfonate in hydrocarbons by the ultracentrifugation/sedimentation method [97]. Spherical micelles or a probate ellipsoid is considered a more thermodynamically favorable micelle shape than oblate ellipsoid. Later Singleterry and his coworkers [98] proposed an alternate micellization theory to explain the micelle size observed. According to this theory, as the solubility parameter of the solvent increases, the micelles tend to assume a small size. This size reduction gives a looser packing of the sulfonate hydrocarbon tails and, thus, exposes the more interactive aromatic and polar parts in such a way as to reduce the difference between the solubility parameter of the solvent and the effective solubility parameter of the solvent-accessible portions of the micelles. Peri found that the state of dispersion of calcium petroleum sulfonate is relatively stable [97]. This was supported by an observation that no change in viscosity could be detected after one and one-half years for a 5 wt% solution in n-dodecane. He further showed that the micellar size and to a certain extent micellar shape of calcium petroleum sulfonate are a function of concentration and temperature. The micellar shape of zinc alkylbenzene sulfonate was found to be less dependent on concentration. The micellar size of lead alkylbenzene sulfonate in lubricating oil was found to be significantly smaller than in simple hydrocarbons, such as dodecane. Unlike sodium di-(2-ethylhexyl)sulfosuccinate (commonly known as AOT), both calcium petroleum sulfonate and lead alkylbenzene sulfonate were found to have a bimodal distribution of micellar sizes in hydrocarbons, consisting of small micelles and larger aggregates.

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B. Counter Ion Effect on Sulfonate Detergent Micellar Stability Kaufman and Singleterry [99] studied the effect of the cation on micelle formation of sulfonates in benzene using the fluorescence depolarization method. Ten cations studied were: Li, Na, Cs, NH4, Mg, Ca, Ba, Zn, Al, and H. The aggregation number (expressed as acid residues per aggregate) was found to depend slightly on the type of cation and varied between 9 and 14. For the commonly used sulfonate cations; i.e., Na, Mg, Ca, and Ba, the aggregation numbers were found to be around 10 or 11 with the exception of Ba, which gave 14. The aggregation number was rather independent of concentration and almost independent of the water content. This indicates that the size of the dinonylnaphthalene sulfonate micelles depends primarily on the geometry of the acid residue. The apparent volume of the cation was inversely related to the coordinating tendency of the cation, suggesting that coordination forces are a factor in micelle stability. Prolate ellipsoid rather than spherical particle was the preferred micelle shape. The asymmetry as measured by the axial ratio depends inversely on the radius of the cation. Inoue et al. [100] discovered that the relative insensitivity of aggregation number of dinonylnaphthalene sulfonate to influences of cation as reported by Kaufman and Singleterry [99] was due to a trace amount of unsulfonated dinonylnaphthalene interfering with the micelle formation. Studying with highly purified dinonylnaphthalene sulfonates associated with monovalent cations, they found a strong correlation between aggregation number and the reciprocal of e2/rI of cation, where e and rI are the charge and radius of the cation, respectively. They attributed the major driving force for micelle formation to the acid-base interaction between the polar groups. The aggregation number associated with a divalent cation was found to deviate from the simple dependence on acid–base interaction [100,101]. They found that the atomic radius of the cation and compactness of the hydrocarbon group significantly contribute to aggregation number. Thus, the aggregation number of dinonylnaphthalene sulfonate increases in the order of Ba ~ Ca > Mg. In addition to cation effect and compactness of the hydrocarbon group, solute-solvent interactions also contribute significantly to aggregation number [98]. C. Thermodynamic Energetics of Micellar Formation Process A more fundamental approach to investigate the micellar formation process in hydrocarbon media was undertaken by Ruckenstein and Nagarajan [102]. They showed that the largest driving force for aggregation of oil-soluble surfactants in nonaqueous media is dipole–dipole attractive interaction between head groups. Increase in dipole–dipole interaction increases aggregation number. This interaction is countered by the free energy increases due to losses of both rotational and translational freedom of motion by surfactant molecules when they are incorporated into an aggregate. In systems where intermolecular hydrogen bonds or metal coordination bonds exist between surfactant head groups, these bonds can significantly contribute to aggregation. Solvent polarity and steric constraint of the hydrocarbon chains of surfactants participated in aggregation, and cation radius, which affects the distance between point charges of the dipole, influence the dipole–dipole interaction between head groups. The study indicated that unlike aqueous systems, the lack of hydrophobic bonding in nonaqueous systems results in the formation of aggregates with a relative broad range of aggregate sizes and without the existence of a clear critical micelle concentration (CMC). Though both small aggregates and large aggregates coexist, the resulting size distribution is such that under all conditions higher amounts of surfactant molecules are contained within the small aggregates than within the large ones. This may explain the relatively insensitivity of sulfonate micelle size to concentration observed by Kaufman and Singleterry [99].

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Hsu and his group [103,104] studied a low base calcium alkarylsulfonate to determine the conditions, under which the theoretical model derived by Rukenstein and Nagarajan [102] is applicable to a typical commercial alkaline earth alkaryl sulfonate commonly used in lubricants. They found that reversed micelle formation by this surfactant can be adequately accounted for by dipole–dipole attractive interaction, which is the most dominant driving force, and the repulsive force created by the loss of the translational and rotational freedom. The micelle size decreases with increasing of solvent chain length because its solubility parameter, which is a good measure of solvent polarity, increases. The polarity of the solvent has a more dramatic effect on the aggregate size than the solvent chain length. They also found that increasing temperature decreases the aggregate size as expected by the theoretical model. D.

Micellar Properties of Other Metallic Detergents in Hydrocarbon Solvents Inoue and Watanabe [105] showed that salicylates form micelles having an apparent aggregation of 15 to 30 in nonaqueous solutions. The apparent aggregation number increases with a decrease in the solubility parameter of the solvent. Increasing chain length of salicylates lowers the aggregation number. A greater steric effect, due to longer chain length, was considered the main factor for the inverse relationship between chain length and aggregation number. However, they found that micellization of salicylates does not follow the solubility rule entirely. For example, calcium polyisobutylsalicylate has an average chain length of 22 with the chain highly branched. The aggregation number of this surfactant should be smaller than that of linear salicylates derived from α-olefin. Inoue and Watanabe [105] also showed that the dependency of apparent aggregation number on the cations of salicylates is stronger than sulfonates and phenates and the order is Ba > Ca > Mg salts. Such cationic dependency is contrary to the micellization driving force responsible for alkali metal salts of dinonylnaphthalenesulfonates. Aggregation numbers of alkali metals of dinonylnaphthalenesulfonates have a linear relationship with the Coulomb force between the ions. The Coulomb force interaction here is considered by them to be the basis of acid–base interaction between the polar groups in micellar cores. Thus, they believe that the driving force for micellization of ionic surfactants with divalent cations as counter ions is different from that of ionic surfactants with monovalent cations. They also showed that the apparent aggregation number of barium nonylphenate (BaNP) depends on its concentration in various hydrocarbon solvents [105]. Like salicylates, the apparent aggregation number of BaNP decreases with increasing solubility parameter of the solvents though its dependency of aggregation number on solvent polarity is much less than that of metal salts of salicylates. Similarly, the cation dependency of phenates is also not as strong as that of salicylates. The aggregation number of calcium nonylphenate (CaNP) is close but slightly larger than that of BaNP. The apparent aggregation number of CaNP and BaNP is 3 to 8, which is similar to that of the metal salts of dinonylnaphthalenesulfonates. This is not surprising since the size and structure of CaNP and BaNP are analogous to those of dinonylnaphthalenesulfonates. The close resemblance between phenates and sulfonates in aggregation state suggests that the strength of interaction force between polar groups of phenates is close to that of sulfonates. E. Micellar Properties of Ashless Dispersants The question of whether succinimide dispersants can form micelles or not had been a controversial issue in the earlier studies of succinimide dispersants in hydrocarbons. Studies by Fontana and Watanabe indicated that this type of ashless dispersants does not

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form micelles as opposed to metallic detergents [106,107]. It was shown that for succinimide dispersants to be capable of forming micelles a relatively polar species must be present to induce the formation [106]. Other studies suggested that succinimide dispersants do form micelles [101,105,108]. Inoue and Watanabe [105] found that polyisobutenylsuccinimides form micelles having an apparent aggregation number of 2 to 10 in nonaqueous solutions. However, contrary to metallic detergents, longer alkyl chain length increases aggregation number. They found that low molecular-weight succinimides do not form micelles. No explanation could be given for the unexpected aggregation behavior. Like most metallic detergents, succinimides containing a branched-chain in the alkenyl group have a smaller aggregation number than analogs having similar carbon atom numbers in the chain. Bis-succinimides have a smaller aggregation number than the corresponding mono-succinimides, exhibiting clearly the steric effect. F. Rigidity of Metallic Detergent Micelles Inoue used 13C-NMR spin-lattice relaxation times to study the mobility of individual carbon atoms on the surfactant tails of calcium dodecylsalicylate in micelles [109]. He found that the local mobility of carbons of the aromatic ring and the five carbons of the dodecyl group nearest the aromatic ring, which constitute the inner part of the reversed micelle of salicylates, was considerably restricted as in the solid state. In contrast, the local mobility of the remaining carbons of the dodecyl group remained as liquidlike. Jao et al. arrived at the similar conclusions from their fluorescence probe study [110]. G. Effect of Overbasing on Micellar Structures Tricaud et al. [111] studied the micellar structure of alkaline earth metal alkylarylsulfonate detergents by ultracentrifugation. They found a good correlation between TBN and the size of the micelle. Calcium and magnesium overbased detergents were found to be very stable in non-polar solvent, such as isooctane, but the micelle can be permanently destroyed in a polar solvent, such as methanol. Overbased magnesium salts are more difficult to dissolve than calcium salts; their micelle sizes are also significantly larger than those of the overbased calcium salts. Both overbased calcium and magnesium salts appear to have 2 to 3 species of different sizes. Whether these different species are actually of different micelle sizes or of different aggregates formed by association between micelles was not established. Klein’s group [112] has used molecular dynamics to simulate the micelle structure of an overbased calcium alkylbenzenesulfonate. They used 102 calcium carbonate, 11 calcium (2-hexadecyl)benzenesulfonate, and 22 water molecules to simulate an overbased micelle in a nonpolar solvent. The overbasing ratio is approximately 9:1, which is normally expected to provide a 300 TBN calcium sulfonate product. In solution, the micelle is roughly spherical with a total diameter of about 41 Å. The inorganic core, consisting of calcium atoms and carbonate molecules, has a clear boundary. Water molecules are tightly bound to the surface of the inorganic core. The anionic surfactant headgroups are tightly bound to the surface of the polar core and the interactions of the surfactant headgroups with the core are not affected by the nonpolar solvent. The nonpolar parts of the surfactants are, on average, predominantly pointed away from the core with the tails mostly extended into the solvent. Conformational distributions of the hexadecyl chains in solution show that the behavior of the middle parts of the surfactant tails is similar to that in aqueous micelles, while the ends of the chains resemble liquid alkanes. The simulations reveal that approximately 25% of the micelle core surface is exposed to an acetic acid–sized molecule in solution. The micelle has on the average a dipole moment of about 20 daltons.

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H. Overbasing Mechanism The mechanism of incorporating calcium carbonate into the inverted micelles of sulfonate detergents to form overbased micelles deserves some discussion since overbased detergents are an important class of metallic detergents. When overbased detergents were first developed, it was generally assumed that the overbasing process involves the formation of an oil-soluble intermediate between a promoter and hydroxide [113]. The study of sulfonate overbasing mechanism was almost nonexistent until the mid-1980s when Jao and Kreuz [114] investigated two possible mechanisms. One possible mechanism was assumed to involve direct carbonation of macroscopic calcium hydroxide particles. The carbonation process was believed to create a separate phase of small carbonate particles, which are then quickly stabilized by sulfonate surfactant molecules. The second possible sulfonate overbasing mechanism was assumed to have preexisting water-in-oil micelles, which can solubilize hydroxide followed by carbonation. The sequential steps of solubilization of hydroxide into the inverted micelles followed by carbonation can be repeated until all hydroxide is consumed. In both cases, methanol was found to be essential to assist in loosening sulfonate from rigid micelles to allow it either to adsorb onto the carbonation product or to solubilize hydroxide particles. Roman et al. [115] reinvestigated the sulfonate overbasing mechanism and found that the model involving preexisting water-in-oil microemulsion was more realistic. Their study concluded that overbasing mechanism involves pre-existing water-in-oil microemulsion, which is capable of incorporating hydroxide into the inverted micelles. Carbonation occurs inside the micelle and initiates the carbonate particle nucleation. The growth of carbonate particles is achieved by a dynamic exchange with the unnucleated micelles, which provide both the necessary lime and the additional surfactant molecules required to stabilize the colloidal particles.

VI. ACTION MECHANISMS OF METALLIC DETERGENTS AND ASHLESS DISPERSANTS A. Acid–Base Neutralization Mechanisms in Lubricating Oils Two neutralization mechanisms of acids in lubricating oils have been proposed. Hone and his coworkers [116,117] proposed that in lubricating oil the neutralization involves base transfer from the overbased detergent micelle into the acid/water-in-oil microemulsion, where the acid-neutralization reaction occurs. The acid/water-in-oil microemulsion is formed because in an engine excess free surfactant and water are often present, which can lead to microemulsification of the acid/water in the oil. Papadopoulos and his coworkers [118,119] proposed an alternate neutralization mechanism based on their study involving marine cylinder lubricating oils, where much greater amounts of acids and water are expected. The model involves the collision of an overbased detergent micelle on the interface of a large droplet of acid and water in oil. A successful (sticky) collision results in the adsorption of the reverse micelle on the interface followed by the formation of a channel between the reverse micelle and the bulk aqueous phase, through which acid is transferred into the core of the reverse micelle and reacts with the base. The main difference between the two mechanisms is that in the former model the acid neutralization occurs in the oil phase while in the latter model the reaction takes place at the interface. Papadopoulos’s group has also studied the effect of dispersant on the neutralization rate [119]. The presence of 1 wt% of polyisobutylene succinimide dispersant slowed down the neutralization, but further increasing the concentration of the dispersant to 4 wt% had no additional effect. They found that nonionic surfactant produces the opposite effect, instead of decreasing the neutralization rate, it actually increases [120].

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Jao and Passut CaCO3 “dimer” CaCO3 CO2 bubbles

Oil phase H+ Oil phase Acid phase Acid

Acid

Acid phase

Model proposed by Lewis [118]

Model proposed by Papadopoulos et al. [118]

B. Rate of Alkalinity Depletion in Oils The rate of depletion of motor oil alkalinity has been shown by Al’tshuler el al. to follow first-order reaction kinetics [121]. They have further shown that the alkalinity depletion processes of all oil formulations independent of the engines being served by the oils are similar. The depletion processes can be described by a simple equation relating two dimensionless variables as follows: η ≈ exp [- ι ln 2]

Eq. 1

Here η is equal to c 0/c, where c 0 and c are initial and current alkaline additiveconcentrations, and ι is equal to t/T, where t is time and T is the time during which the alkaline additive concentration will drop to half of its original level. Figure 1 (Fig. 1 of the paper by Al’tshuler et al) shows the plot of η vs. ι involving different oils, engine types, and test or service conditions. This relationship allows the calculation of oil alkalinity at any time once the time to one half alkalinity is established.

Dimensionless concn., η

1.0

0.5

0

10 11 12 13 14 15 16 17 18

1 2 3 4 5 6 7 8 9

1

2

19 20 21 22 23 24 25 26 27 28

3

3.5

Dimensionless time, T

Figure 1 Depletion of basicity as a function of time in dimensionless units. (Taken from Fig. 1 of the paper by Al’tshuler et al. Teknol. Topl. Masel, 10, 27–28, 1980.)

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C. Peptization Mechanisms to Keep Insoluble Particles in Suspension Two mechanisms have been proposed by which metallic detergents and ashless dispersantskeep insolubles, like carbonaceous materials or coke generated in the piston ring-belt zone, suspended in the oil medium [122]. One is the steric repulsion effect and the other is the electrostatic repulsion effect. In the case of metallic detergents, steric repulsion is effective in peptizing insoluble particles with a diameter in the range of 20 to 50 Å by forming an adsorbed layer of about 20 to 30 Å thick film, which physically prevents coagulation of these small particles. Succinimide dispersants are in general more effective than sulfonate metallic detergents in peptizing particles. They can peptize larger insoluble particles with a diameter ranging between 20 and 500 Å and form an adsorbed film thickness of about 100 Å. Ashless dispersants effect their peptization mainly through hydrogen bonding. The electrostatic repulsion mechanism can be effective in keeping insoluble particles in suspension if the diameter of the particles is sufficiently large and if the surface of the particles can be electrically charged by ionic salts to form an electrical double layer. For electrostatic repulsion to be effective, the diameter of the particles must be in the range of 5,000 and 15,000 Å [122], because if the diameter of the particles is smaller than 5000 Å, the surface is too small to be sufficiently charged. The electrostatic repulsion mechanism is more viable for metallic detergents than ashless dispersants because the former possesses ionic salt structures to produce the electrical double layer while the latter do not. In principle, if the dispersants can be made as ionic salts, then the electrostatic repulsion effect should be a possible mechanism, by which they effect their dispersancy [122].

. . x

x

. x

. x

.x . x x x x. . .

Steric repulsion

x

.

x. x .

Polar part

Apolar part

Metallic detergent or ashless dipersant

Electrostatic repulsion

(From Zalai, A. Proc. 5th Int. Tribol. Collog., 1986.)

Ashless dispersants are used extensively in gasoline engine oil formulations to control sludge and other insolubles created during engine operation from combustion byproducts. Dispersants are also extensively used in diesel engine formulations to control soot agglomeration. If sludge and soot are not properly dispersed, they can thicken the oil and hinder its proper flow. Steric repulsion is generally known to be the most effective mechanism, by which ashless dispersants keep sludge and soot in suspension. Diraison et al. (123) showed that dispersants such as PIB succinimide, dispersant poly-alkylmethacrylate (or DAPMA), dispersant olefin copolymers (or DOCP), and hydrogenated poly(styrene-butadiene) (or HPSB) prevent soot from agglomeration by a common mechanism, namely by formation of a steric repulsive barrier.

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D. Prevention of Varnish and Lacquer Deposition Formation The main source of varnish and lacquer precursors is the polar oxidation products, which can originate from both polar compounds produced by combustion of fuel through blowby and the lubricant thermal-oxidation degradation process. These polar species can be deactivated by metallic detergents as soon as they are formed through micelle solubilization and neutralization [124,125]. Micellization effectively removes them from bulk oil and prevents them from depositing on critical engine parts, such as piston grooves and skirts. It is noteworthy that succinimide dispersants have been shown to have a similar solubilization capacity to remove varnish or lacquer precursors from the bulk oil medium. Another effective way to prevent varnish and lacquer precursors from depositing on the critical engine parts can be effected by pre-coating a strongly adsorbed film on the surfaces by metallic detergent. Adsorption of sulfonate metallic detergents and succinimide ashless dispersants on metal surfaces has been established by Tamura et al. [126,127]. The adsorption is highly influenced by the presence of polar chemicals in the oils. Metallic detergents can adsorb on both metal surfaces and carbonaceous solids, such as soot and sludge surfaces. The adsorption on the former is considerably stronger than on the latter. This may explain why sulfonates are more effective in metal surface detergency than in the dispersion of carbons or related insoluble particles [127]. E. As Friction and Wear Reduction Agents Shirahama and Hirata found that neutral calcium sulfonate does not offer any significant antiwear protection against valve train wear, but overbased calcium sulfonate and overbased calcium phenate do by the formation of calcium carbonate film at the sliding surface [128]. They also found that ashless dispersants do not provide any significant antiwear protection to the valve train, but borated ashless dispersants show excellent antiwear performance. Increasing the overbasing level of overbased detergents is found to improve their friction reduction capability [129]. The mechanism, by which overbased detergents effect their antifriction action, is to increase the lower temperature limit, above which the primary destruction of the boundary lubricating layers will start, and the maximum temperature, beyond which the additive’s antifriction action is no longer effective. Vipper et al. referred to these two temperatures as Tcr1 and Tcr2, respectively. The two characteristic temperatures (Tcr1 and Tcr2) and the antifriction action of the overbased detergents directly influence the structure of triblolayers formed at the contacted metal surfaces. Effective antifriction action reduces the formation of tribolayers, i.e., thinner tribolayers. F. Solubilization of Polar Species Solubilization is one of the two main mechanisms by which ashless dispersants effect their role in crankcase oils. Contaminants of combustion and polar oxidation products from engine blow-by and oxidation degradation of base oil are potential sludge or varnish precursors that can undergo further reaction to produce insoluble resinous products, which will eventually deposit on engine surfaces in the form of sludge or varnish depending on the local temperatures. Ashless dispersants have been found to be a good solubilizing agent that can prevent the formation of sludge or varnish. Hall proposed that succinimide solubilization is the main mechanism in preventing iron corrosion from sulfuric acid [130]. Since the identification of sludge or varnish precursors as hydroxyl, carbonyl, and other polar groups by Rogers [131] and the inclusion of nitro-nitrate and nitro-alcohol chemical species as potential sludge or varnish precursors by Vineyard and Coran [132], several mechanisms have been proposed to effect the solubilization of sludge or varnish precursors. Watanabe proposed that solubilization of water by succinimide ashless dis-

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persants is effected by hydration of water to amino groups of succinimides [107]. Gallopoulos demonstrated by infrared study that succinimides form hydrogen bonds with alcohols [133]. Ranney found that the bonding with sludge or varnish precursors by succinimides through free amino groups can be achieved by neutralization with carboxylic acids, chemical reaction to form a Schiff base with aldehyde, and hydrogen bonding with alcohols [134]. He also suggested that dipolar interactions and dispersion forces are also important bonding mechanisms. The study of Bell and Groszek showed that neutralization by succinimides is not only effective in solubilizing the carboxylic acid type of sludge precursors but also effective in deactivating them [124]. They found that though both barium sulfonate and succinimides can deactivate carboxylic acids by virtue of their basicity, succinimides are more effective than barium sulfonate because they can cause deactivation of the acid-concentration in excess of the base number of the additive. Later Watanabe attributed this effect as due to ion-pair formation between succinimides and carboxylic acids [107]. The question as to whether the solubilized acid exists as a micellar/microemulsion solution or nonmicellar solution has not been completely answered. Nevertheless, in the case of pyruvic acid it appears to be certain that the solubilized acid by succinimides is in a micellar state [106,135].

VII.

ADDITIVE–ADDITIVE INTERACTIONS

Lubricants are generally made by blending an additive package and a viscosity modifier with a base oil. The effectiveness of the additive package is strongly influenced by additiveadditive interactions. Additive–additive interactions can be both beneficial and detrimental. A. Strength and Type of Additive–Additive Interactions Interactions between metallic detergents and ashless succinimide dispersants, metallic detergents and ZDTPs (Zinc dialkyldithiophospate), and ashless succinimide dispersants and ZDTPs have been studied by Inoue and Watanabe [101]. Strong interactions were found between ashless succinimide dispersants and ZDTP. There are moderate interactions between metallic detergents and ashless succinimide dispersants. It was suggested that the interaction between metallic detergents and ashless succinimide dispersants is acid-base type of the anion of metallic detergents and the amino group of the ashless succinimide dispersant. The order of the strength of interactions is salicylate > sulfonate ~ phenate. The stronger interaction with salicylate is believed to be due to the presence of two, rather than one, acidic polar groups in one salicylate molecule. However, Inoue and Watanabe [101] found no such interaction between metallic detergents and ZDTPs. The proposed interaction between ashless succinimide dispersants and ZDTPs is also acid–base type between the anion of the ionic ZDTP and the amino group of the ashless succinimide dispersants, possibly through N-P bonding. The interaction is so strong that infrared absorption of the complex had been observed by Gallopoulos [136]. Both ashless succinimide dispersants and ZDTPs can adsorb onto iron surfaces. Though both additives can compete for the iron surfaces, ZDTPs form irreversible adsorption while the ashless dispersants form reversible adsorption. The irreversibility of ZDTP adsorption can eventually compete more favorably for the surface. Sodium dinonylnaphthalenesulfonate does not interact with either calcium dinonylnaphthalenesulfonate or calcium dodecylsalicylate [101]. However, it was found that sodium dinonylnaphthalenesulfonate interacts slightly with barium nonylphenate. The lack of interaction between metallic detergents was interpreted to mean that each metallic detergent forms its own micelles, which are dissolved independently in the solution.

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B. Effect of Additive–Additive Interactions on Oxidation Stability Dispersants and detergents are known to interact in oil with ZDTPs [137] and influence their antioxidation performance. The interaction patterns at low temperatures (60°C) can be quite different from those at high temperatures (160°C). Within each temperature region, the interactions are heavily dependent on additive concentrations. Often an optimal level of an additive can be identified while in the presence of known concentrations of a number of fixed additives; for example, succinimide dispersants interact with ZDTP and enhances the antioxidant’s effectiveness in controlling oil oxidation. Hsu et al. [138] investigated the level of antioxidant enhancement dependency on the ZDTP concentration, dispersant concentration and base oil chemical composition. They found that at 1% ZDTP, optimal enhancement is achieved with 3.0% succinimide dispersant, but when 2% ZDTP is present, a slightly higher succinimide dispersant concentration is required to produce the optimal interaction. The base oil chemical composition has a large impact on succinimide dispersant-ZDTP interaction. Highly refined base oil by removing almost all heteroatoms is essentially paraffinic base and offers the most favorable solvent medium for the interaction. Two less-refined base oils from Mideast crudes, one with a high sulfur content (0.35% by weight) 150N and another low sulfur content (0.01%) 110N, reduced succinimide dispersant–ZDTP interaction considerably. Overall, the dispersant improves the oxidation stability of the oil, with the best result obtained in highly refined base oils followed by high sulfur base oils and then by low-sulfur base oils. Since dispersant nitrogen acts as an oxidation inhibitor and base oil sulfur as a radical decomposer antioxidant, Hsu et al. [138] attributed the high ZDTP performance in paraffinic base oils to synergistic binary interactions and the lower performance in the two regular sulfurcontaining base oils to a competitive three-way interaction. The interaction appears to be effected through complexation with the nitrogen atoms of the succinimide dispersant [139,140]. A similar study on the effect of overbased calcium sulfonate-ZDTP interaction on the effectiveness of ZDTP as an antioxidant has been conducted by Hsu et al. [138]. As with dispersants, the most favorable overbased calcium sulfonate–ZDTP interaction occurs in paraffinic base oil, followed by high sulfur regular base oil and then by low-sulfur regular base oil. The sulfonate–ZDTP interaction is very dependent on the ZDTP concentration. At 1% ZDTP, the synergistic effect is restricted to 1% overbased calcium sulfonate. At 2% ZDTP, the optimum broadens to between 1 and 2% sulfonate. At the higher ZDTP concentration, the sensitivity of the interaction toward the pro-oxidant sulfonate is also reduced. When succinimide dispersant is added at a constant concentration of 4% to the systems, the nature of the sulfonate–ZDTP interaction radically changes. At 1% ZDTP, it is clear that the addition of calcium sulfonate to the system deteriorates the oxidation resistance. The synergism between ZDTP and sulfonate disappears. However, when the ZDTP level is raised to 2%, the same trend is only observed in the paraffin base oil. In the two regular base oils, favorable interaction between sulfonate and ZDTP recurs around 1% sulfonate. The synergism is better with high-sulfur base oil than with low-sulfur base oil. C.

Effect of Additive–Additive Interactions on Antiwear and Anti-EP Performance Additive–additive interactions between detergents and antiwear and extreme pressure (EP) additives more often produce antagonism. Since both chemical types are surface active, they both compete for the metal surface. Metal detergents, such as calcium sulfonates, lower the activity of AW/EP additives, such as ZDTP, with neutral sulfonate being the worst offender [141]. More dramatic results have been observed in automatic transmission

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fluid (ATF) formulations where addition of moderate amounts of calcium overbased sulfonate brought about failure in AW and EP tests [142]. It is well known that ashless dispersants, such as succinimides, interfere with the AW properties of ZDTP, a fact that places a concentration restriction on their use in many formulations. The dispersant reduces the reaction rate of ZDTP with the metal surface and also the rate of AW/EP film formation [143]. The mechanism for this antagonism is the formation of ZDTP-dispersant complexes, which have lower adsorptivity than the free ZDTP. The reason for this, it is theorized, is that these complexes are both bulkier and more oil-soluble than the components themselves. Long-chain amines behave in a similar manner and the degree of AW decrease worsens with the degree of complex formation. In fact, any excess amine over the 1:1 ratio is worse owing to added competition for the metal surface [144]. Kapsa et al. [145] found in a plane/plane contact friction machine that calcium sulfonate detergents can interfere with ZDTP in boundary lubrication through three main interactions. The first interaction is an acid/base type reaction, which can effectively reduce the concentration of ZDTP. In the second interaction calcium sulfonate soap produces a “dispersant effect,” which prevents basal materials in the antiwear film formed by ZDTP from agglomeration, effectively changing the colloidal nature of the antiwear film. An overbased calcium sulfonate can effect a third interaction, which alters the interface film chemical composition by incorporating CaCO3 particles. The wear rate increases observed in the presence of calcium sulfonate detergents could be the result of changes in the interface film. Yin et al. [146] studied the effect of detergents and dispersants on antiwear films generated by ZDTP. They found that overbased calcium phanate has a greater effect than neutral calcium sulfonate on the chemical nature of the antiwear film, while PIB succinimide dispersant has the largest effect among the three additives studied. They determined that interaction between detergent or dispersant and ZDTP in oil is responsible for the change in antiwear film chemistry. The interaction competes with the adsorption of ZDTP on the surface. Stronger additive-ZDTP interaction in the oil will result in less ZDTP adsorbed. This in turn will cause a greater percentage of the adsorbed ZDTP to decompose to polyphosphate and a greater percentage of the polyphosphate to react with iron oxide to give a shorter chain phosphate. D.

Effect of Additive–Additive Interactions on High-Temperature Deposit Formation Additive–additive interactions of detergents and dispersants with ZDTPs have been studied by Ramakumar et al. [141]. A synergistic effect between overbased calcium sulfonate and ZDTP was found to reduce high temperature deposit in the panel coker detergency test. ZDTP and the overbased calcium sulfonate detergent alone were found to have greater deposits in the same panel coker test. Similar synergistic effects on deposit reduction was found between the pair of ZDTP and a 200 TBN overbased phenate. The optimal concentrations for the synergistic additive-additive interactions are 0.3 wt%, 1.5 wt%, and 3.0 wt% for ZDTP, overbased calcium sulfonate, and overbased calcium phenate, respectively. However, ZDTP and PIB-succinimide dispersant were found to produce an antagonistic additive-additive interaction, giving a rise in deposition formation. In the case of antiwear performance, the synergism between ZDTP and overbased calcium sulfonate and between ZDTP and overbased calcium phenate was retained. Again, the antagonistic effect on wear performance is present between ZDTP and the PIB-succinimide dispersant; however, the effect is not as large as that with detergents. Studies by infrared indicated the synergism between detergents and ZDTP was not effected by complexation, but rather by some “physical cohesion” between ZDTP and detergent [141]. This was not the case for the interaction between ZDTP and PIB-succin-

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imide dispersant. It was found that the interaction was effected by the N-P bond formation through the amino nitrogen of the PIB-succinimide dispersant and phosphorus of ZDTP.

VIII.

GENERAL FORMULATIONS UTILIZING DETERGENTS AND DISPERSANTS IN LUBRICANTS

A. Use of Detergents and Dispersants in Engine Oil Formulations Detergents as defined (metallic soaps) were used first in crankcase engine oils [147]. These detergents provide a basic environment to reduce lubricant oxidation and to neutralizecombustion by-products [148]. Starting in the 1920s the use of tetraethyl lead as an octane improver required the use of halogen compounds in the gasoline to scavenge the lead. Internal combustion engines with conventional pistons and piston rings permit combustion by-products to enter the crankcase (blow-by) and contaminate the engine oil. In gasoline engines, depending on the fuel used and the efficiency of the combustion process, these products can include organic acids, partially burned fuel, sulfuric and nitric acids, and halogen acids from lead scavengers. These corrosive materials required basic compounds to prevent internal rusting, corrosion and oil oxidation. The by-products of oil oxidation can cause deposits on critical engine parts. Detergents are used to prevent deposition of these materials on those critical parts. In diesel engines the fuels do not contain lead but often contain high levels of sulfur which results in sulfur dioxide in the engine blow-by. This is particularly important in marine diesel engines, where high concentrations of mineral acids are expected [148]. Diesel engine blow-by can quickly neutralize engine oils and promote oxidation of the lubricant. Diesel engine piston rings also operate at higher temperatures and pressures which can lead to carbon deposits. These deposits can be reduced with the use of metallic detergents. In addition, for acid neutralization, overbased detergents are also an important class of antiwear agents in marine cylinder oils. In this case, antiwear is achieved by forming a calcium carbonate protective film. Dispersants, or ashless detergents, were developed to prevent deposits in gasoline engines caused by dirty fuel and the reaction of the partially oxidized fuel with the lubricant [149]. These polymeric sludges are often called “cold sludge” since they occur at low temperatures in stop-and-go driving. These sludges are not well dispersed by the metallic detergents and the higher-molecular-weight ashless materials are required. In diesel engines these ashless dispersants are ideal for suspending soot particles which cause oil thickening and sludge deposits. Soot is the major component of sludge in diesel used oils. The increase of soot contaminant in diesel engine used oils is quite dramatic in the last decade. In the last decade the level of soot increased from around 1% to about 10% [150]. One of the first additives used in crankcase engine oils was zinc dialkyldithiophosphate (ZDDP),an oxidation, corrosion and wear inhibitor. Early crankcase oils often contained only the ZDDP as a corrosion and oxidation inhibitor [149]. ZDDP can give insoluble deposits when it oxidizes and these deposits in combination with oil/fuel oxidation products provide the need for engine oil detergents and dispersants. Early crankcase engine oils contained a combination of three components: (1) ZDDP corrosion, wear and oxidation inhibitor, (2) basic metallic detergent for high temperature deposit and rust prevention, and (3) ashless dispersant to suspend low temperature sludge and soot deposits. The performance levels of crankcase engine oils are defined by a variety of engine and bench performance tests. In the North American market these tests are defined in the ASTM test method D 4485 for both gasoline and diesel engines. The levels of performance are determined by an industry consensus of the Original Equipment Manufacturers (OEMs), the American Petroleum Institute (API), and the American Society of Testing

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Formulations of Crankcase Motor Oils

Additives

Diesel Engine oil

Gasoline Engine Oil

*

Dispersant Detergent Antioxidant Antiwear Rust inhibitor Corrosion inhibitor Friction modifier Seal swell agent PP depressant Antifoamer Vis index improver

= contains; = major component; * for some lubricants

Table 2

Typical Engine Oil Compositions API CH-4 Oil

ILSAC GF-3 Oil

15–18 wt% 7–15 wt%

8.5–11.5 wt% 5–12 wt%

45–60% 20–30% 15–22%

45–60% 13–23% 20–30%

Total Treat Rate

DI package VI improver DI Package

Dispersant Detergent Inhibitor

and Materials (ASTM). Oils which meet the requirements set forth in D 4485 and which have passed the tests following the American Chemical Council (ACC) code of practice can be licensed and certified by the API [151]. As the performance levels of engine oils have increased the number of additives and the complexity of engine oil formulations has also increased, Table I. Typical additive treating levels are shown in Table 2. In modern gasoline crankcase engine oils the primary wear and oxidation inhibitor is still ZDDP. This material has been under pressure to be reduced to limit oil phosphorus, which can poison exhaust catalysts. Both ashless and ashcontaining oxidation inhibitors are added to allow lubricants to be used at higher temperatures. Supplemental phosphorus-free wear inhibitors are used to make up for reduced ZDDP levels. Even though leaded gasoline is not in common use in most industrialized countries, ash-containing detergents are still used to prevent rusting and to provide a basic environment to prevent oxidation. Additionally a variety of friction modifiers are added to the oil to provide reduced fuel consumption. Some of the friction modifiers are metallic detergents such as sodium sulfonates. The largest fraction of the additive performance

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package is the ashless dispersant. These materials range in molecular weight from 900 to 10,000 and contain a variety of head groups containing primarily nitrogen and oxygen. These dispersants are often capped with boron to limit the reactivity of the head groups. The variety of tests required for the current performance levels often require mixing several ashless dispersants in combination with metallic detergents. Modern engines require that parts be maintained in essentially clean condition to work efficiently. These modern additive packages also contain antifoam and supplemental non-detergent rust inhibitors. Often the polymer thickening agents which allow the engine oils to be blended as wide temperature grades (i.e., 5W-30) are also functionalized to become very high molecular weight (100,000) dispersants. These dispersant viscosity modifiers will disperse low temperature sludge and provide improved oil film thickness [152]. Modern diesel crankcase oils also become very complex mixtures to meet the latest diesel oil performance requirements. These requirements are also defined in ASTM D 4485. Since fuel generated soot is a major by-product of diesel combustion the diesel crankcase oils contain very high levels of ashless dispersants (some as high as 10%) to disperse soot. The soot levels in the latest diesel engines equipped with exhaust gas recirculation (EGR) have soot levels which approach 10%(m) in the lubricating oil. At one time it was felt that diesel engine oils should not have dispersants and the soot should be separated from the oil by the oil filter. This separation is not practical with the soot levels of modern engines. It leads to filter plugging and insoluble sludge deposits throughout the engine. Because diesels can have very high cylinder pressures the sealing of the piston rings is critical for engine performance. The deposition of carbon deposits in the ring grooves and on the piston lands (between the ring grooves) can increase oil consumption and cause a loss of power because of ring sticking. These deposits can lead to ring and cylinder scuffing and engine failure. To prevent these deposits diesel engine oils often contain a mixture of metallic detergents and ashless oxidation inhibitors. These detergents may include both low base and high base sulfonates for piston cleanliness and acid neutralization. Phenates and salicylates are also added to provide high temperature detergency in the ring groove area. The diesel engine oils usually contain ZDDP and a variety of antioxidants and supplemental wear and rust inhibitors. Antifoam agents are also used in diesel engine oils. The functionalization of the polymer viscosity thickeners used in diesel engine oils can provide a significant boost in soot dispersancy and also provides improved oil film thickness. This improved oil film thickness can provide improved valve train wear performance in high soot systems. Detergents and dispersants also provide critical performance for a variety of other engine types such as marine and railroad diesels, natural gas engines, and two-stroke cycle gasoline engines. The primary purpose of the detergents and dispersants are the same, to maintain engine cleanliness and to neutralize acids. Marine diesel oils are very high in base number to neutralize the residual fuel sulfur levels. Dispersants used in two-stroke cycle gasoline engines must burn cleanly and prevent port plugging engine deposits. B.

Use of Detergents and Dispersants in Automatic Transmission Fluids and Gear Oils When General Motors introduced the first modern automatic transmission in 1939, the transmission fluid was essentially engine oil. These transmissions contain a fluid coupling and wet clutches which activate planetary gear sets. General Motors Type A fluid, introduced in 1949, was the first fluid to be specifically formulated for automatic transmissions. These fluids now contain ashless dispersants and/or metallic detergents to maintain clean part surfaces. Oil lacquer and sludge deposits can interfere with the movement of precision

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parts and fluids often require a basic environment to limit oil oxidation [153]. Metallic detergents and ashless dispersants can provide modification of the static and dynamic coefficients of friction which are critical to the smooth operation of wet clutches. The use of metallic detergents in automatic and off highway power transmissions provide the ability to adsorb contaminant water and hold it in suspension to prevent rusting. This is critical for preventing hydraulic valve sticking in valve control bodies which have close machine tolerances [154]. The roles of metallic detergents and ashless dispersants in automatic transmission fluids, gear oils, and hydraulic fluids can be quite different from those found in engine oils. Unlike their applications in engine oils, metallic detergents and ashless dispersants are used to both improve frictional characteristics of automatic transmission components and to solubilize polar species and disperse contaminants from oil oxidation. Ashless dispersants and metallic detergents can both increase or decrease the static and dynamic coefficients of friction on wet clutches. The change in friction will be different for different clutch materials [155]. In gear oils, ashless dispersants have been used to prevent deposit on shaft to minimize seal degradation, which can lead to seal leakage. The use of ashless dispersants in gear oils in the industry started in the late 1970s led to the introduction of so-called “clean gear chemistry.” Many of the same engine oil style additives are also used in gear oils with the addition of high levels of extreme pressure agents. A special gear oil is required for use in limited slip differentials which require friction modification [156]. A special balance is required for those gear oils with high levels of active sulfur compounds and metallic soap rust inhibitors to prevent additive interactions.

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117. Hone, D. C., Robinson, B. H., Dteytler, D. C., Glyde, R. W., and Cleverly, J. A. (1999). Acid-Base Chemistry in High-Performance Lubricating Oils. Can. J. Chem., 77 (5/6), 842–848. 118. Wu, R. C., Papadopoulos, K. D., and Campbell, C. B. (1999). Visualization Test for Neutralization of Acids by Marine Cylinder Lubricants. AIChE J. 45 (9), 2011–2017. 119. Wu, R. C., Papadopoulos, K. D., Kyriakos, D., and Campbell, C. B. (2000). Acid-Neutralization of Marine Cylinder Lubricants: Measurements and Effects of Dispersants. AIChE J., 46 (7), 1471–1477. 120. Wu, R. C., Campbell, C. B., and Papadopoulos, K. D. (2000). Acid-Neutralizing of Marine Cylinder Lubricants: Effects of Nonionic Surfactants. Ind. Eng. Chem. Res., 39 (10), 3926–3931. 121. Al’tshuler, M. A., Viper, A. B., Zhurba, A. S., Chermenin, P. P., and Lyubomirskii, A. K. (1980). Kinetic Study and Prediction of Exhausion of Alkaline Properties of Motor Oils. Khim. Teknol. Topl. Masel, No. 10, 27–28 (English translation is available from Plenum). Kinetic Study and Prediction of Exhausion of Alkaline Properties of Motor Oils. 122. Zalai, A. (1986). Effect of Detergent-Dispersant Engine Oil Additives. Proc. 5th Int. Tribol. Colloq., Ostfildern, Germany, pp. 9/4/1–9/4/8. 123. Diraison-Ruot, C., Faure, D., Blanc, G. (2000). Adsorption of Engine Lubricant Dispersants and Polymers onto Carbon Black Particles. SAE SP-1550, pp. 215–223. 124. Bell, G. H. and Groszek, A. J. (1965). A Study of Solubilizing Properties of Detergent Additives by Vapor Concentration and Heat of Adsorption Measurements. ACS Mtg. Preprint Div. Petrol. Chem., 10, D-89–D-102. 125. Inoue, K. and Nose, Y. (1987). Solubization by Sulfonates and Related Phenomena. ASLE Preprint No. 87-AM-3B-3, 1–16. 126. Tamura, K., Tse, J. T., and Adamson, A. W. (1983). Adsorption of Lubricating Oil Additives on Solid Surfaces (Part 2). J. Japan Petrol. Inst., 26 (4), 309–317. 127. Tamura, K., Tse, J. T., and Adamson, A. W. (1984). Adsorption of Lubricating Oil Additives on Solid Surfaces (Part 3). J. Japan Petrol. Inst., 27 (5), 385–391. 128. Shirahama, S. and Hirata, M. (1989). The Effects of Engine Oil Additives on Valve Train Wear. Lubr. Sci., 1 (4), 365–384. 129. Vipper, A. B., Bartz, W., Karaulov, A. K., Mischuk, O. A., and Lukinyuk, M. Yu. (1995). Antifriction Action of Lubricant Additives. Lubr. Sci., 7 (3), 247–259. 130. Hall, K. L. (1969). Iron Corrosion by Sulfuric Acid Solubilized in Oil. ACS Mtg. Preprint Div. Petrol. Chem., 14, A93–A101. 131. Rogers, D. T., Rice, W. W, and Jonach, F. L. (1956). Mechanism of Engine Sludge Formation and Additive Action. Soc. Auto. Eng. Trans., 64, 782–796. 132. Vineyard, B. D. and Coran, A. Y. (1969). Gasoline Engine Deposition: I. Blowby Collection and the Identification of Deposit Precursors. ACS Mtg. Prep. Div. Petrol. Chem., 14, A25–A35. 133. Gallopoulos, N. E. (1967). Hydrogen Bonding between Alcohols and Motor Oil Dispersants. I&EC Product Research and Development, 6 (1), 36-39. 134. Ranney, M. W. (1968). Bonding Mechanisms between Lubricating Oil Dispersants and Polar Solvents. ACS Mtg. Preprint Div. Petrol. Chem., 13 (24), B-83–B90. 135. Bradley, R. V. and Jacock, M. J. (1972). Solubilization of Acids by Succinimide-Type Ashless Dispersants. ACS Mtg. Preprint Div. Petrol. Chem., 17 (4), B101–B110. 136. Gallopoulos, N. E. and Murphy, C. K. (1970). Interactions between a Zinc Dialkylphosphorodithioate and Lubricating Oil Dispersants. ASLE Trans., 14, 1–7. 137. Hsu, S. M. and Lin, R. S. (1983). Interactions of Additives and Lubricating Base Oils. SAE Paper No. 831683. 138. Hsu, S. M., Pei, P., Ku, C. S., Lin, R. S., and Hsu, S. T. (1986). Mechanisms of Additive Effectiveness. 5th Int. Tribol. Coll., pp. 3.4/1–3.4/10. 139. Rounds, F. G. (1978). Additive Interactions and Their Effect on the Performance of a Zinc Dialkyl Dithiophosphate. ASLE Trans., 21 (2), 91–101.

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140. Rounds, F. G. (1981). Some Effects of Amines on Zinc Dialkyldithiophosphate Antiwear Performance as Measured in 4-Ball Wear Tests. ASLE Trans.,. 24 (4), 431–440. 141. Ramakumar, S. S. V., Rao, M. A., Srivastava, S. P. (1992). Studies on Additive-Additive Interactions: Formulation of Crankcase Oils towards Rationalization. Wear, 156, 101–120. 142. Papay, A. G. and Sunne, J. P. (1989). Antiwear Characteristics of Automatic Transmission Fluids. SAE Paper 892157. 143. Barcroft, F. T. and Park, D. (1986). Interactions on Heated Metal Surfaces between Zinc Dialkyldithiophosphates and Other Lubricating Oil Additives. Wear, 108 (3), 13–34. 144. Shiomi, M., Tokashiki, M., Tomizawa, H., and Kuribayashi, T. (1989). Interaction between Zinc Dialkyldithiophosphate and Amine. Lubr. Sci., 1(2), 131–147. 145. Kapsa, P., Martin, J. M., Blanc, C., and Georges, J. M. (1981). Antiwear Mechanism of ZDTP in the Presence of Calcium Sulfonate Detergent. J. Lubr. Technol.: Trans. ASME, 103, 486-496. 146. Yin, Z., Karsrai, M., Bancroft, G. M., Fyfe, K., Colaianni, M. L., and Tan, K. H. (1997). Application of Soft X-Ray Absorption Spectroscopy in Chemical Characterization of Antiwear Films Generated by ZDTP. Part II: The Effect of Detergents and Dispersants. Wear, 202, 192–201. 147. Barwell, F. T. (1986). Lubricant Additives—The History of Their Introduction and Assessment. 5th Int. Tribol. Colloq., pp. 1/1/1–1/1/23. 148. O’Connor, S. P. et al. (1994). Interactions between a Zinc Dialkylphosphorodithioate and a Lubricating Oil Dispersants. Lubr. Sci., 6(4), 297–325. 149. Watson, R. W. and McDonnell T. F. (1984). Additives—The Right Stuff for Engine Oils. SAE Paper No. 841208. 150. Kuo, C. C., Passut, C. A., Jao, T. C., Csontos, A. A. and Howe, J. M. (1998). Wear Mechanism in Cummins M-11 High Soot Diesel Test Engines. SAE Paper No. 981372. 151. Clark, H. C., Johnson, D. M. and Swedberg, S. E. (1984). Modern Engine Oils. SAE 841207. 152. Benfaremo, N. and Liu, C. S. (1990). Crankcase Engine Oil Additives. Lubrication, 76 (1), pp. 8–11. 153. Stanek, J. M. and Smith, D. B. (1968). Considerations in Design of a Type F Automatic Transmission Fluid. SAE Paper No. 680040. 154. Deen, H. E. and Ryer, J. (1984). Automatic Transmission Fluids—Properties and Performance. SAE Paper No. 841214. 155. Rodgers, J. J. and Gallopoulos N. E. 1967. Friction Characteristics of Some Automatic Transmission Fluid Components. ASLE Trans., 10, 102–114. 156. Kostelak, R. L. (1970). Limited Slip Differentials. Lubrication, 56 (4), 56–58.

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16 N-Alkyl Amide Sulfates Hiromoto Mizushima

CONTENTS I. II. III.

Synthesis................................................................................................................ 474 Chemical Stability in Water .................................................................................. 475 Micellar Properties ................................................................................................ 475 A. Critical Micellization Concentration (CMC)............................................ 475 B. Micelle Ionization Degree......................................................................... 478 IV. Krafft Temperature ................................................................................................ 478 V. Basic Properties as Shampoo Detergent............................................................... 479 A. Foaming Capacity ..................................................................................... 479 B. Mildness .................................................................................................... 480 VI. Concluding Remarks ............................................................................................. 481 Acknowledgment ............................................................................................................ 481 References ....................................................................................................................... 481

Environmental awareness has led to the development of the environmentally benign “green surfactants” that show high biodegradability and low aquatic toxicity [1]. Also, there is a growing trend toward surfactants for personal care products that are milder and less irritant than conventional surfactants, because such mild surfactants can help to reduce the visible signs of aging and leave the skin feeling moisturized [2–4]. Accordingly, “green and mild” are the important property for personal care products such as shampoos and body washes. In addition, important characteristics of a shampoo detergent are foaming ability, appropriate detergency, and calcium stability [3, 4]. The foaming capacity of the shampoo detergent does not directly determine the performance, but can affect the consumers’ purchasing decisions [4]. Also, when one applies anionic surfactant in shampoo detergent, precipitation of the calcium salts in hard water decreases the detergency and the foaming ability [5,7]. Much effort has been devoted to developing such effective (highly calcium-tolerant and foaming) but gentle (mild and green) anionic surfactants for the shampoos or body473

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cleansers [2–12]. Amide group incorporated anionic surfactants, e.g., N-acylated amino acids [2], amide ether carboxylate [3,6] or N-alkanoyl amide sulfates [7,13–15], have been known to show many excellent properties including lower irritation to the skin and eyes, as well as the higher biodegradability than similar conventional surfactants. Also, the calcium stability can be improved by the incorporation of an amide linkage into anionic surfactant molecules [10-12]. Therefore, the amide-linked surfactants including the amide-linked sulfate seems to be a promising candidate for an effective, mild, and green shampoo detergent. However, some N-alkanoyl amide sulfates derived from long-chain fatty acids are chemically unstable in water [7,13–15]. For example, the sulfated N-(2-hydroxyethyl)lauramide (n-C11H25CONHCH2CH2OSO3Na; MEAS), an excellent lime soap dispersing agent, has been reported to be easily hydrolyzed in water, and can not be used in shampoo detergents. Despite the practical importance of the amide-linked surfactants, there has not been a systematic detailed study of the chemical structure-property relationships for the amide-incorporated anionic surfactants [7]. With this in mind, we have studied the structure-property relationship of amidelinked sulfates to improve the chemical stability in water, and to find out an excellent shampoo detergent. We designed a new series of N-alkyl amide sulfates CmH2m+1NHCO(CH2)nOSO3Me (n = 1, 3, 5; Me = Na, 0.5Ca), derived from long-chain fatty amines. Although their chemical structures are quite simple, there is no report concerning the N-alkyl amide sulfates without our reports [7,16,17]. In this chapter, the synthesis and some physicochemical properties of the N-alkyl amide sulfates CmH2m+1NHCO(CH2)nOSO3Me (n = 1, 3, 5; Me = Na, 0.5Ca) are described. Relationships were discussed between the chemical structure and the physicochemical properties, such as chemical stability in water, Krafft point, micellar properties, and foaming ability. Among them, sodium N-dodecyl glycolic amide sulfate (m = 12, n = 1, Me = Na) shows excellent properties including high foaming ability even in hard water, as well as complete calcium stability, and has been utilized by the authors as a shampoo detergent since 1996 in Japan. In addition, surprisingly, the kraft point (KP) of the calcium salt (m = 12, n = 1, Me = 0.5Ca) was found to be below 0oC and is lower than that of the sodium salt (25.7oC). This is the first observation that the KP of the divalent salt is lower than that of the monovalent salt having the same surface active anion [7].

I. SYNTHESIS The synthetic sequence for the preparation of N-alkyl amide sulfates, outlined in the following Scheme [7], is CmH2m+1NHCO(CH2)nOSO3Me (abbreviated as m-n-Me). Starting

O HOCH2CO2CH3(1.0 eq.) RNHC-CH2OH O O (1.0 eq.) R-NH2

O

O (1) ClSO3H (1.05 eq.), hexane RNHC-(CH2)nOSO3Me

RNHC-(CH2)3OH (2) NaOH or Ca(OH)2

O O (1.3 eq.)

O RNHC-(CH2)5OH

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from primary fatty amines, amidation reaction with methyl glycolate or with lactones gave the three types of amides, that were sulfated by chlorosulfonic acid to afford the amide sulfates. In the amidation step, methylglycolate and primary amines (n-C12H25NH2, nC14H29NH2, n-C16H33NH2) condensed quantitatively to afford the corresponding N-alkyl glycolic amide at relatively low temperature (100oC) without any catalyst. In addition, the reaction of the amines and γ-butyrolactone (100oC) was almost quantitative, and no undesirable by-products were formed. However, in the reaction with ε-captrolactone (120oC), the desired product (III) further reacted with excess lactone to give a by-product, n-CmH2m+1NHCO(CH2)5OCO(CH2)5OH. The sulfation reactions (30 to 60oC) of amide alkanols were achieved completely using an equimolar or slightly excess amount (1.00 to 1.05 eqiv) of chlorosulfonic acid in hexane, although the reactions were heterogeneous. Neutralization with sodium or calcium hydroxide gave the corresponding sodium or calcium sulfates in excellent yield. Sodium salts of N-alkyl amide sulfates were typically prepared as follows: the selected N-alky amide alkanol (0.121 Mol) was suspended in hexane (500 ml) at room temperature with vigorous stirring. Chlorosulfonic acid (0.127 Mol) was added dropwise to the slurry at room temperature. The mixture was then heated at 60oC for 3 hours to remove HCl by introducing nitrogen. After completion of the reaction, the mixture was cooled to 30oC and neutralized with sodium hydroxide (1.52 Mol). The aqueous layer was separated and concentrated in vacuo. If necessary, the residual solid was purified by recrystallizations from a mixture of 2-propanol and water or from water. Similarly, the calcium salts were typically prepared as follows: after completion of the sulfation reaction of the N-alkyl amide alkanol (0.184 Mol), the reaction mixture was cooled to 5oC and added to a mixture of ice water (200 g) and 2-propanol (150 ml). The aqueous layer was separated and neutralized with calcium hydroxide (0.195 Mol) at 5 to 10oC. Excess calcium hydroxide was filtered off, and the resulting solution was evaporated. The residue was crystallized from a mixture of 2-propanol and water or from water.

II. CHEMICAL STABILITY IN WATER Prior to the industrial utilization of surfactants, it is essential to examine their chemical stability in water. As described previously, some classical N-alkanoyl amide sulfates, such as the sulfated N-(2-hydroxyethyl)lauramide (MEAS), structurally related to the present N-alkyl amide sulfates, are easily hydrolyzed in water [14]. Therefore, chemical stability in water was examined of the sodium N-dodecyl amide sulfates (12-1-Na, 12-3-Na, and 12-5-Na). As shown in Fig. 1, for MEAS and 12-3-Na, the surfactant concentrations decreased markedly after 7 days at 50oC, while the concentrations of 12-1-Na and 12-5Na did not change. The HPLC and 1H-NMR analyses suggested the hydrolysis pathway via five-membered ring [7]. However, 12-1-Na and 12-5-Na were apparently stable in water, and can be used for shampoo detergents. The spacer chain length (n), connecting the amide and sulfate groups, exerted an influence on the chemical stability of N-alkyl amide sulfates in water.

III. MICELLAR PROPERTIES A. Critical Micellization Concentration (CMC). The CMCs of N-alkyl amide sulfates, determined by the electrical conductivity method, are presented in Table 1. For the sake of a comparison, the data for n-dodecyl sulfate and

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25 12-1-Na (Surfactant), wt%

20 12-5-Na 15 HN

10

O

HN

12-3-Na

O

5

O HN

OSO3Na OSO3Na OSO3Na MEAS

12-1-Na 12-3-Na MEAS

0 0

10

20

30

Day

Figure 1 Chemical stability of surfactants at 50oC in pH 7.0 phosphate buffer: 12-1-Na (filled circle); 12-3-Na (open triangle); 12-5-Na (open circle); MEAS (filled triangle). (Reprinted with permission from Langmuir 1999, 15, 6664–6670. Copyright 1999 American Chemical Society.)

Table 1

Micellar Properties of Sodium Salts

Surfactant

CMC, mM

α

Temp, °C

n-C12H25NHCOCH2OSO3Na n-C12H25NHCO(CH2)3OSO3Na n-C12H25NHCO(CH2)3OSO3Na n-C12H25OSO3Na n-C12H25COH2CH2OSO3Na

5.2 4.4 3.1 8.3a 4.8a

0.50 0.53 0.66 0.25a 0.32a

35 35 35 35 35

a

From Barry, B.W. and Wilson, R. Collid Polym Sci 256:251, 1978.

n-dodecyloxyethyl sulfate are also presented. The CMC of 12-1-Na (5.2 mmol) at 35oC is smaller than that of sodium sulfate (8.3 mmol), and is nearly equal to that of sodium dodecyloxyethyl sulfate (4.8 mmol). Thus, the introduction of the amide group is seen to decrease the CMC. The CMC depression by introducing amide group has been explained as follows: counterions are not only located on the surface of the micelle but also distributed within a hydrophilic layer consisting of amide groups, spacer methylene chains, sulfate headgroups [7,8]. This results in a decreased electrical potential at the micelle surface and in a decreased solubility of surfactants. Moreover, a linear relationship was found between the log CMC vs. the hydrocarbon chain length (m) of the m-1-Na series and also between the log CMC vs. the spacer chain length (n) of the 12-n-Na homologues at 50oC (see Fig. 2). Empirically, the plots of the logarithm of CMC vs. the hydrocarbon chain length are known to exhibit linear relationships for many ionic surfactant homologues [18–20]. The linear relationship obey the equation: log CMC = A – BN, where N is the hydrocarbon chain length. A and B are constants which depend on the hydrophilic group and the energy transfer of a methylene group from the aqueous to the hydrocarbon phase, respectively [18]. The value of B for m-1-Na amide sulfates (0.32) agrees well with those of CmH2m+1OSO3Na (0.28), and of CmH2m+1OCH2 CH2OCH2CH2OSO3Na (0.29). However,

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1

log CMC

−2

477

n 3

5 12-n-Na

−3 m-1-Na

−4 10

12

14 m

16

18

Figure 2 Plots of log CMC vs. hydrocarbon chain length (m, n) of the 12-n-Na homologues (open circles) and the m-1-Na series (filled circles).

Table 2 Values of Constants A and B, and Free Energy Contribution per Methylene Group Toward Micellization (Φ) of Surfactant Homologues Type of Surfant CmH2m+1NHCOCH2OSO3Na C12H25NHCO(CH2)nOSO3Na CmH2m+1COO(CH2)3SO3Naa C9H19 COO(CH2)nSO3Naa a

A

B

Φ, cal mol -1

Temp, °C

1.63 — 1.78 —

0.32 0.08 0.29 0.15

473 118 420 211

50 50 40 40

From Hikots, T. and Meguro, K. J Am Oil Chem Soc 47:197, 1970.

Source: From Langmuir 1999, 15, 6664–6670. Copyright 1999 American Chemical Society. With permission.

for the 12-n-Na homologues, the constant B is only 0.08. Thus, the ratio of reduction in log CMC for m to n, is just 4:1. Also, the data for CMC as a function of chain length can conveniently be used to determine the Gibbs energy contribution of –CH2- groups toward micellization (Φ) [21]. The Φ value of 473 cal/mol for m-1-Na homologues is comparable to that (418 to 427 cal/mol) reported for sodium alkyl sulfates. On the other hand, Meguro studied the effect of the position of the ester group on CMCs for ester-linked sulfonates, and found the relation of log CMC = –0.147N + 0.011 at 40oC for C9H19COO(CH2)nSO3Na homologues, where n = 2 to 4 [22]. The B value for the spacer methylene chains connecting the ester and sulfonate head group is 0.147 (see Table 2), which is about twice of that (0.08) for the C12H25NHCO(CH2)nOSO3Na series, although there is no large difference in B value with the hydrocarbon chain between CmH2m+1NHCOCH2OSO3Na and CmH2m+1COO(CH2) 3SO3Na homologues (see Table 2). This implies that the spacer chain in the amide-linked sulfates is less hydrophobic than that in the ester surfactants. An amide linkage, recognized as a strong hydrophilic group, was thus shown to decrease

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the hydrophobicity of the spacer methylene chain more strongly than an ester group, when it is incorporated into anionic surfactants [7]. B. Micelle Ionization Degree The micelle ionization degrees α, for the 12-n-Na amide sulfates were found to be extremely larger (e.g., 0.50 for 12-1-Na at 35oC) than that (0.25 at 35oC) for sodium dodecyl sulfate (see Table 1). It must be recalled that for conventional single chain surfactants with about 12 carbon atoms in the hydrocarbon chain, α is usually around 0.20-0.25 [23–26]. An increase in α is also seen for n-C12H25(OCH2CH2)nOSO3Na series (0.25 for n = 0, 0.32 for n = 1, and 0.37 for n = 2 at 35oC), although the degree of the increase is smaller than that of the amide sulfate homologues [18]. For some dimeric or gemini surfactants having long spacer methylene chains, extremely large values of α were observed [27,28]. The head group repulsion of the gemini surfactant molecules within the micelle is small, due to the existence of the long spacer, keeping the headgroups far apart from each other. Thus, for the 12-n-Na amide sulfates, the large micelle ionization value clearly suggests the surface charge density of the micelles is low. This may be due to the attractive interaction between the head groups including the amide group of surfactant molecules [7].

IV. KRAFFT TEMPERATURE The Krafft temperatures and the transition enthalpies, determined by differential scanning calorimetry, are shown in Table 3. The introduction of the amide group along with the spacer methylene chain into surfactant molecules was found to increase the KPs, except for the m-1-0.5Ca homologues, although the incorporation of an oxyethylene chain depresses the KPs. The KP is related to the monomer solubility in the presence of hydrated surfactant crystals [29]. The addition of a hydrophilic group such as a hydroxyl group or an oxyethylene chain will increase the monomer solubility and depress the KP. The decrease in the CMC or in the monomer solubility, and increased KP by the introduction of the amide group should be attributed to stabilization in the hydrated solid state [7]. Also, the most striking and interesting feature of Table 3 is that the KPs of the m-10.5Ca amide sulfates are lower than those for the corresponding sodium counterparts. To our best knowledge, this is the first observation that the Krafft temperature of the divalent salt is lower than that of the univalent salt having the same surface active anion. The KP of anionic surfactants is strongly affected by the type of counterions. If the counterion is strongly hydrated, such as Li+, the surfactants exhibit substantially lower KPs. On the other hand, the increase in valency of counterion generally results in higher KPs. The KPs of divalent salts of conventional anionic surfactants have always been found at higher temperatures than those of the corresponding univalent salts [7,8,30,31]. The KPs of calcium alkyl sulfates are significantly depressed by introducing an oxyethylene chain. However, the KPs of the calcium salts are still higher than those of the sodium salts (see Table 3). In a comparison of the Krafft temperature and the phase transition enthalpy (∆H) for the sodium salts and those of the calcium salts, the higher Krafft temperature is always accompanied by the larger ∆H (see Table 3). The ∆H values of sodium alkyl sulfates are smaller than those for the corresponding calcium salts, and the KPs of the sodium salts are lower than those of the calcium salts. Similar trend were also observed for the m-3Me and m-5-Me amide sulfates. However, larger ∆H values were founded for the m-1-Na amide sulfates than those of the calcium salts. The KP of these anionic surfactants seems to be mainly reflected by the hydrated crystalline state, e.g., the packing [20,29]. The entropy of dissolution (∆S/J mol–1 deg–1)

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Table 3 Krafft Points and Enthalpies of Dissolution of Hydrated Solid Surfactants Surfactants

12-1-Na 12-1-0.5Ca 14-1-NA 14-1-0.5Ca 16-1-Na 16-1-0.5Ca 12-3-Na 12-3-0.5Ca 12-5-Na 12-5-0.5Ca C12H25OSO3Na C12H25OSO30.5Ca C12H25OCH2CH2OSO3Na C12H25OCH2CH2OSO30.5Ca

Krafft Point, °C

DH, KJ mol-1

25.7 below 0 35.8 22.7 47.1 42.3 19.2 55.3 40.9 65.5 9a 50a 5a 15a

85.7 — 63.4 19.5 43.3 23.4 46.7 64.1 49.5 68.8 50a 75a 39.3b 89.4b

a

From Hato, M. and Shinoda, K. J Phys Chem 77:378, 1973.

b

From Tsujii, K. et al. J Phys Chem 84:1842, 1977.

for the 14-1-Me surfactants was calculated from the equation: ∆S= ∆H/T, where T is the Krafft temperature. The entropy value for 14-1-0.5Ca is 65.9 J mol–1 deg-1 and is smaller than that (205.2 J mol–1 deg–1 ) of 14-1-Na. This strongly suggests that the lower KP of m-1-0.5Ca surfactants, compared to those for the corresponding sodium sulfates, would be attributed to the disordered hydrated crystalline state [7]. Moreover, linear relationships between the KP and the hydrocarbon chain length (m) were observed for both the sodium and the calcium salts of m-1-Me amide sulfates (Fig. 3). Empirically, the plots of the KP vs. hydrocarbon chain length are known to exhibit linear relationships for many kinds of ionic surfactant homologues with the same kind of counterion. The linear relationship obey the following equation : KP = Kc N – Ki, where N is the hydrocarbon chain length [20]. Ki is a constant depending on the ionic headgroup, and Kc is a constant mainly depending on the counterion valency. For many anionic surfactants, the Kc value for Ca salt is 11.0 and is twice that (5.5) of the corresponding sodium salts [20]. The Kc value was found to be 5.4 for the sodium salts and 10.6 for the calcium salts; these are nearly equal to those of alkyl sulfates. Thus, the trends in the KP vs. the hydrocarbon chain length (m) for the m-1-Me amide sulfates were consistent with those for the conventional anionic surfactants such as alkyl sulfates.

V. BASIC PROPERTIES AS SHAMPOO DETERGENT A. Foaming Capacity Foaming is an essential quality feature of shampoos which affects purchasing decisions of consumers. Both the foam height and the foam stability of 12-m-Na amide sulfates were studied by essentially the same procedure to the Ross-Miles method [16]. Each

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Krafft Point (°C)

40 Na salt

30 20

Ca salt

10 0 below 0°C

−10 10

12

14

16

18

Hydrocarbon Chain length (m)

Figure 3 Plots of Krafft point vs. hydrocarbon chain length (m) of the m-1-Me surfactants. The open circle is of the sodium salts, and the filled circle the calcium salts. (From Langmuir 1999, 15, 6664–6670. Copyright 1999 American Chemical Society. With permisssion.)

Table 4

Foaming Properties of Surfactants Foam Volume (mL) Surfactant

n-C12H25NHCOCH2OSO3Na n-C12H25NHCO(CH2)5OSO3Na n-C12H25O(CH2CH2)3.0OSO3Na

After 10 sec 190 170 170

After 120 sec 168 95 90

Source: U.S. Patent 5599483, Kao Corporation, 1997.

surfactant solution (0.1%) containing 0.3% of lanolin was prepared by using 4od hard water at 40oC. The surfactant solution was stirred by the reversing stirring technique at 1450 rpm for 6 minutes. The volume of foam formed that remained was measured 10 and 120 seconds after the termination of the stirring. The 12-1-Na amide sulfate showed favorable foaming performance (see Table 4), i.e., higher foaming ability and stability than those of sodium lauryl ether sulfate (SLES). Increasing the spacer methylene chain of the amide sulfate (from 12-1-Na to 12-5-Na) resulted in extensive decrease in the foaming capacity, especially the foam stability. B. Mildness N-Alkyl amide sulfates have been shown to be mild surfactants and less irritating than conventional shampoo detergents such as sodium dodecyl sulfate (SDS) [16]. The quadruple cumulative skin irritation test was carried out by employing guinea pigs. Aqueous solution containing 10% of surfactant was applied to the healthy skin of five guinea pigs four times. The reaction of the skin after fourth application of the aqueous solution was evaluated according to the criteria shown in Table 5. Table 5 shows a comparison of Ndodecyl amide sulfates to sodium dodecyl sulfate (SDS). As can be seen, 12-1-Na and 125-NH4 amide sulfates were less irritating as compared to SDS.

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N-Alkyl Amide Sulfates Table 5

481

Quadruple Cumulative Irritation of Surfactants Surfactant

Average irritation score

n-C12H25NHCOCH2OSO3Na n-C12H25NHCO(CH2)5OSO3NH4 n-C12H25OSO3Na

0.5 0.2 2.6

Evaluation criteria: 0, no reaction; 1, slight erythema; 2, clear erythema; 3, clear erythema accompanied by edema; 4, clear erythema accompanied by necrosis or asphyxia observed. Source: U.S. Patent 5599483, Kao Corporation, 1997.

VI. CONCLUDING REMARKS To develop a highly calcium tolerant, foaming, mild, and green anionic surfactants for the shampoos or body cleansers, chemical structure and physicochemical property relationships were studied for a new series of N-alkyl amide sulfates. The inclusion of an amide linkage in sodium alkyl sulfates results in a decrease in the CMC value and in a marked increase in the micelle ionization degree. From the comparison with the effect of the methylene chain length on CMC and Gibbs energy contribution toward micellization, part of the spacer methylene chain was suggested to behave like a hydrophilic group. A large depression in the KP was observed for the CmH2m+1NHCOCH2OSO3 0.5Ca homologues. Moreover, the Krafft point of C12H25NHCOCH2OSO3 0.5Ca (12-1-0.5Ca) was found to be below 0oC and is lower than that (25.6oC) of C12H25NHCOCH2OSO3 Na (12-1-Na). The 12-1-0.5Ca amide sulfate has a lower CMC (1.4 mmol at 25oC) than that of the sodium salt (5.2 mol at 35oC). These features seem to resemble to dimeric or gemini surfactants, which have a smaller CMC and lower Krafft temperature than the corresponding monomeric surfactants [27,28,32]. The 12-1-Na amide sulfate was shows several excellent properties including high foaming ability even in hard water, mildness to skin, as well as complete calcium stability and biodegradability (data not shown), and has been utilized by the authors as a shampoo detergent in Japan since 1996 [7].

ACKNOWLEDGMENT This article is reprinted (in part) with permission from Langmuir 1999, 15, 6664–6670. Copyright 1999 American Chemical Society.

REFERENCES 1. P A Gilbert. Surfactants and the Environment. Proceedings of 4th World Surfactants Congress, Vol. 1, Barcelona, 1996, pp. 57–66. 2. K Miyazawa, T Takahashi, H Kohashi, M Ishida, S Yoshino, H Kamogawa, H Sakai, M Abe. J Jpn Oil Chem Soc 47:11, 1998.

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Mizushima

3. H Fukusaki, K Isobe, J K Smid. New Mild Surfactant for Hair and Skin Amide Ether Carboxylate. Proceedings of 4th World Surfactants Congress, Vol. 1, Barcelona, 1996, pp. 227–237. 4. B Jewett. Soap & Cosmetics 39, 2001. 5. C H Rodriguez, J F Scamehorn. Surfactants Deterg 2:17, 1999. 6. B M Folmer, K Holmberg, E G Klingskog, K Bergstroem. Surfactants Deterg 4: 175, 2001 7. H Mizushima, T Matsuo, N Satoh, H Hoffmann, D Graebner. Langmuir 15:6664, 1999. 8. K Shinoda, T Hirai. J Phys Chem 81:1842, 1977. 9. K Tsujii, N Saito, T Takeuchi. J Phys Chem 84:2287, 1980. 10. P A Kooreman, J B F N Engberts, N M J Van Os. Surfactants Deterg 1:23, 1998. 11. Y P Zhu, M J Rosen, S W Morrall. Surfactants Deterg 1:1, 1998. 12. W W Schmidt, D R Durante, R Gingell, J W Harbell. J Am Oil Chem Soc 74:25, 1997. 13. P Desnuelle, O Micaelli. Bull Soc Chim Fr 671, 1950. 14. J K Weil, N Parros, A Stirton. J Am Oil Chem Soc 47:91, 1970. 15. S Kuroiwa, H Fujimatsu, K Takagi, S Mukai. J Jpn Oil Chem Soc 40:244, 1981. 16. U.S. Patent 5599483, Kao Corp, 1997. 17. H Mizushima, T Matsuo, N Satoh, H Hoffmann, D Graebner. Synthesis and Properties of N-Alkyl Amide Sulfates. Proceedings of International Conference on Colloid and Surface Science, Tokyo, 2000, p. 493. 18. B W Barry, R Wilson. Colloid Polym Sci 256:251, 1978. 19. H B Klevens. J Am Oil Chem Soc 30:74, 1953. 20. T Gu, J Sjoblom. Colloids Surf 64:39, 1992. 21. M S Celik, P Somasandoran. J Colloid Interface Sci 122:163, 1988. 22. T Hikota, K Meguro. J Am Oil Chem Soc 47:197, 1970. 23. R Zana. J Colloid Interface Sci 78:330, 1980. 24. I Satake, T Tahara, R Matsuura. Bull Chem Soc Jpn 42:319, 1969. 25. T. Sasaki, M. Hattori, J Sasaki, K Nukina. Bull Chem Soc Jpn 42:319, 1969. 26. P Lianos, J Lang. J Colloid Interface Sci 96:222, 1983. 27. R Zana, M Benrrau, R Rueff. Langmuir 7:1072, 1991. 28. R Zana, H Levy. Langmuir 13:402, 1997. 29. T W Davey, W A Ducker, A R Hayman, J Simpson. Langmuir 14:3210, 1998. 30. M Hato, K Shinoda. J Phys Chem 77:378, 1973. 31. M Hato, K Shinoda Bull Chem Soc Jpn 46:3889, 1973. 32. M J Rosen. Chemtech 30, 1993.

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17 Future Outlook for Detergent Formulations Kenneth N. Price

CONTENTS I. II.

Introduction ........................................................................................................... 484 Economics ............................................................................................................. 487 A. Business Environment............................................................................... 487 B. Efﬁciency Breakthroughs .......................................................................... 488 C. More Cost-Effective Design Tools............................................................ 491 1. Predictive High-Throughput Screening and Computational Modeling .................................................................................... 491 2. Formulation Work Process—Virtual Formulation..................... 492 3. Cross Fertilization and Importation of Solutions from Other Industries.......................................................................... 493 III. Consumer Trends—Simplicity and Enhanced Sensory Experiences................... 493 IV. Innovations in Appliances ..................................................................................... 497 V. Compatibility and Complementarity—Innovations in Textiles and Home Hard Surfaces ............................................................................................. 499 A. Hard Surfaces Innovations ........................................................................ 499 B. Textile Innovations .................................................................................... 502 1. What Functional Textiles and Hard Surfaces Imply for Detergents.... 503 2. Other Textile Trends ............................................................................. 503 VI. Innovations in Devices and Substrates—Holistic Solutions ................................ 504 VII. Environmental and Regulatory Considerations .................................................... 505 A. New Chemical Regulations....................................................................... 505 B. Sustainability—Important Design Themes for Detergents ...................... 507 C. Cool Water Performance ........................................................................... 508 D. More Efﬁcient Rinse Processes ................................................................ 510 VIII. Miscellaneous Design Directions ........................................................................ 511 A. “Reinvented” Liquid Detergents ............................................................... 511 B. Home Dry Cleaning .................................................................................. 514 C. Partitioned/Staged Chemistry.................................................................... 515 D. Advances in Catalytic Chemistry ............................................................. 515 References ....................................................................................................................... 517 483

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I. INTRODUCTION What does the future look like for detergent formulations? From a review of the patent literature, inventors and formulators have been proliﬁc. Just considering laundry detergent patent ﬁlings alone from 1998 to 2003 from the major manufacturers, there were over 3000 patent ﬁlings; categorized into the conventional “building block” ingredient categories, these are approximately as summarized in Table 1. No doubt, the near future of laundry detergent formulations will involve many of these inventions becoming commercialized and bringing new beneﬁts to consumers. A similar patent analysis exercise could be done for fabric enhancers, hand and automatic dishwashing detergents, hard surface cleaners, etc., with product form-related and ingredient-related intellectual property (IP) providing indications of how we might expect the landscape of these products to evolve over the next few years. The preceding chapters in this volume should serve to provide the reader with speciﬁc trends and technology directions. Indeed, the approach for this chapter will not be to survey patent trends in detergent building blocks and new product forms and project these into future developments. Rather, the intention of this chapter is to take a step back and look at the broader factors that are changing the playing ﬁeld of how detergents will be designed. The central theme is “drivers of change” and how these may translate into speciﬁc formulation and product design themes. In addition to economic trends, demographic trends, regulatory trends, and consumer trends, the boundaries between “detergent” and other disciplines such as materials science, textile science, and device design, are becoming blurred, and “formulation” is increasingly becoming just one part of the detergent formulator’s job. The ﬁeld of the formulator’s consideration will need to expand past “detergent” into “holistic cleaning products and consumer solutions” in order to stay relevant within the broader context of other factors that are starting to take over some of the functions once delivered by detergents. The upside is that all these changes will create opportunities for the development of proprietary innovations, hence creating continued economic incentive for advances in detergent product design. Table 2 provides an overview of this chapter by showing how these factors will inﬂuence detergent design. Column 1—“drivers of change”—summarizes the key factors that will continue inﬂuencing changes in detergent formulations. Some of these trends have been evident for several years but will continue to intensify and/or make their way into other product

Table 1

Laundry Patent Filings, 1998–2003, Major Manufacturers Category

Surfactant Bleach Polymer Enzyme Builder Perfume Granules form-speciﬁc Liquid form-speciﬁc Tablets/pouches form-speciﬁc

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Number of Filings >900 >450 >350 >200 >100 >100 >600 >400 >216

Future Outlook for Detergent Formulations Table 2

485

Key Emerging Drivers for Detergents and Resulting Implications for Design Drivers of Change

Design Themes

Economics

• Increasing commoditization of historical detergent building blocks • Continued market share growth of lower tier and private label products • Continued retailer consolidation • Demographics—low/no growth in developed markets, high growth in developing markets • Reduced R&D budgets • Increased cost of petrochemicals and related raw materials

ÆÆ ÆÆ ÆÆ ÆÆ

• Continued development of proprietary efﬁciency breakthroughs to deliver better performance at lower chemistry cost • Local ingredient sourcing • Deposition enhancement technologies • Catalytic technologies • Multifunctionality • Polymer technologies • “Reinvented liquid detergents” • Cost-effective design toolbox: virtual formulation, predictive high-throughput screening, predictive computational modeling, and crossfertilization from other industries via eR&D tools • More cost-effective options for non-petrochemical derived surfactants • Technologies which enable signiﬁcant reductions in surfactant and builder

ÆÆ ÆÆ ÆÆ ÆÆ

• • • • •

ÆÆ ÆÆ

• Detergent needs to have “compatibility,” “selectivity,” and “complementarity” in order to avoid dosage reduction or migration to nonpremium products • Detergent must be compatible with surface, and selective toward removing target soils without attacking built-in functionality of the surface/textile • Detergent can be complementary, either by being a vehicle for maintaining or replenishing surface, or by beneﬁting from opportunities to formulating out certain ingredients and hence shifting focus to new performance vectors • Continued and increasing need for antiabrasion, color care, and ﬁber integrity maintaining technologies • Covalently attached metal bleach ligands, surfactants, and enzymes

Consumer trends

• Need for simpliﬁcation (time, number of steps) • Increasing demand for customized sensory experiences • Skepticism toward marketing claims

Holistic solutions, new habits “Reinvented liquid detergents” Through-the-wash softening No-iron or one-pass ironing Continued effort against elusive “holy-grail” targets • Home dry-cleaning • Dry fabric odor • Wellness actives

Innovations in textiles and hard surfaces

• Increased diversity of consumer textiles and home hard surfaces (more synthetic blends, composite hard surfaces, composite material or stone hard surface, etc.) • Smart surfaces & textiles with builtin functionality will continue giving consumers choices beyond or instead of detergents for meeting their cleaning and care needs (soil repellancy, embedded actives, selfcleaning, moisture managing, corrosion protection, wrinkle resistance, antimicrobial, etc.) • Substrates with new surface characteristics and embedded or attached actives will present a changing playing ﬁeld for detergents to manage

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Table 2

Key Emerging Drivers for Detergents and Resulting Implications for Design (continued)

Innovations in appliances

• New functionality and processes will continue giving consumers choices beyond or instead of detergents for meeting their cleaning and care needs • Sensors in conjunction with autodosing • Cartridge-based/chemistry-ready appliances can begin replacing detergent functionality • Web-enabled appliances

ÆÆ ÆÆ ÆÆ ÆÆ

• Detergents that work synergistically with novel energy input modes • Frees detergent to formulate out of certain ingredients and shift focus to new performance vectors • Cool water cleaning • Consumable aspect shifts to cartridges with chemistry and or substrates (e.g., ﬁlters) that are periodically replaces; automatic detection and web-communicated reﬁll order of cartridges • Home dry cleaning

ÆÆ ÆÆ

• Continued shift of cleaning model from “chemistry solution” to “chemistry + device/substrate integrated solution” • Need for successful re-application of holistic solutions from home to fabric care—move beyond the washing machine/dryer • Chemistries must be compatible and synergistic with device/substrates (plastics, nonwovens, metal) • Chemistries that work in conjunction with novel energy input modes

ÆÆ ÆÆ ÆÆ ÆÆ ÆÆ ÆÆ ÆÆ ÆÆ

• • • • •

Innovations in devices & substrates

• Low-cost sourcing from China and elsewhere • Miniaturization • New functions/beneﬁts

Environmental and Regulatory

• • • •

Sustainability Water and energy savings Chemicals management policies Soft instruments/ecolabels

Cool water cleaning Home dry-cleaning Water reuse enablers Compaction Biodegradable ingredients

sectors. These include innovations in hard surfaces, innovations in appliances, trends in retailing, innovations in and low-cost sourcing of substrates and devices, innovations in textiles, emerging consumer trends, changes in the petrochemical industry, commoditization of basic detergent ingredients, and regulatory changes in progress or expected. Speciﬁcally, hard surface, textiles, and appliances are all delivering innovations to the consumer that start to overlap functions that have traditionally been delivered by detergents, and this is expected to continue. All of these factors have profound implications for the makers of cleaning products and detergents. Those who adapt to these effectively will be successful. Column 2—“design themes”—looks at how makers of cleaning products are adapting or could adapt to the foregoing drivers of change. The most immediate and obvious design vectors will continue to be efﬁciency improvements to reduce the total delivered

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cost of cleaning products and the search for the elusive “cost-effective breakthroughs” against the longstanding laundry, dish, and home care cleaning problems. The key subthemes in this area include local sourcing of ingredients and better alignment with emerging lower cost feedstocks, multifunctional ingredients, delivery/deposition technologies, and polymer technology. Other design vectors involve devising new ways to match consumer needs like improved simplicity, enhanced experience, and user wellness. As new, innovative hard surfaces and textiles increase penetration into consumers’ homes, additional requirements of compatibility and “replenishment” will be imposed on cleaning products. As appliances continue to evolve, detergent formulators are faced with potentially overformulating products, but could be freed to shift focus to higher-order beneﬁts or developing chemistries that work cooperatively with novel energy input modes. Some of these directions cascade into speciﬁc design directions such as home dry cleaning, “reinventing liquid detergents,” staged chemistry, and hydrophilic surface modiﬁcation. Regulatory considerations will inﬂuence design toward cool water cleaning, increased weight efﬁciency, catalytic chemistry, and water-reuse. Finally, innovations in devices and substrates will continue to impose compatibility requirements on cleaning chemicals, but more importantly will continue to force “detergents” to evolve more toward holistic cleaning solutions that work in concert with devices and substrates in totally new ways. Throughout the chapter, where possible, emphasis is placed on showing real-world and on-the-market examples in addition to patent ﬁlings. This also serves to highlight the many circumstances where the drivers of change are already providing new choices to consumer, and shaping consumer attitudes, habits, and opinions.

II. ECONOMICS A. Business Environment The most important driver of change for detergents is the challenging current and foreseeable business environment. A telling indicator is global sales of laundry, home care, and personal cleaning products over the period 1993–2003: sales growth averaged less than 1% growth per year. Part of the reason for this is that G7 developed markets are approaching zero population growth and these regions have complete penetration of traditional cleaning products. In developing regions, population is growing rapidly and cleaning products whitespace remains, but affordability issues put limits on sales and proﬁt growth. One school of thought involves the theory that the current paradigms of detergents and detergent chemistry are approaching the upper limit of what consumers will pay for. This model does not mean that all consumer needs are now being met—after all, there are still unmet needs in across laundry and home care . . . stain removal failures, dingy buildup, fabric color care and abrasion, wrinkle reduction, tough soil removal on ﬂoors and other hard surfaces, baked-on food soils, spotty glassware, etc. Rather, the model holds that this upper limit is ﬁxed because of underlying fundamentals of traditional chemistry, in conjunction with the fact that consumers have by and large decided that that majority of cleaning/care tasks they expect to be met by detergents are adaquately achieved by commodity ingredients at their current levels, because of static or shrinking household budgets, because new/innovative chemistries do not provide a beneﬁt that is worth their additional cost, or because consumers have developed compensatory behaviors to meet their needs. In other words, this does not mean that consumers do not want completely clean and like-new clothes and household surfaces—it just means that they are not willing to part with the time, money, and effort to obtain these.

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In developed markets, the growth of private label and lower tier products (mostly based on commodity chemicals and budget-oriented) are dominant factors for detergent makers. Consolidation in the retailing sectors has put severe pressure on detergent makers to hold or even reduce prices. Private labels will continue to exert pressure. In most non-detergent product categories, market share is 20% conversion to private label or higher; the fact that many laundry and household cleaning products are currently only around 10% private label share suggests that the growth of the private label market share will continue. In developing markets, the dominant factor is low purchasing power. India, China, and Southeast Asia represent half the world’s population, the fastest growing economies, yet consumer ability to afford premium products is extremely limited. One statistic lending insight to this is the number of minutes required for a consumer to work in order to acquire the wages necessary to purchase one package of premium product: in western Europe, it is 5 to 10 minutes, yet in developing markets this ﬁgure is 100 to 200 minutes or more. It comes as no surprise that low-tier products are the dominant products and likely to remain so in the coming decade. The bottom line in both developed and developing markets is that detergent makers will generally not be able to pass on cost increases for new raw materials to consumers and that consumers will continue turning to more affordable products. B. Efficiency Breakthroughs The above discussed economic drivers mean that detergent innovations—at least within the traditional forms such as laundry/dish/hard-surface detergent powders, liquids, tablets—must continue to occur within a static or shrinking cost structure. The top innovation targets in the near future will therefore continue to be efﬁciency breakthroughs. This requirement is particularly important for developing geographies where products need to sell for at least half the price vs. developed markets. Rather than being viewed as a negative constraint that dampens enthusiasm for investing new money into new technologies, this can also be viewed as an opportunity for proprietary solutions. Innovation will continue to be the path to ﬂourishing in a challenging mature market. The ﬁrst type of innovation will be proprietary efﬁciency breakthroughs. Detergent formulators have over the years developed an extensive understanding of detergency mechanisms, and this body of knowledge can continue to be used to develop proprietary efﬁciency breakthroughs that challenge previous formulation and raw material models. The second category of innovations will be those that break the mold and move beyond traditional powder/liquid/unit-dose detergents for laundry/dish/hard-surface. These are discussed in more detail in sections IV (“Innovations in Appliances”) and VI (“Innovations in Devices and Substrates”) below. The third category will be those discontinuous innovations that provide a dramatic improvement against a central consumer need even via a traditional liquid/powder/unit-dose product form. These are discussed in sections III (“Consumer Trends”), VII (“Environmental and Regulatory Changes”), and VIII (“Miscellaneous Design Directions”) below. Efﬁciency breakthrough design themes are summarized in Table 3. Local raw material sourcing and development is an important component because it can eliminate currency and duty issues, and drastically reduce total transportation costs. The idea is to maximize alternative materials based on local source or local currency. Clearly, this seems counterintuitive based on previous trends of companies wanting to globalize and centralize their product supply chains. However, it has become increasingly apparent that in many cases, the additional complexity from local sourcing is outweighed by cost savings and other intangible beneﬁts that come from local sourcing. For example,

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Future Outlook for Detergent Formulations Table 3

489

Efﬁciency Breakthrough Design Themes Theme

Local raw materials

Formulation

Deposition technologies

Details • • • • • • • • •

Catalysis

•

Surfactants

• •

Polymers

• • •

Sourcing in local currency Similar substitute materials from local suppliers Align with global shift to Asian raw material production Multifunctionality, synergies, and system approaches Rigorous challenge of existing blocks & levels DOX optimization Cost-effective delivery/deposition technologies for hydrophilic actives Perfume deposition and delivery/release technologies Reduce overformulation and down-the-drain waste of ingredients like perfumes Replace stoichiometric detergency processes with catalytic processes Hardness tolerance Better utilization of capability/toolbox for converting available feedstocks into surfactants (coal and gas derived feedstocks, oleochemicals) Better exploitation of low levels of polymers for high surface modiﬁcation Cost effective soil suspension and whiteness drivers for developing regions Surface modiﬁcation without tactile/visible residues—next-time cleaning assistance, long-lasting antimicrobial beneﬁts

multinational companies are ﬁnding that geopolitical risk can be mitigated by developing sourcing partnerships with local ﬁrms, and local consumers are more likely to overlook foreign ownership if the company plays a positive role in local development [1]. Other aspects to local sourcing involve aligning supply chains with the general shift of global shift raw material sourcing to Asia. For example, approximately 70% of new linear alkyl benzene (LAB) capacity by 2005 will be in Asia. From a formulation point of view, the need for efﬁciency improvements will continue to motivate formulators to take every formulation block and optimize it to maximize the most cost effective investment, and to challenge preconceived ideas for the presence and level of existing ingredient chassis components. Common themes will be to identify and develop synergies and optimal system approaches via combinations of technologies rather than focusing on single ingredient development approaches for drop-in use. In addition to tools like design-of-experiment (“DOX,” “DEX”) methodologies, such optimization will make increasing use of virtual formulation, high-throughput screening, and crossindustry reapplication as described in section II.C (“Cost-Effective Design Tools”). Another theme involves reducing the amount of overformulation and down-the-drain waste that results from poor deposition of these materials where they are needed. The ﬁrst-tomind target here is perfumes which are typically among the most expensive ingredients in the formulation. In a laundry context, many of these—especially perfume top notes that drive overall impression and freshness—are hydrophilic and are lost down the drain or

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during tumble or line drying. Cost-effective perfume delivery technologies thus represent a fertile design target for the future. In addition to perfumes, key formulation blocks to call out for special attention for cost-breakthrough analysis are catalytic chemistry, surfactants, and polymers. Broadening the portfolio of catalytic chemistry that can be used in detergents beyond enzymes represents a huge untapped source of potential efﬁciency breakthrough. This topic is described in section VIII. D (“Advances in Catalytic Chemistry”) below. The chief source of efﬁciency breakthroughs in surfactants will probably involve developing more cost effective routes to existing type surfactants but via novel feedstocks. The premise is that the surfactant industry is still not fully utilizing its capability and toolbox for converting available feedstocks into surfactants and hence there is still room for signiﬁcant improvement in more cost-effective surfactants [2]. Traditionally, surfactants have been derived from oleochemicals or petroleum. Recent advances in Fischer-Tropsch (FT) have now made it possible to produce surfactant feedstocks from coal or natural gas [3]. The latter process is referred to as gas-to-liquid (GTL) and affords an intermediate C10 to 13 range material. The prospect of being able to monetize stranded natural gas represents an extremely attractive opportunity for a cost breakthrough in workhorse surfactants. The key industry need is how to best utilize GTL parafﬁn. Other efﬁciency strategies for surfactants are discussed in sections VII.C. (“Cool Water Cleaning”), and VIII.A. (“Reinvented Liquids Detergents”), below. Polymers represent an especially important area for innovation to deliver efﬁciency improvements to detergents. The central proposition that needs to be better explored by detergent makers is the idea that “low levels of polymers can replace high levels of surfactants.” The bases for this idea are that (1) polymers can sufﬁciently modify surfaces at lower levels (surfactants typically result in 2 to 10 mg/m2 range of surface coverage, whereas surface active polymers typically are able to deliver >10 mg/m2 coverage at a much lower concentrations, usually 2% of formula or less), and (2) polymer design lends itself to multifunctionality via ability to incorporate varied functional groups and hydrophilic/phobic moieties in controlled spatial arrangements (e.g., blockiness, etc.). The accompanying assumption, of course, is that the polymer needs to be inexpensive enough so that the replacement is overall more cost-effective. Formulators need to continue exploring how polymers can replace or enable reduction of surfactants and builders, but also devise new ways for polymer solution and surface behavior to streamline formulas. Some of the challenges include: (1) cost, (2) biodegradability, (3) kinetics (polymers are thermodynamically effective at modifying surfaces but are often be too slow for what is needed during the cleaning process), and (4) achieving surface modiﬁcation without visible or tactile negatives. The need for cost-effective polymers for developing markets is especially worthy to point out. Soil suspension polymers have proven their worth in detergents in developed market. In fact, the need for soil suspension polymers is even greater in developing markets where high pollution and dust lead to an even higher soil load to control, but most developing markets cannot afford the current options for soil suspension polymers, or, not at their optimal levels. The industry needs to design next-generation analogs to current soil suspension polymers that are signiﬁcantly lower in price and hence enable their use at proper levels for developing market detergents. At this writing, high oil prices and tight supplies are exerting tremendous pressure on detergent ingredients such as surfactants (e.g., LAS), polymers (e.g., polyacrylates, ethylene oxide containing polymers), and other adjuncts. While the cyclical nature of the chemical industry and the historical ﬂuctuation of petroleum prices may mitigate raw material prices in coming years, the current circumstances nontheless highlight two long-felt needs in the

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detergent arts. (1) The need to develop a broader portfolio of raw material options – especially surfactants – that can allow detergent makers to transparently shift to hedge against the viscissitudes of global supply and price scenarios from one year to the next. This needs to be accompanied by a thorough understanding of how such shufﬂing impacts the range of cleaning tasks, product rheology, and product stability. (2) The need to substantially reduce the material or chemical “footprint” of detergents, i.e., to reduce large formula percentages of organic materials such as surfactants and solvents, and inorganic materials such as zeolite or phosphate builders. This effectively translates into a vision of relying much more heavily on catalytic chemistries, as are described below in section VIII.D. C. More Cost-Effective Design Tools Detergent formulation is not the only area that will have to manage with a shrinking cost structure. The technology development, formulation, and product discovery process itself will have to operate in the face of more challenging R&D budgets. Fortunately, just as efﬁciencies in formula design and detergency interactions have been developed, new tools are becoming available to make the detergent R&D process more cost-efﬁcient. These include (1) high-throughout screening, (2) virtual formulation, and (3) cross-fertilization and importation/re-application of solutions with other industries via electronic research and development (eR&D) tools. 1. Predictive High-Throughput Screening and Computational Modeling A key challenge for high-throughput screening in the detergent arts is developing benchtop assays or computational methods that are truly predictive of performance in full-scale performance settings. The development of such tools with high correlation to the target settings would be enormously powerful for detergent design, not to mention favorable for R&D budgets, as these could save repetitive performance testing that is labor- and resourceintensive. Unfortunately, the product applications setting are often extremely complex with process parameters that cannot be directly replicated in microscale assays. Detergency phenomena in particular involve complex multiphase systems comprising numerous solution species (polymers, surfactants, chelating agents, metal ions, etc.), numerous substrates (cellulose ﬁbers/fabrics, oily surfaces, proteinaceous surfaces, etc.), most of which are characterized by complex dynamics such as adsorption/desorption processes, surfactant micellization and liquid crystal phase transitions, metal ion induced precipitation, polymersurfactant interactions, clay hydration dynamics, etc. Moreover, most of these phenomena themselves exhibit considerable variation over the range of temperatures, concentrations, and local conditions encountered in real-world cleaning applications. Although much progress has been made in surface chemistry and physical techniques—to the extent that speciﬁc aspects of many cleaning phenomena may be studied at length—the fact remains that most of these techniques fail to fully account for the vicissitudes of these multicomponent systems. Detergent scientists must therefore continue to rely heavily on timeconsuming and expensive full-scale testing methods in order to develop innovative new ingredients and formulations that are beneﬁcial in end-use conditions. Accordingly, the formulator’s toolbox of the future will include predictive new screening tools that account for the abovementioned factors. Such screening tools could include computational modeling packages and high throughput "benchtop" screening methods, e.g. especially those that could support combinatorial arrays of ingredients and/or ranges of condition variables. Progress is being made on both fronts. For the case of computational methods relating to colloid and surface chemistry, the reader is referred to Surfactant Science Series, Vol. 89, [4]. At present, the state of

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Table 4 Current and Future Areas of High-Throughput Screening for Detergent Development Topic Laundry detergents

Dish

Perfume Fabric care Hard surface

Subtopics • • • • • • • • • • • • •

Stain removal Anti-redeposition, whiteness maintenance Solution-phase bleaching Solution-phase enzyme performance Glass corrosion Metal corrosion Suds generation and suppression Oil suspension and interfacial phenomena Headspace optimization Dye safety, color retention Fiber damage/integrity Reﬂectance and shine performance Antimicrobial performance

computational science is limited to modeling simple systems. Additional research of high interest to detergency involves the modeling of clay phenomena. The reader is referred to work, for example, by Teppen et al. [5] and Coveney et al. [6]. Another example moving closer to detergency involves the use of computational modeling to study oil/water/surfactant systems by Lal et al. The computational method (C2·DPD, Dissipative Particle Dynamics, Accelrys Inc. of San Diego, California) used in this study provided estimates of the surface tension and surface excess, as well as information about the kinetics of adsorption, and were used to model the effect of modiﬁcations to the surfactants or to the oil/water system. Results show that the surfactant migrates to the interface, lowering the interfacial tension in the process. In addition, there is a good qualitative agreement with the expected relation between the changes in surface tension and surface excess. [7]. In terms of future developments on computational modeling tools for detergency, the holy grail that the art will likely strive toward is being able to model complex wash or rinse liquor phenomena in a complete formulation setting against textile surfaces, hard surfaces, or soil materials. Development of high-throughput screening tools is being done for numerous other aspects of relevance to detergents and household products, and can be expected to continue in both breadth of topics covered, and improvement in how the results correlate with fullscale application testing (see Table 4). 2. Formulation Work Process—Virtual Formulation A recent development that should have a profound impact on detergent formulation and product design is something that can be called “virtual formulation.” The underlying premise is that research organizations are not tapping the full potential of their existing knowledge and data. Reasons for this include the fact that the data are usually located in isolated pockets that do not fully integrate or interact, that data from various projects are not linked (geographically or chronologically), that there is too much information, that the data exist in different formats, that the “owners” of data are often from different disciplines that “do not speak the same language.”

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Future Outlook for Detergent Formulations

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Advances in information technology and computing are now seeking to rectify this situation by fully integrating a company’s wealth of past data in such a way that mining for trends and insights is fully enabled. The art is still at an early stage. Before describing some real-life examples, a “wish list” of what such a “virtual formulation” or “virtual product design” interface might look like is shown in the schematic in Fig. 1. This ranges from (1) codiﬁcation of existing experimental data (performance data, benchtop data, analytical data, consumer preference data, toxicological/regulatory data, cost data), (2) linking that data with speciﬁc formulations (chassis combinations as well as new molecules) and conditions, and then (3) leveraging computing power and artiﬁcial intelligence to extract useful patterns and trends and to simulate and predict the performance of formulas as yet still “on paper.” The ideal platform would be an evolving system where new experimental data are entered on an ongoing basis to reﬁne predictiveness. Representative examples of virtual formulation are those being developed by Accelrys Inc. of San Diego, California. (www.accelrys.com). In one case study, virtual formulation was used to model ranges of multisurfactant systems for foaming performance [8]. Henkel is also partnering with Accelrys to develop a software system to facilitate product development and formula design, incorporating and compiling databases of existing information on chemical raw materials, pricing information, toxicity data, and other company data [9]. 3. Cross Fertilization and Importation of Solutions from Other Industries Finally, consistent with the theme of the notion of “detergent” becoming blurred with other disciplines as explored in more details below, formulators and product designers will continue to increase reaching into other disciplines and industries for solutions to reapply to their own problems and consumer needs. Of course, this is nothing new, as detergents have a rich history of taking inspiration from other scientiﬁc and technical areas. What is new is that this process will become routine and formalized, especially through the use of “eR&D” tools and external expert networks such as NineSigma (www.ninesigma.com) and Innocentive (www.innocentive.com). Through these vehicles, technology needs can be rapidly diffused through these companies’ networks of experts, with monetary rewards for successful solutions.

III. CONSUMER TRENDS—SIMPLICITY AND ENHANCED SENSORY EXPERIENCES There are a number of consumer trends that are driving change and will continue to drive change in detergents. These will be summarized in a general manner only. The most important trend can be called the “time crunch.” In both developed and developing markets, more households have less time for household tasks such as cleaning, and consumer dollars are going to migrate to cleaning/care products that allow them do this in less time and with less effort, or to other product categories where perceived worth to self and family is greater. For example, the incidence of ironing has decreased by ~40% since 1998. Another result of the time crunch is that there is increased tolerance for lessthan-perfect end results. This does not mean that consumers do not want completely clean and like-new clothes and household surfaces, it just means that they are not willing to part with time, money, and effort to obtain these. In the laundry area, the time crunch is compounded with the general move toward more casual apparel. Accordingly, a key design theme for detergents in the coming years will be the continued move to toward innovations that dramatically simplify the cleaning experience.

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Existing consumer preference data

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Raw material cost data

Formula chassis blocks Safety data and Molecular structure of actives applicable regulatory codes/status Literature data of interest

New data Existing data “On-paper actives” “On-paper formulas” Required performance attributes

Figure 1

-Computing power, - artificial intelligence - chemical algorithms - statistical computations - data management - molecular modeling - models constantly evolves to better fit real data

Predict performance Extract useful trends ... interactions ... evolving models Recommended formulas, actives

Existing known analytical data technical (stability, rheology, performance surface tension, data of polymer-surfactant known formulations binding constants) of actives Existing high-throughput screening data

“Virtual formulation/product design” platform of the future.

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The last decade has seen a number of new product forms whose underlying success is that they bring the consumer a step change in convenience and time/effort reduction. The most dramatic example is in the home care category, where some makers of cleaning products have reinvented the category by moving beyond chemistry and availing themselves of recent advances in — and lost-cost sourcing of — devices and substrates. At ﬁrst glance some of these products such as those in the semidisposable wet-mop category appear to involve higher cost and more complexity, but upon more careful analysis, the reality is that consumers are unsatisﬁed with existing hard-surface cleaning paradigms and their extra investment in the new products gives them a better result with less time & effort. The laundry and dish categories have been less successful in ﬁnding holistic solutions, but can be expected to search for ways to do this, as well as to continue searching for a unit dose form that ﬁnally cracks the US market. Other design themes related to the simpliﬁcation via new product form are described below in sections VIII.A. (“Reinvented Liquid Detergents”) below and section VI (“Innovations in Devices and Substrates”). A speciﬁc area within the laundry category that is ripe for simpliﬁcation or holistic design solutions is wrinkle reduction. Ironing is one of the most hated tasks in the laundry process and for which there is no adequate solution other than elbow grease with iron and ironing board. Some progress has been made on incremental improvements of wrinkling via “through the rinse” or “through the wash” products, but these have not provided a step change in consumer satisfaction. Laundry product makers need to take a holistic look at the entire laundry process and devise new habits and products (of which chemistry may be only part of the solution) to provide a meaningful simpliﬁcation of the wrinkle reduction process. Alternatively, through-the-wash or through-the-rinse chemistry approaches that provide “one pass ironing” represent fertile ground for innovation. One area of simpliﬁcation where recent progress has been made involves throughthe-wash fabric care. This reduces the need for the consumer to purchase two products and to perform two product addition steps during laundering. Traditionally, through-thewash fabric care has been a major challenge due to incompatibility of care actives with surfactants or soils. A recent product innovation delivering discontinuous beneﬁt was introduced by Procter & Gamble in 2003 based on a proprietary cationic silicone fabric ﬁnishing agent that bonds to ﬁbers and delivers a true step change in shape retention and elasticity beneﬁts, as shown in Fig. 2 [10]. The resulting performance on garments resonates with the simpliﬁcation theme in that it allows consumers to wash fabrics that they would previously have to wash via special care methods—“no sort.” A key design trend for the coming years is that this sort of innovation needs to be taken to the next level to include through-the-wash softening to a level of softening equal to what can be achieved via separate addition of a liquid fabric softener. Another key trend can be thought of as “experience seeking.” Aromatherapy, the proliferation of natural ingredient-based products, and customization of products to bring the consumer novel sensory experiences are examples of how this is playing out in consumer products and will play out in detergents. The implications of this consumer trend are that major innovations are needed in the areas of customizing and enhancing the sensory appeal of these experiences. How can detergent design be directed toward this consumer trend? Table 5 lists some targets for detergent formulators and product designers. The primary design targets involve better exploitation of perfume. As discussed above, most perfume is not delivered where and when the consumer wants it. The detergent art is replete with technologies attempting to provide controlled release; however, consumer needs are far from being met, and there is ample room for innovators to develop proprietary solutions. The key technical challenges that need to be overcome are deposition, and the ability to be able to deliver a balanced “signature” accord throughout the entire

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CH3

H3C N +

NCH2CHCH2O(CH1)3

Cl−

OH

O

O

Table 5

CH3 O

CH3

Si

CH3

(CH2)3OCH2CHCH2N

CH3

NCH2CHCH2O(CH2)3 OH

N +

OH

CH3

H3C

(CH2)2CO(CH2CH2O)6-4C(CH2)2 N + Cl−

Figure 2

Si

Si CH3

Cl−

CH3 O

Si

(CH2)3OCH2CHCH2

CH3

OH

Process simpliﬁcation example: through-the-wash fabric care. Sensory Enhancement Vectors for Detergent Products Topic

Laundry—odor

Laundry—user wellness

Hard surface Dish

Details • • • • • • • • • • • • • • • •

Dry fabric odor—long-lasting perfume Long-lasting “Top notes” Balanced accord throughout entire release timeframe Deposition and controlled release technologies “Signature scents,” customizable Malodor reduction during use/storage Skin care active delivery Allergen control Vitamin delivery Personal cooling Whole room malodor control and freshening “Signature scents” Kitchen freshening via dishwasher or sink dishwashing Malodor control in dishwasher Tactile beneﬁts of wash water for hand dish No residual perfume on dishware

release timeframe in the face of complicated mixtures of perfume raw materials possessing varied physicochemical and hedonic properties. Some of the user wellness targets may seem exotic, but aging populations in conjunction with innovations in appliances, substrates, and textiles (gradually assuming functional roles formerly provided by the detergent) may very well bring these to a point where the value equation is right to include them as detergent beneﬁts.

© 2006 by Taylor & Francis Group, LLC

Future Outlook for Detergent Formulations base2 base1 base3

custom selection of care actives & level

497

custom selection of signature perfume & level mixing

selection of base chassis

custom selection of cleaning boosters & level

Figure 3

Individually Personalized Detergent

custom selection of packaging wellness actives & level

“Detergent boutique” for on-the-spot individual-customized liquid detergents.

Consumer desires for customized products have yet to transform detergents in more than a superﬁcial manner. Typically, economies of scale outweigh arguments for highly tailored products, and at best, multiple SKUs with a few variations in fragrance and minors are all that consumers have to choose from. To the extent that detergents enhance their beneﬁt proﬁles beyond functional cleaning and start captivating consumers’ sensory requirements, customization could increase to encompass more options. To prevent the need to ship and maintain inventories of large numbers of SKUs, detergent makers could reapply the “base + on-site mixing” model currently used by paint manufacturers. Figure 3 shows a schematic of what this product making might look like. Finally, not to be overlooked is the consumer trend that can be described as “marketing skepticism.” The key aspects of this are that consumers are increasingly skeptical of product claims, and that incremental beneﬁts that are not obvious in short-term usage will not be successful. The design implications of this trend is simply that detergent formulators need to continue innovating against the holy grails of household cleaning: (1) perfect stain removal, (2) perfect fabric care (color retention & antiabrasion), (3) complete elimination of the need to iron, (4) scrub-free cleaning of hard surfaces, (5) crystal clear shiny glasses, dishes, and other hard surfaces, and (6) long-lasting signature perfume of dry fabrics.

IV. INNOVATIONS IN APPLIANCES For most detergents (laundry detergents, fabric softeners, automatic dishwashing), the appliance is the “playing ﬁeld” in which it performs its job. Hence, the design of the appliance is critical for design of the detergent or cleaning product. An interesting analogy can be made between the above “commoditization” trends of detergents to the situation with washing machines. Twenty years ago the U.S. washing machine market was essentially commoditized with ~$200 toploading machines with basic functions. Over the last decade, appliance manufacturers have been able to decommoditize the market via innovation based on designs, extra beneﬁts, and other features that meet consumer needs such as cleaning, fabric care, energy and water savings, etc. Importantly, these innovations are designed to deliver beneﬁts that detergents are also designed to deliver. Current and continuing appliance trends are summarized in Table 6. In the short-term, the most obvious driver of change for detergents involves the shift toward horizontal axis washing machines and water/energy savings. Energy/water savings aspects will be discussed in section VII (“Environmental and Regulatory Considerations”) below. The move to high efﬁciency (HE) in North America will continue and penetration is actually planned to be faster than expected due to Asian and European machine manufacturers coming into the market and providing more visibility and better/cheaper options

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Price Appliance Trends Driving Change in Detergents Theme

Continued concentration and move to high efﬁciency (HE) Cool-water cleaning Novel energy input modes Innovations to replace traditional detergent functions Sensors (soil, load weight, water hardness) Autodosing Larger capacity Fabric care/garment maintenance

to consumers. Resonating with the above mentioned themes, though, an important driver to the faster than expected adoption by NA consumers of HE is that the appliance—rather than the detergent—is providing consumers a step change in performance. Soil sensors will continue to become part of appliances. These innovations are important because they allow the appliance settings to match the particular details of the task and conditions at hand and avoid waste of water, time, and energy. The fabric load can be determined, and the amount of water adjusted accordingly. To customize cleaning, the water hardness and soil load can be sensed, and wash parameters adjusted accordingly to most efﬁciently deliver the necessary consumer end result. The next stage of sensor technology in appliances will couple these and other types of sensors with autodosing. For example, the amount of detergent matched to the amount of garments or dishes to be washed, or to the water hardness, or to amount of soil present. Larger capacity washing machines are expected to continue. For example, average load sizes in the United States and Europe are around 3 kg. Large capacity machines are raising this to 7 to 10 kg. The consumer need this meets is simplicity and time-savings: fewer larger-capacity loads instead of a larger number of lower-capacity loads. An active area for appliance development with direct impact to detergent makers involves innovative designs for fabric care. Examples already on the market include the following. Merloni has developed technology that “pins” garments to the walls to prevent shrinkage and enable the washing of wool and other ﬁne washables [11]. Whirlpool has developed both horizontal axis and vertical axis based appliance design to deliver reduced fabric damage. Such appliance-driven fabric care solutions are expected to continue and have implications for detergent formulators. Figure 4 shows advertising copy describing these features. In the area of cleaning, innovative designs for enhanced cleaning are also entering the market. Again, the designs utilize novel appliance features rather than chemistry to improve cleaning, which has been the traditional function of the detergent. For example, Whirlpool has introduced a method using a concentrated pretreat [12], and Dyson has introduced a novel horizontal-axis machine involving a split drum design rotating in opposite directions [13]. Figure 5 shows advertising copy describing these features. The above examples illustrate how innovations in appliance design are assuming functions traditionally associated with detergents. However, it is expected that continued innovations will continue this trend. Based on activity in the patent literature and other sources, we can envision the laundry appliance of the future that has assumed many of the functions that are today carried by detergents. This would involve combinations of

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Future Outlook for Detergent Formulations

CASHMERE GOLD Cashmere Gold, an exclusive patent of Merioni Elettrodomestid, is a special program that allows you to wash by machine even wool items labelled “hand wash” This is possible thanks to a cycle that uses a particular drum speed, “satellitizing” the items to prevent the fibres from being rubbed. Cachemire Gold is the first program recognized by the Woolmark Company.

499

REFINING INNOVATION TO REDEFINE THE INDUSTRY. The Whirlpool® Duet® fabric care system has set the industry standard for fabric care through the incorporation of innovative ways to extend the life of fabrics. Duet® washers offer responsive technology, incredible capacity, excellent performance, and amazing resource savings.

Keeps Clothes Looking Newer Longer

Figure 4

Examples of appliance innovations delivering fabric care beneﬁts.

chemical-generating devices novel energy input modes, physical methods to peptize/dissociate soils or sequester soils from bulk wash liquors. Figure 6 shows a schematic of how a combination of such innovations could change the playing ﬁeld for detergents and provide new opportunities for detergents and consumables. Of course, such an appliance is not realistic for the near future. Recently Sanyo launched a “detergentless” washing machine based on electrolysis to generate chlorine bleach from NaCl. The performance of such systems using isolated technology blocks will likely remain poor compared to traditional cleaning. However, the future is to assemble a portfolio of such blocks that complement each other and provide an equal or superior consumer end beneﬁt but with the added beneﬁts of resource conservation or task simpliﬁcation to the consumer. Such approaches could be a signiﬁcant driver/enabler of radically different detergent formulas.

V. COMPATIBILITY AND COMPLEMENTARITY—INNOVATIONS IN TEXTILES AND HOME HARD SURFACES Surfaces are the other “playing ﬁeld” for detergents and other fabric and home care products, from hard surfaces to natural material textiles to synthetic textiles. Interactions between surfaces and soils must be overcome, and wear & tear from use and environmental factors must be mitigated. Innovations in textile and materials science are providing a changing playing ﬁeld for detergents to work on. Durable or semidurable nanotech, polymer, or other coatings, or embedded actives applied during the manufacturing stage of articles/substrates are being explored by most of the major producers of textiles, ﬁbers, coatings, glass, tiles, and other materials for use in apparel or around the home. A. Hard Surfaces Innovations In the area of hard surfaces, the beneﬁts these surfaces are claiming to provide are summarized in Table 7. Two examples involving hard surfaces are shown in Fig. 7. The ﬁrst is a window product on the market by Pilkington that features an invisible titanium dioxide coating. The resulting beneﬁts are self-cleaning (photocatalytic activity of the coating breaks down organic dirt) and water-sheeting action which reduces spotting and allows easy-rinse off

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CATALYST® CLEANING ACTION Virtually eliminates the need to pretreat! Four out of five washer users pretreat stains some of the time. NO MORE! Think of Catalyst® Cleaning Action as washing your hands. For thorough cleaning, you apply soap directly onto your hands and rub them together to form a sudsy lather. Catalyst® Cleaning Action works the same way on your clothes.

The ideal wash action. To replicate the movement of washing by hand Dyson engineers designed two aligned drums and engineered them to rotate in opposite directions at the same time. The effect of this revolutionary action on the clothes is dramatic. Instead of revolving in the old single drum pattern of ‘drop and flop’, the clothes are much more active, moving in an infinitely variable dance, to flex the fabric and open the weave to the detergent. Because the ContrarotatorTM releases dirt more effectively, it can wash clothes cleaner.

Figure 5

Examples of appliance innovations delivering cleaning beneﬁts.

Price

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Future Outlook for Detergent Formulations Electrolysis Cells Ozone Generation (replace bleach)

501 Ion-exchange cartridges (replaces builders)

pH generators alkalinity on demand (replaces some cleaning function)

Untrasonic devices (drive stain removal)

Filtration systems (replace antiredep and DTI chemistry)

Continued fabric care methods (non-chemical methods for antiabrasion, color care, shrinkage control)

Silver ion de-germing (replace/reduce malodor control chem or bleach)

Dryer methods

... less chemicals going down the drain ... detergent needs to radically change ... complement or work with the device/appliance ... fuel/precursors for the devices ... consumable aspect shifts to cartridges ... chemistry based (autodosing) ... electrical or substrate-based

Figure 6.

Table 7

Future washing machine with devices to replace current detergent chemistries.

New Beneﬁts Being Delivered from Innovative Hard Surfaces Theme

Stain repellancy Easy to clean, or self-cleaning Corrosion protection Scratchprooﬁng Nonstick Antimicrobial Water-sheeting and spot reduction

of loosened dirt. Numerous other such products are on the market ranging from glass products to hard-surfaces such as tile products and bathroom ﬁxtures. The second example provides a look into smart materials that could radically change (or marginalize) the role of detergents. Langer et al. from Massachusetts Institute of Technology (MIT) developed a metal surface that can be switched back and forth between hydrophilic and hydrophobic by the application of an electrical signal. In the hydrophilic state, the surface presents carboxyl groups, while in the hydrophobic state, the carboxyl groups bend down to the surface and present a surface comprising alkylene spacers [14]. It remains to be seen how such developmental technologies will manifest themselves in commercialized products, but once they become available for consumers’ home hard surfaces, they could dramatically change (or marginalize) the role of detergents.

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Hydrophilic

Figure 7

Table 8

Hydrophobic

Innovations in hard surface with implications for detergents.

New Beneﬁts Being Delivered from Innovative Textiles Theme

Stain repellancy, soil repellancy Color care Pollution blockers UV protection Wrinkle resistance Health and wellness beneﬁts Antimicrobial Insect repellancy Abrasion resistance Comfort, moisture management, personal cooling Enhanced absorbency Durable softness

B. Textile Innovations Similar innovations are taking place in the textile industry. Detergent formulators are already well aware of soil repellancy and wrinkle resistance coatings. These will continue with better beneﬁts and fewer negatives, and will be joined by other beneﬁt vectors enabled via application of nanotechnology, polymer coatings, active-containing microbeads, and other technical approaches. Some of the end-result beneﬁts being claimed are summarized in Table 8. Examples of current market innovations along these lines are shown in Fig. 8.

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Sara Lee Corporation Hanes Body Enhancers Anti-Cellulite Mid-Thigh No Hose

Purista is the consumer-facing brand name for Avecia’s antimicrobial treatment that helps keep textiles fresh and clean for longer by controlling the growth of bacteria arising in everyday use.

Figure 8

New Ingredients: Ingredients include: soybean oil, butcher’s broom, rutin, horse chestnut, Paraguay tea, caleus forskhalii, gatu kola, grape seed extract. Innovative Delivery System or Packaging: Microbeads are released onto the leg. The waffle weave provides extra effectiveness. Unique Characteristics: It saves having to use a separate anti-cellulite cream.

Innovations in textiles with implications for detergents.

Some of these “user wellness” targets may seen exotic for use in detergents, but aging populations, in conjunction with innovations in delivery and nutraceuticals, may very well bring these to a point where the value equation is right to include them in detergents. 1. What Functional Textiles and Hard Surfaces Imply for Detergents There are several important implications for detergent formulators from these innovations in hard surface and textiles: (1) Consumers are being given alternative choices beyond detergents to meet their needs, thus presenting consumption risk and trade-down risk. Although actual beneﬁts may currently be too small to completely satisfy consumers, continued innovations will reinforce the general trend and provide increasing levels of beneﬁts to consumers that serve to reduce their need for detergent, i.e., either less detergent is needed, or the playing ﬁeld between detergent options is leveled because the consumer can obtain adequate detergency from nonpremium products. (2) Detergents will need to innovate so as to be “compatible,” “selective,” and “complementary” with these surfaces. “Compatible” means that at a minimum, after having invested in the textile or surface in question, the consumer will be looking for a product that is not going to damage or strip away its special properties. Current detergents may be too aggressive toward the surface coatings of the future. “Selectivity” means that the detergent has speciﬁcity for removing or breaking down soil ingredients rather than functional actives integral to the surface. “Complementary” means that the priority of detergents in future may be to preserve and assist the coated surface, and/or to refresh & maintain actives. 2. Other Textile Trends In addition to the above developments in textiles, other textile trends with important design implications for future detergents include the following. (1) White garments will continue to be a smaller and smaller percentage of garments in laundry loads. This will continue to

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Previous paradigm –Wet chemistry during use –Product chemistry (Powders . . . liquids . . . sprays)

Figure 9

New paradigm –Device or substrate (no wet chemistry) –Wet chemistry + device –Wet chemistry + substrate –Wet chemistry + device + substrate

Going beyond chemistry.

increase the need for technologies directed toward color care, antiabrasion, and other appearance beneﬁts. (2) World ﬁber usage will continue migrating toward increased use of polyester. By 2015, polyester is expected to overtake cotton as the top ﬁber in global apparel. This will increase the need for hydrophobic stain removal boosters from hydrophobic polyester surfaces, and may also prompt a new generation of soil-release polymer technology.

VI. INNOVATIONS IN DEVICES AND SUBSTRATES—HOLISTIC SOLUTIONS As discussed above, a key design theme for detergents in the coming years will be the continued move to toward innovations that dramatically simplify the cleaning experience. This consumer need, coupled with the development of new nonwoven technologies, advances in device design, and, importantly, the development of rapid-prototyping and low-cost sourcing of such devices from China and elsewhere, are leading to an underlying paradigm shift in detergency that can be described as “going beyond chemistry.” These are shown in Fig. 9. In addition to the functional beneﬁts and time/effort reduction beneﬁts, these paradigms also introduce an element of novelty and “delightful design” that captivates consumer attention. The best examples have been in the home care category. The reader should be well aware of detergent wipes which have by now become popular in nearly every subsector of cleaning. These involve not only wet wipes that combine conventional or modiﬁed detergent chemistry with a nonwoven substrate, but also dry wipes based on electrostatic or open pore nonwoven technologies that are more effective in dealing with dry particulate soils than wet chemistry. The next generation of products involving the “chemistry + substrate + device” model was successfully deployed in the semidisposable wet mop category, with products such as Swiffer Wet-Jet and Clorox Ready-Mop. Most recently, the new paradigm’s boundaries have been further expanded by a product that replaces sponge/bucket/hose/elbow-grease via a patented holistic solution exploiting device and wash and rinse chemistries, featuring a hydrophilic surface modiﬁcation polymer [15], and a water treatment cartridge, the Mr. Clean AutoDry product for car care, illustrated in Fig. 10. As was the case when the wet ﬂoor mop category was reinvented, this product on ﬁrst glance may appear complicated, but the integration of device and chemistry is designed to intuitively match what the consumer wants from simplifying the current time-consuming multistep process of washing a car, and the end result beneﬁts of a spot-free ﬁnish without hand-drying meets a consumer need that is currently unmet by any other means. In fact, for many household cleaning and care chores, consumers are already practicing their own crude system approaches, so there is a strong opening for holistically designed device/chemistry solutions to give them a more streamlined and functionally satisfying option.

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Future Outlook for Detergent Formulations

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3 Independent Flow Paths and Nozzles Sprays de-ionized water Sprays rinse water Sprays soap solution

X′ R 2

R1 H2C

C

Z

[CH2]n

X′ R

R4 X′

3

N+ [A

N+]m

R3

R3

B

N+

R5

R6

Figure 10. Holistic integrated device + chemistry product for car cleaning.

Figure 11

Innovations in textiles with implications for detergents.

The laundry and dish categories have been less successful in ﬁnding such holistic solutions and using device and substrate chemistry. The challenges here are perhaps greater because existing systems involve appliances that are already entrenched and themselves innovating in other ways (described above). Nonetheless, some early attempts are shown in Fig. 11. Integration of devices, implements, and substrates with detergent chemistry is a key driver of change for the cleaning products industry. Blurring of the distinction between chemistry and these other components will continue, and “detergent innovation” will have to go hand-in-hand with these materials and with holistic design principles. Speciﬁc design implications and opportunities are summarized in Table 9.

VII. ENVIRONMENTAL AND REGULATORY CONSIDERATIONS A. New Chemical Regulations A comprehensive treatment of new chemical regulations is beyond the scope of this chapter. However, this section presents a brief summary of key regulatory elements that will affect detergent formulation in the coming decade. The reader is encouraged to consult guidelines and white papers as summarized on the relevant websites of the governing bodies.

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Table 9

Device/Implement/Substrate Systems Implications for Detergents

Topic Home care opportunity areas Fabric care opportunity areas

New options for solvent chemistry

Details • Outdoor care applications • Air care applications • Successful development of holistic solutions for dishwashing • • • • • • •

More options for hydrophilic surface modiﬁcation General functional requirements of detergent chemistry

• • •

Ironing task simpliﬁcation Garment storage pre/post-laundering Special care items that cannot be washed Immobile fabrics that cannot be easily washed (home or car upholstery, draperies, carpets) Cheaper solvents More selective solvents (stain-selective, therefore mild toward household substrate Compatibility with plastic materials, glues, and novel nonwoven materials No visible or tactile negatives Deliverable beneﬁts w/ lower levels of active Condition-independent technologies (not adversely affected by moisture, hardness, surface type, type of surfactant present)

• Compatibility with plastic materials, glues, and novel nonwoven materials • Chemistries that work in conjunction with novel energy input modes (ultrasonic, UV, electrolysis) • Microparticles or ﬁbers with embedded actives • Durable or semidurable beneﬁts • “No-rinse”-friendly materials

The European Union (EU) detergent directive will involve important considerations for the biodegradability of detergent ingredients. The U.S. Environmental Protection Agency’s (EPA’s) HPV (High Production Volume) Challenge program is part of its Chemical Right to Know Initiative to provide public access to basic hazard information on high production volume chemicals and the risk they may pose, as well as to improve reporting on chemicals that are PBT (persistent, bioaccumulative, and toxic). EU REACH (Registration, Evaluation, and Authorization of Chemicals) Legislation was recently adopted by the European Commission. This legislation, which will replace over 40 existing EU directives and regulations, is based on a single, integrated system for assessing risks to public health and environment of more than 30,000 substances marketed and/or produced in Europe, shifting to industry the burden of the responsibility for safe handling of chemicals all along the supply chain (from producers to the very last downstream users). REACH will require that all chemicals manufactured/imported in Europe at a level 1 t/y/m be registered with submission of a technical dossier including information about the physical-chemical and toxicological properties of each substance. Special reduced registration regimes have been proposed for “intermediates of reaction” chemicals for “R&D purposes,” and polymers have been temporarily exempted. The regulations are expected to come into force around 2005–2007, and registration of all chemicals should be completed in a maximum time frame of about 10 years.

© 2006 by Taylor & Francis Group, LLC

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507

Key Current or Upcoming Regulatory Factors Affecting Detergents Factor

• EU Detergent Directive http://europa.eu.int/comm/ • EU REACH Legislation http://europa.eu.int/comm/enterprise/chemicals/chempol/whitepaper/reach.htm • Canadian DSL http://www.ec.gc.ca/substances/nsb/cpdsl/eng/cg_s1_e.htm • US EPA/OECD HPV Program http://www.epa.gov/chemrtk/volchall.htm

Table 11

Sustainability Drivers for Detergent Design and New Proprietary Solutions

Topic Waste reduction

Water conservation

Energy reduction Biodegradability

Speciﬁc Technology Targets • • • • • • • • • •

Increase options and efﬁciency in catalytic chemistry Formula compaction reduced packaging Water reuse technologies Rinse reduction technologies—surfactants and builders with enhanced rinsability Continued move to HE appliances Cool water cleaning in laundry and dish Drying enhancement technologies Cost-effective innovations in molecular design of polymers and surfactants with equal/better performance vs. current materials Bioroute—develop new technologies for converting biomass into chemical feedstocks and consumer products

B. Sustainability—Important Design Themes for Detergents As detergent manufacturers and other consumer products companies become more proactive in aligning themselves with responsible care of the environment, a key emerging theme is “sustainability.” Indeed, during the August 2002 “World Summit on Sustainable Development“ in Johannesburg, voluntary detergent industry and chemicals sector themes emerged. For example, the voluntary goal of “development and diffusion of environmentally friendly technologies” included such speciﬁc targets as new enzymes, bleach boosters (to enable washing at lower temperatures), and biodegradable surfactants and polymers. Table 11 lists some the key design implications for detergents and other household care/cleaning products. Again, the upside for detergent makers is that these drivers constitute opportunities for proprietary innovations to deliver against. Three of these design themes—“cool water cleaning,” “rinse processes,” and “catalytic chemistry”—are discussed in more detail below in sections VII.C., VII.D., and VIII.D., respectively. Drying enhancement technologies have received some attention in

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Putting the European eco-Label on your products means that they have the following assets: • Reduced amount of total chemicals • Reduction of packaging • Limitation of substances harmful for the aquatic environment • Increased biodegradability

Figure 12

• Safety of the product • User instructions for environmental use • Performance rested and guaranteed

Representative ecolabels.

liquid fabric softeners, but this ﬁeld will continue to represent fertile design opportunities for product designers and detergent technologists, as tumble drying (along with heating water for warm and hot wash cycles) is one of the largest energy consumption steps of household cleaning processes. In terms of surfactant design, inertia of the industry along existing workhorse surfactants will continue to suppress innovation. Though rising oil prices are starting to change this, it is well known that calls for biodegradable materials in the past have come up against consumer needs and failed to materialize: in general, consumers will not accept a tradeoff between environmental friendliness and performance, cost, and convenience. Nonetheless, given the above sustainability arguments, there will be a measurable incentive for taking a fresh look at surfactant design. For some interesting perspective, the reader is referred to papers by Chevalier [16] and Lang [17]. Emerging regulations and sustainability policies imply that innovations that crack the historical performance/cost vs. biodegradability trade-off will enjoy a market advantage. The ﬁnal driver of change relating to environmental considerations involves ecolabels. These “soft instruments” are not legally binding requirements, but their impact on manufacturers can be considerable. A representative ecolabel is the “EU Flower” ecolabel in the European Union, shown in Fig. 12. According to the European Commission’s website, “The European Eco-label is a voluntary scheme enabling European consumers including public and private purchasers to easily identify ofﬁcially approved green products across the European Union . . . It allows producers to show and communicate to their customers that their products respect the environment.” Detailed requirements for being granted use of the labels for various detergent and household product categories may be found at the European Commission’s website (http://europa.eu.int/comm/environment/ecolabel/). The importance of ecolabels and other such third-party endorsements will become an increasingly important consideration for detergent formulation, especially as special interest groups seek to inﬂuence consumer products without having to go through ofﬁcial legislative procedures. C. Cool Water Performance Along the “energy savings” sustainability vector described above, cool water performance will be a major driver of both laundry and dishwashing in the coming years. Regulations are coming into play that will force appliance manufacturers to meet speciﬁed energy consumption levels. The U.S. regulations coming into effect in 2007 governing appliances are representative, involving meeting a “modiﬁed energy factor” (MEF) of 1.26 (current U.S. toploading machines generally have MEFs in the range of 0.8 to 1.0; for calculation of MEF and other aspects of energy regulations, the reader is referred to the US Department of Energy website for more details, at http://www.eere.energy.gov/buildings/ appliance_standards/). Since ~85% of the total energy consumption of washing machines

© 2006 by Taylor & Francis Group, LLC

Future Outlook for Detergent Formulations Table 12

509

Innovation targets for detergents arising from the shift to cool water cleaning Topic

Fundamental Science

Builders Polymers

Plasticizers Catalysis

Surfactants

Speciﬁc Technology Targets • Better understanding of the behavior of all soils in general at low temperature • Better understanding of surfactant kinetics and surfactant aggregate morphologies at low temperature • Better understanding of adsorption/desorption physics and particle behavior of lipids below their melting point • Improved suspension and avoidance of residue/dissolution issues • Hydrophobic dispersants that can peptize and suspend solid lipid particles • Lime soap management to enable more satisfactory use of lipases • Cost-effective plasticizers effective in softening solid lipid soils • Surface active lipid plasticizers • Lipases with better efﬁcacy against solid-phase lipids • Bleach catalysis to offset loss in peroxide activity at lower temperatures • Development of desaturases to shift fatty acid chain proﬁle to lower mp triglycerides • Reinvent surfactancy for cool water • Formulators need to take a fresh look at their existing portfolio of surfactants against the criterion of cold water cleaning and scrutinize if current preferences are really the right ones • Exploitation of mid-chain branched branched surfactants that have demonstrated superior cold-water solubility

comes from heating the water, appliance manufactures are coping with the regulations via a combination of reducing the amount of water used, and by changing settings to consume less hot water. Besides energy considerations, the other driver responsible for the shift to cool water is the desire by consumers to better care for colored garments and other specialty garments. What this translates into is that average wash temperatures are going to drop by about 15 to 20˚C in both Europe and North America. Simplistically, this provides a clear target for detergent formulators: develop solutions that enable a degree of cleaning at cooler temperatures that matches or exceeds what is currently achieved at warm temperatures, e.g. 60˚F cleaning needs to match 90˚F cleaning. Table 12 summarizes some of the key directions in which detergents are going to have to move, in order to meet the demands of cool water cleaning. Surprisingly, there is a scarcity of technical literature on how detergency fundamentals change with a shift toward lower temperatures. A signiﬁcant portion of detergent innovation in the next decade is therefore going to be related to better understanding detergency processes at lower temperatures, and the development of new chemistries that are adapted to cooler temperatures. Some of the traditional detergent blocks are going to need to reinvent themselves to adapt, via revisitation of existing technologies that are currently on the shelf, via identiﬁcation of previously overlooked synergies and system

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510 Table 13

Price Opportunities and Future Directions for Rinse Water Reduction Processes Topic

Water reuse technologies

Rinse reduction technologies

Holistic solutions Hard surface applications Dish applications

Details • • • • • • • • • • • • • •

Additives that transform “gray water” into reusable water Rinse water into water that can be used in the next wash cycle Wash water that can be re-used Flocculation and self-ﬁltering/self-partitioning technologies Surfactants and builders with enhanced rinsability Controlled “rinse-release” technologies (e.g. suds suppressors) Cost-effective “vanishing surfactants” Actives that decrease slippery feel of rinse water Actives that increase water clarity of rinse water Devices and implements Continued development of no-rinse formulations Surfactants and builders with enhanced rinsability Controlled release suds suppression Splittable surfactants

approaches, or via development of new actives. Given that the primary difﬁculty in moving to cool water involves lipid removal, innovations are likely to be concentrated in new surfactants or alternative approaches to surfactants. D. More Efficient Rinse Processes Rinse processes are being called out for special attention given their criticality in developing markets. The demographic arguments above (most future population growth will occur in developing markets) in conjunction with the need for products having high sustainability standards with respect to water supply strongly imply that detergent products and technologies directed toward water savings will be an important growth vector for the industry. Technologies and products directed toward improving the efﬁciency of rinse processes in fact represent signiﬁcant whitespace. The only major products dealing with this stage of the laundry process are fabric enhancers, and these are generally not designed with water conservation in mind. Some design directions for rinse water reduction products are described in Table 13. These could include dish and hard surface applications as well as laundry applications. The additional underlying constraint imposed on all of these would be cost effectiveness in order to assure affordability for developing market consumers. Since the dominant laundry habit in developing geographies is hand-washing, the key qualities that need to be delivered to rinse water are suds suppression, water clarity, and nonslippery feel. Suds control is a special challenge as consumers in hand-wash geographies prefer high levels of suds in the preceding wash water, hence a speciﬁc technical need is to deliver a potent suds suppressor directly to the rinse. This could be via a separate rinse additive, but to improve simplicity and affordability, it would preferably be delivered via the main detergent, either via controlled rinse release or via “vanishing surfactants.” “Vanishing surfactants” mean surfactants whose functionality changes upon entry into the rinse cycle, either via an induced splitting of the molecule into two or more parts (e.g., pH change–induced hydrolysis) each of which is nonfoaming, non-surfaceactive, or highly water soluble, or via a pH-sensitive change in the molecule that renders it nonfoaming, non-surface-active, or highly water soluble. Flocculation methods are

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New Don’t Mop With Dirty Water Again!TM Pine-Sol® Cleaner Only New Don’t Mop with Dirty Water Again!TM Pine-Sol® contains a revolutionary new formula that pulls the dirt to the bottom of the bucket so it doesn’t spread back onto the floor. Now you’ll be mopping with cleaner water.

Dirt gets pulled down to the bottom, so you’re mopping with cleaner water.

Figure 13

Water reuse product.

already being used in products intended for generating potable water in developing countries. Their use in laundry would need to involve some means of preventing massive redeposition and whiteness negatives from the ﬂocculate; self-ﬁltering, self-partitioning technologies, or coupling with devices or inexpensive implements could enable this. Interestingly, in developing markets, there is a product on the market with a water-reuse/clariﬁcation technology, as shown in Fig. 13. This example gives an indication of what the future could look like for water reduction technologies in developing markets. We predict that water conservation-directed products for developing markets will emerge as a future growth category for the laundry sector globally. In addition to being the right thing to do, such products have strong potential for building relationships between product manufacturers and government agencies, as many local governments are under pressure to address the growing water shortages. Table 13 describes some potential directions.

VIII. MISCELLANEOUS DESIGN DIRECTIONS The following three sections are design directions that several of the above drivers of change suggest will be important in the future of detergent and product design, namely, (1) “reinvented liquid detergents,” (2) home dry-cleaning, and (3) advances in catalytic chemistry. A. “Reinvented” Liquid Detergents The shift from powder to liquid detergents in North America is one of the most important business trends in both the laundry and automatic dish detergent sectors. In laundry detergents for example, liquids made up about 60% of the market in 1997, and this rose dramatically to over 70% by 2002, and is expected to continue rising. The primary drivers are convenience, perceived better solubility (which resonates with shift to cooler wash temperatures), the enablement of easy pretreating. Despite this success, there is much more room for innovation, and all signs are that the coming 5 to 10 years will see signiﬁcant improvements in both performance and “experience” vectors for liquid detergents in both dish and laundry. Table 14 summarizes some future design directions. The “holy grail” in liquid detergents is to be able to formulate both bleach and enzymes in an aqueous liquid matrix. Despite the phenomenal market success of liquid detergents, there is still no available cost-effective manner in which to co-formulate both bleach and enzymes in this product form. The key reasons are (1) incompatibility between

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Table 14

Innovation Opportunities for Liquid Detergents

Topic Bleach-in-liquid

Structured liquids

Surfactancy

Higher pH enablement

Details • Cost-effective encapsulation and release technologies for bleach with true long-term stability/integrity in liquid matrix and selective trigger mechanisms • Reliable, quantitative triggered release • Reliable, robust partitioning (no slow-cross contamination) • Encapsulation media capable of maintaining pH or ionic strength gradients over long periods of time and large temperature ranges • Formula stable and color-safe bleach catalysis • Thickening approaches with complete lack of haziness/lumpiness • Cost-effective visible particles with active delivery capability • Neutral pH effective thickeners • Novel and cost effective transparent packaging • More hardness tolerant surfactants • More hydrophobic surfactants • Development of better supply chains to enable alternative workhorse surfactants such as methyl branched hydrophobe-based surfactants, and MES • Surfactants adapted for cool-water cleaning • Better enzyme stability • Technologies to manage color care (compensate for pH) • Nonbuilder hardness management strategies • Cost-effective and environmentally acceptable soluble builders • More cost-effective options in cationic surfactants

enzymes and bleach (bleach’s tendency to denature enzymes), (2) long-term instability of the bleach or bleach activator itself in an aqueous formulation. Although certain bleaches may exhibit satisfactory shelf-life in aqueous liquid formulations, these are often limited to pH ranges which may not be desirable to the formulator. Stability and compatibility of enzymes and bleaches is necessary in two stages: during product storage (“shelf-life”), and during use (i.e., in the wash liquor). Contrasting this to powdered detergents, enzymes and bleaches are easily co-formulated in powdered detergent formulations because they may be delivered in separate, discrete particles, and the dry powder form ensures the stability of water-sensitive bleach actives; for the in-use stage, many enzymes have been developed which are stable in the presence of oxygen bleaches such that upon dissolution of product into water, bleach and enzyme are both long-lived enough in solution to perform their detersive roles during the washing process. In contrast, liquid detergent formulas present difﬁculties for the shelf-life stage, either because the bleach components suffer hydrolysis or decomposition over days/weeks/months, or because the bleach denatures the enzymes during shelf-life such that by the time the product is used, there is little or no enzyme activity remaining, and part of the bleach has been consumed. Current means of co-formulating enzymes and bleaches into liquid detergent compositions include: (1) nonaqueous solvents as the continuous phase (prevents hydrolysis of the bleaching species, while also inhibiting bleach-enzyme interactions by keeping the both species insoluble), (2) dual-compartment packaging, (3) encapsulation of bleach and/or enzyme—bleach and enzyme are protected from each other and from the

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continuous phase. Unfortunately, all of these approaches have drawbacks and have yet to be proven to be commercially effective. Nonaqueous solvents are expensive and often involve safety and environmental issues. Dual-compartment packaging is expensive and often inconvenient. For encapsulation to be effective, the encapsulation material must be robust enough to keep the components partitioned during processing and throughout foreseeable ﬂuctuations in shipping/storage temperatures. On the other hand it must also be sensitive enough to release the actives upon use (via some “trigger” present in the wash conditions but not present in storage conditions). Numerous encapsulation approaches have been developed; to date, however, none has been cost-effective enough for detergent formulations. The functional incentives (breakthrough cleaning, convenience) to bleach + enzymein-liquid formulation are large enough that this will remain a key design direction and innovation opportunity for liquids in the coming decade. The ﬁnancial incentives also support this direction: consumer dollars in North America have recently lavished rewards on the “oxi” category of bleach additives, and those who develop a way to achieve oxygen bleaching via consumers’ preferred liquid detergent form will be amply rewarded in the marketplace. Vigorous activity in the patent literature on structured liquid detergents suggest that totally new generation of heavy duty liquids (HDLs) will enter and reshape the market. Higher viscosity and/or structured liquids offer several beneﬁts: a novel experience and less messiness in pouring, compaction (reduction of transportation/packaging costs, resonance with sustainability objectives), ease in pretreating (detergent stays where you want it), and perhaps most importantly, the enablement to include visible particles with functional and/or aesthetic beneﬁts. The key technology need for structured liquids is thickening approaches that are truly nonhazy and nonlumpy across the spectrum of storage and process temperatures, and over long shelf-life, and with effectiveness at the near-neutral pHs required by some HDLs. Improvements in performance and cost for both internal and external structurants will continue. The reader is referred to the review by Farooq for more details on detergent thickeners [18]. Two other important future design themes for liquid laundry detergents are improved surfactancy and enablement of high-pH HDL formulas. Surfactants need to be hardness tolerant in order to cope with reduced or absent builder systems, and they need enhanced solubility in cooler wash temperatures. In terms of design, these needs are difﬁcult to reconcile with the need for increased hydrophobicity required to drive greasy soil cleaning, and in terms of economics, it is difﬁcult to change workhorse surfactant systems due to supply-chain and feedstock reasons. One attractive option is to exploit the ability of methyl branching in hydrophobes, which allows increased hydrophobicity to drive cleaning while preserving both cool water solubility and hardness tolerance. The industry can therefore expect to see future improvements in the design and availability of such materials. Typically, liquid laundry detergents are formulated at closer to neutral slightly basic pH ranges. The advantages are that enzymes are stabilized, and dye loss from fabrics is reduced. However, the lower pH regime means that the detergency process is deprived of a lot of soil and fabric ionization working in its favor, and hence in many areas liquid detergents are inferior in cleaning to powdered detergents working at higher pH (e.g., particulate cleaning), and this gap is especially pronounced at cooler wash temperatures. Higher-pH HDLs are therefore a fertile design direction for formulators; the technical challenges ripe for proprietary solutions include: (1) enzyme stability during shelf-life, (2) technologies for color to compensate for greater dye loss at higher pH, and (3) Ca/Mg control.

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B. Home Dry Cleaning An area of emerging importance and signiﬁcant recent patent activity is home dry cleaning. On ﬁrst consideration, home dry-cleaning might seem to be an insigniﬁcant future trend due to the use of organic solvents which might pose “chemical concerns” related to safety and disposal. However, dry-cleaning actually resonates with a number of the future drivers of change described in this chapter: • Energy saving—organic solvents can deliver outstanding detergency at cool temperatures against the lipid/hydrophobic stains that are the number one weakness of water-based detergents at cool temperatures • Water savings—no water needed, or very little water needed (e.g., <1% of wash liquor) • Textile trends—inert organic solvents are extremely gentle on fabrics of all sorts, and delight consumers by maintaining garments in a like-new conditions, and can be more compatible with innovative textiles • Convenience—dry cleaning systems enable “no-sort” laundry experience Another driver is that in developed markets, consumers are increasingly willing to pay a premium for innovative appliances, such as high-end washer/dryer systems (some of which total for more than U.S.$1,500), steam-cleaning carpet systems, central home vacuum systems, and commercial grade kitchen appliances. Recent innovations in both chemistry and appliance design have enabled dry cleaning processes to overcome some of their historical issues. Key advances include the development of D5 (cyclopentasiloxane) silicone solvents with improved environmental and safety proﬁles, the development of dry cleaning detergent systems effective on hydrophilic stains without the need for pretreatment, and improvements in miniaturization and efﬁciency of dry cleaning appliances [19–23]. Figure 14 shows potential home dry cleaning appliance described in U.S. Patent 6,045,588. These technical and market factors suggest that home dry cleaning research and innovations will continue during the next 5 to 10 years and make home dry cleaning a real possibility for market introduction.

10 12

15 11

14

13

Figure 14. Example of home dry cleaning apparatus (U.S. Patent 6,045,588).

© 2006 by Taylor & Francis Group, LLC

Future Outlook for Detergent Formulations Table 15

515

Future Design Directions for Partitioned/Staged chemistry

Topic Consumable formats

Key functional beneﬁt targets

Via appliance

Challenges

Details • • • • • • • • • • • • • • • •

Via ﬂexible dose (powder/liquid) Via unit dose Via Devices/substrates Bleach and enzymes (improved performance, enablement in liquid form) Through-the-wash softening Rinse-speciﬁc suds suppression Autodish rinse aid chemistry Two or more consumable cartridges Autodosing by machine at right time Washer, dryer, dishwasher Reliable, fast, and quantitative triggered release Reliable, robust partitioning (no slow-cross contamination) Films and encapsulation media capable of maintaining long-term pH or ionic strength gradients Consumer issues: value impression, dosage control for unit dose Multifunctional ﬁlms Cost-efﬁciency

C. Partitioned/Staged Chemistry The use of partitioned and/or staged chemistry resonates with a number of future trends driving the industry, i.e., simpliﬁcation (combining two or more products into one), efﬁciency (many current ingredients are overformulated more than if they could be delivered at the right time or without competition or attack from other ingredients), and new appliances and devices/substrates (mechanical delivery options for achieving staging or separation of chemistry). Table 15 describes some current and emerging factors that will impact formulation and design. From a conceptual standpoint, staged/triggered release will also become more important because it will unshackle formulators’ creativity. Currently, most formulations are fundamentally restricted to a narrow ﬁeld of options due to the historical product forms: i.e., the formulator chooses a “basic chassis” (powder, liquid, tablet, gel pouch), and from that point on additional degrees of freedom are limited according to what is compatible with what, and what can be processed. This is a profound unconscious constraint on creativity and innovation. Innovations in partitioned detergent chemistry will frees detergent formulators to truly start from detergency mechanisms and consumer needs of the target application and let those dictate ingredient selection and levels. The formulation endpoints at which future formulators arrive may look completely different than the current stock formulas to which most powders, liquids, and tabs currently adhere. D. Advances in Catalytic Chemistry The use of catalytic chemistry resonates with a number of future trends driving the industry, primarily cool water cleaning (need to achieve acceleration of removal, soil breakdown, and decolorization kinetics), and cost-efﬁciency sustainability (smaller amounts of catalysts to replace larger amounts of other detergent ingredients). These powerful drivers, in conjunction with continuing advances in catalysis science, materials science, biotechnol-

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ogy, biomimetics, chemical synthesis, and other areas, indicate that future detergents must and will develop new and improved catalytic processes. Catalysis directions for detergency can be categorized into three general areas: bleach catalysis, enzyme catalysis, and “new catalysis vectors.” It is outside the scope of this chapter to present a detailed overview on the future outlook for bleach and enzyme catalysis, other than to mention some of the key design trends, as summarized in Table 16. For more perspective, the reader is referred to the articles by Reinhardt [24] and Crutzen et al. [25]. One future catalysis design direction that deserves special mention is catalytic utilization of atmospheric molecular oxygen as an oxidant source for bleaching. This is a

Table 16

Future Design Directions for Catalytic Chemistry

Topic Bleach catalysis

Enzyme catalysis

New catalysis

Details • New options for oxidant sources beyond current perborate and percarbonate • Catalysis to enable use of atmospheric oxygen as oxidant source • Reliable color and ﬁber safety [aided by new guidelines from garment industry stakeholders, e.g., fastness laundering test method ISO (International Standards Organization) 105:C09, and new AISE (Associatiòn Internationale de la Savonnerie, de la Détergence et des Produits d’Entretien) fabric dye sets] • Compatible with aqueous liquid detergents and enzymes • Exploration by appliance and device manufacturers of cost-effective methods of using photoactivation as a route to utilizing atmospheric oxygen as a bleach oxygen source • Continued use of new biotechnology tools to deliver cost and activity breakthroughs in current workhorse enzyme classes (proteases, carbohydrases, lipases) • New enzyme classes beyond proteases, carbohydrases, and lipases • Bleaching enzymes • Lipases with increased activity on triglycerides below their melting points • Lipase enabling technologies (fatty acid management—malodor management, Ca soap suspension, etc.) • Transesteriﬁcation processes for in situ generation of surfactants (convert triglycerides into Ca/Mg-tolerant fatty-acid surface active species) • Whole-cell systems containing multienzyme systems for in situ multistep conversions w/o product inhibition • Development of completely new catalytic processes in areas other than enzymes or bleaching • Biomimetic catalysis • Catalytic antibody technology • Catalytic approaches to lipid removal and suspension • Catalytic approaches to converting liberated biopolymer monomers or oligomers (oligo/monosaccharides, amino acids, short peptides) into species with detergency activity

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holy-grail target of the industry and one that promises to remain a research theme for detergents during the next decade. There are currently three routes to using atmospheric oxygen: via enzymatic processes, via light/photoactivation, and via free radical chemistry. Free radical chemistry is problematic due to damage to ﬁbers, dyes, and other detergent ingredients. Photoactivation belongs to the realm of appliance makers but could also be leveraged in consumer or semiconsumable devices in conjunction with detergent products. The key challenge in the enzyme route is developing materials that do not require exotic and expensive cofactors, and that have adequate activity at room temperature.

REFERENCES 1. Gadiesh, O. and Pean, J-M., “How Marketing Locally Boosts your Business,” Wall Street Journal, http://www.careerjournal.com/columnists/managersjournal/20030909-managersjournal.html. 2. Putter, A., “The Future of Surfactant Feedstocks,” 5th World Conference on Detergents, Ed. A. Cahn, 2002, AOCS Press, p. 110. 3. WO Patent 01-02328. 4. Computational Methods in Surface and Colloid Science, Surfactant Science Series, Vol. 89, Ed. M. Borowko. 5. Yu, C. H., Norman, M. A., Newton, S. Q., Miller, D. M., Teppen, B. J., and Schafer, L. “Molecular Dynamics Simulations of the Adsorption of Proteins on Clay Mineral Surfaces,” Journal of Molecular Structure (2000), 556(1–3), 95–103. 6. Bains, A. S., Boek, E. S., Coveney, P. V., Williams, S. J., and Akbar, M. V., “Molecular Modeling of the Mechanism of Action of Organic Clay-swelling Inhibitors,” Molecular Simulation (2001), 26(2), 101–145. 7. Lal, M., Ruddock, N., and Groot, R., Unilever Research, “Mesoscale Modeling of Oil/Water/Surfactant Systems,” http://www.accelrys.com/cases/oilwater.html. 8. Nicolaides, D., “Modeling and Optimization of Detergents,” 5th World Conference on Detergents, Ed. A. Cahn, 2002, AOCS Press, p. 177. 9. http://www.accelrys.com/cases/henkel_whole.html. 10. WO Patent 0218528A1. 11. WO Patent 00102639A1. 12. U.S. Patent 4,784,666. 13. WO Patent 09958753A1. 14. Science, Vol. 299, 2003, p. 231. 15. U.S. Patent 6,562,142 B1. 16. Chevalier, Y., “New Surfactants: New Chemical Functions and Molecular Architectures,” Curr. Opin. Coll. Int. Sci., 7 (2002), 3. 17. Lang, S., “Biological Amphiphiles (Microbial Biosurfactants)”, Curr. Opin. Coll. Int. Sci., 7 (2002). 18. Farooq, A., “Rheological Modiﬁers for Aqueous Solutions,” Chapter 22, Surfactant Science Series, Vol. 82, 1999. 19. U.S. Patent 6,045,588 (Estes et al., “Non-Aqueous Washing Apparatus and Method,” assignee Whirlpool). 20. U.S. Patent 2003/0097718 A1 (Evers et al., “Dry Cleaning Process,” assignee Unilever). 21. U.S. Patent 2003/0046963 A1 (Scheper et al., “Selective Laundry Apparatus Using Water,” assignee Procter & Gamble). 22. WO 02/072939 A2 (Banerjee et al., “Modiﬁed Machine,” assignee Hindustan Lever). 23. WO 03/000833 A1 (Deak et al., “Fabric Care Compositions for Lipophilic Fluid Systems,” assignee Procter & Gamble). 24. Reinhardt, G., “New Oxygen-based Bleach Technology,” 5th World Conference on Detergents, Ed. A. Cahn, 2002, AOCS Press, p. 69.

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25. Crutzen, A. and Douglass, M., “Detergent Enzymes — A Challenge,” Chapter 18 Surfactant Science Series, Vol. 82, 1999.

© 2006 by Taylor & Francis Group, LLC

Index A Accelerated solvent extraction (ASE), 308 Acrylic dyeing, 292–294 Additive-additive interactions, 459–465 effect on antiwear and anti-extreme pressure performance, 460–461 effect on high-temperature deposit formation, 461–462 effect on oxidation stability, 460 strength and type of, 459 See also Lubricants, detergent formulations in Aftertreatment process, in textile applications, 296 Agricultural detergent formulations, 13, 19t Air stripping efficiency, 361–362 Alameda Point Naval Air Station (NAS), supersolubilization studies at, 362–364 Alcohol, defining, 351 Alcohol sulfate (AS), 56, 160 Alkaline water flooding process, 336 Alkyl ethoxy sulfate (AES), 116, 160 Alkyl polyglycoside, shampoos based on, 234 All-purpose cleaners, 159–164 major ingredients in, 160–164 performance profile of, 159–160 suds and aesthetics of, 159 See also Liquid household cleaners Aloe vera, 213 Amine oxide (AO), 113 See also Dishwashing detergents, for household applications Amphoteric surfactants, 4, 58, 113, 116 See also Surfactants Amylolytic enzymes. See Enzymes Anionic surfactants in emulsion polymerization, 401–419 in hand dishwashing detergent, 112, 115–116 in laundry detergent, 4, 56 in textile finishing, 299 See also Surfactants Anticorrosion glass care, 142 Antifilming surface care, 142–143 Antifoam agents, 12 Antimicrobial agents, 164, 166

Antimicrobial textile finishing, 301 Antistatic textile finishing, 300–301 Appliance innovations, 497–499 Aquifer remediation. See Environmental remediation, surfactant-based systems for Armstrong-Nome retention model, 317 Ashless lubricant dispersants, 445–451 esters, 446–447 graft ethylene-propylene copolymers, 449–450 Mannich condensates, 448–449 oxazolines, 447 succinimides, 445–446 thiophosphonates, 450 See also Lubricants, detergent formulations in Atomic force microscopic (AFM) technique, for hair cosmetics, 245–246 Auto care formulations, 262–270 automatic prewash/main wash products, 262–265 conclusion, 276 exterior car care agents/polishes, 267–268 glass/windshield cleansing, 269–270 interior car care/leather care, 268–269 introduction, 262 manual car wash products, 262, 263t rim/tire care, 269 rinse/drying aids, 265–267 Automatic dishwashing detergents bleach catalyst technologies for, 135–138 bleach metal catalyst technology design, 135–137 product performance of Cobalt (III) bleach catalyst, 138 bleach technologies for hydrophobic stains, 138–139 chemistry of, 122, 132–135 key consumer benefits, 133 major ingredients in, 133–135 new product forms, 132–133 process of automatic dishwashing, 122, 132 conclusion, 143 glass surface care technologies, 141–143 anticorrosion glass care, 142 antifilming surface care, 142–143 introduction, 2, 106–109 low-foaming nonionic surfactants, 139–141

519

520

Index

summary of recent patents for, 143, 144–149t See also Dishwashing detergents, for household applications Automatic dishwashing process, 122, 132 Automatic prewash/main wash products, 262–265 See also Auto care formulations Automobile detergent formulations, 13, 20t See also Auto care formulations Automotive lubricants. See Lubricants, detergent formulations in

B Bar laundry detergent, 90–93 Bath oils, microemulsions as, 236, 237t Bathroom cleaners, 164–166 major ingredients in, 165–166 suds and aesthetics of, 164–165 See also Liquid household cleaners Battery-powered dishwashing brush, 122 Beverage stain removal, 138 Biosurfactants, 342 Bleach all-purpose cleaners, 169–170 See also Liquid household cleaners Bleach-containing liquids, 79–81 Bleaching agents in automatic dishwashing detergent, 134, 135–137 chemistry of, 9–10 in hand dishwashing detergent, 121 for hydrophobic stains, 138–139 in laundry detergent, 62–63 performance washing tests for, 180–182 product performance of Cobalt (III) bleach catalyst, 138 in textile processing, 288–289 in toilet bowl cleaners, 167–168 See also Liquid bleach formulations Bleach metal catalyst technology, for automatic dishwashing, 135–137 Bleach performance tests, 180–182 Brightners/fabric whitening actives, 11, 196 Builders in all-purpose cleaners, 162 in automatic dishwashing detergents, 134 chemistry of, 8–9 in glass cleaners, 171 in laundry detergent, 58–59 See also specific detergent formulations

C Calcium carbonate, 59 Calculation of phase inversion in concentrates (CAPICO) system, 224–227 Car exterior care agents/polishes, 267–268 See also Auto care formulations

Car interior care/leather care, 268 Carpet cleaners, 172–174 shampoos, 173 spotters and high traffic cleaners, 172–173 spray extraction machines, 173–174 See also Liquid household cleaners Car polishes, 267–268 Car wash soaps, 263–265 Catalytic chemistry, advances in, 515–517 Cationic surfactants, in emulsion polymerization, 419 See also Surfactants Cellulose dyeing, 290–291 Chelating agents chemistry of, 8–9 in hand dishwashing detergent, 116 in laundry detergent, 58, 63 See also specific detergent formulations Chemical flooding process, 327–328 See also Enhanced oil recovery, surfactant formulations in Chemical regulations, new, 505–507 Chlorinated solvents, 348 Chlorine bleach, 182–191 fabric safety of, 187–191 introduction, 9, 182–183 stability of, 183–187 See also Liquid bleach formulations Citric acid, 8, 59 Cleaning In Place (CIP) products, 275–276 Cleaning mechanisms, of hand dishwashing detergents emulsification, 111 grease "roll-up," 111, 112f solubilization, 111–112 surfactant-rich intermediate phase, 112 Cloud-point (CP) extraction, 309–313 Cobalt (III) bleach catalyst, product performance of, 138 Color, in toilet bowl cleaners, 168 Color care formulas, in laundry detergent, 94–96 Color safety in hydrogen peroxide bleaches, 197, 201–202 in hypochlorite bleaches, 191 Computational modeling, development of, 491–492 Concentrated minisolution (CMS) method, in hand dishwashing, 110 Concentrate robustness study, in heavy duty liquid (HDL) detergent, 45–49 Consumer trends in cosmetic products, 212–213 future outlook in, 493–497 in laundry products, 52–54 Contaminant extraction, maximizing, 354–355, 358–360 See also Environmental remediation, surfactantbased systems for Convenient products, in personal cleansing, 211–212 Cool water performance, advances in, 508–510 Cosmetic cleansing formulations, trends for, 208–214 evolution of cleaning, 208–210

Index

521

future cleansing concepts, 210 improved cleansing conditions, 209 mildness concept, 209–210 product safety, 209 psychological trends, 211–214 See also Personal care formulations Cotton impurities, 284 Cream cleansers (scouring creams), 170–171 See also Liquid household cleaners Creams/lotions, for sensitive skin, 238, 240t Critical micelle concentration (CMC), 31, 116, 475–478

D Defoaming, for textile applications, 295–296 Degree of polymerization (DP) values, 181 Dense nonaqueous phase liquid (DNAPL), 348 Depletion flocculation, 220 Dermatological tests, in body-cleansing formulations, 214–216 Design of Experiments (DOE) software, 31, 38 Design themes for detergents, future. See Detergent formulations, future outlook for Design tools, cost-effective, 491–493 Desizing agents, on textile fibers, 286–287 Detergency theory and mechanisms, 15, 18 soil removal, 19, 21–23 suspension, 23–24 Detergent applications, 3 Detergent categories, 2–3 Detergent formulations, future outlook for appliance innovations, 497–499 consumer trends, 493–497 devices and substrates innovations, 504–505 economic drivers, 487–493 business environment, 487–488 cost-effective design tools, 491–493 efficiency breakthroughs, 488–491 environmental and regulatory considerations, 505–511 cool water performance, 508–510 efficient rinse processes, 510–511 new chemical regulations, 505–507 sustainability design themes, 507–508 home hard surface innovations, 499–502 introduction, 484–487 miscellaneous design directions, 511–517 advances in catalytic chemistry, 515–517 home dry cleaning, 514 partitioned/staged chemistry, 515 reinvented liquid detergents, 511–513 textile innovations, 502–504 Detergent formulations, separation science in introduction, 305–306 micellar electrokinetic capillary chromatography (MECC), 318–319 micellar liquid chromatography (MLC), 316–318

micellar solubilization (MS), 306–308 micelle-mediated separation/preconcentration techniques, 308–316 micellar ultrafiltration, 313–316 microwave-assisted micellar extraction (MAME), 308–309 thermal phase separation (cloud-point extraction), 309–313 Detergent formulations, statistical mixture design of conclusion, 49 examples of, 31–49 concentrate detergent blend, 45–49 heavy duty liquid (HDL) detergent, 32–39 light duty liquid (LDL) detergent, 39–45 introduction, 27–29 mixture design experiments, 29–31 Detergents, overview of common ingredients in, 4–13 bleaching systems, 9–10 builders and chelants, 8–9 dispersing polymers, 4–8 performance enhancing minors, 11–13 solvents, 10–11 surfactants, 4 detergency theory and mechanisms removal mechanisms, 19, 21–23 suspension mechanisms, 23–24 examples of detergent formulations, 13–21 introduction, 2–3 theory and mechanisms, 15–24 See also specific detergent formulations Devices and substrates, innovations in, 504–505 Direct application (DA) method, in hand dishwashing, 110 Dishwashing detergents, for household applications automatic dishwashing detergent, 122, 132–143 bleach catalyst technologies for, 135–138 bleach technologies for hydrophobic stains, 138–139 chemistry of, 122, 132–135 glass surface care technologies, 141–143 low-foaming nonionic surfactants, 139–141 summary of recent patents for, 143, 144–149t conclusion, 143 hand dishwashing detergent, 109–122 chemistry of, 109–112 new product forms, 121–122 recent developments in, 115–121 summary of recent patents for, 122, 123–131t typical ingredients in, 112–115 introduction, 2, 13, 16t, 106–109 busier consumer lifestyles, 108–109 smaller households, 108 trends in residential dishwashers, 107–108 summary, 106 Dish wipes, 121–122 Disinfectancy, in all-purpose cleaners, 160, 164 Dispersing dyeing agents, 294 Dissolution aids, in hand dishwashing detergents, 115, 120–121

522

Index

DLVO theory, 219 Dry cleaning products, 10 Dual-bottle liquids, 81–82 Duhring Chamber Test, 214, 215 Dye fixatives. See Laundry detergent formulations Dyeing assistance, surfactants as dispersing agents, 294 foaming and defoaming, 295–296 introduction, 289–290 leveling agents, 290–294 wetting and penetrating agents, 294–295 See also Textile processing, surfactant applications in Dye-substantive leveling agents, 290

E Economic future outlook, for detergents, 487–493 business environment, 487–488 cost-effective design tools, 491–493 efficiency breakthroughs, 488–491 See also Detergent formulations, future outlook for Efficiency breakthrough design themes, 488–491 Emulsification mechanism, of cleaning by hand, 111 Emulsion formulation technology, 216–227 calculation of phase inversion in concentrates (CAPICO) system, 224–227 high-pressure homogenization (HPH), 222 phase inversion temperature (PIT) procedure, 222–224 physicochemical properties, 216–222 See also Personal care formulations Emulsion polymerization process, 392–419 choice of surfactants, 400–419 composition table, 406–416t homogeneous nucleation mechanism, 396–398 latex stabilization, 398–400 micellar nucleation mechanism, 393–396 See also Polymerization, surfactant formulations in Encapsulation techniques, for cosmetic requirements, 231–233 Encrusted grease removal, test methods for, 157–158 See also Liquid household cleaners Energy savings. See Environmental and regulatory considerations Engine cleaner. See Lubricants, detergent formulations in Enhanced oil recovery, surfactant formulations in alkaline water flooding, 336 applications of, 339–342 acidified oil/surfactant enhanced alkaline system, 341 adsorption of surfactants on kaolinite, 341 biosurfactants, 342 dual surfactants for high salinity reservoir, 341 mixed micelles, 342

neutralizations using low interfacial tension (ITF), 342 spontaneous inhibition of aqueous surfactants, 340–341 surfactant adsorption at reservoir rock, 340 chemical flooding, 327–328 commercial applications, 328 field testing, 328 laboratory methods, 327–328 chemical surfactants, 329–332 cation exchange of, 332 stability of, 332 interfacial tension and residual oil saturation relation, 338–339 introduction, 3, 327 phase behavior in EOR systems, 339 polymer flooding, 335–336 scope primary recovery, 326 secondary recovery, 326 tertiary oil recovery, 326 surfactant flooding, 332–333 surfactant mixtures, 333–335 application of ideal mixing, 334 ideal mixtures, 334 nonideal mixtures, 334–335 surfactant-polymer interaction in solution, 337–338 traditional surfactant/polymer flooding, 336–337 See also Environmental remediation, surfactantbased systems for Environmental and regulatory considerations, 505–511 cool water performance, 508–510 efficient rinse processes, 510–511 new chemical regulations, 505–507 sustainability design themes, 507–508 See also Detergent formulations, future outlook for Environmental Protection Agency (EPA), U. S., 506 Environmental remediation, surfactant-based systems for contamination problem, 348–350 economic/technical factors, 353–358 maximizing contaminant extraction, 354–355 minimizing surfactant losses, 354 mitigating vertical migration concerns, 356–358 surfactant regeneration/reuse, 355–356 field results, 358–364 Alameda Point Naval Air Station (NAS), 362–364 Hill Air Force Base (AFB), 358–360 Tinker Air Force Base (AFB), 361–362 future advances/applications, 364–366 summary, 3, 347–348 surfactant enhanced approach, 350–351 surfactant fundamentals, 351–353 Environmental safety, in cosmetic products, 209 Enzymes

Index

523

in automatic dishwashing detergents, 134 in hand dishwashing detergents, 121 in laundry detergent, 11, 61–62 EO/PO block copolymers, 57 Ester lubricant dispersants, 446–447 Experimental error, 30–31 Experimental mixture design conclusion, 49 defining features of, 29–31 examples of, 31–49 concentrate detergent blend, 45–49 heavy duty liquid (HDL) detergent, 32–39 light duty liquid (LDL) detergent, 39–45 introduction, 27–29 Exterior car care agents/polishes, 267–268 Extraction techniques. See Separation science, detergent formulations in

F Fabric care formulas, in laundry detergent, 94–96 Fabric oxidation, 181–182 Fabric safety in hydrogen peroxide bleaches, 201–202 in hypochlorite bleaches, 187–191 Fabric softeners, 2, 96–99 See also Laundry detergent formulations Facial care creams, 241 Facial cleansers, 236, 237t, 238t Fatty alkanol amides, 113, 115 Fibers. See Textile processing, surfactant applications in Fiber-substantive leveling agents, 290 Fillers (minors), in laundry detergent, 65–66 Finishing processes, surfactant applications in antistactics, 300–301 other applications, 301–302 softeners, 298–300 Fixing process, in textile applications, 296 Floor cleansers, industrial quick dry, 271–272 Floor tile cleansing, industrial, 272 Fluorescent whitening agents (FWA), 65–66 Foam boosters, 11–12, 113, 115 See also specific detergent formulations Foam cosmetic stability test, 247–248 Foaming capacity of shampoos, 479–480 for textile applications, 295–296 Foaming profile test, for surface cleaners, 158–159 Food processing equipment. See Industrial and institutional (I & I) applications Formulation development. See Detergent formulations, statistical mixture design of Formulators, 27 Fountain solutions, surfactants for, 384–385 See also Paints and printing inks Fragrance

in all-purpose cleaners, 159 in hydrogen peroxide bleaches, 197 in toilet bowl cleaners, 168 Full sink (FS) method, in hand dishwashing, 110 Future design directions. See Detergent formulations, future outlook for

G Gardner abrasion scrub tester, 157 Gel cleansing products, industrial, 270–271 Gel permeation chromatography (GPC), 187–188 Glass cleaners, 171–172 See also Liquid household cleaners Glass cleaning, improvements in, 275 Glass surface care technologies, in automatic dishwashers, 141–143 anticorrosion glass care, 142 antifilming surface care, 142 Glass/windshield cleansing, 269–270 Graft-ethylene-propylene copolymers, 449–450 Granular laundry detergent. See Laundry detergent formulations Grease cleaning technologies, in hand dishwashing detergents, 116–117 Grease "roll-up" mechanism, of cleaning by hand, 111, 112f Ground water resources, contamination of. See Environmental remediation, surfactantbased systems for

H Hair conditioner products, 236–237, 238t Hair cosmetic performance tests, 242–247 atomic force microscopy, 245–246 dry combing, 242–243 hair gloss, 247 hair thickness, 244–245 oscillation properties, 246 shadow-image analysis, 245 tensile strength, 243–244 wet combing, 242 See also Personal care formulations Hair styling products, 237–238, 239t Hand dishwashing detergents chemistry of, 109–112 mechanisms of cleaning, 111–112 methods of hand dishwashing, 110–111 process of hand dishwashing, 109–110 conclusion, 143 introduction, 2, 106–109 new product forms, 121–122 battery-powered brush, 122 dish wipes, 121–122 recent developments in, 115–121

524 bleaches, 121 enzymes, 121 low-IFT grease cleaning technologies, 116–117 product dissolution aids, 120–121 suds boosting polymers, 118–120 surfactants, 115–116 summary of recent patents for, 122, 123–131t typical ingredients in, 112–115 foam (suds) stabilizers, 113, 115 hydrotropes and dissolution aids, 115 surfactants, 112–113, 114t See also Dishwashing detergents, for household applications Hand dishwashing methods, 110–111 concentrated minisolution (CMS), 110 direct application (DA), 110 full sink (FS), 110 Hand dishwashing process, 109–110 Handwash vs. machine wash laundry, 70–71 See also Laundry detergent formulations Hard surface cleaning formulations, 13, 17t Hard surface innovations, 499–502 Health and well-being issues, in cosmetics, 213–214 Heavy duty granules (HDG), in laundry detergent introduction, 66–67 low density vs. high density products, 69–70 machine wash vs. handwash laundry, 70–71 phosphate vs. nil-phosphate builders, 67–69 Heavy duty liquids (HDL), in laundry detergent bleach-containing liquids, 79–81 dual-bottle liquids, 81–82 introduction, 71 isotropic liquids, 71–76 mixture design of, 32–39 structured liquids, 76–79 See also Detergent formulations, statistical mixture design of Herbicidal compositions, 13 Herbicidal formulations, 19t High density vs. low density products, 69–70 High-pressure homogenization (HPH), 222 High-throughput screening tools, development of, 491–492 High traffic carpet cleaners, 172–173 See also Liquid household cleaners Hill Air Force Base (AFB), solubilization/mobilization studies at, 358–360 Holistic innovations, 504–505 Home dry cleaning, 514 Home hard surface innovations, 499–502 Home laundry detergent. See Laundry detergent formulations Homogeneous nucleation mechanism, 396–398 Household soil classifications, 154–156 Household surface classifications, 156–157 Household surface cleaners. See Liquid household cleaners Hydrogen peroxide, 62, 168

Index Hydrogen peroxide bleach, 181–202 color and fabric safety, 201–202 introduction, 191–192 stability of, 192–197 stain removal performance of, 198–201 See also Liquid bleach formulations Hydrophobic stains, bleach technologies for, 138–139 Hydrotropes (coupling agents) in all-purpose cleaners, 162–163 in hand dishwashing detergent, 115 Hypochlorite bleach, 182 See also Chlorine bleach

I Industrial and institutional (I & I) applications Cleaning In Place (CIP) products, 275–276 conclusion, 276 gel cleansing products, 270–271 glass cleaning, 275 introduction, 3, 15, 20t, 21t, 262, 270 nanostructured floor tile cleansing, 272, 273t natural raw material cleaners, 276, 277t odor control products, 272–273, 274t quick dry floor cleansers, 271–272 water-based steel cleaner, 273–275 Industrial lubricants. See Lubricants, detergent formulations in Inks. See Paints and printing inks 2-in-1 laundry detergent, 96–99 Innovation targets. See Detergent formulations, future outlook for Inorganic pigments. See Pigment dispersion, surfactants for Institutional applications. See Industrial and institutional (I & I) applications Interior car care/leather care, 268–269 Inverse emulsion polymerization, 426–433 See also Polymerization, surfactant formulations in Isotropic liquids, 71–76

K Krafft temperatures, 478–479

L Latex preparation, 371–374 See also Paints and printing inks Latex stabilization, 398–400 See also Emulsion polymerization, process of Laundry aids. See Laundry detergent formulations Laundry bar detergent, 90–93

Index Laundry detergent formulations heavy duty granules (HDG), 66–71 low density vs. high density, 69–70 machine wash vs. handwash laundry, 70–71 phosphate vs. nil-phosphate, 67–69 heavy duty liquids (HDL), 71–82 bleach-containing liquids, 79–81 dual-bottle liquids, 81–82 isotropic liquids, 71–76 structured liquids, 76–79 introduction, 2, 13, 14t, 15t, 52–54 laundry bars, 90–93 reinvented liquid detergents, 511–513 specialty detergents, 93–100 care formulas, 94–96 2-in-1 detergents, 96–99 summary, 99–100 typical detergent ingredients, 56–66 bleach, 62–63 builders, 58–59 chelating agents, 63 enzymes, 61–62 minors (fillers), 65–66 perfumes, 63–65 polymers, 59–61 surfactants, 56–58 unifying formulation concepts, 54–55 unit dose detergents, 82–90 liqui-tabs, 87–89 sheets, 89–90 tablets, 82–86 See also Detergent formulations, future outlook for Laundry tablets, 82–86 Leather car care, 268–269 Letterpress inks, 371 Leveling dyeing agents, 290–294 Light duty liquids (LDL), mixture design of, 39–45 See also Detergent formulations, statistical mixture design of Limescale removal, test methods for, 158 See also Liquid household cleaners Linear alkylbenzene sulfonate (LAS), 33, 40, 56, 116, 160 Liquid bleach formulations future trends, 202 introduction, 180 liquid chlorine bleach, 182–191 fabric safety of, 187–191 introduction, 182–183 stability of hypochlorite solutions, 183–187 liquid hydrogen peroxide bleach, 191–201 boosting the performance of, 198–201 color and fabric safety of, 201–202 introduction, 191–192 stability of, 192–197 performance assessment of, 180–182 Liquid household cleaners future trends, 174–175 introduction, 2, 154–159

525 background, 154 household soil classifications, 154–156 household surface classifications, 156–157 test methods, 157–159 reinvented liquid detergents, 511–513 surface cleaner formulations all-purpose cleaners, 159–164 bathroom cleaners, 164–166 bleach cleaners, 169–170 carpet cleaners, 172–174 cream cleansers, 170–171 glass cleaners, 171–172 toilet bowl cleaners, 167–169 Liqui-tab detergent, 87–89 Low density vs. high density products, 69–70 Low-foaming nonionic surfactants, 139–141 Low interfacial tension (IFT) technologies, 106, 116–117, 143 Lubricants, detergent formulations in action mechanisms in oils, 455–459 acid-based neutralization mechanisms, 455 friction and wear reduction capability, 458 peptization mechanisms in keeping insoluble particles in suspension, 457 prevention of varnish and lacquer deposition, 458 rate of alkalinity depletion, 456 solubilization of polar species, 458–459 additive-additive interactions, 459–462 effect on antiwear and anti-extreme pressure performance, 460–461 effect on high-temperature deposit formation, 461–462 effect on oxidation stability, 460 strength and type of, 459 ashless dispersants, 445–451 esters, 446–447 graft ethylene-propylene copolymers, 449–450 Mannich condensates, 448–449 other dispersants, 450–451 oxazolines, 447 succinimides, 445–446 thiophosphonates, 450 chemistry of, 20t, 439 general formulations, 462–465 in automatic transmission fluids and gear oils, 464–465 in engine oils, 462–464 introduction, 3, 438–439 metallic detergents, 439–445 other detergents, 444–445 phenates, 442 phosphonates and thiophosphonates, 443–444 salicylates, 442–443 sulfonates, 439–442 solution behavior in oils, 451–455 counter ion effect on sulfonate detergent micellar stability, 452

526

Index effect of overbasing on micellar structures, 454 micellar properties of ashless dispersants, 453–454 micellar properties of sulfonate detergents in hydrocarbons, 451 other metallic detergents in hydrocarbons, 453 overbasing mechanisms, 455 rigidity of metallic detergent micelles, 454 thermodynamic energetics of micellar formation, 452–453

M Machine wash vs. handwash laundry, 70–71 See also Laundry detergent formulations Magnetic resonance imaging (MRI), method of, 255 Mannich lubricant dispersants, 448–449 Manual car wash products, 262, 263t See also Auto care formulations Marble, 158 Market developments, in detergents, 487–488 See also Detergent formulations, future outlook for Metal cleansing pastes, 273–275 Metal component cleaning, 15, 21t Metallic lubricant detergents, 439–445 chemistry of, 439 phenates, 442 phosphonates and thiophosphonates, 443–444 salicylates, 442–443 sulfonates, 439–441 See also Lubricants, detergent formulations in Micellar electrokinetic capillary chromatography (MECC), 307, 308, 318–319 Micellar-enhanced ultrafiltration (MEUF), 313 Micellar liquid chromatography (MLC), 316–318 Micellar nucleation mechanism, 393–396 Micellar solubilization (MS), 306–308 Micellar ultrafiltration, 313–316 Microemulsions, as bath oils, 236, 237t Microemulsions (ME) and PIER, 221, 227–230 See also Emulsion formulation technology Microwave-assisted micellar extraction (MAME), 308–309, 311 Mildness in cosmetic products, 209–210 in shampoo detergents, 480–481 Miniemulsion polymerization, 421–426 See also Polymerization, surfactant formulations in Minors (fillers), in laundry detergent, 65–66 Mixture design. See Detergent formulations, statistical mixture design of

N N-alkyl amide sulfates chemical stability in water, 475 conclusion, 481 introduction, 473–474 micellar properties of, 475–478 critical micellization concentration (CMC), 475–478 Krafft temperature, 478–479 as shampoo detergent, 479–481 foaming capacity, 479–480 mildness, 480–481 synthetic sequence for, 474–475 Nanoemulsions, 221–222 See also Emulsion formulation technology Nanostructured floor tile cleansing, 272, 273t Natural raw materials, cleaning with, 276, 277t Natural sulfonates, as lubricant additives, 439–441 Nil-phosphate vs. phosphate builders, 67–69 Nonionic surfactants in all-purpose cleaners, 161 in automatic dishwashing detergent, 135 in emulsion polymerization, 402–419 in laundry detergent, 56–57 low-foaming, 139–141 in textile finishing, 299, 300 See also Surfactants Nonionic surfactant softener, 299

O Odor control products, 272–273, 274t Oil recovery. See Enhanced oil recovery, surfactant formulations in Optical textile finishing, 302 Oral care detergent formulations, 13, 18t, 19t Overbased lubricant detergent, 444–445 See also Lubricants, detergent formulations in Oxazoline lubricant dispersants, 447

P PAAN catalyst, 136–137, 138 Paints and printing inks introduction, 3, 369–370 paint formulations, 370–371 printing ink formulations, 371 specialty surfactants for paints, 384 surfactants for dispersion stabilization, 371–377 latex (lattices), 371–374 postemulsified binders, 374–377 surfactants for fountain solutions, 384–385 surfactants for pigment dispersion, 377–383 solvent-borne formulations, 383 waterborne formulations, 379–383

Index wetting agents, 383–384 Paraffin sulfonates (PS), 160 Partial phase solu-inversion technology (PPSIT), 226 Partitioned/staged chemistry, 515 Peeling properties, cosmetic formulations with, 235, 236t Penetrating dyeing agents, 294–295 PentaAmmineAcetatocbalt (III) Nitrate (PAAN), 136–137, 138 Performance enhancing minors, 11–13 Perfume ingredients in bleach cleaners, 170 in hypochlorite bleaches, 187 in laundry detergent, 63–65 Permanent wave products, 237–238, 239t Peroxide-based bleaches. See Hydrogen peroxide bleach Personal care formulations examples and concepts, 13, 17t, 18t, 233–241 creams/lotions for sensitive skin, 238, 240t facial care creams, 241 facial cleansers, 236, 237t, 238t hair conditioners, 236–237, 238t microemulsions as bath oils, 236, 237t peeling preparations, 235, 236t shampoos based on alkyl polyglycosides, 234 shower gels, 235, 236t styling and permanent wave products, 237–238, 239t sun protective lotions, 240 formulation techniques, 216–233 emulsions, 216–227 encapsulated systems, 231–233 microemulsions (ME) and PIER, 227–230 surfactant concentrates, 230–231 introduction, 3, 208–216 cosmetic cleansing trends, 208–214 dermatological testing strategies, 214–216 performance properties of, 241–257 cleansing effects, 248–249 foam stability tests, 247–248 hair cosmetic tests, 242–247 skin cosmetic tests, 249–257 trademarks, 257 Personal cleansing products. See Personal care formulations Petroleum hydrocarbons, 348 Petroleum sulfonates, as lubricant additives, 439–441 Phase inversion by emulsifier ration (PIER) microemulsions, 227–230 Phase inversion temperature (PIT) procedure, 222–224 See also Emulsion formulation technology PH control. See specific detergent formulations Phenate lubricant detergent, 442 Phosphate vs. nil-phosphate builders, 67–69 Phosphonate lubricant detergent, 443–444 Pigment dispersion, surfactants for, 377–383

527 solvent-borne formulations, 383 waterborne formulations, 379–382 See also Paints and printing inks Polar decomposition, 192–193 Polishes, exterior car, 267–268 Polyester dyeing, 291–293 Polymer flooding process, 335–336 See also Enhanced oil recovery, surfactant formulations in Polymeric dispersants in automatic dishwashing detergent, 134 chemistry of, 4–8 for solvent-borne formulations, 383 for waterborne formulations, 379–382 See also specific detergent formulations Polymeric foam boosters, 12 Polymerization, surfactant formulations in emulsion polymerization, 392–419 choice of surfactants, 400–419 homogenous nucleation mechanism, 396–398 latex stabilization, 398–400 micellar nucleation mechanism, 393–396 introduction, 387–388 inverse emulsion polymerization, 426–433 miniemulsion polymerization, 421–426 role of surfactants, 388–392 advantages/disadvantages, 388–391 alternatives to using, 391–392 suspension polymerization, 419–421 Polymer latexes, production of, 391–392 See also Polymerization, surfactant formulations in Polymers in all-purpose cleaner, 163–164 in bathroom cleaner, 166 in glass cleaners, 171–172 in hand dishwashing detergent, 118–120 in laundry detergent, 59–61 in textile finishing, 299–300 See also specific detergent formulations Postemulsified binders, 374–377 Post-scoring process, in textile applications, 296 Preblending, 45 Primary oil recovery, 326 See also Enhanced oil recovery, surfactant formulations in Printing inks. See Paints and printing inks Printing process, surfactant applications in, 297–298 See also Textile processing, surfactant applications in Proteolytic enzymes. See Enzymes Pump-and-treat remediation, 349

Q Quick dry floor cleansers, industrial, 271–272

528

Index

R Raw cotton impurities, 284 R & D tools, 491–493 Reactive surfactant softeners, 300 Regulatory considerations. See Environmental and regulatory considerations Research and development (R & D) tools, 491–493 Residual oil saturation, 338–339 Reverse-phase micellar liquid chromatography (RPMLC), 316, 317 Rim/tire care, 269 Rinse/drying aids, in auto care, 265–267 Rinse water reduction processes, 510–511 Rotor-Foam test, 247

S Salicylate lubricant detergent, 442–443 Scale deposits, 142 Scanning electron microscopy (SEM), 181 Scheffé, Henri, 30 Scouring agents, on textile fibers, 287–288 Scouring creams (cream cleansers), 170–171 See also Liquid household cleaners Screen printing, 297 Secondary oil recovery, 326 See also Enhanced oil recovery, surfactant formulations in Sensitive skin, creams/lotions for, 238, 240t See also Personal care formulations Separation science, detergent formulations in introduction, 305–306 micellar electrokinetic capillary chromatography (MECC), 318–319 micellar liquid chromatography (MLC), 316–318 micellar solubilization (MS), 306–308 micelle-mediated separation/preconcentration techniques, 308–316 micellar ultrafiltration, 313–316 microwave-assisted micellar extraction (MAME), 308–309 thermal phase separation (cloud-point extraction), 309–313 Shampoo detergents in auto care, 262–265 based on alkyl polyglycosides, 234 basic properties of, 479–481 in carpet cleaners, 173 ingredient examples, 17t two-in-one products, 211 See also N-alkyl amide sulfates Sheet laundry detergent, 89–90 Shine performance test, for surface cleaners, 158 Shower gel products, 235, 236t Silk impurities, 285 Sizing agents, on textile fibers, 285 Skin cleansing process, 208–209

Skin cosmetic performance tests cosmetic spreading behavior, 251–253 mechanical properties, 253–254 sensory properties/assessment, 254 skin lipids, 256 skin moisture, 255–256 skin surface pH, 256–257 surface structure, 249–251 See also Personal care formulations Skin hydration, measuring, 255 Skin surface lipids, 256 Skin surface pH, 256–257 Soap bars, 90 Soap scum removal, test methods for, 157–158 See also Liquid household cleaners Sodium tripolyphosphate (STPP). See Builders Softeners, in textile finishing, 298–300 Softening agents, in laundry detergent, 2, 96–99 Soil classifications, household, 154–156 Soil release polymers, 12–13 See also Polymers Soil-release textile finishing, 301–302 Soil removal mechanisms, 19, 21–23 Soil removal tests, for surface cleaners encrusted grease and soap scum, 157–158 foaming profile, 158–159 limescale removal, 158 shine performance, 158 Solubilization mechanism, of cleaning by hand, 111–112 Solvents in all-purpose cleaners, 161–162 in bathroom cleaners, 166 chemistry of, 10–11 chlorinated, 348 dispersants for pigments, 383 in glass cleaners, 171 See also specific detergent formulations Spa movement, 213–214 Special purpose cleaning formulations auto care, 262–270 automatic prewash/main wash, 262–265 exterior car care agents/polishes, 267–268 glass/windshield cleansing, 269–270 interior car care/leather care, 268–269 manual car wash, 262 rim/tire care, 269 rinse/drying aids, 265–267 conclusion, 276 industrial and institutional (I & I) products, 270–276, 277t Cleaning In Place (CIP) products, 275–276 cleaning with natural raw materials, 276, 277t gel cleansing products, 270–271 glass cleaning, 275 nanostructured floor tile cleansing, 272 odor control products, 272–273, 274t quick dry floor cleansers, 271–272 water-based steel cleaner, 273–275 introduction, 262

Index Specialty laundry detergent care formulas, 94–96 2-in-1 detergents, 96–99 introduction, 93–94 See also Laundry detergent formulations Spot carpet removal products, 172–173 See also Liquid household cleaners Spray cleaning solutions, 173–174 See also Liquid household cleaners Staged/partitioned chemistry, 515 Steel cleaner, water-based, 273–275 Steric repulsion, 220 Stripping process, in textile applications, 296 Structured liquids, 76–79 Styling mousse products, 237–238, 239t Subsurface remediation. See Environmental remediation, surfactant-based systems for Succinimide lubricant dispersants, 445–446 Suds and aesthetics in all-purpose cleaners, 159 in bathroom cleaners, 164 Suds boosting polymers background, 118 cationic hydrophobic polymers, 118–119 mechanism of, 119–120 Sulfonate lubricant detergent, 439–441 Sun protective lotions, 240 Supercritical fluid extraction (SFE), 308 Supersolubilization concerns, mitigating, 356–358, 362–364 Surface cleaner formulations all-purpose cleaners, 159–164 bathroom cleaners, 164–166 bleach cleaners, 169–170 carpet cleaners, 172–174 glass cleaners, 171–172 toilet bowl cleaners, 167–169 See also Liquid household cleaners Surface cleaning test methods, 157–159 Surface household classifications, 156–157 Surfactant-based separations. See Separation science, detergent formulations in Surfactant decontamination, for reinjection, 361–362 Surfactant enhanced aquifer remediation. See Environmental remediation, surfactantbased systems for Surfactant flooding process, 332–333 See also Enhanced oil recovery, surfactant formulations in Surfactant losses, minimizing, 354 Surfactant mixture properties, 333–335 Surfactant regeneration/reuse, 355–356 Surfactants in all-purpose cleaner, 160–161 amphoteric, 116 in bathroom cleaner, 165–166 in bleach cleaner, 169 in car wash soap, 263–265 cationic softeners, 298–300

529 chelating, 116 classification of, 329–332 in Cleaning In Place (CIP) products, 275–276 concentrated blends, 230–231 dermatological properties of, 214–216 for emulsion polymerization, 400–419 anionic, 401–402 anionic/nonionic mixtures, 405, 418–419 cationic, 419 nonionic, 402–404 for fountain solutions, 384–385 fundamentals of, 4, 18, 351–353 in glass cleaner, 171 in hand dishwashing detergent, 112–113, 114t foam (suds) stabilizers, 113, 115 hydrotropes and dissolution aids, 115 new developments in, 115–116 high-solubility anionic, 115–116 in hydrogen peroxide bleach, 196 in hypochlorite bleach, 185–186 in laundry detergent, 56–58 anionic surfactants, 56 cationic surfactants, 58 new developments in, 58 nonionic surfactants, 56–57 low-foaming nonionic, 139–141 for paints, 384 for pigment dispersion, 377–383 in toilet bowl cleaner, 167, 168 See also specific detergent formulations Suspension mechanisms, 23–24 Suspension polymerization, 419–421 See also Polymerization, surfactant formulations in Synthetic detergent bars, 90–91 Synthetic sulfonates, as lubricant additives, 439–441

T Tablets, laundry, 82–86 Tertiary oil recovery, 326 Textile fiber consumption, 280–281 See also Textile processing, surfactant applications in Textile innovations, 502–504 Textile processing, surfactant applications in introduction, 3, 280–284 surfactant's market in textile chemicals, 283–284 surfactant's role in, 283 textile chemical uniqueness, 282–283 textile fiber consumption, 280–281 textile processes, 281–282 textile dyeing, 289–296 aftertreatment applications, 296 dispersing agents, 294 foaming and defoaming, 295–296 leveling agents, 290–294

530 wetting and penetrating agents, 294–295 textile finishing, 298–302 antistactics, 300–301 other applications, 301–302 softeners, 298–300 textile preparation, 284–289 bleaching assistants, 288–289 desizing agents, 286–287 naturally occurring impurities, 284–285 process-added impurities, 285–286 scouring agents, 287–288 textile printing, 297–298 See also Detergent formulations, future outlook for Theory and mechanisms, detergency, 15, 18 soil removal, 19, 21–23 suspension, 23–24 Thermal phase separation (cloud-point extraction), 309–313 Thickeners, 12 Thiophosphonate lubricant detergent, 443–444 Thiophosphonate lubricant dispersants, 450 Tinker Air Force Base (AFB), air stripping studies at, 361–362, 364 Toilet bowl cleaners, 167–169 See also Liquid household cleaners Toothpaste formulations, 13, 19t See also Personal care formulations Toxicological tests, in body-cleansing formulations, 214–216 Transepidermal water loss (TEWL), of the skin, 254, 255 Trial-and-error approach, in experimental design, 27–28 See also Detergent formulations, statistical mixture design of Trial mixtures. See Detergent formulations, statistical mixture design of Two-in-one skin care products, 211–212

Index

U U. S. Environmental Protection Agency (EPA), 506 Unit dose detergents laundry bars, 90–93 liqui-tabs, 87–89 sheets, 89–90 tablets, 82–86

V Vertical migration concerns, mitigating, 356–358, 362–364 Virtual formulation, advances in, 492–493

W Water-based flushing, 349 Water-based steel cleaner, 273–275 Waterborne paints, dispersants for, 370, 379–382 See also Paints and printing inks Water/oil repelling textile finishing, 301–302 Well-being and health issues, in cosmetics, 213–214 Wetting agents in dyeing, 294–295 i n paints, 383–384 Whitening agents, in hypochlorite bleach, 186 Windshield/glass cleansing, 269–270 Wool dyeing, 292 Wool impurities, 284–285

Y Yarn lubricants, on textile fibers, 286