Modern Tendencies in Organic and Bioorganic Chemistry - Today and Tomorrow

MODERN TENDENCIES IN ORGANIC AND BIOORGANIC CHEMISTRY: TODAY AND TOMORROW

MODERN TENDENCIES IN ORGANIC AND BIOORGANIC CHEMISTRY: TODAY AND TOMORROW

ABDULAKH MIKITAEV MUKHED KH. LIGIDOV AND

GENNADY E. ZAIKOV EDITORS

Nova Science Publishers, Inc. New York

Copyright © 2008 by Nova Science Publishers, Inc.

All rights reserved. No part of this book may be reproduced, stored in a retrieval system or transmitted in any form or by any means: electronic, electrostatic, magnetic, tape, mechanical photocopying, recording or otherwise without the written permission of the Publisher. For permission to use material from this book please contact us: Telephone 631-231-7269; Fax 631-231-8175 Web Site: http://www.novapublishers.com NOTICE TO THE READER The Publisher has taken reasonable care in the preparation of this book, but makes no expressed or implied warranty of any kind and assumes no responsibility for any errors or omissions. No liability is assumed for incidental or consequential damages in connection with or arising out of information contained in this book. The Publisher shall not be liable for any special, consequential, or exemplary damages resulting, in whole or in part, from the readers’ use of, or reliance upon, this material. Any parts of this book based on government reports are so indicated and copyright is claimed for those parts to the extent applicable to compilations of such works. Independent verification should be sought for any data, advice or recommendations contained in this book. In addition, no responsibility is assumed by the publisher for any injury and/or damage to persons or property arising from any methods, products, instructions, ideas or otherwise contained in this publication. This publication is designed to provide accurate and authoritative information with regard to the subject matter covered herein. It is sold with the clear understanding that the Publisher is not engaged in rendering legal or any other professional services. If legal or any other expert assistance is required, the services of a competent person should be sought. FROM A DECLARATION OF PARTICIPANTS JOINTLY ADOPTED BY A COMMITTEE OF THE AMERICAN BAR ASSOCIATION AND A COMMITTEE OF PUBLISHERS. LIBRARY OF CONGRESS CATALOGING-IN-PUBLICATION DATA Modern tendencies in organic and bioorganic chemistry : today and tomorrow / Abdulakh Mikitaev, Mukhed Kh. Ligidov, Gennady E. Zaikov (editor). p. cm. ISBN 978-1-60692-454-9 1. Chemistry, Organic. 2. Bioorganic chemistry. I. Mikitaev, Abdulakh K. II. Ligidov, Mikhail Kh. III. Zaikov, Gennadii Efremovich. QD251.3.M636 2008 547--dc22 2007051490

Published by Nova Science Publishers, Inc.

New York

CONTENTS Preface Chapter 1

Chapter 2

Chapter 3

Chapter 4

ix Thermal and Thermal-oxidative Degradation of Polyethylene Nanocomposite Prepared by Intercalation Polymerization S. M. Lomakin, L. A. Novokshonova, P. N. Brevnov, A. N. Shchegolikhin and G. E. Zaikov Modification of Catalytic Activity of Complexes of Acetylacetonates Fe(II,III) with Quaternary Ammonium Salts in the Ethylbenzene Oxidation with Molecular O2 in the Presence of Small Amounts of H2O L. I. Matienko and L. A. Mosolova

1

33

Modeling the Kinetics of Moisture Adsorption by Wood during the Drying Process A. Farjad, S. H.Rahrovan and A. K. Haghi

51

New Trends, Achievements and Developments on the Effects of Beam Radiation on Different Materials K. Mohammadi and A. K. Haghi

65

Chapter 5

Structural Behavior of Composite Materials О. А. Legonkova, J. L. Gordeeva and E. S. Obolonkova

Chapter 6

Comparative Evaluation of Antioxidant Properties of Spice-aromatic Plant Essential oils A. L. Samusenko

103

The Polymeric Compositions Stabilized Nanodimensions Phosphor Organically by Compounds A. Kh. Shaov, A. N. Teuvazhukova and A. A. Akezheva

113

Composite Materials for Ortopedical Stomatology on the Basis of Utilized Glassy Organically A. Kh. Shaov, E. M. Kushhov and K. A. Sohrokova

117

Chapter 7

Chapter 8

89

vi Chapter 9

Chapter 10

Chapter 11

Chapter 12

Chapter 13

Contents A Preliminary Study on Antimicrobial Edible Films from Pectin and Other Food Hydrocolloids by Extrusion Method LinShu Liu, Tony Jin, Cheng-Kung Liu, Kevin Hicks, Amar K. Mohanty, Rahul Bhardwaj and Manjusri Misra

121

Controlled Release of the Antiseptic from Poly(3-hydroxybutyrate) Films. Combination of Diffusion and Zero-order Kinetics R. Yu. Kosenko, Yu. N. Pankova, A. L. Iordanskii and G. E. Zaikov

139

Photo Composites on the Base of Polymer-monomer Combined System, Modified by Oligomers N. V. Sidorenko, I. M. Gres, N. G. Bulycheva, M. A. Vaniev and I. A. Novakov Stabilization of Cell Membranes by Hybrid Antioxidants in Therapy of Neurodegenerative Diseases L. D. Fatkullina, O. M. Vekshina, E. B. Burlakova, A. N. Goloshchapov and Yu. A. Kim Wear Resistant Composite Polymeric Materials Based on Polyurethanes and Polyisocyanurates L. V. Luchkina, A. A. Askadsky and V. V. Kazantseva

Chapter 14

Photodestruction of Chlorophyll in Non-biological Systems A. V. Lobanov, O. V. Nevrova, Yu. A. Vedeneeva, G. V. Golovina and G. G. Komissarov

Chapter 15

Some Microkinetic Particularities of Deep Hydrolysis Pet Calcium Gidrokside in Bead Mill A. S. Harichkin and A. M. Ivanov

147

151

161 165

171

Chapter 16

Transport Phenomena within Porous Media Sh. Rahrovan and A. K. Haghi

175

Chapter 17

Block-copolysulfonarilates of Polycondensational Type E. B. Barokova, A. M. Kharaev, R. Ch. Bazheva and T. R. Umerova

211

Chapter 18

Liguid-crystalline Polyesthers on the Basis of Terephtaloyl-di(n-oxibenzoat) and Aromatic Polyethers L. A. Asueva, M. A. Nasurova, G. B. Shustov, A. M. Kharaev, A. K. Mikitaev

Chapter 19

Fireproof Aromatic Block Copolymer Resin on the Basis of 1,1- Dichlor-2,2 DI(N-oxyphenyl)ethylene A. M. Kharaev, R. C. Bazheva, E. B. Barokova, O. L. Istepanova, R. A. Kharaeva and A. A.Chaika

215

219

Contents Chapter 20

Chapter 21

Chapter 22

Chapter 23

Chapter 24

Chapter 25

Chapter 26

Chapter 27

Chapter 28

Chapter 29

Increase in Selectivity of Molecular Complex Formation of Metalloporphyrins due to π-π-interactions Nataliya A. Pavlycheva, Nataliya Sh. Lebedeva, Anatoliy I. Vyugin and Elena V. Parfenyuk

vii

223

Influence of Individual Components of Essential Oils and Flavorings on Citral Oxidation А. L. Samusenko

231

Some Aspects of Dynamic Water Vapour and Heat Transport through Fabrics A. K. Haghi

239

A Novel Approach for Measurement of NanoFiber Diameter of Electrospun Webs M. Ziabari, V. Mottaghitalab and A. K. Haghi

271

Lasers Application Boundaries to Stimulate Photochemical Processes R. H. Chaltykian and N. M. Beylerian

295

Quantum-chemical Analysis of the Mechanism of Nucleophilic Substitution of Bromine in Methyl(benzyl)bromide by s-, o-anions Generated from 2-thiouracil A. V. Babkin, A. I. Rakhimov, E. S. Titova, R. G. Fedunov, R. A. Reshetnikov, V. S. Belousova and G. E. Zaikov

311

Conformational Behavior of Propagating Chains of Polyacrylate- and Polymethacrylate Guanidines in Water Solutions N. A. Sivov, A. I. Martynenko, Yu. A. Malkanduev, M. H. Baidaeva, A. A. Zhansitov, O. A. Taov and A. I. Sarbasheva Biocide and Toxicological Properties of Synthesized Guanidine Containing Polymer and their Structure N. A. Sivov, Yu. A. Malkanduev, S. Yu. Khashirova, M. H. Baidaeva, A. I. Sarbasheva, A. A. Zhansitov and O. A. Taov Co-polymerization of Diallyldimethylammonium Chloride and Diallylguanidine Acetates on High Conversion for Creation of New Biocide Materials N. A. Sivov, Yu. A. Malkanduev, A. I. Sarbasheva, M. H. Baidaeva and S. Yu. Khashirova The Approach to Calculation of Different Co-polymers Composition by NMR1H Spectroscopy Method N. A. Sivov, M. Yu. Zaremsky, A. N. Sivov, E. V. Chernikova, D. N. Sivov, A. A. Zhansitov and O. A. Taov

325

335

341

345

viii Chapter 30

Chapter 31

Chapter 32

Chapter 33

Chapter 34

Chapter 35

Chapter 36

Index

Contents Structure Peculiarities of Guanidine Containing Monomers on NMR Spectroscopy Data N. A. Sivov, M. P. Filatova, A. N. Sivov, A. I. Rebrov, D. N. Sivov and E. B. Pomakhina Peculiarities of Radical Polymerization Reactions of Acrylate- and Methacrylate Guanidines N. A. Sivov, A. I. Martynenko, Yu. A. Malkanduev, E. Yu. Kabanova, N. I. Popova, A. A. Zhansitov, O. A. Taov and S. Yu. Khashirova The Strategy of Ionizing Monomers Synthesis and Investigation of their Radical Polymerization for Preparation of New Polyelectrolytes with Useful Properties N. A. Sivov Effect of Vibration on Structure and Properties of Polymeric Membranes V. N. Fomin, A. P. Bobylev, E. B. Malyukova, V. V. Smolyaninov, I. A. Arutyunov and N. A. Bulychev

349

353

361

367

One-stage Synthesis of Polymer Flocculant on the Acrylonitrile Basis N. V. Kozhevnikov, M. D. Goldfein and N. I. Kozhevnikova

379

Ultrasonic Treatment Assisted Surface Modification of Inorganic and Organic Pigments in Aqueous Dispersions N. A. Bulychev, E. V. Kisterev, I. A. Arutunov, and V. P. Zubov

385

Investigation of Antioxidant Activity of Essential Oils from Lemon, Pink Grapefruit, Coriander, Clove and its Mixtures by Capillary Gas Chromatography A. L. Samusenko

397 407

PREFACE “Heroes are born after their death” Sigmund Freid Austria We hope that scientific popularity of those who has taken part in a preparation of the given compilation book, will come earlier, than it declared Sigmund Freid (see an epigraph). The present collection of articles is made of reports which have been reported on four international conferences: •

• • •

The first All-Russia Scientific and Technical Conference “Nanostructures in polymers and polymeric nanocomposites” (the Kabardino-Balkarian State University, Nalchik, Russia, June, 2 - 5 2007); The Thirds All-Russia Scientific conference “New polymeric composite materials” (the Kabardino-Balkarian State University, June, 6 - 9 2007). XIIIth International Conference for Renewable Resources and Plant Biotechnology (Institute of Natural Fibres, Poznan, Poland, June, 18 – 19 2007); IXth International Conference on Frontiers of Polymers and Advanced Materials (Cracow University of Technology, Cracow, Poland, July, 8 – 12 2007).

This volume is including information about thermal and thermooxidative degradation of polyolefine nanocomposites, modeling of catalytic complexes in the oxidation reactions, modeling the kinetics of moisture adsorption by natural and synthetic polymers, new trends, achievements and developments on the effects of beam radiation, structural behaviour of composite materials, comparative evaluation of antioxidants properties, synthesis, properties and application of polymeric composites and nanocomposites, photodegradation and light stabilization of polymers, wear resistant composite polymeric materials, some macrokinetic phenomena, transport phenomena in polymer matrix, liquid crystals, flammability of polymeric materials and new flame retardants. We expect that this information will be useful for students, scientists and engineers who are working in the field of organic and bioorganic chemistry (including monomers, oligomers, polymers, composites and filled polymers as well as in agriculture and biotechnology).

In: Modern Tendencies in Organic and Bioorganic Chemistry ISBN: 978-1-60456-295-8 Editors: A. Mikitaev, M. K. Ligidov, pp. 1-32 © 2008 Nova Science Publishers, Inc.

Chapter 1

THERMAL AND THERMAL-OXIDATIVE DEGRADATION OF POLYETHYLENE NANOCOMPOSITE PREPARED BY INTERCALATION POLYMERIZATION S. M. Lomakin1, L. A. Novokshonova2, P. N. Brevnov2, A. N. Shchegolikhin1 and G. E. Zaikov1 1

N.M. Emanuel Institute of Biochemical Physics of Russian Academy of Sciences, 119991 Kosygin 4, Moscow, Russia, 2 N.N. Semenov Institute of Chemical Physics of Russian Academy of Sciences, 119991 Kosygin 4, Moscow, Russia

ABSTRACT A comparative study of thermal and thermal-oxidative degradation processes for polyethylene/organically modified montmorillonite (PE-MMT) nanocomposites, prepared by the ethylene intercalative polymerization in situ with or without subsequent addition of an antioxidant, is reported. The results of TGA and time/temperature dependent FTIR spectroscopy experiments have provided evidence for an accelerated formation and decomposition of hydroperoxides during the thermal oxidative degradation tests of PE-MMT nanocomposites in the range of 170-200oC as compared to the unfilled PE, thus indicating to a catalytic action of MMT. It has been shown that effective formation of intermolecular chemical cross-links in the PE-MMT nanocomposite has ensued above 200oC as the result of recombination reactions involving the radical products of hydroperoxides decomposition. Apparently, this process is induced by the oxygen deficiency in PE-MMT nanocomposite due to its lowered oxygen permeability. It is shown that the intermolecular cross-linking and dehydrogenation reactions followed by the shear carbonization lead to appreciable increase of thermal-oxidative stability of PE nanocomposite as compared to that of pristine PE. Notably, the TGA traces for the antioxidant-stabilized PE-MMT nanocomposites recorded in air were quite similar to those obtainable for the non-stabilized PE-MMT nanocomposites in argon. The results of treatment of the experimentally acquired TGA data in frames of an advanced model kinetic analysis are reported and discussed.

2

S. M. Lomakin, L. A. Novokshonova, P. N. Brevnov et al.

Keywords: Catalysis; intercalation polymerization; kinetics; layered clay; nanocomposite; oxidation; polyethylene; thermal degradation

1. INTRODUCTION Polyethylene (PE), being the most commercially important thermoplastic commodity, is heavily used for consumer products in many applications, but in a number of cases general applicability of PE turns out to be undermined by its relatively low thermal stability and flame resistance. The concept of compounding polymer matrices with nanoscale fillers (in particular, clays or layered silicates) has already been proved to be an effective method of preparing nanocomposites with excellent physicochemical properties [1 – 11]. It is believed that, in the course of high temperature pyrolysis and/or combustion, clay nanoparticles are capable of promoting formation of protective clay-reinforced carbonaceous char which is responsible for the reduced mass loss rates, and hence the lower flammability. Accordingly, considerable attention has been paid also to polyolefin/layered silicate nanocomposites. Reportedly, the latter have exhibited improved mechanical properties, gas impermeability, thermal stability, and flame retardancy as compared with corresponding pristine polymers [4,5,9,10]. This study deals with polyethylene/layered silicate nanocomposites that can be prepared by intercalative polymerization route. In accordance with the latter [12], the polymer chains growing within the interlayer spacing of montmorillonite (MMT) should be able to exfoliate the original MMT particles down to the nanoscale inorganic monolayers. Here, an experimental study of the universal intercalative approach, involving in the particular case (1) intercalation of a metallorganic catalyst system into the interlayer spacing of organically modified MMT and (2) subsequent polymerization of ethylene on thus intercalated catalyst, will be reported as well as the properties of the correspondingly produced PE/MMT nanocomposites will be discussed. To clarify the mechanisms of the clay-reinforced carbonaceous char formation, which may be responsible for the reduced mass loss rates, and hence the lower flammability of the polymer matrices, a number of thermo-physical characteristics of the PE/MMT nanocomposites have been measured in comparison with those of the pristine PE (which, by itself is not a char former) in both inert and oxidizing atmospheres. The evolution of the thermal and thermal-oxidative degradation processes in these systems was followed dynamically with the aid of TGA and FTIR methods. Proper attention was paid also to the effect of oxygen on the thermal-oxidative stability of PE nanocomposites in their solid state, in both the absence as well as in the presence of an antioxidant. Several sets of experimentally acquired TGA data have provided a basis for accomplishing thorough model-based kinetic analyses of thermal and thermal-oxidative degradation of both pristine PE and PE/MMT nanocomposites prepared in this work.

Thermal and Thermal-oxidative Degradation of Polyethylene Nanocomposite …

3

2. EXPERIMENTAL 2.1. Materials A Cloisite 20A (purchased from Southern Clay Products, Inc.) has been used as the organically modified montmorillonite (MMT) to prepare PE/MMT nanocomposites throughout this study. The content of an organic cation-exchange modifier, N+2CH32HT (HT=hydrogenated tallow, C18≈65%; C16≈30%; C14≈5%; anion: Cl-), in the MMT was of 38 % by weight. VCl4 (vacuum distilled at 40°С before use, TU 48-05-50-71) and Al(i-Bu)3 (Aldrich) have been used for catalytic activation of MMT. Ethylene monomer was of a standard polymerization grade.

2.2. Procedure of Polyethylene Nanocomposite Synthesis Intercalation of the catalyst has been accomplished by treating the freshly dehydrated MMT with Al(i-Bu)3 and then with VCl4. The polymerization reaction was started by admitting ethylene into the reactor and then was carried out until desired amount of PE nanocomposite (PE-n-MMT) was obtained. The polymerization reaction was stopped by adding ethanolic HCl solution (5 wt % HCl) to the reactor. The polymer composite product was filtered off, washed with ethanol and dried under vacuum at 60°C. The weight loads of MMT in the resulting composites were calculated by neglecting the contribution of the organic modifier in MMT. The sample of unfilled polyethylene (PE) was prepared by ethylene polymerization on VCl3 activated with Al(i-Bu)3 at the same conditions as applied to the nanocomposite synthesis. Stabilized samples of both the nanocomposites (st-PE-n-MMT) and pristine PE (st-PE) were prepared by treating them with synergetic composition of Topanol CA and di-lauryl3,3’-thiodipropionate (DLTDP) solutions in heptane [Voigt J., Die Stabilisierung der Kunstoffe Gegen Licht und Wärme, Springer-Verlag, Berlin-Heidelberg-New York, 1966, p.542] at 70°C, followed by drying in vacuum. The concentrations of Topanol and DLTDP in (st-PE-n-MMT) and (st-PE) comprised 0.3 and 0.5 wt.%, respectively. For further testing, the prepared materials were hot-pressed into films at applied pressure of 20 MPa and 160°С.

2.3. Characterization of Materials Small-angle X-ray Scattering (SAXS) The structure of the composites was studied by SAXS using a KRM-1 camera (Cu Kα radiation, λ = 0.154 nm, Ni filter). The test samples were powders or films. The data collected were normalized with due regard to the concentration of MMT and the coefficients of attenuation.

4

S. M. Lomakin, L. A. Novokshonova, P. N. Brevnov et al.

Transmission Electron Microscopy (TEM). Micrograph of PE nanocomposite sample was obtained on a JEM-100B transmission electron microscope at an accelerating voltage of 80 kV. The sample of 70 nm thickness was cut with the aid of LKV-III ultramicrotome from the composite plate prepared by hot pressing. Thermogravimetric Analysis (TGA) A Perkin-Elmer TGA-7 instrument calibrated by Curie points of several metal standards has been employed for non-isothermal thermogravimetric analysis. The measurements were carried out at a desired heating rate (in the range of 3 – 40 K/min) in both inert (argon) and oxidizing (oxygen) atmospheres, as appropriate. Fourier Transform Infrared (FTIR) Spectroscopy Infrared spectra of the investigated materials in their nascent form were acquired with the aid of a Perkin-Elmer 1725X FTIR instrument by using a Spectra-Tech "Collector" DRIFT accessory furnished with a heated sample post, embedded thermo couple and the corresponding external heater/controller providing temperature reading precision of ±1.0C. The series of FTIR spectra for the polymer samples have been recorded at systematically varied temperatures or over predetermined time intervals (in isothermal regimes) by employing a modified diffuse reflectance-absorbance Fourier Transform (DRAFT) spectroscopy technique published elsewhere [13]. All measurements were performed using the instrument DTGS detector and a 4cm-1 resolution. Kinetic analysis of PE compositions thermal degradation was carried out using Thermokinetics software by NETZSCH-Gerätebau GmbH.

3. RESULTS AND DISCUSSION 3.1. Morphology (Structure Evaluation) Small-angle X-ray scattering (SAXS) has been used to evaluate the degree of exfoliation of the organoclay particles in the polymer matrix [12]. SAXS diffractograms of pristine C20A MMT and those of PE nanocomposites prepared by the intercalation polymerization route for MMT contents of 2.0 vol. % (2) and 6.5 vol. % (3) are shown in Figure 1. The SAXS curve for C20A MMT shows a reflection at around of 3.6o corresponding to the interlayer mean distance of 2.46 nm (Figure 1, 1). As can be seen from the same Figure 1 (2, 3), for the PE/clay nanocomposites having different MMT contents, the 3.6o reflection is absent. This result infers that PE chains, while growing in the course of polymerization in the interlayer spacing of the layered filler particles, are able to commit full exfoliation of the MMT particles down to the monolayers.

Intensity, cps

Thermal and Thermal-oxidative Degradation of Polyethylene Nanocomposite …

5

3 2 1

0

2

4

6

8

2θ, degrees Figure 1. SAXS patterns for the original C20A MMT (1) and PE nanocomposites with MMT content of 2.0 vol. % (2) and 6.5 vol. % (3)

Figure 2 shows TEM image of the PE nanocomposite containing 1 vol. % of MMT. The dark features in the micrograph correspond to the exfoliated monolayers and nanostacks of MMT distributed throughout the PE matrix. It can be seen that the nanoscale MMT layers lack any sort of orientation in the matrix of the pressed composite. Moreover, the exfoliated MMT particles exhibit a very high aspect ratio (longitudinal size: thickness).

Figure 2. TEM micrograph of the PE nanocomposite containing 1% by volume of MMT.

S. M. Lomakin, L. A. Novokshonova, P. N. Brevnov et al.

Intensity, cps

6

1 2

0

2

4

6

8

2θ, degrees Figure 3. SAXS patterns for the original C20A MMT (1) and C20A MMT treated with HCl solution in ethanol (5 wt % HCl) (2).

It is worth noting here that the organic ammonium cations present in pristine C20A MMT are susceptible to washing out from the interlayer spacing of MMT under acidic treatment of the latter with ethanolic HCl (5% by wt.). The ammonium cations are substituted for protons, and this leads to a prominent decrease of the interlayer distances in the MMT structure (Figure 3). If the intercalative polymerization of ethylene would not accomplish exfoliation of the MMT particles in the composite to the full extent, the diffractogram should contain a wide reflection positioned somewhere at greater angles than in the pristine C20A MMT. It is obvious also that the acidic after-treatment of the synthesized exfoliated nanocomposites should lead to removal of the major part of the original organic MMT modifier.

3.2. Thermal Degradation of PE Nanocomposite It is generally accepted that thermal stability of polymer nanocomposites is higher than that of pristine polymers, and that this gain is explained by the presence of anisotropic clay layers hindering diffusion of volatile products through the nanocomposite material. It is important to note that the exfoliated nanocomposites, prepared and investigated in this work, had much lower gas permeability in comparison with that of pristine unfilled PE [12]. Thus, the study of purely thermal degradation process of PE nanocomposite seemed to be of interest in terms of estimation of the nanoclay barrier effects on thermal stability of polyolefin/clay nanocomposites. The radical mechanism of thermal degradation of pristine PE has been widely discussed in a framework of random scission type reactions [14-22]. It is known that PE decomposition products comprise a wide range of alkanes, alkenes and dienes. Branching of PE chains causes enhanced intermolecular hydrogen transfer and results in lowering thermal stability. The polymer matrix transformations, usually observed at lower temperatures and involving

Thermal and Thermal-oxidative Degradation of Polyethylene Nanocomposite …

7

molecular weight alteration without formation of volatile products, are principally due to the scission of weak links, e. g. oxygen bridges, incorporated into the main chain as impurities. The kinetics of thermal degradation of PE is frequently described by a first-order model of mass conversion of the sample [21]. A broad variation in Arrhenius parameters can be found in literature, i. e., activation energy (E) ranging from 160 to 320 kJ/mol and pre-exponential factor (A) variations in the range of 1011 and 1021 s-1 [20-22] are not unusual. It is believed that the broad range of E values reported may be explained by the polymers molecular mass variations, by use of various additives, and by different experimental conditions [22] employed by different authors. Previously Bockhorn et al. have reported that thermal degradation of PE leads to a large number of paraffins, dienes and olefins without a residue formation [20]. Analysis of the pyrolysis products with GC-MS revealed high yields of linear n-alkanes and n-alkenes. Neither branched aliphatics, alicyclics or aromatic compounds nor Diels-Alder derivatives of butadiene have been detected [20]. In order to formulate a simple kinetic model adequately explaining the isothermic global kinetic data of the authors, a mechanism embracing only the main reactions has been proposed [20]. The latter is based on a radical chain mechanism (Scheme 1) initiated by random scission of the polymer chains into primary radicals Rp (1). βScission of these radicals leads to ethylene (2). At higher temperatures, the unzip reaction leading to ethylene becomes more evident [15]. At low temperatures, intramolecular hydrogen transfer followed by β-scission occurs (3). This reaction leads to the more stable secondary radicals Rs. The 1,5 rearrangement reaction (3) in Scheme 1 stands for all preferred rearrangement reactions via cyclic intermediates such as 1,9, 1,13, 1,17, etc. Subsequent βscission of the secondary radicals contributes to the radical chain mechanism because the primary radical is produced in each step (propagation). Two β-scission reactions (4, 4’) are possible. Reaction (4) leads to alkenes, whereas reaction (4’) leads to a short primary radical and a polymer with a terminal double bond. It is important that the change in the reaction order is dependent on the intermolecular hydrogen transfer in reaction (5) leading to the alkanes. In this case only the intermolecular hydrogen transfer of the primary radicals is considered because the latter are less stable than the secondary radicals. At high temperatures and at a high degrees of conversion, the alkanes formation via reaction 5 becomes favored and, therefore, the reaction order alters from 0.5 to 1.5 [20]. In the present work, the processes of thermal degradation of both unstabilized PE and PE-n-MMT nanocomposite with MMT content of 4.3 wt.% have been investigated by TGA in an inert (argon) atmosphere at the heating rates of 3, 5, 10 and 20 K/min. According to the dynamic TGA data, the polymer degradation starts at about 300°C and then, through a complex radical chain process (Scheme 1), the material totally destructs and completely volatilizes in the range of 500-550oC (Figure 4). It is obvious that, taken at the same heating rates in argon, the thermograms for pristine PE and PE-n-MMT are practically identical, except that the solid silicate residue amounting to 4-5 % wt. can be seen on the curves for the nanocomposites (Figure 4). This result suggests that the mechanisms of thermal degradation of PE and PE-n-MMT nanocomposites, and hence the global kinetic parameters of their thermal degradation processes are rather similar.

8

S. M. Lomakin, L. A. Novokshonova, P. N. Brevnov et al. Initiation H2 C

H2 C

C H2

C H2

C H2

H2 C

H2 C

k1

+

C H2

C H2

H2 C C H2

C H2

(1)

H 2C

CH2

(2)

2RP

P Propagation H2 C

H2 C

C H2

C H2

H2 C

k2

C H2

C H2

C H2

RP

+

RP Hydrogen transfer (intramolecular)

H2 C

H2 C

H2 C

C H2

C H2

C H2

H2 C

k3

H2 C

C H2

C H2

C H2

C H2

CH3

β-scission H2 C

k4 C H

H2 C

(3)

Rs

RP

H2 C

C H

C H2

CH3

C H2

C H2

H 2C

RP

H2 C C H2

+

H2 C

H C

(4) 3)

alkene/diene

k 4' H2 C

Rs

CH3

C H

C H2

+

CH2

C H2

P

H2 C

(4')

CH3

RP

Hydrogen transfer (intermolecular) H2 C H 3C

n C

H2 C

+

H2

H2 C

RP

n C

H 3C

C H2

C H2

H2 C

k5

H2

alkane

P

CH3

+

H C C H2

C H2

(5) )

Rs

Termination -2nd order (recombination)

H2 C

RP

+

H2 C

k6

RP

Scheme 1. Mechanism of PE thermal degradation [20].

C C H2 H2

P

(6) )

Thermal and Thermal-oxidative Degradation of Polyethylene Nanocomposite …

9

100

Weight, %

80

3

60

1 40

2 4

20

0 200

300

400

500

600

o

Temperature, C Figure 4. TGA thermograms for PE (firm lines) and PE-n-MMT (dotted lines) taken in Ar at the heating rates of: 3K/min - 1, 2 and 10K/min. - 3, 4.

3.3. Kinetic Analysis of PE Nanocomposite Thermal Degradation Based on TGA Data Kinetic studies of materials degradation have long history, and there exists a long list of data analysis techniques employed for the purpose. Often, TGA is the method of choice for acquiring experimental data for subsequent kinetic calculations, and namely this technique was employed here. It is commonly accepted that the degradation of materials follows the base equation (1) [15]. dc/dt = - F(t,T co cf)

(1)

where: t - time, T - temperature, co - initial concentration of the reactant, and cf concentration of the final product. The right-hand part of the equation F(t,T,co,cf) can be represented by the two separable functions, k(T) and f(co,cf): F(t,T,co,cf) = k[T(t)·f(co,cf)]

(2)

Arrhenius equation (4) will be assumed to be valid for the following: k(T) = A·exp(-E/RT)

(3)

10

S. M. Lomakin, L. A. Novokshonova, P. N. Brevnov et al. Therefore, dc/dt= - A·exp(-E/RT)·f(co,cf )

(4)

All feasible reactions can be subdivided onto classic homogeneous reactions and typical solid state reactions, which are listed in Table 1 [23]. The analytical output must provide good fit to measurements with different temperature profiles by means of a common kinetic model. Kinetic analysis of PE and PE-n-MMT thermal degradation at heating rates of 3, 5, 10 and 20K/min was accomplished by using a NETZSCH Thermokinetics software in accordance with a formalism we proposed earlier [7]. In order to assess the activation energy for development of a reasonable model for kinetic analysis of pristine PE and PE-n-MMT thermal degradation processes, a few evaluations by model-free methods have been done as the starting point. As an example, the results of a model-free Friedman analysis for thermal degradation of PE, where the activation energy is a function of partial mass loss change [24], are shown in Figure 5. Table 1. Reaction types and corresponding reaction equations, dc/dt= - A·exp(E/RT)·f(co,cf ) Name F1 F2 Fn

f(co,cf ) c c2 cn

Reaction type first-order reaction second-order reaction nth-order reaction

R2 R3

2 · c1/2 3 · c2/3

two-dimensional phase boundary reaction three-dimensional phase boundary reaction

D1 D2 D3 D4

0.5/(1 - c) -1/ln(c) 1.5 · e1/3(c-1/3 - 1) 1.5/(c-1/3 - 1)

one-dimensional diffusion two-dimensional diffusion three-dimensional diffusion (Jander's type) three-dimensional diffusion (Ginstling-Brounstein type)

B1 Bna

co · cf con · cfa

simple Prout-Tompkins equation expanded Prout-Tompkins equation (na)

C1-X

c · (1+Kcat · X)

first-order reaction with autocatalysis through the reactants, X. X = cf.

Cn-X

cn · (1+Kcat · X)

nth-order reaction with autocatalysis through the reactants, X

A2 A3 An

2 · c · (-ln(c))1/2 3 · c · (-ln(c))2/3 N · c · (-ln(c))(n-

two-dimensional nucleation three-dimensional nucleation n-dimensional nucleation/nucleus growth according to Avrami/Erofeev

1)/n

Thermal and Thermal-oxidative Degradation of Polyethylene Nanocomposite …

E, kJ/ mol

11

log (A,s-1) 2

35

1 25 1 15

5

0

5 0

0. 0. Conversion degree

0.

0.

1.

Figure 5. The graphs for activation energy and pre-exponential factor as the functions of the conversion degree (partial mass loss) for thermal degradation of PE in argon, obtained with the aid of Friedman analysis.

Further, nonlinear model fitting procedure for PE and PE-n-MMT TGA-curves has led to the following triple-stage model scheme of successive reactions (Figure 6 a, b):

Dn

A

Fn

B

C

Fn

D

(5)

Taking this as a reasonable approximation for PE and PE-n-MMT, the fits with the aid of nonlinear regression were attempted by the model (5), where an one-dimensional diffusion type reaction was used for the first step and the nth-order (Fn) reaction - for the two subsequent steps of the overall thermal degradation process (Figure 6, Table 1). Assuming a radical chain mechanism is operative in the process of PE and PE-n-MMT thermal degradation (Scheme 1), the apparent activation energy and the pre-exponential factor values calculated in this work turned out to be in perfect match with the data from isothermal analysis and dynamic TGA published earlier (Ea = 268 ± 3 kJ/mol, log A = 17.7 ± 0.01 min-1 and Ea = 262.1 kJ/mol, log A = 18.09± 0.14 min-1 [25].)

12

S. M. Lomakin, L. A. Novokshonova, P. N. Brevnov et al.

a

100

80 3

Weight, %

2

4 1

60

40

20

0

200

300

400

500

600

o

Temperature, C

b

100

80 3

2

Weight, %

4 1

60

40

20

0

200

300

400

500

600

o

Temperature, C

(b)

Figure 6. Outcome of multiple models-based nonlinear fitting for pristine PE (a) and PE-n-MMT (b). The experimental TGA-data (dots) in comparison with the model calculations results (firm lines) are shown for different heating rates: 3K/min – (1), 5K/min – (2), 10K/min – (3) and 20K/min – (4).

Thermal and Thermal-oxidative Degradation of Polyethylene Nanocomposite …

13

Table 2. The kinetic parameters for the three-step thermal degradation of PE and PE-nMMT as obtained by the multiple-curve analysis of the experimental TGA-data (heating rates 3, 5, 10 and 20 K/min) in frames of the reaction model Fn Dn Fn

A Material

PE

PE-n-MMT

B

C

Parameter

Value

logA1, s-1 E1, kJ/mol

11.7 197.7

logA2, s-1 E2, kJ/mol n2

15.5 253.1 0.50

logA3, s-1 E3, kJ/mol n3

16.6 268.1 1.50

logA1, s-1 E1, kJ/mol

10.3 186.3

logA2, s-1 E2, kJ/mol n2

14.5 237.5 0.50

logA3, s-1 E3, kJ/mol n3

17.6 274.3 1.50

D

Corr. Coeff.

0.9994

0.9992

The TGA data acquired for PE and PE-n-MMT in argon has not provided any evidence in favour of the hypothesis that the barrier effect, being clearly manifested in the gas permeability experiments with the same PE-n-MMT at room temperature [12], is operative also during thermally stimulated degradation of PE-n-MMT. It should be noted that, in an inert atmosphere, degradation/volatilization of both PE and PE-n-MMT starts at about 350°C and is totally completed upto 500-550oC, not taking into account a solid silicate residue amounting to 4-5 % wt. which remains in the case of the nanocomposites (Figure 4, 6). Based on TGA data, the first stage of the degradation process (1D-diffusion limiting stage) develops in the range of 350-410oC corresponding to the overall mass loss of 5-7%. The subsequent steps of the thermal degradation processes (410 - 500oC) for PE and PE-n-MMT proceed in the liquid melt of high molecular weight degradation products (Scheme 1). In the light of the above findings, we believe that during the high-temperature degradation stages (above, e. g., 410oC) in an inert atmosphere, the barrier diffusion restrictions can become insignificant since the viscosity of the pyrolyzed polymer melt at these temperatures is rather low and, because of the intensified mobility of the clay layers in such melt, the overall ‘labyrinth effect’ normally provided by the clay particles in more viscous matrices may be considerably diminished.

14

S. M. Lomakin, L. A. Novokshonova, P. N. Brevnov et al.

Scheme 2. A flow-chart of elementary steps constituting PE thermal-oxidative degradation process.

3.4. Thermal-oxidative Degradation of PE Nanocomposite Thermal oxidative degradation of PE and PE nanocomposites has been extensively studied over the past decades [26-30]. It has been reported that the main oxidation products of PE are aldehydes, ketons, carboxylic acids, esters and lactones [26, 27]. According to Lacoste and Carlsson [28], β-scission plays an important role in thermal oxidation of UHMWPE. Notably, the feasibility of intra-molecular hydrogen abstraction by the peroxy radicals for polyethylene has been questioned in frames of a thermal oxidation mechanism proposed by Gugumus [29, 30]. It is usually supposed that the reaction of hydrogen abstraction from an alkane molecule, R-H, may lead to either hydroperoxide or alkyl radicals according to the overall reaction scheme (Scheme 2). A mechanism describing oxidation of organic molecules by virtue of complex chain reactions has been proposed earlier by Benson [31]. At temperature below 190oC, oxidation of organic compounds involves free-radical chain initiation and the main products are hydroperoxides and oxygenated species indicated in the routes A1 and A2 of Scheme 2. At temperatures below 200oC, the abstraction of H from R· resulting to HO2· + olefin (routes B1 and B2) proceeds at least 200 times slower than the addition of O2 to R· to give RO2·. Above 250oC, the route A2 becomes reversible and the very slow step B2 becomes rate determining. As a consequence, at temperatures above 300oC, there is some retardation of the rate of oxidation of the polymer. The H2O2 can play the same role as ROOH in providing a secondary radical source just above 480oC where the rate of oxidation picks up again.

Thermal and Thermal-oxidative Degradation of Polyethylene Nanocomposite …

15

It is worth noting that simple digital photo camera was of help for qualitative assessment of differences in the processes of thermal oxidation of neat PE as compared to PE-n-MMT. Figure 7 shows color photographs of the neat PE (1) and PE-n-MMT (2) taken after both samples having been heated during 2 minutes at 180oC in air. It can be seen that coloration of the PE-n-MMT sample (2) is much darker than that of the neat PE (1), thus evidencing that MMT is able to induce an oxidative dehydrogenation of PE, resulting in emergence of unsaturated bonds, which subsequently lead to crosslinking, aromatization and carbonization of the polymer. Figure 8 compares the TGA thermograms for neat PE and PE-n-MMT which has been acquired at a 10K/min heating rate in air. Obviously, under the thermal oxidative degradation conditions, these two materials demonstrate strikingly different behavior.

1

2 Figure 7. Differences in coloration of neat PE (1) and PE-n-MMT (2) samples - both heated for two minutes at 180oC in air.

16

S. M. Lomakin, L. A. Novokshonova, P. N. Brevnov et al. 100

Weight, %

80

2

1

60

40

20

0

100

200

300

400

500

600

o

Temperature, C Figure 8. TGA curves for PE (1) and PE-n-MMT (2) recorded in air at the heating rates of 10K/min.

The earliest stage of thermal oxidative degradation of unstabilized samples of PE-nMMT and PE manifests itself as a clear weight gain feature emerging on the TGA curves well below 200oC and is attributed to the oxygen absorption followed by the hydroperoxides formation (Figure 8, 9). Of importance, however, is the fact that for PE-n-MMT this process seems to be accelerated due to the presence of nanosilicate additive as compared with the pristine PE. Dependences of the hydroperoxides formation onset temperatures versus the heating rate, which have been derived from the TGA data for unstabilized PE-n-MMT and PE samples, are presented in Figure 10. O2 H2C

H2C MMT

OO*

+

CH2 H2C

CH2

Δ MMT

OO

H

CH

H2C

Δ MMT

OOH

+

CH2

CH2 H2C

CH2

H C H2C

H2C

CH2

Δ MMT

Scheme 3. The earliest stages of the process of PE thermal oxidative degradation in the presence of exfoliated MMT nanoparticles.

Thermal and Thermal-oxidative Degradation of Polyethylene Nanocomposite …

104 179

o

190

o

204

o

223

o

Weight, %

102

100

98

o

20 /min

o

96

10 /min

o

o

3 /min

5 /min

94 100

150

200

250

300

350

o

Temperature, C Figure 9. Exploded view of TGA traces characterizing the primary stage of PE-n-MMT thermal oxidative degradation at different heating rates.

2

200

1

o

Temperature (Ton), C

190 180 170 160 150 140 0

10

20

30

40

Heating Rate, K/min Figure 10. The onset temperatures of hydroperoxides formation vs. heating rate for: 1 – PE, 2 - PE-nMMT.

17

18

S. M. Lomakin, L. A. Novokshonova, P. N. Brevnov et al.

We believe that O2 molecules, being adsorbed on the defect centers of MMT represented by the traces of transitional metals, transform into more active species which are able to react with PE at lower temperatures, thus inducing formation of active centers on the hydrocarbons chains (Scheme 3). Apparently, this chain of events should result to accelerated formation of PE hydroperoxides. Notably, while the hydroperoxides accumulation starts at lower temperatures in PE-nMMT than in the unfilled PE (cf. e. g., Figure 8), the clearly visible mass loss of the nanocomposite (attributable solely to decomposition of the accumulated hydroperoxides) ensues at lower temperatures as well. It is reasonable to suggest that this effect is caused by a catalytic action of exfoliated MMT nanoparticles on the hydroperoxides decomposition. As it has been mentioned above, the treatment of PE-n-MMT with alcoholic HCl solution led to substitution of the major part of the organic modifier by acidic protonic centers. Moreover, it is widely accepted that MMT-type clay minerals always comprise a plenty of different catalytically capable sites, which may be represented by weakly acidic Brønsted-like Si-OH sites, by strongly acidic -OH groups localized at the edges of the silicate layers, by transition metal cations captured in the galleries, and by crystallographic defect sites within the layers [32,33]. All these sites are able to trigger decomposition of hydroperoxides within the bulk of the PE-n-MMT. It has been shown that acid-catalyzed rearrangements of hydroperoxides can proceed in both polar and non-polar solvents. Hence, such rearrangements can be expected to occur also in PE-n-MMT. Acids can decompose primary and secondary hydroperoxides according to two different pathways [34]. Both these routes are depicted in Scheme 4 for the secondary hydroperoxides most probably present in PE. Since mobility of the methylene units in the PE backbone is rather limited, it is reasonable to assume that reaction (2) in Scheme 4 should be of minor importance. Then the main reaction [reaction (1) in Scheme 4] must lead to transformation of the hydroperoxide into the ketone group with elimination of water. The reaction might proceed according to the general mechanism or be simply dehydration [35]. At the same time, the acidic sites of MMT may turn out to be sufficiently active to abstract single electrons from donor molecules with formation of free radicals, the latter being capable of further accelerating the thermal oxidation of PE chains e. g. by virtue of branching reactions. H2 H C C O

H2 H C C

C H2

AH

H2 C

C O

C H2

+

H2O

(1)

C C H2

(2)

OH

C H2

O

H

AH C OH H2

+ O

OH Scheme 4. Acid-catalyzed decomposition of PE hydroperoxides.

Thermal and Thermal-oxidative Degradation of Polyethylene Nanocomposite …

19

In addition to the accumulation and subsequent decomposition of the hydroperoxides on the earlier stage resulting to emergence of the oxygen-containing groupings, the ensued process of thermal oxidative degradation of the nanocomposite involves the reactions of oxidative dehydrogenation and intermolecular cross-linking. The latter two reactions have been revealed with the aid of the DRAFT FTIR spectra presented below. It seems reasonable to suggest that namely at this step the thermally stable carbonized charred layer on the nanocomposite surface is formed and starts to hinder the diffusion transport of both the volatile degradation products (out of the polymer melt into the gas phase) and the oxygen (from the gas phase into the polymer). The above set of events results in actual increase of the nanocomposite thermal stability in the temperature range of 350-500°C, where normally a shear degradation of the main part of PE takes place. This point is illustrated by TGA and DTG plots presented in Figs. 11 and 12. 100

Weight, %

80

3

60

2

1

40 20 0 200

300

400

500

600

0.0

dm/dT

-0.7

1

-1.4 -2.1

2

-2.8 200

300

3

400

500

600

o

Temperature, C Figure 11. Acquired at 10 K/min heating rate in air or argon TGA and DTG curves for: 1 - PE (air), 2 – st-PE (air), 3 - PE (Ar).

20

S. M. Lomakin, L. A. Novokshonova, P. N. Brevnov et al. 100

3

Weight, %

80

2 60

1

40 20 0 200

300

400

500

600

0.0

dm/dT

-0.7

2

-1.4

1

-2.1

3

-2.8 200

300

400

500

600

o

Temperature, C Figure 12. Acquired at 10 K/min heating rate in air or argon TGA and DTG curves for: 1 - PE-n-MMT (air), 2 – st-PE-n-MMT (air), 3 - PE-n-MMT (Ar).

The diverse behavior of stabilized and unstabilized samples (Figure 11 and 12, curves 1,2 TG and DTG) shows that the addition of antioxidants has resulted to higher thermal-oxidative stability. It can be seen also that the overall thermal oxidative stability of PE-n-MMT irrelevantly of the antioxidant presence was higher that that of the pristine PE. Moreover, incorporation of the antioxidants in PE-n-MMT has led to a notable change in the character of the mass loss process (Figure 12, curves 2,3 of TG and DTG). It is quite probable that the antioxidant is able to “deactivate” the sites of MMT that have been occupied earlier with absorbed oxygen. In the result, the MMT nanolayers could become chemically inert in respect to the hydroperoxides formation and hence to further accelerated PE oxidation. It may be seen as well that, with the exception of the first thermal oxidation step, the TGA and DTG curves for st-PE-n-MMT taken in air become closely resembling those characteristic for PE-n-MMT run in argon. Having taken into account the above findings, it seems reasonable to explain the observed retardation of thermal oxidative degradation of st-PE-n-MMT by the capability of exfoliated MMT nanolayers to hinder the diffusion of oxygen throughout the partly cross-linked and carbonized nanocomposite matrix.

Thermal and Thermal-oxidative Degradation of Polyethylene Nanocomposite …

21

3.5. Kinetic Analysis of PE-n-MMT thermal Oxidative Degradation Kinetic analysis of thermal oxidative degradation of unstabilized PE and PE-n-MMT at the heating rates of 3, 5, 10 and 20K/min. (Figure 13 a, b) (as well as of the same samples stabilized with antioxidants) has been accomplished by using the aforesaid interactive model based nonlinear fitting approach. With best fidelity, the undertaken nonlinear model fitting for the stabilized samples of PE and PE-n-MMT has provided a triple-stage model scheme of successive reactions, wherein an nth-order autocatalysis reaction (Cn) was used at the first step, while a general nthorder (Fn) reaction was used for both the second and the third steps of the overall process of thermal oxidative degradation (Table 1):

Cn

A

Fn

B

C

Fn

D

(8)

For unstabilized PE and PE-n-MMT at the beginning stage of degradation, the degree of conversion depends on the heating rate (Figure 13a), such dependence being a strong evidence in favor of a branched reaction path. For this case, the same approach has provided a dissimilar triple-stage model scheme comprising two competitive reactions: an n-th order autocatalytic reaction (Cn), for the first competing path, and two nth-order (Fn) successive reactions, for the second competing path (9). Cn

A

Fn

B B

Fn

C

(9)

As data in Table 3 for the first stage of thermal oxidative degradation reaction show, the activation energies values for st-PE and st-PE-n-MMT amount to 74 and 96 kJ/mol, while for unstabilized materials those values are of 65 and 51 kJ/mol, correspondingly, thus indicating that the degradation of these samples is initiated by the similar oxygen induced reactions. At this stage, the lower activation energy of PE-n-MMT compared to that of PE may be related to the catalysis exerted by the ММТ during formation and decomposition of hydroperoxides. At the same time, the values of activation energy found at the second and the third stages of thermal-oxidative degradation for PE-n-MMT are higher than those for PE (Table 3, Figure 14). This difference may be attributed to a shift of the PE-n-MMT degradation process to a diffusion-limited mode owing to emergence in the system of a carbonized cross-linked material. The activation energy values of st-PE-n-MMT at the first and the last stages are higher than those of st-PE (Table 3, Figure 14). Actually, at the last stage, the activation energy of stPE-n-MMT rises up to 274.8 kJ/mol, almost reaching the activation energy value found for degradation of PE-n-MMT in inert atmosphere (274.3 kJ/mol) (Table 2). This fact infers that the last stage of the st-PE-n-MMT degradation process is governed mainly by random scission of C-C bonds, rather than by an oxygen catalyzed reactions. On the other hand, these results are also consistent with the barrier model mechanism, which suggests that inorganic

22

S. M. Lomakin, L. A. Novokshonova, P. N. Brevnov et al.

clay layers can play a role of barriers retarding the diffusion of oxygen from gas phase into the nanocomposite. a

3

100

2

Weight, %

80

1

60

40

20

0

100

200

300

400

500

600

o

Tem perature, C

b

100

Weight, %

80

60 2

1

3

40

20

0

100

200

300

400

500

600

700

o

Temperature, C Figure 13. Nonlinear kinetic modelling of PE-n-MMT (a) and st-PE-n-MMT (b) in air. Comparison between experimental TGA data (dots) and the model results (firm lines) at several heating rates: 3K/min – (1), 5K/min – (2) and 10K/min.

Thermal and Thermal-oxidative Degradation of Polyethylene Nanocomposite … Table 3. Results of the multiple-curve kinetic analyses for thermal-oxidative degradation of PE and PE-n-MMT in accordance with the reaction models 8 and 9 Material

St-PE

PE

St-PE-n-MMT

PE-n-MMT

Parameter

Value

logA1, s-1 E1, kJ/mol n1 log Kcat 1

3.6 74.9 0.79 0.59

logA2, s-1 E2, kJ/mol n2

14.9 225.9 0.51

logA3, s-1 E3, kJ/mol n3

16.1 254.4 1.79

logA1, s-1 E1, kJ/mol n1 log Kcat 1

3.6 65.3 1.62 0.14

logA2, s-1 E2, kJ/mol n2 logA3, s-1 E3, kJ/mol n3 logA1, s-1 E1, kJ/mol n1 log Kcat 1

5.1 120.2 0.55 13.7 219.7 1.37 6.3 96.3 2.4 0.15

logA2, s-1 E2, kJ/mol n2

13.8 230.2 0.64

logA3, s-1 E3, kJ/mol n3 logA1, s-1 E1, kJ/mol n1 log Kcat 1

16.8 274.8 1.66 2.2 51.5 2.81 0.12

logA2, s-1 E2, kJ/mol n2

6.8 146.2 0.53

logA3 s-1 E3 kJ/mol n3

14.7 238.2 1.69

Corr. Coeff.

0.9987

0.9953

0.9993

0.9993

23

24

S. M. Lomakin, L. A. Novokshonova, P. N. Brevnov et al.

250

0

PE-n-MMT

PE

3 stage 2 stage 1 stage

1 stage

2 stage

1 stage

50

1 stage

2 stage

100

3 stage

2 stage

3 stage

150

3 stage

En, kJ/mol

200

st-PE

st-PE-n-MMT

Figure 14. Comparative diagram of activation energies for PE and PE-n-MMT thermal-oxidative degradation processes.

Thus, from the results of the kinetic analyses of TGA data for both antioxidant-stabilized and unstabilized PE and PE-MMT nanocomposite it follows that the organoclay nanoparticles can exert two counteracting effects influencing the thermal-oxidative stability of the PEMMT nanocomposite: 1. the barrier effect in partly carbonized cross-linked polymer matrix tending to improve the thermal-oxidative stability of the nanocomposite; 2. observed at the earlier stages the catalytic effect inducing the accumulation and decomposition of hydroperoxides, thus in fact promoting degradation of the polymer matrix and hence impairing the thermal stability of PE-n-MMT.

3.6. Dynamic FTIR Analysis of PE-n-MMT Thermal Oxidative Degradation Simultaneously to TGA measurements, thermal oxidative degradation of non stabilized samples of PE and PE-n-MMT has been monitored in this work with the aid of a dynamic FTIR spectroscopy in a temperature range of 25 – 240oС. The overall evolution of the dynamic FTIR spectra in the course of thermal-oxidative degradation of PE and PE-n-MMT in the condensed phase is shown in Figure 15 (a, b).

Thermal and Thermal-oxidative Degradation of Polyethylene Nanocomposite …

25

a

o

240 C o

230 C o

220 C o

210 C o

200 C o

Absorbance, %

190 C o

180 C o

170 C o

160 C o

150 C o

140 C o

130 C o

120 C o

110 C o

100 C o

90 C o

80 C o

70 C o

60 C o

50 C o

25 C

3500

3000

2500

2000

W avenumber, cm

1500

1000

-1

b

o

240 C o

240 C o

230 C o

220 C o

Absorbance, %

210 C o

200 C o

190 C o

180 C o

170 C o

160 C o

150 C o

140 C o

130 C o

120 C o

110 C o

100 C o

50 C o

25 C

3500

3000

2500

2000

1500

Wavenumber, cm

-1

Figure 15. Dynamic FTIR analysis of PE – (a) and PE-n-MMT – (b).

1000

500

26

S. M. Lomakin, L. A. Novokshonova, P. N. Brevnov et al. Table 4. Assignments of the dynamic FTIR spectra

Wavenumber (cm-1)

Assignment

Reference

3630-3690 3552

-OH hydroxyl groups -OH hydroxyl groups of MMT free hydroperoxide groups (-OOH)

[46] [S] [45]

3410

associated hydroperoxide groups (-OOH)

[45]

3400

ν (-OH) hydroxyl groups of MMT

[S]

2930

ν (CH2)a

[44]

2852

ν (CH2)s

[44]

1790 1746

-lactone C=O stretching ν (C=O) in ester

[43] [45,46]

1734

ν (C=O) in aldehyde

[48]

1717

ν (C=O) in ketone

[45,46]

1700

ν (C=O) in

[45]

1600-1590 1458

ν (C=C) δ (CH2)a

[45] [44]

1363

δ (CH2)s

[44]

1163

ν (C–O-C) in ester

[44,45]

1072

ν (Si–O)

[45,]

1010

ν (Si–O)

[45,]

719

γ (CH2)

[45]

–β unsaturated ketone

Table 4 shows peak positions of the absorption bands monitored during the heating experiment along with the corresponding assignments of the vibrations. At room temperature (25oC), the FTIR spectra of both materials are typical for PE. The absorption bands at 2845-2960 cm-1 are assigned to -CH-, -CH2-, or -CH3 stretching vibration [36]. The absorption at 1472 cm-1 is due to the deformation vibration of -CH2- or -CH3 groups, while that at about 720 cm-1 is due to (CH2)n rock when n ≥ 4 [36, 37]. Beside these, the FTIR spectra of PE-n-MMT revealed the absorptions belonging to MMT (ν (Si–O) 1047 cm-1) [37]. Another MMT absorption band at 3630 cm-1 has been assigned to the structural hydroxyl groups, directed toward the vacant positions in the inner octahedral layer of montmorillonite. Else, a broad absorption band of hydroxyl groups was observed at 3400 cm-1 [38]. During the dynamic recording of the PE and PE-n-MMT spectra under the step-wise heating a sharp growth of the absorption in the range of 1700 - 1800 cm-1 was noted at temperatures above 200oC indicating the emergence and accumulation of carbonyl-containing products resulting from the thermal-oxidative degradation process (Figure 16).

Thermal and Thermal-oxidative Degradation of Polyethylene Nanocomposite … 88

3500

2500

2000

719

1072

1363 1311

1590

920 1041

719

1363 1311 1163

1734 1746 1717

1790

2678

3000

1458

2853 2856

66 64 62 60 58 56

2

1604

2922 2934

1458

2678

1746 1717

3550

1

3550

Transmitance

86 84 82 80 78 76 74 72 70 68

27

1500

1000

Wavenumber, cm

500

-1

Figure 16. FTIR spectra of PE – (1) and of PE-n-MMT – (2) taken at 220oC in the course of the heating runs (Excerpted from the corresponding dynamic FTIR spectra sets).

Obviously, the complex band in the range of 1700-1800 cm-1 comprises (1) a carbonyl absorption (shoulder at 1717 cm-1) belonging to ketone groups embedded into the polymer chain [37, 39], which are known to be the main oxidation products for the neat PE [3], (2) a shoulder peaking close to 1734 cm-1 (Figure 17, Table 3) which is attributed to aldehyde groups [40], (3) another shoulder with maxima in the vicinity of 1746 cm-1 (Figures 17 Table 3) which is normally assigned to ester groups vibrations [37, 39], and (4) an absorption at 1790 cm-1 belonging to the carbonyl in -lactone moiety [41]. Gradual growth of concentration of the vinylene groups absorbing close to 1600 cm-1 has also been noted [37]. The dynamic FTIR spectra show that, while the fractional ratio of different carbonyl absorptions was almost the same for both PE and PE-n-MMT, the apparent concentration of the carbonyl-containing products (overall intensity of the complex absorption band) in PE-nMMT was considerably higher than in pristine PE (Figure 17), other conditions being the same. For non stabilized samples of both PE and PE-n-MMT, temperature dependences of the Carbonyl Index (CI) have been estimated which are shown in Figure 18. The carbonyl index (CI) was defined to illustrate the formation of non-volatile carbonyl containing oxidation products:

CI =

SC=O − CIo S2019

28

S. M. Lomakin, L. A. Novokshonova, P. N. Brevnov et al. 0.025

Absorbance

1717

0.020

1790

1746

0.010

1734

0.015

0.005

0.000

1800

1750

1700

1650

-1

Wavenumbers, cm

Figure 17. An exploded view of the 1700 - 1800 cm-1 infrared region showing the separated modes belonging to different carbonyl-containing groups formed in the course of thermal-oxidative degradation of PE and PE-n-MMT. 14

2

10 8

i

CI = S[C=O] /S2019- CIo

12

6 4

1

2 0 50

100

150

200

250

o

Temperature, C Figure 18. The Carbonyl Index (CI) vs. temperature dependences for: (1) PE; (2) PE-n-MMT.

Thermal and Thermal-oxidative Degradation of Polyethylene Nanocomposite …

29

where SC=O is peaks area of carbonyl containing groups at 1800-1700 cm-1, S2019 is internal reference at 2019 cm-1, which was attributed to the combination of 1300 cm-1 and 720 cm-1 , CIo is initial carbonyl index. Along with the carbonyl absorptions growth, the FTIR spectra have revealed a clear decay of intensities of the bands belonging to -СН2- vibrations as the result of the PE chain scission. Both investigated materials experienced the chain scission during pyrolysis, but with drastically different rates. The relative rates of the decay are illustrated by the overlaid spectra in Figure 19 showing evolution of the symmetrical and asymmetrical –CH2- stretch absorption bands with the pyrolysis temperature for pristine PE as compared to PE-n-MMT. At any given temperature above 200oC, PE-n-MMT has higher content of intact CH2 units than the pristine PE sample, and the apparent rate of disappearance of the aliphatic units in the pyrolysis temperature range of 220-260oC is much higher for pristine PE than for the corresponding nanocomposite. Thus, the observed evolution of the spectra is an extra proof of the fact that, at temperatures above 220oC, PE-n-MMT nanocomposite undergoes thermaloxidative degradation with a considerably slower rate than the neat PE does. The same conclusion has been derived in the preceding section based on the analysis of corresponding TGA data (Figure 10). We explained this fact by the formation of chemical crosslinking between the polyethylene macromolecules in the nanocomposite. Figures 15b and 16 show the medium absorption band at 1162 cm-1 which can be attributed to intermolecular esters groups (>С-ОС<) [ книга ]. At the same time this peak is absent at the spectra of the pristine PE (Figures 15a, 16). a 88

b 75

o

260 C

o

240 C

70

Transmittance

Transmittance

80

o

200 C 72

o

260 C

o

240 C

65

o

200 C o

150 C o

150 C

64 60

2600

2700

2800

2900

3000

3100

2600

2700

2800

2900

3000

3100

-1

-1

Wavenumber, cm

Wavenumber, cm

Figure 19. Comparative evolution of the IR absorption bands attributed to -СН2- units in: (a) neat PE, and (b) PE-n-MMT nanocomposite.

30

S. M. Lomakin, L. A. Novokshonova, P. N. Brevnov et al. (ROOH)

( RO )

OOH

O

C C H C H2 H2

(b)

PE

C H2

H2 C

(RH)

RO C H2

(a)

C H2

H C

(c)

Chain scission (oxygen excess) O

C C H C H2 H2

+ HO (d )

C CH + H2C H2

O2 / RH

C H2

RO

H2 C H C

(e)

O

(R )

C H2

x2

H2 C (ROR)

C H

C H2

Cross-linking (oxygen deficiency)

(f ) H2 C C H2

H C C H

H2 C (R-R) C H2

Scheme 6. Alternative reactions of alkyl radicals during thermal-oxidative degradation of polyethylene [26].

It is known that in low oxygen concentrations, PE nanocomposite undergoes crosslinking processes with the formation of intermolecular >C-C< and >С-О-С< bonds [26]. The difference lies in the subsequent reactions of alkyl macro-radicals after depletion of oxygen which is both dissolved in the polymer and trapped between the clay particles. Increasing the concentration of oxygen leads to the predominance of chain scission in PE (Scheme 6, reactions c, d), whereas at low concentration of oxygen the intermolecular crosslinking followed by carbonization takes place (Scheme 6, reactions e, f). When a silicate is dispersed into a polymer matrix giving a nanocomposite an improvement of the barrier properties of the material is obtained, due to the labyrinth effect of the silicate layers towards the diffusing gas or liquids.

CONCLUSION Performed study of the thermal and thermal-oxidative degradation of PE and its nanocomposites revealed distinguishing features for nanocomposites thermal-oxidative degradation. It is shown that thermal degradation of PE in the inert environment proceeds identical with PE nanocomposite, which is the evidence against the MMT influence on this process. On the other hand, the thermal-oxidative degradation of these materials in the presence of oxygen proceeds in different ways:

Thermal and Thermal-oxidative Degradation of Polyethylene Nanocomposite … •

•

•

• •

31

During the thermal oxidation at 170-200oC for inhibitor-free PE-MMT nanocomposites it was observed the accelerated formation and decomposition of hydroperoxides as compared with unfilled PE which is caused by catalytic action of montmorillonite (at the presence of oxygen). It was registered above 200oC the effective formation of intermolecular chemical cross-links in the PE-MMT nanocomposite, as a result of recombination reactions of the products of radical decomposition of hydroperoxides, caused by deficiency of oxygen in a polymeric matrix due to the lowered oxygen permeability. Cumulative action of chemical cross-linking and catalytic dehydration presents arise a necessary and sufficient condition of carbonization, which is observed in the process of thermal-oxidative degradation of PE-MMT nanocomposites. Carbonized layer formation leads to appreciable increase of thermal stability of PE nanocomposite, owing to a hindrance of the mass transfer in the nanocomposite. An incorporation of the antioxidant in PE and its nanocomposite suppresses the formation and decomposition of hydroperoxides and reduces the catalytic action of MMT on these processes. These facts lead to an increase of thermal-oxidative stability in both materials, at that the nanocomposite thermal stability exceeds PE and approaches the values obtained in inert atmosphere.

REFERENCES [1] [2] [3] [4] [5]

Messersmith PB, Giannelis EP. Chem Mater 1993;5:1064. Zanetti M, Lomakin S, Camino G. Macromol Mater Eng 2000; 279:1-9. M. Alexandre, P. Dubois, Mater. Sci. Eng. R 28 (2000) 1–63. Giannelis EP. Adv Mater. 1996; 8:29-35. Oya A. Polypropylene clay nanocomposites. In: Pinnavaia TJ, Beall GW, editors. Polymer clay nanocomposites. London:Wiley; 2000. [6] J.W. Gilman, T. Kashiwagi, M. Nyden, J.E.T. Brown, C.L. Jackson, S.M. Lomakin, E.P. Gianellis, E. Manias, in: S. Al-Maliaka, A. Golovoy, C.A. Wilkie (Eds.), Chemistry and Technology of Polymer Additives, Blackwell Scientific, London, 1998, pp. 249–265. [7] S.M. Lomakin, I.L. Dubnikova, S.M. Berezina, G.E Zaikov, Polymer International, v.54, 7, (2005), 999-1006. [8] Lomakin SM, Zaikov GE, Modern Polymer Flame Retardancy, VSP Int. Sci. Publ. Utrecht, Boston, 2003, 272. [9] Gilman JW. Applied Clay Sci. 1999. V.15. P.31. [10] Gilman GW, Jackson C L., Morgan A B, Harris R H, Manias E, Giannelis E P, Wuthenow M, Hilton D, Phillips S. Chem. Mater. 2000. V.12. P.1866. [11] T. Kashiwagi, R.H. Harris Jr, Xin Zhang, R.M. Briber, B.H. Cipriano, S. R. Raghavan, W. H. Awad, J. R. Shields. Polymer. 2004. V. 45. P.881. [12] N.Yu. Kovaleva, P.N. Brevnov, V.G. Grinev, S.P. Kuznetsov, I.V. Pozdnyakova, S.N. Chvalun, E.A. Sinevich, L.A. Novokshonova, Polymer Science, Series A, 2004, V. 46, 6, p.651.

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[13] A.N. Shchegolikhin and O.L. Lazareva Int. J. Vib. Spect., [www.ijvs.com] 1, 4, 95-116 (1997). [14] D.J. Lacey, V. Dudler, Polym. Degrad. Stab. 51 (1996) 1011. [15] M. Paabo, B.C. Levin, Fire Mater. 11 (1987) 55. [16] R.P. Lattimer, J. Anal. Appl. Pyrolysis 31 (1995) 203–226. [17] T. Kuroki, T. Sawaguchi, S. Niikuni, T. Ikemura, Macromolecules 15 (1982) 1460– 1462. [18] E. Kiran, J.K. Gillham, J. Anal. Appl. Pyrolysis 20 (1976) 2045–2068. [19] M. Blazso, J. Anal. Appl. Pyrolysis 25 (1993) 25–35. [20] U. Hornung, A. Hornung, H. Bockhorn, Chem. Ing. Tech. 70 (1998) 145–148. [21] U. Hornung, A. Hornung, H. Bockhorn, Chem. Eng. Technol. 21 (1998) 332–337. [22] H. Bockhorn, A. Hornung, U. Horung, J. Anal. Appl. Pyrolysis 46 (1998) 1–13. [23] Opfermann J. J Thermal Anal Cal. 2000. V.60. № 3. P. 641. [24] Friedman H.L. J Polym. Sci. C. 1965. V.6. № 1. P.175. [25] Bockhorn H, A. Hornung A, Hornung U, Schawaller D. Journal of Analytical and Applied Pyrolysis. 1999. V.48. No.2. P.93. [26] N. Grassie, Gerald S. Polymer Degradation and Stabilization, Cambridge University Press, Cambridge - New York – Melbourne – Sydney, 1988, 222 p. [27] Gugumus F. Polym Degrad Stab 2000; 69:23–34. [28] Lacoste L, Carlsson DJ. Gamma-, photo-, and thermally-initiated oxidation of linear low density polyethyleneda quantitative comparison of oxidation products. J Polym Sci Part A Polym Chem 1992;30:493e500. [29] Gugumus F. Re-examination of the thermal oxidation reactions of polymers 2. Thermal oxidation of polyethylene. Polym Degrad Stab 2002;76(2):329-40. [30] Gugumus F. Re-examination of the thermal oxidation reactions of polymers 3. Various reactions in polyethylene and polypropylene. Polym Degrad Stab 2002;77(1):147-55. [31] S.W. Benson, Thermochemical Kinetics, S. 114, Wiley, New York, 1976. [32] Zaragoza D.F. Organic Synthesis on Solid Phase, Wiley, New York, 2000. [33] Xie W, Gao ZM, Pan WP, Hunter D, Singh A, Vaia R., Chem Mater 2001;13:2980. [34] Yablokov VA. Russ Chem Rev 1980;49:833–42. [35] Plesnicar B. In: Patai S, editor. The chemistry of functional groups, peroxides. New York: John Wiley; 1983. p. 521–84. [36] Bugajny M, Bourbigot S, Bras ML, Delobel R. Polym Int 1999; 48:264. [37] Xie RC, Qu BJ, Hu KL. Polym Degrad Stab 2001;72:313. [38] Serratosa J.M., Bradlay W.F., J. Phys. Chem. 62, 1164, 1958 [39] Zanetti M, Bracco P, Costa L. Polym Degrad Stab 2004;85:657. [40] Morlat S, Mailhot B, Gonzalez D, Gardette J. Chem Mater 2004;16:377. [41] S.M .Desai, J.K. Pandey and R.P.Singh, Macromol Symp, 169 (2001), p.121.

In: Modern Tendencies in Organic and Bioorganic Chemistry ISBN: 978-1-60456-295-8 Editors: A. Mikitaev, M. K. Ligidov, pp. 33-49 © 2008 Nova Science Publishers, Inc.

Chapter 2

MODIFICATION OF CATALYTIC ACTIVITY OF COMPLEXES OF ACETYLACETONATES FE(II,III) WITH QUATERNARY AMMONIUM SALTS IN THE ETHYLBENZENE OXIDATION WITH MOLECULAR O2 IN THE PRESENCE OF SMALL AMOUNTS OF H2O L. I. Matienko*, L. A. Mosolova Emanuel Institute of Biochemical Physics, Russian Academy of Sciences, 4 Kosygin str., Moscow, 119991 Russia

ABSTRACT The catalytic effects of small amounts of H2O (~10-3 mol/l), introduced in the ethylbenzene oxidation with molecular O2, catalyzed with {Fe(III)(acac)3 + R4NBr} systems, where R4NBr = exo ligands-modifiers, quaternary ammonium salts CTAB, (С2H5)4NBr, Me4NBr, were discovered by us. The synergetic effects of increase in the selectivity (SPEH) and the conversion degree (C) (parameter S·C) of ethylbenzene oxidation with molecular O2 into α-phenylethylhydroperoxide (PEH) were obtained in the case of the ethylbenzene oxidation, catalyzed with {Fe(III)(acac)3 + CTAB+ H2O} system. The proposed “dioxygenase-like” mechanism of the iron catalyst transformation into new catalytic particles in the course of oxidation process in the presence {Fe(III)(acac)3 + R4NBr} and activating additives of the water is discussed. The method of evaluation of the activity of formed complexes (Fe(II)(acac)2)x·(R4NBr)y (H2O)n in the micro stages of the catalytic chain-radical ethylbenzene oxidations is offered.

Keywords: oxidation, ethylbenzene, α-phenylethylhydroperoxide, homogeneous catalysis, dioxygen, iron (III) tris(acetylacetonate), quaternary ammonium salts, trace amount of H2O. *

E-mail:[email protected]

34

L. I. Matienko and L. A. Mosolova

1. INTRODUCTION The selective oxidation of hydrocarbons into hydroperoxides, primary products of oxidation is the most difficult problem because of the high catalytic activity of the majority of applied catalysts in ROOH decomposition. At the same time, the problem of selective oxidation of alkylarens (ethylbenzene and cumene) with molecular O2 in ROOH, is of current importance from the practical point of view in connection with ROOH use in large-tonnage productions such as production of propylene oxide and styrene (α-phenylethylhydroperoxide, PEH), or phenol and acetone (cumyl hydroperoxide) [1]. In recent decades the interest to fermentative catalysis and investigation of possibility of modeling of biological systems able to carry out selective introduction of oxygen atoms by C−H bond of organic molecules (mono- and dioxygenase) is grown [2,3]. Unfortunately, dioxygenase capable of to realize chemical reactions of alkanes dioxygenation are unknown [2]. The method of modifying of homogeneous catalysts by additives of different electrondonor ligands for increase in the rate, selectivity and conversion degree of alkylarens (ethylbenzene and cumene) oxidations with molecular O2 in corresponding ROOH was proposed by us [4]. The mechanism of control of Ni(II)(L1)2 (L1=(acac)-) complexes catalytic activity by additives of electron-donor monodentate ligands L2 (L2=HMPA, DMF, MP (Nmethyl pyrrolidone-2), MSt (M=Li, Na, K)) was established on the example of ethylbenzene oxidation. The probable mechanisms of catalysis with iron complexes Fe(II,III)(acac)n, activated with L2 (L2= DMF, R4NBr) were offered. On the basis of the established (Ni) and probable (Fe) mechanisms of the catalysis the methods of control of catalytic ethylbenzene oxidation into PEH including of the use of additives of crown-ethers and ammonium quaternary salts as ligands-modifiers were proposed by us. As result the more active catalytic systems were constructed and so the mechanism of the selective catalysis was confirmed. The values of selectivity, conversion degree and ROOH yield reached at the catalysis by {Ni(II)(L1)2+L2} (L2= Me4NBr, 18C6 (18-crown-6)) exceed analogous parameters in the presence of {Ni(II)(L1)2+L2 (L2=monodentate ligand HMPA, DMF, MP (N-methyl pyrrolidone-2), MSt (M=Li, Na, K))} and known catalysts of ethylbenzene oxidation into PEH (homogenous and heterogonous) [5-7]. The relatively low efficiency of Fe(III)(acac)3 and {Fe(III)(acac)3+L2} systems (as a selective catalysts for ethylbenzene oxidation to PEH) as compared to the efficiency of Ni(II) complexes is due to the simultaneous formation of PEH, methylphenylcarbinol (MPC), acetophenone (AP) and the high rates of accumulation of MPC and AP as the principle products. We established that mechanism of the formation of the selective nickel(II) catalyst responsible for the rise in the selectivity SREH in the process of the ethylbenzene oxidation, consisted in the oxygenation of Ni(II)(L1)2·(L2)n complexes with molecular O2. Coordination of electron-donor extra-ligand L2 by nickel complex Ni(L1)2 (L1=acac-) promoting stabilization of intermediate zwitter-ion L2(L1M(L1)+O2⎯ leads to increase of possibility of regio-selective connection of O2 to the γ-C atom of acetylacetonate ligand, activated in complex with nickel (II) ion. Further introduction of O2 into chelate cycle accompanying by proton transfer and bonds redistribution in formed transition complex (Griegee rearrangement) leads to break of cycle configuration with formation of (OAc)⎯ ion, acetaldehyde, elimination of CO, completing by the formation of catalytic particles with

Modification of Catalytic Activity of Complexes of Acetylacetonates Fe(II,III) ...

35

mixed ligands of general formula Ni(II)x(acac)y(OAc)z(L2) (L1ox= MeCOO--) (“A”) [4,7]. Similar change in complexes' ligand environment was observed in reactions, catalyzed with the only known to date a Ni(II)-containing dioxygenase – acireductone dioxygenase, ARD [8], and in reactions of oxygenation simulating the action of quercetin 2,3-dioxygenase (Cu, Fe) [9, 10]. The proposed mechanism of transformation of (Fe(II)(acac)2)x (L2)y complexes formed in the initial stages of the ethylbenzene oxidation catalyzed with {Fe(III)(acac)3 + L2(DMF, R4NBr)} into active selective catalytic species consists in dioxygenation of acetylacetonate ligand. By analogy to the dioxygenation of nickel (II) complexes a regioselective addition of O2 to the γ-C atom of acetylacetonate ligand (controlled by L2 ligand) with the intermediate formation of zwitterions L2(L1ML1+O2⎯) takes place obviously also in this case [11]. However due to the favorable combination of the electronic and steric factors appeared at inner and outer sphere coordination (hydrogen bonding) of R4NBr or DMF with Fe(II)(acac)2 the oxidative degradation of the acetylacetonate ligand may follow another mechanism. Insertion of O2 into C−C bond (not the C=C bond as takes place for nickel(II) complexes) via 1,2dioxetane intermediate can lead to the formation of methylglyoxal as the second destruction product in addition to the (OAc)⎯ ion (by analogy with the action of Fe(II) containing acetylacetone dioxygenase (Dke 1) (Scheme 1) [12]. As in the case of catalysis by Ni(II) complexes an increase in the selectivity of (Fe(II)(acac)2)m (L2)n (L2=R4NBr, DMF) – catalyzed ethylbenzene oxidation to hydroperoxide is presumably due to the formation of a mixed-ligand complex as a dioxygenation intermediate M(II)x(acac)y(OAc)z(L2)n (M = Fe(II), complex “B”), and the final oxygenation product, Fe(II) acetate, is responsible for the decrease in selectivity [11,13]. We considered the possibility of the positive effect of small amounts of water on the rate of the transformation of iron complexes with R4NBr and probably on the parameters SPEH and C in the ethylbenzene oxidation, catalyzed {Fe(III)(acac)3 + R4NBr}. Outer sphere coordination of H2O molecules may promote the stabilization of intermediate zwitterions L2(L1ML1+O2⎯) and as a consequence the increase in the probability of the regioselective addition of O2 to nucleophilic γ-C аtom of (acac)⎯ ligand can be expected [14]. It is wellknown that the stability of zwitterions increases in the presence of the polar solvents [14]. The H – bond formation between H2O molecule and zwitterion may also promote the proton transfer inside of the zwitterion followed by the zwitterion conversion into the products via Scheme 1 [15]. It is known the cases of the increase in the ratio of alkylation’s products on γC atom of the R4N(acac) in the presence of insignificant additives of water (∼10-3 моль/л) as compared to the alkylation’s reaction in the non proton solvents [16]. Few examples are known to date about the influence of small additives of H2O (~10-3 mol/l) on the homogeneous catalysis by transition metal complexes in the hydrocarbon oxidation with molecular O2. The role of H2O as a ligand in metal complex-catalyzed oxidation has not been practically investigated [15,17,18]. And it is unknown examples of catalytic reactions, when addition of water in small amounts enhances the reaction rate and the product yield. Some of known facts are concerned of the use of onium salts QX together with metal catalyst. So the decrease in the rate of the tetralin oxidation, catalyzed with oniumdecavanadate(V) ion-pair complexes in the presense of ~10-3 mol/l H2O was observed[19]. The oxidations are dependent on structural changes in the inverse micelles, in response to concentration changes of ion-pair complexes existing only in the presence of small amounts

L. I. Matienko and L. A. Mosolova

36

of H2O [20]. The most known facts are connected with the influence of small concentrations of H2O on the catalysis of the ROOH homolysis by onium salts (including quaternary ammonium salts). The acceleration of ROOH homolysis may be the consequence of H – bond formation between ROOH, H2O and QX [21]. Also it is important to understand the role of small amounts of water because some water is always formed during the catalytic oxidation of the hydrocarbon. The homogeneity of the hydrocarbon solution remains upon addition of small amounts H2O ([H2O] ∼ 10-3 моль/л) [20].

2. EXPERIMENTAL Ethylbenzene (RH) oxidation was studied at 80°C in glass bubbling-type reactor in the presence of Fe(III)(acac)3(5·10--3 mol/l) and additives of R4NBr(5·10-4 mol/l) (R4NBr = (С2H5)4NBr, Me4NBr, CTAB). The selectivity SPEH and RH conversion degree C of ethylbenzene into PEH oxidation were determined using the formulas: SPEH = [PEH] / Δ[RH]·100% and C = Δ[RH] / [RH]0·100%. H

3

C H

C O

3

O

Fe O H

3

+

H

O

O

O

C

C H H

3

3

H

C

3

C O

O

O O Fe

O H

3

C

C H

3

H

O C H

3

O O

O

H

+

3

C

Fe H

3

O

O

C

O

+

O

O

C H

O O

O

+

Fe H

3

C

3

O

O

C H

3

H

3

C O

Scheme 1. The principle scheme of dioxygen-dependent conversion of 2,4-pentandione catalyzed by acetyl acetone dioxygenase Fe(II).

Modification of Catalytic Activity of Complexes of Acetylacetonates Fe(II,III) ...

37

Analysis of Oxidation Products α-Phenylethylhydroperoxide was analyzed by iodometry. By-products, including methylphenylcarbinol (MPC) acetophenone (AP), and phenol (PhOH), as well as the RH content in the process were examined by GLC [11,22]. The overall rate of the process was determined from the rate of accumulation of all oxidation products. A correlation between RH consumption and product accumulation was established: Δ[RH] = [PEH] + [P] + [PhOH], where P = AP + MPC. The reaction rates were determined with accuracy of ± 0.5 - 5% [11,22]. The catalytic ethylbenzene oxidation with dioxygen was carried out in the O2 – solution two phase systems under kinetic control. The order in which PEH, AP, and MPC formed was determined from the time dependence of product accumulation rate rations at t → 0. The variation of these rations with time was evaluated by graphic differentiation [11,22].

3. RESULTS AND DISCUSSION Previously we established the interesting fact – the catalytic effect of small concentrations of quaternary ammonium salts, [R4NBr] = 5·10-4 mol/l, which in 10 times less than initial catalyst concentration [Fe(III)(acac)3] (synergetic effects of the grow in the parameters – the rate w0, selectivity SPEHmax, conversion degree C (parameter S·C) in the ethylbenzene oxidation, catalyzed with {Fe(III)(acac)3 + R4NBr} [13]. It was established also that the small amounts of CTAB (5·10-4 mol/l) did not form micelles in the ethylbenzene oxidation, catalyzed with {Fe(III)(acac)3 + CTAB} (800 C) [13]. But there are known the facts of the increase in the rate of the ROOH decomposition in the hydrocarbon solvents, catalyzed by the transition metal compounds, in the presence of CTAB due to including of the metal compound and ROOH in micelles of CTAB [23]. So in this article kinetic studies were carried with additives of H2O into the ethylbenzene oxidation, catalyzed with {Fe(III)(acac)3(5·10-4 mol/l)+ R4NBr(5·10-4 mol/l)} (R4NBr = CTAB, and also R4NBr = (С2H5)4NBr, Me4NBr, 800 C). On the addition of 3,7·10-3 mol/l H2O into the ethylbenzene oxidation, catalyzed with Fe(III)(acac)3 and R4NBr (R4NBr = (С2H5)4NBr, Me4NBr) the effectivity of catalytic systems, estimated by the values of parameters SPEHmax (and S·C) decreases (Figure 1, a-c). In the case of catalysis by system {Fe(III)(acac)3 + (С2H5)4NBr + H2O} the decrease in SPEH took place due to the decrease in the PEH concentration. The contents of PhOH, MPC and AP are changing insignificantly (Figure 1, a,b). At the admixed H2O to the ethylbenzene oxidation, catalyzed with {Fe(III)(acac)3 + Me4NBr} the PEH kinetic unchanged in fact. At the same time the increase in concentrations of [AP] and [MPC] was observed (Figure 1, c). The all reactions to investigate proceed in autocatalytic mode due to the transition Fe(III) to Fe(II) [11,22]. The products were formed with auto acceleration period longer than in the case of the H2O additives – free process (Figure 1, a-c). The reaction rates (as well as in the absence of the H2O additives [22]) rapidly becomes equal to w = wlim = wmax (w0). Under these steady – state reaction conditions the changes in oxidation rates in the both

L. I. Matienko and L. A. Mosolova

38

cases were due to the changes in PEH or P (AC+MPC) accumulations [11,22] (Figure 1, a-c; Table 1). The increase in w0 at catalysis by complexes (Fe(II)(acac)2)n(Me4NBr)m in the presence of the H2O is observed (as compared with catalysis by Fe(II)(acac)2, and catalysis by complexes (Fe(II)(acac)2)n(Me4NBr)m without H2O [13]). The rate w0 decreases insignificantly in the case of catalysis by (Fe(II)(acac)2)n((С2H5)4NBr)m and H2O additives (as compared with catalysis by complexes (Fe(II)(acac)2)n((С2H5)4NBr)m without H2O additives [13].

(a)

35 30

mol/l

2

3

[PEH].10 , [PhOH].10 ,

40

25 20 15 10 5 0 0

10

20

30

40

50

t, h

2

[АP], [МPC].10 , mol/l

(b) 45 40 35 30 25 20 15 10 5 0 0

10

20

30

t, h Figure 1. Continued on next page.

40

50

Modification of Catalytic Activity of Complexes of Acetylacetonates Fe(II,III) ...

39

(c)

2

[АP], [МPC].10 , mol/l

100 90 80 70 60 50 40 30 20 10 0 0

20

40

t, h

(d) 70

SPEH, %

60 50 40 30 20 10 0

5

10

15

20

C, % Figure 1. a. Kinetic of PEH (◊-1,-2) and PhOH (∆-3,c-4) communication in the course of the ethylbenzene oxidation, catalyzed with of {Fe(III)(acac)3 + (C2H5)4NBr(5·10-4 mol/l)} (◊-1,∆-2) or {Fe(III)(acac)3 + (C2H5)4NBr(5·10-4 mol/l) + H2O} (-2,c-4). [H2O]=3,7·10-3 mol/l, 800C. b. Kinetic of AP (◊-1,-2) and MPC (∆-3,c-4) communication in the course of the ethylbenzene oxidation, catalyzed with of {Fe(III)(acac)3 + (C2H5)4NBr(5·10-4 mol/l)} (◊-1,∆-2) or {Fe(III)(acac)3 + (C2H5)4NBr(5·10-4 mol/l) + H2O} (-2,c-4). [H2O]=3.7·10-3 mol/l. 800C. c. Kinetic of AP (◊-1,-2) and MPC (∆-3,c-4) communication in the course of the ethylbenzene oxidation, catalyzed with of {Fe(III)(acac)3+Me4NBr (5·10-4 mol/l)} (◊-1,∆-3) or {Fe(III)(acac)3 + Me4NBr (5·10-4 mol/l) + H2O} (-2,c-4). [H2O]=3.7·10-3 mol/l. 800C. d Dependences SPEH от C in the reactions of the ethylbenzene oxidation in the presence systems {Fe(III)(acac)3 + R4NBr} (◊-1,∆-2) or { Fe(III)(acac)3 + R4NBr + H2O} (-3,c-4). R4NBr = Me4NBr (◊-1,-3), (C2H5)4NBr (∆-2,c-4). [Fe(III)(acac)3]=5·10-3 mol/l. [R4NBr (Me4NBr, (C2H5)4NBr)]=5·10-4 mol/l [H2O] = 3.7·10-3mol/l. 800C.

L. I. Matienko and L. A. Mosolova

40

Table 1. The rates (mol·l-1·s-1) of PEH and P accumulations (P = {AC+MPC}) in the presence of systems {Fe(III)(acac)3 + R4NBr(L2)} without admixed H2O (L3) and at the addition of small amounts of H2O (3,7·10-3.mol/l) L2, L3 ⎯ (C2H5)4NBr (C2H5)4NBr + H2O Me4NBr Me4NBr + H2O CTAB CTAB + H2O

wPEH0· ·106 ⎯

wp0· ·106 ⎯

5.9 4.9

8.3 7.7

wPEH· ·106 2.90 (wPEH0=wPEH) 3.3 3.03

wp· ·106 3.40 (wP0=wP) 4.3 4.1

4.2 5.0

3.4 5.87

2.5 2.5

1.87 4.8

4.35 3.75

3.3 1.1

2.5 3.19

1.2 0.85

w0 – The initial rate of the products accumulation. w – The rate of the products accumulation in the course of the ethylbenzene oxidation. [Fe(III)(acac)3]=5·10-3 mol/l. [R4NBr (Me4NBr, (C2H5)4NBr, CTAB )]=5·10-4 mol/l. 800C.

S·C·10-2 (%,%) 8

6,91

7 6

5,46

4,97

5

3,43

4

2,9

3 2

1,14

1

TA

B

+

H

2O

C TA B C

N

Br +

H 2O

Br M e4

M e4 N

(C

2H

(C

5) 4N

2H

Br

+

H

5) 4N

2O

Br

0

Figure 2. Parameter S·C·10-2 (%,%) in the ethylbenzene oxidation at catalysis by Fe(III)(acac)3 and catalytic systems {Fe(III)(acac)3+R4NBr} and {Fe(III)(acac)3+R4NBr+H2O}. [Fe(III)(acac)3]=5·10-3 mol/l, [R4NBr]=0.5·10-3 mol/l, 80°C.

Modification of Catalytic Activity of Complexes of Acetylacetonates Fe(II,III) ...

41

These are unusual results as compared with known facts of inhibiting effects of water, formed in the oxidation process in the absence of Cat, on the hydrocarbon oxidation rates owing to solvatation of RO2• radicals by H2O molecules [24], deactivation of Cat with water in the processes of chain-radical hydrocarbon oxidation by O2 in no polar medium [25]. The dependence of SPEH on the C in the discussed ethylbenzene oxidation, catalyzed with iron complexes in the presence of small amounts of H2O has extremum as well in the absence of H2O additives. The decrease in values of SPEHmax was observed. Thus, SPEHmax ≈ 43% ({Fe(III)(acac)3 + (C2H5)4NBr + H2O}) < SPEHmax = 48% (at the catalysis with {Fe(III)(acac)3 + (C2H5)4NBr (5·10-4 М)} in the absence of H2O) and SPEHmax ≈ 43% ({Fe(III)(acac)3 + Me4NBr + H2O}) < SPEHmax = 64% ({Fe(III)(acac)3 + Me4NBr}) (Figure 4). The growth in SPEH from SPEH0 to SPEHmax was parallel to decrease in wPEH and wP as in the case of catalysis with systems in the absence of H2O additives (Figure 1 a-d, Table 1). The decreases in values of parameter S·C in the ethylbenzene oxidation, catalyzed with catalytic systems {Fe(III)(acac)3 + (C2H5)4NBr(Me4NBr)} (◊, ∆) or {Fe(III)(acac)3 + (C2H5)4NBr(Me4NBr) + H2O}, the most significant at R4NBr = Me4NBr, are presented on the Figure 5. At the catalysis by Fe(III)(acac)3 without L2, L3, the value of S·C = 2.1(·10-2 (%,%) (Figure 3) [22]. The performance of catalysis with iron complexes was compared in terms of the parameter S·C. In this case we assumed: S was averaged selectivity characterizing change of S in the course of oxidation from S0 at the beginning of the reaction to some Slim, selected as a standard for the series of catalyst systems to be matched in efficiency, C was the conversion degree for which SPEH ≤ Slim (80°С). Slim was assumed to be 40%. This value of S approximately corresponds to the selectivity of the ethylbenzene oxidation in the presence of exo ligand – free Fe(III)(acac)3 (5·10-3 mol/l, 800C) under the steady – state reaction conditions (at the catalysis with Fe(II)(acac)2, formed in the process) [11,13,22]. The changes in parameters SPEH, C (S·C), and w0 and w observed in the reactions catalyzed by Fe(III)(acac)3 in the presence of R4NBr and H2O additives, and also obtained kinetics of catalytic ethylbenzene oxidation are evidently caused with the formation of catalytic active complexes of (Fe(II)(acac)2)x(R4NBr)y(H2O)n and products of their transformation in the course of ethylbenzene oxidation. [11,13]. The decrease in SPEHmax (S·C) is assumed due to the increase in the rates of the oxygenation of intermediate products of the (Fe(II)(acac)2)x(R4NBr)y(H2O)n transformation to the end products as a consequence of coordination of H2O molecules with iron complexes. As result, the decrease in steady-state concentrations of selective catalysts Fe(II)x(acac)y(OAc)z(L2)n(H2O)m, took place. Unlike the catalytic ethylbenzene oxidation, presented above, addition of 3.7·10-3 mol/l H2O into the ethylbenzene oxidation, catalyzed with {Fe(III)(acac)3 + CTAB}, results in the increase in parameters SPEHmax and S·C (Figure 2, 3). At the beginning of the reaction (C < 1%) SPEH = 85.4%. Then with the grow in C the selectivity falls to SPEH =70.3% (the catalysis with Fe(II) complexes, formed in the process [22]). After that at C > 1% the dependences SPEH от C has extremum as in the absence of H2O additives (probably as a consequence of the catalysis with products of Fe(II) complexes dioxygenation). At that SPEHmax = 78.2%, and this value is significantly higher than SPEHmax = 65% in the case of the H2O additives – free process. The increase in C (∆C) is observed. ∆C ≈ 8% as compared to catalysis by Fe(II)(acac)2 or is ∆C ≈ 4% as compared to catalysis by complexes (Fe(II)(acac)2)p·(CTAB)q (Figure 3).

L. I. Matienko and L. A. Mosolova

42

95 85

SPEH, %

75 65 55 45 35 25 0

5

10

C, % * The value of Clim at SPEH=40% was estimated by the extrapolation. Figure 3. Dependences SPEH от C in the ethylbenzene oxidation in the presence Fe(III)(acac)3 (∆-1) and systems {Fe(III)(acac)3 + CTAB} (◊-2) and {Fe(III)(acac)3 + CTAB + H2O} (-3)*. 800C.

In this case the increase in SPEHmax at the H2O additives is due to the increase in PEH concentration (from [PEH]max= 0,33 mol/l to [PEH]max = 0,4 mol/l, the rate of PEH accumulation wPEH in the process (in the presence of H2O) > wPEH in the process (in the absence of H2O)). The Decreases in AP and MPC concentration and in the (AP + MPC) accumulation rate wАP+МPC in the course of the ethylbenzene oxidation as compared with the H2O additives – free process took place (Figure 4, Table 1). Unlike the catalysis by {Fe(III)(acac)3+R4NBr} (R4NBr=Me4NBr, (C2H5)4NBr) the significant fall in initial rate of principal products {P=AP+MPC} formation, w0АP+МPC, (in ∼ 3 times) was observed (compare Figure 4 and Figure 1,a-b, and also data in Tables 1, 2). The initial rate of PEH accumulation wPEH0 decreased insignificantly. In the ethylbenzene oxidation in the presence of {Fe(III)(acac)3+CTAB(5·10-4 mol/l)} system without H2O the grow in the rate of PEH accumulation wPEH0 took place (in ∼ 1.5 times) as compared to catalysis with Fe(II)(acac)2, but the rate of P accumulation w0АP+МPC is unchanged in fact (Table 1). In the oxidation in the presence of {Fe(III)(acac)3 + CTAB(5·10-4 mol/l) + H2O (3.7·10-3 mol/l)} system the PhOH as oxidation product was not found right up to 50 hours of the ethylbenzene oxidation. This fact may be explained by the significant decrease in the activity of formed catalyst in the heterolytic decomposition of PEH with formation of phenol (PhOH) and acetaldehyde and by the inhibition of the rate of particles formation (Fe(OAc)2), responsible for PEH heterolysis [4,11,13,22].

Modification of Catalytic Activity of Complexes of Acetylacetonates Fe(II,III) ...

43

(a)

[PEH].10 , [PhOH].10 , mol/l

50

3

40 30

2

20 10 0 0

10 20 30 40 50 60

t, ч

10 8

2

[АP], [MPC].10 , mol/l

(b)

6 4 2 0 0 10 20 30 40 50

t, h Figure 4. a. Kinetics of PEH (◊-1,-2) and PhOH (∆-1) communication in the course of the ethylbenzene oxidation, catalyzed with {Fe(III)(acac)3 + CTAB(5·10-4 mol/l)} (◊,∆) or {Fe(III)(acac)3 + CTAB(5·10-4 mol/l) + H2O} (). [H2O]=3.7·10-3 mol/l. 800C. b. Kinetics of AP (◊-1,-2) and MPC (∆-3,c-4) accumulation in the course of the ethylbenzene oxidation, catalyzed in the presence of {Fe(III)(acac)3+ CTAB (5·10-4 mol/l)} (◊,∆) or {Fe(III)(acac)3 + CTAB (5·10-4 mol/l) + H2O} (,c). [H2O]=3.7·10-3 mol/l. 800C.

The rise in SPEHmax in the course of ethylbenzene oxidation in the presence of {Fe(III)(acac)3 + CTAB(5·10-4 mol/l) + H2O (3.7·10-3 mol/l)} is accompanied by the decrease in the value w of oxidation rate as compared with the value w0 in the initial stage of oxidation process mainly due to decrease in wАP+МPC (Table1,2). These changes in kinetics of {AP + MPC} accumulations and hindering of the heterolytic of PEH decomposition point to the

L. I. Matienko and L. A. Mosolova

44

transformation of complexes (Fe(II)(acac)2)x·(CTAB)y·(H2O)n, into new active selective catalysts (Scheme 1). We established that at the addition of 3.7·10-3 mol/l H2O into the ethylbenzene oxidation, catalyzed with {Fe(III)(acac)3+ CTAB} (and {Fe(III)(acac)3+ R4NBr(Me4NBr, (C2H5)4NBr)} also) the mechanism of products formation is obviously unchanged. As in the absence of H2O the products AP and MPC formed parallel to PEH formation, at parallel stages of chain propagation and chain quadratic termination, AP and MPC formed in parallel stages also (wP/wPEH ≠ 0 at t → 0, wAP/wMPC ≠ 0 at t → 0 (here P= AP or MPC)) [11,22]. The heterolysis of PEH was not observed. These data differed from known facts of catalysis with CTAB and systems, including CTAB and transition metal complexes, consisting in the acceleration of PEH decomposition in the micelles of CTAB [23]. Thus the significant rise in the of value of SPEHmax from 40% (the catalysis with {Fe(III)(acac)3) to SPEHmax ≈ 78.2% at the catalysis with {Fe(III)(acac)3+ CTAB+ H2O (~ 10-3 mol/l)} in the ethylbenzene oxidation may be achieved. The significant increase in SPEHmax, in C, (parameter S·C) (unlike the catalysis with {Fe(III)(acac)3+R4NBr(Me4NBr, (C2H5)4NBr)+H2O} systems) may be connected in this case with the increase in the life time of active selective heteroligand complexes of probable structure Fe(II)x(acac)y(OAc)z(R4NBr)n(H2O)m (“B”), formed perhaps according to Scheme 1. The outspherical coordination of CTAB, may create sterical hindrances from H2O coordination and regio-selective oxidation of (acac)- − ligand by the described earlier mechanism, and the rate of intermediate complex “B” oxygenation to inactive final product Fe(OAc)2 reduced. Besides that the part of H2O molecules may be absorbed by hydrophilic cation nC16H33Me3N+, and as a result the lowering of the rate of the intermediate heteroligand complex “B” conversion to the end products was realized.

4. PARTICIPATION OF CATALYSTS ACTIVE FORMS IN ELEMENTARY

STAGES OF RADICAL-CHAIN ETHYLBENZENE OXIDATION CATALYZED BY {FE(II,III)(ACAC)N+R4NBR} Previously we suggested the method for estimation of catalytic activity of complexes (Fe(II)(acac)2)x(R4NBr)y at the micro stages of radical-chain ethylbenzene oxidation by simplified scheme assuming quadratic termination of chain and equality to zero of rate of homolytic decomposition of ROOH [4,7,11,13,22]. We found that at the catalysis Fe(II,III)(acac)n ([Cat]=(0.5-5)·10-3 mol/l)) products MPC and AP were formed parallel to PEH, at stages of chain propagation Cat + RO2•→ and quadratic termination of chain 2RO2•→, and Cat was inactive in the reaction of PEH homolysis [22]. In the framework of radical-chain mechanism the chain termination rate in this case will be (1):

wterm=k6[RO2•]2=k6

⎧ w PEH ⎫ ⎨ ⎬ ⎩k 2 [RH]⎭

2

(1)

Modification of Catalytic Activity of Complexes of Acetylacetonates Fe(II,III) ...

45

where wPEH − rate of PEH accumulation, k6 − constant of reaction rate of quadratic chain termination (k6=1.9 107 mol-1 s-1); k2 − constant of rate of chain propagation reaction (RO2• + RH) → (k2=5.72 l mol-1 s-1 (800C) [22]). The hydrocarbon consumption was taken into account in the calculations (the initial concentration of the ethylbenzene [RH]0 = 8.2 mol/l) Actually, we found that w0 (wlim, iron(II) complexes) ~ [Cat]1/2, and wi0 ~ [Cat], and linear radicals termination on catalyst may be not taken into account [22]. With allowance for quasisteady-state conditions for RO2• radicals the calculated by formula (1) wterm.= wi can be considered a measure of activation of molecular oxygen with iron(II) complexes. Discrepancy between wAP+MPC and wterm in the case of absence of linear termination of chain is connected with additional formation of alcohol and ketone at the stage of chain propagation Cat + RO2•→ (2): wpr.= wAP+MPC – wterm

(2)

The direct proportional dependence of wpr0 on [Cat] testifies in favor of iron(II) complexes participation at stage of chain propagation Cat + RO2•→. The conditions w0~[Cat]1/2 and wi0~[Cat] are supposed to be fulfill also in the presence of R4NBr additives. The values of wi0 (O2 activation) and wpr0 (Cat + RO2•→) were estimated [22]. The chain initiation in the ethylbenzene oxidation with dioxygen in the presence of Fe(III)(acac)3 or {Fe(III)(acac)3+ R4NBr} can be represented by the following reaction [13,22]: Fe(III)(acac)3 ((Fe(III)(acac)2)m·(R4NBr)n)+ RH → → Fe(II)(acac)2 ((Fe(II)(acac)2)x·(R4NBr)y) … Hacac + R•

(I)

The reaction (I) and interaction of the resulting Fe(II) complex with dioxygen appear to be responsible for chain initiation in the ethylbenzene oxidation, catalyzed by Fe(III)(acac)3 or {Fe(III)(acac)3+ + R4NBr}. The schemes of radical-chain oxidation including reaction of Cat with RO2•-radicals with intermediate formation peroxo-complexes [LM-OOR] [26-29] and further homolytic decomposition of peroxo-complexes ([LM-OOR]→R′C=O (ROH) + R•) (cage “latent radical” mechanism) may explain parallel formation of alcohol and ketone under ethylbenzene oxidation in the presence of M(L1)n (L1 = acac-) and their complexes with R4NBr (wpr0 (Cat + RO2•→)). As mentioned above the mechanism of the ethylbenzene oxidation catalyzed with {Fe(III)(acac)3+ R4NBr} is obviously unchanged at the addition of 3.7·10-3 mol/l H2O. So we proposed that catalysis by complexes (Fe(II)(acac)2)x·(R4NBr)y (H2O)n satisfied the conditions w0~[Cat]1/2 and wi0~[Cat] that allowed wi0 and wpr0 to be calculated by Eqs. (1) and (2) and the catalytic activity of complexes (Fe(II)(acac)2)x·(R4NBr)y (H2O)n at the micro stages of chain initiation (activation of O2, wi0) and chain propagation (Cat + RO2•→, wpr0) can be evaluated. Calculated rates of chain initiation (wi0), chain propagation (wpr0) and (wi0/wpr0)·100%. [Fe(III)(acac)3]=5·10-3 mol/l. [L2] = 0.5·10-3 mol/l). 800 C.

L. I. Matienko and L. A. Mosolova

46

As follows from the data in Table 2 the growth in SPEH0 at the catalysis by complexes Fe(II)(acac)2)x·(CTAB)y (H2O)n is connected mainly with the considerable fall in the value of wpr0 ~ 3.2 times. The value of wi0 decreases by a factor of ~ 1.3. At that the rate of {AP+MPC} accumulation wp0 decreases ~ 3 times, and wPEH0 decreases only by a factor of ~ 1.26. The decrease in the rate of chain propagation wpr0 at the catalysis by complexes Fe(II)(acac)2)x·(CTAB)y (H2O)n seems to be caused by unfavorable steric factors for the RO2• coordination with metal centre appeared in this case. The value of SPEHmax ≈ 78.2% in the process is caused with the transformation of (Fe(II)(acac)2)x·(CTAB)y nH2O in the course of the ethylbenzene oxidation. At the catalysis with complexes Fe(II)(acac)2)x·(CTAB)y (H2O)n the growth in ratio wi0/ wpr0 to a grate extent (by a factor of ~ 2.35 as compared with Fe(II)(acac)2)x·(CTAB)y) was received. In the case of the use of the other R4NBr as ligand-modifier L2 the decrease in parameter wi0/ wpr0 was observed at the H2O addition :~ 1.4 times (L2 = (C2H5)4NBr (mainly in consequence of the decrease in wi0~ 1.5 times)); ~ 1.22 times (L2 = Me4NBr (mainly in consequence of the increase in wpr0~ 1.7 times (wi0 increases ~ 1.4 times))) as compared with catalysis by systems without admixed H2O. The observed insignificant decrease in wi0 (CTAB or (C2H5)4NBr) was assumed to be caused with the outer sphere H2O coordination with acetylacetonate ligand and the structure of the formed complex Fe(II)(acac)2)x·(R4NBr)y nH2O, the steric factors created the hindrance from the O2 coordination with metal centre. At that the possibility of formation of O2-complexes, active in chain-radical oxidation would decrease [30-32]. The rise in wi0 (Me4NBr) may be explained by more stable coordination of Me4NBr with acetylacetonate ligand of Fe(II)(acac)2 as compared with CTAB or (C2H5)4NBr [6]. The role of H2O may be consist in the stabilization of active (L2)δ+Fe(II)(L1)2·O2δ⎯ in consequence of H – bonding [32]. Table 2. The initial rates (mol l-1 s-1) of PEH (wPEH0) and P(AC+MPC) (wp0) accumulations at the catalysis with Fe(III)(acac)3, with systems {Fe(III)(acac)3 + R4NBr(L2)} without admixed H2O (L3) and at the addition of small amounts of H2O (3,7·10-3.mol/l). w0 – The initial rate of {PEH+P} accumulation L2, L3 ⎯ (C2H5)4NBr (C2H5)4NBr +H2O Me4NBr Me4NBr +H2O CTAB CTAB +H2O

wPEH0· ·106 2,90 5,90 4,90

wp0 · ·106 3,40 8,30 7,70

w0 · ·106 6,30 14,20 12,60

wi0· ·107 0,79 3,00 2,07

wpr0· ·106 3,32 8,00 7,50

(wi0/ wpr0) 100% 2,38 3,75 2,66

4,20

3,40

7,60

1,52

3,25

4,67

5,00

5,87

10,87

2,16

5,65

3,82

4,35 3,75

3,30 1,10

7,65 4,85

1.63 1,21

3,14 0,98

5,19 12,24

Modification of Catalytic Activity of Complexes of Acetylacetonates Fe(II,III) ...

47

As seen from the data presented in Table 2, the reaction of the chain propagation (Cat + RO2•→) is evidently the principal reaction of the AP and MPC formation in the ethylbenzene oxidation in the presence of systems {Fe(III)(acac)3 + L2 + H2O}. It took place also in the cases of use of composition of {Fe(III)(acac)3 + L2} or only Fe(III)(acac)3. The contribution of the reaction of chain quadratic termination in the mechanism of AP and MPC formation is inessential.

5. CONCLUSION Thus we first established the increase in catalytic activity of system on basis of transition metal complex and donor ligand-modifier, namely, system {Fe(III)(acac)3 + CTAB}, as catalyst of the ethylbenzene oxidation to PEH at the addition of small amounts of H2O (~10-3 mol/l). It was found that the admixtures of H2O caused a no additive (synergistic) effects of growth in selectivity SPEHmax, conversion degree C (SPEHmax ≈ 78.2%, C ≈ 12%) (parameter S·C), changes that were due to the formation of more active selective (Fe(II)(acac)2)x·(CTAB)y (H2O)n complexes, and products of (Fe(II)(acac)2)x·(CTAB)y (H2O)n transformation [33]. ∆SPEHmax ≈ 14% and ∆C ≈ 4%, as compared with catalysis by {Fe(III)(acac)3 + CTAB} and ∆SPEHmax ≈ 40% and ∆C ≈ 8% as compared with catalysis by Fe(III)(acac)3. The additives of ~10-3 mol/l H2O decreased the activity of systems {Fe(III)(acac)3 + R4NBr} (R = Me или C2H5) as catalysts of the ethylbenzene oxidation to PEH that was expressed in the fall in the parameters SPEHmax and S·C. But the rise in w0 (wi0, wpr0) at the catalysis by complexes (Fe(II)(acac)2)x·(Me4NBr)y (H2O)n formed at the initial stages of the ethylbenzene oxidation was observed. The probable “dioxygenase-like” mechanism of the iron catalyst transformation in the presence H2O is offered. The discovered fact of increase in parameters SPEHmax, C (and S·C) at catalysts of the ethylbenzene oxidation by {Fe(III)(acac)3 + CTAB + H2O(~10-3 mol/l)} system may be result of the increase in stationary concentration of active selective heteroligand complexes of probable structure Fe(II)x(acac)y(OAc)z(CTAB)n(H2O)m, intermediate products of transformation of complexes (Fe(II)(acac)2)x·(CTAB)y (H2O)n in the course of the ethylbenzene oxidation. Upon the addition of 3.7·10-3 mol/l H2O into the ethylbenzene oxidation, catalyzed with {Fe(III)(acac)3 + R4NBr} (R4NBr = CTAB, Me4NBr, C2H5)4NBr) systems the mechanism of principal products acetophenone (AP) and methylphenylcarbinol (MPC) formation is unchanged. As in the absence of H2O, AP and MPC formed parallel to PEH formation, at parallel stages of chain propagation and chain quadratic termination, AP formed parallel to MPC also (wP/wPEH ≠ 0 at t → 0, wAP/wMPC ≠ 0 at t→ 0) in the course of all oxidation process. The system {Fe(III)(acac)3 + CTAB + H2O(~10-3 mol/l)} is inactive in heterolysis of PEH. It was found that the oxidation rate w0 and the hydroperoxide selectivity SPEH0 at the catalysis by complexes (Fe(II)(acac)2)x·(R4NBr)y (H2O)n formed at the initial stages of the ethylbenzene oxidation depend on the catalyst activity in micro stages of chain initiation (activation of O2) and chain propagation mediated by the catalyst (Cat + RO2•→). The growth in PEH selectivity at the catalysis by (Fe(II)(acac)2)x·(CTAB)y (H2O)n is connected mainly with the considerable fall in the rate of chain propagation wpr0 (Cat + RO2•→).

48

L. I. Matienko and L. A. Mosolova

The ratio wi0/ wpr0 ≈ 2.66 – 12.24%, estimated for catalysis by (Fe(II) (acac)2)x·(R4NBr)y (H2O)n, indicates a significant role of the chain propagation (Cat + RO2•→) in the mechanism of catalysis by these complexes pertaining to the ethylbenzene oxidation with molecular oxygen. At the same time the rate of chain initiation at catalysis by (Fe(II)(acac)2)x·(R4NBr)y (H2O)n is higher than in the reaction catalyzed by Fe(II)(acac)2 and much higher than in the no catalytic reaction (wi0 ≈ 10-9 mol l-1 s-1 [7]).

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[4]

[5] [6] [7] [8] [9] [10] [11] [12] [13]

[14] [15] [16] [17] [18] [19]

Weissermel K., Arpe H.-J., Industrial Organic Chemistry, 3nd ed., transl. by Lindley C.R.. New York, VCH, 1997, 427 pp. Karasevich E.I., Kulikova V.S., Shilov A.E., Shteinman A.A. // Uspekhi khimii, V. 67, N 4, PP. 376-398, 1998. Mansuy D. // In: The Activation of Dioxygen and Homogeneous Catalytic Oxidation / Eds. Barton D.H.R., Martell A.E., Sawyer D.T. New York: Plenum Press, 1993, PP.347–358. Matienko L.I. // In: Chemical Reaction In Condensed Phase. The Quantitative Level. / Ed. by Zaikov G.E., Zaikov V.G. and Mikitaev A.K. New York: Nova Science Publ., 2006, PP. 49– 69. Mosolova L.A., Matienko L.I., Skibida I.P. // Kinetika i kataliz.. V.28, N 2, PP.479– 484, 1987. Mosolova L.A., Matienko L.I., Skibida I.P. // Kinetika i kataliz, V.28, N 2, PP.484– 487, 1987. Matienko L.I., Mosolova L.A. // Kinetika i kataliz, V.44, N 2, С.237–245, 2003. Dai Y., Pochapsky Th. C., Abeles R.H., Biochem., V. 40, N 21, PP. 6379-6387, 2001. Gopal B., Madan L.L., Betz S.F., and Kossiakoff A.A. // Biochemistry, V.44, №1, P.193–201, 2005. Balogh-Hergovich É., Kaizer J., Speier G. // J. Mol. Catal. A: Chem. V.159. P.215– 224, 2000. Matienko L.I., Mosolova L.A. // Neftekhimiya. V.47. N 1. PP.42–51, 2007. G. D. Straganz, B. Nidetzky, J. Am. Chem. Soc., V. 127, N 35, PP. 12306-12314, 2005. Matienko L.I., Mosolova L.A. // In: New Aspects of Biochemiсal Physics. Pure and applied sciences / Ed. by Varfolomeev S.D., Burlakova E.B., Popov A.A., Zaikov G.E. New York: Nova Science Publ., 2006, PP. 128–137. Nelson J.H., Howels P.N. Landen G.L., De Lullo G.S., Henry R.A. // In: Fundamental research in homogeneous catalysis. N.Y.-L.: Plenum Press, 1979, V.49, PP.921-928. Pardo L., Osman R., Weinstein H., Rabinowitz J.R. // J. Am. Chem. Soc., V.115, N 18, P.8263-8269, 1993. Demlov E., Demlov Z. Phase-transfer catalysis. М.: Мir Press, 1987, 485 P. Nekipelov V.M., Zamaraev K.I. // Coord. Chem. Rev. V.61, РP.185-240, 1985. Li-Hua, Yangzhong L., Xuhong Z., e.a. // J. Am. Chem. Soc., V.128, N 19, P.63916399, 2006. Csanyi L.J., Jaky K., Galbacs G. // J. Mol. Catal. A: Chem., V.164, P.109-124, 2000.

Modification of Catalytic Activity of Complexes of Acetylacetonates Fe(II,III) ...

49

[20] Csanyi L.J., Jaky K., Dombi G., e.a. // J. Mol. Catal. A: Chem., V.195, P.109-124, 2003. [21] Csanyi L.J., Jaky K., Palinko I., e.a. // Phys. Chem. Chem. Phys., N 2, P.3801-3805, 2000. [22] Matienko L.I., Mosolova L.A. // Kinetika i kataliz.. V.46, N 3, PP.354–359, 2005. [23] Maksiмоvа Т.V., Sirota Т.V., Koverzanova Е.V., Kasaikina O.T. // Neftekhimiya. V. 41. N 5. PP. 289-293, 2001. [24] Emanuel N.M., Zaikov G.E., Maizus Z.K. The role of medium in radical-chain reactions of organic compounds oxidation. // M: Nauka, 1973, 279 P. [25] Partenheimer W. // Catalysis Today, V.23, PP.69–158, 1991. [26] Semenchenko A.E., Solyanikov V.M., Denisov E.T. // Zh. Phiz. Khimii, V. 47, N 5, PP. 1148-1151, 1973. [27] Chavez F.A., Rowland J.M., Olmstead M.M., Mascharak P.K. // J. Am. Chem. Soc., V.120. N 35, PP.9015–9027, 1998. [28] Solomon-Rapaport E., Masarwa A., Cohen H., Meyerstein D. // Inorg. Chim. Acta, N 299, PP.41–46, 2000 [29] Krishnamurthy D., Kasper G.D., Namuswe F., Kerber W.D., e.a. // J. Am. Chem. Soc, V.128, N 44, PP.14222–14223, 2006. [30] Carter M.J., Rillema D.P., Basolo F. // J. Am. Chem. Soc., V. 96, N 2, PP. 392-400, 1974. [31] Martell A.E.. // Acc. Chem. Res, V.15, N 5, PP.155-162, 1982. [32] Stynes D.V., Stynes H.C., Ibers J.A, James B.R. // J. Am. Chem. Soc., V.95, N 4, PP.1142-1149, 1973. [33] Golodov V.A. // Ross. Khim. Zh., V. 44, N 3, PP. 45-57, 2000.

In: Modern Tendencies in Organic and Bioorganic Chemistry ISBN: 978-1-60456-295-8 Editors: A. Mikitaev, M. K. Ligidov, pp. 51-63 © 2008 Nova Science Publishers, Inc.

Chapter 3

MODELING THE KINETICS OF MOISTURE ADSORPTION BY WOOD DURING DRYING PROCESS A. Farjad, S. H.Rahrovan, and A. K. Haghi* Faculty of engineering, The University of Guilan Rasht 41635, P. O. Box 3756, Iran

ABSTRACT A mathematical model was developed for optimization of heat and mass transfer in capillary porous media during drying process to predict the drying constants. The modeling equations verified the experimental results and proved to be an important tool in predicting the drying rate under different drying conditions.

Keywords: Heat transfer, mass transfer, drying time, diffusion, moisture content, mathematical model

INTRODUCTION The importance of heat and mass transfer in capillary porous materials like wood has increased in the last few decades due to its wide industrial as well as research applications. In order to reduce moisture content in woods to a level low enough, to prevent undesirable biochemical reactions and microbiological growth, prolonged drying time and high temperature must often be used. In practice, several different techniques are used; natural drying, vacuum drying, convectional convective drying, high temperature convective drying, and more recently microwave drying [1]. Several physical mechanisms contribute to moisture migration during the process. For a porous solid matrix, with free water, bound water, vapor, and air, moisture transport through the matrix can be in the form of either diffusion or capillary flow driven by individual or

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A. Farjad, S. H.Rahrovan and A. K. Haghi

combined effects of moisture, temperature and pressure gradients. The predominant mechanisms that control moisture transfer depend on the hygroscopic nature and properties of the materials, as well as the heating conditions and the way heat is supplied. In this regard, there is a need to assess the effects of the heat and mass transfer within the wood on the transfer in the fluid adjacent to it. There are three stages of drying: In the first stage when both surface and core MC are greater than the FSP. Moisture movement is by capillary flow. Drying rate is evaporation controlled. In the second stage when surface MC is less than the FSP and core MC is greater than the FSP. Drying is by capillary flow in the core and by bound water diffusion near the surface as fiber saturation line recedes into wood, resistance to drying increases. Drying rate is controlled by bound water diffusion and finally in the third stage when both surface and core MC is less than the FSP. Drying is entirely by diffusion. As the MC gradient between surface and core becomes less, resistance to drying increases and drying rate decreases. For wood, model developments have been based on either a mechanistic approach with the transfer phenomena derived from Fick’s and Fourier’s laws, or on the principles of thermodynamics and entropy production. These models may be divided into three categories: (a) diffusion models [2], (b) models based on transport properties [3,4] and (c) models based on both the transport properties and the physiological properties of wood related to drying [5,6]. Drying adds value to timber but also costs money. Working out the complete cost of drying is a complex process. Timber drying is a critical and costly part of timber processing. Comparing the cost and effectiveness of drying systems and technology is an important exercise, before drying systems are commissioned or are upgraded. Reduction in drying time and energy consumption offers the wood industries a great potential for economic benefit. But the reduction in drying time often results in an increase in drying related defects such as checks, splits and warp. In previous work drying curves were fitted to four drying models and the goodness of fit of each model (Correlation Coefficient and Standard Error) was evaluated [7]. The main aim of this work is to find out a model for drying time and to predict the required time for drying samples to desired moisture content. In the second part the forecast time is compared with the theoretical approach. The predicted values by the theoretical model are compared with experimental data taken under actual drying conditions to demonstrate the efficiency of the predictive model.

2. ANALYTICAL APPROACHES A software tool “Trend Analysis” for analysis the time series was applied. Trend analysis fits a general trend model to time series data and provides forecasts. S-curve is best fitted to our drying case. The S-curve model fits the Pearl-Reed logistic trend model. This accounts for the case where the series follows an S-shaped curve. The model is:

**

[email protected], http://www.guilan.ac.ir

Modeling the Kinetics of Moisture Adsorption

MC =

10 a b0 + b1b2t

53

(1)

This tool is useful when we have dried the wood to moisture content not near to 30% and then predict the time needed to dry it completely. Minitab computes three measures of accuracy of the fitted model: MAPE, MAD, and MSD for each of the simple forecasting and smoothing methods. For all three measures, the smaller the value, the better the fit of the model. These statistics are used to compare the fits of the different methods. Mean Absolute Deviation (MAD) measures the accuracy of fitted time series values. It expresses accuracy in the same units as the data, which helps conceptualize the amount of error: n

MAD =

∑y t =1

t

− yˆ t (2)

n

Where yt equals the actual value at time yˆ t equals the fitted value, and n equals the number of observations. Mean Absolute Percentage Error (MAPE) measures the accuracy of fitted time series values. It expresses accuracy as a percentage.

MAPE =

∑

( yt − yˆ t ) yt

× 100 ( yt ≠ 0)

n

(3)

Where yt equals the actual value at time yˆ t equals the fitted value, and n equals the number of observations. MSD stands for Mean Squared Deviation. MSD is always computed using the same denominator, n, regardless of the model, so we can compare MSD values across models. MSD is a more sensitive measure of an unusually large forecast error than MAD. n

MSD =

∑ t =1

2

yt − yˆ t n

(4)

Where yt equals the actual value, t equals the forecast value, and n equals the number of forecasts.

A. Farjad, S. H.Rahrovan and A. K. Haghi

54

3. GOVERNING EQUATIONS Heat and mass transfer in a body take place simultaneously during the drying process. The time required to go from an initial moisture content, U 0 , to a certain value U is given in[8]: t=

(μ

1.6 × 10 −4 S x2 S y2 2 x1

D x S y2 + μ y21 D y S x2

)

⎛ ⎛ U 0 − U eq Log ⎜ Γx1 Γ y1 ⎜ ⎜ U −U ⎜ eq ⎝ ⎝

⎞⎞ ⎟⎟ ⎟⎟ ⎠⎠

(5)

μ l21 can be defined as: μ l21 =

1

(6)

4

1 + π 2 Bl

Where Bl is the dimensionless constant called the "bio-criterion "of the sample: Bl =

α l Rl

(7)

Dl

Where Rl is half of the length of the rod, l is any of the two coordinates x,y, S x × S y is the width and thickness of sample,

α l is the coefficient of moisture exchange(m/s), Dl is the

2

moisture diffusion coefficient( m /s) which can vary in each of the different directions for the wood sample. The value Γl1 is determined as:

2 Bl2 Γl1 = 2 2 μ l1 Bl + Bl + μ l21

(

)

(8)

and an average dimensionless moisture content E Σ is: EΣ =

U − U eq U 0 − U eq

U eq is the equilibrium moisture content of the wood. Another theoretical approach is presented by [9]:

(9)

Modeling the Kinetics of Moisture Adsorption

t=

65S 2 ⎛ π 2 D ⎞ U 0 − U eq ⎟ log ⎜1 + 2αs ⎟⎠ U − U eq D10 6 ⎜⎝

55

(10)

Where D is the average diffusion coefficient and S is the average length of the dimensions of specimens.

4. EXPERIMENTAL DATA Experimental material was obtained from two types of wood species, Guilan spruce and pine. The wood specimens were selected from Guilan region which is located in the north of Iran. The experiments were performed in a programmable domestic microwave drying system (Deawoo, KOC-1B4k) with a maximum power output of 1000 W at 2450MHz. Samples were dried in four methods: convection drying (150°C), microwave drying (270 W), infrared drying (100% power) and combination of microwave and convection drying. The dryer was run without the sample placed in, for about 30 min to set the desired drying conditions before each drying experiment. Throughout the experimental run the sample weights were continuously recorded at predetermined time intervals until wood reached to 30% of its moisture content.

5. RESULTS AND DISCUSSION Figures 1-8 show the graphs moisture content variation against drying time, the model and the forecasted time for the four methods of drying on pine and Guilan spruce. Drying time is estimated to a moisture content of 14%. Results are relatively in a good agreement with drying curves. Just in some cases in heating up period this model didn’t fit the experimental data closely. Heat is transferred by convection from heated air to the product to raise the temperatures of both the solid and moisture that is present. Moisture transfer occurs as the moisture travels to the evaporative surface of the product and then into the circulating air as water vapor. The heat and moisture transfer rates are therefore related to the velocity and temperature of the circulating drying air. Moreover, the momentum transfer may take place simultaneously coupled with heat and moisture transfer. Convective drying at intermediate temperatures has proved to be very effective from the economical point of view, thanks to the short drying time, the reduced sizes of the kilns, and the better control of the energy consumption and the possibility of a good integration in the production line. Infrared energy is transferred from the heating element to the product surface without heating the surrounding air. When infrared radiation is used to heat or dry moist materials, the radiation impinges the exposed material, penetrates it and the energy of radiation converts into heat. Since the material is heated intensely, the temperature gradient in the material reduces within a short period the depth of penetration of radiation depends upon the property of the material and wavelength of radiation. Further by application of intermittent radiation, wherein the period of heating the material is followed by cooling, intense displacement of moisture from core towards surface can be achieved.

A. Farjad, S. H.Rahrovan and A. K. Haghi

56

Moisture content(%)

120 100

Actual

80

Fits

60

Forecasts

40 20 0 0

20

40

60

80

100

Time(min)

Figure 1. Moisture content vs. time for pine, (Convection drying).

Microwave drying generate heat from within the grains by rapid movement of polar molecules causing molecular friction and help in faster and more uniform heating than does conventional heating. It should be pointed out that by variation of drying conditions (i.e. air temperature, humidity and air velocity) within a lumber stack, it is expected that the drying rate and the moisture content distribution varies as well [10].

Moisture content(%)

120 100

Actual

80

Fits

60

Forecasts

40 20 0 0

10

20

30 Time(min)

Figure 2. Moisture content vs. time for pine, (Infrared drying).

40

50

60

Modeling the Kinetics of Moisture Adsorption

57

Moisture content(%)

120 100

Actual

80

Fits

60

Forecasts

40 20 0 0

100

200

300

400

500

600

Time(s)

Figure 3. Moisture content vs. time for pine (Microwave drying).

Moisture content(%)

120 100

Actual

80

Fits

60

Forecasts

40 20 0 0

50

100 Time(sec)

Figure 4. Moisture content vs. time for pine (Combined dryer).

150

200

A. Farjad, S. H.Rahrovan and A. K. Haghi

58

Moisture content(%)

120 100

Actual

80

Fits

60

Forecasts

40 20 0 0

50

100

150

200

Time(min)

Figure 5. Moisture content vs. time for spruce (Convection drying).

Moisture content(%)

140 120

Actual

100

Fits 80

Forecasts

60 40 20 0 0

200

400

600

800

1000

Time(s)

Figure 6. Moisture content vs. time for spruce (Microwave drying).

The method of drying, type of samples, Mean Absolute Deviation, Mean Absolute Percentage Error, Mean Squared Deviation of these models used for moisture content change with time are presented in Table1.

Modeling the Kinetics of Moisture Adsorption

59

Moisture content(%)

120 100

Actual

80

Fits

60

Forecasts

40 20 0 0

20

40

60

80

Time(min)

Figure 7. Moisture content vs. time for Spruce (Infrared drying).

Moisture content(%)

120 100

Actual

80

Fits

60

Forecasts

40 20 0 0

100

200

300

400

Time(sec)

Figure 8. Moisture content vs. time for spruce (Combined dryer).

It is clear that the MAPE, MAD, MSD values of this model were changed between 0.344.8, 0.22-1.63 and 0.08-33.22 respectively. As it can be seen for pine samples the convection method has a better fitness to the model and for spruce infrared drying model fitted the experimental data properly. The estimated values are based on data from [11] and can be conveniently used for theoretical approach are shown in table 2.

A. Farjad, S. H.Rahrovan and A. K. Haghi

60

Table 1. Results of fitness Type of Samples

pine

spruce

Drying methods

MAPE

MAD

MSD

Convection Microwave Infrared Combined

0.341876 1.08315 1.07610 1.26813

0.221418 0.86600 0.83372 1.00335

0.080966 2.08191 2.51506 3.72067

Convection Microwave Infrared Combined

1.61692 4.8156 0.638023 2.46335

1.16996 3.3411 0.420579 1.63377

4.21973 33.2286 0.342695 9.40387

Table 2. Set of data selected for this study Specifications Sx

value 2.9cm

Reference [11

Sy

10.2cm

[11]

u0

82.5%

[11]

u eq

16.2%

[11]

u

19% 316.15K

α

0.787 × 10 −5 cm / s

[11] [11] [11]

D

8.711× 10 −6 cm / s

Equation(11)

βx

1.3099

Equation(7)

βy

4.6072

Equation(7)

μx

0.925

Equation(6)

μy

1.2676

Equation(6)

Γx

0.99

Equation(8)

Γy

0.985

Equation(8)

A

[11]

B

11.7cm 2 / s 3.14cm 2 / s

[11]

t t t t (real time)

213hr 557.32hr 420hr 550hr

Equation(5) Equation(10) Trend analysis [11]

T

Modeling the Kinetics of Moisture Adsorption

61

It was assumed that the diffusion coefficient bellow FSP can be represented by [11]:

D = A.e

−5280 T

.e

Bu 100

(11)

Where T is the temperature in Kelvin, u is percent moisture content, A and B are experimentally determined. Drying time is calculated from theoretical approach and evaluated model. Results show that real time had best agreement with which was obtained from equation (10) while there was a significant difference between real time and the one obtained from equation (5). Some authors have assumed that the diffusion coefficient depends strongly on moisture content [1214] while others have taken the diffusion coefficient as constant [15-18]. Also, different boundary conditions have been assumed by different authors [19-22]. But Liu. et al concluded that the diffusion coefficient is a function of time, position, moisture content, and moisture gradient, which is at variance with assumptions in the literature that the diffusion coefficient is either a constant or a function of moisture content only [23].The difference in drying time may be due to the fact that diffusion coefficient was assumed to be the same in tangential and radial direction. So this assumption can’t be used for equation (5). The same calculation can be done for other drying methods to predict the drying time.

6. CONCLUSION Selection of the optimum operating conditions to obtain good quality dried products requires knowledge of the effect of the process parameters on the rate of internal-external mass transfer. High temperature heat treatment of wood is a complex process involving simultaneous heat, mass and momentum transfer phenomena and the effective models are necessary for process design, optimization, energy integration, and control. Infrared heating offers many advantages over conventional drying under similar drying conditions. These results in high rate of heat transfer compared to conventional drying and the product is more uniformly heated rendering better quality characteristics. Microwave drying offers a number of advantages such as rapid heating, selective heating and self-limiting reactions which in turn can lead to improved quality and product properties, reduced processing time, and energy consumption and labor savings. For pine samples the convection method has accurate result to the model and for spruce infrared drying model fitted the experimental data properly, thus their model was found to be adequate in predicting drying time of wood samples under different drying methods. The principle reason for drying wood at higher temperatures is because the rate of diffusion increases with the temperature. Water molecules generally diffuse from a region of high moisture content to a region of low moisture content, which reduces the moisture gradient and equalizes the moisture content. Diffusion plays an important role in the drying of lumber, at all moisture content with impermeable timbers and in permeable timber wherever the moisture content is too low for hydrodynamic flow of water through the lumens. Diffusion coefficient is influenced by the drying temperature, density and moisture content of timber.

62

A. Farjad, S. H.Rahrovan and A. K. Haghi

Other factors affecting the diffusion coefficient that are yet to be quantified are the species (specific gravity) and the growth ring orientation.

REFERENCES [1]

[2] [3] [4] [5] [6] [7]

[8] [9] [10]

[11]

[12] [13]

[14] [15]

[16]

Perre. P., Turner. I.W., The use of numerical simulation as a cognitive tool for studying the microwave drying of softwood in an over-sized waveguide, Wood Science and Technology 33, 1999, 445–446. Rosen H.N., Drying of wood and wood products. In: Mujumdaar A.S. (ed.): Handbook of Industrial Drying. Marcel Dekker Inc., New York: 1987, 683-709. Plumb O.A., Spolek G.A., Olmstead B.A., Heat and mass transfer in wood during drying. Intern. J. Heat Mass Transfer 28(9), 1985: 1669-1678. Stanish M.A., Schajer G.S., Kayihan F. A mathematical model of drying for porous hygroscopic media. AIChE J. 32(8): 1986, 1301-1311. Pang S. Moisture content gradient in softwood board during drying: simulation from a 2-D model and measurement. Wood Science and Technology 30, 1996, 165-178. Pang S., Relationship between a diffusion model and a transport model for softwood drying. Wood and Fiber Science 29(1), 1997, 58-67. Naghashzadegan. M., Haghi. A.K., Amanifard. N., Rahrovan. Sh., Microwave drying of wood: Prductivity improvement, Wseas Trans. on Heat and Mass Transfer, Issue 4, Vol.1, 2006, pp. 391-397. Pavlo Bekhta, Igor Ozarkiv , Saman Alavi, Salim Hiziroglu, A theoretical expression for drying time of thin lumber, Bioresource Technology 97, 2006, 1572–1577. Sergovskii, P.S., Heat Treatment and Preservation of Timber, unpublished report, Moscow, Russia, 1975, p 400. Pang, S. "Airflow reversals for kiln drying of softwood lumber: Application of a kilnwide drying model and a stress model", Proceedings of the 14th International Drying Symposium, vol. B, 2004, pp. 1369-1376. Baronas,F. Ivanauskas,M. Sapagovas, R., Modelling of wood drying and an influence of lumber geometry on drying dynamics, Nonlinear Analysis: Modelling and Control, Vilnius, IMI, No 4, 1999, pp.11-22. Meroney, R.N., The State of Moisture Transport Rate Calculations in Wood Drying, Wood Fiber, 1(1), 1969, pp. 64–74. Simpson, W.T., Determination and Use of Moisture Diffusion Coefficient to Characterize Drying of Northern Red Oak, Wood Science and Technology, 27(6), 1993, pp. 409–420. Skaar, C., Analysis of Methods for Determining the Coefficient of Moisture Diffusion in Wood, Journal of Forest Products Research Society, 4(6), 1954, pp. 403–410. Avramidis, S. and Siau, J.F., An Investigation of the External and Internal Resistance to Moisture Diffusion in Wood, Wood Science and Technology, 21(3), 1987, pp. 249– 256. Droin, A., Taverdet, J.L. and Vergnaud, J.M., Modeling the Kinetics of Moisture Adsorption by Wood, Wood Science and Technology, 22(1), 1988, pp. 11–20.

Modeling the Kinetics of Moisture Adsorption

63

[17] Mounji, H., Bouzon, J. and Vergnaud, J.M., Modeling the Process of Absorption and Desorption of Water in Two Dimension (Transverse) ina Square Wood Beam, Wood Science and Technology, 26(1), 1991, pp. 23–37. [18] Soderstro¨ m, O. and Salin, J.G., On Determination of Surface Emission Factors in Wood Drying, Holzforschung, 47(5), 1993, pp. 391–397. [19] Crank, J., The Mathematics of Diffusion, Chap. 9, 2nd ed., ClarendonPress, Oxford. 1975. [20] Plumb, O.A., Spolek, G.A. and Olmstead, B.A., Heat and Mass Transfer in Wood during Drying, International Journal of Heat and Mass Transfer, 28(9), 1985, pp. 1669–1678. [21] Salin, J.-G., Mass Transfer from Wooden Surface and Internal Moisture Nonequilibrium, Drying Technology, 14(10), 1996, pp. 2213–2224. [22] Hukka, A., The Effective Diffusion Coefficient and Mass Transfer Coefficient of Nordic Softwoods as Calculated from Direct Drying Experiments, Holzforschung, 53(5), 1999, pp. 534–540. [23] Jen Y. Liu, William T. Simpson, and Steve P. Verrill, An inverse moisture diffusion algorithm for the determination of diffusion coefficient, Drying Technology, 19(8), 2001, 1555–1568.

In: Modern Tendencies in Organic and Bioorganic Chemistry ISBN: 978-1-60456-295-8 Editors: A. Mikitaev, M. K. Ligidov, pp. 65-87 © 2008 Nova Science Publishers, Inc.

Chapter 4

NEW TRENDS, ACHIEVEMENTS AND DEVELOPMENTS ON THE EFFECTS OF BEAM RADIATION ON DIFFERENT MATERIALS K. Mohammadi, and A. K. Haghi* The University of Guilan, P. O. Box 3756, Rasht, Iran

ABSTRACT To get around the secondary electron generation, it will be imperative to use lowenergy electrons as the primary radiation to expose photoresist. Ideally, these electrons should have energies on the order of not much more than several ev in order to expose the photoresist without generating any secondary electrons, since they will not have sufficient excess energy. Such exposure has been demonstrated using a scanning tunneling microscope as the electron beam source. This article contains the theory relevant to the technique and the practical aspects of the work. We reported the effects of beam radiation on different form of materials such as microwave dried fibers or materials used for lithography.

1. INTRODUCTION After more than 40 years of commercial availability of SEM (Scanning Electron Microscope), it is still largely being known as a “look-see” microscope for many users. Scanning electron microscope is one of the most complete tools for engineers and scientists in order to investigate the materials characteristics. The high magnification ranges of this instrument as well as its X-ray spectrometry can easily provide resolutions of defects on nano-scale ranges. The SEM can focuses at high magnification and play a key role in a *

Corresponding author e-mai: [email protected]

66

K. Mohammadi and A. K. Haghi

variety of materials science studies [1]. Research with the scanning electron microscope (SEM) consists of the study of a wide range of problems in instrumentation, theory, and applications. According to previous investigations by Gao Yu and his colleagues [2] the electron irradiation causes an increase in the tear resistance of the some polymers. However, the electron energy can changes adhesion properties [3] and strength and elongation in the some other polymers as well [4,5]. In essence this is due to the similarity between internal atmosphere an electron microscope (SEM) and space environment in the section of vacuumed and charged particles (i.e. electrons). Meanwhile, the effect of SEM electron beam on fiber is similar to the effect of irradiation of an accelerator on the polymer film

1-2. Electron Beam Technology Electron beam accelerators (or linear accelerators) produce a stream of electrons (negatively charged particles) moving at very high speeds. The electrons are generated when a current is passed through a tungsten wire filament in a vacuum. The wires heat up due to the electrical resistance and emit a cloud of electrons. These electrons are then accelerated by an electric field to over half the speed of light and pass out of the vacuum chamber through a thin titanium window into the atmosphere. Once outside the vacuum chamber, the electron beam can be used for a number of applications including polymerization, sterilization, air treatment and plasma generation, amongst others.

1-3. Commercial Use of Electron Beam Technology Commercial applications for Electron beam technology are based broadly on the electron beam as a source of ionizing energy to initiate chemical reactions (e.g., polymerization) or to break down more complex chemical structures. The commercial potential of electron beams was first recognized in the 1970s. Since then, electron beams have been used in many industrial processes such as for drying or curing inks, adhesives, paints and coatings. Electron beams are also used for liquid, gas and surface sterilization as well as to clean up hazardous waste. These (and other) applications are discussed in more detail below. There are presently around 1,000 electron beam systems in commercial operation worldwide. Of these about 700 are high voltage systems, although the number of low voltage installations is now growing at a much faster rate of acceptance. Conventional electron beam applications for industrial purposes include an electron beam accelerator that directs an electron beam onto the material to be processed. The accelerator has a large lead encased vacuum chamber containing an electron generating filament or filaments powered by a filament power supply. During operation, the vacuum chamber is continuously evacuated by vacuum pumps.Although Electron beams have a number of advantages over possible alternatives, they have historically suffered from the major commercial disadvantage that the systems were large, expensive, and complex to maintain. In particular, Electron beam systems have, until now, required vacuum pumping equipment, large high voltage power supplies and complex shielding, as well as inplant engineering and maintenance expertise. As a result, it has not been easy or sometimes possible at all to integrate the systems into manufacturing equipment.

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1-4. Theory In light microscopy, a specimen is viewed through a series of lenses that magnify the visible-light image. However, the scanning electron microscope (SEM) does not actually view a true image of the specimen, but rather produces an electronic map of the specimen that is displayed on a cathode ray tube (CRT). The electron radiation in the SEM is produced by a thermoyonic effect, which is induced by a tungsten filament.[6] The electron waves have an extra acceleration and the electron wave length is calculated by the equation (1)

λ=

150 V + 10 −6 V 2

(1)

where;

λ = Electron radiation wave length V = The voltage of SEM

The amount of the energy of electron beam is being calculated by Plank equation: E=ν h

(2)

Where; E = Electron wave energy h= Plank coefficient

ν =C λ C = Light speed From (1) and (2) one can observe that an increase in SEM voltage may cause a decrease in electron radiation wave length. In view of the above, the diffusion depth is expected to increase as well.[7] It should be noted that the irradiation of electron beam causes elastic and inelastic diffraction in the sample. On the other hand, the energy of primary electrons are dispersed or transferred to sample electrons. Nearly all of the kinetic energy is changed to heat and just a little of it is transferred to the former Cathodoluminescence and secondary electron. These are based on the images of SEM displayed on a cathode ray tube (CRT) and spots on the CRT mimic and the motion of electron beam on the sample. Hence

P=

10 × 10 M

(3)

where; M= Magnification Based on this relation, with increasing the magnification, the beam scanned area will be decrease.

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When an electron enters the specimen surface it will “see” the atoms of the specimen. If by coincidence the electron travels close to an atom the presence of the atomic and nuclear potential will result in a force affecting the velocity of the electron. This implies that the initial velocity of the electron is disturbed or in other words the electron is scattered. It is important to realize that such a scattering process is a statistical event. moreover the velocity change may be directional only (elastic scattering) or both the direction and the size of the velocity may be changed (inelastic scattering). If an electron penetrates into the atom so that it reaches the nucleus the coulomb potential of this positively charged nucleus has a large influence on its velocity. Classically this interaction mechanism is known as Rutherford scattering and the deviation of the electron from its original track can be calculated with a good accuracy. The force on the electron approaching the nucleus is the classical coulomb force, so it is linearly proportional to the charge of the nucleus. on the atomic number z. it should be noted that the nucleus itself is hardly affected by the movement of the electron as a result of its large mass, compared to that of the electron: for hydrogen the nuclear mass is already 1830 times the electron mass. At the interaction between electron and nucleus there is a conservation of energy and momentum so this is an elastic scattering process. However, for a proper interpretation the screening of the nucleus by the Surrounding atomic electrons has to be taken into account the single scattering models which are available in literature are used as elementary models to describe the successive scattering of an electron as it travels from one atom to the other. This results in the so called multiple scattering model which can be used to calculate elastic electron scattering at a loose energy and this phenomenon has to be dealt with as well. An electron entering the material will also interact with the electron cloud around the nucleus, mainly resulting in inelastic scattering of the electron and a transfer of to the atom. As a result of the interaction electrons in the atomic shell will be released and/or excited. Mostly the outer shell electrons are involved, because of the relatively low energy required to remove them from the shell. These electrons start to drift through the material and are subjected to the inelastic scattering process as well. Moreover, the remaining ionized atom may pick up a drifting electron again. The specimen itself is connected to earth, so electrons may also be added to the sample. The drifting electrons have a low average energy and they can only escape form the material if they are in neighborhood of the surface and have sufficient energy to overcome the work function.The penetration depth of the electrons depends on the material composition which influences both the elastic and the inelastic scattering processes. In particular the inelastic scattering, resulting in slowing down of the electrons (also known as the stopping power) is far better for high z materials than for low z materials. This means that although the elastic scattering increases for high z materials the penetration is smaller than for low z materials. Using both inelastic and elastic multiple scattering models probabilities for scattering angles and energy transfer can be defined and used in Monte-Carlo simulations. In such a simulation many stochastic electron tracks within the specimen are calculated and with the statistics of the tracks a good impression of the interaction volume.

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Figure 1.1. and 1.2. Monte-Carlo simulations of the scattering of 20 Ke v electrons in carbon and iron.

A few of those types of simulations are shown in the figures 2.1-2.4 for C, Fe, Ag and Au from the 0.5 micron bars shown in these figures we see that there is a strong influence of the z value of the material on the interaction volume. For instance, the range of the 20 Kev electrons in carbon is about 3 micron, whereas the corresponding range in silver is about 0.7 micron. The influence of the initial energy of the electron beam is shown in the figures 2.5-2.7 for iron. As shown in these figures the penetration depth increases with increasing electron beam energy Epe For many materials the range of the electrons as a function of the energy has been determined and generally the range r be described by: R= a(Epe)b

Figure 1.3. and 1.4. Monte-Carlo simulations of the scattering of 20 Kev electrons in silver and uranium.

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Where the constants a and b are material constants. From this general relationship again we find that there is an increase of the range, as the energy Epe increases. A good knowledge about the range of the electron beam is important if one is interested in non-homogeneous materials such as layers on an integrated circuit or inclusions in a metal. The range will then provide information about the origin of the signal. Furthermore it is possible to obtain depth information of the specimen for instance for EBIC, using the accelerating voltage as a parameter.

Figure 1.5. –1.7. Monte-Carlo simulations of the scattering of electrons in iron, using Epe as a parameter.

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The shape of the interaction volume is also affected by the internal structure of the sample. In a material such as a crystal the electrons are allowed to pass through certain channels, without a strong energy loss per unit of length. This means that locally the interaction volume changes and that in the scattering models this channeling phenomenon has to be included, thus resulting in a scattering pattern which is strongly peaked into the direction of a channel. If the channels are in the direction of the primary electron beam an increase of the penetration depth will be the result.

1-5. The Origin of the Signals As discussed in the preceding section the electron looses energy on its way through the material. This energy is then released from the specimen in many different forms, depending on the type of interaction between the primary electron and the atoms of the specimen. As a result of the elastic and inelastic interaction the electron may become a back scattered electron with a maximum energy equal to the primary electron energy (in this case there is a single head-on collision). Ionization occurs as well, so electrons are produced throughout the total interaction volume; the electrons escape from the material and have an average energy of 2 to 5 eV. These electrons are called secondary electrons and they come from a small exit depth of about 1 nm for metals, and of the order of 10 nm for carbon. It should be noted that a backscattered electron generated deep in the material is energetic enough to produce a secondary electron on its way back to the surface this means that secondary electrons are also generated outside the actual interaction volume of the primary electron beam. This may even be outside the specimen it self, for instance if a back scattered electron hits the chamber or the pole piece of the electron microscope. These effects are schematically shown in Figure 1.8.

Figure 1.8. The production of secondary electrons by backscattered electrons.

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When the primary electron interaction results in ionization of an atom, the atom is left with a vacancy in one of its shells. One of the ways for the atom to loose the excess of energy is to transfer it to an electron in another shell, thus resulting in the generation of an electron with a energy characteristic for the material of the sample. These electrons have an energy up to about 2 Kev and are called Auger electrons. The spectrum of all electrons coming out of a specimen when it is irradiated with an electron beam of energy Epe is shown in figure 2.9. by convention the electrons with an energy below 50 eV are called secondary electrons (SE) and those remaining are the back scatter electrons (BSE). The large peak around the primary beam energy results from Rutherford scattering and this process increases with increasing atomic number z. therefore the number of BSE coming out of the specimen reflects the average z value of the material: this is the important contrast mechanism for the backscattered electrons (see also section 3.2). A second way an atom can fill the vacancy in one of its shells, is to catch one of the electrons of a higher shell. This electron jumps from one shell to a lower one and the difference in energy is emitted as an x-ray quantum. Since the electronic energy levels of the atom are fixed, and since the allowed jumps from one shell to another are subjected to strong quantum mechanical selection rules, the energy of the emitted x – ray quantum is characteristic for the atom itself. The x-ray quanta are generated everywhere the primary electron has sufficient energy to remove an inner shell electron from the atom on their way to the surface the generated x-ray quanta can be captured by an atom, which in turn may emit an x-ray quantum, usually with a different (lower) energy. This phenomenon is known as fluorescence, and it influences the position at which the x-rays come out of the specimen and it decreases the number of quanta that are originally produced.

Figure 1.9. The spectrum of the electrons leaving the specimen.

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2. SECONDARY ELECTRONS Of all signals that can be used for specimen investigation with a SEM the secondary electron signal are most frequently used. The most important characteristics of the SE signal are discussed below.

a) Energy Range Electrons that are emitted from the specimen with an energy less than 50 eV are defined as secondary electrons. Within this energy range there will always be a small number of backscattered electrons that have lost most of their energy but since their, contribution is small they contribution is small they can effectively be ignored. The maximum number of secondary electrons has an energy of between 2 and 5 eV with the exact peak position and energy spread varying for different materials. With the standard secondary electron detector the position and width of the peak do not effect the collected signal.

b) Angular Distribution When the primary electron beam strikes a specimen set at 0 degrees tilt the yield of secondary electrons for different exit trajectories follows a so called cosine rule [I (a) = I0 cos (a)] as shown in figure 3.1.The maximum yield is for electrons with an exit angle normal to the specimen surface with the intensity decreasing as the cosine of the angle the trajectory path makes with the incident beam.

Figure 1.10. The angular dependence of the secondary electron yield.

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The total yield of secondary electrons will increase as the specimen is tilted but the angular distribution remains the same. This is a consequence of the isotropic nature of secondary electron generation where the path direction of the secondary electrons is independent of the direction of the initiating high energy electrons.

c) Information Depth Electron beam specimen interactions give rise to secondary electrons throughout the total interaction volume but only those that are generated close to the surface will leave the sample and contribute to the signal. The depth is about 1 nm for metals and 10 nm for most insulating (low z) materials. Secondary electrons are generated by the primary beam as it enters the sample and also by backscattered electrons as they leave the sample material (see Figure 1.8). thus although the secondary electrons themselves come from a depth of a few nanometers there is also a contribution to the SE signal as a result of backscattered electrons emerging from several hundred nanometers beneath the specimen surface. When the primary beam impinges on such an area, backscatter electrons are emitted from the specimen surface in the usual way. The backscatter electrons are not influenced significantly by the leakage fields because of their energy is relatively high. However, as a result of their low energy, the secondary electrons will be influenced by the magnetic fields above the specimen. when the secondary electrons emerge from the specimen in a region where there are leakage fields they will experience a force which in some regions will deflect them towards the secondary electron collector and in others, with different fields, will deflect them away from it.

Figure 1.11. The interaction volume and the origin of some signals.

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A reduction in the field strength of the secondary electron detector (by reduction of the grid bias) may help to enhance the contrast since the secondaries deflected away from it are less likely to be collected. as with the crystal orientation, described in the previous section, this contrast mechanism is only normally visible when the stronger effects such as those due to topography are reduced.

3. BACKSCATTERED ELECTRONS This signal is the result of electrons from the primary beam undergoing a sequence of elastic and inelastic scattering events, in which the net change in direction is sufficient to carry them out of the specimen. The most important characteristics of the BSE signal are discussed below.

a) Energy Range As a result of the definition of the SE energy as discussed in previous sections the electrons in the remaining energy interval i.e. 50 eV to the energy Epe of the primary electrons, are referred to as backscattered electrons. The BSE with an energy close to E are the ones that are subject to elastic scattering and they form a substantial part of the total BSE signal.

b)Angular Distribution Normalized angular distributions of the BSE are shown in figure 1.12 for a normal incident beam on Al and on Ag For a given z the BSE yield follows more or less a cosine relationship, so most of the electrons are reflected back in the direction of the primary beam. The shape of the curve does not strongly depend on the primary beam energy for an angle of incidence of 60° the angular distributions of Al and Ag are shown in Figure 1.13 in this case there is a maximum in the direction opposite to the primary beam direction and a” deformed cosine relation” describes the distribution. Moreover, the same normalization is used as in figure 3.6 and as shown in the figures the ratio of the maximum yields of Ag and Al is larger for normal incidence than for 60 o incidence. So tilting the specimen results in a stronger peaked signal, but also in a decrease of the signal difference i.e. the signal contrast.

c) Information Depth As stated, the high energetic backscattered electrons result from a single interaction and are therefore most likely to come from the upper layer of the specimen. So if only the high energetic BSE are detected the information depth is smaller than the penetration depth. If a non-dispersive detector is used all BSE are detected simultaneously, so the information depth becomes a substantial part of the penetration depth of the primary electron beam.

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Figure 1-12. the angular distribution of the backscattered electrons for a normal incident beam on Al and on Ag.

Figure 1.13. The angular distribution of the backscattered electrons for an electron beam on Al and on Ag with an angle of incidence of 60.

4. CATHODOLUMINESCENCE As a result of electron bombardment of the specimen, light may be generated inside the specimen, and if the specimen is transparent for emitted and detectable wavelengths, this Cathodoluminescence signal can be used for imaging as a result of the way excited states of the specimen can decay to lower levels there might be a considerable amount of time between the moment of excitation by the electron beam and the moment the energy is released again by photon emission. The emitted radiation may even cause fluorescence in the specimen and the effective decay time is strongly increased his time between excitation and total decay is the reason why a Cathodoluminescence image might not be clearly visible at the TV scan speed. The total image will then appear blurred, and selection of a slower scan speed is the only remedy for this.

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a) Energy The energy of the emitted radiation is strongly dependant on the material composition and may be somewhere in the total spectrum from the very ultra violet to the far infra-rad. Not all these wavelengths are suited for imaging, since low noise detection with a photomultiplier has to be possible as well; therefore imaging is restricted to those wavelengths which are in the detectable range of the photomultiplier.

b) Angular Distribution As a result of the nature of the photon emission there is no preference for a certain angle. However, the presence of local obstructions and absorption variations of the sample will have an influence on the distribution. Moreover the local variation of the specimen surface (topography)may result in variation of the internal reflection coefficient, and this reduces the efficiency for the light to get out of the specimen (analogous to light in an optical fiber)and induces local polarization of the light.

c) Information Depth The information depth is very large, since as long as the electrons have sufficient energy for the excitation of atoms or molecules of the specimen, Cathodoluminescence may occur. Thus the volume where the photons come from is larger than for instance for backscatter electrons, since these electrons are subject to the same scattering mechanisms as the incoming electrons. For Cathodoluminescence the signal is carried by other elementary particles (photons) than the particles that generated the signal, so the absorption of the signal on its way back will be principally different.

5. THE X–RAY SIGNAL a) Energy Range In the case of characteristic x-rays the energy range depends on the nature of the sample. assuming that many elements are present characteristic x-rays have a theoretical upper energy limit equal to E pe . The probability of emission of that radiation is however very low. The lower limit of the x-ray radiation is less then 0.1 kev and in fact enters the transition region for Cathodoluminescence. In the case of the continuum radiation (bremsstrahlung) the spectrumranges from zero to E pe and here there is also a strong decrease of the emission probability for high energetic xrays. The spectrum is schematically shown in figure 1.14.

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Figure 1.14. The x-ray continuum spectrum obtained with an electron beam of energy E pe .

b) Angular Distribution Principally the characteristic emission is randomly emitted, but as a result of internal absorption (i.e. absorption of the x-rays in the sample on their way from the interaction volume to the surface) the x-ray signal is peaked into the direction of the electron beam; the lower the energy, the stronger the peak. The direction of the continuum radiation is related to the velocity of the decelerated electron, so principally it is related to the initial beam direction, but as a result of the multiple scattering this direction preference is lose. A peak of the signal in the direction of the electron beam comes from absorption phenomena inside the specimen as is the case for the characteristic radiation.

c) Information Depth Assuming that all generated x-rays can escape from the sample, the information depth is related to the primary beam energy, reflecting the interaction volume of the primary and the backscattered electrons. The information depth is also related to the characteristic radiation of interest. By decreasing E pe the interaction volume is decreased as well (thus the information comes from a region that is closer to the surface) but the obtained x-ray spectrum is also different since the maximum energy of the x-rays has decreased. So the reduction of E pe to obtain a decrease of the information depth is accompanied by a reduction of the maximum energy that is emitted, and thus of the number of detectable elements.

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6. TRANSMITTED ELECTRONS Transmission of electrons only takes place if the specimen is very thin The thickness must certainly be less than about 1 micron. Usually the transmission of electrons through the specimen is investigated in a TEM. With this special instrument it is possible to visualize diffraction patterns that contain valuable specimen information such as crystallographic constants and orientation. Since extra lenses below the specimen are required for this, a SEM is not suited to detect diffraction patterns. The most important information for a SEM in transmission mode comes from the locally variable transmission coefficient (the thickness) of the specimen. The various characteristics of the transmission signal will be discussed below.

a) Energy Range Depending on the specimen thickness and/or density the energy of the transmitted electrons ranges from zero to the primary electron energy E pe .The greater the specimen thickness (density),the smaller the averaged energy of the transmitted electrons.

b) Angular Distribution When the specimen is sufficiently thin the signal will be strongly peaked in the direction of the optical axis. As a result of many interactions in a thick sample, this angular spread will become larger. The mentioned diffraction phenomenon is beyond the scope of this basic course. Because of the detection method normally employed in a SEM the angular distribution is of minor importance.

c) Information Depth In fact the transmission signal itself reflects the absorption of electrons in specimen. The information depth thus depends on the combination of specimen thickness (and composition) and applied high voltage.

7. CONVENTIONAL ELECTRON-BEAM LITHOGRAPHY The practice of using a beam of electrons to generate patterns on a surface is known as electron beam lithography. The primary advantage of this technique is that it is one of the ways to beat the diffraction limit of light and make features in the sub-micrometer regime. Beam widths may be on the order of nanometer as of the year 2005. This form of lithography

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has found wide usage in research, but has yet to become a standard technique in industry. The main reason for this is speed. The beam must be scanned across the surface to be patterned -pattern generation is serial. This makes for very slow pattern generation compared with a parallel technique like photolithography (the current standard) in which the entire surface is patterned at once. As an example, to pattern a single layer of semiconductor containing 60 devices (each device consists of many layers) it would take an electron beam system approximately two hours; compared with less than two minutes for an optical system. One caveat: While electron beam lithography is used directly in industry for writing features, the process is used mainly to generate exposure masks to be used with conventional photolithography. However, when it is more cost-effective to avoid the use of masks, low volume production or prototyping, electron-beam direct writing is also used. For commercial applications, electron beam lithography is usually produced using dedicated beam writing systems that are very expensive (>$2M USD). For research applications, it is very common to produce electron beam lithography using an electron microscope with a home-made or relatively low cost lithography accessory. Such systems have produced line widths of ~20 nm since at least 1990, while current systems have produced line widths on the order of 10 nm or smaller. These smallest features have generally been isolated features, as nested features exacerbate the proximity effect, whereby electrons from exposure of an adjacent feature spill over into the exposure of the currently written feature, effectively enlarging its image, and reducing its contrast, i.e., difference between maximum and minimum intensity. Hence, nested feature resolution is harder to control. For most resists, it is difficult to go below 25 nm lines and spaces, and a limit of 20 nm lines and spaces has been cited here[9]. With today's electron optics, electron beam widths can routinely go down to a few nm. This is limited mainly by aberrations and space charge. However, the practical resolution limit is determined not by the beam size but by forward scattering in the photo resist and secondary electron travel in the photoresist [10]. The forward scattering can be decreased by using higher energy electrons or thinner photoresist, but the generation of secondary electron is inevitable. The travel distance of secondary electron is not a fundamentally derived physical value, but a statistical parameter often determined from many experiments or Monte Carlo simulations down to < 1 eV. This is necessary since the energy distribution of secondary electrons peaks well below 10 eV[11]. Hence, the resolution limit is not usually cited as a well-fixed number as with an optical diffraction-limited system[12]. Repeatability and control at the practical resolution limit often require considerations not related to image formation, e.g., photoresist development and intermolecular forces. In addition to secondary electrons, primary electrons from the incident beam with sufficient energy to penetrate the photoresist can be multiply scattered over large distances from underlying films and/or the substrate. This leads to exposure of areas at a significant distance from the desired exposure location. These electrons are called secondary electron and have the same effect as long-range flare in optical projection systems. A large enough dose of backscattered electrons can lead to complete removal of photoresist in the desired pattern area.

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8. NEW FRONTIERS IN ELECTRON-BEAM LITHOGRAPHY To get around the secondary electron generation, it will be imperative to use low-energy electrons as the primary radiation to expose photoresist. Ideally, these electrons should have energies on the order of not much more than several ev in order to expose the photoresist without generating any secondary electrons, since they will not have sufficient excess energy. Such exposure has been demonstrated using a scanning tunneling microscope as the electron beam source[13]. The data suggest that electrons with energies as low as 12 eV can penetrate 50 nm thick polymer photoresist. The drawback to using low energy electrons is that it is hard to prevent spreading of the electron beam in the photoresist[10]. Low energy electron optical systems are also hard to design for high resolution [14,15]. Coulomb inter-electron repulsion always becomes more severe for lower electron energy. Another alternative in electron-beam lithography is to use extremely high electron energies (at least 100 keV) to essentially "drill" or sputter the material. This phenomenon has been observed frequently in transmission electron microscope[16]. However, this is a very inefficient process, due to the inefficient transfer of momentum from the electron beam to the material. As a result it is a slow process, requiring much longer exposure times than conventional electron beam lithography. Also high energy beams always bring up the concern of substrate damage. Interference lithography using electron beams is another possible path for patterning arrays with nanometer-scale periods. A key advantage of using electrons over photons in interferometry is the much shorter wavelength for the same energy. Despite the various intricacies and subtleties of electron beam lithography at different energies, it remains the most practical way to concentrate the most energy into the smallest area.

9. EXPERIMENTAL STUDIES In this experiment, a commercial electron microscope Philips armored to (EDXE) detector. The characteristic of this microscope is presented in the Table 2.1. In order to compare the effect of irradiation on the fibers, four types of fibers are kindly provided by industrial sectors (i.e., acrylic, polyester, cotton and viscose rayon). Table 2.1. The Characteristic of Electron Microscope Model

XL30

The Size Of Chamber

20.×20

Filament

W-gun

Kind of pump

Oil Diffusion Pump

MAX Voltage

30KeV

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At the end of drying process each fiber sample is glued to ample holder with carbon stick and then they are placed in the SME vacuum chamber and the electron gun is switched on. At the first stage each sample is observed by 12800 x magnification with various voltage namely; 12,15, 20,25,30 KV, alter to get to a steady state condition. The photographs are then taken from each sample and the size variations are measured. At the second stage the samples size variations are measured after irradiation with respect to time.

10. RESULTS AND DISCUSSIONS Diagram1 shows the inflation or deflation of different fibers versus different voltages. According to Diagram2.1, increase of beam voltage causes some changes in the fibers diameter, but this change is different for each fiber. The most variation belongs to viscose and the least variation belongs to acrylic. The diameter variation is most likely for inflation of viscose, cotton and polyester, whilst this is shown as deflation for acrylic. Diagram 2.2 to2.5 show diameter changes for polyester, acrylic, cotton and viscose rayon. It can be seen that with increasing the time of irradiation, the destruction of fibers increased significantly. For polyester, cotton and viscose fibers this destruction appears in the form of increase in the fiber diameter whilst for the acrylic fiber, this deformation appears as decrease of the fiber diameter. Series1

Series2

Series3

Series4

Percent of fiber change

60 50 40 30 20 10 0 -10 0

10

20

30

-20 voltage(KeV)

Diagram 2.1. Fiber diameter change verses different voltage at 13000 x.

40

percent of inflation in polyester

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30 25 20 15 10 5 0 0

200

400

600

time (s)

perenct of deflation in acrylic

Diagram 2.2. Polyester fiber diameter change verses time after irradiation at13000 x.

20 15 10 5 0 0

200

400

600

800

time (s)

percent of inflation in cotton

Diagram 2.3. Acrylic fiber diameter change verses time after irradiation at13000 x.

50 40 30 20 10 0 0

50

100

150

200

time(s)

Diagram 2.4. Cotton fiber diameter change verses time after irradiation at13000 x.

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percent of inflation in viscose rayon

84

60 50 40 30 20 10 0 0

10

20

30

40

time(s)

Diagram 2.5. Viscose fiber diameter change verses time after irradiation at13000 x.

The destruction depends electron radiation in vacuumed atmosphere and the formation on the surface of fibers is shown in the Figures 2.1 to 2. 4. Distraction of the polyester fiber is showed in the Figure 2.1 where some sorts of fractures are seen on the surface of fiber. On contrast, in Figure 2.2 the diameter decreased and the necking of fiber is obvious. In Figure 2.3, it is clearly observed that the transverse bonding of cotton has broken.[2,8] In Figure 2.4 the variation of viscose rayon is shown as bulging of fiber cross section.

Figure 2.1. Electron micrograph of polyester.

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Figure 2.2. Electronmicrograph of acrylic.

Figure 2.3. Electron micrograph of cotton.

Figure 2.4. Electron micrograph of viscose rayon.

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K. Mohammadi and A. K. Haghi Table 2.2. The Characteristic of Fiber Changing

Kind of fiber polyester acrylic cotton viscose

Maximum change in fiber diameter 25 -14.5 42 48.7

Minimum time for maximum change 450 S 640S 120S 30S

11. CONCLUSION The radiation modification of fibers by means of the SEM electron beam was studied in this paper. From the pictures captured, it is observed that the proper selection of SEM radiation wavelength and time can have significant effects on the appearance of fibers studied. The effect of time on this variation is summarized in Table 2. For the case of acrylic fiber it takes 640s to get to a maximum deflation whilst this time for viscose rayon is as short as 30s. It is also concluded that electron irradiation has much faster effects on the viscose comparing to the other samples. Nevertheless, the rate and amount of changes for acrylic is least. In essence, it is expected that the irradiation of electrons break the chemical bonds with lower binding energies in the fibers surface layer. (i.e. the C-C, C-H, C-N and C-O bonds)[8]. Hence the tendency and range of changes in the materials depend on the amount of energy absorbed by materials. Meanwhile, as irradiation time increases, the amount of energy absorbed by the fiber will increase as well. This is due to the increase in the duration of surface scanning by electron probe. However, increase of voltage of beam causes decrease in the wavelength and for each case the fibers may absorb more energy. The electron energy may produce some defects and abrupt cross- link bonds. The effect of electron on the different fibers could depend on the length and the type of fiber bonds charges. The deformation of observed in the samples is similar to deformation in the wool and silk fiber which were investigated and reported earlier in

Figure 2.5. Electron micrograph of silk.

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Figure 2.6. Electron micrograph of wool.

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

A. K. Haghi, K. Mahfouzi, K. Mohammadi, J. Univ. Ch. Tech. Metallur. (Sofia), 138, 85 (2002). Y. Gao, S. L. Jiang, M. Sun, D. Yang, S. He &Z. Li, Radiat. Phys. Chem, 73, 384(2005). M. Zenkiewicz, Int. J. Adhesion Adhesive, 25, 61(2005). M. Zenkiewicz, Int. J. Adhesion Adhesive, 24, 256(2004). M. Zenkiewicz, Radiat. Phys. Chem, 69, 373(2004). P. G. Fuochi, M. Lavalle, A. Martelli, U. Corda, A. Kovacs, P. Hargittai&K. Mehta, Radiat. Phys. Chem, 67, 593(2003). B. D. Cullity, Elements of X-Ray diffraction, Addision-Wesley Company, Inc, edn. 2(1978). S. B. Warner, Fiber Science, Prentice hall Inc(1995). J. A. Liddle et. al., Mat. Res. Soc. Symp. Proc. vol. 739, pp. 19-30 (2003). A. N. Broers et. al., Microelectronic Engineering 32, pp. 131-142 (1996). H. Seiler, J. Appl. Phys. 54, R1-R18 (1983). L. Feldman and J. Mayer, Fundamentals of Surface and Thin Film Analysis, pp. 130133 (North-Holland, 1986). C. R. K. Marrian et. al., J. Vac. Sci. Tech. B 10, pp. 2877-2881 (1992). T. M. Mayer et. al., J. Vac. Sci. Tech. B 14, pp. 2438-2444 (1996). L. S. Hordon et. al., J. Vac. Sci. Tech. B 11, pp. 2299-2303 (1993). R. F. Egerton et. al., Micron 35, pp. 399-409 (2004).

In: Modern Tendencies in Organic and Bioorganic Chemistry ISBN: 978-1-60456-295-8 Editors: A. Mikitaev, M. K. Ligidov, pp. 89-101 © 2008 Nova Science Publishers, Inc.

Chapter 5

STRUCTURAL BEHAVIOR OF COMPOSITE MATERIALS О. А. Legonkova1,*, J. L. Gordeeva 1, E. S. Obolonkova2 1

Moscow State University of Applied Biotechnology, Moscow, 109316, Talalikhina str., 33, 2 Institute of synthetic polymer materials RAS named after Enikolopov N.S.

ABSTRACT Physical and mechanical properties of the filled polymer composite materials (PCM) in dependence on the extent of filling, the rate of deformation were investigated. It was found out that structural properties of the filled composite materials are determined with the nature of polymer matrix, filling degree, nature of the fillers, structural organization of FCM, that is being formed in the process of receiving of the composite materials, and conditions of tests.

Keywords: composite materials, physical and mechanical properties, strength Today the overwhelming majority of polymers are applied as composite materials (PCM). Properties PCM, as a rule, are not a sum of properties of the components, and are defined by the variety of chemical and physical processes as the result of interaction of components on the borders of phases. Introduction of fillers into polymers brings essential changes in the mobility of macromolecules on boundary layers, arises various kinds of interaction between polymers and the surface of fillers, influences on chemical structure of the fillers and polymers during reception and exploitation of PCM [1-5]. However insufficient attention is given to research of physical and mechanical properties of highly filled materials consisting of polymeric matrix and mixture of fillers of various nature, giving biodegrability of composition as a whole. At present work the following large-capacity polymers were taken as polymeric basis: acrylate-styrene carboxylated latex - Lentex А4 (TU 2241-001-47923137-01); copolymer of *

[email protected]

90

О. А. Legonkova, J. L. Gordeeva and E. S. Obolonkova

ethylene and vinyl acetate (cevilen, mark #11306-070; polyamide (PA, which is copolymer of hexamethylene diamine, adipate and sebacic acids with melting temperature 1300С); thermoplastic polyurethane (PU), which is produced by "Agropolymer" firm (Russia, TU 5141-003-17823007), polyvinyl spirit (PVS) with the degree of saponification - 88 %. Waste products of thrashing grains(organic filler) of the third category (size of particles 63-240mcm, bulk density of 350 kg / m3; humidity of 4 %), and water-soluble mineral fertilizer (inorganic filler with the following make-up (in %): (NH4) 2SO4- 35, NH4H2PO4 - 6, KNO3 - 32, MgSO4*7H2O - 27) were taken as fillers. Depending on properties of polymeric matrix various ways of reception of composites were applied. Compositions on basis of watersoluble PVS and industrial Lentex А4 have been received via watering of water solutions consisting of organic and inorganic fillers. Compositions on polyurethane basis were received through hardening on air of the component mixture. For reception of samples of PCM on sevilen basis and PA matching of components were carried out by laminar mixture in melt, pressing, and also by making a mixture of components and pressing. Thus samples received as plates with thickness 500 microns. It was noticed while investigating the physical and mechanical properties of PCM on PA basis and speed of deformation at 100 mm/min for two component systems, that at introduction of inorganic filler into composition up to 10 % the breaking point insignificantly falls. It could be explained by the following: the filler at its small concentration in PCM in absence of aggregation powdered particles, carries out role of concentrator of internal pressure and is a potential source of cracks’ growth [1]. At increase of concentration inorganic filler up to 30 % durability of PCM increases in 2, 5 times and that is explained with the creation of more obstacles for development of cracks. Owing to this the breaking processes of destruction stops [1]. Reduction of durability with increase of contents of filler is typical for highly filled PCM. At concentration of inorganic filler in the quantity of 75 % samples become very fragile, have durability on order below, than the initial samples. Relative lengthening at break for all samples decreases, and finally, becomes in 2 times less, than at initial sample. For two componental PCM with organic filler similar law is traced, relative hardening system is observed at small concentration of filler (up to 10 %) which is not so significant as in two-componental system with inorganic filler (increase of durability in 1,5 times). At creation of two component systems on sevilen basis at monoaxial deformation 100mm/mines the «effect of temporary conversion of reinforcing action of fillers», for the first time described in the work [7], wasn’t found: with increase of content of organic and inorganic fillers durability and relative deformation reduced, Figures 1,2. Samples become more rigid (module grows) in case of filling organic filler. At introduction of inorganic filler even at large concentrations (weights of 60 %) samples keep rather high plasticity (deformation at destruction is appr. 400 %).

Structural Behavior of Composite Materials

91

σр, МПа 1

2

σр, МПа

А. εотн, % 3

5

4

B. εотн, % Figure 1. Physical and mechanical properties PCM on basis of sevilen. Content of organic filler, weight in %: 1 - 0 %; 2 - 20 %; 3 - 40 %; 4 - 50 %; 5 - 60 %. Speed of monoaxial deformation is 100 mm / min.

92

О. А. Legonkova, J. L. Gordeeva and E. S. Obolonkova

МПа

1

2

4 3 5

εотн, % Figure 2. Physical and mechanical properties of two componental PCM on basis of sevilen. Content of inorganic of filler, weight in %: 1-0 %; 2 - 20 %; 3 - 40 %; 4 - 50 %; 5 - 60 %. Speed of monoaxial deformations - 100 mm / min.

According to IK-spectroscopy inorganic filler is inert in the relation to polymeric matrix because the identical spectra of absorption of initial unfilled polymer and the polymer filled with inorganic filler are the same. Hence, mechanical behavior of PCM is defined by structural organization of composite materials, its dependence on conditions of formation and test on PCM (in our case, speed of deformation). Electronic- microscopic photos of PCM surface on basis of PA and sevilen are submitted on Figure 3, 4. It is visible, that systems heterogeneous. Introduction of organic filler results in reception of more homogeneous systems, than introduction of inorganic filler. Systems with inorganic filler include as crystallites of salts of filler as their more difficult formations. However distribution of inorganic filler in sevilen environment is distinct from its distribution in PA environment, Figure 3 (1-3). In PCM on basis of PA structure of composite at 20 % filling is more defective on all surface of spalling, creating obstacles for development of cracks. While in PCM systems on basis of sevilen defects "were pressed" in homogeneous structure of composite, therefore decrease in durability PCM occurs due to the reduction of maintenance of polymer in a composition and hardenings PCM is not observed at speed of deformation of 100 mm / min.

Structural Behavior of Composite Materials 1.

4.

10% inorganic filler

10% organic filler

2.

5.

20% inorganic filler

20% organic filler

3.

6.

50% inorganic filler

50% organic filler

93

Figure 3. Electronic - microscopic photos of chips of two component systems PCM on basis of PA and inorganic filler (1,2,3), and organic filler (4,5,6.) (Increase 200 microns)

О. А. Legonkova, J. L. Gordeeva and E. S. Obolonkova

94 1.

20% inorganic filler

4.

tree componental PCM

2.

5.

40% inorganic filler

40% organic filler

3.

6.

60% inorganic filler

60% organic filler

Figure 4. Electronic - microscopic photos of chips of two component systems PCM on basis of sevilen and inorganic filler (1,2,3), and organic filler(5,6), three componental PCM: 50 % organic filler, 35 % inorganic filler. (Increase 200 microns)

Structural Behavior of Composite Materials

95

Physical and mechanical properties of two componental PCM on basis of PU, Lentex А4, PVS are submitted in Tables 1-2, Figure 5. Introduction of organic filler resulting in decrease of elasticity of PCM and introduction of inorganic filler leading to preservation of enough elasticity of composite in comparison with PCM, filled with organic filler are general for all investigated systems. «Effect of temporary conversion of reinforcing action of fillers» was found at filling with organic and inorganic fillers, both in two and three componental systems. Physical and mechanical properties of PCM on basis of PVS with concentration of filling inorganic filler 20 % at various speeds monoxial stretching are presented on Figure 6. While investigating the three component PCM on basis of investigated polymers, Figures 6-7, Tables 3, 4, it should be noted that the basic contribution to durability of three componental PCM brings organic filler. Even in highly filled systems where the general content of fillers reaches 85 %, the given dependence is kept. Inorganic filler, as well as in case with two-component materials gives plasticity of PCM. Table 1. Physical and mechanical properties of two component PCM on the basis of PU at stretching (speed of deformation is 100 mm / min) Maintenance, weight %

durability, МPa

deformation, %

Polimer 90

organic filler 10

inorganic filler -

21,4

480

80

20

-

16,4

360

79

30

-

13,3

270

46

54

-

4,4

6,6

90

-

10

25,0

500

80

-

20

22,6

480

70

-

30

16,3

300

60

-

40

8,6

240

Table 2. Physical and mechanical properties of two componental PCM on basis Lentex А4 at stretching (speed of deformation is 100 mm / min) Maintenance of Lentex А4, %

maintenance organic filler, %

maintenance inorganic filler, %

durability, МPa

100

0

0

3,1

Deformation of destruction, % 600

90 80 60 90 80 60

0 0 0 10 20 40

10 20 40 0 0 0

1,3 1,0 0,8 2,5 1,7 1,6

300 300 180 300 20 12

О. А. Legonkova, J. L. Gordeeva and E. S. Obolonkova

96

300

Pressure, MPa

250

5 1

200

2 3

150

4 5

100

3

6

50

2

4

1

6

0 0

5

10

15

20

25

30

35

Deformation, % Figure 5. Physical and mechanical properties of PCM on the basis of PVS (monoaxial deformation 100 mm/min). Content of inorganic filler, weight in %: 1-0 %; 2 - 10 %; 3 - 20 %; 4 - 50 %; ratiot of organic filler, weight in %: 5 - 20 %; 6 - a parity of polymer, organic filler and inorganic filler in three component PCM is 1:1:1.

120

Pressure, MPa

100 2 80

1 1

60

2 3

40

3

20 0 0

2

4

5

8

10

15

20

25

30

35

40

Deformation, % Figure 6. Physical and mechanical properties of PCM on the basis of PVS, filled inorganic filler (20 % of weights) at various speeds monoaxial deformation: 1-0,5 mm / min; 2 - 10 mm / min; 3 - 100 mm / min.

Structural Behavior of Composite Materials

97

1

5

3 4

2

εотн, % Figure 7. Physical and mechanical properties three component PCM on the basis of sevilen, weight in mass. %: 1 - sevilen/organic filler - 50/50; 2 - sevilen/ inorganic filler - 50/50; 3 - sevilen/ inorganic filler/ organic filler. - 50/37/13; 4 - sevilen/ inorganic filler/ organic filler.-50/25/25; 5 - sevilen/ inorganic filler/ organic filler.-50/13/37. The rate of stretching is 100 mm/ min.

At research of physical and mechanical properties of PCM received via pressing, all the above described dependences in changes of durability depending on degree of filling and conditions of test are kept. Being based on the above discussed results we can estimate that durability dependence on content of each type of the fillers (organic or inorganic) is linear:

( )

f x j = α 0 j + α1 j ⋅ x j ,

(1)

Table 3. Physical and mechanical properties of three componental PCM on basis PU at test for stretching (speed of deformation of 100 mm / min)

80

Content, % Organic filler 10

72

14

14

7,1

94

60

20

20

6,5

63

50

25

25

6,1

26

polymer

Inorganic filler

Durability, МPa

Deformation, %

10

7,3

110

О. А. Legonkova, J. L. Gordeeva and E. S. Obolonkova

98

σ, МPа 1 2

3

4 ε, %

Figure 8. Physical and mechanical properties of three component PCM on the basis of PA. Content of polymer/organic filler/inorganic filler, weight in mass. %: 1 - 50/10/40; 2 - 50/20/30; 3 - 50/25/25; 4 50/40/10.

where j – factor number (filler), α0j, α1j – equation coefficient for the j-factor (j = 1, 2). For example, these dependences for samples based on sevilen are given in the Figure 8 (а, б). Brandon’s method was used to describe the behavior of three component PCM [7,8]. According to this method the approximate function has the following appearance:

y = λ ⋅ f1 ( x 1 ) ⋅ f 2 ( x 2 ) ,

(2)

Table 4. Physical and mechanical properties of the high filled PCM on the basis of sevilen (speed of deformation is 100 mm / min) Content, % polymer

durability, МPa

Deformation, %

Inorganic filler

15

Organic filler 35

50

0,72

5,2

15

45

45

1,06

5,0

15

50

35

1,20

6,3

15

60

25

1,31

4,0

10

55

35

0,80

6,3

Structural Behavior of Composite Materials

99

Durability

2,5 2 1,5 1 0,5 0 0

0,2

0,4

0,6

x1 а) 2,5

Durability

2 1,5 1 0,5 0 0

0,2

0,4

0,6

0,8

x2 b) Figure 8. Dependence durability of filler content: а – of inorganic filler (x1); b – of organic filler (x2).

where

y

–

durability

of

f 2 (x 2 ) = α 02 + α12 ⋅ x 2

PCM;

λ

-

constant;

f1 (x1 ) = α 01 + α11 ⋅ x1 ,

– dependence of PCM durability on filler content,

correspondingly, inorganic (x1) and organic (x2) fillers. The meaning of λ constant equals to the medium experimental meaning of the exit parameter

λ=

1 N ∑ y i , i=1, 2, …, N. N i =1

Where yi – durability for PCM. After normalization of experimental data via division yi on λ according to the formula

(3)

О. А. Legonkova, J. L. Gordeeva and E. S. Obolonkova

100

y*i =

yi λ

(4)

for two pairs of variables

(x

)

* 1i , y i with the help of method of minimum squares, constants

of the first component in the regression equation

f1 (x1 ) = α 01 + α11 ⋅ x1

calculated. Constants of the second component of the function

were

f 2 (x 2 ) = α 02 + α12 ⋅ x 2

for

variable x2 and remaining function yi1 were calculated via excluding the meaning of the first * component of the function f1(x1) out of the normalized meanings of the exit parameter y i according to the formula

y i1 =

y*i f1 ( x1 )

.

(5)

After determination of f1(x1) и f2(x2) the common formula of plural regression was built. As a result, the following regression equations for three component PCM were received: - for PCM based on sevilen

y = 1,82 ⋅ (1,29 − 0,96x1 ) ⋅ (1,36 − 0,95x 2 )

(6)

- for PCM based on PA

y = 8,41 ⋅ (2,07 − 4,08x1 ) ⋅ (0,96 − 0,15x 2 )

(7)

- for PCM based on PU

y = 6,75 ⋅ (1,21 − 1,23x1 ) ⋅ (1,01 − 0,03x 2 )

(8)

- for PCM based on Lentex

y = 1,40 ⋅ (2,01 + 9,64 x1 ) ⋅ (1,27 − 1,01x 2 )

(9)

- for PCM based on PVS

y = 39,63 ⋅ (4,36 − 11,40 x1 ) ⋅ (2,54 − 6,76x 2 )

(10)

Structural Behavior of Composite Materials

101

The quality control of approximation according to Fisher criteria revealed that equations (6-10) sufficiently reflect the behavior of three component PCM at p<0,1 (the level of the meaning). Thus, strength characteristics of PCM are defined with nature of polymeric matrix, degree of filling and nature of fillers, that structural organization which is formed during reception PCM and test specifications (as response PCM to external influence). Fillers bring corrective amendments into mechanical properties of composite material independently from each other, namely: presence of organic filler results in increase of durability, presence of inorganic filler keeps plasticity of systems almost for all investigated materials. For each composite there is the rate of deformation at which “the effect of strengthening action of the filler” realizes. . The equation of regression for three component composite materials based on sevilen, PA, PU, Lentex, PVS were received that let us to forecast the durability properties of PCM and finally properties of industrial articles.

REFERENCES [1] [2] [3] [4] [5] [6] [7] [8]

Lipatov U.S. Physical and chemical of basis of filling of polymers. M.: Chemistry. 1991.260 p. 2 Simonov-Emeljanov I.D., Kuleznev V.N. Basis of creation of composite materials. M.: МИХМ, 1986, 86 p. L.Nilsen. Mechanical properties of polymers and polymeric compositions. М., Chemistry, 1978, 310 p. Physical chemistry of polymeric compositions. collection of articles, "Naukova Dumka", Kiev, 1974, 183 p. V.E.Gul. Structure and properties of polymers. М., Chemistry, 1978, 300 p. SolomkoV.P. Filled crystallized polymers. Kiev, Naukova Dumka, 1980, 263 p. Bondar A.G. Mathematical modeling in chemical technology. Kiev, Vuscha shkola, 1973, 280 p. Podvaljnii S.L. Modelling of industrial processes of polymerization. Moscow, “Chemisty”, 1979, 256 p.

In: Modern Tendencies in Organic and Bioorganic Chemistry ISBN: 978-1-60456-295-8 Editors: A. Mikitaev, M. K. Ligidov, pp. 103-112 © 2008 Nova Science Publishers, Inc.

Chapter 6

COMPARATIVE EVALUATION OF ANTIOXIDANT PROPERTIES OF SPICE-AROMATIC PLANT ESSENTIAL OILS A. L. Samusenko* N. M. Emanuel Institute of Biochemical Physics, Russian Academy of Sciences, 4 Kosygina Street, 119 991 Moscow, Russia

ABSTRACT Antioxidant properties of the essential oils from black pepper (Capsicum nigrum L.) ginger (Zingeber officinale), cardamom (Elettaria cardamomum), berries of juniper (Juniperus pinchoti), fennel (Foeniculum officinale), mace (Myristicia fragans L.), lemongrass (Cymbopogon citratus) and seeds of caraway (Carum carvi) were studied by capillary gas-liquid chromatography using an aldehyde/carboxylic acid assay. The essential oil from mace was found to have the highest antioxidant activity while the essential oil from black pepper possessed the lowest one. The composition changes in the essential oils during long storage in light were studied. The correlation was made between autooxidation of the essential oils under study and their antioxidant properties.

Keywords: spice-aromatic plants, essential oils, antioxidant activity, aldehyde/carboxylic acid test, capillary gas chromatography.

AIMS AND BACKGROUND Using of the essential oils in food stuffs, beverages and perfume industry has significantly increased in consequence of the growing interest of customers to the natural ingredients since the synthetic additives are potentially dangerous for human health [1]. It is *

E-mail: chembio @ sky.chph.ras.ru

104

A. L. Samusenko

known that the essential oils of spice-aromatic plants have a nice flavor, inhibit the oxidation of lipids and microbiological spoilage of products. These undesirable processes are responsible for appearance of off-odors, toxic properties and influence on the shelf-time of products [2]. Until the recent time odor and taste of the essential oils were mainly studied for flavoring of food stuffs, beverages etc. However in recent years the investigation of biological activity, including the antioxidant one, is of a great interest [3-9]. It was shown that antioxidant activity of spice-aromatic plants, in which the essential oils are the important components, is comparable with the activity of traditionally used synthetic antioxidants, such as buthylated hydroxyanisole and hydroxytoluene [7]. The various methods of evaluation of antioxidant activity, i.e. photochemiluminescence [10], bleaching of β-carotene [11], free radical-scavenging test [12] and the reaction of oxidation of aldehyde to carboxylic acid [13] were used for the investigation of antioxidant properties of the thyme, rosemary, ginger, lemon grass, laurel, coriander, fennel, black and green tea essential oils [8-10, 14]. Biological activity of the essential oils depends on its main component composition. It is known that the presence in the oil composition of cyclic monoterpene hydrocarbons having two double bonds in the cycle, i.e. α- and γ-terpinene, α-terpinolene, sabinene, and also eugenol, thymol and carvacrol [15] is responsible for the antioxidant properties of the essential oils. However the oil composition is not a constant, depends on taxonomic variety of plants [16], time and conditions of oil storage [17]. It was shown that the essential oils of sage [18], savory [19], clove and cardamom [20], coriander [21] and marjoran [22] noticeably varied during a storage and the main process was autooxidation. The goal of this work was studying of the antioxidant properties of the black pepper, ginger, cardamom, juniper, fennel, mace, lemon grass and caraway essential oils and comparison of antioxidant activity with essential oil composition and it’s change during the process of autooxidation.

EXPERIMENTAL The fresh samples of the essential oils from black pepper (Capsicum nigrum L.), ginger (Zingiber officinale L.), cardamom (Elettaria cardamomum), berries of juniper (Juniperus pinchoti), fennel (Foeniculum officinale), mace ( Myristicia fragans L.) (“Plant Lipids Ltd”, India), lemon grass (Cymbopogon citratus L.)(“Synthite”, India) and seeds of caraway (Carum carvi) (Lionel Hitchen”, the United Kingdom”) have been studied. For evaluation of antioxidant properties of the essential oils 160 μl of trans-2-hexenal and 160 μl of n-dodecane (internal standard) were dissolved in 20 ml of hexane. The solution was divided to 2 ml aliquots in 10 ml glass vessels and 200 μl of the individual essential oil was added in each vessel. The control sample didn’t contain essential oil. Each sample was prepared twice. The samples in the closed vessels were exposed in light at room temperature. Each week the vessels were opened and stream of air was passed through the sample with help of 10 ml pipette. Quantitative content of 2-hexenal was determined by capillary gas chromatography after each 6 – 8 days and the change of the component content in the essential oil composition was fixed when 50 % of initial quantity of aldehyde in each sample has been oxidized. Gas chromatographic analysis of essential oil samples was carried out using chromatograph “Micromat – 412” (“Nordion Instr.”, Finland), equipped with fused silica

Comparative Evaluation of Antioxidant Properties …

105

capillary column SPB-1 (“Supelco”, USA, 35 m x 0.32 mm, phase film thickness 0.25 μm), at temperature programming of column from 60 [o] up to 250 [o]C with a rate 8 [o] / min. Velocity of carrier gas He was 1 ml/ min, temperature of injector and flame-ionization detector - 250 [o]C. Identification of the components in the oil samples was performed using retention index values by its comparison with published [23] or our experimental data. Quantitative content of hexenal and components of the essential oils was calculated using relationship of the peak areas corresponding to the substances and internal standard, which content was accepted equal to 8 μl/ml.

RESULTS AND DISCUSSION For evaluation of antioxidant (AO) activity of the essential oils we used test “aldehyde/ carboxylic acid” [13], which was successively applied for studying of AO activity of volatile extracts from various plants, such as clove, eucalyptus [24] and some kinds of black and green tea [14]. As aldehyde we used trans-2-hexenal, which oxidized to 2-hexenoic acid. The criterion of AO activity was “time of half-oxidation”(THO) of aldehyde, i.e. oxidation time of a half of aldehyde initial quantity. As seen from Figure 1, all essential oils under study possessed the certain AO activities. THO of aldehyde in control solution was 21 days, while the presence in solution of the essential oils to a great extent inhibited the oxidation of aldehyde. The results, presented in Figure 1, demonstrate wide interval of THO values in different oils. In the oil from black pepper, having minimal activity, this value is equal only to 42 days while in the oil from mace it reaches 103 days, i.e. 2.5 times as large. For other essential oils we have obtained intermediary values of aldehyde THO. Thus the series of decreasing AO activity of 8 essential oils may be presented as follows: mace > lemon grass = ginger > fennel = caraway > cardamom = juniper > black pepper As mentioned above biological activity of the essential oils depends on its composition. The changes in the composition of the essential oils during autooxidation may be directly connected with its AO activity. The results presented in the Figures 2 - 9 demonstrate the changes in composition of all essential oils under study during THO of aldehyde in each oil. The main components of essential oil from black pepper are β-caryophyllene, 1,8cineole, limonene and monoterpene hydrocarbons. As seen from Figure 2, we observed significant oxidation of sesquiterpene hydrocarbons, especially β-caryophyllene, and as a result increasing of it’s oxide content. Monoterpene hydrocarbons, except for α-phellandrene, have been oxidized to less extent. However γ-terpinene and α-terpinolene, which are known to be the strong antioxidants, during oil storage time have been completely oxidized. Their initial content in the oil composition was not high; possibly it is a reason for comparatively low AO activity of the essential oil from black pepper (Figure 1).

A. L. Samusenko

106

120 day 100 80 60 40 20 0 1

2

3

4

5

6

7

8

9

Figure 1. Time of half-oxidation (THO) of trans-2-hexenal in various essential oils: 1 – control, 2 – black pepper, 3 – berries of juniper, 4 – cardamom, 5 – seeds of caraway, 6 – fennel, 7 – lemon grass, 8 – ginger, 9 - mace Change of main component content in studied essential oils during autooxidation.

120 % 100 80 60 40 20 0 1

2

3

4

5

6

7

8

Figure 2. Black pepper: 1 - α-pinene, 2 - sabinene, 3 - β-pinene, 4 - limonene + 1,8-cineole, 5 - γterpinene, 6 - α-terpinolene, 7 - β-caryophellene, 8 – myristicine.

The essential oil from ginger is not only food flavoring, but is used in pharmacology. That is why the study of it’s AO properties is of special interest. AO activity of the extracts from ginger has been investigated in Ref. 25, 26. The data obtained by us showed that change of ginger essential oil composition was mainly connected with oxidation of sesquiterpene hydrocarbons (Figure 3). Content of zingiberene, which is the main component of this oil, decreased nearly to 30 times, content of β-sesquiphellandrene and β-besabolene – to 2 times,

Comparative Evaluation of Antioxidant Properties …

107

whereat we observed significant deterioration of oil odor. Degradation of monoterpenes practically did not occur. We suppose that the main antioxidant of ginger essential oil is zingiberene. AO activity of ginger essential oil was lower only than that of the essential oil from mace (Figure 1).

120 % 100 80 60 40 20 0 1

2

3

4

5

6

Figure 3. Ginger: 1 - 1.8-cineole, 2 - α-terpinolene, 3 - zingiberene, 4 - β-bisabolene, 5 - γ-cadinene, 6 β-sesquiterpene.

120 % 100 80 60 40 20 0 1

2

3

4

5

6

7

8

Figure 4. Cardamom: 1 - α- pinene, 2 – sabinene, 3 - β-myrcene, 4 – 1,8-cineole, 5 - γ-terpinene, 6 - αterpinolene, 7 – 4-terpineol, 8 – terpinyl acetate.

A. L. Samusenko

108

120 % 100 80 60 40 20 0 1

2

3

4

5

6

Figure 5. Berries of juniper: 1 - α-pinene, 2 - β-myrcene, 3 – limonene, 4 - γ-terpinene, 5 - αterpinolene, 6 - β-caryophellene.

The results on change of volatile component composition of the essential oils from cardamom and berries of juniper are presented in Figures 4 and 5. The both oils have the same value of aldehyde THO and, therefore, the same AO activity. The content of main components of cardamom essential oil – 1,8-cineole and terpinyl acetate – insignificantly changed during storage time, monoterpene hydrocarbons underwent to oxidative degradation to a lower extent. The content of citrals didn’t practically changed. As it was expected, α-, γterpinenes and α-terpinolene were completely oxidized. These compounds proved to be the antioxidants in cardamom essential oil. The essential oil from berries of juniper had a lot of the same compounds as compared with cardamom oil, but contained much more monoterpene hydrocarbons, the main of which being α-pinene, β-myrcene and limonene. Its oxidation occurred approximately to the same extent, which we observed in cardamom essential oil (Figure 5). Besides that, the oxidation of sesquiterpenes, for instance β-caryophyllene, took a place. It is of interest that total content of α-, γ-terpinenes and α-terpinolene was the same in the both oils. This compounds have the highest AO activity in comparison with other monoterpenes [15]. Considering all these factors it could be explained the same AO activity of the essential oils from cardamom and juniper (Figure 1) by the similar character of its autooxidation during storage. As seen from Figure 6, the main components of fennel essential oil were trans-anethol, fenchone, estragol and limonene. During storage trans-anethol underwent to noticeable oxidation; it partly was oxidized to anise aldehyde and partly transformed in cis-isomer, having toxicity [17]. Because of low content α-, γ-terpinenes and α-terpinolene in fennel essential oil the main antioxidant in this sample was trans-anethol. However, as shown in Ref. 9, it’s AO activity was significantly lower than that of γ-terpinene. It is a possible reason for low value of aldehyde THO in fennel essential oil, which was equal only to 54 days, while in mace essential oil, having a high γ-terpinene content, the value of THO was 2 times as large (Figure 1). As mentioned above, essential oil from mace possessed the highest AO activity as

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compared with all samples studied in this work. This fact may be explained by mace oil composition: besides a high γ-terpinene content, it also has very high content of other monoterpene hydrocarbons, which is 1 – 2 order as large than that in fennel oil. None from strong antioxidants in essential oil from mace (α-, γ-terpinenes, α-terpinolene) has completely oxidized during storage time, which was longer than 3 months (Figure 7). Except for αphellandrene and some minor components, such as β-caryophyllene, the composition of mace essential oil inconsiderably changed. It is necessary to note that source of mace essential oil is a skin of nutmeg, which is characterized by not only a high AO activity, but used in pharmacology due to antimicrobial properties and improvement of glucose and insulin metabolism [27, 28].

120 % 100 80 60 40 20 0 1

2

3

4

5

6

Figure 6. Fennel: 1 - α-pinene, 2 - β-myrcene, 3 – limonen, 4 – fenchon, 5 – estragol, 6 – trans-anethol.

120 % 100 80 60 40 20 0 1

2

3

4

5

6

7

8

9

Figure 7. Mace: 1 - α-pinene, 2 – sabinene, 3 - β-pinene, 4 - α-terpinene, 5 – limonene + 1,8-cineole, 6 - γ- terpinene, 7 - α-terpinolene, 8 – 4-terpineol, 9 – myristicine.

A. L. Samusenko

110

120 % 100 80 60 40 20 0 1

2

3

4

5

6

7

8

Figure 8. Lemon grass: 1 – camphene, 2 – limonene, 3 - γ-terpinene, 4 - α-terpinolene, 5 – linalool, 6 – neral, 7 – geraniol, 8 – geranial.

120 % 100 80 60 40 20 0 1

2

3

4

5

6

7

8

Figure 9. Seeds of caraway: 1 - α-pinene, 2 – sabinene, 3 - β-myrcene, 4 – limonene, 5 - γ-terpinene, 6 – dihydrocarvon, 7 – dihydrocarveol, 8 – carvone.

Figures 8 – 9 demonstrate the change of composition of the essential oils from lemon grass and seeds of caraway. The main components of lemon grass oil were citrals – neral and geranial, content of which considerably decreased during storage time (Figure 8). Oxidation of limonene and linalool has resulted in increasing of epoxylimonene content and appearance of cis- and trans-linalool oxides correspondingly in the oil composition. The content of γterpinene in lemon grass oil was low and it didn’t change. It could be supposed that citrals were the antioxidants in this sample; oxidation of citrals led to deterioration of oil odor. The

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other aldehydes and alcohols, being the components of lemon grass oil – citronellal and decanal, citronellol and geraniol, were also oxidized (Figure 8). The composition of lemon grass oil drastically changed, but AO activity was keeping relatively high. The data obtained by us were in concordance with those of Ref. 8, where high AO activity was revealed for the oils, having a high content of citrals. The main components of caraway seed essential oil were limonene and carvone. Caraway seed oil, as well as fennel, had a medium value of AO activity in series of the oils studied (Figure 1). The composition of this oil slightly changed during storage time. Oxidation of carvone, though not very considerable, allowed to suppose that it was the main antioxidant in this sample. We observed a stronger oxidation of monoterpene hydrocarbons, especially βmyrcene (Figure 9), but its initial quantity in the oil composition was not quite high.

CONCLUSION The comparison of AO activity of the essential oils studied with the change of its composition during autooxidative process has showed that cyclic monoterpene hydrocarbons - α-, γ-terpinenes, α-terpinolene and citrals – neral and geranial were the most prominent antioxidants. High AO activity of the essential oils was also caused by the presence of significant quantity of sesquiterpene hydrocarbons – zingiberen and β-caryophyllene. The essential oil from mace was found to have the highest antioxidant activity while the essential oil from black pepper possessed the lowest one.

REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]

D.W. Reishe, D.A Lillard, R.R. Eitenmiller: Chemistry, Nutrition and Biotechnology ( Eds. C.C.Ahoh & D.B.Min). Marcel Dekker, New York, 1998, p.423. R.S. Farag, M.N. Ali, S.H. Taha: J.Amer.Oil Chem.Soc., 67, 188 (1990). K.P Svoboda, S.G. Deans: Flavour Fragrance J., 7 ( 2), 81 (1992). H.L. Madsen , G. Bertelsen: Trends Food Sci. and Technol., 6, 271 (1995). M. Sawamura: Aroma Research., 1 (1), 14 (2000). K. Platel, K. Shrinivasan: Nahrung., 44 (1), 42 (2000). M.A. Murcia, I. Egea, F. Romojaro, P. Parras, A.M. Jimenez, M. Martinez-TOME: J.Agric.Food Chem., 52 (7), 1872 (2004). G. Sacchetti, S. Maietti, M. Muzzoli, M. Scaglianti, S. Manfredini, M. Radice, R. Bruni: Food Chem., 91, 621 (2005). Т, А. Мisharina, A.N. Polshkov: Prikladnaya Biokhimiya i Mikrobiologiya, 41 (6), 693 (2005) (in Russian). I. Popov, G. Lewin G.: Methods in Enzymology, 300, 437 (1999). M.S. Taga, E.E. Miller, D.E. Pratt: J.Amer.Oil Chem.Soc., 61, 928 (1984). H.S. Choi, H.S. Song, H. Ukeda, M. Sawamura: J.Agric.Food Chem., 48 (9), 4156 (2000). K.G. Lee, T. Shibamoto: J.Agric.Food Chem., 50 (15), 4947 (2002).

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[14] K. Yanagimito, H. Ochi, K.G. Lee, T. SHIBAMOTO: J.Agric.Food Chem., 51 (25), 7396 (2003). [15] G. Ruberto, M. Baratta: Food Chem., 69, 167 (2002). [16] F. Gong, Y.-S. Fung, Y.-Z. Liang: J.Agric.Food Chem., 52 (21), 6378 (2004). [17] S.A. Voitkevitch: Ephirniyi masla dlya parfyumerii i aromaterapii. Pischevaya prom., Moscow, 1999. [18] A. Sivropoulou, E. Papanikolaou, C. Nikolaou, S. Kokkini, T. Lanaras, M. Arsenakis: J.Agric.Food Chem., 44 (5), 1202 (1996). [19] T.A. Мisharina, R.V.Golovnya, I.V. Beletskii: Zhurnal analit. khimii, 54 (2), 219 (1999) (in Russian). [20] N. Gopolakrishnan: J.Agric.Food Chem., 42 (3), 796 (1994). [21] T.A. Мisharina, A.N. Polshkov: Prikladnaya Biokhimiya i Mikrobiologiya, 37 (6), 726 (2001) (in Russian). [22] T.A. Мisharina, A.N. Polshkov, Е.L. Ruchkina, I.B. Мedvedeva: Prikladnaya Biokhimiya i Mikrobiologiya, 39 (3), 353 (2003) (in Russian). [23] W. Jennings, T. Shibamoto: Qualitative Analysis of the Flavor and Fragrance Volatiles by Glass Capillary Gas Chromatography. Acad.Press, New York, 1980. [24] K.G. Lee, T. Shibamoto: Food Chem.Toxicol., 39, 1199 (2001). [25] C.Z. Kelly, O.M.M. Marcia, J.P. Ademir, A.M.M. Angela: J.Supercrit.Fluids, 24, 57 (2002). [26] G.B. Alexander, T.W. Gordon, C. Byung-Soo: J.Supercrit.Fluids, 13, 319 (1998). [27] C.L. Broadhurst, M.M. Polansky, R.A. Anderson: J.Agric.Food Chem., 48 (2), 849 (2000). [28] S.W. Choi, T. OSAWA: Food Biotechnol., 5, 156 (1996).

In: Modern Tendencies in Organic and Bioorganic Chemistry ISBN: 978-1-60456-295-8 Editors: A. Mikitaev, M. K. Ligidov, pp. 113-115 © 2008 Nova Science Publishers, Inc.

Chapter 7

THE POLYMERIC COMPOSITIONS STABILIZED NANODIMENSIONS PHOSPHOR ORGANICALLY BY COMPOUNDS A. Kh. Shaov*, A. N. Teuvazhukova, and A. A. Akezheva Kabardino-Balkarian state university it. H.M.Berbekov, 173 Chernyshevsky St., 360004, Nalchik, Russia

ABSTRACT Technical progress is impossible without wide use polymeric materials in all areas of human activity. Wide circulation of plastic and synthetic pitches it is impossible without giving of necessary stability by him to ageing, i.e. To deterioration of physical and chemical and physical-mechanical properties in process of processing, operation and storage of polymers. In the present work results of researches are given on to definition of stabilizing and modifying influence cyclohexyl phosphonic acids and her potassium the salts having the size of molecules within the limits of 0,097-0,191 нм3 on polyethylene high density (PEHD), as one of most distributed industrial thermoplastics.

Keywords: polymers, compositions, phosphonates, nanodimensions, polyethylene of high density, potassium, stabilization

Studying of processes of ageing and stabilization of polymers is one of the most important and least developed directions of a modern chemical science. Therefore works of complex research on creation of new stabilizers and modifiers get especially big value. The general tendency in the given area of a science are questions of compatibility of antioxidizers with polymers, their influence on coloring of materials, shock durability and adaptability to manufacture, and also development of target additives for concrete types of *

E-mail: [email protected]

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polymeric materials. Mark, that the mechanism of action phosphor organically compounds (FОС) is defined by type of stabilizing substance and conditions of its oxidation. If to consider a problem, in general as stabilizers of polymeric materials against various kinds of ageing use the inorganic and organic connections promoting delay of processes, operational characteristics of polymers resulting in deterioration under action of various factors : light, heat, mechanical loadings, radiation etc. Widely widespread stabilizers of polymeric materials of a various structure and class are connections of phosphorus. The most investigated as stabilizers of polymers among them are connections of trivalent phosphorus. As to stabilizing properties derivative five-valent phosphorus they are investigated not yet full. The majority of polymeric materials at operation contact to oxygen of air i.e. are in the oxidizing environment. Basically all reactions at ageing in natural conditions are characterized oxidizing деструкции and represent radical - chain oxidizing process. This process is activated by various external factors - thermal, radiating, chemical, mechanical. Lately the attention of researchers to acids and salts of five-valent phosphorus that proves to be true sharp increase of number of the publications devoted to synthesis and studying of stabilizing properties of such substances has strongly increased. Modifying and stabilizing influence phosphonate in relation to polymeric materials is investigated to a lesser degree, than others organic derivative the four-co-ordinates phosphorus. In this connection by the purpose of the present work it was put synthesis and research of stabilizing and modifying properties cyclohexyl phosphonic acids and it potassium salts in relation to polythene of high density (PEHD), as to one of the most widespread industrial thermoplastic. More often phosphonates stabilize polyolefins and various copolymers olefins. The results received at research of character of influence organic phosphorus of compounds on physic-mechanical characteristics PEHD in conditions shock test (Table), allow to assert with the big share of reliability, that FOC show plasticization property, that in turn raises values of sizes of mechanical characteristics. It, apparently, is connected by that organic phosphorus of compounds, borrowing free volumes in macro chain and getting in intermolecular "space", the polar groups strengthen intermolecular interaction a little. As confirmation of such assumption that circumstance, that at van-der-waals volume (VW) polyethylene in 20,6 sm3/mol, found on can serve a known technique, the share of free volume (VE) makes 7,6 sm3/mol, and volumes organic phosphorus of compounds – cyclohexyl phosphonic acids, potassium hydrocyclohexyl phosphonate, potassium cyclohexyl phosphonate - are accordingly equal 0,097 нм3, 0,144 нм3, 0,191 нм3. The effect of small additives, probably, is connected by that at such dosages FOC they in the optimum image "find room" in free volume and intermolecular "space" of polymer. Forces of intermolecular interaction "work" on distance about 0,35 нм so our structures are nanosystems typical.

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Physic-mechanical properties of structures on a basis. PEHD and FOC in conditions of shock test No

Structure

1 2 3 4 5 6

PEHD PEHD+ 0,05 % cyclohexyl phosphonic acid - « - + 0,1 % - «- « - + 0,3 % - «- « - + 0,5 % - «PEHD+0,05 % potassium hydrocyclohexyl phosphonate - « - + 0,1 % - «- « - + 0,3 % - «- « - + 0,5 % - «PEHD + 0,05 % potassium hydrocyclohexyl phosphonate - « - + 0,1 % - «- « + 0,3 % - «- « + 0,5 % - «-

7 8 9 10 11 12 13

А, kJ/m2 11,0 19,5 16,3 18,8 20,0 20,0

Е, GPa 1,06 0,82 0,90 0,81 0,87 1,05

21,1 14,1 18,6 17,1 16,5 29,9

ε, % 5,7 9,5 7,6 7,6 8,7 5,1

19,3 15,0 12,1 20,5

0,85 0,82 0,57 0,92

16,0 16,0 18,7 16,0

8,1 7,5 6,9 8,6

19,0 15,5 15,4

0,85 0,91 0,82

18,0 17,3 18,3

7,6 8,4 8,5

σ МPa

REFERENCES [1] [2] [3] [4] [5] [6] [7]

Tager A.A. Fizikohimya of polymers //M.: Chemistry.-1978.-544 p. Kytaigorodsky A.I. The organically of crystal chemistry //M.: USSR of АN. - 1955 558 p. Askadsky A.A. Structure and properties higher termoresystens polymers //M.: Chemistry.-1981.-320 p. Askadsky A.A., Matveev U.I. Chemical a structure and physical properties of polymers.-M.: Chemistry.-1983.-248 p. Barshtein R.S., Kirillovich V.I., Nosovsky U.E. Softener for polymers.-M.: Chtmistry.1982.-200 p. Kozlov P.V., Papkov S.P. Physical and chemical of a basis of plasticization of polymers.-M.: Chemistry.-1982.-224 p. Korbrig D. Phosphorus: Bases of chemistry, biochemistry, technology //M.: Mir-1982.680 p.

In: Modern Tendencies in Organic and Bioorganic Chemistry ISBN: 978-1-60456-295-8 Editors: A. Mikitaev, M. K. Ligidov, pp. 117-120 © 2008 Nova Science Publishers, Inc.

Chapter 8

COMPOSITE MATERIALS FOR ORTOPEDICAL STOMATOLOGY ON THE BASIS OF UTILIZED GLASSY ORGANICALLY* A. Kh. Shaov*, E. M. Kushhov, K. A. Sohrokova Kabardino-Balkarian State University it. H. M. Berbekov 173 Chernyshevsky st., 360004, Nalchik, Russia

ABSTRACT Use of polymers and the polymeric compositions having property polymeryzated at room temperature, in practice orthopedic stomatology allows to reduce the price of process manufacturing of various products, in particular bugles skeletons, the dental prosthetics. The polymeric composition prepares on to basis methylmethakrylate, received at recycling waste products polymethylmethakrylate. A way of manufacturing bugles skeletons on the basis of a polymeric composition from utilized PMMA allows to reduce quantity of stages of multiphasic process (necessity of manufacturing of fireresistant model is excluded at traditional way) and to improve quality of a product. In result we receive essential economy material and time resources, that, undoubtedly, reduces the cost price of process manufacturing bugles a skeleton.

Keywords: recycling, polymethylmetacrylate, composition, orthopedic stomatology, bugles a skeleton.

*

E-mail: [email protected]

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Life of a modern civilized society cannot be presented without wide use of polymeric materials in all areas of human activity. The volume and rates of growth of manufacture of high-molecular connections and composite materials on their basis have reached very much a high level. To the beginning of 21 centuries manufacture of synthetic plastic in the world has reached more than 130 million tons per one year. The ecological situation will depend on rates of the decision of a problem of plastic waste products in the world, so both intensity and directions of development of manufacture of synthetic plastic in the come century substantially. Otherwise people will bury themselves plastic dust. Problem of protection of an environment - one of the major problems of the modernity. Emissions of the industrial enterprises, power systems and transport in an atmosphere, reservoirs and bowels at the present stage of development of a science and engineering have reached such sizes, that in a number of areas, is especial in large industrial centre, levels of pollution in some times exceed allowable sanitary norms. The problem of preservation of the environment is a complex problem and has global character. The further development of mankind is impossible without the complex account of social, ecological, technical, economic, legal and international aspects of a problem as applied not only to a concrete production cycle, but also in scales of regions, the countries and all world. Despite of prescription and a plenty of researches in the field of non-polluting manufacture, the problem of recycling and processing of industrial wastes remains actual till now. Therefore, all has appeared economically, technologically and ecologically proved necessity for development and introduction of new progressive and safe methods of the decision of a problem of disposal of biosphere from danger of its pollution by waste products of manufacture and consumption. The preliminary account and estimation of waste products is necessary for a choice of more rational way of the decision of a problem. The polymeric materials found wide application in various branches of a science and engineering, polymers on a basis acrylic acids are. Many of them are known under the technical name "glassy organically". Glassy organically (acryl) represents a synthetic material from acryl pitches with some interest of the various additives giving to a material certain properties. In the international literature glassy organically it is designated as PMMA. Glassy organically it is applied in the most various areas: lighting engineering (plafonds, partitions, obverse screens); the outdoor advertising (obverse glasses for box, light letters, molded volumetric products); the trading equipment (supports, show-windows, price lists); the sanitary technician (the equipment of bathrooms); construction and architecture (glaze ion apertures, a partition, a dome, a dance-floor, volumetric molded products); transport (glaze ion planes, boats); instrument making (dials, observation ports, cases, dielectric details, capacities). Glassy organically completely can be used repeatedly after his processing. We both have taken advantage of last circumstance, i.e. an opportunity of repeated processing, and have tried from utilized PMMA to create polymeric composite materials which can be used in orthopedic stomatology at manufacturing bugles skeletons and attachments to them during prosthetics.

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More and more becoming tougher requirements to materials, industrial necessity to have molding materials with stable properties which are not present at natural waxes, result in creation similar wax the synthetic materials used for modeling bugles of artificial limbs. It is necessary to note, that manufacturing of a dental artificial limb is many studies process at which it is practically impossible to use standard forms. Work of the doctor and dental engineering is under construction on the basis of the account of specific features of the patient, in particular morphological and functional his characteristic dental jawing systems. Clearly, that wax as too plastic materials, not absolutely precisely can transfer forms at modeling. Received at recycling glassy organically MMA forms a basis for reception of a polymeric composition, polymerization room temperature which further can be used at manufacturing bugles skeletons in practice of orthopedic stomatology. In volume of the present work process chemical hardened, taking place is comprehensively investigated at room temperature (19-220 С), polymeric compositions on a basis methylmetakcylate and polymethylmetacrylate (plays a role filling). On their base for the first time are developed about 40 structures of the polymeric compositions, distinguished by a various mass parity of a hardener and the accelerator of process of polymerization for which time initial polymerization makes 8-30 minutes, impact strength is within the limits of 1,2-7,4 kJ/m2. Efficiency developed bugles skeletons from polymeric compositions is defined by that a way of manufacturing bugles skeletons on the basis of a polymeric composition from utilized polymethylmetacrylate will allow to reduce quantity of stages of multiphase process (is excluded necessity of manufacturing of fire-resistant model at a traditional way) and to improve quality of a product. Finally we receive essential economy of material and time resources, that, naturally, reduces the cost price of process of manufacturing of all bugles a skeleton, so cost of orthopedic service for the patient.

ACKNOWLEDGEMENTS Work is executed with the financial help of Federal Fund of assistance to development of small forms of the enterprises in scientific and technical sphere under the innovational program "Start -2005" (Government contract No4037р/5987 from 25.05.2006).

REFERENCES [1]

[2] [3] [4]

Shaov A.Kh., Kushhov M.I., Kushhov E.M. Polymeric composite materials cold hardened for orthopedic stomatology //Abstr. VI Russian scientific forum “Stomatology 2004”.-2004.-P.194-195. Shaov A.Kh., Kushhov M.I., Begretov M.M. Way of manufacturing bugles a skeleton //Pat. 2245116, Russia (2005) (a priority from 21.07.2003). Kuznetsov E.V., Divgun S.M., Budaryna L.А etc. //The practical work in chemistry and physics polymers.-M.: Chemistry. - 1977.-256 p. Nikolaev A.F. //Synthetic polymers and plastics on their basis.- M.,L.-1966.-768 p.

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V.N.Kopejkin, L.M.Demner. //Dental orthopedic technical.-M.:"Success".-1988.-416 p. A.I.Dojnikov, V.D.Sinitsyn. //Dental technical material-keeping. - M.: Medicine. 1986. - 208 p. [7] Кushhov M.I. New a method of manufacturing bugles a skeleton //Dental technical. 2001. - No1. – P.36. [8] Kalmykov K.V., Кushhov M.I. Way of manufacturing bugles an artificial limb and container attachments //Pat. 2000754, Russia (1993). [9] Garner M.M., Napadov M.A. etc. //Materiology in stomatology. M.,1969. [10] Napadov M.A., Shturman A.A. etc. //Increase of durability and biological indifference of orthopedic designs from acrylic plastic //Stomatology.-1976.-No1. [11] Shaov A.Kh. Reception of polymeric compositions for orthopedic stomatology on the basis of utilized glassy organically //Abstr. of XXVI international conf. and exhibitions “Composite materials in the industry”.-Yalta (Crimea) .-2006.-P. 239-241. [12] Kushhov E.M., Shaov A.Kh. Polymeric of a composition for orthopedic stomatology //Abstr. XVI Russian youth scientific conf., devote to an 85-anniversary from birthday prof. V.P.Kochergin. - Ekaterinburg.-2006. – P.255.

In: Modern Tendencies in Organic and Bioorganic Chemistry ISBN: 978-1-60456-295-8 Editors: A. Mikitaev, M. K. Ligidov, pp. 121-137 © 2008 Nova Science Publishers, Inc.

Chapter 9

A PRELIMINARY STUDY ON ANTIMICROBIAL EDIBLE FILMS FROM PECTIN AND OTHER FOOD HYDROCOLLOIDS BY EXTRUSION METHOD LinShu Liu1,*, Tony Jin1,†, Cheng-Kung Liu1,‡, Kevin Hicks1,§, Amar K. Mohanty2, Rahul Bhardwaj2, and Manjusri Misra3 1

Eastern Regional Research Center, ARS, U.S. Department of Agriculture, Wyndmoor, PA 19038, USA 2 The School of Packaging, 130 Packaging Building, Michigan State Universities, East Lansing, MI 48824, USA 3 Composite Materials and Structure Center, 2100 Engineering Building, Michigan State University, East Lansing, MI 48824, USA

ABSTRACT Antimicrobial Edible films were prepared from natural fiber of pectin and other food hydrocolloids for food packaging or wrapping by extrusion followed by compression or blown film method. Microscopic analysis revealed a well mixed integrated structure of extruded pellets and an even distribution of the synthetic hydrocolloid in the biopolymers. The resultant composite films possess the mechanical properties that are comparable to films cast from most natural hydrocolloids that consumed as foods or components in processed foods. The inclusion of poly(ethylene oxide) alters the textures of the resultant composite films and therefore, demonstrating a new technique for the modification of film properties. The composite films were produced in mild processing conditions, thus, the films are able to protect the bioactivity of the incorporated nisin, as shown by the inhibition of Listeria monocytogenes bacterial growth by a liquid incubation method. *

E-mail: [email protected] E-mail: [email protected] ‡ E-mail: [email protected] § E-mail: [email protected] †

122

LinShu Liu, Tony Jin, Cheng-Kung Liu et al. Keywords: Pectin, antimicrobial, fiber, films, extrusion

INTRODUCTION Pectin is a branched heterogeneous polysaccharide, consisting of 11 monosaccharides and their methyl or acetylated derivatives (Varagen 1996). Pectin is produced by extraction from cell walls of higher plants. The isolated pectin is water soluble. In water solutions or as the commercially available form of powders, pectin macromolecules aggregate each other to form fibers or small particles (Fishman, Jen 1986). Figure 1A shows the AFM imagine of pectin fibers in aqueous solution; the fibers with the size ranging from 100 nm to 400 nm are further associated to form a network. Soluble pectin readily reacts with most natural polymers to form hydrogels. Thus, pectin has a long history in the use as a gelling agent and film forming material (Liu et al. 2003). In the industry, the sources of pectin include citrus peel, sugar beet pulp, apple pomace, sunflower heads, or grape skins, etc. In the U.S., more than 300 thousand tons of pectin are available annually from the byproducts of fruit juice and beet sugar processing. However, only less than 2% of the available pectin is produced and they are mainly consumed as food additives. We have been interested in new utilizations of pectin and other agricultural commodities. In the previous studies, we showed that the blends of pectin with glycerol, and high amylose starch or poly(vinyl alcohol) can be used to produce biodegradable films with a wide range of mechanical properties and excellent oxygen barrier activity (Coffin, Fishman 1993; Coffin et al. 1995; Fishman, Coffin 1995; Fishman et al. 1996; Coffin et al. 1996). We also explored the medical applications of pectin-derived composites by incorporating with bioactive substances (Liu et al. 2003; Liu et al. 2004; Liu et al. 2005a; Liu et al. 2005b; Liu et al. 2006a). Recently, we extended our research to active packaging materials (Liu et al. 2006b; Liu et al. 2007a; Liu et al. 2007b). A series of pectin cast films have been prepared with the inclusion of various food proteins and a bacteriocin and tested for food packaging and wrapping applications, showing improved mechanical properties, water resistant and sustained antimicrobial activity. Extrusion is a cost effective manufacturing process. Extrusion is popularly used in large scale production of food, plastics and composite materials. Most widely used thermoplastics are processed by extrusion method. Many biopolymers and their composite materials with petroleum-based polymers can also be extruded. These include pectin/starch/poly(vinyl alcohol) (Fishman et al. 2004), poly(lactic acid)/sugar beet pulp (Liu et al. 2005c), and starch/poly(hydroxyl ester ether) (Otey et al. 1980), etc. In this study, composite films of pectin, soybean flour protein and an edible synthetic hydrocolloid, poly(ethylene oxide), were extruded using a twin-screw extruder, palletized and then processed into films by compression molding process or blown film extrusion. The films were analyzed for mechanical and structural properties, as well as antimicrobial activity.

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Figure 1. Atomic force microscopic images of pectin (A), soybean flour protein (B) and poly(ethylene oxide) (C). Concentration of solutions: A and B, 100 μg/ml; C 10 μg/ml. Field width: 2.5 μm.

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EXPERIMENTAL Materials Citrus pectin (MexPec 1400) with the molecular weight (M.W.) of 1.8 × 105 dalton and the degree of esterification of 82 and Nisaplin® (2.5% Nisin) were purchased from DaniscoCultor (Kansas City, KS). Soybean flour protein (SFP), poly(ethylene oxide) (PEO, M.W. 900,000), and glycerol (reagent grade, < 99.5%) were obtained from Aldrich Chemical Corp. (Milwaukee, WI).

Preparation Prior to extrusion, dry ingredients of pectin, SFP, glycerol and Nisaplin were blended using a model C-100-T Hobart heavy-duty blender (Hobart Mfg. Co., Troy, OH). The compositions of blends are shown in Table 1. The blends were freeze-dried for 8 h and stored in a plastic bucket covered with lid at 4°C. The premixed pectin, SFP, glycerol were blended with PEO using a Werner & Pfleiderer ZSK-30 twin screw extruder and processed into pellets. This extruder has co-rotating screws (L/D ratio of 30/1) having variable screw profiles throughout its length. The screw speed was 105 rpm, which gave a torque value of 54%. The temperature profile of this extruder from zone 1 to zone 6 was 83, 90, 90, 88, 87, and 86°C. For formulation I, tap water was fed with solids together into the extruder barrel using a series 6300 Digital Feeder at the weight ratio of 19:81, liquid to solid. For formulation II, no water was used. The film blown was processed using a Killion Extruder (Davis Standards Corporation, Troy, OH). The extruder has a bottom fed blown film die. The die has a concentric air opening for film blowing. The air pressure can be controlled with an air valve. The die is also surrounded by an air ring for cooling. The screw rotation was varied between 25-50 rpm. The rotation speed of rollers on the tower was extremely slow to avoid the breaking of the film. The temperature profile of the extruder was also shown in Table 2. Some pellets were ground with the help of Polymer Machinery B.T.P granulator for 5-10 minutes to get powder for film compression processing. A Carver Laboratory press (Fred S. Carver Inc., Summit, NJ) was used for this purpose. The temperatures of upper and lower plates were controlled at 90°C. Composite powders were placed between the 2 metal plates and pressed for 3 minutes under the load of 15000-20000 lbs. Teflon sheet were used between the metal plates to avoid the sticking of the materials to metal plates. Table 1. Compositions of two formulations* Formulations I II

Pectin 50 35

SFP 19 13

* Date expressed as w% of total solid.

PEO 0 30

Glycerol 30 21

Nisaplin® 1 1

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Table 2. Extrusion temperature profiles (°C)

Zone 1 1000

Barrel Zones Zone 2 Zone 3 100 100

Clamp ring 90

Adaptor 85

Die 1 85

Die 2 80

All samples thus obtained were stored in a desiccator over CaCl2 at room temperature for structural and mechanical examinations.

Microscopic Analysis Confocal laser scanning microscopy. A laser scanning confocal microscope system was used to analyze the microstructure of the film components and films. A model IRBE (inverted) microscope (Leica Microsystems, Bannockburn, IL) with a universal stage and 20X objective lens was coupled to a TCS NT/SP scanner head (Leica Microsystems, Exton, PA). Sheets of samples or powders in MatTek dishes (MatTek Corp., Ashland, MA) were illuminated with the 488 nm line of an Argon laser and fluorescence was collected in one channel (520-580 nm) and reflection at 488 nm was collected in another. Fluorescence emission spectra for the sample powders of SFP and Pectin were collected in the range of 500-680 nm. Atomic force microscope (AFM). Sample solutions at 100 ng/ml or less were cemented onto mica and imaged in a model Nanoscope IIIa scanning probe microscope with TESP cantilevers (Veeco/Digital Instruments, Santa Barbara, CA) operated in the intermittent contact mode on an atomic force microscope. Scanning electron microscopy. A Quanta 200 FEG scanning electronic microscope (SEM, FEI, Hillsboro, OR) was used to collect images. Prior to examination, samples were mounted to specimen stubs and sputtered with a thin layer of gold. Samples were examined in the high vacuum/secondary electron imaging model at 5,000X and 50,000X.

Dynamic Mechanical Analysis (DMA) Small deformation dynamic mechanical analysis on compressed or blown films was done using a Rheometrics Scientific RSA II Solids Analyzer. Samples were tested using an initial applied force of 150 grams, an applied strain of 0.1%, and were heated from -100oC to 200oC at 10oC/min. A triplicate set of tests were performed for each samples

Tensile Test and Acoustic Emission (AE) The mechanical property and AE measurements were performed as previously described (Liu et al. 2005). An upgraded Instron mechanical property tester, model 1122, and Testworks 4 data acquisition software (MTS Systems Corp., Minneapolis, MN) were used throughout this investigation. The strain rate was set at 50 mm/min. Date of tensile strength,

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Young’s modulus, and fracture energy was collected. The tensile tester was also programmed to perform a cyclic test. Samples were repeatedly stretched to 2 % strain at 50 mm/min and back to 0% strain. A total of 5 cycles were tested and the peak stress was recorded for each cycle. AE measurement was performed simultaneously with the stress-strain tests. A small piezoelectric transducer (Model R15, Physical Acoustics Corp., Princeton, NJ) was clipped against the samples. AE signals emanating from this transducer when the Instron stretched samples were processed with an upgraded LOCAN-AT acoustic emission analyzer (Physical Acoustics Corp.), which connected to a PC base with enhanced graphing and data acquisition software with all features and options of the SPARTAN 2000.

Bacterial Inhibition Test Pathogenic bacteria Listeria monocytogenes Scott A 724 was obtained from the in house culture collection. Stock cultures of L. monocytogenes were maintained at -80ºC in BHI medium (Difco Laboratory, Detroit, MI). Working Cultures of L. monocytogenes were maintained on BHI agar at 4 ºC and were sub-cultured bi-weekly and grown aerobically at 37ºC in BHI broth. Prior to inoculation of product the organism was cultured in BHI broth at 37ºC for 16-18 h. Bacterial inhibition by the antimicrobial films was evaluated using a liquid incubation method, 4 pieces of films (1 cm2 each) were placed in a glass test tube with 9 ml BHI broth inoculated with 1 ml L.monocucytogenes overnight culture. The test tubes then placed in a shaker (Innovas 3100, New Brunswick Sci. Inc., Edison, NJ) at room temperature and shaken at 200 rpm. One ml of inoculated sample was taken at 0, 8, 24, and 48 h. The samples were serially diluted by sterile phosphate buffer (Hardy Diagnostics, Santa Maria, CA), then pour plated onto BHI agar. Plates were incubated at 37ºC for 24 h. A film-free inoculated BHI broth served as a control. Plates with 30-300 colonies were enumerated using a manual colony counter (Bantex Colony Counter 920; Bantex, Burlingame, CA).

RESULTS AND DISCUSSION Characterization of raw materials for films was firstly conducted on the three ingredients and their blends. Figure 1 shows the AFM images of pectin, SFP and PEO in diluted solutions. The three macromolecules were in the form of fibers in the size ranging from 100 nm to 10 μm. The fibers associated each other. Both the pectin and SFP have intrinsic fluorescence emission (Figure 2A, B) and show a similar profile in their fluorescence spectra (Figure 2C), except that the protein has a narrow maximal intensive peak at around 530 nm, the pectin has a broad peak extended from 530 to 550 nm. Furthermore, the autofluorescence of protein is stronger than that from pectin. PEO doesn’t emit fluorescently, PEO can be detected by reflection (Figure 2D). The differences of the ingredients in photoemission were used to probe the microstructure of resultant composite films. Figure 3 reveals the homogeneity of extruded pellets. After processing, we are still able to identify specific regions that consist of pectin or SFP alone. Each of these regions stretched

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about 10 μm in width; between the two regions of interest there was a well mixing area, which also sized at about 10 μm. The florescent emission from the mixed area reflects the profiles of each spectrum of the two single biopolymers. Figure 4 shows the microscopic images of one of the final products, compression film of formulation II, obtained by confocal reflection and confocal fluorescence in stereo projection. The red area correlated with PEO reflection; the green area correlated with the pectin and protein. The image indicates a well mixed integrated structure, showing an even distribution of the synthetic hydrocolloid in the biopolymers.

Figure 2. Confocal laser scanning microscopic image: (A) fluorescence of pectin, (B) fluorescence of soybean flour protein, (C) fluorescence spectra of pectin and soybean flour protein, and (D) reflection of poly(ethylene oxide). Field width: A, B and D, 480 μm.

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Figure 3. Structure analysis of extruded pellets: Region I (X) colored with green, indicating more pectin component in the area; regions II (∆) colored with yellow, indicating there is more soybean flour protein; regions III (○) colored with brown, indicating the well mixing areas. Field width, 550 μm.

Small deformation dynamic mechanical analysis is a well known method used as a complement for microscopic examination in material structure study. Figure 5 comprises of DMA curves for samples prepared by compression method from formulations I (PEO-free, Figure 5A), formulation II (PEO included, Figure 5B) and PEO alone (Figure 5C). Two significant differences were seen between the samples. One is the location of the sub-ambient glass transition temperature. This is seen at -55oC in sample of formulation I and at -69oC in sample of formulation II. The other is that samples with PEO shows a melting behavior at about 64oC, while a melting behavior is not seen in the PEO-free samples until about 145oC. These differences are certainly due to the presence of the PEO which has a melting point of 57oC. The PEO-free samples also have a transition at 34oC which is probably related to the protein in the sample.

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Figure 4. Confocal laser scanning microimages of compression film from formulation II. The organization of the biopolymers were resolved by confocal fluorescence (excitation 484 nm, emission 520-580 nm), the PEO was defined by confocal reflection (633 nm). The micrograph was collected in stereo projection in extended focus images of 20-30 micrometer-thick slabs of the film. Field width, 470 μm.

Mechanical properties of tensile strength, Young’s modulus, elongation at break and toughness are important for packaging and wrapping materials. In a variety of end uses, packaging and wrapping materials are often subjected to a force during tensile strain. The materials must be able to resist considerable stress without failing to a fracture at a designed stress. Furthermore, as an edible food wrapping materials, the materials may be taken with foods together either for convenient purpose or to enhance or alter the food texture. In these cases, their mechanical properties directly related to the mouth feeling of accepters, which is an important measurement of food quality. Table 3 shows the mechanical properties of selected samples of compression and blown films. In general, the composite films have mechanical properties that are similar to cast films from most natural hydrocolloids, which consumed in our ordinary life (Liu et al. 2006a). For compression films, the addition of PEO almost doubled the Young’s modulus, which is an indication of stiffness; but only had a minor impact on the tensile strength, maximal elongation, and toughness. In comparison of blown film with compression films with same composition, the blown films seemed to be stiffer, but they were not as strong as the films prepared by compression method. Moreover,

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the replacement of SFP with PSG dramatically enhanced the mechanical properties of the composite films (Table 3). The results of the stress-strain cyclic tests are shown in Figure 6. For the PEO-free samples, the loop created by the first cycle is bigger than those created by following cycles. Among the following cycles, the different in loop size is not significant. For samples containing PEO, the size of loop decreased gradually as cycled, then, became constant in the last two cycles. At the end of the cyclic test, the PEO containing sample expressed a much higher stress than the PEO-free sample. Although the PEO free samples are more resistant to mechanical force and less permanent deformation occurred than the PEOincluded sample; the inclusion of PEO strengthens the composite films.

Figure 5. Continued on next page.

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Figure 5. Dynamic Mechanical Analysis of composites containing with PEO (A) or without PEO (B) and PEO alone (C). The PEO-free samples show a melting point at about 145 °C; while, both the PEO alone samples and PEO-included samples a melting behavior at about 64 °C.

Figure 6. Continued on next page.

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Figure 6. Stress-strain curves obtained from cyclic tensile tests. Samples of soybean flour protein and pectin containing without PEO (A) and with PEO (B). For the PEO free films, the loop created in the first cycle is larger than following cycles. For the PEO included films, the size of loops gradually decreased as cycled, then became constant in the last two cycles.

The addition of PEO has an influence on film destruction caused by an external destructive force (Figure 7). Without PEO, the external force created a clear-cut fracture surface, indicating the good adhesion between the two biopolymers. With the inclusion of PEO, the deformation created a fibrous surface. This can be seen more clearly from SEM and fluorescent microscopy. As shown in Figure 8 A and B, fibers were pulled out, extended, and then, broken, but still embedded in the matrix phase. We examine the fibers with confocal reflection and confocal fluorescence in two channels. It confirms that the main component of the fibers is PEO; however, the biopolymers were either inserted or encapsulated within the fibers (Figure 8C). Table 3. Mechanical properties Samples, processing method I, compression I-b, compression* II, compression II, blown

Tensile strength (MPa) 2.35 ± 0.09 8.8 ± 0.3 3.1 ± 0.8 2.3 ± 0.3

Elongation at break (%) 6.14 ± 0.6 13.1 ± 2.0 7.3 ± 1.5 2.8 ± 0.3

* I-b, PSG was used to replace SFP in this composite film.

Young’s modulus (MPa) 77.2 ± 4.49 353.4 ± 26.9 125.2 ± 25.3 151.2 ± 20.8

Toughness (J/cm3) 0.16 ± 0.08 0.90 ± 0.12 0.20 ± 0.07 0.03 ± 0.01

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Figure 7. Photographs of fractural surfaces of samples of PEO-Free (a and b) and PEO-included composite films (c and d).

To probe the structural changes of a composite film that subjected to a destructive force, we measured the AE event simultaneously with the tensile test. Figure 9 shows the correlation between the stress-strain curve and the AE hit pattern. For the PEO-free samples, AE activity detected only at the peak stress, when the samples were completely destructed. This confirms the homogeneity of the composite films. Since the two biopolymers are compatible, they are able to transfer stress evenly. For the samples containing with PEO, the phenomena are similar, the samples emitted sound at the peak stress; however, signals were continually collected as the PEO fiber were pulled and broken, being consistent with the results shown in Figures 7 and 8.

Figure 8. Microscopic images of the fractural surfaces of PEO-included composite samples obtained by scanning electron microscope (left), laser microscope (middle), and confocal laser scanning microscope in confocal fluorescence and confocal reflection two channels (right). Field width: 520 μm (left) and 480 μm (middle and right).

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Figure 9. Correlation between Stress-strain curves and AE patterns of PEO-free samples (A) and the samples containing with PEO (B).

In the colorful family of food packaging and wrapping materials, antimicrobial film is a new member. Besides providing a physical barrel, the films function in prohibition, protection and suppression of microbial migration to or growth in the packages by creating antimicrobial surfaces or releasing antimicrobial substances. The use of antimicrobial materials in food packaging improves food safety and is more convenient to the consumers; therefore, the

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market for antimicrobial food packaging has a fast growth (Cutter 2006; Ozdemir, Floros 2004). In the present study, we incorporated an antimicrobial polypeptide, nisin, into the film formulation. The antimicrobial activity of resultant films is shown in Figure 10. Nisin alone was firstly tested for stability and the results were compared to that treated in the conditions as same as film compression. No statistically significant differences could be detected. Then, we compared the activity of nisin incorporated in blown films and compression films with that of non-treated nisin. As shown in Figure 9, the non-treated nisin was little more active than that formulated in pectin films at the fist 24 hours; however, the difference disappeared in 48 hours incubation. This result indicates that the extrusion conditions applied in the current experiments are mild and not harmful to nisin. Thus, the resultant composite films are able to retain nisin activity.

CONCLUSION The current study provides a new type of edible, antimicrobial food packaging or wrapping films from food-grade natural fibers or hydrocolloid. Besides film casting, the films can also be produced by compression, extrusion blown methods. The inclusion of PEO hydrocolloid in natural fiber formulations makes films tougher and caused less permanent deformation when the films were subjected to an external force. Since the extrusion and compression were performed in mild conditions, nisin can be incorporated into films without diminishing its antimicrobial activity.

Figure 10. Growth of Listeria monocytogenes in BHI broth at 24 °C. Control (diamond), nisaplin prior to extrusion (square), nisaplin post extrusion (circle), nisaplin in compress film (up triangle), and nisaplin in blown film (down triangle).

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ACKNOWLEDGMENTS Authors acknowledge Dr. Peter H. Cooke, Mr. Nicholas Latona, Ms. Guo-ping Bao, Dr. David R. Coffin and Dr. Vitoria L. Finkensdadt for their technical assistant.

REFERENCES Coffin, D. R., Fishman, M. L. 1993. Viscoelastic Properties of Pectin/Starch Blends. Journal of Agricultural and Food Chemistry, Vol. 41, pp. 1192-1197. Coffin, D. R., Fishman, M. L. Cooke, P. H. 1995. Mechanical and Microstructural Properties of pectin/Starch Films. Journal of Agricultural and Food Chemistry, Vol. 57, pp. 663670. Coffin, D. R., Fishman, M. L., Ly, T.V. 1996. Thermomechanical Properties of Blends of Pectin and Poly(vinyl alcohol). Journal of Applied Polymer Science, Vol. 61, 663-670. Cutter, C. N. 2006. Opportunities for Bio-Based Packaging Technologies to Improve the Quality and Safety of Fresh and Further Processed Muscle Foods. Meat Science, Vol. 74, 131-142. Fishman, M. L., Coffin, D. R. 1995. Films Fabricated form Mixtures of Pectin and Starch. US Patent 5,451,673. Fishman, M. L., Jen, J. J. 1986. Chemistry and Function of Pectins. ACS Series 310, American Chemical Society press, Washington D.C. Fishman, M. L., Coffin, D. R., Unruh, J. J., Ly, T. 1996. Pectin/Starch/Glycerol Films: Blends or Composites. Journal of Macromolecular Science: Pure and Applied Chemistry, Vol. A33, pp. 639-654. Fishman, M. L., Coffin, D. R., Onwulata, C. I., Konstance, R. P. 2004. Extrusion of Pectin and Glycerol with Various Combinations of Orange Albedo and Starch. Carbohydrate Polymers, Vol. 57, pp. 401-413. Liu, L. S., Fishman, M. L., Kost, J., Hicks, K. B. 2003. Pectin-Based Systems for ColonSpecific Drug Delivery via Oral Route. Biomaterials, Vol. 24, 3333-3343.doi: Liu, L. S.; Won, Y.-J.; Cooke, P. H., Coffin, D. R., Fishman, M. L., Hicks, B. K., Ma, P. X. 2004. Pectin/Poly(lactide-co-glycolide) Composite Matrices for Biomedical Applications. Biomaterials, Vol. 25, pp. 3201-3210. Liu, L. S., Chen, G., Fishman, M. L., Hicks, K. B. 2005a. Pectin Gel Vehicles for Controlled Fragrance Delivery. Drug Delivery, Vol. 12, pp. 149-157. Liu, L. S., Fishman, M. L., Hicks, K. B., Kende, M. 2005b. Interaction of Various pectin Formulations with Porcine Colonic Tissues. Biomaterials, Vol. 26, pp. 5907-5916. Liu, L. S., Fishman, M. L., Hicks, K. B., Liu, C.-K. 2005c. Biodegradable Composites from Sugar Beet Pulp and Poly(lactic acid). Journal of Agricultural and Food Chemistry, Vol. 53, No. 23, pp. 9017-9022.doi:10.1021/jf058083w. Liu, L. S., Fishman, M. L., Hicks, K. B., Kende, M., Ruthel, G. 2006a. Pectin/Zein Beads for Potential Colon-Specific Drug Delivery: Synthesis and in vitro Evaluation 13:417-423. Liu, L. S., Liu, C.-K., Finkenstadt, V. L., Jin, T. Z., Fishman, M. L., Hicks, K. B. 2006b. Pectin Films for Various Applications. Proceedings of the 35th United States – Japan Cooperative Program in Natural Resources PR31-34.

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Liu, L. S., Finkenstadt, V. L., Liu, C.-K., Jin, T. Z., Fishman, M. L., Hicks, K. B. 2007a. Preparation of Poly(Lactic acid) and Pectin Composite Films for Application in Antimicrobial Packaging. Journal of Applied Polymer Science, in press. Liu, L. S., Liu, C.-K., Fishman, M. L., Hicks, K. B. 2007b. Composite Films from Pectin and Fish Skin Gelatin or Soybean Flour Protein. Journal of Agricultural and Food Chemistry, 55(6), 2349-2355. doi: 10.1021/jf062612u. Otey, F. H., Westhoff, R. P., Doane, W. M. 1980. Starch-Based Blown Films. Industrial Engineering Chemical Products Research and Development, Vol. 19, pp. 592-595. Ozdemir, M., Floros, J. H. 2004. Active Food Packaging Technologies Critical Reviews in Food and Nutrition, Vol. 44, pp. 185-193. Voragen, A. G. J. 1996. Pectin and Pectinases. Elsevier Science Publisher, New York, NY.

In: Modern Tendencies in Organic and Bioorganic Chemistry ISBN: 978-1-60456-295-8 Editors: A. Mikitaev, M. K. Ligidov, pp. 139-146 © 2008 Nova Science Publishers, Inc.

Chapter 10

CONTROLLED RELEASE OF THE ANTISEPTIC FROM POLY(3-HYDROXYBUTYRATE) FILMS. COMBINATION OF DIFFUSION AND ZERO-ORDER KINETICS R. Yu. Kosenko1, Yu. N. Pankova1, A. L. Iordanskii1,*, and G. E. Zaikov2 1

Semenov’s Institute of Chemical Physics. 4 Kosygin str., B-334, Moscow 119991, Russia 2 Emanuel’s Institute of Biochemical Physics. 4 Kosygin str., B-334, Moscow 119991, Russia

ABSTRACT The modeling polymer system based on biocompatible and biodegradable poly (3hydroxybutyrate) [PHB] and antiseptic (5- nitrofurfuryliden semicarbazone) [Fr] has been devised. The system PHB - Fr is potentially destined for study of drug controlled release from degradable matrices. Release kinetics from membranes of PHB loaded by 0, 5 – 5, 0 wt % Fr into aqueous media have been investigated by UV spectroscopy technique at 25oC. Profiles of the release comprise diffusion and kinetic impacts. Diffusion component of the release has been analyzed and diffusivity dependence on the drug concentrations has been determined. Kinetics constants of release are directly related with hydrolytic destruction of PHB and dependence on initial concentration of the drug. The destruction of PHB is clearly demonstrated at long-term experiments (after first week of release). These results are required for further elaboration of novel drug delivery systems including a combination of several drugs that will give combined action on tissues and organs in biological systems.

*

E-mail: [email protected]

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INTRODUCTION A dramatic rise of the cost for liquid and gaseous hydrocarbons stimulates development of novel biopolymers which production is not depended on fossil fuels. Fermentative biosynthesis of poly(3-hydroxybutyrate) [PHB] and its homologues – poly(3hydroxyalkonoates) [PHAs] bases on using renewable organic substrates. Hydrocarbons’ wastes of food- and wine/juice industries (sugars, melissa, starch et al.) present the basic “structural material” for bacterial PHB (and PHA). Utilization of hydrocarbons during biosynthesis of PHA is favorable to eco-efficiency. In the last decade, PHB and its copolymers begin productively to use in medicine. For example, the composites of PHB are master of high biocompatibility with bone tissues that allows using such composites as bioresorbable osteo implants [1]. The modified PHB works as high effective scaffold in tissue engineering and promotes proliferation, adhesion, and production of cells [2,3]. The PHB materials [4] have good hemocompatibility. Authors [5] have reported that, under blood contact, surfaces of PHB and PHBcoHV films do not activate hemostatic changes on the cell-level. The great progress for poly(4-hydroxybutyrate) [P4HB] is observed in cardio implantation [6]. The artificial heart valves are produced by stereolithography [7] with P4HB and controlled by x-ray tomography. They have demonstrated a relevant combination of mechanical properties and hemocompatibility [8]. In [9] the stent fabrication based on PHB is described. By this means, PHB and its derivatives can be considered as a novel perspective medical materials for tissue engineering [10], design of osteoprostheses with progressive replacement of biodegradable material by germinated bone tissues [11], and hemocompatible coatings for cardiovascular surgery [12]. In framework of this paper it should be emphasize especially that there is a further area of PHB application : design of matrices, reservoirs, and micro/nanoparticles for controlled drug release [13 – 15]. In this case, information on biocompatibility, rate of resorption and diffusion characteristics of the polymer systems is required. On this basis the object of this paper is design and study of therapeutical PHB system loaded by the antiseptic (furacelin), and destined for drug release into modeling aqueous media. Recently [16] we have shown that water diffusion in the PHB films with 100 µm thick was completed in several tens of minutes, whereupon the films absorbed the limiting equilibrium concentration of water (ca. 1 wt %). Structural relaxation in PHB under humid conditions is finished in longer period of time (nearly 1000 minutes). We have investigated kinetics of release for several tens of days, therefore, to a first approximation, a water transport phenomenon in PHB is not essential. However, long-term kinetics of drug release from PHB films has an intricate form and demands special analysis for both diffusion modeling and drug delivery application.

EXPERIMENTAL PART We used PHB supplied by the company “Biomer” (Krailing Germany) : Lot F16. Initial powder of PHB was solved in chloroform under long-term boiling. Hot polymer solution was filtered and after filtration, molecular weight of PHB was determined by viscosimetry technique in accordance with procedure desribed in [17]. Averaged value of Mw is 183.5×103

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g/mol. As aseptic drug we used furacilin (Fr) (MW = 198 g/mol) qualified as Medical grade and with general formula of 5- nitrofurfuryliden semicarbazone:

Basic characteristics of the polymer include density = 1,25 g/cm3; Tm = 178oC; Tg = 9 o C; crystallinity degree = 70% (determined by WAXS data). Films of PHB containing Fr were prepared by two different methods: 1-stage procedure. 1g of the polymer powder was mixed with 50 ml of chloroform and boiled in retort with reverse glass refrigerator. After heating, saturated solution of Fr was added. The mixture was allowed to cool down till room temperature and then cast on glass surface for slow removal of solvent. 2-stage procedure. 1g of powder was mixed with 50 ml of 1,4-dioxane and boiled in retort with reverse glass refrigerator as well. Then after cooling and the removal of 1,4dioxane by the vacuum pump, the PHB and Fr were solved in chloroform and procedure looked like 1st stage operation. Thickness of cast PHB films varied from 120±10 µm to 180±15 µm and concentration of loaded Fr changed in the set 0,5; 1,0; 1,5; 1,75; 2,0; 3,0 и 5,0 wt % . The drug release profiles of PHB were registered in water and phosphate buffer (pH = 7.4) by UV technique with UV spectrophotometer Beckman DU65 at 25 oC.

RESULTS AND DISCUSSION The typical kinetic profiles of Fr release from PHB films are illustrated in Figure 1. As is clear from the graph, for PHB release systems loaded by the drug at the concentrations exceeding 1% there are no constant limiting values of equilibrium concentration that would be typical for Fick-law diffusion picture. These kinetic curves are characterized by initial nonlinear range and final range where the drug release profile is linear relative to time (zero-order kinetics). Analyze of data in Figure 1. gives ground to expect that the superposition of the proper diffusion and a linear kinetic process defines the complicated character of release. Most clearly the linear ranges are manifested after completion of drug diffusion and observed for last 8 – 10 days. Based on aforesaid, the release profile is described by the following equation ∂Ct/∂t = D[∂2Ct/∂x2] + k ,

(1)

where D is drug diffusion coefficient, cm2/sec; k is kinetic constant of hydrolytic destruction, sec-1; Ct is drug concentration in the polymer; wt %, x (cm) and t (sec) are coordinate and time of diffusion respectively. After subtraction of linear impact on the profile of release (k·t) from the integral values of concentration Сt Сt – kt ≡ Gt ,

(2)

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142 0,45

5

0,40 0,35 0,30

3

Dt

0,25 0,20 0,15

1

0,10 0,05 0,00 0

5

10

15

20

25

30

time, days Figure 1. Kinetic profiles of aseptic release. The figures show the initial concentrations of the drug (% wt) ; Dt is optical density of the dug in liquid medium at 373 nm.

the equation 1 takes a traditional diffusion form ∂Gt/∂t = D[∂2Gt/∂x2]

(3)

Numerical subtraction of linear contribution in release kinetics from total concentration of the drug (shown in Figure 1) has been performed for separation of the diffusion and kinetic impacts. The solution of Eq 3 for plane sheet diffusion and small times (i.e. under condition 0 < Gt/Goo < 0.60) has the classical form Gt/Goo ≈ 4/π2(D·t/L2)0,5,

(4)

where L is the film thickness, cm; Gt and Goo are concentrations of the drug being available for diffusion and determined by eq.2 at any time t or t → ∞ respectively. Finding the slop of linear part of the curves on Figure 2 in coordinates Gt/Goo - t0,5 and solving this equation graphically, we can calculate the diffusion coefficients of Fr in the PHB films. We emphasize two features of drug release profiles : 1) the linear character of data in the above diffusion coordinates holds within limits 0 < Gt/Goo < 0.65 that attests a predominance of diffusion in initial stage of release; 2) the slope of lines in the same coordinates depends on the initial concentration of the drug that demonstrates the dependence of diffusivity on drug concentration. Limiting (equilibrium) values of the drug (Goo) dissolved in the PHB films are needed for construction of the curves in Figure 3. Additionally, these values show the portion of the drug taking part in molecular diffusion.

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1

1,0

2

3

0,8

Gt/Goo

3 0,6

5 0,4

0,2

0,0 0

5

10

15

20

25 1/2

30

35

40

1/2

(Time) , (h)

Figure 2. Impact of diffusion in total drug release kinetics for PHB films (thickness = 180 mkm). Initial concentration of the aseptic are 1 : 1,75%; 2 : 2,5%; 3 : 3%; 5 : 5 wt. %.

Mobile fraction of furaciline, % wt

3,0

2,5

2,0

1,5

1,0

0,5

0,0 0

1

2

3

4

5

Total furaciline concentration, % Figure 3. Relation between loaded (total) and mobile (Goo) concentrations of the drug in films of PHB.

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2

Drug diffusion coefficient*10 , cm /s

1,6

10

1,2

0,8

0,4

0,0 0,0

0,5

1,0

1,5

2,0

2,5

3,0

Aseptic concentration, % wt. Figure 4. Diffusivity dependence on mobile fraction of antiseptic concentration in drug release process.

The impact of initially loaded concentration of Fr sorption on equilibrium drug sorption is shown in the Figure 3. From this Figure it follows that till 3 wt % both concentrations are related by the linear function. The deviation from the linearity is observed at maximal concentration (5 wt %) of the loaded Fr. At this point the drug forms its proper phase in the polymer that looks as yellow crystals, while the effect of phase formation does not distort the general manner of kinetic curve (compare in Figure 2, curve3 for 3% and curve 5 for 5%). Summarizing results presented in Figures 1 and 2 we can estimate effective diffusion coefficients for all initial concentrations of the drug. Figure 4 shows the concentration dependence of diffusivities (D) on mobile fraction of the drug (Goo) which has maximum defined clearly in the drug concentration area 1.0 – 1.5 wt %. The rising branch of the curve D(C) results likely from disordering of the PHB structure after drug loading. In contrast, the dropping branch is related with the drug crystal formation in the PHB matrix that bring to the decrease of low-molecular-weight component mobility. The formation of Fr crystals in PHB has been observed recently in our work by Krivandin with WAXS technique [18]. Above we have mentioned that simultaneously with diffusion kinetics the linear kinetic process of Fr release is observed. In this case, the greater initial concentration of loaded drug, the higher is the constant rate of drug release. More informatively this effect is shown in Figure 5, where the exponential dependence of degradation constant (k) on drug concentration is observed. Simultaneously with measurement of the concentration in the drug desorbing from films PHB we have determined the loss of weight for the polymer samples. Gravimetric measurements shown that the polymer sample loses its weight in accordance with the linear low as well. Initial polymer with no content of the drug has the stable weight

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for all time of release. Preliminary experiments show that, in contrast to enzymatic biodegradation of PHB going on the polymer surface [19], hydrolytic destruction involves all accessible volume of PHB that supported by the increase in brittleness and the decrease in the strength of PHB films.

CONCLUSION We suggested a polymer system for aseptic controlled release that includes films of PHB and furaciline. The release goes on simultaneously in accordance with kinetic (polymer degradation) and diffusion mechanism. The rates of kinetic mode for release obey a zero degree curves relative to time. The diffusion mode which determines the profiles of release in the initial range of time (about a first week) were analyzed in more detail. The dependences of both diffusion coefficients (D) and kinetic constant (k) of release on the drug concentrations were demonstrated. These results are requisite for further development of the drug release systems with multicomponent action when several drugs simultaneously have a local action on biological tissues and cells.

3

Destruction constant of PHB film x10 , g/cm /h

7

2

6 5 4 3 2 1 0 1

2

3

4

5

Initial drug concentration, wt % Figure 5. Dependence of release destruction constant (k) on loaded drug concentration for PHB films.

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REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17]

[18]

[19]

C. Doyle, E.T. Tanner, and W. Bonfield. Biomaterials. 12, 841 – 847 (1991). S.G. Hu, C.H. Jou, and M.C. Yang. Carbohydr.Polym. 58, 173 – 179 (2004). S.G. Hu, C.H. Jou, and M.C. Yang. Biomaterials .24, 2685 – 2693 (2003). G.X. Cheng, Z.J. Cai, and L.Wang. J. Mater. Sci. 14, 1073 – 1078 (2003). V.I.Sevastianov, N.V.Perova, E.I. Shishatskaya, G.S.Kalacheva, T.G. Volova. J.Biomater Sci. Polymer Ed. 14, 1029 – 1042 (2003). D.P.Martin and S.F. Williams. Biochem Eng. J. 16, 97 – 105 (2003). R. Sodian, M.Loebe, A.Hein, D.P.Martin, S.P. Hoerstrup, E.V.Potapov et al. ASAIO J. 48, 12 – 16 (2002). R.Sodian, S.P. Hoerstrup, J.S. Sperling, et al. Ann. Thorac. Surg. 70, 140 – 144 (2000). M.Unverdorben, A.Spielberger, A. Schywalsky et al. Cardiovasc. Intervent. Radiol. 25, 127 – 132, (2002). G.T. Köse, S.Ber, F.Korkusuz, et al. Biomaterials .24, 4998 – 5007 (2003). L.J.Chen and M.Wang. Biomaterials .23, 2631 – 2639 (2002). G.-Q. Chen and Q.Wu. Biomaterials .26, №33, 6565 – 6578 (2005). D.P.Martin, F.Skraly, and S.F. Williams. US Patent 403242 2003. C.W.Pouton and S. Akhtar. Adv.Drug.Deliver. Rev. .18, 133 – 162 (1996). D.Sendil, I.Gürsel, D.L.Wise, and V.Hasirci. J.Controlled Release 59, 207 – 217 (1999). A.L.Iordanskii, P.P.Kamaev J.Macrom.Chem. (Rus) V.41, Ser.B. #1-2, 39-43 (1999). R. H Marchessault, K. Okamura,., C.J Su. Physical properties of poly(βhydroxybutyrate). II. Conformational Aspects in Solution. // Macromolecules. 1970. V.3. №6. 735-740. Shatalova, A.V.Krivandin, and A.L. Iordanskii. 6th European Symposium on Polymer Blends. Program and Abstracts. May 16-19, 1999 Max-Planck-Institut fur Polymerforschung. Mainz, PC90, p.69. Germany. X-ray diffraction study of films prepared from polyethylene-poly(3-hydroxybutyrate) blends. Tamao Hisano, Ken-ichi Kasuya , Yoko Tezuka , Nariaki Ishii , Teruyuki Kobayash , Mari Shiraki , Emin Oroudjev , Helen Hansma , Tadahisa Iwata , Yoshiharu Doi , Terumi Saito and Kunio Miki . Journal of Molecular Biology V356, #4 , 993-1004 (2006).

In: Modern Tendencies in Organic and Bioorganic Chemistry ISBN: 978-1-60456-295-8 Editors: A. Mikitaev, M. K. Ligidov, pp. 147-150 © 2008 Nova Science Publishers, Inc.

Chapter 11

PHOTO COMPOSITES ON THE BASE OF POLYMERMONOMER COMBINED SYSTEM, MODIFIED BY OLIGOMERS N. V. Sidorenko, I. M. Gres, N. G. Bulycheva, M. A. Vaniev*, I. A. Novakov Volgorad State Technical University, 28 Lenin Av., Volgograd, 400131, Russia

ABSTRACT Composite materials based on monomer-polymeric systems have been obtained by UV-initiated polymerization method. The flow characteristics of these compositions and their effect on further polymerization have been studied. The polymerization of monomers in the presence of dissolved polymers and properties of the materials have been investigated.

Keywords: photopolymerization, monomer-polymeric systems, polymer solutions, gel-effect, polymeric composite materials.

Perspective course in the case of creation new polymeric composite materials is combining of two or more various high-molecular compounds. This principle may be realized by dissolution or swelling of polymer component in monomer and further polymerization of the last. The diversity of possible polymer-monomer combinations permits to vary a wide range of compounds structure and properties. The employment of such systems makes it possible to design materials with a new complex of characteristics [1, 2, 3].

*

e-mail: [email protected]

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The subjects of inquiry of this research have been methacrylic and styrene solutions of polyurethane- and fluoroelastomers and polysulphone accordingly in combination with diand three- methacrylic comonomers. The reological properties of investigated solutions have been studied. It has been shown that such compositions have non-Newtonian flow mode, structural nature of flow becomes more expressed with decrease of temperature and increase of solution concentration. It has been shown that viscosity of the composition may be varied in wide range (1.6 – 500 mPa·s). It makes possible to apply different production techniques. Influence of dimethacrylic comonomer concentration on dynamic viscosity and flow activation parameters of compositions has been analyzed. The polymerization of monomer in the presence of dissolved polymers has been studied. It has been shown that the rate of polymerization of monomer-polymer solutions is higher compared to that of pure monomer (Figure 1). The influence of the content of dissolved polymers on the conversion of monomers corresponding to the onset of the gel effect has been estimated. In the presence of the polymer being added, this phenomenon manifests itself at a lower fractional conversion of the monomer. The greater the content of the polymer and the higher the viscosity of the reaction system, the sooner the rise in the rate of polymerization. The effect of the photoinitiator type and amount on the reaction rate, degree of polymerization and structural characteristics of the material has been considered. By using UV-spectroscopy method, it has been shown that initiation efficiency depends on polymeric influence on initiator absorption spectrum. 100

1

3 2

G,%

75

50

25

0 250

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7250

9000

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12500 Time,s

Figure 1. Effect of the amount of fluoroelastomer on degree of methyl methacrylate polymerization: 1- without polymer, 2- 5% , 3 – 15% of polymer.

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It has been determined that polymerization rate may be increased by application of oligomer. Influence of backbone chain and finite groups nature of methacrylic additives on polymerization process and properties of the derivable materials has been studied. Variation of oligomer chemical structure allows improving heat stability, chemical resistance, wear resistant by three-dimensional structure formation. For example in the case of polysulphonestyrene systems, we can vary these characteristics in wide range by using oligomer that illustrated in the Figure 2 (a, b). 40 35

Tensile strength, MPa

30 25 20 15 10 5 0 0

10

20

30

40

50

60

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(a)

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VST, ºС

160 150 140 130 120 110 100 0

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35

40

45

Сontents of comonomer, %

(b) Figure 2. Effect of the amount of methacrylic olygomer on the properties of polysulphone-styrene composite materials: (a) tensile strength, (b) heat stability (VST).

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O

CH

Cl CH2

O

CH2

O

O

CH3

C

C

CH2

C

C

CH2

O

CH3

P O

CH H2 C

Cl

enables to produce materials with high incombustibility. Thus, new materials on the base of polymer-monomer system have been produced. The results of researches have allowed to develop methods of creating shock-resistant, heatresistant, abrasion-resistant and aggression resistant compounds.

REFERENCES [1] [2] [3]

Vaniev M. A., Candidate’s Dissertation in Technical Sciences (Volgograd, 1996). Polymer Science Series A. Volume 48, Number 7 / July, 2006. - p. 707-711. Polymer Science Series A. Volume 49, Number 4 / April, 2007. - p. 388-394.

In: Modern Tendencies in Organic and Bioorganic Chemistry ISBN: 978-1-60456-295-8 Editors: A. Mikitaev, M. K. Ligidov, pp. 151-159 © 2008 Nova Science Publishers, Inc.

Chapter 12

STABILIZATION OF CELL MEMBRANES BY HYBRID ANTIOXIDANTS IN THERAPY OF NEURODEGENERATIVE DISEASES L. D. Fatkullinaa,*, O. M. Vekshinaa, E. B. Burlakovaa, A. N. Goloshchapova, and Yu. A. Kimb a

Emanuel Institute of Biochemical Physics, Russian Academy of Sciences, Moscow, Russia b Institute of Biophysics of Cell, Russian Academy of Sciences ,Pushchino, Russia

ABSTRACT A hybrid antioxidant of new generation – ichfan is suggested for the therapy of membrane-pathologies associated with neurodegenerative diseases. It was shown that the compound applied in a wide range of concentrations modifies the properties of erythrocyte membranes and cells of Ehrlich ascitic carcinoma and changes the functional state of cells. Incorporated in the lipid phase and near-protein lipids of membranes, the antioxidant affects the structural state of the lipid bilayer, the structure and functional activity of proteins, in particular, the functions of ionic channels. Recommendations were made as to the compound doses responsible for the pronounced antioxidant and stabilizing effects and the absence of unfavorable side-effects.

Keywords: antioxidants, Alzheimer's disease, membranes, microviscosity, 2+ neurodegeneration, light scattering, thermodenaturation, Ca -dependent K+-channels

*

4, Kosygin Str., Moscow, 119334, Russia. Fax: (495) 137 41 01; E-mail: [email protected]

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INTRODUCTION As is known, the Alzheimer's disease (AD) is associated with membrane pathologies that are characterized by the oxidative stress and drastic changes in the structural state, lipid composition, and functions of membranes. The Alzheimer's disease is often characterized by increasing nonsaturation and fluidity of the membrane lipid phase and promotion of oxidation [1,2]. The microviscosity of the membrane lipid bilayer controls the functions of membranebound proteins responsible for the general cellular response and, particularly, the work of ionic channels of plasmalemma, activated by increased intracellular concentration of Ca2+, which is characteristic of many pathologies [3, 4]. Hybrid antioxidants (HA) ichfans [β-4oxy- (3.5-ditertbutyl-4-oxyphenyl) potassium propionate] derivatives of antioxidant phenozan) were synthesized at the Emanuel Institute of Biochemical Physics, Russian Academy of Sciences. These are potential agents in the therapy of neurodegenerative diseases. Ichfan is a combined antioxidant aimed at several targets of a pathological process. Its protective effect is enhanced due to addition of the saturated fatty-acid tail into the phenozan molecule; the incorporation of the tail in the membrane increases the rigidity of the corresponding sites of the membrane and increases the probability for the compound to pass through the hematoencephalic barrier. The choline residue imparts the hybrid antioxidant the anticholine activity [5, 6]. Ichfan exhibits a high antioxidizing activity and inhibits the cholinesterase activity in human erythrocytes and in cytosol and membrane fractions of animal brain [7]. The task was to determine the contribution of membrane modification to the mechanisms of AD occurrence and development and to the drugs efficiency for AD. The aim of this work was to study the effect of ichfan on the structure and functions of membranes in model experiments. We tested the lipid bilayer microviscosity, thermo stability of protein domains of membranes, and K+ - release through Ca2+-dependent K+-channels (CaK channels) in the presence of HA in concentrations from 10-4 M to 10-17 M and determined the ranges of applicability of the compound. We used erythrocytes and cells of Ehrlich ascitic carcinoma (EAC). Erythrocytes are the primary targets for drugs getting into blood vessels. The structural elements of erythrocyte membranes are similar to those of other cells of organism. However, erythrocytes are devoid of the whole system of signal transduction that is characteristic of other less specialized cells. Therefore, experiments were performed in EAC cells that give a typical cellular response to a signal and possess the system of transduction of signal from the cell surface to inside.

MATERIALS AND METHODS The structural state of membranes was studied by EPR-spectroscopy using paramagnetic spin probes [8]. Rat and mice blood erythrocytes and mice EAC cells were incubated in the presence of ichfan for 45 min; then, probes were inserted. The microviscosity of various membrane sites was measured on an ER 200D-SRC spectrometer (Bruker, Germany). Probe I (2.2.6.6-tetramethyl-4-capryloyl-oxypiperidine-1-oxyl) is localized mainly in the surface lipid bilayer of membrane; probe II (5.6-benzo-2.2.6.6-tetramethyl-1.2.3.4-tetrahydro-γ-carboline3-oxyl) permeates into deep-located near-protein sites of the lipid bilayer. From the EPR spectra obtained, using the formula for rapidly rotating probes, the rotation correlation time

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that has the meaning of the period of the radical reorientation by the angle π/2 was calculated (τc x 10-10 s) [9]. The results were expressed in arbitrary units (samples without the compound were used as the control). Isolation of erythrocytes and erythrocyte ghosts of mongrel white rats and determining the cell stability degree with regard to the level of hemolysis of erythrocytes were performed by the methods described in [10,11]. The releasing activity of Ca-K channels was measured potentiometrically using the K+ -selecting electrode [12]. The thermograms of erythrocyte ghosts were recorded with the aid of a DASM-4 differential adiabatic scanning microcalorimeter [13]. Isolation of EAC cells and recording of right angle light scattering of dilute suspension of EAC cells were performed on a Perkin–Elmer-44B spectrofluorometer at a wavelength of 510 nm by the method described in [14].

RESULTS AND DISCUSSION

1,2

1,2 microviscozity of AKE (rel.un.)

microviscozity of erythrocites (rel.un.)

The EPR-spectroscopy data obtained showed that ichfan applied in various concentrations modifies the microviscosity of both layers (probes I and II) of erythrocyte membranes and EAC cells (Figure 1). We discovered a complex nonlinear character of the dose–effect dependence. In all cases, the membrane microviscosity increased by 18% relative to the control at the HA concentrations 10-16–10-14 M and 10-6–10-4 M. For EAC cells, under the action of the compound, the microviscosity of both layers of the membrane lipid bilayer decreased on the average by 20% with the exception of the extreme concentrations. Consequently, in vitro experiments showed that ichfan modifies the structural state of biomembranes; the effect depends on the compound dose and type of membranes.

1,15 1,1 1,05 1 0,95 0,9

1,1 1 0,9 0,8 0,7 0,6

-16 -14 -12 -10

-8

lg[ichfan-10] М

-6

-4

-16

-14

-12

-10

-8

-6

-4

lg[ichfan-10] M

Figure 1. Dose-response diagram for the effect of ichfan on microviscosity of the erythrocyte (A), and of the cell of Ehrlich ascitic carcinoma (B). Probe I (light) (2,2,6,6-tetramethyl-4-capryloyloxypiperidin-1-oxyl) is localized in the surface layer of the membrane lipid bilayer; Probe II (dark) (5,6-benzo-2,2,6,6-tetramethyl-1,2.3,4-tetrahydro-γ-carbolin-3-oxyl) in the deep near-protein sites of lipids.

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-1 6

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A hemolysis of erythrocytes (rel.un.)

4 3,5 3 2,5 2 1,5 1 0,5

-4

-6

-8

-1 0

-1 2

-1 4

0 -1 6

0

lg[ichfan-10] M

B Figure 2. a. Dose-response curve for the effect of ichfan on the erythrocyte Ca-K-channels. Before the potentiometric assays of the dependence of intensity of K+ releasing from erythrocytes on the concentration of ichfan the red blood cells were preincubated in the absence or presence of ichfan at 37o C for 45 minutes. Than cells were precipitated by centrifugation and were resuspended. Ca-K-channels are activated by the A23187 adding .b. Dose- response curve for the effect of ichfan on the hemolysis of erythrocytes. Before spectrophotometric assays of the dependence of intensity of haemoglobin releasing from erythrocytes on the concentration of ichfan the red blood cells were preincubated in the absence or presence of ichfan at 37o C for 45 minutes. Than cells were precipitated by centrifugation and supernatant was tested. Axis of ordinates – optical density upon the λ of haemoglobin absorbency (575 nm).

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The effect of HA on the Ca-K channels (Figure 2a) and the cells stability (Figure 2b) was studied in erythrocytes. The Ca2+-activated release of K+ was initiated by adding a calcium ionophore A23187 (from 2 to 4 μM) under condition of a low content of K+ (up to 1 μM) [12]. At the ichfan concentration 10-4 M, we observed a complete hemolysis of erythrocytes and the maximum release of K+ to the incubation medium. At low concentrations of the compound, the dose–effect curves of release of K+ ions and the curves of the hemolysis degree differed. The curve of dependence of the K+ release is of the S-shape: about 20% of K+ is released at the HA concentrations 10-10–10-6 M; at 10-15–10-11 M, the K+ release decreases; at 10-17–10-16 M, a slight increase is observed. The values of hemolysis do not differ from the control over the range from 10-17 M to 10-6 M. Thus the membrane stability is disrupted at high concentrations of ichfan (10-5–10-4 M). At the doses of 10-17–10-6 M, we observed no effect but discovered two maxima of activation of the Ca-K channels. The effect of the compound on the system of signal transduction in cell was studied by recording the light scattering in a dilute suspension of EAC cells; the light scattering correlated with a change in the cell volume. The cell volume is controlled considerably by functioning of the Ca2+-dependent - K+- and -Cl--channels of the plasmalemma. The regulation of these channels proceeds by several transduction pathways. We used the ATPdependent pathway of enhancement of intracellular Ca2+ concentration by activating EAC cells purinoreceptors by means of ATP additives [14]. The ichfan concentrations 10-5 M modify the light scattering considerably; the effect points to changes in the cell form and, correspondingly in the Ca-K and Ca-Cl channels (Figure 3). The Ca2+ - signal transduction initiated by the ATP effect on plasmalemma purinoreceptors is inhibited by HA applied in the dose 10-5 M; the ichfan concentrations 10-8 M and lower produce no effect. Thus, we observed no side effects at the cellular level produced by ichfan in the concentration 10-8 M. The effect of the compound on the structural organization of membrane proteins was studied by means of the differential scanning microcalorimetry of erythrocyte ghosts. The thermograms exhibited five identified thermo induced transitions depending on the denaturation of certain domains of the membrane framework: A (a complex of α- and βspectrine and actine), B1 (anchirine, proteins of bands 4.1 and 4.2, and dematine), B2 (a cytoplasmic fragment of protein of band 3), C (a membrane fragment of 55 kDa of protein of band 3 – ionic channels), and D (unidentified proteins and vesiculation of membrane [15, 16]. The preincubation of erythrocyte ghosts with ichfan for 45 min results in a slight shift in the temperature of the transitions (Figure 4a). A is shifted to the region of higher temperatures, B1 is retained, B2, C and D are shifted to the region of lower temperatures The treatment of ghosts with ethanol (Figure 4b) results in lowering of the peaks of the B1, B2, and D transitions. After treatment of membranes with HA at a dose of 10-6 M results in returning of the thermograms to their almost initial form with the exception of the D transition. A conclusion was drawn about the stabilizing effect of ichfan applied in the dose 10-6 M on the structure of isolated membranes.

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Figure 3. Effect of ichfan on the ATP-depended Ca2+- transduction system of cells of Ehrlich ascitic carcinoma. The kinetic curves of light – scattering of a dilute suspension of cells. The succession of adding: the medium of incubation, (1) – AKE; (2) – ATP; (3) – ichfan(10-5 M); (4) – Triton –X100.

The effect of a biologically active substance on an isolated membrane and an intact cell membrane may differ considerably as to the concentration dependence and qualitatively. Therefore, we performed a preliminary treatment of whole cells of erythrocytes with ichfan; then, we isolated ghosts. The thermogram of erythrocyte ghosts (Figure 4c) varies considerably upon the preincubation of erythrocytes with HA at doses of 10-6–10-5 M. The thermogram of erythrocyte ghosts preincubated with ethanol (this additive is equivalent to

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that of HA dissolved in ethanol) exhibits a decrease in the peak of the A transition as compared with untreated ghosts. In fact, the A transition disappearing is associated with a loss of deformation of erythrocytes and ghost membranes [17,18]. The treatment of erythrocytes with ichfan results in restoration of the A transition peak, i.e., restoration of the cytoskeleton. In a similar way, the temperature maxima are shifted to the region of lower temperatures; the peaks amplitudes vary. At a higher HA concentration of 10-5 M, the peaks of the B1 and B2 transitions converge into one junctional B transition; normally, this effect is observed on an ionic strength decreasing [15,16]. Hence, ichfan (at doses of 10-6–10-5 M) causes significant changes in the protein structure of the whole erythrocyte membrane and protects from damages. Thus, the maximum changes in the viscosity of the lipid bilayer of erythrocyte membranes are observed for the HA concentrations 10-16–10-14 M and 10-6–10-4 M, which correlate with two peaks of K+ releasing from erythrocytes. At higher ichfan concentrations, along with enhancement of the membrane viscosity, the organization of cytoskeletal proteins and functioning of the Ca-K channels are modified. At very high HA doses (10-4 M), the integrity of erythrocytes cells is disrupted. At low ichfan concentrations, the microviscosity increases and the K+ channels are activated, although no significant structural changes are observed (according to testing of hemolysis of erythrocytes). For EAC cells membranes, the compound (almost over the entire concentration range) decreases significantly the microviscosity of surface lipids and near-protein domains of the lipid bilayer; only at the HA concentrations 10-16 and 10-4 M, the viscosity increases. In particular, the compound dose 10-5 M affects the Ca2+ signal system of EAC cells. At lower ichfan concentrations (10-8 M), the membrane microviscosity decreases and the compound produces no effect on the cell volume. Evidently, over this concentration range, the compound produces no effect on the membrane and Ca2+ signal system. The studies on the effect of HA on EAC cells made it possible to determine the concentration range, within which the compound produces no side effects. On the basis of data obtained, we suggest using ichfan in concentrations no higher than 10-8 M that causes no side effects. Using the compound at higher doses (10-5 M) cause considerable changes in the characteristics of the Ca2+ signal system. Also, we detected changes in the structural organization of ghost membranes of erythrocytes after a preliminary incubation of them with HA at concentrations 10-5–10-6 M, which correlate with changes in the degree of hemolysis and activity of the Ca-K channels. A similar dependence of changes in the erythrocyte cell form and hemolysis degree was shown previously in [19]. Over the range of lower concentrations, the compound effect decreases and disappears completely, although the cytoskeletal structure and functions of cell ionic channels do not experience significant changes. A certain increase in the activity of the K+ channels is observed over the range of ultra-low concentrations (10-15–10-17 M). At these concentrations of ichfan, the integrity of cell is retained and the viscosity of the upper leaf of the bilayer increases significantly; the viscosity of deep proteins-permeated layers of the lipid bilayer increases insignificantly.

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b

c

Figure 4. a. Differential scanning calorimetric thermogram of red blood cells ghosts: (1) - ghosts of erythrocytes preincubated with phenozan before the preparation of red blood cells membranes; (2) – with ichfan; (3) – control, intact ghosts. b. Differential scanning calorimetric thermogram of red blood cells ghosts: (1) – control, intact ghosts; (2) - ghosts of erythrocytes preincubated with ethanol, before the preparation of red blood cells membranes; (3) – ghosts of erythrocytes preincubated with ichfan, before the preparation of red blood cells membranes. c. Differential scanning calorimetric thermogram of ghosts, preincubated with ichfan, before the preparation of red blood cells membranes. (1) – with ichfan (10-5 M); (2) - with ichfan (10-6 M); (3) – control, ghosts of erythrocytes preincubated with ethanol. Axis of ordinates - ΔCp – the change of relative thermal capacity (J g-1 k-1).

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Consequently, at high concentrations, ichfan may form its own phase and drastically digitizes the membrane; indirectly (through lipids) it modifies the activity of membranebound proteins, which leads to destruction, i.e., the integrity of cells is disrupted as a result of the lipid bilayer disordering. It is possible that the compound in low concentrations is distributed in the bilayer in the proximity to proteins as a raft-forming substance. The HAinduced changes detected in the structure of membranes of erythrocytes are possible to occur in membranes of other cells, because the families of structural proteins studied are characteristic of many other cells of organism. Thus, the discovered stabilizing efficiency of hybrid antioxidant ichfan on cell membranes with regard to its pronounced antioxidizing effect and feasibility of permeation through the hematoencephalic barrier may be of primary importance for the membrane therapy of neurodegenerative diseases.

REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19]

M.R. Prasad, M.A. Lovell, M. Yatin et al.: Neurochem. Res., 23 (1), 81 (1998). L. Ginsberg, J.H. Xuereb, N.L. Gershfield: J. Neurochem., 70 (3), 2533 (1998). L. Bolis, D.F. Hofmann, A. LIF: Membranes and diseases, Мedicine, Мoscow, 1980. 341 p. (in Russian). Yu.V. Postnov, S.N. Orlov: Primary hypertension as pathology of cell membranes, Мedicine, Moscow, 1987. 237 p. (in Russian). E.M. Molochkina, I.B. Ozerova, E.B. Burlakova: Free Rad. Biol. Med.,33, 229 (2002). E.M. Molochkina, I.B. Ozerova: Radiation Biol./Radioecol., 43 (3), 294 (2003) (in Russian). E.M. Molochkina, N.Yu. Gerasimov, L.D. Fatkullina et al.: Chem. and Phys. of Lipids, 143, 94 (2006). A.N. Kuznetsov: Method of spine probes, Nauka, Moscow, 1976. 209 p.(in Russian). A.N. Goloshchapov, E.B. Burlakova: Biofizica, 20 (5), 816 (1975)(in Russian). A.K. Gulevskiy, V.V. Ryazantsev, A.M. Belous: Scientific Proceedings Higher Schools, Biol. Scien., 29 (1990) (in Russian). E. Beutler, C. West: J.Lab.Clin.Med., 88 (2), 328 (1976). N.V. Maksimova, S.Yu. Tchizhevskaya, Yu. A. Karpov et al.: Kardiologiya, 5, 45 (1999)(in Russian). P. L. Privalov, V.V. Plotnikov: Therm. Acta, 139, 257 (1989). V.P. Zintchenko, V.A. Kasimov, V.V. LI et. al.: Biofizica, 50 (5), 1055 (2005)(in Russian). W.M. Jackson, J. Kostyla, J.H. Nordin et al.: Biochemistry, 12, 3662 (1973). J.F. Brandts, K.A Lysko, A.T. Schwartz et al.: Colloques internationaux. C. R. S., 246, 169 (1976). N. Mohandas, A.C. Greenquist, S.B. Shohet: The Red Cell, Alan R. Liss, Inc., New York,1978. 453 p. B.P. Heath, N. Mohandas, J.L. Wyatt et al.: Biochim. Biophys. Acta, 691, 211 (1982). E.Yu. Parshina, L.Ya. Gendel, A.B. Rubin: Biofizica, 49 (6), 1094 (2004) (in Russian).

In: Modern Tendencies in Organic and Bioorganic Chemistry ISBN: 978-1-60456-295-8 Editors: A. Mikitaev, M. K. Ligidov, pp. 161-163 © 2008 Nova Science Publishers, Inc.

Chapter 13

WEAR RESISTANT COMPOSITE POLYMERIC MATERIALS BASED ON POLYURETHANES AND POLYISOCYANURATES L. V. Luchkina, A. A. Askadsky, and V. V. Kazantseva A.N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 28 Vavilov street, 119991 Moscow, Russia

ABSTRACT Reaction molding method has given composite impact and wear resistant reinforced gradient polymeric materials, based on polyisocyanurates (PIC) and polyurethanes (PU). The materials are good for mechanical processing that allowed production of wear resistant gears, working practically noiselessly.

Keywords: polyurethanes, polyisocyanurates, gradient materials, impact resistance, wear resistance, gears At the present time, the traditional methods of property control for polymeric materials is their level-to-level alignment using expensive welding or adhesion processes that represents a labor-intensive and multistage process, which also may lead to obtaining materials with defective interlayer adhesion. To our opinion, there is possible and perspective method for production of materials with controllable properties in the given directions, which is synthesis of gradient polymeric materials based on PU and PIC composites. Their technology includes the use of a “solution” method for combining a binder and a carrier, and their processing to articles using the reaction molding method. These are materials without interfaces, having elastic rather than viscoelastic properties typical of all known polymers present in the transition zone from the glassy-like to the rubbery state. This work is targeted at the study of impact resistance and wearability in gradient polymeric materials based on PU and PIC composites, produced by reaction molding method, with respect to the composition. Two types of composite gradient polymeric materials: the

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ones reinforced by strengthening fillers and composite ones with a carrier which does not change the polymer properties. In this work, the polymeric binders are network polyurethane isocyanurates of the controlled composition based on polypropylene glycol (PPG) having MM = 2200, polyester urethane diisocyanate (PEUD) having MM = 3800, 2,4-toluylene diisocyanate (TDI), and diamine (di(3-chlor-4-aminophenyl)methane) [1, 2]. The reinforcement fillers in this case fibrous carbon material based on hydrated cellulose fibers (carbon tissue of UVIS-T, UVIS-TM/4 trademarks); the carriers causing no changes in properties of produced materials which are highly porous systems, such as elastic polyurethane foam of PPU-EM-1 trademark (PUF), have been used. The use of one or another type of carrier or filler has predetermined the ranges for application of gradient polyurethane isocyanurate polymeric materials. Based on the composite polyurethane isocyanurate gradient materials, shock absorbing layings and supports for household appliances (refrigerators, laundry washers, ventilators and so on), which perceive high vibration, have been developed under laboratory conditions. In this case, the rigid polyisocyanurate part of the material provides the ability of strong connection between parts of the article, and the rubber-like part acts as a shock absorber. A possibility of production of comfortable, including the orthopedic one, footwear based on composite materials, in which tensile loads are perceived by the rubber-like material, and compressing loads are perceived by the rigid material to which rubber-like material is gradually transferred. However, if materials with strengthened properties have been required than, as mentioned above, carbon fabric was used to create reinforced materials. The reinforced gradient materials obtained are well mechanically processed; as a result, gears are obtained which teeth have much lower modulus of elasticity than the core. For 350 h of operation the wear of such gears equaled 0.25% only. It is found that as polyurethane component content in the elastic part of gradient composite materials increases to 50-60 wt.%, impact strength obtain the highest values (16.9 and 13.7 kg⋅cm/cm2, respectively). Hence, flexural strength at the same ratio of polyisocyanurate and polyurethane is maximal in the rigid part of the material rather than in the elastic one. Mechanical tests of reinforced gradient materials have shown that impact strength of such materials, measured at the elastic side, is several time higher than for composite materials with a carrier. In the second series of experiments, the impact strength measured at the elastic side of the reinforced material specimen is higher than for the rigid part irrespective of PU content. It is found that impact strength of the samples tested at impacting the elastic side affects concentration of the PU component, because isocyanurate network crosslink points in these samples are linked by PU fragments containing propylene oxide group. It is noted that the impact strength, determined at impacting the rigid side of the samples, changes in the concentration of TDI and PU had a low effect: it has changed in the range of 11.1 to 17.6 kg⋅cm/cm2. The bending strength of reinforced gradient materials remains practically equal for rigid and elastic sides. Only in some cases its value is higher for the elastic side rather than for the rigid side. The abrasion value of gradient composite and reinforced polymeric materials has been estimated on a Schopper-Schloban type device (Table 1). Samples 1-7 shown in the Table contain polyurethane foam as the carrier of polymeric composite, and the sample 8 contains

Wear Resistant Composite Polymeric Materials et al.

163

carbon tissue UVIS-T. The sample 5 contains 2 wt.% of K 354 trademark technical carbon, and the sample 6 2 wt.% of P803. It is found that the abrasion value is minimal at a side of the gradient sample contained from PU only or its content is greater in relation to the PIC component, and obtains the values typical of standard rubbers [3]. As PIC concentration in the rigid part increases, the abrasion value also increases to significant values (6-7⋅10−3 cm3/m). It is found that the abrasion value also is affected the technical carbon trademark. As the trademark P803 is used, the abrasion index is insignificantly lower compared with K354 trademark use. For a gradient reinforced material, the following regularity is observed: abrasion is maximal for the rigid side consisting of PIC only. As the PU component in the material increases, the abrasion index becomes minimal exceeding insignificantly abrasion indices typical of standard rubbers. This indicates that PU component addition to polyisocyanurate materials increases wearability of the materials obtained. Thus, reinforced impact resistant and wear resistant gradient polymeric materials based on PU and PIC. Specific impact strength and flexural strength of such samples depend on the quantity of PU component in the gradient materials, and the articles produced (gears) work almost noiselessly and do not show any wear. Table 1. Abrasion values for gradient polymeric materials No.

TDI concentration in PIC

Sample side composition PIC:PU

1 2 3 4 5

50 50 50 60 60

Elastic PU PU PU PU PU

6

60

PU

7 8

60 50

50:50 20:80

rigid 80:20 60:40 20:80 PIC 80:20 K354 80:20 P803 60:40 PIC

Side abrasion index I·103, cm3/m elastic rigid 1.0 5.4 2.3 4.9 3.4 3.4 1.5 5.6 1.7 6.4 1.2

5.9

4.7 4.7

7.2 7.4

REFERENCES [1] [2] [3]

Luchkina L.V., Askadsky A.A., Bychko K.A., and Kazantseva V.V. // Plastich. Massy. 2005. No. 9. P. 21. (Rus). Luchkina L.V., Bychko K.A., Kovriga O.V. et al. // Plastich. Massy. 2005. No. 10. P. 19. (Rus). Reznikovsky M.M. and Lukomskaya A.I. // Mechanical tests of natural and artificial rubbers. M.: Khimia. 1968. 359 p. (Rus).

In: Modern Tendencies in Organic and Bioorganic Chemistry ISBN: 978-1-60456-295-8 Editors: A. Mikitaev, M. K. Ligidov, pp. 165-169 © 2008 Nova Science Publishers, Inc.

Chapter 14

PHOTODESTRUCTION OF CHLOROPHYLL IN NON-BIOLOGICAL SYSTEMS A. V. Lobanov1,2, O. V. Nevrova1, Yu. A. Vedeneeva1, G. V. Golovina3, and G. G. Komissarov1 1

Semenov Institute of Chemical Physics RAS, Kosygina st. 4, Moscow 119991, Russia; 2 Lomonosov Moscow State University, Chemistry Department, Leninskie Gory 1-3, Moscow 119899, Russia; 3 Emanuel Institute of Biochemical Physics RAS, Kosygina st. 4, Moscow 119991, Russia

1. INTRODUCTION The structure of plant photosynthetic systems is interrogated by numerous methods [1-3], but there are not comprehensive information about factors influencing on stability of chlorophyll (Chl). Furthermore the data of photodestruction of Chl are important for development of structure functional models of photosynthesis. The study of effect of hydrogen peroxide on Chl photodestruction intensity is of particular interest because the active role of H2О2 in photosynthesis mechanism was shown [4] and Н2О2 was used in several artificial photosynthetic systems [5, 6]. Transformations of Chl under the visible light irradiation include in opening of chlorine macrocycle (Figure 1) which results to formation of colourless oxygen-containig compounds (λabs ≤ 350 nm) [7] and/or elimination of Mg2+ ion that leads to production of pheophytin (Pheo) with another absorption spectrum. This work is concerned with the investigation of photodestruction of Chl in a number of non-biological systems.

2. EXPERIMENTAL Extraction of Chl from dry nettle leaves and its purification were carried out by methods [4]. Ethanol (50 or 100 vol.%), micelles of cetyltrimethylammonium bromide (CTAB), liposomes of 1,2-diacyl-sn-glycero-3-phosphocholine (PC), complexes based on bovine

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166

serum albumin (BSA) and poli-N-vinylpyrrolidone (PVP), adsorption layers on silica gel as well as Photosystem I (PSI) extracted from spinach chloroplasts were used as the systems for the study of Chl photodestruction. To elucidate the effect of hydrogen peroxide on Chl photodestruction kinetics H2O2 (0.1 M) was added to the samples. The samples (solutions or suspensions), 10 ml, were agitated by a stirrer at visible light irradiation. The lighter consisted of halogen tube (150 W), lens and condenser. The concentration of Chl was measured by spectrophotometer Beckman DU-8. X X = CH3 N

N

Chl a

X = CH=O Chl b

Mg N

N

H3C H H H3COOC O

H

O

O CH3 H CH3 H

Figure 1. The structure of Chl molecules.

3. RESULTS AND DISCUSSION During studying of Chl photodestruction its concentration varied in the systems. General peculiarity of photodestruction is its acceleration at Chl aggregation, e.g. at [Chl] > 10-4 М in ethanol, at ≥20 molecules of Chl on one micelle in CTAB micelles, at monolayer exceeding on silica gel. Consequently, in Chl aggregates photodestruction occurs as Chl* + Chl. It is quite possible that singlet oxygen participates in photodestruction because 1O2 can be produced by triplet excited chlorophyll molecules 3Chl*. The photodestruction of smaller quantity of Chl depends on concentration of solved oxygen or other oxidant. As it turned out the type of Chl photodestruction is affected by polarity of the systems. The formation of Pheo takes place at high degree of Chl photodestruction in only polar systems (ethanol, water/ethanol, PSI, BSA, PVP), when bindig of Mg2+ and medium ligands

Photodestruction of Chlorophyll in Non-biological Systems

167

(Figure 2). But producing of Pheo does not happen at non-polar environment (PC, CTAB), in which Chl molecules are in hydrophobic region. Individual Pheo is stable at experimental conditions. However Pheo formed by Chl photodestruction is subjected to photodestruction. The reason of this fact is possibility of Mg-containing Chl as well as complexes of porphyrines and nontransition metals to generate long-living triplet excited states 3Chl* (1 ms) with high quantum yield (≥60%) in contrast to free Pheo. 3.5 3.0

1

2.5

D

2.0 1.5 1.0

2 0.5 0.0 400

500

600

700

800

nm Figure 2. Adsorption spectra of Chl in BSA (10-6 M) before (1) and after 180 min of irradiation (2). 1,1

1.01,0 0.90,9

D / D0

0.80,8 0.70,7 0.60,6

1

0.50,5 0.40,4

2

0.30,3 0.2 0 0

20

40

20

40

60

60

80

100

80

120

100

140

120

140

160

180

t, min Figure 3. Kinetics of Chl photodestruction in 1.2 · 10-3 M CTAB (1) and in 1.2 · 10-3 M CTAB with 0.1 M H2O2(2).

A. V. Lobanov, O. V. Nevrova and Yu. A. Vedeneeva

168 1.0 0.9

D / D0

0.8

5

0.7 0.6 0.5

12 3

0.4 0

20

40

4 60

80

100

t, min Figure 4. Kinetics of Chl photodestruction in ethanol (1), ethanol-PVP (2), ethanol-PVP-H2O2 (3), water-PVP (4), water-PVP-H2O2 (5). Content of PVP is 10 weight %.

Addition of Н2О2 to the Chl systems accelerates Chl photodestruction in all cases except PVP system (Figure 3). It unexpectedly proved that of Chl associated with PVP is more stable in presence of Н2О2 (Figure 4). Obviously this effect are explained by high affinity between PVP and Н2О2 [8], when Н2О2 molecules bind polymer chain by hydrogen bond and steric factor protecting Chl appears. In artificial systems Chl is more stable than one in PSI. Adsorbed Chl molecules are the most stable.

ACKNOWLEDGEMENTS The research was supported by grant NSh-5236.2006.3.

REFERENCES [1] [2] [3] [4]

S. Iwata, J. Barber. Current Opinion in Structure Biology. 2004. V. 14. № 4. P. 447453. W. Hillier, T. Wydrzynski. Biochim. Biophys. Acta. 2001. V. 1503. P. 197-209. R.D. Britt, K.A. Campbell, J.M. Peloquin et al. Biochim. Biophys. Acta. 2004. V. 1655. P. 158-171. G.G. Komissarov. Fotosintez: fiziko-khimicheskiy podkhod. Мoscow: Editorial URSS, 2003. 224 p. (in Russian).

Photodestruction of Chlorophyll in Non-biological Systems [5] [6] [7] [8]

169

A.V. Lobanov, S.N. Kholuiskaya, G.G. Komissarov. Doklady Akademii Nauk. 2004. V. 399. № 1. P. 73-75 (in Russian). A.V. Lobanov, S.N. Kholuiskaya, G.G. Komissarov. Khim. Fizika. 2004. V. 23. № 5. P. 44-47 (in Russian). B.D. Berezin. Koordinatsionnye soedineniya porfirinov i ftalotsianina. Мoscow: Nauka, 1978. 280 p. (in Russian). E.F. Panarin, K.K. Kalninsh, D.V. Pestov. Doklady Akademii Nauk. 1998. V. 363. № 2. P. 208-210 (in Russian).

In: Modern Tendencies in Organic and Bioorganic Chemistry ISBN: 978-1-60456-295-8 Editors: A. Mikitaev, M. K. Ligidov, pp. 171-174 © 2008 Nova Science Publishers, Inc.

Chapter 15

SOME MAKROKINETICHESKIE PARTICULARITIES OF DEEP HYDROLYSIS PET CALCIUM GIDROKSIDE IN BEAD MILL A. S. Harichkin*and A. M. Ivanov Kursk State Technical University, 94, 50 years October Str., 305040, Kursk, Russia

ABSTRACT The variant of hydrolysis PET calcium hydroxide interesting in that plan that both components in reactionary mixture are present in the manner of independent hard phases, but fluid phase needs for ensuring the mobilities reactionary mixture, as well as for carrying alkali on surface PET way to adsorptions from solution. Chemical reaction occurs on surfaces PET itself.

Keywords: Hydrolysis, polyethyleneterephthalate (PET), calcium hydroxide, bead mill, salvaging, ethyleneglycol

One method of a polymer utilization is its decomposition into monomers. Considering that PET is ester the easiest way of its decomposition will be a deep alkali hydrolysis. The cheapest and most available alkali is calcium hydroxide. However, it is slightly soluble in water. That makes significant difficulties for its using for the mentioned purpose. An attempt has been made to overcome this problem by carring out the process in the beaded mill in accordance with the following scheme:

*

[email protected], [email protected]

A. S. Harichkin and A. M. Ivanov

172

PET (granules) Ca(OH)2 (CaO) distilled water

beaded mill

samples of the reaction mixture for analyses

powder

screening

heating of finedispersed suspension being stirred up to working temperature proceeding the process in thebeaded-mill up to self-stopping

fraction of fixed sizes dosage mixing initial reaction mixture

addition of distilled water or another liquid phase or

Ca(OH)2 Ca(OH)2 stirring and heating up to working temperature distilled water final reaction mixture

PET fraction of fixed sizes

water

hydrolysis Ca(OH)2

Ca(OH)2

distilled water

The process was controlled by taking samples for analysis and determining amount of alkali in them (total amount in all phases and alkali concentration in liquid phase of the reaction mixture (using a conductometric method)). Samples were taken without stopping stirring the reaction mixture that excluded significant phase division of the system into layers and change of the phase ratio in samples to be taken because of the stated reason. As a whole such an attempt was successful. PET was decomposed into ethylene glycol and calcium salt of terephthalic acid astheproducts. However, the process was found to be not simple. Considerable growth in viscosity of the reaction mixture and progressing self-braking that may be followed by untimely self-stopping in case of untaking effective actions could be observed (Figure 1). Under model conditions ethyleneglycol as a hydrolysis product increases solubility of Ca (OH)2. However, its accumulation or introduction into the beaded mill as a component of the liquid phase does not lead to hydrolysis intensification. Probably it occurs because presence of ethyleneglycol promotes the growth of liquid phase viscosity that may be connected with increase in solubility of calcium salt of terephthalic acid in liquid phase of the reaction mixture. In consequence of this significant drop in efficiency of the beaded mill work is observed.

Some Makrokineticheskie Particularities …

173

Simultaneos reduction of PET and Ca(OH)2 dosage was found to be unproductive. The process being considered is heterogenous and the place of its proceeding is a polymer surface. Reduction of the latter undoubtedly leads to decrease of the process. Farther investigations were directed to understanding what prevents the process from fast proceeding at deep stages. For this purpose the following results were estimated: • use of fractional introduction of stechiometric amount of calcium hydroxide or its excess instead of introduction for one time; • various programmes of dillution the reaction mixture becoming thick during the course of the process with distilled water, ethyleneglycol, aqueous solutions of ethyleneglycol etc.; • use of calcium oxide that could interact with water giving finer-dispersed Ca(OH)2 instead of calcium hydroxide; • substitution distilled water or aqueous solution of calcium hydroxide for a part of liquid phase of the reaction mixture during the course of the process; • variation of initial content of PET and Ca(OH)2; • variation of temperature of carrying out the process; • variation of operations succession while introducing the reagents; As mentioned above the process being considered is heterogenous and the place of its proceeding is a polymer surface from liquid phase by means of adsorbtion in the form of both Ca(OH)2 molecules and Ca(OH)+ and OH- ions. In other words the following displacement of the alkali reagent takes place:

Ca(OH)2

Ca(OH)2sol

PET surface

adsorption +

-

Ca(OH) + OH

Various chemical reactions occur on the surface of PET, for instance

~C6H4C(O)O- + Ca(OH)+

~ C6H4C(O)OCaOH

~CH2CH2OC(O)C6H4C(O)OCa+ + OH-

~C6H4C(O)OCH2CH2OH + OHetc.

~C6H4C(O)OCa+ + OH-

~CH2CH2OH- + OC(O)C6H4C(O)OCa+ Ca(OC(O))2C6H4

~C6H4C(O)O- + OHCH2CH2OH

174

A. S. Harichkin and A. M. Ivanov

Calcium salt of terephthalic acid that is slightly soluble in water remains on the surface of the solid part of the polymer and ethylene glycol that is soluble in water mainly goes into the liquid phase. Finally surface sediments of the products arise on particles of PET. Under conditions of intensive mechanical stirring and interaction of the particles with each other the sediments can move from particles of PET to ones of Ca(OH)2. It will lead to blocking of both particles of PET and ones of Ca(OH)2.In consequence of this the concentration of Ca(OH)2 in solution decreases that may be a reason of self-stopping to be met practice.

Drawing 1. Kinetic curves of the spending calcium hydroxide on hydrolysis PET in bead mill of the vertical type; the fluid phase: 1 - water; 2,3 - water-whine solution ethyleneglycol; 4 - ethyleneglycol.

Drawing 2. Influence of the contents ethyleneglycol (EG) in fluid phase on soluble calcium hydroxide.

In: Modern Tendencies in Organic and Bioorganic Chemistry ISBN: 978-1-60456-295-8 Editors: A. Mikitaev, M. K. Ligidov, pp. 175-210 © 2008 Nova Science Publishers, Inc.

Chapter 16

TRANSPORT PHENOMENA WITHIN POROUS MEDIA Sh. Rahrovan and A. K. Haghi* Faculty of engineering, The University of Guilan Rasht 41635, P. O. Box 3756, Iran

ABSTRACT Wood is a hygroscopic, porous, anisotropic and non-homogenous material. Microwave drying generate heat from within the grains by rapid movement of polar molecules causing molecular friction and help in faster and more uniform heating than does conventional heating. In this paper, a comprehensive review is presented on the researches and developments related to drying processes of wood. Other issues regarding the technology limitation, research challenges, and future trends are also discussed.

NOMENCLATURE

**

A= a= e a* = b* = CP =

area; xposed area per unit volume of the stack; color parameters; color parameters; specific heat;

D=

Da =

diffusion coefficient; inter diffusion coefficient of vapor in air;

Dbt =

transverse bound water diffusion coefficient of wood;

Eb =

activation energy;

f= G=

relative drying rate; dry air mass flow rate;

[email protected]

Sh. Rahrovan and A. K. Haghi

176 h=

heat transfer coefficient;

hD =

mass transfer coefficient;

Jb =

bound water diffusion flux;

Jf =

liquid free water flow flux;

J vf =

water vapor flow flux;

j0 =

constant drying rate;

K=

thermal conductivity;

KL =

longitudinal thermal conductivity;

KT =

transverse conductivity;

k= k0 =

permeability; mass transfer coefficient;

kr =

relative permeability;

L= L* = Le = MC =

M cr1 =

length of specimen parallel to the direction of flow; lightness; Lewis number; moisture content; first critical moisture content;

M cr 2 =

second critical moisture content;

Me =

equilibrium moisture content;

Mw= m& = m& ij =

molecular weight of water; mass flow rate per unit surface area;

Nν =

moisture flux;

P=

Pressure;

P = pc = Q& =

Average pressure across the specimen; capillary pressure;

q= R=

Ra =

heat flux; gas constant; average roughness;

Rq =

root mean square (RMS) roughness;

Rz =

average maximum height of the profile;

r= SG =

SGd =

latent heat of vaporization of water; specific gravity of wood; nominal specific gravity of wood substance;

T=

temperature;

transition from phases i and j;

heat flow rate;

Transport Phenomena within Porous Media t= u= V= v= X= x= Y=

177

time; moisture content; volume; fluid velocity; Distance in x coordinate axis; water transfer distance; air humidity;

Greek Symbols

αR = α LS = β= ν= ΔE * = ΔΗ wv = ε = μ= ρ= ρ0 =

coefficients to reflect effects of heat radiation; coefficients to reflect effects of heat loss; mass transfer coefficient when vapor partial pressure difference is taken as driving force; porosity of wood; total color change; Latent heat of vaporization; void fraction in the lumber stack; viscosity; density; density of oven-dry wood;

ρs =

wood basic density;

ρ Gν =

vapor partial pressure in the air stream;

ρ νs = ϕ= φ = φi = χ=

vapor partial pressure at the wood surface; humidity coefficient relative humidity; volumetric fraction; water transfer distance;

Subscripts a _ air; b _ bound water; c_ capillary; C _ Celsius; conv _ convection; cs _cross sectional; cw _ cell wall;

178

Sh. Rahrovan and A. K. Haghi DB _ dry Bulb; evap _ evaporation; ex _ exit; f_after drying; f.s.p._fiber saturation point; G _main stream; i_before drying; in _ initial; k _ kelvin; L _ longitudinal; l _liquid phase; m _ mean value; mt _ moisture or wet; r _ relative; s _ solid skeleton of wood; sat _ Wood, at saturation; surf _ surface of wood board; so _ wood segment o; T_ transverse; v _ vapor; ν _gas phase; w _ free water; wood _ wood; wv _ water vapor;

1. WOOD AS A POROUS MEDIA Wood is a hygroscopic, porous, anisotropic and non-homogeneous material. After log sawing, the lumber contains liquid water in fiber cavities (capillary water) and bound water inside the fiber wall (hygroscopic water). Porosity refers to volume fraction of void space. This void space can be actual space filled with air or space filled with both water and air. Capillary-porous materials are sometimes defined as those having pore diameter less than

10 −7 m. Capillary porous materials were defined as those having a clearly recognizable pore space. In capillary porous material, transport of water is a more complex phenomena. In addition to molecular diffusion, water transport can be due to vapor diffusion, surface diffusion, Knudsen diffusion, capillary flow, and purely hydrodynamic flow. In hygroscopic materials, there is large amount of physically bound water and the material often shrinks during heating. In hygroscopic materials there is a level of moisture saturation below which the internal vapor pressure is a function of saturation and temperature. These relationships are called equilibrium moisture isotherms. Above this moisture saturation, the vapor pressure is a function of temperature only (as expressed by the Clapeyron equation) and is independent of the moisture level. Thus, above certain moisture level, all materials behave non-hygroscopic. Green wood contains a lot of water. In the outer parts of the stem, in the sapwood, spruce and pine have average moisture content of about 130%, and in the inner parts, in the

Transport Phenomena within Porous Media

179

heartwood, the average moisture content is about 35%. Wood drying is the art of getting rid of that surplus water under controlled forms. It will dry to an equilibrium moisture content of 8–16% fluid content when left in air which improves its stability, reduces its weight for transport, prepares it for chemical treatment or painting and improves its mechanical strength. Water in wood is found in the cell cavities and cell walls. All void spaces in wood can be filled with liquid water called free water. Free water is held by adhesion and surface tension forces. Water in the cell walls is called bound water. Bound water is held by forces at the molecular level. Water molecules attach themselves to sites on the cellulose chain molecules. It is an intimate part of the cell wall but does not alter the chemical properties of wood. Hydrogen bonding is the predominant fixing mechanism. If wood is allowed to dry, the first water to be removed is free water. No bound water is evaporated until all free water has been removed. During removal of water, molecular energy is expended. Energy requirement for vaporization of bound water is higher than free water. Moisture content at which only the cell walls are completely saturated (all bound water) but no free water exists in all lumens is called the fiber saturation point (F.S.P). Typically the F.S.P of wood is within the range of 2040 % moisture content depending on temperature and wood species. Water in wood normally moves from high to low zones of moisture content. The surface of the wood must be drier than the interior if moisture is to be removed. Drying can be divided into two phases: movement of water from the interior to the surface of the wood, and removal of water from the surface. Water moves through the interior of the wood as a liquid or water vapor through various air passageways in the cellular structure of wood and through the cell walls. Drying is a process of simultaneous heat and moisture transfer with a transient nature. The evolution process of the temperature and moisture with time must be predicted and actively controlled in order to ensure an effective and efficient drying operation. Lumber drying can de understood as the balance between heat transfer from air flow to wood surface and water transport from the wood surface to the air flow. Reduction in drying time and energy consumption offers the wood industries a great potential for economic benefit. In hygroscopic porous material like wood, mathematical models describing moisture and heat movements may be used to facilitate experimental testing and to explain the physical mechanisms underlying such mass transfer processes. The process of wood drying can be interpreted as simultaneous heat and moisture transfer with local thermodynamic equilibrium at each point within the timber. Drying of wood is in its nature an unsteady-state nonisothermal diffusion of heat and moisture, where temperature gradients may counteract with the moisture gradient.

2. SOME ASPECTS OF HEAT FLOW DURING DRYING PROCESS 2.1. Stages of Drying First stage: When both surface and core MC are greater than the F.S.P. Moisture movement is by capillary flow. Drying rate is evaporation controlled. Second stage: When surface MC is less than the FSP and core MC is greater than the F.S.P. Drying is by capillary flow in the core and by bound water diffusion near the surface as

180

Sh. Rahrovan and A. K. Haghi

fiber saturation line recedes into wood, resistance to drying increases. Drying rate is controlled by bound water diffusion. Third stage: When both surface and core MC are less than the F.S.P. Drying is entirely by diffusion. As the MC gradient between surface and core becomes less, resistance to drying increases and drying rate decreases.

2.2. Capillary Capillary pressure is a driving force in convective wood drying at mild conditions [1]. The temperature is higher outside than inside. The moisture profile during convective drying is in the opposite direction, namely, the drier part is toward the exposed surface of wood. This opposite pattern of moisture and temperature profiles lead to the concept of the wet front that separates the outer area, where the water is bound to the cell wall, from the inner area, where free water exists in liquid and vapor form. A wet front that moves slowly from the surface toward the center of a board during convective drying leads to subsequent enhancement of the capillary transportation. Capillary transportation can then be justified due to the moisture gradients developed around that area. When the drying conditions are mild, the drying period is longer so the relative portion of the total moisture removal, due to the capillary phenomena, is high, and it seems that this is the most important mass transfer mechanism [2].

2.3. Bound Water Diffusion Credible data on the bound water diffusion coefficient in wood and the boundary condition for the interface between moist air and wood surface are very important for accurate description of timber drying as well as for the proper design and use of products, structures and buildings made of wood already dried below the fiber saturation point. During the last century, two groups of methods for measuring the bound water diffusion coefficient in wood were developed. The first one, traditionally called the cup method, uses data from the steadystate experiments of bound water transfer and is based on Fick’s first law of diffusion. Unfortunately, the method is not valid for the bound water diffusion coefficient determination in wood because it cannot satisfy the requirements of the boundary condition of the first kind and the constant value of the diffusion coefficient [3]. The second group of methods is based on the unsteady-state experiments and Fick’s second law of diffusion. The common name of this group is the sorption method and it was developed to overcome the disadvantages of the cup technique [4].

2.4. Diffusion In solving the diffusion equation for moisture variations in wood, some authors have assumed that the diffusion coefficient depends strongly on moisture content [5-9] while others have taken the diffusion coefficient as constant [10-14]. It has been reported [15-19] that the diffusion coefficient is influenced by the drying temperature, density and moisture content of timber. The diffusion coefficient of water in cellophane and wood substance was shown by

Transport Phenomena within Porous Media

181

[20] to increase with temperature in proportion to the increase in vapor pressure of water. Stamm and Nelson also observed that the diffusion coefficient decreased with increasing wood density [21]. Simpson recorded an exponential relationship for the diffusion coefficient in the moisture content range of 5 to 30 % [17]. Other factors affecting the diffusion coefficient that are yet to be quantified are the species (specific gravity) and the growth ring orientation. Literature has suggested that the ratios of radial and tangential diffusion coefficients vary for different tree species [16]. The radial diffusion coefficient of New Zealand Pinus radiate has been estimated to be approximately 1.4 times the tangential diffusion coefficient [22]. Jen Y. Liu et al observed that for northern red oak, the diffusion coefficient is a function of moisture content only. It increases dramatically at low moisture content and tends to level off as the fiber saturation point is approached [23]. Also, different boundary conditions have been assumed by different authors [24-27]. In a one-dimensional formulation with moisture moving in the direction normal to a specimen of a slice of wood of thickness 2a, the diffusion equation can be written as:

∂ ( MC ) ∂ ⎛ ∂ ( MC ) ⎞ = ⎜D ⎟ (0 < X < a, t > 0) ∂t ∂X ⎝ ∂X ⎠

(1)

Where MC is moisture content, t is time, D is diffusion coefficient, and X is space coordinate measured from the center of the specimen. The moisture content influences on the coefficient D only if the moisture content is below the fiber saturation point (F.S.P.) (typically 20%-30% for softwoods) [28]:

⎧ f D (u ) , u < u fsp ⎪ D(u ) = ⎨ ⎪ f (u ) , u ≥ u fsp ⎩ D fsp

(2)

Where u fsp denotes the F.S.P. and f D (u ) is a function which expresses diffusion coefficient in moisture content, temperature and may be some other parameters of ambient air climate [7], [29]. The expression of f D (u ) depends on variety of wood.

It was assumed that the diffusion coefficient bellow F.S.P. can be represented by:

f D (u ) = A.e

−

5280 T

.e

B .u 100

(3)

Where T is the temperature in Kelvin, u is percent moisture content, A and B are experimentally determined [30]. The regression equation of diffusion coefficient of Pinus radiata timber using the dry bulb temperature and the density is [31]:

(

)

D 10 −9 = 1.89 + 0127 × TDB − 0.00213 × ρ S ( R 2 =0. 499)

(4)

Sh. Rahrovan and A. K. Haghi

182

The regression equations of diffusion coefficients below of Masson’s pine during high temperature drying are [32]:

D = 0.0046 MC 2 + 0.1753MC + 4.2850 (R 2 = 0.9391)

(5)

Tangential diffusion

D = 0.0092MC 2 + 0.3065MC + 4.9243 (R 2 = 0.9284 )

(6)

Radial diffusion The transverse diffusion coefficient D can be expressed by the porosity of wood ν , the transverse bound water diffusion coefficient Dbt of wood and the vapor diffusion coefficient

Dν in the lumens [33]: D=

ν Dbt Dν

(1 −ν )( ν Dbt + (1 − ν )Dν )

(7)

The vapor diffusion coefficient Dν in the lumens can be expressed as:

M w Da Ps dφ . SGd ρ w RTk du

Dν =

(8)

Where M w (kg/kmol) is the molecular weight of water.

Da =

9.2.10 −9 Tk2.5 (Tk + 245.18)

(9)

is the inter diffusion coefficient of vapor in air [34].

SGd =

1.54 (1 + 1.54u )

(10)

is the nominal specific gravity of wood substance at the given bound water content [35].

ρw

3

= 103 kg / m is the density of water, R = 8314.3 kmol, K is the gas constant, Tk is the Kelvin temperature,

φ is the relative humidity (%/100), and Psat is saturated vapor pressure

given by [36, 37]:

(

p sat = 3390 exp − 1.74 + 0.0759TC − 0.000424 TC2 + 2.44 .10 −6 TC3

)

(11)

Transport Phenomena within Porous Media The derivative of air relative humidity

183

φ with respect to moisture content u is calculated

from the Hailwood-Horrobin equation adopted for wood by Simpson [37] and given as:

u=

k Φ ⎞ 18 ⎛ k1k 2 Φ ⎜⎜ ⎟ + 2 w ⎝ 1 + k1k 2 Φ 1 − k 2 Φ ⎟⎠

(12)

Where:

k1 = 4.737 + 0.04773TC − 0.00050012TC2

(13)

k 2 = 0.7059 + 0.001695TC + −0.000005638TC2

(14)

W = 223.4 + .6942TC + 0.01853TC2

(15)

The diffusion coefficient Dbt of bound water in cell walls is defined according to the Arrhenius equation as:

Dbt = 7.10 −6 exp(− Eb / RTk )

(16)

Where:

(

)

Eb = 40.195 − 71.179u + 291u 2 − 669.92u 3 .10 6

(17)

is the activation energy [38]. The porosity of wood is expressed as:

ν = 1 − SG(0.667 + u )

(18)

Where specific gravity of wood SG at the given moisture content u is defined as:

SG =

Where

ρS

ρW (1 + u )

=

ρ0

(19)

ρW + 0.883 ρ 0 u

ρ s is density of wood, ρ 0 is density of oven-dry wood (density of wood that has 0

been dried in a ventilated oven at approximately 104 C until there is no additional loss in weight) [35].

Sh. Rahrovan and A. K. Haghi

184

Table 1. Thermal conductivity of selected hardwoods and softwoods Species Hardwoods Ash Black White Aspen Big tooth Quaking Basswood, American Beech, American Birch Sweet Yellow Cherry, black Chestnut, American

Cottonwood Black Eastern Elm American Rock Slippery Hackberry Hickory, pecan Hickory, true Mockernut Shagbark Magnolia, Southern Maple Black Red Silver Sugar Oak, red Black Northern red Southern red Oak, white Bur White Sweetgum Sycamore, American Tupelo Black

Specific gravity

Conductivity(W/m·K) Oven dry

Conductivity(W/m·K) 12% MC

0.53 0.63

0.12 0.14

0.15 0.17

0.41 0.40 0.38 0.68

0.10 0.10 0.092 0.15

0.12 0.12 0.11 0.18

0.71 0.66 0.53 0.45

0.16 0.15 0.12 0.11

0.19 0.18 0.15 0.13

0.35 0.43

0.087 0.10

0.10 0.12

0.54 0.67 0.56 0.57 0.69

0.12 0.15 0.13 0.13 0.15

0.15 0.18 0.15 0.16 0.19

0.78 0.77 0.52

0.17 0.17 0.12

0.21 0.21 0.14

0.60 0.56 0.50 0.66

0.14 0.13 0.12 0.15

0.16 0.15 0.14 0.18

0.66 0.65 0.62

0.15 0.14 0.14

0.18 0.18 0.17

0.66 0.72 0.55 0.54

0.15 0.16 0.13 0.12

0.18 0.19 0.15 0.15

0.54

0.12

0.15

Transport Phenomena within Porous Media

185

Table 1. Continued Species

Specific gravity 0.53 0.46

Conductivity(W/m·K) Oven dry 0.12 0.11

Conductivity(W/m·K) 12% MC 0.15 0.13

Water Yellow-poplar Softwoods Baldcypress Cedar Atlantic white Eastern red Northern white Port-Orford Western red Yellow Douglas-fir Coast Interior north Interior west Fir Balsam White Hemlock Eastern Western Larch, western Pine Eastern white Jack Loblolly Lodgepole Longleaf Pitch Ponderosa Red Shortleaf Slash Sugar Western white Redwood Old growth Young growth Spruce Black Engelmann Red Sitka White

0.47

0.11

0.13

0.34 0.48 0.31 0.43 0.33 0.46

0.085 0.11 0.079 0.10 0.083 0.11

0.10 0.14 0.094 0.12 0.10 0.13

0.51 0.50 0.52

0.12 0.12 0.12

0.14 0.14 0.14

0.37 0.41

0.090 0.10

0.11 0.12

0.42 0.48 0.56

0.10 0.11 0.13

0.12 0.14 0.15

0.37 0.45 0.54 0.43 0.62 0.53 0.42 0.46 0.54 0.61 0.37 0.40

0.090 0.11 0.12 0.10 0.14 0.12 0.10 0.11 0.12 0.14 0.09 0.10

0.11 0.13 0.15 0.12 0.17 0.15 0.12 0.13 0.15 0.17 0.11 0.12

0.41 0.37

0.10 0.090

0.12 0.11

0.43 0.37 0.42 0.42 0.37

0.10 0.090 0.10 0.10 0.090

0.12 0.11 0.12 0.12 0.11

Sh. Rahrovan and A. K. Haghi

186

2.5. Thermal Conductivity Wood thermal conductivity ( K wood ) is the ratio of the heat flux to the temperature gradient through a wood sample [39]. Wood has a relatively low thermal conductivity due to its porous structure, and cell wall properties. The density, moisture content, and temperature dependence of thermal conductivity of wood and wood-based composites were demonstrated by several researchers [40-44]. MacLean [40] measured the thermal conductivities of various woods with a large range of MC and specific gravities (SG). He presented two empirical equations which gave the best agreement with his experimental data. The transverse thermal conductivity can be expressed as:

K wood = [SG × (4.8 + 0.09 × MC ) + 0.57]× 10 −4

cal cm * Cs

(20)

cal cm * Cs

(21)

When moisture content of wood is below 40%.

K wood = [SG × (4.8 + 0.125 × MC ) + 0.57]× 10 −4 When moisture content of wood is above 40%.

The specific gravity and moisture content dependence of the solid wood thermal conductivity in the transverse (radial and tangential) direction is given by Siau [45] as:

K T = SG (K cw + K w .M ) + K aν

(22)

Where: SG= specific gravity of wood, K cw = Conductivity of cell wall substance (0.217 J /m/s/K),

K w = conductivity of water (0.4 J / m/s /K), K a = conductivity of air (0.024 J /m/s /K), M = moisture content of wood (fraction),

ν = porosity of wood.

The thermal conductivity of wood is affected by a number of basic factors: density, moisture content, extractive content, grain direction, structural irregularities such as checks and knots, fibril angle, and temperature. Thermal conductivity increases as density, moisture content, temperature, or extractive content of the wood increases. Thermal conductivity is nearly the same in the radial and tangential directions with respect to the growth rings. The longitudinal thermal conductivity of solid wood is approximately 2.5 times higher than the transverse conductivity [45]:

Transport Phenomena within Porous Media

K L = 2.5K T

187 (23)

For moisture content levels below 25%, approximate thermal conductivity K across the grain can be calculated with a linear equation of the form [46]:

K wood = G (B + CM ) + A

(24)

Where SG is specific gravity based on oven dry weight and volume at a given moisture content MC (%) and A, B, and C are constants. For specific gravity >0.3, temperatures around 24°C, and moisture content values <25%, A = 0.01864, B = 0.1941, and C = 0.004064 (with k in W/(m·K)). Equation (24) was derived from measurements made by several researchers on a variety of species. Table 1 provides average approximate conductivity values for selected wood species, based on Equation (24). However, actual conductivity may vary as much as 20% from the tabulated values [46].

3. DRYING RATES During the early stages of drying the material consists of so much water that liquid surfaces exist and drying proceeds at a constant rate [47-50]. Constant drying rates are achieved when surface free water is maintained and the only resistance to mass transfer is external to the wood. The liquid water moves by capillary forces to the surface in same proportion of moisture evaporation. Moisture movement across the lumber will depend on the wood permeability and the drying rate itself is controlled by external conditions in this period. Part of energy received by the surface increase temperature in this region, and the heat transfer to the inner part of lumber starts [51-53]. Since the moisture source for the surface is internal moisture, constant drying rates can only be maintained if there is sufficient moisture transport to keep the surface moisture content above the F.S.P. If this level is not maintained then some of the resistance to mass transfer becomes internal and neither the drying rate nor the surface temperature remains constant and drying proceeds to the falling rate period [54]. As the lumber dries, the liquid water or wet line recedes into wood and the internal moisture movement involves the liquid flow and diffusion of water vapor and hygroscopic water. The effect of internal resistance on the drying rate increases. In the last phase (second falling rate period) there is no more liquid water in the lumber, and the drying rate is controlled only by internal resistance (material characteristics) until an equilibrium moisture content is reached [55]. A typical drying curve showing three stages of drying characteristic is illustrated in figure 1. Pang et al. proposed that the three drying periods (constant rate, first falling rate and second falling rate) based on simulated drying of veneer be expressed by the following equations [56]:

−

d ( MC ) = j 0 For MC> M Cr1 dt

(25)

Sh. Rahrovan and A. K. Haghi

188

Figure1. Drying characteristic of porous media: (A) constant rate region; (B) first falling rate region; (C) second falling rate region.

−

d ( MC ) = A + B * MC For M cr1 > MC > M cr 2 dt

(26)

−

d ( MC ) A + B * M cr 2 = * (MC − M e ) For MC< M cr 2 dt M cr 2 − M e

(27)

Where: j 0 is constant drying rate, M Cr1 is the first critical moisture content, M cr 2 is the second critical moisture content, constants A and B also vary with wood thickness, wood density, and drying conditions.

4. MOISTURE CONTENT AND PERMEABILITY Moisture content of wood is defined as the weight of water in wood expressed as a fraction, usually a percentage, of the weight of oven dry wood. Moisture exists in wood as bound water within the cell wall, capillary water in liquid form and water vapor in gas form in the voids of wood. Capillary water bulk flow refers to the flow of liquid through the interconnected voids and over the surface of a solid due to molecular attraction between the liquid and the solid [57]. Moisture content varies widely between species and within species of wood [57-59]. It varies particularly between heartwood and sapwood. The amount of moisture in the cell wall may decrease as a result of extractive deposition when a tree undergoes change from sapwood to heartwood. The butt logs of trees may contain more water than the top logs. Variability of moisture content exists even within individual boards cut

Transport Phenomena within Porous Media

189

from the same tree. Green wood is often defined as freshly sawn wood in which the cell walls are completely saturated with water. Usually green wood contains additional water in the lumens. Moisture content at which both the cell lumens and cell walls are completely saturated with water is the maximum moisture content. An average green moisture content value taken from the Wood Handbook [59] and Dry Kiln Operator’s Manual [58] of southern yellow pine (loblolly) is 33 and 110% for heartwood and sapwood, respectively. Sweetgum is 79 and 137% while yellow-poplar is 83 and 106% for heartwood and sapwood, respectively [58, 59]. Permeability refers to the capability of a solid substance to allow the passage of gases or liquids under pressure [60]. Permeability assumes the mass movement of molecules in which the pressure or driving force may be supplied by such sources as mechanically applied pressure, vacuum, thermal expansion, gravity, or surface tension [61]. Under this condition, the permeability of wood is the dominant factor controlling moisture movement. Fluid movement in wood is a very important process in wood products industries [62]. An understanding of wood permeability is essential for determining lumber drying schedules for treating lumber and for producing high-quality wood products. The flow of gas inside the wood particle is limited due to the fact that wood consists of a large number of clustered small pores. The pore walls act as barriers largely preventing convective flow between adjacent pores. The wood annular rings also act as barriers for flow in the radial direction which makes flow in the axial direction more favorable and giving a lower permeability in the radial direction than in the axial direction where the axial flow is regarded as flow parallel to the wood fiber grains and the radial flow as flow perpendicular to the wood grains. The permeability in the wood cylinder is therefore an important parameter for the velocity field in the wood. From [63] the dry wood radial permeability is 10000 times lower than the dry wood axial permeability. The chemical composition of the wood/ char structure also affects the permeability, where the permeability in char is in order of 1000 times larger than for wood [64]. Longitudinal flow becomes important, particularly in specimens having a low ratio of length to diameter, because of the high ratio of longitudinal to transverse permeability [65]. Longitudinal permeability was found to be dependent upon specimen length in the flow direction [66], i.e. the decrease of specimen length appears result in greater permeability in less permeable species. For example, Sebastian et al. [67] found that the permeability of white spruce decreased with increasing specimen length. Bramhall [68] observed a negative relationship between the gas permeability and the lengths of Douglas fir specimens ranging from 0.5-3.5 cm. Siau [69] also reported similar results for Douglas fir and loblolly pine specimens of 2-30 cm in length. Banks [70] described that (due to decreased permeability with increases in specimen length) some flow paths may remain unchanged as length is increased while others may totally be blocked with a wide variation in pore diameter. Liquid, therefore, penetrates into some flow paths more rapidly than others, giving rise to the occurrence of surface forces resisting penetration with both wetting and non wetting liquids [71]. The effect of drying conditions on gas permeability and preservative treatability was assessed on western hemlock lumber. Although there were no differences in gas permeability between lumber dried at conventional and high temperatures, there were differences in preservative penetration. High temperature drying significantly reduced drying time, but did not appear to affect permeability or shell-to-core MC differences compared with drying at conventional temperature [72]. Pits have a major influence on softwood permeability [73].

Sh. Rahrovan and A. K. Haghi

190

Across pits can be impeded by aspiration or occlusion by deposition extractives on the membrane. Drying conditions can significantly affect pit condition, sometimes inducing aspiration that blocks both air and fluid flow [74]. Pressure treatment is presumed to enhance preservative uptake and flow across pits, but the exact impact of pit condition (i.e., open or aspirated) is unknown. Drying conditions may also alter the state of materials deposited on pits, thereby altering the effects of pressure and perhaps the nature of preservative wood interactions [75]. The latter effect may be especially important, since changes in wood chemistry could affect the rates of preservative fixation, which could produce more rapid preservative deposition on pit membranes that would slow further fluid ingress. Peter Y.S et al measured vessel lumen area and the longitudinal and radial permeabilities of the sapwood of each species to evaluate the effect of diameter growth rate on vessel lumen area percentage and on the intrinsic permeability. The longitudinal permeability of the outer heartwood of each species also was determined to evaluate the effect of growth rate on the decrease in longitudinal permeability following sapwood conversion to heartwood. Faster diameter growth produced higher longitudinal permeability in the sapwood of yellow-poplar, but not in the sapwood of northern red oak or black walnut. Growth rate had no effect on either vessel lumen area percentage or decrease in longitudinal permeability in newly formed heartwood for all three species [76]. Table 2 represents typical values for gas permeability. Values are given in orders of magnitude [77]. Darcy’s law for liquid flow:

V flux (t × A) = V × L k= = ΔP t × A × ΔP gradient L

(28)

Table 2. Typical values for gas permeability Type of sample

Longitudinal gas permeability 3

Red oak (R = 150 micrometers)

[ cm (gas)/(cm at sec)] 10,000

Basswood (R = 20 micrometers)

1,000

Maple, Pine sapwood, Coast Douglas-fir sapwood

100

Yellow-poplar sapwood, Spruce sapwood, Cedar sapwood

10

Coast Douglas-fir heartwood

1

White oak heartwood, Beech heartwood

0.1

Yellow-poplar heartwood, Cedar heartwood, Inland Douglasfir heartwood Transverse Permeabilities(In approx. same species order as longitudinal)

0.01 0.001 - 0.0001

Transport Phenomena within Porous Media

191

Where: 3

k = Permeability [ cm (liquid)/ (cm atm sec)] 3

V = Volume of liquid flowing through the specimen ( cm ) t = Time of flow (sec) A = Cross-sectional area of the specimen perpendicular to the direction of flow 2

( cm ) ΔP = Pressure difference between ends of the specimen (atm) L = Length of specimen parallel to the direction of flow (cm) Darcy’s law for gaseous flow:

kg =

V × L× P t × A × ΔP × P

(29)

Where:

k g = Superficial gas permeability [ cm 3 (gas)/ (cm atm sec)] 3

V = Volume of gas flowing through the specimen ( cm (gas)) P = Pressure at which V is measured (atm) t = Time of flow (sec) A = Cross-sectional area of the specimen perpendicular to the direction of flow 2

( cm ) ΔP = Pressure difference between ends of the specimen (atm) L = Length of specimen parallel to the direction of flow (cm)

P = Average pressure across the specimen (atm)

5. BASIC THEORETICAL CONCEPTS 5.1. Mass Conservation Equations To simulate the heat and mass transport in drying, conservation equations for general non-hygroscopic porous media have been developed in Whitaker [78] based on averaging procedures of all of the variables. These equations were further employed and modified for wood drying by Perre´ et al. [79] Mass conservation equations for the three phases of moisture in local form are summarized in equations (30-32). Water vapor:

∂ (φ g ρV ) = −div ρV VV + m& WV + m& bV ∂t

(

)

(30)

Sh. Rahrovan and A. K. Haghi

192 Bound water:

∂ (φ s ρ b ) = −div(ρ bVb ) + m& bV + m& wb ∂t

(31)

Free water:

∂ (φ w ρ w ) = −div(ρ wVw ) − m& wv − m& wb ∂t Where the velocity of the transported quantity is denoted by Vi ,

(32)

ρ i is the density, and

m& ij denotes the transition from phases i and j. From here on, the subscripts w, b, v, and s refer, respectively, to free water, bound water, water vapor, and the solid skeleton of wood. Denoting the total volume by V and the volume of the phase i by Vi , the volumetric fraction of this phase is:

φi =

Vi V

(33)

with the geometrical constraint:

φ g + φs + φw = 1

(34)

5.2. The Generalized Darcy’s Law Darcy’s law, by using relative permeabilities, provides expressions for the free liquid and gas phase velocities as follows: vl = −

K l K rl

∇Pl

(35)

vv= −

K v K rv

∇Pv

(36)

μl

and

μv

Where K is the intrinsic permeability ( m 2 ), k r is the relative permeability, P is the

pressure (Pa), and μ is the viscosity (Pa .s).

Transport Phenomena within Porous Media

193

5.3. External heat and Mass Transfer Coefficients The heat flux (q) and the moisture flux ( Nν

(

q = h TG − Tsurf

) are estimated by:

)

(37)

(

Nν = ϕK 0 (Ysurf − YG ) = β pνG − pνats

)

(38)

In which Tsurf , Υsurf andpνs are respectively, the wood temperature, the air humidity and the vapor partial pressure at the wood surface and, TG , ΥG andp νG are the corresponding parameters in the air stream. The heat-transfer coefficient is represented by h. The masstransfer coefficient is β when vapor partial pressure difference is taken as driving force and is k 0 when humidity difference is taken as the driving force with ϕ being the humidity factor. The mass-transfer coefficient related to humidity difference is a function of distance along the airflow direction from the inlet side [80]. The heat-transfer coefficient is correlated to the mass-transfer coefficient, as shown by and can be calculated from it [81]. The humidity coefficient ϕ has been found to vary from 0.70 to 0.76, depending on the drying schedules and board thickness [82].

5.4. Moisture and Heat Balance Equations For the moisture mass transfer and balance, the moisture loss from wood equals the moisture gain by the hot air, and the moisture transfer rate from the board is described by mass transfer coefficient multiplied by driving force (humidity difference, for example). These considerations yield:

−

⎧− ϕK .a.(Υ − Υ )(condensation) ∂ [MC.ρ s .(1 − ε )] = G. ∂Υ = ⎨ 0 surf G ∂τ ∂X ⎩ϕK 0 .a. f .(Υsat − ΥG )(evaporation)

Where MC is the wood moisture content,

(39)

ρ s is the wood basic density, ε is the void

fraction in the lumber stack, a is the exposed area per unit volume of the stack and G is the dry air mass flow rate. In order to solve the above equations, the relative drying rate (f) needs to be defined which is a function of moisture content [83, 84]. For the heat transfer and balance, the energy loss from the hot air equals the heat gain by the moist wood. The convective heat transfer is described by product of heat transfer coefficient and the temperature difference between the hot air and the wood surface. The resultant relationships are as follows:

Sh. Rahrovan and A. K. Haghi

194

(1 + α R − α LS ) ∂Twood = ∂τ ρ s .(1 − ε ).C Pwood

∂Υ ⎤ ⎡ .⎢h.a.(TG − Twood ) − G.ΔH wv . G ⎥ ∂X ⎦ ⎣

∂ΥG ⎞ ⎛ ⎟.(TG − Twood ) ⎜ h.a + G.C Pν ∂TG ⎝ ∂Ζ ⎠ = G.(C Pν + ΥG .C Pν ) ∂X In the above equations, Twood is the wood temperature,

(40)

α R and α LS are coefficients to

reflect effects of heat radiation and heat loss, C Pwood is the specific heat of wood, and ΔΗ wv is the of water evaporation. These equations have been solved to determine the changes of air temperature and wood temperature along the airflow direction and with time [85].

5.5. Energy rate Balance on Drying Air and Wood The energy rate balance (kW) of a drying air adjacent to the wood throughout the wood board can be represented as follows [86]:

dT 1 1 Va ρ a ,mt cp a ,mt a = νAcs cp a ,mt (Ta ,in −Ta ,ex ) + Q& evap − Q& conv dt 2 2

(41)

Where Q& evap and Q& conv (kW) are the evaporation and convection heat transfer rates between the drying air and wood, which can be calculated as follows:

Q& evap = rm& wv ,s Asurf

(42)

Q& conv = hA(Ta − TSO )

(43) 2

& wv ,surf ) (kg/ m s) to the drying air can be The specific water vapor mass flow rate ( m calculated as follows:

m& wv ,surf =

hD (Pwv,surf − Pwv,a ) RwvTSO

(44)

The vapor pressure on the wood surface can be determined from the sorption isotherms of wood [87]. The mass transfer coefficient ( hD ) (m/s) can be calculated from the convection 2

heat transfer coefficient (h) (kW/ m K) as follows [88]:

Transport Phenomena within Porous Media

hD = h

1

ρ a ,mt cpa ,mt Le

0.58

⎛ ρ wv ,m / ⎜⎜1 − P ⎝

⎞ ⎟⎟ ⎠

195

(45)

5.6. Water Transfer model above F.S.P. Water transfer in wood involves liquid free water and water vapor flow while MC of lumber is above the F.S.P. According to Darcy’s law the liquid free water flux is in proportion to pressure gradient and permeability. So Darcy’s law for liquid free water may be written as:

Jf =

k l ρ l ∂Pc . μ l ∂χ

(46)

Where:

J f =liquid free water flow flux, kg/ m 2 ·s,

k l =specific permeability of liquid water, m 3 (liquid ) / m ,

ρ l = density of liquid water, kg / m 3 , μ l = viscosity of liquid water, pa .s , pc = capillary pressure, pa , χ = water transfer distance, m, ∂pc / ∂χ = capillary pressure gradient, pa / m . The water vapor flow flux is also proportional to pressure gradient and permeability as follows:

J vf =

kV ρ v ∂PV . μV ∂χ

Where:

J vf = water vapor flow flux, kg/ m 2 ·s,

kV = specific permeability of water vapor, m 3 (vapor ) / m ,

ρ v , μ v = density and viscosity of water vapor respectively, kg / m 3 and pa .s , ∂pV / ∂χ =vapor partial pressure gradient, pa / m .

(47)

Sh. Rahrovan and A. K. Haghi

196

Therefore the water transfer equation above F.S.P. during high temperature drying can be written as:

ρs

∂ ( MC ) ∂ = (J f + J vf ∂t ∂x

)

(48)

Where:

ρ S = basic density of wood, kg / m 3 , MC = moisture content of wood, %, t = time, s, ∂ ( MC ) / ∂t = the rate of moisture content change, %/s, x = water transfer distance, m.

5.7. Water Transfer Model below F.S.P. Water transfer in wood below F.S.P. involves bound water diffusion and water vapor diffusion. The bound water diffusion in lumber usually is unsteady diffusion; the diffusion equation follows Fick’s second law as follows:

∂ ( MC ) ∂ ⎛ ∂ ( MC ) ⎞ = ⎜ Db ⎟ ∂t ∂x ⎝ ∂x ⎠

(49)

Where Db is bound water diffusion coefficient, m 2 /s, ∂ (MC)/ ∂x is MC gradient of lumber, %/m. The bound water diffusion flux J b can be expressed as:

J b = Db ρ s

∂ ( MC ) ∂x

(50)

Where:

ρ S is basic density of wood, kg/ m 3 . The water vapor diffusion equation is similar to bound water diffusion equation as follows

∂ ( MC ) ∂ ⎛ ∂ ( MC ) ⎞ = ⎜ DV ⎟ ∂t ∂ ( MC ) ⎝ ∂x ⎠ Where DV is water vapor diffusion coefficient, m 2 /s.

(51)

Transport Phenomena within Porous Media

197

The water vapor diffusion flux can be expressed as:

J V = DV ρ s

∂ ( MC ) ∂x

(52)

Therefore the water transfer equation below F.S.P. during high temperature drying can be expressed as:

ρs

∂ ( MC ) ∂ = (J b + J V ) ∂t ∂x

(53)

6. EXPERIMENTAL APPROACHES Two types of wood samples (namely; Guilan spruce and pine) were selected for drying investigation. Natural defects such as knots, checks, splits, etc which would reduce strength of wood are avoided. All wood samples were dried to a moisture content of approximately 30%. The effect of drying temperature and drying modes on the surface roughness, hardness and color development of wood samples are evaluated.

6.1. Surface Roughness The average roughness is the area between the roughness profile and its mean line, or the integral of the absolute value of the roughness profile height over the evaluation length: L

1 Ra = ∫ r ( x)dx L0

(54)

When evaluated from digital data, the integral is normally approximated by a trapezoidal rule:

Ra =

1 N

N

∑r n =1

n

(55)

The root-mean-square (rms) average roughness of a surface is calculated from another integral of the roughness profile: L

Rq =

1 2 r ( x)dx L ∫0

The digital equivalent normally used is:

(56)

Sh. Rahrovan and A. K. Haghi

198

Rq =

1 N 2 ∑ rn N n=1

(57)

Rz (ISO) is a parameter that averages the height of the five highest peaks plus the depth of the five deepest valleys over the evaluation length. These parameters which are characterized by ISO 4287 were employed to evaluate influence of drying methods on the surface roughness of the samples. [89]. ÜNSAL, Ö. et al investigated the influence of drying temperatures on the surface roughness characteristics of veneer samples. The results showed that the effect of drying temperatures used in practice is not remarkable on surface roughness of the sliced veneer and maximum drying temperature (130°C) applied to sliced veneers did not affect significantly surface roughness of the veneers [90]. Results obtained from previous similar studies supported the findings of this study [91, 92]. Ismail Aydin and Gursel Colakoglu conducted a study on veneer. Veneer sheets were classified into four groups and dried at 20, 110, 150, and 180°C. According to the results, the smoothest surfaces were obtained for 20°C drying temperature while the highest values of surface roughness were obtained for 180°C [93]. Because some surface checks may develop in the oven-drying process [94]. It was also found in a study that the surface roughness values of beech veneers dried at 110°C was higher than that of dried at 20°C [95]. Ismail Aydin et al. performed an experimental study on Alder and beech. Veneer sheets were oven-dried in a veneer dryer at 110°C (normal drying temperature) and 180° C (high drying temperature) after peeling process. The surfaces of some veneers were then exposed at indoor laboratory conditions to obtain inactive wood surfaces for glue bonds, and some veneers were treated with borax, boric acid and ammonium acetate solutions. After these treatments, surface roughness measurements were made on veneer surfaces. Alder veneers were found to be smoother than beech veneers. They concluded that the values mean roughness profile ( Ra ) decreased slightly or no clear changes were obtained in Ra values after the natural inactivation process. However, little increases were obtained for surface roughness parameters, no clear changes were found especially for beech veneers. It was concluded in a study that the surface of CCAtreated wood was rougher than that of untreated and water-treated wood [96, 97]. Ali Temiz et al. investigated the changes created by weathering on impregnated wood with several different wood preservatives. The study was performed on the accelerated weathering test cycle, using UV irradiation and water spray in order to simulate natural weathering. Wood samples were treated with ammonium copper quat (ACQ 1900 and ACQ 2200), chromated copper arsenate (CCA), Tanalith E 3491 and Wolmanit CX-8 in accelerated weathering experiment. The changes on the surface of the weathered samples were characterized by roughness measurements on the samples with 0, 200, 400 and 600 h of total weathering. Generally the surface values of alder wood treated with copper-containing preservatives decreased with over the irradiation time except for treated Wolmanit CX-82% when comparing unweathered values. Surface values of pine treated samples generally increased with increasing irradiation time except for ACQ-1900 groups [98]. Because the stylus of detector was so sensitive first each sample was smoothened with emery paper then measurement test was performed before and after drying. The Mitutoyo

Transport Phenomena within Porous Media

199

Surface roughness tester SJ-201P instrument was employed for surface roughness measurements. Cut-off length was 2.5 mm, sampling length was 12.5 mm and detector tip radius was 5 μm in the surface roughness measurements. Table 3 and Table 4 displays the changes in surface roughness parameters ( Ra , R z and Rq ) of the Pine and Guilan spruce at varying drying methods. In both cases the surface roughness becomes higher during microwave and infrared heating while surface smoothness of both pine and Guilan spruce increased during convection and combined drying [99]. However, the roughness of wood is a complex phenomenon because wood is an anisotropic and heterogeneous material. Several factors such as anatomical differences, growing characteristics, machining properties of wood, pre-treatments (e.g. steaming, drying, etc.) applied to wood before machining should be considered for the evaluation of the surface roughness of wood [100]. Table 3. Surface roughness (μm) for pine Drying methods

Drying conditions

Microwave

Before drying After drying Before drying After drying

4.525.46

24.6830.21

5.396.62

4.42 4.87

25.52 26.55

5.43 5.69

Convection

Before drying After drying

4.66 4.08

26.87 24.64

5.86 5.12

Combined

Before drying After drying

5.23 3.41

32.59 21.7

6.42 4.27

Infrared

Ra

Rz

Rq

Table 4. Surface roughness (μm) for Guilan spruce Drying methods

Drying conditions

Microwave

Before drying After drying Before drying After drying Before drying After drying Before drying After drying

Infrared Convection Combined

Ra

Rz

Rq

6.44 7.77 4.92 6.42 4.97 4.78 10.41 9.11

34.18 44.3 30.61 38.93 32.41 32.27 59.5 54.31

7.85 9.82 6.30 8.17 6.5 6.34 13.37 11.5

6.2. Hardness Hardness represents the resistance of wood to indentation and marring. In order to measure the hardness of wood samples, the Brinell hardness method was applied. In this

Sh. Rahrovan and A. K. Haghi

200

method a steel hemisphere of diameter 10 mm was forced into the surface under test. The Brinell method measures the diameter of the mark caused by the steel ball in the specimens. The specimens were loaded parallel and perpendicular to the direction of wood grains. After applying the force the steel ball was kept on the surface for about 30 seconds. The values of hardness are shown in figures 2, 3 respectively. In both type of samples the hardness measured in longitudinal direction is reported to be higher than tangential. The amount of fibers and its stiffness carrying the load are expected to be lower when the load direction is angled to the grain. Results showed that hardness of wood increased in combined drying. The hardness of wood is proportional to its density [101]. The hardness of wood varies, depending on the position of the measurement. Latewood is harder than early wood and the lower part of a stem is harder than the upper part. Increase in moisture content decreases the hardness of wood [102]. Selhlstedt_Persson has observed the effect of different drying temperatures during air circulation drying. The result indicates no significant influence of temperature on hardness; still the specimens dried at higher temperature gave a hard and brittle impression [103]. L.Hansson and A.L.Antti investigated whether wood hardness is affected by temperature level during microwave drying and whether the response is different from that of conventionally dried wood. They concluded that there is a significant difference in wood hardness parallel to the grain between methods when drying progresses to relatively lower level of moisture content, i.e. wood hardness becomes higher during microwave drying. Variables such as density and moisture content have a greater influence on wood hardness than does the drying method or the drying temperature [104].

perpendicular to the grain

C

In fra re d C om bi ne d

parallel to the grain

on ve ct io n M icr ow av e

Hardness(Mpa)

30 25 20 15 10 5 0

DIFFERENT DRYING METHODS Figure 2. Brinell hardness for Guilan spruce.

Transport Phenomena within Porous Media

Hardness(Mpa)

25

201

perpendicular to the grain

20 15

parallel to the grain

10 5

bi ne d om

C

In fra re d

C

on ve ct io n M icr ow av e

0

DIFFERENT DRYING METHODS Figure 3. Brinell hardness for pine.

6.3. Color Development Measurement Color development of wood surfaces can be measured by using optical devices such as spectrophotometers. With optical measurement methods, the uniformity of color can be objectively evaluated and presented as L*, a* and b* coordinates named by CIEL*a*b* color space values [105]. Measurements were made both on fresh and dried boards and always from the freshly planed surface. Three measurements in each sample board were made avoiding knots and other defects and averaged to one recording. The spectrum of reflected light in the visible region (400-750 nm) was measured and transformed to the CIEL*a*b* color scale using a 10º standard observer and D65 standard illuminant. These color space values were used to calculate the total color change ( ΔE ) applied to samples according to the following equations: *

ΔL* = L*f − L*i Δa * = a *f − ai* Δb * = b *f − bi*

(58)

ΔE * = (ΔL* ) 2 + (Δa * ) 2 + (Δb * ) 2 f and i are subscripts after and before drying respectively. In this three dimensional coordinates, L* axis represents non-chromatic changes in lightness from an L* value of 0 (black) to an L* value of 100 (white), +a* represents red, -a* represents green, +b* represents yellow and -b* represents blue [106]. As can be seen from figure4 and figure5 color space values of both pine and Guilan spruce changed after drying.

Sh. Rahrovan and A. K. Haghi

Surface color

202 7 6 5 4 3 2 1 0 -1 -2 -3

o i cr M

ΔL* Δa* Δb* d n tio ine c b e m In nv o Co C Different drying methods

ve wa

ΔE*

d re a r f

Surface color

Figure 4. Surface color of Pine. 6 5 4 3 2 1 0 -1 -2 -3 -4

o i cr M

ΔL* Δa* Δb* d n ne tio i c b e In nv om o C C Different drying methods

ve a w

re fra

d

ΔE*

Figure 5. Surface color of Guilan spruce.

Results shows that Δa ∗ generally decreased but Δb ∗ increased for both pine and Guilan spruce wood samples except for Guilan spruce during combined heating. The lightness values ΔL increased during drying. The L of wood species such as tropical woods which originally have dark color increases by exposure to light [107, 108]. This is due to the special species and climate condition of Guilan spruce and pines wood. Positive values of Δb* indicate an increment of yellow color and negative values an increase of blue color. Negative values of Δa* indicate a tendency of wood surface to greenish. A low ΔE* corresponds to a *

*

low color change or a stable color. The biggest changes in color appeared in ΔE values of pine samples during infrared drying while for Guilan spruce it was reversed. Due to differences in composition of wood components, the color of fresh, untreated wood varies between different species, between different trees of the same species and even within a tree. *

Transport Phenomena within Porous Media

203

Within a species wood color can vary due to the genetic factors [109, 110] and environmental conditions [111, 112]. In discoloration, chemical reactions take place in wood, changing the number and type of chromophores. Discolorations caused by the drying process are those which actually occur during drying and are mainly caused by non-microbial factors [113]. Many environmental factors such as solar radiation, moisture and temperature cause weathering or oxidative degradation of wooden products during their normal use; these ambient phenomena can eventually change the chemical, physical, optical and mechanical properties of wood surfaces [114]. A number of studies have been conducted that have attempted to find a solution to kiln brown stain, the majority of them being pre-treatment processes. Biological treatment [115], compression rolling [116], sap displacement [117, 118] and chemical inhibitors [119] have all been used as pre-treatments. In all cases these processes were successful in reducing or eliminating stain but were not considered economically viable. Vacuum drying [120] and modified schedules [121] have been tried as modified drying processes with only limited success. Within industry various schedules have been developed, though these are generally kept secret and it is difficult to gauge their success. Generally it seems that industry has adopted a post-drying process involving the mechanical removal of the kiln brown stain layer as recommended by Kreber and Haslett [121].

7. CONCLUDING REMARKS Microwave processing of materials is a relatively new technology that provides new approaches to improve the physical properties of materials. Microwave drying generate heat from within the grains by rapid movement of polar molecules causing molecular friction and help in faster and more uniform heating than does conventional heating. If wood is exposed to an electromagnetic field with such high frequency as is characteristic for microwaves, the water molecules, which are dipoles, begin to turn at the same frequency as the electromagnetic field. Wood is a complex composite material, which consists mainly of cellulose (40–45%), hemicelluloses (20–30%) and lignin (20–30%). These polymers are also polar molecules, and therefore even they are likely to be affected by the electromagnetic field. This could possibly cause degradation in terms wood hardness. For Guilan spruce the average of hardness is shown to be much higher than pine. From the experimental results it can be observed that in combined microwave dryer, the hardness was relatively improved in comparison to the other drying methods. Microwave and infrared drying can increase wood surface roughness while the smoothness of wood increases during convection and combined drying. The effect varies with the wood species. Thus this work suggests keeping the core temperature below the critical value until the wood has dried below fiber saturation as one way of ensuring that the dried wood is acceptably bright and light in color.

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[57] Haygreen, J.G. and Bowyer. J.L. Forest Products and Wood Science: An Introduction. Iowa State University Press, Ames, Iowa, 1996. [58] Forest Products Society (FPS). Dry Kiln Operator’s Manual. Reprinted from USDA Agricultural Handbook 1997. No. 188. [59] Forest Products Society (FPS). Wood Handbook: Wood as an Engineering Material. Reprinted from USDA Forest Service Forest Products Laboratory General Technical Report FPL-GTR 113. 1999. [60] Erickson, H.D. Permeability of southern pine. Wood Science, 1970, 2(3):149-157. [61] Waananen, K.M., and Okos. M.R. Analysis of Mass Transfer Mechanisms during Drying of Extruded Semolina. Proceedings of the 5th International Congress on Engineering and Food. 1989. May 28-June 3, Cologne, Germany. [62] Petty, J. A. The Relation of Wood Structure to Preservative Treatment. The wood we grow, Society of Forestry Britain, 29-35, University Press, Oxford. 1970. [63] Larfeldt, J., Leckner, B., Melaaen, M.C. Modelling and Measurements of Drying and Pyrolysis of Large Wood Particles. Fuel, 2000, 79(13):1637–1643. [64] U. Sand , J. Sandberg, R. Bel Fdhila, Two-Phase Transport Model for the Pyrolysis Process of a Vertical Wood Cylinder, Including the Surrounding Flow Field, International Journal of Green Energy, 2006, 3: 63–78. [65] Siau, J. F. Flow in Wood. Syracuse University Press, London, 1971, pp:131. [66] Siau, J. F. The Effects of Specimen Length and Impregnation Time upon the Retention of Oils in Wood. Wood Science, 1972, 4 (3): 163-170. [67] Sebastian, L. P., Cote, W. A., J. R., Skaar, C. Relationship of Gas Phase Permeability to Ultrastructure of White Spruce Wood. Forest Products Journal, 1965, 15 (9): 394404. [68] Bramhall, G. The validity of Darcy’s law in the axial penetration of wood. Wood Science and Technology, 1971, 5 (2): 121- 134. [69] SIau, J. F. Pressure Impregnation of Refractory Woods. Wood Science, 1970, 3 (1): 17. [70] Banks, W. B.Addressing the problem of non-steady state liquid flow in wood. Wood Science and Technology, 1981, 15: 171 177. [71] lker USTA, Arif GÜRAY., The Effect of Wood Specimen Length on the Proportional Saturation of Preservative Fluid in Sitka Spruce (Picea sitchensis(Bong.) and Corsican Pine (Pinus nigravar. mantima), Ankara-TURKEY Turk J Agric For 25, 2001, 1-4 . [72] Rhatigan, R.G. Milota, M.R. Morrell, J.J. Lavery, M.R., Effect of High Temperature Drying on Permeability and Treatment of Western Hemlock Lumber, Forest Products Journal, 2003, Vol. 53, No. 9, pages 55-58. [73] Siau, J.F. Wood: Influence of moisture on physical properties. Dept. of Wood Sci. and Forest Prod., Virginia Polytechnic Institute and State Univ., Blacksburg, VA. 1995, pp: 227. [74] Bao, F., J. Lu, and Y. Zhao. Effect of Bordered Pit Torus Position on Permeability in Chinese Yezo spruce. Wood and Fiber Sci., 2001, 33(2):193-199. [75] Forsyth, P.G. and J.J. Morrell. Hexavalent Chromium Reduction in Chromated Copper Arsenate-treated Douglas-fir and Western Hemlock. Forest Prod. J.1990, 40(6):48-50. [76] Peter Y.S. Chen, Guoqiang Zhang J.W., Van Sambeek, Relationships Among Growth Rate, Vessel Lumen Area, and Wood Permeability for Three Central Hardwood Species. Forest Products Journal, 1998, VOL. 48, NO. 3, pages 87-90.

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[77] Siau, J.F. Transport Processes in Wood. Springer-Verlag. New York, 1984. [78] Whitaker, S. Simultaneous Heat, Mass and Momentum Transfer in Porous Media: A Theory of Drying. Advances in Heat Transfer 1977, 13, 119–203. [79] Perre´, P.; Fohr, J.-P.; Arnaud, G. A model of drying applied to softwoods: The effect of gaseous pressure below the boiling point. In Drying ‘89; Mujumdar, A.S., Roques, M.A., Eds.; Hemisphere: New York, 1990; 91–98. [80] Kho, P.C.S.; Keey, R.B. and Walker, J.C.F. Effects of Minor Irregularities and on Drying Rate of Softwood Timber Boards in Kilns. Proceedings of 2nd IUFRO Wood Drying Conference, Seattle, 1989, pp. 150-157. [81] Pang, S., External Heat and Mass Transfer Coefficients for Kiln Drying of Timber, Drying Technology, 1996, 14(3&4), pp.859-871. [82] Pang, S. High temperature Drying of Pinus Radiate Boards in a Batch Kiln, PhD Thesis, University of Canterbury, Christchurch, New Zealand, 1994. [83] Keey, R.B. and Pang, S. The high Temperature Drying of Softwood Boards: A Kiln Wide Model, Chemical Engineering Research and Design, 1994, Vol.72, No. A6, pp.741-753. [84] Pang, S. Development and validation of a kiln-wide model for drying of softwood lumber, Proceedings of 5th International IUFRO Wood Drying Conference, Quebec, Canada, 1996, pp.103-110. [85] Pang ,Airflow Reversals for Kiln Drying of Softwood Lumber: Application of a KilnWide Drying Model and a Stress Model, Proceedings of the 14th International Drying Symposium, 2004, vol. B, pp. 1369-1376. [86] Awadalla, H.S.F., El-Dib, A.F. Mohamad, M.A. Reuss, M. Hussein, , H.M.S. Mathematical Modelling and Experimental Verification of Wood Drying Process , Energy Conversion and Management , 2004, 45, 197–207. [87] Kollmann F. Principles of wood science and technology. Berlin, Germany: SpringerVerlag; 1968. [88] Krischer O, Kröll AJ. Trocknungstechnik. Berlin, Germany: Springer-Verlag; 1992. [89] International Standard ISO 4287. Geometrical Product Specifications (GPS) Surface Texture: Profile Method - Terms, Definitions and Surface Texture Parameters. International Organization for Standardization, Geneva, Switzerland, 1997. [90] Ünsal, Ö. Ayrilmi, N.; Korkut, S., 2005: Effect of Drying Temperature on Surface Roughness of Beech (Fagus orientalis Lipsky L.)Veneer, 9th International IUFRO Wood Drying Conference, Quality Control and Energy Saving in Wood Drying, 2005, pp. 316-319. [91] Aydin, I.; Colakoglu, G. The Effects of Veneer Drying Temperature on Wettability, Surface Roughness and Some Properties of Plywood, Proceedings of the Sixth Panel Products Symposium, 2002, pp. 60-70, 9-11. [92] Aydin, I.; Colakoglu, G. The Effect of Steaming and Veneer Drying Temperature on the Weathering Reactions, Wood-based materials, wood composites and chemistry, International Symposium. 2002, pp: 1-9. [93] Ismail Aydin and Gursel Colakoglu, Formaldehyde Emission, Surface Roughness, and Some Properties of Plywood as Function of Veneer Drying Temperature, Drying Technology, 2005, 23: 1107–1117. [94] Reeb, J.E. Drying Wood; University of Kentucky, College of Agriculture. Cooperative Extension Service, USA, 1997.

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[95] Aydin, I. Activation of wood surfaces for glue bonds by mechanical pretreatment and its effects on some properties of veneer surfaces and plywood panels. Applied Surface Science 2004, 233 (1=4), 268–274. [96] Aydin, I. Colakoglu, G. Effects of Surface Inactivation, High Temperature Drying and Preservative Treatment on Surface Roughness and Color of Alder and Beech Wood, Applied Surface Science, 2005, 252, 430–440. [97] D.C. Maldas, D.P. Kamdem, Surface Characterization of Chromated Copper Arsenate (CCA)-Treated Red Maple, J. Adhes. Sci. Technol., 1998, 12 (7) 763–772. [98] A. Temiz, U.C. Yildiz, I. Aydin, M. Eikenes, G. Alfredsen, G., Colakoglu, Surface roughness and color characteristics of wood treated with preservatives after accelerated weathering test, Appl. Surf. Sci. (in print). [99] Naghashzadegan, M. Haghi, A.K. Amanifard, N. Rahrovan, Sh. Microwave drying of wood: Prductivity improvement, Wseas Trans. on Heat and Mass Transfer, Issue 4, Vol.1, pp. 391-397, 2006. [100] I. Aydin, G. Colakoglu, Roughness on Wood Surfaces and Roughness Measurement Methods, J. Artvin For. Faculty Kafkas Univ. 4 (1–2), 2003, 92–102. [101] F. Kollmann, A. Cote, Principles of wood science and Technology. Part 1, Solid Wood, Springer, Berlin, 1968. [102] J.Kopac, S. Sali, Wood an Important Material in Manufacturing Technology, Journal of Material Processing Technology 133 ,2003, 134-142. [103] S.M.B. Selhlstedt-Persson, High-Temperature Drying of Scots Pine. A comparison between HT and LT drying, Holtz als Roh- und Werkstoff 53, 1995, 95-99. [104] L.Hansson and A.L.Antti, The Effect of Drying Method and Temperature Level on the Hardness of Wood, Journal of Materials Processing Technology, 2005. [105] Toivonen, R.and Laurila, R. Tree species information in marketing of solid wood products, in: Proceedings of XI World Forestry Congress, Antalya, Turkey, 1997. [106] Hunt, R.W.G. Measuring Color. Third edition. Fountain Press, Kingston-upon-Thames, England, 1998, pp. 53-72. [107] Mitsui. K., Tsuchikawa.S. Low Atmospheric Temperature Dependence on Photo Degradation of Wood, Journal of Photochemistry and Photobiology B:Biology 81, 2005, pp. 84 –88. [108] Kishino.M.,Nakano.T.,Holzforschung, 2004, ,58 pp. 558 –565. [109] Rink, G. & Phelps, J.E. Variation in Heartwood and Sapwood Properties Among 10year Old Black Walnut Ttrees. Wood and Fiber Science 21:1989, pp.177-182. [110] Mosedale, J.R., Charrier, B. & Janin, G. Genetic Control of Wood Color, Density and Heartwood Ellagitannin Content of European Oak (Quercus petraea and Quercus robur).Forestry 69:1996, pp.111-124. [111] Phelps, J.E., McGinnes, E.A., Garret, H.E. & Cox, G.S. Growth Quality Evaluation of Black Walnut Wood. II. Color Analyses of Veneer Produced on Different Sites. Wood and Fiber Science 15: 1982, pp.177-185. [112] Wilkins, A.P. & Stamp, C.M. Relationship Between Wood Color, Silvicultural Treatment and Rate of Growth in Eucalyptus Grandis Hill (Maiden). Wood Science and Technology 24:1990, pp. 297-304. [113] Amburgey, T.L. Color, Stain, and the Drying Process. Profitable Solutions for Quality Drying of Softwoods and Hardwoods, proceedings. May 25-27, 1 Charlotte, NorthCarolina. Forest Products Society, 1994, pp. 66-68.

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[114] Hon, D.N.-S. Weathering and photochemistry of wood. In: Hon, D.N.-S. & Shiraishi, N. (eds.). Wood and cellulosic chemistry. 2nd ed., rev. and expanded. Marcel Dekker, New York, 2001, pp. 513-546. [115] McCurdy, M.C.; Nijdam, J.J.; Keey, R.B. Biological Control of Kiln Brown Stain in Radiata Pine. Maderas: Ciencia Y Tecnologia, 2002, 4(2):140-147. [116] Kreber, B.; Haslett, A. N. A Study of Some Factors Promoting Kiln Brown Stain Formation in Radiate Pine. Holz als Roh und Werkstoff 55 (4): 1997, 215-220. [117] Dieste, A. Colour Development in Pinus Radiata D. Don under kiln-drying Conditions. ME thesis, Department of Chemical and Process Engineering, University of Canterbury, New Zealand, 2002. [118] Kreber, B.; Stahl, M.R, Haslett, A.N. Application of a Novel de-Watering Process to Control Kiln Brown Stain in Radiata Pine. Holz als Roh und Werkstoff 59:2001, 29-34. [119] Kreber, B., Haslett, A.N., McDonald, A.G. Kiln Brown Stain in Radiata Pine: A Short Review on Cause and Methods for Prevention. Forest Products Journal, 1999, 49(4): 66-70. [120] Wastney, S., Bates, R., Kreber, B. and Haslett, A. Potential of vacuum drying to control kiln brown stain in radiata pine. Holzforschung und Holzverwertung, 1997, 49(3): 56-58. [121] Kreber, B.; Haslett, A. N. The Current Story on Kiln Brown Stain. FRI Bulletin Issue No.23, 1998.

In: Modern Tendencies in Organic and Bioorganic Chemistry ISBN: 978-1-60456-295-8 Editors: A. Mikitaev, M. K. Ligidov, pp. 211-214 © 2008 Nova Science Publishers, Inc.

Chapter 17

BLOCK-COPOLYSULFONARILATES OF POLYCONDENSATIONAL TYPE E. B. Barokova, A. M. Kharaev, R. Ch. Bazheva, T. R. Umerova Kabardino-Balkarian State University, Nalchik, 173 Chernishevskaye street, KBR, Russia

ABSTRACT The review on the ways of receiving, properties and the use of some blockcopolysulfonarilates on the basis of bisphenols of different kinds of construction is represented here.

Keywords: block-copolysulfonarilates, bisphenols, dichloranhydride, sulphonoxide, 1,1-dichloro-2,2-di(n-oxyphenyl)ethylene.

oligoarilen-

The production of polymers of prefabricated construction – one of the ways of creation of high-molecular compounds with a beforehand given complex of properties. The perspective in this direction is the synthesis of chemically active bifunctional oligomers, able to react with polycondensations. Polycondensational pokymers, as a rule, have valuable operational characteristics, as a high heat-, fire-, thermo-, chemicalstability in combination with good strengthening indices. Polysulfonarilates belong to such ones. Block-copolysulfonarilates may be received in several ways, for instance, by the interaction of separately received macrodychlorinehydride on the basis of oligoarylate of needed molecular weight and oligoarylensulfoxide (OASO) with terminal hydroxyl groups. It is obvious that this way may be realised by the method of acceptor- catalytic polycondensation. Oligomers of both types of the given molecular weight with terminal hydroxyl groups may be also received and their transformation into block-copolymers may be realised by interaction with dichloranhydride of dicarboxylic acid – the extender of the chain. There is also a possibility of introducing one of the beforehand received olygomers, for instance,

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212

oligoarylensulfoxide as a macrobisphenol into the reactionary compound, containing lowmolecular bisphenol and dichloranhydride of dicarboxylic acid. At the same time there is a formation of olygoarialate blocks of an indeterminate molecular weight which are chemically connected with blocks of oligoarylensulfoxide of the given molecular weight, and also the lengthening of oligoarylensulfoxide blocks through dichloranhydride of dicarboxylic acid, that is the block-copolymers are noticeably of less well-ordered structure. These two ways of receiving block-copolymers may be realised by acceptor- catalytic, emulsive and high-temperature polycondensation. For receiving different block-copolysulfonarilates the initial monomers are, as a rule, such widespread monomers as diphenylolpropane, phenolphtalein, dichloranhydrides of phthalic acid, and also OASO of different degree of condensation on the basis of these bisphenols and 4,4'-dichlorodiphenilsulfon. As the investigations of properties of block-copolymers datas, received by different ways, show that if having OASO – blocks till 10-15% the thermic properties of samples remain on the level of polyarilates, and the mechanical properties noticeably improve. Simultaneously the viscosity of fluxes of block-copolymers greatly decrease, and that has a great practical significance as it leads to a considerable simplification of heat-resistant polymers. With the aim of getting block-copolysulfonarilates with a smaller degree of fusion, and with good physio-mechanical properties the block-copolymers are synthesized on the basis of dian or phenolphtalein oligoarilensulphonoxides and dichloranhydrides of different structure [1-6]. The received block-copolysulfonarilates, on the basis of dian OASO and dichloranhydride 1,1-dichlor-2,2-di(n-oxyphenyl)ethylene, have the following structure:

C CH3

CH3

O

CH3 O

O

S O

O

C CH3

O n

C

C

C

O

CCI2

O m

where n = 1,5,7,10 and 20 The use of 1,1-dichloro-2,2-di(n-oxyphenyl)ethylene as an acid agent leads to an improvement of a number of mechanical datas. The block-copolymers are soluble in chlorinated hydrocarbons and are not soluble in alcohol and in aliphatic hydrocarbon, have stability in deluted and concentrated solutions of alkali, in strong mineral acids, but resolve in a concetrated sulphuric acid. The films received by the method of watering in chloroform, are transparent and have good physio-mechanical properties. If compared the mechanical properties of the given layer of block-copolysulfonarilates it is evident that with a increase of the length of initial oligoether the significance of the breaking-down voltage doesn’t change greatly, while the percent elongation increases greatly. The block-copolysulfonarilates o the basis of OASO –20D have good plasticity. High datas of deformation- strengthening properties of given block-copolysulfonarilates are explained that the last ones combine inflexibility of polyarilates as well as elasticity of polysulfones. In this case the elasticity is gained by OASO of different degree of polycondensation, which makes the system in the hole more plastic.

Block-copolysulfonarilates of Polycondensational Type

213

Commparatively low datas of temperatures of glass transition and the flow of this level of block-copolysulfonarilates are explained by the content of a big number of flexible simple ether bonds. The size of permittivity of all investigated samples of block-copolymers~3 – 3,6 and is stable in the interval of temperatures 20-200 °C. The characteristics of inflammation and combustibility of polymer materials are connected closely with the existance of macromolecules haloidcontaining groupings in the chain. The introduction of a macromolecule >C=CCl2 groupings into the chain and the increase of their percentage in block-copolymers promote the increase of the index of the oxygen index (OI). The ramp OI of block-copolymers with the increase of the content of chlorinated components, is apparently connected with the changes of the amount of combustible products, exuded from unit of volume of block-copolymers when burning. The other group of block-copolysulfonarilates – are block-copolymers on the basis of phenophthalein oligoarilensulphonoxides (OASO) of different length and dichloranhydride 1,1-dichlor-2,2-di(n-oxyphenyl)ethylene, having the following structure: O O

C

O

O

O C

S

O

O

O

C

C O

O C

O

n

R

C O m

The use of phenolphtalein oligoethers, intruduction of volumetric carded classifications as a bridge group into the structure of oligoethers noticeably increases the temperature of glass transition and the flow of block-copolysulfonarilates in comparison with blockcopolysulfonarilates on the basis of OASO. The investigation of the temperature dependence of dielectric characteristics of these block-copolysulfonarilates showed that the permittivity in the interval 20-250°C is stable. When higher than this temperature its increase is seen, which is explained by the transition to a hyperelastic state. These block-copolysulfonarilates are steady in diluted solutions of acids and alkalies. A big degree of turgescence of polyethers on the basis of phenolphtalein oligoethers is connected with a lesser density of the packaging materials of these block-copolysulfonarilates in comparison with block-copolysulfonarilates on the basis of OASO. A high chemical stability, refractoriness, good dielectric characteristics in a wide interval of temperatures receivings of linear and structural polymers make them suitable as insulating, chemicaly stable, fire-resistant coverages, and high physio-mechanical characteristics – as constructive materials. An important characteristic for polyarilatesulfones and their derivatives is their incombustibility, refractoriness and thermal stability. In the work [7] with the aim to receive incombustible polymeric materials some polyarilatsulfon block-sopolymers on the basis of halogen containing bisphenols are synthesized and their properties are investigated. The BSP datas have a high refractoriness, rising with an increase of the halogen content in BSP. When the initial halogen containing

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bisphenol is changed for bromide the refractoriness of received block-sopolymers increase greately. The datas of oxygen index for given block-sopolymers are in the interval 30-55%. In last three decades prof. Mikitaev and his pupils in the Kabardino-Balkarian State university hundreds of different block-copolysulfonarilates with high exploitation characteristics. Olygoarilensulfonoxides of different construction and structure are used in them, making a high heat resistance in combination with a high explosive solidity and plasticity. In the scientific works of these scientists it is shown that the introduction of some elements of olygosulfons into the macrochain of blok-sopolyethers influence positively some properties of the last ones. Different polyarilates and block-copolysulfonarilates based on the different unsaturated halogen containing monomers are also created - chloral derivatives, characterised by a complex of important properties, including an especially high fire- and chemicalstability. The use of such monomers helps to enlarge greatly the assortment of constructive and insulating polyesters. Besides, the egsistense of an unsaturated bond in these monomers makes it possible to thermoset block-copolysulfonarilates, thus improoving a number of operational characteristics. Taking into consideration the above-stated, we synthesized a number of blockcopolysulfonarilates on the basis of different bisphenols, the results of which will be presented in the subsequent works.

REFERENCES [1] [2]

[3]

[4] [5]

[6] [7] [8] [9]

Mikitaev A.K., Shustov G.B., Kharaev A.M. Synthesis and properties of blockcopolysulfonarilates. // Vysokomolek. Soed., 1984, 26A, №1, - P. 75-78. Kharaev A.M., Mikitaev A.K., Shustov G.B. and others. Synthesis and properties of block-copolysulfonarilates on the basis of oligoarilensulfophenolphthalein. // Vysokomolek. Soed., 1984, V.26B №14. – P. 271-274. Mikitaev A.K., Kharaev A.M., Shustov G.B. Unsaturated aromatic compound polyesters on the basis of chloral’s derivatives as constructive and membraneous materials. // Vysokomolek. Soed.,. 1998, v.39 №15, P.228-236. Kharaev A.M. Aromatic polyesters as thermostable constructive and membraneous materials: thesis for a Doctor's degree in chemistry, - Nalchik, 1993. 297 p. Mikitaev A.K., Korshak V.V., Shustov G.B. and others. Synthesis and investigations of some properties of halogen containing block-copolymers on the basis of oligomeric sulfone. Thes. Rep. of rep. conf. “Polymeric materials and the use in national economy”. Nalchik, 1976, publication 3, P. 49-50. Ozden S, Charaev A.M., Shaov A.H. High impact thermally stable blok- copolyethers. J. Mater. Sci. – 2001.-36.-P. 4479-4484. Mikitaev A. K., Shustov G. B, Charaev A. M., Korshak V. V., Kunizhev B. I. and. Dorofeev V. T. Vysokomolek. Soed. 1984.A, V.26, 75. Ozden S., Charaev A. M., Shaov A. H. and Shustov G.B., J. Appl. Polym. Sci.,1998, V.68, 1013. Shustov G.B., Mikitaev A. K., Charaev A. M., Dorofeev V. T. Patent 1485642, МКИ4 С08G 75/20.

In: Modern Tendencies in Organic and Bioorganic Chemistry ISBN: 978-1-60456-295-8 Editors: A. Mikitaev, M. K. Ligidov, pp. 215-218 © 2008 Nova Science Publishers, Inc.

Chapter 18

LIGUID-CRYSTALLINE POLYESTHERS ON THE BASIS OF TEREPHTALOYL-DI(N-OXIBENZOAT) AND AROMATIC POLYETHERS L. A. Asueva*, M. A. Nasurova, G. B. Shustov, A. M. Kharaev, and A. K. Mikitaev Khasbulatova Z. S.-Chechen State Pedagogical Institute, Grozny, 33 Kievskaya Str., Russia Kabardino-Balkar State University, Nalchic, 173 Chernishevskogo Str, Russia

ABSTRACT The briet review of coming out of liguid-grystalline poyethers, containing terephtaloyl-di(n-oxybenzoat) links and description of oligoethers, oligoketons, oligosulphoneketons which are used by the authors to get liguid-crystalline blokcopolymers is given.

Keywords: Liguid-crystalline, polycondensation, termotropic, terefhtaloyl-di(n-oxibenzoat) links, mesohenic groups, spacers, nematic, smectic, cholesteric structures, oligoethers, blockcopolymers

Nowadays we know several types of polymers, which are capable of liguid-crystalline solutions and m elts formation. Termotropic liguid-crystalline polymers with meso-henic rigid and flexible parts in the bacic chain is a comparatively new class of hing-molecular compounds. Changes in the chemical nature and length of flexible parts spacers, and structures of mesohenic groups allow to get polymers exhibiting liguid-crystalline properties in the wide temperature interval. Polyethers are examples of such compounds. Low temperatures of transformation into liguid-crystalline state in comparison to polyarylats and *

E-mail: [email protected]

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216

conseguently low temperatures of processing, high solubility in available solvenst on the one hand, and subbiciently. Ligh resistance on the other hand let to use them as necessary material and takes these systems guite attractive. Liguid-crystalline polymers can have nematic, smectic and cholesteric structure, theu are called termotropic liguid-crystalles. Scientists all over the world work on making liguid-grystalline polymers. So blockcopolymers containing terephtaloyl-di(n-oxybenzoat) and polyarylat has been got by polycondensation of corresponding oligomers [1]. Thermal properties and structure of blockcopolymers have been studied by means of IRS and DSK. Termotropic liguid-crystalline nematic phase of these block-copolymers was identified by means of DSK. It was found out that biphase olivision is seen at the temperature ligher than 2800C. Description of termotropic liguid-crystalline copolyether polyethyleneterephtalat and terephtaloyl-di(n-oxybenzoat) is given in this work [2]. Microstructure of given blockcopolymer is characterized by means of IR-spectroscopy with fourie-transformation. Pictures of polarization microscopy show, that copolyether is nematic liguid-crystalline polymer. Molecular properties and structure of termotropic liguid-crystalline polymers containing terephtaloyl-di(n-oxybenzoat) are studied in the works [3, 4, 5]:

C O

O

C

C

O

O

O

C O

n

So, is has been found out that poly(terephtaloyl-di-n-oxybenzoat) polymer with flexible methylene and siloxane spacers takes smectic structures with folded molcule dispositoon in the loyers in the melt. Polymer was got by heating chlorophorme in the atmosphere of agon 1,1,3,3-tetramethyle-1,3-bis-(3-hydroxypropyl)disiloloxane [6], chloranhydrite terephtaloyldi(n-oxybenzoic acid) [7] triethylamin in the ratio 1:1:2 correspondingly. X-ray studies were done for poly(terephtaloyl-di-n-ozybenzoat) with decamethilene flexible spacers [8]. Atter several heating-cooling cycles it was found that polymer transforms into melt at T=1100C. Disorder of layer structures and transformation of system into isotropic state from liguid-crystalline occurs at temperature rise up to 1900C. When polymer is cooled at 1800C melt transforms from isotropic state into liguid-crystalline-state with the structure of smectic type. Description of liguid-crystalline polyethers properties researches containing mesohenic links of terephtaloyl-di(n-oxybenzoat) in the basic chain and methylene spacers of different length is giver in the work [9]. It is found that share of more movable cycles for oxybenzol groups in polyethers with terephtaloyl-di(n-oxibenzoat) mesogen is higher than in terephtaloyl ones. Share of more movable terephtaloyl groups is higher in polyethers with nonamethylene spacer, than in polyether with decamethylene spacer (exhibition of even effect). In decamethylene spacer flexibility of CH2-groups grows with removal from mesohen. Polyethers have smectic type structures. Polymers containing mesohenic groups of terephtaloyl-di(n-oxybenzoat) are synthesized in the work [10]. 1,6-hexanediol, 1,10-decandiol, oligomers of ethylene oxide and propylene oxide of different molecular weight, playing the role of spacers in the macromolecule has

Liguid-crystalline Polyesthers …

217

been used in the polycondensation. Segmenteo liguid-crystalline polyethers, containing seven or nine para-phenylene parts in the mesohenic link were got. It was shown that part of synthesized polyethers was processed into products by means of fiber formation and melting under pressure we synthesized oligoformals, oligoketons, oligosulphones, oligosulphoneketons, terephtaloyl-di-n-oxybenzoic acid and dichloranhydrite of terephtaloyl-di-n-oxibenzoic acid to get termotropic liguid-crystalline polyethers [11]. Oligoformals of different level of condensation were synthesized by excess of bisphenole with digaloidmethylene of common formula interaction: HO-Ar-[-CH2-O-Ar-O-]-H, С(ССl2)=; n=5, 10, 20.

where

Ar=n-C6H4-R-C6H4-;

m-C6H4-;

R=-C(CH3)2-;

Oligoketons, oligosulphoneketons, oligosulphones of different level of condensation were synthesized by method of high temperature polycondensation in the aprotonic dipolar solvent medium in the atmosphere of inert gase. 4,4/- dioxydiphenylpropans, phenolphthalein, 4,4/dichlordiphenylsulphon, 4,4/-dichlorbenzophenon were used as initial materials. Dichloranhydrite terephtaloyl-di(n-oxybenzoat) was synthesized by effect of thionyl chloride on terephtaloyl-di-n-oxybenzoic acid. Composition of polyethers whick were got on the basis of different aromatic oligoethers and dichloranhydrites of terephtaloyl-di-n-oxybenzoic acid were confirmed by IRspectroscopy data, the properties were studied by different physico-chemical methods.

BIBLIOGRAPHY [1]

He Xiao-hua, Wang Xia-yu // Xiangtan daxue ziran kexue xuebau-Netur. Sci. J. Xiangtan Univ., 2001, 23, №1, p. 49-52. [2] Wang Jiu-fen, Zhu Long-xin, Huo Hong-xing // Ctongneng gaofensi xuebao=J. Funct. Polym., 2003, 16, №2, p. 233-237. [3] Grigoryev A. P., Andreeva N. A., Bylibyn A. J., Skorohodov S. S., Eskin V. E. // Highmolecular compounds, B 1985, V. 27, №1, p. 4. [4] Grigoryev A. P., Andreeva N. A., Bylibyn A. J., Skorohodov S. S., Eskin V. E. // Highmolecular compounds, B 1985, V. 27, №10, p. 758. [5] Grigoryev A. P., Andreeva N. A., Volkov A. J., Smirnova G. S., Skorohodov S. S., Eskin V. E. // High-molecular compounds, A 1987, №6, p. 1158-1161. [6] Knath W. H., jr., Lindsey R. V.,jr., // J. Amer. Chem. Soc. 1985, V. 80, №15, p. 4106. [7] Bylibyn A. J., Tenkovtsev A. V., Pyraner O. N., Skorohodov S. S. // High-molecular compounds, A 1984, V. 26, №12, p. 2570. [8] Grigoryev A. P., Andreeva N. A., Skorohodov S. S., Eskin V. E. // High-molecular compounds, B 1984, V. 26, №8, p. 591. [9] Kapralova V. M. Dynamics of liguid-crystalline alkylnonaromatic polyethers and its development in NMR // Abstract of Physico-Chemestry Masters. Thesis. St. Peterburg, 1992. [10] Stepanova A. R. Liguid-crystalline polyethers synthesis on the basis of biphenyl derivatives. // Abstract of Chemistry Masters. Thesis. St. Peterburg 1992.

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[11] Bylibyn A. J., Shepelevski A. A., Savinova T. E., Skorohodov S. S. // Patent № 792834 USSR Published V.1, 1982, №12, p. 284.

In: Modern Tendencies in Organic and Bioorganic Chemistry ISBN: 978-1-60456-295-8 Editors: A. Mikitaev, M. K. Ligidov, pp. 219-222 © 2008 Nova Science Publishers, Inc.

Chapter 19

FIREPROOF AROMATIC BLOCK COPOLYMER RESIN ON THE BASIS OF 1,1- DICHLOR-2,2 DI(NOXYPHENYL)ETHYLENE A. M. Kharaev*, R. C. Bazheva, E. B. Barokova, O. L. Istepanova, R. A. Kharaeva, and A. A.Chaika Kabardino-Balkar State University, 360004, Nalchik, Chernishevsky st. 173, KBR, Russia

ABSTRACT By the method of p-type-catalytic polycondensation the block- copolysulfonearylates on the basis of 1,1- dichlor-2,2 di(n-oxyphenyl) ethylene were received. The physicalchemical properties of block copolymer resins are investigated.

Keywords: Polycondensation, monomers, oligomers, block- copolysulfonearylates, physicalchemical properties.

At present time the limited flammable, heat- and thermostable polymers with a high mechanical and dielectric properties are widely adopted in different spheres of science and technics [1]. The lowering of inflammability with a simultaneous improvement of other operational characteristics of polymeric materials remains to be an actual problem today. This task is also actual for such perspective highheatproof thermoplastics and reactive layers, as polyarylates, polysulphones, blockcopolysulfonearylates and polyesterketone. The acquisition of such polymeric materials may be realized in two ways – by the creation of new ones or by the modification of the existent polymers, which are released in production quantities. The both ways are effective depending on the concrete current task [2]. *

[email protected]

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The usage of halogen containing monomers for making fireproof polymeric materials is a traditional way for solving the problems of improovement of the flame retarded constructive and membranous materials. One of the ways of solving this actual and important scientific problem is the utilization of the chloral and the usage of monomers on its basis, such as 1,1- dichlor-2,2 di(noxyphenyl)ethylene and the dichloranhydride of the 1,1- dichlor-2,2 di(n-oxyphenyl)ethylene [3]. The supplies of this raw material are big and have no any practical application. Thus, we have a number of blockcopolysulfonearylates (BSN–7D) according to the following scheme: C H3 n HO

C

OH

m HO

C

C H3 (n m k ) C l

OH

k HO

R

OH

C C l2

C

C

O

O

Cl

2 (n m k )E t 3 N - 2 (n m k ) E t 3 N HC l

C H3 O

C

O

C H3

C

C

O

O n

O

C

O

C C l2

C

C

O

O

O m

R

O

C

C

O

O

k

z

there O

C H3 R =

C C H3

O

S O

C H3 O

C 10

CH 3

For that we used a highly perspective, in terms of small expenses of time and energy, ptype-catalytic method of polycondensation. The mechanism of synthesis of these unsaturated polyesters was investigated. The influence of some parameters on the given viscosity and the outlet of polyesters was studied. The main parameters, which define the properties of polymers, received in conditions of ptype-catalytic polycondensation, are the nature of vehicle, the temperature and the duration of the metathesis, and also the concentration of initial substances. As a result of the conducted investigation the following conditions of synthesis of block-copoly sulfone on the basis of 1,1dichlor-2,2 di(n-oxyphenyl)ethylene and 4,4΄-dioxidephenylpropane, oligoarylensulfoneoxide OASO – 10D and mixture (50:50) dichloranhydride izo- and teraphthalic acids: vehicle – 1,2-dichlorethane; synthesis temperature is 20 ˚C; synthesis duration is 1 hour, triethylamine’s quantity - double spillover relative to bisphenols; solution’s concentration is 0,6 mole/l. Selecting the correlation of initial monomers, using first of all oligosulfone OASO – 10D in in the small (10 weight %) quantity, the compounding of polyesters, characterised by high deformation-strengthening properties (74 – 102 Mfa and relative lengthening 13,5 – 60,0 %). The initial bisphenols are taken in equimol correlations. The particular dignity of polymeric materials, derived in such a way, is that these polyesters in heat treatment make a spatial structure, because of the existance of unsaturated bond in the macrochain, and the last ones,

Fireproof Aromatic Block Copolymer Resin …

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as a rule, differ from linear structures in several properties. In heat treatment of these polymers a partial structuring is observed, which helps to raise their disconnected strength till 150 Mfa and more. The investigations showed that the given block- copolymers are characterised by a sufficiently low polydispersity. It is shown that the threshold of the coagulation BSN–7D increases with the increase of the content of the chloride-bearing bisphenol, which is apparently connected with the polarity >C=CCl2 – group, and thus, a better solubility of these polymers. Polyesters are soluble in such organic vehicles as chloroform, dichlorethane, tetrachloroethane, tetrahydrofuran and others. Synthesized copolysulfonarilats have stable indices of inductive capacity in the interval of temperatures 20-200 ˚C and sufficiently persistent in deluted and concentrated solutions H2SO4, HCl, NaOH. The characteristics of these indexes considerably improve for heat-treated blockcopolymers, which is of no small importance for membranous materials. The thermomechanical tests of synthesized BSN showed, that the temperature magnitudes of glass transition and fluidity greatly depend on the composition and construction of the initial substances and are in in the interval 207-217 ˚C and 250-350 ˚C correspondingly. Such low indices of Ttr. May be explained by a presence of the remains of dichloranhydride of isophthalic acid and oligoarylensulfonoxidation OASO-10D in the structure of macrochain. Besides, it should be mentioned that the polyarylates on the basis of dian and DHDOFA, having in their structure isopropyliden and >C=CCl2 groups, are characterised not by high indices of glass transition. Things go differently with fluidity temperature. In the BSN–7D layer with the increase of the bisphenol DHDOFA part the fluidity temperature changes from 250 ˚C to 350˚C. Probably, the reason of such increase is a saturation of the macrochain by a >C=CCl2 group, which contains a dangling bond and polymers are inclined to structuring. All the received block-copolymers relate to the class of thermostable polymers. It is ascertained that the introduction of some quantity of oligoarylensulfonoxidation OASO-10D into the structure positively influence the heat resistance of polyesters, rising it for 10-20 ˚C in comparison with polyarylates on the basis of dian and 1,1- dichlor-2,2 di(noxyphenyl)ethylene [4]. For some BSN the noticeable destructive process begins at 400˚C and more, which correspond to good thermostable polymeric materials. Observing the regimen of optimal heat treatment, the heat resistance of the materials may be raisen for 3050˚C. Table 1. The results of thermomechanical analysis of block-copolysulfonarilats BSN BSN–7D

BSN on the basis of bisphenols, mol % Dian DHDOFA 0 100 25 75 50 50 75 25 100 0

Ttr. ˚C 207 210 210 215 217

Tfl. ˚C 250 255 270 310 350

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Table 2. Refractoriness of block-copolysulfonarilats BSN BSN–7D

BSN on the basis of bisphenols, mol % Dian DHDOFA 0 100 25 75 50 50 75 25 100 0

Chlorine content, % 4,79 9,24 13,39 17,27

Oxygen index, % 27,0 30,0 35,0 37,5 43,5

The refractoriness of polymer samples were evaluated by amount of oxygen index. From the acquired results it follows that the presented block-copolysulfonarilats possess an increased refractoriness (Table 2). As it seen from Table 2 the greatest significance of the oxygen index has BSN, where as an acid component only 1,1- dichlor-2,2 di(n-oxyphenyl)ethylene was used, each molecule of which has two atoms of chlorine as an residue. In this layer because of the inconstancy of content of halogen value of the oxygen index change fundamentally. For a layer of block-copolysulfonarilats, containing remains of a monomer 1,1- dichlor2,2 di(n-oxyphenyl)ethylene, it is determined, that with the increase of the chlorinated content the oxygen index rises for 50% and more, that is a sufficiently considerable result and makes this approach attractive and perspective for solving the problem. The acquired polymers do not form inflammation drops, that is they are not the secondary source of inflammation, they are self-extinguishing and nonflammable materials. The complex of physical-chemical properties enable to hold out the unsaturated halogen containing block-copolysulfonarilats as warm-, thermo- and fire-proof constructive and membranous materials. The accessibility of the feedstock for receiving monomers on the basis of chloral, and also the manufacturability acceptor-catalytic polycondensation mekes it possible to refer the new halogen containing unsaturated block-copolysulfonarilats to industrialy-perspective polymeric materials.

REFERENCES [1] [2] [3]

[4]

Korshak V.V., Kzireva N.M. The progresses of synthetic chemistry of high-molecular compounds. The progresses of chemistry. 1979, T.48, №1, c.5-29. Korshak V.V., Vinogradova S.V. Nonequilibrium polycondensation. M., Science, 1972. Kharaev A.M., Kekharsaeva E.R., Mikitaev A.K. The properties of aromatic unsaturated polyesters on the basis of 1,1- dichlor-2,2 di(n-oxyphenyl)ethylene. Plast. Masses. 1985, №7, c.22. Kharaev A.M. Aromatic polyesters as thermostable constructive and membranous materials. Thesis for a Doctor of Chemistry Science, 1993, 297c.

In: Modern Tendencies in Organic and Bioorganic Chemistry ISBN: 978-1-60456-295-8 Editors: A. Mikitaev, M. K. Ligidov, pp. 223-230 © 2008 Nova Science Publishers, Inc.

Chapter 20

INCREASE IN SELECTIVITY OF MOLECULAR COMPLEX FORMATION OF METALLOPORPHYRINS DUE TO π-π-INTERACTIONS Nataliya A. Pavlycheva, Nataliya Sh. Lebedeva*, Anatoliy I. Vyugin, and Elena V. Parfenyuk Institute of Solution Chemistry, Russian Academy of Sciences, 1, Akademicheskaya St., Ivanovo, 153045, Russia

ABSTRACT Peculiarities of desolvation of crystallosovates of zinc(II)porphyrins with benzene, npropylamine and their mixtures have been studied by method of thermogravimetric analysis. It has been found that in two component systems zinc(II)porphyrin-ligand coordination properties of the metalloporphyrins increase in the following order: ZnTPhPZnDP>ZnHP>ZnTPhP and are inversely proportional to an ability of the macrocycle to π-π-interactions with benzene. Thus, the new approach to molecular recognition based on specific salvation π-πinteractions is demonstrated on example of znc(II)porphyrins.

Keywords: Thermogravimetric analysis; Molecular complexes; Metalloporphyrins

*

E-mail: [email protected]

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1. INTRODUCTION The metalloporphyrins as macrocyclic compounds have a few sites for specific and universal solvation and are able to axial coordination of some ligands. At the present time chemical modification of macrocycle is a main way of increasing of selectivity of molecular complex formation. The data obtained earlier [1,2] show that the selectivity may be increased due to specific π-π interactions of the metalloporphyrins with aromatic molecules. Aromatic molecules coplanar to the macrocycle will rise geometrical requirements to axial coordinating ligands. In particular, the results of the thermodynamic study of the axial coordination of npropylamine by zinc(II) porphyrins in benzene have demonstrated the formation of the complexes of the metalloporphyrin containing both n-propylamine and benzene [2]. The aim of this work is to study the molecular complexes of zinc(II) porphyrins prepared by slow crystallization from saturated solutions in benzene, n-propylamine and mixed solvent benzene - n-propylamine.

2. EXPERIMENTAL The objects of this study are the synthetic symmetrically substituted zinc(II)tetraphenylporphyrin (I) – ZnTPhP and the porphyrins of heme blood: zinc(II) hematoporphyrin t.m.e.(II) - ZnHP, zinc(II)deuteroporphyrin IX d.m.e.(III) - ZnDP, zinc(II)protoporphyrin IX d.m.e. (IV) - ZnPP having different peripheral substitutes.

II. ZnHP M=Zn, R=CH(OCH3)CH3 III. ZnDP M=Zn, R=H IV. ZnPP M=Zn, R=CH=CH2

I. ZnTPhP M=Zn

Benzene (analytical grade) was dried by molecular sieves of 4Å size and distillated. NPolyamine (Aldrich, 98%) was double distillated under vacuum. Purity of the reagents was checked chromatographically. It was 99.95 % for CH3(CH2)2NH2 and 99.98% for C6H6. The content of water was determined by Karl Fisher method It was not greater than 0.01%. Thermogravimetric measurements were made with thermoanalytical set. The detail description of the equipment, procedures of the measurements and software for treatment of the experimental data and calculations of uncertainties were reported earlier [3]. The chemical analysis of content of C,N,H was performed with CHNS-O Analyzer Flash TF 1112 Series.

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Table 1. Physicochemical properties of molecular complexes of ZnP with benzene and n-propylamine

ZnP

ZnHP ZnDP ZnPP ZnTPhP

Benzene Compos. of ZnP:L 1:2 1:1 1:1 1:1 1:2

Тdestr, 0С 60 122 72 49 60

Solvent n-propylamine * ΔevpН , kJ Compos.of mol-1 ZnP:L 39 1:2 96 1:1 62 1:2 1:1 38 1:1 150 1:1

Тdestr, 0С 70 113 67 81 82 114

ΔevpH*, kJ mol-1 58 199 53 171 168 113

*

Uncertainty in ΔevpН is ±(3÷8) kJ mol-1.

3. RESULTS AND DISCUSSION The results of the thermogravimetric analysis of crystallosolvates of the porphyrins with benzene and n-propylamine are presented in Table 1. As an example, typical thermograms of the crystallosolvates of ZnTPhP and ZnPP are shown in Fig.1 and 2. For all zinc(II)porphyrins studied, the process of removing of n-propylamine from the crystallosolvates has several steps. In the first step, the ΔevpH value of the organic solvent for the crystallosolvates giffers slightly from that for pure solvent. This may be explained by destruction of the solvates formed due to universal interactions. The peaks at higher temperatures are characterized by a significantly greater ΔevpH values than for pure npropylamine. This may be due to destruction of the specific molecular complexes in these steps. ΔevpH consists of two contributions: (i) the energy losses associated with breaking of macrocycle-ligand bonds and (ii) the work of expansion at transition of the substance to the gas phase [4]. The last contribution is negligible (2-3 kJ mol-1). Thus, in the first approach the ΔevpH value reflects energetic strength of the macrocycle – ligand bonds. Clear stoichiometry and high repeatability of the results testifies about destruction of the specific molecular complexes but not inclusion complexes. As can be seen from Table 1, the energetic strength of the metalloporphyrin complexes with n-propylamine increases in the following order: ZnTPhP +I (CH3CH=). CH3Ogroup is able to both +C and –I effects. But as a component of CH(OCH3)CH3 substitute, it can exhibit only –I effect because of the presence of CH—group excluding a possibility of conjugation of pz- electrons of oxygen atom with π-system of the macrocycle. CH2=CH-group has +C and +I effects. The position of ZnTPhP in the order mentioned above results from +I effect of phenyl groups [7]. This fact indicates that the coordination ability of the metalloporphyrins in binary systems is determined by residual positive charge on the metal ion and hence, basicity of the macrocyclic ligand.

Nataliya A. Pavlycheva, Nataliya Sh. Lebedeva, Anatoliy I. Vyugin et al.

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Table 2. Results of chemical analysis of complexes of ZnP with benzene and npropypamine Formula ZnTPhP·С6Н6·РА ZnНP·С6Н6·2РА ZnDP·С6Н6·РА ZnPP·PA

С% 78.08 65.67 66.62 65.68

Calculated H% 5.31 7,49 6.40 6.35

N% 8.59 9.19 9.47 9.82

C% 78.20 65.38 66.17 65.42

Observed H% 5.20 7.48 6.23 6.34

N% 8.46 9.35 9.80 9.77

As can be seen from the obtained calorimetric data [2], the coordination ability of ZnP in relation to n-propylamine in benzene increases in the following order: ZnPP
(b)

Differences between the orders (a) and (b) may be associated with an effect of the solvent (benzene). Therefore, desolvation processes of ZnP in benzene and n-propylamine and their mixtures were studied. Specific complexes ZnP·(C6H6)x· (n-propylamine)y were isolated. Their compositions were confirmed by element analysis. Let us consider the obtained results. The process of removing of benzene from the crystallosolvates of zinc(II)porphyrins has two (ZnTPhP, ZnDP, ZnPP) or three steps (ZnHP) (Fig.1,2). It should be noted that the physicochemical properties of the molecular complexes of zinc(II)porphyrins with benzene obtained in this study are in agreement (within uncertainty) with those obtained earlier [5,7]. They are also presented in Tables 1 and 2. Let us consider the results of the thermogravimetric study of tree-component system ZnTPhP-benzene-n-propylamine. The DTA curve of the crystallosolvate of ZnTPhP with benzene and n-propylamine exhibits peaks characterizing evaporation process of the solvent molecules specifically bonded with the macrocycle. The temperatures of the beginning of these processes coincide within uncertainties with corresponding temperatures of destruction of axial and specific π-π complexes (Fig.1). The method of thermogravimetric analysis of crystallosolvates provides a clear picture of their step by step destruction but unfortunately in mixed solvents mole ratio of ZnTPhP : benzene : n-propylamine can not be calculated. The step beginning at 60 0C indicates that an axial coordination of n-propylamine does not lead to a complete destruction of ZnTPhP 2·C6H6 π -π complex. However it is impossible to exclude that upon the coordination of n-propylamine, only one molecule of benzene specifically solvating the ZnTPhP is removed. This supposition seems to be reasonable taking into account numerous X-ray studies of π -π complexes of ZnTPhP with aromatic molecules [8,9]. These data have shown that small aromatic molecules occupy coplanar to the macrocycle plane position and partially blockage a central metal ion. It also should be noted that in most π -π complexes of natural and synthetic porphyrins, the small aromatic molecules are located above trans-pyrrol fragments. Thus, a reactive center of the porphyrin is not screened [10]. Such unusual location of the small aromatic molecules in π -π complexes of ZnTPhP may be explained by a presence of phenyl substitutes, which are located at an angle to the macrocycle plane and sterically hinder from an orientation of the small aromatic molecules above the pyrrol fragments. Moreover, a different distribution of electron density in the macrocycles of

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227

synthetic and natural porphyrins [11] may play a certain role. That is why in order to ascertain a composition of the molecular complex of ZnTPhP with benzene and n-propylamine, the element analysis of the corresponding crystallosolvate which was prepared by heating up to 55-58 0C and kept at this temperature up to constant TG curve. Chemical analysis of C,N,H showed most accordance with ZnTPhP C6H6 PA formula. Thus, the coordination of npropylamine by ZnTPhP ·2 C6H6 leads to partial destruction of the specific π -π complex with benzene and formation of ZnTPhP C6H6 PA complex.

Figure 1. TG and DTG curres for the thermal decomposition crystallosolvaty of ZnTPhP with benzene and n-propylamine.

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Nataliya A. Pavlycheva, Nataliya Sh. Lebedeva, Anatoliy I. Vyugin et al.

Figure 2. TG and DTG curres for the thermal decomposition crystallosolvaty of ZnPP with benzene and n-propylamine.

A composition of the molecular complex of ZnDP with benzene and n-propylamine can not be fixed from the thermogram because temperatures of destruction of ZnDP π -π complex with benzene and an axial complex with n-propylamine are slightly different (Table 1). That is why for three-component system ZnDP- benzene- n-propylamine, the peak on the DTG curve at 62 0C may be explained by both evaporation of benzene and n-propylamine. Chemical analysis of C,N,H indicate most accordance with ZnDP·С6Н6·РА. formula. Thus, in the three-component in comparison with ZnDP-n-propylamine binary system, the coordination of the second n-propylamine molecule does not occur.

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Zn(II)hematoporphyrin is characterized by the most ability to complex formation with both n-propylamine and benzene among all natural porphyrins studied (Table 1). Three peaks are observed on the thermogram of the crystallosolvate of ZnHP with benzene and npropylamine at the temperatures above 60 0C. These data and results of chemical analysis allow to conclude about formation of ZnHP · C6H6 · 2PA specific complex. The results of thermogravimetric study of the crystallosolvate of ZnPP with benzene and n-propylamine are similar to those obtained for ZnPP-n-propylamine. This may be due to low ability of ZnPP to complex formation with benzene (Table 1).

4. CONCLUSION Thus, the results of this study indicate that using some aromatic solvents as solvating medium can lead to the formation of molecular complexes containing both an axial coordinated ligand and π – π bonded molecules of the aromatic solvents. A lower thermodynamic stability of the axial complexes of ZnHP, ZnDP and ZnTPhP with npropylamine in benzene in comparison with ZnPP [2] is connected with the formation of stable ZnHP 2C6H6 and ZnDP C6H6 π -π complexes. Thus, the specific π -π interactions of metalloporphyrins with benzene have a greater influence on the coordination properties of the macrocycles than modification of their structures. It is one of the ways to increase the selectivity of the molecular complex formation of metalloporphyrins with ligands.

ACKNOWLEDGEMENTS This work was supported by Russian Academy of Sciences (Program of federal budget of RAS " Directional synthesis of compounds with prescribed properties and creation of functional materials on their basis N 8P) and Russian science Support Foundation.

REFERENCES [1] [2] [3] [4] [5] [6]

N. Sh. Lebedeva, S. P. Yakubov, A. I. Vyugin and E.V. Parfenyuk. Thermochim. Acta. 402 (2003) 19. N. Sh. Lebedeva, N. A. Pavlycheva, A. I. Vyugin, O. I. Davydova, S. P. Yakubov. Bull. Russ. Acad. Sci. 2 (2004) 317. N. Sh. Lebedeva, S. P. Yakubov, A. N. Kinchin, A. I. Vyugin. Russ. J. Phys. Chem. 79 (2005) 958. А.V. Suvorov, Termodynamicheskaya chimia paroobraznogo sostoyania (Thermodynamic chemistry of vapour state). Leningrad: Chimia. 1970. 208 p. Е. V. Аntinа, N. Sh. Lebedeva, A. I. Vyugin, I. К. Stroykova, Russ. J. Phys. Chem. 72 (1998) 721. Е. V. Аntinа, N. Sh. Lebedeva, М. B. Berezin, A. I. Vyugin, G. А. Кrestov. Russ. J. Phys. Chem. 70 (1996) 1625.

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N. Sh. Lebedeva, К. V. Мichaylovskii, A. I. Vyugin. Russ. J. Coord. Chem. 27 (2001) 795. [8] C.A. Reed, T. Mashiko, S.P. Bentley, M.E. Kastner, W.R. Scheidt, K. Spartalian and G. Lang. J. Am.Chem. Soc. 101 (1979) 2948. [9] J. F. Kirner, C.A. Reed and W.R. Scheidt. J. Am.Chem. Soc. 99 (1977) 1093. [10] G. Fulton and G.N.La Mar. J. Am.Chem. Soc. 98 (1976) 2124. [11] Y. Murakami, J-I. Kikuchi and Y. Hisaeda. Chem. Rev. 96 (1996) 721.

In: Modern Tendencies in Organic and Bioorganic Chemistry ISBN: 978-1-60456-295-8 Editors: A. Mikitaev, M. K. Ligidov, pp. 231-238 © 2008 Nova Science Publishers, Inc.

Chapter 21

INFLUENCE OF INDIVIDUAL COMPONENTS OF ESSENTIAL OILS AND FLAVORINGS ON CITRAL OXIDATION А. L. Samusenko* N. M. Emanuel Institute of Biochemical Physics, Russian Academy of Sciences, 4 Kosygina Street, 119 991 Moscow, Russia

ABSTRACT Antioxidant properties of individual components of the essential oils and flavorings, which are widely used in food and perfume industry – linalool, lemonene, octyl acetate, anise aldehyde. vanillin and eugenol – have been investigated by capillary gas chromatography. The evaluation of antioxidant activity was performed using the method of citral oxidation during it storage in light in presence of the substances under study. It was found that eugenol possessed the maximal antioxidant activity while octyl acetate didn’t inhibit the citral oxidation. The substantial difference in antioxidant activity of lemon and clove essential oils and its main components – lemonene and eugenol was noted. Synergetic effect in the mixture of anise aldehyde and vanillin was observed.

Keywords: antioxidant activity, citral oxidation, linalool, lemonene, octyl acetate, anise aldehyde, vanillin, eugenol, capillary gas chromatography.

AIMS AND BACKGROUND In recent years using of the essential oils of spice-aromatic plants as flavorings in food, pharmacological and perfume industry is of great interest. Until the recent time odor and taste of the essential oils were mainly studied for flavoring of food stuffs, beverages etc. However *

E-mail: chembio @ sky.chph.ras.ru

232

А. L. Samusenko

biological activity, including the antioxidant (AO) one, is an important characteristics of essential oils, especially with the point of view of its influence on human health [1-5]. The studying of the biological properties of essential oils [6-12] showed that its AO activity is comparable with activity of traditionally used synthetic antioxidants and sometimes even outdoes it [10]. Biological activity of essential oils depends on the properties of its main components. It was found that eugenol, carvacrol, thymol and guaiacol, which are the components of essential oils, possessed a high AO activity, being comparable with activity of α-tocoferrol. Cyclic monoterpene hydrocarbons, having two double bonds in the cycle - α- and γterpinenes, α-terpinolene and sabinene, possessed very high AO activity [13]. Each essential oil is a multi component system, having certain red-ox potential, which determines it’s AO activity. That is why it is of interest to turn out the role of individual components of essential oils in inhibition of oxidation process. The goal of this work is studying of AO properties of individual compounds, containing in the composition of different essential oils and flavorings, which are used in food and perfume industry.

EXPERIMENTAL The substances of different classes of organic compounds – monoterpene hydrocarbons, alcohols, esters, aldehydes, aldehyde-alcohols and phenols were selected as antioxidants. The next substances have been investigated: lemonene (“Lluch”, Spain), linalool (“Moellhausen”, Italy), octyl acetate (“Ventos”, Spain), anise aldehyde (“Lluch”, Spain), vanillin (“Dinos”, China) and eugenol (“Ventos”, Spain). All compounds, including test-substance – citral (“Moellhausen”, Italy), were characterized by gas chromatography. For evaluation of AO properties of selected compounds 150 μl of citral (neral + geranial) and 50μl of undecane (internal standard) were dissolved in 30 ml of hexane. The solution was divided to 2 ml aliquots in 10 ml glass vessels – total amount 13 samples. The substances studied were added in the samples in the next order: 1 –4 μl of linalool; 2 – 3 μl of lemonene; 3 – 3 μl of octyl acetate; 4,5,6 and 7 – 0.5; 1; 2 and 4 μl of anise aldehyde correspondingly; 8,9,10 and 11 – 1; 2; 3 and 4 mg of vanillin correspondingly; 12 – mixture of 1 μl of anise aldehyde and 2 mg of vanillin (see Figure 1). Control sample did not contain the substances. Each sample was prepared twice. The samples prepared were exposed in light in closed vessels at room temperature during 63 days. Each week the vessels were opened and stream of air was passed through the sample with help of 10 ml pipette. Quantitative content of citral and the substances was determined by capillary gas chromatography each 7 days. The samples, containing eugenol, were prepared separately: 60 μl of citral and 12 μl of undecane were dissolved in 12 ml of hexane. In 2-ml aliquots of solution obtained 0.5; 1; 2; 5 and 20 μl of eugenol were added (correspondingly samples 1 –5, Figure 2). control sample did not contain eugenol. The samples were exposed in sunlight in closed vessels during 63 days. Quantitative content of citral and eugenol in the samples were determined by gas chromatography each 7 –14 days.

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%

60 50 40 30 20 10 0 1

2

3

4

5

6

7

8

9

10 11 12 13

Figure 1. Final content of citral (neral – black, geranial - grey) in solution after 8 weeks of storage in light in the presence of different substances-antioxidants: 1 – control, 2 – linalool, 3 – lemonene, 4 – octyl acetate, 5 - 8 - anise aldehyde (0.25; 0.50; 1 and 2 μl/ml correspondingly), 9 – 12 –vanillin (0.5; 1; 1.5 and 2 mg/ml correspondingly), 13 – anise aldehyde + vanillin.

Citral content, %

100

80

1 60

C 40

2

1 B 2 2 1A

20

0 0

20

40

60

80

100

120

140

160

days

Figure 2. Influence of lemonene on citral oxidation: А – control solution, В – individual lemonene, С – lemon essential oil. (1 – neral, 2 – geranial).

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Gas chromatographic analysis of samples was carried out using chromatograph “Micromat – 412” (“Nordion Instr.”, Finland), equipped with fused silica capillary column SPB-1 (“Supelco”, USA, 35 m x 0.32 mm, phase film thickness 0.25 μm). Temperature of analysis was 140oC. The samples, containing eugenol, have been analyzed at temperature programming of column from 100o up to 250oC with a rate 8o / min. Velocity of carrier gas He was 1 ml/ min, temperature of injector and flameionization detector - 250oC. Quantitative content of citral and substances was calculated using relationship of the peak areas corresponding to the substances and internal standard, which content was accepted equal to 100 units of concentration.

RESULTS AND DISCUSSION To evaluate AO activity of the substances under study we used test “aldehyde/ carboxylic acid” [14] . Citral (neral + geranial), which is a component of lemon, orange, mandarin, lemon grass and other essential oils, served as aldehyde. Such test-substance allowed to evaluate the reciprocal influence of different substances, being the components of the same essential oil, during autooxidation . Influence of the substances under study on citral oxidation during 8-week storage in light is presented in Figure 1. The data obtained showed that all substances, except for octyl acetate, possessed the certain AO activity and inhibited citral oxidation. The rate of citral oxidation in presence of octyl acetate and in control solution was the same, therefore octyl acetate was not an antioxidant. Linalool and lemonene were found to have approximately equal AO activity. The results obtained allowed to consider its as quite strong antioxidants only during 6 weeks of storage, then rate of citral oxidation in the presence of linalool and lemonene increased. Possibly it may be explained by decreasing of content of these substances due its autooxidation, since we observed the appearance of epoxylemonene, which was the product of lemonene oxidation. It is necessary to note that all the substances: lemonene, linalool and citral are the components of lemon essential oil. The data presented in Table 1 demonstrate the content change of all compounds mentioned above during lemon oil autooxidation in light. In Table 1 we also show the content change of strong antioxidants of lemon oil - α- and γ-terpinenes and α-terpinolene. As it is seen from Table 1 and Figure 2, during the same storage time citral was oxidized to a significantly less extent in lemon oil, than in model mixtures, which contained individual lemonene or individual linalool (Figure 1, samples 1 and 2), while lemonene and linalool content in the oil didn’t practically change. It is obviously that the reason of this fact is the presence of the strong antioxidants in the essential oil, especially γ-terpinene, which underwent to p-cymene as a result of it’s oxidation (Table 1). So in spite of lemonene was the main component of lemon essential oil, it didn’t serve as antioxidant in relation to citral, yielding this role to a stronger antioxidant, i.e. γterpinene. In the absence of γ-terpinene lemonene was able to inhibit citral oxidation (see Figure 1).

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Table 1. Change of main component content (μl/ml) in the composition of lemon essential oil during autooxidation in light Compound 0 0.18 0.70 76.76 12.07 0.48 0.17 0.80 1.21

α-terpinene p-cymene Limonene γ- terpinene α-terpinolene Linalool Neral Geranial

time, days 60 9.12 78.27 4.47 0.24 0.82 0.52

27 4.87 83.28 9.15 0.04 0.25 0.80 0.91

145 12.84 62.40 0.02 0.18 0.59 0.29

Citral content, %

100

80

60

1

40

2

B

20

1 0 0

10

20

30

40

50

60

2

A 70

days

Figure 3. Influence of vanillin on citral oxidation: А – control solution, В – vanillin (1 – neral, 2 – geranial).

We have tried to study the influence of antioxidant concentration in the samples, containing anise aldehyde and vanillin. Figure 1 (samples 4 – 7) demonstrates that anise aldehyde possesed AO properties only at relatively high concentration (sample 6 and 7), but at low concentration it was oxidized and didn’t inhibit citral oxidation as compared with control sample. We observed another situation in the case of vanillin. This compound is a component of numerous flavorings, which are used in food and perfume industry. That is why studying of it’s AO properties is of special interest. In fact, the data obtained by us (Figure 1,

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sample 8 – 11) showed that vanillin possessed a high AO activity even at low concentration. This activity increased with increasing of it’s concentration in model mixture. For instance, citral in the presence of vanillin was oxidized less than to 50% after 8 weeks of storage in light, while in control solution for the same time it’s content didn’t exceed 5 – 8 % (Figure 3). We observed synergetic effect in the mixture vanillin and anise aldehyde (Figure 1, sample 12). The inhibition of citral oxidation in the mixture: anise aldehyde + vanillin occurred to a more extent than in the case of individual anise aldehyde at the same concentration (Figure 1, sample 5). The high AO activity of phenol derivatives, containing in different essential oils, was noted in Ref. 7, 13. We have investigated influence of eugenol on citral oxidation, using a wide interval of it’s content in the samples – from 0.25 up to 10 μl/ml. To investigate AO properties of eugenol the vessels with samples were exposed in direct sunlight. Due this procedure citral oxidation occurred more rapidly than in previous experiments (Figure 4). The results, presented in Figure 5, showed that eugenol significantly inhibit citral oxidation and this effect increased with increasing of it’s content in the sample. Taking into consideration the rate of citral oxidation in control solution and in the samples, containing eugenol, and comparing these data with the results obtained for other substances under study, one may conclude that eugenol proved to be the strongest antioxidant of all compounds studied in this work.

Citral content, %

100

80

60

1 2 1 2

40

20

2

В А

1 Control

0 0

10

20

30

40

50

60

70

days

Figure 4. Influence of eugenol on citral oxidation: Concentration of eugenol: А – 0.25 μl/ml, В – 10 μl/ml (1 – neral, 2 – geranial).

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60 % 50 40 30 20 10 0 1

2

3

4

5

6

Figure 5. Final content of citral (neral – black, geranial - grey) in solution after 9 weeks of storage in light in presence of eugenol: 1 – control solution, 2 – 6 –concentration of eugenol: 0.25; 0.50; 1.0; 2.5 and 10 μl/ml correspondingly.

Table 2. Influence of individual clove essential oil and oil mixtures on oxidation of hexanal* Essential oil or oil mixture Control Clove Clove + Lemon Clove + Lemon + Coriander

0 100 100 100 100

7 91 100 100 100

time, days 28 45 100 100 77

60 13 100 100 77

* content of hexanal is given in % of it’s initial concentration in solution.

Since eugenol is a component of basil, nutmeg, black pepper essential oils and the main component of clove essential oil [15] we have compared it’s AO activity in the samples, containing citral, with the results [16] on oxidation of other aldehyde – hexanal in the presence of clove essential oil (Table 2). The data presented show the complete inhibition of hexanal oxidation during 60 days of storage in light. The practically same results were obtained for the mixtures, containing clove oil. It is interesting to note that in all samples we observed noticeable oxidation of individual eugenol, but in the clove essential oil, where eugenol is the main component, it’s content didn’t change during 60 days of storage (Table 3). This fact may be explained: at first - by very high concentration of eugenol in essential oil and at second - by stabilization of red-ox potential in oil system. These factors may increase AO activity of essential oil system as compared with individual components of essential oils.

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Table 3. Change of main component content (μl/ml) in composition of clove essential oil during it’s autooxidation in light Compound Eugenol β-caryophillene Farnezene Eugenyl acetate δ-Cadinene Caryophillene oxide

0 91.59 7.23 0.87 13.07 0.36 0.43

time, days 28 100.78 7.25 0.88 15.57 0.32 0.53

60 94.84 6.74 0.80 14.78 0.34 0.58

The data obtained allowed to present the decreasing series of AO activity of substances studied as follows: eugenol > vanillin > anise aldehyde > limonene > linalool > octyl acetate

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

P.D. Duh , D.B. Yeh, G.C. Yeh: J.Amer.Chem.Soc., 69, 814 (1992). M.N. Dang, M. Takascova, D.V.Nguyen, K. Kristianova: Nahrung / Food, 45 (1), 64 (2001). M.F.Ramadan, L.W. Kroh, J.-T. Morsel: J.Agric.Food Chem., 51 (24), 6961 (2003). M. Sawamura, S.H. Sun, K. Ozaki, J. Ishikawa, H. Ukeda: J.Agric.Food Chem., 47 (12), 4868 (1999). L. Calucci, C. Pinzino, M. Zandomeneghi, A. Capocchi, S. Ghiringhelli, F. Saviozzi, S. Tozzi, L. Galleschi: J.Agric.Food Chem., 51 (4), 927 (2003). K.P. Svoboda, S.G. Deans: Flavour Fragrance J., 7 (2), 81 (1992). H.L. Madsen, G. Bertelsen: Trends Food Sci. and Technolog., 6 , 271 (1995). M. Sawamura: Aroma Research. 1, 14 ( 2000). K. Platel, K. Shrinivasan: Nahrung., 44 (1), 42 (2000). M.A. Murcia, L. Egea, F. Romojaro, P. Parras, A.M. Jimenez, M. Martinez-TOME: J.Agric.Food Chem., 52 (7), 1872 (2004). G. Sacchetti, S. Maietti, M. Muzzoli, M. Scaglianti, S. Manfredini, M. Radice, R. Bruni: Food Chem., 91, 621 (2005). T.A.Misharina, A.N. Polshkov: Prikladnaya Biokhimiya i Mikrobiologiya. Mikrobiologiya, 41 (6), 693 (2005) (in Russian). G. Ruberto, M. Barrata: Food Chem., 69 (1), 167 (2002). K.G. Lee, T. Shibamoto: J.Agric.Food Chem., 50 (15), 4947 (2002). S.A. Voitkevitch: Ephirniyi masla dlya parfyumerii i aromaterapii. Pischevaya prom., Moscow, 1999. Т.А. Мisharina, A.L. Samusenko: Prikladnaya Biokhimiya i Mikrobiologiya, 44 (2), (2008) (in Russian), in press.

In: Modern Tendencies in Organic and Bioorganic Chemistry ISBN: 978-1-60456-295-8 Editors: A. Mikitaev, M. K. Ligidov, pp. 239-270 © 2008 Nova Science Publishers, Inc.

Chapter 22

SOME ASPECTS OF DYNAMIC WATER VAPOUR AND HEAT TRANSPORT THROUGH FABRICS A. K. Haghi* The University of Guilan P. O. Box 3756, Rasht, Iran

ABSTRACT The thermal environment is sometimes very complex. Convection, radiation and conduction are the common means of heat exchange and they vary independently over time and location. The final effects on the surface heat exchange of the human body are important factors for heat balance and for perception of the thermal conditions. Assessment of the thermal environment in a modern office or a car can create difficulties due to the complex interaction of the ventilation system with the situation close to the person and the external, environmental factors (e.g. radiation, air temperature and air movements). Furthermore, measurements in reality, as well as in the laboratory, contain various methodological problems. In this chapter some important aspects of dynamic water vapour and heat transport through fabrics are discussed.

1. INTRODUCTION During physical activity the body provides cooling partly by producing insensible perspiration. If the water vapour cannot escape to the surrounding atmosphere the relative humidity of the microclimate inside the clothing increases causing a corresponding increased thermal conductivity of the insulating air, and the clothing becomes uncomfortable. In extreme cases hypothermia can result if the body loses heat more rapidly than it is able to produce it, for example when physical activity has stopped, causing a decrease in core temperature. If perspiration cannot evaporate and liquid sweat (sensible perspiration) is *

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produced, the body is prevented from cooling at the same rate as heat is produced, for example during physical activity, and hyperthermia can result as the body core temperature increases. Table.1 shows heat energy produced by various activities and corresponding perspiration rates. The ability of fabric to allow water vapour to penetrate is commonly known as breathability. This should more scientifically be referred to as water vapour permeability. Although perspiration rates and water vapour permeability are usually quoted in units of grams per day and grams per square meter per day, respectively, the maximum work rate can only be endured for a very short time. During rest, most surplus body heat is lost by conduction and radiation, whereas during physical activity, the dominant means of losing excess body heat is by evaporation of perspiration. It has been found that the length of time the body can endure arduous work decreases linearly with decrease in fabric water vapour permeability. It has also been shown that the maximum performance of a subject wearing clothing with a vapour barrier is some 60% less than that of a subject wearing the same clothing but without a vapour barrier. Even with two sets of clothing that exhibit a small variation in water vapour permeability, the differences in the wearer's performance are significant[1]. In an environment where body temperature cannot be regulated without a lot of sweating, we often try to get rid of heat from our body by turning on the air conditioning systems or moving into a conditioned room. Just after the change of the environment, we will feel "cool" or "comfortable". But the sweat accumulated in clothing evaporates gradually, until the heat loss from our body can be more than needed and at last we might feel "cold" or "uncomfortable". A review of clothing studies has shown that moisture collection in cold weather clothing, even after heavy exercise, seldom exceeds 10% by weight of added water [2]. One of the measurements are used to calculate values related to water vapour transmission properties is "water vapour resistance". This is the water vapour pressure difference across the two faces of the fabric divided by the heat flux per unit area, measured in square meters pascal per watt. Some water vapour resistance data on different types of outwear fabrics are presented in Table 2. The measurement of water vapour resistance in thickness unit (mm) is the thickness of a still air layer having the same resistance as the fabric. The use of thickness units facilitates the calculations of resistance values for clothing assemblies comprising textile and air layers. Table 1. Heat energy produced by various activities and corresponding perspiration rates[1] Activity Sleeping Sitting Gentle Walking Active Walking With light pack With heavy pack Mountain walking with heavy pack Maximum work rate

Work rate (watts) 60 100 200 300 400 500 600-800 1000-1200

Perspiration rate (g/day) 2280 3800 7600 11500 15200 19000 22800-30400 38000-45600

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Table 2. Typical water vapour resistance(WVR) of fabrics[1] Fabric, Outer (shell) material Neoprene, rubber or PVC coated Conventional PVC coated Waxed cotton Wool overcoating Leather Woven microfiber Closely woven cotton Ventile L28 Other Ventile Two-layer PTFE laminates Three-layer laminates (PTFE, polyester) Microporous polyurethane (various types)

WVR(mm still air) 1000-1200 300-400 1000+ 6-13 7-8 3-5 2-4 3.5 1-3 2-3 3-6 3-14

This observation is generally explained by noting that the major transfer mechanism from wet skin to underwear is one of distillation. An initial observation noting the surprisingly strong discomfort sensations associated with small amounts of water in the skin-clothing interface [3]. It has been confirmed in a number of studies in which either moisture from sweating or added moisture generates these clothing contact sensations. The procedures for these measurements [4] emphasize again that very little moisture is required to stimulate sensations of discomfort. Often 3% to 5% added moisture is ample to develop discomfort [5]. Simultaneous differential equations for the transfer of heat and moisture in porous medial under combined influence of gravity and gradients of temperature and moisture content were developed by D.A. De Vries [6]. These equations are a generalization of those drived by philip et al. [7]. Eckert and Faghri [8] have performed a general analysis of moisture migration in a slab of an unsaturated porous material for a condition where the temperature of one surface is suddenly increased to a higher value whereas the temperature of the other surface is maintained constant. Udell [9], [10] has derived a general, one-dimensional, steadystate model describing the heat and mass transfer within a homogeneous porous medium, saturated with a wetting liquid, its vapor and a non-condensible gas. The effects of gas diffusion, phase change, conduction, liquid and vapor transport, capillarity, and gravity are included. The analysis is based on a general thermodynamic description of the unique equilibrium states characteristics of liquid wetting porous media. Bouddor et al. [11] have provided a systematic, rigorous and unified treatment of the governing equations for simultaneous heat and mass transfer within a wide range of porous media. Some work has also been done in the area of coupled diffusion of moisture and heat in hygroscopic textile materials. Gibson [12] has given a review of numerical modeling of convection, diffusion and phase changes in textiles. The paper summarizes current and past work aimed at utilizing CFD techniques for clothing applications. It was shown that water in a hygroscopic porous textile may exist in vapor or liquid form in the pore spaces. Phase changes associated with water include liquid evaporation/condensation in the pore spaces and sorption/desorption from polymer fibers. Additional factors such as swelling of solid polymer due to water and heat of sorption was incorporated into the appropriate conservation and transport equations. Nordon and David [13] have attempted to solve the non-linear

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differential equations which describe coupled diffusion of heat and mass (moisture) in hygroscopic textile materials. In addition to the diffusion equations, a rate equation was introduced describing the rate of exchange of moisture between the solid (textile fibers) and the gas phase. The predictions compared favorably with experimental observations on wool bales and wool fabrics [14]. Farnworth [15] has developed a simple model of combined heat and water vapor transport in clothing. Transport by forced convection was not included in this model. Osczevski and Dolhan [16] and Farnworth et al [17] reported a strong dependency of water vapour resistance of hydrophilic membranes or coatings: the higher the relative humidity at the membrane, the lower the water vapour resistance (i.e., the higher the water vapour permeability or breathability). In a temperature dependent experiment, Osczevski[18] placed a hydrophilic film on an ice block. Water vapour sublimating from the ice could diffuse only through the film and was collected by a desiccant. Osczevski measured mass transport through the film, and he found that water vapour resistance is an exponential function of temperature. In this experiment, water vapour permeability varnishes nearly completely with decreasing textile temperature. Because diffusion in hydrophilic materials is non-Fickian, he also derived from his results a theory of diffusion speed depending on activation energy, and he accounted for different relative humidities. Additionally, Gretton et al [19] reported an increase in the moisture vapour transmission rate of hydrophilic and microporous textiles when measuring with a heated dish instead of unheated dish. They interpreted their results by the increased motion of water vapour and polymer molecules, which they claimed would also work for microporous constructions. Galbraith et al [20] compared cotton, water repellent cotton, and acrylic garments through wearing tests and concluded that the major factor causing discomfort was the excess amount of sweat remaining on the skin surface. Niwa [21] stated that the ability of fabrics to absorb liquid water (sweat) is more important than water vapour permeability in determining the comfort factor of fabrics. Morooka and Niwa [22] postulated physiological factors related to the wearing comfort of fabrics as follows: sweating occurs whenever there is a tendency for the body temperature to rise, such as high temperature in the surrounding air and physical exercise, etc. If liquid water (sweat) cannot be dissipated quickly, the humidity of the air in the space in between the skin and the fabric that contacts with the skin rises. This increased humidity prevents rapid evaporation of liquid water on the skin and gives the body the sensation of “heat” that triggered the sweating in the first place. Consequently, the body responds with increased sweating to dissipate excess thermal energy. Thus a fabric’s inability to remove liquid water seems to be the major factor causing uncomfortable feelings for the wearer. Hollies [23] conducted wearer trails for shirts made of various fibers. They concluded that the largest factor that influenced wearing comfort was the ability of fibers to absorb water, regardless of weather fibers were synthetic or natural. All of these studies indicate that the transient state phenomenon responding to the physiological demand to cause sweating is most relevant to comfort or discomfort associated with fabrics. When work is performed in heavy clothing, evaporation of sweat from the skin to the environment is limited by layers of wet clothing and air. The magnitude of decrement in evaporative cooling is a function of the clothing’s resistance to permeation of water vapour.

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King and Cassie [24] conducted an experimental study on the rate of absorption of water vapor by wool fibers. They observed that, if a textile is immersed in a humid atmosphere, the time required for the fibers to come to equilibrium with this atmosphere is negligible compared with the time required for the dissipation of heat generated or absorbed when the regain changes. Gretton [25] investigated the effects of heat of sorption in the wool-water sorption system. They observed that the equilibrium value of the water content was directly determined by the humidity but that the rate of absorption and desorption decreased as the heat-transfer efficiency decreased. Heat transfer was influenced by the mass of the sample, the packing density of the fiber assembly, and the geometry of the constituent fibers. Crank [26] pointed out that the water-vapor-uptake rate of wool is reduced by a rise in temperature that is due to the heat of sorption. The dynamic-water-vapor-sorption behavior of fabrics in the transient state will therefore not be the same as that of single fibers owing to the heat of sorption and the process to dissipate the heat released or absorbed. Henry [27,28] was who the first started theoretical investigation of this phenomenon. He proposed a system of differential equations to describe the coupled heat and moisture diffusion into bales of cotton. Two of the equations involve the conservation of mass and energy, and the third relates fiber moisture content with the moisture in the adjacent air. Since these equations are non-linear, Henry made a number of simplifying assumptions to derive an analytical solution. In order to model the two-stage sorption process of wool fibers, David and Nordon [13] proposed three empirical expressions for a description of the dynamic relationship between fiber moisture content and the surrounding relative humidity. By incorporating several features omitted by Henry into the three equations, David and Nordon were able to solve the model numerically. Since their sorption mechanisms (i.e. sorption kinetics) of fibers were neglected, the constants in their sorption-rate equations had to be determined by comparing theoretical predictions with experimental results. Based on conservation equations, this global model consists of two differential coupled equations with variables for temperature and water

( )

concentration in air ( Ca ) and in the fibers of the textile C f , which is generally the water

adsorbed by hygroscopic fibers. C f is not in equilibrium with Ca , but an empirical relation between the adjustable parameters is assumed: the rate of sorption is a linear function of the difference between the actual C f and the equilibrium value. The introduced coefficients are not directly linked to the physical properties of the clothes[29]. Farnworth [14] reported a numerical model describing the combined heat and watervapor transport through clothing. The assumptions in the model did not allow for the complexity of the moisture-sorption isotherm and the sorption kinetics of fibers. Wehner et al [30] presented two mechanical models to simulate the interaction between moisture sorption by fibers and moisture flux through the void spaces of a fabric. In the first model, diffusion within the fiber was considered to be so rapid that the fiber moisture content was always in equilibrium with the adjacent air. In the second model, the sorption kinetics of the fiber were assumed to follow Fickian diffusion. In these models, the effect of heat of sorption and the complicated sorption behavior of the fibers were neglected. Li and Holcombe [31] developed a two -stage model, which takes into account watervapor-sorption kinetics of wool fibers and can be used to describe the coupled heat and moisture transfer in wool fabrics. The predictions from the model showed good agreement

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with experimental observations obtained from a sorption-cell experiment. More recently, Li and Luo [32] further improved the method of mathematical simulation of the coupled diffusion of the moisture and heat in wool fabric by using a direct numerical solution of the moisture-diffusion equation in the fibers with two sets of variable diffusion coefficients. These research publications were focused on fabrics made from one type of fiber. The features and differences in the physical mechanisms of coupled moisture and heat diffusion into fabrics made from different fibers have not been systematically investigated. Holmer [33] compared the heat exchange and thermal insulation of two ensembles, one made from wool, the other from nylon, worn by subjects who exercised either lightly (dry condition) or strenuously (wet condition) for 60 minutes, then rested 60 minutes. He found that there was a significant difference in physiological and subjective responses between dry and wet conditions, but not between the two fiber types. Further, there was no significant difference between the ratings of temperature and humidity sensations for the wool and nylon garments. The wool garment picked up more water than the nylon garment (245 g versus 198 g) for the wet condition. However, the wool fabric may have been slightly thicker than the nylon fabric, since it was reported to have a slightly greater thermal resistance and therefore hold more water [34]. Nielsen and Edrusick [29] evaluated the effect of five kinds of knit structures, all made from 100% polypropylene were evaluated. On subjects exercising for 40 minutes at 5°C followed by 20 minutes at rest, and then repeated. The thickest knit, a fleece, caused the greatest total sweat production, retained the most moisture, and wetted skin the most. They stated that the hydrophobic polypropylene prevented extensive sweat accumulation in the underwear (10 to22%) causing the sweat to accumulate in the outer garments. Bakkevig and Nielsen [35] repeated the protocol above, but used low and high work rates with three kinds of underwear (a polypropylene 1×1 knit, a wool 1×1 knit, and a fishnet polypropylene) worn under wool fleece covered by polyester/cotton outer garments. Total sweat production and evaporated sweat were the same for all three underwear fabrics, but where the sweat accumulated differed significantly. More sweat accumulated in the wool underwear than either polypropylene at both work rates. At the higher work rate, more sweat moved into the fleece layer from both kinds of polypropylene underwear than for the wool. Most likely for the 1×1 knits, the thicker wool underwear(1.95 mm) simply holds more water than the polypropylene underwear (1.41 mm) and based on outer layer-to layer wicking results, needs a greater volume of sweat to fill it pores before it starts to donate the excess to the layer above it. Galbraith et al [34] conducted wear trails for shirts made of various fibers. They concluded that the largest factor that influenced wearing comfort was the ability of fibers to absorb water, regardless of whether fibers were synthetic or natural. All of these studies indicates that the transient state phenomenon responding to the physiological demand to cause sweating is most relevant to comfort or discomfort associated with this general principle. It is important to point out that a highly water absorbing fabric placed in the first layer keeps the partial pressure of water vapor near the skin low, which helps dissipate water at the skin surface, although the water vapor transport rate is smaller than for non-absorbing fabrics. In the other words, the dissipation of water by means of absorption by fabrics appears to be much more efficient way to keep the water vapor pressure near the skin low than

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dissipation by permeation through fabrics. Highly water absorbing fabrics raise the temperature of the air space near the skin. The temperature rise will further decrease relative humidity; however, the higher temperature may or may not desirable depending on environmental conditions [37]. In the literature, the emphasis has been placed on the correlation between sweating and discomfort associated with wearing fabrics. However, there is relatively less emphasis placed on the influence of changes in the surrounding conditions, that is, the influence of the seasons. Many comfort studies are conducted with a single layer of fabric at relatively warm and moderately humid conditions. Severe winter conditions, which mandate the use of layered fabrics, would necessitate totally different kinds of testing procedures. Consequently, it is necessary to distinguish the comfort factor and the survival factor, and to investigate these factors with different perspective[38]. The evaporation process is also influenced by the liquid transport process. When liquid water cannot diffuse into the fabric, it can only evaporate at the lower surface of the fabric. As the liquid diffuses into the fabric due to capillary action, evaporation can take place throughout the fabric[39]. Moreover, the heat transfer process has significant impact on the evaporation process in cotton fabrics but not in polyester fabrics. The process of moisture sorption is largely affected by water vapor diffusion and liquid water diffusion, but not by heat transfer. When there is liquid diffusion in the fabric, the moisture sorption of fibers is mainly determined by the liquid transport process, because the fiber surfaces are covered by liquid water quickly. Meanwhile, the water content distributions in the fibers are not significantly related to temperature distributions. All moisture transport processes, on the other hand, affect heat transfer significantly. Evaporation and moisture sorption have a direct impact on heat transfer, which in turn is influenced by water vapor diffusion and liquid diffusion. The temperature rise during the transient period is caused by the balance of heat released during fiber moisture sorption and the heat absorbed during the evaporation process[40]. As a whole, a dry fabric exhibits three stages of transport behavior in responding to external humidity transients. The first stage is dominated by two fast processes: water vapor diffusion and liquid water diffusion in the air filling the interfiber void spaces, which can reach new steady states within fractions of seconds. During this period, water vapor diffuses into the fabric due to the concentration gradient across the two surfaces. Meanwhile, liquid water starts to flow out of the regions of higher liquid content to the dryer regions due to surface tension force [41]. The second stage features the moisture sorption of fibers, which is relatively slow and takes a few minutes to a few hours to complete. In this period, water sorption into the fibers takes place as the water vapor diffuses into the fabric, which increases the relative humidity at the surfaces of fibers. After liquid water diffuses into the fabric, the surfaces of the fibers are saturated due to the film of water on them, which again will enhance the sorption process. During these two transient stages, heat transfer is coupled with the four different forms of liquid transfer due to the heat released or absorbed during sorption/desorption and evaporation/condensation. Sorption/ desorption and evaporation/condensation, in turn, are affected by the efficiency of the heat transfer. For instance, sorption and evaporation in thick cotton fabric take a longer time to reach steady states than in thin cotton fabrics.

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Finally, the third stage is reached as a steady state, in which all four forms of moisture transport and the heat transfer process become steady, and the coupling effects among them become less significant. The distributions of temperature, water vapor concentration, fiber water content, and liquid volume fraction and evaporation rate become invariant in time. With the evaporation of liquid water at the upper surface of the fabrics, liquid water is drawn from capillaries to the upper surface.

2. EFFECTIVE THERMAL CONDUCTIVITY One way of expressing the insulating performance of a textile is to quote "effective thermal conductivity". Here the term "effective" refers to the fact that conductivity is calculated from the rate of heat flow per unit area of the fabric divided by the temperature gradient between opposite faces. It is not true condition, because heat transfer takes place by a combination of conduction through fibers and air and infrared radiation. If moisture is present, other mechanisms may be also involved. Research on the thermal resistance of apparel textiles [42-47], has established that the thermal resistance of a dry fabric or one containing very small amounts of water depends on its thickness, and to lesser extent on fabric construction and fiber conductivity. Indeed, measurements of effective thermal conductivity by standard steady-state methods show that differences between fabrics and mainly attributable to thickness. Despite these findings, consumers continue to regard wool as "warmer" than other fibers, and show preference for wearing wool garments in cold weather, particularly when light rain or sea spray is involved.

Effective thermal conductivity

acrylic

Wool Cotton Porous Polypropylene

%regain

Figure 1. Comparison of effective thermal conductivities for porous acrylic, polypropylene, wool and cotton.

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Meanwhile, the effective thermal conductivites of fabrics can be studied for varying regains. Regain is the mass of water present expressed as a percentage of the dry weight of the material. The effective thermal conductivities for porous acrylic, polypropylene, wool, and cotton is shown in Figure 1.

Figure 2.a. Cross sections of nonabsorbent material at different regains.

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Figure 2.b. Cross sections of absorbent material at different regains.

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The curves indicate that changes in "effective thermal conductivity" with increasing regain are not linear, but can be explained in terms of water within the fibers of fabrics with regain. Figure 2 presents the various phases diagrammatically. When fabrics containing water are subjected to a temperature gradient, three different modes of heat flow can be distinguished; • • •

the presence of condensed water vapor transport, and condensation.

Fiber sorption properties influence the heat and mass transfer up to the point when the rate of increased conductivity with regain is low in the curves, and then all fiber types behave similarly. Generally heat transfer increases with increasing regain, but in this initial regain the rise is most pronounces for the nonabsorbent polypropylene. The fiber with the lowest effective conductivity over the regain 0-200% regain is wool, an effect that is especially pronounced in the region of low regains from zero to saturation. This is mostly influenced by fiber sorption properties. Low regains are most common in real wear situation. This is mostly influenced by fiber sorption properties. Low regains are most common in real wear situations. This explains the popular association between wool and warmth in situations such as yachting, where the garment will very likely become wet. Cotton fabric has the highest effective thermal conductivity for almost the whole regain.

3. TRANSPORT PHENOMENA FOR SWEAT Fabrics to protect human body are, in most cases used under nonequilibrium conditions; therefore, characteristics of fabrics under nonisothermal and nonequilibrium conditions are important in evaluating overall performance. Furthermore, in colder environments, layered fabrics rather than a single fabric are used in most cases. Under such conditions, the two most important characteristics of fabrics are water vapour and heat transport. However, the water vapour transport may not influenced significantly by surface characteristics-the hydrophilic or hydrophobic nature of fabrics. On the other hand, when liquid water contacted a fabric, such as in the case of sweating, the surface wetability of fabric play a dominant role in determining the water vapour transport through layered fabrics[48-50]. In such a case, the wicking characteristics, which determines how quickly and how widely liquid water spreads out laterally on the surface of or within the matrix of the fabric, determines the overall water vapour transport rate through the layered fabrics. It should be noted that the overall water vapour and heat transport characteristics of a fabric should depend on other factors such as the water vapour absorbability of the fibers, the porosity, density, and thickness of the fabric, etc[51-53]. Moreover, transport phenomena for the sweat case are much more complicated than the water vapour case because wetting of the surface by liquid water precedes water wetting of the surface by liquid water precedes water vapour transmission. Note that there is an important difference in water absorbing characterizing of wool and cotton, although both fibers have relatively high water vapour absorption rates. Because of the hydrophobic surface

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of wool fibers, a liquid droplet in contact with a wool fabric does not spread out laterally within a fabric layer. The water vapour transport rate, in the sweat case, can be indicated by the size of liquid water spread out on the surface or within a fabric matrix[54,55]. Moreover, the term "breathable" implies that the fabric is actively ventilated. This is not the case. Breathable fabrics passively allow water vapour to diffuse through them yet still prevent the penetration of liquid water. Production of water vapour by the skin is essential for maintenance of body temperature. The normal body core temperature is 37˚C, and skin temperature is between 33 and 35˚C, depending on conditions. If the core temperature goes beyond critical limits of about 24˚C and 45˚C then death results. The narrower limits of 34˚C and 42˚C can cause adverse effects such as disorientation and convulsions. If the sufferer is engaged in a hazardous pastime or occupation then this could have disastrous consequences.

4. FACTORS INFLUENCING THE COMFORT ASSOCIATED WITH WEARING FABRICS As it was mentioned earlier, if liquid water (sweat (sweat) cannot be dissipated quickly, the humidity of the air in the space in between the skin and the fabric that contacts with the skin rises. This increased humidity prevents rapid evaporation of liquid water on the skin and gives the body the sensation of "heat" that triggered the sweating in the first place. Consequently, the body responds with increased sweating to dissipate excess thermal energy. Thus a fabric's inability to remove liquid water seems to be the major factor causing uncomfortable feeling for the wearer. Hollies et al. [38] conducted wearer trails for shirts made of various fibers. They concluded that the largest factor that influence wearing comfort was the ability of fibers to absorb water, regardless of whether fibers were synthetic or natural. All of these studies indicate that the transient state phenomenon responding to the physiological demand to cause sweating is most relevant to comfort or discomfort associated with fabrics. It is important to point out that a highly water absorbing fabric placed in the first layer keeps the partial pressure of water vapour near the skin low, which helps to dissipate water at the skin surface, although the vapour transport rate is smaller than for non-absorbing fabrics. In other words, the dissipation of water by means of absorption by fabrics appears to be much more efficient way to keep water vapour pressure near the skin low than dissipation by permeation through fabrics. Highly water absorbing fabrics raise the temperature of the air space near the skin. The temperature rise will further decreases relative humidity; however, the higher temperature may or may not be desirable depending on environmental conditions.

5. INTERACTION OF MOISTURE WITH FABRICS Trying to stay warm and dry while active outdoors in winter has always been a challenge. In the worst case, an individual exercises strenuously, sweats profusely, then rests. During exercise, liquid water accumulates on the skin and starts to wet the clothing layers above skin. Some of the sweat evaporates from both the skin and the clothing. Depending on the

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temperature and humidity gradient across the clothing, the water vapor either leaves the clothing or condenses and freezes somewhere in its outer layers. When one stops exercising and begins to rest, active sweating soon ceases, allowing the skin and clothing layers eventually dry. During this time, however, the heat loss from body can be considerable. Heat is taken from the body to evaporate the sweat, both that on the skin and that in the clothing. The heat flow from the skin through the clothing can be considerably greater when the clothing is very wet, since water decreases clothing’s thermal insulation. This post-exercise chill can be exceedingly comfortable and can lead to dangerous hypothermia. A dry layer next to the skin is more comfortable than a wet one. If one can wear clothing next to the skin that does not pick up any moisture, but rather passes it through to a layer away from the skin, heat loss at rest will be reduced. For such reasons, synthetic fibers have gained popularity with winter enthusiasts such as hikers and skiers. Advertising the popular press would have us believe that synthetic materials pick up very little moisture, dry quickly, and so leave the wearer warm and dry. In contrast, warnings are given against wearing cotton or wool next to skin, since these fibers absorb sweat and so "lower body temperature". A further property credited to synthetics, in particular polypropylene, is that they wick water away from the skin, leaving one dry and comfortable. In the early fifties, when synthetic fibers such as nylon and the acrylics were first coming onto the consumer market, Fourt et al. [56] and Coplan [57] compared the water absorption and drying properties of these "miracle" fibers with those of conventional wool and cotton. Forty-five years latter, the water absorption and drying properties of synthetics were compared with natural fibers and it was found that all fabrics pick up water, and the time they take to dry is proportional to the amount of water they initially pick up [58,59]. It was also found that properties relevant to clothing on an exercising person, that is, the energy required to evaporated water from under and through a dry fabric or to dry a wet fabric and layer-to-layer wicking [60]. Holmer [61] compared the heat exchange and thermal insulation of two ensembles, one made from wool, the other from nylon, worn by subjects who exercised either lightly (dry condition) or strenuously(wet condition) for 60 minutes, then rested 60 minutes. He found that there was a significant difference in the physiological and subjective responses between dry and wet conditions, but not between the two fiber types. Further, there was no significant difference between the ratings of temperature and humidity sensations for the wool and nylon garments. The wool garment picked up more water than the nylon garment (245 g versus 198 g) for the wet condition. However, the wool fabric may have been slightly thicker than the nylon fabric, since it was reported to have a slightly greater thermal resistance and would therefore, hold more water.

6. MOISTURE TRANSFER IN TEXTILES In nude man any increase of sweating is immediately accompanied by an increase in heat loss due to evaporation. Similarly any decrease in sweating is immediately accompanied by a decrease in heat loss. Thus, nude man has a control of his heat loss which has no appreciable time lag. This is shown diagrammatically in Figure 3.

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252

Rate of heat transfer

Period A

Period C Period B

Further limit due to moisture accumulation Desired heat transfer (heat production). Heat transfer limit of fabric.

Time Figure 3. Rate of heat transfer versus time.

In this figure time is plotted as abscissa and rate of heat produced or lost as ordinate. To maintain perfect heat balance and a constant temperature, heat loss should equal heat production so that the heat production and heat loss curves should be the same. Suppose a man is initially at rest with a low heat production and a like heat loss as represented by the solid line in period A. When he exercises and produce more heat, the heat loss should rise as represented by the solid line in period B. Again, when he returns to the resting condition, period C, heat loss should return to the solid base line. If sweating is the mechanism bringing about increasing heat loss but evaporation is limited, the increased heat loss might only be sufficient to match an increased heat production represented by the dashed line in period B. The position of this dashed line will depend on the equilibrium vapor transfer characteristics of the clothing. If , however, the hypothetical man is clothed in absorbent clothing, some of the sweat initially evaporated at the skin at the start of the exercise period will be absorbed by the clothing and its heat of absorption will appear in the clothing as sensible heat. This source of sensible heat will temporarily reduce the heat loss so that it follows the dotted line. Eventually a new equilibrium moisture content will be established and the dotted and dashed lines will coincide. When exercise and sweating stop, period C, moisture accumulated in the clothing will be desorbed or evaporated and tend to cool the clothing and the man wearing it. Thus, there is a time lag, and the heat loss curve will tend to follow the dotted curve during the after-exercise period. Since in Figure 5.3 heat loss per unit time is plotted against time, the area between the dotted line and the solid line represents an amount of heat, as distinguished from rate of heat loss, which can be regarded as a quantitative value of after exercise chill [62].

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It should be noted that the moisture contained in the clothing need not be only that which is collected by absorption. It is also possible in cold damp or extreme cold environments that sweat which is evaporated at the skin will recondense when it reaches colder layers of clothing. Alternatively the sweat rate may be so high that some of it will not evaporate from the skin. In nude man this drips off, but in clothed man it is blotted up by clothing to evaporate after sweating ceases. Meanwhile, measurements of water vapour permeability of woven fabrics have indicated that in the lower ranges of fabric density, the main path of water vapour transfer is through the air spaces between fibers and yarns. This covers the densities characteristic of most apparel fabrics made from staple fibers, although filament yarn fabrics may be woven to higher densities in which the kind of fiber itself in the passage of water vapour , it is necessary to account for the water vapour passage through air spaces.

7. WATER VAPOUR SORPTION MECHANISM IN FABRICS In 1393, Henry [63] proposed a mathematical model for describing heat and moisture transfer in fabric, as shown in Equations 1 and 2 , and the further analysed the model in 1948 [64];

∂C f ∂C a Da ε ∂ 2 C a ε + (1 − ε ) = ∂t ∂t τ ∂x 2 Cv

∂C f ∂ 2T ∂T −λ =K 2 ∂t ∂t ∂x

(1)

(2)

In these equations, both C v and λ are functions of the concentration of water absorbed by the fibers. Most textile fibers have very small diameters and very large surface/volume ratios. The assumption in the second equation of instantaneous thermal equilibrium between the fibers and the gas in the interfiber space does not therefore lead to appreciable error. The two equations in the model are not linear and contain three unknown, i.e., C f , T, and C a . A third equation should be established appropriately in order to solve the model. Henry [63, 64] derived a third equation to obtain an analytical solution by assuming that C f is linearly dependent on T and C a , and that fibers reach equilibrium with adjacent air instantaneously. Considering the two-stage sorption process of wool, David and Nordon [65] proposed an exponential relationship to describe the rate of water content change in the fibers, as shown in equations (3) and (4);

1 ∂C f ( H a − H f )γ ε ∂t where

(3)

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254

γ = k1 (1 − exp(k 2 H a − H f )

(4)

and k1 and k 2 are adjustable parameters that are evaluated by comparing the prediction of the model and measured moisture content of the fabric. Farnworth [66] reported a numerical model describing combined heat and water vapour transport through clothing. The assumptions in his model do not allow for the complexity of the moisture sorption isotherm and the sorption kinetics of fibers. Wehner et a.l [67] presented two mathematical models to simulate the interaction between moisture sorption by fiber and moisture flux through the air spaces of a fabric. In the first model, they considered diffusion within the fiber to be so rapid that the fiber moisture content is always in equilibrium with the adjacent air. In the second model, they assumed that the sorption kinetics of the fiber follows a Fickian diffusion. Their model neglected the effect of heat of sorption behavior of the fiber. Li and Luo [32] developed a new sorption equation that takes into account the two-stage sorption kinetics of wool fibers, and incorporated this with more realistic boundary conditions to simulate the sorption behavior of wool fabrics. They assumed that water vapour uptake rate of fiber consists of a two components associated with the two stages of sorption identified by Downes and Mackay [68] and described by Watt [69]. The first stage is represented by Fickian diffusion with a constant coefficient. Secondstage sorption is much slower than the first and follows an exponential relationship. The relative contributions of the two stages to the total uptake vary with the sorption stage and the initial regain of the fibers. Thus, the sorption rate equation can be written as;

∂C f ∂t

(1 − p) R1 + pR2

(5)

where R1 is the first-stage sorption rate, R2 is the second-stage rate sorption rate, and p is a proportional of uptake in the second stage. Equation (5) assumes that the sorption rate is a linear average of the first and second sorption rates. The first-stage sorption rate R1 can be derived using Crank's truncated solution [26]. Which may lead to a corresponding algorithm that needs a strict time striction and hence long computation times. The second-stage sorption rate R2 , which relates local temperature, humidity, and the sorption history of the fabric, is assumed to have the following form;

R2 ( x, t ) = s1 sign( H a ( x, t ) − H a ( x, t ) − H f ( x, t )) ⎛ ⎞ s2 ⎟ × exp⎜ ⎜ H ( x, t ) − H ( x, t ) ⎟ f ⎝ a ⎠

(6)

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255

where s1 and s 2 are constants. No values for s1 and s 2 have been reported in the literature for any textile fibers. This is also an empirical equation that has an unclear physical meaning, which makes it inconvenient to predict and simulate heat and moisture transport in a fabric. These equations were improved substantially by Li and Luo [32]. The numerical values and approximate relationships they used are listed in Table 3. They assumed that moisture sorption by a wool fiber can be generally described by a uniform diffusion equation for both stages of sorption;

∂C f ( x, r , t ) ∂t

=

∂C f ( x, r , t ⎞ 1 ∂ ⎛ ⎟⎟ ⎜⎜ rD f ( x, t ) r ∂r ⎝ ∂r ⎠

(7)

C fs ( x, R f , t ) = f ( H a ( x, t ), T ( x, t )) Table 3. Numerical values of wool and physical properties Parameters Thermal conductivity of fabric (KJ/m.K)

Initial values

Volumetric heat capacity of

1609.7

38493 . e

−2

373.3+4661 Wc +4.221 T

fabric ( kJ / m . K ) 2

fiber ( m / s) Diffusion coefficient of water vapor in fabric

(38.493 − 0.72Wc + 0.113Wc2 − 0.002Wc3 )10 − 3

3

Diffusion coefficient of

Mathematical relationship

2.4435 e 1.91 e

−14

1.0637 arc tan(1541.1933) 2

(3600/ t ) 10

−14

−5

______

2

( m / s) Heat of sorption or desorption of water by fibers ( KJ / Kg )

4124.5

1602.5exp(-11.72 Wc ) +2522

Porosity of fabric

0.925

______

Density of fabric

1330

______

Radius of wool fiber (m)

104 . e −5

______

Mass transfer coefficient (m/s) Heat transfer coefficient

0.137

______

99.4

______

3

( Kg / m )

2

(W / m . K )

Wc =Water content of the fibers in the fabric.

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where D f ( x, t ) are the diffusion coefficients that have different presentations at different stages of sorption, and x is the coordinate of a fiber in the given fabric. The boundary condition is determined by the relative humidity of the air surrounding a fiber at x. In a wool fabric, D f ( x, t ) is a function of Wc ( x, t ) , which depends on the sorption time and the fiber location.

8. MODELING The fabric model simulates the transport of a liquid and vapor-phase fluid that can undergo phase change (e.g., water) and an inert gas (air) in a textile layer. Several new models and capabilities were added to a standard commercial CFD code (FLUENT Version 6.0, Fluent Inc., Lebanon, NH) [47]. These capabilities include: • • • • •

Vapor phase transport (variable permeability). Liquid phase transport (wicking). Fabric property dependence on moisture content. Vapor/liquid phase change (evaporation/condensation). Sorption to fabric fibers.

In the fabric, transport equations are derived for mass, momentum, and energy in the gas and liquid phases by volume-averaging techniques. Definitions for intrinsic phase average, global phase average, and spatial average for porous media are those given by Whitaker [48]. Since the fabric porosity is not constant due to changing amounts of liquid and bound water, the source term for each transport equation includes quantities that arise due to the variable porosity. These equations are summarized in general form below [47]. Gas phase continuity equation:

∂ ((1 − ε ds )ργ ) + ∇.(ργ vγ ) = Sγ ∂t S y = m' sv + m' lv +

∂ (ε + ε β ) ρ γ ∂t bl

(

(8)

)

(9)

Vapor continuity equation:

∂ ((1 − ε ds )ργ mν ) + ∇.(ργ m ν γ ) = ∇.{ργ Deff ∇(mν )}+ Sν ∂t v

Sν = m© msν + m©lmν +

∂ {(ε bl + ε β )ργ mν } ∂t

(10)

(11)

Some Aspects of Dynamic Water Vapour …

mν =

ρν ργ

257

(12)

Gas phase momentum equation:

∂ (ρ γ ν γ ) + ∇.(ρ γ ν γ ) = ∇.{μ γ ∇(ν γ )}− ∇pγ + S γ ∂t Sγ = −ν γ

μγ

(13)

(14)

Kγ k γ

Liquid transport:

⎛ k K ⎞ ∂ [ (1 − ε ds )ργ s ] = ∇.⎜⎜ − β β ∂Pc ⎟⎟∇s + Sl ∂t ⎝ μ β ∂s ⎠

(15)

⎛k K ⎞ m©lsm m©lmν ∂ Sl = −∇.⎜ β β ρ β g ⎟ − − + [(ε bl )s ] + ⎜ μ ⎟ ρ ρ ∂t β β β ⎝ ⎠

[

∂ (1 − ε ds )( ρ γ − 1)s ∂t

]

(16)

∂ [(1 − ε ds )ργ hγ + ε ds ρds hds ]+ ∇.(ργν γ hγ ) + ∇.(ρβν β (hν − Δhν )) ∂t

[

]

= ∇. k eff ∇(T ) + ∇. ( − ha J a − hν J ν ) + S T

(17)

ST =

∂ [(ε β + ε bl )ργ hγ − ε β ρβ (hν − Δhν ) − ε bl ρβ (hν − Δhν − Q )] ∂t

(18)

νβ =

k β K β ⎡ ∂Pc ⎤ ∇s + ρ β g ⎥ ⎢ μ β ⎣ ∂s ⎦

(19)

In summery, due to the intensive body activity, the wearer perspires and the cloth worn next to skin will get wet. These moisture fabric reduces the body heat and makes the wearer to become tired. So the cloth worn next to the skin should assist for the moisture release quickly to the atmosphere. The fabric worn next to the skin should have two important properties. The initial and fore most property is to evaporate the perspiration from the skin surface and the second property is to transfer the moisture to the atmosphere and make the

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258

Relative humidity %

wearer to feel comfort. Diffusion and wicking are the two ways by which the moisture is transferred to the atmosphere. These two are mostly governed by the fiber type and fabric stricture. The air flow through the fabric makes the moisture to evaporate to the atmosphere. The capillary path plays a vital role in the transfer of moisture and this depends on the wicking behavior of the fabric. In the development of protective clothing and other textiles, modeling offers a powerful companion to experiments and testing. It should be noted that condensation occurs when the vapor density of the steam is higher that its saturation vapor density. The condensation rate is proportional to the vapor density difference between that in the gas phase and that at the condensing surface. The relative hygrometry is quite different due to the action (water vapor pressure) of the airs on each side of the fabric (Figure 4). Sorption and desorption have not opposite kinetics, the former faster in temperature and in charge of humidity during the first minutes, the latter more completer in discharge of humidity after a long time (figure 5). Figure 6 shows experimental results of hygrometry for the internal and external surfaces of wool fabric(between skin and fabric). Meanwhile, the internal gap has a considerable effect on the moisture transmission rate. The internal air gap has been identified as being a source of potential errors in most experimental works due to its changing resistance (Figure 7). Figure 8 shows the effect of thickness on the amount of water can be held in a fabric.

100 80 60 40 20 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Time (min)

Relative humidity %

Figure 4. Relative hygrometry of wool fiber during desorption.

100 80 60 40 20 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Time (min)

Figure 5. Relative hygrometry of wool fiber during sorption.

Relative humidity %

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259

100 80 60

External surface

40

Internal surface

20 0 1

2

3

4

5

Time (min)

MVTR(g/sq m/24hr)

Figure 6. Experimental results of hygrometry for the internal and external surfaces of wool fabric(between skin and fabric).

4000 3000 2000 1000 0 0

10

20

30

40

Air gap (mm)

Water held in fabric (mg/m2)

Figure 7. Effect of the internal air gap size on the moisture Vapor transmission (MVTR).

300 250 200 150 100 50 0 1

2

3

4

5

6

Relative thickness (mm)

Figure 8. Thickness versus the amount of water held in fabric.

7

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260

Figure A-1. Overall Thermal Model for Human Comfort.

CONCLUDING REMARKS Information on the transmission of water vapour by textiles fibers is desirable for better understanding of the problems of comfort, and data for design in special applications such as upholstery, footwear, immersion suits and other protective clothing, and wrapping or packaging, where high resistance to liquid water is desired, combined with considerable permeability of water vapour. Some of the issues of clothing comfort that are most readily understood involve the mechanisms by which clothing materials influence heat and moisture transfer from the skin to the environment. Heat transfer by convection, conduction and radiation and moisture transfer by vapor diffusion are the most important mechanisms in very cool or warm environments.

APPENDIX A. HUMAN THERMAL COMFORT A- 1. Overall Thermal Model The thermal model is shown below in Figure A-1. Note the variable resistor which represents the variable perfusion (blood flow) between the core and the skin of the body. Also, note the respiration, RES, and evaporation, E, which represent heat flows but are not driven directly by a temperature difference. Thus, there are no thermal resistances involved in the model of these two flows.

A- 2. Variable Definitions ACEEbi -

area of the naked body (m2) convective heat flux (W/m2 of naked body area) evaporative heat flux (W/m2 of naked body area) radiative emissive power of surface i (W/m2-K4)

Some Aspects of Dynamic Water Vapour … hhfg Icl KL= Mmmair PRRi RES STW-

Subscripts accl dkmrt rssat sw w*-

261

body height (m) latent heat of vaporization of water (J/kg) thermal resistance of clothing, 1 "clo" = 0.155 m2-C/W ("clo") conductive heat flux (W/m2 of naked body area) thermal load (W/m2 of naked body area) metabolic heat generation flux ("met", or W/m2 of naked body area) body mass (kg) mass flow rate of air due to respiration (kg/s) pressure (Pa) radiative heat flux (W/m2 of naked body area) radiative thermal resistance of node i (K4/W) respirative heat flux (W/m2 of naked body area) source term, net rate of heat addition to the body (W/m22 of naked body area) temperature (C or K for radiation) rate of work done by the body (W/m2 of naked body area), or humidity ratio (kg of water vapor/kg of dry air)

denotes ambient denotes "core," i.e. deep within the body denotes clothing denotes diffusion denotes conductive sink temperature denotes mean radiant temperature denotes radiative denotes skin denotes saturated denotes sweat denotes water vapor denotes value needed to achieve comfort

A- 3. Models of Transport Below are presented the individual thermal models for the transport shown in the overall thermal model above in Figure 1. The models are presented one by one. All models are based upon the naked body area, A, which is correlated to mass, m, and height, h, by A = 0.202 m0.425h0.725 For the standard body of mass, m - 70 kg, and height, h = 1.72 m, the "standard" naked body area is Astd = 0.202 (70)0.425(1.73)0.725 = 1.8 m2

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Table A-1. Metabolic Heat Generation Rates Activity

met

W/m2

Lying down

0.8

47

Quietly seated

1.0

58

Sedentary activity (office, home, school)

1.2

58

Standing, relaxed

1.2

70

Light activity (shopping, laboratory, light work)

1.6

93

Medium activity (shop work, domestic work, machine work)

2.0

117

Heavy activity (heavy machine work, garage work)

3.0

175

Heavy exercise (running)

9.0

525

A- 3.1. Metabolic Heat Generation, M The units of M, the metabolic heat generation rate, are met, where 1 met = 58.15 W/m2. The following table provides M for various activity levels. Example For the "standard" body, seated quietly M = (58.15 W/m2) (1.8 m2) = 105 W

A- 3.2. Evaporation, E E consists of Ed, due to diffusion, and Esw, due to sweating. A model exists for Ed: Ed = 3.05 x 10-3 (Pw,sat(Ts) - Pw,a) [Pa, W/m2] ASHRAE provides a curve fit for Pw,sat(T), as ln(Pw,sat(T))= c6/T + c7 + c8 T + c9 T2 + c10 T3 + c11 ln(T) [kPa, K] where: c6 = 5.800 e 03 c7= -5.516 e 00 c8= -4.864 e-02 c9= 4.176 e-05 c10= -1.445 e-08 c11 = 6.546 Note that here the units of P are kPa (not Pa), and the units of T are K (not C).

Example At Ta = 23 C and 50% RH, Pw,a = 1,400 Pa; and for Ts = 33 C, Pw,sat(Ts) = 5,039 Pa

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Then, Ed = 3.05 x 10-3 (5.039 - 1,400) = 11.1 W/m2

A- 3.3. Respiration, RES The model for respiration includes a sensible component, RS, and a latent component (due to evaporation), RE, for heat transport. RS = mair cp,air (Tair,out -Ta) [W/m2, kg/s-m2, C] RE = mair hfg (Wair,out -Wa) [W/m2, kg/s-m2, J/kg] Experiments indicate that mair depends linearly on M. Substituting the curve fit for this, and for the thermodynamic properties (Wair,out is taken as saturated at 34 C): RS = 0.0014 M (Tair,out -Ta) [W/m2, C] RE = 1.72 x 10-5 M (5,867 - Pw,a) [W/m2, Pa]

Example At 1 met, and using Tair,out = 34 C, and the ambient conditions of 23 C and 50% RH: RS = 0.0014 (58.15)(34 -23) = 0.87 W/m2 RE = 1.72 x 10-5 (58.15) (5,867 - 1,400) = 4.47 W/m2

A- 3.4. Heat Transfer through Clothing, Kcl Using a classical thermal resistance model: Kcl = (Ts - Tcl)/[0.155 Icl] [W/m2, C, "clo"] Values for Iclo are given in Table A-2. Table A-2. Thermal Resistance of Various Attires Clothing Combination

Iclo

m2-K/W

Naked

0

0

Shorts

0.1

0.016

Tropical attire (briefs, shorts, open- necked shirt, light socks and sandals)

0.3

0.047

Light summer attire (briefs, long lightweight trousers, short-sleeved shirt, light socks and shoes)

0.5

0.078

Working attire (briefs, long-sleeved shirt, trousers, woolen socks and shoes) 0.8

0.124

Typical indoor winter attire (briefs, long-sleeved shirt, trousers, longsleeved sweater, heavy socks and shoes)

1.0

0.155

Heavy indoor winter attire (long underwear, long-sleeved shirt, suit with vest, heavy socks and shoes)

1.5

0.233

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A- 3.5 Radiation, R From a radiative thermal network, normalizing the heat transfer to surface i of area Ai, and where all other surface resistances Rj << Ri, then qi/Ai = εi (Ebi - Eb,MRT) where εi is the emittance (absorptance) of surface i, and the Mean Radiant Temperature, MRT is defined as MRT4 = Σ Fij Tj4 Note that here, i is the outside area of the clothing, as it is the clothing which exchanges energy radiatively with the surrounding surfaces j. Also, the temperature of surface i must then be the temperature of the outside of the clothing. The relation above may be further simplified and normalized to the naked body area by linearizing the emissive powers, valid if all temperatures are near room temperature (recall that, when dealing with radiation, all temperatures must be in absolute units of K): R = 3.9 fcl (Tcl - MRT) [W/m2, C or K] where fcl is the ratio of clothing area to naked body area, and 1 < fcl < 1.5.

Example For fcl = 1.2, Tcl = 21 C (70 F), and MRT = 18 C (65 F): R = 3.9 (1.2) (21 - 18) = 14 W/m2 A- 3.6. Convection Convection is modeled using classical heat transfer relationships for free and forced convection. Normalized to naked body area, and using the temperature difference between the clothing and the ambient as the driving potential: C = fcl hc (Tcl - Ta) [W/m2, W/m2-C, C] where hc is the convective heat transfer coefficient. For natural convection (i.e. Va = 0), hc is proportional to Ra1/4. Substituting the properties of air at room temperature: hc = 2.38 (Tcl - Ta)1/4 [W/m2-C, C] and for forced convection, hc is proportional to Ra1/2. Substituting the properties for air at room temperature: hc = 12.1 (Va)1/2 [W/m2-C, m/s]

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Example 1. For still air with Tcl = 21 C, Ta = 18 C, and fcl = 1.2: hc = 2.38 (21 - 18)1/4 = 3.13 W/m2-C C = (1.2) (3.13) (21 - 18) = 11.3 W/m2 2. For the above conditions, except with the air moving at Va = 1 m/s (2.2 mph): hc = 12.1 (1)1/2 = 12.1 W/m2-C C = (1.2) (12.1) (21 - 18) = 43.6 W/m2 Note how a small velocity dramatically increases the heat flux. This is the reason that folks use Casablanca style ceiling fans during the summer.

A- 3.7. Conduction, K This is normally very small, so is neglected.

A- 4. Conditions for Human Comfort Comfort is attained with Ts and Esw at fixed levels, depending linearly upon (M-W). These values are denoted by starred superscripts, as those necessary, but not sufficient. for comfort. The curve-fits are: Ts* = 35.7 - 0.0275 (M-W) [C, W/m2] and Esw* = 0.42 (M - W - 58.15) [W/m2]

Example For a person seated, at rest, i.e. M = 58.15 W/m2 and W = 0 W/m2: Ts* = 35.7 - 0.0275 (58.15 - 0) = 34.1 C and Esw* = 0.42 (58.15 - 0 - 58.15) = 0 [W/m2] Note that this implies that no sweating occurs at or below M - W = 58.15 W/m2. Now, by plugging Ts* and Esw* into the heat balance equation (first law), we can determine the ambient conditions, i.e. Ta, Va, RHa, MRT and Iclo, necessary for thermal comfort.

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A- 5. Thermal Discomfort Thermal comfort may not be attainable because: 1) the heat balance is unable to be satisfied for Ts* and Esw*, or 2) asymmetries such as drafts, asymmetric radiation, etc., exist. Defining the thermal load, L, as L = (M - W) - (Kcl + RES + E)* = (M - W) - (R + C + RES + E)*, Fanger correlated L with the Predicted Mean Vote (PMV) to determine comfort: PMV = [0.303 exp(-0.036(M-W)) + 0.028] L where the PMV values are associated with sensation in Table A-3. A correlation exists between PMV and Predicted Percentage Dissatisfied (PPD). Normally, "comfort" is assumed when 85% of respondents are comfortable. Table A-4 provides values read from the graph of PPD vs. PMV. Putting PMV = +/- 0.7 in the correlation of the thermal load with PMV will allow the comfort limits for 85% of people comfortable to be determined from the energy balance, L. Table A-3. PMV and Sensation PMV

Associated Sensation

+3

Hot

+2

Warm

+1

Slightly Warm

0

Comfortable

-1

Slightly Cool

-2

Cool

-3

Cold

Table A-4. PPD vs. PMV PPD

PMV

5%

0

6%

+/- 0.2

8%

+/- 0.35

10%

+/- 0.5

15%

+/- 0.7 ("comfort")

20%

+/- 0.8

30%

+/- 1.07

40%

+/- 1.3

60%

+/- 1.7

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[5] [6] [7] [8]

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A.R. Horrocks and S.C.Anand, Handbook of technical textiles, Woodhead publishing Ltd, England, 2000. Hollies, N.R.S., Mt. Washington feasibility test, Report #20 contract DA-19-129-qm 331, Natick R&D Center, June 1956, AD 698, 450. Hollies, N.R.S., Cotton clothing attributes in subject comfort, 15th textile chemistry and processing conference, USDA New Orleans, 1975. Hollies, N.R.S., Psycological scaling in comfort assessment, ch. 8 in "Clothing Comfort", N.R.S. Hollies and R.F. Goldman, Eds, Ann Arbor Science, Ann Arbor, 1977. D.M. Scheurell, S.M. Spivak, and N. R.S. Hollies, Dynamic surface wetness of fabrics in relation to clothing comfort, Text Res. J., 394-399, 1985. D.A.De Vries, Transactions, American Geophysical Union, 39(5), 909-916, 1958. J.R. Philip and D.A. DE Vries, Transactions, American Geophysical Union, 38, 222232, 1957. Eckert E. and Faghri M. (1980): A general analysis of moisture migration caused by temperature difference in an unsaturated porous medium, Int. J. Heat Mass Transfer, vol. 23, pp.1613-1623. Int. J. Heat Mass Transfer, 23, 1613-1623, 1980. Udell K.S. (1985): Heat transfer in porous media considering phase change and capillarity-the heat pipe effect, Int. J. Heat Mass Transfer, vol. 28(2), pp.485-495. Udell K.S. (1983): Heat transfer in porous media heat from above with evaporation, condensation and capillary effects, J. Heat Transfer, vol.105, pp.485-492. Bouddour A. , Auriault J.L. , Mhamadi M. and Bloch J.F. (1998): Heat and mass transfer in wet porous media in presence of evaporation-condensation, Int. J. Heat Mass Transfer, vol. 41(15), pp. 2263-2277. P.W. Gibson, In Computational Technologies for Fluid/Thermal/Structural/Chemical Systems with Industrial Applications, Volume II, pages 125-139, ASME, 1999. Nordon P. and David H.G. (1967): Coupled diffusion of moisture and heat in hygroscopic textile materials, Int. J. Heat Mass Transfer, vol. 10, pp. 853-866. Farnworth B. (1983): Mechanics of heat flow through clothing insulation, Tex. Res. J. vol. 56, pp. 581-587. Farnworth B. (1986): A numerical model of the combined diffusion of heat and water vapor through clothing. - Tex. Res. J., vol. 56, pp.653-665. Osczevski, R.J. and Dolhan, P.A., J. Coated Fabrics 18, 255-258 (1989). Osczevski, R.J. (1966): Water Vapour Transfer Through a Hydrophilic Film at Subzero Temperatures, Tex. Res. J. vol. 66(1), pp. 24-29. Farnworth B., Lotens, W.A., and Wittgen, P. (1990): Variation of Water Vapour Resistance of Microporous and Hydrophilic Films with Relative Humidity, Tex. Res. J. vol. 60(1), pp. 50-53. Osczevski R.J. and Dolhan, P.A.(1989): Anomatous Diffusion in a Water Vapor Permeable, waterproff Coating, J. Coated Fabrics vol. 18, pp. 255-258. Gretton, J.C., Brook, D.B., Dyson, H.M., and Harlock, S.C. (1998): Moisture Vapour transport Through Waterproof Breathable Fabrics and Clothing Systems Under a Temperature Gradient, Tex. Res, J. vol. 68(12), pp. 936-941.

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[20] Galbraith R.L., Werden, J.E., Fahnestock, M.K. (1962): Comfort of Subjects Clothed in Cotton, Water Repellent Cotton and Orlon Suits, Tex. Res. J., vol. 32, pp. 236-243. [21] Niwa M. (1968): Water Vapor Permeability of Underwear, J. Jpn. Res. Assn. Textile End Uses. Vol. 9, pp.446 450. [22] Morooka, H., and Niwa, M., Moisture and Water Transport Properties of Clothing Materials and Comfort Sensations, J. Home Econ. Jpn, 30, 320 (1979) [23] Hollies, N., Improved Comfort Polyester, Textile Res. J. 54, 544(1984). [24] King G. and Cassie A.,(1940): Propagation of temperature changes through textiles in humid atmospheres. Trans Faraday Soc., vol. 36, pp. 445-453. [25] Gretton J.C. and Brook D.B. (2000): Moisture vapor Transport through Clothing System, Tex. Res. J., vol.56, pp.872-879. [26] J. Crank, The Mathematics of Diffusion, Clarendon Press, Oxford, UK 1975. [27] P. Henry, Proc. Roy. Soc., 171A(1939) 215., Diffusion in absorbing media. [28] P. Henry, Disc. Faraday Soc., 3(1948) 243., The diffusion of moisture and heat through textiles. [29] Nielsen, R., and Edrusick, T.L. (1990): Thermoregulatory Responses to Intermittent Exercise are Influenced by Knit Structure of Underwear, Eur. J. Appl. Physiol., vol.60, pp.15-25. [30] J. Wehner, B. Miller and L. Rebenfeld, Dynamics of water vapour transmission through fabric barrier, Tex. Res. J., 58(1988) 581. [31] Y. Li, and B. Holcombe, A two stage sorption model of the coupled diffusion of moisture and heat in wool fabrics, Text. Res. J., 62 (1992) 211. [32] Y. Li and Z. Luo, An improved mathematical simulation of the coupled diffusion of moisture and heat in wool fabric, Text. Res. J., 69(1999) 760. [33] Holmer I. (1985): A study of heat transfer through fabrics, Tex. Res. J., vol. 55,pp.511518. [34] Snycerski M and Wasiak I.F. (2002): Influence of Furniture Covering Textiles on Moisture Transport in a Car Seat Upholstery Package, Autex Res. J. vol. 2 , pp.126131. [35] Bakkerig M.K. and Nielsen R. (1995): Some aspects of clothing comfort.-Ergonomics vol. 38, pp.926-934. [36] Galbraith R.L., Werden, J.E., Fahnestock, M.K. (1962): Comfort of Subjects Clothed in Cotton, Water Repellent Cotton and Orlon Suits, Tex. Res. J., vol. 32, pp. 236-243. [37] Niwa M. (1968): Water Vapor Permeability of Underwear, J. Jpn. Res. Assn. Textile End Uses. Vol. 9, pp.446 450. [38] Hollies, N., Demartino, R., Yoon, H., Buckley,a., Becker, C., and Jackson, W. (1984): Improved Comfort Polyester, Tex. Res. J., vol. 54, pp.544-551. [39] M. Adler, and W.K. Walsh, Mechanisms of Moisture Transport between Fabrics, Tex. Res. J.,84 (1984), 334-343. [40] M. Day, and P.Z. Sturgeon, Water Vapor Transmission Rates Throuh Materials as Measured by Differential Scanning Calorimetry, Tex. Res. J., 86 (1986)157-161. [41] A.M. Schneider, and B.N.Hoschke, Heat Transfer Through Moist Fabrics, Textile Res. J., 62 (1992), 61-66. [42] P. Gibson, D. Rivin, C. Kendrick, and H. Schreuder, Humidity- Dependent Air Permeability of Textile Materials, Textile Res. J., 69(1999), 311-317.

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[43] R.M.Crow and R. J. Osczevski, The Interaction of Water with Fabrics, Textile Res. J., 68(1998), 280-288. [44] M. Snycerski, I.F. Wasiak, Influence of Furniture Covering Textiles on Moisture Transport in a Car Seat Upholstery Package, Autex Res. J. 2(2002), 126-131. [45] K.Prasad, W.Twilley, and J.R. Lawson, Thermal Performance of Fire Fighters’ Protective Clothing, NISTIR Report No 6881, 1-32, (2004). [46] M. Sozen and K. Vafai, Analysis of the non-thermal equilibrium condensing Flow of a Gas Through a Packed bed, International J. of Heat Mass Transfer, 33, 1990, 12471261. [47] J.J.Barry, R.W. Hill, Computational Modeling of Protective Clothing, INJ Report, 2003, 25-34. [48] S. Whitaker, in advances in Heat Transfer, Vol.31, edited by J. Hartnett, (Academic Press, New York, 1998), p.1. [49] Holcombe, B.V., and Hoschke, B.N., Dry Heat transfer characteristics of underwear fabrics, Textile Res. J. 53, 368-374 (1983). [50] Marsh, M.C., The thermal insulating properties of fabrics, proc. Phys. Soc. (London) 42, 570 (1930). [51] Monego, C.J., Golub, S. J., Insulating values of fabrics, Foams and Laminates, Am. Dyest. Rep. 52(1), 21-32 (1963). [52] Morris, M.A., Thermal Insalation of single and multiple layer of fabrics, Textile Res. J. 25, 766-773 (1955). [53] Peirce, F. T., and Rees, W.H., The transmission of heat through textile fabrics, Part II, J. Textile Inst. 37, T181-T204 (1946)., [54] Rees, W.H., The protective value of Clothing, J. Textile Inst, 37, 132-152 (1946). [55] T. Yasuda, M. Miyama and H. Yasuda, Dynamic water vapour and heat transport through layered fabrics, Textile Res. J., 62(4), 227-235, 1992. [56] Fourt, L., Stooknee, A.M., Fisherman, D., and Harris, M., The rate of drying of fabrics, Textile Res. J. 21, 26-33 (1951). [57] Coplan, M. J., Some moisture relations of Wool and several synthetic fibers and blends, Textile Res. J. 23, 897-916 (1953). [58] Crow, R. M., and Dewar, M. M., Wicking, Regain, Hydrophilicity and drying of textiles, Defence Research Establishment Ottawa Report No. 1180, 1993. [59] Crow, R.M. and Dewar, M.M., The effect of fiber and fabric properties on fabric drying times, Defense Research Establishment Ottawa Report No. 1182, 1993. [60] Crow, R. M., and Dewar, M.M., Liquid transport across fabric layers, Defense Research Establishment Ottawa Report No. 1002, 1989. [61] Holmer, I, Heat exchange and thermal insulation compared in woolen and nylon garments during wearing trial, Textile Res. J. 55, 511-518, 1985. [62] A.H. Woodcock, Moisture transfer in textile systems, Textile Res. J. 32, 719-723, 1962. [63] Henry, P.S.H., The diffusion in absorbing media, Proc. Roy. Soc., 171, 215-241, 1939. [64] Henry, P.S.H, The diffusion of moisture and heat through textiles, Discuss. Farad. Soc. 3, 243-257, 1948. [65] David, H.G., and Nordon, P., Case studies of coupled heat and moisture diffusion in wool beds, Textile Res. J. 39, 166-172 (1969). [66] Farnworth, B., A numerical model of the combined diffusion of heat and water vapour through clothing, Textile Res. J. 56, 653-665, 1986.

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[67] Wehner, J. A., Miller, B., and Rebenfeld, L., Dynamics of water vapour transmission through fabric barriers, Textile Res. J. 58, 581-592, 1988. [68] Downes, J. G., and Mackay, B. H., Sorption kinetics of water vapour in wool fibers, J. Polym. Sci. , 28, 45-67, 1958. [69] Watt, I.C., Kinetic study of the wool-water system, Part I: the mechanisms of two-stage sorption, Textile Res. J. 58, 581-592, 1988.

In: Modern Tendencies in Organic and Bioorganic Chemistry ISBN: 978-1-60456-295-8 Editors: A. Mikitaev, M. K. Ligidov, pp. 271-294 © 2008 Nova Science Publishers, Inc.

Chapter 23

A NOVEL APPROACH FOR MEASUREMENT OF NANOFIBER DIAMETER OF ELECTROSPUN WEBS M. Ziabari, V. Mottaghitalab and A. K. Haghi* The University of Guilan, P. O. Box 3756, Rasht, Iran

ABSTRACT In this chapter, a novel approach is presented for determination of nanofiber diameter of electrospun webs. In this approach we have demonstrated the general applicability of a method using real webs, taking into account 5 real electrospun nonwoven webs, which were obtained by electrospinning of PVA. The application of image analysis has been reviewed and successfully applied using this new approach.

INTRODUCTION Fibers with a diameter of around 100 nm are generally classified as nanofibers. What makes nanofibers of great interest is their extremely small size. Nanofibers compared to larger fibers, with higher surface area to volume ratios and smaller pore size, offer an opportunity for use in a wide variety of applications. To date, the most successful method of producing nanofibers is through the process of electrospinning. The electrospinning process uses high voltage to create an electric field between a droplet of polymer solution at the tip of a needle and a collector plate. When the electrostatic force overcomes the surface tension of the drop, a charged, continuous jet of solution is ejected. As the solution moves away from the needle and toward the collector, the solvent evaporates and jet rapidly thins and dries. On the surface of the collector, a nonwoven web of randomly oriented solid nanofibers is deposited. Figure 1 illustrates the electrospinning setup [1]-[5].

*

Corresponding author E-Mail: [email protected]

272

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Figure 1. Electrospinning Setup.

Fiber diameter is an important structural characteristic in electrospun nonwoven webs. Clearly, the properties of nonwovens will depend on the nature of the component fiber as well as its structural characteristics such as fiber orientation [6]-[11], fiber diameter [12], pore size [13] and other structural features [14]. In modeling the performance of nonwovens, it is desirable to understand the effect of fiber diameter on performance. Therefore, there is a need for determining fiber diameter reliably and accurately. More recently, image analysis has been employed to identify fibers and measure structural characteristics in nonwovens. However, the accuracy and indeed the limitations of these techniques have not been verified. A reliable evaluation of the algorithm requires samples with known characteristics. To accommodate this, a simulation scheme that generates specific nonwoven structures (images) has been developed. This investigation explores the use of image analysis in evaluating electrospun fiber diameter.

METHODOLOGY Simulation of Electrospun Nonwoven Web The use of simulation is not a new idea. It was used by Abdel-Ghani and Davis [15] and Pourdeyhimi [6] for simulation of nonwovens with both continuous and discontinuous fibers which are made by the use of idealized straight lines. The most important component of simulation is the way in which lines or curves are generated. Abdel-Ghani and Davis [15] presented three methods for generating a random network of lines. 1. Surface randomness known as S-randomness 2. Mean free path known as µ-randomness 3. Internal randomness known as I-randomness

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They assumed that the lines were infinitely long (continuous filament) so that, at least in the image plane, all lines would intersect the boundaries. Lately it was discovered by Pourdeyhimi et.al. [6] that the best way to simulate nonwovens of continuous fibers is through the second method. The aim is to obtain unbiased arrays and both of the first and third methods produce biased samples and are not appropriate for simulating continuous filaments. Under the second scheme known as µ-randomness, a line is defined by the perpendicular distance d from a fixed reference point O (preferably located in the center of the image) and the angular position of the perpendicular α. Distance d is limited to the diagonal of the image and is sampled from a random distribution. The slope α is sampled from an appropriate distribution as discussed above, A line is then drawn perpendicular to the α direction, distance d away from the reference point [6], [15]. As Figure 2 shows, this procedure produces an unbiased sample which is spatially homogeneous for infinitely long lines (continuous filaments).

Simulation Variables The performance properties of fiber assemblies depend on the structural characteristics associated with the web. Some of the key structural parameters are web density, fiber orientation distribution, fiber diameter distribution. These variables are allowed to be controlled during the simulation [6]. Web Density The web density can be controlled using the line density which is the number of lines to be generated in the image. Angular Density This is useful for generating fibrous structures with specific orientation distribution. The orientation may be sampled from either a normal distribution or a uniform random distribution. For a normal distribution, the mean angle and its standard deviation are needed. In a uniform random distribution, the maximum and minimum values for the angular range need to be specified. Otherwise, the range will lie between 0 and 2π. Distance from the Reference Point Distance d varies between 0 and the diagonal of the image and is restricted by the boundary of the image; it is sampled from a uniform random distribution.

α

d

O

Figure 2. Procedure for µ-randomness.

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M. Ziabari, V. Mottaghitalab and A. K. Haghi

Fiber Diameter The fiber diameter is also sampled from either a normal distribution or a uniform random distribution. For a normal distribution, the mean diameter and its standard deviation are needed. In a uniform random distribution, the maximum and minimum values for the diameter need to be specified. Image Size The image size can also be chosen as required. We typically choose an image size 720×480 pixels, which is a typical size for frame capture. The simulations are therefore of the same dimension as real web images. With real webs, the magnification needs to be chosen carefully.

Fiber Diameter Measurement Electrospinning process produces very fine fibers and this is one of the very few methods from which fibers of sub-micron size can be produced. So it becomes immensely important to understand the behavior of fiber diameter and fiber diameter distribution in the electrospun web as impacted by the independent variables (processing parameters). Understanding how fiber diameter and diameter distribution are affected by the processing parameters is essential to produce webs with desired fiber diameter and distribution. The measurement of fiber diameter in the electrospun webs that have been reported in the literature is based using various techniques. The measurement of the fiber diameter and the analyses has been done using various instruments, mainly scanning electron microscope, transmission electron microscope and atomic force microscopes. The analyses have been done by capturing of images through these devices called the micrographs. There is no standard technique to measure the fiber diameter and analyze its distribution.

Manual Method The conventional method of measuring the fiber diameter of electrospun webs would be to produce a good image of the web at a suitable magnification using the electron microscopy techniques and then analyze the image manually using suitable calibration scale. The manual analysis usually consists of the following steps, determining the length of a pixel of the image (setting the scale), identifying the edges of the fibers in the image and counting the number of pixels between two edges of the fiber (the measurements are made perpendicular to the direction of the fiber-axis). Typically 100 measurements are carried out. Figure 3 illustrates this process. The data can be directly used for measuring fiber diameter distribution. Distance Transform This method uses a binary image to create a "distance map" of the image, which records the distance from each pixel to the background. From the distance map, the fiber diameter at any pixel location can be determined [12].

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Figure 3. Manual method.

The distance transform of a binary image is a relatively simple concept: It is the distance from every pixel to the nearest nonzero-valued pixel. Figure 4 illustrates the distance transform. Figure 4a shows a small binary image matrix and Figure 4b the corresponding distance transform. Not that 1-valued pixels have a distance transform value of 0 [16]. 1

1

0

0

0

0.000

0.000

1.000

2.000

3.000

1

1

0

0

0

0.000

0.000

1.000

2.000

3.000

0

0

0

0

0

1.000

1.000

1.414

2.000

2.236

0

0

0

0

0

1.414

1.000

1.000

1.000

1.414

0

1

1

1

0

1.000

0.000

0.000

0.000

1.000

Figure 4. a) Small binary image b) Distance transform.

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20

Distance

15

10

5

0 70 60

70

50 40

50 30 30

20

20

10 0

Height

60

40

0

10

Width

Figure 5. An image and its distance transform.

Since in the images used in this study, objects (fibers) are white on a black background, the images first need to be complemented. In the complement of a binary image, zeros become ones and ones become zeros; black and white are reversed. Thus in the complement of the image, fibers are black and background is white. Afterwards, the distance between each pixel and its nearest nonzero pixel is found by using Euclidean distance transform. The Euclidean distance is the straight line distance between two pixels. The Euclidean distance between (x1,y1) and (x2,y2) is defined by

( x1 − x2 ) 2 + ( y1 − y 2 ) 2

(1)

The center of an object in the distance transform image will have the highest value, as shown in Figure 5. For example, if a transformed line has a value of five in the center as the highest for that object, the line thickness will be nine. The peaks coincide with the axis of the object; that is, an object's skeleton will lie exactly over the maximum of the distance for that object [12].

Skeletonizing (Thinning) An important approach for representing the structural shape of a plane region is to reduce it to a graph. This reduction may be accomplished by obtaining the skeleton of the region via a skeletonization (also called thinning) algorithm. The skeleton of a region may be defined via the medial axis transformation (MAT). The MAT of a region R with border b is as follows. For each point p in R, its closest neighbor in b is found. If p has more than one such neighbor, it is said to belong to the medial axis (skeleton) of R. This algorithm removes pixels on the boundaries of objects but does not allow objects to break apart. This reduces a thick object to its corresponding object with one pixel wide.

A Novel Approach for Measurement …

a)

b)

277

c)

Figure 6. Skeletonization: a) input image, b) skeleton obtained by skeletonization, c) resulting skeleton after pruning.

Skeletonization and thinning often produce short extraneous spurs, sometimes called parasitic components. Spurs are caused during erosion by non uniformities in the strokes composing the characters. The process of cleaning up (or removing) these spurs is called pruning. Pruning is an essential complement to skeletonization and thinning algorithms because it tends to leave parasitic components that need to be cleaned up by postprocessing. Assuming that the length of a parasitic component does not exceed a specified number of pixels, the method iteratively identifies and removes endpoints [16]-[19]. Figure 6 shows an image, its skeleton obtained by skeletonization and resulting skeleton after pruning.

a)

b)

c)

d)

Figure 7. a) a simple simulated image, b) its distance transform, c) its skeleton after pruning d) its skeleton overlaid on its distance transform.

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Figure 8. Histogram of fiber diameter distribution obtained by distance transform.

The algorithm for determining fiber diameter uses the skeleton and a distance transformed image and the skeleton acts as a guide for tracking the distance transformed image by recording the intensities to compute the diameter at all points along the skeleton [12]. Figure 7 demonstrates the procedure used in this method for a simple simulated image and Figure 8 the histogram of fiber diameter obtained by this method.

Direct Tracking In this method in which binary images are used, fiber diameter is measured on the basis of two scans; first a horizontal scan and then a vertical scan. Top left corner of the image is set as the reference. Down and right were chosen as the default directions for vertical and horizontal scans respectively. Black pixels (0s) are representative of background and white pixels (1s) are representative of fibers. If the first pixel is white, horizontal scanning carries out to find the first black pixel. Then the process continues to reach the first white pixel. Pixel counting is started from the first white pixel and it goes on until the first black pixel is reached. But if the first pixel is black, scanning carries out to find the first white pixel. Then the process continues by counting the white pixels to the first black. Therefore horizontal pixels of fiber are numbered. From now on, vertical scanning carries out. From the mid point of horizontal scan, a vertical scanning to the down (default vertical direction) is started. Scanning continues and pixels are counted until the first black is reached. Otherwise, the vertical scanning direction changes and a scan to up direction is started and white pixels are counted until first black pixel is reached. In each stage, if black pixel isn't found, the method fails. The process is illustrated in Figure 9.

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Figure 9. Direct tracking.

Having the numbers of vertical and horizontal pixels, one can measure the number of pixels in perpendicular direction (which is the fiber diameter) through a simple geometrical relationship as shown in Figure 10.

x y

d

Figure 10. Fiber diameter from the number of vertical and horizontal pixels

d=

xy x2 + y2

⇒ D = 2d

(2)

Fibers in webs obtained by electrospinning method are in random order and cross each other at intersection points. This causes problem in algorithm. An attempt was made in order to solve the problem. Figure 11a shows a simple simulated image which its diameter distribution is supposed to be measured. First of all, background regions which aren't consisting fibers are labeled; this step which is called labeling shown in Figure 11b. Afterward, it is explored which couple of regions contain fiber; this step is called regions selecting. Two possible selections are shown in Figure 11c. Then the size of the image is reduced to the size of image obtained from these regions in order to increase processing speed. Finally, fiber diameter is measured according to the algorithm explained above.

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4

5

1

8 2 7 3 a)

b)

6

c) Figure 11. a) a simple simulated image for direct tracking, b) labeling, c) Regions selecting (left: between 1 and 2, right: between 7 and 8)

In the end, the diameters in pixels converted to nm using the scale of the image and then the histogram of fiber diameter distribution is plotted. In this case, since the scale of image is arbitrary, the diameter reported in pixel (Figure 12).

Figure 12. Histogram of fiber diameter distribution.

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Real Webs Treatment Segmentation (Thresholding) Both of distance transform and direct tracking algorithms developed for measuring fiber diameter require a binary images as their input. Thus, the images first need to be thresholded to separate the fibers from the background (white from black). This is done by segmentation (or thresholding) which produces a binary image from a grayscale (intensity) image. A pixel has the value 1 if it belongs to object (fiber); otherwise it is 0. After segmentation we know which pixel belongs to which object [16], [17]. This is a critical step because the segmentation significantly affects the result [10]. Assuming that the image composed of light objects on a dark background, which is the case here, the typical way to extract the object from the background is to select a threshold that separates these modes. Then all the pixels up to and including the pixels equal to the threshold belong to the first class (object, fiber here) and the remaining pixels belong to the other class (background). The simplest of all thresholding techniques is to partition the image by using a single constant threshold. Segmentation is then accomplishes by scanning the image pixel by pixel and labeling each pixel as object or background, depending on whether the gray level of that pixel is grater or less than the value of threshold. This approach is called global thresholding. One simple way to choose a threshold is by trial and error; picking different threshold s until one is found that produces a good result as judged by the observer [16]-[19]. The important problem is how to decide upon the optimum threshold value so that the desired classification of objects is achieved. This is often difficult, especially in the presence of non-uniform illumination or local gray level unevenness. In global thresholding (the most widely used method) a pixel is thresholded without any consideration of its neighbors. Typically, the mean intensity is selected as the threshold value. This method works well when the image histogram is bimodal, with sufficient separation of the dark and light objects [10]. Consider the image given in Figure 13 and its gray level histogram. Although the contrast in the image appears to be fairly high, thresholding with the mean intensity as the threshold value results in some broken fiber segments. An approach for handling such a situation is to divide the original image into subimages and then utilize a different threshold to segment each subimage. The key issues in this approach are how to subdivide the image and how to estimate the threshold for each resulting subimage [16]. In this study, morphological opening operation is used to estimate the background illumination. Morphological opening is an erosion followed by a dilation, using the same structuring element for both operations. The opening operation has the effect of removing objects that cannot completely contain the structuring element. So the structuring element must be of sufficiently large size so that it cannot fit entirely inside the objects in the image. Prior to this step, in order to enhance its contrast and remove noise in the image, an intensity adjustment operation and a two dimensional median filter were employed. Median filtering is a specific case of order-statistic filtering, also known as rank filtering. The value of the output pixel is determined by the median (recall that median, M, of a set of values is such that half the values in the set are less than or equal to M, and half are grater than or equal to M) of the pixel values in the neighborhood of the corresponding input pixel.

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Figure 13. A real web (left), its intensity histogram (up) and after thresholding (right).

Then in order to create a more uniform background for the image, the background obtained from morphological opening operation is subtracted from the original image. After subtraction, the image has a uniform background but it is a bit dark. In order to solve this problem, an intensity adjustment operation is used to enhance the contrast of the image. The next step is to find an optimum threshold needed for segmentation. This is done according to Ostu's method. This method chooses the threshold to minimize the interaclass variance of the black and white pixels. The algorithm automatically computes an appropriate threshold to convert the grayscale image to binary. Finally the binary version of the image is created by using a global thresholding with the threshold value found in previous step [16]-[19]. This process is illustrated in Figure 14. It can be shown that this process is equivalent to segment the image with a locally varying threshold [16].

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f)

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Figure 14. Thresholding process: a) input image, b) median filtering, c) background, d) subtracting the background from the image, e) intensity adjustment and f) binary image produced by thresholding.

EXPERIMENTAL PVA with molecular weight of 72000 g/mol, purchased from MERCK Company, was used to prepare solutions needed for electrospinning. The micrographs of electrospun PVA fibers, used in image analysis, were obtained using Philips (XL-30) environmental Scanning Electron Microscope (SEM) after being gold coated.

MATERIALS Two sets each composed of five simulated images were used to demonstrate the validity of the techniques. Table 1 and Table 2 show the structural features of the simulated images generated using µ-randomness procedure. The simulated images are shown in Figure 16 and Figure 17. The first set of simulated images has random orientation with increasing constant

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diameters; the other set is also random but varies in fiber diameter. For the second set, the diameter values are sampled from normal distributions with a mean of 15 pixels and standard deviations ranging from 2 to 10 pixels. In addition, there are five real webs in this report shown in Figure 18. They were obtained from electrospinning of PVA. To obtain the image analysis results, all images have been processed using the procedures described before and the diameter distributions determined using the distance transform and direct tracking methods as described above. Table 1. Structural characteristics of image series 1 Image No. C1 C2 C3 C4 C5

Angular Range 0-360 0-360 0-360 0-360 0-360

Line Density 30 30 30 30 30

Line Thickness 5 10 15 20 25

Table 2. Structural characteristics of image series 2

C1

C3

Image No.

Angular Range

Line Density

V1 V2 V3 V4 V5

0-360 0-360 0-360 0-360 0-360

30 30 30 30 30

C2

C4 Figure 15. Continued on next page.

Line Thickness Mean 15 15 15 15 15

Std 2 4 6 8 10

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C5 Figure 16. Simulated images with constant diameter.

V1

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V4

V5 Figure 17. Simulated images with varying diameter.

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R1

R2

R3

R4

R5 Figure 18. Real webs.

RESULTS AND DISCUSSION Mean and standard deviation of the simulated images in series 1 and series 2 are shown in Table 3 and Table 4. Table 5 and Table 6 show the results for real webs in term of pixel for the former and nm for the later. Figure 20 and Figure 22 show histograms for simulated images in series 1 and series 2 respectively. Histograms for real webs are given in Figure 24. In series 1, for simulated images with the line thickness (diameter) of 5 and 10 pixels, distance transform presents results closer to the simulation. For the line thickness of 15, the standard deviation of diameter for direct tracking method is closer to that of the simulation. However, distance transform measured the average diameter more accurately. For the simulated webs with line thickness more than 15 in series 1, direct tracking method resulted in better estimation of the mean and standard deviation of fiber diameter. This is due to the fact that as the lines get thicker, there is higher possibility of branching during the skeletonization (or thinning) and these branches remain even after pruning. Although these

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branches are small, since their orientation is typically normal to that of the backbone of the fiber; thus causing widening the distribution. Furthermore, distance transform method fails in measuring the diameter of fiber in intersections. The intersections cause to overestimate fiber diameter. Since in direct tracking method, image is divided into parts where single fibers exist, the effect of intersections which causes in inaccurate measurement of fiber diameter is eliminated. Therefore, there will be a better estimate of fiber diameter. Table 3. Mean and standard deviation for series 1 Simulation Distance Transform Direct Tracking

mean std mean std mean std

5 0 5.486 1.089 5.625 1.113

10 0 10.450 2.300 11.313 2.370

15 0 16.573 5.137 17.589 4.492

20 0 23.016 6.913 22.864 5.655

25 0 30.063 10.205 29.469 7.241

Table 4. Mean and standard deviation for series 2 Simulation Distance Transform Direct Tracking

mean std mean std mean std

15.247 1.998 16.517 5.350 16.075 2.606

15.350 4.466 16.593 6.165 15.803 5.007

15.243 5.766 17.135 7.597 16.252 6.129

15.367 8.129 17.865 9.553 16.770 9.319

16.628 9.799 19.394 11.961 18.756 10.251

Table 5. Mean and standard deviation for real webs (pixel) Manual Distance Transform Direct Tracking

mean std mean std mean std

24.358 3.193 27.250 8.125 27.195 4.123

24.633 3.179 27.870 7.462 27.606 5.409

18.583 2.163 20.028 4.906 20.638 4.148

18.827 1.984 23.079 7.005 21.913 4.214

17.437 2.230 20.345 6.207 20.145 3.800

Table 6. Mean and standard deviation for real webs (nm) Manual Distance Transform Direct Tracking

mean std mean std mean std

318.67 41.77 356.49 106.30 355.78 53.94

322.27 41.59 364.61 97.62 361.15 70.77

243.11 28.30 262.01 64.18 269.99 54.27

246.31 25.96 301.94 91.64 286.68 55.14

228.12 29.18 266.17 81.21 263.55 49.72

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In series 2, independent of the line thickness in the simulation, for all simulated webs, direct tracking resulted in better measurement of mean and standard deviation of fiber diameter. For the real webs, mean and standard deviation of fiber diameter for direct tracking were closer to those of manual method which means better results. 0.7 Distance Transform Direct Tracking Distance Transform Direct Tracking

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Figure 19. Continued on next page.

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Figure 20. Histograms for simulated images with constant diameter.

CONCLUSION µ-randomness procedure was used in order to simulate the electrospun nonwoven webs. Based on this method, two sets of simulated images, each contained 5 webs, were produced. The first set of simulated images had random orientation with increasing constant diameter. For the second set, the diameter values were sampled from normal distributions with a mean of 15 and standard deviation ranging from 2 to 10 pixels. Two image analysis based methods were presented; distance transform and direct tracking.

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0.2 0.2 Simulation Simulation Distance Distance Transform Transform Direct Direct Tracking Tracking Simulation Simulation Distance Distance Transform Transform Direct Direct Tracking Tracking

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Figure 21. Continued on next page.

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Figure 22. Histograms for simulated images with varying diameter.

For all the simulated webs with varying diameter and for those with constant diameter more than 15, direct tracking method resulted in the mean and standard deviation closer to the simulation. However, for the simulated webs with smaller constant diameter, distance transform measured the mean and standard deviation of fiber diameter more accurately. The results suggest that the direct tracking method is an accurate, direct measurement technique, because it extracts the fiber diameter for the samples by tracking fixed segment of the fiber and eliminates the effect of intersections. We have demonstrated the general applicability of the method using real webs. To that end, 5 real electrospun nonwoven webs, which were obtained by electrospinning of PVA, were used. Since both of the methods needed binary images as their input, the images first had to be thresholded. A local thresholding method together with otsu's method in order to automatically compute the appropriate threshold was employed. The results obtained for real webs confirm the trends suggested by simulated images. The results show that the use of image analysis in order to determine the fiber diameter in electrospun nonwoven webs has been successful.

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0.012 Manual Distance Transform Direct Tracking Manual Distance Transform Direct Tracking

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Figure 23. Continued on next page.

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Figure 24. Histograms for real webs.

REFERENCES [1] [2] [3] [4]

[5]

Haghi, A. K., Akbari, M., Trends in Electrospinning of Natural Nanofibers, Physica Status Solidi (a), In Press (2007). Reneker, D. H., Chun, I., Nanometre Diameter Fibers of Polymer, Produced by Electrospinning, Nonotechnology 7, 216-223 (1996). Salem, D. R., Structure Formation in polymeric Fibers, Hanser, Cincinnati , Chapter 6, Fong, H., Reneker, D. H., Electrospinning and the Formation of Nanofibers (2001). Subbiah, Th., Bhat, G. S., Tock, R. W., Parameswaran, S., Ramkumar S. S., Electrospinning of Nanofibers, Journal of Applied Polymer Science 96, 557-569 (2005). Frenot, A., Chronakis, I. S., Polymer Nanofibers Assembled by Electrsopinning, Current Opinion in Colloid and Interface Science 8, 64-75 (2003).

294 [6] [7]

[8] [9] [10]

[11] [12] [13]

[14] [15] [16] [17] [18] [19]

M. Ziabari, V. Mottaghitalab and A. K. Haghi Pourdeyhimi, B., Ramanathan, R., and Dent, R., Measuring Fiber Orientation in Nonwovens, Part I: Simulation, Textile Research Journal 66, (11), 713-722 (1996). Pourdeyhimi, B., Ramanathan, R., and Dent, R., Measuring Fiber Orientation in Nonwovens, Part II: Direct Tracking, Textile Research Journal 66, (12), 747-753 (1996). Pourdeyhimi, B., Dent, R., and Davis, H., Measuring Fiber Orientation in Nonwovens, Part III: Fourier Transform, Textile Research Journal 67, (2), 143-151 (1997). Pourdeyhimi, B., and Dent, R., Measuring Fiber Orientation in Nonwovens, Part IV: Flow Field Analysis, Textile Research Journal 67 (3), 181-190 (1997). Pourdeyhimi, B., Dent, R., Jerbi, A., Tanaka, S., and Deshpande, A., Measuring Fiber Orientation in Nonwovens, Part V: Real Fabrics, Textile Research Journal 69, 185-92 (1999). Pourdeyhimi, B., Kim, H.S., Measuring Fiber Orientation in Nonwovens: The Hough Transform, Textile Research Journal 72, (9), 803-809 (2002). Pourdeyhimi, B., Dent, R., Measuring Fiber Diameter Distribution in Nonwovens, Textile Research Journal 69, (4), 233-236 (1999). Aydilek, A.H., Oguz, S.H., Edil, T.B., Digital Image Analysis to Determine Pore Opening Size Distribution of Nonwoven Geotextiles, Journal of Computing in Civil engineering, 280-290 (2002). Chhabra, R., Nonwoven Uniformity-Measurements Using Image Analysis, International Nonwoven Journal, 43-50 (2003). Abdel-Ghani, M. S. and Davis, G. A., Simulation of Nonwoven Fiber Mats and the Application to Coalescers, Chemical Engineering Science, 117 (1985). Gonzalez, R. C., Woods, R. E., Digital Image Processing, Prentice Hall, Second Edition (2001). Jähne, B., Digital Image Processing, Springer, 5th Revised and Extended Edition (2002). Petrou, M., Bosdogianni, P., Image Processing the Fundamentals, John Wiley and Sons (1999). Serra, J., Image Analysis and Mathematical Morphology, Academic Press, London (1982).

In: Modern Tendencies in Organic and Bioorganic Chemistry ISBN: 978-1-60456-295-8 Editors: A. Mikitaev, M. K. Ligidov, pp. 295-309 © 2008 Nova Science Publishers, Inc.

Chapter 24

LASERS APPLICATION BOUNDARIES TO STIMULATE PHOTOCHEMICAL PROCESSES R. H. Chaltykian and N. M. Beylerian

ABSTRACT Stimulating lasers application boundaries by their intensivity are studied in detail on the known example consisting in 2,2′ azobisisobutyronitrile (AIBN)+vinylacetate (VA). It is shoun that up to photons beam densities of order 1017 photons / (cm2. sec.) AIBN is being decomposed. The process may be described by classical photochemistry laws. But the increase of photons beam density up to 1024 ÷1028 photons / (cm2. sec.) results in nonlinear process manifestation concerning emission absorption and in distortion of kinetic behavior of reaction if it is stimulated at noticed conditions. The second component of the studied system the VA up to photons beam densities of nanosecond emission ∼1029photons /(cm2. sec.) is ”clear “with respect to emission. But at the substitution of impulses of nanosecond duration by piconsecond emission of YAGNd(|||) laser threshold, “explosion type” absorption is being observed which results in VA ”laserolysis”. Therefore before any application of a laser as process stimulating source their boundaries by intensivities must be studied in detail to determine them.

INTRODUCTION Unlike to usual photosources lasers differ from them at their use to stimulate photochemical reactions by their photons beam high density. This circumstance provokes extreme necessity to determine the boundaries of lasers application. This means to study lasers intinsity regions for which either classical photochemistry laws are applicable or distortions may be observed as result of nonlinear effects superposition due to nonusual light emission absorption by the system.

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To solve the presented problem as study object well investigated vinylacetate (VA) polymerization system initiated by AIBN photodecomposition has been choiced.At first let us discuss some literature data concerning AIBN decomposition. According to [1] Kd = 1.58. 1015 exp(-218750/RT) s -1 in benzene, toluene at temperature interval 310÷373 K. It has been shown that light (λ=366nm) induces AIBN decomposition which initiates VA, as well styrene polymerization [2]. The authors of [3,4] have established the likeness of AIBN thermo- and photodecomposition mechanisms with formation of methyl –N-2-cyano-2-propylketenimine which has absorption in the region λ=290-300nm.The quantum yield of AIBN photodecomposition is equal to φ=0.47±0.02 mol/Einstein.This result is confirmed also in [5,6]. It is established too [7-9] that the photoradiation of azocompounds results in cis-trans isomerization around-N=N-bond. The trans isomers are more stable and have absorption in the region of short wave lengths but with less extinction coefficients(ε). For example, trans AIBN has absorption at λ max=345nm with ε=15.0 M-1cm-1 and for AIBN cis isomer λ -1 -1. The activation energy (E a) of cis- AIBN homolysis is less max=385nm with ε=140,0 M cm by 29,3-33,5 kJ with respect to trans-AIBN homolysis Ea. According to [11-13] the photochemically induced azocompounds isomerization occurs via triplet state for simple acyclic azocompounds and there is not photodecomposition in solutions. It has been shown [14,15] that AIBN may be successfully used in experiments when in ruby laser’s second harmonics (λ=347nm) is being applied. It must be noticed that nanosecond laser impuls emission allows to obtain high concentrations of free radicals in solutions. But in cited and in [16-18] investigations the photolysis kinetics as well the specificities of laser absorption by matter are not studied. As is shown in [14,19] at intensive laser emission the intiation rate diminishes, which (according to [14,16] )is due to high rate of primary radicals recombination. But the extistence of nonlinear effects can’t be excluded [20]. But it is not considered. Thus, it has been studied azoethane decomposition [21] stimulated by ruby laser (λ=694.3nm) with power density equal to 70÷175 MW/cm2. It has been established that the N2 yield is proportional to the order 2.2±0.1 with respect to the light intensity. The authors of [22] suppose that after photon absorption the excited molecules from the first excited singlet state A* are transfered to an other excited singlet state B* from which fluorescence is forbidden. The both states are at close range. The excited molecules which are on B* level may be decomposed with a rate which depends on the nature of radicals linked with azo group. The authors of [23] assume that both mechanisms (thermo-and photo) are identic, but only in the case of photolysis transfer to triplet (T) state is possible. Data concerning the AIBN ability to quench excited molecules are contradictory [24,25]. In [26] it has been stated that AIBN quenches excited antracene molecules. It is shown that the quenching is diffusion controlled and it occurs at every collosion between donor and acceptor molecules. So the fact that azocompounds, in particular AIBN, as photostimulators are well studied, allows to use them to study in detail stimulated by lasers photoprocesses. It gives the possibility at each stage of studies to compare data obtained using lasers with data obtained using usual photosources. This concerns also literature data. As was stated in literature there are some divergences and not clear moments concerning matter-laser interaction mechanism.

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To bring in the cited problem some clearness we have studied [27] AIBN photo and laserinduced decomposition in solutions, including vinylacetate (VA) as solvent, as well as reagent.

OBTAINED RESULTS AND GENERAL DISCUSSION 1. Study of AIBN Decomposition Mechanism Induced by Light and by Laser, AIBN as Quencher. The Specificity of Laser Action AIBN is manifold recrystallized from absolute methanol solution and dried at 293K. Chlorobenzene (ChB) is distilled just before it’s use. AIBN decomposition rate is studied making use gasometric [21] and spectrophotometric(SPECORD M-40) [3] methods. The temperature range was 313÷343K. At [AIBN] o=4.2. 10-2 M kd =1.5.1017⋅exp[-(130300±4200) / RT] min-1 (1) which is in good agreement with literature data [28]. It shows the purity grade of the used reagents and reliability of applied methods. As photosource high pressure mercury lamp (DRSh-500) has been used combined with light filter (10% copper sulfate aqueous solution + glass UFS-3). λ=365nm, (∆ λ=40nm). As laser source nitrogen laser (AL-202) is used [λ = 337,1nm, pulse duration τimp = 5 ns, frequency of pulse reiteration was ν = 1 ÷ 60 Hz]. In all experiments single pulse’s power was 140 KW [1016÷17 photons /(cm2.s)]. The frequency of following pulses is changed. The AIBN initial concentration range was 0,022 ÷ 0,1M. The absorption data obey Buger-Lambert-Beer law. It is established [29] that the rate of initiator decomposition Win=β. Iabs (2), where I abs is the absorbed light intensity (either photo, or laser ). β is the initiation efficiency. At 303 K β photo=0,49 ± 0,03 and β laser=0,26 ± 0,02. Such a divergence between β values for both cases may be explained assuming that: a. between excited particles occur singlet-singlet interactions with different extents; b. the concentration of excited particles in triplet state depends on the light source nature. On this factor depends the rate of spontanous and concentration inactivation. For this reason the influence of concentration quenching by means of AIBN molecules on the efficiency of AIBN photo and laser induced decomposition has been studied [30]. The discussed in [29] kinetic scheme is the following. k1 ⎯⎯ → AIBN k2 AIBN + hv → ( AIBN ) * ⎯⎯ → 2 AIBN

⎯⎯→ 2 R ⋅ + N 2

(2)

k3

where k1 and k2 are the rate constants of spontanous and concentration inactivation correspondingly, k3 – is the rate constant of AIBN homolysis.

R. H. Chaltykian and N. M. Beylerian

298

When the process occurs in steady state regime one has: I abs= (k1 + k2 [ AIBN ] + k3 ) [ AIBN ]*

(3)

It follows: Rin =β I abs = k3 [AIBN]*

(4)

Where β= k3/ (k1+ k2 [AIBN] + k3)

(5)

(3) and (5) allow to determine β values for both cases (photo and laser induced processes. It is obvious that the increase of [ AIBN]o results in β decrease. β= f[AIBN]o function study allows to determine k1/ k3 and k2/ k3 ratios, the ratio k1/ k2 too (see Table 1). Table 1. β dependence on [AIBN] o (T=303 K) 102·[AIBN]oM 1.87 3.73

β photo 0.59 0.53

β laser 0.37 0.27

ki/ k j k1/ k3 k2/ k3

photo 1.25 26.67

laser 3.1 88.88

4.20

0.49

0.26

k1/ k2

0.035

0.047

Relative values laser/photo (k1/ k3) l / (k1/ k3)ph =2.5 (k2/ k3) l / (k2/ k3)ph =3.3

From presented data it follows that k2> k1. So it is established that AIBN is a quencher too. Taking into consideration this fact the quenching coefficient (kQ) for AIBN has been determined by fluorescent analysis method making use ‘‘Perkin-Elmer-43 A ’’ fluorometer with two diffraction monochromators. The exciting light source was Xe lamp (320nm ). AIBN excited molecules fluoresence was registrated at wave lengths: λ=400,450 and 470nm. Figure 1 shows that experimental data obey Stern-Folmer equation: α o/ α c=1+k [AIBN]

(6)

where α o and α c are fluorescence quantum yields at [AIBN] o=0(α o) and α c at [AIBN] o=c. Making use Figure 1 kQ values are determined kQ = (0.26±0.02) ·102 M-1 in ChB and kQ =(0.22±0.03) ·102M-1 in VA, This question is not discussed in literature. One may conclude that laser action is 1.8 time less efficient with respect to photo action, monitored for the same [AIBN]o. (See table 1). It may be the result of the fact that in the case of laser stimulation the concentration of formed excited molecules is 107÷8 times more than in the case of photo excitation.This results in increase of quenching rate (spontanous and concentration). Apart in the case of laser stimulation one cannot exclude sharp enhance of S1→T1 intercombination conversion, resulting in direct enhance of ‘‘populations number’’ on T1 level [31]. The nondependence of kQ in ChB and VA on solvent nature once more underlines the AIBN importance as quencher.

Lasers Application Boundaries …

ao/ac

299

2

3.2

2.4

1

1.6

0.8

2

10 [AIBN] M 0.0 2

4

6

8

10

Figure 1. Dependence of αo/αc (in orbitrary units) on [AIBN]0 in vinylacetate (VA), 2.in chlorbenzene(ChB) at λ=320nm and T=303 K.

Our, as well literature, data show that when the intensity(I) of the used photo source is~1016÷17 photons / (cm2. s) non linear effects concerning light absorption by matter, are not observed. This means that in such cases classic photochemistry laws can be used and laser sources in the frame of mentioned intinsities of light emission also may be used to initiate polymerisation without distortion of the initiation mechanism. Ruby laser with I=10 19÷20 photons/(cm 2.s) is used to stimulate methylmethacrylate polymerization in AIBN and diacetyl presence [14,19,32].The authors do attempt to explain the obtained experimental data without considering the specificities and pecularities of high intensive light beam + matter interaction. We assume that such approach is not correct.

2. High Intensity Laser +AIBN Interaction Study by Fluorescent Analysis Method. Non Linear Effects [33,34] The experiments are carried out making use nanosecond laser emission source with I=1024÷28 photons / (cm2, s). The substrate was AIBN. Figure 2 concerns the device which is used. Nanosecond laser has been used with “good quality, durability” electrooptical modulator collected on the ground of yttrium orthoaluminate with Nd(III). The 3-rd ground emission has the follouing parameters: λ = 360 nm, Eimp = 3.0 mJ, τ imp=20 ns, ν =5.0 Hz, the beam diameter on the substrate sample 1 mm. The experimental data are collected and worked up by means of special microcomputing system which is marked in the figure′s 2 subscription, In all cases [AIBN] 0 =4.2 ⋅ 10-2 M, T=298 K.

R. H. Chaltykian and N. M. Beylerian

300

12 2

3 4

1

7 5

4

6

8 9

11

10

Figure 2. 1.laser source, 2. light filter, 3.quartz glass,4.quartz lens, 5. quartz cuvette which is the reacting vessel, 6.monochromater DMR-4, 7.photomultiplier FEOu-79, 8.quartz prism, 9. photodiode FD-2, 10.computing system KAMAK, 11.microcomputer DVK-2, 12.manometer.

Our publications [33,34] show that the existence of nonlinear effects is fact. The experimental data concerning fluorescence dependence on exciting emission photons beam density are depicted in figure 3. P is the fluorescent intensivity in arbitrary units. The fluorescent level decrease at high photons beam density indicates that the “ population” on the fluorescent level diminishes as result of S1→S N transfers whith further inactivation of molecules via higher singlet states. The following equations describe the process: dN1/dt=NoI σ1,2 –N1(Iσ2,3φ+k1) – N1Iσ1,2

1.2

Pfl

0.8

0.4

2

I(GW/cm ) 0.0 5

10

15

20

25

30

Figure 3. Dependence of excited AIBN fluorescence intensivity in arbitrary units on exciting emission photons beam density ( in GW/cm2).

Lasers Application Boundaries …

301

dNT/dt= N1kST – NTk2

(7)

dR۠/dt=I σ2,3φN1 + NTφ 2 + NIφ N=N0 + N1 +NT +R۟ where N,N0,N1 and NT—are the initial densities and the “ population number” of S0, S1 and T1 states, corrspondigly, R· - the concentration of decomposed molecules in the reaction volume, k1, k2 – the rate constants of relaxation rates of S1 and T1 levels, kST – the rate constant of intercombination conversion process, φ1, φ2 and φ – the quantum yields of photo reactions via S1, T1 and Sn states- correspondingly, σ1,2, σ 2,3 cross sections of absorption from S0 and S1 levels, I-the density of photons beam. The integration of the differentral equations system (7) gives the following expression concerning the “population number “ in N1 state: N1 = N0 / (λ 1 –λ 2) (eλt – e- λt ), where λ1,2=-A±√A2-4B; A=I σ1,2; β=I σ2,3+k1

(8)

For intensive fluorescence one may obtain: Pfl= ~ 0∫∞ N1dt= No / (λ1-λ2) ( e λ1 τ imp / λ1 - eλ2τimp / λ2 -1/λ1 - 1/λ2)

(9)

where τp is the duration of nanosecond pulse. Comparing (9) with presented in figure 3 experimental data the product of absorption cross section of S1 level with photoreaction from SN level the quantum yield, as well the mean lifetime value of S1 state at above mentioned conditions are determined: σ2, 3. φ =10-17cm2,τ1=1/k1= 4,10-9s. According to [35] σ1, 2=4,6.10-20cm2.

ϕ0/ϕΙ 3

2

1

-2

I(GW.cm )

0 0

5

10

15

20

25

30

35

Figure 4. Dependence of ϕI -1 (ϕI- fluorescence yield) on absorbed light intensity.

R. H. Chaltykian and N. M. Beylerian

302

The dependence of φ-1 I (Fl) on photons beam intensity has been studied. The experimental data are depicted in figure 4. ϕo is the fluorescence quantum yield at I →0. From figure 4 it follows that at I~6.1028 photons/ (cm2.s) the fluorescence yield diminishes approximatly 3 times. Such inactivation of S1state is identic with concentration quenching. At our experimental conditions when τ1<τimp and I. σ 1, 2. τimp <<1 one may assume that the process of levels “ population growth’’ is steady state. In this carse from (8) one can obtain: N1 = I σ 1,2 No / (k1 + I σ 1,2 + I σ 1,2 ϕ ) (10) and ϕ 0 /ϕI =1+ ( σ1,2 + σ2,3) I / k1

(11)

Eq.(II) is identic with Stern-Folmer equation. It describes molecules fluorescence quenching in the field of high intensive laser emission. Studies are carried out to determine if AIBN can permeate (allow to pass) high intensivity laser light impulses with nanosecond duration (see figure 5) through the system which is being studied Putting (10) in k = k0 (N0 / N + N1σ 2,3 / (N,σ 1,2 )

(12) [36]

we obtain: k (I) = k0 [1+ I σ 1,2 / (k1 + I σ 1,2 + I σ 2,3 ϕ). ( σ 2,3 -σ 1,2 / σ 1,2) ]

(13)

The problem concerning the nonlinear light absorption by optically dense layer may be solved by integration the absorption differential law:

50

T(%)

40

30

20

10 -2

I(GW.cm )

0 2

4

6

8

10

12

14

16

Figure 5. Dependence of permeability coefficient (T %) on photons beam density.

18

Lasers Application Boundaries … dI / dx = - kI

303 (14)

Putting (13) in (14) and after integration one may obtain: T0 / T = [ 1+Io ε (1+ϕ ) ] / [1+ IoT ε (1+ϕ)]1-γ / 1+γ

(15)

where γ ≅ σ 1,2 / σ 2,3, ε ≅ σ 2,3 / k1, T1 ≅ I1 / I0, T0 = e – ko l (l-is the solution contating cuvettes thikness ). The particular solution of eq (15) and its combination with experimental data obtained making use computer technik (DVK-2) gives the following values for the meanlife time of excited state and for absorption cross seetion from intermediate state, as well the value of fluorescence quantum yield from upper excited state: σ 1=1/ k1= (4±0.6).10-9 s, σ 2,3 =(1.5±0.2).10-17 cm 2, φ=0.7±0.15 It is obvious that in the frame of experimental errors both methods (nonlinear fluorometry and absorption spectroscopy) give near values for spectral magnitudes. This fact evidences that the choice of the experimental methods and the corresponding mathematical model are adequate. The experimental data show also that in the field of high intensivity laser emission occurs singlet-singlet transfer. The cross section of S1 state absorption(σ 2,3) is sometimes more than the cross section of absorption from So state. Considering the quantum yield from the upper excited state ( φ =0.7) it is impossible to answer the question what portion of excited molecules is being decomposed and what part is being inactivated. For this aim the AIBN decomposition is studied at same conditions, stimulated by the third harmonic of IAG-ND (III) laser with nano and picoseconds impulse duration (see Figure 2). The characteristics of nanosecond light emission are: λ=360nm, τimp=20ns, the mean pulse power 0,005 W, ν=2,0Hz, the diameter (d) of the light beam falling on the sample which is being studied 7,5mm. In the case of picosecond laser λ=355nm,τimp=40 picos, the mean pulse power 0,004 W, ν=2,0Hz, d=4,7mm. AIBN decomposition is studied measuring the volume of evaluated N2 at [AIBN] 0=4, 2, 10-2 M, T=303K.The efficiency coefficient of AIBN decomposition was:βns=0,315±0,042 and βps=0,142±0,038. The difference between β values may be due to the enhance of S1→SN transfer rate in the case when picosecond laser is used. It is possible also existence a supplementary chanel of photons discharge which results in AIBN decomposition efficiency decrease [34]. So the study of high intensive laser emission absorption by AIBN shows that two photons absorption process as S1→SN transfer occurs. So the fluorescence level becomes less”populated”. As I=6, 1028 photons /cm2 the fluorescence quantum yield decreases 3-fold. Like to concentration quenching, such inactivation of the S1 state, brings to efficient decrease of single quantiec photoprocesses occurring from the first excited singlet state. This phenomenon, as well the highintensive laser light absorption by AIBN may be described making use mathematical simulation. Photons absorption from state S1 approximately is 320 times more than from state So. Two photon absorptions lead to higher SN states, are more probable. Excited molecules in SN state, participate in photoprocesses with probability equal to 0.7. This means that in this

304

R. H. Chaltykian and N. M. Beylerian

case the decomposition efficiency (β) with respect to one photon must be not less ν, than β=0.35. But in the case of nanosecond laseraction β=0.315 and β=0.142 in the case of picosecond laseraction.So β experimental value is less than calculated one. That difference may be the result of difference in S1→SN transfer numbers which depends on the power difference which exist between the used two laser sources. The obtained data concerning β values show that occurs either AIBN heterolysis or its ionization without N2 evolution. This is few probable. Fast conversion from SN state to more low states is probable. The existence of such supplementary chanels of absorbed photons expenses must bring to inevitable decrease in β values. From the stated it follows that the use of highintensivity lasers (I~1024±28 photons/(cm2.s) results in the change of radical chain processes initiation mechanism as result of nonlinear effects rised dy AIBN emission absorption. It is to be noted that according to literature data [14,16,19,32,37] usually lasers with I≤1020 photons/ (cm2.s) are being used in research work to initiate radical chain reactions. The laser intensity is changed in narrow interval. Our data show that in the case of use of lasers with such intensivities nonlinear processes are not observed. This means that in such experiments to meet distortions in kinetic regularities is few probable.

3. Study of Laser Liquid Organic Compound Interactions. A Particular Case: Laser- vinylacetate Interaction. A New Phenomenon: Multiphoton Absorption. Laserolysis Let us discuss the behavior of the second component of polymerization system – the VA in the laser field. VA is purified by distillation in presence of hydroquinone. The distilled liquid is degassed and exposed to initiated forpolymerization. After 4-6 % conversion the polymerization is stopped. The remained monomer is distilled [39]. The obtained compound′s purity is determined using chromatography. The sample is studied by UV-spectroscopy too. During 150 min there is not volume contraction under laser action (I=1017 photons/cm2.s) with λ=694.3, 347,360,355,270 and 266 nm. According to [39.40] pure VA may be polymerized only in frozen state. In this state the system is nontransparent. Ruby laser is used (λ=694,3 and347nm). It is very important to note that VA polymerization can be initiated under the action of light whith λ=303-313 exclusively in presence of partly oxidized VA(oligo peroxi vinylacetate)which has absorption in the cited wave length region [29]. The conclusion is the following: when the intensity of the photosource is of the order 1017photons /(cm2.s) the system AIBN-VA may be considered as classical from photopolymerization point of vue. It obeys usual photochemistry laws. It is interesting to discuss VA behavior in high intensivity laser fields when the selection rule for vibration-rotation transfers to some vitrational states for homopolar molecules becomes possible absorption in such a region of wave length where they have not optical activity if they are in a field of low intensivity [41, 42]. For example, threshold phenomenons are known in laser chemical reactions when in the system there are thermal or vibrational instabilities [43, 44].It is assumed that in this case under laser action with in crease of polyatom molecules vibrational energy the V-A relaxation rate is being enhancated in more

Lasers Application Boundaries …

305

little extent than molecules‘ excitation rate. This results in manifestation of threshold phenomenons. The explanation is the following [45]; the molecule which is on the level ν=1 after excitation moves on to ν=2. By means of ν i→ν j exchange relaxation two particles in state ν=1 may be formed (0+2→1+1). By the same mechanism such two particles induce the formation of 4 particles and so on. So an “explosive”-avalanche type light absorption arises at isothermal conditions. This phenomenon may be used to realize selective action on chemical systems. We have for the first time observed nonlinear, multiphoton ”explosion type” absorption [46-48] by VA in liquid phase and by other matters under the action of high intensity picosecond IR laser emission (λ=1,06nm, Ep=50mI, IN 1029-30photons /(cm2.s) τimp = 40 picos). The molecule is decomposed by formation of CH4, CO2(traces). In the case of hexane the main product is H2. The observed phenomenon we called ”laserolysis”. The studied liquids were degassed. The volumes of evolved gaslike products are measured by gasometric method. They are indentified making use gasliquid chromatograph. Divergent laser beams(with divergency coefficient equal to α=(1+2)10-2)are used to diminish selffocusing effect. The beam diameter at its entrance into the reaction cuvette was changed in the interval 1,5-3,0mm. The experiments are carried out making use the device shown by scheme. The following regularities have been established. 1) there is no photodecomposition and gasformation under the action of picosecond laser jet, even at 5-fold increase of the density(ED)comparing with laser, working in the regime of single pulses with picosecond duration. No effect is observed even under the action of nanosecond focused light beam with same energy /YAGNd(III)laser, 5.109 W/cm2.[I 1029÷30 photons /(cm2.s)]. This shows that there is no pyrolysis. 2) the gasformation efficiency dependence on the picosecond emission energy density has threshold character. The energy density threshold(EDT)depends on the compound(liquid)nature (see table 2). As result of laserolysis gasformation dependence on ED is shown in Figure 6. In the case when ED>EDT ∆V~In, where n=1.6-1.9. Gasformation quantum yield is equal to 0.20-0.25. It decreases with emission intensity increase. When there is gasformation with enhance of threshold energy density value strong absorption of laser emission is being observed (see figure 7). Table 2. The energy density threshold values for some compounds.( T=298 K) Compound C2H5OH EDT ρ\ cm2 2.15

CH3COOH (CH3)2CO C6H14 CH3COOC2H5 1.3 1.2 1.1 0.9

CH2=CH(CH3COO) 0.65

R. H. Chaltykian and N. M. Beylerian

306

δV(ml/imp) 0.16

2

0.12

1 0.08

0.04

2

ED(J/cm )

0.00 0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Figure 6. Gasformation volume dependence on picosecond laser ED(J/cm2) for: 1.acetic acid (curve 1), 2.vinylacetate (curve 2).

T 1,0

1

0,5

2

2

ED(J/cm ) 0,0 0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

1,8

2,0

2,2

2,4

2,6

Figure 7. Dependence of the difference between entrance and exit emission intensivities from cuvette(T) on ED for: acetic acid (curve 1) and vinylacetate (curve 2).

Lasers Application Boundaries …

307

The solid line corresponds to dependence established at measuring T of picosecond pulses jet. It follows that the nonlinear absorption strongly restricts picosecond laser permeability(T)through liquid. Some observed scatterings in pulse energies is due to fluetuatious of durations and energy partition concerning the cross section of laser pulses. Stocks frequency in the region of 1,55hm efficiently is being generated in studied liquids. For this reason photodiode FD-2 is used to measure the energy of exciting from the cuvette emission. FD-2 diode together with CC-6 type photofilter has the same sensibility with respect to laser and Stocks component frequencies. Antistocks component was weak, for this reason in caleulations it is not taken into consideration. In the case of VA the analysis of IR spectrums of intradiated liquids by laser emission showed absorption decrease in the region 3090cm-1 and increase in the region 2900cm-1. Absorption new regions at 760cm-1and 1720cm-1are being abserved. They do not concern new compounds. For ethylacetate new absorption weak picks are being obtained at 890cm-1, an “arm” at 1650cm-1and a large pick at 3550-3560cm-1. The situation is the same in the case of acetone, which may be due to Ke to-enol tautomerization. In acetie acid, ethanol and hexane IR spectrums there are not essential changes. Only the main vibrations intensities relatively are being decreased. So, the studied liquids absorb 1÷2 photons, but to excite their molecules’ first electron levels it needs 5-6 photons because they are in the region of 180-220nm. Therefore one may assume that vibrational levels excitation(~2ev)occurs which is enough to realize chemical reactions with formation of new, as well gas like products in condensed mediums. It is probable that the nature of reactions products will depend on the stimulation mechanism: thermal way or induced by high intensivity laser action. So such studies are actual because they are opening new ways to realize purposeful reactions, in particular synthesis. From this statement it follows that the second component polymerization systems (e.g.VA in a particular system ) may cause to obtain distored polymerization kinetics data when the process stimulator- the laser is not carefully choiced.

CONCLUSION To use high intensivity lasers emissions as sources of chemical reactions stimulators it is indispensable to take into consideration the boundaries of the applicability concerning their intensities with respect to each reagent separately. Only such approach can guarantee to obtain correct experimental data.

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Idage B.B. Verneker S.P., Chatge N.D., J. Polym. Sci., 1983, v.21,p.2145-2156. Vichutinsky A.A., Prokofev A.I. Shabalkin V.A., J. Phys Chem (Russia) 1964, v.38, issue 4, p.983-985. Smith P.,Rosenberg A.M., J.Am Chem. Soc.,1959, v.21, N 5,p.2037-2045. Ayscough P.B. Brooks B.R. Evans H.E.,J. Phys.Chem.,1964,v.68,N12, p.3889-3890.

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R. H. Chaltykian and N. M. Beylerian Hansmond G.S., Fox J.R., J.Am.Chem.Soc., 1964, v.86, N10, p.1918-1921. Smith P., Sheats J.E., Miller P.E., J.Org.Chem., 1962., v.27., N11, p.4053-4054. Organic photocromes(by edition of Eltsova A.V)Leningrad “Chemistry”,1982, p.288.(in Russian) Baltrop J., Coll J., Excited states in Organic Chemistry. Moscow, “Mir”,1978, p.380386.. (in Russian) Lewis G.E., J.Org.Chem., 1974, v.25, N12, p.2193-2195. Engel P.S., Bishop D.J.,J.Am.Chem.Soc., 1975, v.93, N10, p.6754-6762. Abram.I.I., Milne G.S., Solomon B.S., Steel C.,J.Am.Chem.Soe. , 1969, v91, N5, p.1220-1222. Engel P.S., J.Am.Chem.Soc., 1970, v.92, N6, p.5883-5887. Gary W. Byere, Green H.,Giles H. G. Scott H.N.Kampmeter J.A., J.Am.Chem. Soc. 1972, v. 94, N.3, p.1016-1018. Genkin V. N., Sokolov V.V., Dokladi Acad.Sci. USSR, 1977, v. 234,N 1, p. 94-96. (in Russian) Patent N 3.405.045.(USA), Hoskins H., Calif S. P., CA, 1969, v.70, N 2., 4798j. Ganachaud F., Balic R., Maiteiro M.J. and R. G.Gilbert R. G., Macromolecules, 2000, v.33, p.8589-8596 Junkers T., Theis A, Buback M, Davis T. R., M.H. Stenzel M.H, P. Vana P., BarnerKowollik C., Macromolecules, 2005,v.38, p.9497-9508. Buback M., Hesse P., Junkers T., Vana P., Macromol. Rapid. Commun, 2006, v.27.p.182-187 Bityurin N.M., Genkin V. N.Smirnova I.M., Sokolov V.V., Highmolecular comp., Russia, “B’, 1982, v.24, N 12, p.898-901. (in Russian) Harutunian A. G., Hovhanesian V. A., News of Acad. Sci. USSR, (Phys)., 1985, v.49., N.3, p.588-591. Speiser S., Oref I., Goldstein T., Kimel S., Chem. Phys. Lett, 1971, v.11,N1,p.117-119 Jano I., Chem. Phys. Lett., 1968, v.2, N6, p.643-644 Fox J. R., Hausmond G.S., J. Am. Chem. Soc., 1964, v.86, N.19, p.4031-4035. Shljapintoch V.J., Karpukhin O.N., Postnikov L.M.,Zakharov I.V.,Vichutinsky A.A.,Tsepalov V.F., Chemilumiscent Methods of Study of slow chemical Processes. Moskow, “Science”, 1966,p.299 Burkhart R. D., Merrill J. C., J.Phys. Chem., 1969, v.73, N8, p.2699-2703 Ponomareva V.A., Leplyarin G.V., J. Appl, Spectros. (Russia), 1984, v.40, N6, p.10231026 Chaltykian R.H., Safarian G. E., Beylerian N. M., Arm.J. Chem.(Armenia), 1985,v.38, N11, p.729-730 28Denisov E.T., Reaction Rate Constants of Homolytic Liquid Phase Reactions. Moskow, “Science”, 1971, p.51,117. Bagdasarian Kh. S., Moskow, Theory of Radical Polymerization. (in Russian) “Science “, 1966, p.208. Chaltykian R.H., Safarian G. E., Beylerian N.M., Sci.Transactions of YSU (Armenia), 1985, N2(159)p.152-154. Hakopian M.E., Vilesov F.I., Potapov V.K., J. Chem. High Energy (Russia) 1972, v.6.,N4, p.291-303. (in Russian).

Lasers Application Boundaries …

309

[32] Sokolov V.V., tes. Reports of XI All-Union conf. on coherent and conbinear optics, 1982,p.693-694,Yerevan (Armenia). [33] Safarian G.E., Chaltykian R.H., Hovhanesian V.A., Rep. of conf. “Science to Tech. Progress”, Tbilisy (Georgia), 1986,p.35-36. [34] Chaltykian R.H., Armenian Chem.J.,1987,v.40,N7,p.407-429. [35] 3Calvert J.,Pitts J. Photochemistry (Russian trans.), Moskow, “Mir”,1968,p.671. [36] Tikhonov E.A., Shpak M.T., Nonlinear optical Phenomenon in Organic Compounds. Kiev, “Naukova Dumka”,1979,p.384. [37] Aleksandrov A.P., Genkin V.N., Kitaj M. S., Smirnova I.M.,Sokolov V.V., J. Quant. Electron (Russia), 1977,V.4,N.5, p.976-981. [38] Veisberg A., Proskauer E., Riddik J., Tups E., organic Solvents, Moskow, “ Foreign. Literature.” 1958,p.518. [39] Chaltykian R.H., Beylerian N.M. Selected reports (YSU 60-years old anniversary) Yerevan (Armenia),1981,p.170-180. (in Russian) [40] Nersesian K.A., Chaltykian R.H., Beylerian N.M., Armenian Chem. J.,1987, v.40, N8,p.533-534. [41] Askarian G. A., J. Experim. And Theoret.Phys. (Russia), 1965,v.48,N2,p. 666-668.. (in Russian) [42] Prokhorov A. M., Shigorin V. D., Shipulo G.P.,Dokladi of Acad of Science (URSS)(in Russian)1967,v.175, N.4, p.793-796. [43] Gorlevsky V.V., Oraevsky A. N., Pankratov A.V., Skachkov A.H., Shabarshin V.M, J. High Energy., (Russia),1976, V.10,N5,p.443-446.. (in Russian) [44] Sazonov V. N., J.Exper. and Theoret. Phys. (Russia), 1980, v. 79, N1. p.39-45.(in Russian) [45] Oraevsky A.N., Protsenko I. E. J.Quant Electr. (Russia), 1985,v.12,N1, p.26342637.(in Russian) [46] Haroutunian A.G., Hovhanesian V.A., Sarkisian K. A., Safarian G.E., Chaltykian R.H., Collection of Sci. Reports N.I.I. FKS, Yerevan (Armenia), 1987,p.164-173. [47] Haroutunian A.G., Hovhanesian V.A., Sarkisian K.A., Safarian G.E., Chaltykian R.H., Abstracts of Papers V the Internat. Simp. On “Super” fast processes in spectroscopy. Vilnius (Litva),1987,p.206. [48] G.E.Safarian, R.H.Chaltykian, V.A. Hovhanesian, J.of Inform. Tekhnologies and Manengment (Armenia),2002,v.3-2, p.196.

In: Modern Tendencies in Organic and Bioorganic Chemistry ISBN: 978-1-60456-295-8 Editors: A. Mikitaev, M. K. Ligidov, pp. 311-323 © 2008 Nova Science Publishers, Inc.

Chapter 25

QUANTUM-CHEMICAL ANALYSIS OF THE

MECHANISM OF NUCLEOPHILIC SUBSTITUTION OF BROMINE IN METHYL(BENZYL)BROMIDE BY S-, OANIONS GENERATED FROM 2-THIOURACIL A. V. Babkin1, A. I. Rakhimov2,*, E. S. Titova2, R. G. Fedunov3, R. A. Reshetnikov1, V. S. Belousova1, and G. E. Zaikov4 1

Volgograd State Architect-Build University Sebrykov Departament, Michailovka, Volgograd region; Russia 2 Volgograd State Technical University, Volgograd; Russia 3 Institute of Environmental Chemical Problems, Volgograd, Russua 4 Institute of Biochemical Physics Russian Academy of Sciences; Moscow, Russia

ABSTRACT Quantum-chemical analysis (the method ab initio on base 6-311 G **) of SN2 nucleophilic substitution of bromine in methyl(benzyl)bromide by S-, O-aniones, generated from 2-thiouracil, was made and was studied syntheses of 2methyl(benzil)thio-4-methyl(benzil)oxypyrimidins .

Keywords: 2-thiouracil, 2-metyl(benzil)thio-4-methyl(benzil)oxypyrimidins, chemical calculation, method AB INITIO

*

e-mail [email protected]; [email protected]; [email protected]

quantum-

A. V. Babkin, A. I. Rakhimov, E. S. Titova et al.

312

AIMS AND BACKGROUNDS Nucleophilic substitution of halogen in alkyl(benzyl)halogenides by ions, generated from 2-thiouracil, is leading to S- and O-derivatives of 2-thiouracil, which perspective as material with broad spectrum of the biological activity [1-17]. In this connection analysis of the electronic structure aniones generated from 2-thiouracil and elementary stage given to reactions is necessary. The aim of this work is a study by method ab initio electronic structure of the heterocyclic systems as uracil, thiouracil, also aniones, generated from them and reaction SN2- substitution of halogen in methyl(benzyl)galogenids with their participation.

METHODICAL PART Classical method ab initio was used for quantum-chemical analysis on base 6-311 G ** [18]. The choice of the base is motivated by need of the study mechanism of reaction nucleophilic substitution, as this base gives best correlation dependencies for ion processes. The calculation was executed in approach the insulated molecule in gas phase. In some cases quantum-chemical calculations was compared with standard method CNDO/2 in parametrization of Santri-Poppla-Segala [19]. The chemical conversions were leaded on the following scheme (S-sodium compound of 2-thiouracil → 2-methyl(benzyl)thio-4-pyrimidinon → O-sodium compound of 2methyl(benzyl)thio-4-pyrimidinon → 2-methyl(benzyl)thio-4-methyl(benzyl)oxypyrimidin):

NH

NH NaOH(в) N H

O

O

O

S

N

S

NH

RBr Na

- NaBr

N

OR

ONa Br R

N N

R

2-methyl(benzyl)thio4-pyrimidinon

S-sodium 2-thiouracil

NaOH (в)

S

S

- NaBr R

N N

S

R

2-methyl(benzyl)thioO-sodium 2-methyl(benzyl)thio4-methyl(benzyl)oxypyrimidin 4-pyrimidin R = CH3, CH2C6H5 The syntheses goes in four stages:

Quantum-chemical Analysis of the Mechanism of Nucleophilic Substitution …

313

I. The reaction of formation of S-sodium compound of 2-thiouracil from 2-thiouracil. II. The reaction of nucleophilic substitution of bromine in methyl(benzyl)bromide by anion generated from 2-thiourucil. III. The reaction of formation of O-sodiumt compounds of 2-methyl(benzyl)thio-4pyrimidinon. IV. The reaction of nucleofilic substitution bromine in methyl (benzyl)bromid by Oanion generated from 2-methyl(benzyl)thio-4- pyrimidinon.

I. The Reaction of Formation of Sodium Compound of 2-thiouracil from 2thiouracil The reaction of formation of salts goes with participation S-anion in accordance with their greater stability in contrast with O-anion.

O

NH N H

NH

OH

O

N

N

S

N

SH

I S

Na

O Na N N H

II S

The general energy of the S-anion generated from 2-thiouracil E0=-1926727.5 kDg/mol, dipole moment D= 4.2 dB. For O-anion E0 = -1926671,7 kDg/mol, D = 8.5 dB. The full energy E0 of S-anion on 55.8 kDg/mol less, than E0 of O-anion, consequently occurs formation to salts on scheme I, rather then on scheme II, as also evidenced by calculation by method CNDO/2 corresponding to sodium uracil. Results of quantum-chemical calculation О- sodium compound of 2-thiouracil, its optimized geometric and electronic structure, energy E0, total energy of the bonds Eof bond, dipole moments D are presented on Figure 1. For S-sodium 2-thiouracil E0 = -219882 kDg/mol, Eof bond = -15895, D = 5.59 dB. From meanings E0 and Eof bond for O- and S-sodium 2-thiouracil are seen that shaping S-sodium compound of 2-thiouracil has energy on 157 kDg/mol less than О-sodium compound. So, reaction of 2-thiouracil with NaOH has less energy for formation S-sodium compound (reaction goes on scheme I). The similar result give calculation by method ab initio in base 6311 G **.

A. V. Babkin, A. I. Rakhimov, E. S. Titova et al.

314

Na

0.78

нм

0.22 4

26

нм

2 0. 90

0

-0.74

23

1 N-0.830.135 0. нм нм 32 C0.82 0 .1

S-0.42 0.169 нм

121

0 0

C

114

0.47

1200 0

118

N-0.7 0.136 н

м

0.34 122

1 0.

33

C-0.31

нм

0

122

H0.18

C0.22

0

H

1200

0.145 нм

0.137 нм

0.099 нм

нм O

1160

0.107 нм

H0.19 Figure 1. Geometric and electronic structure of О- sodium compound of 2-thiouracil (E0 = -219725 kDg/mol, Eof bond = -15738, D = 5.38 dB).

II. The Reaction of Nucleophilic Substitution of Bromine in Methyl(benzyl)bromid by Anion Generated from 2-thiouracil The second stage is a reaction S-sodium compound of 2-thiouracil with methyl(benzyl)bromid and obtaining of 2-thiomethyl(benzyl)-4-pyrimidinon. Reaction of nucleophilic substitutiof bromine in methyl(benzyl)bromid by anion, generated from 2thiouracil is shown on scheme

O

O RBr

NH N H

S Na

-NaBr

S-sodium salt of 2-thioracil

NH N H

S R

2-methyl(benzyl)thio-3(H)-4-pyrimidinin R = CH3, CH2C6H5

Quantum-chemical Analysis of the Mechanism of Nucleophilic Substitution … H0.17

H0.17

0.107 нм

С-0.36

0.194 нм

0

Br-0.15

111

0

108

H0.17 H

0.18

105

Br -0.15

315

110

0

0.197 нм 11 2

С -0.26 0

H

0

А)

0.18

0.10 7 нм 11 2

0

0.15 нм

H

0.15

12 0 0

С -0.00

С -0.14

12 0

0

120

0

H 0.15

С -0.14 0.13 85 нм

С -0.14

С -0.14 H 0.15

H 0.15

С -0.14 0.107 нм

H 0.15

В)

Figure 2. Geometric and electronic structures RBr. Results of quantum-chemical calculation ab initio in base 6-311 G **. a) R=CH3, E0= -2609.5455 AU, D = 2.17 dB; b) R=C6H5CH2, E0 = -2839.1005 AU, D = 2.48 dB.

It was calculated methyl bromid and benzyl bromid and finel structures by quantumchemical method ab initio in base 6-G 311**. Geometric and electronic structures are submitted for Figure 2. For study of the mechanism of nucleophilic substitution atom of the bromine in methyl(benzyl)bromid by anion generated from 2-thiouracil was chose coordinate at C2-S. Initial coordinate betweenC2 and S was 0.300 nm. Than the meaning of C2-S chandged (tables 3 and 4). The complex S-anion + BrCH3(CH2C6H5) and the complex S-anion +C6H5CH2Br are submitted for Figures 3 and 4.

A. V. Babkin, A. I. Rakhimov, E. S. Titova et al.

316

H0.34

0. 34 3

12 0.17

1020

нм

0.182 нм

H

0.18

-0.5

С2

H0.18

0

112

С0.79

нм

0.26

6

S

0.

N-0.76 0.139 нм

нм 5 нм

1250

125

13

0.353

нм

0.099 нм

0.

Br-0.94

O-0.64

С10.4

0

0

122

0.129 нм

13 0.

0

109

0.144 нм

N-0.64

4

нм

С-0.33

H0.15

0.136 нмС0.17

0.107 нм

H0.16

0.107 нм

H0.15 Figure 3. Geometric and electronic structure of the complex S-anion + BrCH3 (Q = -1). Results of quantum-chemical calculation ab initio in base 6-311G**. E0= -3344.1264 AU, D = 11.3 dB.

Change charge on atoms, which directly participate in reactions qC1, qC2, qS, qBr are also presented in tabl. 1, 2. Change E0 molecular system of the complex along coordinate of the reactions C2-S is indicative of that this reaction goes with obtaning of the energy (for CH3Br advantage to energy as a result of reactions is 16.2629 kDg/mol, but for BrCH2C6H5 50.623 kDg/mol). The energy barrier for CH3Br is 63.9998 kDg/mol, for C6H5CH2Br 51.9344 kDg/mol, accordingly (refer to the Figures 5, 6). Meanings of E0 in complex S-anion + BrCH3 and S-anion + BrCH2C6H5 are accepted for 0 as for buildings graph of energy profiles of reactions. The behaviour atoms in this study complexes is indicative of smaller reactionary ability atom of the bromine in methylbromid in nucleophilic substitution on classical SN2 mechanism by S-anion, generated from 2-thiouracil, in contrast with benzylbromid. That will with experimental given [20]. The reaction goes with obtaning of the energy and has little energy barrier. Table 1. Results of quantum-chemical calculation of forming the complex Sanion+BrCH3 by ab initio in base 6-311G** № 1 2 3 4 5 6 7 8

RC2-S *, nm 0.300 0.280 0.260 0.240 0.220 0.200 0.190 0.182

RC2-Br, nm 0.200 0.198 0.201 0.261 0.302 0.329 0.343 0.343

* The coordinate of the reactions.

RBr-S, nm 0.500 0.478 0.460 0.501 0.521 0.525 0.518 0.353

qC1

qS

qC2

qBr

E0, AU

0.46 0.44 0.44 0.46 0.45 0.44 0.44 0.40

-0.53 -0.52 -0.51 -0.34 -0.14 0.02 0.10 0.26

-0.30 -0.33 -0.34 -0.20 -0.27 -0.39 -0.44 -0.50

-0.32 -0.27 -0.30 -0.78 -0.92 -0.96 -0.96 -0.94

-3344.1202 -3344.1125 -3344.1030 -3344.0958 -3344.1037 -3344.1167 -3344.1216 -3344.1264

Quantum-chemical Analysis of the Mechanism of Nucleophilic Substitution … H 0.34

O -0.64

9 нм

102

0

С2

0.151 нм

5 нм

0

125 0.183 нм

H 0.24 111

0 .1 7

-0.41 107

125 0

6

0.26

0

13

35 0.

S

С 0.79

нм

N -0.76 0 .1 39 н м

0. 12

6 нм

0.

0 .3 6

нм

0.099 нм

Br-0.9

С 1 0.42

122

0.144 нм

0

0.129 нм

0

1 0.

N -0.63

0.107 нм

317

34

нм

С -0.33

H 0.15

0 .1 3 6 н м С 0.17

H 0.17

0.107 нм

H 0.15

Figure 4. Geometric and electronic structure of the complex S-anion + C6H5CH2Br (Q= -1). Results of quantum-chemical calculation ab initio in base 6-311G**. The full energy E0 = -3573.6892 AU, dipole moment D = 11.54 dB.

Table 2. Results of quantum-chemical calculation of forming the complex S-anion + C6H5CH2Br by ab -initio in base 6-311G** №

RC2-Br, nm 0.199

RBr-S, nm 0.473

qC1

qS

qC2

qBr

E0, AU

1

RC2-S *, nm 0.300

0.44

-0.52

-0.24

-0.23

-3573.6699

2

0.280

0.201

0.461

0.44

-0.51

-0.26

-0.25

-3573.6635

3

0.260

0.205

0.450

0.44

-0.50

-0.27

-0.29

-3573.6521

4

0.240

0.291

0.520

0.46

-0.27

-0.11

-0.87

-3573.6501

5

0.220

0.365

0.440

0.44

0.00

-0.27

-0.90

-3573.6670

6

0.200

0.359

0.376

0.42

0.18

-0.35

-0.90

-3573.6825

7

0.190

0.359

0.369

0.42

0.23

-0.39

-0.90

-3573.6879

8

0.183

0.359

0.366

0.42

0.26

-0.41

-0.90

-3573.6892

* - the coordinate of the reactions.

A. V. Babkin, A. I. Rakhimov, E. S. Titova et al.

318 -3344,09

-3344,095

-3344,1

Е0, AU

-3344,105

-3344,11

-3344,115

-3344,12 0,29

0,27

0,25

0,23

0,21

0,19

0,17

-3344,125

-3344,13

Lengths of bond RC2-S, nm Figure 5. The energy profile of the reaction of nucleophilic substitution atom of the bromine in methylbromid by S-anion generated from 2-thiouracil. -3573,645 -3573,65 -3573,655

Е0, AU

-3573,66 -3573,665 -3573,67 0,29 -3573,675

0,27

0,25

0,23

0,21

0,19

0,17

-3573,68 -3573,685 -3573,69 -3573,695

Lenghts of bond R C2-S, nm Figure 6. The energy profile of the reaction of nucleophilic substitution atom of the bromine in benzylbromid by S-anion generated from 2-thiouracil.

Quantum-chemical Analysis of the Mechanism of Nucleophilic Substitution …

H0.35

O-0.61

1020

0 .1 35

нм

N-0.770.139 нм

С 0.45 0 1

123 0.182 нм

H0.16 0.16

H

1100

0

124

С0.79

0

112

0.145 нм

0

123

0.128 нм

0 С2-0.52 109

0 .1

2н

м

0.099 нм

S0.19 0.17 7 нм

319

N-0.63

4 13 0.

нм

-0.31

С

H0.18

0.137 нмС0.16

0.108 нм

H0.23

0.107 нм

H0.17 Figure 7. Geometric and electronic structure of the S-methylderivative. The results of quantumchemical calculation ab initio in base 6-311G**. E0= -774.1292 AU, D = 3.97 dB.

III Stage. The Reaction of Formation О-sodium 2-methyl(benzyl)thio-4pyrimidinon Since O-sodium compound of 2-methyl(benzyl)thio-4-pyrimidinon is easy formed, and in this instance there is no need to in undertaking quantum-chemical calculation.

IV Stage. The Reaction of Nucleophilic Substitution Atom of the Bromine in Methyl(benzyl)bromid by O-anion 2-methyl(benzyl)thio-4-pyrimidinon The fourth stage connected with obtaning of 2-methyl(benzyl)thio-4methyl(benzyl)oxipirimidin by reaction O-sodium t 2-methyl(benzyl)thio-4-pyrimidinon with methyl and benzylbromid: Table 3. Charges and full enerdgy for ions of Br-1 , Na and molecule NaBr calculated by method ab initio in base 6-311G** № 1 2 3

System Br -1 Na +1 NaBr

RNa-Br, nm 0.251

qBr -1.00 -0.58

qNa 1.00 0.58

D, dB 9.27

E0, AU -2569.9757 -161.6593 -2731.8574

A. V. Babkin, A. I. Rakhimov, E. S. Titova et al.

320

Table 4. Charges and full energy calculated for S-methylderivative + CH3Br by ab initio in base 6-311G** №

RC2-O*

RC2-Br

RC1-O

RBr-H

qC1

qO

qC2

qBr

E0

1

0.300

0.198

0.121

0.251

0.71

-0.73

-0.30

-0.29

-3383.1274

2

0.280

0.198

0.122

0.251

0.72

-0.73

-0.29

-0.30

-3383.1272

3

0.260

0.200

0.122

0.252

0.72

-0.74

-0.28

-0.32

-3383.1256

4

0.240

0.203

0.123

0.252

0.72

-0.75

-0.25

-0.36

-3383.1214

5

0.220

0.211

0.123

0.254

0.73

-0.76

-0.21

-0.44

-3383.1129

6

0.200

0.254

0.125

0.272

0.76

-0.77

-0.05

-0.76

-3383.1049

7

0.180

0.299

0.127

0.293

0.77

-0.76

-0.01

-0.92

-3383.1163

8

0.170

0.315

0.128

0.293

0.76

-0.74

0.01

-0.94

-3383.1266

9

0.160

0.328

0.129

0.293

0.75

-0.71

0.00

-0.96

-3383.1364

10

0.150

0.342

0.129

0.290

0.74

-0.68

-0.01

-0.96

-3383.1436

11

0.143

0.377

0.130

0.274

0.73

-0.64

-0.05

-0.96

-3383.1453

* - the coordinate of the reactions.

Quantum-chemical calculations of ions, participating in this reactions, as well as complex S-anion + BrCH3, S-anion + BrCH2C6H5 are submitted for Figures 8 - 11 and in tables 3- 5. This stage also goes on classical mechanism of nucleophilic substitution SN2. The reactions are exotermic (the advantage to energy in the event of methylbromid and benzylbromid forms accordingly 46.9508 kDg/mol and 51.4098 kDg/mol). Table 5. Charges and full energy calculated for S-benzylderivative + C6H5CH2Br by ab initio in base 6-311G** №

RC2-O *

RC2-Br

RC1-O

RBr-H

qC1

qO

qC2

qBr

E0

1

0.300

0.198

0.123

0.249

0.72

-0.74

-0.27

-0.22

-3842.2383

2

0.280

0.199

0.123

0.249

0.73

-0.75

-0.27

-0.24

-3842.2347

3

0.260

0.201

0.123

0.249

0.73

-0.74

-0.19

-0.28

-3842.2348

4

0.240

0.205

0.123

0.250

0.74

-0.74

-0.18

-0.33

-3842.2289

5

0.220

0.216

0.123

0.252

0.75

-0.75

-0.14

-0.43

-3842.2189

6

0.200

0.280

0.125

0.273

0.77

-0.76

0.06

-0.84

-3842.2139

7

0.190

0.364

0.127

0.265

0.78

-0.73

0.05

-0.91

-3842.2215

8

0.180

0.368

0.127

0.267

0.78

-0.72

0.05

-0.91

-3842.2306

9

0.170

0.373

0.128

0.270

0.78

-0.71

0.05

-0.92

-3842.2406

10

0.160

0.377

0.129

0.273

0.77

-0.69

0.05

-0.92

-3842.2501

11

0.150

0.381

0.130

0.276

0.76

-0.66

0.05

-0.92

-3842.2568

12

0.145

0.383

0.130

0.278

0.75

-0.64

0.05

-0.92

-3842.2579

* - The coordinate of the reactions.

Quantum-chemical Analysis of the Mechanism of Nucleophilic Substitution …

321

0.13

H

1060 -0.48

1100 C

H

0.15

0 .1 8

1 нм S

1110

H

0.19 0.12

1020

0.133 нм

0.15

1200 0.131 нм

0.35

N

C

1270

0 N-0.6 115

0.134 нм

-0.64

C1-0.73

1160

C

0.136 нм

0.108 нм

C2-0.05

1210

1110

1600

Br-0.96

0.23

0.274 нм

H

1070 0.144 нм

0.13 нм

O

-0.64

0.141 нм

-0.28

C0.16

109

0

H

0.131 нм

1170 1210

1230

0.12

H

0.177 нм

1200

H0.15

H0.17

Figure 8. Geometric and electronic structure of the complex S- methylderivativ e + BrCH3 (Q= -1). Results of quantum-chemical calculation ab initio in base 6-31G**. E0= -3383.1453 AU, D = 19.26 dB.

H 0.14

1060

0 .1 8

-0.49 111 0 110 C 0

H 0.16

H 0.16

0.2 1 нм S

102 0

H 0.14

0.176 нм 0.133 нм

120 0

C 0.35

0.131 нм

127 0

0 N -0.58 115

0.134 нм

123 0

C 0.17 0.108 нм

H 0.17

111 0

N -0.65

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-0.02

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105 0

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H 0.13

0.142 нм

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-0.65

0.141 нм

C -0.28 120 0

0.136 нм

H 0.18

Figure 9. Geometric and electronic structure of the S,O-dimethylderivative Results of quantumchemical calculation ab initio in base 6-311G**. E0= -813.1550 A.U., D = 1.39 dB.

CONCLUSION Nukleophilic substitution in alkyl(benzyl)galogenids on S- and O-aniones generated from 2-thiouracil was studed by quantum-chemical method ab initio in base 6-311 G**. Electronic structures of heterocyclic aniones, the complex S-anion + BrCH3(CH2C6H5) and the complex S-anion +C6H5CH2Br, the complex S-methylderivative + BrCH3, the complex S-

A. V. Babkin, A. I. Rakhimov, E. S. Titova et al.

322

benzylderivative + C6H5CH2 were calculated. Results of quantum-chemical calculation and results of syntheses of S-, O-dederivatives of 2-thiouracil are coordinating.

H0.15

1060

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-0.42

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H

Figure 10. Geometric and electronic construction of the complex S-benzylderivative + C6H5CH2Br (Q= -1). Results of quantum-chemical calculation ab initio in base 6-311G**. E0= -3842.2579 A.U. ,D = 22.88 dB. H0.15 H

0.15

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C

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-0.15

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1100

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-0.05

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0.16

110 0 C

0.108 нм

C -0.14

0.17

H0.15

0

H0.14

0.143 нм

O-0.66

0.132 нм

0.141 нм 120 0

0.15

H

0.17

H

0.18

Figure 11. Geometric and electronic construction of the S,O-dibenzylderivative. Results of quantumchemical calculation ab initio in base 6-311G**. E0= -1272.2609 AU, D = 1.48 dB.

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323

REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20]

Abdel-Rahman A.-H. // Afinidad.1997. V.54. № 468. P. 135. Rahman A.A.-H., Abdel Al M.T.// Pharmazie. 1998. 53. № 6.P.377. Besada Amir, Tadros N.B., Gawargyious Y.A. Egypt. J. Pharm. Sci. 1989. 30. №1. P. 251. Adav Geo, Kolczeцылш Sabine, Mutel Vincent, Wichmann Jurden Derivatives of 5Hthiazolo[3,2-a]-pyrimidina, Pat 0891978 (1998). USA, 1999. Maccha Marko, Antonell Guido, Balsamo Aldo, et.al. Farmaco(Amsterdam). 1999. V. 54. № 4. P. 242. Larson Janus S., Abdel Abl Mohammed Taha, et. Al. J. Heterocycl. Chem. 2001. V. 38. № 3. P. 679. Morris Joel, Adams Wade, Fris Janis, Wishka Donn. Pat. 6124306 (1999). USA, 2000. Mai A., Sbardella G., Artico M., et.al. J. Med. Chem. 2001. V 44. № 16. P.2544. Mai A., Sbardella G., Artico M., et.al. J. Med. Chem. 1999. V 42. № 4. P.619. Quaglia M., Mai A., Artico M., et.al. Chirality. 2001. V 13. P.75. Sudbeck E.A., Mao C., Venkatachalam T.K., et. al. Antimicrob. Agents Chemther.1998. V. 42. № 12. P. 3225. Ole S. Pedersen, Lene Petersen, Malene Brandt, et.al. Monatsh Chem. 130. 199. P. 1499. Mitsuya. H., Broder. S. Nature. 325. 1987. P. 773. Goff S.P. Acquired Immune Defic. Syndr. № 3. 1990. P. 817. Vorbruggen H., Bennua B.A. Chem Ber. 114. 1981. P. 1270. De Clercq E. J. Med. Chem.38. 1995. P. 2491. Baba M., Tanaka H., Miysaka T., et.al.Nucleosides Nucleotides. 14. 1995. P. 497. Shmidt M.W., Baladridge K.K., Boatz J.A., et.al. J. Comput. Chem. 1993, 14, 1347. V.A. Babkin and e.c.t. Oxidation Communication, 2002, 25, № 1, P. 21. Rakhimov A.I., Titova E.S.J. Organic Chem. V. 43. № 1. 2007.

In: Modern Tendencies in Organic and Bioorganic Chemistry ISBN: 978-1-60456-295-8 Editors: A. Mikitaev, M. K. Ligidov, pp. 325-333 © 2008 Nova Science Publishers, Inc.

Chapter 26

CONFORMATIONAL BEHAVIOR OF PROPAGATING CHAINS OF POLYACRYLATEAND POLYMETHACRYLATE GUANIDINES IN WATER SOLUTIONS N. A. Sivova,*, A. I. Martynenkoa, Yu. A. Malkanduevb,†, M. H. Baidaevab, A. A. Zhansitovb, O. A. Taovb, A. I. Sarbashevab а

A.V.Topchiev Institute of Petrochemical Synthesis, Russian Academy of Science, 29 Leninsky prosp., 119991 Moscow, Russian Federation b Kh.M.Berbekov Kabardinian Balkarien University, 173 Chernyshevsky st., 360004 Nal’chik, Russian Federation

ABSTRACT The influence of composition of acrylate- and methacrylate guanidines reaction solutions in radical polymerization in aqueous solutions (0.2 ≤ [M] ≤ 2.5 mol l-1; [APS] = 5×10-3 mol l-1; pH ∼ 6.5; 600C) on conformational behavior peculiarities of investigated systems was studied. It was established that observing micro-heterogeneity under certain conditions is caused by coagulation of propagating polymer chains as a result of specific complex formation between monomer and polymer molecules (in particular under interaction of functional and guanidine groups of monomer and polymer molecules)

Keywords: acrylate- and methacrylate guanidines; radical polymerization; poly (meth) acrylate guanidines, conformational behavior, micro-heterogeneity

* †

E-mail: [email protected] E-mail: [email protected]

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2,5

ηred

2

1,5

1

0,5

-1

[GA]mole l

0 0

0,5

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1,5

2

Figure 1. The dependence of reduced viscosity of PAG on AG concentration in water at 30°C; [η]PAG = 0,27 dl g-1; [PAG] = 0,12 mole l-1 (1,62% solution), ///// − the region of heterogeneity. 3,5

ηred

3

2,5

2

1,5

1

0,5 [MAG], [GHC], mole l

-1

0 0

0,1

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0,3

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0,5

Figure 2. The dependence of reduced viscosity of PMAG model solution in systems: 1 − PMAG + MAG; 2 − PMAG + GHC ([η]PMAG = 0,27 dl g-1; 1,7% solution of PMAG in water; 0,1 mole⋅l-1; 30°C, hydroquinone), ///// − the region of heterogeneity.

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The very important characteristic of physical-chemical behavior of polyelectrolytes in solution is conformational state which depends on a great number of factors including nature of solvents, polymer ionization degree, solution ion force, etc… Investigation of conformational behavior of macromolecules containing charged fragments in the chain causes significant interest of researches not only from theoretical point of view, but also from positions of possible application of such polymers for solution of medical-biological, ecological and other problems [1]. For revealing of influence of conformational state of macro-radicals on kinetics of radical polymerization of acrylate- and methacrylate-guanidines in water mediums with the help of viscosimetry method the values of macroscopic viscosities in solutions modeling reaction mixtures at low conversion degrees were measured and obtained data were compared with kinetic ones. By measuring of reduced viscosity ηred = ηsp / с in dependence on monomer concentration in model systems we showed that even at small additions into investigated polymers PAG and PMAG water solutions of corresponding to them monomer salt the sharp change of linear sizes of polymers chains, i.e. their "compression" was observed, and at high concentrations the solution became opaque (Figures 1 and 2). We also established that in the case of PMAG the opalescence of model solution was observed in monomer solutions diluted enough at concentration [MAG] > 0.3 mole⋅l-1 (Figure 2); for the PAG insignificant haze of solution was observed at essentially bigger concentrations of monomer [AG] > 1.3 mole⋅l-1 (Figure 1). We should note that close to these concentration regions (regions of transition from total homogeneity to micro-heterogeneity), according to viscosimetry data, the maximum compression of balls of PAG and PMAG macromolecules occurs and the lowest value of ηred corresponds to this fact. In given region with the rise of ion force of model solution together with the appearance of micro-heterogeneity the increase of ηred is obviously occurs that may be the consequence of two phenomena − either of transition of system to micro-heterogeneity, or of the reduction of PAG chains sizes as a result of specific complex formation between monomer and polymer molecules (in particular under interaction of functional and guanidine groups of monomer and polymer molecules, Figure 3). In the other model system PMAG + MAG at the transition of ηred through the minimum value ([MAG] > 0.3 mole⋅l-1) complete turning of PMAG chain with phase separation is observed (precipitation of white residue is clearly observed visually) that is revealed at relatively low (thrice-repeated) excess of MAG monomer in relation to PMAG. Since due to PMAG sediment precipitation the further carrying out of viscosimetry investigations becomes impossible (viscosimeter capillary is clogged) the further measurements were stopped at relatively low concentrations of monomer. Nevertheless, the analysis of data received by viscosimeter investigations allows concluding that there was a good coincidence with kinetic data. Actually, in both cases the interval of monomers concentrations in which reaction systems keep their homogeneity is practically coincides (of course with definite correction by temperature course of investigated processes since polymerization kinetics as it was mentioned earlier was measured at 60°C, and viscosimetry studies were carried out at 30°C). Moreover, undoubtedly the correspondence of "transition region" of monomer concentrations values was also traced at which compression of macroradicals balls and their turning obtained by mentioned independent methods (dilatometer and viscosimetry) was observed.

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polymer anion

polymer cation

monomer molecule

HO H

water molecule

H I A hydrophobic interactions area for PMAG Figure 3. The change of PAG and PMAG balls' form under the action of monomer or guanidinehydrochloride (model system).

H

O

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Conformational Behavior of Propagating Chains …

329

For revealing of possible reasons explaining so uncharacteristic for ionogenic polymers in water solutions "salting-out" at low degrees of transformation under the action of proper monomer we carried out kinetic investigations of AG and MAG polymerization from initial up to high conversions (for a number of samples up to 80%) by dilatometry method. At that the solution's transparency at investigated conditions was fixed visually. We should note that for some monomer concentrations at high conversion degrees as it is known due to high viscosity of reaction solution such measurements by dilatometry method are impossible. In other cases when viscosity of reaction solution is significantly increased with conversion but solution keeps fluidity such measurements are possible however they reflect mainly the qualitative picture of proceeding processes. As it was shown, under AG polymerization ([AG] ≤ 1.3 mole⋅l-1) kinetic dependences of Vp on q % were linear, and polymerization solution remained completely transparent up to high conversions. At higher monomer concentration [AG] > 1.5 mole⋅l-1 from the initial conversions the micro-heterogeneity is appeared. As far as the monomer is spent in reaction solution at high conversion degrees solution turbidity is gradually reduced and solution becomes absolutely transparent. The given phenomenon observed under AG polymerization in water is completely uncharacteristic for MAG. The homogeneity in the case of MAG was fixed only in diluted solutions [M] ≤ 0.4 mole⋅l-1 (but remained up to high conversion degrees 80%). At high initial MAG concentrations at the initial section of kinetic curve the micro-heterogeneity was observed (at Vр ≈ const, q ≤ 5%). At q ≥ 20% the PMAG sediment is precipitated in dilatometer and complete heterogeneity remains up to deep conversions (to complete monomer spending in reaction system).

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(a) Compressed hydrated ball-shaped structure of PMAG at the expense of strong hydrogen bonding methyl groups) interactions (the regions of hydration and hydrogen and hydrophobic ( bonding are shown fragmentary). Figure 4. Continued on next page.

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H

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(b) Hydrated flocculent ball-shaped structure of PAG (the regions of hydration and bonding are shown also fragmentary). Figure 4. The structures of PMAG (a) and PAG (b) homopolymers (---- − hydrogen bonds, the rest legend as in Figure 3).

The analysis of results described above shows that MAG behavior in polymerization reaction has the features differed from AG behavior at the same conditions. The main feature of these differences as we assume is in special structure of PMAG chains in water mediums (Figure 4). It is known that degree of interaction between water molecules and functional groups of PE, i.e. PE hydration degree is the factor determining its basic physical-chemical parameters and first of all macromolecules conformation in water solutions. In the case of PMAG and PAG molecules of H2O also participate in stabilization of structure organized in such way that macromolecule takes the shape of swollen ball stabilized by hydrogen and hydrophobic interactions (Figure 5). Introduction of monomer containing guanidine groups leads to "disorientation" of mentioned structure at the expense of primary interaction of NH2-groups with carboxyl group as a result of which the water molecules are removed from inter-chain interactions, functional carbon chain groups are "blocked" and finally the macromolecule is compressed becoming more compact in the shape of coagulated conformation of globular type (Figure 3). The intrinsic viscosity of polymer solution at that is reduced: in the case of PAG the solution becomes opaque (turbid) and in the case of PMAG at high conversions q% or at high monomer concentrations the separate phase is formed. Thus, we assume that the observing in the radical polymerization of MAG microheterogeneity is the consequence of the fact that MAG monomer at the expense of guanidine groups content leads to coagulation of PMAG propagating chains as a result of cooperative conformational transition.

Conformational Behavior of Propagating Chains … H

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Figure 5. Change of conformation and form of homopolymer (PAG and PMAG) under the action of mutual monomer in the course of polymerization as a result of specific interactions between polymer, monomer and water molecules (legend as in Figure 3).

Of course if we shall draw an analogy close to mechanism of guanidine salts action on macromolecules of synthetic (or nature) proteins and considered polymer systems then the PMAG to a definite degree may be considered as such analogue. Since stability of proteins and proteins-similar synthetic polymers structures is provided mainly not by hydrogen bonds (their role is undoubtedly in the creation of proteins structure), but by hydrophobic

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interactions. That is why as we assume the presence of MAG monomer "excess" in polymerization process leads to the change of "ordered" PMAG structure which is formed in water solutions in the absence of monomer or at its low content (less than 0,4 mole⋅l-1) (Figure 5). In the case of PAG the total destruction of macromolecule structure is not observed and it is more labile since as we discussed earlier even at significant excess of AG monomer in PAG solution the system remained homogeneous (sediment was not formed) and at the decrease of GA monomer concentration in reaction solution (during its consumption in polymerization process) the polymerization solution gradually became transparent again and "micro-saltingout" of macromolecules was stopped. The analysis of data obtained by us allows concluding that observing changes of macromolecules conformations (at any case for PAG) are determined mainly by the concentration of monomer salt in reaction solution, and weakly depend on molecular mass of corresponding polymer (that we may expect a priory). Otherwise it is difficult to explain the observing in polymerization process phenomenon of transition of reaction system PAG + AG (at high AG monomer concentrations and higher q%) from completely opaque to totally transparent (homogeneous). It is interesting to estimate also possible influence on conformation of PMAG in water solution of its low-molecular analogue. With this aim we select guanidine hydrochloride (GHC). As it is obvious (Figure 2 curve 2) the dependence of reduced viscosity on salt concentration in system PMAG + GHC and dependence in model system PMAG + MAG (Figure 2.9 curve 1) are symbate. In both cases under addition of salt the coagulation of PMAG chains in a narrow interval of solution's ion force change (∼ 0,10–0,15) is observed that is caused probably by phase transition of system as a result of disorientation of macromolecules structure, by the way this process is irreversible. It is interesting that in the system PMAG + GHC at [GHC] > 0,3 mole⋅l-1 the gelatinous opaque mass is formed that is caused probably by the formation of spatial network structure. Thus, the characteristic for investigated polymer systems conformational transformations accompanying by reconstruction of chain local structure are caused as it is obvious by "blocking" action of guanidine monomer groups leading to essential coagulation of PMAG macromolecules, and particularities of conformational behavior of PMAG in contrast to PAG are explained by significant contribution of hydrophobic interaction in PMAG chains that impacts to given macromolecules order in structure organization and lower lability in comparison with PAG.

ACKNOWLEDGEMENETS This work was carried out under partial financial supporting of RAS, Division of chemistry and sciences on materials, project No DCSM-04.

Conformational Behavior of Propagating Chains …

REFERENCES [1]

I.Yu. Galaev, Uspekhi khimii, 64, No.5, 505 (1995) (in Russian).

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In: Modern Tendencies in Organic and Bioorganic Chemistry ISBN: 978-1-60456-295-8 Editors: A. Mikitaev, M. K. Ligidov, pp. 335-340 © 2008 Nova Science Publishers, Inc.

Chapter 27

BIOCIDE AND TOXICOLOGICAL PROPERTIES OF SYNTHESIZED GUANIDINE CONTAINING POLYMER AND THEIR STRUCTURE N. A. Sivova,*, Yu. A. Malkanduevb,†, S. Yu. Khashirovab, M. H. Baidaevab, A. I. Sarbashevab, A. A. Zhansitovb, and O. A. Taovb а

A.V.Topchiev Institute of Petrochemical Synthesis, Russian Academy of Science, 29 Leninsky prosp., 119991 Moscow, Russian Federation b Kh.M.Berbekov Kabardinian Balkarien University, 173 Chernyshevsky st., 360004 Nal’chik, Russian Federation

ABSTRACT In the work there were investigated biocide and toxicological properties of guanidine containing homo- and co-polymers of diallyl and vinyl nature: poly (meth) acrylate guanidines, co-polymers of (meth) acrylate guanidines and diallylguanidine acetate with diallyldimethylammonium chloride, and also model polymers for comparison: polydiallyldimethylammonium chloride and polyhexamethyleneguanidine hydrochloride. It was shown that co-polymers display considerable biocide activity in relation to E.coli and St.Aureus, co-polymers of diallylguanidine acetate demonstrate maximum indices. Co-polymers of (meth) acrylate guanidines, containing 30 – 70 mol% of acrylate comonomer, have close indices. It was shown that homo-polymers and co-polymers on the base of (meth) acrylate guanidines with less than 40 mol% of diallyldimethylammonium chloride links are non-toxic. When content of diallyldimethylammonium chloride links is more than 40 mol% (up to 65 – 70%) co-polymers have low toxicity. Co-polymers of diallylguanidine acetate are the exceptions and their toxicity is close to polydiallyldimethylammonium chloride toxicity. * †

e-Mail: [email protected] E-mail: [email protected]

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Keywords: poly (meth) acrylate guanidines, poly (diallyldimethylammonium chloride)copolyacrylate guanidines, poly (diallyldimethylammonium chloride)copolymethacrylate guanidines, poly (diallyldimethylammonium chloride)copolydiallylguanidine acetates, biocide properties, toxicity

Creation of novel biocide polymers represents important direction in present-day chemistry of high-molecular compounds. This problem became especially relevant recently when wide spreading of stable to various bactericidal substances strains and possibility of their epidemic spreading was the serious problem for the formation of effective anti-bacterial therapy. That is why the search of means providing blocking of several factors of stability of pathogenic microorganisms becomes necessary. Application of polymers able to reveal combined effect on bacterial cell which are more effective and less dangerous for person in comparison with low-molecular biocide substances traditionally used for protection of microorganisms seems to be perspective for the solution of this problem. On the base of said above we may conclude that synthesis of novel guanidine containing polyelectrolytes on the base of monomers of acrylic type and dialkyldiallylammonium derivatives with the use of radical polymerization and investigation of scientific bases of these processes, and also the developing of methods of novel guanidine containing biocide polyelectrolytes reception are very relevant problems. Synthesis of polyacrylate guanidines (PAG), polymethacrylate guanidines (PMAG), copolymers of AG and MAG with diallyldimethylammonium chloride (PDADMAC-co-PAG and PDADMAC-co-PMAG), and also co-polymers of diallylguanidine acetate with DADMAC (PDADMAC-co-PDAGA) and determination of their structure and composition was fulfilled by authors earlier [1 – 7]. We should note, that these polymers meet the number of requirements which are made of modern preparations of such type: good solubility in water and physiological solution (1% solutions of polymers have pH = 6.5 − 7.0); the solutions are colorless, don't have smell, don't cause destruction of treated materials and polymer nature of these compounds promotes the absence of inhalation toxicity and formation on treated surfaces of continuing polymer film providing prolonged biocide effect. Investigations of bactericide activity and toxicity of synthesized homo- and copolymers showed that these preparations were very active and posses biocide action in relation to grampositive (St.Aureus) and gram-negative (E.coli) microorganisms and that a lot of samples had low toxicity (Table 1). On the base of obtained data we may conclude the following. Polyacrylic acids (PAA and PMAA) (Table 1, entries 1 and 6), and also homopolymers PAG and PMAG (Table 1, entries 2 and 8) possess low toxicity, and polymer derivatives of acrylic acid posses the lowest toxicity. This fact may be explained probably by additional hydrophobic interaction of polymers on the base of methacrylic derivatives (MAA and MAG) with cellular wall. The same regularity is observed for copolymers (Table 1, entries 3−4 and 9−13): copolymers with AG are less toxic, at that toxicity of samples is the higher, the higher the content of DADMAC units in copolymers (Figure 1). The presented Figure needs the following explanation. Since the criterion of non-toxicity according to technique of investigation is the value of index of toxicity in the interval from 60 up to 120 (Table 1, column 4), than for

Biocide and Toxicological Properties of Synthesized Guanidine …

337

clearness during comparing the low level equal to 60 was subtracted from the value of this index. Table 1. The data on biocidicity and toxicity of polymer derivatives of AG, MAG and DAGA and some model polymersa Entry

Compound

М1:М2b

It

E. coli c

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

PAA PAG PDADMAC-co-PAG PDADMAC-co-PAG PDADMAC-co-PAG PMAA PMAA(G) PMAG PDADMAC-co-PMAG PDADMAC-co-PMAG PDADMAC-co-PMAG PDADMAC-co-PMAG PDADMAC-co-PMAG PDADMAC PHMG HC PDADMAC-co-PDAGA PDADMAC-co-PDAGA

0:100 18:82 36:64 75:25 0:100 11:89 28:72 34:66 43:57 61:39 100:0 85:15 95:5

87.1 67.6 75.2 98.8 122.4 93.2 76.1 104.6 88.7 101.5 119.1 131.3 143.4 29.7 27.5 38.6 33.5

------+ -++ +++ -------++ -++ +++ -++ -++ --+ -++ +++ +++

St. aureus c ---++ +++ +++ +++ ---++ -++ -++ +++ +++ +++ +++ ---++ +++ +++

MSC ×103 d 8.5 1.9 2.0 2.3 9.8 9.2 2.2 2.7 1.4 1.9 3.2 0.4 1.5

a

the samples of copolymers DADMAC with AG (entries 3−5), copolymers DADMAC with MAG (entries 9−13), polyacrylic acid (PAA) (entry 1), PAG (entry 2), polymethacrylic acid (PMAA) (entry 6), PMAA modified by guanidine (entry 7), PAG (entry 8), PDADMAC (entry 14), polyhexamethylene guanidine hydrochloride (PHMG HC) (experiment 15), copolymers DADMAC with DAGA (entries 16, 17). It − index of toxicity; b according to 1H NMR spectroscopy data; c Escherichia coli is colon bacillus, representative of gram-negative bacteria and Staphylococcus Aureus 906 is golden staphylococcus, representative of gram-positive bacteria. (+++) continuous lysis of bacterial cell, hinders growth of given culture completely; (--+) partial lysis of bacterial cell, the zones of growth suppression are observed after 48 hours; (--+) partial lysis of bacterial cell, the zones of growth suppression are observed after 72 hours; (---) inactive; d minimum suppression concentration, mass %.

This result was expected for polyamphylic copolymers if one took into account the fact that derivative of acrylic acids had low toxicity, whereas PDADMAC possessed high toxicity (Table 1, entry 14) due to its polycation nature. High toxicity was revealed also by samples of copolymers of DADMAC with DAGA however it was lower than for PDADMAC (Table 1, entries 16, 17 and 14). The other polycation taken for comparison polyhexamethyleneguanidine hydrochloride (PHMG HC) also showed high toxicity (Table 1, entry 15). So, we may conclude that when select the copolymer as biocide preparation one should take into account the copolymer composition.

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100

Reduced index of toxicity

80

60 2 1

40

20

Content of DADM AC in copolymer 0 0

20

40

60

80

100

Figure 1. The change of toxicity index in dependence on change of DADMAC content in copolymers with AG (curve 1) and MAG (curve 2).

As it is obvious from data of Table 1 the synthesized guanidine-containing preparations reveal bactericide activity in relation to studied cellular structures and for copolymers the most expressed biocide activity was observed (the highest biocidity was revealed by copolymers of DADMAC with DAGA, Table 1, entries 16 and 17). As it is known, it is connected with the fact that polyelectrolytes in water medium form electrically charged groups, fixed along the lengthy polymer chain and able to "multipoint" (cooperative) interactions with bacterial cell and transport function first of all is fulfilled by positively charged units of DADMAC. This fact is also confirmed by the fact that PAA and PMAA polyacids (Table 1, entries 1 and 6) don't possess biocide properties in relation to investigated cultures; copolymer of MAG with MAA obtained by modifying of PMAA by guanidine at low toxicity possesses weak biocide properties (Table 1, entry 7). Essentially weaker biocide properties of homopolymers are also explained by given facts (Table 1, entries 2 and 8).

Biocide and Toxicological Properties of Synthesized Guanidine …

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On the whole for MAG and PMAG more expressed activity was noticed in relation to gram-positive micro-organisms, and gram-negative-cultures turned to be more stable to these compounds (Table 1, entries 2 and 8). We should also note the following. When we discuss biological activity of synthesized by us guanidine-containing polymers we don't mean medicine preparations. We speak about biocide preparations designed for treatment of various surfaces and introduction of them into various compositions for imparting of biocidity. So, under influencing on bacteria the effect of biocidity will be supplemented with toxic influence of these compounds. That is why in the raw of synthezised polymers the samples with higher toxicity possess higher biocidity. In the raw presented below both toxicity and biocidity are decreased from left to right: PDADMAC-co-PDAGA > PDADMAC-co-PMAG > PDADMAC-co-PAG > P(M)AG At that we clearly understand that it is important to take into account the toxicity index in the case of contact with preparations of warm-blooded animal. Thus, combination of high bactericide activity (at the expense of guanidine groups presence) with high ability to bond with bacterial cells due to DADMAC units in obtained copolymers allows us to synthesis the novel effective guanidine-containing biocide polymers. The presence in copolymer chain of acrylate units allows obtaining of such preparations with low toxicity.

ACKNOWLEDGEMENTS This work was carried out under partial financial supporting of RAS, Division of chemistry and sciences on materials, project No DCSM-04.

REFERENCES [1]

[2] [3]

[4]

[5] [6]

S.Yu. Khashirova, N.A. Sivov, N.I. Popova, E.Yu. Kabanova, A.I. Martynenko, Yu.A. Malkanduev, D.A. Topchiev // Izvestia VUZov, sev.-kavk. Region, ser. Estestv. Nauki, 2002, No. 4, p. 45. (in Russian). G.E.Zaikov, Yu.A.Malkanduev, S.Yu.Khashirova, A.M.Esmurziev, A.I.Martynenko, L.I.Sivova, N.A.Sivov, J.Appl.Pol.Sci., 2004, v.91, p. 439. A.M.Esmurziev, S.Yu.Khashirova, A.I.Martynenko, E.Yu. Kabanova, N.I. Popova, N.A. Sivov, Yu.A.Malkanduev // Izvestia VUZov, sev.-kavk. Region, ser. Estestv. Nauki, 2003, No. 6, p. 56. (in Russian). S.Yu.Khashirova, A.I. Martynenko, N.A. Sivov, A.M. Esmurziev, N.I. Popova, E.Yu. Kabanova, Yu.A. Malkanduev // Thesises of 2nd All-Russian scientific-practical conference “New polymer composition materials” Nal’chik, 2005, p. 73. (in Russian). Yu.A. Malkanduev, N.A. Sivov, A.N.Sivov, S.Yu. Khashirova, A.M. Esmurziev, A.A. Zhansitov, O.A. Taov, ibid, p. 239. (in Russian). N.A. Sivov, A.N. Sivov, Yu.A. Malkanduev, S.Yu. Khashirova, A.M. Esmurziev, A.A. Zhansitov, O.A. Taov, ibid, p. 245. (in Russian).

340 [7]

N. A. Sivov, Yu. A. Malkanduev, S. Yu. Khashirova et al. N.A. Sivov, A.I. Martynenko, G.N. Bondarenko, M.P. Filatova, E.Yu. Kabanova, N.I. Popova, A.N. Sivov, E.B. Krut’ko // Petroleum Chemistry, 2006, V. 46, No 1, p. 41.

In: Modern Tendencies in Organic and Bioorganic Chemistry ISBN: 978-1-60456-295-8 Editors: A. Mikitaev, M. K. Ligidov, pp. 341-344 © 2008 Nova Science Publishers, Inc.

Chapter 28

CO-POLYMERIZATION OF DIALLYLDIMETHYLAMMONIUM CHLORIDE AND DIALLYLGUANIDINE ACETATES ON HIGH CONVERSION FOR CREATION OF NEW BIOCIDE MATERIALS N. A. Sivova,*, Yu. A. Malkanduevb,†, A. I. Sarbashevab, M. H. Baidaevab amd S. Yu. Khashirovab а

A.V.Topchiev Institute of Petrochemical Synthesis, Russian Academy of Science, 29 Leninsky prosp., 119991 Moscow, Russian Federation b Kh.M.Berbekov Kabardinian Balkarien University, 173 Chernyshevsky st., 360004 Nal’chik, Russian Federation

ABSTRACT The investigation of radical co-polymerization of diallyldimethylammonium chloride (DADMAC) and diallylguanidine acetate (DAGA) on high conversion in aqueous solutions was carried out. It was shown that co-polymers enriched with DADMAC links in comparison with initial mixture of co-monomers for all compositions of reaction mixtures and deep conversion is observed for high content of DADMAC in initial reaction mixtures. Evidently, it is connected with degradative chain transfer on monomer that character for DAGA. Polymer products of different composition and molecular weight were obtained and considerable biocide activity of synthesized copolymers was demonstrated.

Keywords: co-polymerization, poly (diallyldimethylammonium chloride)copolydiallylguanidine acetates, degradative chain transfer on monomer, biocide activity * †

E-mail: [email protected] E-mail: [email protected]

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Table 1. The dependence of co-polymer composition on initial composition of reaction solution and reaction conditions under copolymerization of DADMAC (M1) with DAGA (M2) Entry 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 a d

Initial conditions [M] a, [I] b, -1 mol L mol L-1 4.00 0.040 4.00 0.040 4.00 0.004 4.00 0.004 4.00 0.004 4.00 0.004 4.26 0.004 4.26 0.008 4.17 0.004 4.12 0.004 4.00 0.040 4.00 0.040 4.00 0.040 4.29 0.043 4.17 0.042 4.17 0.042 4.08 0.040 4.08 0.040 4.08 0.040 4.08 0.040 4.08 0.040 4.08 0.040 4.08 0.040 4.08 0.040 4.08 0.040 4.08 0.040

М1 : М2, mol % 0:100 50:50 50:50 20:80 40:60 50:50 70:30 70:30 80:20 90:10 20:80 40:60 50:50 70:30 80:20 90:10 70:30 70:30 70:30 70:30 70:30 70:30 70:30 70:30 70:30 70:30

T c, 0 C 60 55-60 50-60 60 60 60 60 60 60 60 60 60 60 60 60 60 60 60 60 60 60 60 60 30 40 50

t d, hour 72 200 150 40 40 40 40 40 40 40 40 40 32 33 33 33 0.5 1 2 4 8 15 32 16 4 1

Reaction products Conver- М1 : М2 e sion, % , mol % 4 0:100 28 83:17 29 76:24 2 30:70 3 56:44 6 68:32 18 93:7 30 86:14 31 97:3 52 98:2 10 38:62 23 75:25 33 76:24 74 87:13 80 91:9 93 94:6 64 89:11 64 65 89:11 63 65 65 60 89:11 41 94:6 41 92:8 44 88:12

[η] f, dL g-1 0.04 0.08 0.07 0.08 0.12 0.12 0.32 0.37 0.45 0.60 0.07 0.12 0.15 0.20 0.31 0.52 0.21 0.23 0.26 0.27 0.20 0.15 0.17 0.29 0.37 0.42

Total co-monomers concentration. b APS concentration. c Reaction temperature. Reaction time. e According to NMR1H data. f In 1N NaCl aqueous solution at 300C.

Investigation of co-polymerization processes of various comonomers except scientific interest of reveling of particularities of comonomers behavior under copolymerization proposes possibility of combination of positive in practical aspect features of separate monomers revealing in corresponding homopolymers. From this point of view study of radical copolymerization of synthesized by us diallylguanidine acetates (DAGA) [1 – 3] with diallyldimethylammonium chloride (DADMAC) − well known cationogenic monomer was of great interest. This article devotes to investigation co-polymerization DADMAC and DAGA on high conversion for creation of new biocide materials. Kinetic studying is carried out on low conversion (less than 10%), that it doesn’t allow using this method for producing of such

Co-polymerization of Diallyldimethylammonium Chloride et al.

343

polymers. Investigation of co-polymerization to high conversion degrees can bring important results for practical purposes. Radical co-polymerization of DAGA and DADMAC under action of initiators ammonium persulfate (APS) and dinitrilazobis isobutyric acid (AIBN) was carried out in ampoules in vacuo in aqueous media ([M] = 4.0 – 4.3 mol L-1; initiators [APS], [AIBN] ∼ 4⋅10-2 – 4⋅10-3 mol L-1; 600C). The co-monomers reaction solutions with initiator was degassed (10-3 mm Hg) three time and then sealed and heated. Precipitated in acetone copolymers were separated on glassy filter, dried in vacuo and twice reprecipitated from methanol in diethyl ether. Co-polymer composition was determined on NMR1H data (spectra were measured in D2O, the signal of methyl group of acetate counter-ion DAGA was the reference signal [1 – 3]); intrinsic viscosity was measured on Ubelode-type viscosimeter in 1N NaCl aqueous solution at 300C. The wide set of copolymers of various composition in enough for further physicalchemical and biological investigations quantities was obtained as a result of carried out studies (table 1). Copolymerization was carried out up to high conversion degrees. However as investigations of isolated samples showed, transformation of co-monomers in co-polymers with good yield was observed under following conditions: DADMAC content is more than 70%, initiator concentration is 4⋅10-2 mol L-1 and reaction temperature is 600C (table 1, entries 14 – 23). Evidently, it is connected with degradative chain transfer on monomer that character for DAGA [4 – 5]: We can’t prepare DAGA homo-polymer with high intrinsic viscosity (table 1, entry 1). In all cases including those at small conversions q ≤ 5% the formation of copolymers enriched by DADMAC units in comparison with initial mixture of co-monomers is observed (Table 1) that conformed high reaction ability of DADMAC in chain propagation reactions. We should note that co-polymerization reaction was observed only in the presence of radical initiators and was completely inhibited under introduction of effective radical inhibitors. When radical co-polymerization conditions were changed we found following interesting appropriatenesses. By the decrease of initiator concentration (table 1, entries 14, 7, 8 and entries 7, 9 – 10 and 14 – 16) intrinsic viscosity of isolated co-polymers, that is expected result. However by the change of reaction time and the equal co-monomer ratios the conversion degrees change weakly but intrinsic viscosity have maximum (table 1, entries 17 – 23). Additionally by the increase of temperature with simultaneous decrease of time reaction (table 1, entries 24 – 26) co-polymers intrinsic viscosity increase, although usually temperature decrease during radical polymerization leads to increase of intrinsic viscosity. Probably this phenomenon connects with conformation changes of co-polymer molecules. Also we should note that the decrease of initiator concentration results in decrease of monomer in co-polymer conversion (table 1, entries 4 – 10 and 11 – 16). Thus, on the base of obtained data we may consider comparable reaction ability of considered co-monomers that allows developing the methods of direct synthesis of novel cationogenic polymer products with prescribed characteristics (structure, molecular mass, hydrophilic-hydrophobic balance) that may be changed in a large diapason with consideration of this factor. At the end we should note, that considerable bactericide activity of copolymers has been elucidated for a few compositions (table 2). The prepared copolymers demonstrate considerably greater biocide activity than both polyDADMAC and

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polyhexamethyleneguanidine containing guanidine in each link. It is probably connected with combined action: biocide function of guanidine-containing links and transport function of DADMAC segments of polycation. Table 2. Biocide activity of some copolymers Entry 1 2 a

Biocide b

Copolymer Copolymer c

E-coli 1.5⋅10-3 3.5⋅10-4

MSC, wt.% a St. aureus 4.0⋅10-3 4.5⋅10-4

Minimum suppressing concentration of biocide. b DADMAC:DAGA = 94:6, [η] = 0.52 dL g-1 (table 1, entry 16). c DADMAC:DAGA = 83:17, [η] = 0.08 dL g-1 (table 1, entry 2).

REFERENCES [1] [2]

[3] [4]

[5]

Zaikov G.E., Malkanduev Yu.A., Khashirova S.Yu., Esmurziev A.M., Martynenko A.I., Sivova L.I., Sivov N.A. // Russian Polymer News, 2003, V. 8, No. 4, p. 1. Zaikov G.E., Malkanduev Yu.A., Khashirova S.Yu., Esmurziev A.M., Martynenko A.I., Sivova L.I., Sivov N.A. // J. Environ. Protect. And Ecology, 2003, V. 4, No. 4, p.863. Zaikov G.E., Malkanduev Yu.A., Khashirova S.Yu., Esmurziev A.M., Martynenko A.I., Sivova L.I., Sivov N.A. // J.Appl.Pol.Sci., 2004, V.91, pp. 439. Khashirova S.Yu., Sivov N.A., Popova N.I., Kabanova E.Yu., Martynenko A.I., Malkanduev Yu.A., Topchiev D.A. // Izvestia VUZov, sev.-kavk. Region, ser. Estestv. Nauki, 2002, No. 4, p. 45. (in Russian) Zaikov G.E., Malkanduev Yu.A., Khashirova S.Yu., Esmurziev A.M., Martynenko A.I., Sivova L.I., Sivov N.A., in Biochemistry and Chemistry: Research and Developments, Nova Science Publishers, New York, 2003, p.39.

In: Modern Tendencies in Organic and Bioorganic Chemistry ISBN: 978-1-60456-295-8 Editors: A. Mikitaev, M. K. Ligidov, pp. 345-348 © 2008 Nova Science Publishers, Inc.

Chapter 29

THE APPROACH TO CALCULATION OF DIFFERENT CO-POLYMERS COMPOSITION BY NMR1H SPECTROSCOPY METHOD N. A. Sivova,*, M. Yu. Zaremskyb, A. N. Sivova, E. V. Chernikovab, D. N. Sivova, A. A. Zhansitovc, and O. A. Taovc a

A.V.Topchiev Institute of Petrochemical Synthesis, Russian Academy of Science, 29 Leninsky prosp., 119991 Moscow, Russian Federation b M.V. Lomonosov Moscow State University, Chemistry Faculty, Leninsky gory, 119899 Moscow, Russian Federation c Kh.M.Berbekov Kabardinian Balkarien University, 173 Chernyshevsky st., 360004 Nal’chik, Russian Federation

ABSTRACT The approach to determination of co-polymers composition by NMR1H spectroscopy data on examples of a number of co-polymers with different structure and chemical nature was proposed. The basis of method is the selection of signals or signal kits corresponding to appointed proton quantity of different structural elements of copolymer.

Keywords: co-polymers, homo-polymers, reactivity ratios, NMR1H spectroscopy

Investigation of co-polymerization processes allows determining basic regularities of preparation of new perspective high-molecular products that can combine of useful features revealing for corresponding homo-polymers.

*

e-mail: [email protected]; [email protected]

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One of the most important characteristic of co-monomers in radical co-polymerization processes is the reactivity ratios (RR). Their determination gives the opportunity to characterize co-monomers reaction ability. To determine RR it is necessary to know copolymers compositions that were obtained in co-polymerization reactions from systems with different co-monomers compositions. One of the most convenient and informative method for this purpose is NMR1H spectroscopy. In dependence on taken co-monomers pair it is important to select corresponding signals and / or signal kits that will be base to determine prepared co-polymers compositions. This selection connects with both co-polymers structure and lines position in NMR1H spectra of corresponding homo-polymers and solvent in which measuring of co-polymers spectra were carried out. We should note that determination of copolymers composition by NMR1H spectroscopy method is possible for samples that were obtained under polymerization both with low conversion and high conversion. In first case we investigate the samples that were obtained under kinetic measuring; these data are need for RR determination. In second case we investigate enlarged samples that were obtained for studying of different practical useful properties. In this case co-monomers distribution along polymer chain will differ for first and second samples, but total co-monomers composition will be determined precisely. In this article basic moments will be stated. These principal propositions were elaborated on example a number of co-polymerization systems. These appropriatenesses can be used for other numerous co-polymers under critical analysis and correct interpretation. As examples of co-polymers for determination of general regularities following copolymers were selected (Table 1; number in table 1 corresponds to number in list) 1. Poly (diallyldimethylammonium chloride)-co-polydiallylguanidine acetate (PDADMAC-co-PDAGA), 2. Poly (styrene)-co-polytertbutylacrylate (PSt-PBA), 3. Poly (sodium styrenesulfonate)-copolyacrylamide (PSSN-PAAm) 4. Poly (diallyldimethylammonium chloride)-copolyacrylate guanidines (PDADMACco-PAG), 5. Poly (diallyldimethylammonium chloride)-copolymethacrylate guanidines PDADMAC-co-PMAG), 6. Poly (diallyldimethylammonium chloride)-copolyvinylpirrolidone (PDADMAC-coPVP) The most simple cases among these systems are the first tree examples (systems 1 – 3): a) DAGA content in PDADMAC-co-PDAGA are calculated on protons of DAGA methyl group, b) styrene co-monomers content in PSt-PBA and PSSN-PAAm are calculated on aryl protons, c) other protons signals appear in upfield region; it is need to take into account protons (appearing in aliphatic protons region) quantity of each co-monomers under calculation of “one mole proton”. There are three ones for styrene co-monomers in both cases; there are twelve protons for tert-butylacrylate co-monomer and three for acrylamide co-monomer. In the cases of PDADMAC-co-PAG and PDADMAC-co-PMAG (systems 4 and 5) ten co-monomer DADMAC protons binding to carbon atoms neighboring nitrogen appear in downfield region. In upfield region six protons of this co-monomer and three protons of AG and five protons of MAG appears.

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Table 1. Structural formulas of co-polymers 1

( CH2

HC CH2

+

CH CH2 ) ( CH2

CH

CH CH2)

CH2

CH2

CH2 N

N Cl H3C CH3

C NH2

M1 ( CH2 CH) ( CH2

2

+

NH2 CH3COO

CH )

M2 ( CH2 CH) ( CH2

3

CONH2

COOC(CH3)3 M1 4 and 5

M2

M1

SO3-Na+

M2

R ( CH2

CH CH2 ) ( CH2

HC CH2

CH2

+

N Cl H3C CH3

( CH2

HC CH2

+

C)

AG: R = H MAG: R = CH3

COO +

(H2N)2C=NH2

M2

M1 6

CH )

CH CH2 ) ( CH2

CH)

CH2

N

O

N Cl H3C CH3 M1

M2

For all these cases it can be concluded simple formulas that allow calculating copolymers compositions; ones can know some details in our works [1 – 4]. The most complicated systems for analysis is 6th system for PDADMAC-co-PVP. Analysis of proton spectra of corresponding homo-polymers and co-polymers allows determining a number of spectrum areas in which different quantity of co-monomers protons appear (Table 2). If x is one proton of DADMAC and y is one proton of VP therefore we obtain following equations system (1 – 3): I1 = 4x +2y

(1)

I2 = 2x +4y

(2)

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Table 2. Data of NMR1H spectroscopy for calculation of mole shares of co-monomers DADMAC (M1) and VP (M2) in poly (diallyldimethylammonium chloride)copolyvinylpirrolidone Integral intensities

Spectrum area

I1 I2 I3

1.0 – 2.1 2.1 – 3.1 3.1 – 4.3

Quantity of co-monomers protons appearing in corresponding area For M2 For M1 4 2 2 4 10 3

I3 = 10x +3y

(3)

We obtain equations 4 and 5 for calculation of mole shares of co-monomers in copolymers if we solved this system: y = (I1 +I2) : 6 – x

(4)

x = [I3 – (I1 +I2) : 2] : 7

(5)

As a conclusion we should note that the approach to determination of co-polymers composition by NMR1H spectroscopy data on examples of a number of co-polymers with different structure and chemical nature was proposed with taking to account co-polymers structure and signals position in NMR1H spectra of corresponding homo-polymers.

REFERENCES [1] [2] [3] [4]

S.Yu. Khashirova // Dissertation of candidate of chemical sciences, Moscow: Russian chemical technological university (2002) (in Russian). A.M. Esmurziev // Dissertation of candidate of chemical sciences, Moscow: Institute of Petrochemical Synthesis of RAS (2004) (in Russian). N.A. Sivov, A.I. Martynenko, G.N. Bondarenko, M.P. Filatova, E.Yu. Kabanova, N.I. Popova, A.N. Sivov, E.B. Krut’ko // Petroleum Chemistry, 2006, V. 46, No 1, p. 41. N.A. Sivov, A.N. Sivov, Yu.A. Malkanduev, A.I. Martynenko, S.Yu. Khashirova, A.M. Esmurziev, A.A. Zhansitov, O.A. Taov // Izvestia VUZov, sev.-kavk. Region, ser. Estestv. Nauki, 2006, No. 4, p. 53. (in Russian).

In: Modern Tendencies in Organic and Bioorganic Chemistry ISBN: 978-1-60456-295-8 Editors: A. Mikitaev, M. K. Ligidov, pp. 349-352 © 2008 Nova Science Publishers, Inc.

Chapter 30

STRUCTURE PECULIARITIES OF GUANIDINE CONTAINING MONOMERS ON NMR SPECTROSCOPY DATA N. A. Sivov*, M. P. Filatova, A. N. Sivov, A. I. Rebrov, D. N. Sivov, and E. B. Pomakhina A. V. Topchiev Institute of Petrochemical Synthesis, Russian Academy of Science, 29 Leninsky prosp., 119991 Moscow, Russian Federation

ABSTRACT New acrylate and methacrylate monomer derivatives: (meth) acrylate guanidines, methacryloyl guanidine and it’s hydrochloride and also a number of model (meth) acrylate compounds (corresponding acids, salts and amides, methacryloyl chloride, methylmethacrylate, guanidine and it’s hydrochloride) were investigated by NMR spectroscopy method. Structure of synthesized monomers was determined, and dependence of spectral characteristics on structure of investigated compounds and used solvent was shown.

Keywords: NMR spectroscopy, (meth) acrylate guanidines, methacryloyl guanidines, methacryloyl guanidines hydrochloride, (meth) acrylic acids, (meth)acryl amides, guanidine hydrochloride, chemical shifts

The investigation of monomers structure is necessary for correct choice of pomerization system for concrete monomer. In this work NMR spectral characteristics were studied for a number of new guanidine containing monomer compounds, and also for a number of (meth) acrylic acids derivatives (scheme 1) and guanidine (G) and guanidine hydrochloride (GHC).

*

E-mail: [email protected]

N. A. Sivov, M. P. Filatova, A. N. Sivov et al.

350

Hb

O 1 C X 3 2 C C

Ha

H(CH3)

Õ=Í

X = O- H2+N C(NH2)2 (M)AG

(M)AA

Õ = NH2 (M)AAm

X = N C(NH2)2

MGU

Õ = Î Na (M)ANa

X = NH C NH2+ Cl- MGHC NH2

Scheme 1. 1

H NMR spectra of acrylic acid (AA), it’s amide (AAm) and sodium (ANa) and guanidine salt (AG) relate to ABC type; characteristics of signals are summarized in Table 1 Analysis of the character of AG signals and their chemical shifts (Table 1, entries 2, 3) and also their comparison with data on AA derivatives (Table 1, entries 1, 4 – 6) completely confirm the structure of synthesized monomer salt − acrylate guanidine. A number of spectral peculiarities of these compounds were revealed. In all cases 1H NMR spectra measured in DMSO-d6 have completely resolved type, i.e. the signal of each proton has 4 lines (the socalled doublets of doublets). The small upfield shift of the AG methylene proton (3C) signals relative to the AA signals is presumably due to the fact that GA in water preferably has the structure of the single-hydrogen-bond complex and/or the dimer (scheme 2), so that the deshielding effect of the carboxylic group is weakened only to an insignificant extent. The 2C proton signals in the spectrum of AG are shifted downfield relative to the AA signals; this is likely caused by variation in the GA conformation in a solution compared with AA, and 2C proton transfers from the positive region of C=O group anisotropy cone to the negative region. The spectra in D2O and DMSO-d6 indicate that the first bonding type (scheme 2) involving two hydrogen bonds is realized in less polar DMSO, because the signals of all protons have a significant upfield shift. This indicates weakening of the deshielding effect of the carboxylic group (Table 1, entries 2 and 3).

H2N

H

O

H2N C N +

C H

CR=CH2

O

Scheme 2. 1

H NMR spectra of methacrylic acid (MAA), methyl ether (MMA), chloroanhydride (MAC), amide (MAAm), sodium (MANa) and guanidine salt (MAG), methacryloyl guanidine (MGU) and it’s hydrochloride (MGHC) relate to АВХ3 type, characteristics of signals are summarized in Table 2. The analysis of character of MAG, MGU and MGHC signals and their chemical shifts (Table 2, entries 5 and 6, 9 and 10, 13) and also their comparison with the data on MAA derivatives (Table 2, entries 1 – 4, 7 and 8, 11 and 12) completely confirm the structure of synthesized monomers − methacrylate guanidine, amide derivative of guanidine and it’s hydrochloride. A number of spectral features of these compounds were revealed.

Structure Peculiarities of Guanidine Containing Monomers …

351

Table 1. NMR1H spectral characteristics of acrylate derivatives Entry

Compound

Chemical shift, δ, ppm 2 Hb H 6.36 6.11 6.27 6.41 5.79 5.96 6.06 6.19 6.25 6.24 6.06 6.19

Solvent 3

1 2 3 4 5 6

AA AG AG ANa AAm AAm

D 2О D 2О DMSO-d6 D 2О D 2О DMSO-d6

3

Ha 5.94 5.91 5.28 5.71 5.82 5.58

NH 7.74 7.03 / 7.49

We should note that signals were not completely resolved, i.e. there was degenerated АВХ3 type of spectra. It may be connected with the fact that protons of methyl and methylene groups interacted via 4 bonds (allyl interaction) and constants of spin-spin coupling had in this case (as well as for heminal protons HA and HB) low values (for the 4J magnitude about 3,0 – -0,5 Hz, and for Jhem for protons of СН2= group -3,0 – +2,0 Hz). The upfield shift of the MAG vinyl proton signals (Table 2, entries 5, 6 and 2, 3) as compared with MAA can be explained by the formation of delocalized system (scheme 2), leading to a decrease in the deshielding effect of the COOX group on these protons. This assumption is supported by an even larger upfield shift of the MAG vinyl proton signals measured in DMSO-d6 (Table 2, entries 6 and 3) as compared with that in D2O (Table 2, entries 5 and 2). The delocalization of negative charge over the carboxylate anion bonds in DMSO, which is less polar than D2O, becomes very significant (hydrogen bonding with the guanidine counterion is likely enhanced), and the chemical shifts of all signals (including CH3 groups) are close to those of CH2=C(CH3)R compounds, where R is an alkyl-type group. Analogous downfield shift is observed in row MAG – MGU – MGHC both in D2O and DMSO-d6 (Table 2, entries 5, 6, 9, 10, 13). Table 2. NMR1H spectral characteristics of methacrylate derivatives Entry 1 2 3 4 5 6 7 8 9 10 11 12 13

Compound MMA MAA MAA MAC MAG MAG MANa MANa MGU MGU MAAm MAAm MGHC

Solvent DMSO-d6 D2О DMSO-d6 DMSO-d6 D2О DMSO-d6 D2О DMSO-d6 D2О DMSO-d6 D2О DMSO-d6 DMSO-d6

CH3 1.88 2.10 1.83 1.77 2.05 1.76 1.91 1.73 2.08 1.81 2.11 1.82 1.91

3

Ha 5.67 5.90 5.56 5.52 5.50 5.04 5.37 5.04 5.62 5.25 5.69 5.32 5.87

Chemical shift, δ, ppm 3 Hb NH 6.02 3.68 (осн3) 6.31 5.96 12.31 (соон) 5.91 5.82 5.59 7.79 5.69 5.54 6.02 5.92 6.78 / 7.66 5.98 5.69 7.02 / 7.43 6.37 8.65 / 8.79 / 11.81

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352

Table 3. NMR1H spectral characteristics of methacrylate derivatives Entry 1 2 3 4 5 6

Compound G GHC MAG MAG MAAm MGHC

СН3

=CH2

=C(CH3)

Guan1

Guan2

СOХ

Amide1

Amide2

19.95 19.20 18.66 17.88

117.65 120.05 119.65 126.02

144.30 144.44 139.81 137.47

158.43 158.20 158.98 155.57

162.87 -

172.49 -

169.54 168.41

178.00 -

O guan2 H amide2 C N C(NH2)2 C C H MGU CH3

O guan1 H amide1C NH C NH2+ ClC C NH2 H CH3 MGHC

Scheme 3.

It was occurred also that amide MGU and it’s hydrochloride salt MGHC have different structure of amido-guanidine part of molecule (Table 3 and Scheme 3). Such differences in structures of these compounds were confirmed by NMR13C spectroscopy data (Table 3). Guan 1 and amide 1 mean the features of amido-guanidine fragment of MGHC, and guan 2 and amide 2 mean the features of amido-guanidine fragment of MGU. At the end it is necessary to indicate the spectral features of protons bonded to nitrogen atoms, which signals appear when spectra were measured only in DMSO. For amides AAm, MAAm and MGU are non-equivalent and in spectra these signals appear as two close lines for all compounds although in the case of MGU (Scheme 3) these protons are amine ones (Table 1, entry 6, Table 2, entries 10, 12). Two analogous amine proton signals and one amide signal (with most downfield shift) are in MGHC spectrum (Table 2, entry 2). Whereas all protons in AG (Table 1, entry 3) and MAG (Table 2, entry 6) are equivalent as in guanidine (4.96 ppm) and in GHC (7.18 ppm), and these protons appear as one line.

In: Modern Tendencies in Organic and Bioorganic Chemistry ISBN: 978-1-60456-295-8 Editors: A. Mikitaev, M. K. Ligidov, pp. 353-360 © 2008 Nova Science Publishers, Inc.

Chapter 31

PECULIARITIES OF RADICAL POLYMERIZATION REACTIONS OF ACRYLATE- AND METHACRYLATE GUANIDINES N. A. Sivova,*, A. I. Martynenkoa, Yu. A. Malkanduevb,†, E. Yu. Kabanovaa, N. I. Popovaa, A. A. Zhansitovb, O. A. Taovb, and S. Yu. Khashirovab а

A.V.Topchiev Institute of Petrochemical Synthesis, Russian Academy of Science, 29 Leninsky prosp., 119991 Moscow, Russian Federation b Kh.M.Berbekov Kabardinian Balkarien University, 173 Chernyshevsky st., 360004 Nal’chik, Russian Federation

ABSTRACT The kinetic peculiarities of acrylate guanidine (AG) and methacrylate guanidine (MAG) radical polymerization were studied in aqueous solutions. It was revealed the homogeneity of reaction medium remain during polymerization not in all scale of monomer concentration but for following ranges: [AG] ≤ 1.30 mol l-1 and [MAG] ≤ 0.40 mol l-1 ([APS] = 5×10-3 mol l-1; pH ∼ 6.5; 600C). In more concentrated water solutions of considered monomers even at low conversions q ∼ 3 – 5% the turbidity of reaction medium is observed (without phase separation). In spite of this for these systems in all studied concentration range (0.20 – 2.50 mol l-1) orders of reactions with respect to monomer (1 for MAG and 1.5 for AG) and initiator (0.5 for both systems) concentration have the same values as for corresponding acrylic acids. The influence of reaction solution compositions on the change of polymerization initial rates was studied.

Keywords: acrylate- and methacrylate guanidines; radical polymerization; polymerization initial rates

* †

E-mail: [email protected] E-mail: [email protected]

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N. A. Sivov, A. I. Martynenko, Yu. A. Malkanduev et al.

Synthetic polyelectrolytes attract more and more attention of investigators recently as from theoretical, so from practical point of view. They play the important role in science, technique, medicine. At that we observe constant expansion of application fields of polymers of this class. This implies the growth of requirements to production of novel polyelectrolytes (PE), polymers and copolymers of given chemical and stereochemical structure and molecular mass that stimulates studies concerning structure, synthesis and mechanism of formation of various representatives of this class of polymer compounds. In this work kinetic aspects and mechanism of radical polymerization of new guanidine containing monomer salts acrylate- and methacrylate guanidines (AG and MAG) were investigated. The selection of acrylic monomers as initial systems for guanidine containing monomer preparation was made because of corresponding polymers practical value, guanidine compounds high biocide activity, initial substances availability and simplicity of synthesis that allowing to prepare corresponding guanidine containing monomer salts. Acrylate- and methacrylate guanidines (AG and MAG) were prepared with high yield (to 80%) by reaction of acrylic acids and guanidine according to method elaborated by authors of this article and described in work [1]. Kinetics of AG and MAG monomers polymerization was studied by dilatometry method in bidistillated water (pH ∼ 6.5, 600C) on low conversion degrees (< 5%) after preliminary degassing of reaction mixtures on vacuum equipment (10-3 millimeters of mercury). Ammonium persulfate (APS) was used as initiator. The degree of conversion of monomer into polymer was determined on the base of contraction values determined by densimetry method which for GA polymerization reaction in water was 10.8%, and for MAG – 7.0%. Intrinsic viscosities [η] of polymers were determined 1N solution of NaCl in water at 30°C. Relative viscosities ηrel of reaction solutions were determined at 30°C. Carried out kinetic investigations of radical polymerization of AG and MAG in water and organic mediums showed that polymerization processes of mentioned monomers were characterized by the number of specific particularities. In all organic solvents (methanol, ethanol, dioxane, initiator AIBN) AG and MAG polymerization is heterogeneous. The appearance of white flaky sediment in reaction volume of dilatometer beginning from the initial (practically from zero) conversion testifies to the last fact. By AG and MAG polymerization in water solutions the homogeneity (complete transparence of the solution) up to high conversions q ∼ 50 – 70% remains only in definite concentration interval of monomers which is equal for [AG] ≤ 1.30 mole l-1 and for [MAG] ≤ 0.40 mole l-1. In more concentrated water solutions of considered monomers even at low conversions q ∼ 3 – 5% the turbidity of reaction medium is observed (without phase separation). We proposed that the probable reason of found effect was formation in water solution in the course of AG and MAG polymerization of associative structures stabilized by hydrogen bonds and (or) hydrophobic interactions. Since as it is known [2] during the polymerization process of ionogenic monomers the influence of a number of factors (dissociation of monomers and macro radicals, specific and non-specific bonding of ions, electrostatic and hydrophobic interactions, etc.) on the state of polyelectrolytes chains in solution was possible it was naturally to expect the revealing of analogous effects also during the propagation of PAG and PMAG chains. But in polymerization of other inogenic monomers (in the case of acrylic and methacrylic acids in methanol and dioxane also) the homogeneity of reaction solutions remains to high conversion as a rule [3].

Peculiarities of Radical Polymerization Reactions …

355

lg V+5

It is important to note that synthesized polymers PAG and PMAG are insoluble and even don’t swell in any of investigated by us organic solvents − methanol, ethanol, dioxane, DMSO, DMFA. At the same time we established that when the values of synthesized polymers intrinsic viscosity were high enough − 2.5 dl g-1 for PMAG and 0.9 dl g-1 for PAG they were easily solved in water that indicated on their linearity. The data of element analysis and NMR1H spectroscopy of polymers confirmed that their structure corresponds to theoretical. As kinetic investigations showed micro-heterogeneity of process (i.e. appearance of opalescence) was observed by sight at the following monomers concentrations: [AG] > 1.3 mole l-1 and [MAG] > 0.4 mole l-1, at q ≤ 5%. At that nevertheless as at conditions of complete homogeneity of system under AG polymerization, so at micro-heterogeneity under AG and MAG polymerization the half order of reaction by initiator (APS) concentration is maintained, as it is obvious from (Figure 1). Investigation of kinetic orders of considered polymerization reactions by monomer showed that with the increase of initial AG and MAG concentrations the initial polymerization rate was increased sharply and non-linearly and reaction was characterized by exceeding the first variable order by monomer (Figures 2 and 3). As it is obvious from Figures 2 and 3 the dependence of intrinsic viscosity of resulted PAG and PMAG polymers is symbatic to the change of polymerization rate for both polymerization systems. It is known that observing in radical polymerization processes change of chains bimolecular termination rate constant kt (reaction is controlled by diffusion) is often connected with the change of reaction solution viscosity [4, 5] which is naturally increased by the accumulation of reaction product in system − polymer. And then the contribution of viscosity factor is significant and that is why the reduction of rate constant of chains bimolecular termination kt is observed first of all. However, for a number of monomers it is necessary to consider the factor of influence of initial reaction solution viscosity on polymerization parameters. 3

3

2,5 2 1,5

2

1 1

0,5 lg[I] +3

0 0,4

0,6

0,8

1

1,2

Figure 1. The dependence of AG and MAG polymerization initial rate on concentration of initiator APS; 1 − [MAG] = 1.0 mole⋅l-1; 2 − [AG] = 1.0 mole⋅l-1; 3 − [AG] = 1.5 mole⋅l-1; H2O; 60°C.

N. A. Sivov, A. I. Martynenko, Yu. A. Malkanduev et al.

356

Vp 104 mole l-1

[η] dl g-1

18

1

16

0,9 0,8

14

0,7

12

0,6 10 0,5 8 0,4 6

0,3

2

4

0,2

1

2

0,1

-1

[M] моль л 0 0,25

0 0,75

1

1,25

1,5

2

Figure 2. The dependence of AG polymerization initial rate (curve 1) ([APS] = 5×10-3 mole l-1; 60°С) and intrinsic viscosity of resulted polymers (curve 2) (1N NaCl solution in H2O; 30°C) on monomer concentration.

1

2

Figure 3. The dependence of MAG polymerization initial rate (curve 1) ([APS] = 5×10-3 mole l-1; 60°С) and intrinsic viscosity of resulted polymers (curve 2) (1N NaCl solution in H2O; 30°C) on monomer concentration.

Peculiarities of Radical Polymerization Reactions … 14

357 3,5

ηrel

Vр×104 mole l-1 sec-

12 3

1 2

10

2,5

8

6

2

4 1,5 2 [M] mole l

0 0

1

2

3

4

-1

1 5

Figure 4. The dependence of AG polymerization initial rate (curve 1) ([APS] = 5×10-3 mole l-1; 60°С) and relative viscosity of initial AG solutions (curve 2) (1% hydroquinone; 30°C) on monomer concentration in water solutions.

For revealing of reasons causing the found non-linear dependence of Vp on [M] in our case it was interesting to clear up the character of dependence of macroscopic viscosity of initial solutions of investigated monomers on their concentration (Figures 4, 5). It is obvious from Figures 4 and 5 that for mentioned monomer salts AG and MAG the non-linear increase of relative viscosity (ηrel.) is naturally observed with the rise of monomer concentration in initial reaction solution. (As it was already mentioned the solution remained transparent.) Thus, there is definite correlation in the character of polymerization initial rate change and values of ηrel.. The obtained data (namely the non-linearity of change of Vp on [M]) may be explained by the fact that due to comparatively high values of ηrel. of initial solutions of monomer salts (at [M] > 1 mole⋅l-1) the constant of chains bimolecular termination rate kt even at conditions of very small conversions is turned to be sensitive to the viscosity of initial reaction solutions and consequently to monomer concentration. Mentioned change of values of relative viscosity with the rise of initial monomer concentration should lead to symbatic reduction of constant kt and thus to mentioned non-linear increase of polymerization initial rate. The suggested explanation may be checked experimentally. If we assume that in the studied system the constant kt is naturally depended on monomer solution viscosity then in accordance with North's conceptions [4, 5] we should take that kо ∼ η-1. Then polymerization rate may be calculated by equation 1

N. A. Sivov, A. I. Martynenko, Yu. A. Malkanduev et al.

358 60

4

5

Vр х10 -1

mole l ·sec

-1

1

50

3,5

2

40

3

30

2,5

20

2

10

1,5 -1

[M] mole l

0 0

1

2

3

1 4

Figure 5. The dependence of MAG polymerization initial rate (curve 1) ([APS] = 5×10-3 mole l-1; 60°С) and relative viscosity of initial MAG solutions (curve 2) (1% hydroquinone; 30°C) on monomer concentration in water solutions.

V = kр × Vин 1/2 × ηотн1/2 × [М]

(1)

It turned out that these non-linear dependences are straighten (Figures 6 and 7) in coordinates lgV / lg{[M] ηrel1/2 }. The fact of good straighten of experimental curves in coordinates of given equation tells us about correctness of assuming that under determination of reaction order by monomer in given systems it is necessary to consider the viscosity factor. Then obviously considering this factor the studied reaction of polymerization is characterized by the first order by monomer in the whole investigated interval of MAG monomer concentration (Figure 6), in spite of observing micro-heterogeneity for given system. In the case of AG polymerization (Figure 7) even with correct for "viscosity" factor reaction order by monomer concentration is more than one and is equal to ≈ 1,5. For polymerization systems considered by us the deviation from single reaction order by monomer for AG as we think connected with specific influence of reaction medium on reactivity of monomer and propagation radical in polymerization processes. On the base of said above we suppose that presented formulation of polymerization rate with consideration of viscosity effect (equation 1) allows satisfactorily describing of initial stage of AG and MAG polymerization reaction at studied conditions.

Peculiarities of Radical Polymerization Reactions …

359

2

lgV+5

1,5

tg ≈ 1.0 1

lg([M]•η1/2)+1 0,5 0,5

1

1,5

2

Figure 6. The dependence of lgV on lg{[M]⋅η1/2} under MAG polymerization in water solutions, [APS] = 5⋅10-3 mole l-1; 60°C.

2,5

lgV+5

2 1,5

tgα ≈ 1,5

1 0,5

1/2

lg([M]•η )+1

0,5

1

1,5

2

Figure 7. The dependence of lgV on lg{[M]⋅η1/2} under AG polymerization in water solutions, [APS] = 5⋅10-3 mole l-1; 60°C.

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N. A. Sivov, A. I. Martynenko, Yu. A. Malkanduev et al.

ACKNOWLEDGEMENTS This work was carried out under partial financial supporting of RAS, Division of chemistry and sciences on materials, project No DCSM-04.

REFERENCES [1] [2] [3] [4] [5]

N.A. Sivov, A.I. Martynenko, E.Yu. Kabanova, N.I. Popova, S.Yu. Khashirova, A.M. Esmurziev, Petroleum Chemistry, V. 44, No.1, 43 (2004). V.A. Kabanov, D.A. Topchiev, Polymerization of ionized monomers, Moscow: Nauka (1975) (in Russian). D.A. Topchiev, Dissertation of doctor of chemical sciences, Moscow: Institute of Petrochemical Synthesis of RAS (1973) (in Russian). North A.M. Reed G.A. // J. Polym. Sci. A. 1963, V.1, P. 1311. North A.M. // Chemistry and Industry, 1968, P. 1295.

In: Modern Tendencies in Organic and Bioorganic Chemistry ISBN: 978-1-60456-295-8 Editors: A. Mikitaev, M. K. Ligidov, pp. 361-365 © 2008 Nova Science Publishers, Inc.

Chapter 32

THE STRATEGY OF IONIZING MONOMERS SYNTHESIS AND INVESTIGATION OF THEIR RADICAL POLYMERIZATION FOR PREPARATION OF NEW POLYELECTROLYTES WITH USEFUL PROPERTIES N. A. Sivov* A. V. Topchiev Institute of Petrochemical Synthesis, Russian Academy of Science, 29 Leninsky prosp., 119991 Moscow, Russian Federation

ABSTRACT The strategy of new ionizing monomers and polymers and also the approaches to the synthesis of new generation perspective monomers of different structures are gave in account in this article.

Keywords: polyelectrolytes, diallylguanidine (tryfluoro)acetates, diallyl(methyl)ammonium tryfluoroacetates, (meth)acrylate guanidines, guanidine containing (co) polymers, (meth)acryloyl guanidines

Synthetic polyelectrolytes (PEs) play a very important role in science, technique and medicine at present. At the same time constant broadening of these polymers application spheres is observed. As a consequence we observe the growth of requirements for creation of novel polyelectrolytes − polymers and copolymers of prescribed chemical and stereochemical structure and molecular mass. This fact stimulates investigations of synthesis and formation mechanism of this class of polymer compounds. It is also obvious that the most simple and convenient methods of PEs preparation are the reactions of ionizing monomers radical polymerization and copolymerization. *

E-mail: [email protected]

N. A. Sivov

362

The strategy of new ionizing monomers synthesis and new PEs preparation is very simple because of the clear aim – PEs with determined properties. Therefore the strategy includes itself some important points: -

the introducing of polymerazable fragment in the structure of created substance; the presence or the introducing of ionogenic group in the structure of created monomer if the purpose is PEs preparation.

It is necessary for imparting of special properties to new polymers: -

the presence of groups responsible for these properties or the presence of groups that have ability to modification for introduction mentioned above groups, the modification can be carried out both on stage of monomer synthesis and on prepared polymer (last aspect is very important circumstance in native PEs modification).

After synthesis of monomers responsible for these demands it is necessary to carry out -

-

the investigation of general peculiarities of polymerization, co-polymerization and modification, and also the study of composition and structure, physical chemical and applied properties of synthesized substances for search of optimal conditions to create novel polymer systems with practical useful properties; the adaptation of laboratory methods of polymer products preparation to possible industrial use

In last years in the Laboratory of chemistry of polyelectrolytes and surface active polymers, Institute of Petrochemical Synthesis RAS the works on synthesis and modification of ionogenic polymers of different structure that prepared in Laboratory. Simultaneously both general peculiarities of its preparation are investigated and search of synthesized substances use are carried out taking into account possible useful properties. So, considerable successes in that direction were achieved in last years [for example, 1 – 3]: it were synthesized new diallyl and acrylic monomers: diallylguanidine acetates (DAGA) and tryfluoroacetates (DAGTFA), diallylammonium- (DAATFA) and diallylmethylammonium tryfluoroacetates (DAMATFA), acrylate- (AG), methacrylate guanidines (MAG); it were determined their composition and structure. And it were carried out -

-

the investigations of quantitative physical chemical appropriatenesses of polyelectrolytes formation processes in water media; the studying of kinetic peculiarities (initial rates, orders of reaction on monomer and initiator, co-polymerization reactivity ratios) of homo-polymerization and copolymerization with diallyldimethylammonium chloride (DADMAC) in water media; simultaneously some interesting phenomena were revealed: spontaneous “upgrowing” of macromolecules of isolated polydiallylmethylamines in free base form; micro heterogeneity and appearance of multiform ion bonded intra-molecular structures in (co) polymerization AG and MAG with DADMAC;

The Strategy of Ionizing Monomers Synthesis and Investigation … -

363

also, simultaneously it was carried out search of possibilities for regulation of their composition, structure, chemical links distribution in macromolecules, molecular masses and properties.

From the point of view on biocide properties, for instance, we can mark several moments on the base of general strategy: -

charge of polymer chain and introducing of the groups responsible for biocide action; the most optimum their combination and the optimum molecular mass characteristics to achieve maximum high biocidity and minimum toxicity.

As a result from synthesized monomers corresponding homopolymers and co-polymers with DADMAC were prepared and their high biocide and fungicide activity were shown. Many modern biocide preparations both rather effective ones and harmful ones for people, plants and animals because toxic compounds of copper, cadmium, tin, lead, arsenic, chlorine. Biocide preparations of home production polyhexamethyleneguanidine hydrochloride (PGMG, it was elaborated in our laboratory more than 20 year ago) less toxic compared with these compounds. New biocide preparations on the base of AG and MAG, synthesized in laboratory possess higher biocidity and less toxicity compared with PGMG. Comparison novel (co) polymers with PGMG derivatives gives follow line on minimum suppression concentration (MSC) from 10-1 (left) to 10-4 (right) wt.%: DADMAC < PAG, PMAG < PGMG < PDADMAC-co-P(M)AG < PDADMAC-co-PDAGA, PDA(M)ATFA Toxicity of synthesized compounds decreases (from left to right) in follow line: PDA(M)ATFA < DADMAC, PGMG, PDADMAC-co-PDAGA < PDADMAC-co-P(M)AG < PAG, PMAG Another example of imparting of necessary biological properties is the introducing of antioxidant substituent groups in native polyelectrolyte chitozan. As a result of investigation carried out in Laboratory new water soluble macromolecule systems on the base of chitozan, and and its quaternized derivative and antioxidant of plant origin were synthesized. The carried out investigations elucidated a number of appropriatenesses of these systems formation and behavior and allowed to develop the approaches to selection of bioactive substances for purposeful synthesis of effective antioxidants and antimutagenes and for their composition optimization. Leaned on the previous laboratory works experience of last several years and on the developed strategy of monomer synthesis, we have begun the investigations of perspective objects – novel derivatives of acrylic acids – (meth) acryloylguanidines, containing covalently combined guanidine groups of different structure. We note as we demonstrated earlier in comparison of PDADMAC-co-PDAGA and PDADMAC-co-P(M)AG biocide properties that covalently combined guanidine groups impart higher biocide activity to first co-polymers.

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Also (meth) acryloylguanidines have groups which give the possibility to change the structure within wide limits both for monomer itself and for polymer thereof. There were investigated following methods of (meth) acryloylguanidines synthesis: from corresponding chloroanhydrides, from methyl(meth) acrylates, from corresponding acids (two approach). The most perspective methods are the first two ones as it shows the data obtained to present moment. In the near future we propose to carry out the investigation on following directions, connecting with monomers synthesis, polymerization, modification, and revealing the possibilities of prepared systems use. 1. Methods elaboration of new monomer synthesis and modification. 2. Studying of polymerization and co-polymerization peculiarities with use of different systems including the pseudo-living radical polymerization technique, for example, reversible addition-fragmentation chain transfer polymerization (RAFT) to regulate different parameters of obtained polymers such as, for instance, structure, molecular mass, molecular-mass distribution. RAFT agents were synthesized and investigation of this polymerization system was begun. 3. Investigation of medium influence on radical polymerization of cationogenic monomers. 4. Investigation of formation mechanism of polymer networks and gels. 5. Studying physical chemical and applied properties of synthesized substances for preparation polymers with necessary characteristics. 6. Modification of (meth) acryloylguanidines and polyguanidines for imparting additional properties. 7. Synthesis of di(meth)acryloylguanidines (in the case of symmetric ones – new crosslinking agents). 8. Synthesis of non-symmetric di”vinyl”guanidines with unsaturated groups that can polymerize under different condition. 9. Preparation of graft-co-polymers from non-symmetric di”vinyl”guanidines. 10. Preparation of graft-co-polymers from poly(meth)acryloylguanidines after their modification (obtaining of macro-monomers) followed by co-polymerization of macro-monomers. 11. Creation on the base of graft-co-polymers of biocide gels for purifying and disinfection of water and other nutritive liquids (these gels as a variant of toxicity problem solution). 12. Creation of the system to prepare similar gels by polymerization of the mixture of mono- and di-substituted guanidines, synthesized in one synthesis simultaneously. 13. Creation of cross-linked polymers with molecular imprinting for separation and concentrating of organic compounds, for analysis of different liquids, for instance, of native origin. 14. Use of these novel guanidine containing polymers as carriers of biological objects and medicinal substances. 15. Imparting of biocide properties to different objects (for example, surfaces, membranes, paintings, etc.). 16. Elaboration schemes close up to technological ones (as an example we can call synthesis of PDADMAC-co-PMAG.

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REFERENCES [1] [2]

[3]

N.A. Sivov, A.I. Martynenko, E.Yu. Kabanova, N.I. Popova, S.Yu. Khashirova, A.M. Esmurziev, Petroleum Chemistry, 2004, V. 44, No.1, 43. N. A. Sivov, A. I. Martynenko, G. N. Bondarenko, M. P. Filatova,E. Yu. Kabanova, N. I. Popova, A. N. Sivov, and E. B. Krut’ko, Petroleum Chemistry, 2006, Vol. 46, No. 1, pp. 41. N.A.Sivov “Biocide Guanidine containing Polymers: Synthesis, Structure and Properties”, 2006, Brill Academic Publishers and VSP, Leiden Boston, 152 p.

In: Modern Tendencies in Organic and Bioorganic Chemistry ISBN: 978-1-60456-295-8 Editors: A. Mikitaev, M. K. Ligidov, pp. 367-377 © 2008 Nova Science Publishers, Inc.

Chapter 33

EFFECT OF VIBRATION ON STRUCTURE AND PROPERTIES OF POLYMERIC MEMBRANES V. N. Fomin1, A. P. Bobylev2, E. B. Malyukova3, V. V. Smolyaninov4, I. A. Arutyunov5 and N. A. Bulychev5,6 1

Nonlinear Wave Mechanics and Technology Centre of Russian Academy of Sciences, Bardina str., 4, 119991, Moscow, Russia 2 A.A. Blagonravov Mechanical Engineering Research Institute of Russian Academy of Sciences, 4 Bardina str., 119991, Moscow, Russia 3 A.N.Kosygin Moscow State Textile University, 1 M. Kaluzhskaya str., 119071, Moscow, Russia 4 M.V.Lomonosov Moscow State University, 1 Leninskie gory, 119992, Moscow, Russia 5 Lomonosov Moscow State Academy of Fine Chemical Technology, 86. Vernadskogo pr., 119451, Moscow, Russia 6 University of Stuttgart, Institute for Polymer Chemistry, Pfaffenwaldring 55, 70569, Stuttgart, Germany

ABSTRACT The effect of structural memory in a wave field has been exsemplarily studied by the IR-spectroscopy method on films made from mixtures of butadiene-styrene and acrylic latex as models of polymeric membranes. The strengthening of the interphase interaction in heterophase systems that can cause change of their local and transmitting mobility has been observed. It has been shown, that the response of polymeric dispersed systems and compositions on influence of nonlinear vibrations proves their influence on deformation properties, like orientation phenomena in solid polymers (where Rebinder’s effect can take place) that it is possible to consider as a way of polymer modifications, including the obtaining of nanicomposites, polymeric biocarriers, etc.

Keywords: vibrowave treatment, heterophase latex systems,, membran systems, relaxation phenomena, IR-spectroskopy, nanocomposites

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INTRODUCTION Aqueous dispersed systems like latexes have been being widely applied as polymeric composite materials in technics, construction and various branches of industry. Specific features of properties of such systems cause their great value for biology and medicine, too. Among other applications, latex systems are being used as composite materials in chemical, pharmaceutical, food-processing industry, in medicine, including their application as various membranes (dividing and ionic) and also as the modelling systems, allowing to study exchange processes in alive organisms, microbiology, biochemistry, etc. Biomaterials of type “artificial skin” in which latex are components of the composite materials which are carrying out functions of a skeleton for biocarriers, are also of great interest. Membran systems are known to play an important role in functioning biological objects (in mass transfer processes, passive and active transport of substance, regulation of an endocellular metabolism, in bio-energetics, etc.). Unique properties of biomembranes are caused by their structure, in particular, presence of bimolecular focused layers of lipids. At the same time, one of the main disadvantages of modelling lipid membran systems (monolayers, flat bilayers, liposomes), is their low stability in time and to action of external factors. Polymeric focused membranes have an enhanced stability as well as structural and functional similarity with lipid membranes. High-organized polymeric systems with small sizes (micelles, vesicules, mono- and polylayers), and also polymeric dispersions are important for modelling various functions of biomembranes and are perspective as materials and functional elements for biotechnology, medicine etc. Their substantial sensitivity to external influences is due to the microheterogeneity of such multiphase and multicomponent systems. Therefore, the study of dynamic behaviour of latex systems under generation of nonlinear vibrations in a sound range of frequencies attracts a geat deal of interest. It is essential, that the use of latexes in these conditions is aimed to study of wave influence on multiphase systems at different structural levels. Consideration of structural-morphological features of polymers, local and transmitting mobility of the kinetic units describing relaxation spectrum of a system, interphase interaction and the state of an interphase surface can be a basis for elucidation of the mechanism of influence of nonlinear vibrations on mass transfer processes in multiphase and multicomponent systems, and also interrelation of relaxation and resonant absorption of energy. It is necessary to note, that the study of wave influence on latexes as biomedical objects can promote the obtaining the additional information about the relationship of the oscillatory phenomena with biochemical and biophysical processes [1].

EXPERIMENTAL PART Materials Mixtures of butadiene-styrene latex DL-940 (styrene content 65%) and acrylic AK-525B, as well as butadiene-styrene latex CKC-65 and acrylic AK-252B.

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Techniques The influence of vibrowave treatment on the film properties obtained from latex mixtures has been studied as described elsewhere [2]. IR examination of latex films has been carried out by using PE 1600 FTIR instrument in the field of 400-4000 cm-1. For vibrowave treatment, the vibrowave shaker EDVK-250 was applied.

RESULTS AND DISCUSSION The study of influence of vibrating treatment on dynamic behaviour of multiphase systems allowed to establish that the intensification of heat and mass transfer under the generation of nonlinear vibrations in polymeric dispersions can be accompanied by the relaxation phenomena (such as vibrorelaxation, vibroflowing, vibrotixotropy) [1,3]. Considering the crucial role of relaxation processes in behaviour of real polymeric materials, it is necessary to emphasize that the sensitivity of relaxation characteristics to structural inhomogeneties and to transformations under external influences that is most pronounced in such heterogeneous systems as polymeric mixtures and polymeric composite materials [4-6]. Features of a structure of macromolecules and supramolecular formations, causing variety of forms of molecular mobility in polymers, lead to a number of relaxation processes; all of them are related to a heat movement of kinetic units of the certain kind and can be described by a spectrum of times of a relaxation. Therefore, spectral representations have been used by consideration of structural changes under influence of vibrating influence on polymers and polymeric composite materials. In this work, the film properties made from mixtures of latex based on hard-chain and elastic copolymers, undergone by vibrowave treatment have been considered. Process of a film formation in this case is known to start with the evaporation of the dispersion media (water) and finishes with transformation of a dispersion into a coating. The period between the change of the film sizes during the coating formation and achievement of an equilibrium condition is governed by relaxation processes [7]. Relaxation phenomena arise already during the moment of a film drawing on a substrate when a shift pressure appears and possibilities for the cohesion break of an interface between the film and the substrate are created. During the drying, the coating should relax, forming a thin and smooth layer, thus the module of elasticity increases. Thus, the mechanical relaxation promotes decrease of the probability of fragile destruction and exfoliation of the film from the substrate [7]. Processes of mechanical and dielectrical relaxation as well as structural-morphological self-organization in these systems under vibrowave treatment have been already described in our previous work [8]. In the presented work the major attention is paid to an estimation of elastic-strenght properties of latex films and their IR-spectra. Figures 1 and 2 illustrate the dependence of physicomechanical properties of films on their composition, and also change of these dependences at simple mechanical influence (stirring of a latex by means of a mechanical stirrer) and under vibrowave treatment.

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1000 800

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Mixture composition (DL-940/АК-252B), %

Figure 1. Dependence of the break stress and relative elongation at the moment of a film break on the mixture composition DL-940/АК-252 B.

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Figure 2. Dependence of the break stress and relative elongation at the moment of a film break on the mixture composition СКС-65/АК-252 B.

Preliminary tests on search of optimum conditions of vibrowave stirring for obtaining mixtures with improved physicomechanical properties have shown that from three varied factors (ratio of latexes in a mixture, frequency and time of vibrowave treatment) crucial factor is a composition of mixtures.

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Changes of time of the treatment and frequency in the considered limits (5-10 min. and 50-150 Hz, respectively) lead to less prononced effects (the confidential interval is ±10 %). On the basis of the results gained, optimal compositions of latex mixtures and conditions of vibrowave stirring (ratio of latexes poly(butadiene-styrene):poly(butadieneacrylate) = 75:25 vol., duration of vibrowave stirring - 7,5 min., frequency-150 Hz) have been chosen. Curves structure vs. physicomechanical property (break stress and relative elongation at the moment of break) for films made from latex treated by nonlinear vibrations demonstrate a deviation from the additive dependence in the form of an extremum which corresponds to mixtures with the dominating content of relatively more hard-chain polymer, which relaxation characteristics cause its greater sensitivity to vibrowave treatment (Figure 1, 2). Composition dependences have parameters of the module at 200% stretching received from ratios σ-ε have similar character (Figure 3). IR-spectra of samples demonstrate characteristic tendencies for multiphase systems in the presence of interphase interactions (Figure 4). Intensive bands of valent vibrations are observed for νСН benzene rings in the region 3000-3100 cm-1, methyl and methylene groups in the region 2848-2954 cm-1, a band of deformation vibrations of these groups in the region 1380-1491 cm-1, intensive bands of vibrations of benzene rings in the region 1500-1640 cm-1 [9-11]. Location and intensity of these bands vary slightly for different frequencies and times of stirring. In the region 760-670 cm-1, there are bands which concern to pendular vibrations of methylene groups (-CH2-); their presence in spectra of polymers in the solid state is caused by the interaction between the next molecules. Location and the form of these bands depend also on connection of various functional groups to a chain. For the sample treated by mechanical stirring, these bands are very intensive and narrow.

14

М200%

12 1

10 8 6 4 2

2

0 100

80

60

40

20

0

Mixture composition (DL-940/АК-252B), % Figure 3. Dependence of the module at 200% elongation on the mixture composition DL-940/АК-252 B.

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1

2

3

1 4

5

6

Figure 4. IR-spectra of latex films. 1 – without vibrowave treatment 2 – treatment for 5 min., 50 Hz. 3 – treatment for 10 min., 50 Hz. 4 – treatment for 5 min., 100 Hz. 5 – treatment for 7,5 min., 100 Hz. 6 – treatment for 10 min., 100 Hz.

In the samples received after vibrowave stirring, these bands dilate. This dilation is more pronounced at a frequency of vibrowave stirring of 100 Hz. The dilation increases with the increase of the time of wave treatment. The increase of the time and frequency of stirring leads to decrease of intensity of bands at 700 cm-1 and 759 cm-1 and to occurrence of a band at 670 cm-1 which intensity becomes close to intensity of bands at 700 cm-1 and 759 cm-1 at frequency 100 Hz and time of stirring 10 min.

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Dilation of bands under the wave influence has also been observed for the region 10001300 cm-1 where there are bands of skeletal vibrations of chains -C-C-C- and CH2- and CH3groups, as well as vibrations of aromatic systems. Interesting feature of the studied spectra is a decrease of the intensity of bands at 910 cm-1, 967 cm-1, 1640 cm-1, 1660 cm-1 and occurrence after vibrating influence of bands at 3440 cm-1 and 3238 cm-1, which intensity increases with increase of time and frequency of treatment. These bands belong to vibrations of O-H bond in water and hydroxylic compounds. Interpretating the character of the dependence of elastic-strength properties of polymeric compositions on structure, two factors can be taken into consideration at least. Taking into account a defining role of a continuous phase in the formation of properties of a mixture, Sshaped structure-property curve is based on the phase inversion [12]. It is also noted, that relative elongation at a break and a limit of fluidity better characterize the nature of a continuous phase, than relative strength at the stretching. At the same time, the deviation of the curve “break stress – composition” from additivity (nonmonotonic dependence) – relative strength under the stretching – can be considered as a proof of strengthening of interaction in an interphase layer in mixtures of polymers under the influence of nonlinear vibrations. It is quite characteristic, that the effect of nonmonotonic dependence is more pronounced as an extremum in compositions with the preferential content of more hard-chain polymer, which relaxation characteristics cause its greater sensitivity to vibrowave influence (Figure 1,2). Considering an increase of shift deformations under the influence of vibrations, it is possible to believe that vibrating influence in this case leads to the effect similar to that under plastification on rollers, where there are conditions for orientation of structural formations of a filler and polymer and strengthening of their interaction in an interphase layer. Similar effects have been noted earlier in solid mixturing of hard-chain crystallizing flourinecontaining copolymers with flourine rubber [13]. It is obvious, that correlation of anisotropy of structure and physicomechanical parameters of properties is most pronouced in the presence of anisodiametric morphological formations. Comparison of physicomechanical properties of films obtained from latex treated by vibrowave action and in solid-phase mixturing of the same polymers, where defining criteria are stress and deformations of a shift, allows to prove the efficiency of vibrowave influence. The wave effects concerning the organization of a controlled tubulization in a resonance regime in multiphase systems, three-dimensional current and deagglomeration of associates, lead to obtaining dispersions with narrower particle size distribution and, consequently, more homogeneous films with an increased level of physicomechanical properties. Strengthening of interphase interaction under the influence of so-called vibrating force can be explained by the occurrence of additional chemical bonds. In the case of polymers containing nonsaturated bonds, excitation of nonlinear vibrations can lead to the crossinking of polymeric chains with non-saturated bonds, that can be confirmed by the data about the decrease of swelling velocity (Figure 5).

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swelling, %

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Figure 5. Swelling of latex films in cyclohexanone.

Reduction of the vapor transmittance of latex films as a result of vibrowave influences on the latex, measured by diffusion method, also confirms the change of a film structure under the influence of nonlinear vibrations [8]. It is necessary to emphasize, that the influence of vibrowave treatment observed already at a stage of synthesis of polymers [14] is efficient at the subsequent stages of formation of a complex of properties of polymeric composite materials. Relaxation processes in latex systems are in the interplay with the regulation of process of a film formation when it is necessary to create high gradient of velocity in the dispersed systems. In this process, three stages of process of a film formation are known to be determined: concentrating of suspensions and transition of low-viscosity mobile system in capillary structure, transformation of capillary structure into a film in which local contacts between particles convert in continuous, dense contact (driving force of particle coalescence can be an interphase tension on border polymer-water, and also force of capillary pressure); and, finally, the third stage (having the greatest value for maintenance of film continuesity and its high physicomechanical properties) where processes of mutual diffusion take place, as well as adhesive interaction and formation of hydrogen or chemical bonds between particles (physical and chemical crosslinking) [15]. As it has been pointed out, IR-spectra of samples look very characteristic for multiphase systems in the presence of interphase interactions. Change of positions and contours of bands after vibrating influence in a resonant regime, including the decrease in intensity of bands at 910 cm-1, 967 cm-1, 1640 cm-1, 1660 cm-1 and occurrence of bands at 3440 cm-1 and 3238 cm1 after vibrating influence can reveal the strengthening of interphase interaction with formation of cross-bonds in butadiene blocks and occurrence of hydrogen bonds in interphase space. By IR-spectroscopic studies of latex films of acrylic copolymers, it has been shown that at the formation of latex films, an intensive interphase interaction and formation of intermolecular hydrogen bonds can appear that leads to the change of morphological structures of latex particles and to the increase of their strength properties.

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The explanation of observed effects of modifying influence of vibrowave treatment on multiphase systems which is carried out by the direct excitation of nonlinear vibrations in a resonant regime and is observed further at the formation of properties of films and other compositions based on the dispersions, undergone by the vibrowave treatment, it is possible to explain by the occurance of the factor of "memory" as an element of hereditary mechanics [16-18]. The carrier of such a "memory" is the structural-morphological organization of the examined multiphase systems, and the influence of wave action in a sound range of frequencies is observed at different levels of the structural organization.

CONCLUSION Thus, the discovered features of physicomechanical properties of latex systems in a wide range of component ratios, and their IR-spectra show the strengthening of interphase interaction in compositions under the influence of vibrowave treatment in a resonant regime in a sound range of frequencies. Alongside with the data describing the dynamic behaviour of investigated systems, which were obtained by means of various structurally-sensitive methods [19], the revealed effects (change of dispersity, structural-morphological organization, local and translation mobility) can be considered as a proof of the suggested mechanism of wave influence on the dispersed polymeric systems, leading to an intensification of mass-transfer processes, and also can be used for studying the interrelation of relaxation and resonant absorption of energy [20]. To sum up it is necessary to note, that latex systems considered in the presented work as well as water-soluble physiologically active polymers and microparticles (type of liposomes) [21], other polymeric dispersions (for example, monodispersed latex for immunological studies, diagnostics etc., as binders and polymeric carriers of bioobjects [22] represent doubtless interest for a farmaceutical industry, medicine, etc.

REFERENCES [1]

[2]

[3]

[4] [5]

Fomin V.N. Vliyanie mekhanicheskikh vozdeistvii na formirovanie svoistv mnogokomponentnykh sistem (Effect of Mechanical Treatments on Adjustment of Properties of Multicomponent Systems), Moscow, Nauka, 2004 (in Russian). Ganiev R.F., Kashnikov A.M., Malyukova E.B., Fomin V.N., Berlin A.A., Lakokrasochnye Materialy i Ikh Primenenie (Paint and Varnish Materials and Their Application), 2003, 12, 25 (in Russian). Ganiev R.F., Ukrainsky L.E., Vibratsii v tekhnike. Vibratsionnye protsessy i mashiny (Vibrations in Technics. Vibration Processes and Machines), Moscow, Machinostroenie, 1981, vol. 4 (in Russian). Bartenev G.M., Zelenev Yu.V. Relaksatsyonnye yavleniya v polimerakh (Relaxation Phenomena in Polymers), Leningrad, Khimiya, 1972, 376 (in Russian). Transitions and relaxations in polymers. ed. R.Boyer, Journal of Polymer Science, (C), 14, 1966, Amer. Chem. Soc. Symp. Atlantic Cit., New Jersey, Sept.13-14, 1965, Intersc. Publ. Div. of John Wiley&Sons, 1966.

Effect of Vibration on Structure and Properties … [6] [7] [8] [9] [10] [11]

[12] [13] [14] [15] [16] [17] [18] [19]

[20] [21] [22]

377

Kabanov V.A., Doklady Chemistry (translated from Doklady Akademii Nauk), 1970, 195 (2), 402. Schen M. Viscoelastic Relaxation in Polymers, Journal of Polymer Science, (C), 35, Interscience Publischer Division of John Wiley & Sons, Inc. 1971. Fomin V.N., Malyukova E.B., Lomovskaya N.Yu., Petrova T.F., Barteneva A.G., Chalykh A.E., Materialovedenie, 2006, 6 (in Russian). Elliott A. Infra-red Spectra and Structure of Organic Long-chain Polymers, London, Edward Arnold (Publishers) Ltd. 1969. Bellamy L.J., The infra-red spectra of complex molecules. London, New Jork 1954, Methnen and Co. Ltd., John Wiley & Sons, Inc. Dechant J. (unter Mitarbeit von Rudi Danz, Wolfgang Kimmer und Rudolf Schmolke) Ultrarotspektroskopische Untersuchungen an Polymeren (Ultra-Red Spectroskopic Stydies of Polymers). Akademie - Verlag - Berlin 1972 (in German). Kuleznev V.N. Smesi polimerov (struktura i svoistva) (Polymer Mixtures (Structure and Properties)). Moscow, Khimiya, 1980 (in Russian). Vomin V.N. PhD Thesis, Moscow, 1997 (in Russian). Ganiev R.F., Fomin V.N., Malyukova E.B., Doklady Chemistry (translated from Doklady Akademii Nauk), 2005, 402 (3), 359. Eliseeva V.I. Polimernye dispersii (Polymeric Dispersions), Moscow, Khimiya, 1980 (in Russian). Rabotnov Yu. N. Elementy nasledstvennoi mekhaniki tverdykh tel (Elements of Hereditary Mechanics in Solid State). Moscow, Nauka, 1977 (in Russian). Suvorova Yu. V., Mekhanika polimerov (Polymer Mechanics), 1977, 6, 976 (in Russian). Alexeeva S.I. PhD Thesis, Мoscow, 2002 (in Russian). Ganiev R.F., Fomin V.N., Malyukova E.B., Ponomarenko A.T., Sergeev A.I., Matveev V.V., Chalykh A.E., Doklady Chemistry (translated from Doklady Akademii Nauk), 2005, 403 (6) 777. Amrhein E., Kolloid Z. u. Z. Polym., 1967, Bd. 216-217, 38. Plate N.A., Vasilev A.E. Fiziologicheski aktivnye polimery (Physiologically Active Polymers). Moscow, Khimiya, 1986 (in Russian). Davydova G.A. PhD Thesis, Pushino, 2005 (in Russian).

In: Modern Tendencies in Organic and Bioorganic Chemistry ISBN: 978-1-60456-295-8 Editors: A. Mikitaev, M. K. Ligidov, pp. 379-384 © 2008 Nova Science Publishers, Inc.

Chapter 34

ONE-STAGE SYNTHESIS OF POLYMER FLOCCULANT ON THE ACRYLONITRILE BASIS N. V. Kozhevnikov*, M. D. Goldfein, and N. I. Kozhevnikova Saratov State University, 410012, Astrakhanskaya st. 83, Saratov, Russia

ABSTRACT The process of formation of polyacrylamide flocculant on the basis of acrylonitrile and sulphuric acid in one stage was investigated. The required properties of flocculant can be obtained as result of achievement of the optimal rates' ratio of reactions of polymerization and hydrolysis, which proceeds in the synthesis conditions simultaneously.

Keywords: water purification, flocculant, synthesis, acrylonitrile, polymerization, hydrolysis, kinetics, mechanism

The increase in size of water consumption and decrease of water quality due to man’s impact make the problem of water purification and treatment from different contaminants, such as suspended and colloidal disperse particles, more acute. The efficiency of dispersion precipitation can be greatly improved with the use of flocculants – high-molecular compounds that have the ability to adsorb themselves on disperse particles and form fast precipitating aggregates [1]. Both natural and synthetical water soluble polymers can be used as flocculants. The most commonly used and the most active of these polymers are polyacrylamide (PAA) and some of its derivatives. Polyacrylamide type flocculants are prepared by polymerization of acrylamide (AA) or by copolymerization it with some other monomers in water, organic or mixed (water and organic) solutions as well as emulsions in presence of radical initiators [2]. AA can be distinguished from other mogomers by high polymerization activity [3] and molecules of *

E-mail: [email protected]

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PAA can form associates even in much diluted solutions because of interaction between polar groups of different molecular chains which results in appearance of spatial grid and formation of a gel. The polyacrylamide flocculant can be produced by hydrolysis the polymer which contains acrylonitrile groups [4]. The product of such reaction has much less molecular mass (approx. 5*104) and flocculating activity, than the product of AA polymerization. Besides, the flocculant can be obtained as a result of multistage transformations of acrylonitrile (AN). AA is produced during these transformations as an intermediate product. For example, it can be obtained as a result of three-stage synthesis: sulphuric acid hydrolysis of AN – neutralization of acid excess with lime or ammonia and isolation of intermediate products – polymerization of monomers. A gel-like flocculant, which contains 5–8% of polymer, can be obtained as a result of such transformations [1]. It should be noted that many synthetic organic flocculants are produced under their brand names and their precise chemical composition is not yet known. The quantitative characteristics of their flocculating activity are lacking in scientific literature (including patents), thus making it more difficult to compare these compounds. In this work we have investigated kinetics and mechanism of processes that occur during the synthesis of polymeric flocculants from acrylonitrile in presence of sulphuric acid and modified this process into one-stage synthesis without isolation of any intermediate or byproducts. If we take into account that only small quantities of precipitating agents are used during water purification and that this water may contain alkaline impurities, then we can skip the neutralization stage and leave some sulphuric acid in the flocculant. In presence of sulphuric acid and radical initiators both processes – hydrolysis and polymerization – occur simultaneously. The process of copolymerization of AA and AN occur during the formation of AA from AN. During the investigation it was found out that water solubility and flocculation activity of copolymer were depend on contribution of reactions of hydrolysis and polymerization in polymer formation. If we found the optimal ratio of these two reactions rates, then we can obtain a polymer with required properties. We have investigated the kinetics of process by dilatometric method which allowed us to measure total bulk effect of reaction. In presence of sulphuric acid and polymerization initiator total bulk effect is formed from bulk effect of hydrolysis and bulk effect of polymerization. If the initiator is not present, then we have to measure only bulk effect of hydrolysis. In this case the process rate (R) was gradually decreasing due to the consumption of the initial monomer (AN). But if the initiator is present at first the rate is increasing and only after some time it began to decrease. This fact validates the following conception: reactions of hydrolysis and polymerization occur simultaneously, transformation from AN to AA which is characterized by higher rate of chain propagation [3], leads to speeding the polymerization up as the reaction occurs despite the consumption of monomer. The polymer molecular mass was measured with the use of viscosimetric method. Flocculating ability was measured as velocity (V) of precipitation of suspended disperse particles of a specific imitator – black copper oxide. Besides, residual suspended materials concentration (turbidity – T) was measured with the use gravimetric method after passing through the front of depositing flakes.

One-stage Synthesis of Polymer Flocculant

t, min

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80 [H2SO4], %

Figure 1. The rate of synthesis of flocculant from acrylonitrile in presence of different concentration of sulphuric acid (1), duration of process (4), velocity of precipitation of suspended particles of copper oxide by action flocculant (3) and residual suspended materials concentration (2) versus the concentration of water solution of acid. [AN]=10 vol. %, [APS]= 10 g/l, 60 oC.

Changes in the mix proportion of reaction medium, temperature and duration of the process affect reactions of polymerization and hydrolysis both separately and jointly, thus allowing us to find conditions required to prepare the flocculant in one stage. We have found out that increase in sulphuric acid concentration results in increase of AN hydrolysis rate (AA formation rate) as well as in much lesser increase of polymerization rate. Meanwhile, polymer molecular mass ( M ) decreases and duration of the process (t) as well (Figure 1). We continued flocculant synthesis until the volume of reaction solution stopped decreasing. The further prolongation of synthesis results in gradual increase of that volume due to hydrolysis of amide groups and formation of acrylic acid elements in the polymer. Sulphuric acid concentration also affects solubility and flocculating properties of the product. It should be noted that if the flocculant is water soluble then diapason of acid content is rather narrow. The width of this diapason depends of initial concentration of AN and the higher concentration is the narrower is diapason. It makes synthesis of water soluble flocculant with high polymer content more difficult. As the acid concentration increased flocculating properties of product kept increasing at first (due to increase in velocity of precipitation of suspended particles of black copper oxide and decrease of residual suspended materials concentration), but then started to decrease. Both characteristics of flocculating activity reached their extreme value during the same acid concentration which did not depend on initial AN content. The optimal ratio between hydrolysis and polymerization velocities can be obtained not only by changing sulphuric acid concentration, but also by changing initiate’s (ammonium persulfate (APS)) concentration. It’s concentration doesn’t affect the process velocity much (order of reaction’s initiation rate is 0.24), but it greatly affects polymer’s molecular mass – much more than it can expected according to classical concepts [3]. We think that detected deviations from ideal kinetics exist because processes of polymerization and hydrolysis of AN occur simultaneously which results in formation of a more reactive monomer – AA.

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Increase of initiator’s concentration results in increasing flocculant’s water solubility, velocity of precipitation of suspended particles of black copper oxide can be characterized by extreme dependence (Figure 2). The flocculant that is obtained as a product of aforementioned process contained a small amount of polymer that plays an integral role in the process of suspended particles precipitation. To find out if we can increase its content in the product we investigated how initial concentration of AN affects synthesis kinetics and flocculant’s properties. We found out that increase of concentration of initial monomer results in increase of reaction’s rate, polymer’s content (P) and its molecular mass and in decrease of duration of process and improvement of flocculating properties (Figure 3). But it also results in decrease of water solubility of flocculant (even if we increase initiator’s concentration) which impedes further increase in polymer’s content. Nevertheless, we managed to synthesize a flocculant which contains 1.5–2 times as much polymer as the product obtained as a result of aforementioned three-stage synthesis. Increase in temperature results in increase of reaction’s rate (active activation energy ~ 83 kJ per mole), decrease of its duration and of polymer’s molecular mass as well as flocculating properties: both velocity of precipitation of suspended particles and purification rate decreased (residual suspended materials concentration increased) (Figure 4). As a result of our investigation we have found out that changing such factors as temperature or monomer’s content equally affect hydrolysis and polymerization rate and do not lead to a significant change in structure of a polymer obtained as a result of one-stage synthesis. On the contrary, concentration of acid of initiator predominantly affects one of these reactions which results in change of polymer’s molecular mass, structure of polymer molecules and brings about extreme dependence of flocculating activity from these factors. Extremum locations are not affected by initial concentration of AN and temperature (activation energies of hydrolysis and polymerization are very similar).

_ -5 4 R .10 М.10 1

30 8 20

4

6 2

4 10 0

V, mm/s 6

2 2 0

3

10

20

30

40 [APS], g/l

Figure 2. The rate of synthesis of flocculant in presence of different concentration of initiator (1), molecular mass of polymer that is obtained in this process (3) and velocity of precipitation of suspended particles of copper oxide by action flocculant (2) versus the concentration of ammonium persulfate. [AN]=16 vol. %, [H2SO4]=74 %, 60 oC.

One-stage Synthesis of Polymer Flocculant

t, min [P], %

T, % V, mm/s 1 20 8

200 15

6

2

10

10 4

100 5 0

383

3

2

4

0

5

10

15

20 [АN], %

Figure 3. The duration of synthesis of flocculant in presence of different concentration of acrylonitrile (3), contents of polymer in flocculant (1), velocity of precipitation of suspended particles of copper oxide by action flocculant (2) and residual suspended materials concentration (4) versus the initial concentration of monomer. [APS]=10 g/l, [H2SO4]=74 %, 60 oC.

The presence of extreme dependencies makes the selection of optimal conditions for the reaction of flocculant formation much easier. This method is characterized by high efficiency as well as simplicity and low labour intensity of synthesis. We can obtain a product with similar properties if we use other polymerization initiators including the oil-soluble ones. For example, we synthesized the flocculent in presence of azoisobutyric acid dinitrile, which was introduced into reaction system in AN solution.

t, min

T, % V, mm/s 1

300

4

2 3

200 2 100 50

55

60

65 70 o Temperature, C

Figure 4. The influence of reaction temperature on the duration of synthesis of flocculant (1), velocity of precipitation of suspended particles of copper oxide by action flocculant (2) and residual suspended materials concentration (3). [AN]=16 vol. %, [APS]=10 g/l, [H2SO4]=74 %.

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REFERENCES [1] [2] [3] [4]

Weizer Yu. I., Mintz D.M. The Use of High-molecular Flocculants in Processes of Natural Water and Sewage Purification. Moscow: Stroiizdat, 1984. 200 p. Abramova L.I., Baiburdov T.A., Grigoryan E.P., Zilberman E.N., Kurenkov V.F., Myagchenkov V.A. Polyacrylamide. Moscow: Khimia. 1992. 189 p. Bagdasariyan Kh. S. The Theory of Radical Polymerization. Moscow: Nauka. 1966. 300 p. Nebera V.P. Flocculation of mineral suspensions. Moscow: Nedra. 1983. 288 p.

In: Modern Tendencies in Organic and Bioorganic Chemistry ISBN: 978-1-60456-295-8 Editors: A. Mikitaev, M. K. Ligidov, pp. 385-395 © 2008 Nova Science Publishers, Inc.

Chapter 35

ULTRASONIC TREATMENT ASSISTED SURFACE MODIFICATION OF INORGANIC AND ORGANIC PIGMENTS IN AQUEOUS DISPERSIONS N. A. Bulychev1,3, E. V. Kisterev2, I. A. Arutunov 1, and V. P. Zubov1 1

Lomonosov Moscow State Academy of Fine Chemical Technology, 119571, pr. Vernadskogo, 86, Moscow, Russia 2 Kurnakov Institute of General and Inorganic Chemistry of the Russian Academy of Sciences, 113334, Leninsky pr., 31, Moscow, Russia 3 Institute for Polymer Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany

ABSTRACT The colloidal stability and pigment surface modification of aqueous dispersions of inorganic pigments TiO2 (rutile) and Fe2О3 (red) as well as organic pigment copper phthalocyanine CuPc (blue) treated in an ultrasonic field in the presence of water-soluble polymers and surfactants was studied. It has been shown that for inorganic pigments ТiO2 and Fе2О3 in the absence of polymers and surfactants, ultrasonic treatment results in a fast coagulation of aqueous dispersion. In the presence of ethylhydroxyethylcellulose (EHEC), ultrasonic treatment leads to a significant increase in the stability of aqueous dispersions of TiO2 and Fe2O3, decrease of pigment particles size from 1,5 mcm to 0,2 mcm, and narrowing the particle size distribution. Experimental results on measuring the ζ-potential of the particle surface of ТiO2 pigment have verified the assumption that the ultrasonic treatment of aqueous dispersions of pigment in the presence of EHEC not only results in effective deagglomeration of particles but also activates the adsorption of polymer on freshly-formed surface and facilitates the formation of protective adsorption-solvation layers. For aqueous dispersions of organic pigment CuPc, there is a problem of the wetting of its surface. It has been shown that this problem is effectively removed in the presence

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N. A. Bulychev, E. V. Kisterev, I. A. Arutunov et al. of polyvinyl alcohol (PVA) with the content of residual acetyl groups of 10-17 % and molecular weight of 10000 -11000. The presence of anionogenic dispersant NF gives the same effect. The wetting of CuPc surface results in the colouring of its aqueous dispersion into a bright-blue colour. The colour intensity can be used as a measure of the stability of CuPc aqueous dispersions. It is demonstrated that the value of optical density of CuPc dispersions with the separated solid phase in the presence of PVA and dispersant NF becomes significantly higher as a result of ultrasonic treatment, which indicates an increase in the stability of CuPc aqueous dispersions.

Keywords: pigment, surface modification, ultrasound, surface active polymers

INTRODUCTION The colloidal stabilization of aqueous dispersions by polymer surfactants is believed to be a result of the adsorption of the amphiphilic macromolecules on the particle surface. This adsorption results in the formation of mono- or multi-layers of certain structure and thickness which provide sterical and/or electrostatic stabilization effects [1-5]. Polymer adsorption from aqueous solution on a particle surface is a result of specific interactions of various active sites on the particle surface with corresponding sites (groups) of the macromolecule. Therefore the adsorption behaviour and the colloidal stabilization may be used as a sensitive approach (tool) to elucidate the effects of the polymers structural differences on their behaviour on the liquidsolid interface [6-9]. Aqueous dispersions of inorganic pigments ТiO2 (rutile) and Fe2O3 (red) and organic pigment copper phthalocyanine CuPc (blue) are widely used in the printing as well as in varnish and paint industries. Therefore the stabilization of environmentally friendly aqueous dispersions of these pigments is an important problem from the scientific and practical points of view [10,11]. Previously, it was shown [12, 13] that the stability of aqueous dispersions of inorganic and organic pigments could be increased in the presence of water-soluble polymers. Dispersing effect of an ultrasonic field on colloidal systems is well known. It is based on the phenomenon of cavitation which arises in a liquid as a result of local pressure decrease during the passage of acoustic wave of high intensity. Cavitation bubbles formed, moving into the region of higher pressure, collapse, creating a shock wave. The deagglomerution of particles can occur during several seconds. However, in order to prevent a subsequent coagulation of particles, the effect of ultrasound must be fixed by forming the protective layers of a stabilizer (polymeric or low-molecular surfactant). For organic pigment CuPc, the formation of adsorption-solvation layers of polymers or surfactants allows to eliminate the problem of the wetting of its surface in aqueous dispersions. The objective of the present work is to obtain stable aqueous dispersions of inorganic pigments ТiO2 и Fe2O3 and organic pigment CuPc in the presence of water-soluble polymers and surfactants under conditions of treatment in an ultrasonic field.

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EXPERIMENTAL PART Materials In the work, TiO2 (rutile) from company "Kronos" and Fe2O3 (red) from company "Bayer" were used. The particle surface of pigment TiO2 was treated with the oxides of aluminium, silicon and zirconium, and the surface of pigment Fe2O3 - with aluminium and silicon oxides. Pure phthalocyanine pigment - p-CuPc was used in the work. As a stabilizer of aqueous dispersions of TiO2 and Fe2O3, ethylhydroxvethylcellulose (EHEC) from company "Berol" with molecular weight 60000 was used. For the stabilization of aqueous dispersions of CuPc, poly vinyl alcohol (PVA) from company "Sigma" with the acetyl groups content of 2 % and 17 % and molecular weight of 10000 and anionogenic dispersant NF were used. Dispersant NF is disodium-methylene-bisnaphthalenesulfonate – NaO3SC10H17CH2C10H17SO3Na.

Techniques To study the sedimentation behaviour of Fe2O3, 0,25 % vol. pigment was mixed with 10 ml. of water or aqueous solution of EHEC. Dispersion was predispersed for 15 min using a laboratory stirrer (700 rpm), then ultrasonically treated and placed into glass cylinders with scale divisions, and the movement of the interface between the solid phase and the pure dispersion medium was monitored. Sedimentation curves were constructed as a dependence of sedimentation volume Vsed (ml) on sedimentation time (min, logarithmical coordinates). To measure the particle size and ζ-potential of pigment ТiO2 by the ESA (Electrokinetic Sonic Amplitude) method, the Acoustosizer 2 device (“Colloidal Dynamics”, Sydney) was used. The average size of ТiO2 and Fe2O3 particles was estimated using a Coulter-N-4-particle size analyzer. For ultrasonic treatment, an ultrasonic generator “UZDN-2” with frequency 22 kHz and maximum intensity 30 W/cm2 was employed. The value of optical density of the CuPc liquid phase was measured calorimetrically after keeping 0,1 % CuPc dispersion in the solution of a stabilizer during 1 hour and separating the solid phase by filtration. Keeping time was time for which the optical density of the liquid phase reaches a constant value. This time was about 1 hour. Optical density was measured at a wave length of 364 nm and temperature of 18 °C.

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RESULTS AND DISCUSSION 1. Effect of Ultrasonic Treatment on Stability of Aqueous Dispersions of Inorganic Pigments TiO2 and Fe2O3. Figures 1 and 2 show the influence of ultrasonic treatment of aqueous dispersions of TiO2 and Fe2О3, respectively, on their sedimentation stability in the absence and presence of ethylhydroxyethylcellulose (EHEC). The particle size of obtained dispersions is given for Fe2О3 in Table 1 and for TiO2 in Table 2. From Figures 1 and 2 it is seen that in the absence of polymer the treatment of dispersions in an ultrasonic field leads to their fast coagulation (curve 1). It can be assumed that ultrasonic treatment results in the deagglomeration of pigment particles and the formation of "fresh" surface with uncompensated charges. The system tends to decrease surface energy, which leads to a sharp reduction of the system stability. The presence of EHEC in the system increases the stability of dispersions (compare curves 2 and 3 in Fig. 1 and 2), and particle size decreases from 1,2 mcm to 0,4 – 0,6 mcm. This is due to the formation of protective adsorption-solvation layers of the polymer on the pigment surface, which leads to an increase in aggregation and sedimentation stability of TiO2 and Fe2О3 dispersions. Under ultrasonic treatment of dispersions in the presence of EHEC, their stability increases considerably (by nearly two orders of magnitude) - curves 4 in Figures 1 and 2. At the same time, particle size (see Table 1 for Fe2O3 and Table 2 for ТiO2) decreases almost to the original size of pigment particles (0,2-0,3 mcm). Table 1. Effect of ultrasonic treatment on the particle size of Fe203 (1% wt.) aqueous dispersions № 1 2 3 4

Polymer EHEC EHEC

US-treatment, min. 2 2

Particle size, μm. 1,5 1,2 0,6 0,3

Table 2. ξ-potential and particle size of TiO2 (1% wt.) obtained by ESA method № 1 2 3 4

System TiO2, H2O TiO2, EHEC (1%) TiO2, EHEC (1%) + UStreatment 2 min. №3 after 3 days (Т = 40°С)

ξ-potential, mV. -35,90 -19,70 -3,160

D50, μm. 0,356 0,405 0,215

Dmin, μm. 0,103 0,367 0,194

Dmax, μm. 1,240 0,488 0,238

-0,972

0,278

0,251

0,307

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12

Fall height, cm.

10

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1

2 0 1

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Sedimentation time, min. Figure 1. Sedimentation curves for TiO2 pigment in absence and in presence of EHEC. 1 – without EHEC, ultrasonic treatment 2 min., 2 – without EHEC, no ultrasonic treatment, 3 – with EHEC, no ultrasonic treatment, 4 – with EHEC, ultrasonic treatment 2 min. Concentration of TiO2 and EHEC – 1% wt.

From the data given in Table 2 and Figure 3, it can be seen that as a consequence of ultrasonic treatment of aqueous dispersions of TiO2 and Fe2O3, the narrowing of particle size distribution occurs, that indicates the obtaining more uniform dispersions. 12

Fall height, cm.

10 8

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2 0 1

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Sedimentation time, min.

Figure 2. Sedimentation curves for Fe 2O3 pigment in absence and in presence of EHEC. 1 – without EHEC, ultrasonic treatment 2 min., 2 – without EHEC, no ultrasonic treatment, 3 – with EHEC, no ultrasonic treatment, 4 – with EHEC, ultrasonic treatment 2 min. Concentration of Fe 2O3 and EHEC – 1% wt.

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Figure 3. Particle size distribution for Fe2O3 aqueous dispersions in presence of EHEC (1% wt.). a) without ultrasonic treatment. b) ultrasonic treatment 2 min.

Figure 4 illustrates the influence of a polymer concentration on the stability of aqueous dispersions of pigment ТiO2 (ultrasonic treatment time - 2 min). It is seen from the figure that with increasing the concentration of EHEC, sedimentation stability of dispersions increases. 12

Fall height, cm.

10 8

3

6

1

2

4 2 0 1

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100 1000 10000 Sedimentation time, min.

100000

1000000

Figure 4. Sedimentation curves for TiO2 pigment by different concentrations of EHEC and ultrasonic treatment for 2 min. 1 – 0,1% wt. 2 – 0,5% wt. 3 – 1,0% wt. Concentration of TiO2 – 1% wt.

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It should be noted that approximately similar behaviour of aqueous dispersions of pigments ТiO2 and Fe2O3 can be due to similarity of the chemical nature of these oxides and to the method of their production - the surface of both pigments, as indicated in the experimental section, was treated with silicon and aluminium oxides. Thus, ultrasonic treatment of aqueous dispersions of pigments TiO2 and Fe2O3 in the presence of polymer leads to a significant increase in their stability and uniformity, that is due to the deagglomeration of pigment particles and the formation of a stabilizing layer on their surface as a result of the activation of polymer adsorption. It can be said that the surface of pigment particles is undergone to mechanochemical modification. The evidence of the polymer adsorption on the surface of pigment particles and the formation of protective layers has been obtained by ESA method by experiments on measuring the ζ-potential of the ТiO2 surface in aqueous dispersions in the presence of EHEC (Table 2). It can be seen from the table that ζ-potential becomes less negative in the presence of EHEC and still more approaches zero as a result of the treatment of dispersions in an ultrasonic field. This indicates the activation of polymer adsorption and the formation of stabilizing layers due to mechanochemical modification of particles. From the table it is also seen that as a consequence of mechanochemical treatment, the size of pigment particles in dispersions decreases, and dispersion becomes structurally more uniform, which leads to an increase of its stability even at increased temperature (experiment 4). Additional evidences of the intensification of the polymer adsorption on the surface of pigment particles as a result of ultrasonic treatment, which were obtained using spectral techniques of analysis, have been published earlier [7]. 12

Fall height, cm.

10 8

2-3-4

6

1

4 2 0 100

1000

10000 100000 Sedimentation time, min.

1000000

Figure 5. Sedimentation curves for TiO2 pigment in 1% wt. aqueous solution of EHEC by different duration of the ultrasonic treatment. 1 – no ultrasonic treatment, 2 – ultrasonic treatment for 30 min., 3 – ultrasonic treatment for 10 min., 4 – ultrasonic treatment for 2 min. Concentration of TiO2 – 1% wt.

N. A. Bulychev, E. V. Kisterev, I. A. Arutunov et al.

392 12

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8 6

1-2-3

4 2 0 10

100

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10000

100000

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Sedimentation time, min. Figure 6. Sedimentation curves for Fe 2O3 pigment in 1% wt. aqueous solution of EHEC by different duration of the ultrasonic treatment. 1 – no ultrasonic treatment, 2 – ultrasonic treatment for 30 min., 3 – ultrasonic treatment for 10 min., 4 – ultrasonic treatment for 2 min. Concentration of Fe 2O3 – 1% wt.

The important factor that influences the efficiency of the ultrasonic treatment is its duration. According to the data given in work [14], polymers during ultrasonic treatment can be destructed, the degree of destruction depending substantially on the chemical structure of polymer – more flexible polymers are destructed to a lesser extent. Figures 5 and 6 show sedimentation curves for aqueous dispersions of TiO2 and Fe2O3, respectively, in the presence of 1 % solution of EHEC at different times of ultrasonic treatment. It is seen from the figures that the optimum time of treatment for obtaining the most stable dispersions is 2 minutes. An increase in the time of ultrasonic treatment leads to a considerable reduction in the system stability. It can be shown that EHEC, being an insufficiently flexible polymer, undergoes mechanodestruction, which weakens its stabilizing effect on the system.

2. EFFECT OF ULTRASONIC TREATMENT ON STABILITY OF AQUEOUS DISPERSIONS OF ORGANIC PIGMENT - COPPER PHTHALOCYANINE Copper phthalocyanine (CuPc) is one of the most important blue organic pigments that are widely used in the varnish-, paint- and printing industries. Its surface is hydrophobic and weakly charged. The particles of CuPc during contact with water without a stabilizer are not wetted and float on the water surface. In work [13] it was shown that the compounds allowing to solve the problem of the wetting of CuPc to a certain extent are the samples of polyvinyl alcohol (PVA) with a high content of acetyl groups and low molecular weight. The optimum parameters are 10 – 17%

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acetyl groups and molecular weight 10000 — 11000. The authors have suggested that the maximum effect of increasing the dispersion stability of nonpolar pigments is achieved due to steric stabilization, where hydrophobic fragments of stabilizer are adsorbed on the surface of particles and hydrophilic fragments are oriented into the dispersion medium. This accounts for a stabilizing effect of PVA with the specified composition. The experiments carried out in this work have shown that dispersant NF (disodiummethylene-bis-naphthalenesulfonate - NaO3SC10H17CH2C10H17SO3Na) which has, in spite of good solubility in water, powerful hydrophobic groups possesses the same property. Thus, the stability of aqueous dispersions of CuPc depends on the efficiency of the stabilizer adsorption on its surface. Treatment in an ultrasonic field allows to increase the efficiency of the stabilizer adsorption and therefore to increase the stability of pigment dispersions. Experiments have shown that the use of ultrasonic treatment of CuPc aqueous dispersions in the presence of PVA and dispersant NF results in the improvement of the wetting of the pigment surface and facilitates its transition into a medium, which is accompanied by the colouring of water into bright-blue colour. The colour intensity can be used as a measure of the stability of CuPc aqueous dispersions. The results of experiments on measuring the optical density of aqueous dispersion of CuPc with PVA, with the separated solid phase, without and after ultrasonic treatment are shown in Figure 7. It is seen from the figure that the use of PVA with the acetyl groups content of 2 % in the absence of ultrasonic treatment, the solution colouring is small, and low values of optical density are observed (curve 1). An increase in the acetyl groups content of PVA up to 17 % leads to a rise in the value of optical density even without ultrasonic treatment (curve 3). Curves 2 and 4 corresponding to the experiments with ultrasonic treatment of CuPc aqueous dispersions indicate a high efficiency of influence on the properties of the pigment surface even in the presence of 2 % acetyl groups in PVA. Particularly intensive colouring of the aqueous medium into blue colour is observed in the presence of PVA with the acetyl groups content of 17 % under ultrasonic treatment (curve 4). Figure 8 shows the results of measuring the optical density of CuPc aqueous dispersion with the separated solid phase in the presence of dispersant NF without ultrasonic treatment (curve 1) and after it (curve 2). In this case a positive role of ultrasonic treatment for increasing the intensity of the colouring of CuPc aqueous dispersions is proven as well. On the basis of the results obtained, it can be assumed that during the ultrasonic treatment of CuPc aqueous dispersions the deagglomeration of pigment panicles that is accompanied by the formation of "fresh" surface with increased energy takes place, which leads to an activation of the stabilizer adsorption and the increased stability of dispersions. For aqueous dispersions of CuPc, a mechanochemical modification of surface results in the elimination of the problem of wetting and the obtaining of intensively coloured stable aqueous dispersions of this pigment.

N. A. Bulychev, E. V. Kisterev, I. A. Arutunov et al.

394 1,8 1,6

4

Optical density

1,4

2

1,2

3

1 0,8 0,6 0,4

1

0,2 0 0

0,2

0,4

0,6

0,8

1

1,2

Concentration of PVA, % wt.

Figure 7. Optical density of 0,1% wt. copper phthalocyanine (Cu Pc) aquous dispersions with separated solid phase in presence/absence of ultrasonic treatment in depending on concentration of PVA (% wt.). 1 – PVA with 2% of acetyl groups, without US-treatment. 2 – PVA with 2% of acetyl groups, with US-treatment. 3 – PVA with 17% of acetyl groups, without US-treatment. 4 – PVA with 17% of acetyl groups, with US-treatment.

1,8 1,6 1,4

2

Optical density

1,2 1 0,8

1

0,6 0,4 0,2 0 0

0,2

0,4

0,6

0,8

1

1,2

Concentration of DNF, % wt. Figure 8. Optical density of 0,1% wt. copper phthalocyanine (Cu Pc) aquous dispersions with separated solid phase in presence/absence of ultrasonic treatment in depending on concentration of DNF (% wt.) 1 – without US-treatment. 2 – with US-treatment.

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CONCLUSION Thus, it can be concluded that ultrasonic treatment of aqueous dispersions of both inorganic pigments ТiO2 and Fe2O3 and organic pigment copper phthalocyanine CuPc in combination with the use of polymeric and low-molecular surfactants is an effective method of increasing their stability. It is evident that the application of this technology can substantially improve the efficiency of industrial processes with the application of pigments.

REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14]

“Surfactants and Polymers in Aqueous Solution”, 2nd edition, K. Holmberg, B. Jönsson, B. Kronberg, B Lindman, J. Wiley & Sons, Chichester, UK 2003. R.R. Netz, D. Andelman. Physics Reports, 380, 2003, 1-95. P. Somasundaran, S. Krishnakumar. Colloids and Surfaces, A: Physicochemical and Engineering Aspects, 123, 1997, 491-513. Theo G.M. Van de Ven. Advances in Colloid and Interface Science, 48, 1994, 121-140. P. Somasundaran, Xiang Yu. Advances in Colloid and Interface Science, 53, 1994, 3349. M. Antonietti, M. C. Weissenberger, Macromol. Rapid. Com. 1997, 18, 295. V. P. Zubov, N. V. Serebryakova, I. A. Arutyunov, I. F. Kuzkina, N. A. Bulychev and Yu. A. Khrustalev, Colloid Journal, 2004, 66, 302. N. A. Bulychev, I. A. Arutunov, V. P. Zubov, B. Verdonck, T. Zhang, E. J. Goethals, F. E. Du Prez, Macromol. Chem. Phys., 2004, 205 (18), 2457-2463. N. Bulychev, K. Dirnberger, I.A. Arutunov, P. Kopold, T. Schauer, V. Zubov, C.D. Eisenbach, Progr. Org. Coat., in press. K.-Ch. Ullman, Stabilisation of TiO2 dispersions with non-ionic water-soluble molecules. Thesis, University of Stuttgart, 1989. L. Dulog, M. Hilt. Farbe & Lack 95, 1989, p. 793. V. P. Zubov, I. F. Kuzkina, 1.1. Ivankova, 0. J. Schmitz; European Coating Journal, 1998, No. 11, p. 856. V. P. Zubov, I. F. Kuzkina, 1.1. Ivankova, 0. J. Schmitz; European Coating Journal, 1998, No. -12, p. 954. N. Grassie, G. Scott; Polymer Degradation and Stabilization, Cambridge University Press, Cambridge, 1985, p.221.

In: Modern Tendencies in Organic and Bioorganic Chemistry ISBN: 978-1-60456-295-8 Editors: A. Mikitaev, M. K. Ligidov, pp. 397-405 © 2008 Nova Science Publishers, Inc.

Chapter 36

INVESTIGATION OF ANTIOXIDANT ACTIVITY OF ESSENTIAL OILS FROM LEMON, PINK GRAPEFRUIT, CORIANDER, CLOVE AND ITS MIXTURES BY CAPILLARY GAS CHROMATOGRAPHY A. L. Samusenko* N. M. Emanuel Institute of Biochemical Physics, Russian Academy of Sciences, 4 Kosygina Street, 119 991 Moscow, Russia

ABSTRACT Antioxidant properties of individual essential oils from lemon (Citrus limon), pink grapefruit (Citrus paradisi ), coriander (Coriandrum sativum L.), clove buds (Caryophyllus aromaticus L.) and their mixtures have been investigated by capillary gas chromatography. Evaluation of antioxidant activity was carried out using the reaction of oxidation of aliphatic aldehyde (hexanal) to carboxylic acid. Essential oil from clove buds was found to have the most antioxidant activity, while pink grapefruit oil had the minimal one. The mixtures of the essential oils, containing clove oil, also effectively inhibited hexanal oxidation. The changes in composition of essential oils and its mixtures have been studied during prolonged storage in light. It was found increasing of component stability in the mixtures of essential oils from lemon and coriander as compared with individual oils.

Keywords: lemon, pink grapefruit, coriander and clove essential oils, antioxidant activity, aldehyde/carboxylic acid test, capillary gas chromatography

*

E-mail: chembio @ sky.chph.ras.ru

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A. L. Samusenko

AIMS AND BACKGROUND Essential oils are widely used in the composition of medicines, biological and food additives, in aroma therapy, food and cosmetic industry [1 - 4]. Applying of the oils is caused by its nice or spice flavor. Biological activity of essential oils was recently established as a result of numerous investigations. The oils possessed antimicrobial, antioxidant and radical absorbing properties [1 - 15] . Essential oils mainly consist of low molecular mono- and sesquiterpene hydrocarbons , its oxygen analogs and phenol derivatives [3, 4, 16]. Small sides of the molecules allow them to penetrate through the cell walls and influence on various biochemical processes. Biological activity of essential oils depends on its composition. The essential oils, containing substituted phenols – eugenol, thymol, carvacrol and guaiacol [2, 6 8, 14 - 17] were shown to have pronounced antimicrobial and antioxidant properties. Studying of individual terpenes and phenols, being the components of various essential oils, has showed that numerous terpenes possessed antioxidant and radical absorbing activity. The activity of cyclic monoterpene hydrocarbons, having two double bonds in the cycle, is comparable with activity of phenols and α-tocopherol [18 – 20]. It is of importance the stability of essential oil composition during its using. However, the data on changes of oil composition during its storage are limited. It was estimated that the essential oils from sage [21], savory [22], clove, cardamom [23], coriander[ 24], marjoran[ 25], laurel and fennel[ 26] significantly changed during its storage and the main process was oxidation of individual oil components. It was shown that the stability of labile components of fennel oil noticeably increased in mixture with coriander and laurel essential oils [26]. The goal of work is studying of antioxidant properties of lemon, pink grapefruit, coriander, clove essential oils and its mixtures and comparison of antioxidant activity with the change of essential oil composition during a process of autooxidation.

EXPERIMENTAL Fresh samples of the essential oils from: lemon (Citrus limon) (“R.C.TREATT”, the United Kingdom), pink grapefruit (Citrus paradisi) (“Frutarom”, Israel), coriander (Coriandrum sativum L.) and clove buds (Caryophyllus aromaticus L.) (“Plant Lipids Ltd.”, India), and the mixtures of lemon and clove (1:1), lemon and coriander (1:1), lemon, coriander and clove (1:1:1) oils were investigated. For evaluation of antioxidant properties of the essential oils 400 μl of hexanal and 400 μl of n-dodecane (internal standard) were dissolved in 50 ml of hexane. The solution was divided to 5 ml aliquots in 10 ml glass vessels and 600 μl of the individual essential oil was added in each vessel. The control sample didn’t contain essential oil. Each sample was prepared twice. The samples in the closed vessels were exposed in light at room temperature during 145 days. Each week the vessels were opened and stream of air was passed through the sample with a help of 10 ml pipette. Quantitative content of hexanal was determined by capillary gas chromatography after each 8 – 12 days during first 3 months of storage and then interval of determination increased up to 1 month. The changes of the component content in the essential oil composition were fixed after 1, 2 and 5 months of storage.

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Gas chromatographic analysis of essential oil samples was carried out using chromatograph “Micromat – 412” (“Nordion Instr.”, Finland), equipped with fused silica capillary column SPB-1 (“Supelco”, USA, 35 m x 0.32 mm, phase film thickness 0.25 μm), at temperature programming of column from 60o up to 250oC with a rate 8o / min. Velocity of carrier gas He was 1 ml/ min, temperature of injector and flame-ionization detector - 250oC. Identification of the components in the oil samples was performed using retention index values by its comparison with published [23] or our experimental data. Quantitative content of hexanal and components of the essential oils was calculated using relationship of the peak areas corresponding to the substances and internal standard, which content was accepted equal to 8 μl/ml. The degree of oxidation of hexanal and essential oil components (%) was determined in relation to its content in initial samples.

RESULTS AND DISCUSSION For evaluation of antioxidant (AO) activity of essential oils under study and its mixtures we used test “aldehyde/carboxylic acid” [2, 8, 12, 28 ]. The method is based on inhibition of autooxidation of aldehyde to carboxylic acid in presence of substances having AO activity. This method in tandem with gas chromatography allows to study AO properties and determine quantitative changes in content of each component of essential oils during a process of its autooxidation.. Hexanal didn’t influence on autooxidation of essential oil because of the relationship hexanal/essential oil was equal 1:15. In control solution hexanal has completely oxidized to hexanoic acid after 145 days of storage. Essential oils and its mixtures significantly inhibited the oxidation of hexanal. In Figure 1 is given the quantity (%) of non-oxidized hexanal in the systems studied after 110 days. This value we used as criterion for evaluation of AO activity of essential oils and its mixtures. As seen from Figure 1, clove oil possessed the maximal AO activity of all individual oils. 84% of hexanal has remained non-oxidized after 110 days and it’s oxidation started only after 90 days of storage in presence of clove oil. Pink grapefruit oil possessed the minimal AO activity and noticeable hexanal oxidation was observed already after one week of storage. The oxidation rate of hexanal in this essential oil was much higher than in other oils. Coriander oil practically completely inhibited the oxidation of aldehyde during 60 days, but then it’s oxidation occurred at increasing rate. Lemon oil possessed the same AO activity, but rate of hexanal oxidation was less than one in coriander essential oil system. In our opinion it may be explained by different content of γ-terpinene in the oils: coriander oil contained only 2 % of γterpinene, while in lemon one it’s content was equal to 12.5 %. The mixture of lemon and coriander oils has demonstrated antagonistic effect, i.e. it’s AO activity was less than the one of individual oils from lemon or coriander. This phenomenon obviously is not connected with the content of γ-terpinene, because the mixture of lemon and coriander oils has to contain about 7 % of γ-terpinene. As was shown in Refs 17, 24, γ-terpinene possesses AO activity comparable with the one of phenol antioxidants. According to data [17] practically all compounds, containing in the composition of essential oils under study, possessed the antioxidant properties, but its activity significantly differed. So, in model system of methyl linoleate oxidation AO activity of individual α- and γ- terpinenes, terpinolene was equal to 80 – 95 %, limonene, α- and β-pinenes – to 30 % [17] . Grapefruit essential oil contained about

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94 % of limonene and it’s AO activity, found by us, was equal to 32 % (Figure 1), which was in accordance with literature data [17]. We have watched over the changes of each component content in essential oils during a process of its autoxidation and evaluated the influence of essential oil composition on the oxidation rate of main components (Figures 2 – 5) and AO activity (Figure 1). The content of limonene in grapefruit essential oil was equal to 96 %; during storage it monotonously decreased and after 145 days has fallen to 46 % of initial value (Figure 4). Simultaneously it was noted increasing of epoxylimonene, carvon and α- terpineol content, formed as a result of limonene oxidation. At the end of storage we observed dimness of the solution and noticeable deterioration of oil odor. Perhaps the absence of compounds, having pronounced AO activity, in composition of grapefruit essential oil makes it the weakest antioxidant of all oils studied.

100

%

90 80 70 60 50 40 30 20 10 0 1

2

3

4

5

6

7

8

Figure 1. Content of hexanal (%) in solution after storage in light during 110 days in presence of individual essential oils and its mixtures: 1 – control, 2 – lemon, 3 – pink grapefruit, 4 – coriander, 5 – clove, 6 – lemon + clove, 7 – lemon + coriander, 8 – lemon + coriander + clove

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Content of linalool, % 110

5

100 90

4 80

3

70

2

60 50 40 30

1

days

20 0

20

40

60

80

100

120

140

160

Figure 2. Change of main component content (%) in the composition of essential oils and its mixtures during autooxidation in light: Linalool: 1 – pink grapefruit , 2 – lemon + coriander , 3 – coriander, 4 – lemon + coriander + clove , 5 – lemon.

The main components of lemon oil were limonene, β-pinene and γ-terpinene. Besides that lemon oil contained 2 % of citral (neral and geranial). Comparison of the oxidation rates of lemon oil components and hexanal showed that hexanal oxidized slower than γ-terpinene, which oxidized to p-cymene completely. The concentration of p-cymene increased and concentation of γ-terpinene decreased to the same extent. The cyclic monoterpene hydrocarbons: α-terpinene and α-terpinolene have undergone the complete oxidation, though its content in lemon oil was not quite high before storage. The content of the main component – limonene has begun to decrease after 60 days of storage, but nevertheless remained enough high (Figure 4). As distinct from grapefruit oil, terpinenes and also citral (Figure 3), being the components of lemon oil, inhibited limonene oxidation. We didn’t observed the degradation of other monoterpene hydrocarbons, which contained in lemon oil. The essential oil from coriander, as well as lemon oil, contained active antioxidant - γterpinene, but it’s content was significantly less, about 2 %. During the oil storage γ-terpinene almost completely oxidized after 60 days (Figure 5). It is interesting to note that during these 60 days the content of other components of coriander oil didn’t change and hexanal didn’t oxidize. However after complete disappearance of γ-terpinene hexanal oxidation occurred at high rate; quantity decreased of limonene (Figure 4) and linalool (Figure 2), which oxidized to terpineol, carvon and linalool oxides. So, γ-terpinene, citral, limonene and linalool possessed AO properties in the essential oils from lemon and coriander. In the mixture of these oils the concentration of γ-terpinene and limonene was higher than in coriander oil, but less than in lemon oil. The concentrations of citral and linalool was also less. As a result

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hexanal (Figure 1), limonene (Figure 4) and linalool (Figure 2) in this mixture oxidized to a higher extent than in the systems with individual oils, but degree of geranial oxidation was less (Figure 3). Thus, addition of coriander essential oil to lemon oil decreased stability of limonene and linalool as compared with the individual oils, but increased the keeping of key component of lemon odor – citral. It’s content in this mixture after 145 days of storage was equal to 52 % , while in individual lemon oil – only 24 %. As distinct from lemon, pink grapefruit and coriander oils the essential oil from clove has not undergone to noticeable change of it’s composition even during prolonged storage in light. Insignificant oxidation was observed only for β-caryophillene and content of it’s oxide increased (Figure 6). Essential oil from clove contained about 80 % of eugenol, that is why it proved to be strong antioxidant (Figure 1) [1, 16 – 20]. The mixture of two “AO-leaders”, i.e. essential oils from clove and lemon also possessed the high AO activity (Figure 1). Moreover, the composition of this mixture practically didn’t change during a process of storage. The degradation of monoterpene hydrocarbons was insignificant and oxidation of γ-terpinene to pcymene occurred slower than in individual lemon oil (Figure 5). It may be supposed that in mixture “clove + lemon” essential oil from clove increased the stability of lemon oil components and also was responsible for high AO activity of the mixture on the whole (synergetic effect). In the mixture of three essential oils: lemon, clove and coriander the stability of limonene and γ-terpinene was considerably higher than in the individual oils, but less as compared with mixture of the oils from lemon and clove (Figures 4 and 5). The presence of eugenol in the mixtures didn’t influence on the stability of geranial (Figure 3) and insignificantly increased the stability of linalool (Figure 2).

Content of geranial, % 100

80

60

4 40

3 2

20

1 0 0

20

40

60

80

100

120

140

days 160

Figure 3. Geranial: 1– lemon, 2 – lemon + clove, 3 – lemon + coriander + clove, 4 – lemon + coriander.

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Content of limonene, %

105

6

100 95 90

5

85 80

4

75

3

70

2

65 60 55 50

1

45

days

40 0

20

40

60

80

100

120

140

160

Figure 4. Limonene: 1 – pink grapefruit, 2 – lemon + coriander, 3 – coriander, 4 – lemon, 5 – lemon + coriander + clove, 6 – lemon + clove.

Content of gamma-terpinene, % 100

80

60

5 40

4 3

2

20

1

days

0 0

20

40

60

80

100

120

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Figure 5. γ-Terpinene: 1 – coriander, 2 – lemon + coriander, 3 – lemon, 4 – lemon + coriander + clove, 5 – lemon + clove.

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140

% 0125

120 100

0125

0125

0125

0125

0125

2

3

4

5

80 60 40 20 0 1

6

Figure 6. Change of main component content (%) in the composition of clove essential oil during 5 months of storage in light: 1 – eugenol, 2 - β-caryophyllene, 3 – farnezene, 4 – eugenyl acetate, 5 - δcadinene, 6 – caryophyllene oxide.

CONCLUSION The investigation carried out has shown that the essential oils possess AO activity, which to a considerable extent depends on oil composition. AO activity of the oils, oil stability during a process of storage, oxidation rate of individual oil components by complex means are connected with the composition of the oils and its mixtures, also with concentration and relationship of the most active components. The knowledge of reciprocal influence of components on the properties and stability of the system on the whole allow to regulate these features by preparation of the mixtures of the essential oils or its components, having beforehand targeted AO properties.

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INDEX

A absorption spectroscopy, 303 AC, 38, 40, 46 accelerator, 66, 119 accessibility, 222 accuracy, 37, 53, 68, 272 acetic acid, 306 acetone, 34, 36, 307, 343 acetophenone, 34, 37, 47 achievement, 369, 379 acid, 18, 103, 104, 105, 115, 137, 152, 172, 174, 211, 212, 216, 217, 222, 234, 307, 337, 343, 379, 380, 381, 382, 383, 397, 399 acidic, 6, 18 acrylate, 89, 325, 327, 335, 336, 339, 349, 350, 351, 353, 354, 361, 362 acrylic acid, 118, 336, 337, 349, 350, 353, 354, 363, 381 acrylonitrile, 379, 380, 381, 383 activation, 3, 7, 10, 11, 21, 24, 45, 47, 148, 155, 175, 183, 242, 296, 382, 391, 393 activation energy, 7, 10, 11, 21, 175, 183, 242, 296, 382 activation parameters, 148 active centers, 18 active site, 386 active transport, 368 activity level, 262 adaptability, 113 adaptation, 362 additives, 7, 33, 34, 35, 36, 37, 38, 41, 42, 45, 47, 103, 113, 114, 118, 149, 155 adhesion, 66, 132, 140, 161, 179 adhesion properties, 66 adhesive interaction, 375 adhesives, 66

adjustment, 281, 282, 283 adsorption, ix, 166, 385, 386, 388, 391, 393 advertising, 118 AFM, 122, 125, 126 agar, 126 ageing, 113, 114 agent, 122, 212 aggregates, 166, 379 aggregation, 90, 166, 388 aggression, 150 agriculture, ix AIBN, 295, 296, 297, 298, 299, 300, 302, 303, 304, 343, 354 alcohol(s), 45, 111, 122, 136, 212, 232, 387 aldehydes, 14, 111, 232 algorithm, 63, 254, 272, 276, 278, 279, 282 alkaline, 380 alkane, 14 alkenes, 6, 7 alkylarens, 34 alternative, 81 alternatives, 66 aluminium, 387, 391 Alzheimer's disease, 151, 152 ambient air, 181 amendments, 101 amide, 350, 352, 381 ammonia, 380 ammonium, 6, 34, 198, 343, 361, 381, 382 Amsterdam, 323 AN, 380, 381, 382, 383 animals, 363 anion, 3, 313, 314, 315, 316, 317, 318, 319, 320, 321, 351 anise aldehyde, 108, 231, 232, 233, 235, 238 anisotropic, 6, 175, 178, 199 anisotropy, 350, 374 annular rings, 189

Index

408

antimicrobial, 109, 122, 126, 134, 135, 398 antioxidant(s), ix, 1, 2, 20, 21, 24, 31, 103, 104, 105, 107, 108, 109, 110, 111, 151, 152, 159, 231, 232, 233, 234, 235, 236, 363, 397, 398, 399, 400, 401, 402 AP, 34, 37, 39, 42, 43, 44, 46, 47 apparel, 246, 253 apple, 122 APS, 325, 342, 343, 353, 354, 355, 356, 357, 358, 359, 381, 383 aqueous solutions, 173, 325, 341, 353 argon, 1, 4, 7, 11, 13, 19, 20 Armenia, 308, 309 aromatic compounds, 7 Arrhenius equation, 9, 183 Arrhenius parameters, 7 arsenic, 363 artificial heart valve, 140 aseptic, 141, 142, 143, 145 aspect ratio, 5 aspiration, 190 assessment, 15, 267 assumptions, 61, 243, 254 atmosphere, 7, 13, 21, 31, 66, 84, 118, 216, 217, 239, 243, 257 atomic force microscope, 125, 274 atoms, 34, 68, 71, 77, 222, 316, 352 ATP, 155, 156 attention, 2, 89, 114, 354, 369 Austria, ix auto acceleration, 37 autocatalysis, 10, 21 autooxidation, 103, 104, 105, 106, 108, 234, 235, 238, 398, 399, 401 availability, 65, 354 averaging, 191, 256

B bacillus, 337 bacteria, 126, 339 bacterial cells, 339 bacteriocin, 122 barriers, 22, 189, 270 basicity, 225 bead mill, 171, 174 beam radiation, ix, 65 beams, 66, 81, 305 beet sugar, 122 behavior, 15, 20, 98, 101, 128, 131, 243, 245, 254, 258, 274, 295, 304, 325, 327, 330, 332, 342, 363 bending, 162 benzene, 223, 224, 225, 226, 227, 228, 229, 296, 372

berries of juniper, 103, 104, 106, 108 beverages, 103, 231 bias, 75 binding, 86, 346 binding energies, 86 biochemistry, 115, 368 biocide activity, 335, 338, 341, 343, 354, 363 biocompatibility, 140 biodegradable, 122, 139, 140 biodegradation, 145 biological activity, 104, 105, 232, 312, 339 biological systems, 34, 139, 165 biomer, 140 biopolymers, 121, 122, 127, 129, 132, 133, 140 biosphere, 118 biosynthesis, 140 biotechnology, ix, 368 bisphenol(s), 211, 212, 213, 214, 220, 221, 222 bleaching, 104 blends, 122, 124, 126, 146, 269 blockcopolymers, 215, 221 blocks, 190, 212, 375 blood, 140, 152, 154, 158, 224, 260 blood flow, 260 blood vessels, 152 body temperature, 240, 242, 250, 251 bonding, 35, 46, 84, 179, 329, 330, 350, 351, 354 bonds, 15, 21, 30, 34, 86, 198, 209, 213, 225, 313, 351, 374, 375 boric acid, 198 borrowing, 114 brain, 152 branching, 18, 286 Britain, 207 bromine, 311, 313, 314, 315, 316, 318 buffer, 126, 141 burning, 213 butadiene, 7, 367, 368, 372, 375 butadiene-styrene, 367, 368, 372 by-products, 380

C Ca2+, 151, 152, 155, 156, 157 cadmium, 363 calcium, 155, 171, 172, 173, 174 calibration, 274 Canada, 208 capillary, 51, 52, 103, 104, 105, 176, 177, 178, 179, 180, 187, 188, 195, 231, 232, 234, 245, 258, 267, 327, 375, 397, 398, 399 caraway, 103, 104, 105, 106, 110, 111 carbon, 69, 71, 82, 162, 163, 330, 346

Index carbon atoms, 346 carbonization, 1, 15, 30, 31 carbonyl, 27, 28 carboxylic acid(s), 14, 397 carcinoma, 151, 152, 153, 156 cardamom, 103, 104, 105, 106, 108, 398 carotene, 104 carrier, 105, 161, 162, 234, 376, 399 cast, 121, 122, 129, 141 casting, 135 catalysis, 21, 33, 34, 35, 37, 38, 40, 41, 42, 44, 45, 46, 47, 48 catalyst(s), 2, 3, 33, 34, 35, 37, 41, 42, 44, 45, 47 catalytic activity, 34, 44, 45, 47 catalytic effect, 24, 33, 37 catalytic system, 34, 37, 40, 41 C-C, 21, 30, 86, 374 CCA, 198, 209 cell, 122, 140, 152, 153, 155, 156, 157, 159, 177, 179, 180, 183, 186, 188, 244, 336, 337, 338, 398 cell membranes, 159 cell surface, 152 cellulose, 162, 179, 203 CFD, 241, 256 CH2-groups, 216 CH3COOH, 305 chain molecules, 179 chain propagation, 44, 45, 46, 47, 48, 343, 380 chain scission, 29, 30 chain transfer, 341, 343, 364 channels, 71, 132, 133, 151, 152, 153, 154, 155, 157 chemical bonds, 86, 374, 375 chemical composition, 189, 380 chemical cross-links, 1, 31 chemical properties, 179, 219, 222 chemical reactions, 34, 66, 173, 203, 304, 307 chemical stability, 213 chemical structures, 66 China, 232 Chinese, 207 chloral, 214, 220, 222 chloride, 217, 221, 335, 336, 341, 349 chlorinated hydrocarbons, 212 chlorine, 165, 222, 363 chloroanhydrides, 364 chloroform, 140, 141, 212, 221 chlorophyll, 165, 166 cholesteric, 215, 216 cholinesterase, 152 chromatography, 103, 104, 231, 232, 304, 397, 398, 399 chromium, 207 Cincinnati, 293

409

circulation, 113, 200 citrus peel, 122 classes, 232 classification, 281 cleaning, 277 clove buds, 397, 398 C-N, 86 CO2, 305 coagulation, 221, 325, 330, 332, 385, 386, 388 coatings, 66, 140, 242 cognitive tool, 62 cohesion, 369 colon, 337 combined effect, 52, 336 combustibility, 213 combustion, 2 commodity(ies), 2, 122 communication, 39, 43 compatibility, 113 complement, 128, 276, 277 complexity, 243, 254 components, 89, 90, 104, 105, 108, 110, 111, 121, 125, 171, 202, 213, 231, 232, 234, 237, 254, 277, 368, 398, 399, 400, 401, 402, 404 composites, ix, 3, 90, 122, 131, 140, 161, 186, 208 composition(s), 3, 4, 47, 68, 77, 79, 89, 90, 92, 101, 103, 104, 105, 106, 108, 109, 110, 111, 113, 117, 119, 120, 124, 129, 147, 148, 152, 161, 163, 202, 221, 226, 227, 228, 232, 235, 238, 325, 336, 337, 339, 341, 342, 343, 345, 346, 347, 348, 353, 362, 363, 367, 369, 370, 371, 372, 374, 376, 393, 397, 398, 399, 400, 401, 402, 404 compounds, 37, 108, 114, 147, 150, 165, 215, 217, 224, 229, 232, 234, 236, 305, 307, 313, 336, 339, 349, 350, 351, 352, 354, 361, 363, 374, 380, 392, 399, 400 computation, 254 computing, 300 concentration, 3, 9, 27, 30, 35, 37, 42, 45, 47, 90, 95, 139, 140, 141, 142, 143, 144, 145, 148, 152, 154, 155, 156, 157, 162, 163, 166, 172, 174, 220, 234, 235, 237, 243, 245, 246, 253, 297, 298, 301, 302, 303, 326, 327, 329, 332, 337, 342, 343, 344, 353, 354, 355, 356, 357, 358, 363, 380, 381, 382, 383, 390, 394, 401, 404 conception, 380 concordance, 111 concrete, 113, 118, 219, 349 condensation, 212, 217, 241, 245, 249, 256, 258, 267 conditioning, 240 conduction, 239, 240, 241, 246, 260 conductivity, 176, 184, 186, 187, 239, 246, 249, 255 configuration, 34

Index

410

Congress, 207, 209 conjugation, 225 Connecticut, 206 conservation, 68, 191, 241, 243 constant rate, 144, 187, 188, 206 construction, 118, 119, 142, 211, 214, 221, 246, 322, 368 consumers, 134, 246 consumption, 37, 45, 118, 332, 379, 380 contaminants, 379 continuity, 256 control, 34, 37, 52, 55, 61, 80, 104, 105, 106, 126, 153, 155, 158, 161, 210, 232, 233, 234, 235, 236, 237, 251, 398, 399, 400 convection, 55, 59, 61, 177, 194, 199, 203, 241, 260, 264 convection drying, 55 conversion, 7, 11, 21, 33, 34, 35, 36, 37, 41, 44, 47, 90, 95, 148, 190, 298, 301, 304, 327, 329, 341, 342, 343, 346, 354 conversion degrees, 327, 329, 343, 354 cooling, 55, 124, 141, 216, 239, 242 copolymers, 114, 140, 211, 212, 213, 214, 215, 216, 221, 336, 337, 338, 339, 343, 344, 354, 361, 369, 374, 375 copper, 198, 297, 363, 380, 381, 382, 383, 385, 386, 392, 394, 395 copper oxide, 380, 381, 382, 383 correlation(s), 37, 103, 133, 152, 220, 245, 266, 312, 357, 374 costs, 52 cotton, 81, 82, 84, 85, 86, 241, 242, 243, 244, 245, 246, 247, 249, 251 Coulomb, 81 coupling, 246, 351 critical analysis, 346 critical value, 203 cross-linked polymers, 364 crystalline, 215, 216, 217, 218 crystallinity, 141 crystallites, 92 crystallization, 224 crystals, 144 culture, 126, 337 curing, 66 customers, 103 cycles, 126, 130, 132, 216 cyclohexanone, 375 cytoskeleton, 157

D danger, 118

Darcy’s law, 190, 191, 192, 195, 207 data analysis, 9 death, ix, 250 decay, 29, 76 decomposition, 1, 6, 18, 19, 21, 24, 31, 34, 37, 42, 43, 44, 45, 171, 296, 297, 303, 304 defects, 52, 65, 86, 92, 197, 201 deficiency, 1, 31 definition, 75, 113 deflation, 82, 86 deformation, 26, 82, 86, 89, 90, 91, 92, 95, 96, 97, 98, 101, 125, 128, 130, 132, 135, 157, 212, 220, 367, 372 degradation, 1, 2, 7, 9, 10, 13, 14, 19, 21, 23, 24, 26, 28, 29, 30, 31, 35, 108, 144, 145, 203, 401, 402 degradation process, 1, 2, 7, 13, 14, 21, 24, 26 dehydration, 18, 31 dehydrogenation, 1, 15, 19 demand, 242, 244, 250 denaturation, 155 density, 61, 79, 90, 113, 114, 141, 177, 180, 181, 182, 183, 186, 192, 193, 195, 196, 200, 213, 243, 249, 253, 258, 273, 295, 296, 300, 301, 302, 305, 387, 393, 394 Department of Agriculture, 121, 205, 206 deposition, 188, 190 derivatives, 7, 122, 140, 152, 213, 214, 218, 236, 312, 336, 337, 349, 350, 351, 352, 363, 379, 398 desorption, 241, 243, 245, 255, 258 desorption of water, 255 destruction, 35, 82, 84, 90, 95, 132, 139, 141, 145, 159, 225, 226, 228, 332, 336, 369, 392 destructive process, 221 detection, 77, 79 deviation, 68, 144, 286, 288, 291, 358, 372, 374 diallyl, 335, 361, 362 diallyldimethylammonium chloride, 335, 336, 341, 342, 346, 348, 362 diallylguanidine acetate, 335, 336, 341, 342, 362 diamond, 135 dichloranhydride, 211, 212, 213, 220, 221 dielectric, 118, 213, 219 dienes, 6, 7 differential equations, 241, 242, 243 differential scanning, 155 differentiation, 37 diffraction, 67, 79, 80, 87, 298 diffuse reflectance, 4 diffusion, 6, 10, 11, 13, 19, 20, 21, 22, 51, 52, 54, 55, 61, 62, 63, 67, 139, 140, 141, 142, 143, 144, 145, 175, 178, 179, 180, 181, 182, 183, 187, 196, 197, 206, 241, 242, 243, 244, 245, 254, 255, 256, 260, 261, 262, 267, 268, 269, 296, 355, 375

Index diffusivities, 144 diffusivity, 139, 142 dignity, 220 dilation, 281, 373 dimer, 350 diphenylolpropane, 212 dipole, 313, 317 dipole moment(s), 313, 317 direct measure, 291 discomfort, 241, 242, 244, 245, 250 disinfection, 364 dispersion, 369, 379, 385, 386, 387, 391, 393 dispersity, 376 displacement, 55, 173, 203 dissociation, 354 distillation, 241, 304 distilled water, 173 distortions, 295, 304 distribution, 56, 74, 75, 76, 77, 79, 80, 92, 121, 127, 226, 273, 274, 278, 279, 280, 287, 346, 363, 364, 374, 385, 389, 390 divergence, 297 diversity, 147 division, 99, 172 DMF, 34, 35 DMFA, 355 dosage, 173 double bonds, 104, 232, 398 DRIFT, 4 drug delivery, 139, 140 drug delivery systems, 139 drug release, 140, 141, 142, 143, 144, 145 drugs, 139, 145, 152 drying, 3, 51, 52, 54, 55, 56, 57, 58, 59, 61, 62, 66, 82, 175, 176, 178, 179, 180, 182, 187, 188, 189, 191, 193, 194, 196, 197, 198, 199, 200, 201, 202, 203, 205, 206, 208, 209, 210, 251, 269, 369 drying time, 51, 52, 55, 61, 62, 179, 189, 269 DTA curve, 226 durability, 90, 92, 95, 97, 98, 99, 101, 113, 120, 299 duration, 86, 220, 295, 297, 301, 302, 303, 305, 372, 381, 382, 383, 391, 392 dynamic mechanical analysis, 125, 128 dynamic viscosity, 148

E E. coli, 335, 336, 337 earth, 68 Egypt, 323 Einstein, 296 elaboration, 139, 364 elasticity, 95, 162, 212, 369

411

electric field, 66, 271 electrical resistance, 66 electromagnetic, 203 electron(s), 4, 18, 34, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 84, 86, 125, 133, 223, 225, 226, 274, 307 electron beam lithography, 79, 81 electron density, 226 electron microscopy, 274 electronic structure, 312, 313, 314, 315, 316, 317, 319, 321 electrospinning, 271, 279, 283, 284, 291 electrospun, 271, 272, 274, 283, 289, 291 electrostatic force, 271 elementary particle, 77 elongation, 66, 129, 212, 370, 371, 372, 374 emission, 76, 77, 78, 125, 126, 129, 295, 296, 299, 300, 302, 303, 304, 305, 306, 307 emission source, 299 employment, 147 emulsions, 379 energy, 10, 21, 52, 55, 61, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 86, 126, 179, 187, 193, 194, 220, 225, 240, 243, 251, 256, 264, 266, 304, 305, 307, 313, 316, 317, 318, 320, 368, 376, 393 energy consumption, 52, 55, 61, 179 energy density, 305 energy transfer, 68 England, 209, 267 entropy, 52 environment, 30, 35, 92, 114, 118, 167, 239, 240, 242, 260 environmental conditions, 203, 245, 250 environmental factors, 203, 239 epidemic, 336 EPR-spectroscopy, 152, 153 equality, 44 equilibrium, 54, 63, 140, 141, 142, 144, 176, 178, 179, 187, 205, 241, 243, 252, 253, 254, 369 equipment, 66, 118, 224, 354 erosion, 277, 281 erythrocyte membranes, 151, 152, 153, 157 erythrocytes, 152, 153, 154, 155, 156, 157, 158, 159 Escherichia coli, 337 essential oils, 103, 104, 105, 106, 108, 110, 111, 231, 232, 234, 236, 237, 397, 398, 399, 400, 401, 402, 404 ester(s), 14, 26, 27, 29, 122, 171, 232 ethanol, 3, 6, 155, 156, 158, 165, 166, 168, 307, 354, 355 ethers, 34

Index

412

ethylbenzene, 33, 34, 35, 36, 37, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48 ethylene, 1, 2, 3, 6, 7, 90, 121, 122, 123, 124, 127, 172, 174, 211, 212, 213, 216, 219, 220, 221, 222 ethylene glycol, 172, 174 ethylene oxide, 121, 122, 123, 124, 127, 216 ethyleneglycol, 171, 172, 173, 174 ethylhydroxyethylcellulose (EHEC), 385, 387, 388, 389, 390, 391, 392 eucalyptus, 105 eugenol, 104, 231, 232, 234, 236, 237, 238, 398, 402, 404 evaporation, 52, 178, 179, 187, 194, 226, 228, 240, 241, 242, 245, 246, 250, 251, 252, 256, 260, 263, 267, 369 evidence, 1, 13, 21, 30, 391 evolution, 2, 24, 29, 179, 304 examinations, 125 excitation, 76, 77, 129, 298, 305, 307, 374, 376 exercise, 52, 240, 250, 251, 252, 262 experimental condition, 7, 167, 302 expertise, 66 exploitation, 89, 214 exposure, 65, 80, 81, 202 external influences, 368, 369 extinction, 296 extraction, 122 extrapolation, 42 extreme cold, 253 extrusion, 121, 122, 124, 135

F fabric, 162, 240, 242, 243, 244, 245, 246, 249, 250, 251, 253, 254, 255, 256, 257, 258, 259, 268, 269, 270 fabrication, 140 family, 134 fast processes, 245, 309 federal budget, 229 feelings, 242 fennel, 103, 104, 105, 106, 108, 111, 398 fibers, 65, 81, 82, 84, 86, 122, 126, 132, 135, 162, 200, 241, 242, 243, 244, 245, 246, 249, 250, 251, 253, 254, 255, 256, 260, 270, 271, 272, 273, 274, 276, 278, 279, 281, 283, 287 fidelity, 21 filament, 66, 67, 253, 273 filled polymer composite materials, 89 filled polymers, ix filler particles, 4 fillers, 2, 89, 90, 95, 97, 99, 101, 162

film(s), 3, 80, 105, 121, 122, 124, 125, 126, 127, 129, 132, 133, 134, 135, 140, 141, 142, 143, 144, 145, 146, 212, 234, 242, 245, 367, 369, 370, 371, 372, 373, 374, 375, 376, 399 film formation, 369, 375 film thickness, 105, 142, 234, 399 filtration, 140, 387 financial support, 332, 339, 360 Finland, 104, 234, 399 fitness, 59, 60 fixation, 190 flame, ix, 2, 105, 220, 234, 399 flame retardants, ix flammability, ix, 2 flavor, 104, 398 flexibility, 216 flexible polymers, 392 flexural strength, 162, 163 float, 392 flocculant, 379, 380, 381, 382, 383 flocculation, 380 fluid, 52, 171, 174, 177, 179, 190, 256 fluorescence, 72, 76, 125, 126, 127, 129, 132, 133, 296, 298, 300, 301, 302, 303 fluorescent microscopy, 132 food, 103, 106, 121, 122, 129, 134, 135, 140, 231, 232, 235, 368, 398 food additives, 122, 398 food safety, 134 footwear, 162, 260 forecasting, 53 Forest Service, 206, 207 fossil, 140 fossil fuels, 140 Fourier, 4, 294 fractures, 84 fragmentation, 364 free radicals, 18, 296 free volume, 114 friction, 56, 175, 203 fruit juice, 122 FTIR, 1, 2, 4, 19, 24, 25, 26, 27, 29, 369 FTIR spectroscopy, 1, 24 fusion, 212

G gas diffusion, 241 gas phase, 19, 22, 178, 192, 225, 242, 258, 312 gases, 189 gauge, 203 gel, 147, 148, 166, 380 gel-effect, 147

Index generalization, 241 generation, 65, 66, 72, 74, 80, 81, 151, 261, 262, 361, 368, 369 genetic factors, 203 Geneva, 208 Georgia, 309 Germany, 140, 146, 152, 207, 208, 367, 385 ginger, 103, 104, 105, 106 glass, 36, 104, 126, 128, 141, 213, 221, 232, 297, 300, 387, 398 glass transition, 128, 213, 221 glass transition temperature, 128 glasses, 118 glucose, 109 glycerol, 122, 124 glycol, 162 gold, 125, 283 government, iv GPS, 208 grains, 56, 90, 175, 189, 200, 203 gram-negative bacteria, 337 gram-positive bacteria, 337 grape skins, 122 graph, 141, 266, 276, 316 grass, 104, 105, 106, 110, 234 gravity, 184, 185, 187, 189, 241 green tea, 104, 105 groups, 18, 26, 27, 28, 29, 32, 149, 180, 198, 215, 216, 221, 225, 330, 332, 338, 351, 362, 363, 364, 372, 374, 380, 381, 386, 387, 392, 393, 394 growth, 10, 26, 27, 29, 41, 46, 47, 51, 62, 90, 118, 121, 134, 172, 181, 185, 186, 190, 337, 354, 361 growth rate, 190 growth rings, 186 guanidine, 325, 327, 330, 331, 332, 335, 336, 337, 338, 339, 344, 349, 350, 351, 352, 353, 354, 361, 363, 364 guanidine groups, 325, 327, 330, 339, 363

H haemoglobin, 154 halogen, 166, 213, 214, 220, 222, 312 hardener, 119 hardness, 197, 199, 200, 201, 203 hardwoods, 184 haze, 327 health, 103, 232 heat, 51, 52, 55, 56, 61, 66, 67, 114, 149, 150, 175, 176, 177, 179, 186, 187, 191, 193, 194, 203, 211, 212, 214, 219, 220, 221, 239, 240, 241, 242, 243, 244, 245, 246, 249, 250, 251, 252, 253, 254, 255,

413

257, 260, 261, 262, 263, 264, 265, 266, 267, 268, 269, 369 heat capacity, 255 heat exchange, 239 heat loss, 177, 194, 240, 251, 252 heat release, 243, 245 heat transfer, 61, 176, 179, 187, 193, 194, 245, 246, 249, 252, 264, 268 heating, 4, 7, 9, 10, 12, 13, 15, 16, 17, 19, 20, 21, 22, 26, 27, 52, 55, 56, 61, 141, 175, 178, 199, 202, 203, 216, 227 heating rate, 4, 7, 9, 10, 12, 13, 15, 16, 17, 19, 20, 21, 22 height, 176, 197, 198, 261 heme, 224 hemisphere, 200 hemocompatibility, 140 heptane, 3 heterogeneity, 325, 326, 327, 329, 330, 355, 358, 362 heterogeneous systems, 369 hexane, 104, 232, 305, 307, 398 high-molecular compounds, 147, 211, 222, 336, 379 hip, 189 histogram, 278, 280, 281, 282, 286 homogeneity, 36, 126, 133, 327, 329, 353, 354, 355 homogeneous catalyst, 34 homolytic, 44, 45 homopolymers, 330, 336, 338, 342, 363 hot pressing, 4 human activity, 113, 118 humidity, 56, 90, 177, 182, 183, 193, 239, 242, 243, 244, 245, 250, 251, 254, 256, 258, 261 hybrid, 151, 152, 159 hydrocarbons, 18, 34, 104, 105, 106, 108, 109, 111, 140, 232, 398, 401, 402 hydrochloride, 332, 335, 337, 349, 350, 352, 363 hydrocolloids, 121, 129 hydrogels, 122 hydrogen, 6, 7, 14, 35, 68, 165, 166, 168, 329, 330, 331, 350, 351, 354, 375 hydrogen abstraction, 14 hydrogen bonds, 330, 331, 350, 354, 375 hydrogen peroxide, 165, 166 hydrolysis, 171, 172, 174, 379, 380, 381, 382 hydroperoxides, 1, 14, 16, 17, 18, 19, 20, 21, 24, 31, 34 hydrophilic, 44, 242, 249, 343, 393 hydrophilic, 267 hydrophilic materials, 242 hydrophobic, 167, 244, 249, 329, 330, 331, 332, 336, 343, 354, 392, 393 hydrophobic groups, 393

Index

414 hydrophobic interactions, 330, 332, 354 hydroquinone, 304, 326, 357, 358 hydroxide, 171, 173, 174 hydroxyl, 26, 122, 211 hydroxypropyl, 216 hygroscopic, 52, 62, 175, 178, 179, 187, 191, 241, 243, 267 hypertension, 159 hyperthermia, 240 hypothermia, 239, 251 hypothesis, 13

I illumination, 281 image analysis, 271, 272, 283, 284, 289, 291 images, 67, 123, 125, 126, 127, 129, 133, 272, 274, 276, 278, 281, 283, 285, 286, 289, 291 imaging, 76, 77, 125 immersion, 260 immunological, 376 impact strength, 119, 162, 163 implants, 140 imprinting, 364 impurities, 7, 380 in situ, 1, 249 in vitro, 136, 153 incidence, 75, 76 inclusion, 121, 122, 130, 132, 135, 225 independent variable, 274 India, 104, 398 indication, 129 indices, 163, 211, 221, 335 industrial sectors, 81 industrial wastes, 118 industry, 80, 103, 120, 122, 203, 231, 232, 235, 368, 376, 398 inelastic, 67, 68, 71, 75 inflammation, 213, 222 inflation, 82 inhibition, 42, 121, 126, 232, 236, 237, 399 inhibitor, 31 inhomogeneties, 369 initiation, 14, 45, 47, 48, 148, 297, 299, 304, 381 injury, iv inoculation, 126 inorganic fillers, 90, 95 Instron, 125, 126 instruments, 274 insulation, 244, 251, 267, 269 insulin, 109 integration, 55, 61, 301, 302, 303 integrity, 157, 159

intensity, 27, 73, 80, 118, 154, 165, 281, 282, 283, 296, 297, 299, 301, 302, 304, 305, 372, 373, 374, 375, 383, 386, 387, 393 interaction(s), 45, 68, 69, 71, 72, 74, 75, 78, 79, 89, 114, 136, 174, 190, 206, 211, 217, 223, 224, 225, 229, 239, 243, 250, 254, 269, 296, 297, 299, 304, 325, 327, 329, 330, 331, 332, 336, 338, 351, 367, 368, 372, 374, 375, 376, 380, 386 intercalation, 2, 4 interface, 180, 241, 369, 386, 387 interphase, 367, 368, 372, 374, 375, 376 interpretation, 68, 346 interval, 75, 105, 213, 214, 215, 221, 236, 296, 304, 305, 327, 332, 336, 354, 358, 372, 398 intrinsic viscosity, 330, 343, 355, 356 ionization, 72, 105, 234, 304, 327, 399 ions, 155, 173, 312, 319, 320, 354 IR, 29, 216, 217, 305, 307, 367, 369, 372, 373, 375, 376 Iran, 51, 55, 65, 175, 239, 271 iron, 33, 34, 35, 41, 45, 47, 69, 70 irradiation, 66, 67, 81, 82, 83, 84, 86, 165, 166, 167, 198 IR-spectra, 369, 372, 373, 375, 376 IR-spectroscopy, 216, 217, 367 isolation, 380 isomerization, 296 isomers, 296 isophthalic acid, 221 isothermal, 4, 11, 179, 305 isotherms, 178 Israel, 398 Italy, 232

J Japan, 136

K K+, 151, 152, 153, 154, 155, 157 kinetic curves, 141, 156 kinetic energy, 67 kinetic model, 7, 10, 22 kinetic parameters, 7, 13 kinetic regularities, 304 kinetic studies, 37 kinetics, ix, 2, 7, 41, 43, 139, 140, 141, 142, 143, 144, 166, 206, 243, 254, 258, 270, 296, 327, 379, 380, 381, 382 King, 243, 268 knots, 186, 197, 201

Index

L labeling, 279, 280, 281 labor, 61, 161, 383 lactic acid, 122, 136 lactones, 14 laminar, 90 laser(s), 125, 127, 129, 133, 295, 296, 297, 298, 299, 300, 302, 303, 304, 305, 306, 307 latex, 89, 367, 368, 369, 372, 373, 374, 375, 376 laundry, 162 laws, 52, 295, 299, 304 lead, 1, 6, 14, 15, 18, 31, 35, 61, 66, 80, 161, 172, 174, 180, 226, 229, 251, 253, 254, 303, 357, 363, 369, 372, 374, 382 leakage, 74 Lebanon, 256 lemonene, 231, 232, 233, 234 lemongrass, 103 lens, 125, 166, 300 LIF, 159 lifetime, 301 ligand(s), 33, 34, 35, 41, 44, 46, 47, 166, 223, 224, 225, 229 light beam, 299, 303, 305 light scattering, 151, 153, 155 light stabilization, ix lignin, 203 limitation, 175 linalool, 110, 231, 232, 233, 234, 238, 401, 402 linear dependence, 357, 358 linear function, 144, 243 links, 7, 215, 216, 335, 341, 344, 363 lipid(s), 104, 151, 152, 153, 157, 159, 368 liposomes, 165, 368, 376 liquid chromatography, 103 liquid crystals, ix liquid phase, 172, 173, 174, 178, 256, 305, 387 liquids, 30, 189, 305, 307, 364 Listeria monocytogenes, 121, 126, 135 literature, 7, 61, 68, 118, 245, 255, 274, 296, 297, 298, 299, 304, 380, 400 lithography, 65, 79, 81 living radical polymerization, 364 local action, 145 location, 80, 128, 226, 239, 256, 274 London, 31, 207, 269, 294, 377 low density polyethylene, 32 low temperatures, 7, 216 lumen, 190 lysis, 337

415

M mace, 103, 104, 105, 106, 107, 108, 111 macrocycle, 165, 223, 224, 225, 226 macromolecules, 29, 89, 122, 126, 213, 327, 330, 331, 332, 362, 363, 369, 386 macroradicals, 327 magnetic field, 74 manufacturing, 66, 117, 118, 119, 120, 122 market, 135, 251 marketing, 209 mass loss, 2, 10, 11, 13, 18, 20 mass transfer process, 179, 368 materials science, 66 matrix, 5, 20, 31, 51, 89, 90, 92, 101, 132, 144, 249, 250, 275 meanings, 100, 313 measurement, 62, 126, 129, 144, 198, 200, 201, 240, 274, 287, 288 measures, 53, 200 mechanical behavior, 92 mechanical loadings, 114 mechanical properties, 2, 89, 91, 92, 95, 96, 97, 98, 101, 115, 121, 122, 129, 140, 203, 212 media, 62, 139, 140, 241, 268, 269, 343, 362, 369 median, 281, 283 medicine, 140, 339, 354, 361, 368, 376 melt, 13, 19, 90, 216 melting, 90, 128, 131, 217 melting temperature, 90 membranes, 139, 151, 152, 153, 155, 157, 158, 159, 190, 242, 364, 368 memory, 367, 376 mercury, 297, 354 metabolism, 109, 368 metalloporphyrins, 223, 224, 225, 229 metals, 18, 71, 74, 167 methacrylic acid, 350, 354 methane, 162 methanol, 297, 343, 354, 355 methyl group(s), 329, 343, 346 methyl methacrylate, 148 methylene, 18, 216, 350, 351, 372, 387, 393 methylene group, 351, 372 methylmethacrylate, 299, 349 Mg2+, 165, 166 mice, 152 micelles, 35, 37, 44, 165, 166, 368 microcalorimetry, 155 microclimate, 239 microheterogeneity, 368 micrometer, 79, 129 microorganisms, 336

416

Index

microscope, 4, 65, 67, 71, 80, 81, 125, 133, 274 microscopy, 67, 125 microstructure, 125, 126 microviscosity, 151, 152, 153, 157 microwave(s), 51, 55, 62, 65, 199, 200, 203 migration, 51, 134, 241, 267 minerals, 18 mixing, 127, 128 MMA, 119, 350, 351 mobility, 13, 18, 89, 144, 367, 368, 376 model system, 327, 328, 332, 399 modeling, ix, 34, 51, 101, 119, 139, 140, 241, 258, 272, 327 models, 12, 23, 52, 53, 58, 61, 68, 71, 165, 179, 243, 254, 256, 261, 367 modernity, 118 modulus, 126, 129, 132, 162 moisture, ix, 51, 52, 53, 54, 55, 56, 58, 61, 63, 176, 177, 178, 179, 180, 181, 183, 186, 187, 188, 189, 191, 193, 196, 197, 200, 203, 207, 240, 241, 242, 243, 244, 245, 246, 251, 252, 253, 254, 255, 256, 257, 258, 259, 260, 267, 268, 269 moisture content, 51, 52, 53, 54, 55, 56, 58, 61, 176, 177, 178, 179, 180, 181, 183, 186, 187, 188, 193, 196, 197, 200, 241, 243, 252, 254, 256 moisture sorption, 243, 245, 254, 255 mole, 220, 226, 326, 327, 329, 332, 346, 348, 354, 355, 356, 357, 358, 359, 382 molecular mass, 7, 332, 343, 354, 361, 363, 364, 380, 381, 382 molecular mobility, 369 molecular oxygen, 45, 48 molecular structure, 362 molecular weight, 7, 13, 124, 140, 176, 182, 211, 217, 283, 341, 386, 387, 392 molecules, 14, 18, 34, 35, 41, 44, 56, 61, 77, 113, 166, 167, 168, 173, 175, 179, 189, 203, 224, 226, 229, 296, 297, 298, 300, 301, 302, 303, 304, 325, 327, 330, 331, 372, 377, 379, 395, 398 momentum, 55, 61, 68, 81, 256, 257 money, 52 monolayer, 166 monomer(s), ix, 3, 147, 148, 150, 171, 212, 214, 219, 220, 222, 304, 325, 327, 328, 329, 330, 331, 332, 335, 336, 341, 342, 343, 346, 347, 348, 349, 350, 353, 354, 355, 356, 357, 358, 360, 362, 363, 364, 379, 380, 381, 382, 383 monomer salts, 354, 357 monosaccharides, 122 monoterpenes, 107, 108 Monte Carlo, 80 Monte-Carlo simulation, 68, 69, 70 Moon, 405

Moscow, 1, 33, 62, 89, 101, 103, 112, 139, 151, 159, 161, 165, 231, 238, 308, 311, 325, 335, 341, 345, 348, 349, 353, 360, 361, 367, 376, 377, 384, 385, 397, 404 motion, 67, 242 movement, 52, 56, 68, 175, 179, 187, 189, 203, 369, 387 MTS, 125

N NaCl, 342, 343, 354, 356 nanicomposites, 367 nanocomposite(s). ix, 1, 2, 3, 4, 5, 6, 7, 13, 14, 18, 19, 20, 22, 24, 29, 30, 31, 367 nanodimensions, 113 nanofibers, 271 nanolayers, 20 nanometer(s), 74, 79, 81 nanoparticles, 2, 16, 18, 24 nanostructures, ix nanosystems, 114 natural polymers, 122 Nd, 295, 299, 305 negative relation, 189 nematic, 215, 216 network, 122, 162, 264, 272, 332 neurodegeneration, 151 neurodegenerative diseases, 151, 152, 159 New Jersey, 376 New Orleans, 267 New York, 3, 32, 48, 62, 111, 112, 137, 159, 204, 205, 208, 210, 269, 344, 405 New Zealand, 181, 205, 208, 210 Newtonian, 148 nickel, 34, 35 nitrogen, 297, 346, 352 NMR, 217, 337, 349, 350 NMR1H spectroscopy, 345, 346, 348, 355 noise, 77, 281 nonequilibrium, 249 normal distribution, 273, 274, 284, 289 nucleation, 10 nucleus, 10, 68

O observations, 53, 242, 244 occlusion, 190 octyl acetate, 231, 232, 233, 234, 238

Index oil(s), 103, 104, 105, 106, 108, 110, 111, 231, 232, 233, 234, 235, 237, 238, 383, 397, 398, 399, 400, 401, 402, 404 oil samples, 104, 399 oil storage, 104, 105, 401 olefins, 7, 114 oligoarilen-sulphonoxide, 211 oligoethers, 213, 215, 217 oligomers, ix, 211, 216, 219 optical activity, 304 optical density, 142, 154, 386, 387, 393 optical fiber, 77 optical systems, 81 optics, 80, 309 optimization, 51, 61, 363 organ, 4, 24 organic compounds, 14, 49, 232, 364 organic mediums, 354 organic solvent(s), 225, 354, 355 organism, 126, 152, 159 organization, 89, 92, 101, 129, 155, 157, 332, 374, 376 organoclay, 4, 24 orientation, 5, 62, 75, 79, 181, 226, 272, 273, 283, 287, 289, 367, 374 orthopedic stomatology, 117, 118, 119, 120 Ottawa, 269 oxidation, ix, 2, 14, 20, 27, 32, 33, 34, 35, 36, 37, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 104, 105, 106, 108, 110, 111, 114, 152, 231, 232, 233, 234, 235, 236, 237, 397, 398, 399, 400, 401, 402, 404 oxidation products, 14, 27, 32, 37 oxidation rate, 37, 41, 43, 47, 399, 400, 401, 404 oxidative stress, 152 oxides, 110, 387, 391, 401 oxygen, 1, 2, 4, 7, 16, 19, 20, 21, 30, 31, 34, 114, 122, 165, 166, 213, 214, 222, 225, 398 oxygen absorption, 16 oxygenation, 34, 35, 41, 44

P PAA, 336, 337, 338, 379, 380 packaging, 121, 122, 129, 134, 135, 213, 260 paints, 66 parameter, 33, 37, 41, 44, 46, 47, 70, 80, 99, 100, 189, 198 particles, 2, 4, 5, 6, 13, 30, 33, 34, 42, 66, 77, 90, 122, 140, 174, 297, 305, 375, 379, 380, 381, 382, 383, 385, 386, 387, 388, 391, 392, 393 partition, 118, 281, 307 passive, 368 patents, 380

417

pathogenic, 336 pathology, 159 pathways, 18, 155 patterning, 81 PCM, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101 pectin, 121, 122, 123, 124, 126, 127, 128, 132, 135, 136 pectin, 121, 122, 124, 125, 136, 137 PEHD, 113, 114, 115 perception, 239 performance, 41, 240, 246, 249, 272, 273 perfusion, 260 permeability, 1, 6, 13, 31, 176, 187, 189, 190, 191, 192, 195, 240, 242, 253, 256, 260, 302, 307 permeation, 159, 242, 245, 250 permittivity, 213 PET, 171, 172, 173, 174 Petroleum, 340, 348, 360, 365 pH, 141, 325, 336, 353, 354 pharmacology, 106, 109 phase inversion, 374 PHB, 139, 140, 141, 142, 143, 144, 145 phenol, 34, 37, 42, 236, 398, 399 phenolphthalein, 217 PhOH, 37, 39, 42, 43 phosphate, 126, 141 phosphonates, 113, 114 phosphorus, 114 photodegradation, ix photodestruction, 165, 166, 167, 168 photoemission, 126 photographs, 15, 82 photolithography, 80 photolysis, 296 photons, 77, 81, 295, 297, 299, 300, 301, 302, 303, 304, 305, 307 photopolymerization, 147, 304 photoresist, 65, 80, 81 photosynthesis, 165 photosynthetic systems, 165 physical activity, 239, 240 physical and mechanical properties, 89, 90, 97 physical exercise, 242 physical mechanisms, 51, 179, 244 physical properties, 115, 203, 207, 243, 255 physical-mechanical properties, 113 physicochemical properties, 2, 226 physics, 119 physiological factors, 242 piezoelectric, 126 pigments, 385, 386, 391, 392, 393, 395 pink grapefruit, 397, 398, 400, 401, 402, 403

418

Index

plants, 103, 104, 105, 122, 231, 363 plasma, 66 plasticity, 90, 95, 101, 212, 214 plasticization, 114, 115 plastics, 119, 122 Plywood, 208 PMMA, 117, 118 Poland, ix polar groups, 114, 380 polar molecules, 175, 203 polarity, 166, 221 polarization, 77, 216 polarization microscopy, 216 pollution, 118 poly(3-hydroxybutyrate), 140, 146 polyacrylamide, 379, 380 polyamide, 90 polyarylates, 219, 221 polycondensation, 211, 212, 215, 216, 217, 219, 220, 222 polydispersity, 221 polyelectrolytes, 327, 336, 338, 354, 361, 362 polyesters, 214, 220, 221, 222 polyether, 216 polyethylene, 1, 2, 3, 14, 29, 30, 32, 113, 114, 146 polyethyleneterephthalate, 171 polyisocyanurates, 161 polymer chains, 2, 7, 325 polymer film, 66, 336 polymer materials, 89, 213 polymer matrix, ix, 4, 6, 24, 30, 89 polymer molecule, 242, 325, 327, 343, 382 polymer nanocomposites, 6 polymer networks, 364 polymer properties, 162 polymer solutions, 147, 148 polymer systems, 140, 331, 332, 362 polymeric chains, 374 polymeric composites, ix polymeric materials, ix, 113, 114, 118, 161, 162, 163, 213, 219, 220, 221, 222, 369 polymeric membranes, 367 polymerization, 1, 2, 3, 4, 6, 66, 101, 119, 147, 148, 149, 296, 299, 304, 307, 327, 329, 330, 331, 332, 341, 342, 343, 345, 346, 353, 354, 355, 356, 357, 358, 359, 362, 364, 379, 380, 381, 382, 383 polymerization kinetics, 307, 327 polymerization process, 149, 332, 342, 345, 346, 354, 358 polymerization processes, 342, 345, 346, 354, 358 polymethylmethakrylate, 117 polyolefin(s), 2, 6, 114 polypeptide, 135

polypropylene, 32, 162, 244, 246, 247, 249, 251 polysaccharide, 122 polythene, 114 polyurethane(s), 90, 148, 161, 162, 241 polyurethane foam, 162 polyvinyl alcohol, 386, 392 polyvinyl spirit, 90 pomace, 122 population, 300, 301, 302 population growth, 302 porosity, 177, 182, 183, 186, 249, 256 porous materials, 51, 178 porous media, 51, 188, 191, 241, 256, 267 porphyrins, 223, 224, 225, 226, 229 ports, 118 potassium, 113, 114, 115, 152 power, 55, 66, 68, 118, 260, 296, 297, 303, 304 precipitation, 327, 379, 380, 381, 382, 383 prediction, 254 preference, 77, 78, 246 preservative, 189 pressure, 3, 52, 90, 124, 176, 177, 178, 180, 181, 182, 189, 190, 191, 192, 193, 194, 195, 208, 217, 240, 244, 250, 258, 261, 297, 369, 375, 386 primary products, 34 probability, 35, 77, 152, 303, 369 probe, 86, 125, 126, 133, 152 production, 34, 52, 55, 71, 80, 118, 122, 140, 148, 161, 162, 165, 211, 219, 244, 252, 354, 363, 391 program, 119 programming, 105, 234, 399 proliferation, 140 promote, 35, 213, 368 propagation, 7, 47, 354, 358 propylene, 34, 162, 216 prosthetics, 117, 118 protein(s), 122, 123, 124, 126, 127, 128, 132, 151, 152, 153, 155, 157, 159, 331 protein structure, 157 protocol, 244 protons, 6, 346, 347, 348, 350, 351, 352 pruning, 277, 286 PSG, 130, 132 PTFE, 241 pulse, 297, 301, 303, 307 pulses, 297, 305, 307 pumps, 66 purification, 165, 379, 380, 382, 384 PVA, 271, 283, 284, 291, 386, 387, 392, 393, 394 PVC, 241 PVP, 166, 168, 346, 347 PVS, 90, 95, 96, 100, 101 pyrolysis, 2, 7, 29, 305

Index

Q quality control, 101 quanta, 72 quantum yields, 298, 301 quantum-chemical calculations, 312 quartz, 300 quaternary ammonium, 33, 36, 37

R radiation, ix, 3, 55, 65, 67, 76, 77, 78, 81, 84, 86, 114, 159, 177, 194, 203, 239, 240, 246, 260, 261, 264, 266 radical copolymerization, 342 radical mechanism, 6 radical polymerization, 325, 327, 330, 336, 343, 353, 354, 355, 361, 364, 384 radius, 199 rain, 246 Ramadan, 238, 405 range, 1, 4, 6, 7, 13, 19, 24, 26, 27, 29, 66, 69, 70, 73, 77, 80, 86, 122, 125, 141, 145, 147, 148, 149, 151, 155, 157, 162, 179, 181, 186, 241, 273, 296, 297, 353, 368, 376 ratings, 244, 251 raw materials, 126 reactant(s), 9, 10 reaction medium, 353, 354, 358, 381 reaction order, 7, 358 reaction rate, 35, 37, 45, 148 reaction temperature, 343, 383 reaction time, 343 reactivity, 345, 346, 358, 362 reading, 4 reagents, 173, 224, 297 real time, 60, 61 reality, 239 recall, 264, 281 reception, 89, 90, 92, 101, 119, 336 recognition, 223 recombination, 1, 31, 296 reconstruction, 332 recycling, 117, 118, 119 red blood cells, 154, 158 redistribution, 34 reduction, 52, 75, 78, 92, 173, 276, 327, 355, 357, 388, 392 reflection, 4, 6, 77, 125, 126, 127, 129, 132, 133 regression, 11, 100, 101, 181, 182 regression equation, 100, 181, 182 regulation, 155, 363, 368, 375

419

reinforcement, 162 relationship(s), 70, 75, 105, 178, 181, 193, 234, 243, 253, 254, 255, 264, 279, 368, 399, 404 relaxation, 140, 301, 304, 367, 368, 369, 372, 374, 376 relaxation processes, 369 relaxation rate, 301, 304 reliability, 114, 297 resins, 219 resistance, 2, 52, 66, 149, 161, 180, 187, 199, 214, 216, 221, 240, 241, 242, 246, 258, 260 resolution, 4, 80, 81 resources, 117, 119 respiration, 260, 261, 263 retardation, 14, 20 retention, 105, 399 returns, 252 rigidity, 152 rings, 372 rolling, 203 ROOH, 14, 34, 36, 37, 44 room temperature, 13, 26, 104, 117, 119, 125, 126, 141, 232, 264, 398 root-mean-square, 197 roughness, 176, 197, 198, 199, 203, 209 roughness measurements, 198, 199 rubber(s), 162, 163, 241, 374 rubbery state, 161 Russia, ix, 1, 33, 62, 90, 103, 113, 117, 119, 120, 139, 147, 151, 161, 165, 171, 211, 215, 219, 223, 231, 307, 308, 309, 311, 367, 379, 385, 397 rutile, 385, 386, 387

S SA, 166 salt(s), 33, 34, 35, 37, 92, 113, 114, 172, 174, 313, 327, 331, 332, 349, 350, 352, 354 sample, 3, 4, 7, 15, 29, 54, 55, 67, 68, 71, 72, 74, 77, 78, 79, 82, 90, 104, 108, 110, 111, 125, 126, 128, 130, 144, 162, 163, 186, 190, 198, 201, 232, 235, 236, 243, 273, 299, 303, 304, 372, 398 sampling, 199 saturated fat, 152 saturation, 52, 178, 179, 180, 181, 203, 221, 249, 258 savings, 61 scaling, 267 scanning electronic microscope, 125 scanning tunneling microscope, 65, 81 scatter, 72 scattering, 4, 68, 69, 70, 71, 72, 75, 77, 78, 80, 155, 156

420

Index

school, 262 science, 113, 118, 206, 208, 209, 219, 229, 354, 361 sea spray, 246 search, 336, 362, 363, 371 sediment(s), 174, 327, 329, 332, 354 sedimentation, 387, 388, 390, 392 seed(s), 111, 103, 104, 106, 110 segmentation, 281, 282 selecting, 153, 279, 280 selectivity, 33, 34, 35, 36, 37, 41, 47, 224, 229 self-organization, 369 semiconductor, 80 sensation(s), 241, 242, 244, 250, 251, 266 sensitivity, 368, 369, 372, 374 separation, 142, 281, 327, 353, 354, 364 series, 4, 41, 52, 67, 105, 111, 122, 124, 162, 238, 284, 286, 287, 288 serum, 166 serum albumin, 166 sewage, 384 shape, 71, 75, 155, 276, 330 shaping, 313 shares, 348 shear, 1, 19 shock, 113, 114, 115, 150, 162, 386 side effects, 155, 157 signal transduction, 152, 155 signals, 73, 74, 126, 133, 345, 346, 348, 350, 351, 352 silica, 104, 166, 234, 399 silicate, 2, 7, 13, 18, 30 silicon, 387, 391 silk, 86 siloxane, 216 silver, 69 similarity, 66, 368, 391 simulation, 62, 68, 244, 268, 272, 273, 286, 288, 291, 303 sites, 18, 20, 152, 153, 179, 224, 386 skeleton, 117, 119, 120, 178, 192, 276, 277, 278, 368 skin, 109, 241, 242, 244, 250, 251, 252, 253, 257, 258, 259, 260, 261, 368 smectic, 215, 216 smoothing, 53 smoothness, 199, 203 society, 118 sodium, 312, 313, 314, 319, 346, 350 software, 4, 10, 52, 125, 126, 224 softwoods, 181, 184, 208 solid matrix, 51 solid phase, 386, 387, 393, 394 solid polymers, 367 solid state, 2, 10, 372

solubility, 172, 216, 221, 336, 380, 381, 382, 393 solvation, 224, 385, 386, 388 solvent(s), 18, 35, 37, 141, 217, 224, 225, 226, 229, 271, 297, 298, 327, 346, 349 solvent molecules, 226 sorption, 144, 180, 194, 241, 243, 245, 249, 253, 254, 255, 256, 258, 268, 270 sorption isotherms, 194 sorption kinetics, 243, 254 sorption method, 180 sorption process, 243, 245, 253 soybean, 122, 123, 127, 128, 132 space environment, 66 spacers, 215, 216, 217 Spain, 232 specialized cells, 152 species, 14, 18, 35, 62, 181, 187, 188, 189, 190, 202, 209 specific gravity, 62, 176, 181, 182, 183, 186, 187 specific heat, 175, 194 spectral techniques, 391 spectroscopy, 4, 92, 139, 148, 304, 309, 337, 346, 349, 352 spectrum, 72, 77, 78, 127, 148, 165, 201, 312, 347, 350, 352, 368, 369 speed, 66, 67, 76, 80, 90, 92, 95, 97, 98, 124, 242, 279 speed of light, 66 spin, 152, 351 spine, 159 stability, 1, 2, 6, 20, 24, 31, 35, 113, 135, 149, 152, 153, 155, 165, 179, 212, 313, 331, 336, 368, 385, 386, 388, 390, 391, 392, 393, 395, 397, 398, 402, 404 stabilization, ix, 34, 35, 46, 113, 237, 330, 386, 387, 393 stabilizers, 113, 114 stages, 13, 16, 21, 24, 33, 35, 44, 45, 47, 52, 117, 119, 173, 187, 245, 254, 255, 256, 312, 375 standard deviation, 273, 274, 284, 286, 287, 288, 289, 291 standards, 4 Staphylococcus, 337 starch, 122, 140 statistics, 53, 68 steel, 200 stent, 140 sterile, 126 stoichiometry, 225 storage, 103, 104, 108, 110, 111, 113, 231, 233, 234, 236, 237, 397, 398, 399, 400, 401, 402, 404 strain, 125, 126, 129, 132, 133, 134

Index strength, 66, 75, 89, 101, 129, 132, 145, 157, 162, 179, 197, 221, 225, 374, 375 stress, 62, 126, 129, 133, 370, 371, 372, 374 stretching, 26, 95, 97, 372, 374 strikes, 73 structural changes, 35, 133, 157, 369 structural characteristics, 148, 272, 273 structural formation, 374 structural protein, 159 structure formation, 149 structuring, 221, 281 students, ix styrene, 34, 89, 148, 149, 296, 346, 368 styrene polymerization, 296 substitutes, 223, 224, 225, 226 substitution, 18, 173, 295, 311, 312, 313, 315, 316, 318, 320, 321 substrates, 140 subtraction, 141, 142, 282 sugar beet, 122 sulfate, 297 summer, 263, 265 Sun, 87, 238 sunflower heads, 122 supply, 66 suppression, 134, 337, 363 surface area, 176, 271 surface diffusion, 178 surface energy, 388 surface layer, 86, 153 surface modification, 385, 386 surface tension, 179, 189, 245, 271 surfactant, 386 surfactants, 385, 386, 395 surplus, 179, 240 survival, 245 suspensions, 166, 375, 384 sweat, 239, 240, 242, 244, 249, 250, 251, 252, 253, 261 Sweden, 206 swelling, 147, 241, 374 Switzerland, 208 synthesis, ix, 3, 114, 161, 211, 218, 220, 229, 307, 336, 339, 343, 354, 361, 362, 363, 364, 375, 379, 380, 381, 382, 383 synthesized copolymers, 341 synthetic fiber, 251, 269 synthetic polymers, ix, 331 systems, 2, 33, 34, 37, 39, 40, 41, 42, 44, 46, 47, 52, 66, 80, 90, 92, 93, 94, 95, 101, 118, 119, 141, 145, 147, 149, 162, 165, 166, 168, 216, 223, 225, 240, 269, 305, 307, 312, 325, 326, 327, 346, 347,

421 353, 354, 355, 358, 363, 364, 367, 368, 369, 372, 374, 375, 376, 386, 399, 402

T targets, 152 TDI, 162, 163 technical carbon, 163 technician, 118 technology, 52, 66, 101, 115, 161, 175, 203, 208, 395 teeth, 162 TEM, 5, 79 temperature, 1, 2, 4, 9, 10, 13, 14, 19, 24, 27, 28, 29, 51, 52, 55, 56, 61, 105, 124, 125, 148, 155, 157, 173, 176, 178, 179, 180, 181, 182, 186, 187, 189, 193, 194, 196, 197, 198, 200, 203, 206, 208, 212, 213, 215, 216, 217, 220, 221, 227, 234, 239, 241, 242, 243, 244, 245, 246, 249, 250, 251, 252, 254, 258, 260, 261, 264, 267, 268, 296, 297, 327, 342, 343, 381, 382, 387, 391, 399 temperature dependence, 27, 28, 186, 213 temperature gradient, 55, 179, 186, 246, 249 tensile strength, 125, 129, 149 tension, 375 terpenes, 398 tetrachloroethane, 221 tetrahydrofuran, 221 textiles, 241, 242, 246, 258, 260, 267, 268, 269 TGA, 1, 2, 4, 7, 9, 11, 12, 13, 15, 16, 17, 19, 20, 22, 24, 29 theory, 65, 66, 242, 384 therapy, 151, 152, 159, 336, 398 thermal decomposition, 227, 228 thermal degradation, 2, 4, 6, 7, 8, 10, 11, 13, 30 thermal energy, 242, 250 thermal equilibrium, 253, 269 thermal expansion, 189 thermal oxidation, 14, 15, 18, 20, 31, 32 thermal oxidative degradation, 1, 15, 16, 17, 19, 20, 21, 24 thermal resistance, 244, 246, 251, 260, 261, 263 thermal stability, 2, 6, 19, 24, 31, 213 thermodenaturation, 151 thermodynamic, 179, 224, 229, 241, 263 thermodynamic equilibrium, 179 thermodynamic properties, 263 thermodynamic stability, 229 thermodynamics, 52 thermograms, 7, 9, 15, 153, 155, 225 thermogravimetric, 4, 223, 225, 226, 229 thermogravimetric analysis, 4, 223, 225, 226 thermooxidative degradation, ix

Index

422

thermoplastic, 2, 90, 114 thermoplastic polyurethane, 90 thermoplastics, 113, 122, 219 thermostable polymers, 219, 221 threshold, 221, 281, 282, 291, 295, 304, 305 timber, 52, 61, 179, 180, 181, 206 time series, 52, 53 tin, 363 tissue, 140, 162, 163 titanium, 66 toluene, 296 total energy, 313 toxicity, 108, 335, 336, 337, 338, 339, 363, 364 tracking, 278, 279, 280, 281, 284, 286, 287, 288, 289, 291 trademarks, 162 trading, 118 trajectory, 73 transducer, 126 transduction, 152, 155, 156 transformation(s), 6, 18, 33, 35, 41, 44, 46, 47, 211, 216, 276, 329, 332, 343, 369, 375, 380 transition(s), 18, 34, 35, 37, 44, 47, 77, 128, 155, 157, 161, 176, 192, 213, 225, 327, 330, 332, 375, 393 transition metal, 18, 35, 37, 44, 47 translation, 204, 376 transmission, 4, 79, 81, 240, 242, 249, 258, 259, 260, 268, 269, 270, 274 Transmission Electron Microscopy (TEM), 4 transparency, 329 transport, ix, 19, 51, 52, 62, 118, 140, 178, 179, 187, 191, 239, 241, 242, 243, 244, 245, 246, 249, 250, 254, 255, 256, 257, 261, 263, 267, 269, 338, 344 transport processes, 245 transportation, 180 trees, 188, 202 trend, 52 trial, 269, 281 trial and error, 281 tungsten, 66, 67 Turkey, 209

United States, 136 upholstery, 260 uranium, 69 urethane, 162 USDA, 206, 207, 267 users, 65 USSR, 115, 218, 308 UV, 139, 141, 147, 148, 198, 304 UV irradiation, 198

V vacuum, 3, 51, 66, 82, 125, 141, 189, 210, 224, 354 validation, 208 validity, 207, 283 values, 7, 11, 21, 31, 34, 37, 41, 45, 52, 53, 59, 105, 114, 141, 142, 155, 162, 163, 187, 190, 198, 200, 201, 202, 225, 240, 255, 265, 266, 269, 273, 274, 281, 284, 289, 297, 298, 303, 304, 305, 327, 351, 353, 354, 355, 357, 393, 399 vanillin, 231, 232, 233, 235, 238 vapor, 51, 175, 177, 178, 180, 181, 182, 191, 193, 194, 195, 241, 243, 244, 245, 249, 252, 256, 258, 260, 268, 375 variable(s), 79, 100, 124, 191, 243, 244, 256, 260, 273, 355 variance, 61, 282 variation, 7, 37, 55, 56, 77, 82, 84, 86, 173, 189, 240, 350 vehicles, 221 velocity, 55, 56, 68, 78, 177, 189, 192, 265, 374, 375, 380, 381, 382, 383 ventilation, 239 vessels, 104, 232, 236, 398 vibration, 26, 162, 304 vinyl, 90, 122, 136, 335, 351, 364, 387 Virginia, 207 viscoelastic, 136, 377 viscoelastic properties, 161 viscose, 81, 82, 84, 85, 86 viscosity, 13, 148, 157, 172, 177, 192, 195, 212, 220, 326, 327, 329, 332, 343, 355, 357, 358, 375 volatilization, 13

U UK, 204, 268, 395 ultrasonic, 385, 386, 387, 388, 389, 390, 391, 392, 393, 394, 395 ultrasound, 386 uncertainty, 226 uniform, 56, 175, 203, 255, 273, 274, 281, 282, 389, 391 United Kingdom, 104, 398

W walking, 240 Washington, 136, 205, 267 water absorption, 251 water diffusion, 52, 140, 175, 176, 179, 180, 182, 196, 245 water evaporation, 194

Index water purification, 379 water quality, 379 water sorption, 243, 245 water vapor, 55, 176, 178, 179, 187, 188, 192, 194, 195, 196, 197, 242, 243, 244, 245, 246, 251, 255, 258, 261, 267 water-soluble polymers, 385, 386 wavelengths, 76, 77 WAXS, 141, 144 wear, ix, 149, 161, 162, 163, 244, 249, 251 web, 271, 273, 274, 282 weight gain, 16 weight ratio, 124 welding, 161 wetting, 189, 241, 249, 385, 386, 392, 393 windows, 118 wine, 140 winter, 245, 250, 251, 263 wires, 66 wood, 51, 52, 53, 54, 55, 61, 62, 175, 176, 177, 178, 179, 180, 181, 182, 183, 186, 187, 188, 189, 190, 191, 192, 193, 194, 195, 196, 197, 198, 199, 201, 202, 203, 206, 207, 208, 209, 210 wood density, 181, 188 wood products, 62, 189, 209 wood species, 55, 179, 187, 202, 203

423

wool, 86, 87, 242, 243, 244, 246, 247, 249, 251, 253, 254, 255, 256, 258, 259, 268, 269, 270 writing, 80

X x-ray, 72, 77, 78, 140 X-ray diffraction, 146 x-ray(s), 72, 77, 78

Y yarn, 253 yield, 34, 35, 73, 74, 75, 167, 193, 296, 301, 302, 303, 305, 343, 354 yttrium, 299

Z zinc, 223, 224, 225, 226 zirconium, 387 Zone 1, 125 Zone 2, 125 Zone 3, 125 zwitterions, 35