Wool: Science and Technology

Wool: Science and technology

Other titles in the Woodhead Publishing Limited series on fibres, published in association with The Textile Institute: Series Editor: Professor J E McIntyre Bast and other leaf fibres Cotton: Science and technology High-performance fibres Regenerated cellulose fibres Silk, mohair, cashmere and other luxury fibres Smart fibres, fabrics and clothing Synthetic fibres

Wool: Science and technology Edited by W S Simpson and G H Crawshaw

Cambridge England

Published by Woodhead Publishing Limited in association with The Textile Institute Woodhead Publishing Ltd Abington Hall, Abington Cambridge CB1 6AH, England www.woodhead-publishing.com Published in North America by CRC Press LLC 2000 Corporate Blvd, NW Boca Raton FL 33431, USA First published 2002, Woodhead Publishing Ltd and CRC Press LLC © Woodhead Publishing Ltd 2002 Chapter 9 and Chapter 11 © The Woolmark Company 2002 The authors have asserted their moral rights. This book contains information obtained from authentic and highly regarded sources. Reprinted material is quoted with permission, and sources are indicated. Reasonable efforts have been made to publish reliable data and information, but the authors and the publishers cannot assume responsibility for the validity of all materials. Neither the authors nor the publishers, nor anyone else associated with this publication, shall be liable for any loss, damage or liability directly or indirectly caused or alleged to be caused by this book. Neither this book nor any part may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, microfilming and recording, or by any information storage or retrieval system, without permission in writing from the publishers. The consent of Woodhead Publishing and CRC Press does not extend to copying for general distribution, for promotion, for creating new works, or for resale. Specific permission must be obtained in writing from Woodhead Publishing or CRC Press for such copying. Trademark notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation, without intent to infringe. British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library. Library of Congress Cataloging in Publication Data A catalog record for this book is available from the Library of Congress. Woodhead Publishing ISBN 1 85573 574 1 CRC Press ISBN 0-8493-2820-9 CRC Press order number: WP2820 Cover design by The ColourStudio Typeset by SNP Best-set Typesetter Ltd., Hong Kong Printed by TJ International Ltd, Cornwall, England

Contents

Preface List of contributors

xi xiii

1

Wool production and fibre marketing w s simpson

1

1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 1.10 1.11 1.12 1.13 1.14 1.15 1.16

General introduction World wool production Wool harvesting Clip preparation Participants in the wool trade Wool sampling Fibre diameter Fibre length Wool colour Bulk testing Dark fibre contamination Specification of woolscour deliveries Computer blend selection Wool promotion The Fernmark brand Marketing of distinctive wool types References

1 3 5 5 5 11 13 14 15 16 16 17 18 18 19 19 20

2

Woolscouring, carbonising and effluent treatment l a halliday

21

2.1 2.2 2.3 2.4 2.5

Introduction Nature of contaminants Historical overview of scouring methods Unit operations Scouring chemistry

21 21 22 23 33 v

vi

Contents

2.6 2.7 2.8 2.9 2.10 2.11 2.12 2.13

Development of scouring systems Chemical treatments in woolscours Drying Solvent scouring Woolgrease and its recovery Effluent Process control and quality assurance Energy conservation References

35 39 42 45 46 49 55 56 57

3

Fibre morphology h höcker

60

3.1 3.2 3.3

Introduction General chemical composition Composition and structure of morphological components of wool Outlook References

60 61

4

Physical properties of wool j w s hearle

80

4.1 4.2 4.3 4.4 4.5 4.6

The wool fibre Effects of water Observed mechanical properties Structural mechanics Electrical properties Yarns and fabrics References

80 80 84 106 118 122 126

5

Wool chemistry w s simpson

130

5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 5.10 5.11 5.12

General introduction Chemical composition Degradation by radiation and heat Photobleaching and photoyellowing Absorption of acids Absorption of alkalis Dyeing with acid dyestuffs Acid, alkali and enzymic hydrolysis Oxidation with peracids Chlorine-based oxidation Reduction Sulphitolysis

130 131 131 132 135 137 139 141 143 145 145 146

3.4

67 76 78

Contents

vii

5.13 5.14 5.15

Metal salts Miscellaneous reactions Crosslinking References

147 150 151 156

6

Mechanical processing for yarn production l hunter

160

6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 6.10

Introduction Worsted processing system Preparation for spinning (drawing) Semi-worsted processing system Woollen processing system Spinning Twisting Winding, clearing and lubrication Yarn steaming (setting) Top dyeing References Bibliography

160 161 177 180 181 192 206 207 208 208 209 213

7

Chemical processes for enhanced appearance and performance w s simpson

215

7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9 7.10 7.11 7.12 7.13

Introduction Bleaching Prevention of dyebath yellowing Insect-resist treatments Shrinkproofing Antistatic properties Flame-retardant wool Photostabilisers Stainblocking Multi-purpose finishes Polymer grafting Removal of vegetable matter by carbonising Setting References

215 215 216 217 219 224 225 226 228 229 230 232 232 234

8

Practical wool dyeing k parton

237

8.1 8.2

Introduction Dyestuff chemistry

237 238

viii

Contents

8.3 8.4 8.5 8.6 8.7 8.8 8.9 8.10 8.11

Dyeing of different substrate forms Classification of wool dyestuffs Commercial forms of dyestuffs Levelness Dyeing fibre blends Treatments to improve colour fastness Environmental issues Fibre protection Summary References

240 242 247 248 251 252 252 256 256 257

9

Manufacture of wool products k russell, d m cdowell, i ryder and c smith

258

9.1 9.2 9.3 9.4 9.5 9.6 9.7 9.8

Introduction Twisting Winding Warp preparation for weaving Weaving yarns Fabric design Weaving machinery Knitting and knitwear Bibliography

258 258 264 266 269 270 273 275 289

10

Carpets, felts and nonwoven fabrics g h crawshaw and s j russell

290

10.1 10.2

Carpets Felts and nonwoven fabrics References

290 304 312

11

Finishing s a myers

314

11.1 11.2 11.3

Finishing of woven fabrics Finishing of knitted fabrics Finishing of knitwear Reference

314 328 330 332

12

Overview of global dynamics in the wool textile industry p d f kilduff

333

Introduction Overview of trends in world textiles

333 333

12.1 12.2

12.3 12.4 12.5 12.6 12.7

Contents

ix

Factors shaping global integration in textiles Overview of trends in wool textile production and trade Factors behind the declining importance of wool and wool textiles Patterns of industry development and adjustment Outlook for the wool textile industry References

335 337 342 349 355 357

Index

360

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Preface

Werner von Bergen and his collaborators released Volume 1 of their Wool Handbook in 1963, and two further volumes followed soon after. This series was unique in presenting a broad-spectrum description of every pertinent aspect from sheep-raising to wool consumer products. These texts were subsequently enlarged and reprinted in several editions. Another notable previous publication was Wool. Its Chemistry and Physics by Alexander and Hudson, first published in 1954. More recently, two more narrowly focused texts have appeared, both highly valued in industry and academia. They are Maclaren and Milligan’s Wool Science. The Chemical Reactivity of the Wool Fibre (NSW Science Press 1981) and Lewis’ Wool Dyeing (Soc. Dyers and Colourists, Bradford, 1992). The present text is therefore the first attempt in almost 40 years to present a comprehensive view of the wool industry from fibre marketing through to manufacture of consumer products. In Chapter 1, I briefly describe a major overhaul that has occurred of the methods of trading wool, basically moving the entire system from one of individual intuitive skill to one based on laboratory measurements of sale lots. Wool-scouring also has improved enormously in efficiency with a host of small and a few large innovations. Chapter 2 describes this modern technology, which reflects a strong emphasis on environmental concerns such as treating effluent discharges and energy conservation, coupled with far better quality control and capabilities for new add-on processes. Chapters 3, 4 and 5 describe the principal sectors of current wool science. Understanding of wool fibre morphology, and of physical and chemical properties continues to progress and, in doing so, highlights just how intricate and complex is the wool fibre. Instrumentation, now available for isolating and sequencing wool proteins and for determining their structural arrangement, is beginning to offer a better-informed basis for technologists to devise improved wool products and processes. Chapters 6 onwards deal in turn with each major aspect of wool proxi

xii

Preface

cessing technology. I have to say the contributing authors have been, and in most cases still are, working in the heartlands of these industries. Spinning, weaving and knitting are the three really major physical processes. The Chapter on wool carpets exemplifies how one particular consumer product may be woven, tufted, knotted, or needled to create a great variety of pattern and texture. Chemical processes that improve appearance or performance of wool products have been brought together in Chapter 7 to better highlight the technical options available to meet special specifications. The development of synthetic fibres with specialised performance features, allied with higher expectations of consumers, has been a strong motivation for creative new processes for wool. Flameproof protective clothing and antistatic carpets are just two fairly recent examples where wool products meet the most demanding requirements. Wool dyeing innovation is similar to wool-scouring in some respects in that it has been driven by a greater emphasis on energy conservation, shorter treatment times, and better management of effluents, in addition to the publicly more visible competitive demands for high standards of stylish and stable colouration of wool products. The final chapter is intended to put these modern developments in the wool industry into a global context amongst other fibres and textile technologies. I wish to sincerely thank my co-authors for their efforts to make available an up-to-date text for wool technologists, textile students and so many others interested in this old, yet modern, industry. W S Simpson

Contributors

Editors: Dr W S Simpson 19 Longmuir Street Christchurch 4 New Zealand E-mail: [email protected]

Dr G H Crawshaw Flat 5 Chapel House Wells Road Ilkley West Yorkshire LS29 9JD UK

Chapter 1:

Wool production and fibre marketing Dr W S Simpson, 19 Longmuir Street, Christchurch 4, New Zealand E-mail: [email protected]

Chapter 2:

Woolscouring, carbonising and effluent treatment Mr Lindsay A Halliday, 145 Bells Road, West Melton, Christchurch RD1, New Zealand E-mail: [email protected]

Chapter 3:

Fibre morphology Professor D H Höcker, German Wool Research Institute, 52062 Aachen, Veltmanplatz 8, Germany E-mail: [email protected]

Chapter 4:

Physical properties of wool Professor J W S Hearle, The Old Vicarage, Church Lane, Mellor, Stockport, SK6 5LX, UK E-mail: [email protected]

Chapter 5:

Wool chemistry Dr W S Simpson, 19 Longmuir Street, Christchurch 4, New Zealand E-mail: [email protected] xiii

xiv

Contributors

Chapter 6:

Mechanical processing for yarn production Professor Lawrance Hunter, CSIR Division of Manufacturing and Materials Technology, PO Box 1124, Port Elizabeth, South Africa E-mail: [email protected]

Chapter 7:

Chemical processes for enhanced appearance and performance Dr W S Simpson, 19 Longmuir Street, Christchurch 4, New Zealand E-mail: [email protected]

Chapter 8:

Practical wool dyeing Mr Keith Parton, Clariant UK Ltd, PO Box 42, Calverley Lane, Horsforth, Leeds, LS18 4RP, UK E-mail: [email protected]

Chapter 9:

Manufacture of wool products Mr Kevin Russell, Mr David McDowell, Mr Ian Ryder, and Mr Colin Smith, The Woolmark Company, Valley Drive, Ilkley, West Yorkshire, LS29 8PB, UK E-mail: [email protected] [email protected] [email protected] [email protected]

Chapter 10:

Carpets, felts and nonwoven fabrics Dr G H Crawshaw, Flat 5, Chapel House, Wells Road, Ilkley, West Yorkshire, LS29 9JD, UK, and Dr Stephen Russell, School of Textiles and Design, University of Leeds, Leeds, UK E-mail: [email protected] [email protected]

Chapter 11:

Finishing Mr Steven A Myers, The Woolmark Company, Valley Drive, Ilkley, West Yorkshire, LS29 8PB, UK E-mail: [email protected]

Chapter 12:

Overview of global dynamics in the wool textile industry Dr P D F Kilduff, Department of Textile and Apparel Technology, School of Textiles, NCSU, 240 Research Drive, Raleigh, NC 227695-8301, USA E-mail: [email protected]

1 Wool production and fibre marketing W S SIMPSON

1.1

General introduction

Sheep husbandry is an important pastoral activity across most of Europe, the Americas and Asia. Its purpose nowadays is primarily meat production, although the wool harvest has for centuries been an important basis of local textile industries. European colonisation of large areas of the southern hemisphere suitable for pastoral production led to much larger numbers of sheep and a more dominant emphasis on wool production. A large proportion of the wool harvest from Australia, New Zealand, South Africa, Argentina and Uruguay is exported to textile manufacturers in the northern hemisphere. For about a century (from 1860–1960) these manufacturers were almost entirely to be found in Western Europe. Since 1960, wool manufacture has declined in some of these countries and more volatile trading patterns have emerged. Russia, Japan, Iran and China are some of the countries that have fluctuated between minor and major importers of southern hemisphere wool. Another trend, which gathered momentum since the end of the 1939–45 war, has been the drive for greater productivity from textile machines and consistent high-quality standards for textile products, so that standardised raw material is demanded. This turned the spotlight on wool marketing practices. Competition from synthetic fibres intensified. Their prices were usually stable, or actually reduced as the scale of production increased. Particularly important were technological advances in converting petroleum gases into reactive monomers suitable as starting materials for synthetic fibre production. Moreover, the consistent and precisely specified properties of synthetic fibres were very much in harmony with the ability to finetune textile machinery for high production rates. In the face of this growing competition it was inevitable that the historic reliance of buyers and sellers of raw wool on intuitive judgement and experience in making trades came under pressure for change. Basically, the onus for developing, testing and implementing more sophisticated wool 1

2

Wool: Science and technology

marketing systems fell mainly on Australia and New Zealand. Australia is by far the dominant producer of fine Merino wool and accounts for almost half the quantity of wool worldwide that comes onto the open market. The Australian Wool Corporation (AWC), over the approximate period of 1950–1990, chaperoned the wool producers towards more efficient fleece preparation, and the wool trade into more efficient wool handling, packaging, transportation and sale methods. The AWC would also fund a considerable portion of the R&D efforts of Australian CSIRO scientists who were to verify new test methods and develop equipment for wool-brokers and test houses. In Australia, numerical specification of wool would focus on those measurements of most importance to the worsted industry. New Zealand had a closely parallel responsibility as the predominant producer of crossbred wool for open sale. These wools, in many respects, posed a greater problem in sampling and testing because of the greater variability within and between sale lots and the diversity of end-uses. Although carpets were mainstay products after the 1939–45 war, considerable segments of the crossbred wool clip were destined for woven and knitted clothing, blankets, furnishing fabrics and many other products. In similar fashion to the AWC role in Australia, the New Zealand Wool Board (NZWB) encouraged the wool trade to participate in trials of new marketing procedures, and contributed a high proportion of funds to enable scientists at the Wool Research Organisation of New Zealand (WRONZ), formally incorporated in 1961, to develop sampling and testing methods and equipment, as well as scientific, manufacturing and product research relevant to coarser wools. The numerical specifications would emphasise those features of most importance for spinning on the woollen system. By about 1990, almost all the testing and marketing procedures had been implemented in both Australia, New Zealand and South Africa. The last had a very similar fine wool profile to that of Australia and co-operated very closely in all aspects of wool testing, adoption of standards and marketing procedures. The regular meetings of the International Wool Textile Organisation (IWTO) meant reviews of outstanding concerns to the wool textile industries could be aired and responsibility for redress taken by the appropriate research laboratories, test houses, or trade committees. Representatives of long-established wool manufacturers could expand their historic emphasis on such things as tariffs and regulation of trading in woollen goods to participate in IWTO sub-committees examining the technical and practical issues involved in routinely using the proposed new wool specifications. These were not all the problems to be addressed. Not only were the major traditional wool manufacturers confronting stiff competition from a burgeoning type of new textile industry featuring relatively cheap synthetic fibre products, but consumer interests increasingly required proof of product performance. On the one hand, the primary fibre needed

Wool production and fibre marketing

3

to be free from agricultural chemical residues, and on the other, retailers of wool products wanted a performance endorsement. Both aspects were fairly solidly secured in the 1980s, particularly through a very successful promotion campaign headed by the Woolmark label on products approved according to International Wool Secretariat (IWS) Standards. New problems have arisen during the 1990s, not so much with sales and test methods, where continued improvements in equipment and computer technology remain in vogue, but rather a renewed competitive pressure on wool prices. This has occasioned calls for relief from wool growers who wish to see wool marketing overhead costs, such as levies collected by AWC and the NZWB, to be much reduced. Another change is some revival of direct sales between consortiums of specialist wool producers and corresponding clubs of manufacturers in Europe or Asia. Irrespective of these continual shifting patterns in wool trading, the wool industry does now possess a sophisticated array of sampling and testing procedures that provide reliable support in terms of technical data. Whether the transaction is made through the auction system, private treaty or increasingly, one would expect, through electronic means such as the Internet, the packages of wool test methods described later in this chapter will remain relevant.

1.2

World wool production

Table 1.1 is reproduced from the 1998/99 Statistical Handbook of New Zealand Wool Group, a division of the NZWB.1 The major trend is a reduction in Australian wool production in the 1990s due to poor prices, which in turn was initiated by a recession in Japan and other important wool consumers. Recovery has been hindered by acquisition of a considerable stockpile in Australia early in the decade. Economic disruption has also halved wool production in the Soviet Union (now CIS), but it is growing significantly in China. New Zealand production is fairly stable, in spite of modest prices and several droughts during the 1990s. The slow downward trend is, in part, a result of buoyant investment in dairying as a more profitable use of grassland. There are several features of world wool production worthy of additional comment. Australian wool production is highly concentrated on the Merino breed and it therefore has a very dominant position in fine wools, accounting for about half of world supplies. Although approximately 75% of New Zealand production is categorised as crossbred type, i.e. about 140 000 clean tonnes, this represents just 30% of world supplies. The UK is a very substantial producer of coarse carpet wools and most of its 46 000 tonne production competes directly with New Zealand offerings to the carpet industries in Europe and elsewhere. Halfbred wools comprise a quite high

Table 1.1 World wool production [Reproduced from the 1998/99 Statistical Handbook of New Zealand Wool Group, Wool House, Wellington] Country

World wool production (thousand tonnes clean) 1992– 1993– 1994– 93r 94r 95r

1995– 1996– 1997– 96r 97r 98r

1998– % 99p change 1997–98 to 1998–99

Australia

573

544

473

452

472

455

443

-3%

New Zealand

193

214

213

199

203

197

185

-6%

China

119

120

128

139

149

146

151

3%

Soviet Union/CIS

207

194

157

124

118

103

90

-13%

United Kingdom

47

45

45

44

43

44

46

5%

Uruguay

64

66

60

56

60

55

45

-18%

Argentina

60

52

48

43

41

37

37

0%

Turkey

38

38

37

37

36

36

36

0%

South Africa

44

43

38

38

36

33

34

3%

India

28

28

28

28

28

28

28

0%

Pakistan

21

21

22

22

23

23

24

4%

Iran

21

21

22

23

23

23

23

0%

Ireland

18

18

18

18

17

18

18

0%

Spain

16

17

17

16

16

16

15

-6%

Morocco

14

14

14

14

14

15

15

0%

USA

23

22

19

18

15

15

14

-7%

Mongolia

12

12

11

11

11

11

11

0%

Romania

13

12

11

11

10

10

10

0%

France

12

11

11

11

11

11

10

-9%

Chile

11

11

11

11

9

9

9

0% -27%

Brazil

17

13

11

11

11

11

8

Peru

7

6

7

7

7

8

8

0%

Germany

7

7

7

8

8

8

7

-13%

Greece

6

6

6

6

6

7

7

0%

Iraq

7

7

7

6

6

6

6

0%

Italy

6

6

6

5

5

5

5

0%

Portugal

5

5

5

5

5

5

5

0%

132

124

127

126

125

127

127

0%

1721

1677

1559

1489

1508

1462

1417

-3%

Merino

813

777

681

643

653

626

609

-3%

Halfbred

405

388

383

365

368

363

350

-4%

Crossbred

503

512

495

480

487

473

458

-3%

Other countries World total of which:

r = revised; p = provisional; Source: IWTO. Data extracted from 1998/99 Statistical Handbook of New Zealand Wool Group.

Wool production and fibre marketing

5

fraction (25%) of the total world wool production. This classification notably includes a large proportion of the predominant Corriedales and Merino cross wools sold out of Argentina and Uruguay. World wool production in total is, however, modest compared to the volumes of cotton and synthetic fibres. Wool available for manufacturing from all sources at the end of the twentieth century accounts probably for no more than 3% of total world fibre supply.

1.3

Wool harvesting

Most wool is harvested by shearing live sheep using powered hand clippers. Blade shears are still preferred for flocks run where harsh weather can occur, because about 10 mm of fleece can be left on the sheep for protection. Slipe wools are produced at meat-works. Woolly sheepskins from slaughtered sheep and lambs are chemically treated to weaken the fibre roots so that the wool can be pulled off the pelt. The main wool classifications are full fleece (a year’s growth), second shear and early shorn (part-year’s growth), and crutchings (shorn from the hindquarters before lambing). Lambswool (shorn at about six months), woolly hogget (shorn at one year) and shorn hogget (shorn as lambs and then at 18 months) are other descriptions used in New Zealand. Each woolproducing country uses a variety of other classifications.

1.4

Clip preparation

During shearing, each fleece is examined with the objective of removing faults relating to colour, length and contamination, and collecting each separately. The main categories are belly wool, short discoloured crutch wool, stains and dags. Vegetable matter and cotted (i.e. felted) parts of the fleece are also separated. Skirted fleeces are sorted into uniform groups or lines. Fine wool lines will discriminate on the variables of fibre diameter, length, strength, colour and vegetable contamination. The main sorting principles for carpet wools are discolouration and fleece tenderness. Slipe wools, produced in meat works, are classed along similar lines, the main difference being a wash that removes most of the woolgrease and suint, as well as any sodium sulphide depilatory adhering to the wool.

1.5

Participants in the wool trade

1.5.1 Woolgrowers Sheep farmers have been constantly urged to improve their performance with respect to putting a better product into the start of the wool market-

6

Wool: Science and technology

ing and manufacturing chain. Apart from the obvious requirement for good sheep husbandry and a breeding and selection strategy, there are several aspects involving responsible farm management. Some pasture weeds produce burrs and seeds that become entangled in the growing fleece. Substantial contamination cannot be taken out by conventional mechanical processing, and carbonising (an acid process which embrittles vegetable matter) is required, adding costs in wool classing and processing. Environmental concerns are another issue where the woolgrower is ultimately responsible for using approved pesticides, drenches and agricultural sprays, so that the shorn wool contains no unwanted residues. Finally, workers in the shearing shed need to be well informed on best practices and skilled in classing and skirting (Section 1.4) before loading the wool harvest into farm bales. Provided these responsibilities of the woolgrowers are reliably fulfilled, the onward task of taking the clip to auction, usually via a wool broker, or a direct sale at the farm gate, is much facilitated.

1.5.2 Wool brokers and wool buyers For wool sold at auction, a reputable wool broker is the traditional intermediary who prepares farm lots. Nowadays, this entails aggregating similar sale lots, particularly small lots, weighing, sampling and cataloguing. There are formal procedures for core sampling and obtaining a pre-sale test certificate from a test house to be available at the auction. A grab sample of full-length wool is also obtained, which is displayed alongside the test certificate at the auction room. This is an enormous transformation that has mainly been effected since 1970, after which time the means for improved testing and their ratification by IWTO (Section 1.1) have come to dominate wool marketing. Previously, a few large and many small wool-broking companies had relied upon the personal expertise of their staff. Their ability to judge the yield (i.e. the weight of clean wool remaining after scouring) and mean diameter, for example, were extraordinary. In the latter case, staff in both wool broking and wool buying companies were adept at assigning a fineness estimate for each sale lot in their notebooks prior to auction. For fine wool products, where wool mean fibre diameter is a critical parameter, these assessment experts were capable of discriminating readily between 18, 20, and 22 micron wools, and more often than not their subjective assessments correlated with laboratory measurements to within a fraction of a micron. They also included other judgements on ‘style’, which meant a synthesis of fibre crimp and other fleece characteristics that they and their clients believed to be a superior judgement of processing and product performance as compared to a limited array of objective measurements.

Wool production and fibre marketing

7

Efficient sampling and testing procedures (Sections 1.6–1.12) have largely eliminated this bias, and basically in the 21st century most wool trading will be underwritten by physical measurements. Exceptions will still exist, typically where a wool-buyer and a wool-grower agree at the farm gate on a transaction price. Direct selling has the attraction of very low transaction costs. It is seen to best advantage when an atmosphere of mutual trust is developed between a manufacturer and a number of wool-grower clients. For example, Cavalier Corporation is a prominent New Zealand carpet manufacturer. The company has a subsidiary which has established a good record in arranging direct acquisition of wool on a regular basis. Many of the woolgrowers became directly involved with individual carpet manufacturers about 1950 when the first commercial flocks of Drysdale sheep were taking shape. The Drysdale breed was named after Dr Dry, a geneticist who discovered a gene which led to remarkably coarse wool from the sheep which carried it, and it is particularly sought after for some styles of carpets. In Australia in 1997, approximately 80% of the wool clip was sold at auction using the services of one of about 30 wool-broking companies operating in that country.2 Private buyers account for the remaining 20% of the wool market, the larger companies being affiliated to the national Private Treaty Wool Merchants Association.

1.5.3 Test houses The Australian Wool Testing Authority (AWTA) was established as a statutory body by an Act of the Commonwealth Government in 1937. With the advent of large-scale sampling and testing of wool sale lots, the activities of AWTA expanded greatly. The form of governance was changed, and since 1982 AWTA Ltd has operated as a public company limited by guarantee, without shareholders. Its guarantors nominate directors with an additional director representing CSIRO. They are as follows: • • • • • • •

Australian Council of Wool Exporters Federal Council of Private Treaty Merchants National Council of Wool Selling Brokers of Australia Wool Council of Australia Wool Scourers and Carbonisers Association of Australia Wool Textile Manufacturers of Australia Australian Wool Corporation

Pre-sale wool test certificates comprise about 66% of all documents issued by AWTA Ltd since 1984. The remainder are certificates for scoured and carbonised wool, and the company is also active in testing of imported

8

Wool: Science and technology

woolpack materials. Very similar organisations operate in New Zealand (NZ Wool Testing Authority) and South Africa. They are, themselves, subject to regular quality control audits. The issue of reliable sampling was at the heart of introducing fundamental changes in wool marketing methods. Sampling technology is described in more detail in Section 1.6. It should, however, be emphasised here there are two basic methods of sampling, which have quite different and explicit purposes. Objective measurements of core samples comprise yield (i.e. percentage of clean wool), diameter, colour and vegetable matter content. Pre-sale certificates are shown adjacent to a grab-sample of the same lot prior to auction. Post-sale test certificates for greasy wool may also be issued, notably when several sale lots are later combined. Most New Zealand wool is scoured prior to export and the pre-sale certificate is redundant. A different sampling and test regime applies to scoured wool shipments, and a notable replacement for the yield test of greasy wool is the ‘residuals’ test, i.e. the result of a solvent extraction of a representative sample in order to quantify wool fats and residues not totally removed by the scouring process.

1.5.4 British wool marketing There are many similarities between marketing arrangements in Australia, New Zealand and South Africa and that in the UK, notably a strong reliance on the auction system and a Board which takes a broad overview of the industry.3 The most recent report of the British Wool Marketing Board indicates there are about 75 000 farmers contributing to an annual wool production in the UK of 46 million kilos. Amongst their activities, the Board organises regular auctions, supports training of shearers and promotes British wools in carpets manufactured in the UK. In the northern hemisphere, institutions such as the Bradford Conditioning House have for many years offered a weighing and testing service; in their case for the large number of wool manufacturers concentrated in the West Riding of Yorkshire. The application of objective specifications of wool lots is clearly gaining increased support as the British Wool Marketing Board indicates3 considerable investment in equipment for the purpose, and a stated interest in future marketing of British wools internationally using the Internet.

1.5.5 Wool exporters including wool scourers There are two methods for obtaining wool from exporting companies. Under the ‘indent buying’ system, the overseas buyer nominates an upper price, wool type and quantity, and the exporter attempts to fill the order on

Wool production and fibre marketing

9

essentially a commission basis. Under the ‘firm offer’ system, the exporter takes the initiative and makes a firm offer to a buyer including price and other details. If the offer, usually open for 24 hours, is accepted, the onus is on the exporter to fill the order on the terms of the offer. In cases of dispute, the IWTO have regulations applying to trading, such as ordering retests when the specification of the delivery is questioned. A good number of powerful European and Asian textile companies bid at auction, and essentially can be regarded as exporters who principally buy on behalf of their own wool manufacturing mills. Wool scouring companies have several different objectives according to their ownership and, to some extent, their location. For some, their predominant business is scouring on commission for an exporter or a local manufacturer. Others may be owned in part or in whole by wool manufacturers, and a sizeable part of their business is essentially ‘in house’. Some of the largest wool scouring companies have a wool trading operation including wool exporting. One of the advantages of a wool scour is the ability to blend wool lots to make up large consignments to specifications of overseas clients. The technology supporting this type of wool export operation is described in Sections 1.12 and 1.13. The major southern hemisphere wool exporting countries have wellestablished test houses (Section 1.5.3), which are regularly subjected to quality-control audits. Objective measurements of core samples comprise yield (i.e. percentage of clean wool), diameter, colour and vegetable matter content. Formal pre-sale and post-sale test certificates are issued for greasy wool. Scoured wool shipments have a somewhat different sampling and test regime before issue of a scoured wool test certificate. This would include a ‘residuals’ test, i.e. the result of a solvent extraction of selected samples in order to evaluate the presence of wool fats and other residues not removed during the scouring process. Wool scouring presents a good opportunity to pool and blend similar lots purchased by a particular exporter. Following scouring, the wool is baled at medium or high density and commonly paralleled in container-sized lots of about 20 tonnes. Therefore, the principal advantage is an intelligent amalgamation of wool into consignments of a specification and regular tonnage appropriate to manufacturers.

1.5.6 Central wool facility Central wool facilities are essentially strategically-placed port storage and packaging depots where greasy or scoured wool is made up into shipments. Greasy wool, for example, has traditionally been ‘double-dumped’, i.e. two bales pressed into one dense package to reduce shipping space. Ports

10

Wool: Science and technology

around Australia with wool-handling facilities are serviced by three companies who specialise in this business. Dumping has some technical problems that will be just touched upon here. The presses are themselves remarkable, working almost continuously for several months with thrusts of 300 or even 500 tonnes. The compression of two 150 kg bales together is demanding on the pack material, which must comply with strict specifications. Tensile strength is only one consideration. One of the problems discovered with polypropylene packs, for instance, is shattering of fibres, which contaminate fine wool and are visible faults in finished fabrics.Another problem with highly compressed wool bales is that, after some months in a compressed conditions, the wool is difficult to ‘open’, i.e. to break up into a manageable form for scouring. Bale-warmers and various opening machines have been devised to solve this problem. Packaging of wool from farm bale to densely compressed shipping containers is itself an interesting topic. Jute was the dominant material until the advent of synthetic fibres. As noted above, these have not been troublefree. Nylon packs seemed likely prospects, because fibre contamination would essentially be invisible owing to the similar dyeing properties of wool and nylon. However, cost considerations are important too. It seems likely polyethylene will continue to develop as a preferred woolpack material.

1.5.7 Wool flow patterns and the auction system The full flow diagram for shorn wool sold at auction is shown in Fig. 1.1. The important auction process lies essentially between wool broker and exporter on the right of the diagram. Data flow describing wool samples involve a test house, shown on the left of the diagram. Auctions remain the dominant feature of wool sales in Australia and South Africa, but as mentioned in the general introduction, in New Zealand in the final few years of the 1990s there has been a very significant movement towards private sales. Woolscouring companies are among those taking a more aggressive approach to acquiring greasy wool direct from the woolgrower, particularly in New Zealand. In 1998/99 in New Zealand, the total sales of new greasy wool was about 185 300 tonnes, of which just 83 700 tonnes were sold at auction. Of the balance, growers sold 75 000 tonnes privately, and most of the remaining 26 600 tonnes was recovered as slipe wools.1 The latter enters the international wool market as a specialty product favoured by particular wool manufacturers, or is sold to one of the prominent wool exporters.

1.5.8 Historic form of the wool auction system Until changes began to be introduced after 1960, the historic form of the wool auction was identical in most respects to the commodity marketing of

Wool production and fibre marketing

11

Wool grower Test house

Wool broker

Wool exporter

Wool scour

Central wool facility Mill

1.1 Flow diagram for shorn wool to be sold at auction. Samples and test data involve a test-house.

a great many agricultural products. There was a roster of sale dates for all the wool producing regions and, on the day, all the product put up for sale was in full view for inspection, i.e. wool bales were cut open before lot-bylot sale to bidders representing the international wool manufacturing community. Other than the weight of each greasy wool lot, buyers had no other factual information, but in practice they were highly skilled in judging the relevant attributes of each lot (Fig. 1.2). The International Wool Textile Organisation (IWTO) had evolved over many years to become something close to a regulatory body. Delegates from all the member countries represent all the commercial interests to be found in the flow chart for the auction system (Fig. 1.1). Adoption of regulations governing wool trading, accreditation and dispute procedures essentially gave IWTO the status of professional governance of the wool industry, with particular emphasis on standards and accreditation of wool supplies coming onto the international market.

1.6

Wool sampling

The largest obstacle to overcoming the cumbersome features of the old traditional auction system was the highly variable quality of sale lots. This could commonly be exacerbated by poor growing conditions or sloppy classing and skirting. Therefore, it was hardly surprising that wool buyers and manufacturers insisted on extensive and repetitive technical trials before they could be convinced on the key issue of sampling. Wool sampling, in essence, replaces the opportunity for buyers to exercise their skills and judgement whereby they view the whole contents of every bale, by presenting to them a small sample attached to some test house measurements (Fig. 1.3). Nevertheless, this crucial victory in

12

Wool: Science and technology

1.2 Photograph of a traditional New Zealand wool-broker’s store taken about 1957. Bales were opened for inspection several days before auction.

obtaining the confidence of all parties has rested upon the development of two methods of sampling greasy wool lots. Grab sampling entails slitting open each bale and drawing out a regulated number of full-length wool staples to make up a composite sample of about 5 kg of greasy wool representative of a typical line of 3 to 20 bales (or even much larger lines in Australia). The entire wool lot is then weighed before undergoing the second method of sampling. Core sampling, as it is called, entails punching a sharp-ended tube through at least 97% of the length of each bale, sufficiently often to provide five samples of 150 g each, the cores being immediately sealed in a plastic bag for test house measurements complying with Core Test Regulations IWTO-19. To set up the greasy wool auction, the grab samples are assembled in long lines of trays in a display hall, each rejoined by a test certificate derived from the core sample. This enables the buyer to see both a representative full-length staple display and have accurate data on fibre diameter, yield, colour, clean weight and vegetable matter content. To give some idea of the speed at which buyers must operate to fill their buying orders, about 300 lots are sold every hour, and up to 3400 lots in a single day, comprising up

Wool production and fibre marketing

13

1.3 Photograph of a complete assembly of representative grab samples of New Zealand wool lots to be auctioned. Each numbered viewing box has a data sheet from a test-house and other information.

to 35 000 bales of wool. In Australia, at peak times these volumes are greatly exceeded.

1.7

Fibre diameter

No measurement could better exemplify the divergence in priorities between fine and coarse wools than measurement of fibre diameter. For fine Merino wools, the predominant average within a lot lies between 18 and 21 microns and there is a useful price premium at the finer end of that range. The mean diameter, of course, relates closely to both the spinning limit and the luxury handle, where every micron finer creates an advantage. Increasingly in recent years, a new niche sector has developed in production of super-fine wool with breeders going to extraordinary pains to produce tiny amounts of wool in the 14 to 17 micron range, which can sell at extreme prices. For crossbred wools destined for carpets, the mean diameters are most commonly in the 30–38 micron range and the New Zealand Romney and Coopworth wools that dominate this class have a good reputation for efficient processing. For some products in the carpet market the fibre blends

14

Wool: Science and technology

are actually improved by addition of very coarse wools, e.g. Drysdale or British moorland sheep fleece wools. (For a better appraisal of matching wool blends to carpet styles see Chapter 10.) However, there is a significant intermediate diameter range (halfbreds, Corriedale and Down breeds) of 25–30 microns where diameter variability becomes a significant issue. A few very coarse fibres can affect the comfort of wearers of knitwear constructed from these wools. The airflow method has been almost exclusively employed by test houses to measure mean fibre diameter until recent times. It is calibrated to record mean diameter of a wool lot reduced to a plug of clean core sample material through which air is forced under pressure. The method depends on a pressure drop principle; the greater the drop, the finer the wool. It is a simple, cheap measurement but has the drawback of inaccuracy when testing lambswools and medullated wools, where the diameter is increased relative to sample weight by empty spaces and hollow cells within the fibres. Much painstaking work over many years was required to produce calibration samples that were fully acceptable to wool manufacturers. Definitive measurement of mean fibre diameter and variability has, for many years, depended on expensive microscope measurements of fibre snippets. This laborious technique has been employed by test houses but was generally regarded as suitable mainly for research workers. Since about 1970 however, there has been a series of brave attempts to master the problem of providing a representative array of fibre snippets and analysing them with a scanning instrument. Computation of the fibre profile of the sample is rapidly becoming a trivial procedure with the advent of powerful computers. Presently, it seems inevitable that there will soon be complete reliance on cost-effective equipment to record wool fibre diameter profiles using laser-scanning devices, such as OFDA (Optical Fibre Diameter Analyser), a development of BSC Electronics in Perth.

1.8

Fibre length

Objective testing of fine Merino wools has come to include a measurement of wool staple length and strength (IWTO-30 test method) applied to greasy wool samples. The Atlas machine developed about 1985 for this purpose has since been somewhat improved but essentially it has remained a fairly daunting and expensive test. Individual wool tufts are fed into a grip-break device. In addition to a calculated fibre tenacity it also records the position of break along the sample. Attention given to this technically difficult measurement reflects the desire of manufacturers to know, in advance, every feature of processing performance. For manufacturers, the results of this test can indicate the percentage of fibre that breaks during processing. Short fibres unsuited to further worsted processing are extracted in the form of noils in the combing process to prepare tops.

Wool production and fibre marketing

15

For New Zealand crossbred wools, where a very high percentage of the clip arrives via the auction or other routes at a woolscour prior to export, the more useful index of fibre length is actually a critical test of fibre entanglement induced by the scouring process, in addition to accounting for breakage at weak or thin places in some or all of the fleeces making up the scourment. Consequently, WRONZ developed a test based on processing representative samples through a dedicated, narrow-width wool carding machine. A minimum of five samples of the output sliver are analysed by the well-known Almeter equipment, which then produces a statement of short fibre percentage, mean fibre length, and a coefficient of variation of hauteur. This ‘length after carding’ test (NZ Standard 8719:1992) is essentially only available using equipment tested and validated in New Zealand. However, with active collaboration from other countries this test is steadily becoming recognised and applied on an international basis. Testing wool scourments in this way results in a substantial consolidation of the data at the ‘sale-by-sample’ stage provided to auction buyers. Whereas the latter lots are commonly in the range 500–2000 kg, scourments are generally exported as one or several container loads of dense-packed bales, each holding about 16–20 tonnes.

1.9

Wool colour

A colour parameter in wool specification has no relevance to dozens of wool breeds around the world where the wool harvest is a great mixture of brown, yellow and white colours. However, it has a strong relationship with the value put on New Zealand wool sale lots since these vary widely in the incidence of yellowness (Section 5.4) in otherwise basically white fibre. Australian fine wools are very substantially protected from yellowing during wool growth because of the dense structure of a Merino fleece so that colour measurement at point-of-sale of fleece wools is of minor commercial interest. A relatively low priority for colour testing of Merino fleece is not to be confused with the importance of exceptionally good whiteness, often achieved by bleaching, for many fine wool products. A New Zealand Standard (NZS 8707:1984) developed by WRONZ has progressed to the status of an IWTO Draft Test Method (IWTO-DTM-56).4 The actual measurements are made by observing the reflectance from a chopped fibre wool sample packed into an observation cell. Strictly speaking, all three CIE tristimulus X, Y, and Z values are needed to construct a total description of wool colour. It should be seriously emphasised there are two aspects of wool fibre colour measurement which are important in the context of the appearance of final textile products. Rather than resort to complex equations, the simple difference between green and blue tristimulus measurements (i.e. Y–Z) is an adequate measure of wool yellowness. The other important discriminator among wool lots is their total light

16

Wool: Science and technology

reflectance or brightness and for this, the tristimulus Y value has satisfied all requirements. To summarise, (Y–Z) yellowness measurements will usually rank between 0 (very good whiteness) to 8–12 (very yellow) and the brightness index Y will range from about 70 at best down to about 40 for very dull wools. These figures are, or are closely related to, the percentage of incident light reflected back to reach the eyes of the observer.

1.10

Bulk testing

Bulk testing has assumed considerable importance right through the chain from sheep breeder to manufacturer. The essence of the test is essentially to quantify the loftiness or space-filling capabilities of particular wool lines. This, in turn, is largely dependent on the degree of crimpiness, which is almost non-existent in some wool types and in general increases as the wool gets finer. However, the correlation with mean diameter is not always satisfactory. For example, carpet wools with a broad spectrum of fibre diameters will yield a bulkier yarn than those with a narrow range, even though the mean diameters are similar. The procedure for the Core Bulk Test involves running a scoured core sample through a small card, loading 2.5 g into a cylinder, applying a loaded piston and measuring the volume occupied by the sample. The Core Bulk Test is one where it is mandatory for the wool sample to be held in an airconditioned environment (65% RH and 20 °C) for at least 24 hours before testing. The regulations pertaining to some of the other tests described earlier also require the wools to be held and tested in the same conditioned environment.

1.11

Dark fibre contamination

Merino wools are particularly affected by even minute contamination with dark fibres. In fine white or pale shades of fabric, every dark fibre is a visible fault that entails close inspection and individual removal with tweezers by a mill operative. Down breeds of sheep with a black face and legs present a problem of contamination too, as the main part of their fleece is white. The problem is largely pursued through training in fleece skirting procedures in the shearing shed and generally avoiding contamination along the processing chain. Counting individual coloured fibres on a microscope slide has been the traditional laborious method, appropriate mainly for research purposes. With the advent of laser scanning equipment for fibre diameter measurement, there are now better prospects for including a statistical measure of dark fibre contamination.

Wool production and fibre marketing

1.12

17

Specification of woolscour deliveries

Most New Zealand woolscours have acquired Near Infrared Reflectance Analysis (NIRA) instruments. These greatly improved in-house quality control, although an external certification is still necessary from a test house before the measurements are formally recognised by clients and manufacturers. The NIRA equipment provides rapid measurements of moisture regain, residual grease content and scoured wool colour. The instrumentation can also produce an unofficial measure of fibre diameter, wool bulk and fibre medullation.5 Predictive equations are required for each of the measurements, derived from very extensive sampling and validation experiments. Considerable precautions are also needed in order to transfer the predictive data base between instruments sited in other laboratories.6 The measurement of fibre length of scoured wool is very important, and the relevant ‘length after carding’ test was described in Section 1.8. The wool may have had faults such as cotting and the scouring process itself introduces some degree of fibre entanglement. By emulating, with carefully controlled equipment, the opening and carding process in industrial processing, the ‘length-after-carding’ test breaks a comparable proportion of fibres and provides important guidance about the future processing performance of the scourment. In summary then, a scoured wool specification has test information on the variables of colour, fibre diameter, fibre length after carding, bulk, medullation content, and vegetable matter content. These six parameters have been shown to be a necessary and sufficient data set for predictive expectations of scourments.7 Most of these tests have already been briefly described. However, in the context of specifying relatively large scourments some additional points should be made. These have particular significance for on-line quality control in the woolscour. Although wool colour is measured as for auction lots of greasy wool (NZS 8707:1984 and IWTO(E)-14-88, which is based on the NZ Standard method), a significant additional development is the use of on-line colour monitoring. A video camera and computer display ‘as-is’ wool colour by viewing the wool-flow, thus facilitating corrective action and avoiding re-scouring if the scouring process deteriorates in quality. The vegetable matter test (IWTO-19-85) has some problems when applied to most New Zealand scourments, because the commonly low levels of contamination make it difficult to carry out representative sampling. The most important technology to come into use in woolscours in recent years is the adoption of Near Infra Red (NIR) equipment for quality control purposes. Modern NIR equipment scans a wide spectral range, extending into the visible region, so that ‘as is’ colour can be measured by this method. Predictive equations for bulk and medullation are constantly

18

Wool: Science and technology

being improved. The core bulk test (NZ 8716:1994) may ultimately be replaced in test houses by an NIR test. Similarly, the long-standing method of measuring medullation by the definitive but expensive projection microscope method will ultimately be replaced. Although NIR instruments can be calibrated to obtain a measure of medullation, the newer forms of laser scanning instruments for fibre diameter measurement (see Section 1.7) are most likely to also quantify medullation.

1.13

Computer blend selection

A computer expert system has been developed to define objective fibre specifications appropriate for carpet yarns according to the processing route and product specification.8,9 The system can be customised to suit the machinery and processing conditions in yarn manufacturing plants. By way of example, if the product has been manufactured in the past, the customary blend, if still available, is sampled and measured to quantify its properties. This information can then be applied to currently available lines of wool to determine a computer-selected blend using least-cost-blending software. However, using a least-cost strategy for purchasing wool may not be the ideal solution because processors may find machine settings, processing efficiency and product properties need to be revised to take full advantage of the technology. One of the interesting outcomes of relying on computer selection of lots comprising a blend has been the observation that visually different unscoured blends do indeed conform after processing to the end result sought. A significant advantage of computer blend technology is the assistance that can be provided to new entrants into wool processing, or to processors wanting to quickly develop a new product using their existing equipment. Following a series of successful validation trials8,9 it became possible for wool exporters in New Zealand to provide an enhanced service to clients using 100% New Zealand wool in their product. It also offered a new marketing opportunity whereby mills unfamiliar with these wools, for example in emerging markets in China, could be supplied with blends suited to their equipment and the desired final product.

1.14

Wool promotion

The International Wool Secretariat (IWS) was formed in 1946, the three signatories being Australia, New Zealand and South Africa. In later years, Uruguay showed an interest and was eventually admitted to membership. Levies from their woolgrowers supported a head office in London, and somewhat later a large technical centre in Ilkley, Yorkshire. Branches in

Wool production and fibre marketing

19

most leading countries provided technical and marketing support for their local wool manufacturers. They also had considerably autonomy in developing promotional campaigns appropriate for their particular market and these were usually strongly identified with the Woolmark, a quality certification mark. The quality assurance aspect involved labelling garments, textiles and carpets that met set standards of performance. This very extensive programme was generally admired and supported by retailers as well as manufacturers. Brand recognition by consumers worldwide was one of the highest for any type of product. Section 12.7 highlights the extremely competitive environment faced by wool products in achieving consumer awareness. An effort by the Australian Wool Corporation to intervene and maintain high wool prices in 1991 led to stockpiling of almost a year’s supply of Merino wool, followed by a long period of very slow recovery. New Zealand had experienced a long-term slow decline in wool prices and this was exacerbated by economic crises in Asia in the 1990s. They subsequently withdrew from the IWS and developed their own marketing strategy.

1.15

The Fernmark brand

New Zealand’s share of world carpet wool usage had declined significantly in recent years and with that decline came a move from generic promotion under the Woolmark logo to a brand marketing programme that more specifically identified New Zealand as the country of origin of the pile fibre. This fundamental change in marketing philosophy saw Wools of New Zealand in 1994 take over the Interior Textiles Division of IWS, which it had previously fully funded, and strike out on its own with the new Fernmark brand entity. The fern leaf image was selected for its general association with New Zealand. Initially, the emphasis for branding has been on carpet wools with the development of segmented brandnames for various classes of product, to be used in conjunction with the Fernmark brand. Other segment brands have been developed, such as Isolana, for use with bedding products. Ultimately, all major product segments that use New Zealand wool are likely to have specific brands used with the Fernmark.

1.16

Marketing of distinctive wool types

Over the past 30 years, the major thrust in wool marketing has clearly been driven by the objective measurements of important wool fibre variables. In the case of coarse and medium diameter wool types, the sheep breed and flock discriminations such as ewes, wethers and lambs have, in principle, become of minor importance compared to the physical specifications of

20

Wool: Science and technology

wool lots. However, in a similar fashion to the emergence of direct selling to reduce transaction costs associated with wool auctions, there has been some revival of marketing based on particular features of fleece from certain breeds. Superfine Merino wools are the best example of what is essentially niche marketing. It combines the commercial interests of woolgrowers who specialise in producing very fine lines of wool (<18 micron) and manufacturers with a capability and reputation for creating luxurious wool products. Another instance is the development of breeding strategies for Perendale wool. Perendale sheep are the outcome of a long term breeding and selection programme at Massey University, New Zealand, led by Professor Peren. The notable marketing attribute of Perendale sheep is the additional bulkiness (see Section 1.10) of yarns made from their wool as compared to the general run of crossbred wools of otherwise comparable quality. The sheep farmers involved with the breed have formed a marketing alliance to promote their wools with the intention of extracting some price premium for their product. Comparable marketing strategies have been extensively used in the UK to promote not just a brand name for knitwear or distinctive clothing such as tartans, but to put forward the particular credentials of British wools.

References 1 Anon., New Zealand Wool Statistical Handbook, 1998/99 edition. Prepared by New Zealand Wool Group, Wool House, Wellington, New Zealand. 2 Anon., Objective Measurement of New Zealand Wool. Prepared by Fibre Technology Section, Wools of New Zealand and extracted from The New Zealand Wool Industry Manual, 2000 update. ISSN 1173-6402. 3 Anon., British Wool Marketing Board. Report and Accounts: 2000. 4 IWTO Draft Test Method IWTO-DTM-56, Internat. Wool Text. Org., Brussels, Belgium. 5 Hammersley M J, ‘NIR Analysis of Wool’, in Near-Infrared Analysis, Eds: D A Burns and E Ciurczak, Marcel Decker Inc., New York, 1991. 6 Hammersley M J, Ranford S L and Townsend P E, ‘Near-Infrared Analysis of Wool; The Calibration Transfer Problem’. Proc. 8th Int. Wool Text. Res. Conf., Christchurch, New Zealand, 1990, II, 218–29. 7 Wood E J, Burling-Claridge G R, Ranford S L, Hammersley M J, Edmunds A R and Thomas B L, ‘Recent Developments in the Objective Measurement of New Zealand Wool’, 9th Int. Wool Text. Res. Conf., Biella, Italy, II, 44–52. 8 Carnaby G A, Maddever D C and Ford A M, ‘The Application of Linear Programming to Wool Blending and Specification’. Proc. 7th Int. Wool Text. Res. Conf., Tokyo, Japan, 1985, II, 186–94. 9 Maddever D C, Cuthbertson I M and Edwards S, ‘An Expert System Tool for Specification of New Zealand Wool to be Used in the Manufacture of Carpet Yarn’, 9th Int. Wool Text. Res. Conf., Biella, Italy, 1995, I, 18–25.

2 Woolscouring, carbonising and effluent treatment L A HALLIDAY

2.1

Introduction

Raw or ‘greasy’ wool is contaminated with impurities, the type depending on the breed of sheep, the area in which the sheep are raised, and husbandry methods. The role of woolscouring is to: • •

•

clean the contaminants from the wool by means of an economic process ensure that the wool is in a physical and chemical condition to suit the intended processing route (e.g. for topmaking to minimise entanglement and retain the staple structure) comply with environmental requirements (this requirement has become much more important over the last 20 years).

The term ‘scouring’ is used here in the generic sense of a process that removes contaminants from raw wool. Thus, it includes all processes which aim to clean wool including those which use solvents other than water and those which use solids as a carrier for removing the contaminants. Scouring clearly is a critically important step in wool processing. It must be carried out using technology that enables the wool to attain its optimum performance in further processing.

2.2

Nature of contaminants

The main contaminants are woolgrease, suint and dirt. Woolgrease, technically a wax, is produced by the sebaceous glands in the skin of sheep, while suint is produced by the sudoriferous (sweat) glands. A more precise way of defining woolgrease and suint in relation to the analysis of greasy wool relates to their solubilities in organic solvents and water respectively. Thus suint can be defined as the water-soluble fraction of the fleece and woolgrease as the solvent-soluble fraction.1 Woolgrease is comprised principally of high molecular weight esters formed from a mixture of sterols (including cholesterol) and aliphatic alco21

22

Wool: Science and technology

Table 2.1 Typical concentrations of non-wool contaminants (Percent by mass on greasy wool) Maximum

Minimum

Average

10.0

16.1

Australian (New South Wales) Merino52 Grease

25.4

Suint

12.0

2.0

6.1

Dirt

43.8

6.3

19.6

New Zealand crossbred 53 Grease

8.5

1.6

5.2

Suint

12.1

2.2

8.0

Dirt + suint moisture

—

—

7.9

hols with straight and branched chain fatty acids. The amount present on the wool depends upon the sheep breed, with Merinos recording the highest amounts (Table 2.1). Crossbred wool usually has substantially less. For most processing routes, the requirement is to reduce the grease on the fibre to below 0.5%. Suint is mainly potassium salts of organic acids: potassium comprises 90% of the cations present and this represents 25–27% on the weight of dry suint. In scouring liquors, at alkaline pH levels, suint has detergent properties. The amount present also depends on the breed type, with crossbreds tending to have more than merino. The range of the levels of the contaminants is notably wide; especially for the dirt. The differences in type and level of contaminants help to explain why different hardware and processes have proven necessary in woolscouring. For example, the large amount of fine dirt on some of the fine wools from Western Australia is very difficult to remove, and low scouring throughputs are often necessary; whereas a high yielding coarse wool from New Zealand represents the other extreme of being very easy to scour. Raw wool may also be contaminated with vegetable matter (VM). Where the wools are heavily contaminated with VM, they may have to be carbonised to remove it (Section 2.7.1). A major proportion of the wools requiring carbonising are from Australia and South Africa.2

2.3

Historical overview of scouring methods

Traditionally, wool was scoured in hot, aqueous solutions of soap and alkali. Synthetic detergents have largely displaced soap, but aqueous scouring has remained the principal method. However, the use of volatile solvents

Woolscouring, carbonising and effluent treatment

23

to scour wool in batchwise processes was introduced about 1900.1,3 Conventional aqueous scouring removes the woolgrease in emulsion, the suint in solution and the dirt in suspension. Solvent scouring removes the woolgrease in solution, and removes both the dirt and suint in suspension. Various dry-powder-type processes have been employed or advocated in the past, where solids are used as carriers to remove the contaminants from the wool.1 Types of materials used have included gypsum, kieselguhr, aluminium silicate, and bran. A method currently under development in Australia uses microwave energy to heat the greasy wool while it is being contacted with a powder.4 Many developments in woolscouring and effluent treatment have been commercialised over the last 30 years, several of which originated in work carried out in the research laboratories of WRONZ (New Zealand) and CSIRO (Australia). Other research organisations, technical centres, machinery manufacturers and processors themselves have also contributed. More recently, with the reduction in bulk funding available for research and development laboratories, a greater proportion of the work has been commercial and has not been reported in the literature.

2.4

Unit operations

2.4.1 General overview A woolscouring works typically includes facilities for blending and mechanically cleaning greasy wool, and drying and blending the scoured wool, as well as the scouring machine itself. The possibility of carrying out additional chemical processing may also be provided.

2.4.2 Blending systems for greasy wool Two basic types of blending systems may be identified: i)

ii)

In-line blending systems (Fig. 2.1) are used where the wools being blended have similar characteristics. Partially opened wools are layered horizontally into an accumulator (blending bin) and an inclined spiked lattice empties the bin from one end, providing effective mixing. Such systems are often used by scourers of fine wools. Computerised weighbelt blending systems (Fig. 2.2) are used for blending wools that have different characteristics. Such systems include multiple weighbelt lines that deliver the wool onto a conveyor for mixing. Further opening-dusting followed by layered blending may also be included.

24

Wool: Science and technology

Bale breaker

Conveyor

Blending accumulator

Hopper feeder

2.1 Typical in-line blending system.54 [Courtesy of ANDAR.]

Accumulator Accumulator Accumulator hopper hopper hopper feeder feeder feeder weighbelt weighbelt weighbelt

Hopper feeder / accumulator

Weighbelt

Accumulator conveyor

Hopper feeder

2.2 Typical computerised weighbelt blending system.54 [Courtesy of ANDAR.]

Blending systems are usually built-up from standard items of equipment (e.g. hopper feeders and weighbelts), and may be customised to suit the requirements of the user. Dimensions of existing buildings often impose constraints on the layout.

2.4.3 Preheating bales of fine wool Before densely packed fine wool is blended, preheating may be necessary to facilitate opening of the wool. Fine wools are often compressed to high densities to facilitate storage and to lower the cost of transport. Australian greasy wools are usually exported in ‘tripacks’, at roughly three times the density of a farm bale. Where ambient temperatures in the scouring plant are low, the packed wool remains very hard and difficult to process. It may be necessary to heat the wool to relax strains and enable efficient opening and blending; also to reduce wear and tear on the processing equipment. It has been suggested that the temperature of the greasy wool needs to be at least 15–25 °C to allow adequate opening and blending.5 There are three main methods of heating the bales of wool: i) warm rooms ii) steam injection iii) microwave and ‘dielectric’ heating methods.6

Woolscouring, carbonising and effluent treatment

25

Warm rooms have long been used to prepare farm bales for processing. With tripacks, a longer holding time is necessary and access for forklifts is necessary. The rate of heating can be increased by increasing the temperature, but mills set an upper limit of about 75 °C to avoid damage to the wool.5 Disadvantages are the high labour costs, potentially high heating costs and the space requirements. Injection of steam into tripacks has been practised, but yellowing of the wool at the point of injection has been a problem, especially if high temperature steam is used.5 The Australian Wool Corporation developed the Forced Convection Bale Warmer to overcome the problems of conventional steam injection. This unit used two fluids – low temperature dry steam and warm air – which were applied to the tripack sequentially.5 Although the unit was technically successful it has not sold in numbers. Radio frequency heating techniques have been used in the wool industry for some time, mainly using the dielectric frequency range; typically 13.56 or 27.12 MHz. Although commercial use of bale heaters utilising dielectric heating has been reported in the literature, their use has not become widespread. Presumably, this has mainly been because of their high capital and running costs. More recently, the successful commercialisation of bale heating systems using radio frequency power in the low microwave range (915–922 MHz) has been reported.7

2.4.4 Opening and dusting Wool may be opened and dusted before and after scouring, and there are generally benefits for all types of wool if both of these processes are carried out appropriately. Greasy wool is opened to facilitate the removal of contaminants in the scour, and to assist the blending process. Opener-duster machines are also used to remove dirt and VM prior to scouring, which reduces the solids loadings in the liquors and effluent. After scouring and drying, wool is opened to assist its transport by pneumatic conveying, to help even-out the moisture distribution in the wool mat, and to facilitate further dusting of the wool. There are results to indicate that mild opening of fine wool after drying may be beneficial to the worsted carding process8 but further testing has indicated that such pre-opening has advantages only when the scoured wool is notably entangled.9 Any opening of wet fine wool, even the relatively gentle action of a feed-hopper, has been shown to reduce the top length and should be avoided.8 Coarse wools generally can withstand quite intensive opening, both before and after washing.1 Dag and slipe wools in particular will benefit from such treatment. It is interesting to note that the most recent commercial developments in opening equipment mainly for coarse wools – the

26

Wool: Science and technology

Short Wool Processor and the Scoured Wool Cleaner – have been high intensity machines. The following types of machine are commonly used, listed approximately in order of increasing intensity of opening: Bale-breakers are strongly-built, large machines for breaking open bales prior to opening/dusting in a drum opener. The mechanical action may be derived from drums with teeth (see Fig. 2.1) or from large flails rigidly attached to shafts.The former types are often used by scourers of fine wools, while the latter are favoured by the commission scourers in the UK for handling rolled fleeces. Feed-hoppers are machines with multiple roles of feed-rate regulation, opening and wool containment. They have a spiked lattice which carries the wool out of the hopper for delivery to the next stage of the process (see Fig. 2.3). Drum openers most commonly have two drums (Fig. 2.3), but configurations have ranged from one to four drums (Fig. 2.4). New Zealand scourers have recently favoured three-drum units for their flexibility and additional cleaning capacity. Many of these openers are now supplied with screens that are cleaned automatically as they slide sideways out of the machine under the power of hydraulic rams. There are also various options available for handling the waste from openers, including straightforward gravity discharge into waste containers, pneumatic conveying, and mechanical systems such as augers and belt conveyors. Measurements by WRONZ on the performance of multi-drum openers in industry showed that they removed 5 to 16% of the dirt on the wool, depending on the wool type, provided the screens were cleaned regularly.10 These measurements were carried out on New Zealand wools and a

Variable speed motor drive

Wool flow

Variable speed motor drive

Hoppermatic

Lattice motor speed

Feedrate controller

Lattice motor speed

Ultrasonic sensor

Loadcell

No 1 hopper feeder

Drum opener

No 2 hopper feeder

2.3 Opening and feeding system.

54

Weighbelt

[Courtesy of ANDAR.]

Woolscouring, carbonising and effluent treatment

27

2.4 Three-drum greasy wool opener. [Courtesy of Kaputone Wool Scour (1994) Ltd.]

lesser performance would be expected on fine wools, which contain more grease. The opening process carried out by rotating drum openers appears to occur in three main ways.10 Intense opening takes place firstly at the feed or ‘nip’ rollers at the entry to the opener, as the teeth on the drum tear or ‘pick’ at the constrained wool mat. Secondly, fixed teeth on the screens will break up the wool flow with a strong effect since they are normally designed to intersect with the rotating teeth on the drums. An important innovation from WRONZ was the development of a self-cleaning-teeth assembly, which provides a self-cleaning capability and a means to adjust the number of rows of fixed teeth in the ‘up’ position while the opener is in operation.11 Thirdly, there is less severe opening as the wool changes direction on transferring from one section of the opener to the next. One of the outcomes of the considerable amount of work carried out at WRONZ on the opening and dusting of greasy wool was the design of a self-cleaning machine, the WRONZ Autoclean, which reached the commercial prototype stage.12 Although its opening and dusting performance was up to expectation, it has not achieved commercial success. Stepped opener-dusters use a smaller diameter rotor than drum openers (Fig. 2.5). Their usage at the greasy end of the scour has much reduced during the last 20 years, mainly because the dusting screens became rapidly

28

Wool: Science and technology

blocked with dirt, and they essentially become an expensive inclined conveyor. They are better suited to the cleaning of scoured wool. The Short Wool Processor is based on the principle of hinged flails (as in a dag crusher) attached to a rotor. It may be used in continuous or batch processing modes. The Short Wool Processor is used off-line mainly to pre-open and dust dag wools and slipe wools. Cott Openers are used for breaking apart cotted fleeces. The main working part is usually a rotor fitted with angled teeth or pins which combs a fringe away from the fleece as it is fed at a controlled rate.1 The feeding system is usually a conveyor belt that delivers the fleece to a pair of restraining spiked rollers, or to a spiked roller working in combination with a ‘piano key’ set-up. Cyclic Openers have a large diameter drum fitted with teeth, with intersecting workers located above it. It is fed via conveyor and feed rollers. In New Zealand, it was used mainly on slipe and dag wools; elsewhere it was also used to open wools prior to carbonising. It may be used in batch or continuous mode.1 In New Zealand, the Short Wool Processor has largely superseded the Cyclic Opener. The less demanding duty on scoured rather than greasy wool suits the Stepped Opener-Duster machine. The degree of opening is determined at the design stage by the selection of the number of drums, their speed, and whether feed rollers are required. Figure 2.5 shows a scoured wool dedusting system that includes a three-drum stepped opener-duster. In this example, the wool is delivered onto a picking conveyor before it is transported by pneumatic conveying to its destination for discharge by a condensor. The air from the condensor is exhausted to atmosphere via filter bags or cyclones. Scoured Wool Cleaners are a WRONZ development commercialised by Mentec.13 Unlike most opener-dusters for wool, which have multiple drums or rotors with the wool being fed from one drum to the next, the Scoured Wool Cleaner is a single-rotor machine, with the wool being fed near one end and discharged at the other end. Thus, the wool has an axial flow

Wool flow

Air & dust out

Wool Dryer

Picking Stepped opener/duster conveyor

Condenser & conveyor

Fan

Dust Collection

2.5 Scoured wool finishing system.54 [Courtesy of ANDAR.]

Woolscouring, carbonising and effluent treatment

29

component as well as a rotational component. In this respect, the Scoured Wool Cleaner is similar to the willows or ‘beater-scutchers’ used for dedusting in the carbonising process.14 It achieved rapid penetration into the New Zealand scouring industry, owing to its proven wool cleaning capability. A smaller machine operating on a similar principle is available for recovering fibre from the waste of the main unit. Fearnought machines operate like a card with swift, workers, and strippers. They are mainly used by scourers in the UK for opening and blending.

2.4.5 Washing wool in scouring trains A scouring train comprises a number of wash bowls and squeeze heads, and is usually linked to an in-line dryer and a woolgrease recovery system. Figure 2.6 shows a typical plant layout for a scour for fine (e.g. Merino) wools; while Fig. 2.7 shows a typical plant layout for coarse (e.g. NZ crossbred) wools. Older conventional scouring lines typically include four bowls having rake or harrow mechanisms that dunk and transport the wool. The scoured product from such designs is satisfactory for most purposes so that the basic mechanical motions of aqueous scour bowl design have not changed greatly over the last 100 years. Most of the greasy wool processed throughout the world is still scoured in aqueous systems using rake and harrow machines.15 Details of the bowls have, however, changed significantly. Over the years, various major innovations in scour bowl design have reached commercial prototype stage but only a few have gained ultimate commercial acceptance. Of particular note were the different designs of aqueous jet scours during the 1960s by CSIRO and the University of New

80 610 Bowl 1 Bale breaker

Bowl 2

Bowl 3

Bowl 4

Bowl 5

Bowl 6

8 Drum dryer

3 Drum stepped opener

Feeder Opener Feeder

Weighbelt

2.6 Scour plant for fine wools.54 [Courtesy of ANDAR.]

62 715 Bowl 1 Feeder Opener Feeder Weighbelt

Bowl 2 Bowl 3 Bowl 4

Bowl 5

Bowl 6 Feeder

2.7 Scour plant for coarse wools.54 [Courtesy of ANDAR.]

6 Drum dryer

3 Drum stepped opener

30

Wool: Science and technology

South Wales.1 These designs were aimed at improving the combing results when compared with scouring on conventional machinery and while they achieved that aim, it was also shown that conventional scouring mechanisms could be developed to achieve a similar improvement in processing performance (e.g. in the Petrie-Wira Improved Scour).16 An important scouring development commercialised during the 1960s was the Fleissner suction drum scouring bowl.17 Perforated suction drums are used to transport the wool and also to wash it by means of liquor flow from outside to the inside of the drums. In the original design, the liquor circulation pumps were located inside the drums. In later designs, an axial flow pump was installed in a side space of the bowl. It is interesting that the original design allowed for flexibility in bowl length, ranging from one to three suction drums long.17 During the late 1980s, a 3 m-wide suction drum scour was installed in Uruguay,15 which remains the largest working width of woolscour available from any manufacturer. The suction drum design has been successful mainly for high yielding fine wools; on dirtier wools, product cleanliness becomes an issue. The wool mat acts as a filter for fine dirt, some of which may remain in the wool mat at the exit of the final suction drum bowl. For this reason, a ‘hybrid’ scour has been installed by some mills with a selection of suction drum and rake bowls being fitted into the scour train. Hence, the particular bowls are chosen depending on their prime function: grease and suint removal or dirt removal. Rake and harrow bowls fulfil most of the requirements for the washing of fine and coarse wools. Rake systems using three-throw crank drives have proven most popular, since they can be set up to have a lesser felting effect than a square action single harrow, and their compact dimensions makes the bowl easier to cover. A small number of machines have used swing-rake mechanisms, which simulate the movement of a hand-held fork,1 to move the wool through the bowls, but they are only suitable for blends that demand a particularly strong mechanical action. A hopper-bottomed scour bowl of recent design (ANDAR) is shown in Fig. 2.8. The wool is fed into the bowl and is submerged and wet-out by means of the suction drum, which is mechanically driven at the required speed. Liquor within the scour bowl is circulated from the spraybox to the squeeze press by means of the flow-around pump. A heat exchanger may be installed within the spraybox or installed separately to heat the liquor flow between the flow-around pump and the spraybox. The main rake moves the wool through the bowl where it is picked up by the head rake, which in turn delivers the wool to the drain tray. The squeeze press removes liquor from the wool and then transfers it to the outfeed conveyor for delivery to the next step in the process.

Woolscouring, carbonising and effluent treatment Suction drum

Main rake Head rake

Wool in

Squeeze ool W press

31 t ou

Spraybox

Flowback from next bowl

Flowback to previous bowl Heavy solids

2.8 ANDAR bowl flow diagram.54 [Courtesy of ANDAR.]

During early 1978, two ‘mini-bowls’ designed by WRONZ were installed by ANDAR as a replacement for the first scouring bowl at the original installation of the WRONZ Comprehensive Scouring System (see Scouring Systems) in Timaru, New Zealand. The impetus for this development was the general trend towards shorter scouring bowls, the knowledge that many raw wools are easy to wash, and the stimulus given to the industry in New Zealand by the demonstration of the Lo-Flo wash-plate process to the trade at Geelong in 1977.18 Comparative trials showed that the scouring efficiency of two mini-bowls was comparable with that of two bowls of conventional length (the mini-bowl was 2.7 m long, while the conventional bowls were 6.7 m and 5.8 m long).19 The benefits due to mini-bowls were several including: space savings, reduction in energy losses, reduced volume, reduced capital cost, reduced maintenance, and ease of operation.18 Commercialisation was successful, with ANDAR/WRONZ mini-bowls installed in New Zealand and overseas soon afterwards. Subsequent experience showed that mini-bowls were not ideal for washing low yielding fine wools, mainly because dirt removal could be a limiting factor. However, they were still chosen by some processors for scouring and rinsing applications of high yielding fine wools on the basis of their own experience, and they are widely installed for the processing of New Zealand coarse wools, often in combinations with long conventional bowls. The mini-bowl hopper design, with its hopper of full scour working width, became the basis for the ANDAR

32

Wool: Science and technology

multi-hopper designs to follow. Scour lines comprising bowls of one, two, three, and sometimes four hoppers long were installed, mainly in Australia, Asia, and the USA.

2.4.6 Squeeze heads The action of the squeeze rollers (Fig. 2.9) is critical to the efficiency of removal of contaminants from the wool. As the wool mat enters the nip of the squeeze rollers, it is subjected to intense hydrodynamic forces which are particularly efficient at removing woolgrease and suint from the wool fibres, but less efficient at removing dirt. Efficient squeeze rolling also minimises the carryover of contaminants entrained in the wool mat to the next bowl in the scouring line. The efficiency of the squeeze rollers of the last bowl in the scouring line is also very important. By reducing the regain of the wool entering the dryer, the energy usage of the dryer is reduced while its wool throughput capacity is increased. The squeezing efficiency of rollers in a scouring line increases with temperature and with the applied downforce on the top roller. Typical industrial squeeze rollers are designed for a maximum downforce in the range of 5 to 10 tonnes per metre of scour width. Thus, a 2 m-wide

2.9 Squeeze press. [Courtesy of Jandakot Wool Washing Pty Ltd.]

Woolscouring, carbonising and effluent treatment

33

scour line will normally have a squeeze roller set capable of 20 tonnes total downforce at the exit of the final scouring bowl. Other bowls in the line may be equipped with so-called ‘10 tonne’ presses. Most modern squeeze rollers are pressurised via pneumatic systems. The bottom rollers are commonly of solid steel with a stainless steel coating. The top rollers are also commonly made of steel with a lapping of polyamide rope of square cross section. Where acid conditions are expected (e.g. in the final bowl, where insect resist treatments may be applied, or in the acid bowl of the carbonising process), the lapping should consist of polyester rope owing to its superior acid resistance. Historically, the top rollers were lapped with wool top or nylon tow but such lapping has been largely superseded due to the superior durability of square rope. A few scourers, mainly in Europe, have chosen to use polyurethane coatings for the top squeeze rollers. The regain of wool from squeeze rollers is between 50 and 100% depending on the efficiency of squeezing.1 The main factors affecting the result are the liquor temperature, the downforce on the top roller, the type and condition of the lapping on the top roller, and the evenness of wool flow through the rollers. It is useful to consider what results might be expected for some specific processing conditions. Wool regains in the range 60–70% should be achieved with 10 tonne squeeze rollers with top roller lapping of nylon rope on 2 m-wide scouring lines with bowl temperature of about 60 °C. Figures in the range 50–60% should be achieved for 20 tonne presses with similar operating conditions.

2.5

Scouring chemistry

2.5.1 Detergents and builders Before the 1950s, the main detergent used to scour wool was soap, which was used with an alkaline builder, usually soda ash.20 The propensity of soaps to form insoluble salts with calcium and magnesium ions in hard water areas prompted the development of synthetic detergents and the most common ones used in the scouring industry today are non-ionic types.15 Until recently, nonyl or octylphenol ethoxylates have been most popular. However, they are not readily biodegradable and concerns regarding the environmental effects of such detergents and their breakdown products has resulted in voluntary and legislative restrictions on their use in several countries. As a result, the usage of the more biodegradable fatty alcohol ethoxylates is increasing. Soda ash (sodium carbonate) remains the most common builder used, although sodium chloride or sodium sulphate are sometimes used. The

34

Wool: Science and technology

action of the builder is to stabilise the emulsified woolgrease and dirt, and prevent redeposition back onto the wool.15 Suint has soap-like detergent properties when either natural alkalinity is present in the fleece or alkali is added to the washing liquors.1 Greasy crossbred wools contain more suint than fine wools and, unlike such wools, are naturally alkaline, as well as containing much less woolgrease. This explains why crossbred wools are usually scoured with a hot first bowl without any addition of soda ash. In contrast, soda ash may sometimes be added to the early bowls of fine wool scours. Table 2.2 shows typical bowl operating temperatures for scouring with neutral non-ionic detergent. The optimum temperature depends on the actual detergent used, but is usually within the range 50–65 °C.15 Where alkaline scouring conditions are employed, temperatures less than 55 °C should be used. Desuinting is favoured by many scourers in Europe, in part because the contaminants removed in Bowl 1 are thereby eliminated from the woolgrease recovery system connected to the following bowl(s). This has potential benefits in terms of reduced wear on pumps and centrifuges in the woolgrease recovery system. Siroscour in 3-stage mode uses a modified desuinting bowl (see Section 2.6 for details). The rate of detergent usage depends on the type of wool being scoured, but should be less than 9 litres/tonne greasy weight for merino wools and less than 3 litres/tonne greasy weight for crossbred wools. More of the detergent should be added to the second and third hot scouring bowls to enable the countercurrent flowback system to have greatest effect. However, when scouring merino wools this approach may have to be tempered if the detergent foams excessively in the later scouring bowls. The rate at which wool can be scoured depends greatly on the type of wool. Thus, a relatively clean crossbred wool from NZ usually can be scoured at more than twice the throughput of a low-yielding Merino type Table 2.2 Typical bowl temperatures for aqueous woolscouring (°C) Bowl No.

1

2

3

4

5

Desuinting

<35

60

60

55

50

6 50

(fine wool)

D

S

S

S

R

R

Conventional

60

60

60

50

50

50

(fine wool)

S

S

S

R

R

R

Conventional

65

60

60

cold

cold

60

(NZ crossbred)

S

S

S

R

R

R

Where D = desuint, S = scour (with detergent addition to bowl), R = rinse.

Woolscouring, carbonising and effluent treatment

35

from Western Australia. The latter wools have a greater surface area to clean owing to the smaller fibre diameter, have more woolgrease, and commonly have much more fine dirt which is difficult to remove. Wool throughputs have increased markedly over the last 30 years owing to improvements in scour and dryer design, process control, and increase in scour working width. Thus, a 3 m-wide scour is capable of washing good quality NZ crossbred wools at a rate of 5.5 tonnes/h. It is of interest to note that, as the working width of woolscour increases, the throughput per metre of width also increases, probably because edge effects are less important for wider scours.

2.5.2 Water quality There are two main sources of problems associated with water quality: hardness and the presence of multivalent metal ions.20 While hardness, in the form of calcium and magnesium ions in the water, does not interfere directly with the action of non-ionic detergents, their presence could cause redeposition of fibre contaminants and dyeing problems. It has been suggested that it is possible to scour greasy wool satisfactorily in water of total hardness up to 70 mg CaCO3 /litre, while unsatisfactory scouring is likely to occur over 100 mg/litre.15 In hard water areas it may be necessary to install a softening plant in order to prevent such problems. Apart from calcium and magnesium, the presence of metal ions such as iron can cause severe dyeing problems by interacting with dyestuffs.20

2.6

Development of scouring systems

For many years, woolscouring of the wide range of wools available was viewed as an art rather than a science. Even wools of the same breed and micron range vary widely in their scouring properties, depending on where the sheep were raised and the methods of husbandry. An early system of note was the Duhamel process, which was introduced in France during the 1920s.1 The system included several elements that were to become cornerstones of woolscouring in the future, e.g. bowls with conical shaped bottoms and the use of decanter and nozzle-disc centrifuges to remove dirt and woolgrease from the liquors, respectively. The process never received universal acceptance, perhaps because poor scouring could have been expected under the liquor conditions used;1 but it is also likely that maintenance problems on many items of equipment would have been severe. Even today, with the major advances in materials and design, the selection of pumps, fibre screens, solids removal systems and centrifuges must be approached warily.

36

Wool: Science and technology

During the 1960s, research and development on scouring machinery concentrated on the design of individual scour bowls. During the 1970s, while such developments continued, they became viewed in the context of a systems approach to woolscouring. This was necessary as energy and pollution discharge costs soared,21 while there was also new environmental awareness. This process probably began with the WRONZ Comprehensive Scouring System (see Fig. 2.10), which was first installed at a new woolscour in Timaru, New Zealand in 1972.1,22 The system was designed after the main deficiencies of typical plant design and operation had been identified.1 The major outcomes were to integrate the contaminant removal systems into the operation of the scour so that all heavy effluent (i.e. that originating from the hot scouring bowls rather than from the rinsing bowls) received treatment before discharge. Such treatment included removal of fibre and heavy solids, and recovery of woolgrease. Batchwise operation, where the scour bowls were ‘dumped’ to drain from time to time, was replaced by a fully continuous process. Liquor management was ‘tight’, with avoidance of bowl overflows and use of bowl-to-bowl ‘flowback’ running countercurrent to the wool flow. The ‘flowdown’ of heavy liquor to drain was at a controlled rate that could be set manually or automatically via measurement of a particular property of the liquor (e.g. density or turbidity). Heat was recovered from the flowdown and used to preheat fresh water being fed to the scour. During 1977, CSIRO released the Lo-Flo process to industry.23 This had a high level of effluent treatment integrated into the scour process. The LoFlo process relied on the phenomenon of ‘concentration destabilisation’. When this liquor condition was reached, all of the suspended solids were

Greasy wool

Scoured wool Fresh water from heat recovery system

Product wool grease

Sludge Effluent to drain

2.10 Simplified flow diagram of WRONZ comprehensive scouring system.54 [Courtesy of ANDAR.]

Woolscouring, carbonising and effluent treatment

37

able to be removed by centrifuging, and the liquor was then able to be re-used indefinitely. It was considered that several substances were involved in causing the destabilisation of the liquor. One was suint, another was the detergent added to scour the wool and the builders such as soda ash that were added to the liquors.23 Destabilisation was said to be enhanced by high temperatures, and the liquors were heated almost to boiling point before centrifuging. During equilibrium operation, a mass balance for soluble substances (suint, builder, and detergent) was said to be achieved where the mass of such substances discharged with the sludge from the decanter and with the cream from the disc separator(s) equalled their rate of introduction to the machine.23 There would also be a significant mass of soluble substances carried forward from the Lo-Flo unit to the next washing stage. The Lo-Flo process was trialled by IWS at full-scale in a mill in the UK. To facilitate the transport of wet wool through squeeze rollers at very high liquor concentrations, wash plate systems were used both in the CSIRO laboratory machine and in the IWS full-scale machine. Wash plates include a perforated metal sheet down which the wool is caused to slide by a jet of liquor into the nip of the squeeze rollers.21 In practice, IWS found that it was necessary to maintain a small flowdown from the Lo-Flo unit.21 For dirty wools, the decanter sludge production increased and the suint removal was improved so that the flowdown could be eliminated. Guided by experience in operating their full-scale Lo-Flo installation for two years, the Mini-Flo process was introduced by the IWS, mainly to address the low rates of dirt removal of the wash-plates.21 Their Lo-Flo installation was modified to trial the process, and achieved 65% recovery of woolgrease and 59% recovery of dirt.21 The Mini-Flo prototype used conventional bowls to remove dirt from the wool after the wash plates, while the commercial design used mini-bowls for the purpose. While the results from the commercial prototype were promising, neither Mini-Flo nor LoFlo achieved continued commercial success. An early reference to Siroscour (Fig. 2.11) highlighted the need for cleaner wool and better dirt recovery, both of which had been problems with Lo-Flo.24 Residual contaminants could affect processing performance in several ways, including contributing to dust and fly in the mill, affecting the performance of processing additives, leading to increased wear and tear on machines, and visual effects on both topmaking and subsequent processing (e.g. in spinning and dyeing).25 Studies by CSIRO scientists had also shown that each of the usual wool contaminants, i.e. grease, dirt and suint, had easy-to-remove and hard-to-remove fractions. The model of contaminant removal was as follows:25

38

Wool: Science and technology Greasy wool

Scoured wool Fresh water from heat recovery system Product wool grease

Sludge Effluent to drain

2.11 Simplified flow diagram of Siroscour.54 [Courtesy of ANDAR.]

1) 2)

the contaminant mass is penetrated by water and detergent; the contaminants begin to swell as the water penetrates the mass (the rates of penetration and swelling vary considerably for different contaminants); 3) wool grease globules are formed within the swollen mass; 4) the complexed and uncomplexed easy-to-remove contaminants are removed from the surface of the wool; 5) the hard-to-remove contaminants, which may either be only partially swollen or adhering strongly to the fibre surface, are partially removed. Easy-to-remove contaminants comprised the unoxidised woolgrease, readily soluble suint and loosely held minerals, together with organic and proteinaceous dirt. The remaining hard-to-remove contaminants comprised a small fraction of the total oxidised grease, slowly soluble suint, sub-micron mineral dirt and flakes of protein contaminant.26 To facilitate the scouring of most of the contaminants, and to assist in the removal of the contaminants from the liquors, ‘two-stage’ and ‘three-stage’ scouring was promoted. Three-stage scouring was the preferred mode of operation.25 The first stage (Bowl 1) removed dirt without removing woolgrease by using a modified suint bowl. Small additions of detergent and soda ash were made and the temperature was kept below 35 °C. This improved the recovery of dirt via settling tanks or hydrocyclones in the liquor treatment loop connected to Bowl 1, since there was less chance that non-settleable greasedirt complexes could be formed. In the second stage (Bowls 2–4), the easyto-remove contaminants were removed. Bowls 2 and 3 were scouring bowls containing hot detergent liquor while Bowl 4 acted as both a rinsing bowl to remove the easy-to-remove contaminants entrained in the wool mass and as a soaking bowl to encourage further swelling and hydration of the hard-to-remove contaminants. The third and final stage (Bowls 5 and 6) removed the hard-to-remove contaminants. Siroscour provided a system which will effectively wash the full range of

Woolscouring, carbonising and effluent treatment

39

fine wools, much in the same way that the WRONZ System provided a similar outcome for New Zealand wools. While the WRONZ System with mini-bowls was indeed capable of efficiently and effectively washing the better types of fine wool, it was not capable of washing all types. A happy marriage of CSIRO and WRONZ technologies took place in the first ANDAR Siroscour, where Bowls 3 and 4 were mini-bowls, as there were space constraints at that particular site. A comprehensive series of trials comparing the performances of different woolscours in industry was reported by the IWS in 1993.27 This was actually the second series of such trials, carried out because there were a number of weaknesses in the first series of trials.25 They were carried out by running four-tonne (greasy) batches each of fleece and skirtings through five different scours: a conventional rake/harrow scour, a suction drum scour (Fleissner), a Siroscour, a short-bowl (mini-bowl) scour, and a solvent scour (de Smet). The results showed strong relationships between specific opening energy and top length (hauteur), and between specific opening energy and noil. Specific opening energy has proven to be a useful measure of the degree of entanglement of wool presented to the card. This measurement technique was developed and used at CSIRO, Geelong. By suitably instrumenting their card, they were able to determine the work done per kilogram of wool carded, i.e. ‘the specific opening energy’.9 Since there are so many variables at play in any particular scour, only a proportion of which can be measured and reported, it is difficult to confirm causal relationships. The method of changing only one or a few variables on a particular scour is therefore preferable, and such tests were carried out on a Siroscour in Asia.25 These tests confirmed the better performance of 3-stage scouring, compared with conventional scouring, both in terms of increased top length and better whiteness (Table 2.3). This is the type of result that scourers have always aimed for and disproves the proposition that better colour can only be achieved at the expense of a more felted product (e.g. via increased mechanical energy input through the scouring process) and hence reduced top length. A subsidiary trial using three-stage scouring was carried out where the degree of mechanical action both in greasy wool opening and in agitation in the bowls was reduced. This had the expected effect of improving the top length but with a small reduction in whiteness (Table 2.3).

2.7

Chemical treatments in woolscours

2.7.1 Carbonising Raw wools are contaminated with amounts of vegetable matter (VM) depending on the environment in which the sheep were raised. The VM

40

Wool: Science and technology

Table 2.3 Comparison between conventional and three-stage scouring for wool scoured at a commercial topmaking plant (Mill A)25 Topmaking

Hauteur (mm) Conventional

Whiteness of tops (Y)

3-stage

Conventional

3-stage

Mill A

65.6

67.3

65.1

65.5

CSIRO

68.7

69.1 (70.6)

66.4

67.0 (66.2)

includes burrs, seeds, twigs, and straw.28 While the woolscouring process is very efficient at removing grease, dirt and suint from the raw wool, it is not effective at removing much vegetable matter. Pre- and post-scour opening and dusting machines can be specified or customised to remove small amounts of VM, but its removal is usually regarded as one of the functions of the card.2 Where the level of VM contamination is high, or where a VM-free product is required, a chemical treatment known as carbonising is necessary. A recent estimate puts the total volume of raw wool carbonised at more than 100 million kg per annum.2 The carbonising process takes advantage of the difference in chemical stability of wool keratin and VM (mainly cellulose and lignin) towards mineral acids. The carbonising process comprises conventional scouring, acidising, drying, crushing, beating, neutralising and final drying of the product. If alkaline scouring conditions are employed by means of additions of sodium carbonate, it is necessary to rinse the wool well before it is acidified.2 Sulphuric acid is the usual choice, applied at a concentration in the treatment bowl in the range 4.5–7.5%,depending on the bowl temperature and on the residence time of the wool in the bowl.2,28 A wetting agent effective under acid conditions is selected to obtain maximum penetration of acid into the VM, while minimising the acid content of the wool. Materials of construction are selected to resist damage by the acidic liquors. The acid concentration in the bowl is best measured by acid-base titration: Knott showed that the densitometric method overestimated the acid concentration by more than 20 g/l for most of a trial week. Moisture removal prior to drying traditionally used squeeze rollers. More recently, it has become accepted practice to install a continuous centrifuge after the acid squeeze roller and before the dryer feed-hopper. Centrifugal moisture removal provides a lower and more even regain distribution in the acidified wool, reducing the loss of fibre strength. Modern high-throughput plants use a separate dryer and baker rather than an integrated unit. Thus, the dryer is designed for rapid drying at low

Woolscouring, carbonising and effluent treatment

41

temperature but with significant heat inputs, while the baker is designed for higher temperatures but with lower heat inputs. This provides improved flexibility in control, including an opportunity to redistribute the wool mat by means of a feed-hopper prior to the baker. The drying stage is critical in the process,2,28 since acid hydrolysis of the protein chains may occur. Damage can be minimised by drying at low temperatures (60–70 °C) with high air flow rates through the wool mat. After drying, the wool is baked at a temperature in the range 105– 130 °C. Baking times in industry are typically 3–10 minutes depending on factors including openness of the wool mat, wool mat thickness, throughflow air velocity, and the amount of acid on the VM.28 Under the influence of the concentrated sulphuric acid, the VM becomes brittle and charred, which facilitates its removal in the crushing and beating stages. During baking, some acid may react with the wool to form covalently bound sulphate, which can cause problems in subsequent dyeing processes. The amount increases with temperature, baking time and acid concentration on the wool.2 It is necessary to crush the VM directly after baking because its crushability decreases when moisture is reabsorbed.2 Crushing is carried out by passing the wool between sets of pressurised rollers arranged in series, and there is a trade-off between efficient crushing and length reduction in the wool fibre. Beating (dedusting) of the wool entails mechanical action in willows or stepped opener-dusters.2,14,28 Much of the now friable vegetable matter is removed at this stage. After beating, the carbonised wool retains an acid content that can cause damage to the fibre if it is not properly neutralised. Neutralisation is usually carried out in a scouring train comprising 4 to 5 bowls.2 The first bowl contains water, in order to remove free acid and to allow hydration of the wool. The next 2 bowls usually contain sodium carbonate solution to neutralise the wool. Nonionic detergents may also be added to the neutralising bowls.28 The fourth and sometimes the fifth bowls contain rinse water to remove residual sodium carbonate.

2.7.2 Bleaching, insect-proofing and control of photo bleaching Certain chemical processes normally carried out in textile and carpet mills can be applied within the constraints of a continuous scouring regime. Bleaching with sodium metabisulphite or peroxide, insect-resist treatments and a photobleaching control process are those most commonly applied. The chemistry and treatment conditions are described in detail in Chapter 7.

42

Wool: Science and technology

2.8

Drying

2.8.1 General The clean, wet wool from the final squeeze roller set of the woolscouring line carries 50–100% of its bone dry mass as water, depending mainly on the temperature of the water in the bowl, the squeeze pressure and the type and condition of the covering (‘lapping’) on the top roller. The percentage of moisture based on the wool base is termed ‘regain’, and this parameter must be reduced to a typical target value of 16% at the exit of the dryer. Drying is responsible for 30–60% of the heat usage of a typical woolscour1 and ways of reducing the usage of heat have constantly been sought.29 A future approach to energy conservation is ‘airless’ drying, where the material is dried in an atmosphere of superheated steam rather than in hot humid air.30 Energy usage may be much reduced by recompressing and reusing the water vapour,29 or by merely using the recovered heat in wet processing.30 It was found that colour changes on drying should not be a problem but that only thin layers of wool could be handled by the technology. The latter requirement is likely to limit the applications, particularly in the drying of loose fine wool. Applications of superheated steam drying have been hindered by lack of suitable equipment and the corrosive conditions encountered.29

2.8.2 Commercial dryers The dryers used in the scouring and carbonising industry are of the continuous throughput type with throughflow air circulation. The air and material flows within a wool dryer are normally worked in counterflow to maximise the thermal efficiency and drying capacity. Dryers are classified according to the mode of transport of the wool. A suction drum dryer (Fig. 2.12) is fed by means of a belt and the wool is conveyed through it by perforated suction drums. Fixed baffles located inside the drums restrict the air flow to the upper or lower half of each drum alternately. The air circulation may be heated by steam or hot water coils located above and below fans mounted at the ends of the drums. Alternatively, the air circulation heating may be via direct gas firing. Suction drum dryers are compact, are easily controlled and have reasonable capital cost. Conveyor dryers carry wool through the dryer on a perforated slat conveyor through which hot air is circulated downwards (Fig. 2.12). Heating may be via steam or hot water coils or via direct gas firing. Such dryers occupy a larger floor area than drum dryers of the same production capacity since the rate of air circulation through the wool is lower. Upwards air

Woolscouring, carbonising and effluent treatment

43

Exhaust

Fresh air in

Wool in

Wool out Suction drum dryer

Exhaust Fresh air in Wool out

Wool in

Conveyor dryer

Exhaust

Fresh air in Wool in Wool out

Unidryer

2.12 Types of wool dryer, not drawn to scale.54 [Courtesy of ANDAR.]

flow has the aim of improving the evenness of drying but only very low airflow rates can be used before the wool is lifted off the conveyor. Capital costs of conveyor dryers are higher than for drum dryers and they usually have a slower response in temperature control. Fig. 2.13 shows a conveyor

44

Wool: Science and technology

dryer of recent design, where the wool is conveyed by means of porous sandwich belts. The Unidryer (Fig. 2.12) is a more recent introduction, and was originally intended to be a rapid (‘high intensity’) dryer for carbonising loose wool.31 The wool is carried through the dryer between two woven polyester conveyors while being subjected to reversing airflows in alternate sections of the dryer. The original design used air temperatures up to 150 °C, and relatively heavy bed weights of wool. Lower operating temperatures were used in later designs mainly due to industry concerns about wool yellowing. Because the wool mat is totally contained, throughflow air velocities may be adjusted without the wool drop-off problems that might occur in a suction drum dryer. This means that control of air velocity with possible energy savings is a viable means of regain control. Cleaning requirements should be less frequent because it is less likely that fugitive wool will accumulate in the dryer. It was originally commercialised in the UK on loose wool and then hanks, but achieved little market penetration. Early applications of the Unidryer included the drying of hanks, coils of yarn in the WRONZ Twistset process, and loose stock in dyehouses.1 The Unidryer was succesfully installed in a

2.13 Modern sandwich-conveyor dryer. [Courtesy of Jandakot Wool Washing Pty Ltd.]

Woolscouring, carbonising and effluent treatment

45

woolscour of 3 m working width in New Zealand during 1996 and further sales followed. Historically, most of the dryers in the wool industry have been heated by means of steam coils. More recently there has been a trend towards heating by means of direct firing with natural gas where it is available. This trend has been driven by improvements in dryer capacity, speed of response in control, and savings in process heat owing to the elimination of transmission and boiler losses that characterise steam systems. Heating by means of radio frequency power has a theoretical advantage in that the energy should be preferentially absorbed by the moisture in the wool, which should result in a more evenly dried product. However, suitably controlled and well maintained hot air dryers produce wool that is sufficiently uniform for baling directly, with lower capital and running costs than radio frequency drying.

2.9

Solvent scouring

There are several major advantages of solvent scouring. Felting and entanglement associated with aqueous scouring are largely eliminated, woolgrease recovery is much increased, suint recovery may be designed into the process, and aqueous effluent problems are avoided. At first sight then, there are several clear cut advantages to be gained from solvent scouring, with only minor disadvantages – the necessity for solvent recovery, possible toxicity and fire hazards to be set against it.32 Several different processes reached commercial prototype status during the 1950s–1970s without achieving significant commercial success. These included a process developed at the Swedish Institute for Textile Research,33 the CSIRO solvent jet process,32 and a process developed in Yorkshire at the West Riding Woollen and Worsted Mills Ltd.34 The Swedish and CSIRO processes both used a relatively high boiling point petroleum fraction, while the Yorkshire process used tetrachloroethylene. The most successful solvent scouring technology has been the de Smet process, with seven plants in commercial operation in 1990.35 It uses a combination of non-polar (hexane) and polar (isopropyl alcohol) solvents to target woolgrease and suint removal from the wool respectively. However, despite the acceptable results obtained for the de Smet plant in comparative testing of woolscour performance,27 there has been little further market success for this technology in the 1990s. A contributing factor is the high capital cost for such plant compared to conventional aqueous plant, during a time of low profitability in the wool industry generally. A new type of solvent scour was commissioned in Japan during 1983.This was the Toa-Asahi process and the solvent used was 1,1,1 trichloroethane. The wool was solvent degreased, dedusted and then given a conventional

46

Wool: Science and technology

soap/soda scour to remove residual suint and dirt. Only one plant was ever installed, and it has ceased operation. Part of the problem with this process was that the chosen solvent both depletes ozone and is a greenhouse gas.36 Historically, high capital costs have militated against the installation of solvent scouring systems. Additionally, because many of the investments in scouring during the 1990s have been for plant upgrades or plant relocations rather than for ‘greenfield’ installations, the opportunities for a step-change in technology have been limited. An exception is the solvent scouring technology from Wooltech Ltd, of Brisbane, Australia,37 who have developed a system using a formulation of 1,1,2 trichloroethylene (TCE). This solvent is non-flammable and does not deplete ozone, since it chemically degrades before reaching the ozone layer. However, TCE is toxic to humans and requires appropriate handling, as described in material safety data sheets (MSDSs) which are available on-line.38 A full-scale topmaking plant including a complete Wooltech solvent scouring system was installed in Trieste, Italy in time for the ITMA Exhibition of 1995 in Milan. Enhancements of fibre properties have been claimed by the treatment using TCE, including increased tenacity, elongation and resilience.37 It has also been claimed that such enhancements combined with the very low residual grease content of the scoured product enables good quality yarns to be spun using the rotor system. When compared with conventional aqueous scouring equipment, which is simple, robust, and has a long working life, solvent scouring equipment is much more sophisticated, and requires a chemical process engineering approach to its operation. However, if the aqueous scouring plant has a comprehensive effluent treatment system added to comply with strict environmental regulations, the levels of engineering sophistication are similar. It will always be difficult to remove the suint and to a lesser extent the dirt, from the raw wool by means of TCE. However, subsequent processing may be arranged to include further cleaning and obtain a satisfactory product (e.g. by backwashing). Capital and operating costs, as well as processing performance, will ultimately determine the success of this technology. At the time of writing, there have been no further installations of the Wooltech system.

2.10

Woolgrease and its recovery

It is useful to clarify terminology relating to woolgrease.1 The material secreted from the sebaceous glands of sheep is ‘wool wax’. The material recovered from woolscouring liquors or by solvent extraction from greasy wool is known as ‘woolgrease’ which, as well as wool wax, may contain pesticide residues, dirt, suint components, and detergent. When the crude wool-

Woolscouring, carbonising and effluent treatment

47

grease is refined, the product is known as ‘lanolin’. The major components of lanolin are high-molecular-weight esters formed from a mixture of sterols, aliphatic alcohols, and diols combined with straight chain, branched chain, and hydroxy fatty acids. Minor components are free alcohols and acids.1 Acid cracking is a long-established process which includes woolgrease recovery, but because it is applied at ‘end-of-pipe’, it is described in the effluent treatment section. Centrifuging is almost universally used and is most efficiently employed by integrating the operation with the liquor circulation in the scour train as in the WRONZ System or Siroscour. The design of the woolgrease recovery system depends on the quantity and quality of the woolgrease available on the raw wool. For coarse wools (e.g. New Zealand Romney types), two-stage recovery is used. In this type of plant, the liquor is first pumped to a nozzle/disc centrifuge set up as a concentrator to produce a cream for subsequent feeding to a disc separator set up as a purifier. This is usually a self-desludging machine rather than a nozzle machine since there is only a small quantity of dirt in the feed. For Merino wools, a three-stage recovery plant is used, where three centrifuging stages are used in series. Again, the first stage is concentration using nozzle/disc centrifuge(s) and the third stage is purification; but interposed is an additional concentration stage, typically using a self-desludging disc centrifuge. Fig. 2.14 shows a recently installed woolgrease recovery plant for Merino wools. For practical reasons of centrifuge operation and to assist the removal of water-soluble contaminants and dirt, water at almost boiling temperature is added with the cream being fed to the purifier. The product from the purifier centrifuge should be woolgrease at less than 1% moisture. Part only of the grease present in woolscouring liquors can be recovered by centrifuging and this fraction differs in composition from that remaining in the liquor.39 The recovered material is relatively unoxidised while the remainder is relatively oxidised and tends to be darker and of less commercial value. Recycling the clean phase from the separators back to the first hot scouring bowl is usually carried out as part of a system to control the level of total solids in the bowl and this favours the recovery of woolgrease.40 Feeding the liquors to the primary centrifuges at elevated temperatures assists recovery, but there appears to be little benefit in using temperatures above about 75 °C. However, it is claimed that a feed temperature close to boiling point enhances recovery when operating in the Lo-Flo regime.23 Only a minority of commercial centrifuges are suitable for use on woolscour liquor, which brings technical challenges for high-throughput (2.4–3.0 m width) scouring machines. Solvent extraction and aeration have been very rarely used for woolgrease extraction.

48

Wool: Science and technology

2.14 Woolgrease recovery plant. [Courtesy of Jandakot Wool Washing Pty Ltd.]

Woolgrease has an enormous diversity of uses whether as the material recovered in scouring plants, as the refined product (lanolin), or as chemical derivatives of woolgrease1,40 and lanolin. Crude woolgrease has been used for anti-corrosive coatings or additives, leather processing aids, release agents, and tree-wound dressings. It is refined to lanolin by a process of deodorisation, bleaching, and neutralising to provide a lighter coloured product with little odour and low free fatty acid and moisture contents. Lanolin is used widely in the pharmaceutical and cosmetic industries. In pharmaceutical uses, the desired properties of lanolin and its derivatives include their general inertness and ease of emulsification. Cosmetic uses take advantage of the material’s ability to absorb large quantities of water as water-in-oil emulsions or when suitably modified, to stabilise oil-in-water emulsions. Lanolin may be saponified to the constituent acids and alcohols. Cholesterol is one of the most frequently sought after products of saponification, and is one of several that can be further transformed for cosmetic and pharmaceutical use. The wool wax acids are useful in protective surface coatings, corrosion inhibitors, and when converted to metallic soaps, as lubricants.

Woolscouring, carbonising and effluent treatment

2.11

49

Effluent

2.11.1 Effluent components It is useful to group unit operations and processes together to provide what are known as primary, secondary, and advanced (or tertiary) treatments of effluent.41 In primary treatment, physical operations such as screening, sedimentation, and centrifugation, are used to remove floating and settleable solids found in the effluent. In secondary treatment, biological and chemical processes are used to remove most of the organic matter.The most widely-used measure of organic pollution in effluents is the 5-day biochemical oxygen demand (5-day BOD or BOD[5]). In advanced treatment, additional combinations of unit operations and processes are used to remove other constituents, such as nitrogen- and phosphorus-containing compounds, that are not significantly reduced by secondary treatment. Land treatment processes, now more commonly termed ‘natural systems’, combine physical, chemical, and biological treatment mechanisms and produce-water with quality similar to or better than that of advanced wastewater treatment.41 Woolgrease recovery and dirt recovery are now integrated with the operation of the scour line. However, after such primary treatment the effluent remains highly polluting and difficult to treat. The effluent from a 2 metre-wide woolscour can give a pollution load similar to that of a town with over 30 000 people.42 Effluent discharge from an efficient scouring plant contains these components: i) An oxidised less biodegradable fraction of woolgrease.43 ii) A dissolved organic component (suint) relatively easy to biodegrade. iii) A dirt content which varies tremendously. Fine particles associated with residual woolgrease cannot be completely removed by mechanical means. iv) Minor components such as detergents, insect resist agents, bisulphite, peroxide, and builders (e.g. sodium carbonate). Jamieson and Stewart identified the contributions of the main contaminants to the pollution load and summarised the results in the following formulae:1 BOD[5] = 2400 ¥ Suint + 5100 ¥ Oxidised grease + 11 350 ¥ Top grease + 185 COD = 8267 ¥ Suint + 30 980 ¥ Oxidised grease + 28 326 ¥ Top grease + 6454 ¥ Dirt + 1536

50

Wool: Science and technology

BOD[5] and COD are given in mg/litre and the contaminant concentrations are percentages by mass in the effluent. BOD[5] is the Biochemical Oxygen Demand: it is the quantity of oxygen needed to oxidise one litre of the waste under the conditions likely to be met with in natural receiving waters; the [5] refers to the length of time for which the sample is incubated, namely 5 days. COD is the Chemical Oxygen Demand; it is the amount of oxygen in milligrams required to chemically oxidise one litre of the waste under specified conditions. The formulae illustrate that the oxidised grease is indeed more difficult to degrade by biological means than the top (or unoxidised) grease.

2.11.2 Primary methods of effluent treatment Minimisation of water usage and production of relatively concentrated effluent streams is part of efficient scour management.A concentrated effluent is more conveniently treated than a high-volume waste stream. Primary treatment should, therefore, be integrated with scouring. Modern scouring systems such as the WRONZ or Siroscour systems incorporate primary treatments. Sedimentation (settling of particles by gravity) in settling tanks is still practised industrially, but the use of settling tanks in liquor treatment loops may cause scour liquors to become anaerobic and discoloured due to microbial activity. The use of hydrocyclones has become more widespread as pump and hydrocyclone design have improved. The Lemar Stage 1 Process may be used to increase the rate of woolgrease recovery and to dewater the sludges produced by a typical WRONZ System.1 In this process, the flowdown effluent and sludges are combined and pumped via a hydrocyclone to a decanter centrifuge. The centrate from the decanter is fed to a disc centrifuge where woolgrease (an additional 8–10%) is recovered. Dissolved air flotation has been tested at full scale as a treatment for heavy liquors. It was found that the liquors from a modern scouring system were too concentrated and the results were no better than sedimentation or thickening.44

2.11.3 Secondary treatments Chemical destabilisation by acid cracking is the oldest industrial method for treating woolscour effluents, and is still used by several mills,42 mainly in Europe. It involves adding sulphuric acid to the effluent to provide a pH of 2–3.5, and allowing the resulting sludge to settle. A low grade woolgrease is recovered from the sludge by boiling followed by filter pressing. The method works efficiently for effluents from soap/soda scouring, but is

Woolscouring, carbonising and effluent treatment

51

unreliable for effluents from scours which use non-ionic synthetic detergents. Acid cracking at the boil has been shown to overcome the difficulties encountered with non-ionic detergents.42 There have been many variations of chemical coagulation and flocculation, regarding both the chemicals used and the process details. Generally, chemical coagulation produces a voluminous sludge that requires dewatering. Simple filtration is not possible since the woolgrease in the sludge causes the filters to clog. Historically, rotary drum vacuum filters using precoats have been employed for dewatering, at considerable running cost. Recent advances in this type of process have included the additional use of polymeric flocculants in a multi-pronged chemical approach, along with decanter centrifuges for sludge dewatering.42,45 Generally, processes using large amounts of chemicals are now considered ecologically undesirable. Alternative approaches treating wastes as a resource are coming to the fore.46,47 Sirolan CF is a chemical flocculation process developed to treat heavy effluent, i.e. the flowdown from hot scouring bowls combined with the sludges from the heavy solids loops. After pH adjustment with acid and flocculation with a polymer, effluent is fed to a decanter centrifuge where suspended solids are removed as a sludge with 50–70% total solids. This process removes over 95% of the solvent extractable and suspended solids, and reduces COD by about 75%. It is used commercially by several scours in the UK and Australia. SWIMS47 is an acronym for Scour Waste Integrated Management System. Its features are: i)

effluent treatment is closely integrated with the operation of the scouring line; ii) each waste stream is treated separately; iii) the wastewater treatment systems are modular; and iv) the scouring wastes are considered as a resource. As well as the heavy liquor flowdown from the hot scouring bowls, in three-stage Siroscour operation there are discharges from the modified desuinting bowl and from the rinsing bowls. Evaporation of the desuinting flowdown produces a potassium fertiliser, while the rinsewater is subjected to microfiltration or other membrane treatment. Suint in the effluent produced by Sirolan CF still has substantial COD. Laboratory and pilot plant trials have substantially removed this by aerobic treatment (Sirolan CFB) except for some bio-refractory material which still exerts a COD. Sludge from Sirolan CF has proved satisfactory as an ingredient for the making of compost when mixed with a variety of materials.47 Alcohol destabilisation occurs if water-soluble alcohols are added to woolscour liquor, to give three phases:1

52

Wool: Science and technology

i) Grease/alcohol phase saturated with water; ii) Dirt/water phase saturated with alcohol; and iii) Water phase containing suint and saturated with alcohol. Alcohols including n-butanol and n-hexanol have been used in laboratory and pilot plant studies, while a full-scale plant using n-pentanol ran for 5 years before the woolscour ceased operation for reasons unrelated to the effluent process.1 Woolscour emulsions may also be destabilised by short-term aerobic or anaerobic treatments, and the woolgrease flocculates into a sludge.43 A twostage laboratory process working on Australian scouring liquors removed 70–90% of the woolgrease (without significantly biodegrading it) at a combined hydraulic retention time of 4–10 days. Such destabilisation is apparently not robust enough for commercial processes to have been developed based on it alone, but anaerobic pretreatments have been used as precursors to full scale coagulation and flocculation processes,1,42 and there are probably opportunities for more leverage to be gained from such low cost destabilisation, perhaps incorporating chemical treatments or electrocoagulation. By way of contrast, aerobic digestion uses free oxygen to convert wastes into carbon dioxide and water, plus biomass. Long residence times are necessary and the feedstock must generally be dilute. Process variables that need to be monitored include temperature, oxygen levels, pH, nutrient levels and degree of mixing. Scours in Germany and Australia have successfully used such treatments. A topmaking plant in Germany reported BOD reductions from 1100 to 80 mg/l and COD reductions from 2500 to 1200 mg/l.46 Commercial anaerobic digestion plants have been reported, but generally the process requires long treatment times and is prone to upsets in the feed.1 A conventional sludge digestion plant has been operating in New Zealand fed with flowdown liquors in admixture with domestic effluent since the early 1980s.1 When operated at a retention time of 20 days, 80–95% reductions in BOD and suspended solids were achieved. Ultrafiltration is a membrane process which is used to separate suspended solids from dissolved solids. On heavy liquors, it produces a suint solution and a concentrated grease-dirt sludge (concentrate). Ultrafiltration plants have been used in the UK scouring industry on heavy liquors for some years, with the concentrate trucked away to appropriate disposal sites and the ultrafiltrate discharged for further treatment at the local sewage works.42 Ultrafiltration and microfiltration have also been used successfully to treat rinsewaters to enable recycling of water in the scouring process. Microfiltration membranes have a larger pore size than ultrafiltration membranes, and hence exhibit higher flux rates.

Woolscouring, carbonising and effluent treatment

53

Evaporation may be carried out as a stand-alone effluent treatment if suitable outlets for the sludge are available. Various commercial plants are available, and are in use in Europe, Asia and Australia (Fig. 2.15). The efficiency of energy usage may be improved by a number of means, e.g. multiple effect evaporation, use of the steam produced to heat the scour, or by mechanical or thermal vapour recompression.

2.11.4 Tertiary treatments Several systems using biological lagoons are in operation in rural areas of Australia.42 A typical process involves a number of pits and lagoons in series as follows: i) A sludge pit to remove settleable solids. ii) A deep anaerobic pond, sealed by a floating crust of woolgrease. This pond receives the heavy flowdown effluent. Retention time is approximately two to four weeks.

2.15 Effluent treatment plant incorporating an evaporation system. [Courtesy of Jandakot Wool Washing Pty Ltd.]

54

Wool: Science and technology

iii) An aerated lagoon, perhaps using floating aerators. iv) A large holding lagoon, which also receives the dilute rinsewater effluent from the scour. It acts as an evaporation pond or as a holding pond for subsequent irrigation to land. One scour in Australia combines the anaerobic pond and aerated lagoon into a facultative41 lagoon. The dilute effluent is recycled to the scour via a trickling filter, settling and chlorination.42 The main disadvantages with lagooning systems are occasional odour problems and the need for unpleasant cleaning out of the sludge pit and anaerobic ponds.

2.11.5 Total treatments Evaporation and incineration eliminates all aqueous effluent. During the 1970s, over 22 mills in Japan which operated woolscours installed various evaporation and incineration plants.1 Discharge requirements of increasing severity stimulated such expensive measures. Unlike the situation for a stand-alone woolscour plant, the capital and running costs were spread over a large operating base. At the time of writing, all of the scouring operations within Japan have been replaced by lower cost processing options outside Japan. Today’s evaporation plants are typically of the multiple effect falling film type, sometimes operating under vacuum.42,46 Sludges are often burnt in a two-stage process, where the first stage generates a combustible gas by pyrolysis. This approach minimises problems associated with fusion of potassium compounds in the combustion zone and with deposition of particulates downstream of the combustion zone. The performance of a very comprehensive effluent treatment plant at a topmaking mill in Germany has been described.46 Evaporation/incineration is used to treat the heavy effluent while the rinsewaters are treated separately in an aerobic biological system. Condensate from the evaporation plant is reused in the scour rinsing process after stripping ammonia by steam and removing odours and pesticides via a fixed bed bioreactor. Main routes for disposal have been to landfill or for more dilute sludges to be spread on land. Landfill disposal is becoming less favoured as dumping charges increase.47 Suitably conditioned sludges have some value as a fertiliser in agriculture,46 but there may be adverse effects in some cases of sludge disposal on land.48 Composting of sludges is already being carried out commercially by a topmaker in Australia, and it is likely that this method will become more widely used. It has been shown that the sludge from Sirolan CF may be readily composted and that the woolgrease and associated pesticide

Woolscouring, carbonising and effluent treatment

55

residues arising from on-farm treatments to control lice, flystrike etc are broken down in the process.47 It has also been shown that composting of woolscour sludges and solid wastes must be carried out with care to avoid inadequate results.48 Trials on the pelletising of sludge for use as a fuel or slow release soil improver/conditioner have also been reported.47

2.12

Process control and quality assurance

Over the last 30 years in particular, there has been sustained development in control and instrumentation systems in woolscouring. Often, such developments have been mainly applications of generic innovations from outside the industry (e.g. weighbelt feeding) but significant innovations have also derived from the special needs of the industry (e.g. the Drycom moisture meter). A brief mention of the more significant developments of both types will be given here. Weighbelt feeding of the greasy wool to the scour is now regarded as essential, to provide an even feed-rate of wool with benefits in terms of consistent scouring and drying, increased productivity and provision of management information. Scourcom set the standard for state-of-the-art computerised control systems for woolscours (Fig. 2.16).1,49

2.16 Scourcom computer monitors. [Courtesy of Jandakot Wool Washing Pty Ltd.]

56

Wool: Science and technology

Hoppermatic control of the level of greasy wool in feed-hoppers has allowed for improved control of the opening and feeding stages.1,49 Various on-line monitors have been developed to measure the regain of wool at the exit of the dryer with the most successful unit being the Drycom moisture meter.1,20,49 Control of liquor quality is now practicable by means of density or turbidity sensors.1,20,49 Suitably rugged and reliable sensors are now available commercially for scouring and rinsing applications. The Trimwaste system controls the discharge of sludge from settling tanks.1,20,49 The potential number of applications for this system has reduced as hydrocyclones have become more widely used instead of settling tanks. Continued development has taken place in the measurement of scoured wool properties by means of Near Infra Red Analysis (NIRA). A ‘Generation III’ instrument has recently been successfully installed in a woolscour.50 This instrument has detectors operating in the visible region as well as the near infra red, which has enabled accurate measurement of the ‘as is’ and ‘base’ colour of the scoured wool. In addition, residual grease and moisture levels are monitored simultaneously, with most of the information for these measurements originating from the near infra red detectors. Since the measurement time is now down to 45 seconds, the information is valuable as a guide to the operation of the scour itself. Integrity of the wool sample has been achieved by automated sample coring, transport, loading into the instrument, measurement and sample sealing.

2.13

Energy conservation

Woolscouring is an energy intensive process. In terms of the operating costs for a woolscouring plant, energy is second only to labour. Considerable work was carried out on energy efficiency in woolscouring during the 1970s and early 1980s in response to the rapid fuel price rises of the time.1,51 While there was little scope for reducing the electricity usage in woolscouring, there was considerable potential for savings of process heat by improved design of the heating system, improved control and by installing heat recovery systems. Taking advantage of heat recovery from heavy effluents and from rinsewater is now routine, but heat recovery from dryer exhaust air is less common due to a longer payback time and more demanding practical requirements. Owing to the installation of new, higher productivity scours of 2.4 m and 3.0 m working width during the last 20 years, average energy costs per kilogram of wool scoured have fallen. Improved process control whereby throughputs can be maintained at higher average levels has assisted this result.

Woolscouring, carbonising and effluent treatment

57

References 1 Stewart R G, Woolscouring and Allied Technology, Wool Research Organisation of New Zealand, Third Ed., 1988. 2 Knott J and Robinson B, Wool Carbonising, Guimares, Eurotex, 1994. 3 Roberts Beaumont, Woollen and Worsted, London, G Bell and Sons Ltd, Third Ed., 1919. 4 Lennox-Kerr P, ‘Clean, green and dry’, Wool Record, 158, (3657), 44, 1999. 5 Christoe J R and Napper G J, ‘The warming of fine wools using the AWC Forced Convection Bale Warmer’, Proc. 8th Int. Wool Text. Res. Conf., Christchurch, Wool Res. Org. of NZ, 1990. 6 Gibson M, The application of radio frequency heating techniques in wool processing, part 2, Wool. Sci. Rev. 46, 1973, 30–43. 7 Nadj L et al, ‘Microwave wool bale warming’, Text. Asia, July 1998, 42. 8 Eley J R et al, Report to Topmakers I, Report No G50, CSIRO, Geelong, 1985. 9 Robinson G A, ‘The Nature of Scoured Wool and its Preparation for Carding’, Proc. Symposium on Woolscouring and Worsted Carding, 38–43, CSIRO Div. Text. Ind., Geelong, 1986. 10 Taylor M E, Improvements to greasy wool openers – II, dusting performance of three multi-drum openers, WRONZ Report No 85, 1981. 11 Taylor M E, Improvements to greasy wool openers – IV, fixed self-cleaning teeth, WRONZ Report No 93, 1982. 12 Taylor M E, The WRONZ Autoclean Opener, WRONZ Report No 149, 1987. 13 Tucker S G, ‘Survival of the fittest’, Wool Annual, (Massey Wool Association of NZ (Inc.)) 1996, 18–23. 14 Lipenkov Y, Wool Spinning Vol 1, Moscow, Mir, English translation, 1983. 15 Robinson B, A basic guide to raw scouring, IWS Technical Information Letter, Ilkley, Report TIL/ET-6, 1991. 16 Atha K E, Commercial development of the CSIRO aqueous jet scourer and the Petrie/Wira improved wool scourer, Appl. Polym. Symp., 1971, 18, 1147–56. 17 Karsch F, Development trends in wool scouring, Mell. Textilber., 1968, 49, 885–9. 18 Chisnall P E and Stewart R G, ‘Studies in Woolscouring Part IV: Commercial Scouring with Mini-Bowls’, Text. Inst. Ind., 17, 68–9, 1979. 19 Jamieson R G, ‘Studies in Woolscouring Part V: The Scouring Efficiency of MiniBowls’, Text. Inst. Ind., 17, 70–1, 1979. 20 Christoe J R, ‘Developments in wool scouring – an Australian view’, Wool Sci. Rev., 1987, 64, 25–43. 21 Morgan W V, Gibson J D and Robinson B,‘How soaring effluent costs have influenced scouring techniques’, Wool Record, 137 (3427) 18–19, 54, 1980. 22 Gibson J M D, Morgan W V and Robinson B, ‘Aspects of wool scouring and effluent treatment’, Text. Inst. Ind., 17, 31–7, 1979. 23 Wood G F, Pearson A J C and Christoe J R, The CSIRO Lo-flo Process, An In-process Effluent Treatment for Aqueous Woolscouring, CSIRO Div. of Text. Ind. Report No G39, 1979. 24 Christoe J R, ‘New Approaches in Wool Scouring’, Aust. Textiles, 7 (2), 37–8, 1987. 25 Bateup B O and Christoe J R, ‘Siroscour: Study of Technical Innovation’, Proc. Top-Tech ’96, 419–31, Geelong, CSIRO Div Wool Tech, 1996.

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26 Anon., ‘CSIRO Scouring System Commercialised’, CSIRO Text. News, No 17, 1–2, 1987. 27 Robinson B and Lee C S P, ‘A Comparative Study of Raw Wool Scouring Systems’, IWS Environmental Technical Bulletin ETB-27, Ilkley, 1993. 28 Mozes T E, ‘Raw-wool carbonizing’, Text. Prog. 17, 3, 1988. 29 Keey R B, Introduction to Industrial Drying Operations, Oxford, Pergamon Press, 1978. 30 Schwartze J P, Evaluation of the superheated steam drying process for wool, Aachen, Shaker Verlag, 1999. 31 Nossar M S and Chaikin M, ‘A new development in the drying of textile fibres with air’, Proc. 5th Int. Wool Text. Res. Conf., Vol 5, 635–46, Aachen, DWI, 1975. 32 ‘Solvent scouring of raw wool’, Wool Sci. Rev., 1963, 23, 40–54. 33 Lindberg J and Ekegren S, ‘A new method for solvent scouring of raw wool’, Proc. Int. Wool Text. Res. Conf., Melbourne, CSIRO, 1955, E, 342–6. 34 Saville N, Shelton W J, Ward R and Sewell J, ‘A system of wool scouring using chlorinated solvents’, Appl. Polym. Symp., 1971, 18, 1157–61. 35 Barker G V and Davin F, ‘A focus on solvent scouring with special reference to the de Smet plant in Western Australia’, Proc. 8th Int. Wool Text. Res. Conf., Christchurch, Wool Res. Org. of NZ, 1990. 36 Robinson B, Recent developments in raw wool scouring and carbonising, IWS Technical Information Letter, Ilkley, Report TIL/ET-7, 1991. 37 Hopkins P, Solvent Cleaning of Wool: Some Recent Developments, Deutsches Wollforschungsinstitut Report No 119, pp 128–135, 1997. 38 http://www.msds.pdc.cornell.edu/ 39 Anderson C A and Wood G F, ‘Fractionation of wool wax in the centrifugal recovery process’, Nature, 193, 742–4, 1962. 40 Stewart R G and Story L F (eds), ‘Woolgrease A review of its recovery and utilisation’, Tech. Papers, Vol 4, WRONZ, 1980. 41 Metcalf & Eddy Inc., Wastewater Engineering: treatment, disposal, and reuse, New York, McGraw-Hill, Third Ed., 1991. 42 Robinson B, Effluent treatments for raw wool scour liquors, IWS Technical Information Letter, Ilkley, Report TIL/ET-8, 1991. 43 Lapsirikul W, Cord-Ruwisch R and Ho G, ‘Anaerobic bioflocculation of wool scouring effluent’, Water Research, 28, 8, 1743–47, 1994. 44 Halliday L A, Pollution control and by-product recovery in the New Zealand woolscouring industry, MSc thesis, Joint Centre for Environmental Sciences, University of Canterbury and Lincoln College, 1976. 45 Aronsson G and Turner G, ‘Reductions in woolgrease and COD levels of woolscouring effluents by combined chemical coagulation and centrifugation’, Proc. 9th Int. Wool Text. Conf., Biella, 1995. 46 Hoffman R, Timmer G and Becker K, ‘The environmentally friendly production of wool tops – waste water treatment at BWK’, Proc. 9th Int. Wool Text. Conf., Biella, 1995. 47 Bateup B O, Christoe J R, Jones F W, Poole A J, Skourtis C and Westmoreland D J, ‘Effluent management’, Proc. Top-Tech ’96, 388–407, Geelong, CSIRO, 1996. 48 Williamson W M, ‘The decomposition of woolscour and fellmongery sludges’, PhD thesis, Plant and Microbial Sciences Department, University of Canterbury, 1998.

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59

49 Stewart R G and Jamieson R G, ‘Raw wool scouring – a New Zealand perspective’, Wool Sci. Rev., 1987, 64, 16–24. 50 Ranford S L, Marsh C, Schuler L P, Ellery M W, Walls R J and Piper C F, ‘Advances in visible/near infra red scoured wool process control technology’, Proc. 10th Int. Wool Text. Conf., Aachen, 2000. 51 Halliday L A, Barker G V, and Stewart R G, ‘Energy Use in the New Zealand Textile Industry’, Report No 29, NZERDC, Auckland, 1977. 52 Lipson M and Black U A F, J. Proc. Roy. Soc. NSW, 1944, 78, 84–93. 53 Ross D A, NZ J. Agric. Res., 1959, 2, 214–28. 54 Halliday L A, ‘Future opportunities in the scouring industry’, Wool Annual, (Massey Wool Association of NZ (Inc.)) 1994, 27–30.

3 Fibre morphology H HÖCKER

3.1

Introduction

Wool is the generally accepted generic description of the hair of various breeds of domesticated sheep (Ovis aries), although it is also commonly used as the generic name of all animal hair, particularly including the socalled fine animal hair, i.e. the hair of the cashmere and angora (mohair) goat as well as the cross-breeds of both (cashgora), of camel, vicuna and alpaca, of the angora rabbit, and of many others including the hair of the yak. The morphology and composition of human hair also closely resembles that of wool. While wool contains a-keratins (protein molecules in a-helix conformation,1 in a complex mixture with proteins of irregular structure), silk and feathers are composed of b-keratins (protein molecules partially in b-pleated sheet conformation2) (see Fig. 3.1). From a macromolecular point of view, wool is a composite fibre, i.e. a fibril-reinforced matrix material with both the fibrils and the matrix consisting of polypeptides (thus of chemically similar nature), interconnected physically and chemically. From a morphological point of view, the wool fibre is a nanocomposite (the reinforcing fibrils have a diameter of about 10 nm) of high complexity with a clear hierarchy indicating an enormous degree of self-organisation. A detailed description of its structure is given in Sections 3.3.4 and 3.3.5. From a protein structural point of view, only the fibrils are regarded as a-keratins, they being embedded into a protein matrix of irregular structural conformation. The fibrils (microfibrils) are typical intermediate filaments, i.e. one type of protein constituting the cytoskeleton, others being actin filaments and microtubuli. They are generally called keratinintermediate filaments (KIF) and the matrix materials in which they are embedded are called keratin associated proteins (KAP).

60

Fibre morphology

61

(b)

(a) 3.1 a-Helical1 (a) and b-sheet2 (b) conformation of polypeptide chains. [Reproduced from Pauling, Corey and Bronson.1,2]

3.2

General chemical composition

Wool is a protein fibre and as such consists of the elements carbon, hydrogen, oxygen, nitrogen and sulphur (see Table 3.1).3 Except for the large sulphur content, the elemental composition is typical of proteins. The sulphur mainly derives from the amino acid cystine, which has two sulphur atoms forming a disulphide bond, this being the most important crosslinking element of wool. Beside cystine, 20 other amino acid residues are found in wool (see Table 3.2). They are distinguished by their side chain, which imparts a special character, being either hydrophilic or hydrophobic, acidic or basic. Note that, in their ionised state, a deprotonated carboxylic acid group may be regarded as basic, and a protonated amino group as acidic. From Table 3.2 it can be seen the proportions of acidic and basic groups are approximately the same (800–850 mmol/g of each).

62

Wool: Science and technology Table 3.1 Elemental composition of dry wool [From: Zahn, Wortmann and Höcker3] Element

Weight (%)

Carbon

50–52

Hydrogen

6.5–7.5

Oxygen

22–25

Nitrogen

16–17

Sulphur

3–4

Ash

0.5

This high content of oppositely charged side chains facilitates a second kind of crosslinking, i.e. salt-bridges between a glutamate or aspartate residue and a protonated lysine or arginine residue. Salt-bridges will obviously be sensitive to the pH-value of the fibre. A third kind of crosslinking element is the isodipeptide bond between a glutamic or an aspartic acid and a lysine residue. Additionaly, hydrogen bonds have to be included as stabilising elements of wool, notably between amide groups but also between a variety of other hydrogen donating and accepting groups. Hydrogen bonds render wool sensitive to all kinds of hydrogen bond-breaking reagents. Absorption of water, for example, has a major effect on the physical properties of wool fibres (see Chapter 4). After reduction and carboxymethylation (to protect thiol groups), four fractions of proteins can be extracted from wool, namely the low sulphur fraction (LSF), the high (HSF) and ultrahigh sulphur fraction (USF), and the high Gly/Tyr fraction (HGT). The approximate portions, molar masses, and sulphur contents of these proteins are given in Table 3.3. The LSF fraction originates from the KIF.4,5 The amino acid composition of wool, as compared with that of the above mentioned fractions, is given in Table 3.4. Each fraction consists of a number of protein families, each one of them made up by closely related members.6–12 In addition to proteins, wool contains about two percent of internal lipids and external lipids as well. The latter are generally known as woolgrease and are almost completely removed on scouring. There are many fractionated and refined forms of woolgrease, the most widely known of which is lanolin. Internal lipids consist mainly of cholesterol, fatty acids and polar lipids such as ceramides, cerabrosides and cholesterol sulphate (Table 3.5). These lipids originate from all kinds of membranes surrounding living cells and separating the different compartments within the cell such as the

Amino acids with hydroxyl groups in the side chain

Y

Tyrosine

Tryptophan

S T

W

Lysine Histidine

Serine Threonine

K H

Aspartic acid Glutamic acid Asparagine Glutamine Arginine

‘Acidic’ amino acids and their w-amides

‘Basic’ amino acids and tryptophan

D E N Q R

Name and abbreviation

Chemical character of side group

Table 3.2 Amino acid composition of fine Merino wool [From: Lindley4]

CH2

CH3

—CH2—OH CH OH

CH2

CH2 N

—(CH2)4—NH2

N H

H N

NH

OH

350

900 570

40

250 80

200 600 360 450 600

—CH2—COOH —(CH2)2—COOH —CH2—CONH2 —(CH2)2—CONH2 (CH2)3 NHC NH2

Concentration (mmol/g)

Side chain

Fibre morphology 63

G A V P

L I

F

Glycine Alanine Valine Proline

Leucine Isoleucine

Phenylalanine

Amino acids without reactive groups in the side chain

M

Cysteine Thiocysteine Cysteic acid Cystine Lanthionine Methionine

Sulphur-containing amino acids

C

Name and abbreviation

Chemical character of side group

Table 3.2 (cont.)

CH2

CH3

CH2 —CH2—CH(CH3)2 CH CH2 CH3

CH2

260

680 270

760 470 490 520

10 5 10 460 5 50

—CH2—SH —CH2—S—SH —CH2—SO3H —CH2—S—S—CH2— —CH2—S—CH2— —(CH2)2—S—CH3 —H —CH3 —CH(CH3)2 CH2

Concentration (mmol/g)

Side chain

64 Wool: Science and technology

Fibre morphology

65

Table 3.3 Approximate portions, sulphur contents and molecular masses of protein fractions obtained from Merino wool (see text) Protein fraction

Portion (%)

Sulphur content (%)

Molecular mass (kg/mol)

Ref.

Low sulphur

58

1.5–2

45–50 45–60

6 7

High sulphur

18

4–6

14–28 11–23

8 9

Ultrahigh sulphur

8

8

28 37

8 10

High Gly/Tyr

6

0.5–2

9–13 11–12

11 12

Table 3.4 Amino acid composition (mmol/g) of Merino wool and three protein fractions extracted [From: Crewther5] Amino acid

Merino wool

LSF

HSF

USF

Ala

417

518

238

275

Arg

602

585

398

248

Asp

503

655

60

82 1734

Cys*

943

546

1859

Glu

1020

1138

772

905

Gly

688

709

497

702

Ile

234

295

215

330

Leu

583

826

144

151

Lys

193

326

38

1

Met

37

44

0

0

Phe

208

243

50

103

Pro

633

342

969

853

Ser

860

588

1163

1100

Thr

547

354

893

832

Tyr

353

345

164

151

Val

423

477

331

317

LSF = low sulphur fraction, HSF = high sulphur fraction, USF = ultra high sulphur fraction. * Cysteine and half cystine.

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Wool: Science and technology

Table 3.5 Wool lipids [From: Zahn,Wortmann and Hoffmann14] Class/Name

Formula

Fatty acids Palmitic acid Stearic acid Oleic acid Protein bound fatty acid 18-Methyleicosanoic acid

CH3—(CH2)14—COOH CH3—(CH2)16—COOH CH3—(CH2)7—CH=CH—(CH2)7—COOH CH3—CH2—CH(CH3)—(CH2)16—COOH 24

Sterols Cholesterol Desmosterol (= 24-Dehydrocholesterol)

HO Polar lipids

O

Ceramide HN

(CH2)16

CH3 (CH2)12

HOH2C Cerebroside (Sphingolipid)

CH3

O HN

(CH2)21

CH2OH O O

CH3 (CH2)12

C H2

CH3

OH

Cholesterol sulfate

24

NaO3SO

Fibre morphology

67

nucleus, the endoplasmatic reticulum, the Golgi apparatus, etc. At the termination of the keratinisation process, lipids are trapped in various locations within the compacted mass of wool proteins. It is specially to be noted that there is one fatty acid, 18-methyl eicosanoic acid (18-MEA), that is covalently bound to the surface of the fibre.13 One percent of wool consists of mineral salts, nucleic acid residues and carbohydrates.14 The content of mineral salts is partially nutrition dependent. Nucleic acids can be isolated from wool and used to discriminate between wool of different origins, and particularly between sheepswool, cashmere, and yak fibre.15 Carbohydrates originate from glycoproteins representing former membrane proteins.

3.3

Composition and structure of morphological components of wool

The classical morphology of wool is represented by Fig. 3.2, showing the gross hierarchy of morphological elements.16 The fibre is surrounded by cuticle cells which overlap in one direction and which consist at least of four layers, the epicuticle, the A-layer and the B-layer of the exocuticle, and the endocuticle. The cuticle surrounds a compacted mass of cortical cells of spindle form aligned with the fibre axis and with their fringed ends interdigitating with each other.17 Both cuticle and cortical cells are separated by the so-called cell membrane complex comprising internal lipids and proteins. This cell membrane complex is the component between the cells that guarantees strong intercellular bonding via proteins generally called desmosomes. Transmission electron micrographs of cross-sections of the cortex cells (Fig. 3.3) clearly demonstrate the presence of macrofibrils oriented in the direction of the fibre axis and embedded into the intermacrofibrillar matrix which contains cytoplasmic residues and nuclear remnants. The macrofibrils themselves consist of hundreds of microfibrils (KIF) embedded in a matrix of interfilament material (KAP). The fine structure of the intermediate filaments will be described in more detail later. Clearly, at least two kinds of cortex cells can be distinguished due to different intensity of staining, namely the orthocortex cells, which appear lighter, and the paracortex cells, which appear darker upon staining with silver nitrate in ammonia solution.18

3.3.1 The cuticle The cuticle cell is a nearly rectangular sheet, slightly bent, with a width of about 20 mm, a length of 30 mm, and a thickness of 0.5–0.8 mm (at the scale

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Wool: Science and technology

2 nm

Dimer

2.8 nm

Protofilament

4.5 nm

Protofibril

10 nm

Microfibril keratin intermediate filament KIF Interfilament material

300 nm Macrofibril

Paracortex cell Orthocortex

Endocuticle Exocuticle Epicuticle

Paracortex

3.2 Hierarchy of a merino fibre with a diameter of 20 mm. The intermediate filament shows three fibrillar subunits. [According to Eichner et al.16]

edge). From cross-sections of about 50 fibres, it was determined that the weight fraction of the cuticle with respect to the whole fibre is between 6 and 16%.18 Transmission electron microscopy of longitudinal sections provides other structural information. There is only a single layer of cuticle cells surrounding the orthocortex while neighbouring the paracortical cells two to three cuticle layers can be detected. The outer cuticle cell generally is thicker than the cuticle cells lying below it. Fibres with extremely small diameter (15 mm and smaller) show single cuticle cells surrounding the fibre stem like a spiral. The cuticle cells have some overlap, with the

Fibre morphology

69

Macro-fibrils

Micro-fibrils Matrixproteins

3.3 Cross-section of cortex cells.

transition from one cuticle cell to the next being either planar or stepwise. While the tip end of the cuticle cell is clearly separated from the cuticle cell below it, the root end of the lower cuticle cell becomes decreasingly thinner and neighbouring cells seem to merge, exhibiting a common endocuticle. Cuticle cells overlaying the paracortex are longer by 40% than those neighbouring the orthocortex. Another distinction is the extent of overlapping. Next to the orthocortex, about 20% of the total length of the cuticle cells are covered by neighbouring cuticle cells while next to the paracortex there is 30% overlap.18 The surface of the cuticle cells contains a covalently bound fatty acid, the chiral 18-methyl eicosanoic acid (18-MEA), very probably bound via a thioester linkage. This has sometimes been called the F-layer, although from transmission electron microscopy it seems more plausible that the fatty acid is integrated into the surface rather than forming a separate layer. The epicuticle, though not yet precisely described, is highly resistant to attack from alkalis, oxidizing agents, and proteolytic enzymes. It is about 2.5 nm thick and amounts to approximately 0.1% of the weight of the fibre. It has been

70

Wool: Science and technology

considered to consist of lipids (including the 18-MEA), proteins, and/or carbohydrates, and, due to its chemical inertness, has been called a resistant membrane containing small proline-rich proteins (SPRPs) typical of proteins of the cornified envelope (CE) of the stratum corneum. The skin19 (cutis) consists of two components: the external epidermis and the connecting tissue containing corium. The epidermis is a cornified layered plate epithelium consisting of several morphologically distinguishable living cell layers such as the stratum basale, the stratum spinosum, the stratum granulosum, and the stratum lucidum covered by a dead cornified cell layer, the stratum corneum, a filament matrix composite.20 The fibrils represent a-keratins or intermediate filaments.21 The plasma membrane of the stratum corneum in conjunction with the protein layer represents the cornified envelope. The A-layer is sulphur-rich (35% S) and characterized by a high degree of crosslinking via disulfide and isodipeptide bonds. There is a marked similarity between the A-layer and the CE, characterized by a similarly high content of the protein loricrin (65–70%) which is rich in Gly, Ser, and Cys. When wool is exposed to chlorine water, oxidation of some of the cuticle proteins lifts up surface bubbles known, since this reaction was first described, as the Allwörden membrane. The formation of the Allwörden membrane occurs as a result of an osmotic effect due to the oxidative cleavage (by means of Cl+) of proteins in the A and B-layer forming degradation products that are too large to diffuse out of the fibre through the resistant membrane with isodipeptide crosslinks. The A-layer-rich Allwörden membrane was found to contain 42% loricrin, 51% ultrahigh-sulphur cuticle proteins and 7% involucrin.3 Thus, the Allwörden membrane is a complex aggregate and may be considered to consist of the epicuticle and part of the A-layer. The B-layer contains 20% S and is correspondingly less cross-linked than the A-layer. The endocuticle, finally, is very low in sulphur and, being more readily permeable, is the usual diffusion pathway for water and other reagents.

3.3.2 The cortex The cortex, comprising 90% of the fibre, consists of different kinds of cortex cells, ortho- (60–90%) and paracortex cells (40–10%), the latter containing a larger amount of sulphur than the former and hence being tougher and more highly cross-linked, as clearly seen upon staining with silver nitrate and transmission electron microscopical inspection. Moreover, in fibres from fine wool breeds, e.g. Merino sheep, the two different cortex cells are arranged in a bilateral manner and the borderline between ortho- and paracortex proceeds in a helical manner along the fibre axis. This results in a

Fibre morphology

71

3.4 Ortho- and paracortex by scanning electron microscopy in conjunction with energy dispersive X-ray fluorescence; light pixels: Sfluorescence (above). Organization of ortho- and paracortex along the wool fibre (below).

stable crimp, the paracortex always being situated in the inner part and the orthocortex in the outer part of the curvature (Fig. 3.4). The cortex is composed of spindle-like cortex cells with a length of 45–95 mm and a width of 2–6 mm. In orthocortex cells, cytoplasmatic residues and nuclear remnants are rarely present. The macrofibrils are clearly separated and show a hexagonal arrangement of microfibrils.

72

Wool: Science and technology

The paracortex cells do not only show the macrofibrils but also clearly distinguishable microfibrils with high density of packing exhibiting both random distribution and hexagonal packing. The borderline between the macrofibrils is less clear than in orthocortex cells. Cytoplasmic residues and nuclear remnants are found in every paracortical cell.22

3.3.3 The macrofibrils Each cortical cell is composed of 5–20 macrofibrils at the widest point with a diameter of 100–300 nm embedded into the intermacrofibrillar matrix material comprising cytoplasmatic and nuclear remnants of the keratinocytes.

3.3.4 The microfibrils The macrofibrils are composed of bundles of 500–800 microfibrils (KIF), each of them being enveloped by KAPs. There are five acidic Type I KIF and five basic Type II KIF, and more than a hundred KAPs, some of which are heavily crosslinked.23 The structure and composition of these components are discussed in more detail in following sections. Two dimensional SDS-polyacrylamide gel electrophoresis allows separation of the proteins (Fig. 3.5), obtained upon exhaustive mercaptolysis of wool and carboxymethylation of the resulting thiol groups.24 The types of proteins obtained are listed in Table 3.6. The most impressive example of self-organisation is the structure of the intermediate filaments. The Type I and Type II keratins are expressed just above the bulbus in the wool follicle as the first components of the fibre (Fig. 3.6). In higher areas of the follicle, the isthmus and the infundibulum, glycine-tyrosine rich proteins KAP 6, 7, 8 of the orthocortex and the sulphur-rich proteins KAP 1, 2, 3 and 4 of the paracortex, and eventually the ultra sulphur-rich proteins KAP 5 and 10 of the cuticle cells are expressed.

3.3.5 Primary structure of the wool protein 8c-125 The primary structure of wool keratins has been evaluated from protein sequencing as well as from DNA sequencing. The primary structure of the wool protein KIP 8c-1 is given in Fig. 3.7. It is characterized by an Nterminal and a C-terminal domain. Both are rich in proline and cystine residues. The residues inbetween constitute four a-helical segments, 1A, 1B, 2A and 2B, separated by linkers L1, L12, and L2. The combined segments 1A, L1 and 1B as well as 2A, L2 and 2B have equal length of 20 to 21 nm. The amino acid residues in the helical segments are organised in

Fibre morphology

73

pH 8.9

Type II

UHS

LS

SDS Type I HS

Unknown HGT Type I

Type II

LS = low sulphur; HS = high sulphur; UHS = ultrahigh sulphur; HGT = high glycine tyrosine proteins

3.5 Separation of wool proteins after extraction from Merino wool and subjection to two-dimensional polyacrylamide gel electrophoresis at pH 8.9 in one direction and in the presence of SDS in the other one. [Reproduced from Dowling, Crewther and Parry.24]

heptades; thus the columns are numbered from a to g. The amino acid residues a and d have predominantly hydrophobic side chains. 3.3.5.1 Dimer formation This is the basis of the formation of a heterodimer in the form of a coiled coil. As indicated in Fig. 3.8, the hydrophobic effect is primarily responsible for the formation of the dimer, which additionally is stabilised by saltbridges (Coulombic forces) between the amino acid residues c and g.

74

Wool: Science and technology

Table 3.6 Wool proteins [From: Haylett, Swart, Parris, and Joubert9] Protein family

Number of amino acid residues

Properties

5 acid Type-I KIF

392–416

276 amino acid residues

5 basic Type-II KIF

479–506

80–100 sulphur-rich KAP

94–211

in a-helical central rod domain consisting of 4 segments 16–24 mol% half cysteine

3–15 ultra sulphur-rich KAP

168–197

33–37 mol% half cysteine

10 Type-I-glycinetyrosine-rich KAP

61–84

35–40 mol% Gly + Tyr

5 Type II-glycine-tyrosinerich KAP

ca. 80

60 mol% Gly + Tyr

Outer root sheath

Gene family cell type KAP 5,10 cuticle

Inner root sheath

KAP 4 paracortex KAP 1,2,3 cortex KAP 6,7,8 orthocortex Type I and II keratins cortex

3.6 Expression of KIF (Type I and II) and KAP genes in the wool follicle. Protein genes are activated and transcribed in different cell types in the sequence indicated.

Fibre morphology N-terminal domain 1A

L12

L1

5 Heptades

NAc S F P S S S P P C T P C P V C F G D E

F C N F S S C S C T G N A G N C S G

N L L R C R V S G L A I N S W E F N

2A

1B

L2

2–3 Heptades

14–15 Heptades

C-terminal domain 2B 17 Heptades

20–21 nm

20–21 nm

a b c d e f g

a b c d e f g

M L V N I

QF AS RQ AE L E

L Y L L R

Y I I N I A Y R I L K V L H L

Q E L A D D E Q D D S E I E R

S E C R N D T L G E D S C E S

Y L A L A F E V L L L L L E

K N L E E

F Q K V K R L E R T E K K V

E D E R S

R Q S V L T G S R L A E S N

T R K E R

Q QQ E S P N L PCV T K E Q A K L D I C Q E N T

V T P A A D V E V N L R D G L Q

75

D L N R V L N E T R A Q RR D Y E A L V E T N W V EE Y I R Q T E E L N K Q V V S S S E Q L QS C Q T E I I E L R R T V N A L Q V E L QA Q H N L R D S L E N T L T E T E A R Y S C Q L NQ V Q S L I S N V E S Q L A E I R G D L E R Q N Q E Y QV L L D V R A R L E C E I N T Y R G L L D S E D C K L

P P T A K T I P P P P P R P S R

C C T C T P S C A C C R C C Y

N A N G I C S A A T V S G N V

3.7 Secondary structure and primary structure of an a-keratin monomer, wool protein 8c-1 of the wool intermediate filament. The bold lines characterize the a-helical segments 1A, 1B, 2A, 2B. a-helical segments, the linkers L1, L12, L2, are found. As indicated in the primary structure, the proline and cysteine concentration is particularly high in the terminal domains. The hydrophobic amino acid residues are characterized by vertical lines in the primary structure (amino acid residues a and d within the sequence of heptades) [Reproduced from Parry and Fraser.25]

Two different KIPs, one of acidic and the other of basic nature, form the dimer, a heterodimer. In the helical domains 1B and 2B, six pairs of salt-bridges are formed and between a cationic and an anionic amino acid residue always three non-ionic residues are found. Molecular dynamic simulations showed that the a-helical structure of the segment 1A is inherently stable. In contrast, an a-helical structure superimposed on the linker segment L12 almost instantaneously breaks down upon dynamic simulation.26

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Wool: Science and technology

N

1A

b

L2

L12

L1 1B

e

2A

2B

C

g a

d

d

a

c

f f c

g

e

b

3.8 a) Schematic representation of a heterodimer of two KIFs as a coiled coil, i.e. a left-turned superhelix. b) Cross-section of a dimer; the amino acid residues a and d are in close contact (hydrophobic effect) while the positions g and e are further apart, interacting via Colombic forces between cationic (g) and anionic (c) residues.

3.3.5.2 The packing of dimers The packing of dimers is end-on and the stabilisation occurs via antiparallel combination with another end-on row of dimers shifted against the first row in such a way that the 2B segments overlap. Thus, a protofilament is formed with four KIF molecules in the cross-section and with a diameter of 2.8 nm. The interaction between the 2B segments is stabilised by lateral formation of disulfide bonds (Fig. 3.9).27 The protofilament then is doubled to form the protofibril with eight KIF chains in the cross-section, and two protofibrils form a half-filament. Eventually, two half-filaments form the intermediate filament with a diameter between 8 and 10 nm.28 Thus, the intermediate filament is an excellent example of a self-organised nanostructured fibre that is the reinforcing element in wool.

3.4

Outlook

The morphology and composition of the morphological constituents of wool are still under investigation. An enormous impact came from genomics, which helped to clarify the proteom of wool, in particular of the keratin intermediate filaments. A second, very strong innovative impulse

Fibre morphology

77

Coiled-coil-dimer

Protofilament (Tetramer)

Protofibril (Octamer)

Half filament (2 protofibrils)

Protofibril: 4.5 nm

10-nm-Filament 8–12 nm

Protofilament: 2-3 nm

3.9 Packing of dimers to form the intermediate filament.

came from the comparison of wool with the cornified envelope of the stratum corneum (see Section 3.3.1), the amino acid composition of which was determined using cultured human epidermal keratinocytes. As indicated in Fig. 3.10, the model proposed by Steinert29 for the outer two thirds of the epidermal cornified envelope comprises a lipid envelope followed by isodipeptide-crosslinked involucrin and crosslinked loricrin above the cytoplasma surface, and is finally integrated by the keratin intermediate filaments that are themselves connected by the protein filaggrin. Wool is definitely the most complex fibre one could imagine. Its morphology and chemical structure, as well as its physical properties, are of utmost importance for a thorough understanding of industrial chemical

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Wool: Science and technology

Lipid envelope

Involucrin

Loricrin

Cytoplasmatic surface

Keratin filaments

Filaggrin

3.10 Model of Steinert representing the outer two thirds of the human epidermal cornified envelope. The cytoplasmatic surface consists of cross-linked loricrin. Keratin filaments are linked via filaggrin. The isodipeptide cross-linked involucrin is situated below the lipid envelope [Reproduced from Steinert and Marekov.29]

treatments, and dyeing and finishing processes, as well as of its appearance and performance.

References 1 Pauling L, Corey R B and Bronson H R, Proc. Nat. Acad. Sci. USA, 1951, 37, 205–11.

Fibre morphology

79

2 Pauling L, Corey R B and Bronson H R, Proc. Nat. Acad. Sci. USA, 1953, 39, 253. 3 Zahn H, Wortmann F-J and Höcker H, Chemie in Unserer Zeit, 1997, 31, 280–90. 4 Lindley H, in Chemistry of Natural Fibres, ed. Asquith R S, Plenum Press, London, 1977, p 147. 5 Crewther W G, Proc. Int. Wool Text. Res. Conf., Aachen, 1975, I, 1. 6 O’Donnel I J and Woods E F, J. Polymer Sci., 1956, 21, 397. 7 Jeffry P D, J. Text. Inst., 1972, 63, 91. 8 Gillespie J M, in Biology of the Skin and Hair Growth, ed. Lyne A G and Short B F, Angus and Robertson, Sydney, 1965, p 377. 9 Haylett T, Swart L S, Parris D, and Joubert F J, Appl. Polym. Symp., 1971, 18, 37. 10 Lindley H, Gillespie J M, and Haylett T, Symposium on Fibrous Proteins, ed. Crewther, Butterworth, Sydney, 1967, p 535. 11 Zahn H and Biela M, Eur. J. Biochem, 968, 5, 567. 12 Gillespie J M and Reis P J, Biochem J, 1966, 98, 669. 13 Negri A P, Cornell H J, Rivett D E, Textile Res. J., 1993, 63, 109. 14 Zahn H, Wortmann F-J, Wortmann G and Hoffmann R, Ullmann’s Encyclopedia of Indus. Chem., 1996, A 28, 395–421. 15 Kalbe J, Kuropka R, Meyer-Stork L S, Sauter S L, Loss P, Henco K, Riesner D, Höcker H and Berndt H, Biol. Chem. Hoppe-Seyler, 1988, 369, 413. 16 Eichner R, Rew P, Engel A and Aebi U, Ann. NY Acad. Sci., 1985, 455, 381. 17 Rogers G E, Ann. NY Acad. Sci., 1959, 83, 378–399 and J. Ultrastruct. Res., 1959, 2, 309–30. 18 Phan K-H, PhD Thesis D 82, Aachen, 1994, Mainz, Wissenschaftsverlag Aachen, ISBN 3-930085-72-0. 19 Ackermann A B, Histologic Diagnosis of Inflammatory Skin Diseases. Lea and Febiger, Philadelphia, 1978. 20 Brody E, J. Ultrastruct. Res., 1959, 2, 482–511. 21 Matoltsy A G, ‘Structure and Function of the Mammalian Epidermal Horny Layer’, in The Skin of Vertebrates, ed. R J C Spearman and P A Riley, Linnean Society Symposium Theories (London), 9, 1979, 57, and Osbourne M, J. Invest. Derm., 81, 1983, 104. 22 Powell B C and Rogers G E, Formation and Structure of Human Hair, eds Jolles P, Zahn H and Höcker H, Birkhäuser, Basel, 1997, p 59, and Parry D A D, ibid, p 177. 23 Marshall R C, Text. Res. J., 1981, 51, 106–108, and Rogers G E, Kuczek E S, Mackinnon P J, Presland R B and Fietz M J in The Biology of Wool and Hair, Chapman & Hall, London, NY 1988, eds Rogers G E, Reis P J, Ward K A, Marshall R C, p 69–85. 24 Dowling L M, Crewther W G and Parry D A D, Biochem J., 1986, 236, 705–712. 25 Parry D A D and Fraser R D B, Int. J. Biol. Macromol., 1985, 7, 203–13. 26 Knopp B, Jung B and Wortmann F-J, Macromol. Theory Simul., 1996, 5, 947–956. 27 Sparrow L G, Dowling L M, Loke V Y and Strike P M, in The Biology of Wool and Hair, (see Ref. 23), p 145–55. 28 Franke W F, Margin T M and Hermann H, in Verhandlungen der Gesellschaft Deutscher Naturforscher und Ärzte, 115. Versammlung, Freiburg 1988, Wissenschaft Verlagsges Stuttgart 1988, p 153–164. 29 Steinert P M and Marekov L N, J. Biol. Chem., 1995, 270, 17702.

4 Physical properties of wool J W S HEARLE

4.1

The wool fibre

4.1.1 Structural complexity As is clear from Chapter 3, wool and other hair fibres have the most complicated structures of all textile fibres. All of the many levels of structure described in Chapter 3 have an influence on the physical properties of the fibres, and the mechanisms are now mostly understood qualitatively and, in many parts, supported by quantitative analysis. For convenience, the wool structure is summarised in Fig. 4.1, which is similar to Fig. 3.2 but emphasises aspects that are relevant to a discussion of the physical properties of fibres.

4.1.2 Dimensional and other features An idealised wool fibre has a circular cross-section, with diameters for different wools covering a range that can roughly be put as 20 to 40 mm. In reality, the cross-section is slightly and imperfectly elliptical. Fibre lengths range roughly from 5 to 50 cm. The fibres are helically crimped to varying degrees. The differences between different wool types and the methods of measuring dimensions are discussed in Chapter 1. In general, this Chapter will deal with generic features of wool fibres and will not cover differences between different wools. The density of wool is 1.3 g/cm3. The refractive indices of wool are reported1 as 1.553 parallel to the fibre axis, 1.542 perpendicular, and a birefringence of 0.010.

4.2

Effects of water

4.2.1 Moisture absorption The proteins in wool contain —CO.NH— and other groups that attract water. Figure 4.2 shows the change in moisture regain (mass of absorbed 80

Physical properties of wool

81

Epicuticle

Nuclear remnant

Low-S High-S proteins proteins high-tyr proteins

Lefthanded Righthanded coiled-coil α-helix rope

Exocuticle Endocuticle a Cuticle

Matrix Microfibril

Macrofibril

I 7

I 200

Cell membrane complex Para cell Ortho cell Cortex

I 1

I 2

I 2 000

I 20 000 nm

4.1 Wool fibre structure. Note that many wool fibres have a mesocortex, as well as ortho- and para-cortex, and in some coarse wools there is a medulla. [Drawn by Robert C Marshall, CSIRO.]

water/mass of dry fibre) with relative humidity.2 In a standard atmosphere of 65% RH and 20 °C, regain values range from 14 to 18%. Preston and Nimkar3 found that loose wool retained 133% regain when suctioned at -30 cm of mercury from the wet state but only 45% when centrifuged at 1000 g for 5 minutes. This contrasts with other fibres where the two methods give similar values. As can be seen in Fig. 4.2, there is hysteresis in moisture absorption, with the desorption curve being higher than the absorption curve. The shorter intermediate curves show the changeover from absorption to desorption at different humidities. Regain at a given relative humidity varies with temperature; at 70% RH, Darling and Belding4 found values between 17 and 18% from -29 °C to 4 °C, but then it fell to 13% at 71 °C. There have been a number of thermodynamic and mechanistic theories of moisture absorption in wool.5 There is general agreement that the sigmoidal shape of the absorption curve is a combination of water directly held on hydrophilic sites in the protein molecules, which increases rapidly from zero relative humidity and then levels off, and more loosely held water, which increases rapidly at high humidiites. Speakman6 divides the absorption into three types as shown in Fig. 4.3. The first type (a) is

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Regain (%)

30

20

10

0

20

40

60

80

100

Relative humidity (%)

4.2 Change of moisture regain of wool with humidity. [After Speakman et al.2]

assumed to be bound to hydrophilic groups in protein side-chains, and has little effect on torsional rigidity or, according to Hearle,7 on dielectric constant and electrical resistance. The second type (b) is attached to groups in the main chain, where it replaces intermolecular hydrogen bonds, and is linearly related to rigidity. The third type (c) is absorbed on top of types (a) and (b). When wool takes up water, the swelling is almost entirely radial, with little change in length. The overall volume increases, initially by a lower amount than the volume of absorbed water, but above about 15% regain the volumes are additive. Table 4.1 shows a set of values for radial and volume swelling, together with the change in fibre density.8 The swelling behaviour is explained on the presumption that most or all of the water is absorbed by the matrix, due to the presence of accessible hydrophilic groups, and that this increases the lateral spacing between fibrils, whose length does not change. The first molecules to be absorbed can pack efficiently with the protein molecules, but the later ones merely increase the volume.

4.2.2 Heat of sorption Table 4.2 gives values for the heat of wetting of wool, namely the amount of heat evolved when the wool is completely wetted out from different regains.8 From this, the differential heat of sorption, namely the heat evolved when one gram of water is absorbed, is calculated. The initial bonding of water to hydrophilic groups generates a large amount of

Physical properties of wool

83

Regain (%)

30

20 Total

10

a 0

b

20

40

c 80

60

100

Relative humidity (%)

4.3 Absorption of water in three types. [After Speakman.6]

Table 4.1 Moisture absorption and swelling of wool [From: WIRA8] Moisture regain (%)

0

2

5

7

10

15

20

25

30

15

27

42

68

85

94

98.5

11.7

14.6

16.3

26.2

32.8

36.8

Approximate 0 RH (%)

2.5

Radial swelling (%)

0

0.66

1.82

2.62

4.00

Volume swelling (%)

0

1.57

4.24

6.10

9.07

Density (g/cm3)

1.304

1.310

1.314

1.315

1.315

6.32

14.3

1.313

8.88

20.0

1.304

1.291

1.277

33 100

1.268

heat, but near saturation the effect is small. It has been found that the differential heat of sorption H follows equation [4.1], which is based on Kirchoff’s equation for dilution of solutions. This is expressed in terms of the relative humidities, h1 and h2, at temperatures, T1 and T2, for a constant regain: 2.3 log(h1/h2) = 9 H(1/T2 - 1/T1)

[4.1]

The values in Table 4.2 are for take-up of liquid water. For absorption of water vapour, the latent heat of condensation (2450 kJ/kg at 20 °C), which is three times the maximum heat of sorption from liquid water, must be added to the values. This evolution of heat has an important influence in clothing. When 1 kilogram of wool is taken from 40 to 70% RH, 160 kJ of

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Wool: Science and technology

Table 4.2 Heat of absorption of wool from liquid water [From: WIRA8] Regain (%)

0

5

10

15

20

25

30

Approximate RH (%)

0

15

42

68

85

94

98.5

Heat of wetting (kJ/kg) Diff’l heat of sorption (kJ/kg)

101 854

64.5 624

38.1 431

20.5 276

10.0 159

4.19 100

1.13 41.9

33 100 0 33.5

heat are evolved. The main effect of this is to slow down the impact of moving between hot dry atmospheres indoors and cold damp atmospheres outdoors.

4.3

Observed mechanical properties

NOTE: Much of the data in the literature is reported as conventional stress, based on area, in N/mm2 = MPa or, for older work, in dyne/cm2 = 0.1 Pa. Generally, in the textile literature, it is preferable to use specific stress, namely (force/linear density) based on fibre mass. For wool, assuming a density of 1.3 g/cm3, 1000 MPa = 0.77 N/tex, 7.7 cN/dtex or 7 g/den. Stresses are also often normalised in terms of the tension at 15% extension in wet wool, which is the middle of the yield region; this is typically around 35 MPa (27 mN/tex or 0.25 g/den).

4.3.1 Load–extension properties The most extensive study of the mechanical properties of wool was carried out by Max Feughelman and his colleagues at CSIRO Ryde9 from the 1950s onwards. A special feature of their work is that, provided the fibre is not strained by more than 30% or for longer than 1 hour, it can be returned to its virgin state by soaking in water at 52 °C for 1 hour, so that many tests can be made on one fibre. Most of their tests were on fibres from sheep housed and fed in controlled conditions. These factors reduce the problems of variability within and between fibres. Figure 4.4 shows a typical load–extension curve of a wet wool fibre. The features of the curve are: (i) a low-stress decrimping extension near A; (ii) an initial stiff region up to B, usually referred to as the Hookean region – but, though linear, it is visco-elastic, not elastic; (iii) a yield region up to C; (iv) a stiffer region up to break at D. In tests on different fibres, there is little variation in the points B and C at 2% and 30% extension respectively, but the break extension varies more widely, since it is less if there is any weakness or damage in the fibre. Break extensions of 50 to 60% are typical of a good fibre. From the

Physical properties of wool

85

start of the yield region, there is a progressive loss of the X-ray diffraction pattern corresponding to the a-helix and a growth of the pattern for the extended b-chains.10 Variability along the fibre length changes the shape of the curve, because thin portions extend more easily than thick portions. Consequently, part of the fibre may be suffering high extension in the yield region, while other parts are still in the Hookean region and only yield at a higher load. These features were studied in detail by Collins and Chaikin,11 and Fig. 4.5 illustrates the stress–strain curves of fibres that are more or less regular. Their theoretical calculations12 indicate that a perfectly uniform fibre would have a constant yield stress, i.e. zero slope between B and C in Fig. 4.4, and that the changes of slope at B and C would be sharper than are usually found. If the change in cross-section along the fibre is continuous, the effect is to give a higher yield slope, but, if it is discontinuous, there will be steps in the yield region. Figure 4.6 shows how the stress–strain curve changes with humidity and temperature.13 As the wool becomes drier, the main effects are to raise the yield stress, and there is some increase in yield slope. The initial modulus decreases with increasing moisture regain, as shown in Fig. 4.7.14 It has been

D

8 7

Load (gf)

6 C

5

B

4 3 2 1 A

0 0

10

20

30

40

50

Extension (%)

4.4 Load–extension curve of a Corriedale wool fibre in water at 20 °C. AB is the Hookean region, BC the yield region, and CD the post-yield region. Up to B, the rate of extension was 0.375% per hour, and beyond B, 1.875% per day; the whole test took 25 days. [From Feughelman.9]

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Wool: Science and technology

Stress (kg/mm2)

10 2

2

5

1

1 2

0

50

0 Extension (%)

4.5 Stress–strain curves of wool fibres: (1) with good uniformity; (2) a more irregular fibre. [From Collins and Chaikin.11]

noted15 that although the change to the yield region occurs at higher strains in drier fibres, it is at the same fibre length as at 100% RH, indicating that the additional extension is due to axial shrinkage of the fibre on drying, with some compression of the internal structure. Strength increases in line with the increase in yield stress, but to a lesser extent because of a reduction in break extension. An increase in temperature lowers the stress over the whole curve, with a large change between 40 and 80 °C. The shape of the curve is markedly different at 100 °C (Fig. 4.8). The stress–strain curve is affected by the chemical environment. Figure 4.9(a) shows the effect of alcohols. Because the molecules are larger, they do not cause as much lowering of the stress–strain curve as water. The higher the alcohol, the higher is the stress, with an effect similar to reduction of humidity. Acids inherently tend to lower the stress–strain curve, as shown by formic and acetic acids in Fig. 4.9(b), but this is counterbalanced by the difficulty of the larger acid molecules penetrating the fibre.

4.3.2 Recovery behaviour The shape of the stress–strain curve of wool in extension is not unusual for polymers, though the changes at B and C are particularly sharp. The recovery behaviour is completely different; in most polymers there is no recovery from yielding. In wet wool, as shown in Fig. 4.10, there is complete recovery from extensions up to 30%, but the recovery follows a different curve and only joins the extension curve at about 1/3 of the yield stress. In the post-yield region above 30%, the recovery curve has a similar shape,

Physical properties of wool

0 8.3 27.5 41.0

Stress (N/mm2)

250 200

68.0 84.4 100% RH

150 100

2 Stress (N/mm )

200

87

0°C 20°C 40°C

150

60°C 100 80°C 50

100°C

50 10

0

20 30 40 Extension (%)

50

(a)

0

60

20

40

60

80

Extension (%) (b)

4.6 Change of stress–strain curves with test conditions:13 (a) influence of moisture at room temperature; (b) influence of temperature for wet wool.

Relative Young's modulus

3

2

1

0

20 10 30 Moisture regain (%)

4.7 Change of initial modulus with regain. [From Peters and Woods.14]

but at zero stress there is a small unrecovered extension, which increases with the imposed extension. In his extensive tests at 65% RH, Meredith16 found that the elastic recovery of wool decreased with increasing imposed extension. From 30% extension, the elastic recovery (recovered extension/imposed extension) was 0.6. Table 4.3 gives other recovery data, showing the effect of humidity and imposed extension.17

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Wool: Science and technology

Stress (108 dyn/cm2)

8

22°C

6

4 100°C 2

0

40 80 Extension (%)

4.8 Stress–strain curves of wet wool at 22 and 100 °C. [From Peters and Woods.14]

3 2 1 10

0

Stress (108 dyn/cm2)

Stress (108 dyn/cm2)

20

5 4 20

3 10

0

20 40 60 Extension (%)

(a)

1

4 5

20 40 Extension (%)

60

(b)

4.9 Effect of chemicals on stress–strain curves. (a) 1 – water, and alcohols, 2 – methyl, 3 – ethyl, 4 – n-propyl, 5 – n-butyl or n-amyl. (b) 3 – water, and acids 1 – n-butyric, 2 – propionic, 4 – acetic, 5 – formic. [From Peters and Woods.14]

4.3.3 Time dependence Wool fibres contain many bonds sensitive to time under load, so that viscoelasticity shows up in reduced stress as rate-of-extension is decreased, in creep under constant load, in stress relaxation at constant extension and in changes in dynamic properties.

89

Stress

Physical properties of wool

0

10

20

30

40

Strain (%)

4.10 Stress–strain curve of wet wool in extension and recovery. The stress is in arbitrary units. [From Morton and Hearle.5]

Table 4.3 Elastic recovery of wool [From: Beste and Hoffman17] Humidity

Elastic recovery from extension of 1%

5%

10%

60% RH

99%

69%

51%

90% RH

94%

82%

56%

In the low-strain Hookean region, Fig. 4.11, from studies by Feughelman and Robinson,18 shows that the higher stress at lower humidities relaxes with time towards the stress in the wet state. From larger strains, Fig. 4.12 shows the stress relaxation of human hair, which will be generally similar to wool, from different extensions in water at 35 °C and from 40% extension at different temperatures.14 The curves divide into four regions, which shows that there are different relaxation mechanisms within the fibre structure. There is rapid decay in less than a second, which, if it were the only mechanism, would lead to an asymptotic approach to a limiting tension. This is followed by a slow decay to 100 seconds, then a faster decay from 100 to 10 000 seconds, before the curve begins to flatten out. The increase in rate at higher temperatures is also shown in Fig. 4.13 for relaxation from the mid-point of the yield region.19

90

Wool: Science and technology 5

RH

Tensile modulus E′, (GPa)

0 4

32

65 3 91 2 100 1 E′• 10–1

10o

101

102

103

104

Relaxation time (min)

4.11 Stress relaxation of a wool fibre from 0.8% extension at different relative humidities.18 The stress, calculated on the basis of the wet cross-sectional area, is normalised to the stress at 0.8% extension in a wet fibre. [From Postle et al.26]

Figure 4.14 shows the creep in a wet wool fibre for short times (2.5 minutes) under different loads in the yield region at 18.5 °C and in the yield region at different temperatures.20 The rate decreases with time and, on a linear time scale, appears to become asymptotic to a constant value. Creep is faster at higher temperatures. Feughelman20 found that the results fitted the empirical equation: 1/e = (a/t) + b

[4.2]

where e is extension at time t, and a and b are constants dependent on load and temperature. When tested over longer times and plotted on a logarithmic scale, Fig. 4.15 shows that another mechanism appears to take over at around 100 minutes and begins to level off in a typical sigmoidal plot at about one week.18 The creep, or stress relaxation, in wool will show up as higher extensions at a given stress in load–extension testing. Figure 4.16 shows the effect on Young’s modulus, which decreases as the rate of extension is decreased.18 As can be seen in Fig. 4.17(a), the dynamic modulus, measured by small oscillations at 116 Hz,21 is highest at a small mean strain level in the Hookean region, is lower through the yield region, and rises again in the post-yield

Physical properties of wool

91

Stress (108 dyn/cm2)

16 12

49%

8

39% 30%

4 20% 0 –2 10 10–1

(a)

10 102 103 104 Time (seconds)

1

Stress (108 dyn/cm2)

12

8

105

25°C 35° 45° 55°

4

65° 75°

85° 95°

0 1

10

(b)

102 Time (seconds)

103

4.12 Stress relaxation of wet human hair: (a) at 35 °C from different extensions; (b) from 40% extension at different temperatures. [From Peters and Woods.14]

3

f / f1

80°C 2

70°C 50°C

1

30°C

30°C 80°C

0

10

102

50°C 70°C

103

Time (min)

4.13 Relaxation of wet wool from 15% extension at different temperatures.19 f/f1 is the ratio of the stress after the given time to the stress after 1 hour. [From Morton and Hearle.5]

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Wool: Science and technology

Extension (%)

30

Load(g) 6.7 6.5 6.3 6.1 5.9 5.7

20

10

(a) 0

50

100

150

Time (seconds)

°C 25.3 20.5 14.8 9.8

Extension (%)

20

4.4 10

(b) 0

50

100

150

Time (seconds)

4.14 Creep in a wet wool fibre with a diameter of 44.5 mm:20 (a) under various loads at 18.5 °C; (b) under 6 gram load at various temperatures. Note that 6 gram equals 38.5 MPa, which is towards the end of the yield region.

region. Conversely, the plots of loss angle d in Fig. 4.17(b) are roughly mirror images of the modulus plots, being highest in the yield region. Figure 4.18 shows the change in tan d in dry fibres with temperature, as measured by Meredith in bending.22 For wool, there is a rise, presumably to a peak characteristic of many polymers around -100 °C, at low temperature; a peak at about 20 °C; and then a rise at high temperature.

4.3.4 Directional effects The bending behaviour of fibres relates to their tensile properties, with the outside of the bend being in tension and the inside in compression. For

Physical properties of wool

93

90 80 a

Extension (%)

70

b

60 50 40 30 20 10

1

10

102 103 Time (minutes)

104

Young's modulus (⫻107g wt/cm2)

4.15 Creep of keratin fibres in water: (a) human hair at 72 MPa; (b) Cotswold wool at 69 MPa. [From Peters and Woods.14]

2.0

20°C 1.8

40°C 1.6

10

1

0.1

0.01

Rate of extension (% per min)

4.16 Change of Young’s modulus in wet Cotswold wool with rate of extension at 20 °C and 40 °C.18 [From Morton and Hearle.5]

small curvatures with a constant modulus, there is a central neutral plane and the maximum strain is ±(r/R), where r is the fibre radius and R is the radius of curvature. If there is yielding, the neutral plane is displaced in order to minimise the deformation energy. In most polymers, yielding is

94

Wool: Science and technology 2.4 Modulus E' (relative units)

2.2 2.0

0 11

1.8 1.6

33 52.9

1.4

73.8

1.2 85

1.0

92.5 98

.8

100

.6 .4 (a)

10

20

30

40

50

60

Strain ε (%)

Loss angle d (degrees)

6 5 4 3 2

73.8 52.9 11 33 0

1

98 85 92.5

100

0 0 (b)

10

20

30

40

50

60

Strain ε (%)

4.17 Dynamic mechanical properties of Lincoln wool at different humidities at 25 °C and 116 Hz: (a) Dynamic modulus E¢. Unit modulus at 0.6% extension equals 2 GPa. (b) Loss angle d. [From Danilatos and Feughelman.21]

easier in compression than extension, so that the neutral plane moves out and a plot of equivalent stress against strain in bending falls below that in extension, as found for several fibres by Chapman.23 However, for Lincoln wool, the bending curve goes above the tensile curve, as shown in Fig. 4.19(a). Experiments up to higher curvatures on a coarser horse hair fibre show the effect of the eventual yielding in compression, Fig. 4.19(b). The initial identity of both curves shows that the tension and compression moduli are the same in the Hookean region. Figure 4.20 shows the effect

Physical properties of wool

95

0.05 b

Tan δ

0.04 0.03

a d

0.02 0.01

–50

0

50

100

150

Temperature (°C)

4.18 Loss factor for several fibres measured in bending by Meredith22. Curve (d) is for wool. The others are: (a) mercerised cotton, (b) viscose rayon, (c) secondary acetate [From Morton and Hearle.5]

of temperature and humidity on the nominal initial bending modulus: the black circles are repeats at 20 °C after tests at 60 °C; the dotted line is calculated from tensile modulus and swelling data of Bendit and Feughelman,24 and shows good agreement despite being on different wools at different rates. The changes in differential axial length of wool on drying, as discussed in Section 4.4.3, cause wool to bend on drying from the form in which it grows from the follicle, and this leads to the helical crimp of wool fibres. The torsional properties of wool were measured by Mitchell and Feughelman.25 Figure 4.21 shows that there is a linear relation between the reciprocal of torque and the reciprocal of twist angle. The resistance to twisting decreases with increasing humidity. Speakman6 showed that the reduction in torsional rigidity followed a sigmoidal plot against moisture regain, Fig. 4.22, but was linear when plotted against the intermediate absorption, shown as type (b) in Fig. 4.3. The shear modulus, as measured in torsion, is reported26 to be 1.7 GPa at 0% RH, 1.1 GPa at 65% RH, and 0.13 GPa at 100% RH. The effects of temperature, strain and moisture on torsional stress relaxation are shown in Fig. 4.23. Figure 4.24 shows the transverse load–extension curve of wet porcupine quill.27 The initial modulus of 0.37 GPa should be valid as a measure of the properties of the material of the wool fibre, but, as suggested by Hearle,28 the yielding is probably due to breakdown of the composite structure at some level. Kawabata has developed sensitive methods for measuring the properties of fibres in different directions. He reports the following values

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Wool: Science and technology

Bending Stress (MPa)

100

Tensile

0

10

(a)

20

Strain (%)

200 Bending Stress (MPa)

100

Tensile

0 (b)

10 Strain (%)

20

4.19 Nominal stress–strain curves in bending compared with tensile curves: (a) Lincoln wool; (b) horsehair. [From Chapman.23]

Physical properties of wool

97

5

4 Nominal bending modulus (GPa) 3 20°C 40°C 60°C

2

0

10

20

30

40

50

60

70

80

90

100

R.H. (%)

4.20 Effect of temperature and humidity on nominal bending modulus of Lincoln wool. See text for explanation of black circles and dotted line. [From Chapman.23]

at 25 °C and 55.3% RH: axial modulus EL = 3.33 GPa; transverse modulus ET = 1.09 GPa; shear modulus GLT = 1.47 GPa.29

4.3.5 Fibre strength: fracture and fatigue For ‘good’ wool, the evidence indicates that wet fibres break at an extension of 50 to 60% at a stress of about 100 MPa. Figure 4.25 shows a plot of break load in a standard atmosphere against the local area of cross-section at the break point of wool fibres.30 The slope of the upper bound line indicates an intrinsic strength of 300 MPa. However, the break load of individual fibres, when related to their average diameter or linear density, may be much lower than this due to variability, which causes failure to occur at a thin place. The points falling below the line in Fig. 4.25 can be attributed to

Wool: Science and technology 10 ty mi di

8

Re 0%

5 4

H. R.

lat

6

90 %

ive

Hu

7

. R.H 58% .H. 0% R

10

Torque–1 (dyne-cm)–1

9

3 2 1 0 0

0.1

0.2

0.3

0.4

0.5

Twist–1 (radians–1)

4.21 Reciprocal of torque plotted against reciprocal of twist angle for a wool fibre of diameter 44.6 mm when wet.25 [From Feughelman.9]

1.0

Relative modulus of rigidity

98

0.8

Cotton

Total regain

Cotton Wool

a-Phase only Total regain

Wool

b-Phase only

0.6

0.4

0.2

0

10 20 Moisture regain (%)

30

4.22 Relative torsional rigidity plotted against moisture regain. The upper plots are for wool; the comparison for cotton shows a plot against the first absorbed water in a two-phase model. [From Morton and Hearle.5]

Physical properties of wool

99

100 % R.H.

1.4

9.1°C 21.5°C Tt T60 35°C 1.0 42°C 10–1

1 10 Time (minutes)

1.7 rads. 84.5 1.5 16.1 16.1 Tt 9.0 1.3 34.5 T60 69.1 401 1.1 1.0 –1 100 10

(a)

0 % R.H. 100 % R.H.

1 10 Time (minutes)

100

(b)

4.23 Torsional stress relaxation, plotted relative to stress after 60 minutes: (a) effect of temperature at 100% RH; (b) effect of strain at 0% and 100% RH. [From Chapman.15]

Lateral stress (MPa)

15

10

5

0 0

2

4

6

8

10

Lateral strain (%)

4.24 Stress–strain curve for porcupine quill in lateral extension.28 [From Feughelman.9]

some defect in the fibre, which may be a surface crack, an internal flaw, or some general weakness in the fibre. The form of tensile fracture is a granular break perpendicular to the fibre axis, Fig. 4.26(a).31 In some fibres, the break is in short or long steps joined by an axial split, Fig. 4.26(b,c). The two transverse cracks are an indication

Wool: Science and technology 35 30 Load (gf)

100

25 20 15 10 5 0

0

200

400

600

800

1000

1200

1400

1600

2 CSA (µm )

4.25 Break load of wool fibres plotted against area of cross-section at point of break.30

(a)

(b)

(c)

4.26 Three views of the tensile fracture of wool fibres. [From Hearle et al.31]

Physical properties of wool

101

of prior damage to the fibre, either a pre-existing split or flaws in two places along the fibre. When wool is repeatedly flexed by pulling to-and-fro over a pin, there is a combination of axial splitting and surface wear,32 as shown in Fig. 4.27. Severe repeated buckling, either in a laboratory test or in a carpet, leads to the formation of axial cracks due to internal buckling in axial compression,32 as shown in Fig. 4.28(a). This leads to rupture, Fig. 4.28(b), and is followed by axial splitting.

(a)

(b)

4.27 Failure in wool fibres on flexing over a pin. [From Hearle et al.31]

(a)

(b)

(c)

(d)

4.28 Failure in repeated severe buckling of a wool yarn. (a) transverse crack; (b) ruptured end; (c,d) subsequent axial splitting. [From Hearle et al.31]

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4.3.6 Thermal properties, transitions, supercontraction The thermal conductivity of horn, which is a similar material to wool, increases from 194 mWm-1K-1 at 0% moisture regain to 290 mWm-1K-1 at 30% regain.32 For fibre assemblies, the trapped air leads to much lower values of thermal conductivity. Figure 4.29 shows the variation of specific heat of wool with temperature at various regains.33 The peak below 0 °C at higher regains will be due to the latent heat of ‘freezing’ of loosely bound absorbed water. There is also an indication of a step increase at around 40 °C, which would correspond to a second-order glass transition. A differential scanning calorimetry study by Phillips34 showed that the change in specific heat was considerably affected by fibre ageing. Wool with 15% regain stored at 20 °C for 52 days showed a pronounced endotherm near 60 °C on the first heating cycle, which disappeared in a second run after rapid cooling, but reappeared after 15 days reageing. Figure 4.30 shows how the transition temperature falls with increasing water content. The effect of the second-order transition on mechanical properties is shown by the large drop in the stress–strain curve of wet wool between 40 °C and 80 °C, as seen in Fig. 4.6. The position of the transition is clearly 3.5 33.9 % 30.7 %

3.0

Specific heat (Jg–1 K–1)

28.4 % 2.5 24.8 %

2.0

16.9 % 7.6 %

2.5 Dry 1.0

0.5 –100

–50

0

50

100

Temperature (°C)

4.29 Variation of specific heat of wool with temperature and regain.33 [From Morton and Hearle.5]

Physical properties of wool

103

Transition temperature (°C)

160 140 120 100 80 60 40 20 0 0

10 20 Water content (%)

30

4.30 Variation of transition temperature of wool with water content. [From Phillips.34]

shown in Fig. 4.31 by the change in the strain at the end of the yield region in wet wool. There is no change up to 60 °C, but then there is a rapid increase. The plot of initial modulus against temperature shows a reduction associated with the glass transition, but it then drops rapidly above 100 °C to almost zero at 130 °C, Fig. 4.32. The effects above 100 °C are attributed to a first-order transition and are associated with the phenomenon of supercontraction, which may be brought about in various ways. A fibre that has been stretched to above 40% extension, steamed and released, will contract to less than its original length. Irreversible supercontraction occurs when wool is immersed in a boiling solution of phenol or a lithium halide in water, and reversible supercontraction occurs in cuprammonium hydroxide or a lithium halide solution in milder conditions. In a hot solution of lithium halide, the fibre contracts in a first stage to around -15% extension, with a complete loss of crystallinity, as shown by X-ray diffraction, and of birefringence. After a few minutes, second-stage supercontraction goes to a final value between -30% and -50% extension. Washing the fibre after the first stage restores the fibre to its original state, but this does not occur after the second stage. First-stage supercontraction occurs after many hours in a cold lithium bromide solution above a critical concentration; second-stage supercontraction occurs when the concentration is increased and heat is applied. Chapman35 used this procedure to investigate the change in tensile properties. Figure 4.33 shows the stress–strain curves in water and in cold LiBr solution after first- and second-stage supercontraction.

Wool: Science and technology

Strain at point C

104

0

20

40

60 Temp. (°C)

80

100

Hookean modulus ¥ 10–10 (dyn.cm–8)

4.31 Change in strain at end of yield region in wet wool (point C in Fig. 4.4). [From Chapman.15]

2.0 Rate of strain (8%/min.)

1.0

0

20

40

60

80 100 120 Temp. (°C)

4.32 Change in initial modulus of wet wool with temperature. [From Chapman.15]

In wet wool, the X-ray diffraction pattern of a-keratin is lost at about 130 °C, indicating a melting of the intermediate filaments (IFs). In dry fibres, a melting endotherm occurs at around 225 °C.

4.3.7 Ageing and setting The stress relaxation of wool has been referred to in Section 4.3.3. However, it can be viewed in another context as ‘ageing’ of the fibre. This is particularly important in relation to wrinkling and wrinkle recovery in wool fabrics. In effect, the ageing of bent fibres in the fabric, due to stress relaxation, means that they have been ‘set’ in a new form with changed properties. Setting can be accomplished more rapidly by other treatments. Feughelman36 studied the behaviour after setting in boiling water for 1 hour. Figure 4.34 shows the stress–strain curves in water at 20 °C for the original unset fibre and a fibre that had been set at 10% extension. Both because of the increased set length and a reduction in the initial modulus, the start of the

Load F15 冣

1st stage

Water

1.0

Strain (%)

2nd stage –30

–20

–10

105

冢

Normalised stress

Physical properties of wool

0

10

20

30

4.33 Stress–strain curves in water and in LiBr solution after first- and second-stage supercontraction. [From Chapman.35]

yield region at A is shifted to a much higher extension, when based on the original length. The yield slope is unchanged and the end of the yield region at B is shifted only slightly to a higher extension. Feughelman found that the change was only partial after setting for just one minute. The points A and B were in the same positions as in Fig. 4.34, but the fibre was not set: its length under zero stress was unchanged. The initial part of the curve started from 0% extension and followed a sigmoidal path, with high-lowhigh slopes, to the start of the yield region at A. Feughelman also found that releasing the fibre, after 1 hour set, in water at 100 °C for 1 hour, restored the fibre almost to its original length and stress–strain curve. Release at 120 °C led to supercontraction. As described in Section 7.13, setting is assisted by chemical treatments that attack disulphide bonds, and may be locked in if more permanent chemical cross-links are formed.

4.3.8 Fibre friction Wool has the unusual feature of a directional frictional effect (DFE). It is harder to pull against the scales than with them. For wool on wool, there are three options: (1,2) fibres with roots and tips opposed, pulled with or against the scales; (3) fibres with roots and tips at same end, pulled either

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Stress (108 d/cm2)

4

Setting strain Original

A

B

3 2 1 0

0

10

20 Strain (%)

30

40

4.34 Stress–strain curves, unset and set at 10% extension in boiling water. [From Hearle et al.37, based on measurements by Feughelman.]

way. For wool on another substrate, there are the two options of with or against the scales. Typical experimental results are given in Table 4.4. As with all fibres, the values of the coefficient of friction m depend on the state of the surfaces, particularly the presence of lubricants, and the environmental conditions. It is also found that Amontons’ Law is not strictly followed, so that m is not a constant independent of normal load, but is merely a ratio of friction force to normal load.

4.4

Structural mechanics

4.4.1 The chemical background As is clear from other chapters in this book, wool is composed of a complicated cocktail of proteins and other chemical substances. This means that the thermal and mechanical responses of the fibres are determined by a variety of interatomic and intermolecular bonds and a diversity of structural forms. The mechanics of most of the properties is understood qualitatively, and there are some quantitative theories. Much detail remains to be worked out, but this should be achieved through advances in computer modelling and in analytical techniques, which define structure more precisely. The different parts of wool fibres that influence mechanical properties are shown in Fig. 4.1. The keratin proteins in the intermediate filaments (IFs) can, to a first approximation, be regarded as forming microfibrillar crystals with a-helical chains intra-molecularly linked by hydrogen bonds, though an idealised behaviour will be modified by the presence of various side-groups. Under

Physical properties of wool

107

Table 4.4 Friction of wool [From: Morton and Hearle5] with scales

against scales

same direction

Wool on wool – static – kinetic

0.13 0.11

0.61 0.38

0.21 0.15

Wool on rayon – static – kinetic

0.11 0.09

0.39 0.35

Wool on nylon – static – kinetic

0.26 0.21

0.43 0.35

Wool on wool – crossed fibres

0.20–0.25

0.38–0.49

Pair of twisted wool fibres – dry – wet

0.11 0.15

0.14 0.32

Unswollen wool, swollen** ebonite

0.58

0.79

Swollen* wool, unswollen ebonite

0.62

0.72

Swollen* wool, swollen** ebonite

0.65

0.88

Wool on ebonite – polished surface – rough surface

0.60 0.50

0.62 0.61

Wool on horn: dry

0.3

0.5

Wool on horn: wet, pH 4.0 – untreated – chlorine treated – alcoholic KOH treated – sulphuryl chloride treated

0.3 0.1 0.4 0.6

0.6 0.1 0.6 0.7

* in water ** in benzene.

tension, a crystal lattice transition is observed, extended-chain b-crystals form and the hydrogen bonds become inter-molecular. Terminal domains (tails) of the keratin molecules contain cystine and project into the matrix. The keratin-associated proteins of the matrix are more complicated. The mechanical role of the glycine-tyrosine-rich proteins is not understood, but the cystine-rich proteins constitute a cross-linked network, within the globular molecules, between globules and connecting to the terminal domains of the IF proteins. In the dry state there will be hydrogen bonding between matrix protein segments, but, in wet fibres, absorbed water will give a mobile structure. Other intermolecular bonds will also influence the mechanical response. The cell membrane complex has a different chemistry. The link to mechanics has been little investigated, but the presence of lipids means that it is probably a fairly weak material. The mechanical responses of the various layers of the cuticle also need more study.

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Wool: Science and technology

4.4.2 The fibril–matrix composite The main features of the stress–strain relations can be explained in terms of an axially oriented, parallel assembly of fibrils (IFs) in an amorphous matrix. Feughelman38 laid the foundations of the theory with the two-phase model shown in Fig. 4.35. Swelling of the matrix by absorbed water, which pushed the fibrils apart, explained the high transverse swelling and low axial swelling of wool. The initial extension in the Hookean region is resisted mainly by the deformation energy of the hydrogen-bonded a-helices in the fibrils, with a small contribution from the matrix. Lower shear and transverse moduli are determined mainly by the softer matrix. Quantitative analysis of the anisotropic mechanical properties would follow composite theory. For elements in parallel, which applies to the axial extension of the two-phase model, the mixture law adds forces or averages moduli. For elements in series, extensions are added or compliances averaged. Across circular units in a matrix, as applies to the shear and transverse response of the two-phase model, the stress distribution is more complicated, but the predictions tend to be closer to the series model. A three-dimensional finite-element analysis of the anisotropic elasticity was carried out by Curiskis39,40, but the detailed predictions have been criticised by Postle et al.26 page 23. The possible role of breakdown of the cell membrane complex or elsewhere, which would give the observed yielding under transverse stress, is discussed in Section 4.4.4. The two-phase model was extended to cover the large-strain extension and recovery behaviour by Chapman.41* The model results from a proper analysis of the mechanics of the composite system of fibrils and matrix, both of which have specific load–extension properties. For the fibrils, a plot of free energy against extension will have the form shown in Fig. 4.36(a), which is based on a diagram by Feughelman.9 The energy minima at A and B correspond to the coiled and extended crystal forms. Differentiation gives the force–extension curve shown in Fig. 4.36(b). OA is the extension of the a-helices and FC of the b-crystals. For infinitely large crystals, the extension would jump from A to C, because of the instability of a decreasing force region. At intermediate extensions, both forms * There was an earlier theory by Feughelman and Haly42, based on an alternation of X-zones, which extended in the yield region, and Y-zones, which extended in the post-yield region. There were subsequent detailed variations of this model, and in 1994 Wortmann and Zahn43 suggested an explanation in terms of the IF structure. In the same year, Feughelman44 suggested another model, which was based on separate globular molecules surrounded by water in the matrix. A review by Hearle28 concludes that the Chapman model and its later developments, as described here, are basically correct, though enhancements are needed to take account of more complicated structural details.

Physical properties of wool

109

would be present along DF at the force for equilibrium between a and b, which is given by the slope of the line AB in Fig. 4.36(a). In small crystals, thermal vibrations will cause the jump to occur at the lower force H in Fig. 4.36(b).The expected force–extension relation for the fibrils is thus OHJFC. Along JF, the fraction of a will be decreasing and of b increasing. For the ideal a-helix, the extension to F is 120%, but, for the actual IFs, it is probably only 80%, as some parts are not able to change to the b-crystalline form. In practice, wool fibres will break at around 50% extension, marked by the point G. On the Chapman model, the matrix in the wet state is assumed to act as a rather highly cross-linked, swollen rubber. The matrix stress–strain curve can be derived from the supercontraction experiments shown in Fig. 4.33. Following the X-ray diffraction evidence, it is assumed that the a-crystals are disrupted in first-stage supercontraction, so that the stress–strain curve

Filament

Matrix

4.35 Feughelman’s38 two-phase microfibril–matrix model. [As drawn in Postle et al.26]

(a)

(b) Activated state ∆F

B ∆F* A Length of unit in state B (unfolded) Length of unit in state A (folded) Extension of Burte-Halsey unit

A Force

Free energy

Stress field ‘F’

Fc Fe

C

H EJ D O

G

F

B Extension

4.36 (a) Free-energy diagram for a Æ b transition. (b) Force diagram. [From Hearle.28]

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Wool: Science and technology

is then dominated by the matrix. If the matrix ceases to contribute after second-stage supercontraction, the small resistance to extension is the residual effect of the disrupted IFs. Subtraction of the stress–strain curve after the second stage from that after the first stage thus gives a prediction of the matrix stress–strain curve, as shown in Fig. 4.37(a). In Fig. 4.37(b), it is shown that this curve is close to a theoretical rubber elasticity curve, based on the inverse Langevin function form, with two free links between junction points. The deviation at high stress can be attributed to some rupture of cross-links, which leads to the observed loss of some recovery from extensions over 30%. The maximum extension of the rubber-elasticity curve is about 50%, and this defines the limit at which the matrix will rupture and wool fibres will break. Higher extensions can be achieved, as was done by Bendit45, if cystine cross-links are allowed to break by treatment in hot water. This leads to the maximum extension of 80% for completion of the a Æ b transition. In the Chapman model, the composite fine structure is treated as a fibril, with helical chains, in parallel with an amorphous matrix, with the two linked at intervals to give a series of zones, as shown in Fig. 4.38. Originally, this form was chosen for simplicity in modelling, but now the links correspond to the IF keratin tails, which are cross-linked to the KAPs in the matrix. The stress–strain curves of the two components of the wet fibre are shown in Fig. 4.39(a), based on the above arguments. Up to 2% extension, Fig. 4.38(a), both components extend together, but, as described above, almost all the stress comes from the fibrils. When the critical stress is reached, one of the zones, arbitrarily selected either due to variability or thermal vibration, opens from the a helix to the b extended chain. The tension in the fibril drops to the lower equilibrium value and the matrix extends to make up the tension. There would be an infinitesimal drop in tension, but this is picked up by further extension, so that further zones continue to open. The stress through the yield region, Fig. 4.38(b), remains constant and equal to the IF critical stress plus the small contribution of the matrix at 2% extension. At 30% extension, Fig. 4.38(c), all zones have opened. Further extension in the post-yield region, Fig. 4.38(d), causes the matrix stress to increase. In recovery, Fig. 4.38(e), there is no critical factor and the zones all contract together until they disappear and the initial stress–strain curve is rejoined. With the values shown in Table 4.5, the predicted stress–strain curve is shown in Fig. 4.39(b). This is identical with the experimental stress–strain and recovery curves, if the variability that causes the slope in the yield region is absent. At humidities below 100%, intermolecular hydrogen bonds stiffen the matrix. This gives a larger matrix contribution to the stress and thus increases the initial slope and the yield stress. In the initial and post-yield regions, the matrix stress can be calculated by subtracting the assumed fibril

Normalised stress Load 冢 F15 冣

Water

1st stage 1st stage

冢–2nd stage冣

1.0

2nd stage extrapolated

0

10

20 30 Strain (%)

(a)

40

50

Theoretical rubber elasticity

Nominalised stress

Experimental matrix curve

1.0

(b)

0

10

20 30 Extension (%)

40

4.37 (a) Stress–strain curves of wool after first- and second-stage supercontraction, and for (first stage – second stage), which is assumed to be the matrix curve. The curve for wool in water, which in recovery is almost parallel to the matrix curve, is shown for comparison. (b) Comparison with theoretical rubber-elasticity curve. [From Chapman.35]

112

Wool: Science and technology From 0% to 2%: uniform extension at 2%: IFs reach critical stress

From 2 to 30%: zones open in succession in open zone: IF at eq. stress, matrix at 30%

At 30% extension, all zones open

Beyond 30%, IF at eq., matrix stress rises

In recovery, IFs at eq. stress all zones contract until they disappear

4.38 Schematic representation of the sequence of changes in the Chapman model. [From Hearle.28]

stress from the experimental curves shown in Fig. 4.6. For the intermediate extensions, calculation is not possible, but Fig. 4.40 shows matrix stress– strain curves interpolated in this region.37 They are typical of an amorphous polymer with hydrogen bonds that are broken at a yield stress. Setting can be explained37 on the assumption that the rupture and reformation of cross-links relieves the stress and shifts the origin of the matrix

113

Stress

Stress

Physical properties of wool

M c

b eq

a

Strain

(a)

0

Strain (b)

4.39 (a) Stress–strain curves for fibril and matrix; (b) Predicted stress–strain curve of composite. [From Hearle.28]

Table 4.5 Controlling parameters for Chapman model [From: Hearle28] Parameter

Value

Determines

Notes

Microfibrils a modulus

1.75 GPa

Initial fibre modulus (plus small matrix contribution)

Similar to theoretical calculation

Critical stress a Æ b trans’n

0.035 GPa

Fibre yield stress (plus small matrix contribution)

Reasonable at 2% strain

Equil’m stress a Æ b trans’n

0.07 GPa

Junction of extension and recovery curves

Reasonable on basis of Fig. 4.36

b modulus

1.75 GPa

Additional microfibril extension in post-yield region

Actually higher; negligible effect

a Æ b strain

80%

Extension in opened zones

From X-ray diffr’n expt’s; less than ideal a-helix

Matrix # Nonlinear stress/strain

See Fig. 4.37(b)

Post-yield and recovery curves (plus microfibril contribution)

From supercontr’n expt’s & rubber elasticity theory

In’l modulus

0.35 GPa

Addition to microfibril tension

Follows from #

Extension at critical stress

30%

End of yield region

Follows from #

Ideal max’m extension

40%

Limiting extension if no cross-link failure

Follows from #

Actual max’m extension

50%

Fibre break extension and strength

Greater than ideal max’m due to cystine bond break

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Wool: Science and technology

0 8.3 27.5 41.0

Stress (108 dynes/cm2)

25

20

100% R.H. 68.0

84.4

15

10

5

0

10

20

30 Strain (%)

40

50

60

4.40 Predicted matrix stress–strain curves at different humidities. Dotted lines are interpolated between calculated curves from model. [From Hearle et al.37]

stress–strain curve to the setting strain, as shown in Fig. 4.41(a). Application of a sequence similar to that shown in Fig. 4.34 gives the new stress–strain curve, shown in Fig. 4.41(b). The positions of the points A and B are found to be the same as in the experimental curves of Fig. 4.34, but something different happens in the low-stress region. Visco-elasticity in dry wool in the Hookean region is explained by the progressive breakage of hydrogen bonds in the matrix due to thermal vibrations. This will be intensified at larger strains. If the thermal and chemical conditions are right, other bonds, such as cystine cross-links, will also show time-dependent breakage. The lowering of the critical condition for the a Æ b transition due to thermal vibrations, as shown in Fig. 4.36(a), is another source of time-dependence. Detailed theoretical treatments of these effects follow the classical visco-elastic models, either in their mathematical formulations26 or by adding viscous elements to the computation of the two-phase model.46 By adjusting parameters, it is possible to fit experimental results, but more detailed understanding and modelling is needed in order to derive predictions from first principles.

4.4.3 The ortho-cortex and fibre crimp The two-phase model with fibrils parallel to the axis of the fibre, as shown in Fig. 4.35, and the subsequent treament of the fibre mechanics, applies

Physical properties of wool Stress

115

Original

X

Y

Strain

Stress (Arb.units)

(a)

15 X 10 Original

Y

Setting strain A A'

B

5 X

(b)

0

10

B'

Y 20 30 Strain (%)

40

4.41 (a) Postulated changes in matrix stress–strain curve after setting. (b) Calculated behaviour of set fibres. [From Hearle et al.37] Note: The X lines, which do not give a reasonable prediction, follow a vertical shift of the stress–strain curve; the Y lines with a horizontal shift give a prediction similar to the experimental results.

strictly only to the para-cortex of wool and, with some detailed modification of input parameters, to the meso-cortex. In the ortho-cortex of wool, the IFs (microfibrils) are bundled together in macrofibrils. Electron microscope pictures show circular IF cross-sections at the centres of macrofibrils, becoming increasingly elliptical towards the circumference. This implies that the IFs and the associated matrix follow helical paths in the macrofibrils. Electron microscope tomography47 enables quantitative measurements of twist angles to be made. The structure is like that of a twisted yarn. Similar theory will apply, though account must be taken of the shear stress between IFs and this will lead to a change in tensile properties, which can

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be approximated as a reduction of stress at a given extension by the factor cos2 a, where a is the twist angle at the surface of a macrofibril. A more important consequence is the influence of dimensional changes associated with moisture content, as analysed by Munro and Carnaby.48 The simplest assumption is that the wool fibre is straight when wet, since this is the state in which it is formed. The IFs are then widely separated by the swollen matrix. Drying the fibre will cause a lateral contraction that will reduce the twist angle and cause the macrofibril to extend. The increased stress-free length of an isolated macrofibril would depend on a balance of contraction at the circumference and extension at the centre. However, on the other side of the wool fibre, the lateral contraction of the para-cortex will not cause any extension, because the IFs are parallel to the fibre axis. Consequently, the fibre acts like a bimetallic strip and bends to minimise the deformation energy. The longer orthocortex will take the outside of the bend and the shorter paracortex the inside, as is observed experimentally.49,50 This is the source of crimp in wool fibres. There is some uncertainty about the detail of the helical form. If the ortho–para boundary rotates along the fibre, it would automatically generate a helix. However, if the boundary remains in the same transverse direction, the minimum energy state would be a tight coil, but, to form this from the straight fibre, it is necessary for the fibre to twist. If twisting is allowed, the intermediate state at a given fibre length would be a unidirectional helix; if it is not, alternating right- and left-handed helices would form, as in bicomponent synthetic fibres.

4.4.4 Fibre strength and the cell membrane complex On the Chapman model, as described in Section 4.4.2, the matrix would break at a lower extension than the IFs, and would trigger fibre breakage at around 50% extension. However, the wool fibre is a composite at a number of levels, and it is likely that the system of cells bonded together by the cell membrane complex (CMC) plays a part in determining the form of breakage. Once a crack started in the matrix of one cell, it would be expected to propagate across the cell. The CMC will act as a weak bond, which, as in fibre composites, blocks crack propagation. However, there will be stress transfer from the ruptured cell to neighbouring cells, which causes them to break in a nearby region. This gives rise to the granular breaks shown in Fig. 4.26. The above argument applies to the intrinsic strength, which gives the upper bound in Fig. 4.25. There are many possible causes of lower values of strength. As already mentioned, if the fibre is variable, failure at the weakest link will give a lower apparent strength when related to the average

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117

fibre thickness. Lower intrinsic strength will result from any damage or defects in the fibres. Weakness in the CMC is another, more fundamental, possibility.51 For short fibre composites, the strength is reduced, compared to a system without slip, by a slippage factor SF, which is given by equation [4.3]: SF = 1 - (1/4)(S/B)(D/L)

[4.3]

where S is the tensile strength of the cell, acting as a short fibre in the composite, B is the bond strength of the CMC between cells, D is the cell diameter and L is the cell length. In ‘good wool’, with B reasonably high and (D/L) small, SF should be close to 1, but, if there are thick, short cells with weak CMC, then there will be appreciable loss of strength. The slippage effect will be greater in the transverse direction when (D/L) is equal to one. This is the most likely cause of the yielding in transverse extension of porcupine quill, as found by Feughelman and Druhalla.27 Breakdown of the CMC will lead to the multiple split ends that are often seen in failure of wool in fatigue situations. The transverse axial cracks are a natural consequence of the buckling of aligned elements within the structure.52

4.4.5 Fibre friction and the scales Qualitatively, the scales on the wool fibre would be expected to give a ratchet-like action, due to scales interlocking with one another or catching on asperities on a surface. This would give rise to the directional frictional effect. Figure 4.42 shows the various possible interactions, and from the geometry it is intuitively obvious that motions against scales, Fig. 4.42(b,d), will give more resistance than with scales, Fig. 4.42(c,e). For fibres in the same direction, Fig. 4.42(a), the friction will have an intermediate value. Lincoln53 has given a more detailed analysis based on the components of normal load and frictional force, as shown in Fig. 4.43(a). If F is the frictional force and N is the normal load, Amontons’ Law, F = mN, has a constant coefficent of friction m. Polymeric fibres are generally found to follow a power law: F = aNn. This formulation implicitly assumes that the normal load and frictional force are respectively perpendicular and parallel to the surfaces, both locally and generally. For the scales on wool, this is not so. In Fig. 4.43(a), W and F are the components related to the overall surface, N and P are the components related to the local plane of contact, which makes an angle q with the overall surface plane. Putting P = aNn, the forces are related by equation [4.4].

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Tip

Root (a)

(b)

(d)

(c)

(e)

4.42 Directional friction in wool: (a) between fibres lying in same direction; (b) between fibres against scales; (c) between fibres with scales; (d) on plane surface against scales; (e) on plane surface with scales. [From Morton and Hearle.5]

F cos q - W sin q = a(W cos q + F sin q)n

[4.4]

The frictional force increases rapidly as q goes from negative values, i.e. moving away from the slope, to positive values, as in Fig. 4.43(a). Contact with a wool fibre as shown in Fig. 4.43(b) will have different angles, depending on which part of the scale is in contact. These may be simplified as a saw-tooth with two angles, a and b. Combining positive and negative values of a and b, as appropriate, leads to the frictional forces shown in Fig. 4.43(c), in which the mean force against the scales is higher than the mean force with the scales.

4.5

Electrical properties

4.5.1 Dielectric constant and loss factor At the base level for dry wool, the dielectric constant of wool is about 1.5, and this will result from dipolar groups in the protein and other molecules. In practice, the major influence is that of water. H2O is a permanent dipole, and its orientation in an electric field determines the dielectric constant e. The lag in responding to an alternating field determines the loss factor tan d. The structural features that influence these values are the amount of absorbed water and the firmness with which it is bound; the test conditions that change the values are frequency and temperature. A measurement problem is that the only easy way to measure dielectric properties is on a fibre assembly. Hearle7,54 made tests on yarns wound

Physical properties of wool W

Motion

N

R

119

F

q F

P

With scales

(a) W

W -b

a

b

-a

0 +a

Against scales q +b

a (b)

b

(c)

4.43 (a) Frictional contact at an angle to the overall surface. (b) Different angles of contact on wool scales. (c) Combined effect with and against scales. [From Morton and Hearle.5]

between two cones. The results are shown in Fig. 4.44. The dielectric constant and power factor rise steeply at higher moisture contents and lower frequencies.

4.5.2 Electrical resistance Electrical current in wool is carried either by charged ions present as impurities or by the mobility of protons in hydrogen bonds. According to a theory by Hearle55, only dissociated ions are free to move, and the degree of dissociation depends on the dielectric constant e through its influence on the dissociation energy of two charged particles. Application of the Law of Mass Action leads to equation [4.5]: log R = (A/e) + B

[4.5]

where R is the electrical resistivity and A and B are constants. Changes in e cause orders-of-magnitude changes in resistance, because of the logarithmic dependence. Empirically, it was found that at higher values of moisture content M, log R varied linearly with log M. Figure 4.45 shows the variation of resistance with moisture content and compares the theoretical and experimental results. Up to about 6% moisture content, the resistivity of wool is constant with a value over 1012 ohm cm or, in mass terms, 1012 ohm g/cm2. The drop in resistance starts at a higher moisture content than in cotton and this reflects the way in which the first absorbed water is firmly bound. A comparison against relative humidity is shown in Fig. 4.46. Wool lies between the more conductive cellulose fibres and the less conductive synthetic fibres.

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64% R.H.

4

0.4 cosf

em

64% R.H.

47% R.H. 0% R.H.

2

0.2

47% R.H. 0% R.H. 0

0.1

1

a)

100 10 f kc/s

0

0.1

1

10 100 f kc/s

3.0 em a 2.5 b c

d e f g

2.0

0.1 tan d

a

0.05

cb d

h i 1.5 b)

0.1

1.0

f Mc/s

10

0

i 0.1 3¢s

e f g h

10

1.0

f Mc/s

4.44 Dielectric constant and loss factor of wool yarns with a packing factor of 52–53%. (a) By bridge method at lower frequencies7 (the loss is expressed by the power factor cos f, which equals sin d); (b) By a resonance method at higher frequencies.54

Physical properties of wool

121

14

y Log Rs or e–r + c

12

Wool

10 Cotton 8 6 4 1.9

0.1

0.3

0.5

0.7 Log M

1.1

0.9

1.3

1.5

4.45 Log–log plot of resistance against moisture content, showing a comparison of experimental values (full lines) and theoretical predictions from equation [4.5] (dotted lines). [From Morton and Hearle.5]

14

Acetate

12 Log Rs

Terylene

Nylon

Orlon Silk

10 Wool 8 Cotton

Viscose

6 4 10

20

30

40 50 60 70 Relative humidity (%)

80

90

4.46 Plot of resistance on a logarithmic scale against relative humidity for a variety of fibres. [From Morton and Hearle.5]

4.5.3 Static electrification Static electricity is easily generated when two different surfaces are separated. Typically this occurs in rubbing or in walking on wool carpets. A determining factor in the detection of static charging is how fast the charge can leak away. If the material is a perfect insulator, the limiting charge is given by conduction across the gap between the surfaces as they separate but, if the material is a moderate conductor, conduction can occur back through the material to the unseparated region. If the material is a good conductor, all the charge can flow back and none is left on the material. For practical time scales, static charges begin to drop from the maximum

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limiting value when the resistivity falls to 1010 ohm cm, and will be very small below 106 ohm cm. The values in Fig. 4.46 show that wool will suffer from appreciable static charging below 60 to 70% RH. Static electrification is described in detail by Morton and Hearle.5

4.6

Yarns and fabrics

4.6.1 Structural mechanics of fibre assemblies In general terms, the mechanics of wool yarns and fabrics follows treatments that are common to all textiles. These are described in books.56,57 An account that is specifically related to wool is given by Postle et al.26 Hearle58 includes nonwovens. The extensive work on fabric hand and the KES-F testing system, which is particularly relevant to the effects of finishing of wool fabrics, has been reviewed by Kawabata and Niwa.59 In addition to the particular tensile and other properties, the special features of wool are fibre crimp, which leads to high bulk and softness, and scales, which lead to felting. Good recovery properties are also beneficial, and especially the regeneration of properties by washing. Setting, whether temporary by drying or permanent by chemical cross-linking, maintains the form of yarns, fabrics and garments.

4.6.2 Wool yarns Most wool yarns are twisted structures. Twist, or the alternative of entanglement by felting, is necessary to hold staple fibres together. The effect of obliquity is to reduce the stress at a given extension, but wrapping round in a curved path generates transverse pressure and hence axial friction, which grips the fibres. An approximate analysis56 gives the effect on the yarn stress–strain curve in terms of the surface twist angle a and a factor k that depends on the resistance to slip: (yarn stress at given extension/fibre stress at same extension) = cos2 a(1 - k cosec a) [4.6] The first term is the direct effect of obliquity. The second term is the reduction in stress due to slip from fibre ends. The factor k is proportional to 1 (a Q/mL2) /2. This shows the more effective gripping of fibres with small radius a, large length L, and high coefficient of friction m, in yarns with a short migration period Q and high twist a. The twist is given in operational terms by: 1

tan a = 0.0112(1/jr)C /2T

[4.7] 3

where j is the packing factor, r is fibre density in g/cm , C is yarn linear density in tex, and T is twist in turns/cm.

Physical properties of wool

123

As (1 - k cosec a) decreases from a limiting value when k cosec a << 1, the central length of fully gripped fibre becomes smaller. Equation [4.6] breaks down below (1 - k cosec a) equal to 1/2. The fibres are no longer fully gripped anywhere and there is cumulative slippage.This is the turnover condition between self-locking yarns and draftable rovings. Figure 4.47(a) gives examples of the stress–strain curves for worsted and woollen rovings twisted on a laboratory twister60, and Fig. 4.47(b) gives a comparison of the experimental values of modulus and strength with values predicted from equation [4.6] with fitted values of k. The more irregular woollen structure does not fit the theory and is much weaker than the worsted structure. Modulus results for the worsted yarn can be fitted to equation [4.6], but the strength values require an additional numerical factor, which reflects a higher effective fibre strength in yarns than in fibre tests. A more detailed theory for wool yarns in which there is negligible slip from fibre ends is given in Postle et al.26 This takes account of the bulkiness of wool yarns, and the reduction in volume during extension as the outer fibres compress the underlying structure. The shortest path hypothesis provides a useful procedure. Because fibres are slender, the energy needed to bend and twist them is small and can be neglected, so that they take up the shortest available path. Once a fibre has been pulled into such a path, any further yarn extension requires fibre extension, which is much more strongly resisted and dominates the deformation energy. Following the early work of Carnaby and Grosberg,61–63 a number of more detailed analyses have been made using more elaborate mathematical and computational techniques. However, the underlying difficulty is to have an adequate description of the complex fibre arrangement in wool yarns, which can have a major influence on when the structure jams so that fibres are forced into extension. The more difficult problem of the formation of yarn structure needs to be solved as a prelude to analysing the mechanics of the structure.

4.6.3 Fabric mechanics Postle et al.26 provide a full account of work on the mechanics of woven and knitted fabrics. In general, deformation under low forces depends on the resistance to bending and twisting of yarns, so that the initial modulus is low. When tensions are high enough to straighten yarns or jam the fabric, the forces increase and follow the resistance to yarn extension. Because fabrics are thin, they have a low bending resistance. However, the double curvature needed for good drape and handle also requires in-plane deformation.64 This is found in woven fabrics by a trellis action, which gives very low resistance to shear, and in knitted fabrics by the loop structure, which gives a low resistance in all directions.

3

20

1 Specific stress (g wt/tex)

Fiber

15°

2 g/tex

10°

15 0

2

4

6 % 8 No.1

No.2

Fiber

10

35°

5 15°

30°

40°

20°

40° 35° a = 50° 30° 25° 20° 15°

a = 50°

10°

(a)

20

0

60

40

0

20

40

60

Extension (%)

Yarn/fibre ratios

1·0

0·5

(b) 0

20

40

60

Helix angle a (°)

4.47 a) Stress–strain curves of fibres and twisted rovings. No. 1 – worsted. No. 2 – woollen. (b) Comparison of theory and experiment. No. 1 – worsted. Yarn modulus: black circles, experimental; short dash line, theoretical plot of cos2 a(1 - 0.133 cosec a). Yarn strength: open circles, experimental; long dash line, theoretical plot of 2.3 cos2 a(1 0.24 cosec a). No. 2 – woollen. Yarn modulus: black triangles, experimental. Yarn strength: open triangles, experimental. The two lines coming down from top left are for two theories of effect of obliquity without slip. [From Hearle and EL-Sheikh.60]

Physical properties of wool

125

An aspect of particular importance to wool fabrics is the relaxed state of the fabric. After manufacture or finishing, the fabric will have certain dimensions, but relaxation will change these. For knitted fabrics, Munden65 defined two relaxed states: dry-relaxed for fabrics allowed to recover from knitting stress for at least 24 hours; wet relaxed after wetting and subsequent conditioning. Wrinkling, creasing and crease recovery in wool fabrics, which involve the bending response of wool fibres, have been modelled by Chapman.66,67 Wool is used in needled nonwoven fabrics, in which the fibre arrangement generates the friction to provide fabric strength. The active geometry consists of curved fibre paths in the plane of the fabric passing round the ‘pegs’ (tufts of fibres) that result from the needling action.68 Needled fabrics are necessarily rather thick and, if they are to be stable self-locking structures, must be compacted, so they lack low in-plane resistance and therefore are limited in drape capability. Felts are a long-established form of wool fabric, made possible because of the directional frictional effect in wool (see Section 4.4.5). When a mass of wool fibres is agitated, particularly in hot wet conditions when the fibres are very flexible, each fibre moves in the low-friction direction. The roots move forward followed by the tips – in other words, if the fibre direction is defined as root-to-tip, the fibre as a whole moves progressively backward. Each step involves an increase of interlacing with neighbouring fibres. Eventually a highly interlaced, self-locking felt is produced.

4.6.4 Carpets Wool is used as a carpet fibre because of its bulk, resilience and durability. Carnaby and Wood69 have reviewed the physics of carpets. Important aspects are comfort and compression, appearance retention, and wear resistance. The compression behaviour is determined by the bending and bending recovery of fibres within the carpet pile. An aspect of this related to appearance is the problem of shading, which can cause great concern to customers. It has been shown that this is due to patches of fibres lying in different directions. In some cases, the cause is clear. For example, the movement in turning a corner provides shear forces in a particular direction, which causes the fibres to bend over from their initial direction to follow the shear. Neighbouring regions which are not walked on, or are subject to a symmetrical pattern of treads, will have fibres that remain lying in the original direction. In cases where there is no obvious cause, it is presumed that there is some asymmetric action at an early stage of the use of the laydown or use of the carpet, which causes the pile to reverse, and that this is intensified by subsequent treading.

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Carpet wear has been modelled in terms of fatigue sites that are moreor-less randomly distributed through the carpet pile. This leads to a progressive loss of fibre material. Wear is much more severe in turning-walk trials than in straight walk. The commonest form of fibre breakage is the development of cracks in severely kinked fibres.70

References 1 Preston J M, Modern Textile Microscopy, Emmott, London, 1933. 2 Speakman J B, Cooper C A and Stott E, ‘Wool: moisture relations’, J. Text. Inst., 1936, 27, T183–96. 3 Preston J M and Nimkar M V, ‘Measuring the swelling of fibres in water’, J. Text. Inst., 1949, 40, P674–88. 4 Darling R C and Belding H S, ‘Textile yarns: moisture absorption at low temperatures’, Industr. Eng. Chem., 1946, 328, 524–9. 5 Morton W E and Hearle J W S, Physical Properties of Textile Fibres, 3rd edition, The Textile Institute, Manchester, 1993. 6 Speakman J B, ‘An analysis of the water adsorption isotherm of wool’, Trans. Faraday Soc., 1944, 40, 6–10. 7 Hearle J W S, ‘Capacity, dielectric constant and power factor of fibre assemblies’, Text. Res. J., 1954, 24, 307–21. 8 WIRA, Wool Research Vol 2: Physical Properties of Wool Fibres and Fabrics, Wool Industries Research Association, Leeds, 1955. 9 Feughelman M, Mechanical Properties and Structure of Alpha-keratin Fibres, UNSW Press, Sydney, 1997. 10 Bendit E G, ‘A quantitative X-ray diffraction study of the alpha-beta transformation in wool keratin’, Text. Res. J., 1960, 30, 547–55. 11 Collins J D and Chaikin M, ‘The stress–strain behaviour of dimensionally and structurally non-uniform wool fibres in water’, Text. Res. J., 1965, 35, 777– 87. 12 Collins J D and Chaikin M, ‘Structural and non-structural effects in the observed stress–strain curve for wet wool fibres’, J. Text. Inst., 1968, 59, 379–400. 13 Speakman J B, ‘Intracellular structure of the wool fibre’, J. Text. Inst., 1927, 18, T431–53. 14 Peters L and Woods H J, Protein Fibres in Meredith R (editor), Mechanical properties of textile fibres, North-Holland, Amsterdam, 1956. 15 Chapman B M, ‘A review of the mechanical properties of keratin fibres’, J. Text. Inst., 1969, 60, 181–207. 16 Meredith R, ‘Textile fibres: comparison of tensile elasticity’, J. Text. Inst., 1945, 36, T147–64. 17 Beste L F and Hoffman R M, ‘Resilience of fibres and fabrics: quantitative study’, Text. Res. J., 1950, 20, 441–53. 18 Feughelman M and Robinson M S, ‘Some mechanical properties of wool fibers in the “Hookean” region from zero to 100% relative humidity’, Text. Res. J., 1971, 41, 469–74. 19 Katz S M and Tobolsky A V, ‘Wool fibres: relaxation of stress’, Text. Res. J., 1950, 20, 87–94.

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20 Feughelman M, ‘The creep of wool fibres in water’, J. Text. Inst., 1954, 45, T630–41. 21 Danilatos G and Feughelman M, ‘Dynamic mechanical properties of a-keratin fibers during extension’, J. Macromol. Sci. – Phys., 1979, B16, 581–602. 22 Meredith R, ‘Dynamic mechanical properties of textile fibres’, Proc. 5th Int. Congress in Rheology 1968, University of Tokyo Press, 1969, Vol 1, 43–60. 23 Chapman B M, ‘The bending stress–strain properties of single fibres and the effect of temperature and relative humidity’, J. Text. Inst., 1973, 64, 312–27. 24 Bendit E G and Feughelman M, ‘Keratin’ in Encyclopaedia of Polymer Science and Technology, Vol 8, 1–44, Wiley, New York, 1968. 25 Mitchell T W and Feughelman M, ‘Torsional properties of single wool fibres. Part I: Torque–twist relationships and torsional relaxation in wet and dry fibres’, Text. Res. J., 1960, 30, 662–7. 26 Postle R, Carnaby G A and de Jong S, The Mechanics of Wool Structures, Ellis Horwood, Chichester, 1988. 27 Feughelman M and Druhalla M, ‘The lateral mechanical properties of alphakeratin’, Proc. 5th Int. Wool Text. Res. Conf., Aachen, 1975, 2, 340–9. 28 Hearle J W S, ‘A critical review of the structural mechanics of wool and hair fibres’, Int. J. Biological Macromol., 2000, 27, 123–38. 29 Kawabata S and Kawashima Y, ‘Measurement of the anisotropy in the elastic modulus of cotton and silk fibres’, Proc. 29th Text. Res. Symp., Mount Fuji, 2000, 51–8. 30 Woods J, Orwin D F G and Nelson W G, Proc. 8th Int. Wool Text. Res. Conf., 1990, 557–68. 31 Hearle J W S, Lomas B and Cooke W D, ‘Atlas of Fibre Fracture and Damage to Textiles’, 2nd edition, Woodhead Publishing, Cambridge, 1998. 32 Baxter S, ‘Textiles: thermal conductivity’, Proc. Phys. Soc., 1946, 58, 105–18. 33 Haly A R and Snaith J W, ‘Specific heat studies of various wool–water systems’, Biopolymers, 1968, 6, 1355–77. 34 Phillips D G, ‘Detecting a glass transition in wool by differential scanning calorimetry’, Text. Res. J., 1985, 55, 171–4. 35 Chapman B M, ‘Observations on the mechanical behaviour of Lincoln-wool fibres supercontracted in lithium bromide solution’, J.Text. Inst., 1970, 61, 448–57. 36 Feughelman M, ‘The mechanical properties of set wool fibres and the structure of keratin’. J. Text. Inst., 1960, 51, T589–600. 37 Hearle J W S, Chapman B M and Senior G S, ‘The interpretation of the mechanical properties of wool’, Appl. Polymer Symp., No. 18, 1971, 775–94. 38 Feughelman M, ‘Two-phase structure for keratin fibres’, Text. Res. J., 1959, 29, 223–8. 39 Curiskis J I, ‘A study of the micromechanics of fibrous reinforced composite materials using finite-element techniques’, PhD thesis, University of New South Wales, 1978. 40 Curiskis J I and Feughelman M, ‘Finite element analysis of the composite fibre, alpha keratin’, Text. Res. J., 1983, 53, 271–4. 41 Chapman B M, ‘A mechanical model for wool and other keratin fibres’, Text. Res. J., 1969, 39, 1102–9. 42 Feughelman M and Haly A R, ‘The mechanical properties of wool keratin and its molecular configuration’, Kolloid Z., 1960, 168, 107–17.

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43 Wortmann F-J and Zahn H, ‘The stress–strain curve of a-keratin fibers and the structure of the intermediate filaments’, Text. Res. J., 1994, 64, 737–43. 44 Feughelman M, ‘A model for the mechanical properties of the a-keratin cortex’, Text. Res. J., 1994, 64, 236–9. 45 Bendit E G, ‘Quantitative X-ray diffraction of the a-b transformation in wool keratin’, Text. Res. J., 1960, 30, 547–55. 46 Hearle J W S and Susutoglu M, ‘Interpretation of the mechanical properties of wool fibres’, Proc. 7th Int Wool Text. Res. Conf., Tokyo, 1985, 1, 214–23. 47 Bryson W G, Mastronarde D N, Caldwell J P, Nelson W G and Woods J L, ‘High voltage microscopical imaging of the macrofibril ultrastructure reveals the threedimensional spatial arrangement of intermediate filaments in Romney wool cortical cells – a causative factor in fibre curvature’, Proc. 10th Int. Wool Text. Res. Conf., Aachen, 2000 (on CD from DWI, Aachen). 48 Munro W A and Carnaby G A, ‘Wool-fibre crimp. Part I: The effects of microfibrillar geometry’, J. Text. Inst., 1999, 90, 123–36. 49 Horio M and Kondo T, ‘Crimping of wool fibres’, Text. Res. J., 1953, 23, 373–87. 50 Mercer E H, ‘The heterogeneity of the keratin fibers’, Text. Res. J., 1953, 23, 388–97. 51 Hearle J W S, ‘Can genetic engineering enhance the miracle of wool? Part 3: Why worry about fibre strength?’ Text. Horizons, 1997,August/September 12–16. 52 Hobbs R E, Overington M S, Hearle J W S and Banfield S J, Buckling of fibres and yarns within ropes and other assemblies, J. Text. Inst., 2000, 91, 335–58. 53 Lincoln B, ‘The frictional properties of the wool fibre’, J. Text. Inst., 1954, 45, T92–107. 54 Hearle J W S, ‘The dielectric properties of fibre assemblies’, Text. Res. J., 1956, 26, 108–11. 55 Hearle J W S, ‘The electrical resistance of textile materials: IV. Theory’, J Textile Inst, 1953, 44, T177–98. 56 Hearle J W S, Grosberg P and Backer S, Structural Mechanics of Fibers, Yarns and Fabrics, Wiley-Interscience, New York, 1969. 57 Hearle J W S, Thwaites J J and Amirbayat J, Mechanics of Flexible Fibre Assemblies, Sijthoff & Noordhoff, Alphen an den Rijn, Netherlands, 1980. 58 Hearle J W S, ‘Mechanics of yarns and nonwoven fabrics’, in Chou T-W and Ko F K (editors) Textile Structural Composites, Elsevier, Amsterdam, 1989. 59 Kawabata S and Niwa M, ‘Fabric performance in clothing and clothing manufacture’, J. Text. Inst., 1989, 80, 19–51. 60 Hearle J W S and El-Sheikh A, ‘The mechanics of wool yarns’, Proc. 3rd Int. Wool Text. Res. Conf., Paris, 1965, IV, 267–76. 61 Carnaby G A and Grosberg P, ‘The tensile behaviour of staple-fibre yarns at small extensions’, J. Text. Inst., 1976, 67, 299–308. 62 Carnaby G A and Grosberg P, ‘The mechanics of the relaxation of wool carpet yarns. Part I: Theoretical analysis’, J. Text. Inst., 1977, 68, 24–32. 63 Carnaby G A and Grosberg P, ‘The mechanics of the relaxation of wool carpet yarns. Part II: Experimental evaluation of theory’, J. Text. Inst., 1977, 68, 33–6. 64 Amirbayat J and Hearle J W S, ‘The anatomy of buckling of textile fabrics’, J. Text. Inst., 1989, 80, 52–70. 65 Munden D L, ‘The geometry and dimensional properties of plain-knit fabrics’, J. Text. Inst., 1959, 50, T448–71.

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66 Chapman B M, ‘A model for the crease recovery of fabrics’, Text. Res. J., 1974, 44, 531–8. 67 Chapman B M, ‘The relationship between single fibre bending behaviour and fabric wrinkle recovery’, Proc. 5th Int. Wool Text. Res. Conf., Aachen, 1975, III, 483–92. 68 Hearle J W S, ‘A theory of the mechanics of needled fabrics’, in Lennox-Kerr (editor), Needle-felted Fabrics, The Textile Trade Press, Manchester, 1972, 51–64. 69 Carnaby G A and Wood E J, ‘The physics of carpets’, J. Text. Inst., 1989, 80, 71–90. 70 Hearle JWS, Liu H, Tandon S K and Wood E J, ‘Fibre Fatigue mechanisms in wool carpet near and the modelling of carpet durability’, Proc. 10 th Int. Wool Text. Res. Conf., Aachen, 2000 (on CD from DWJ, Aachen).

5 Wool chemistry W S SIMPSON

5.1

General introduction

This chapter describes the effects of radiation and heat on wool and its response to acids, alkalis, oxidants, reductants, followed by a brief treatment of specific reactions of its amino acid side chains. Chapter 7 is basically concerned with chemical modifications of wool designed to enhance one or more textile attributes such as flame-resistance. Over the full range of wool types, fibre diameters vary between about 10 and 80 mm. Diffusion of reactant chemicals from an immersion solvent, which most commonly is water, may be slow. In addition to fibre diameter variations, diffusion is also moderated by the hydrophobic epicuticle on the external face of wool scale cells, with the path of least resistance usually along the junctions between these cells and the interior cortical cells. Within each cell there are more variations in protein organisation, resulting in micro-heterogeneous regions of both hydrophobic and hydrophilic character. A direct result of these complex variations in wool morphology is that kinetics of diffusion and polarity of the reactants may be at least as important as inherent reactivity. For example, highly reactive chlorine water preferentially attacks the surface of wool fibres within seconds, whereas immersion in an excess of cold dilute acid could take an hour or more to achieve an equilibrium uptake. Provided the constraints to diffusion are taken into account, the chemical reactions of amino acid sidechains of wool proteins are consistent with those of proteins in general. Cystine (CYS) crosslinkages are a special feature of keratin fibres. Reactions of CYS with oxidants and reductants are of major importance, being an integral part of the chemistry involved in isolating wool proteins, in the physical behaviour of wool, and in technical processes such as shrinkproofing and bleaching. CYS is also one of the amino acids principally affected by radiation and heat, as described in Section 5.3. 130

Wool chemistry

5.2

131

Chemical composition

Wool is one of a large group of animal fibres that are almost entirely composed of a family of proteins generally known as a-keratins. Although there are some chemical variations between species, there are also remarkable similarities of structure and composition between comparable types of proteins in animal fibres. The physical form of keratin fibres is as diverse as porcupine quills, various horns and antlers, and extremely soft fine coats of small mammals such as the mouse. The overall amino acid composition of keratins depends, to a large part, on the relative proportions of the two major types of protein, namely the high- and low-sulphur proteins (see Chapter 3). Merino wool, for example, has a notably higher cystine (CYS) content than coarse wools as a result of having a larger proportion of high-sulphur proteins. One of the earliest reliable amino acid analyses was that of Corfield and Robson.1 It remains an adequate description of wool composition and is reproduced in Table 5.1.

5.3

Degradation by radiation and heat

Most of the radiation chemistry of wool is concerned with the effects of exposure to sunlight. Weathering during wool growth varies greatly according to the type of fleece. A dense, fine wool Merino fleece is damaged almost exclusively at staple tips, with heavy secretions of woolgrease and suint contributing to the protection. Coarse open fleeces are more generally exposed to sunlight. Severe weathering implies brittle fibre tips, loss of staple strength and dull or yellow discolouration. Photo-oxidation of CYS is the most damaging reaction, weakening the fibre. Other residues extensively damaged by prolonged exposure to sunlight are TYR, TRP, PHE, THR, MET, ILEU, LEU, PRO and HIS. Additional carbonyl and amide groups are formed following cleavage of the peptide N–Ca bond, as shown in equation [5.1]. R

R¢

hu

CH C

NH CH C

O

O

O

R

R¢

CH C O

NH2 +

C

C

O

O

[5.1]

This reaction is implicated both with fibre strength loss and subsequent susceptibility to hydrothermal yellowing (Section 7.3). Meybeck and Meybeck2 suggested that aromatic amino acids absorb UV light and, after energy transfer to glycine and alanine, there is a photochemical conversion to glyoxylyl and pyruvyl peptides according to the mechanism of equation [5.2].

132

Wool: Science and technology R C

NH CH C

O

O

hu R

C R C O

O2

NH C

C

O

+ H

O R

C

C

OO O

O

NH C

R C O

NH C

C

C

OOH O

N

C

C

+ H

[5.2]

O H2O NH2 + R C

O

C

O O

R C O

NH C

C

OH O

The intermediate structures on the left-hand side arise from further H atom transfers with additional wool protein chains. Minor amounts of other a-ketoacids are detectable in wool following irradiation in the dry state. Few carbonyl groups are detectable when wool is irradiated in water, despite pronounced yellowing. Photochemical damage also increases the susceptibility of wool to discolouration when subsequently exposed to dry heat. Even undamaged wool will develop brownish discolouration when exposed to temperatures over 110 °C for a prolonged period. Just as the dry heat yellowing of silk has been attributed to a dehydration reaction of the SER side chain, similar dehydrations leading to unsaturated carbon bonds have been suggested as the principal source of dry heat discolouration of wool.3

5.4

Photobleaching and photoyellowing

In Section 5.3, photochemical degradation has been implicated in sensitising wool to subsequent discolouration when boiled, as in dyeing, or exposed to dry heat. Depending on the conditions of exposure, sunlight may either yellow wool or bleach it. Irradiation of wool in ambient conditions with 254 nm UV light, causes wool to appear green, due to formation of two chromophores, which fade rapidly in post-irradiation reactions to leave a residual yellow colour.4 Irradiation of wool with different UV wavebands selected from sunlight or artificial sources5 demonstrated that UV below 331 nm increases wool yellowness, whereas visible light above 398 nm induces photobleaching. In the transition range, neither effect is markedly dominant

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133

Table 5.1 Amino acid composition of wool [From: Corfield and Robson1] Amino acid

Abbreviation

Alanine

ALA

Amide N Arginine

N as % of total N of wool 4.12 6.73

ARG

19.1

Aspartic acid

ASP

4.38

Cystine

CYS

7.3

Glutamic acid

GLU

8.48

Glycine

GLY

6.29

Histidine

HIS

1.91

iso-Leucine

ILEU

2.44

Leucine

LEU

5.85

Lysine

LYS

3.92

Methionine

MET

0.32

Phenylalanine

PHE

2.12*

Proline

PRO

5.05

Serine

SER

8.66*

Threonine

THR

5.12*

Tryptophan

TRY

0.82

Tyrosine

TYR

2.62

Valine

VAL

4.16

Total

99.39

* Corrected by the factors 1.02, 1.10, 1.09 for PHE, SER and THR respectively for loss during hydrolysis.

although physical damage to the wool is strongly promoted by these intermediate wavelengths. Window glass absorbs radiation shorter than 305 nm so that wool carpets and furnishings exposed to transmitted sunlight noticeably whiten and brighten due to photobleaching of the wool substrate. Control measures for shade changes are described in Section 7.8. Photobleaching by visible light has been considered as an alternative to chemical bleaching,6 and this idea has been extended to evaluating bluelight sources for wool bleaching. Wet wool bleaches more rapidly than in the air-dry state, and King showed that thioglycollic acid enhanced still further the rate of photobleaching,7 but the chemical residues are troublesome. More dramatic photobleaching results from blue-light irradiation of wool soaked in a dilute hydrogen peroxide solution. If the solution is also made alkaline, extraordinary levels of whiteness can be attained within a minute or so.8 The results were sufficiently encouraging to develop a prototype bleaching machine for continuous treatment of wool sliver. Indus-

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Wool: Science and technology

trial take-up of this technology has not occurred, quite probably because manufacturers would prefer raw material improvements to be the responsibility of wool suppliers, particularly as in this instance a substantial investment is required for equipment that, in turn, requires specially trained operators. Major research efforts have been devoted to understanding the chemistry underlying photoyellowing. The summary of much of this work9 highlights the problems of assigning yellowness to specific chromophores. TRP was long regarded as the most reactive aromatic absorber, with some known yellow decomposition products. One of the earliest correlations was found to be between the TRP content of a range of keratins and their rate of yellowing when irradiated at 310 nm in the dry state.10 More direct evidence was derived by radiolabelling TRP in wool, prior to UV irradiation. After solubilising the wool by reduction, alkylation and proteolytic digestion, a radioactive yellow fraction was isolated by ionexchange chromatography.11 Recent attempts to isolate and identify the yellow components of wool, however, exclude the possibility that TRP decomposition products are the main contributors.9 The principal reason is that most of the known products of TRP degradation, including the major one, kynurenine, are colourless, and the minor coloured products such as N-formylkynurenine are very weak chromophores. Semi-quantitative calculations were sufficient to suggest they could not account for more than 20% of wool yellowness. Isolation and characterisation of yellow wool components entails a difficult first step, i.e. solubilising wool in a manner which neither destroys them nor introduces new artifactual coloured compounds. Wool sufficiently damaged to be significantly yellow is inherently unstable, and dissolution with strong acid or alkaline treatments is visibly accompanied by substantial additional yellowing.9 Simpson9 found papain/bisulphite treatments were also questionable because a significant amount of enzyme is introduced as a contaminant. The pale yellow material in the solution of wool extracts is apparently destabilised by the reducing agent and the colour tends to bleach on standing and often disappears entirely within a day or so. Simpson9 considered the most satisfactory method was dilute acid hydrolysis at 60–80 °C for several days. Almost all the yellow colour was released in the first 5–10% of the wool to be solubilised, and, following a series of enzyme hydrolyses and chromatographic separations, the yellow fractions could be substantially purified. The main fraction was hydrophobic and was eluted from a reverse-phase chromatographic column as three components of very similar amino acid composition, optical density profile and very weak fluorescence. They appeared to be different levels of polymerisation of peptides, notable for very high proline content, about 22 mol %, and low in aromatic amino acid content.

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135

Small proline-rich proteins (sprs) have been found in the cornified cell envelope of keratins and in the epidermis of many mammalian species,12 and are notable for very low amounts of the aromatic acids TRP, TYR and PHE.These proteins are claimed to be particularly associated with wool epicuticle (Section 3.3.1). A major portion of wool yellowness thus appears to be derived from a minor wool protein. The method of extraction and purification results in a kind of hydrophobic complex, resistant to complete enzymatic hydrolysis. In pure aqueous solutions for example, the coloured material condenses into dark brown treacle-like droplets. A yellow-brown solution is restored by addition of methanol but alcoholic solutions are incompatible with further enzymatic hydrolyses. Another aspect of interest in this investigation9 was the chromatographic separation of the high-proline fractions from a high-TYR/GLY fraction that was completely colourless. A clear, yellow component representing perhaps 10% of the total colour was also retrieved, which had fluorescence and optical density properties suggestive of a TRP degradation product incorporated in a mixture of chromatographically similar peptides.

5.5

Absorption of acids

At room temperature, immersion of wool in aqueous solutions of strong acids or alkalis is essentially an ion-exchange titration of the 0.8 mM/g of both carboxyl and amino groups on amino acid sidechains. Ionic interactions between —COO- and —NH4+ groups play an important part in stabilising the protein structure of wool in the vicinity of its isolectronic point at about pH 6.5. Equilibration in an excess of either acidic or alkaline solution is slow, particularly in the pH 3–10 range, where a time of the order of an hour is required even with regular agitation of the solution. Equilibrium rates are slow as a consequence of an electronic barrier formed at fibre surfaces, following an initial absorption, and can be greatly reduced by addition of a neutral salt. Figure 5.1 illustrates the effect of adding KCl on the shape of the titration curve of wool with HCl and KOH.13 There has been considerable interest and effort devoted to providing a theoretical understanding of the acid/base behaviour of wool fibres. Essentially, wool is a fine example of a highly consolidated protein whose behaviour might usefully be compared to soluble proteins of similar acidic and basic amino acid content. The latter have titration characteristics more akin to simple acids and bases. The two principal theoretical models for absorption of acids and bases by wool are those of Gilbert and Rideal,17 and of Donnan. Both have been critically examined in several textbooks.14–16 In the light of current knowledge, the former has been the most successful in terms of prediction of wool titration behaviour, and an abbreviated account of its application follows.

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Wool: Science and technology

KOH-Millimoles per gram dry wool-HCl

0.8

Ionic strength 0.2 Ionic strength 0.02 No salt

0.6 0.4 0.2 0 0.2 0.4 0.6 0.8 1

3

5

9

7

11

13

PH

5.1 Combination of wool with hydrochloric acid and with potassium hydroxide as a function of pH. The influence of a salt on shifting the acidic side of the curve is shown. [From Steinhardt and Harris.13]

Gilbert and Rideal17 made these assumptions: i)

All positively charged groups (mainly amines) have identical properties. ii) All carboxylic groups have similar affinities for protons. iii) Absorbed anions may occupy any positively charged site. Thus, the anions and protons in an aqueous solution can be regarded as being independently absorbed by immersed wool samples. The only other formal requirement of the theory is that electrical neutrality of the fibre must be maintained. The thermodynamic analysis that followed culminated in their well-known equation for titration of wool with hydrochloric acid. log10

(Dm H + Dm Cl ) qH = - pH 1 - qH 4 ◊ 6RT

[5.3]

(qH is the fraction of sites filled by protons, and the final term incorporates changes in the chemical potential of hydrogen and chloride ions respectively). Steinhardt and Harris13 were able to confirm that the equation did fit the experimental data for the titration of wool with hydrochloric acid. More

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137

significantly still, if sodium chloride is added so that the titration is carried out at essentially constant ionic strength, Gilbert and Rideal derived the secondary equation pH 0.5 = log10 [Cl] -

Dm H + Dm Cl 2◊3RT

[5.4]

The subscript 0.5 refers to an equilibrium pH, when half the proton binding sites are filled. When the chloride concentration is increased, so also is the pH at the point of half saturation. Therefore, less acid is required to achieve a given equilibrium pH when the chloride concentration is increased. It becomes difficult to extrapolate this result in a quantitative fashion for more complex wool–acid–salt combinations, but this basic result is a fundamental factor in devising good conditions for processes such as wool dyeing. Stated in the simplest terms, it affords a scientific basis for the advantages of adding salts in order to raise the ionic strength of dyebaths. This approach is taken further in Section 5.6. Long exposure at room temperature to an excess of strong acid will hydrolyse some of the amide groups in wool, releasing ammonia and creating additional carboxylate groups, thereby increasing the measured acid uptake of wool. At pH values greater than 11, alkaline degradation reactions of cystine and peptide bond hydrolysis become increasingly likely for even brief exposure at room temperature. Acids with more complex anions considerably alter the position of the titration curve as compared to HCl, but not its general shape, the changes reflecting a greater affinity of organic anions for wool compared to the chloride ion. For example, several dyestuff-like anions, such as diphenylbenzenesulphonate, are taken up as strongly at pH 4 as chloride ion at pH 2. An extreme example of supra-stoichiometric absorption results from immersion of wool in pure formic acid, which grossly inflates the fibres to several times their original diameters. After rinsing well with water they return to their initial state. The textbook by Alexander and Hudson14 provides an extensive review of every aspect of absorption of both weak and strong acids. A majority of the original papers to which they refer were written as long ago as 1930–1950 but, for the most part, they have not been materially updated by more recent research.

5.6

Absorption of alkalis

Titration data for absorption of alkalis by wool mirrors, in many respects, absorption of acids but with one substantial difference. Alkalis degrade proteins at low concentrations and temperatures, at a significant rate, so that it is very difficult to attempt reversible alkaline titrations beyond a very restricted range by comparison with acids.

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Wool: Science and technology

Chemical groups in wool that alter their state of ionisation in increasingly alkaline conditions are listed below. Their approximate concentration in most wool types, in milliequivalents/kg, and their normal titration range vary widely. • HIS, (68), pH 5.5–7.0 • Terminal amino groups, (25), pH 7.5–8.5 • TYR, (260), pH 9.8–10.4 • LYS, (190), pH 9.5–10.5 • ARG, (600), pH 11.5–12.5 Addition of salts in an alkaline titration of wool has a similar effect in displacing the uptake curve as with acids, so that more alkali is taken up at less extreme pH values when neutral salts are added. The reactions of cystine and other disulphides in alkaline conditions have attracted a great deal of research attention. Maclaren and Milligan list over 40 references yet conclude that there is still room for some disagreement about the mechanism.18 In the case of combined cystine in wool, attack at the b-carbon offers a plausible mechanism for the degradation products that have been identified. The principal reaction steps are illustrated in equation [5.5] (R = wool protein chain). NH

C

CH CH2 C

S

S

CH2

O

O

CH (cystine) NH

OH– NH

C

CH CH2 C

S

O

S– + HO CH2 CH

C

C

O

S

CH2

[5.5]

NH

OH– –S

NH CH CH2

O

O

CH (lanthionine) NH

Lanthionine is one of the main products of alkaline degradation, and the selection of reaction steps shown also account for the appearance of some

Wool chemistry

139

free sulphur. Dehydroalanine is also formed as a minor product when some of the intermediate product sidechain HO—CH2 loses water. The latter product is also known to be capable of reacting with lysine in alkaline conditions to form lysinoalanine. These examples are just indicative of the sequential and complex variations of degradative reactions possible when wool is exposed to strongly alkaline solutions.

5.7

Dyeing with acid dyestuffs

5.7.1 General The theoretical background of absorption of low molecular weight mineral and organic acids is the same as that of the absorption of high molecular weight acids. However, as might be expected, the coulombic forces which substantially explain absorption of hydrochloric acid by wool, and the influence of salts added to the aqueous acid, fall short of explaining all the features of absorption of high molecular weight dyes. For these larger molecules, the principles of fixation in wool fibres is decidedly more complex. The morphological structure of wool is itself a mediating factor, as discussed in the next section. The detailed technology and practical aspects of wool dying are described in Chapter 8.

5.7.2 Morphological structure of wool and its influence on dyeing The three steps in dye transfer from an aqueous dyebath are: i) Diffusion of dye to fibre surfaces ii) Dye transfer across the surfaces iii) Diffusion of dye through wool fibre structures Good dyeing equipment, affording thorough liquor circulation, should eliminate the delays and uneven access to dyes implied in the first step. For the second step, the wool epicuticle offers a significant resistance to dye penetration. It is now accepted that dyes gain access to undamaged wool fibres mainly via junctions between wool cuticle scales.19 Lipids are present to varying degree at the surface and in intercellular interstices, and they present an obstacle to entry of dyes into wool fibres. Wool that has previously been scoured in the normal aqueous fashion, when extracted with a good solvent for lipids or alternatively stripped with anhydrous sodium tertbutoxide, responds with faster rates of dye uptake and better uniformity of dyeing.20 Wools with surface damage, or degraded by sunlight, chlorination or carbonising treatments for example, will respond differently when exposed to dyebath conditions.

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Wool: Science and technology

Dyestuffs, which first penetrate into wool between cuticle cell junctions as mentioned, are now known to next diffuse throughout all the nonkeratinous regions, and also the endocuticle and intermacrofibrillar material regions of the cell membrane complex.21,22 The final stages of dyestuff diffusion inside wool fibres entails a progressive transfer of dye into the sulphur-rich matrix proteins surrounding microfibrils in cortical cells. Even when dye exhaustion is virtually complete, the internal fibre–dye equilibration process is not, and in practical situations an industrial dyeing process may justify an extended dyeing time. A further curious but informative observation from optical and electron microscope studies of dye location in wool fibres is that the initial favoured entry of dye through the cuticle scale junctions is also followed by dye transfer into the adjacent exocuticle and A-layer. The non-keratinous regions, which are so important in the early part of the dye cycle, are found to be almost totally devoid of dye at the completion of the dyeing process.

5.7.3 Dye uptake chemistry The Gilbert and Rideal model was briefly described in the context of acid–base equilibria when wool is immersed in an aqueous solution (Section 5.5). Both this theory and the alternative approach based on the Donnan theory have been tested to find the extent to which they explain dye absorption. Lewis23 concluded that neither theory is particularly successful, especially for dyes with a highly hydrophobic character. However, some of the concepts of the ionic attractions driving absorption of simple acid dyes are a logical extension of titration of wool with common organic acids. A good example of this is the uptake of a fairly simple acid dye. Experimentally it could be demonstrated24 that, from a dyebath containing just Crystal Ponceau and hydrochloric acid, there is an initial rapid absorption of both hydrogen and chloride ions. Over time, the slower diffusing dye anions displace chloride in the fibre, as demonstrated by first a rapid fall in chloride concentration in the bath followed by a more gradual rise again. The influence of a salt on shifting the acidic side of the titration curve of wool is shown in Fig 5.1. Basically, at higher ionic strengths, hydrogen ions are more readily absorbed because the repulsive electrical charge which develops at the surface boundary of the fibres is substantially masked. Exactly the same effects explain why salts, commonly sodium acetate or sulphate, are to be found in most acid dyebaths. Less acid is required for a given uptake of hydrogen ions. This facilitates dye anion absorption at less extremely acid conditions and conveniently also reduces the risk of acid damage to the wool substrate.

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141

Zollinger25 expanded on these ionic aspects of dyestuff affinity for wool and distinguished between coulombic, van der Waals and hydrophobic binding forces. For three carefully selected acid dyes, there was a clear indication of the hydrophobic bonding interaction of an aliphatic sidechain. These studies were based on comparisons of dyeing behaviour between normal and modified wools, notably by blocking ionic sites. Meybeck and Galafassi26 contributed considerably to an understanding of the nature of acid dyestuff binding on wool. They showed that few salt anions (chloride) are released from wool in the course of dyeing compared to the amount of dye absorbed. For slightly hydrophobic dyes, of the order of 10% of bound chloride ions are released, while for more strongly hydrophobic dyes, release of chloride ions is negligible. This result, along with a variety of contributory studies,23,pp68–72 added further weight to their propositions. On the basis of these results, Meybeck and Galafassi formed three principles in relation to wool dyeing: i) Hydrogen bonds are not formed between the dye and the fibre. ii) Coulombic forces play a part in attracting dye anions into the wool fibres but then they locate to hydrophobic sites where they then become strongly fixed. iii) To have a high affinity for the wool, anionic dyes must have a hydrophobic character.The structure of the dye molecule must be such that the hydrophobic substituents are situated some distance from the polar groups.

5.8

Acid, alkali and enzymic hydrolysis

5.8.1 Acid hydrolysis Complete acid hydrolysis is the most common method of preparing solutions of amino acids from wool and other proteins for quantitative analysis. Evacuated, sealed tubes containing the sample and 6 M HCl are typically treated at 105 °C for 24 hours. TRP is destroyed and correction factors are applied to calculate SER, THR and TYR contents (see Table 5.1). This analytical routine is questionable for detection of amino acids modified by exposure of wool to sunlight. Partial oxidation products of cystine disproportionate to cysteic acid and cystine, and quite certainly unstable carbonyl groups (Section 5.3) notably glyoxylyl and pyruvyl either react with other side chains or simply decompose. Amides of GLU and ASP are hydrolysed and the ammonia released is also measured. The whole procedure is, of course, now a routine one for proteins in general. Amino acids and ammonia react with ninhydrin to form blue derivatives, which are quantified as they emerge from a chromatographic column.

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Wool: Science and technology

Partial acid hydrolysis has been evaluated as a general method for selectively producing wool peptides suitable for gaining amino acid sequence information.27 Maclaren and Milligan18 summarised all the results, including hydrolysis in more dilute solutions and lower temperatures, and concluded that this approach was not useful for extensive sequencing of wool proteins. In weaker acid hydrolytic conditions, the amides of GLU and ASP are the most readily hydrolysed and a standard method has been developed for the analytical determination of amide nitrogen as ammonia and other amino groups so released. The peptide bond adjacent to ASP is the most labile, with GLY and SER the next most easily released amino acids. Mild acid hydrolysis for the purpose of providing an analytical determination of amide groups in wool has been specifically developed because the drastic conditions employed for complete acid hydrolysis of wool and wool protein fractions (i.e. the preliminary step before amino analysis, typically 6 M HCl at 105 °C) compromises the measurement. The reason is that a significant fraction of other amino acids, notably SER and THR, decompose as well and, in so doing, release additional ammonia. Acid hydrolysis aimed more specifically at wool amide groups, therefore, should be sufficiently mild to avoid these complications. Inglis et al. judged that a treatment with 2 M HCl at 100 °C for 14 hours in sealed evacuated tubes is adequate for the release of ammonia from all amide groups in wool (and silk), with no significant hydrolysis of other potential contaminants.18 Attempts to isolate yellow compounds from wool, as discussed in Section 5.4, seem likely now to employ variations of conditions for mild acid hydrolysis to advance the prospects for complete chemical characterisation. In particular, the emphasis should be on keeping the temperature low, possibly at the expense of longer reaction times of the order of several days, in order to avoid the loss of unstable compounds.

5.8.2 Alkaline hydrolysis and alkali solubility Alkaline hydrolysis of proteins, including wool, destroys much of the CYS and lesser amounts of ARG, HIS and SER, but unlike acid hydrolysis it conserves the TRP content. In the context of wool chemistry, the most useful application of alkaline treatments is the alkali solubility test, the UK version being BS 3568:1988. This relatively mild treatment with 0.1 M NaOH at 65 °C for 1 hour is a standard test for assessing wool damage. It is particularly useful for detecting loss of CYS crosslinkages, acid damage and sunlight degradation, all of which increase solubility beyond about 10%, which is a figure typical for undamaged wool. Oxidative bleaching processes for example (Section 7.2) must be carefully managed to avoid

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143

excessive oxidation of CYS (see also Sections 5.9 and 5.10) and the alkali solubility test is very commonly used as a quality control check. Conversely the test is very sensitive to the introduction of new stable crosslinkages, which reduce the amount of extractable peptides. A mild alkaline treatment will itself convert some CYS to lanthionine crosslinkages and lower the amount extractable in a subsequent alkali solubility test.

5.8.3 Enzymic hydrolysis The solid, crosslinked structure of wool is resistant to proteolytic enzymes. In the general introduction (Section 5.1) attention was drawn to the difficulties of large molecules permeating the wool structure. Trypsin does diffuse slowly along cell membranes and after several days incubation the fibres readily disintegrate into a dispersion of cortical and scale cells.28 However, if wool is first reduced and alkylated, it is much more accessible to enzymes. Because enzymes afford a relatively mild form of digestion, novel crosslinkages or amino acid derivatives unstable to acid hydrolysis can be released and characterised.29 In this way the reaction of phenylisocyanate with LYS, SER, THR and GLU residues could be detected30 and the unusual peptide bond e-(g-glutamyl) lysine could be isolated and identified.31,32 At least three proteolytic enzymes are necessary for near-complete hydrolysis following the reduction/alkylation step.33 Typically, widespectrum enzymes such as papain, pepsin and pronase, used in combinations or sequential digestions, produce peptide mixtures that are ultimately cleaved to form a solution of individual amino acids. Prolidase is required to break proline bonds and amino peptidase removes Nterminal residues in step-wise fashion. Whilst these more complex procedures have identified some relatively unstable modified amino acids, they are not a universal panacea for resolution of all the questions about wool degradation. Essentially, the proteolytic enzymes are inactive when introduced to the solutions of yellow extracts obtained as described in Section 5.4. It is worth re-emphasizing that enzymes are effective in normal aqueous media but that they are unable to penetrate and degrade hydrophobic aggregates of complex wool peptides.

5.9

Oxidation with peracids

TRY, CYS, and cysteine (CYSH) are the amino acids most susceptible to oxidation. Because of its importance in crosslinking wool proteins and directly influencing the strength and elasticity of wool fibres, the detailed chemistry of CYS oxidation has been very extensively studied.

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Wool: Science and technology

Complete oxidation of CYS to cysteic acid (CYSA) in wool is best achieved with either peracetic or, better still, performic acid. This method forms the basis for post-oxidation procedures beginning with ammonia extraction followed by successive precipitations and purifications in order to prepare well differentiated fractions of soluble wool proteins. The products of these separations have been described as a-, b- and g-keratoses.34 Although both the oxidising acids are likely to rupture some peptide bonds and possibly slowly attack other side chains, O’Donnell and Woods34 found peracetic acid was the more likely of the two to have non-specific effects, possibly because there is a significant amount of hydrogen peroxide in its aqueous solutions. Prolonged oxidation with performic acid does, however, convert MET to its sulphoxide, TRP is converted to N-formyl kynurenine and other products, and some SER, THR and TYR may be affected by vigorous treatments.18 The principal present use of peracetic acid is as a component in the peracetic/ammonia solubility test. Under carefully controlled conditions, the test detects the presence of crosslinkages remaining in wool after cleavage of disulphide bonds.27 When a sufficient excess of oxidant is present, the end product of oxidation of CYS is combined CYSA, i.e. W—CH2—SO3H, where W represents a wool protein chain. Exposure to lesser amounts of chemical oxidant, or photo-oxidising sunlight for that matter (see Section 5.3), results in formation of intermediate products. Chemical structures of those believed to be present1 are shown in equation [5.6] O W CH2

S

S

CH2 W

W CH2

O

S

CH2 W

O

O W CH2

S

[5.6]

O

SH

W CH2

S

O

S

OH

O

Treatment of partially oxidised wool with strong acids leads to disproportionation reactions of intermediate sulphoxides. A typical stoichiometric relationship is given by equation [5.7]. O 5 W CH2

S

S

CH2

W + 2 H2O

O [5.7]

O 3 W CH2

S

S

CH2 W + 4 W CH2

S O

OH

Wool chemistry

5.10

145

Chlorine-based oxidation

Partial oxidation of wool is commonly observed as a result of industrial processes for bleaching (see Section 7.2) and shrinkproofing wool (see Section 7.5). Hydrogen peroxide is a favoured bleaching agent, applied using conditions that limit damage to CYS within acceptable values. Present-day technology essentially confines the industrial use of chlorine and its oxidative derivatives to acidic processes that principally modify wool surface properties. Therefore, they are primarily pretreatments for shrinkproofing, with a second-stage application of polymers (Section 7.5.7). There is a very extensive literature describing oxidation of wool with gaseous chlorine, chlorine water and numerous chlorine-release compounds. One of the earliest observations was that of von Allwörden.35 Wool fibres immersed in either chlorine- or bromine-water develop sacs on individual scales of the fibre surfaces. Osmotic pressure can develop due to oxidation and dissolution of some protein components of cuticle scale cells, provided the epicuticle is undamaged and prevents their diffusion into the immersion liquid. This reaction is therefore the basis of a simple laboratory test using a microscope to detect surface damage of immersed wool fibres. Chlorine derived from hypochlorite solutions has a markedly different reaction with wool depending on the pH of the treatment. This is because the active agent in a solution of calcium hypochlorite, commonly known as bleaching powder, is the hypochlorous ion, ClO- at pH values above 8.5, mainly undissociated HClO in near neutral conditions, while at pH 2 free chlorine accounts for about 70% of the total active chlorine in a dilute solution.Alkaline conditions result in high CYSA levels in the cuticle, whereas acidic treatments promote extraction of soluble acidic peptides from cuticle cells. The alkaline treatment results in a resist to acid dye uptake, whereas the acid method enhances it compared to untreated wool. These differences have been exploited in patterned fabrics to afford cross-dyed effects.36

5.11

Reduction

Wool keratins are structurally stabilised by the disulphide crosslinkages of cystine. Reductive cleavage of cystine, followed by structural reshaping of a fabric and then reforming the bonds, is the basis of chemical setting of pleats and creases. The same principles apply to the permanent waving of human hair. Complete reduction entails two successive nucleophilic displacement reactions – see equation [5.8] (W = wool protein chain and RS- is the reductant thiol).

146

Wool: Science and technology W CH2 S

S

CH2 W + RS–

W CH2 S

W CH2 S

S

R + RS–

R

S

S

S

R + W CH2 S–

R + W CH2 S–

[5.8]

A high concentration of a thiol, such as thioglycollic acid, would be required to achieve full reduction in acid conditions. By adjusting to pH 9–10, which is the pK value for thiol groups, adding a proportion of an organic solvent such as n-propanol, and using a high concentration of a protein disaggregating medium such as urea, total reduction of cystine is readily attained. Maclaren and Milligan18 emphasise the importance of pure reagents. For example, freshly distilled thioglycollic acid avoids acylation of amino groups by thiolactone impurities, and urea should be free of ammonium cyanate, likely to form carbamoyl derivatives with amino groups. Sodium borohydride is another reductant offering high yields of thiol but there is also some peptide bond hydrolysis.37 Extensive reduction of wool cystine may also be achieved with tetrakis (hydroxymethyl) phosphonium chloride (THPC) (see equation [5.9]). The active agent is the phosphine derivative formed by dissociation of THPC in aqueous solution.38 R

R W CH2

S

S

CH2 W + R

P + H2O

2W

R (R = hydroxymethyl group)

CH2

SH + R

P R

O

[5.9]

By way of contrast with the reversible equilibrium reduction characteristics of thiol solutions, the reaction with THPC is irreversible and requires but a small excess of reagent. Because phosphines react slowly with alkylating agents, it is also possible to carry out alkylation of thiol groups derived from cystine with chloroacetate in the same solution.39 Some undesirable modifications of TYR and cysteine can occur38 with THPC, whereas near-quantitative reduction can be achieved with tri-n-butyl phosphine, without unwanted side reactions.40

5.12

Sulphitolysis

Sulphitolysis of cystine in wool is of major industrial importance in processes such as the setting of yarns and fabrics, mild bleaching methods, and after-treatments following oxidative shrinkproofing and bleaching processes. Sulphite (SO32-), bisulphite (HSO3-) and disulphite (S2O52-) exist in equilibrium in aqueous solution. HSO3- is predominant in acid conditions and SO32- is the main species above pH 7. At pH >9 sulphitolysis of cystine is a reversible bimolecular displacement reaction,41 see equation [5.10]

Wool chemistry O– W

CH2

S

S

CH2 W + 2 O

S

147

O 2 W CH2

S

O–

[5.10]

O–

S O

Below pH 9 the reaction is more complex, that with bisulphite forming thiol and S-sulphonate anions (equation [5.11]). O W

CH2

S

S

CH2 W + HS

O O–

W

CH2

SH + W CH2

O

S

S

O–

[5.11]

O

Oxidative sulphitolysis is also possible (equation [5.12]) O W

CH2

S

S

CH2

W + 2S O–

O O–

2W

CH2

S

S

O–

[5.12]

O–

Sulphitolysis reactions reverse readily with rinsing in water but reversal is slower in acidic conditions. There have been long-standing speculations about wool cystine being divisible into four fractions of different reactivity, but Maclaren and Milligan18 conclude, after reviewing all the evidence, that there is not a sound case for this proposition.

5.13

Metal salts

Chrome dyeing is by far the most widely used process involving metal complexes in wool and is dealt with in Chapter 8. More recently, zirconium and titanium salts have featured in the development of flame-retardant wool products (see Section 7.7).Wool does, however, interact strongly with a wide variety of metal salts useful in more limited applications. As might be anticipated, the principal binding sites are carboxyl and sulphydryl groups for metal cations. Sometimes, more elaborate metal complexes with amino, guanidine and imidazole groups have been proposed in order to account for large uptakes. Maclaren and Milligan18 provide a comprehensive description of metal–wool reactions. The principal studies and applications are summarised here.

5.13.1 Mercury Methyl mercuric iodide is generally used in quantitative analysis of thiol and disulphide groups in wool.42 Mercury salts bind in large amounts, e.g. over 2000 mmol g-1, of the chloride.43,44 However, Hg binding is suppressed by excess chloride, which obviates the use of wool as a sorbent for mercury salts in sea water. Mercuric salts are well known for their ability to form

148

Wool: Science and technology

complexes with nitrogen compounds such as amines. Extended multinuclear complexes are likely in the water-swollen matrix proteins of wool, and these would account for the supra-stoichiometric absorption observed with mercuric chloride solutions. Thiol groups would react readily and completely with mercuric ions.

5.13.2 Silver Silver ion is taken up in greater amount as the pH is increased, and is reversibly bound on carboxyl groups with a small amount irreversibly reacting with all the thiol groups present to form a mercaptide.45 In alkaline conditions, silver ions appear to catalyse degradation of cystine, resulting in H2S and additional thiol groups being formed, which in turn convert to mercaptides. This conclusion was supported by evidence for a stoichiometric release of hydrogen ions into solution as silver was absorbed in acidic conditions, where decomposition of cystine by silver salts is negligible. There is close to complete binding of Ag+ ion on carboxyl groups at pH 6, this falling to about 22% at pH 1.5.45 The additional uptake of silver in alkaline conditions due to extra mercaptide formation has led to some useful applications. There has been some exploitation of silver ion in histochemistry, notably as a heavy-metal stain useful as a marker in electron microscopy. Weight increases of the order of 16% are achieved with treatments of wool in ammoniacal silver nitrate solutions at pH 10.5.46 Electron micrographs of wool sections subsequently show dense crystallites of silver sulphide in sulphur-rich regions of the fine structure of wool, presumably formed by reactions involving hydrogen sulphide released by alkaline hydrolysis of cystine. Similar deposits of lead sulphide were observed following alkaline sodium plumbite treatments of wool.47

5.13.3 Copper About 280 mmol g-1 Cu(II) is taken up by wool from a perchlorate solution,48 forming a green complex with carboxyl groups. Treatment with cuprammonium hydroxide in concentrated ammonia results in a 40% weight increase, contraction of the fibres, and loss of the normal keratin structure.49 A brief treatment is fully reversible by rinsing in dilute acid. These two widely different outcomes, the first essentially reflecting the affinity of cupric ions for carboxyl groups in mildly acidic conditions, and the second the supra-stoichiometric absorption possible in strongly alkaline conditions, favour cupric ion interaction with presumably amino and other nitrogencontaining side chains.

Wool chemistry

149

Copper salts are well known for their ability to form complex amines, the affinity being markedly stronger than is the case for silver. On the other hand, the susceptibility of cystine to degradation in alkaline solutions containing silver ion is much greater than for comparable solutions containing copper complexes. Provided the treatment of wool in ammoniacal copper is not too prolonged, as mentioned earlier, the absorbed salts can be washed out and the fibres return to their normal state without a residual amount of copper sulphide or combined copper mercaptide. Supercontraction is the historic description of the structural collapse, and in this respect the treatment is an excellent demonstration of the dependence of wool proteins on hydrogen bonding and amino–carboxyl salt linkages in order to maintain a stable structural form. Interactions which alter the structural stability of wool are described in detail in Chapter 4.

5.13.4 Aluminium Aluminium ions bind on carboxyl groups, and also on sulphonic acid groups produced by oxidative bleaching processes which modify a proportion of the cystine.The rate and extent of binding is increased by adding n-propanol to the solution, with a pronounced effect on the mechanical properties of the fibres. Basically the treatments reduce the stress required to produce an initial strain, or, in other words, the wool is more easily extended yet loses nothing in ultimate strength or recovery from extension. There are some subtleties of Al/alcohol treatments such that the ultimate effects are sensitive to the percentage of water in the ethanol, propanol or butanol mixture, and the actual quantity of Al absorbed appear to be less important than the absorption locations opened up by the particular solvent mixture.50 Unlike Ag+ and Cu+2, Al+3 has a very low affinity for nitrogenous groups. Just as the ammoniacal copper treatment of wool (Section 5.13.3) offers an example of structural destabilisation due to very extensive destruction of crosslinking hydrogen bonds, so, too, the more easily extendable wools treated in some Al/water/organic solvent mixtures highlights another structural feature. In such solutions, the Al+3 ion is sufficiently small to be transported into hydrophobic parts of the wool structure opened up by the organic solvent. Interference with the hydrogen bond cross linkages in these regions is therefore demonstrably a significant factor in the physical properties of wool. Since Al ions hydrolyse at pH values greater than 4, the optimum pH for wool treatments is in the pH 3–4 range, where the rate of hydrolysis is low and wool has sufficient negative character to strongly absorb Al cations.

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Wool: Science and technology

5.13.5 Other metals Wool modified by polymer grafting of methacrylic acid to increase its carboxylic acid content has been evaluated for removing iron, and potentially other metal ion pollutants, present in water. Heavy metal complexes, including uranyl acetate, phosphotungstic acid and osmic acid have been used for examination of wool by X-ray diffraction and electron microscopy.18 There does not appear to be much specificity attached to these treatments. Following some initial absorption, which may well have a specific type of binding site, what appears to follow is a time-dependent accretion of more heavy metal ions on the original binding template. These accretions build up most readily in the most accessible regions of the fibre structure and clearly delineate cell boundaries and other features readily observable in electron micrographs.

5.14

Miscellaneous reactions

5.14.1 Iodination Iodine dissolved in alcohol or potassium iodide reacts with wool in two ways. There is formation of a complex with amino groups which is reversible51 and irreversible di-substitution in the TYR side chain. Richards and Speakman52 found the latter reaction converted up to 96% of TYR to 2 : 4 diiodotyrosine, from treatments in alcoholic solutions of iodine.

5.14.2 Ninhydrin Ninhydrin has a well-known reaction with the amino groups of amino acids in solution, forming a strong blue colour used in quantitative analysis of the amino acids in hydrolysed proteins. Wool boiled in ninhydrin takes up sufficient for a weight increase of 15%, and this results in changes in fibre mechanical properties.53 The main physical effect is a large increase in the work needed to extend the fibres in water. At first, this was thought to be due to ninhydrin forming additional crosslinkages, but a more likely reason is the lower absorption of water by the treated wool when immersed. The weight change, however, indicates that reactions additional to those with the free amino groups in intact wool must occur, as they would account only for a theoretical 3% weight increase. This is most likely a parallel situation to the accumulation of heavy metals such as osmium (Section 5.13.5) in wool, owing to successive reactions or condensations of more reagent upon an original group-specific template of reactions with wool fibres.

Wool chemistry

151

5.14.3 Diazonium salts and staining tests Pauly54 first demonstrated the reaction of diazotised sulphanilic acid with TYR and HIS residues of soluble proteins. Depending on pH and other reaction conditions, other residues are also modified.18 The principal interest in this reaction in wool chemistry is its adaptation as a visual test of fibre damage. Undamaged fibres remain colourless under conditions where damaged fibres rapidly develop red-brown colouration. Glynn55 preferred 2-nitroaniline as the base of a diazonium salt for this test. Allied with a microscope, this very simple test reaction is an extremely useful one in wool quality control. Staining tests can be very informative regarding the sites and extent of damage sustained by wool fibres and fabrics. Simpson and Page56 found it was possible to mix a selected high-molecular weight acid dye and a lowmolecular weight basic dye to form a staining solution that showed no tendency to co-precipitate. This proved to be very useful in delineating progressive damage to wool fabrics exposed to sunlight degradation behind window glass. The standard staining solution was as follows: • • •

0.06% CI Acid Red 52 0.025% CI Basic Blue 3 0.12% acetic acid

Application conditions were 15 minutes at 20 °C followed by 1 minute rinsing. The colours of surface and shielded fibres showed every variation from red, pink, mauve to blue according to changes in ionic character and permeability.

5.14.4 Esterification Alexander et al. demonstrated that wool treated with boiling methanol (65 °C), n-propanol (97 °C), and n-butanol (117 °C) for 6 hours with 0.1 M HCl as catalyst, resulted in 60, 50, 35% esterification respectively of the carboxyl sidechains.57 Some amide groups are converted to esters and some susceptible peptide bonds may succumb to N- and O-methylation.58

5.15

Crosslinking

5.15.1 Effects of crosslinking Potential practical applications of crosslinking reactions include the restoration of physical properties such as depletion of natural cystine crosslinking

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Wool: Science and technology

due to degradation by sunlight. Industrial processes such as oxidative bleaching also damage cystine and suggest that some repair mechanism may be helpful. A treatment which utilises a bifunctional reagent reactive with wool protein sidechains is the obvious approach to take. In many instances, however, there is no discernable effect on fibre properties because only one functional group reacts with a pendant group on a protein chain or alternatively the predominant bifunctional reactions are with the same protein chain. A long chain molecule with reactive end-groups may be more successful at crosslinking than rigid aromatic bifunctional reagents,59 which require more precise positioning of reactive groups on wool proteins to effect a cross-linking reaction. Definitive proof of crosslinking requires isolation and characterisation of the relevant amino acid–reagent linkages. A majority of potential crosslinkages would hydrolyse should the wool be solubilised. Isolation by following a reduction/alkylation route followed by extraction and several steps of enzymic hydrolysis is always a lengthy and difficult procedure with no certainty of eventual success. Changes in fibre solubility (in various reagents), swelling, setting, tensile behaviour, abrasion resistance and supercontraction are alternative indicators, which most commonly can be reasonably reliable measures of crosslinking. Their disadvantage, of course, is that they do not identify the particular fibre protein end-groups involved in crosslinking. Of the several recognised solubility tests, the performic acid/ammonia test is probably the best in most circumstances.60 The first step is oxidation of all the cystine with performic acid, followed by an extraction of soluble proteins with dilute ammonia. New crosslinkages stable to oxidation reduce the amount of extractable material. Concentrated urea solutions are well-known swelling and disaggregating solvents for proteins, in combination with a reductant, such as urea/thioglycollate61 or urea/bisulphite.62 The alkali solubility test63 has the longest history and is a standard method still (0.1 M sodium hydroxide at 65 °C for 1 hour) but can be difficult to interpret. Urea/reductant methods are valuable when crosslinkages are likely to be unstable to oxidising agents or alkalis.

5.15.2 Formaldehyde Formaldehyde reactions with wool have been the subject of numerous studies, in large part because formaldehyde is capable of introducing

Wool chemistry

153

crosslinkages in wool, as well as being cheap and being a small molecule that diffuses rapidly into wool fibres. Although formaldehyde appears to confer no measurable improvements to fibre strength or fabric abrasion resistance when used either as a pre-treatment or included in dyebaths and bleaching processes,18 it can be successfully used to replace a dye carrier when wool/polyester blends are dyed at high temperature.64 There is a considerable history of formaldehyde usage with wool products that do not involve crosslinking, but depend essentially on disinfection. Some examples include dusting greasy wool bales with paraformaldehyde to inhibit growth of microorganisms in storage, disinfection of blankets during laundering, and sterilising Indian wool suspected of containing Anthrax spores.18 Sidechains of ARG, LYS, TYR, TRP, HIS, cysteine, and the amide derivatives of ASP and GLU are known to be capable of reaction with formaldehyde. Some of these reactions can be bi-functional as well as mono-functional, so that new wool protein crosslinkages are likely. In addition to simple —CH2—, i.e. methylene crosslinkages, formaldehyde has a known propensity for self-condensation so that —CH2—(OCH2)n— or oxymethylene crosslinkages are feasible. Verifying the sites and extent of formaldehyde reactions with wool has proved to be difficult since most of the modified amino acid sidechains are unstable under the hydrolytic conditions required to release them for analysis. McPhee65 did, however, conclude that ARG residues are extensively modified under all conditions, whereas the amide derivatives of ASP and GLU react only in acid or in alkaline solutions. Whereas formaldehyde treatments of wool in acid conditions did not improve resistance to attack by insects, McPhee found that treatments at pH 12 modified most of the TRP and roughly half of the ARG and primary amino and amide groups. The treated wool, after neutralisation, showed good resistance to clothes moth larvae and newly hatched carpet beetles. Table 5.2, reproduced by Maclaren and Milligan18 from the primary data of McPhee65 and Reddie and Nicholls,66 illustrates the complexity of the formaldehyde reactions with wool under different conditions. Maclaren and Milligan18 discuss in detail the experimental difficulties in identifying amino acid modifications caused by formaldehyde treatments, essentially because the hydrolytic reagents needed to release individual amino acids may in themselves induce additional modifications. Modified amino acids isolated from acid hydrolysates of formaldehydetreated wool include Ne-methyllysine (A), thiazolidine-4-carboxylic acid (B) and djenkolic acid (C), the latter being the only example of a crosslinkage so far identified (Equation [5.13]).66–68

0.5

7.0

12.2

0.1

6.7

3.0

0.33

2.7

2.7

0.35

0.35

3.5

98

60

60

20

20

35

Temp. (°C)

24

2

2

0.5

48

20

Time (h)

—

870

1270

1200

450

770

Amount of HCHO bound (mmol.g-1)

—

—

—

400

50

300

AMIDEb

300 300 — — —

50c 80d 140d d

210

150

400

c

ARGe

0c

LYS

160

d

25d

55d

0

0

50f

TYR

Groups modified (mmol.g-1)a

40h

25h

40h

50

50

50g

TRP

46

46

46

45

45

45

Ref.

a

The initial amide, lysine, arginine, tyrosine, and tryptophan contents found by McPhee65 were 670, 210, 600, 350, and 54 mmol.g-1, respectively; the initial lysine, tyrosine, and tryptophan contents found by Reddie and Nicholls66 were 240, 420, and 40 mmol.g-1 respectively. b By ammonia determination after partial hydrolysis. c By colorimetry after ninhydrin treatment. d By indirect analysis after treatment with 1-fluoro-2,4-dinitrobenzene. e By reflectance spectrophotometry after applying Sakaguchi reagent. f By colorimetry after applying Pauly reagent and dissolution in alkali. g By reflectance spectrophotometry after applying Ehrlich reagent. h By colourimetry (Spies and Chambers method).

pH

Conc. (M)

Conditions of treatment

Table 5.2 The extent of reaction of formaldehyde with various residues in wool

154 Wool: Science and technology

Wool chemistry

155

O C CH3

NH(CH2)4

OH

S

CH

CH2

NH2

CH C

HN

(A)

(B)

O H2N CH CH2 C

S

CH2

S

CH2

O

OH

[5.13]

OH

NH2

OH

O

CH C

CH2

(C)

5.15.3 Dialdehydes Dialdehydes have attracted research and practical interest because of their obvious potential for crosslinking proteins in general. Glutaraldehyde is clearly the most successful. It has been applied in treatments of woolly sheepskins, where it has a dual role in tanning the leather and protecting the wool from felting during laundering.69 Glutaraldehyde reacts predominantly with LYS residues, although there is an unresolved debate about the nature of the crosslinkages.18,p192 The main disadvantage of the process is that it imparts a golden colour to the wool, although this can be mitigated to some extent by adding bisulphite to the treatment bath.

5.15.4 Other bifunctional reagents One of the early papers describing a crosslinking process for wool employed various alkyl dibromide solutions applied in a one-step treatment which included dithionite. This reducing agent opened up the fibre by cleavage of some cystine, allowing the dibromide to reform this crosslink and add a variety of other bifunctional reactions.70 Acyl and aryl dihalides, dimaleimides and bifunctional acid chlorides, isocyanates and active esters have all been reacted with wool from both aqueous and organic solvents. An example of this type of treatment is that of cyanuric chloride (2,4,6 trichloro-s-triazine), which is a relatively cheap industrial reagent, applied from an aqueous acetone solution at room temperature.71 About 300 m mol/g of wool of the reagent is incorporated and there is reduced solubility in all the regular alkali, urea-bisulphite and acid solubility tests, which is strong circumstantial evidence for crosslinking. Apart from the commercial use of glutaraldehyde as a tanning and fibre stabilisation process (Section 5.15.3) and the regular re-discovery of useful applications for formaldehyde treatments, there has been no

156

Wool: Science and technology

sustained development of crosslinking processes, presumably as any product performance advantages are insufficient to justify their industrial development.

References 1 Corfield M C and Robson A, ‘The amino acid composition of wool’, Proc. Int. Wool Text. Res. Conf., Australia, 1955, C79–86. 2 Meybeck A and Meybeck J, ‘Photo-oxidation of the peptide group, I. Fibrous Proteins’, Photochem. Photobiol., 1967, 6, 355–63. 3 Hoare J L, ‘Chemical aspects of wool yellowing’, WRONZ Communication 2, 1968. 4 Launer H F, Effect of light upon wool, ‘Part I, Greening and yellowing by germicidal ultraviolet.’ ‘Part II, Post-irradiation loss of colour in the dark after germicidal ultraviolet’, Text. Res. J., 1963, 33, 258–63, 910–18: ‘Part IV, Bleaching and yellowing by sunlight.’ ‘Part V, Yellowing and bleaching by ultraviolet and visible arc light’, Text. Res. J., 1965, 35, 395–400, 813–19. 5 Inglis A S and Lennox F G, ‘Studies in wool yellowing, Part IX, Irradiation with different UV wavebands’, Text. Res. J., 1965, 35, 104–9. 6 Launer H F, ‘Rapid bleaching of wool with extremely intense visible light’, Text. Res. J., 1971, 41, 311–14. 7 King M G, ‘The effects of reducing agents on the photobleaching and photoyellowing of wool’, J. Text. Inst., 1971, 62, 251–60. 8 Simpson W S, ‘Comparison of chemical and photochemical bleaches for wool’, Proc. 8th Int. Wool Text. Res. Conf., Christchurch, NZ, IV, 279–87, 1990. 9 Simpson W S, ‘Physics and chemistry of wool yellowing’, WRONZ Report R217, 1999. 10 Lennox F G and Rowlands R J, ‘Photochemical degradation of proteins’, Photochem. Photobiol., 1969, 9, 359–67. 11 Holt L A and Milligan B, ‘Application of enzymic hydrolysis and tritium labelling to a study of the modification of tryptophyl residues in proteins’, Aust. J. Biol. Sci., 1973, 26, 871–6. 12 Steinert P M, Kartasova T and Marekov L N, ‘Biochemical evidence that small proline-rich proteins and trichohyalin function in epithelia by modulation of the biochemical properties of their cornified cell envelopes’, J. Biol. Chem., 1998, 273, 11758–69. 13 Steinhardt J and Harris M, ‘Combination of wool protein with acid and base – HCl and KOH’, J. Res. Natl. Bur. Standards, 1940, 24, 335–67. 14 Alexander P and Hudson R F, Wool: Its Chemistry and Physics, London, Chapman and Hall, 1954. 15 Vickerstaff T, The Physical Chemistry of Dyeing, London, Oliver and Boyd, 1954. 16 Peters R H, Textile Chemistry – The Physical Chemistry of Dyeing, Vol. 3, Amsterdam, Elsevier, 1975. 17 Gilbert G A and Rideal E K, ‘The combination of fibrous proteins with acids’, Proc. Roy. Soc., 1944, A182, 335–46. 18 Maclaren J A and Milligan B, Wool Science. The Chemical Reactivity of the Wool Fibre. NSW Science Press, 1981.

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19 Hall R O, ‘Fibre structure in relation to dyeing’, J. Soc. Dyers and Col., 1937, 53, 341–4. 20 Joko K, Koga J and Koroki N, ‘The interaction of dyes with wool keratin – the effect of solvent treatment on dyeing behaviour’, Proc. 7th Int. Wool Text. Conf., Vol. 5, 1985, 23–32. 21 Leeder J D, Rippon J A and Rivett D E, ‘Modification of the surface properties of wool by treatment with anhydrous alkali’, ibid, Vol. 4, 312–21. 22 Leeder J D, Rippon J A, Rothery F E and Stapleton I W, ‘Use of the transmission microscope to study dyeing and diffusion processes’, ibid, Vol. 5, 99–108. 23 Lewis D M, Wool dyeing, Soc. Dyers and Col., Bradford, 1992. 24 Elod E, ‘Theory of the dyeing process. Influence of acid dyes on animal fibres’, Trans. Farad. Soc., 1933, 327–47. 25 Zollinger H, ‘The dye and the substrate: The role of hydrophobic bonding in dyeing processes’, J. Soc. Dyers and Col., 1965, 81, 345–50. 26 Meybeck J and Galafassi P, ‘The effects of hydrocarbon substituents in azo dyes on wool dyeing’, 4th Int. Wool Text. Res. Conf., Berkeley, Calif, App. Polymer Symp., No. 18, Part 1, 463–72, 1971. 27 Consden R and Gordon A H, ‘The peptides of cystine in partial hydrolysates of wool’, Biochem. J., 1950, 46, 8–20. 28 Burgess R, ‘The use of trypsin for the determination of the resistance of wool fibres to bacterial disintegration’, J. Text. Inst., 1934, 25, T289–94. 29 Holt L A, Milligan B and Roxburgh C M, ‘ASP, ASN, GLU and GLN contents of wool and two derived protein fractions’, Aust. J. Biol. Sci., 1971, 24, 509– 14. 30 Caldwell J B, Milligan B and Roxburgh C M, ‘The sites of reaction of phenylisocyanate with wool’, J. Text. Inst., 1973, 64, 461–7. 31 Asquith R S, Otterburn M S, Buchanan J H, Cole M, Fletcher J C and Gardner K L, ‘Identification of eN (g-glutamyl) lysine crosslinks in native wool keratins’, Biochim. Biophys. Acta, 1970, 221, 342–8. 32 Milligan B, Holt L A and Caldwell J B,‘The enzymic hydrolysis of wool for amino acid analysis’, 4th Int. Wool Text. Res. Conf., Berkeley, Calif., Appl. Polymer Symp., No. 18, Part 1, 1971, 113–25. 33 Schmitz I, Baumann H and Zahn H, ‘Ein Beitrag zur enzymatschen Totalhydrolyse von Wollkeratin’, Proc. 5th Int. Wool Text. Res. Conf., Aachen, II, 313–25, 1975. 34 O’Donnell I J, and Woods E F, ‘The preparation of wool protein solutions’, Proc. Int. Wool Text. Res. Conf., Australia, CSIRO, 1955, Vol. B, 48–55. 35 von Allwörden K, ‘Properties of wool – detection of damaged wool by chemical means’, Z. Angewandte Chem., 1916, 29, 27–32. 36 Simpson W S, ‘Effect of chlorination under different conditions on the dyeing of wool’, WRONZ Communication 47, 1976. 37 Gillespie J M, O’Donnell I J, Thompson E O P and Woods E F, ‘Preparation and properties of wool proteins’, J. Text. Inst., 1960, 51, T703–9. 38 Wolfram L K, ‘The reaction of tris(hydroxymethyl) phosphine with keratin’, Proc. 3rd Int. Wool Text. Res. Conf., Paris, 1965, II, 505–12. 39 Maclaren J A, ‘Quantitative reduction and alkylation of wool’, Text. Res. J., 1971, 41, 713–14. 40 Maclaren J A and Sweetman B J, ‘Preparation of reduced wool and S-alkylated wool keratins using tri-butylphosphine’, Austr. J. Chem., 1966, 19, 2355–60.

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41 Cecil R in The Proteins, ed. H Neurath. Academic Press, NY, Vol. 1, 1963, p. 438. 42 Leach S J, Meachers A and Springell P H, ‘Micro- and submicro methods for the estimation of thiol and disulphide groups in insoluble proteins using radioactive mercurials’, Anal. Biochem., 1966, 15, 18–30. 43 Friedman M and Mavri M S, ‘Sorption behaviour of mercuric salts on chemically modified wools and polyamino acids’, J. Appl. Polymer Sci., 1973, 17, 2183–90. 44 Friedman M, Harrison C S, Ward W H and Lundgren H P, ‘Sorption behaviour of mercuric and methylmercuric salts on wool’, J. Appl. Polymer Sci., 1973, 17, 337–90. 45 Simpson W S and Mason P C R, ‘Absorption of silver ions by wool’, Text. Res. J., 1969, 39, 434–41. 46 Kassenbeck P and Hagege R, ‘Development Des Methods D. Analyses Histochemique’, 3rd Int. Congr. Wool Textile Res., Paris, 1965, I, 245–58. 47 Sikorski J and Simpson W S, ‘Studies of the reactivity of keratin with heavy metals’, J. Roy. Microscopical Soc., 1959, 68, 35–40. 48 Guthrie R E and Laurie S H, ‘Binding of copper II to mohair keratin’, Austr. J. Chem., 1968, 21, 2437–43. 49 Whewell C S and Woods H J, ‘A reversible contraction phenomenon in animal hairs’, Nature, 1944, 54, 546–9. 50 Edgar J S and Simpson W S, ‘The effect of aluminium on the load – extension characteristics of some wool yarns’ and ‘The absorption of aluminium by wool from water alcohol mixtures’, Text. Res. J., 1975, 45, 809–11 and 281–4. 51 Blackburn S and Phillips H, ‘The action of iodine on wool’, J. Soc. Dyers and Col., 1945, 61, 100–3. 52 Richards H R and Speakman J B, ‘The iodination of wool’, J. Soc. Dyers and Col., 1955, 71, 537–44. 53 Cockburn R and Speakman J B, ‘Cross-linking reactions in keratin III. The action of ninhydrin on wool’, Proc. Int. Wool Text. Res. Conf., Australia, 1955, C315–39. 54 Pauly H, ‘The diazo reactions of proteins’, Z. Physiol. Chem., 1915, 94, 284–90. 55 Glynn M V, ‘Diazo compounds in the determination of wool damage’, J. Soc. Dyers Col., 1952, 68, 16–20. 56 Simpson W S and Page C T, ‘The effect of light on wool and the inhibition of light tendering’, WRONZ Report No 60, 1979, pp. 3–5. 57 Alexander P, Carter D, Earland C and Ford O E, ‘Esterification of the carboxyl groups in wool’, Biochem. J., 1951, 48, 629–32. 58 Holt L A and Milligan B, ‘Esterification of wool’, Austr. J. Biol. Sci., 1970, 23, 165–73. 59 Hinton E H Jnr, ‘A survey and critique of the literature on crosslinking agents and mechanisms as related to wool keratin’, Text. Res. J., 1974, 44, 233–92. 60 Caldwell J B, Leach S J and Milligan B, ‘Solubility as a criterion of crosslinking in wool’, Text. Res. J., 1966, 36, 1091–5. 61 Gillespie J M, ‘The isolation and properties of some soluble proteins from wool’, Austr. J. Biol. Sci., 1964, 17, 282–300. 62 Lees K, Peryman R V and Elsworth F F, ‘The solubility of wool in ureabisulphite solutions and its use as a measure of fibre modification – Part II’, J. Text. Inst., 1960, 51, T717–32. 63 Harris M and Smith A L, ‘Oxidation of wool IV. Alkali solubility test for determining the extent of oxidation’, Amer. Dyest. Rep., 1936, 25, 542–5.

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64 Baumann H, Muller H, Mochel L and Spiegelmacher P, ‘Chemische veränderungen und schutz der Wolle beim HT-Färben von Polyester/wolle – Stückware, Melliand Textilber., 1977, 58, 420–2. 65 McPhee J R, ‘The reaction of formaldehyde with wool and its effect on digestion by insects’, Text. Res. J., 1958, 28, 303–14. 66 Reddie R N and Nicholls C H, ‘Some reactions between wool and formaldehyde’, Text. Res. J., 1971, 41, 841–52. 67 Trézl L, Heiszman J and Tyihák E, ‘Changes in the thermal behaviour of wool due to pretreatments. Formation of heat resistant crosslinkage’, 5th Int. Wool Text. Res. Conf., Aachen, 1975, II, 488–98. 68 Middlebrook W R and Phillips H, ‘The action of formaldehyde on the cystine disulphide linkages of wool’, Biochem. J., 1947, 41, 218–23. 69 Happich W F, ‘New process expands uses for woolskins’, 4th Int. Wool Text. Res. Conf., Berkeley, Calif., Appl. Polymer Symp., No. 18, 1971, Part 2, 1483–90. 70 Marzona M, Di Modica G and Marzona M, ‘Crosslinking of wool keratin with bifunctional aldehydes’, Text. Res. J., 1971, 41, 701–5. 71 Harris M and Brown A E, ‘New developments in the chemical modification of wool’, Amer. Dyest. Rep., 1947, 36, 316–19.

6 Mechanical processing for yarn production L HUNTER

6.1

Introduction

The mechanical processing stage in the wool pipeline commences with the clean scoured wool and ends with the yarn ready for the fabric manufacturing stage. The main objectives of this stage are to disentangle the fibres, remove vegetable matter, mix (blend) the fibres, form a uniform coherent strand of fibres (sliver or slubbing) and then attenuate the fibre strand and impart cohesion to form a yarn of the desired linear density (count), quality and character. Other operations that can also take place during the mechanical processing stage include short fibre and residual vegetable matter removal (combing), dyeing (loose stock, sliver/top or yarn) and shrink-proofing (loose stock or sliver). Folding (plying), winding, clearing, waxing, etc. are final operations that may be required to produce a yarn and yarn package suitable for the fabric forming stage. All the above need to take place with the maximum efficiency and quality and with the minimum cost, fibre breakage and fibre loss. The mechanical processing of wool can be divided into the following three main stages: •

•

•

Sliver or slubbing formation – Involves disentangling (individualising) and mixing the fibres, removing vegetable matter and forming a continuous web, sliver or slubbing, this being accomplished by carding. Preparing the carded sliver for spinning – Entails fibre alignment (parallelisation), evening (doubling), drafting and the removal of short fibres, neps and vegetable and other contaminants – Accomplished by gilling, combing and drawing Yarn formation – Drafting and imparting cohesion, usually through twist insertion, this being the spinning stage.

The middle, or intermediate stage (i.e. preparing for spinning) is omitted from the woollen processing route and it is the differences in this stage (namely combing and the associated additional gilling operations) that 160

Mechanical processing for yarn production

161

also essentially distinguish the worsted from the semi-worsted processing route. There are basically three different routes or systems used in the mechanical processing of wool (Fig. 6.1), namely worsted, semi-worsted and woollen.1 The essential differences in the products of the three systems are the levels of short fibres and the alignment of the fibres in the yarn, the fibres in worsted yarns being far more parallel than those in either semi-worsted or woollen yarns, resulting in a far leaner (less bulky) and less hairy yarn. Close on 90% of Australian and South African Merino type apparel wools are processed on the worsted system while some 80% of New Zealand wool is processed on the woollen system. It should be mentioned that short wools, mainly in blends with either cotton or polyester, are also processed on the cotton (short staple) system, being occasionally rotor-spun (open-end) rather than ring spun. Wool with a mean fibre length around 40 mm can generally be processed without any major alteration to the cotton machinery, while wool with a mean fibre length of around 50 mm generally requires slip drafting at the drawframe, speedframe and ringframe. Iype et al.2 have reviewed the processing of wool and wool-rich blends on the cotton system and this processing route will not be dealt with in this chapter.

6.2

Worsted processing system

6.2.1 Introduction The name ‘Worsted’ is a slight corruption of ‘Worstead’, the name of a village in Norfolk where expert cloth-workers who entered England in the early fourteenth century, introduced novel methods for the production of superior and finer cloth than was previously produced in Britain.3 As already mentioned, the essential and differentiating element of the worsted system is combing. Generally, only virgin wool, typically ranging in length from about 40 to 100 mm, is used in manufacturing worsteds, the term worsted-spun yarn, as opposed to worsted yarn, being used for the yarns in those cases where man-made fibres are processed. Virtually since the start of worsted processing, two main systems have been used, namely the English (oil combed or Bradford) system, involving Noble combing, and the French or Continental (dry-combed) system, involving Rectilinear combing. The former was primarily developed and used for longer wools and the latter for shorter wools. Nevertheless, Noble (and also Lister) combs, employed in the Bradford system, are no longer being manufactured and the industry has moved almost entirely to the Rectilinear or French combing route. Essentially, the latter route entails carding followed by Intermediate or Preparer Gilling, then Rectilinear

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Worsted flow chart Raw wool and hairs Blending Dust removal (if needed)

Drying Fibres shorter than 200 mm maximum fibre length

Fibres longer than 200 mm maximum fibre length

Carding

Preparer gilling (6 operations)

Intermediate gilling (usually 3 gill boxes) Combing (Lister or Noble)

Combing (usually rectilinear, sometimes Noble)

Combing factory processes

Scouring

Top finishing (usually 2 gill boxes)

Recombing factory processes (usually omitted if piece-dyeing or yarn dyeing is to be used)

Top dyeing (or bleaching) Backwashing Drying Blending 56’s wool quality and coarser

58’s wool quality and finer

Gill mixing (2 operations)

Comb preparing (3 gill boxes) Recombing (rectilinear or Noble) Top finishing (2 operations) Spinning factory processes

Drawing (2 to 5 operations) Spinning Winding and clearing Folding and re-winding if required

Semi-worsted flow chart

Woollen flow chart

Man-made fibres

Raw wool Raw wool

Remanufactured fibres Threads

Rags Scouring Drying

Pulling (or grinding)

Worsted by-products (soft waste)

Other fibres (e.g. hairs, cotton, silk, man-made fibres)

Dust removal (if required) Scouring Drying Blending High-production carding

Garnetting

Drawing (2 or 3 gill boxes)

Carbonizing if required Dyeing if required Blending Carding

Roving (no roving process for thick count yarns for end-products (bobbin lead, for knitting yarns and some upholstery) such as carpets) Spinning

Spinning Winding and clearing Folding and re-winding if required

Winding and clearing Folding and re-winding if required

6.1 Processing routes for wool. [From Oxtoby.1]

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163

Combing (very occasionally Noble combing) and then Top Finishing, which usually comprises two Finisher Gilling operations. The stage from greasy wool to top is referred to as the ‘early processing’ or ‘topmaking’ stage. Papers at the Top-Tech ’96 Conference in Australia4 dealt with various aspects of topmaking, including the potential and merits of automation in topmaking, cost and flexibility being important aspects in this regard. The Worsted Flow Chart is shown in Fig. 6.1.1

6.2.2 Carding Carding generally represents the first stage of the mechanical processing of scoured wool, worsted cards typically being available in widths between 2.5 and 3.5 m. If any opening is applied prior to carding, care must be taken not to entangle the fibres, particularly for fine wools. Lubricants (generally 0.4 to 0.5%) are applied prior to carding to provide a well-balanced static and dynamic fibre-to-fibre and fibre-to-metal friction, and cohesion and antistatic properties.5 Best results are generally obtained with boundary layer lubrication for carding, the main effect being at the swift. The lubricants should be emulsifiable and preferably bio-degradable, and often also contain bactericides/fungicides, complexing agents and anti-odourants. The worsted, semi-worsted and woollen cards entail similar carding principles, although the last has more carding elements as well as an intermediate feed. Automatic linkages between carding, intermediate gilling and combing have also been developed. In essence, carding is aimed at opening up or disentangling the scoured wool staples (clusters or tufts), individualizing the fibres, mixing the fibres, removing residual dirt and vegetable matter, such as burrs and seeds, and forming the wool fibres into a continuous form (web); this is then condensed into a card sliver, and, in the case of worsted carding (Fig. 6.2), delivered into a ball or can. These actions need to be carried out in such a way that fibre breakage is minimised and as even a web and sliver as possible are produced. In the case of the worsted route, the wool is virtually always carded in the undyed state. The card essentially consists of the following separate mechanical sections, each playing a different part in the process:7 • • • •

Feeding Licker-in, including burr removal etc. Swift-worker-stripper section Fancy doffer section

The exact configuration of the card (Fig. 6.2) depends upon the nature of the fibre being processed, notably the level of vegetable matter. For example, when wools of relatively high vegetable matter levels are carded, the card could have more morels and burr-rollers.

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Burr beaters Swift Licker Volumetric hopper

Breast

Morels

Doffer Drafting head

6.2 Worsted Card. [From Harrowfield.6]

The feed system plays a critical role in the uniformity of the card web and sliver. Examples are continuous flow volumetric feeders or gravimetric feeders, incorporating automatic monitoring and regulating devices (autolevelling). The card essentially consists of rollers with surfaces covered in pins (card clothing). There are two main types of card clothing, flexible steel wire mounted into a firm foundation and rigid (non-flexible) metallic wire. The latter is a continuous steel ribbon with saw teeth which is wound around the card rollers, and this form of card clothing is presently the most popular. The following carding actions take place (Fig. 6.3): • • • • •

Carding (working) Dividing Stripping Doffing Brushing or Raising

The action on the fibres present between the pins of two adjacent rollers on a card is determined by the following factors:1 • • •

Relative speed and direction (i.e. same or opposite) of the movement of the roller surfaces Direction of inclination of the pins, i.e. points leading or backs leading Distance (setting) between points on the adjacent rollers

The intensity of the carding action can be altered by changing one or more of the above factors. Increasing the overall speed of the card generally does not increase the carding action (or fibre breakage) as such, although it can increase fly waste and air currents. There are three pin relationships in carding, namely point to point, point to back and back to back1 (Fig. 6.3):

Mechanical processing for yarn production Fibres leaving

Fibres leaving

Fibres entering

Fibres entering

165

Slow

Slow Fast Fibres entering

(a)

Fibres Fibres Fast leaving entering (b)

Fibres leaving

Fibres leaving

Point-to-point working actions

(a)

(b)

Fibres leaving

Point to back: stripping action

(a) surfaces moving in opposite directions; (b) surfaces moving in the same direction Embedded fibres

Fibres entering Swift (fast)

Fancy Swift

Fibres remaining on the swift

Doffer (slow) Raised fibres

Fibres collected by the doffer Doffing action (point to point)

Back to back: raising action; conventional worsted application with flexible swift clothing

6.3 Carding actions. [From Oxtoby.1]

Point to point, when used to open and disentangle the tufts of fibres, is called working or carding (e.g. at the licker and divider). This action always results in some fibres being retained on both surfaces. It is also used by the doffer to collect fibres from the fast moving swift, normally following the action of the fancy. Point to back provides a stripping action, i.e. transfers all the fibres from the one surface to the other. Back to back results in a raising action, which moves the fibres carried by the swift towards the tips of the pins by the action of the long fancy wire pins as they intersect with the pins on the swift.1 Burr beaters are used to remove burrs and other vegetable matter. They have steel blades and are usually run at the highest feasible speed in the opposite direction to the card roller surface. They are at their most effective during the earlier stages of the carding process, before the burrs have been opened out, and when they are used in conjunction with Morel rollers. Morel rollers are clothed with rigid wire clothing that cause the fibres to bed into the wires (assisted by the action of brush rollers) whereas the vegetable matter particles protrude from the surface and are knocked off into trays by fast revolving burr beaters, sharp blades offering certain

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advantages.8 A modern card with two Morels typically removes over 90% by weight of burr and close on 90% of shive. The full width web from the doffer, which can be monitored and corrected for evenness, is condensed into a sliver as it passes through a funnel and between a pair of pressure rollers, the latter running at a slightly higher speed than the doffer. Card sliver linear density monitoring and autolevelling (open and closed loop) take place at this stage, a drafting head at the delivery end of the card allowing the sliver linear density to be controlled. When carding with rigid metallic wire clothing, wool regain should not exceed 25%,1 and ideally should be between 20 and 25%. Residual grease content of the wool should not exceed 0.6%.1 Carding is a fairly severe action, typically breaking between about 20 and 40% of the fibres, with an average breakage rate of about 30%; as much as 90% of the fibre breakage that takes place in converting scoured wool into top takes place during carding.9 The card also breaks about 90% of the weathered wool tip. These short degraded fibre fragments either fall from the web as carding waste or are taken out of the sliver when subsequently combed. The level of fibre breakage is influenced by the degree of fibre entanglement developed during scouring, the fibre fineness, strength, length (Fig. 6.4)10 and friction (lubrication), as well as on the thickness of the fibre layer on the swift, an increase in fresh fibre density on the swift increasing fibre breakage. It is perhaps worth noting that storage and pressing of scoured wool to high density, lead to additional fibre breakage during subsequent processing. Table 6.1 illustrates the potential effects of changes in certain parameters on fibre breakage during carding, summarising results obtained during various experimental studies (some on processed wool) at SAWTRI.11 The disentangling and opening processes may be inadequate to the extent that small tangled balls (tight clusters) of fibres, described as neps, are present in the card web. Poor carding, often indicated by increasing nep content, can be due to damaged or inadequately ground (blunt) card clothing and incorrect settings. Card wire should not be blunt, bent over, flattened or damaged in any other way. Incorrect setting of burr-beaters and crushing rollers may also lead to unacceptable levels of vegetable matter. Reducing the ‘fresh fibre density’ by increasing swift speed, reduces neps and combing waste.12 The quality of the carding operation can be assessed in terms of the following web characteristics: • • • •

Degree of individualisation of the fibres. Uniformity in weight per unit area. Uniformity of blending. Degree of alignment of the fibres.

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167

Mean fibre length of card sliver (mm)

100 34.5 90 27

ge

80

21

ka

re

a re

b

ib of

16

N

70

12 9.5

60 50

40 50

60

70

80

90

100

110

Mean fibre length of raw wool (mm)

6.4 Mean Fibre Length of Card Sliver after 3rd Gilling vs Mean Fibre Length of Raw Wool. [From Aldrich et al.10]

Table 6.1 Summary of breakage results obtained in various experimental carding studies at SAWTRI11 Parameter*

Change in value of parameter

Change in fibre breakage

Style

Spinners to Inferior

6% to 36%

Length

57 mm to 109 mm

19% to 43%

Vegetable impurity

0.5% to 2.0%

10% to 19%

Temp. of scouring

45 °C to 70 °C

12% to 18%

pH of scour liquor

3.4 to 10.8

10% to 24%

Residual grease

0.4% to 1.6%

26% to 40%

Lubricant added

0.4% to 2.1%

2% to 10%

Worker settings

26 gauge to 30 gauge

27% to 42%

* Only one parameter changed in each case.

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Wool: Science and technology

Level of hooks (most hooks occur at the trailing ends of the fibres as they leave the card). Level of neps and vegetable matter.

Although the card can remove pre-existing neps resulting from fibre entanglement in the scoured wool it also forms new neps and fibre structures that tend to form neps during subsequent gilling. The number of neps decrease with an increase in the number of workers, sharpness of card wire, closer worker settings and with a decrease in recycled fibre density/ swift load.12 The number of neps also increase with increasing scoured wool entanglement and with increasing fibre fineness, crimp and length. Neps generally increase from the card to the comb (i.e. during gilling), affecting the amount of noil. Reducing neps by 50% could reduce noil by some 25%. The basic principles of carding remained virtually unchanged for the entire 20th century, probably the most notable changes taking place in the last two decades of the 20th century. These include the development of Very High Speed Carding (VHSC) by the CSIRO (Australia), the IWS and G H Michell (Australian topmaker) in collaboration with Thibeau (France), and the high speed Hercules card by Octir. The former development virtually doubled the carding speed and resulted in the Thibeau CA7 Card, which was exhibited at the 1995 ITMA, a compact version being shown at the 1999 ITMA. On such a card (2.5 m wide), typical production rates achieved are 220 kg/hr for 22 mm wool and 160 kg/hr for 19.5 mm wool. This substantial increase in speed was brought about essentially by two breakthroughs. The first was the development of tandem burr beaters, which overcame the speed limitations of the single burr beater and enabled much higher carding speeds without any sacrifice in vegetable matter removal efficiency. The second innovation involved the use of two doffers at the swift, which maintained the transfer efficiency from swift to doffer (traditionally about 50%) at the higher carding speeds used. Overall, the increase in production speed was achieved by: • • • • • •

Increase in swift speed and diameter. Increase in the number of carding points. Optimising speed ratios between different rollers and fibre diameters. Improved vegetable matter removal. Double doffer. Efficient suction systems to keep the environment clean.

For superfine wools to achieve the longest Hauteur* and lowest noil, the ratio of swift worker pinning density to fibre density should be as high as * Hauteur is the mean fibre length of a top, based upon a length biased distribution.

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169

possible; this can be achieved by increasing pin density or reducing fibre density, but it is not sufficient to reduce fibre density at some stage before the final swift.13 Developments that have helped to reduce the number, frequency and time required for setting and maintenance include: • • • •

Centralised read-out and control of the different production parameters from the operator console. Variable-speed motor drive to allow operational changes of sliver weight, rate of production and carding intensity. Automatic doffing of full cans. Remote card (gap) settings.

Meng et al.14 critically reviewed the studies undertaken on fibre distribution and movement on the various carding elements, these governing carding efficiency, fibre mixing and levelling, productivity and web quality. They noted the pioneering work of Montfort15 in mathematically modelling the fibre transfer process in a roller-top card as a finite Markov chain, this having been extended by other workers to cover other stochastic features of carding.They concluded that, according to theory, fibre mixing and equalising are improved by increasing the collecting power of workers and decreasing doffer transfer efficiency, but that the theory was not always supported by experimental work. Work has also been done to measure the fibre density on the various carding elements, one example being the optical system developed by Rust and Koella.16 The combined carding and combing operations remove some 99.5% of the vegetable matter present in the scoured wool.17 Particularly troublesome, however, is contamination by polypropylene fibres from twine and by polyethylene wool pack fragments; the latter can be avoided by the use of nylon packs.

6.2.3 Preparer (intermediate) gilling Generally, three preparer (intermediate) gilling operations follow carding (i.e. precede combing), coarser pinning generally being used for preparer than for finisher gilling. The purpose of gilling the card sliver prior to combing is to remove hooks, align, straighten and blend the fibres and improve sliver uniformity (by doubling) so as to reduce fibre breakage and noil during combing as well any excessive extensibility of the card sliver. The more aligned the fibres and the fewer the fibre hooks, the lower the chances of fibre breakage during combing. Significant fibre breakage, however, can occur on high-speed intersecting gill boxes when using close front-roller settings.18 Gilling tends to increase neps from fibre structures formed during carding. The gilling

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Feed rollers

Delivery rollers

Typical draft 6

6.5 Intersecting Gill Box. [From Harrowfield.6]

operation mostly removes trailing hooks, hence the need to reverse the direction of the sliver in subsequent operations. Gilling also creates some hooks.19 It is generally recognised that, in terms of the gilling operations, intersecting pins are necessary to ensure the proper drafting of wool. Intersecting (or intersector) gills (Fig. 6.5) generally have either screw-driven or chain-driven fallers or pinned rollers and rotary gills, and can have either single or double heads. Very few screw gills are now manufactured, chain gills dominating the market. The latter are versatile and have a production rate around double that of the screw gills, the pin paths being similar. Screw gills are, however, still preferred for very short fibres and where high loads are required. There are essentially four gilling machine manufacturers, namely NSC Schlumberger, OKK, Cognetex and Sant’ Andrea Novara. Gills can be equipped with either mechanical or electronic autolevellers and also can be fitted with spraying devices. Adding moisture during high speed gilling, e.g. by spraying, is important for achieving the desired regain for subsequent processing. A lubricant (0.1 to 0.3%) can also be sprayed onto the sliver during the first or second gilling operations, to assist in maintaining or increasing regain, minimising static and modifying static fibre-tofibre cohesion.5 Integrated suction and blowing systems keep the heads clean. Okamura et al.20 investigated the competing effects of draft and doubling on sliver evenness, evenness improving with doubling up to 12 slivers, after which it remains largely constant.

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171

Direct linking of the card to the first gill and the third gill to the comb was found to reduce Hauteur but did not affect noil, neps, vegetable matter or fibre length distribution.19 Introducing a fourth gilling operation in such a set up had a beneficial effect on Hauteur and noil.

6.2.4 Combing Combing enables finer, stronger more uniform and less hairy yarns to be spun at better efficiency. Combing aligns the fibres and removes, as noil, fibres generally shorter than about 20 to 30 mm, vegetable matter and neps. Typically, Hauteur is increased by 10 to 15 mm and its coefficient of variation (CVH) is reduced by 10 to 20%,21 while more than 95% of VM and neps are generally removed. Most of the short fibres removed by the comb as noil arise from fibre breakage during carding. Noil removed during combing has a market value about 40% of that of the top and is mainly utilized by the woollen industry. Originally, four types of combing machines, namely Noble (circular), Rectilinear (intermittent), Lister (nip-motion) and Holden (square motion), were used, but today combing is largely done on the rectilinear comb, also called a Continental, French, Heilmann or Schlumberger comb, the other types of combs no longer being manufactured. The move to rectilinear combing is mainly due to the increasing use of dry-combed as opposed to oil-combed tops and the shorter mean fibre lengths of the wool typically being processed nowadays. Rectilinear combing is the only type described here. The principles of combing introduced during the mid 1800s were so good that they are still used today. The rectilinear comb was invented by Heilmann around 1845 and there are now two main manufacturers of wool combing machines, namely NSC Schlumberger and Sant’ Andrea Novara. Examples of modern rectilinear combs are the Sant’ Andrea P100 (production 1.2 to 1.6 kg/mm) and the Schlumberger PB33, combing speeds being as high as 260 nips/min and visual readout providing instant information on virtually all aspects of the combing operation. The basic operations of a combing machine are:1 • •

•

Feeding the slivers, typically 24 to 32, from balls or cans into the machine. Holding the fibres and combing the free fibre ends by means of a cylinder covered with progressively finer pins, any fibres not held being combed out as ‘noil’, along with neps and vegetable matter (Fig. 6.6). Gripping, by means of detaching (drawing off) rollers, and detaching the combed fringe of parallel fibres (which is now free of short fibres and entanglements), holding it, inserting the top comb, and pulling the

172

Wool: Science and technology (a) Circular combing Feed gill Feed grid Wool Nipper brush Beard

Top comb

(b) Detaching phase Upper nipper

Detaching rollers

Detaching apron

Shovel plate

Lower nipper

Circular comb

6.6 Two phases of Rectilinear Combing. [From Harrowfield.6]

•

fibres through the pins of the top comb, which consists of a single row of pins, thereby removing any ungripped fibres as noil as well as neps and vegetable matter (Fig. 6.6). Laying the combed fringe on the previously combed fringes and forming a continuous ‘combed’ sliver from the tufts that have just been combed.

Brushes play an important role in combing; for example, in cleaning the circular and top combs and drawing-off cylinder, and pressing the fibres into the circular comb. Automatic adjustment of brushes, such as the nipper and circular brushes, and the simplified reversal and removal of the latter represent important developments.

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173

A good measure of combing quality for Merino type wools is the percentage of fibres shorter than 15 mm in the top, which should preferably be below 1.8 to 2.0%.22 It is affected by the total fatty matter content of the sliver (minimum 0.6 to 0.7%), the relative humidity (ideally 70 to 75%) and temperature (ideally 20° to 24 °C) of the combing shed, as well as by the regain of the wool (ideally around 20%) and the comb setting. The comb also breaks fibres, the breakage rate decreasing with decreasing fibre length, friction, combing intensity and with increasing fibre alignment and fibre strength. Fibre breakage during combing can range from around 17 to 31%.23 Trailing hooks in the sliver fed to the comb are less likely to be broken during combing,19 hence the importance of an uneven (odd) number of gilling operations between carding and combing, assuming cans are used. The percentage of fibres shorter than 30 mm and of noil are influenced by the following factors:24 •

• • •

Raw wool characteristics (e.g. fineness, staple length uniformity, staple strength, character or style, including levels of vegetable matter and other impurities). Quality of scouring and associated processes (greasy wool opening, wool felting. etc.). Quality of carding (card production, setting, speed). Quality of combing (comb setting, maintenance).

The amount of noil removed during combing may be expressed either as percentage noil or Tear (ratio) as follows: Noil (%) =

mass of noil ¥ 100 mass of (noil + comb sliver)

[6.1]

Ê mass of comb sliver ˆ :1 Ë ¯ mass of noil

[6.2]

Tear ratio = It follows that: Noil (%) =

100

(tear + 1)

[6.3]

6.2.5 Backwashing Backwashing is the process of treating wool slivers and tops in an aqueous detergent solution to remove any remaining unwanted impurities, such as residual grease and lubricants, and also to straighten the fibres (i.e. reduce fibre crimp). A lubricant is added at the end of the process, and also a fugitive tint to produce a temporary improvement in the colour (whiteness) of

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the wool. Typically, 36 slivers are fed to the backwashing machine, which consists of two scouring bowls and one rinse bowl followed by a suction drum dryer. A gilling process normally follows the backwashing process. Backwashing can either precede or follow the combing process, the former option normally being used for oil-combed tops (e.g. to remove dirt prior to Noble combing) and the latter for dry-combed tops (e.g. to reduce residual fatty matter and improve the appearance of the top). Top shrink-resist treatment (e.g. chlorine-Hercosett) is carried out in a machine similar to a backwashing machine except that there are extra bowls for chlorine and resin application (i.e. a total of five bowls) and an extra dryer to cure the resin.

6.2.6 Recombing Recombing was originally introduced for dyed tops, in order to separate and align fibres which became entangled during dyeing and also to remove neps and slubs formed during dyeing, as well as any other remaining short fibres and neps; the neps in the top are generally reduced by over 80% (small neps by 70 to 80% and larger neps by 90 to 95%). A crimping box was introduced at the comb delivery to improve the cohesion and crimp of dyed tops and it is today often also used in first combing, particularly if chain gills are to be used subsequently. Recombing is carried out after top-dyeing, when fibre blends are involved and also when producing high quality tops, and is particularly important when spinning fine high quality weaving yarns (25 tex and finer). In fact, recombing is increasingly being regarded as a cost-effective means of improving spinning and weaving efficiencies and improving fine yarn and fabric quality in terms of yarn faults (neps and slubs). In the case of pure wool, a recombing line typically has four operations, two preparatory gillings preceding combing (often three in the case of dyed tops and four where different fibre types and colours are involved). Combing is followed by two finisher gillings, the chain gill increasingly being preferred. Six operations are typical for wool/polyester blends. The two gillings prior to recombing are aimed at improving fibre alignment, thereby reducing noil, as well as achieving the correct fibre regain and sliver linear density (weight). The first finishing gill after recombing needs to randomize the fibre ends, which have been aligned at the comb, so as to facilitate subsequent drafting. On modern combs, recombing production (kg/hr) for ecru wool is around 2.3 times the mean fibre diameter of the wool being processed. Noil produced during recombing varies from about 2 to 5%, depending upon factors such as the degree of entanglement of the top.

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6.2.7 Top finishing (finisher gilling) Top finishing refers to the ‘finisher’ gilling operations (generally two) subsequent to combing. Combing aligns the leading ends of the fibres, which adversely affects the sliver cohesion and subsequent processing. One of the main objectives of finisher gilling is to again randomise the leading fibre ends by drafting. Additional objectives are further blending, straightening and aligning of the fibres, the addition of moisture (and oil) according to the trade allowances and producing a top of the required linear density and evenness. A sliver (top) that is uniform in its linear density (weight per unit length) is produced and formed into a ball or bump top of specified size and weight. The main actions are drafting and doubling with pin control. Normally, the first finisher operation (gill box) has an autoleveller unit.The first gilling operation generally involves up to 30 doublings and drafts of between 5 and 10, with the second only involving around 4 or 5 doublings.

6.2.8 Prediction of top properties A quality specification for tops could include the following:25 • • • • • • • • • • • • •

Mean fibre diameter Fibre diameter distribution (e.g. CV and Coarse Edge) Minimum (or mean) fibre length (Hauteur) Fibre length distribution (e.g. Max CV and Short Fibres) Oil (extractable or total fatty matter) content (IWTO value is 1%, but normally around 0.7% for dry-combed tops) Moisture content (18.25% IWTO) Colour Maximum coloured (dark) fibres (e.g. 100/kg) Neps and vegetable matter content Linear density Evenness Ash content pH

Considerable experimental work has been done at the CSIR in South Africa26 and the CSIRO in Australia to quantify the effects of raw wool properties on top properties. These studies have led to empirical equations (e.g. CSIRO TEAM formulae) being derived that quantitatively relate the top properties, such as Hauteur, to those of the raw or greasy wool. Two examples are given for purposes of illustration:

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Wool: Science and technology

CSIR (SAWTRI)27 Hauteur (mm ) = 1.89 ¥ SL - 0.075 ¥ D ¥ Cr + 0.085 ¥ St ¥ D - 0.0048 ¥ SL2 - 0.127SL ¥ Cr + 7.44 ¥ Cr - 39.7 [6.4] where SL = Staple Length (mm) D = Mean Fibre Diameter (mm) Cr = Staple Crimp Frequency (No/cm) St = Style Index CSIRO TEAM Formula28,29 H = 0.52 ¥ SL + 0.47 ¥ SS + 0.95 ¥ D - 0.45 ¥ VM - 0.19 ¥ M - 3.5 [6.5] CV(H) = 0.12 ¥ SL - 0.41 ¥ SS - 0.35 ¥ D + 0.20 ¥ M + 49.3

[6.6]

Noil (%) = -0.11 ¥ SL - 0.14 ¥ SS - 0.35 ¥ D + 0.94 ¥ VM + 27.7 [6.7] 2

Ï CV(H) ˆ ¸ Barbe (mm ) = Hauteur Ì1+ Ê Ë 100 ¯ ˝˛ Ó

[6.8]

where H = Hauteur (mm) CV(H) = CV of Hauteur (%) SL = Staple Length (mm) SS = Staple Strength (N/ktex) D = Mean Fibre Diameter (mm) VM = Vegetable Matter Base (%) M = Adjusted Percentage of Middle Breaks, which is given the value of 45 when M < 45% and the actual value when M > 45% Noil = Romaine The constant of 3.5 in eq. [6.5] can be adjusted according to the mill specific conditions. Also

H= where

1.17 ¥ SL 1+ p

[6.9]

eY 1+ e Y

[6.10]

p=

Y = 0.561 - 0.113 ¥ D + 0.0276 ¥ SL - 0.0331 ¥ SS + 0.0125 ¥ M

[6.11]

and 1 - p is the probability that a fibre will not break during processing.

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177

Another formula, requiring a computer program, also provides a measure of fibre length distribution.28,29 The work carried out at the CSIRO led to the development of the Sirolan-TOPSpec processing prediction software,30 which allows Hauteur, CV(H), Noil, short and long fibres and the shape of the fibre length distribution graph to be predicted from the raw wool test results for mean fibre diameter, VM base, staple length, staple strength and the position of staple break. A Topmaker System software was also developed; this also includes a Topmaker Data Management Program.31 These have now been combined in the Topspin computer program, which can be used to predict and model an infinite array of performance and costs for greasy wool, tops and yarn. It is PC-based and can be configured for network. The Internet-based program can be licensed (desk-top licensing model). Generally, Merino type tops for the pastel trade are expected to have fewer than 100 dark fibres per kilogram to be deemed ‘commercially free from dark fibre’. Longree and Delfosse32 reported on the latest results obtained with the Optalyser measurement of dark fibre and other contaminants, including neps, in wool tops. The Optalyser is an instrument that automatically measures and grades into different classes, coloured fibres, neps and vegetable matter particles in wool tops.

6.3

Preparation for spinning (drawing)

Although direct spinning of sliver into relatively coarse yarn is carried out on the semi-worsted system, thereby eliminating intermediate stages such as the roving stage, this requires high drafts, precise drafting and also good fibre control. Nevertheless, it is not yet possible to spin good quality and relatively fine yarn in this manner, partly because it eliminates the beneficial effects of sliver feed reversal and doubling. A sequence of processes, called drawing, is required to gradually and in a controlled manner, through a process of drafting, reduce the sliver linear density while controlling the movement and alignment of the fibres and the sliver linear density and evenness. This enables a roving (twisted or twistless) to be produced, of the linear density and evenness required for the efficient spinning of a yarn of the desired linear density and quality. Worsted drawing is the process of converting the top into a roving suitable for spinning, this also being referred to as ‘preparation for spinning’. Within the present context, drawing can be defined as the series of operations involving doubling and drafting, the machines which work together for this purpose being called the ‘drawing set’.1 Drafting essentially involves two sets of rollers that run at different surface speeds, the surface speed of the front rollers (delivery) being higher than that of the back (feed) rollers. The ratio of the surface speed of the

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delivery rollers to that of the feed rollers represents the numerical draft. The difference in surface speed causes the fibres to slide past one another, thereby reducing the number of fibres in the sliver cross section and its linear density correspondingly. It also helps to align the fibres. The distance between the nips of the front and back rollers is termed the ratch. The amount of draft which can be applied at any one stage is dependent upon the degree of fibre control, and can vary from as low as four to over 25, there generally being an optimum draft, depending upon the fibres and type of system used. The fibres that are not held by either the front roller nip or the back roller nip are called floating fibres; these fibres are not positively controlled, being controlled only by the frictional forces of adjacent fibres. It is these uncontrolled floating fibres that prevent perfect drafting (i.e. where the random fibre arrangement is preserved). Various techniques are used to improve control over the floating fibres, including additives to increase interfibre friction, pins, twist and direct pressure (e.g. double aprons) and certain combinations of these. Most commonly, pins are used to control the fibres during the early stage of drawing and aprons during the final stages, pinned drafting systems generally being able to handle heavier loads and delivery than apron drafting systems (whereas the latter can handle higher drafts). Accurate settings on apron drafting systems are generally also more critical than on pinned drafting systems because the latter tend to be a more ‘tolerant’. Although drafting is an effective means of aligning the fibres and reducing sliver linear density, it increases sliver unevenness. This problem is overcome by combining the actions of doubling and drafting. Doubling is the action of combining (feeding) two or more slivers into a drafting zone, which results in a more even output sliver. If no draft is applied, the irregularity of the output sliver equals that of the input sliver divided by the square root of the number of input slivers, assuming all input slivers have the same linear density. Nevertheless, to achieve the main objective of drawing, namely to reduce the sliver linear density, the overall draft needs to exceed the number of doublings. Typically, four operations, more for finer yarns and for finer and shorter wools, are used – for example, three gillings (e.g. screw or chain gills) and one roving. Factors, such as lower drafts, individual fibre movement, parallel fibres, fibre control, good lubrication and fewer short fibres, contribute towards good roller drafting and evenness of the drafted material. The reversal of the slivers, and consequently also the direction of fibre hooks, improves fibre randomisation during roller drafting and the removal of fibre hooks. This reduces the short-term irregularity of the sliver. Autolevellers, introduced in the early 1950s, are used to improve the evenness of slivers by measuring the sliver thickness/linear density variation and then continuously altering the draft in such a way that more draft is applied to the thicker than to the thinner sections. Autolevellers, using

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179

2 Rovings crosswound on bobbin

Drafting assembly

Rubbing assembly

Winding assembly

6.7 Rubbing Frame. [From Grosberg and Iype.33]

either mechanical or electronic measurement and draft control systems, can correct short, medium and long term variations, including the mean sliver linear density. The final stage of spinning preparation is the roving or finisher stage. The roving is given the required cohesion, either by inserting low levels of twist (flyer) or, more commonly, by a twistless rubbing action (rubbing-frame), illustrated in Fig. 6.7.33 In the case of the production of twisted rovings, the sliver is generally drafted using an apron drafting system, after which twist is inserted by means of a flyer that inserts one turn of twist per revolution. The twisted roving is then wound onto the bobbin, which rotates with a higher surface speed than the flyer. The flyer also avoids balloon formation and any adverse effect on the fibre assembly due to air currents. Electronic flyer roving frames with integrated automatic doffing are amongst the latest developments. In the case of the rubbing-frame, two slivers are normally fed to each drafting head, the strands remaining separate as they are consolidated and given cohesion by means of the oscillating rubbing action of the aprons. The pairs of consolidated rovings are cross-wound onto a double-meche package which is then used to feed two spindles on the spinning frame. In some cases, e.g. for automatic spinning frames, it is also possible to produce a single meche package from a single sliver. Horizontal and vertical rubbing frames are available. High-speed finisher rubbing frames can now also incorporate automatic bobbin doffing (and ticketing) and have spiral guides after the rubbing zone that improve roving cohesion and enable high-speed winding and also trouble-free unwinding on the spinning frame. Electronic

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contactless stop motions between the rubbing aprons and winding rollers can be fitted. Suction systems achieve good cleaning. Speeds of up to 275 m/min can be achieved on vertical rubbing frames with one rubbing zone (single pair of aprons), and up to 220 m/min on horizontal rubbing frames. Different drafting systems are also interchangeable. Flyer rovings and rubbed rovings essentially produce yarn of virtually equivalent quality, although the former generally enable higher drafts, fewer end breakages and higher speeds in spinning. However, the capital investment costs for rubbing-frames are considerably lower than for flyer frames and the production higher, while fibre breakage also tends to be lower. The flyer roving frame, which can accommodate heavier packages (bobbins), has certain advantages over the rubbing-frames when processing fibres with low cohesion and crimp, such as mohair and certain coarse wools, and in some cases also when using spinning frames with broken end detectors or automatic pieceners.

6.4

Semi-worsted processing system

The semi-worsted system, developed in the first half of the 20th century mainly for synthetics and blends, essentially consists of carding, gilling and spinning, and, when spinning medium and fine yarns, also a roving process prior to spinning. Raw wools are scoured and dried, opened, blended and lubricated prior to carding. The machinery used is very similar to that employed in worsted processing. This system has production and economic advantages over both the woollen and worsted system, but generally cannot produce yarns of the same fineness, character or quality. The character of semi-worsted yarns is somewhere between that of the worsted and woollen yarns, being bulkier, weaker and less regular than worsted yarns. A flow chart for the Semi-Worsted System is shown in Fig. 6.1, the absence of a combing operation being the main feature that distinguishes it from the Worsted System. The absence of combing and the very high production levels make it economically attractive and suitable for producing relatively coarse yarns (about 50 to 500 tex) destined for certain end-uses, particularly carpets but also upholstery and hand-knitting yarns. Best results are generally obtained with between about 80 and 120 fibres in the yarn cross-section, the latter being more typical. The Semi-Worsted System is used for medium to long, relatively coarse wools and man-made fibres, and it handles fibres with finenesses between about 9 and 16.5 dtex and with mean fibre length ranging roughly between 150 and 75 mm (but generally not shorter than 60 mm, and with 15% or fewer of fibres shorter than 30 mm). The semi-worsted system does not offer the opportunity to remove postcarding short fibres and neps, making the carding operation a very critical

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one, nep removal increasing with increasing carding power. The subsequent gilling operations can reduce vegetable matter slightly but can also create neps. The configuration of the high-production semi-worsted cards, which are generally covered with rigid metallic wire, depends upon fibre type and characteristics, such as length and fineness, as well as upon the production rate required. A semi-worsted card typically has only one swift, with four or five sets of workers and strippers and usually twin doffers to ensure high production rates.1 Depending upon applications, they can be supplied with morel rollers, a burr roller on the licker-in, with a fancy, with an intermediate doffer and with one or two delivery doffers. Carding is followed by two to three drawing operations, mostly using chain gills, preferably three if no roving operation is involved, so that a majority of trailing hooks enter the spinning frame as leading hooks. The first and/or second passages can be autolevelling. The sliver is then either attenuated further into roving or spun directly on a ring frame, where drafts can be as high as 300 in a multiple (e.g. three) drafting zone, the main drafting taking place in the final double apron drafting zone.34 Correct fibre lubrication, for low fibre-to-metal dynamic friction, good fibre-to-fibre static friction and antistatic properties, is important. The optimum fatty matter content lies between about 0.7 and 1.2%.35 A regain of about 19.5% appears acceptable for carding. Atmospheric conditions of 23 to 24°C and 70 to 75% RH can be regarded as suitable for the processing of wool, while for spinning it is 21 to 25°C and 55 to 60% RH.35 Elliott et al.,35 building upon the work of Richards and Batwin to develop the concept of ‘Total Carding Power’, describe a computer model based upon published empirical and theoretical studies, for simulating the semi-worsted processing of wool, which predicts how changes in scoured wool properties and processing variables affect yarn irregularity, breaking strength and bulk, spinning performance, card waste and card mixing power. They assumed that most fibre breakage occurred when fibres were withdrawn from tufts during opening. Maddever et al.36 reported on an Expert System which can be used to determine a suitable objective blend specification for the manufacture of wool carpet yarn by the woollen or semi-worsted routes, the fibre property specification depending upon the processing route, product specification and technical data.

6.5

Woollen processing system

6.5.1 Introduction The woollen system represents the shortest processing route for staple fibres, essentially entailing only two primary stages, namely carding and spinning, although there is an important preliminary stage involving blend-

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ing, opening and lubrication. Yarns ranging in linear density from about 30 to 2000 tex can be spun on the woollen system. A woollen yarn is defined37,38 as a yarn made from any fibre processed on a card with at least two parts, and at least one intermediate feed, a condenser dividing the card web into slubbings or rovings, which are subsequently spun at drafts of up to 1.6 (or at most 2). Because spinning follows immediately after carding, the fibres are not very well aligned, and woollen yarns tend to be characterised by their bulkiness, low density, less orientated fibres, softness, low twist and hairiness. A ‘woollen yarn’ would normally refer to 100% wool, whereas a ‘woollen-spun yarn’ would refer to a yarn spun on the woollen system but which contains other fibres. Virgin wool represents a relatively low proportion of the total fibres processed world-wide on the woollen system, the bulk being materials such as noils, re-used and reprocessed wools, man-made fibres, cotton etc. It is a very versatile system and represents one of the major systems for processing noils and other forms of fibre waste and recovered fibres into yarn, although capital and labour costs relative to its productivity impact negatively on its competitive position, particularly for medium to fine yarns. The continuing trend towards lighter-weight fabrics has also impacted negatively on the woollen system, although the move towards a more informal or casual form of dress favours it. Purely from an economic point of view, woollen processing compares unfavourably with semi-worsted processing. Nevertheless, these systems generally process widely different fibres and also produce yarns very different in character.The advantage of the woollen system is that it can handle natural and man-made fibres of almost any type, fineness and length, it being stated that any fibre can be processed, ‘provided it has two ends’. In the case of wool, the woollen system handles from lambswool, 19 mm or even finer, to Shetland and crossbred wools 35 mm and coarser. In the main, fibres ranging in mean fibre length from about 25 to 80 mm33 are processed on the woollen system. The wool processed on the woollen system is also referred to as carding wools (e.g. crutchings, locks, lambs and skirtings), generally having staple lengths ranging from about 30 to 50 mm. Woollen carding generally requires a low level of vegetable matter, vegetable matter adversely affecting carding and spinning, and it is important that only wool with little, if any, vegetable matter is processed on this system. This can be achieved by carbonising, a large proportion of wool processed on the woollen system being carbonised. Atmospheric conditions of 65% RH and 20°C are normally acceptable for processing wool on this system.

6.5.2 Pre-carding Good opening and cleaning of the wool prior to carding are beneficial, the pre-carding operation generally involving blending, opening (willeying) and

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183

lubrication (oiling and antistatics). The blending operation, crucial for achieving quality woollen yarns and products, can be either manual or automatic, generally employing ‘sandwich’ (horizontal) layers and ‘vertical slice’ removal. Bin blending is still widely used for wool although various improved feeding and bin-emptying methods (e.g. automatic and continuous) have been introduced, with continuous inclined step blenders of increasing importance. It is vital that the components of the blend be similar in their degree of openness, composition and density. WRONZ applied the concept of linear programming (computer blending) for optimising wool blends for spinning carpet yarns, taking into consideration the relevant wool characteristics, such as diameter, length, bulk, medullation, colour and vegetable matter content.39 The Fearnought (coarse metallic toothed roller) type of machine, automatic or hand-fed, for example, is widely used for opening and blending, particularly at the final willeying (opening) stage prior to carding. It imparts a carding (fibre working) action, tufts being partially opened by the action of the fast moving cylinder and slower moving worker teeth, there often being four workers. Some fibre cleaning also takes place. Oiling/lubrication, generally takes place here, preferably at the exit, which is more effective, does not lead to the contamination of the Fearnought and does not interfere with its cleaning efficiency.

6.5.3 Lubrication (oiling) The effectiveness and efficiency of woollen carding, and in particular fibre breakage, are dependent upon various factors, notably fibre lubrication. It is critically important that the wool is optimally lubricated prior to carding in order to minimize fibre breakage, fly waste and static electricity, provide additional fibre cohesion and facilitate drafting, condensing and spinning. Between about 5 and 10% of oil is usually applied, either as a straight oil or preferably a 50/50 oil/water emulsion, the card generally being key in the even distribution of the lubricants/additives. Lubricants are used to:40 • • • •

Reduce static, fibre breakage and friction against the condenser rubber Lubricate the fibres for drawing and twisting Increase fibre cohesion Control the rate of build-up of trash on the card.

The essential requirements of a wool lubricant are as follows: • • •

Must have good lubrication and anti-static characteristics in carding and spinning within the temperature ranges experienced Should not discolour the wool Should not impair the strength of the fibre

184 • • • • • • •

Wool: Science and technology

Must not cause rusting or corrosion of the clothing (surfaces) with which it comes into contact Should not reduce the life-span of the leather aprons or condenser tapes Should form a stable and uniform emulsion with soft or moderately hard water Must remain stable in storage under various conditions of temperature Must be easily removed by scouring Should not cause or support spontaneous combustion Should not have or create an objectionable odour.

A further requirement today is that the lubricants should be environmentally friendly (e.g. bio-degradeable).

6.5.4 Carding Because of the very shortness of the woollen processing route, the carding stage is critical and the woollen card is very sophisticated, particularly when relatively fine yarns are being produced. The card web needs to be uniform, both in terms of fibre blend and density (mass), across its width and along its length. The card needs to separate (individualise) and mix the fibres and this requirement largely determines the number of carding units.42 The production of a woollen card is greatly dependent upon its width, which can vary from 1 to 4 m (typically around 3 m), and the fineness of the fibre being processed, increasing the card production rate tending to cause a deterioration in slubbing and yarn quality and neppiness. Neps increase as the wool becomes finer, carding rate increases and number of swifts decrease. Over the years there has been little real improvement in the basic productivity of the worker, stripper, swift and doffer actions, increased production largely coming from the increased width of the card. Uniform feed, by a feed hopper, to the card is very important in terms of productivity and web and yarn quality, notably evenness. Feed can be manual, semi-automatic or automatic. The hopper feeds the tufts of fibres to the card, the aim being as uniform a feed of fibres as possible (in terms of both composition and weight), often achieved by weighing or otherwise monitoring and controlling the tufts and their rate of supply to the card. Automatic hopper feeds can provide either ‘weigh’ (gravimetric) or volumetric ‘chute’ delivery, with or without control systems, the latter entailing monitoring, correcting and controlling. There has been a significant move to chute feed-hoppers, hopper-fed via spiked lattice or automatically from a bin. Examples of advanced feed control systems are the Tathams Microweigh 2000 system for a weigh hopper feed and the Microfeed 2000 and HDB Servolap for volumetric chute hopper feeds. Double hoppers, microprocessor-controlled hoppers and volumetric feeds with autolevellers

Mechanical processing for yarn production Feed section

Scribbler

To carder

185

Peralta rollers Swift Doffer

Swift Doffer

Swift Doffer

Condenser Carder From scribbler

Slubbing on bobbins

Swift Doffer

Swift Doffer

6.8 Woollen card. [From Grosberg and Iype.33]

provide good long-term evenness, although some medium- and short-term variation remains.41 The composition of the woollen card (Fig. 6.8) depends upon the type of fibres to be processed, as well as the range of yarn linear densities to be produced, the card generally consisting of between two and seven units, typically four, each with a swift. The two-card set, with an intermediate feed, is becoming increasingly popular. The major differences between woollen carding sets are as follows: • • • • • •

Number of Sections Number of Swifts Number of Workers per Swift Type of Intermediate Feed Type of Condenser Type of Card Clothing

As shown in Fig. 6.8, a typical woollen card essentially consists of two parts or sections, namely the scribbler (breaker card) and carder (finisher card), there typically being two or three cylinders (swifts), each with a doffer (and four or five pairs of worker and stripper rollers each) in each section. The density of card clothing pinning increases along the machine, thereby increasing the opening of the fibre tufts correspondingly. Typically, the carding unit is made up of a breast section clothed with metallic wire with two workers and strippers; this is where the opening and disentangling of tufts commences. From the scribbler the sliver is fed, crosslapped (cross-

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fed) to improve blending, to the next section, i.e. to the carder. Various combinations of metallic and flexible card wire are supplied with woollen cards, the combinations depending upon the nature of the fibre being processed. Because of the high levels of oil used, flexible wire clothing, as opposed to metallic wire, was traditionally used on woollen cards, but there has been a significant move towards rigid metallic wire (garnett) clothing, the early part of the card (feed and breast sections) having been metallic for many years. Metallic wire is used extensively for synthetics and well-scoured coarse wools, semi-rigid or fillet wire being more popular for relatively ‘greasy’ and fine wools, although even in the case of fine wools there is a move towards metallic wire, particularly for the scribbler section (A G Brydon, private communication). After the scribbler, the fibrous web can be passed through crush (‘Peralta’) rollers. The Peralta hardened steel rollers (precision ground and perfectly set) at the end of the scribbler section, crush vegetable matter, such as burr, in the open fibre web, the smaller crushed particles being easier to remove. The much finer fibres are not damaged to any significant extent. On a woollen card there are typically around 15 to 30 positions where a carding or working action (closely set point-to-point) takes place, which breaks down the tufts into individual fibres, a typical fibre passing through such an action between 100 and 300 times.42 Fibre separation (working) generally takes place where two card-clothed surfaces, set closely to each other and the teeth pointing towards each other, move at different speeds. The stripping action occurs when a faster moving roller, with the clothing tips pointing in the direction of movement, removes all the fibres from the backs of the teeth of a slower moving roller. Fibre opening takes place at the interfaces between the feedrollers and licker-in, the swift and the workers, and the doffer and swift, being completed when the fibre reaches the last swift of the scribbler section. The main opening at the swift–worker interface is due to the combing action of the swift wires on the tufts of fibres held by the slower moving workers. Work by WRONZ43,44 has modelled fibre breakage on the basis of fibre tensile properties and the mechanics of tuft opening. In addition to fibre separation, during which process significant fibre breakage takes place, the carding operation is also crucial for blending (mixing) the fibres, the collecting power of the doffer playing an important role in this respect. According to Richards,45 the Delay Factor (D), or time constant, which is a measure of the average time that fibres take to pass through a part (excluding time on doffers), may be calculated as follows: Ê ˆ D (Delay Factor) = 1 f Á 1 + Â np 1 - p˜ Ë ¯

[6.12]

Mechanical processing for yarn production

187

where f = collecting fraction of the doffer p = collecting fraction of the worker n = number of swift revolutions during which the fibre spends on a worker, stripper and swift from when it is picked up until it is released again. In the case of four workers this becomes: 4 np ˆ D = 1 f Ê1 + Ë 1 - p¯ Ê ˆ C (Carding Power) = 1 f Á 1 + Â 1 1 - p˜ Ë ¯ C, a measure of the card–opening ability and determined by the average number of times a fibre passes through the setting region between swift and workers and swift and doffer, is the same as the average number of workings (t) received by a fibre as derived by Montfort.46 Carding power increases as the delay factor increases. The Intermediate feed (intermittent or continuous) transfers the output of the one carding machine (section) to the next, the objectives being: • • • •

to convert the fibres emerging from the one carding section into a convenient form for transfer to the next carding machine or section to reduce irregularities in the rate of flow of fibres through the card to improve fibre blending to produce a uniform shade where fibres of different colours are involved

Examples of the different types or combinations of feeds are: • • • • •

Pull-away Centre-Draw and Cross Feed Wide Side-Draw and Cross Feed Pull-away Centre-Draw Scotch Feed (finer yarns) Parallel-Fibre Feed (bulkier fibre and coarser yarns)

The pull-away centre-draw, reciprocating overhead and Scotch feed is considered to offer a simple, yet effective, operation. The Scotch feed is popular as it is simple, versatile and convenient for small lots. The wider cards have resulted in a move away from the side-draw Scotch feed system to centre-draw cross-feed and broad-band or parallel-fibre feed systems. The Condenser divides the web of fibres emerging from the last (final) carding machine into a number of continuous ribbons, consolidates these ribbons into cylindrical, twistless slubbings and winds the slubbings onto individual cheeses positioned side by side on condenser bobbins (posi-

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tioned in a creel) for transfer to the spinning frame. There are two different methods of condensing, namely by Ring Doffers or by Tape Condensers, the latter being more common. Ring Doffers (single or double) separate the web into ribbons by a carding action, producing strong, straight and uniform slubbings while Tape Condensers (Series or Endless) separate the web into ribbons by a tearing action. Tape condensers can be offered with single (fine yarn), tandem/double (medium yarns), or triple (coarse yarns) rub arrangements. Tape condensers are generally manufactured with four or six heights (tiers), the latter increasing the production and number of ends, or the end spacing, and package size. Condenser rubbing leathers, used for condensing the narrow strip of materials, are made in various designs; leather aprons have largely been replaced by either grooved or smooth fabric/rubber/ synthetic aprons. A well-rubbed slubbing has good cohesion and wraps onto the condenser bobbin well and unwinds easily and cleanly during spinning, different creel assemblies being used for mule spinning and ring spinning creel assemblies including Ordinary, Traverse and Tandem. Doffing of the condenser bobbins can be either manual or automatic, being one of the most costly operations in woollen processing. Automatic doffing can increase card productivity by up to 12%. Two systems are available to increase the length of slubbings (by up to 50%) on the condenser spool, thereby extending the time cards, and spinning frames can run between creel changes. They are the Tathams Denspak Creel System and the High Density Spooling (HDS) System. The latter was first shown at ITMA in 1987, utilising friction in a groove and a difference in the surface speed of the bobbin/spool and the rubbing apron to create controlled tension and drafts (about 6% actual), enabling increased card production. It also has a beneficial effect on spinning performance and yarn properties. Optical- and capacitance-based devices are used to automatically monitor the evenness of the slubbings or rovings at the output of the card, between the rub apron and the package. One such system (Rovingtex), using a capacitance measuring system, has an alarm should the values exceed preset limits. Open and closed loop automatic controllers are used to correct variations in card web mass per unit area. Automatic setting of the machine when changing slubbing weight (linear density) is also available. The use of electronics for control and automation has been one of the main areas of development, it now being possible to electronically programme and control the main functions of the woollen card. Significant fibre breakage takes place during carding, the amount of fibre breakage depending upon factors such as fibre entanglement, fibre lubrication (friction), fibre strength, fibre length, fibre crimp, fibre regain and the severity of the carding action.

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6.5.5 Woollen spinning* Although ring frames dominate woollen spinning, the mule frame still occupies an important position. The ring frame produces about 2.5 times per spindle more than the mule frame and occupies about a third of the floorspace per spindle. The mule can, however, spin lower twist, bulkier, softer, more even and less hairy yarn, and can handle more difficult fibres and blends than the ring frame. Mule spinning enables finer yarns to be spun than ring spinning, due to the lower tensions involved and the advantages of spindle drafting over roller drafting, drafts often being about 5% higher. Mule spinning, however, is more labour intensive and requires greater operator skills than ring spinning. It is generally accepted that commercial woollen spinning limits are about 100 fibres (125 being more typical) in the yarn cross-section, compared to 40 for worsted spinning, Lee22 suggesting a minimum of 120 per strand for two-ply yarn and 200 for singles yarn. In woollen spinning, draft (normally at least 1.2 but less than 1.6, with a maximum of 2) is usually effected against twist, its main function being to straighten rather than to relatively displace the fibres.

6.5.5.1 Ring spinning A false twist device in the drafting zone close to the front rollers, inserting about 80 to 160 turns/m (typically 40% of the spindle speed), reduces the strand irregularity by preferentially drafting thick places with low twist, since twist generally runs into thinner places thereby increasing inter-fibre cohesion. Drafting is affected by the orientation of the hooks in the slubbing, best being when the slubbing is fed with the majority of hooks trailing, a draft of around 1.5 appearing to be desirable. Collapsed balloons (e.g. using a spindle top extension probe or finger or else a modified spindle top) have become popular and rings with diameters of up to 300 mm are used, traveller speeds peaking at around 40 m/s. Automation in ring spinning, e.g. automatic doffing of full packages, fitting of new tubes, replacing slubbing packages, joining of slubbings, underwinding, stopping and restarting, represent notable developments. Automatic doffing reduces labour and improves productivity, and so have end-break detectors and monitors that allow rogue spindles to be identified, 3 to 4% of such spindles often being responsible for 30 to 40% of end breaks. Information on traveller, roller and spindle speeds enables yarn production and twist to be determined by monitoring systems, such as the Uster

* Note: See also Section 6.6 Spinning

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Ringdata. Electronic console adjustment of the various spinning operations and parameters is also possible. 6.5.5.2 Mule spinning This system of intermittent spinning was invented by Samuel Crompton in 1774, the self-acting mule being patented by Roberts in 1825, and is now virtually only used for spinning fine woollen yarns (woollen mule) from woollen slubbings. The mule frame, utilising draft-against-twist, comprises two parts: a fixed part (headstock) and a moving part (carriage) that moves backwards and forwards on rails (although in some cases, the carriage remains stationary while the headstock moves, while in others, both systems move). The operation of the woollen mule consists of the following five stages (Fig. 6.9): i) Slubbing Delivery: The carriage moves forward at approximately the same speed as the slubbing is delivered and the spindles rotate at a slow speed to insert twist into the slubbing. ii) Drafting: At this stage the delivery rollers stop but the carriage continues to move and the spindle continues to rotate at the same speed, thereby causing a draft-against-twist of the twisted slubbing. iii) Final Twist Insertion: At this stage the carriage is stationary at its most forward position but then moves slightly towards the stationary delivery rollers to compensate for yarn shortening due to the twist, and the spindles are now rotating at full speed to complete twist insertion (the faller wires out of operation). iv) Backing-off: With the carriage stationary, the spindle now rotates in the opposite direction, thereby unwinding the yarn remaining on the spindle when twisting stopped. The winding faller is lowered and the counter faller raised so as to take-up the slack in the yarn, the winding faller being level with the nose of the cop. v) Winding-on: The carriage returns towards the rollers to assume its original position at the start of the cycle; the spindles rotate to wind the yarn onto the cop under the guiding of the winding faller. Today, electronic (computer-controlled), totally-automated self-acting Mule spinning frames are produced, modern examples attaining speeds of 15 to 18 m/min and featuring automatic doffing, fitting of empty tubes, yarn tension control, slubbing replacement and piecening, the complete cycle taking less than four minutes. 6.5.5.3 General Woollen yarn properties can be predicted from the wool fibre properties, very much as is the case for worsted yarns.47,48,49 On the basis of their

Mechanical processing for yarn production

191

Condensed slubbing Condenser bobbin Delivery rollers Winding-faller Yarn Spindle Carriage

Surface drum Counterfaller (a) Condensed slubbing

Twisted slubbing

(b)

Yarn

(c) Winding-faller Counter-faller

(d) Counter-faller Winding-faller (e)

(f)

6.9 Mule Spinning [From Octoby1].

processing trials on 68 wool lots, and using multiple regression analysis, van der Merwe and Gee47 established empirical relationships between on the one hand, carding and spinning performance and yarn and knitted fabric performance, and on the other hand, fibre properties. They showed that mean fibre diameter and its CV were the most important fibre properties influencing processing performance and yarn and fabric properties. The next most important property was fibre bulk resistance to compression followed by mean fibre length. An increase in either mean fibre diameter or

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CV of diameter, more specifically the former, in most cases had an adverse effect on carding performance and yarn properties. An increase in bulk resistance to compression had an adverse effect on yarn and fabric strength, fibre breakage during carding, fabric abrasion resistance and spinnability but had a beneficial effect on yarn extension, bulk and hairiness and on cross-card variation. An increase in mean fibre length, within the ranges covered, generally had a beneficial effect. A ‘length after carding’ test has also been developed in which a small scale card and double draft gill system are used to convert the scoured wool into a sliver suitable for Almeter fibre length measurement.50 It correlates well with actual results.

6.6

Spinning

6.6.1 Introduction The ultimate aim of spinning is to produce yarn (i.e. a coherent and cohesive fibre strand) of the required linear density (count) and which has good evenness, tensile properties and a minimum number of faults. Spinning can be divided into the following three basic operations: i) Attenuation (drafting) of the roving, sliver (semi-worsted) or slubbing (woollen) to the required linear density. ii) Imparting cohesion to the fibrous strand, usually by twist insertion. iii) Winding the yarn onto an appropriate package. Spinning machines can be divided1 into two main groups, namely intermittent (e.g. mule) and continuous (e.g. ring, flyer, cap, open-end, self-twist, twistless, wrap-spinning). It should be noted that wool is not commonly spun on the open-end (rotor) spinning system, although a recent paper51 indicates progress in this direction, 42 tex to 111 tex yarns being spun successfully from 20.5 mm wool at speeds of around 100 m/min. Nevertheless, the wool has to meet very strict requirements in terms of residual grease levels (0.1 to 0.3%) and fibre length; for example, an average fibre length of 30 to 40 mm is required for a 46 mm rotor diameter, with the longest 1% of fibres not exceeding about 60 mm.

6.6.2 Ring spinning Because of its versatility in terms of yarn linear density and fibre type, and also the superior quality and character of the yarn it produces, ring spinning (Fig. 6.10) remains by far the most popular system for spinning wool, particularly for fine yarns, there being some 16 million long-staple ring spindles installed worldwide. It includes two-strand and compact/ condensed type spinning.

Mechanical processing for yarn production

193

Front drafting rollers

Lappet guide

Yarn Bobbin Ring

Traveller

Ring rail

Package Drive

6.10 Ring Spinning [From Grosberg and lype 33].

The input into the ring-frame can be twistless (rubbed) or twisted (flyer) rovings in the case of the worsted and semi-worsted system, slivers in the case of the semi-worsted system, and slubbings in the case of the woollen system. Double apron drafting, draft typically 20, is generally used in modern ring-frames, except in low-draft woollen spinning and some of the high-draft spinning systems. The yarn production of ring-frames is limited largely because of limitations in the speed of the traveller on the ring (around 40 m/s maximum), due to excessive wear and heat being generated by the traveller at high speeds, as well as by the yarn tension and tension variability (peaks) generated during spinning. The maximum spindle speed is normally around 13 000 r/min and yarn production 40 m/min. The tension on the yarn can be controlled by the traveller, largely depending upon the frictional resist-

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ance of the traveller against the ring, which in turn is largely determined by the rotational speed. Requirements of the traveller include good heat dissipation, sufficient thread space, matching of traveller size and shape to the ring flange and good sliding properties.1 Yarn spinning tension is affected by the length and diameter of the balloon, the use of balloon control or suppression devices (e.g. rings, and spindle attachments) enabling the yarn tensions in the balloon to be reduced by reducing (semi-collapsing) or collapsing the balloon, thereby allowing spinning speeds and/or package sizes to be increased and power consumption to be reduced. Traveller speeds as high as 45 m/s become possible when, for example, using sintered rings and nylon travellers. The use of collapsed balloons is particularly important for the larger packages used in woollen and semi-worsted spinning systems. Rotating rings were explored as another way to overcome traveller speed and yarn tension limitations, but they have not yet found wide application. According to Oxtoby1, about 85% of the total power requirements of a ring-frame is consumed in driving the spindles (depending on yarn density, package size, spindle speed, etc.), the balance being consumed by the drafting and lifter mechanisms. The following factors have the main influence on spinning conditions:1 • •

• •

Ring diameter (affects package size, yarn tension, traveller and spindle speeds, power consumption, capital costs, floorspace and doffing costs). Balloon height (affects power consumption, capital cost, floorspace, doffing costs, balloon collapse). Longest balloon height without balloon collapse is the most economical. Spindle speed. Traveller mass.

Spinning production and cost are related to the level of twist inserted, which in turn is related to spinning efficiency (end breakage rate) and yarn properties (notably tensile, bulk, hairiness and stiffness). The minimum twist required to produce acceptable spinning performance and yarn properties is normally selected. It is generally held that surface fibres have the same angle of inclination to the yarn axis when yarns have the same twist factor (turns/cm ÷tex), and that such yarns therefore have a similar geometry. Fibre migration (variable helix angle at different positions along the fibre length) determines the yarn structure, and properties and can be characterised by:1 • • •

Mean fibre radial position Migration amplitude Mean migration intensity (i.e. rate of change of radial position)

Mechanical processing for yarn production

195

Modern ring frames can incorporate automatic doffing, sliver/roving stop motions, thread break indicators, electronic speed and package building programs, and automatic piecening, data collection, ring cleaning. They can also be linked to the winders, with a cop steamer stage between spinning and winding.52 Turpie53 developed the MSS accelerated spinnability test while Huang et al.54,55 developed a model for predicting end breaks in worsted spinning. Yarn strength variation, followed by mean yarn strength and spinning tension were the main factors in the model. They found that the spinning tension varied considerably, the CV being typically 15 to 20%. End breaks are caused either by the yarn spinning tension exceeding the yarn strength (more particularly that of the yarn weak places) or by flaws, such as neps, vegetable matter and short fibres, in the input material. Various studies,26,56 have shown that mean fibre diameter is by far the most important fibre property in terms of spinning performance and limits, and yarn quality, this largely because of its effect on the number of fibres in the yarn cross-section when yarn linear density is constant. It is followed in importance by mean fibre length (a 10 mm change in mean fibre length having approximately the same effect as a 1 mm change in mean fibre diameter), then fibre length distribution (CV and short fibres), fibre crimp (lower crimp generally beneficial), fibre strength and CV of diameter (a 5% absolute change in CV having approximately the same effect as a 1 mm change in mean fibre diameter). For worsted ring spinning, spinning limits are normally taken to be 35 fibres in the yarn cross-section although commercial spinning limits range between 40 and 50 fibres, generally 50 for dyed fibres. Normally, around 40 to 50 end breaks per 1000 spindle hours represent the maximum acceptable limit for commercial spinning of wool. The average number of fibres (n) in the yarn cross-section can be calculated as follows: n=

972 ¥ yarn linear density 2

Ï CVD ˆ ¸ D2 Ì1 + Ê Ë 100 ¯ ˝˛ Ó

where yarn linear density is in tex units, D = mean fibre diameter (mm), and CVD = CV of fibre diameter (%) For a fairly typical CVD of 24.5%, equation [6.13] becomes: n = 917 tex/D2.

[6.13]

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Wool: Science and technology

According to Martindale,57 the limiting (or ideal) yarn irregularity (CVL) assuming completely random distribution of fibres, can be calculated as follows: 2

Ï Ê CVD ˆ ¸ Ì1 + 4Ë ˝ 100 ¯ ˛ CVL (%) = 100 Ó n

[6.14]

which becomes 2

Ï Ê CVD ˆ ¸ Ì1 + 5Ë ˝ 100 ¯ ˛ Ó CVL = 3.208D tex

[6.15]

or CVL =

3.208 Fe tex

[6.16]

where Fe is the effective fineness as termed by Anderson.58 CVD ˆ Fe = D 1 + 5Ê Ë 100 ¯

2

[6.17]

Fe illustrates the relative effects of D and CVD on yarn irregularity as well as on yarn and fabric stiffness.59,60 An irregularity index (I) for yarns and slivers is also often used to provide a measure of the yarn unevenness relative to the fibre used. I can be calculated as follows: I=

CV(%) CVL

[6.18]

If CVD = 25% this becomes: I=

CV(%) n 112

[6.19]

where CV(%) = actual or measured yarn or sliver irregularity and n = the number of fibres in the yarn (or sliver) cross-section, calculated according to eq. [6.13]. I = 1.2 is regarded as very even for worsted yarns and 1.4 for fine woollen yarns.22 Bona61 gave the following empirical relationship, based upon an important worsted spinning mill in Biella, which enables the optimum fibre fineness (diameter) to be calculated if the desired yarn linear density is known,

Mechanical processing for yarn production

197

and the optimum yarn linear density to be calculated for a given fibre fineness or diameter: ns =

150 3

Nm

0.33

= 15( 3 tex ) = 15(tex)

[6.20]

where ns = optimum average number of fibres in the yarn cross-section. Comprehensive empirical studies have been carried out at the CSIR in South Africa26 and the CSIRO in Australia to relate ring spinning performance and yarn properties to top fibre properties and to derive empirical relationships that quantify the various effects and enable prediction. The following are examples26 of the empirical relationships derived in South Africa on the bases of the results obtained on more than 1000 wool worsted yarns.

where

Irregularity (CV%) a D 0.8 L-0.2Compr. 0.1 tex -0.4

[6.21]

Tenacity ( cN tex ) a D -0.8 L0.4 Compr. -0.2 tex 0.2

[6.22]

D = Mean fibre diameter (mm) Compr. = Resistance to compression (mm) L = Mean fibre length (mm)

The general empirical relationship between Irregularity and number of fibres (n) in the yarn cross-section and mean fibre length (L) was found to be: Irregularity (CV%) a L-0.2 n -0.4

[6.23]

The CSIRO work has led to the Sirolan Yarnspec prediction software,62 which has been superseded by the Topspin computer program that combines top prediction from greasy wool and prediction of spinning performance and singles worsted yarn properties, also including commercial costing details. It also enables the spinning mill to benchmark itself against ‘best commercial practice’. According to the work of Gore et al.,63 the fibre tensile properties do not significantly affect processing performance, from re-combing to yarn and fabric, until the fibre extension at break falls below about 28 to 32% (corresponding to a bundle tenacity of 7 to 9 cN/tex), after which a significant deterioration in performance may be found. Nevertheless, some work64 indicates that a 10% change in fibre bundle strength has approximately the same effect on spinning end breaks as a 6 to 9 mm change in Hauteur. Cheng et al.,65 applied Neural Networks to successfully predict spinning performance and yarn quality.

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Wool: Science and technology

6.6.3 Two-strand spinning (Twin-spun) Considerable efforts have been directed towards eliminating two-folding (plying) in the production of weaving yarns, the ultimate aim being to produce as fine a yarn as possible on the spinning frame, which can be woven without resorting to either two-plying or sizing. In the main, two approaches have been followed, namely: Two-strand spinning (e.g. Sirospun and Duospun) and Compact (condensed) spinning. Two-strand spinning, also referred to as spin-twist or double-rove spinning, involves two rovings being fed separately to the same double apron drafting system, each strand receiving some twist before they are combined at the convergence point after the front rollers. Two examples are Sirospun (Fig. 6.11)68 and Duospun, the former using a mechanical break-out device and the latter suction and automatic repiecening to prevent spinning when one strand breaks. It is also possible to include a filament (flat, stretch or textured). In the case of Sirospun, the only modifications required to the ringframe are the following:

ste

m

Rovings

Dr aft

ing

sy

Spacing guides

Break out device

Spindle

6.11 Two strand (Sirospun) spinning. [From Plate.68]

Mechanical processing for yarn production • • • • •

199

New rear roving guide to feed the two rovings separately to the rear rollers Central roving guide, fitted behind the aprons, which controls the strandspacing A front zone condenser with two condensing slots at the correct strand spacing Break-out device Provision for double creels

The strand length (thread length between the convergence point and the nip of the front rollers) should be a minimum, it being related to the strand spacing.The strand spacing needs to be optimal, as large strand spacing beneficially affects yarn hairiness and abrasion resistance but adversely affects spinning performance. Spinning limits are about 35 fibres per strand crosssection, a low short fibre content being important. A minimum of 0.8% lubricant prior to combing is required, and 4 drawing passages are desirable. A draft of 20 appears optimum.67 Sirospun reduces spinning costs by some 55% on average but increases weaving costs by about 1% because of slightly higher yarn breakage rates. Maximum yarn strength occurs at a tex twist factor of between 38 and 41, increasing to about 44 for very fine yarns.67 The recommended tex twist factor for a Sirospun yarn is around 38 (a m = 120).67 Typically, the tenacity of the two-strand yarn is equal to, or slightly greater than, that of the corresponding two-ply yarn, its extension 10 to 30% greater, its irregularity slightly greater, its hairiness slightly less and it contains more thin places. It also produces a more streaky fabric. Its abrasion resistance falls between that of two-ply yarn and that of a singles yarn of similar tex and twist.68 Compared to a two-ply yarn, however, it is twist-lively (similar to a singles yarn). It is also more circular and less easily deformed. Yarn joint quality is very important, splicing (thermal and pneumatic) generally being preferred, particularly for medium and coarse yarns. Z/Z Fisherman’s knots also give good performance, particularly for fine yarns. Approximately 2% of a suitable lubricant (e.g. anionic) in the final rinse of the package dyeing cycle reduces yarn-to-metal friction and improves warping and weaving efficiencies. The application of a suitable lubricant during beaming also improves weavability. Double-rove spinning of woollen slubbings (lambswool) on a woollen ringframe has also met with some success.69

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Wool: Science and technology

6.6.4 Compact (condensed) and related spinning systems 6.6.4.1 Compact (condensed) spinning Following upon the two-strand spinning developments, further work has been undertaken to produce ring-spun singles yarns with superior properties (notably tensile, hairiness, abrasion and pilling). The ultimate aim was to be able to weave the yarn without plying or sizing. Considerable success has been achieved, although it is not yet possible to produce, in one operation, ring-spun wool yarn with the same weaving performance as the traditional two-ply yarn. It has been stated, however,70 that such yarns are not necessarily a direct substitute for the traditional yarns but that the fabric structure may have to be adapted to the new yarns. A number of papers70–74 at the 2000 International Wool Textile Research Conference in Aachen dealt with Compact and related spinning techniques. The width of the spinning triangle (fibre beard) has been shown to be related to the spinning tension as well as to the hairiness and imperfect integration of the fibres into the yarn.75 Considerable effort has therefore been directed towards narrowing (condensing) the spinning triangle at the exit of the front rollers. Most of the resulting systems, also referred to as condensed spinning, involve a condensed, narrow spinning triangle at the front roller nip (Fig. 6.12),76 and better control of the fibres at the exit of the front roller nip and their integration (binding) into the yarn, eliminating peripheral fibres. This has been done by introducing an intermediate (condensing) zone between the front roller delivery and the yarn formation (twist insertion) point, in which the fibrous ribbon width and spinning triangle are reduced, giving improved spinning efficiencies, fibre alignment, smoothness, hairiness, tensile properties and compactness in the yarn, as well as less fibre waste. The condensing systems used to accomplish this, and which are generally easily attached to, and dismantled from, the spinning frame, generally involve pneumatics (vacuum), applied, for example to a perforated front roller, lattice or apron. Examples include the EliTe spinning system of Suessen, ComforSpun (Com4) of Rieter, and Air-Com-Tex of Zinser. 6.6.4.2 Solospun73,74 Solospun (developed by WRONZ, CSIRO and IWS) merely entails the clipping of a pair of grooved plastic rollers to the drafting arms of the spinning frame, in front of the delivery rollers. These split the fibre ribbon emerging from the front rollers, and do not permit twist to reach the front roller nip, allowing the fibres (substrands) to twist and recombine in such a way as to increase the localized twist (cohesion) and compactness of the

Mechanical processing for yarn production Fibre strand

201

Fibre strand

Main draft zone

Main draft zone

Nip of front rolls

First nip

Compacting zone Second nip

Yarn Yarn

Ring spinning

Compact spinning

6.12 Compact spinning. [From Hill and Brayshaw.76]

substrands and yarn, as well as the fibre integration into the yarn. Thermosplicing (hot air) is recommended, the average splice strength should be 80% that of the yarn. Relatively even yarns of 25 tex to 50 tex and tex twist factors from 33 to 43 (at least 38 for weaving yarns) can be spun, and coarser fibres utilised (65 fibres in yarn cross-section), longer fibres being preferable. Compared to two-fold yarns, yarn production costs can be reduced by up to 50%.

6.6.5 Bicomponent spinning Bicomponent yarns, also referred to as bound yarn, have found a niche in the market, these generally combining pre-spun continuous filament yarns with staple fibres to provide improved properties, such as stretch (e.g. Lycra) and strength. Bicomponent spinning77 (see Fig. 6.13)66 normally involves twisting together either a filament (sometimes water-soluble) or pre-spun staple yarn and a conventionally drafted staple (wool) strand during the spinning operation. It is particularly attractive for the costeffective production of superior yarns, which can, for example, be woven or knitted without any further operations (i.e. eliminating plying, sizing and

202

Wool: Science and technology Filament guide Secondary component (filament or pre-spun yarn)

Roving

Drafting zone

Ring spindle

6.13 Bicomponent spinning. [From IWS.66]

steaming). It also enables coarser fibres to be spun into finer yarns, reduces spinning end breakages, allows higher winding speeds and enables yarn and fabric properties to be engineered by suitable selection of the two components and the way in which they are combined. On the negative side, bicomponent yarns are generally not pure wool or torque-balanced and produce fabrics that are generally more streaky and air permeable and have more conspicuous joints. A suitable type of ‘break-out device’ can be used to prevent the production of a single component yarn. Steam setting at 80 to 85 °C is recommended (55 to 60 °C if a water-soluble filament is used).

6.6.6 Self-twist spinning On the Repco self-twist spinning machines (Fig. 6.14), S and Z twist is inserted alternately into each of a pair of strands, which are then brought together, out of phase, along their length to wrap around each other, thereby forming an alternating twist two-ply structure (22 cm total cycle length) in which the torque of the two strands is balanced by the folding torque of the pair. The drafting zone is a modified double-apron system (back rollers, aprons and front rollers), optimum draft being around 25 for wool. Twistless or lightly twisted (maximum twist in turns/metre = 644 tex-0.5) rovings can be used.

Mechanical processing for yarn production Back rollers

Drafting zone with doubleapron control

Front rollers

203

Point where yarn becomes twofold

Oscillating rollers inserting S and Z twist

6.14 Self-twist spinning. [From Grosberg and Iype.33]

When the pair of strands leave the drafting zone, they pass between a pair of synthetic rubber covered rollers which cooperatively rotate and axially oscillate in opposition.1 The self-twist yarn that is produced is wound directly onto cheeses (yarn tension in cN = 0.3 ¥ tex). This system circumvents the limitations associated with package rotation and balloon formation that apply in ring spinning. The self-twist is dependent upon the tension applied to the yarn. Such self-twist wool yarns can withstand tensions of up to 60 mN/tex but need to be up-twisted for weaving, giving what is termed twisted self-twist (STT) yarn. Some useful definitions and concepts follow: Self-Twist-Factor (STF) = Average self-twist per half cycle (t/m) ¥ tex Generally STF = 1550 Pairing twist (PT) is the minimum amount of uni-directional twist required to make all the ply twist either zero or unidirectional. It is proportional to the average self-twist per half cycle. Pairing Twist Factor (PTF) = pairing twist (t/m) ¥ tex on average = 1.55 ¥ STF For twisted self-twist (STT) yarn the uptwist factor or added twist factor (ATF) may be calculated as follows: ATF = PTF + 880 The above twist factors can be converted to tex twist factor (i.e. t/cmx tex ) by dividing them by 100. In addition to the original self-twist (ST) yarn, a number of other versions of self-twist yarns exist, including the use of one filament (STm) or two filaments (STm)m, as well as their uptwisted and plied versions.79

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Wool: Science and technology

Although self-twist spinning has many advantages over ring spinning, such as production rate, floor space, waste levels, cleanliness, spinning limits (35 fibres per strand), noise levels, power consumption, it is not used much today for spinning wool, but rather for spinning high bulk acrylic for knitting.

6.6.7 Wrap (hollow spindle) spinning Hollow spindle wrap-spinning (Fig. 6.15)66 shown at the 1975 Milan ITMA, in which continuous filament yarn, on a hollow spindle, is wrapped around

Sliver input

Draft zone

Filament binder

Filament cop

Hollow spindle

Take off rollers

Delivery rollers

Take up package

6.15 Wrap spinning. [From IWS.66]

Mechanical processing for yarn production

205

an untwisted wool core (the latter accounting for typically 80 to 95% of the yarn composition), has also found some application for wool. In plain yarns, the number of wraps required per unit length is generally very similar to the number of turns (twists) per unit length used for the equivalent ring-spun yarns. The economics tend to favour wrap-spinning for yarns coarser than about 50 tex. Such yarn is not twist lively and has a soft handle, the yarn being more suitable for coarse count knitting than for weaving. Wrap-spun yarns tend to be less hairy and bulky and equal to, or better, in strength and evenness, and can be spun finer than the ring yarn equivalent. Spinning limits generally lie between about 30 and 60 fibres in the yarn cross-section. The fine filament wrapper is expensive, however. Nunes et al.80 established empirical equations relating wool core/nylon wrapper yarn properties to the yarn structural parameters, separating the effects of the staple fibre from those of the filament wrapper. Naik and Galvan81 also empirically related wrap yarn properties to spinning machine variables. Xie et al.82 showed that the strength of a wrap yarn was largely due to lateral pressure generated in the staple core by the binder helix. Choi83 also presented a yarn model that accurately predicted how wrapping pitch affected the yarn load – extension properties. In a study on woollen wrap-spun yarns, Cheung and Cheng84 found that wrapped yarn elongation was higher than that of ring yarn, increasing with wrapping density and also with yarn linear density, being higher without than with a false twister.

6.6.8 Other spinning systems 6.6.8.1 Treotek Treotek is a WRONZ developed variation of the Sirofil, adding two filaments, which can be water soluble (or one filament plus a pre-spun yarn), to staple wool fibres. The number of wool fibres in the yarn cross-section can be as low as 20 (or even 15). 6.6.8.2 Cerifil The Cerifil (Bigagli) system replaces the traditional ring and traveller with an inverted funnel-(cone)-shaped winder, resembling a cap, which is rotated by the yarn itself. It performs two basic functions, namely retarding the winding of the yarn and acting as a rotary balloon limiter, reducing yarn tension (which is adjustable) and end-breakage rate. The Cerifil system, which also eliminates the balloon break, can be incorporated into both semi-worsted and woollen ring frames.

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Wool: Science and technology

2 yarns

PLY yarn

Assembly wound

Doubled ring yarn

Doubled PLY yarn

6.16 Plyfil. [From Fischer.85]

6.6.8.3 Plyfil The Plyfil (Suessen) system (Fig. 6.16), first unveiled at the 1987 ITMA, consists of a five-roller, two pairs of apron drafting system, with drafts of up to 400, being fed by slivers. The Plyfil machine has been referred to as a ‘spin assembly winder’. Yarns are consolidated by a sheath of helically wound fibre ends, wrapped around the fibre core in one direction by air-spinning jets behind the drafting system. The two twistless yarns produced on the Plyfil machine are wound onto each cross-wound package, assembly wound fashion. Generally, two-for-one twisting follows, the folding twist being in the opposite direction to the wrapped fibre sheath but lower than that for conventional two-ply yarn. It can also be used for the worsted spinning of wool, preferably using combed sliver.

6.7

Twisting

The twisting operation, also referred to as plying or folding, is the process where two (sometimes more) yarns are twisted to form a two-ply (or multiply) yarn. Traditionally this was done on a ring-frame (ring-twister) but today it is almost exclusively carried out on a two-for-one twisting machine (Fig. 6.17),33 three-for-one twisting systems having also been developed. Assembly winding is used to assemble two ends of yarn on one package in preparation for two-for-one twisting. It is particularly important to ensure that the two yarns are wound at the same tension. The assembly wound package remains stationary, the yarn passing through a guide mounted on a rotating arm which can freely rotate, through the hollow rotating spindle,

Mechanical processing for yarn production

207

Yarn-winding head

Yarn take-up roller

Yarn guide

Balloon separator

Stationary assemblywound supply package

Rotating spindle Yarn outlet hole

6.17 Two-for-one twisting. [From Grosberg and Iype.33]

then through an eyelet (outlet hole) and from there, via a yarn guide and yarn take-up rollers, to the yarn winding head. One revolution of the spindle inserts one turn of twist into the yarn while the rotating eyelet simultaneously inserts a turn of twist in the yarn in the balloon. Thus two turns are inserted per spindle revolution. (For a detailed description of twisting technology relevant to various textile products see Section 9.2.)

6.8

Winding, clearing and lubrication

Winding (re-winding as it is sometimes called) is aimed at transferring the yarn from the spinning packages (referred to as tubes, cops or bobbins), which normally hold relatively short lengths of yarn, into packages (cones, cheeses, etc.) that can hold considerably longer lengths of yarn more suitable for the subsequent processes, such as yarn preparation, weaving, knitting, package dyeing, etc. The winding process also provides an opportunity for unwanted yarn faults (e.g. slubs and thin or weak places) to be removed

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Wool: Science and technology

(yarn clearing) and the yarn to be lubricated. The latter is often referred to as waxing in the case of knitting, since it entails the use of a solid wax disc for lubricating the yarn. Clearers may be either of the capacitance or optical types, or even a combination of these. (Other aspects of winding and related technology are described in Section 9.3.) Splicing, notably pneumatic, is widely used today, giving joints of acceptable strength and appearance, thermal splicing being considered particularly suitable for wool. On-line monitoring of winding is carried out mainly to provide exact length measurement and control, yarn path control and winding speed control, as well as to provide the necessary management information. On-line monitoring of yarn quality (e.g. hairiness) has also been introduced. Automation (package changing, yarn jointing, etc.), higher speeds, and yarn monitoring and clearing systems characterise modern winders. Automatic linkages between spinning machines and winders, together with inline steaming (setting) of yarn, are also increasingly being used. Maintaining yarn tension also enables twist-lively (i.e. unsteamed) yarn to be wound.

6.9

Yarn steaming (setting)

Yarn is steamed (heat set) in an autoclave after spinning so as to reduce or eliminate the twist liveliness (torque) and snarling tendency of the yarn and thereby facilitate the subsequent winding and twisting (folding) of the yarn, and to avoid fabric distortion (e.g. spirality in knitted fabric). Some modern winders do, however, enable twist-lively yarn to be wound. Different steaming conditions can be employed to achieve the desired effect but it is important to regulate the setting temperature and time, particularly the former, in order to avoid yellowing of the wool. The following is an example of steaming conditions that can be used: • • • • •

Evacuate to 88 kPa (26 inch Hg) Steam at 80 °C for 5 mins Evacuate again to 88 kPa Steam at 80 °C for 15 mins Evacuate to 88 kPa for 15 mins

Longer steaming times, rather than higher temperatures, are preferred if the setting effect is not adequate. In-line steaming on conveyers has also been introduced.

6.10

Top dyeing

Top dyeing is described in Chapter 8. Suffice it to say that it can adversely affect the fibre properties and subsequent processing performance. Work

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by Gore et al.86 indicated that the fibre tensile properties do not significantly affect subsequent processing performance until the fibre extension falls below about 28 to 32%. Recombing improves winding and spinning performance significantly.

References 1 Oxtoby E, Spun Yarn Technology, Butterworths & Co., London (1987). 2 Iype C, Lawrence C A, Mahmoudi M R, Greenwood B D and Delghani A, ‘Cotton System Processing of Wool and Wool-Rich Blends’, Text. Asia, 31, 51 (Oct. 2000). 3 Brearley A and Iredale J A, The Worsted Industry, WIRA, Leeds, UK (1980). 4 Proc. Top-Tech ’96 Conf., Geelong, Australia (1996). 5 Becker W, ‘Lubricants in Wool Top Making’, Proc. 10th Int. Wool Text. Res. Conf., CD-ROM, Aachen, Germany (2000). 6 Harrowfield B V, ‘Early-Stage Worsted Processing – From Scoured Wool to Top’, Wool. Sci. Rev., No. 64, 44 (Dec. 1987). 7 Grosberg P, ‘The Mechanical Processing of Wool’, Proc. 5th Int. Wool Text. Res. Conf., I, 341, Aachen, Germany (1975). 8 Atkinson K R and Saunders R J, ‘Burr Beater Design and Operation Part I: Investigations Using a Mechanical Model’, J. Text. Inst., 82, 433 (1991). 9 Eley J R and Harrowfield B V, ‘Factors Affecting the Maintenance of Fibre Length in Worsted Carding’, Proc. 7th Int. Wool Text. Res. Conf., II, 282, Tokyo, Japan (1985). 10 Aldrich De V, Kruger P J and Turpie D W F, ‘The Carding and Combing of Wools of Different Fibre Lengths’, SAWTRI Techn. Rep. No. 136 (June 1970). 11 Turpie D W F, Private Communication. 12 Harrowfield B V, Robinson G A and Eley J R, ‘The Removal of Entanglements in Carding’, Proc. Symp. Wool Scouring Worsted Carding: New Approaches, 64, CSIRO, Geelong, Australia (1986). 13 Haigh M G, ‘Superfine Wool Processing’, Proc. Top-Tech ’96, 234, Geelong, Australia (1996). 14 Meng J, Seyam A M and Batra S K, ‘Carding Dynamics, Part I: Previous Studies of Fiber Distribution and Movement in Carding’, Text. Res. J., 69, 90 (1999). 15 Montfort F, Carding as a Markovian Process, J. Text. Inst., 53, T379 (1962). 16 Rust J P and Koella E, ‘Carding Fiber Load Measurement’, Text. Res. J., 64, 364 (1994). 17 Robinson G A, CSIRO Division of Wool Technology, Geelong Laboratory, ‘Recent Developments in the Physical Processing of Wool’, Wool and Woollens of India, 25, 41 (Oct./Dec. 1989). 18 Bownass R, ‘Changes in Fibre Length During Early Worsted Processing’, IWTO Techn. Comm. Meeting, Paris, France (Jan. 1984). 19 Atkinson K R, ‘Mill Organisation and Automation’, Proc. Top-Tech ’96, 208, Geelong, Australia (1996). 20 Okamura M, Merati A A, Hasegawa E, Asano Y and Tanaka H, ‘The Role of Fallers in Gill-Box’, Proc. 10th Int. Wool Text. Res. Conf., CD-ROM, Aachen, Germany (2000).

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21 Lee C S P, ‘Early Stage Processing and Spinning with Emphasis on Yarn Quality and Efficiency’, Proc. 1st China Int. Wool Text. Conf., I, 201, Xi’am, P.R. China (April 1994). 22 Lee C S P, ‘Quality Control Aspects of Worsted Processing’, IWS Mech. Process. Techn. Publ., 05.05.92/Release 4 (1992). 23 Kruger P J and Aldrich De V, ‘Fiber Breakage in Rectilinear Combing’, Appl. Polym. Symp., No. 18, Proc. 4th Int., Wool Text. Res. Conf., II, 1375, Berkley, USA (1970). 24 Lee C S P, ‘Quality Control Aspects of Worsted Processing’, IWS Special Publication, Release 5 (1993). 25 Bell P J M, ‘Topmaking Today’, Wool Technol. Sheep Br., 35, 101 (June/July 1987). 26 Hunter L, ‘A Summary of SAWTRI’S Research on Wool and Wool Blends 1952–1987’, SAWTRI Special Publication, WOL 78 (1987). 27 Turpie D W F and Gee E, ‘The Properties and Performance During Topmaking and Spinning of a Wide Range of South African Wools’, Proc. 6th Int. Wool Text. Res. Conf., III, 293, Pretoria, South Africa (1980). 28 Allen D J, Mooy L M, Brown G H and Rottenbury R A, ‘Development of Techniques for Predicting the Processing Performance of Sale Lots, Nice, France’, IWTO Techn. Comm. Rep., No. 12 (Dec. 1990). 29 Allen D J, Mooy L M, Brown G H and Rottenbury R A, ‘Evaluation of Techniques to Predict the Processing Performance of Sale Lots, Nice, France’, IWTO Techn. Comm. Rep., No. 13 (Dec. 1990). 30 Hansford K A, Humphries W and Charlton D, ‘Introducing Sirolan-TOPSpec Processing Prediction Technology: A Review of Sirolan-TOPSpec Development’, Proc. Top-Tech ’96, 332, Geelong, Australia (1996). 31 Couchman R C, ‘Topmaker Data Management Program – The Topmaker System: A Case Study of CSIRO/IWS Technology Adoption’, Proc. Top-Tech ’96, 341, Geelong, Australia (1996). 32 Longree M and Delfosse P, ‘Improvements of the Reliability of Cleanliness Tests on Wool Tops’, Proc. 10th Int.Wool Text. Res. Conf., CD-ROM,Aachen, Germany (2000). 33 Grosberg P and Iype C, Yarn Production, Theoretical Aspects, The Textile Institute, Manchester, UK (1999). 34 Haddad N, ‘Modern Semi-Worsted Technology’, Canadian Text. J., 100, 41 (March 1983). 35 Elliott K H, Carnaby G A and Dent J B, ‘A Computer Model for Simulating the Semi-Worsted Processing of Wool’, J. Text. Inst., 78, 392 (1987). 36 Maddever D C, Cuthbertson I M and Edwards S, ‘An Expert System Tool for Specification of New Zealand Wool to be Used in the Manufacture of Carpet Yarn’, Proc. 9th Int. Wool Text. Res. Conf., IV, 18, Biella, Italy (1995). 37 Ross D A, ‘Review of Woollen Yarn Manufacture’, Proc. 11th Ann. TI Conf., Measurement, Construction and Performance, 79, Christchurch, New Zealand (1983). 38 Ross D A, Carnaby G A and Lappage J, ‘Woollen-Yarn Manufacture’, Text. Prog., 15(1/2) (1986). 39 Carnaby G A, Maddever D C and Ford A M, ‘The Application of Linear Programming to Wool Blending and Specification’, Proc. 7th Int. Wool Text. Res. Conf., II, 186, Tokyo, Japan (1985).

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40 Hayes D, ‘Fibre and Yarn Lubrication’, Text. Month, 38 (July 1972) and 46 (Aug. 1972). 41 Smith P, ‘Control in Carding’, Text. Horiz., 6(5), 25 (May 1986). 42 Richards R T D and Sykes A B, ‘Woollen Yarn Manufacture’, The Textile Institute Manual of Textile Technology, The Textile Institute, Manchester, UK (1994). 43 Carnaby G A, ‘Fibre Breakage During Carding Part I: Theory’, Text. Res. J., 54, 366 (1984). 44 Wood E J, Stanley-Boden P and Carnaby G A, ‘Fibre Breakage During Carding Part II: Evaluation’, Text. Res. J., 54, 419 (1984). 45 Richards R T D, ‘Fibre Motion on a Woollen Card’, J. Text. Inst., 50, P182 (1959). 46 Montfort F, ‘Carding as a Markovian Process’, J. Text. Inst., 53, T379 (1962). 47 van der Merwe J P and Gee E, ‘The Effect of Fibre Physical Properties on Woollen Processing Performance and on Yarn and Plain Knitted Fabric Properties’, Proc. 7th Int. Wool Text. Res. Conf., II, 95, Tokyo, Japan (1985). 48 Mahar T, ‘The Role of Objective Specification for Carding Wools’, Wool Technol. Sheep Br., 37, 20 (March/April 1989). 49 Wood E J and Carnaby G A, ‘Analysis of Spinning-plant Processing Data – I Woollen Carpet Yarn Production’, WRONZ Rep., No. R94 (1982). 50 Grignet J, ‘The Measurement of the Fibre Length Distribution on Wools Used for Woollen Spinning at Several Stages of the Processing: Greasy Wool, Scoured Wool, Slubbings Before Spinning, Made on the Almeter Using a Sliver Preparation Technique’, IWTO Techn. Comm. Rep. to W.G., Length on Raw Wool, Paris, France (Dec. 1988). 51 Krähe U and Schmidt R, ‘Spinning of Pure New Wool on Autocoro Rotor Spinning Machines – An Opportunity for Classic Woollen Yarn Spinning’, Proc. 10th Int. Wool Text. Res. Conf., CD-ROM, Aachen, Germany (2000). 52 Tautenhahn K, ‘Worsted, Semi-Worsted and Woollen Spinning and Recycling Processes’, Int. Text. Bull., (ITB) Yarn Forming, (4/91), 20 (1991). 53 Turpie D W F, ‘A Rapid Measure of Spinning Potential, Mean Spindle Speed at Break’, SAWTRI Techn. Rep., No. 240 (Feb. 1975). 54 Huang X C and Oxenham W, ‘Predicting End Breakage Rates in Worsted Spinning, Part I: Measuring Dynamic Yarn Strength and Tension’, Text. Res. J., 64, 619 (1994). 55 Huang X C, Oxenham W and Grosberg P, ‘Predicting End Breakage Rates in Worsted Spinning, Part II: A New Model for End Break Prediction’, Text. Res. J., 64, 717 (1994). 56 Hunter L, ‘The Effects of Wool Fibre Properties on Processing Performance and Yarn and Fabric Properties’, Proc. 6th Int. Wool Text. Res. Conf., I, 133, Pretoria, South Africa (1980). 57 Martindale J G, ‘A New Method of Measuring the Irregularity of Yarns with Some Observations of the Origins of Irregularities in Worsted Slivers and Yarns’, J. Text. Inst., 36, T35 (1945). 58 Anderson S L, ‘The Measurement of Fibre Fineness and Length: The Present Position’, J. Text. Inst., 67, 175 (1976). 59 de Groot G J J B, ‘The Effect of Coefficient of Variation of Fibre Diameter in Wool Tops on Yarn and Fabric Properties’, Wool Technol. Sheep Breed., 40, 60 (1992).

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60 de Groot G J J B, ‘The Use of Effective Fineness to Determine the Effect of Wool-Fibre-Diameter Distribution on Yarn Properties’, J. Text. Inst., 86, 33 (1995). 61 Bona M, ‘Trends in the Wool Industry from Superfine Yarns to Superlight Fabrics’, Int. Text. Bull., (ITB), Yarn and Fabric Forming, 43(1/97), 12 (1997). 62 Lamb P R and Yang S, ‘Choosing the Right Top for Spinning’, Proc. Top-Tech ’96, 258, Geelong, Australia (1996). 63 Gore C E, Lee C S P and Van Haaften G K, ‘Measurement of the Physical Properties of Wool Fibre and their Relevance in Subsequent Processing Performance’, Proc. Int. Symp., 187, Ghent, Belgium (March 1990). 64 Yang S, De Ravin M, Lamb P R and Blenman N G, ‘Wool Fibre Bundle Strength Measurement with Sirolan Tensor’, Proc. Top-Tech ’96, 293, Geelong, Australia (1996). 65 Cheng W, Lu K and Zhou Q, Applications of Neural Networks in Spinning Prediction, Proc. 10th Int. Wool Text. Res. Conf., CD-ROM, Aachen, Germany (2000). 66 Anon., IWS Wool Profiles, Training Programme (1988). 67 Lee C S P, Improvements in Sirospinning, IWS, Ilkley UK (1985). 68 Plate D E A, ‘Sirospun: Goodbye to the Twofold?’, Text. Horiz., 2(2), 34 (Feb. 1982). 69 Cassidy T, Timmins P and Lee C S P, ‘An Evaluation of Double-Rove Lambswool Woollen Yarns’, J. Text. Inst., 79, 264 (1988). 70 Artz P and Betz D, ‘Compact Spinning – Chance for Wool Processing – With New Yarn Structure to Innovative Products’, Proc. 10th Int. Wool Text. Res. Conf., CD-ROM, Aachen, Germany (2000). 71 Hountondji A, ‘Elite Spinning System for Long Fibres’, Proc. 10th Int. Wool Text. Res. Conf., CD-ROM, Aachen, Germany (2000). 72 Dinkelmann F and Olbricht A, ‘Opportunities and Risks of New Technologies in the Spinning of Wool and Wool-like Fibres’, Proc. 10th Int. Wool Text. Res. Conf., CD-ROM, Aachen, Germany (2000). 73 Fukuhara S, Endo S and Hori M, ‘The Effects of Spinning Conditions and Yarn Composition onto Yarn and Fabric Performance in Solospun (Weavable Single Yarn Spinning)’, Proc. 10th Int. Wool Text. Res. Conf., CD-ROM, Aachen, Germany (2000). 74 Kim S J and Park S H, ‘Solo Spinning Technology – The Physical Properties of the Worsted Yarns and Fabrics’, Proc. 10th Int. Wool Text. Res. Conf., CD-ROM, Aachen, Germany (2000). 75 Stalder H, ‘ComforSpin – A New Spinning Process’, African Text., 16 (April/May 2000). 76 Hill M and Brayshaw J, ‘Innovations in Short-staple Yarn Spinning Technology’, Text. Technol. Int., 33 (2000). 77 Anon., ‘Bi-component Spinning’, IWS Textile Technology Technical Information Bulletin, Issue I (1991). 78 Parkin W and Iredale J A, Contemporary Textile Engineering, (F. Happey Editor), Chapter 3, Academic Press, London (1982). 79 Walls G W, ‘Recent Research and Industrial Application of Self-Twist Spinning and Related Techniques’, The Yarn Revolution, 142 (1976).

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80 Nunes M F, Manich A M, de Castellar M D and Barella A, ‘Optimization of Wool and Acryl/Polyamide Wrap-Spun Yarns’, Proc. 9th Int. Wool Text. Res. Conf., IV, 301, Biella, Italy (1995). 81 Naik A and Galvan F, ‘Response of Spinning Machine Variables to Wool Core Wrapped Yarn Characteristics’, IWTO Techn. Comm. Rep., No. 3, CavtatDubrovnic, Yugoslavia (June 1990). 82 Xie Y, Oxenham W and Grosberg P, ‘A Study of the Strength of Wrapped Yarns, Part I: The Theoretical Model’, J. Text. Inst., 77, 295 (Sept./Oct. 1986). 83 Choi K F, ‘Mechanical Properties of Wrapped Yarn’, Text. Asia., 22(4), 33 (April 1991). 84 Cheung C W and Cheng K P S, ‘Woollen Wrapped Yarn Properties’, Text. Asia, 25(11), 44 (Nov. 1994). 85 Fischer J, ‘Plyfil Gives Wool Spinners New Competitive Advantage’, Wool Rec., 153, 12 (Aug. 1994). 86 Gore C E, Lee C S P and Rogers R V, ‘The Influence of Strength and Extension of Top Dyed Fibre in Subsequent Processing Performance’, Proc. 8th Int. Wool Text. Res. Conf., III, 329, Christchurch, New Zealand (1990).

Bibliography The following are recommended for further reading: Worsted Henshaw D E, ‘Worsted Spinning’, Text., Prog., 11(2) (1981). Harrowfield B V, ‘Early-Stage Worsted Processing – From Scoured Wool to Top’, Wool Sci. Rev., No. 64, 81 (Dec. 1987). Van Rensburg D J J and Hunter L, ‘A Review of the Influence of Certain Raw Wool Characteristics on Worsted Processing’, TexRep. No. 4, Division of Textile Technology, CSIR, Port Elizabeth, South Africa (March 1992). Van Rensburg D J J,‘The Influence of Certain Raw Wool Characteristics on Worsted Processing’, MSc Thesis, University of Port Elizabeth, South Africa (Jan. 1993). Van Rensburg D J J, ‘The Prediction of Wool Worsted Spinning Performance and Yarn Properties’, PhD Thesis, University of Port Elizabeth, South Africa (Jan. 1998). Woollen Roberts G, ‘A New Approach to the Science of Woollen Carding Part I’, Text. Inst. Ind., 17, 246 (July 1979) and Part II, 290 (Aug. 1979). van der Merwe J P, ‘The Woollen System – Development and Basic Principles’, SAWTRI Special Publ., WOL 63 (March 1984). Ross D A, Carnaby G A and Lappage J, ‘Woollen-Yarn Manufacture’, Text. Progr., 15(1/2) (1986). Richards R T D and Sykes A B, ‘Woollen Yarn Manufacture, Manual of Textile Technology’, The Textile Institute, Manchester, UK (1994).

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Lubrication Henshaw B W and Plumb R A, ‘Textile Fibre Lubricants and Developments of Emulsion Compounds’, Text. Manuf., 102, 475 (Nov. 1965). Haigh N, ‘Fibre Lubricants for Woollen Processing, Part I: What They Are and What They Do’, Wool Rec., 110, 39 (9 Sept. 1966) and Part II: ‘Selecting a Fibre Lubricant’, Wool Rec., 110, 24 (16 Sept. 1966). Strathoff V, Lee C S P and Dittrich J-H, ‘The Effect of Finishes in Worsted Spinning and Results of Processing Trials with Wool Tops Using Different Finishes’, Mell. Textilber., 74, E151 and 323 (1993). Aymanns M, Körner A and Höcker H, ‘Action of Different Types and Quantities of Fibre Lubricant in Drafting Wool Tops’, Mell. Textilber., 81, E62 and 263 (2000). General Happey F, (Editor), Contemporary Textile Engineering, Academic Press, London (1982). Oxtoby E, Spun Yarn Technology, Butterworths, London (1987). Oxenham W and Huang X C, ‘New Spinning Developments’, Wool Sci. Rev., No. 68, 1 (Jan. 1992). Grosberg P and Iype C, Yarn Production: Theoretical Aspects, The Textile Institute, Manchester, UK (1999). Meng J, Seyam A M and Batra S K, ‘Carding Dynamics, Part I: Previous Studies of Fiber Distribution and Movement in Carding’, Text. Res. J., 69(2), 90 (1999).

7 Chemical processes for enhanced appearance and performance W S SIMPSON

7.1

Introduction

Chapter 5 describes the chemistry of wool as it interacts with radiation, acids, alkalis, oxidants, reductants and metal ions. It also includes some useful reactions that modify particular amino acid residues. This accumulation of knowledge of the absorption and reactivity characteristics of wool has facilitated the development of practical treatments that enhance some aspect of the performance of wool products. Generally, the process descriptions that follow are those in current practice. A more historical perspective of wool process developments can be found in text books, e.g. that edited by von Bergen.1

7.2

Bleaching

Raw wool can be segregated at the marketing point so that the whitest material is channelled towards products dependent on a good natural colour. Nevertheless, bleaching is a very common process and may be enhanced by fluorescent brightening agents for some fashionable wool products that are in competition with synthetic and cotton textiles. Bleaching processes may be carried out continuously, as in conjunction with raw wool scouring, or batchwise on fibre, yarn and fabric. Reduction bleaches cause little damage to wool by comparison with oxidative methods. Sodium metabisulphite treatments enhance wool brightness, but the preferred reductive bleaching treatment today utilises stabilised sodium dithionite-based products or, alternatively, thiourea dioxide.2 Better whiteness can be achieved using formulations based on hydrogen peroxide at the expense of increased damage, particularly to cystine (CYS). Peroxide used in wool bleaching is usually stabilised by sodium pyrophosphate or chemically-related proprietary products. A typical process3 would be a solution of 20 ml/l (35%) H2O2 at pH 8.5, with 215

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0.4 g/l sodium pyrophosphate as a stabiliser. The treatment bath would slowly be raised to 65 °C and maintained there for about 3 hours. Wool bleached as an ancillary process during raw wool scouring is usually treated with lower levels of hydrogen peroxide than in the batchwise processes mentioned earlier. Typically the final bowl of the woolscouring train would be maintained at 0.5–1.1% peroxide in mildly acidic conditions of pH4–6 and a temperature not exceeding about 40 °C. A fraction of unreacted peroxide is held by the wool and it continues an exothermic reaction even after drying. Caution is therefore essential when wool is baled after scouring and bleaching if thermal damage to the wool is to be avoided. A modest bleaching effect in conjunction with scouring can also be obtained under reactive conditions. With the last scouring bowl set at about 0.4% sodium metabisulphite concentration and a pH of 5.7–6.3, the operating temperature should not exceed 55 °C.

7.3

Prevention of dyebath yellowing

A disappointing aspect of wool bleaching is that the products are less stable in colour than before. Colour reversion in a dyebath is particularly unfortunate. One of the obvious reasons for bleaching in the first instance is to achieve bright, pale shades after dyeing, and should the wool material lose half of more of the original improvement it can be most disappointing. Fortunately, there is now greater appreciation of the reasons for colour reversion, this form of it often being referred to as hydrothermal yellowing. All wools have detectable amounts of a-keto acids and the quantity is greatly increased when they have been damaged by exposure to sunlight (see Section 5.3). Simpson investigated hydrothermal yellowing and considered these carbonyl groups were major contributors.4 Inclusion of hydroxylamine (HA) salts at 0.2% concentration in a conventional mildly acidic dyebath reduces hydrothermal yellowing by at least 50–70%. Simpson considered carbonyl groups were the active agents because they are liable to be quite reactive in boiling water, although the end products of their reactions are unknown. The chemical explanation for the success of the preventative treatment is almost certainly the well-known general reaction of HA with carbonyl groups to form aldoximes and ketoximes. In the case of wool, this intervention avoids colour-forming reactions, although it must be acknowledged there is no material evidence of how these may involve carbonyl groups. A consolidating point in favour of this theory is that the HA-carbonyl reaction is reversible in mildly acidic conditions. Pretreatments of wool with HA and subsequent dyeing in HA-free acidic dyebaths offer only transient protection against yellowing. Boiling in neutral conditions does not cause

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217

yellowing of HA pretreated wool, because the reverse reaction cannot be catalysed by hydrogen ions. Acidic dyeing conditions predominate in wool dyeings and HA must be present at an adequate dyebath concentration in order to minimise hydrothermal yellowing. Simpson also emphasised the importance of high temperatures in hydrothermal yellowing. Dyeing assistants and dyestuff selection which permitted dyeing at 80 °C rather than at the boil, in conjunction with HA usage, would completely eliminate hydrothermal yellowing.5

7.4

Insect-resist treatments

Wool and other animal fibres are attacked by the larvae of particular moths and beetles. Tineola bissiella (Hummel), the common clothes moth, is found worldwide and is used as a laboratory test insect. Other moths found in temperate and sub-tropical regions are also significant pests, notably a number of species within the Tinea genera (Linnaeus) and Hofmannophila pseudosprettella (brown house moth) (Stainton). Several species of beetle attack carpets, and that generally used in laboratory testing is Anthrenus flavipes (LeConte). Damage caused by carpet beetles accounts for more than half the total insect damage to wool products,6 so it is essential to test treatments against several insect species. For many years it was thought the mechanism of digestion of wool by insects originated with highly reducing conditions in the larval midgut. Disulphide bonds in the ingested wool were cleaved, allowing complete digestion with proteolytic enzymes. Powning and Irzykiewicz7 revised this theory and suggested that wool is partially broken down by protease releasing some free cystine which is then reduced to cysteine by the enzyme system. Cysteine promotes rapid subsequent proteolysis by reducing more disulphide bonds. Both chemical modifications of cystine and biological antagonists that inhibit the metabolic enzyme cycle have been considered as potential methods of insect-proofing, but none have gone on to commercial adoption. Environmental constraints have become increasingly important in recent years, so that some of the earliest chemical insect-resist (IR) treatments have now been largely abandoned. A considerable number of very demanding criteria must be met if a treatment is both to comply with environmental regulation and to be effective through the lifetime of the wool textile or carpet. IR agents must survive many different processes, including resistance to hydrolysis in boiling dyebaths, and possess adequate stability to sunlight and laundering or cleaning. The shampoo-fastness requirements for carpets are less stringent than machine-washable standards for wool garments, where an excess of IR may be necessary to compensate for subsequent losses.

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Wool: Science and technology

Concerns for the health of mill workers, consumer safety and environmental protection lead to regular revisions of standards. In most countries there is strict control of permissible IR agents and their concentration in mill discharge of treatment residues into sewage systems. Lewis prepared an extensive list of insect-resist agents used at some time on woollen goods.8,p128 The most important commercial products are listed in Table 7.1. Absent from the list are the first widely used IR agents based on formulations of dieldrin. Its high toxicity to mammals and fish, and longevity in the environment, led to a ban on its use in most markets. Mitin FF has been used since 1939 and, in spite of a high cost, its excellent fastness to washing and light, and exhaustion properties comparable to acid dyes has meant it retains a place, for example, in the treatments of uniforms. Increasing pressure to reduce organochlorine residues in the environment has led steadily to replacement of the older products. Permethrin has a lower chlorine content and low mammalian toxicity but is toxic to fish and aquatic invertebrates vital to the nutritional food-chain of fresh-water fish. This has put pressure on development of application methods that generate little waste chemical discharge. Mitin AL combines permethrin with a hexahydropyrimidine derivative that has good properties of beetle protection. Wherever feasible, the preferred method of application would be to add the IR agent to dyebath formulations. In the case of wool–nylon blend yarns commonly used in carpets, the IR agent may be taken up predominantly by the polyamide and this portion is ineffective in terms of protection of wool. Some IR agents favour the wool component9 and are clearly to be preferred for such products. Table 7.1 Commercial products for insect-proofing wool Product/Manufacturer

Chemical name

Year of introduction

Mitin FF (Ciba Geigy)

Sulcoferon

1939

Molantin P (Chemapol)

Chlorphenylid*

—

Perigen (Glaxo/Wellcome)

Permethrin

1980

SMA-V (Vickers)

≤

1980

Antitarma NTC (Dalton)

≤

1982

Mitin BC (Ciba Geigy)

≤

1982

Eulan SPN (Bayer)

≤

1983

Eulan SP (Bayer)

Cyfluthrin

1982

Mitin AL (Ciba Geigy)

Permethrin/Hexahydro

Cirrasol MPW (ICI,Aust.)

pyrimidine derivative

1983

Cyhalothrin

1985

* Chlorphenylid products from Ciba Geigy and Bayer were withdrawn from the market in 1989.

Chemical processes for enhanced appearance and performance

219

One method devised to limit IR agent discharge in mill effluent is massive overtreatment of a portion of the wool prior to blending it with a larger quantity of untreated fibre.10 This approach is particularly useful for Berberstyle carpets. Finished carpets may also be treated rather than fibre or yarn. Ingham and Rowan describe foam and spray/vacuum procedures, and a dry process involving talc containing the IR agent dusted onto a carpet prior to steam fixation.11 Such processes do not create any aqueous effluent and essentially solve the potential environmental problem. Insect-resist treatments may also be applied during processing in woolscouring plants, provided effluent discharge constraints in their particular location can be met concerning residual chemical in rinsings, etc. Very large quantities of wool have been treated, most commonly with synthetic pyrethroids present in the last scouring bowl, which would be maintained at about 70% and pH 4–6 for the purpose.

7.5

Shrinkproofing

7.5.1 General Apart from dyeing, shrinkproofing processes are the most common chemical treatments applied to wool. In the absence of any preventative treatment, almost all types of woven and knitted wool products will shrink, although the propensity to do so varies widely. Felting is the usual descriptive term for the progressive fibre entanglement of wool products subjected to mechanical action, most particularly during laundering. Felting has been exploited for centuries as a means of manufacturing unique products. Loose wool carded and formed into batting can be compacted and hardened to create felts for a variety of uses, including floor coverings (see Section 10.2). Woollen spun fabrics are often finished with a less drastic felting process described as milling or fulling. For most of the past century, the need to reduce or completely eliminate shrinkage of fabrics as a result of felting has become a necessity. This has required a good understanding of the mechanisms involved in wool fibre entanglement, and the development of a range of treatments appropriate to particular wool products and manufacturing routes. The processes presently favoured for particular wool products are described in Sections 11.1.12 and 11.3.3.

7.5.2 Fibre morphology It is the distinctive cuticle or scale cell structure of wool fibres that is primarily responsible for felting by fibre entanglement, causing a corresponding shrinkage of wool fabrics, most particularly in laundering. The overlapping cells that make up the cuticle are tightly cemented to each

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other and to the underlying cortex. For Merino wool, the exposed length of each cell is 10–20 mm, and the cuticle is 0.5–1.5 mm thick. These scale cells have raised edges and often several ridges or false edges, the pattern varying quite a lot between sheep breeds. The outer membrane of scale cells has often been referred to in past literature as the epicuticle, but it definitely encloses individual cells and not the whole fibre. In the Allwörden test, described in Section 5.8, this outer membrane of each scale cell is inflated by brief immersion of wool fibres in chlorine water. Underlying it is a sulphur-rich layer, the exocuticle, which itself is usually differentiated into an outer ‘a’ layer and a ‘b’ layer. The ‘a’ layer has the highest cystine (CYS) content which may be as much as one residue in five. By way of contrast, the innermost layer or endocuticle has a very low cystine content, of the order of 3% of amino acid residues. More details of the morphology of the wool cuticle are given in Section 3.3.1.

7.5.3 Frictional properties of wool fibres Makinson12 has provided a comprehensive description of the several frictional mechanisms likely to be operative in the dynamic situation when a fibre assembly such as a wool fabric is subjected to mechanical action. Noting the uni-directional layering of scale cells with leading sharp edges, one would logically anticipate differential frictional effects (DFEs) according to the direction in which a fibre is pulled over another surface. The term ‘ratchet mechanism’ has often been used to describe how a particular fibre may readily move one way within a fabric but cannot return. It has, however, proved very difficult to assign precise values to frictional parameters because of the irregular asperities on fibre surfaces, and the complex patterns of interfibre contacts. The contrast between air-dry fibres and water-saturated material is very great. The physics of interfibre friction in air-dry situations is described in Section 4.4.5. Viscoelastic properties and fibre swelling, as well as surface characteristics, would be quite different during laundering. Although inter-fibre frictional properties are acknowledged as of crucial importance, the theoretical difficulties generally mean development of shrinkproofing technology has largely moved along on an empirical basis.

7.5.4 Chlorination Makinson12 lists about 40 patented variations of wet chlorination and there are probably almost as many wool surface treatments based on alternative oxidants. Similarly there is a comparable diversity of polymers designed to be applied either as a one-step shrink resist process or, more commonly, as an aftertreatment following some form of wet chlorination. A relatively

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small number of these processes are in current use and the descriptions that follow are mainly confined to them. Treatments with chlorinating agents stand well above all others as either sole or preparatory processes in shrinkproofing. There are some very different reactions possible (Section 5.10), but in shrinkproofing technology the primary modification sought is either to alter wool fibre surfaces so as to facilitate polymer adhesion or alternatively to oxidise some CYS in the exocuticle in order to alter fibre swelling (in water) and other viscoelastic properties of the scale cells. Dry chlorination, i.e. exposure of wool products and typically knitwear to chlorine gas in sealed vessels has been a major technology, probably peaking in volume useage over the period 1930–1950, especially for blankets and hosiery. Wet chlorination, on the other hand, continues to be used in several variations up to the present day, according to whether a mild preparatory treatment of fibre surfaces is required for subsequent polymer applications, or a more thorough oxidation of the wool epicuticle is sought as a stand-alone shrinkproofing process. Simple acidified hypochlorite treatments are now limited to a preparatory process for subsequent application of polymers. The nature of the attack on wool differs for free chlorine in water, HOCl and OCl-, which predominate at pH 2, pH 5 and pH 8 respectively (see Section 5). In the crucial pH 2–5 range, the speed of the reaction (and therefore the possible diffusion range into the fibres) can be moderated by pH, temperature and inclusion of other chemicals. A major survivor of all these chlorination processes is the use of the sodium or potassium salt of dichloroisocyanuric acid (DCCA) applied under mildly acidic conditions, typically about pH5. The chemical mechanism by which it works appears to be a slow hydrolysis of the salt to yield hypochlorous acid (HClO) at pH 3–6.13 DCCA is essentially a chloroamide, so that its controlled interaction with wool is not very distant from many earlier attempts to moderate hypochlorite activity by inclusion of nitrogencontaining compounds to act as retardants.1,p308

7.5.5 Permanganate Potassium permanganate (KMnO4) is a well known strong oxidant. Although it has probably declined to minor commercial usage, it did have its hey-day in wool shrinkproofing technology and the chemical processes underpinning its success are instructive. Normally KMnO4 would diffuse right through wool fibres and readily oxidise all the accessible CYS. In a concentrated solution of a salt (NaCl or Na2SO4) however, wool swelling is suppressed, so that the KMnO4 reacts mainly with the high densities of CYS

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in the epicuticle. At the termination of this reaction, the black near-surface deposits of manganese have to be cleared by a bisulphite rinse, which rapidly dissolves them.

7.5.6 Permonosulphuric acid Sometimes this acid is described as peroxymonosulphuric acid or more simply as Caro’s acid, so that many of the wool treatments derived from its usage are called Caroic methods. There are a number of favoured processes using this acid (H2SO5) under the label of Dylan treatments. The treatment in 10% H2SO5 is at pH 0.46. Irrespective of whether it is applied as a batch or a continuous top process, it is terminated by a reductive step with sulphite or bisulphite, which is thought to yield a useful improvement to the primary oxidation in terms of shrinkproofing performance.14

7.5.7 Polymer deposition processes for wool tops Feldtman and McPhee produced one of the first publications that clearly demonstrated the advantages of an appropriate surface treatment of wool fibres as a preparatory step for a subsequent application of a solution of a polymeric resin.15 The advent of combined pre-treatment/polymer application processes was a timely opportunity to improve shrinkproofing up to machine-washable standards for many wool products. One of the first to be widely adopted for continuous treatment of tops was the chlorine/Hercosett process. An array of tops is passed around a sequence of six or more suction drums, each in its own treatment bath. The sequence of treatments in successive baths is scour-rinse-chlorinate-neutralise-polymer-softener, and finally passage through a dryer. In more modern versions of the process, the neutralise step after chlorination is often expanded to a bisulphite antichlor bath, a carbonate neutralising bath and then a rinse bowl, before polymer application. Hercosett 57 is a polyamide–epichlorhydrin resin, and another successful polymer, Dylan GRC, is a similar cationic resin suitable for application to wool tops. These treatments do not rely on interfibre bonding to combat felting, and scale masking appears to be the principal mechanism involved. Their outstanding success prompted detailed analysis of the reactions occurring at each stage.16 One of the problems with the process is that the tops harden when dyed, and the extent of hardening is related to the presence on wool fibre surfaces of degraded exocuticle proteins. Most of this material, about 7.5 g/kg of wool treated, is removed in the carbonate neutralising bath.16 Perfecting this step and the subsequent rinse appears to be the key to reducing the top hardening problem.

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7.5.8 Fabric and garment treatments with polymers One of the concerns about chlorine-based shrinkproofing processes is the discharge of some harmful compounds such as chloroamines in the waste liquor. It would also be desirable to avoid the fibre degradation inherent in chlorination. There is a regular demand for simple, versatile treatments that could be applied, for example, to batches of knitwear garments. Many of the polymers developed for woven or knitted products do not exhaust from dilute aqueous baths, so that a common method of application is padding the fabric followed by curing. Shrinkproofing is achieved by inter-fibre bonding and, not surprisingly, the potential drawback of these processes is the loss of flexibility and soft handle. The types of resin that have found popularity include polyurethanes with free isocyanate groups (Synthappret LKF, and its bisulphite adduct Synthappret BAP, Bayer), self-crosslinking polyacrylates, and a variety of silicones. Refinements to treatments are constantly being made, with particular attention to improved curing and fabric handle.17 A detailed study of variations in applications of Synthappret LKF and Synthappret BAP (Bayer) on a knitted wool fabric afforded an insight into the role of surfactants in optimising the treatments. Synthappret LKF is a trifunctional polyether-based urethane prepolymer containing terminal isocyanate groups. It is supplied as a solution in perchloroethylene and applied to the fabric by padding from perchloroethylene, followed by curing in saturated steam for an hour. Solvent-based processes of this general kind have been popular because they are versatile and can be applied to batches of garments in drycleaning machines. Their continued use is in doubt due to increasing restrictions on chlorinated solvents. Environmental concerns are based on the belief some solvent escapes into the atmosphere from industrial processes and chlorinated solvents are one class implicated in changes in the ozone layer. Synthappret BAP is a water-soluble bisulphite adduct of a trifunctional isocyanate-terminated urethane prepolymer and is applied by padding from aqueous solution with bicarbonate as a curing assistant. The curing process typically dries the fabric at 150 °C for about 3 min. in a stenter. All polymer applications to fabrics depend for their shrinkproofing action on forming interfibre bonds. These must be sufficiently strong to withstand domestic laundering, so that adhesive forces are the most relevant to shrink-resist efficiency. Less commonly, some polymers fail because of cohesive fracture within the polymer itself. With Synthappret LKF, failure occurs at the interfacial bond, whereas both mechanisms were observed with Synthappret BAP. Interfibre bonding effectiveness can be quantified by measuring the work to break untwisted yarns.

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Surfactants have a substantial effect in increasing interfibre bonding and a plausible reason is that they stabilise Synthappret BAP solutions and, by delaying precipitation of polymer in the high temperature curing step, a larger number of bonding sites are formed.

7.5.9 Testing regimes for shrinkproof fabrics and garments Most of the shrinkage tests utilise a programmable front loading washing machine. Usually called a Wascator, it has a horizontal rotating drum. The British Standard BS 4923: 1991 also includes test regimes based on a toploading agitator type of machine. Many countries adopt the same general principles of testing, but the exact choice of test routine is closely linked to labelling regulations and instructions appropriate to each product. For example, under the Fernmark licence issued by Wools of New Zealand Inc., eight levels of Wascator operation are recognised. The 7A test is appropriate for knitwear with a handwash label, whereas 5A applies to machinewash knitwear. Woolmark specifications, for example as controlled within Australia by the Australian Wool Corporation, nominate a selection of Wascator routines for each type of garment.

7.6

Antistatic properties

Static electrical charging of wool and other textile fibres during mechanical processing is mitigated by operating in a high-humidity environment and choice of suitably conductive process lubricants. Static electricity became more of a problem in homes and workplaces with the widespread introduction of central heating systems, which lower room humidity or dry out carpets with underfloor heating. Although wool fibres are predominately composed of hydrophilic proteins, the relatively hydrophobic epicuticular layer is prone to developing a frictional static charge at low humidities. The original solution to this problem for floorcoverings was to introduce metal filaments into the wool pile and conductive chemicals or fibres into the carpet backing, but this approach was quite difficult to accommodate in many production routes. Mild oxidation of wool carpets with peroxide increases the hydrophilicity of wool epicuticle and lowers static-propensity18 but, probably because of unwanted bleaching effects, this idea has not yet been applied commercially. Chlorination has much the same effect on wool fibre surfaces but there has never been a thorough evaluation of its potential as an antistatic process. During the development of a chemical antistatic treatment for wool, it was found that a wide variety of topical treatments with anionic and cationic compounds at add-ons of about 1% on weight of wool treated would

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provide excellent performance.19 However, the majority of these chemicals, which are generally similar to or are actually used as detergents, are water soluble and are therefore readily lost during carpet shampooing. Cationic antistatic agents were generally the most effective, quaternary ammonium salts being the best sub-group of this class. As the amount of quaternary salt is increased from 0 to 1.4%, body-voltages developed in the standard Stroll Test typically decrease from -16 000 V to zero at 0.8–1.2%, dependent on the particular compound tested. Positive voltages up to +3000 can be developed after excessive treatments. The mechanism of action of topical antistats is believed to be due to their ability to spread evenly on the low-energy hydrophobic surfaces of clean wool and so form an electrically conductive continuum. Discharges of body voltages of the order of ±1500 V are barely noticed by most individuals, so this sets an approximate objective for antistatic performance at the lowest humidities likely to be encountered. The natural hydrophobicity of wool fibre surfaces has most conspicuously been turned to advantage in a relatively cheap and simple antistatic treatment. An emulsion of trioctylammonium chloride (Aliquat 336, General Mills) breaks on wool fibre surfaces.20 Ammonium groups provide the necessary polar properties and strong bonding of the trioctyl structure with surface hydrophobic groups render the process stable to shampooing and wear. Stringent standards for antistatic performance (conductivity specification) also entail applying a conductive latex as part of the carpet backing. Wear tests equivalent to several years’ heavy traffic and a typical repeat shampooing routine show that the treatment is essentially permanent and does not impair soil-resistance. The process has therefore found regular application, notably in contract carpet installations in static-sensitive situations such as hospitals, aircraft, hotels and other public buildings.

7.7

Flame-retardant wool

Wool has relatively good natural flame-retardant properties, but many wool products fail test specifications where stringent safety requirements are enforced. Fabrics and carpets for aircraft interiors, protective clothing, children’s nightwear and furnishings of public buildings are some examples. Sulphamates and phosphates are very cheap, effective chemicals applied to wool products such as fillings and insulation, where there is no washfastness requirement.21 Flame-retardants primarily developed for cotton, based on the use of tetrakis (hydroxymethyl) phosphonium chloride, or THPC, reacted with urea in situ, provided the first washfast process applied to wool.22 This process was displaced from the mid 1970s by one or other of a family of Zirpro processes. These are based on either zirconium or titanium complexes with citrates, oxalates and hexafluoro compounds.23 Tita-

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nium complexes are cheaper and more effective but cause significant yellowing of wool products and the residues are more toxic. Some variants of Zirpro processes reduce smoke emission and meet specifications for aircraft furnishings.24 Neither Zirpro nor simple inorganic processes based on phosphate, sulphamate or boric acid increase risk due to toxic gas emission. Their effects on the kinetics of decomposition and gas release has been studied by thermogravimetric analysis.25 The weight loss curves for untreated wool are similar in both air and nitrogen up to 440 °C. After the loss of regain water, the initial decomposition begins at about 210 °C, and at temperatures beyond 440 °C, wool in air or oxygen decomposes more rapidly than in nitrogen. Wool samples treated with phosphoric acid, ammonium dihydrogen phosphate, and tris (1-aziridinyl) phosphine oxide exhibited a decrease in both the rate and magnitude of mass loss at temperatures over 440 °C by comparison with an untreated sample.26 A more extensive study which included Zirpro and other metal complexes, revealed a markedly different weight-loss curve when comparing a group of phosphorus-based treatments with those based on tin, tungsten, zirconium and titanium complexes. For the latter group, the final decomposition temperature of wool is lowered and rapid loss of mass ensues.27 It is not unusual for flame retardant treatments of textiles to owe their efficacy to one of several different decomposition mechanisms when exposed to a source of ignition. Fluorozirconate-based processes have been the most popular choice since their refinement in the mid-1970s, and extra attention has been given to understanding their mode of action. It was found that fluoride is not essential for flame-retardance, and indeed is slowly lost by repeated laundering. However, if the F/Zr ratio is less than 2, there must be complex formation between zirconium and wool carboxyl groups. Zirconium dioxide is ineffective as a flame retardant27 because there is no such bonding interaction between zirconium and the wool protein structure.

7.8

Photostabilisers

7.8.1 Stability of wool-base colour The complexities of sunlight degradation of wool were described in Section 5.4, and these notably include either yellowing or bleaching according to the relative amounts of UV and near-UV radiation. Bleached wool yellows more rapidly than unbleached wool. Of the methods tried to reduce this colour reversion, incorporating thiourea formaldehyde resins into the wool is the most successful, and retains some protection after repeated laundering. The mechanism of protection appears to be quenching of singlet and

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triplet excited states in irradiated wool, supplemented by some catalysed photobleaching.28 This process is really only relevant for undyed or very pale shades on wool fabrics, and predominantly these would be fine wool products. Colour stability of wool carpets and knitwear dyed in pale shades is a significant problem where both photobleaching and photoyellowing are undesirable. A process based on the proprietary chemical Lanalbin APB is designed to balance the two effects.29 Note that this is an entirely different solution as it predominantly relates to coarse wools that have not been chemically bleached, and the main problem is to successfully counter photobleaching rather than photoyellowing. The process can be carried out most economically in the last bowl of a scouring train. Licencing control of the treatment is held by Wools of New Zealand and it is marketed under the brandname Fernplus APB. Fine Merino wools are so densely compacted during their growth on the sheep’s back that they do not suffer significantly from photodegradation effects such as yellowing. Subsequently, therefore, fine wool products have a minor propensity for the reversionary process of photobleaching.

7.8.2 Protection from photodegradation Extending the useful life of wool products by curbing the loss of physical strength and elasticity caused by exposure to sunlight is clearly a desirable objective. It is a truism to say this is against nature, for, in the absence of this destructive mechanism, recycling of discarded keratins such as animal hair and feathers would be seriously impaired. For example, discoveries of mammoth hair or similar remnants from other animals are very rare compared to skeletal remains. When they have been subject to the natural elements of sunshine and rainfall, the constituent proteins are reduced to amino acids and their degradation products within about three years. There is a radical difference in the problem according to the wool product. Fine wool apparel products are rarely exposed to sunlight for long periods, but wool furnishings such as carpets, drapes, and upholstery fabrics constructed from mid-micron and coarse wools are often exposed daily to long hours of sunlight transmitted through window glass. There is also a growing consumer interest in apparel that protects skin from excessive exposure to the full spectrum of UV radiation in sunlight. Protection of interior textiles such as curtains is therefore not against UV radiation shorter than 305 nm, which is absorbed by window glass, but the very penetrative and abundant radiation band of sunlight, especially 350–385 nm wavelengths. An obvious strategy is to apply a colourless near UV absorber, rather like protecting people from sunburn with a screening chemical. The most appropriate for easy application are those that simulate

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acid dyestuffs. Most commonly used in current industrial practice are sulphonated 2-hydroxybenzophenones and a sulphonated 2-hydroxybenzotriazole.30,31 Another commercial product is also available.31a There are two serious difficulties in developing and testing protective treatments against photodegradation for wool. Firstly, there are substantial differences between results obtained with conventional sunlamps, including the whole environment of accelerated testing (temperature, humidity, etc.) and exposure of samples in various sorts of glasshouse environments with natural sunlight. Secondly, the sequence of wool degradation may commonly begin with strength improvement, followed by a fairly stable period, then a rapid deterioration. Also, abrasion resistance measurements or tests of elasticity are unlikely to follow the same trend lines over various exposure times as may be found with the simpler fabric strength tests, so that relevant performance evaluations require some experience. These assessment variables were described in studies primarily designed to identify dyestuffs that might usefully be recruited to offer photoprotection to wool.32 Yellow and brown dyes optimally absorb in the low part of the visible spectrum, i.e. 400–420 nm, and because of this, their overall absorption band extends back into the near-UV region most destructive of wool strength. Dyestuff absorption in this critical region can protect wool to the extent that serious deterioration of physical properties can be postponed for periods of the order of 1000 hours of sunlight exposure. Although it is technically possible to include modest amounts of the most protective yellow dyes in a variety of product colourations such as olive, and various shades of tan and brown, there is little evidence that this opportunity has been seriously addressed by carpet and furnishings manufacturers. Another potential industrial innovation is the incorporation of some aluminium in wool (see Section 5.13.4), which has the effect of repairing the loss of elastic properties caused by photodegradation.33

7.9

Stainblocking

Since 1980 there has been a sustained interest in improving appearance retention and easy-care characteristics of textile products. A prominent objective within that generalisation is to eliminate residual staining of carpet pile that has suffered spillage of food and liquids. Nylon fibre manufacturers have perceived branding of their product with a proprietary stainblocking finish as an important competitive opportunity. Many of the chemical aspects of adventitious staining of nylon and wool pile carpets are similar, so that much of the stainblocking technology is relevant to both fibres and the competitive motivation is equally cogent for wool.

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The predominant source of carpet stains are acid dyes included as food and drink colourants. Wine and tea contain polyphenolic tannins that can be even more difficult to combat. Initially, it was envisaged that the effectiveness of stainblocking treatments could be attributed to repulsion of anionic (i.e. food and drink acid) stains by applying a chemical that contained sulphonic acid groups. More recently, for both wool and nylon a supplementary mechanism has been recognised. Rather than simply and solely relying on a fibre surface repulsion effect, longer and higher temperature treatments result in diffusion of some stainblocking chemicals into the fibres where their intimate bonding interactions with the fibre substrate results in a diffusion barrier for incident stains.34 The dual objective of stainblocking finishes is therefore to firstly repel aqueous and oily spills, secondly to inhibit stain retention of (mainly) acidic colourants, and thirdly to restrict diffusion further into the fibres by forming an interlocked stainblocker/fibre layer. A major group of stainblocker chemicals are reaction products of sulphonated phenols and formaldehyde. Syntans, as these compounds are generally known, have been evaluated for their stainblocking attributes.35 Acrylic polymers incorporating carboxylate groups were included in the review, both types obviously designed to repel acid dye spillage by a charge repulsion mechanism. Increased liquid repellancy is commonly consolidated by a post-application of a fluorochemical. Fluorochemical treatments of woven and knitted apparel have improved to the point where they frequently meet both the stain and water repellancy performance standards for easy-care products, thus obviating the need to apply stain-resist chemicals as well. Wool carpets are subject to more stringent abrasive wear, which damages the surface layer of fluorochemical so that, for this reason alone, chemical stain blocking remains an important modern technology. A standard test for staining of carpets involves exposure to the Food and Colouring dye F and C Red 40, applied under standard conditions described in AATCC Test Method 175-1998.36 Stainblocking treatments range from application during yarn dyeing, an aftertreatment to that process, or a product treatment such as applying a foam or spray finish to carpets.

7.10

Multi-purpose finishes

Successful development of versatile flame retardant processes based on Zirpro treatments has encouraged development of treatments suited to a wider range of protective wool clothing, which may also require washability and oil-, petrol-, water- and acid-repellency.37 Silicone-based shrink-resist polymer treatments are incompatible with

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exhaustion of the fluorocarbons required for multi-purpose liquid repellency finishes. This problem can be resolved by applying the Bayer shrinkproofing product Synthappret BAP and Neoprene 400.38 The latter has a sufficient chlorine content to counteract the inherent flammability of the shrink-resist finish. Various other combinations are possible, such as flameproofing with tetrabromophthalic acid, co-applied with Zirpro chemicals and an anionic fluorocarbon39 such as Nuva F (Hoechst) or FC217 (3M). Securing good adhesion of a fluorocarbon to wool fibre surfaces is the key requirements for conferring repellancy properties against most liquids. In simpler situations where flame resistance is not a requirement, coapplication of the fluorocarbon and a shrink-resist polymer improves their adhesion and fastness to abrasion, washing and drycleaning.40

7.11

Polymer grafting

One of the earliest methods of incorporating a polymer within wool fibres took advantage of the natural small proportion of thiol groups in wool to catalyse polymerisation of ethylene sulphide.41 The main problem with most free-radical catalytic systems is to confine the catalyst in the fibres and avoid wholesale formation of homopolymer in the monomer bath. This was attempted with the well-known ferrous ion/peroxide combination for generating free radicals. A two step process starting with impregnating wool with ferrous sulphate, then including peroxide in the aqueous monomer bath, has been tried with various monomers. In practice it is difficult to avoid some diffusion of ferrous ion back into solution and therefore formation of non-grafted polymer. During the 1960s, many new, relatively cheap monomers entered the market and were evaluated as graft polymers in wool. Acrylonitrile and some methacrylates crosslinked with butadiene, styrene and several acrylates were prominent candidates.42 A lack of solubility in water is not a particular problem if the monomers are first converted to an emulsion which subsequently begins to preferentially crack on wool fibre surfaces as the reaction temperature is increased. This affinity of the hydrophobic surface of wool fibres for water-insoluble monomers is analogous to the success in coating them with a trioctyl antistatic agent (Section 7.6). Powerful irradiation facilities using Co60 X-rays or 500 kV electrons introduce the possibility of intimate polymer grafting on a wider range of free radical sites in wool proteins.43,44 Such experiments have generally been disappointing as the free radicals that are first formed transmute rapidly to low activity forms and result in small add-ons of graft co-polymers. The most sophisticated and flexible approach to polymer formation in wool is the discovery of a catalytic system uniquely dependent on the small

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natural thiol content of wool. Copper acetylacetonate and trichloroacetic acid form a water-soluble complex that degrades by reaction with wool thiol groups and generates both CCl3. radicals and CCl3- ions at temperatures above 60 °C. Excess trichloroacetate decomposes to form CO2 and HCCl3, and this concurrent evolution of some gas flushes air (and therefore freeradical inhibitor oxygen) from the reaction vessel.45,46 This catalytic and flushing system is economically formed from small amounts of acetyl acetone, copper sulphate and an excess amount of trichloroacetic acid, added individually to wool immersed in water, typically in a dyeing vessel equipped with a close-fitting lid. Both water-soluble and insoluble monomers can be introduced into the dye vessel, the insoluble ones being first converted into an emulsion with a detergent stabiliser in a side tank. Processes developed from this system include grafting 20–130% polymethacrylic acid in loose wool, subsequently converted into needlepunched batting in the form of a continuous sheet.47 This was mounted in a prototype cation-exchange water treatment plant designed for rapid removal of metal ion pollutants captured by carboxylate groups within a continuous cycle of metal recovery and Na2CO3 regeneration.48 Potential large-scale utilisation of polymer grafting, specifically aimed towards the carpet industry, was evaluated with up to 1.5 tonne lots of carpet wools treated to exhaustion with 750 kg of various butyl acrylate, methyl methacrylate, styrene and methacrylic acid mixtures in a sealed dyeing vessel. A great advantage of this polymerisation process is that it is readily adapted to suit conventional metal complex dyeing48 in a combined process. Other unique features of the process include the complete absence of unwanted homopolymer in the immersion liquor and the total utilisation of available monomer. The latter feature is not just unusual amongst grafting reactions, but very importantly permits normal discharge of the spent treatment liquor to drain. Its success arises from the fact that polymer accretions within wool fibres preferentially attract monomers from the external aqueous phase. Wool–polymer composites produced in this way process normally from spinning right through to carpet tufting. Performance comparisons with pure wool carpets of the same construction and pile weight are satisfactory,49 and the low price of monomers gives a cost advantage.50 However, these processes have not been used commercially, a major reason at the time of their development being the promotion by wool interests of 100% wool products. Nevertheless, the prospect remains of preparing novel woolbased materials by applying a proven, facile process. Polymer grafting in straight long-staple wools, such as those from the Lincoln breed, had some brief commercial success for the manufacture of ladies’ wigs, where the addition of the polymer conferred advantages in setting structure and waves in the product.

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7.12

Removal of vegetable matter by carbonising

Very often burrs, seeds and other vegetable matter are removed mechanically during the carding process. However, some types of vegetable matter and heavily contaminated wools require carbonising. This process involves padding scoured wool with dilute sulphuric acid (5–7% w/w and approximately 65% pick-up). After first drying at 70–90 °C to concentrate the acid, the wool is baked for about a minute at 120–125 °C. This chars and embrittles the vegetable matter so that when the treated wool is passed through rollers it is basically crushed to powder and falls out either directly or on subsequent mechanical processing. Many woolscouring companies readily incorporate carbonising within their regular scouring service to clients (Section 2.7.1). Without careful control, carbonising may cause serious damage to the wool. In particular, its initial moisture content must be sufficiently low, and the low-temperature drying step carried out carefully. A more uniform distribution of the acid is achieved with the assistance of a detergent. Nonionic agents containing an alkyl or aryl hydrocarbon group are generally the best choice.51 Carbonised wool should not be stored without first rinsing and neutralising. The most notable chemical modification of wool induced by carbonising is described as a peptidyl shift. This is a reversible reaction whereby the peptide bonds adjacent to serine (SER) and threonine (THR) residues are cleaved and are detected as an increase in terminal amino groups at those sites. Prompt neutralisation has the effect of reforming up to 80% of the SER and about 70% of the THR peptide bonds.52 Successful management of this step essentially means that carbonising should result in minor main chain peptide cleavage and trivial deterioration of the physical properties of the treated wool.

7.13

Setting

Setting is the general description given to a variety of chemical, and combinations of chemical and physical, processes that are designed to stabilise yarns and fabrics so that they will remain permanently in a particular configuration. Part of the important history of wool science aimed at understanding the factors involved in the physical stability were fundamental studies of the setting properties of individual fibres. Wool fibres held while extended 30–40% and immersed in boiling aqueous solutions, which may also contain setting assistants, for periods up to 2 hours retain most of the extension when released. When the free fibres are again boiled for an hour, some contraction occurs and the residual

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extension is defined as ‘permanent set’. A full account of setting properties of wool fibres and the associated physical and structural changes is given in Section 4.3.7. Introduction of synthetic fibre fabrics produced a great stimulus for development of setting processes applicable to wool fabrics. The synthetic competing fibres are thermoplastic so that durable creases and pleats are readily formed under compression at an appropriate temperature. Imparting flat finishes to fabrics with short steaming times, as is generally practiced in industrial setting, results in minor setting of individual fibres. Assessment of industrial setting of pleats and creases is commonly studied by removing yarns from the crease area and releasing them in hot water. Poorly-set fabrics give crease angles of 170–180° and well-set examples have crease angles less than 50–60°. Setting treatments that provide the best permanent set of single fibres are also the best for imparting well-set pleats and creases. The important step is relaxation of molecular stresses by conformational rearrangement of wool fibre proteins. This requires breaking and reforming both hydrogen bonds and disulphide crosslinkages. Reducing agents such as ammonium thioglycollate promote disulphide bond rearrangements, the active agent being the thiol anion. This is RS- in the following equation, and not the parent RSH thiol.53 WSSW + RS- Æ WSSR + WS - [W = Wool protein chain]

[7.1]

Accordingly, wool is not readily set in acidic conditions, but sets well in neutral or alkaline solutions where thiols largely exist in their ionised state. A more extensive account of the various chemical reactions between wool and reducing agents is presented in Section 5.11. In terms of industrial milestones, one of the most famous would be Siroset, introduced by CSIRO in Australia in 1959. The most common application of this technology is to spray a reducing agent, monoethanolamine sulphite, on the relevant areas of the garment and steam it for a few minutes. This was a major success for basically permanent setting of creases in men’s trousers as well as ladies’ pleated skirts. Following the same general principles, flat-setting of fabrics that have also been adequately shrinkproofed, affords a method for producing washable, minimum-iron garments. They were first introduced in Australia under the Sironise label, but since then, many similar product treatment variations have come into the marketplace. In recent times the setting of permanent creases in wool trousers has moved away from chemical treatments to be replaced by methods based on applying a thermosetting resin along the crease line and on the reverse side of the fabric.

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References 1 von Bergen W, Wool Handbook. Interscience Publishers, New York, J Wiley and Sons, Vol. 2, Part 2, 3rd ed., 1963. 2 Duffield P A and Lewis D M, ‘The yellowing and bleaching of wool’, Review of Progress in Coloration, 1985, 15, 38–51. 3 Cegarra J and Gacen J, ‘The bleaching of wool with hydrogen peroxide’, Wool Science Review, 59, Int. Wool Secretariat Technical Centre, 1984. 4 Simpson W S, ‘The effect of hydroxylamine on wool properties’, WRONZ Report, 213, 1999. 5 Simpson W S, ‘Methods to reduce dyebath yellowing of wool’, WRONZ Technical Bulletin, March 1997. 6 McPhee J R, ‘The mothproofing of wool’, A Merrow Monograph, Watford, Merrow Publishing, 1971. 7 Powning R F and Irzykiewicz H, ‘The digestive proteinase of clothes moth larvae II. Digestion of wool and other substrates by Tineola proteinase and comparison with trypsin’, J. Insect Physiol., 1962, 8, 275–84. 8 Lewis D M, Wool Dyeing, Soc. Dyers and Colourists, Bradford, UK, 1992. 9 Mayfield R J, ‘Insect-proofing wool/nylon blends – the distribution of insectproofing reagents between wool and nylon and its effects on insect-resistance’, J. Soc. Dyers and Col., 1985, 101, 17–21. 10 Jones F W, ‘Protection of wool products from insect damage by blending untreated and insect-proofed wool’, J. Soc. Dyers and Col., 1985, 101, 137–9. 11 Ingham P E and Rowan C K, ‘Alternatives to traditional insect-resist treatment techniques’, Proc. 8th Int. Wool Text. Res. Conf., Christchurch, New Zealand, 1980, IV, 578–86. 12 Makinson K R, ‘Shrinkproofing of wool’, in Fibre Science Series, ed. L Rebenfeld, Marcel Dekker, NY and Basel, 1979. 13 Mazingue G, Ponchel P and Lubrez J P, ‘The composition & properties of the wool cuticle’, Proc. 4th Int. Wool Text. Conf., Berkeley, Calif, App. Polymer Symp., No. 18, 209–16, 1971. 14 Anon., ‘Shrink resist processes for wool. Part 2: Commercial methods’, Wool Sci. Rev., No. 18, 18–37, 1960. 15 Feldtman H D and McPhee J R, ‘The spreading and adhesion of polymers on wool’, Text. Res. J., 64, 634–9. 16 Jackson J, Rushforth M A and Thomas H, ‘The chemistry of the chlorineHercosett shrinkproofing process’, Proc. 8th Int. Wool Text. Res. Conf., Christchurch 1990, IV, 360–9. 17 Guise G B and Freeland G N, ‘Soft handle shrink-resist treatments for wool fabrics’, ibid, IV, 401–7. 18 Satlow G and Shröer S, ‘Über electrostatische Aufladungen von Teppichen aus Wolle und modifizierter (Chemisch Veränderter) Wolle’, Proc. 5th Int.Wool Text. Res. Conf., Aachen, 1975, IV, 483–96. 19 Simpson W S, ‘Wool carpets with antistatic properties’, Text. Inst. and Ind., 1978, 16, 84–5. 20 Rankin D A, Vivian A J and McKinnon A J, ‘Antistatic treatments for wool carpets: the application of a water-soluble cationic antistatic agent to wool in conjunction with a solubilising surfactant’, WRONZ Communication, 97, 1985.

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21 Simpson W S, ‘Efficient flameproofing agents for wool’, Proc. 4th Int. Wool Text. Conf., Berkeley, Calif., App. Polymer Symp., 1971, 18, 1177–82. 22 Basch A, Zvilichovsky B, Hirshmann B and Lewin M, ‘The chemistry of THPCurea polymers and relationship to flame-retardance on wool and wool-polyester blends’, J. Polymer Sci. (Chem.), 1979, 17(1), 39–47. 23 Benisek L, ‘Improvement of the natural flame-resistance of wool, Part I: Metalcomplex applications Part II: Multi-purpose finishes’, J. Text. Inst., 1974, 65, 102–8, 140–5. 24 Benisek L, ‘Part III Vanadium, molybdenum and tungsten complexes’, ibid, 1976, 67, 226–7. 25 Beck P J, Gordon P G and Ingham P E, ‘Thermogravimetric analysis of flame retardant treated wools’, Text. Res. J., 1976, 46, 478–83. 26 Ingham P E, ‘The pyrolysis of wool and the action of flame retardants’, J. Appl. Polymer Sci., 1971, 15, 3025–41. 27 Ingham P E and Benisek L, ‘The hydrolysis of fluorozirconate on wool’, J. Text. Inst., 1977, 68, 176–83. 28 Leaver I, ‘Photo-protective mechanisms in wool. A study of the photo-protective effect of a thiourea/formaldehyde treatment’, Text. Res. J., 1978, 48, 610–8. 29 Dodds M M, ‘Stable colours for wool carpets’, WRONZ Technical Bulletin, November 1996. 30 Cegarra J, Ribe J and Miro P, ‘Use of 2,4 Dihydroxybenzophenone-2-ammonium sulphonate to prevent the yellowing of wool by ultra-violet radiation’, J. Soc. Dyers and Col., 88, 293–6. 31 Waters P J and Evans N A, ‘The effect of phenylbenzotriazole derivatives on the photoyellowing of wool’, Text. Res. J., 1978, 48, 251–5. 31a Anon., ‘Launch of new UV-absorber for wool’, Australasian Text., 1991, 11, No. 2, 33. 32 Simpson W S, ‘Photoprotection of wool fabrics by dyestuffs’, WRONZ Communication, 77, 1982. 33 Simpson W S and Page C T, Inhibition of light tendering of wool, 6th Int. Wool Text. Res. Conf., Pretoria, 1980, V, 183–93. 34 Namath Y K, ‘Mechanisms of stainblocking’, Notes on research No. 481, Text. Res. Inst., Princeton, USA, 1994. 35 Anon., ‘Stainblockers for nylon fabrics’, Report No. 31, Technical Information Centre, Text. Res. Inst., Princeton, USA, 1989. 36 Anon., ‘Stain Resistance: Pile Floor Coverings’, AATCC Tech. Manual, Vol. 75, 2000, Amer. Assoc. of Text. Chem. and Col., USA, 319–21. 37 Benisek L and Craven P C, ‘Machine-washable, water- and oil-repellant, flameretardant wool’, Text. Res. J., 1980, 50, 705–10. 38 Ibid. ‘Machine washable, flame-retardant water, oil, petrol and acid repellent wool’. 1984, 54, 350–2. 39 Ibid. ‘Flame-retardant multi-purpose finishes for wool’, 1979, 49, 395–7. 40 Guise G B and Freeland G N, ‘Treatment of wool fabrics with mixtures of fluorochemicals and shrink-resist polymers’, Text. Res. J., 1982, 52, 182–5. 41 Barr T and Speakman J B, ‘The action of ethylene sulphide on wool’, 1944, J. Soc. Dyers and Col., 60, 238–45. 42 McKinnon A J, ‘The formation of co-polymers of butadiene with acrylonitrile and methacrylate by iron-salt–hydrogen peroxide initiation’, J. Appl. Polymer Sci., 1970, 14, 3033–47.

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43 Burke M, Kenny P and Nicholls C H, ‘Free radicals in irradiated wool: Estimation and role in polymerisation of acrylonitrile’, J. Text. Inst., 1962, 53, T370–8. 44 Stannett V, Araki K, Gervasi J A and McLesky S W, ‘Radiation grafting of vinyl monomers to wool’, J. Polymer Sci., 1965, A3, 3768–74. 45 Simpson W S and van Pelt W B, ‘New catalysts for graft copolymer formation in wool fibres’, J. Text. Inst., 1966, 57, T493–504. 46 Ibid. ‘Graft copolymerisation of acrylonitrile in wool’, 1967, 58, T316–25. 47 Early D B and Simpson W S, ‘Wool copolymer ion-exchange materials’, Proc. 5th Int. Wool. Text. Res. Conf., Aachen, 1975, II, 52–62. 48 Simpson W S, ‘Polymer deposition in wool’, IWS Product Development Report No. 143, Parts I and II, 1971 (copies available from WRONZ). 49 Simpson W S, Bratt R L and Noonan K K, ‘The wear performance of carpets made from wool’, J. Text. Inst., 1973, 64, 449–53. 50 Simpson W S, ‘Production and properties of wool with incorporated polymers’, Proc. 4th Int. Wool Text. Conf., Berkeley, Calif, Appl. Polymer Symp., No. 18. J Wiley and Sons, NY, 585–92, 1971. 51 Crewther W G and Pressley T A, ‘Carbonising investigations, Part VI: A comparison of different types of surface active agents in laboratory carbonising’, Text. Res. J., 1959, 29, 482–6. 52 Hille E and Zahn H, ‘Peptidyl shift during wool carbonising’, J. Text. Inst., 1960, 51, Part II, T1162–7. 53 Crewther W G, ‘Thiol-disulphide interchange reactions in the setting of single wool fibres’, J. Soc. Dyers Col., 1966, 82, 54–8.

8 Practical wool dyeing K PARTON

8.1

Introduction

The physical and chemical properties of wool vary greatly between breeds of sheep, the climates in which the wools are grown and the diet and health of the sheep. The physical properties vary in terms of fibre diameter, length and crimp whereas the chemical properties exhibit variety in terms of amino acid content. Additionally, wools also vary in base colour and have root tip differences that affect both dyestuff diffusion rates and mechanical properties. It is also common to blend wools having different base colours, diameters and fibre lengths. Such blends often exhibit markedly different dyeing properties and careful selection of dyestuff and dyeing auxiliary are required to ensure that the appearance of the coloured fibre is acceptable. Dyeing can take place at a number of points in the production process. Wool can be dyed in either loose, slubbing, yarn, fashioned garment or piece form, and the fibre may be treated to impart shrink resistance either before or after dyeing. Wool is often blended with other natural and synthetic fibres to combine the properties of handle, comfort and drape of the wool fibre with the additional properties of the other fibre. For example, wool is often blended with nylon to improve the resistance to wear in carpets and footwear. Blending polyester with wool is also common in apparel, as it allows the production of permanent-press tailored garments. Polyurethane elastomeric fibres are increasingly used in many apparel fabrics and when blended with wool provide additional comfort by allowing a degree of recoverable stretch. The use of both natural and synthetic fibres in blends with wool provides an additional challenge to the wool dyer. Wool dyeing, like all forms of dyeing, is becoming more regulated. Shades need to be matched under a variety of illuminants, often to a spectral rather than a physical standard. The use of spectrophotometers to measure and specify colour has become commonplace and several colour difference 237

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equations have been developed to improve the quality control in colour matching. As a consequence, the dyer often has to use a wider choice of dyes in order to ensure a satisfactory match under the specified illuminants and colour difference equations. Environmental requirements are also becoming more regulated and the dyer must take care to apply safe working practices whilst ensuring that production meets the environmental legislation relating to effluent, consumer protection and disposal or recycleability. The market is demanding a quicker development and production cycle and, for this reason, there is an increasing demand for delaying colouration to a later stage in the process sequence from loose fibre to garment or carpet. This chapter examines the types of dyestuffs available to the wool dyer to ensure that the dyeing process meets the necessary shade, level dyeing and environmental requirements, and that the resultant fibre has sufficient colour fastness to withstand both processing and consumer fastness demands, without adversely affecting the fibre quality.

8.2

Dyestuff chemistry

8.2.1 Natural dyestuffs Before the introduction of synthetic dyes, the most important dyestuffs used for colouring wool were the natural dyes, such as those extracted from insects and plants. In ancient times, the dyestuffs applied to wool were chosen not only on the availability of natural dyes but also the culture. For example, green was the colour of Mohammed’s coat and as such is sacred, so a Muslim would not produce a carpet with green as the principal colour. In Persia, blue was popular as it depicts heaven, whilst further east in Mongolia it symbolises power and authority. Red generally stands for wealth and joy whilst in China yellow is the Emperor’s colour. The availability of natural dyes varied from region to region. The main source of dye was from vegetable or animal origin and a range of hues was available as follows: Madder (Rubia Tinctorum) Fustic (Morus Tinctoria) Logwood Oak apples Indigo (Indigofera – I. Tinctoria) Cochineal Resedon plant Saffron crocus

Red, crimson, maroon Yellow, olive with chrome Black with chrome Black Blue Scarlet Yellow Yellow

Browns and greys were produced by blending naturally coloured wools.

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Cochineal is the only dye listed from animal origin. It is the extract of the female beetle that lives on the Coccus Cacti plant, and its main use is to produce scarlet uniform cloths. Red was the principal colour used on oriental wool carpets, and the natural dye most widely available. It comes mainly from madder, which is a perennial plant that grows some 3–4 feet high, and the dye called Alizarin can be extracted from the root of the plant after it is 3 years old. The dye is extracted by boiling the rasped root in water, followed by filtering to give the impure dissolved dye.1 This solution is evaporated to dryness and the residue is powdered and spread on a cellulose cloth. Heat is applied and the impurities are adsorbed by the cellulose whilst the colour – Alizarin – sublimes onto the surface in the form of red/orange crystals. The ancient dyers had only a limited number of dyes to work with. Their quality and strength varied considerably from one manufacturer to another and impurities affected the shade, making shade matching and shade reproducibility difficult. Most natural dyes require a mordant, which means that they combine with a metal to produce strong intense colours. Most mordant dyes are polygenetic which means that they produce a different shade with different metal mordants. Alizarin, for example, produces a bright red shade with either a calcium or an aluminium mordant, whilst a chrome mordant gives a maroon shade and an iron mordant produces a dull violet. The metal mordant can also affect the colour fastness properties of the dyed wool. The aluminium complex is of low light fastness, iron and chrome complexes are light fast but the chrome complex is superior, being both wetfast and lightfast.

8.2.2 Synthetic dyes In 1869, Alizarin was synthesised and its commercial production commenced in 1871. The synthetic version of this anthraquinone-based dyestuff soon replaced the natural product. Following this, the increased knowledge of dyestuff chemists led to the production of many synthetic dyestuffs that were suitable for application to either mordanted wool or as acid dyes to unmordanted wool. As well as anthraquinone, the azo chromophore became established, as well as triphenylmethane based chromophores, for special shades such as bright greens, turquoise and violet hues. Further developments of synthetic dyestuffs continued with the development of afterchrome, acid levelling, fast acid (half milling), acid milling and 1 : 1 metal complex dyestuff ranges. Until the 1960s, wool was traditionally used for both clothing and furnishings. In apparel, wool is mainly used for outerwear, overcoats, hats, suiting, knitwear, socks and uniforms. In furnishings, wool is used for

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bedding, carpets and upholstery. However, in recent years significant lifestyle changes have occurred. With the advent of the domestic washing machine the requirements for clothing for a large proportion of consumers have changed from one of formal attire to a wash-and-wear culture. Consumers require fabrics that have easycare properties in terms of washabilty, ease of tumble drying and minimum iron, whilst maintaining garment quality. Synthetic fibres such as nylon, polyester and blends of polyester with cotton and viscose were able to conform to this wash-and-wear culture, whereas wool had a marked disadvantage in that finished wool garments, whether they were woven or knitted, woollen or worsted, exhibited a marked tendency to shrink during even mild hand or machine washing. This problem has been overcome by the development of effective shrink-resist processes and by expanding the use of wool into fibre blends. These shrink-resist processes modify the wool fibre to restrict the fibre’s natural ability to undergo felting shrinkage. An additional application of a polymer resin renders wool knitwear fully machine-washable. This shrink resistant fibre is more receptive to dyestuff, but also exhibits a markedly lower colour fastness. Blends of wool with synthetic fibres have also been developed. In this way the natural properties such as handle, comfort, and drape of wool have been complemented by the additional easycare properties of synthetic fibres that impart strength, washability and stability. Also, elastomeric fibres such as Lycra are becoming important. These developments led to a need for faster dyestuffs that could withstand domestic washing, even in deep intense shades on either plain or multicoloured garments. To cope with these domestic changes, the industry had to quickly refocus on the types of dyes available. In response to these demands for higher colour fastness, new dyestuff ranges were developed and 1:2 metal complex and reactive dyes were introduced.

8.3

Dyeing of different substrate forms

Wool can be dyed at a number of stages in the production process (see Fig. 8.1). The properties of the wool dyestuffs employed must meet both the fastness requirements of subsequent processing and the consumer fastness standards. Loose stock and slubbing undergo considerable processing after dyeing, such as scouring to remove spinning oils and, often, milling treatments. Therefore, the dyestuffs employed must meet the demands of these processes and, to do so, the higher fastness dyestuffs are applied. In wool fabric dyeing, levelness is essential and dyestuffs with adequate migration properties are preferred. However, this is not always feasible. For example, if

Practical wool dyeing Dye

Scouring carding

Dye

Spinning

Dye

Twisting knitting / weaving

Dye

Finishing – including S/R treatments

241

8.1 Different stages of the production process at which wool can be dyed.

wool fabric is to be dyed prior to milling, then it must be dyed with dyestuffs that are fast to milling. If the dyer cannot be sure of achieving a level fabric with such dyestuffs, then the only option is to alter the point in the processing route at which the wool is dyed. This can be achieved by electing to dye the wool in loose fibre form with faster, less level dyeing dyestuffs. Extensive fibre mixing during mechanical processing from loose stock to yarn achieves the essential visual evenness of colouration. Hence, generally, the processing route will determine dye selection but in certain instances the lack of a suitable dye class will re-determine the point in the processing route that the fibre is dyed. When dyeing wool to be used in a multicoloured fabric, the fibre must be dyed in either loose fibre, slubbing or yarn form, and dyestuffs must be carefully selected to ensure the integrity of each shade throughout subsequent processing. In the area of machine-washable wools, the effect of the shrink-resist process can have a marked effect on colour fastness. Machinewashable wool is normally dyed at one of three stages of the production process, namely: • • •

As fully shrink-resist fibre, e.g. chlorine/resin-treated slubbing or yarn. As partially shrink-resist fibre, followed by a resin application after dyeing. As untreated wool that will undergo a subsequent oxidative shrinkresist treatment.

The first route is the most demanding in terms of level dyeing properties because the resin often contains a cationic charge that greatly increases the rate of dyestuff exhaustion. Conversely, in the third route the wool is normally dyed in either loose or slubbing form. The dyeing does not need to be perfectly level because subsequent blending will improve levelness, but colour fastness is vital because the subsequent oxidative shrink resist treatment will markedly lower the wet fastness properties of the wool substrate.

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8.4

Classification of wool dyestuffs

The commercially available ranges of wool dyestuffs have differing dyeing properties. Wool dyestuffs vary in terms of molecular size and the polarity of the molecule. Most wool dyestuffs contain ionic solubilising groups that are based on the sodium salts of either sulphonic or caboxylic acid groups. The number of solubilising groups present within the dye molecule influences the solubility, dyeing properties, and wet fastness. Generally, dyestuffs with lower relative molecular mass and high polarity have the highest migration properties, whilst exhibiting the lowest wet-fastness properties. The classification of dyestuff ranges in terms of migration and wet-fastness properties is illustrated in Fig. 8.2. With the exception of afterchrome dyes, the dyestuffs with the highest wet fastness have the lowest migration properties. Afterchrome dyestuffs do not follow this trend because this class of dye is initially applied as an acid levelling dye and then, during the separate chroming stage, the dye forms coordinate bonds with the fibre. These bonds bring about a substantially improved wet fastness. For example, C.I. Mordant Blue 79 is both an acid dye and an afterchrome mordant dye. When applied as an acid levelling dye it produces a bright red shade, but as an afterchrome dye it produces a deep blue shade. The red acid dye has poor wet fastness whilst the blue chromed dye has exceptionally high wet fastness. Both dyes are equally level dyeing as they are applied in the same way, prior to chroming.

Levelling properties

Acid levelling

Acid half milling

After chrome

1:1 metal complex Acid milling

1:2 metal complex Reactive

Processing fastness properties End user fastness properties

8.2 Classification of wool dyestuffs.

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8.4.1 Mordant dyestuffs An increase in the availability of dyestuffs exhibiting a range of hues meant that their polygenetic potential, i.e. their ability to complex with a variety of metal ions resulting in different colours of mordant dyes was no longer necessary and chromium became established as the main mordant. Chromium produces dyes of high wet fastness and generally good light fastness. The first synthetic dyestuffs were applied to wool in three ways: • • •

as pre-mordant dyes as metachrome dyes as afterchrome dyes

In each case, an excess of chromium is added either before, during or after the application of dyestuff. The results of all three methods is thought to be production of metal complex dyestuffs tightly bound within the fibre in the form of an insoluble dyestuff lake. The metachrome dyes are the easier to apply as this involves a single application procedure, but some dyeings have a tendency to exhibit poor rubbing fastness due to the precipitation of complexed dyestuff in the dyebath, and subsequently some of it being deposited on wool fibre surfaces. The afterchrome process was the most widely used because it gives the highest wet fastness properties and the best levelling properties. The afterchrome dyestuffs give good coverage of different wools but are difficult to strip or reprocess due to the stability of the fibre bonds.

8.4.2 Acid levelling dyestuffs Acid levelling dyes have relative molecular mass (r.m.m.) values of around 300–600. The dye molecules rapidly diffuse into the wool fibre2 and, although exhaustion can be so rapid as to be initially unlevel, the dyes readily migrate at the boil to give a level appearance. The levelling properties of this class of dyestuff are good because during dyeing at the boil an equilibrium level of exhaustion exists. The degree to which this equilibrium favours the fibre or the solution phase is determined by the pH, the temperature, the amount of anionic sulphate ions added in the form of Glaubers salt and the number of solubilising groups on the dye molecule. As the pH, the temperature, the number of sulphate ions and the number of anionic solubilising groups increase, the equilibrium shifts towards the solution phase and consequently the degree of dyebath exhaustion decreases. This class of dyestuff is ideally suited to application on fabrics and yarns where levelness is paramount. They exhibit moderate wet-contact fastness but are not fast to either hand or machine washing. They are widely

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used for dyeing pale to medium depth shades on wool and wool/nylon carpet yarn in hank form. The dyes give acceptable penetration of both velvet and high twist yarns and adequate levelness, even under the adverse conditions encountered in hank dyeing caused by unpredictable flow due to poor packing and channelling. Dye molecules can be either mono or disulphonated. The two solubilising groups on the disulphonated molecule renders it more level dyeing than the monosulphonated dye as its equilibrium level of exhaustion at the boil favours the solution phase to a greater extent than that of monosulphonated dyes. However, the wool exhibits an increase in affinity for disulphonated levelling dyestuffs during cooling from the boil to about 70 °C. This can lead to an increase in the uptake of dyestuff as the dyebath cools, which potentially affects the reproducibility of shade from batch to batch. Careful control of the dyeing process, including the rate of cooling, is recommended to ensure that the final yarn is level and on shade. Acid levelling dyes are applied from an acidic bath at around pH 3.5 in the presence of 10% sodium sulphate. The sulphate anions compete with the dye anions for the protonated cationic sites on the wool. If sulphate anions are not present, then the level of migration in the boiling phase will reduce and the dyeing time required to achieve adequate levelness and penetration will increase. Dyed wool can be stripped or relevelled by re-boiling for 30–60 minutes in a bath containing sodium sulphate. In severe cases of unlevelness, for example that caused when a circulation pump fails, the wool can be relevelled by stripping the dye with a cationic levelling auxiliary, followed by redyeing.

8.4.3 Fast acid dyes This group of dyes have a higher r.m.m. (typically 500–700) than acid levelling dyes and hence exhibit improved levels of wet contact fastness. They are typically applied to wool fabric and yarn in medium to deep shades and, although they are not fast to washing, achieve acceptable fastness to carpet water and shampoo contact tests and to perspiration tests. Their migration properties are lower than those of levelling dyes and dyeing is carried out from acetic acid at around pH 4–5. This slightly higher pH reduces the rate of dye exhaustion and improves the migration properties. An example of the modern range of fast acid dyes is the Sandolan MF range (Clariant). This type of dye has excellent migration properties relative to the molecular size because levelling properties are greatly enhanced by the addition of a mildly cationic dye substantive levelling agent.3 The dye-levelling agent complex acts to reduce the rate of dye uptake during the heating phase and promote migration during the boiling phase. This type of dye is widely used for producing both brilliant and trichromatic combination shades on wool

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fabrics and on carpet yarns. The dyes are usually monosulphonated and give good partition of wool/nylon blends providing a reserving agent is employed to balance the shade depth on each fibre.

8.4.4 Acid milling dyes These are larger dye molecules with typical r.m.m. values of 600–1000. Due to the higher r.m.m., two or more solubilising groups are common in order to impart adequate solubility. Some dyes in this group also have an additional hydrophobic alkyl chain that further increases the molecular weight and provides additional fibre attraction in the form of van der Waals forces. This class of dyestuff has limited levels of migration but extremely high wet fastness properties. The dyes are generally fast to wet contact tests and have good fastness to washing up to medium depths of shade and, as their name suggests, have a degree of fastness to milling processes. Adequate levelling cannot be achieved by allowing for migration at the boil and hence the rate of dyestuff exhaustion during the heating phase needs careful control. The choice of application method is important. Loose fibre dyeing is normally carried out at a fixed pH in the range of 4 to 6, with a weakly cationic levelling auxiliary. Wool yarn, piece goods and fully fashioned garments are often dyed with an acid donor and a weakly cationic levelling axiliary. The weakly cationic leveller forms a complex with the anionic groups within the dyestuff and this complex will exhaust onto the fibre more slowly. The acid donor can be an ammonium compound that breaks down at or near the atmospheric boil to expel ammonia into the atmosphere and liberate an acid into the dyebath. The resultant lowering of the dyebath pH causes the dye to exhaust onto the fibre. Another commonly used type of acid donor is based on organic esters. These products decompose as a function of time and temperature and the dyebath pH is gradually lowered to around pH 5, which helps ensure the gradual level uptake of dyestuff. Acid milling dyestuffs are generally brilliant in shade but have a tendency towards poor combinability. They are normally applied as self shades or as binary combinations to achieve brilliant shades. The limited combinability of acid milling dyes has restricted their use in trichromatic combination shades. They also have a tendency to highlight the naturally occuring root tip differences within the fibre, so some attention must be given to wool blend selection.

8.4.5 1:1 Metal complex dyestuffs The first commercial metal complex dye ranges were introduced early in the twentieth century. The original type used a dye molecule capable of forming a complex with a chromium atom in the ratio 1 : 1. Typically, an

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o,o¢-dihydroxy azo dye was combined with a single chromium atom that carried a cationic charge, and was partially quenched by water. The dye usually contains an ionic sulphonic acid group, which imparts solubility and neutralises the cationic charge on the chromium atom. This class of dye has very good levelling properties when applied to wool at pH levels of around 1.8–2.0 and is ideal for the level dyeing of acid milled and pre-carbonised fabrics. Carbonising is an acid bake process to remove vegetable matter (see Sections 2.7.1 and 7.12), which tends to make wool fibre surfaces more anionic in character. The means by which such dyes are absorbed by the fibre is unclear but the most likely mechanism is that the dye attraction is initially ionic, via the sulphonic acid group. This would explain the high migration properties. It is also thought likely that the dye may form larger 1:2 metal complexes within the fibre. There is no evidence that this class of dye can form coordinate links with the fibre and, as such, their fastness properties are not as good as afterchrome dyes. Indeed, the use of 1:1 metal complex dyes on washable wools is restricted because their shade is unstable when the wool dyeings are washed with modern detergents containing perborate.

8.4.6 1 :2 metal complex dyestuffs Metal complex dyes are dull in shade by comparison with many acid dyes but, providing the right dyes are selected, they are combinable. 1:2 metal complex dyestuffs are formed by the complexing of a metallic atom such as chromium or cobalt with two dye molecules (Fig. 8.3). The resultant larger dye molecule can form strong links with the fibre and so they tend to have low migration properties. There are typically three distinct types of 1:2 metal complex dye, unsulphonated, monosulphonated and disulphonated. The disulphonated type are the most soluble and have a greater pH dependence. This means they have a low neutral affinity and require more acid to achieve exhaustion, but in practice they have the advantage of the highest fastness to domestic washing since any desorbed dye has only limited affinity for adjacent fibres at the pH conditions experienced with domestic detergents. Disulphonated dyes are, however, more fibre selective than the mono or unsulphonated dyes and care must be taken to avoid skittery dyeing. Modern commercial ranges, such as Lanaset (Ciba) and Lanasan CF (Clariant), consist of optimised mixtures of the three different types of 1:2 metal complex dye, and are formulated to give good combinability, good coverage of fibre irregularities and good overall fastness properties. Acid milling and 1:2 metal complex dyes have similar application requirements and are often applied in combination to brighten the shades obtainable with metal complex recipes.

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N=N

O O

Cr

O O

N=N

8.3 A typical structure of a 1 :2 metal complex dyestuff. Molecular weight is usually 500–1000. Chromium is 2–5% by weight of the dye molecule for the commercially-traded product.

8.4.7 Reactive dyestuffs Reactive dyes are medium molecular weight acid dyes with a reactive group capable of reacting with wool amino groups. This reaction involves the formation of a covalent bond, which means the dye becomes attached to the fibre and once fixed cannot normally be removed in subsequent processing. The degree of fixation of reactive dyes depends upon the type of reactive group employed and upon the application conditions. Clearing is necessary to remove unfixed dye, and the ease of clearing of individual dyes is an important factor in achieving high wet fastness. Reactive dyes usually have brilliant hues and have become ideally suited to dyeing bright shades for machine-washable wools. The high colour fastness of 1:2 metal complex and reactive dyes is to some extent negated by the poor level dyeing properties and, as such, their use has traditionally been restricted to dyeing loose fibre and slubbing. However, the increasing importance of machine-washable wools in knitted articles has led to a requirement to apply reactive dyestuffs to other fibre forms such as yarn and garment. In wool garment dyeing, special application processes have been developed to ensure that adequate levelness can be achieved in garment dyeing. The dye is applied at the boil at neutral pH until the garment seams are penetrated and then the dyebath is gradually acidified to allow the dye to feed slowly onto the fibre.

8.5

Commercial forms of dyestuffs

Traditionally, wool dyestuffs have been supplied as powders with adequate solubility to ensure that they dissolve readily in hot water. The dye is manufacture as a wet presscake and then dried. Diluents are added to standardise the dyestuff to the required selling strength and the final solubility of the commercial product depends upon the molecular mass, the

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number of solubilising groups present and the influence of the diluents. Commercial products are often supplied at more than one selling strength and the solubility of the different strengths can vary due to the influence of the diluent. Common salt and Glaubers salt can reduce the solubility of some dyestuffs when used as a diluent whereas naphthalene sulphonate can improve the solubility. Hence, when a particular dyestuff is sourced from two different suppliers, it is not uncommon to find that the solubility can vary greatly. Dyestuffs are now also supplied in both liquid and granular forms. The liquid form is ideally suited to dyes that are applied in large quantities, but the dyestuff must have sufficient solubility to prevent precipitation during storage, and stirring prior to use is advisable. Protection from frost is also important to prevent precipitation. Granular forms are the product of modern spray-drying techniques. They have a lower surface area compared to the powder form and, as such, tend to be less hygroscopic. An advantage of this property is that the dyesuffs are easier to handle during weighing because they flow more readily than powder forms and can even be used in automatic dispensers. The lower moisture regain of the granular form can improve the accuracy and reproducibility of dyestuff weighing, particularly when dyestuffs are stored in moist storage areas.

8.6

Levelness

The importance of achieving satisfactory levelness of wool dyeings has been noted in previous descriptions of dye selection and application methods. This subject is of such fundamental importance for consumer acceptance that the practical problems and means of overcoming them are dealt with in more detail here. It cannot be too often stressed that wool presents very special problems in achieving appropriately uniformly dyed products because of raw material variations between fibres, between fleeces and between large amalgamated wool lots. The four factors which need to be considered are: • • • •

Substrate form and substrate preparation Dyeing machinery Dyestuff selection Application method

The substrate form and the appropriate machine required to dye it govern the dyestuff selection, which in turn governs the choice of application method.

8.6.1 Substrate In terms of the substrate, the dyer often takes the blame for faults that were present in the substrate prior to dyeing but which only became apparent

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during dyeing. Hence the old saying of ‘well prepared is half dyed’ is always true. Typical causes of these dyeability variations are insufficiently scoured fabric and pre-carbonised wools. In the case of pre-carbonised wool, residual acid within the fibre will facilitate a more rapid rate of dye uptake. Dyestuffs with limited migration properties such as fast acid and acid milling dyes can only be applied to such fabrics after complete neutralisation of residual acid. In practice, pre-carbonised fabrics are neutralised with either dilute sodium hydroxide or by treating in a solution of 5–10% sodium acetate. Wool exhibits naturally occurring root tip differences. Fibre tips are damaged by exposure to weathering from wind, rain and light. The tips are more hydrophilic than the fibre root so they exhibit a higher affinity for dyestuff. Initially, the fibre tip appears deeper in shade and the overall appearance can be unsatisfactory. During prolonged boiling, the fibre degrades and this affinity difference is reduced. Hence, migrating dyestuffs will tend to cover root tip difference more readily than dyes that have limited migration properties. Acid levelling, 1:1 metal complex and fast acid dyes give good coverage of root tip affinity differences whereas acid milling, 1:2 metal complex and fibre reactive dyes highlight such differences. Some dyes can actually migrate from tip to root during boiling to such an extent that it is possible to achieve reverse tippiness where the fibre root finally dyes more deeply than the fibre tip. In practice, levelling auxiliaries reduce the effects of tippiness. This type of auxiliary is fibre substantive and increases the rate of dye uptake on both the fibre tip and root, and promotes coverage of such dyeability variations.

8.6.2 Machinery In yarn, piece and garment dyeing, levelness is paramount and, as such, most of the machinery developments of recent years have focused on improving levelness. In yarn dyeing, hank dyeing is still popular because of the bulky handle it produces, but the winding and unwinding operations are inefficient and the restricted liquor circulation and liquor channelling can lead to unlevelness. Package dyeing provides a much more uniformly distributed substrate and therefore overcomes some of the unlevelness caused by poor packing and poor liquor circulation in hank dyeing. Horizontal package machines also have the flexibility to keep liquor ratios constant with varying batch sizes by blocking individual tubes, and this also saves water. In fabric dyeing, the limited liquor circulation found in winch machines has restricted their use to applying acid levelling and fast acid type (half milling) dyes, but with modern jet machines it has been proven that acid milling, 1:1 and 2:1 metal complex dyes can be applied level to wool fabrics. In wool garment dyeing, protection of the garment face is important. Garments are normally dyed inside-out in a side paddle machine. Its gentle

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action ensures that the fabric surface is protected whilst maintaining a liquor circulation sufficient to achieve a level appearance.

8.6.3 Process control Process control specifies that the starting temperature, the rate of temperature rise and the time at top temperature have to be ‘controlled’ in order to achieve a level dyeing.The word ‘control’, of course, has always depended upon state-of-the-art technology and fortunately has progressed from cracking the steam valve, through the use of cam controllers, to the sophisticated microprocessor controls in use today. The benefit of the cam type control and the modern microprocessor control is that they can keep a record of the whole dyeing process, which is useful when examining the levelness and handle of the dyed substrate. The microprocessor has the added benefit of being able to follow a precise, pre-programmed method. Computer programs are now available that predict cycle time, heating rates, pump pressures and flow rates required to assess if a particular dye recipe is likely to be level.

8.6.4 Levelling auxiliaries Levelling auxiliaries have always been used in wool dyeing. Glaubers salt is the long standing traditional levelling agent. It promotes migration with acid levelling type dyes but its use is not recommended with large molecular weight acid milling and 1:2 metal complex dyes because it also promotes aggregation, which can lead to the precipitation of dyestuff. Generally, the levelling auxiliaries in use today consist of the dye substantive cationic type, which can complex with dyestuffs and will therefore reduce the rate of dye uptake and promote migration of adsorbed dye. Fibre-substantive amphoteric types are also employed. This type of product actually accelerates the rate of dye uptake but improves coverage of the inherent variations within the fibre (such as tippiness) and, with some dyes, this gives an increase dye yield.

8.6.5 pH control pH control once consisted of applying gallons of sulphuric or formic acid in order to achieve exhaustion of acid levelling, 1 : 1 metal complex and chrome dyes. The use of such acids has reduced for two main reasons: i) ii)

The low pH values obtained (1.0–3.8) are below the isoelectric region of the wool fibre and can impart wool damage. The move to more neutral dyeing dyes has required higher application pH levels in order to guarantee levelness.

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Even sulphuric acid type acid levelling dyes and 1:1 metal complex dyes are now normally applied with formic acid, whilst the monosulphonated acid levelling dyes that were traditionally applied from formic acid are now often applied from acetic acid. pH control is critical with neutral dyeing dyes. In certain situations, such as yarn hank dyeing, where levelness is difficult and circulation is limited, acid donors are applied. These products allow dyeing to commence at a higher pH (say 7.0–8.0) but gradually break down to liberate acid during heating and boiling, thereby lowering the pH and allowing the dye to gradually feed onto the fibre. Traditional acid donors such as ammonium sulphate are still used but the more modern acid donors such as the Sandacid (Clariant) products give a much more reliable, gradual fall in dyebath pH because, as organic esters, they hydrolyse at a known rate in water. Control of all these factors in both the laboratory and under bulk conditions has not only led to improved levelness but also to improved laboratory-to-bulk, and bulk batch-to-batch reproducibility.

8.7

Dyeing fibre blends

When dyeing blends of wool and other fibres, the dyeing process must ensure that the resultant dyed fibre meets the consumer requirements of shade, levelness and colour fastness, and that the integrity of each fibre is not compromised. Polyester fibre is normally dyed at 130 °C but this temperature damages the wool fibre. In practice wool/polyester blends are dyed in pressure vessels at 115–120 °C for a period of up to 20 minutes. A fibreprotective agent is added to help maintain the quality of the wool. The disperse dyestuffs applied to the polyester component must achieve adequate build up and give minimal cross staining of the wool to ensure adequate colour fastness. When dyeing blends of wool and cellulosic materials under weakly acid conditions, the wool has a high affinity for direct dye. The main requirement is to prevent the cellulosic dyestuff from cross-staining the wool. With direct dyestuffs this is achieved by applying an anionic blocking agent, which is taken up by the wool fibre prior to the addition of dyestuff. When polyurethane elastomeric fibres are used to build a degree of comfort stretch into a garment, it is important to select wool dyestuffs that do not give excessive cross-staining of the elastomeric component, otherwise colour fastness levels will be reduced. Generally, the application process employed is a compromise between the methods employed for each of the blend components. An exception is when dyeing blends of wool and nylon. These two fibres have similar dyeing properties with most classes of wool dyestuffs and, in practice, the wool application method can be employed. There are different types of nylon

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used in wool blends and they can have differing affinity for the wool dyestuff. Generally the nylon component of the blend dyes slightly darker than the wool. With monosulphonated acid dyes, this shade depth difference is enhanced and blocking agents are required to reduce the uptake of dyestuff on the nylon. By controlling the application level of blocking agent, the shade depth between the wool and the nylon can be controlled. This is important when dyeing carpet fibres to ensure that the nylon fibre does not grin, i.e. predominate in visual appearance, particularly in heavy traffic areas, where the wool fibre wears more quickly than the nylon.

8.8

Treatments to improve colour fastness

Washable fabrics made of both wool and wool blends are required to be fast both to long liquor washing and contact colour fastness tests. The fastness of acid milling and 1:2 premetallised dyes can be improved by the addition of a cationic fixing agent. The cationic fixing agent forms a complex with the dyestuff and the fibre. The resultant contact fastness to water and perspiration can illustrate a marked improvement, whilst the washing fastness can be improved by around 1 point. Some cationic fixing agents are able to react with wool to form a permanent bond. This type of fix gives a more durable fastness improvement. Light fastness of wool is particularly important when used in carpet and upholstery furnishing fabrics. The wool fibre can exhibit a rapid fade when exposed to daylight, and in pale shades this can lead to an unacceptable level of light fastness. Generally, such wools are dyed with dyes that have a good light fastness but additional products can be applied to improve light fastness properties and these have been discussed in Section 7.8.1.

8.9

Environmental issues

Ecological issues were initially driven by environmentalists but they have since become more generally endorsed by consumers. The underlying concepts are becoming more widely accepted and this is perhaps best illustrated by society’s changing attitude to recycling. The colouration industry is being affected by these changes. New and proposed laws are impacting upon day-to-day dyeing activities. Headlines containing such terms as ‘heavy metals’, ‘AOX’, ‘banned azo dyes’, ‘consent limits’, ‘air pollution’, etc. are common and concern issues that must be thoroughly addressed by processing companies and standard-setting agencies alike. The hazards presented by all these factors can be categorised into four groups related to the hazards associated with processing, effluent, finished articles and fabric disposal.

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8.9.1 Processing In any manufacturing process, care must be taken to protect the local environment by controlling gas emissions and odours. Employees in the dyeing process must be protected from application hazards, including dyestuff dust and exposure to acids, alkalis and other toxic compounds. Further along the chain, workers who process dyed fibre must be protected from hazards such as residual chemicals.

8.9.2 Effluent The effluent hazards of heavy metals, AOX, as well as C.O.D., B.O.D. and colour are important. All these factors are carefully monitored by the environmental agencies in order to determine the effluent treatment requirements. Generally, each area has different consent levels; the cost of ensuring that these consent levels are met can be excessive and are normally passed on to the dyehouse. Heavy metals are very difficult to extract, even by reverse osmosis, and as such must be dumped as sludge.

8.9.3 The finished article The products applied during dyeing must not present a hazard to the consumer. This includes not using banned dyes such as some of the azo types (see Section 8.9.7) and limiting the amount of extractable heavy metals resident upon fabrics. Free formaldehyde is also an issue.

8.9.4 Disposal Care must be taken to ensure that a product can be disposed of safely at the end of its useful life. (An example of this is CFC gases in fridge freezers.) In textiles, heavy metals are a concern because they can leach out of fibres in landfill sites and survive disposal by incineration. The processing risks are covered by the health and safety at work acts, the finished article risk is covered by consumer law, whilst effluent is covered by the work of the environmental agencies. In Germany, legislation focuses on an ‘emission protection ordinance’ which covers emissions, either gas or effluent, from the processing plant, and the ‘ordinance on materials and articles’, which covers the product. Eco labels have also come to the fore; these set down minimum standards applying to finished articles and in some cases effluent.

8.9.5 The use of water in wool dyeing In wool processing and effluent treatment, water remains the standard solvent. It has always been perceived to be freely available and inexpen-

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sive. The wet processing of wool requires an abundant supply of soft water. However, the amount of water available is finite and ever-increasing demand is leading to variations in supply quality as water is pumped from one area to another. The cost of treated municipal water supplies continues to increase and the textile industry is now incurring additional costs because this water often requires further softening to be suitable for dyeing. The cost of the disposal of water is also increasing and it is important for industrial efficiency to monitor what is discharged in terms of content and volume. One of the most important wool dyeing environmental issues under debate is the restriction on the use of mordant dyes.This restriction is prevalent throughout the western world, with a typical effluent limit of 1 mg/l total chromium. The concern is that chromium, and especially hexavalent chromium, will enter the water supply or the food chain. Afterchrome dyes need a minimum amount of chrome to produce the desired shade. Insufficient chrome gives poor reproducibility and, in practice, a slight excess is required. This excess of chromium still has to be applied because lower levels do not achieve the fully-chromed shade. C.I. Mordant Blue 79, for example, requires a minimum of 1.8% chrome and, in practice, a low chrome addition of 2% on weight of fibre is recommended. However, even at low chrome levels, 1 g/l of hydrated sodium dichromate, which equates to over 300 mg/l of chromium, must be applied. Even when special application methods are employed that involve reduction of chrome VI to chrome III and encourage the chrome to complex with the carboxyl groups within the fibre, and allowing for further effluent dilution from rinsing, it is still indeed a challenge to reduce the chromium level from >300 mg/l to 1 mg/l during the dyeing process. Metal complex dyes are also of concern and the dyer must achieve high levels of dyebath exhaustion to ensure that the effluent discharge is within the specified limits. If one considers dyeing 100 kg of wool to a 2.5% navy shade with 1:2 metal complex dyes at a liquor ratio of 10 : 1 followed by rinsing with 2000 litres of water, the chromium contents during dyeing would be as follows: • • • • • •

weight of dyestuff applied – 2500 g dyebath exhaustion – 96% dyestuff remaining in exhausted dyebath – 100 g the dye powder typically contains 3% chromium on weight of powder this leaves 3 g of chromium in the exhausted dyebath this 3 g will go to effluent with 3000 l of water, which is 1 mg/l

The residual level of chromium discharged just satisfies the water authority discharge requirement. However, dyeing deeper shades, or using less

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rinse water, or achieving lower exhaustion will cause the discharge to exceed the limit. Recent studies have assessed how dyehouse water can be re-cycled in order to reduce the levels of effluent discharge. In the case of the metal complex dye illustrated previously, the rinse water will be fairly clean and will not present an effluent hazard. Most of the contamination is in the exhausted dyebath and, if this water is re-used in subsequent dyeings, there will be an effluent reduction of colour, heavy metal and even pH chemicals. The extent to which the amount of heavy metal discharged to effluent can be reduced by this technique then becomes dependent upon the amount of free, unbound metal present in the commercial dyestuff.

8.9.6 Extractable heavy metal limits on garments The issue of chromium is not just related to effluent discharge. It is clear that residual unbound chromium present on the fibre is also a potential hazard. Various Eco standards quote maximum permissible residual metal limits, e.g. Oeko-Tex

100-I 100-II-IV

2 ppm Cr (4 ppm Cobalt) 1 ppm Cr (1 ppm Cobalt)

These figures are a measure of the amount of free metal that is extracted in a perspiration solution under standard test conditions (Oeko-Tex Standard 1004), which are intended to simulate potential exposure of the wearer of the garment concerned. These standards apply not just to afterchrome dyes but also to other metal complex dyes. Generally, the amount of extractable metal increases with increasing depth of shade. The 1:1 metal complex dyes usually satisfy the Oeko-tex label in pale shades, the 1:2 metal complex dyes satisfy the label in all shades, whilst the chrome dyes satisfy at least to medium depths. Oeko-tex is only one label; other labels are similar and all results rely on best practice in terms of application and exhaustion.

8.9.7 Banned azo dyestuffs Another issue which is perceived as being a hazard to the consumer relates to cleavage of certain azo dyes into amines that can be considered to be potentially carcinogenic. The German ban relates to certain azo compounds, including dyes, in some consumer goods. The only dyes affected are those that are likely to break down to produce one of 20 carcinogenic amines. It is not illegal to manufacture and sell such dyes and the emphasis is on the processor or dyer to avoid using prohibited azo colorants.

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C.I. Acid Red 114 is an example of a dye which will cleave to produce o-toluidine. Only articles that are likely to come into more than temporary contact with the human body are affected. Prohibited dyes can be used for other applications. Environmental issues must be considered when selecting dyestuffs and dyebath auxiliary products. If the wrong products are selected, then there will be a cost penalty incurred to treat affected effluent or to correct faulty garments. Great emphasis has been placed on researching new application techniques and new products that can assist in reducing the environmental impact of the dyeing operation. It is expected that this trend will continue and that issues such as metal-free dyeing and fibre protection will remain as important challenges to the wool dyer.

8.10

Fibre protection

Wool is renowned as being a quality fibre and, as such, it carries a premium price. The value of the fibre demands great care during processing to ensure that the inherent properties of the fibre are maintained. During loose fibre dyeing, the degree of fibre damage must be minimised in order to reduce the amount of waste in carding and to prevent an excessive number of end breaks during spinning. The dyer must ensure that the dyeing time at the boil is kept to a minimum, but it is also an option to dye at temperatures below the boil. Acid milling and metal complex dyes are successfully applied at temperatures of 80–90 °C in conjunction with a low temperature dyeing auxiliary. The auxiliary5 promotes dyestuff exhaustion and diffusion, and produces fast, well penetrated results. A particular property of wool is the structural changes that readily occur in boiling water. Thiol and cystine disulphide bonds can undergo interchange reactions that essentially set wool fibres in their conformation in compacted loose wool and yarns. A full description of permanent setting of wool can be found in Section 7.13. Colourless chemicals capable of reacting with thiol groups have been suggested as a means of restricting permanent set developing during dyeing. Fibre reactive dyes have also been shown to reduce permanent set because thiol groups are a favoured point of their attachment to the wool substrate. The major advantage of restricting permanent set development in loose wool dyeings is the superior spinning properties as compared with afterchrome wool dyeings for example.

8.11

Summary

The wool dyer’s job has changed. It no longer involves carefully cracking open steam valves and tweaking dyeings with skilful shading additions. The

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dyer must select the correct dyestuffs and the most appropriate dyeing technique to ensure that the dyed substrate will be processed with maximum productivity through efficient use of bulk machinery and a substrate that will suit the intended purpose for the lifetime of the product in terms of fastness and environmental characteristics. It is likely that the wool dyer will, in future, rely on modern computer programs that can determine the dyebath conditions required to ensure levelness, that can predict an eco profile for a chosen recipe and recommend a dyebath chemical system that can help protect the fibre during dyeing.

References 1 Liebetrau P, Oriental Carpets, Collier-Macmillan, 1984. 2 Duffield P A, Wool Dyeing, (D M Lewis, ed.), Soc. of Dyers and Colourists, 1992. 3 Frauenknecht J, Hextall P C and Welham A, ‘Sandolan MF dyestuffs’, Textilveredlung, 21, (1986), 331. 4 www.oeko-tex.com. 5 Clariant, ‘Lanasan LT liquid’, Clariant Technical Information, 17th April 2001.

9 Manufacture of wool products K RUSSELL, D McDOWELL, I RYDER AND C SMITH © T H E W O O L M A R K C O M PA N Y

9.1

Introduction

Opportunities for introducing variety into wool products are provided by the fact that wools of different origin vary considerably in terms of mean fibre diameter, distribution of diameter, fibre length, crimp and medullation. Such extensive variations result from the fact that many different breeds have evolved over the years, either through natural selection or through the efforts of man. Different breeds have adapted to particular habitats, and the wools from each breed have their own characteristics and physical properties. In textile processing, wools of different types may be blended together or with other fibres to create special product features, but usually within a fairly narrow average diameter range. Figure 9.1 illustrates the typical usage of wools of different diameters in 11 broad product areas. The darker colour in each band indicates major usage and the lighter areas in the bands indicate some usage. Most apparel products are made by weaving or knitting, although carpets and felts may use other processing methods (see Chapter 10). Chapter 6 covers the processing of wool fibre into singles yarns. This chapter now outlines the machinery used when processing from singles yarns into woven and knitted materials. The various processes are applicable to all fibres, but some are more suited to wool than others, and special conditions appertaining to wool may sometimes be required to ensure production of a satisfactory wool product.

9.2

Twisting

Yarn twisting or folding is a relatively expensive and non-productive operation but for weaving yarns it was, until relatively recently, the only way to produce a final yarn that could withstand the rigours of the weaving process and provide fabrics that exhibited good performance in wear. 258

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Strong wool Superfine merino Merino Fine crossbred Medium crossbred 32 mic and stronger 19 mic and finer 20–24 mic 29–32 mic 25–28 mic Men’s woven outerwear Women’s woven outerwear Knitwear Underwear Socks HK yarns Blankets Upholstery Filled bedding Rugs Carpets

9.1 Allocation of wool by fibre diameter in 11 broad product areas. [Source: The Woolmark Co.]

Since the mid-1980s, considerable efforts have been made to eliminate the need to twist yarns together and several methods have evolved that have taken a small but significant share of the market (see Chapter 6 Yarn Production).

9.2.1 The need for twisting Yarns are twisted together for the following reasons: i) To improve quality (regularity). As with the doubling of slivers (see Chapter 6), twisting two or more yarns together improves regularity. Good regularity is essential to produce fabrics with non-streaky appearance and good physical properties. When one yarn is brought alongside another, chance dictates that it is highly unlikely that a thin place in one yarn will coincide with a thin place in another, or that a thick place will coincide with a thick place, so that such variations are reduced by twisting. ii) Design. Twisting yarns of different colour, count, fibre type or twist can give interesting design opportunities for marl and fancy textural fabrics that, because of the relatively late stage of implementation, can be attractive in terms of delivery options.

260 iii)

Wool: Science and technology To improve the efficiency of later processes. Twisting usually improves the strength (tenacity and elongation) of a yarn but the vast majority of single yarns have sufficient strength to withstand the forces of later processes. However, in the case of weaving, single warp yarns often lack the abrasion resistance that is required to withstand the loom motions such as the reciprocating action of the reed and the rubbing action of the healds which, when coupled with the flexing action of the loom, can lead to yarn failure. The yarn breaks because the weaving process disturbs and then removes the surface fibres, exposing deeper and deeper layers of fibre until the yarn becomes weaker than the operating tensions of the loom. Additionally, relatively small levels of surface disturbance at the reed lead to entanglement of raised fibre from adjacent ends of yarn. This entanglement (‘buttoning’) can affect loom efficiency and can escalate into a situation where the loom can not operate.

Yarn twisting enhances abrasion resistance by trapping the fibre ends and increasing the general security of individual fibres within the yarn structure, both the single and twisted elements. Splices or knots in the single yarn are also to some extent protected from failure by twisting. Yarn performance in knitting (Chapter 9) or tufting (Chapter 10) requires elasticity as well as strength. Twisting can improve the elasticity (elongation) of a yarn compared to that of a single yarn. However, many singles yarns are used for tufting and knitting, the required elasticity being achieved by selection of raw materials and twist levels. Because wool is generally used in high value products that have a quality image, and because yarn twisting tends to improve quality, the economic advantages of using single yarns in worsted products have not yet gained widespread acceptance. By contrast, many yarns produced from short staple fibres such as cotton are woven without twisting, size being applied to the single yarns to improve abrasion resistance at weaving. Although sizing is a long established technology, it has evolved in a way that favours large process lots. These are usually found in markets for short staple products but very rarely in the long staple process areas where wool is used. However, the pressure to reduce the fabric weights and costs of long staple worsted products have resulted in the use of single wool yarns that have waxes or lubricants applied to the warp to enable efficient weaving to take place in specific fabric designs. Also, spinning developments such as Plyfil, Duospun, Sirospun and Solospun have evolved that provide greater fibre security within the yarn without the need for a separate twisting operation. However, as with conventional single yarn, the regularity may not be as good as that of plied (twisted) yarns. For this reason, and despite the acceptance of Sirospun yarns for worsted suitings trousers, jackets, etc.,

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these types of yarn have not yet taken a major share of the market for wool yarns, although they do provide effective routes to producing lightweight fabrics that have good performance in wear.

9.2.2 Twisting machinery Three main methods are used to twist yarns together: ring, two-for-one, and two-stage twisting, with some other systems being used in a small way. 9.2.2.1 Ring twisting The oldest of the three main methods uses a ring and traveller system to insert yarn twist and to wind the yarn onto a spindle. It is relatively slow but is versatile and flexible. Ring twisting machinery is available in different guises, some of which use prepared feed packages in order to maximise efficiency, and others which can twist several single yarns together. Some simple machines have only a creel, feed roller system, spindles and ring; while other more complex machines have individual end detectors and stop motions to halt the spindle for ends to be repaired. Although less productive than other methods, ring twisting tends to produce yarns with low twist variation and is still used for quality reasons and when very fine or very heavy count yarns are required. A few ring machines use assembly wound packages in order to reduce creeling time, thus increasing efficiency and productivity. 9.2.2.2 Two-for-one twisting Two-for-one twisting (TFO) has taken the major share of yarn production since its introduction in the 1960s and is used in all production areas, apart from perhaps the very heavy yarn count market. The system is ideally suited for the production of two-fold yarns in the mid-to-fine count area (a high volume area for wool worsted yarns). A hollow spindle inserts two turns of twist for each rotation of the spindle, thus doubling the production compared to ring twisting. The system is usually fed from cone or PSP (parallel-sided package) and also delivers onto cone or PSP, enabling the machine to run for extended periods without stops for donning or doffing. There is little positive control of feed rate and this tends to result in higher twist variation than from other production methods. Variation may be controlled within acceptable limits for weaving yarns but may be considered too high for some knitting yarns. Generally, but not exclusively, the system uses assembly winding to prepare the yarn for twisting.

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In an alternative procedure, two special cones are clipped together and the yarn taken from each package in the normal way. Unfortunately, this ‘Clip Cone’ system suffers from two disadvantages: variation in tension between the two ends, which can create quality problems, and the possibility of one package emptying before the other, which creates waste. Despite these problems, the system has gained some market share, not least because of the improvements to yarn length measurement during winding, which has reduced variations to a few metres in feed cones that may contain more than 30 km of yarn. 9.2.2.3 Two-stage twisting Two machines are used. The first prepares the feed package, imparting a small amount of twist to the two single yarns as they are assembled. The second machine brings the total twist to the required level. The system arguably provides the lowest twist variation of any twisting method, and is used for product areas where twist variation is critical, e.g. hosiery yarns. 9.2.2.4 Other twisting systems Fancy twisting. The production of ‘fancy’ yarns is a significant area. By definition, such yarns offer the textile designer a virtually limitless range of possibilities to introduce textural and colour effects into a fabric. As a consequence, machines can be very complex mechanically and are often controlled by computer in order that they can be quickly and easily set up. The machines use multiple feed systems that can stop, feed or overfeed yarns and filaments in many combinations. Some machines have one or more drafting units at each spindle so that slub and flame effects can be introduced into a yarn. Tritec. Tritec technology augments two-for-one technology by adding a further yarn loop into the spindle area to produce three turns of twist for every rotation of the spindle (see Fig. 9.2). Although much more complex mechanically and technically than TFO, the system has spindle components revolving at relatively low speed, and it is claimed that this reduces the stress placed on the yarn. Parafil. The Parafil system combines spinning and twisting. It delivers an untwisted fibre stream from the draft zone, which is wrapped as it leaves the draft roller by a filament that gives the strength and abrasion resistance for weaving. This yarn method seems to have been accepted by the industry as more suited to knitted products.

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Inner rotation

Outer rotation

9.2 Principle of the Tritec twisting system for inserting three turns of twist for each rotation of the spindle. [Source: The Saurer Group.]

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Other systems for incorporating filament yarns during spinning, e.g. Sirofil or Bi-component, have a small niche market in lightweight wool blend fabrics for suitings, trouserings etc., that have good abrasion performance.

9.2.3 Yarn structures Conventions on yarn structures become blurred when styling takes precedence over technical performance, so that rules on twist levels cannot be formulated. However, there is a general difference between knitting yarns and weaving yarns. Knitting yarns are usually required to be bulky so that twist factors, both singles and folding, are relatively low. To avoid twist liveliness, folding twists may be selected so as to provide torque balance, or twist imbalance may be corrected by setting. Weaving yarns can be more compact, and the essential requirement for low hairiness can be met by using high levels of twist, especially folding twist, and controlling twist liveliness by steam setting. Some spinners provide special high twist yarns for fabrics that are variously claimed to provide good wrinkle resistance and comfort properties.

9.3

Winding

9.3.1 Objectives of winding The various aims of winding include the following. •

•

• • • •

To provide the size and form of package required for subsequent processing or handling. For example, fine yarns may be spun on 50 g cops but may be wound into 1 kg packages for twisting; twisted yarns may be wound onto cones for knitting or parallel-sided packages (PSP) for weaving; packages may be required to withstand the rigours of packing and transportation. To improve yarn quality by clearing faults. Sophisticated optical or capacitative devices detect yarn mass (or colour) outside the pre-set limits and activate a cutter. The fault is removed and the yarn is joined using a knot or splice. To provide packages suitable for dyeing. To re-wind dyed packages or hanks for further processing. To assemble two or more yarns for twisting. To apply processing aids such as size or wax.

Often, several of these requirements may be satisfied in one winding operation.Winding is sometimes linked with other processes, e.g. automated

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spinning on one side and twisting on the other. Some machines such as open-end spinning frames or TFO twisters often have sophisticated winding equipment at each production point and can provide a variety of quality packages suitable for subsequent processing.

9.3.2 Manual winding Manual winding machines are still used because they are flexible, easy to operate and adjust, and simple to maintain and repair. The tasks of the operative are to: • • • •

load feed packages and remove empties remove delivery packages and replace formers tie or splice yarns that break or have been cut by clearers clean and provide general housekeeping

After the yarn leaves the feed package it is tensioned, often by a dual disc system, to control package density in a uniform way. Lubrication, usually required for knitting yarns, is by controlled contact with a wax disc. The take-up package is supported and surface-driven by a drum that has a helical groove so as to traverse the yarn onto the package. Alternatively, the drum may have a plain surface, and a small guide in front of the drum is then used to traverse the yarn.

9.3.3 Automatic winding For this operation, fully-automatic winding machines take over the tasks of the operative and require only a container of feed packages at one end of the machine and the removal of pallets loaded with delivery packages from the other. Automatic winding machines usually wind and clear spun yarns onto cone ready for twisting. They are less flexible than manual machines.

9.3.4 Yarn jointing Yarn jointing is now mostly by pneumatic splicing. A refinement is thermal splicing, which uses heated compressed air, resulting in reduced variability between splices as well as improving the appearance of the splice. Spliced joints have been widely accepted since their introduction in the late 1970s and have almost replaced knots, except in the fine count area around 13 tex (Nm 80) and finer, and also in some knitting applications, especially for products having a plain smooth surface where the visual appearance of a splice may be unacceptable. In such cases, a knot may be pulled to the back (knitwear) or be replaced by a mend (woven fabrics).

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Knots are usually weaver’s (paradoxically for knitting) or fisherman’s (for weaving).

9.3.5 Twist setting Weaving yarns are usually subjected to a mild steam-setting process to stabilise the twist and prevent snarling in later processes. Setting is carried out in an autoclave, ideally using a multiple steam/vacuum cycle to achieve uniform penetration of steam. Generally, temperatures not exceeding 85 °C are used for wool, to avoid yellowing the wool and losing yarn strength. In-line autoclaves have been developed for setting yarn in linked spinning/winding systems.

9.3.6 Package types Since 1970, the variety of yarn packages used in the wool textile industry has been rationalised from more than 30 to about 10, only five of which are in widespread use. Parallel-sided packages and cones are used for dyeing. The most common knitting package has a conicity of 4 ° 20 ¢, although 5 ° 57¢ is becoming the preferred package for knitting. The traverse length of these packages is usually 150 mm (6 inches) although 125 mm (5 inches) is still used by some companies. A small (70 mm traverse) cone is used as a clip cone for feeding two-for-one twisters. Packages may be random wound (constant winding angle and variable traverses per revolution) or precision wound (constant traverses per package revolution and variable winding angle). Because of the relationship between package diameter and traverse length in random winding, the yarn layers tend to create intermittent diamond shaped patterning or ribboning (local areas of high density) that can be detrimental to uniform dyeing in dye packages and unwinding performance. Precision winding does not give such local variations in density but gradually changes density from the inside to the outside of the package as the yarn build up. ‘Step’ precision winding uses an electronic system to change the traverse angle in a series of small steps to obviate the problem of inside to outside density variation.

9.4

Warp preparation for weaving

Good warp preparation is an essential requirement to reach optimised efficiency and wool fabric quality from high-speed weaving machines. The two main types of warping systems used for wool and worsted yarn preparation are section warping and beam or direct warping.

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9.4.1 Sectional warping Sectional warping is the most commonly used system for producing woollen and worsted warps. It is a very flexible system that not only allows for full warp preparation from an individual yarn, but also can allow warps to be made with a combination of yarns of different count or colour. In sectional warping, a given number of warp threads, known as sections, are wound side by side onto a cylindrical drum (see Fig. 9.3). One end of the cylindrical drum is conical in shape and may be either a fixed angle (usually 11 ° or 14 °) or variable angle type. To commence warping, the yarn packages required to form the section band are mounted onto pegs in the creel. Each thread is passed through its tensioning unit, leasing device and finally through the warping reed where the threads are dented to the required sectional width. Using as an example a warp with a total of 3400 ends and a width of 68 inches (172.7 cm), this gives 3400/68 = 50 ends per inch, and the warp is made as follows: With 200 warp packages, 17 full sections are required to complete the warp, each section being 1727/17 = 4 inches (approx. 10.2 cm) wide.

9.3 The Ben-tronic sectional warping machine and creel. [Source: Benninger.]

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All relevant data, such as total warp ends, ends per section, warp width required, yarn counts in d/tex, warp density, and warp length, are entered at the input station, and the machine positions itself for winding the first section. During winding, the section band is traversed unidirectionally so that the warp threads build-up along the incline of the cone. Subsequent sections are built-up on the angled platform provided by the previous section. Quality requirements are accurate build-up of each section, precise fit of the different sections, and equal length and tension of all warp ends. The sectional warp is then beamed-off onto the weaving machine’s warp beam. Optional waxing/cold sizing may be performed at this stage.

9.4.2 Beam warping Beam warping is occasionally used in the preparation of single-count wool warps for lightweight, plain, piece-dyed fabrics, and may be associated with sizing. Usually, a number of individual warp beams (back beams) with an equal number of warp ends are produced. The back beams are then mounted in the beam creel at the rear of the sizing machine. The total contained number of warp ends from the back beams are then run together through the sizing and drying units, and the required warp length wound onto the weaver’s beam. This volume type of warp preparation is common in the cotton industry, but, as stated above, may be used for worsted warps requiring sizing as a means to improve weaving efficiency and quality, e.g. single or fine count yarns.

9.4.3 Drawing-in of the warp threads Different circumstances in weaving dictate three different ways in which warps are drawn in for weaving: Follow-on warp. When the warp is identical in quality (total number of ends, width and pattern repeat) to the one previously woven, it is tied in at the weaving machine with the aid of a knotting machine. Prior preparation. The warp is knotted into a previously prepared harness set, off the loom. Empty loom. Each individual yarn end is drawn through an eye of a heald wire (or jacquard harness) in the sequence required by the design, and then through the weaving reed. Automatic machines are available that accomplish the entire drawing-in operation reproducibly under computer control, facilitating short runs (see Fig. 9.4).

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9.4 The Uster Delta 200 automatic drawing-in machine. [Source: Staubli.]

The reed is selected according to the cloth construction: it determines the spacing of the warp threads, guides the shuttle and beats up the weft. There may be two (plain weave), three (2 ¥ 1 twill) or four (2 ¥ 2 twill) yarns in each dent space.

9.5

Weaving yarns

Warp yarns. Warp yarns need to be strong, elastic and of low hairiness. As a consequence of this, twofold yarns having high levels of folding twist are usually used (e.g. single twist factor 85–90; folding twist factor 110–120). Some single yarns may be used for lightweight fabrics, but their hairiness should be reduced by waxing or sizing. Crepe yarns are usually single yarns with very high levels of twist (e.g. twist factor 200) and are used for specialised fabrics. Weft yarns. The requirements for physical properties are a little less stringent than for warp yarns, so that singles yarns are more often used (for reasons of economy).

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9.6

Fabric design

Patterns are produced in the cloth by passing each weft yarn under or over a varying number of warp threads, forming the weave. Most simple weaves, which repeat over a small number of ends and picks, are drawn up using squared paper (point paper). The squares marked by a cross (¥) indicate where a warp thread should be raised over the weft pick at that point of the design weave. From the design weave, the drafting plan is created, indicating the order that the warp threads should be drawn into the heald harness frames. Where two or more warp threads have the same weaving or interlacing order throughout the design repeat, they can be drawn onto the same heald frame. During weaving, the heald shafts are raised and lowered, alternately, and opposed to each other, after each successive weft pick insertion.

9.6.1 Plain weave In Fig. 9.5, the first and third warp threads of the plain weave design ‘A’ are the same, so they can, if desired, be drawn into the first heald frame. The second and fourth warp threads of the design also have the same order of interlacing as each other, but opposite to the interlacing order of threads 1 and 3, so must be placed into the second heald shaft, as at ‘C’. Design plan ‘D’ illustrates that all four yarns can alternatively be placed onto four separate heald frames. In this instance is necessary to have frames 1 and 3 working as one unit, being raised and lowered together, and to have frames 2 and 4 working together but in the opposite direction.

4 3 2

2

2

1

1

1

C 4 3

X 2

3 A

X X

X

X

X

X

X X

1

X

X

X X

2 1

D

X X

X 4

1

2

3

4

B

9.5 The same plain weave designs ‘A’ and ‘B’ may have alternative design plans, ‘C’ and ‘D’.

Manufacture of wool products X

X

X X

X X

X

X

X

X

X

X 4 3

X

X

X

X

X X

X

6 5

X X

271

2

X X

X

1

Draft plan 1 2 3 4 5 6 X X X X X X X

X X X X X X X X X X X X X X X

X X X

X X

X X X X X X X X X

X X X X X X X X X

X X X X X X

X X X X X X

X X X

X X X X X X Design weave

X X X X X X

X X X X X X X X X X X X X X X

X X X

Peg plan

9.6 Herringbone 3 ¥ 3 weave.

9.6.2 3 ¥ 3 twill herringbone effect The herringbone effect is achieved by simply reversing the diagonal direction of the twill line, as illustrated in Fig. 9.6, periodically across the width of the fabric. The warp threads are drawn 12 to right and 12 to left alternately across the whole warp width, and the design weave is complete on 6 picks.

9.6.3 Colour and weave effects A combination of colour arrangement and design weave provides patterns in two or more colours. In Fig. 9.7 a plain weave design in one colour is shown at ‘E’. The same structure, woven with black and white yarns in the order 2 and 2 in both the warp and weft directions, produces the well known crows foot check pattern shown at ‘F’. A specification of any fabric pattern requires: • • •

the colour arrangement of warping the colour or sequence of weft insertion the draft, peg plan, and design weave

9.6.4 Fabric structure (sett) The main parameters that influence the structure of a woven fabric are the design weave, warp and weft yarn counts, and fabric sett. The term ‘fabric

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X X

X X

X X X

X

X

X

X

E

X

X

X X X X

X X

X

X

X X

X X

X

X

X X

X

X

X

X X

X X

X

X X

X

X

X

X X

X X

X X

F

9.7 Left: A plain weave design in a single colour. Right: The same structure woven in two colours.

sett’ is used to indicate the number of warp threads and weft pick density required during the warping and weaving process, to enable the fabric finisher to achieve the correct fabric firmness and cover, weight, handle, drape, and stability, etc. after final finishing. There are many setting theories to enable designers to calculate weave density (ends and picks per cm) for the many different weave and yarn types. The first was by Thomas Ashenhurst in 1896. Others, such as Law, Armitage and Brierley, concentrated mainly on formulating setting/ construction theories for woollen and worsted fabrics. Brierley’s setting theory postulates that maximum achievable sett with worsted yarns is 73.5% of the maximum geometric setting. Brierley’s formula for square set fabric (73.5% maximum sett of maximum density) is: T = K ¥ C ¥ Fm where, T = Threads per inch each way (warp and weft) K = Constant depending on yarn count system (118.7 for metric count system) C = Average count warp and weft F = Average float of weave m = Constant according to type of weave. m for plain weave = 0.00 for twill weaves = 0.39 for satin = 0.42 for hopsack = 0.45

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Example: A worsted fabric in 2 ¥ 2 twill using 2/60 Nm yarn warp and weft yarn counts set to Brierley’s formula would require: Max. sett = 118.7 ¥ 30 ¥ F m = 59.67 ¥ Fm = 59.67 ¥ 20.39 = 59.67 ¥ 1.3 = 77.6 ends and picks per inch. In practice this figure may be reduced slightly by the designer according to quality requirements. Note that picks and ends are commonly specified per inch in the USA and UK, and that these figures are easily converted into yarns per cm, when applying the formula in other countries.

9.7

Weaving machinery

Woollen and worsted fabrics are mostly woven on rapier or projectile gripper machines, although shuttle looms are still widely used in some sectors and some countries. Air-jet looms are used for producing wool fabrics to a minor extent.

9.7.1 Projectile weaving The multi-gripper projectile weaving machine, introduced by Sulzer Brothers in 1953, was the first system to begin to displace shuttle weaving. The company and its successors have remained the sole suppliers of projectile weaving machinery. Pick lengths of weft yarn are drawn from large cones by a weft accumulator. The free end is held in the jaws of a weft carrier gripper (projectile), 88 mm long weighing 40 g, and the accumulated yarn is threaded to a sophisticated tensioning and braking system. The projectile is lifted to the picking position, and is propelled across the warp shed by a torsion bar system. At the other side of the loom, the projectile is received, the yarn is released and the projectile is ejected for eventual return to the picking side. The weft is cut at the picking side and is held at both sides by selvedge grippers during beat up and shed change. During the next machine cycle, tucking needles draw the outer ends of weft yarn into the fabric to form selvedges. Usually, 10–12 projectiles are associated with a single-width loom. Picking rates are typically 380–420 ppm for worsted yarns and 250– 300 ppm for woollen yarns.

9.7.2 Rapier weaving Rapier weaving is offered by many loom manufacturers and consequently is in widespread use in the worsted and woollen industry. It offers the same

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9.8 A rigid rapier weaving machine, Type HTVS8/S20. [Source: Dornier.]

advantages as projectile weaving in terms of large weft supply packages, linked on the creel for continuous operation, and supply of weft yarn at minimum tension. Rigid rapier machinery (Fig. 9.8). This machinery employs a weft handover system having opposing carrier and receiver rapiers. The rigid rapier racks are driven via teeth cut to their undersides and carry heads that grip the wefts. In a typical machine, weft transfer is positive: cams activate the operation of clamp levers. Timing is such that the receiving rapier arrives at the central position slightly in advance of the carrier rapier and its clamp is opened to receive the yarn, immediately gripping it. Both rapiers begin to withdraw from the shed as the carrier clamp is released. The receiver rapier takes the weft just beyond catch threads to complete the insertion sequence. Flexible rapier machinery (Fig. 9.9). As with rigid rapier weaving, a handover system is used, but weft transfer is achieved by a negative action. The gripper clamps are mounted on flexible tapes that are radiused at the sides of the loom to economise on floor space. Weft yarn stress is minimised by gentle acceleration of the rapiers during critical stages of the insertion cycle. Such looms operate reliably on virtually all types of yarn.

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9.9 A flexible rapier weaving machine, Type G6300. Note the radiused rapier housing. [Source: Sulzer Textil.]

Operating speeds of 700 ppm have been achieved on 1900 mm rapier looms. Typical picking rates for worsted yarns are 450–550 ppm and for woollen yarns 300–350 ppm.

9.7.3 Air-jet weaving Current systems for inserting weft by jets of air offer more rapid weft insertion than rapier or projectile systems, but are less flexible and have more stringent requirements for yarn. Because of the diverse nature of the woollen and worsted industry, air-jet weaving has not been accepted as widely as other systems. Air-jet weaving of worsted fabric has been accomplished at 850 ppm. The technology may be expected to be improved in terms of performance, flexibility and energy saving, and could become more widely applied for weaving wool/synthetic blend yarns.

9.8

Knitting and knitwear

9.8.1 Knitting machine types The knitting industry as a whole can be divided into four manufacturing sectors: fully fashioned, flat knitting, circular knitting and warp knitting. Within the wool industry both fully fashioned and flat knitting are widely

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used. Circular knitting is limited to certain markets and warp knitting is seldom used for wool. 9.8.1.1 Fully fashioned machines Fully fashioned machines have been used extensively for producing plain classical wool knitwear such as sweaters and cardigans, and there are many machines of this type in existence today throughout the world. Such machines produce panels that are fully shaped and styled during knitting. After knitting, the front, back and sleeve panels are linked to form the garment. The basic principle of loop formation is unique and has changed little since its invention. Fully fashioned machines are sometimes referred to as ‘Cottons Patent’ or ‘Cotton machines’ as a result of William Cotton’s patents in the mid-1800s. A row of bearded needles is set into a straight bar and the entire bar is reciprocated by rotary cams, causing the knitting action. The yarn is laid across the width of the needles and sinkers/dividers immediately push the yarn firmly against the stem of the needles, ready for loop formation. Edge stitches can be transferred to narrow the panel, leaving ‘fashion marks’ and creating a shape. Generally fully fashioned machines have only one set of needles and therefore can only produce plain knit fabric, making it necessary to produce the welts/cuffs on special ribbing knitting machines. The ribs are stored on ‘running-on’ bars and can either be transferred onto the needles of the fully fashioned machine by hand, or automatically. Often, the ribs are knit wider than the body panel to compensate for the difference in characteristics between rib and plain knit. This results in a series of tiny pleats between the rib and the plain stitching, known as doublings, i.e. two rib stitches knitted to one plain stitch. The patterning capability of fully fashioned machines is limited to plain knit fully fashioned panels with stitch transfer and intarsia capabilities. Wrap stitches or ‘rakers’ are also possible. These are usually one-needlewidth diagonal lines in contrasting colours and may create diamond patterns (argyle styles). Gauges range from a relatively coarse 9 gg (generally best suited to heavy yarns in the range 9/2–12/2 Nm) to super-fine 33 gg. Note that fully fashioned gauge is the number of needles per 1.5 inches. The machines are multi-sectioned and the number of knitting sections can vary from 4 up to 16 (normally) and all sections knit identical panels simultaneously. Figure 9.10 shows a section of a fully fashioned knitting machine. Fully fashioned machines are used to produce high-quality wool knitwear: their gentle action allows delicate, fine count woollen spun yarns,

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9.10 A section of a fully fashioned machine. [Source: Monk Cotton, UK.]

e.g. Merino lambswool, to be knitted. The gentle action also provides good knitting efficiency. 9.8.1.2 Flat knitting machines Flat knitting machines (‘Flatbeds’ or ‘V-beds’) are the most versatile knitting machines available as a result of recent technological developments. Machines are ultra-compact (see Fig. 9.11) and are supported by impressive computer design stations. Gauge is the number of needles per inch. Two opposing needle beds are positioned so that the upper ends form an inverted ‘V’ (Fig. 9.12). Needles slide down the beds in slots known as tricks. The carriage of the cam box traverses across the needle beds, selecting needles for knitting. Modern machines have variable traverse cam boxes that can travel only as far as the knitting width. The carriage effectively raises and lowers the needles on both beds simultaneously as it passes over them, depending on the desired pattern. Needle bed lengths can vary from 1.0 m to 2.2 m. They are designed for specific purposes.

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9.11 Flatbed knitting machine with computer control facility. [Source: Shima Seiko, Japan.]

9.12 Needle bed layout of a flatbed knitting machine. [Source: Shima Seiko, Japan.]

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It is possible to produce either shaped panels (fully fashioned) or body lengths of knitted fabrics, which are then cut to the required shape. The panels are then linked to form the garment. Patterning. Stitches can be passed from one bed to the other, and the machines offer virtually unlimited patterning capability. The beds can be moved linearly in relation to each other, which not only allows panels to be shaped, but provides patterning possibilities using stitch transfer, as in Aran-style sweaters. The structured work can be combined with intarsia techniques similar to those produced on fully fashioned machines, although flat machines are limited as to the maximum number of colours and yarn carriers. Servo-motors are increasingly used to drive the yarn carriers, enhancing the scope not only for intarsia but also for knitting of integral garment parts. Integral knitting has closely shadowed machine developments. Garment parts such as pockets, collars, stolling, trims and V-necks can be knit as an integral part of the panel. Expertise devoted to programming and setting up a machine for such detailed work saves time at making-up. Complete garment machines. Complete garments may be knitted on specialised machines, without the need for any making-up. There are two techniques: using an adapted V-bed, or using four needle beds (for finer options). The two-bed machine is quite similar to the conventional machine, but uses coarser needles having larger hooks for the gauge (e.g. 5 gg needles in a 10 gg machine) so that heavier yarns can be knitted. The yarn is knit on every second needle leaving a needle available for transfer. Each stitch has an empty needle in the opposite bed to enable stitches to be transferred back and forth as required. The resultant effect is a 5 gauge fabric from a 10 gauge knitting machine. Two-bed complete garment machines are wider than single panel width to allow for the body and two sleeves to be knit side by side as tubes, which are shaped and linked as required. Four-bed machines (Fig. 9.13) utilise two of the beds for stitch transfer and knitting of ribs. The gauges are the same as for conventional machines and hence finer options than on two-bed machines are available. Complete garment technology is highly sophisticated and requires considerable skill. 9.8.1.3 Circular knitting machines Circular knitting produces lengths of tubular fabric rather than panels or panel lengths. This method is less popular for wool than fully fashioned or flat bed knitting. Garments have to be made via the cut and sew route, which creates waste; and there are technical limitations in knitting, dyeing and finishing.

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9.13 Layout of a four-bed knitting machine. [Source: Shima Seiko, Japan.]

9.14 A typical single jersey knitting machine, showing cylinder of needles. [Source: Pailung, Taiwan.]

Generally, circular knitting produces finer gauge products than the knitwear machines, although available gauges range from 5 to 32 gauge (needles/inch). Gauges suitable for wool jersey knitting are in the region 12–22 gauge, however. Many types of circular knitting machine are dedicated to specific end uses, e.g. interlock or terry loop. There are models that are more versatile, i.e. that allow knit, miss and tuck selections at each feeder, and even stitch transfer, but none match the versatility of flat knitting machines. Single jersey machines. Single jersey machines are equipped with a single cylinder of needles (see Fig. 9.14) that produce plain fabrics (single thick-

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ness) and plain-knit-based derivatives such as float jacquards and piqués. Needle selection can vary from two-needle through to full electronic needle selection with knit-miss-tuck capabilities. The horizontal stripe depth of these machines is usually governed by the number of yarn feeders around the circumference of the cylinder. Wool fabric production on single jersey machines tends to be limited to 20 gauge or coarser, as these gauges can utilise two-fold wool yarns up to 48/2 Nm, the balanced twist giving spirality-free fabrics. Finer gauges require single yarns which induce spirality and, although this can be partially ‘set’ during finishing, the garment may subsequently twist during laundering. Fabrics are used in cut-and-sew garment manufacture, and an inherent feature of wool single jersey fabrics is that the fabric edges tend to curl inwards after cutting. Terry loop is a basis for fleece fabrics and is produced by knitting two yarns into the same stitch, one ground yarn and one loop yarn. The loop yarn is controlled by sinkers which press on the stitch to create a large loop. These protruding loops are then brushed or raised during finishing. Sliver knitting machines are single jersey machines that have been adapted to feed in a sliver of staple wool fibre. The drafted sliver is hooked over the raised needle via card wire rollers. The fibres are then held in place and laid by a jet of compressed air until locked in place by the stitches. Double jersey machines. Double jersey machines have a dial of horizontal needles positioned adjacent to a cylinder of vertical needles (see Fig. 9.15). The pattern/structure possibilities are enhanced dramatically

9.15 A double jersey machine having a cylinder of vertical needles that interact with a dial of horizontal needles. [Source: Terrot, Germany.]

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9.16 A combined fabric slitting and rolling device. [Source: Vignoni, Italy.]

compared with single jersey. Generally, the dial knits the inner face of a fabric and the cylinder the outer face. Wool double jersey fabric is more commonly seen than single jersey. Typical examples are interlock structures for soft Merino wool underwear/base layer garments and 1 ¥ 1 rib fabrics for leggings and outerwear products. Double jersey fabrics tend to be heavy so that fine yarn counts have to be used. A typical yarn providing a compromise between knitting efficiency and cost is Nm 48/1 spun from 21 m or finer Merino wool. Single yarns do not give spirality problems as the double layer construction balances the yarn torque. Extremely high rates of production (25–50 mm of fabric per revolution) are available from machines having 72, 96 or 108 yarn feeders. Such machines are less suitable for knitting delicate wool yarns. A recent development is combined fabric slitting and open width roll-up (as shown in Fig. 9.16), aimed at eliminating crease marks.

9.8.2 Common wool knitted structures Single jersey (plain knit or stocking stitch) is formed by the inter-meshing of a number of loops from side to side and top to bottom (Fig. 9.17). The characteristics of a single jersey fabric are: • • • • •

single sided thin/light weight fast and efficient production edges curl, difficult to handle partially unstable, stitch distortion.

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9.17 A single jersey structure. [Source: Knitting Technology, D J Spencer, Woodhead Publishing.]

9.18 Structure of 1¥1 rib fabric. [Source: Knitting Technology, D J Spencer, Woodhead Publishing.]

Rib fabric covers a broad range of knitted structures including 1 ¥ 1, 2 ¥ 1, 2 ¥ 2, and half gauged and fancy ribs. The simplest rib fabric is 1 ¥ 1 (Fig. 9.18) formed using two beds of needles, passing yarn from one bed to the other alternately. The characteristics of a 1 ¥ 1 rib fabric are: • • • •

double sided fabric thick/medium weight excellent width stretch/recovery balanced structure/fairly stable.

Interlock fabric is similar to 1 ¥ 1 rib fabric in that it is knitted alternately on opposite needle beds, but on alternate needles and requires two

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9.19 Structure of interlock fabric. [Source: Knitting Technology, D J Spencer, Woodhead Publishing.]

opposing knitted courses or traverses to complete one row (Fig. 9.19). Interlock is mostly produced on circular machines. The characteristics of interlock fabric are: • • • •

double side fabric (same face and reverse) thick/heavy weight good width stretch/recovery balanced structure/very stable.

Milano fabric can come in the form of milano rib, milano jacquard, milano and full milano, but all are quite similar in construction. The milano structure combines the 1 ¥ 1 rib with an additional single bed row to improve stability. All variations of milano are widely used, mainly from knitwear machines. The characteristics of a wool milano fabric are: • • • • • •

single sided fabric thick/medium weight limited stretch recovery reasonably balanced structure fairly stable suitable for jacquards.

9.8.3 Fabric quality Fabric quality in wool knitwear can refer to the fabric density or cover factor; it can sometimes apply to the incidence of faults; or to the fineness (micron) of the wool.

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9.8.3.1 Fabric density Stitch density is directly related to the length of yarn in a knitted loop. Factors affected by adjusting loop length are: • • • • •

stitch density/fabric density fabric weight and fabric cost fabric dimensions and panel size (shaped knitwear) dimensional stability; relaxation shrinkage physical performance; pilling, burst strength.

Wool yarn count and loop length of a fabric should be correlated by the cover factor, CF: CF =

1 R ¥ LL

Where: R = resultant count of yarn LL = loop length The cover factor is selected to achieve the best possible compromise between fabric performance and softness/drape. The yarn count must also be matched to the knitting machine type and gauge (see Table 9.1).

9.8.3.2 Fabric faults Fabric faults associated with wool knitwear are: • • • •

stitch distortion fabric spirality yarn irregularity (thick/thin) and neps barré (horizontal stripes/bands).

Stitch distortion and fabric cockling tends to be associated with plain knit shaped garments. Yarn properties are one possible cause. Yarn irregularities or yarn faults can give intermittent thick/thin horizontal stripes across the fabric, and neps can look rather like small lumps of fibre or knots. Fabric spirality results when singles yarns or unbalanced 2-fold yarns are knit into single-bed structures. The fabric twists on steaming or wetting (see Fig. 9.20) leading to garment seams that are no longer vertical. Yarn irregularity. Some poor quality yarns are uneven, having thick and thin places, resulting in irregular effects within the fabric. Visually these faults appear as a streaky effect in the fabric and can quite often contribute to stitch distortion.

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Wool: Science and technology Table 9.1 Examples of yarn count/machine gauge relationships Straight Bar

Nm

9

9/2–12/2

12

12/2–17/2

15

13/2–20/2

18

20/2–28/2

21

22/2–32/2

24

28/2–26/2

27

32/2–40/2

V-Bed

Nm

3

2/2–2/4

5

2/4–2/9

7

2/10–2/14

8

2/12–2/17

10

2/20–2/24

12

2/24–2/32

Single Jersey

Nm

8

17/2–24/2

10

22/2–36/2

12

28/2–40/2

14

32/2–48/2

18

40/2–30/1

20

48/2–32/1

22

28/1–36/1

24

32/1–40/1

26

36/1–44/1

28

48/1–55/1

Double Jersey

Nm

12

18/1–26/1

14

22/1–32/1

16

28/1–36/1

18

32/1–40/1

22

36/1–48/1

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A

9.20 Fabric spirality. [Source: The Woolmark Co.]

Barré can be caused by incorrectly set or badly adjusted knitting equipment. Machines with multiple feeders (both circular and flat machines), if not well controlled, can knit vastly different loop lengths from one feeder (or system) to the next. This problem is more applicable to older generations of circular machinery and hand-operated flat bed machines that have ineffective or no yarn feed control devices.

9.8.4 Garment manufacture Three manufacturing routes are used, depending on the knitting technology:

288 • • •

Wool: Science and technology

fully fashioned (shaped knitwear) cut and sew complete garment

Some are more suited to wool products than others. 9.8.4.1 Fully fashioned Fully fashioned (shaped) knitwear is engineered to size and shape at the point of knitting. Some machines produce only symmetrical designs, whereas others can produce asymmetric styles, enabling shapes such as front panels for cardigans to be produced. As the welts and cuffs are incorporated at knitting, only the collars remain to be added during make-up. Usually, the garment sides, sleeves and underarms are cup seamed using a fine thread, and the shoulders and collars are linked with the same yarn used for knitting. 9.8.4.2 Cut and sew Individual panel shapes are cut to size from panels (V-bed or flat bed) or from a length of fabric (circular knitting machines), and are sewn together with overlocking. Cutting waste may be as much as 25% of the total fabric, which makes the technique unattractive for wool. The cut and sew route is, however, used for relatively fine gauge wool circular jersey products, but the bulky seams in heavier knitwear are more appropriate to down-market qualities. 9.8.4.3 Complete garment Products from complete garment machinery effectively require no further making-up, except for sewing into the seam of loose ends of yarn. The adoption of complete garment technology has been focused on high quality knitwear, using wool, cashmere, silk, etc.

9.8.5 Summary Wool knitwear of high quality has traditionally been made on fully fashioned machines (fine gauges) and flatbed machines (coarser gauges). More limited volumes of knitwear and tailored garments are made from circular-knitted fabrics. Progressive developments in patterning systems for flatbed machines have enabled designs that could once be accomplished only by hand knitting to be produced. The most recent developments in the knitting of complete garments on one machine are strongly associated

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with wool. For information about finishing knitwear and knitted fabrics, see Chapter 11.

Bibliography Ormerod A and Sondhelm W S, Weaving–Technology and Operations, The Textile Institute, Machester, 1995. Spencer D, Knitting Technology, Woodhead Publishing, Cambridge, 2001.

10 Carpets, felts and nonwoven fabrics G H CRAWSHAW AND S J RUSSELL

10.1

Carpets1,2

10.1.1 Introduction The oldest existing carpet, the Pazyryk carpet, believed to be 2400 years old, has a knotted wool pile. Wool has remained the mainstream fibre for hand-knotted carpets and it was natural that, when mechanical weaving of carpets was introduced, wool was adopted as the pile material. Wool and wool blend pile yarns still dominate the carpet weaving industry. In contrast, cotton was the pile material used for ‘candlewick’ tufted bedspreads and its use continued when the tufting industry turned its attention to carpets in the 1940s. It was the low cost of tufted carpets that encouraged consumers to carpet living rooms wall-to-wall and to carpet other areas of the home, so that tufting zoomed into prominence to produce the greatest volumes of carpet worldwide. Rayon quickly displaced cotton and a little later nylon became the dominant pile material: wool was introduced to the tufting industry at a relatively late stage, when the industry expanded up-market. IWTO Wool Statistics (ISSN 0260-216) classify around 470 m kg (clean equivalent) of world wool production as carpet wool (coarser than 32.4 micron). A proportion of this is used in outlets other than carpet manufacture, e.g. fillings for furniture and mattresses, coarse apparel, low-grade blankets, so that a very rough estimate of global wool consumption in carpet manufacture may be 300 m kg. New Zealand is the largest supplier of carpet wools that are traded internationally, contributing 110 m kg. Wools of New Zealand, an organisation that has an oversight of NZ wool production and utilisation, estimates the following allocation of NZ wool between the principal methods of carpet manufacture in 2000: • •

Tufting Weaving

290

52% 27%

Carpets, felts and nonwoven fabrics • •

Handcraft (knotting & tufting) Other

291

19% 2%

Within the area of weaving, use of New Zealand wool is biased towards face-to-face weaving, which requires relatively fine yarns and therefore carefully specified wool, but the broad allocation of all carpet wools in manufacture is probably not very different from the above figures. Although tufting progressively displaced weaving during the period 1960–1990, there has since been a revival of weaving largely owing to adoption of new technical developments.

10.1.2 Hand knotting Since the first oil shock, consumers have been influenced by environmentalism and one consequence has been an increased demand for handknotted carpets. In particular, the small hand-knotting industries of India and Nepal expanded in the 1970s and 1980s to join Iran and Turkey as major producers. Hand-knotted carpets are mainly produced by knotting the pile round the warp using the symmetrical Turkish (Ghiordes) knot or the asymmetrical Persian (Sehna) knot. In Nepal, the technique of ‘weaving round the iron rod’ is used. A sequence of knots in one colour is created by first knotting a continuous length of yarn over a combination of the required warps and an iron rod. The resulting loops are subsequently cut with a knife and the rod is withdrawn. In New Zealand, a technique of knotting two carpets face to face has been developed, thereby accelerating production.3 Machine-spun woollen yarns are widely used in hand-knotted carpets, although semi-worsted or worsted yarns may be applied in the finer constructions. Nomadic weavers commonly use hand-spun yarns, produced using the traditional whorl. Hand-spun yarns are also used in Nepal. Hand-knotted carpets are usually washed in water to cleanse them and improve the uniformity of pile lay. Often, the washing process is boosted by chemicals to increase the lustre, to soften the colours, and generally impart an antique appearance. A typical chemical washing procedure consists in soaking the carpet in caustic soda solution, working the pile unidirectionally with a stiff brush or wooden blade, rinsing with further working, and then repeating the procedure with sodium hypochlorite solution. Lustre is enhanced not only by parallelisation of the pile but by removal of cutical cells. Chemical damage is severe on the pile surface, but the high pile density of the carpets to which the process is applied preserves the greater proportion of the pile from excessive chemical damage.

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10.1.3 Axminster weaving Axminster weaving emulates the hand-knotting once used in the town of Axminster, UK, i.e. tufts of individually coloured yarns are incorporated in the backing as it is being woven (but round the weft, rather than round the warp as in hand-knotting). There are two principal systems: spool-gripper Axminster and gripper-jacquard Axminster. The spool-gripper system is capable of introducing an infinite number of colours into the design, but it is rather inflexible, so that it is most commonly used for long production runs for the residential market of carpets that require subtle shadings of colour, e.g. floral and chintz designs. The pile yarns for each row of the design are assembled on a table creel in the required sequence of colours and are wound parallel onto spools typically holding 15 m of yarn. (Computerisation of this slow operation has been attempted). The various spools representing the rows of tufts in the design are assembled in order on a gantry that leads them to the point of weaving. A line of grippers resembling birds’ beaks takes the yarn ends from the spools, withdraws tuft lengths which are cut off, and transports them to be folded over a double shot of jute or polypropylene weft from an eyed ‘needle’ (the traditional method of weft insertion). Yarn tufts are finally locked in place by a further shot or shots of weft. The gripper-jacquard system was the subject of intense technical development in the late 1980s and 1990s. Weft insertion in a modern loom is by projectile (Griffith) or handover rapier (Crabtree) and colour selection is by electronic jacquard that can be interfaced with a computer aided design (CAD) system. The pile yarns are introduced from a creel having layers (frames) for each colour. Typically, creels hold 8 or 12 colours, although additional colours may be ‘planted’ in a frame if the designer wishes to use localised extra colour. From the creel, yarns are led to carriers that can move horizontally close to the point of weaving, and the electronic jacquard positions these carriers in the required colour sequence so that grippers can withdraw a row of tufts, as in the spool-gripper system, and take them the short distance to be woven into the backing fabric. Weft insertion rates of modern Axminster looms are 120–200 ppm. Rugs and squares are usually produced using a Kardax weave that shows the design on the back, as in knotted carpets. Broadloom carpets are produced with a Corinthian weave that is more economical in the use of pile yarns (see Fig. 10.1). The versatility of electronic gripper-jacquard looms, coupled with their ability to weave dense, hard-wearing carpets, has stimulated their application in the hospitality contract market for carpets. Spectacular designs with long repeats or no repeats can be produced quickly to clients’ requirements.

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10.1 Axminster weave structures. Kardax weaves show the pattern on the back of the carpet as in hand-knotted carpets and are used for squares: Corinthian weaves are usually used for wall-to-wall carpets. [Source: David Crabtree & Son.]

A marked revival of Axminster weaving was a consequence of the new technology. Yarns for Axminster weaving are typically woollen-spun around R600 tex/2 and are hank dyed. Because of the multi-coloured nature of the product, the composition of the wool blend is not as critical as for some other methods of carpet manufacture. For reasons of economy, it is advantageous to blend wools for three grades of yarn: white, yellow and grey, to be used for dyeing light, medium and dark colours, respectively. Moorland wools in the micron range 30–45 are commonly used. Blends may also contain oddments (short, cheap wools). A proportion of well-grown New

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Zealand second shear wools or slipes is included, particularly when a good white colour is required, and to provide a good basis for consistent carding and spinning. Blends of 80% wool and 20% nylon are commonly used in the lower pile weights of Axminster carpets to enhance durability. A niche market exists for Axminster carpets having patterns of texture rather than colour, achieved by the use of light and heavy yarns in different areas of the design, using coarse pitch looms. The very coarse yarns are advantageously felted so as to retain tuft definition in wear.

10.1.4 Wireloom weaving Wireloom weaving pre-dates Axminster weaving by many years. It takes two forms: Brussels weaving for loop-pile constructions and Wilton for cut pile. Creeling of the pile yarns in frames is similar to the creeling for Axminster weaving, but the wool yarn is introduced as a warp rather than as individual tufts, and all the colours are present in every dent of the weave throughout the length of the carpet. Heald frames control the weaving of the backing and a jacquard mechanism causes pile yarn to be lifted over a ‘wire’ when its colour is required in the design. Wires carrying a blade cut the pile on removal to create Wilton carpet, whereas ‘round’ wires leave loops to create Brussels carpet. Heat is generated by friction as wires are withdrawn and metal temperatures may become high enough to fuse synthetic fibres so that wireloom weaving has been confined to wool and wool-rich blends. Pile that lays ‘dead’ in the backing may contribute to the cushioning effect of the carpet, but increases the cost of the product, especially in multi-frame constructions. Figure 10.2 shows a typical weave structure. For economic reasons,Wilton weaving has become focused on two- or three-frame designs woven in dense constructions for the contract market and to some extent on plain carpets. Classical styles of five- and six-frame Brussels and Wilton carpets are still in demand in the upper market brackets. Although modern designs of wireloom are available having handover rapier weft insertion and electronic jacquards, many existing wirelooms have shuttle weft insertion and sometimes traditional jacquard patterning. Because the large areas of plain colour in most wireloom carpets can expose defects, the wools in the blend must not be too diverse in terms of colour, dyeability, medullation and kemp content. Wirelooms are unique in their flexibility for producing textured surface effects in both cut pile and loop pile. Possibilities include tonal patterns of cut and loop pile, carved effects, and textured loops, including huge loops formed from extremely heavy (e.g. 5000 tex) yarns floated over several wires. A special ‘wireless’ loom for producing loop-pile textures and pat-

Carpets, felts and nonwoven fabrics

295

terns has been invented. The loops are formed over temporary wefts, which in turn are supported by lancets – strips of metal suspended parallel to the warps at the point of weaving (Fig. 10.3). The lancets, in effect, function as gauges that determine pile height. Warpwise wireloom weaving has been supported by a small international club of carpet manufacturers. The Karaloc loom is produced in two basic versions: for loop pile and cut pile respectively. Some versions can produce cut/loop styles. Hand-wire weaving is used in Greece to produce unique flokati rugs. Both backing and pile are composed of 100% wool. During weaving, wooden ‘shag bars’ are inserted manually into the shed of the loom every 5–12 picks to create high loops. The operative runs a knife along a groove in the bar to create high cut pile. Traditionally, the rugs are finished by churning them in deep cylindrical vats located by waterfalls. The simple shag pile as woven is transformed into a lofty fleece-like structure in which groups of tufts are felted into pointed strands. As flokati rugs are usually undyed, the wool used must be free from stains and dark fibres. Fibre tends to be lost in the milling process so that sound wool of good length is essential. These requirements favour New Zealand Romney fleece or early shorn wool.

10.2 Weave structure of a three-frame Wilton carpet, showing the location of the dead pile in the backing. [Source: Michel Van de Wiele.]

10.3 Principle of the LoopPile Master 32 wireless weaving machine, showing a lancet supporting false picks (hollow circles), and a carpet structure having high loops formed over false picks and low loops formed over the backing weave. [Source: Michel Van de Wiele.]

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10.1.5 Face-to-face weaving The weaving of two carpets face to face was pioneered by Van de Wiele in the 1920s, and the technique has benefited from a sustained programme of technical development so that it is now arguably the most sophisticated system of carpet manufacture. Face-to-face weaving is the principal system for manufacturing carpet squares and rugs in both traditional and modern designs, and is increasingly used for producing wall-to-wall carpets. Two backing fabrics are woven in parallel and, as in wireloom weaving, the wool pile yarns are led to the point of weaving as warps. When a colour is required in the design, the designated yarn is lifted (or dropped) from one backing to the other while the yarns not required lay dead in the backing (or on the back surface in some constructions). An example weave structure is shown in Fig. 10.4. The resulting sandwich is sliced on the loom into two carpets. The principal advantages of face-to-face weaving compared with wire Wilton are: • • •

higher rates of production in patterned carpets the consumption of dead pile yarn is roughly halved (it is shared between the top and bottom carpets) the cutting mechanism gives a very level surface.

Modern looms are equipped with electronic jacquard, and weft insertion may be by single-rapier, double-rapier, or triple-rapier systems: each has its particular advantages, depending on the quality and style of the carpet to be woven.

2 5 6

TC

5 1 4

3 2 BC

1 6 3 4 Patented

10.4 Cross-section of one of the many weave structures possible from face-to-face weaving, illustrating the principle of the system. [Source: Michel Van de Wiele.]

Carpets, felts and nonwoven fabrics

TC

3 4 4 6 3

BC

2 5 2 1

297

1

Patented weave structure

10.5 Principle of the production of sisal-look loop-pile carpets using a triple-rapier face-to-face weaving machine. The heavier picks are inserted by the middle rapier alternately into the top and bottom carpets. [Source: Michel Van de Wiele.]

A unique way of using a triple rapier loom is to produce loop-pile wool carpets having a sisal look. The middle rapier carries a heavy weft, often destined to be visible in the carpet, and pile yarns first from one backing and, in the next cycle, from the other backing, are lifted towards but not into the opposite backing so that they become looped over the middle weft. The result is two loop-pile carpets that interlock (Fig. 10.5), and which can simply be pulled apart at the exit from the loom. Constructions of face-to-face carpet squares are mostly selected to provide fine definition of design so that particularly fine yarns (in comparison with other styles of carpet) are required. Commonly used yarns are 10/2 Nm and 18/3 Nm semi-worsted or worsted. Wool selection is critical because of the need to compromise between a firm pile and spinning efficiently near the limits. Typically, fleece and second shear blends in the 30–35 micron range are used.

10.1.6 Flat-woven carpets Flat-woven floorcoverings are mainly composed of sisal or coir. Recently, wool and wool-blend products have become popular in some countries, often woven from mixed colour tufting yarns and laminated to a secondary backing fabric. Very simple constructions, e.g. hopsack weave (yarns interlaced in pairs in both warp and weft) may be used. Alternatively, special weave structures providing a distinction between pile warp and backing can be engineered. A particularly sophisticated example with an integral backing is the DuraliteTM weave (Fig. 10.6). Duralite carpets are recommended for use as aircraft carpeting because of the high density (good durability) and low mass per unit area that can be achieved.

298

Wool: Science and technology pile warp yarn support weft (usually a stipple of 2 or 3 shades)

top weft

stuffer bottom weft binding chains

10.6 Weave structure produced on a DuraliteTM loom. [Source: Duralite Corporation.]

10.1.7 Tufting Tufting is a much more productive process than weaving, particularly for plain carpet, but is not as versatile in terms of patterning. As the level of sophistication of patterning increases, production rates become slower, but are still faster than weaving. Note however that the total cost of producing a carpet is heavily dependent on the cost of the raw materials. Tufted carpets are formed by stitching loops of pile yarn from a bar carrying 1000–2000 needles into, usually, a pre-woven or spunbonded polypropylene primary backing fabric. The pile is locked in place by means of synthetic latex, and a secondary backing fabric is laminated to the tufted cloth to provide stability and additional mass. As an alternative to the secondary backing fabric, an integral underlay in the form of foamed latex or needlefelt may be applied. A cutting mechanism is integrated with the loopers when cut pile is required (Fig. 10.7). 10.1.7.1 Plain and semi-plain carpets Most wool tufted carpets are manufactured without a patterning mechanism, so that product variety is to a large extent provided by the texture. Textures widely used in the wool carpet industry include friezé, loop pile variants, tweed effects, plain velours, saxonies and cut/loop styles. Yarn engineering plays a key part in the development of tufted textures. Arguably the most difficult style of tufted carpet to produce is the plain velour. The carpet must have a uniform appearance and the tufts should be individually defined. The wools in the blend should be very similar in dyeing properties, and free from stains, dark fibres, kemp and medullated fibre, and should be thoroughly blended. Blends of wool and synthetic fibres are commonly 80/10/10 wool/nylon/melt-bonding fibre (to enhance durability and set). Dyeing in hank form is desirable in that setting of the twist in the yarn (to achieve tuft definition) is achieved by the immersion in boiling water. Careful control of dyeing is necessary if the colour is to be level within indi-

Carpets, felts and nonwoven fabrics

299

Knife

10.7 The principle of cut-pile tufting. [Source: Cobble (Blackburn).]

vidual dye batches. Stressing the fibres by overtwisting two-ply yarn slightly and incorporating crimpy wools in the blend improve the level of set achieved. Stock-dyed yarns may be chemically set in the form of a coiled warp using the WRONZ Twistset process. The Twistset machine may be used as a key component of the engineering of ecru carpets that can withstand the heat, water and mechanical action that are features of piece coloration techniques (batch or continuous). Shearing is a key process in the production of high quality cut-pile carpets, and is usually carried out before backcoating. The cut-pile friezé texture is a popular style of wool tufted carpet. It is produced by overtwisting two-ply woollen-spun yarn to the extent that the yarn snarls and is set in this configuration during hank dyeing. Short and cheap wools can be included in the blend, as they are firmly held by the high level of folding twist. Tweed yarns from stock-dyed wool (often called berber yarns when in natural colours) are commonly used to provide colour effects in wool tufted

300

Wool: Science and technology

carpets, especially in loop-pile constructions.Another ‘natural look’ that has been widely used in wool is the sisal look. The berber style and its variants were exploited in a major way to introduce wool to the tufting industry during the period 1970–1980. Such semi-plain carpets proved more acceptable than patterned styles of wool tufted carpet during that period. 10.1.7.2 Patterned carpets Screen printing, widely used for nylon carpets, is rarely applied for wool carpets because it is associated with long production runs and the mass market. A minority of wool carpets is patterned using the more versatile computer-controlled jet printing. The two principal techniques for mechanical patterning in tufting are yarn tensioning and crossover tufting. Tensioning systems can be used to provide sculptured carpets composed of high and low loops; and colours in a low loop may be buried under high loops of a different colour to achieve two-colour designs. Using two needlebars that can slide laterally under the control of stepping motors, and with different colours of pile yarn creeled up in sequence, the colours in a carpet can be transposed in position to create, most commonly, small geometric designs. The crossover technique is widely used to produce wool carpets. Elaborate effects can be achieved by combinations of yarn tensioning and crossover patterning systems. A closer resemblance to Axminster carpets can be obtained with the Colortec system of Cobble, which operates through a combination of the Individually Controlled Needle and a sliding needlebar, or the Computer Yarn Placement (CYP) system of Tapistron. The Colortec machine is faster than an Axminster loom while the CYP machine is more versatile. The latter utilises air-assisted hollow needles located two inches apart on a bar, which moves weftwise to stitch in the two-inch gaps as well as being inched forwards in the direction of manufacture. The zig-zag stitch structure from the CYP machine can simulate a wide range of tufting gauges; additional versatility in terms of short runs of patterns is provided by the small number of needles and consequent ease of re-creeling. Hand-held gun tufting is a technique of manufacture that is virtually dedicated to wool. One of its applications is its use by artists to produce individually designed rugs or wall hangings. At the other extreme it may be used to produce spectacular designs in heavy constructions to furnish the floors in the public areas of luxury hotels.

10.1.8 Other methods of carpet manufacture Felting. Needlefelts are widely used to provide contract carpeting in the lower price brackets and as a basis of carpet tiles. There are very few examples of needled wool floorcoverings on the market. However, true wool felts

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(pressed felts) are used as surfaces for indoor bowls – in large areas for the professional game and for roll-up mats for carpet bowls. Bonding. A face-to-face adhesive bonding technique that originated around the French–Belgian border employs two backing fabrics coated with PVC plastisol which are led vertically downwards, close to and parallel with each other (Fig. 10.8). A warp sheet of pile yarn is folded at the entry and pressed into the adhesive. The resulting sandwich is bonded by infra-red heating and then slit into two carpets. Wool velours of good quality are produced on such systems. There are many variants on the face-to-face bonding process, some producing U-tufts and some I-tufts.

Blade

Blade

Heat

Box

Backing

Backing

Carpet

Carpet Knife

10.8 The principle of face-to-face bonding. [Source: David Crabtree & Son.]

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Wool: Science and technology

Two bonding systems that can produce patterned wool products are dedicated to the manufacture of tiles. In the Bondax (UK) process, the pattern is formed by a spool-gripper system. In the Axtile (Japan) process, yarns from a creel are selected for patterning by an electronic jacquard mechanism. Knitting. Extremely irregular effect yarns can be converted into carpet by laying them into the backing fabric as it is formed on a warp knitting loom, resulting in products of unique design. A knitting machine of relatively recent design can produce patterned loop-pile carpets in up to five colours.

10.1.9 Performance features of wool in carpets Herzog4 focused attention on the need to market carpets in terms of their immediate usefulness to the consumer. His list of relevant factors has since been extended to include the following: • • • • • •

psychological usefulness (aesthetics, prestige) walking comfort safety acoustic comfort thermal comfort control of indoor air quality

Wool carpets tend to fall in the thicker and heavier categories, which confer benefits in terms of walking comfort, acoustic comfort and thermal comfort; thick carpets cushion people from falling injuries; and psychological benefits have been attributed to well-designed wool carpets. Some of the positive attributes of wool carpets derive from the properties of the fibre.

10.1.9.1 Safety Wool carpets are inherently difficult to ignite. They have a low heat of combustion and the intumescent char generated on exposure to flame confers insulating properties. Damage from minor burns can often be removed by abrading the carpet, without the need for repairs. Good flammability properties account for the widespread use of wool carpets in passenger aircraft and in many other contract applications such as high-rise buildings. Where the carpet construction and relevant specifications require it, additional flame retardency can be achieved using wool-specific treatments (Section 7.7).

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303

Risk of build-up of electrostatic charge on persons walking over a carpet in a dry atmosphere is a problem that wool shares with nylon. A simple solution based on a wool-specific dressing on the pile is described in Section 7.6. When a conductive carpet is specified, as it often is for computer rooms, the pile and backing must be engineered accordingly. A small proportion (0.2–0.5%) of stainless steel fibre or conductive synthetic fibre is combined with the wool pile: the backing may also be augmented with conductive fibres and/or conductive latex may be applied. 10.1.9.2 Indoor air quality Wool carpets have beneficial effects on indoor air quality owing to the fibre’s large capacity for absorbing toxic gases, notably sulphur dioxide, formaldehyde and oxides of nitrogen.5 10.1.9.3 Deterioration of carpets The deterioration of carpets in general can involve the following aspects: i) ii) iii) iv) v) vi)

durability dimensional stability appearance retention, texture appearance retention, colour appearance retention, soiling appearance retention, pattern

The deterioration of wool carpets in particular deserves special mention with regard to durability, texture retention and soiling. Durability. In laboratory abrasion testing, wool carpets are shown to be less durable than nylon, and wool should not be used in carpets of low pile mass unless they are to be installed in domestic bedrooms. However, wool carpets can be engineered to be highly durable. A rough guide to durability is the pile mass ¥ density factor P2/t*, i.e. carpets having a low, dense pile perform best. Most hand-knotted carpets fall into this category, which accounts for their lasting long enough to become antiques. Resistance to pile reversal (shading). The watermarking effect that can occur particularly in cut-pile carpets (one aspect of texture change) has been shown to be an optical effect caused by random laying of the pile as it is crushed during wear, during storage and handling, or during fitting.6 The TrutrakTM machine for laying and setting the pile of wool carpets so as to

* P = pile mass per unit area and t = pile thickness

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Wool: Science and technology 500

400

300

Acrylic

Polyamide

Polyester

Cellulose

100 Wool

Degree of soiling

200

10.9 Soiling in service (colour change) of comparable carpets in various pile fibres. [Source: L. Benisek.7]

give a more pronounced initial pile lean than is normally produced in manufacture produces a marked resistance to shading. Resistance to soiling. Practical floor trials have shown that wool carpets resist soiling better than carpets from other common pile fibres (see Fig. 10.9) and are more easily cleaned by standard wet cleaning processes.7 The surface structure and composition of the wool fibre may play a role in the resistance to soiling: the swelling of the fibre in detergent solutions is likely to assist the removal of soil in cleaning.

10.2

Felts and nonwoven fabrics

10.2.1 Historical background of pressed felts Pressed felt is produced from wool or animal hairs by mechanical agitation and compression of the fibres in warm, moist conditions. No spinning, weaving or knitting is used in the production of such felts and simple mechanical interlocking of fibres in a batt structure is capable of producing a dimensionally-stable fabric with densities up to 0.7 g/cm3. Commercially, dilute sulphuric acid may be used to accelerate the felting process.8 Animal felts have been used since ancient times and there are various legends about how the felting process was discovered.9 It has been sug-

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gested that Noah lined the floor of his ark with wool to make it more comfortable. After forty days and nights, the pressure and moisture from the animals turned the loose wool into a matted fabric. Another legend tells of a monk from Caen in France who, after setting out for a distant shrine in his new sandals, decided to put loose wool in them to ease his sore feet. After fifteen days of walking he arrived at his destination and found that a strong, soft fabric had formed by the pressure and moisture of his feet. A similar story is told about a camel driver in the Middle East who used camel hair to line his sandals.9 It is known that the ancient nomads used felts. From the eighth to the fourth century BC, the Nomadic Scythian people of Central Asia travelled in felt-covered wagons and lived in tents made of felt.10 Felts composed of wool or camel hair were also used to make carpets in ancient China,11 and in parts of Asia decorative rugs made from pressed felts are still made. Around 900 BC, in Greece, felts were produced to make caps, blankets and helmet linings for soldiers, and in Europe animal felts were used for couching and pressing wet-laid pulp in the hand-processing of paper.12

10.2.2 Manufacture of wool pressed felts The fashion and craft industries still produce items of clothing using traditional felting techniques but, in addition to hats, slippers, interlinings and handbags, many of the fabrics supplied by the modern pressed-felt-making industry are used in a wide range of industrial applications. End-uses include the polishing and de-burring of metals, optical surfaces, plastics and jewellery, the manufacture of seals, gaskets (Fig. 10.10) washers, felt nibs and markers, air and liquid filters (including bag filtration13), oil wicks, piano cushion felts, shoes, toys, pennants, table covers, notice boards, bookbinding and furniture components. Felts are also used in orthopaedic applications and in inking devices found in printers. A mechanical process for making felt was introduced by Williams in 1820 and this provided the basis for industrial development of precision products.14 There have been some excellent reviews of the processes involved in the manufacture of pressed felts.15,16 Commercially, the first stage of felt production is blend selection. Generally, fine wools felt more readily, and appropriate blending of different wool or hair qualities, including waste and noils, allows fabric properties such as abrasion resistance, drape and strength in the final fabric to be engineered as required. Blends of wool and man-made fibres such as viscose rayon are also commonly used to improve fabric performance, as well as to reduce cost. Man-made fibres with a low wet Young’s modulus have been shown to enhance the rate of felting in wool blends, even though such fibres have no intrinsic felting properties.17

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10.10 A selection of pressed felt gaskets. [Source: Anglofelt Ltd, UK]

Following pre-opening and carding of the blend, the web is mechanically lapped to produce a multi-layer web structure or batt. The type of lapping process used determines the predominant fibre orientation in the batt structure (which influences the isotropy of tensile properties) and the weight per unit area of the resulting fabric. Consolidation (or hardening) of the batt is then undertaken using flat or roller hardening machines, and it is at this stage that multiple batts may be brought together to make thicker structures. In both the flat and roller hardening processes the wool is subjected to a combination of pressure and agitation in moist, warm conditions. Repeat treatments or the use of multi-roller machines allows the required degree of consolidation to be achieved on the face and back of the felt. Following hardening, the felt may be subjected to a fulling or bumping stage where, traditionally, heavy wooden hammers are used to pound the felt and increase its density. The thickness of commercially available felts ranges from about 1.5 mm–25 mm, but extra hard felts up to 100 mm are also produced.18 It is possible to produce felts of graduated density in the cross-section, and the surface structure can be modified during the process as required by setting adjustments. The effects of process conditions on the properties of pressed felts have been systematically studied with a view to establishing a means of quantifying felt quality. Fabric tensile strength,

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apparent density and the felted fibre modulus are believed to be the key quality indicators of pressed felts.19 After felting, the fabric is washed and neutralised and may be chemically or mechanically finished. Lightweight felts are often tentered to the required dimensions and subsequently sheared or ground to obtain the correct thickness. Dyeing, mothproofing and resin impregnation are also undertaken, as required by the intended end-use application. Cutting, fabrication and pre-forming of various 3D components is also carried out by the felt manufacturers to produce a wide range of off-the shelf products such as washers, piano hammers and other industrial components for direct supply to the customer.15 Since wool pressed felts are produced by entanglement of fibres to provide a self-supporting fabric, it is reasonable to think of them as a type of mechanically bonded nonwoven fabric. However, strictly speaking felts are not classed as nonwoven materials. The ISO definition of a nonwoven fabric specifically excludes felted or wet milled structures together with paper and fabrics containing binding yarns or filaments, e.g. stitch bonded materials.20

10.2.3 Needlepunched fabrics Around 1870, the commercial production of needlepunching machines was established for driving barbed needles through fibrous webs to introduce the mechanical entanglement needed to form a fabric that is commonly referred to as a ‘needlefelt’. After preparation of the wool blend and the formation of a web on either a Garnett or carding machine, the web is normally cross-lapped before needlepunching. Many other fibres, as well as a wide range of wool types, can be converted into fabric using this approach. Early machines were capable of about 100 punches/min compared to over 3000 punches/min possible on some modern systems. In basic form, a needlepunching machine consists of a perforated bed-plate, which supports the batt during the process, and a perforated stripper plate set immediately above which assists in stripping the reciprocating needles on their return stroke (as the needles withdraw from the batt). The barbed needles are designed to collect and transfer fibres perpendicular (or at preset angles) to the surface of the fabric and then release them when they withdraw from the batt. Different bedplate arrangements, needle designs and needle board layouts are used for making the structured or patterned fabrics needed to produce floorcoverings and upholstery. The properties of needlepunched fabrics are greatly influenced by the punch density, needle penetration depth, needle gauge and needle barb configuration, as well as fibre properties. Originally, needlepunching was used to make comparatively cheap

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fabrics from waste natural fibres such as wool, other animal hairs, cotton and jute. The waste trade still uses needlepunching to make such products with mixed synthetic fibre waste as well as wool. The manufacture of lowcost needled blankets was a major end-use application until the 1970s and such fabrics usually contained a woven scrim or aligned reinforcing filaments in the centre to increase dimensional stability. Wool blankets were characterised by excellent flame retardancy but washing presented technical problems because of high wet shrinkage (for example 5–50%), even after the use of a standard oxidative shrink-resist treatment.21 Such shrinkage led to cockling and poor after-wash appearance. Needlepunched blankets containing wool were the subject of research undertaken by Smith.22 Hung23 investigated the effects of fibre length and blend proportions on the properties of needled blankets containing wool blends and established that a 40% wool/60% man-made fibre composition was the most satisfactory blend, giving pilling performance similar to woven blankets. Needlepunched floorcoverings were first produced from wool in the USA, and later in Europe. Wool products could be printed and were perceived to have good wear characteristics. Development work on wool products of this type was reported in the early 1970s, as well as upholstery.21 In the 1970s, research was completed on the production of needlepunched blazer cloths composed of wool (short 64s quality lambswool and broken tops 60/64s), reinforced with a 45 g/m2 nylon woven scrim.24 Milled needlepunched fabrics were produced with a mean area density of 350 g/m2. Generally, the fabric properties compared well with woven blazer fabric. Intensive raising was suggested as a means of further improving the bending properties of the fabric but this had an adverse effect on abrasion resistance. The best results with respect to abrasion resistance, strength and drape were obtained when raising a damp fabric containing 1% of a softening agent. Alternative methods of improving the surface integrity and dimensional stability of wool needlepunched fabrics include secondary bonding or chemical after-treatments, but these approaches are limited because of the resulting increases in manufacturing costs and fabric stiffness. For domestic textile products, for example floorcoverings and clothing applications, the ability to pattern and colour fabrics is important and, generally, nonwoven materials offer less scope than traditional fabrics. Structuring of needlepunched fabrics to produce relief patterns on the surface is well known and is common in the manufacture of floorcoverings and upholstery, but colouration of such fabrics is limited to the use of colour blends and fabric printing. Dyeing and printing of needlefelts is feasible but the complex structural patterns that can be achieved with yarn dyed wovens is difficult to replicate using existing nonwoven technology. The further penetration of nonwoven fabrics in outerwear will be partly dependent on

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advancements in patterning opportunities, as well as improved tensile and attritional properties in lighter-weight fabrics (<150 g/m2). In addition to domestic and clothing applications, wool needlefelts and other wool filled products are marketed as oil sorbents for cleaning up spillages25,26 and find uses in horticulture, for example in hanging basket liners.27 It is also feasible to introduce plant seeds in such products. When laid on the ground, biodegradable fabrics containing wool are used to aid germination of grass seeds by providing an appropriate microclimate under the fabric, and in mulch mats wool is used to inhibit the growth of weeds around young plants. Additionally, mulch mat products containing wool are believed to be useful as erosion control materials.28 Libraries also use wool needlepunched fabrics to assist in the preservation of books placed in storage archives.

10.2.4 Hydroentangled fabrics In recent years, the production of serviceable, lightweight wool fabrics of 70–150 g/m2 for apparel applications using a process known as hydroentanglement has been commercialised. Hydroentanglement is based on technology introduced in the late 1950s and further developed during the 1960s and 1970s in the USA. The technology is well established in the production of nonwovens from man-made fibres such as polyester, polypropylene and viscose rayon, as well as blends containing cotton, wood pulp and other fibres for applications in the medical and hygiene industries. Wool is a relative latecomer to this process. Following the formation of a fibrous web (or batt) usually (but not exclusively) by carding (and/or cross lapping), the bulk of the web is decreased by prewetting using various means, or mechanical compression, prior to the main process. The web transported by a porous belt or drum is passed below a series of injector heads (typically 6–8 in total depending on requirements), which produce single or multiple rows of closely spaced, fine columnar water jets of about 60–140 microns diameter as required. Commercially, these jets operate at pressures of about 25–250 bar, although much higher pressures up to 1000 bar are now possible depending on machine design. The jet pressures used depends on web weight, line speed and fibre properties, and normally the pressure is profiled so that it tends to increase as the web passes toward the machine exit. Usually, the web is treated face and back to achieve a homogeneously bonded structure, although single-sided treatments are possible using lightweight webs. A key consideration is the total specific energy applied to the web, which is a function of water pressure, flow rate, fabric weight and dwell time. At each injector, suction is applied from below to remove excess water from the surface of the conveyor. The design and surface structure of the conveyor belt influences the resulting

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fabric structure. The production of apertured, mock-lace (spunlace), structured or patterned fabrics is achieved by increasing the open-area of the belt so that there are larger openings in the belt. After bonding, the fabric is removed from the belt and is dried, wound and slit to the required width. Secondary bonding by chemical or thermal means can be undertaken as required before or after drying.A large volume of water is used in hydroentanglement, which has to be recirculated and filtered to remove particulates before it is returned to the injectors. Filtration accounts for a major part of the total cost of a hydroentanglement installation and it needs to be appropriately designed, based on a consideration of the particular chemical and particulate impurities that will be encountered for different fibre types to avoid blockage of jet orifices. Following joint development work in the UK, lightweight hydroentangled fabrics containing Merino wool are now marketed by The Woolmark Company (Europe) under the Sportwool Outdoor Trademark. Such fabrics form part of a breathable, insulating lining fabric for use in outdoor performance garments.29

10.2.5 Thermally and chemically bonded fabrics Commercially, fabrics for thermal and acoustic insulation (see Fig. 10.11) are produced by impregnating or spraying wool batts prepared by carding and cross-lapping, or air-laying with a cross-linking binder (usually acrylic based) which, when heat cured, produces a stable matrix. Coarse, low grade and waste wools are generally, but not exclusively, used and it is possible to introduce pigments, fire retardants, insecticides, fungicides and deodorants as resin-additives to modify the performance of such fabrics. Resin-bonded fabrics of this type have been made in New Zealand for many years.30 Similar structures are also made using thermal bonding techniques in which batts containing a proportion of thermoplastic fibres are blended with wool and are subsequently through-air bonded to produce a stable structure. In Germany, drylaid thermal insulation mats containing 30% binder, 21–35% wool and 35–49% wood fibre have also been developed.31 When mixed with a proportion of thermoplastic fibres (or powders) such as polypropylene, or bicomponents, it is possible to produce a thermally-bonded nonwoven fabric by heating the structure. Commercially, this is normally achieved using through-air methods (e.g. an oven) rather than contact heating methods. Wool blend STRUTO fabrics are also manufactured. STRUTO fabrics are produced from perpendicular-laid webs in which many fibres in the carded web are oriented perpendicular to the plane of the fabric surface. In the STRUTO process, the carded web is formed into corrugations or ‘knuckles’ of a predetermined height, frequency and orientation angle, depending on

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10.11 Wool insulation being installed in the wall of a new building. [Source: Second Nature Ltd, UK ]

machine conditions. Subsequently, the structure is through-air bonded, using hot air, to stabilise the fabric.Therefore, a pre-requisite for the process is that the blend contains a proportion of thermoplastic fibres. Owing to the corrugated structure of STRUTO fabrics, they are generally characterised by comparatively high resistance to compression and are therefore considered suitable as foam replacement products.

10.2.6 Miscellaneous nonwoven fabrics containing wool There is some evidence to suggest that the thermo-regulatory properties of wool are beneficial in promoting sleep. In some countries, wool-filled quilts, underblankets32 and pillows have been introduced and, compared to alter-

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native materials, are claimed to provide improved comfort and resilience as well as more restful sleep.33 For individuals suffering from atopic eczema (a skin disease that causes loss of sleep through itching), bedding composed of wool and kapok and containing no other chemical additives has been evaluated. In this application, Kapok is believed to offer significant advantages because of its hollow cross-section.34 The quilting industry also uses wool waddings to line jackets, oven gloves and sleeping bags.35 Other existing applications for wool nonwovens include vehicle seat padding, where wool is claimed to provide improved physiological comfort as compared to foam,36,37 horse blankets, shoe lining fabrics, absorbent pads for ink cartridges38 and filters39.

References 1 Crawshaw G H, Carpet Manufacture, Christchurch NZ, WRONZ Developments, in press. 2 Crawshaw G H, ‘Textile Floorcoverings’, Textile Progress, The Textile Institute, Manchester, in press. 3 Feng Lui, ‘Novel techniques for manufacturing hand knotted/woven carpet’, PhD Thesis, Lincoln University, New Zealand, 2000. 4 Herzog W, ‘Textile floorcoverings: The Usefulness Index and its testing. Part 1: Walking comfort; Part 2: The action of walking’, Text. Inst. and Industry, 1971, 9, 126–8; 153–7. 5 Ingham P E, ‘The role of wool carpets in controlling indoor air pollution’, Proc. Tifcon’94, The Textile Institute, Manchester, 1994. 6 Hearle J W S and Carnaby G A, ‘Carpet shading explained’, Proc. Tifcon’92, The Textile Institute, Manchester, 1992. 7 Benisek L, ‘Service soiling of wool, man-made fibre and blended carpets’, Text. Res. J., 1972, 42, 490–6. 8 Mizell L R, ‘The Manufacture of Wool Felts’, Interior Textiles Technical Information Letter, Internat. Wool Secretariat, No 15, March 1984. 9 Batra S K, Hersh S P, Barker R L, Buchanan D R, Gupta B S, George T W and Mohamed M H, ‘A New System for Classifying Textiles’, Nonwovens An Advanced Tutorial, TAPPI Press, ISBN 0-89852-457-1, pp. 1–2 (1989). 10 Ryder M L, Sheep and Man, Gerald Duckworth, ISBN 0-7156-1655-2, p. 114 (1983). 11 http://asia-art.net/chinese_carpet.html. 12 Albany International Corporation, Paper Machine Felts and Fabrics, Vail-Ballou Press Inc., New York, pp. 3–5 (1976). 13 USP 5,705,076:1998. 14 Lauterbach H G, ‘Felt from Man-Made Fibers’, Text. Res. J., vol. 25, no. 2, pp. 143–149, (1955). 15 Anon., ‘The Manufacture of Pressed Felts’, Wool Sci. Rev., no. 26, pp. 15–24, (1964). 16 Sharif A K, ‘The Effects of Mechanical Finishing Upon Wool Pressed Felt Fabric Properties’, MSc Dissertation, Department of Textile Industries, University of Leeds, 1984.

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17 Blankenburg G, ‘The Feltability of Wool-Man-Made-Fibre Blends and the Interpretation of the Felting Mechanism’, J. Text. Inst., vol. 56, pp. T145–155, (1965). 18 http://www.britishfelt.co.uk 19 Baines A, Barr T and Smith R L, ‘Physical Properties of Felt: Measurement of Felt Quality’, J. Text. Inst., vol. 51, pp. 1247–1256, (1960). 20 ISO 9092:1998. 21 Winterburn S M, (Lennox-Kerr P L – Editor) ‘The Use of Wool in Needled Fabrics’, Needle-felted Fabrics, The Textile Trade Press, Manchester, pp. 101–118, (1972). 22 Smith P A, (Lennox-Kerr P L – Editor) ‘The Production of Needled Blankets and Carpets’, Needle-felted Fabrics, The Textile Trade Press, Manchester, pp. 65–99, (1972). 23 Hung J, ‘The Use of Wool Blends in Blankets made by the Needle-loom Process’, MPhil Thesis, Department of Textile Industries, University of Leeds, UK (1977). 24 Larsen S A and Smith P A, ‘The Production and Finishing of Needle-Felted NonWoven Blazer Cloths’, WIRA Report no. 261, March (1976). 25 http://www.firstpage.com.au/woolsorb/ 26 http://www.usasorb.com 27 http://www.appleseedwool.com 28 http://www.wronz.org.nz/wronz-linclabnz/news-nov2.htm 29 Anon, Nonwovens Report International, Feb, p. 16 (2001). 30 http://www.woolbloc.co.nz 31 Anon., ‘Insulation Mats made from Wool and Wood Fibres’, Tech. Text. Internat., October, p. 9 (1998). 32 http://www.exton.com/awg/advant.html 33 http://www.chsdirect.com 34 Wollina U, Willmer A and Karamfilov Th, ‘Practical Applications of Kawoll’, Melliand Textilberichte (Melliand English) 3, p. E60 (1999). 35 http://www.westernwadding.com 36 Faust E et al. ‘Vehicle Seat Padding’, USP 6,189,966, 20 February (2001). 37 Umbach K H, ‘Parameters for the Physiological Comfort on Car Seats’, 38th International Man-Made Fibres Congress, Dornbirn, Austria, September (1999). 38 Price L C, ‘Ink Cartridge’, USP 4,484,827, 27 November (1984). 39 Evans DJ, Lipson M, Mayfield RJ, ‘Wool Cigarette Filters, PART 1: A Study of the Parameters that Affect Filter Performance’, J. Text Inst., vol. 66, pp. 325–331, (1975).

11 Finishing S A MYERS © T H E

11.1

W O O L M A R K C O M PA N Y

Finishing of woven fabrics

Finishing machinery and practices vary from one company to another, depending upon the type of fabrics being produced. Finishing starts once the fabrics have been inspected, after being received from the weaving department. The fabrics, described as ‘grey’ at this stage, are generally dirty and can contain lubricants and waxes from spinning and weaving. They may also be stiff and feel thin and flat. On receiving the fabrics, the finisher has to design a finishing procedure, based around several individual operations, that will produce a finished fabric that: • • • • • •

is clean from contaminants has a soft handle and desired aesthetics is the correct working width has the correct dimensional stability for successful manufacture has additional performance features if required, and is at the required cost

garment

The finishing manager, therefore, must have an intimate working knowledge of all machinery-operating parameters and of which are most suited for a particular fabric quality. A finishing procedure can contain many steps to achieve the desired finish. Many of the individual finishing processes are unique to wool, and finishing can contribute in a major way towards product variety in wool fabrics.

11.1.1 Fabric setting (crabbing) Setting or crabbing is mainly applicable to worsted fabrics and is required to relax and set the strains introduced into the yarns and fabric during spin314

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ning and weaving. If some weave structures are not set in this way, they may be susceptible to the formation of distortions (e.g. ‘crowsfooting’) during subsequent wet finishing. The crabbing operation is carried out in the presence of heat and moisture, during which the intermolecular bonds in wool are broken and then reformed in a more relaxed configuration. Setting is arrested by shock cooling. The chemistry of setting when assisted by reducing agents is described in Section 5.12 of Chapter 5, and the physics of stress relaxation is discussed in Section 4.4.3 of Chapter 4. Two basic types of set, cohesive and permanent, may be induced by finishing procedures, depending on the severity of operating conditions used. Many processes will incur some of both. Moisture (and fabric moisture content) is a pre-requisite of setting and the degree of setting is also dependent upon temperature and time. Fabric pH is also important, for example in pressure decatising, a higher level of set can be expected at pH values neutral to slightly alkaline than strongly acid. Cohesive set is believed to be due to rearrangement of hydrogen bonds within the wool structure and occurs when wool is distorted at temperatures above its glass transition temperature (Tg) and cooled whilst distorted. This set is largely temporary. For example, the dimensions of a fabric stretched during tenter drying are mainly held by cohesive set. Permanent setting occurs when conditions are sufficient to disturb and reform, primarily, both disulphide and hydrogen bonds. Permanent set occurs mainly in finishing operations such as crabbing and pressure decatising and is generally defined as the set remaining in a fabric which is stable to release by hot water (70 °C) – conditions that would release cohesive set. 11.1.1.1 Batch crabbing In a traditional batch crabbing machine, the fabric is wound onto a cylinder (covered with a cotton wrapper) which is rotated, whilst half immersed in hot or boiling water, for a predetermined time. To ensure even treatment, the fabric is reversed and the treatment repeated. The fabric may then be steamed and finally passed through a tank of cold water to arrest the setting process. Batch machines allow for long treatment times and, at appropriate temperatures and pH, high levels of set can be achieved. Despite reversing the fabric direction, traditional batch crabbing machines remain associated with uneven treatment which, for piece dye qualities, can result in end-to-end or piece-to-piece variation. Improvements on traditional machines include the use of large crabbing cylinders and bigger treatment lots, minimising variation. Absolute control of loading tensions, centring devices and anti-slipping compacting rollers, ensure uniform package build up.

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11.1.1.2 Continuous crabbing Continuous crabbing machines are now widely established in the industry and offer faster production and even fabric treatment. However, the treatment time is generally quite short and the levels of set can be lower than those attainable with batch systems. Two basic types of continuous crabbing machine are available. Cylinder types. The fabric is initially wetted through a trough of hot water and then passed around a large, rotating, heated cylinder. The fabric is pressed at high pressure against the heated cylinder by a specially engineered impermeable belt. Special seals resist escape of steam and entry of air at the edges of the belt. Fabric operating temperatures as high as 135–140 °C are claimed and superheated steam is created in situ, setting the fabric. Setting is arrested by shock cooling. Chemical setting agents are sometimes added to the wetting tank to promote higher levels of set. Superheated water machines. These differ in design from the cylinder types in having no pressure belt to maintain fabric/cylinder contact and use superheated water to facilitate setting. A possible advantage for fabric quality is that yarns are claimed to fully swell with minimal fabric compacting. The fabric enters and exits through barometric columns. Water temperatures are around 110 °C, although a series of steam battery heaters situated around the main cylinder are claimed to elevate the fabric temperature during its contact time with the cylinder, promoting fabric set. Choice of machinery depends on the level of set required, which in turn depends on the fabric type and subsequent processing. For example, a colour woven plain weave fabric for rope scouring will generally require lower levels of set than a plain weave fabric for piece dyeing.

11.1.2 Scouring Scouring to remove spinning lubricants and soil is mainly carried out in aqueous media with the addition of a suitable detergent. If fabrics are heavily stained, for example with mineral oil, solvent scouring (or padding with solvent-based detergents and storing) prior to aque-ous scouring can be used to ensure a clean fabric, particularly for piece dye qualities. Alternatively, spot solvent guns are used for localised staining. Concurrently with cleaning the fabric, handle and cover can also be developed during the scouring process, which influences the quality and appearance of the finished fabric.

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11.1.2.1 Detergents Anionic and non-ionic detergents are used for scouring wool and wool/blend fabrics. Synthetic detergents have largely replaced traditional soaps, mainly because they have better all-round stability to variations in water supply (particularly hard water supplies), are cheaper, easier to remove from fabrics during rinsing and are usually fluids and easier to handle. Anionic detergents work by electrostatic repulsion. Scouring pH is important and should be pH 8.5–9.0, with the addition of ammonia or sodium carbonate to the scouring bath. With non-ionic detergents, scouring pH is not as critical. However, alkaline scour baths are recommended as alkaline conditions aid fibre swelling, allowing release of soil, and enhance the stability of the scouring emulsion. Non-ionic detergents have a strong de-greasing effect and can give firmer handling fabrics than those scoured with anionic detergents. They are also effective for scouring-off surface dye residues and are useful for colour woven fabrics which may be prone to bleeding, since scouring may be carried out at slightly acid pH values. With both detergent types, concentrations of 1% (owf) are normally used and the cycle may be single or double bath, depending upon the degree of soiling. Scouring conditions are typically 40–45 °C for 30–60 minutes for batch operations, depending on fabric length and processing speed, followed by thorough rinsing. Slightly higher temperatures are used for continuous scouring operations to compensate for the reduced processing times.

11.1.2.2 Batch scouring machines During batch scouring, the fabric in rope form is sewn into an endless loop. Nip rollers facilitate fabric transport. As the fabric passes through the nip rollers, scouring liquor is interchanged, promoting scouring action and developing cover and handle. Traditional rope scouring machines ran at relatively slow speeds (80–100 m/min) with a risk of fabrics running continually in the same folds, causing processing marks and creases that could be difficult to remove in subsequent processing. Modern rope scouring machines can scour at speeds of 200 m/min or more. At increased speeds, scouring times are reduced and fabrics are more effectively opened before the nip, reducing the tendency for processing marks. Many machines include pneumatic opening jets, to further encourage fabric opening during processing. Baffle plates or similar may be located

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at the back of the machine to allow for rapid scouring/semi-milling procedures. Independent channel control with automatic seam monitoring and knock off for fabrics of differing lengths ensure consistency of finish. Alternatively, different fabric qualities and weights can be processed in the same lot. Milling is described in Section 11.1.3. Combined scour/milling machinery allows for scouring and milling in the same machine, combining two traditionally separate operations. This type of machine has facility for scouring, i.e. a scouring bowl to retain liquor, a sud box to collect expressed liquor from the nip rollers, and a milling spout or trough to facilitate milling. Increasing nip pressure enables the fabric moisture content to be lowered for milling operations. Alternative designs for transporting the fabric, particularly for lighter weight fabrics that would be susceptible to creasing with nip transport systems, include transport between lightly-pressured conveyor aprons or ‘lungs’, or transport around large slatted drums. Such profiled drums are designed to provide processing without slippage. Some designs include a lightly pressurised air lung or brush, to ensure drum/fabric contact. Increased processing speeds and baffle plates allow for semi-milled finishes to be achieved. After rope processing, fabrics are opened and plaited, a process known as ‘scutching’. 11.1.2.3 Open-width scouring machines Open-width scouring machines may be batch machines (for small lots), but are more usually continuous machines. Both are used mainly for processing lightweight fabrics in open width, where rope scouring would cause unacceptable creasing or fabric damage. Continuous scouring machines scour fabric evenly and effectively, with high productivity, and produce a clean, clear finish. Open-width machinery with slight felting action is available, for example by the use of ‘V’ shaped baffle plates against which the fabric is processed during scouring. Different modes of scouring action are available. The most conventional design for wool fabrics involves tangential jets of scouring and rinsing liqours, followed by squeeze rollers or suction slots. Complete immersion systems are also available, having liquor interchanged by sucking large volumes of scouring solution through the fabric. Suction drum type designs are also available, with varying flow direction. Machines are generally modular in construction, allowing lines to be assembled, depending upon the fabric qualities processed. Driven guide rollers, relaxation zones or overfeeding onto drums ensure minimum processing tensions, important for lightweight fabrics and fabrics containing elastane filaments.

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Continuous open width scouring machines are often used in-line with crabbing tanks to effect cleaning and setting of fabrics.

11.1.3 Milling The purpose of milling is to provide: • • • • •

interfibre felting and fabric consolidation, e.g. as preparation for raising increased fibre cover and an increase in fabric strength, particularly with woollen fabrics subduing or totally obscuring of the weave structure increase in fabric weight and density, and improved handle (providing milling levels are not too high)

During milling, much lower levels of liquor are used than for scouring; detergent levels are generally higher, typically 5–6% on the weight of fibre (owf); and greater mechanical action is applied. The differential friction effect derived from the surface scale structure of wool, as described in Sections 4.4.5 and 7.5.3, is the primary reason why wool fabrics consolidate and ultimately become felted by a ratchet mechanism. Traditional milling machines are equipped with nip rollers to transport the fabric into a tapering milling box (spout) having a weighted lid. In the milling box (with the milling lid lowered) the passage of the fabric is restricted, encouraging fabric shrinkage in the length direction. To aid milling, fabrics are milled at low liquor content (typically 100–120% owf) as excess liquor can reduce mechanical action and also cause slippage. Heat promotes milling (felting) and temperatures of 40–45 °C are normally used. pH is also important as wool mills (felts) least in neutral to slightly acid conditions (near its isoelecric point) so that milling is generally carried out with alkali to pH 9.5–10. Acid milling at pH 2–3 for very dense felts is also carried out. To control fabric dimensions during milling, nip roller and milling box pressures are adjusted. For example, if greater width shrinkage is required, the milling lid is lifted and the mouthpiece narrowed so that pressure is applied only by the nip rollers. Fabrics are regularly opened out or may be bagged (sewn selvedge-to-selvedge) to reduce milling lines or rigs. When milling is complete, fabrics require thorough rinsing. New developments in milling machinery include the use of pneumatic fabric transport (jet type), eliminating the need for nip rollers. The fabric is transported to a traditional style milling box with milling speeds up to 200 m/min. Elimination of nip rollers removes the problems of processing marks.

11.1.4 Carbonising Carbonising is mainly applicable to woollen fabrics that are contaminated with vegetable matter. Its purpose is to break down (hydrolyse) cellulosic

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impurities to brittle residues that can be removed mechanically, while retaining the properties of the wool as far as possible. Carbonising is carried out by treating the fabric with acid (usually sulphuric acid) followed by drying, baking, beating (dry milling), and neutralising. Fabrics for carbonising are usually scoured but carbonising may be carried out on loom-state or dyed fabrics. Typically, fabric is impregnated with sulphuric acid containing an acidresistant wetting agent. Drying is carried out quickly, and baking follows at 130–140 °C. ‘Dry milling’ consists in crushing and beating the fabric to remove vegetable residues. Solvent carbonising procedures are available, where the fabric is initially solvent scoured in open width, prior to entering the carbonising bath. Advantages claimed are prevention of contamination of the acid bath by oils etc., low absorption and reduced usage of acid, and less fibre damage due to the ‘protective’ action of the solvent. By increasing solvent scour temperatures and duration times, removal of polypropylene contaminants is also claimed.

11.1.5 Drying Prior to tenter (stenter) drying, excess water is removed using hydroextractors, mangle or vacuum type systems. Tenters work by hot air convection currents blowing through and/or across the fabric, whilst it is held at the edges by pins or clips. The process is continuous, with width settings and overfeed adjustments made to control fabric dimensions. Two basic types of tenter frames are available, single-layer and multi-layer. Single-layer tenters are common in the worsted industry whereas multilayer tenters are more common for woollen or heavier fabrics. Multi-layer tenters allow longer drying duration and also gentler air circulation, preferred for pile and raised surfaces. Drying temperatures depend upon processing speed but generally 120–140 °C is used for wool fabrics: 140 °C should be regarded as the uppermost limit. It is important that wool fabrics are not overdried because this affects fabric quality. Residual moisture contents of 7–8% after drying should be attainable. Wool fabrics should always be dried close to relaxed dimensions as excessive stretching can affect finish quality and cause problems of relaxation shrinkage if the stretched dimensions are not stabilised in decatise finishing. Modern single-layer tenters are equipped with video display of operating parameters such as width settings, overfeed, temperature and speed. Further developments include optimised airflow systems to ensure energyefficient and uniform drying, guide plates to direct heat away from fabrics if the machine is stopped, and valves to divert airflow to upper or lower

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fabric surfaces as required. Monitoring of residual fabric moisture content allows control of drying parameters. Other developments include automatic or minimum maintenance chains, ease of removal and cleaning (or selfcleaning) of lint screens, and pyrometers to control heat setting operations. Modern tenters are environmentally-friendly, with heat-recovery units and systems to purify exhaust air gases.

11.1.6 Raising Raising is mainly used for woollen fabrics, the aim being to produce a ‘pile’ surface, enabling a wide range of fabric styles to be produced. Depending upon the raising parameters used, the pile can be upright or laid, markedly changing the surface of the fabric. The general procedure is to subject the fabric, which may be dry or wet, to the action of raising wire, although traditional teasel (or metallic teasel) raising is still used for specialised fabrics. Raising is often carried out on fabrics that have been prepared by milling. Emphasis has been placed by manufacturers on optimising the main factors affecting raising, e.g. drum rotation speeds, speeds of pile and counterpile rollers, fabric speed and most importantly, absolute control of tension along and across the fabric at input, exit and throughout the raising operation. Synchronisation of all these parameters produces uniform and controlled raising, minimising fabric extension and strength loss. All parameters are stored on computer. Automatic systems advise lubrication and maintenance requirements. Raising machines are often double drum, with one drum situated above the other. This provides high productivity with minimum floor space usage. Shearing machines are often incorporated into raising lines for intermediate shearing to ensure an even pile, or for final shearing. Machinery designs are available to offer increased flexibility in the raising operation. Using a three 1-star arrangement of raising rollers around the raising drum, 24 out of 36 rollers can be brought into working position. By changing roller configuration, different raising effects can be produced.

11.1.7 Shearing (and singeing) After wet finishing and drying, surface fibre is present on wool fabrics. Whilst some surface is beneficial for the handle, excessive fibre left on the finished fabric can rub up in wear, causing the formation of pills. Excess surface fibre is normally removed by shearing (cropping). During shearing the fabric is initially brushed (or steam brushed) to raise loose surface fibre before passing to the shearing cylinder. The shearing

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cylinder is wound with helical blades and rotates at high speed. Prior to reaching the shearing cylinder, the fabric passes over an angled bed, where fibres are made to stand erect. These are caught by the rapidly rotating blades and cut against a stationery (ledger) blade. The machine operates with strong suction to remove cut fibres (and cool the shearing elements), and is equipped with metal detectors and anti-stat bars. Modern shearing machines are normally 3-head, allowing one cut on the back initially and two on the face in a single passage. Computer control and video display allows for data storage and exact repeat of operating parameters for different lots. Piano beds (for bulky selvedges) with edge detectors and guiders and automatic seam detectors are normally standard. Careful control of tension during processing is paramount for even shearing. Parameters in shearing include cylinder speed (typically 1000 rpm), number of helical blades, fabric speed, etc. Normally around 40–45 cuts per cm is the maximum requirement, e.g. for warp-faced worsted structures. In some areas of the industry, singeing is also used to remove surface fibre and reduce the propensity for pilling. During singeing, protruding fibres are removed by an intensive flame. Alternative designs use reflected or radiated heat. Singeing parameters require very careful control to minimise possible damage and faults, e.g. singeing bar marks. After singeing, fabrics are rapid cooled. They require post-scouring to remove singeing residues and smell.

11.1.8 Relaxation and pressing Prior to pressing, woven fabrics are usually passed over a steam table to relax processing tensions such as length tensions from shearing. The fabric is overfed onto a vibrating belt and passed through steaming zones. Developments in this area include the use of hoods to enclose the steaming zones. Heated elements prevent condensation. The hoods provide more intensive, controlled and uniform steaming (little dilution with air), maximising steam usage and reducing energy costs. An alternative machinery design is based on the traditional London Shrinkage process. The fabrics pass in a festooned manner through steaming chambers. The manufacturers of such equipment claim relaxation free from any restraint. Festoon folds increase dwell times, to achieve maximum shrinkage. Pressing operations are carried out to modify handle and as preparation for pressure decatising. Rotary presses were widely used, but these machines can stretch lightweight fabrics by 5–6%. Other traditional systems include paper pressing (batchwise pressing against firm, lustrous papers),

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which is still used due to the superior handle and improved stability of effect when compared to continuous systems, but is slow. Modern continuous pressing machines pass the fabric around a small diameter heated cylinder, applying high pressure by an impermeable belt. The belt is driven and cylinder and guide roller speeds are synchronised to permit pressing under minimum tension. Fabric may be conditioned, e.g. by spray systems, prior to pressing.

11.1.9 Decatising Decatising is a term applied to a family of fabric setting processes that can provide a range of levels of set and modifications to handle and finish. Decatising is a key tool in the development of the final finish of worsted fabrics in particular. Machinery, process conditions and combinations of different setting, pressing and relaxation processes are selected to give the result that is appropriate to a particular fabric. 11.1.9.1 Batchwise pressure decatising Pressure decatising is a setting process that provides conditions for achieving high levels of set. The principal objectives are: • • •

to stabilise lustre to set the finished aesthetics of the fabric to stabilize dimensional stability

The process involves winding the fabric with controlled tension onto a perforated beam (previously covered with a wrapper) interleaved with a decatising wrapper. When the batch is complete, it is loaded into a steaming chamber, sealed and steamed under pressure. Typical conditions for wool fabrics are 0.8–1.0 bar (120–125 °C) for 2 minutes, followed by cooling to arrest the setting process. High levels of permanent set can be imparted, producing a ‘permanent’ finish. This is important for stability of finish (to steaming during making up), for control of fabric dimensional properties, and for handle and lustre. It is important that wool fabrics are at the correct pH and moisture content prior to all pressing and decatising procedures, particularly pressure decatising. Fabric pH is ideally around pH 6: more strongly acid reduces set, and more strongly alkaline may cause yellowing. Moisture content for all-wool fabrics is ideally 12–15%, since low moisture levels can result in low levels of set. Modern pressure decatising machines offer a variety of steam cycles and choice of steam directions (in to out, out to in) to produce variations in handle, lustre and finish. Computers are used to store and retrieve data,

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including fault monitoring. Various wrapper types are available, e.g. satin (firm) for worsted fabrics, molleton (soft) for bulkier woollen fabrics or more matt finishes. Large diameter decatising cylinders (with tubes to reduce air volume) reduce the problem of end marking, allow more rapid steam penetration of the package and permit more even treatment. Absolute control of fabric and processing wrapper tensions and axial movement during winding ensures even package build-up, to minimise problems of wrapper collapse, moiré and problems with bulky selvedges. Minimum tension loading and tension control at stops is particularly important for lightweight and elastane-containing fabrics. Other developments include input steam regulating valves to control small fluctuations in steam supply, and anticondense cradle designs. Modern machines have three stations: one batch loading, one cooling/ unloading and one steaming. Production rates up to 1500–2000 m/hour are claimed. Pressure decatising is often the final process of a finishing procedure. However, for fabrics requiring further handle or finish modification or to ensure even processing, a continuous post-decatising operation is often used. For elastane-containing fabrics it is often necessary to finally steam relax and re-dress on a continuous decatising machine, to ensure full relaxation. 11.1.9.2 Continuous decatising Most modern decatising machines offer continuous processing. They generally provide lower levels of set than batchwise pressure decatising. Three basic types of machine are available: Pressing/decatising machines. Fabrics are passed around a large heated cylinder and are pressed against it by an impermeable belt. Fabrics are prewetted, normally using spray-type systems. The larger cylinder design gives longer treatment periods than the pressing machines described in Section 11.1.8. By controlling operating parameters such as moisture content, speed, and pressures, handle and lustre variations can be achieved on finished fabrics. Alternatively, the machines are used as preparation for pressure decatising. Specially designed machines allow for additional ‘wet’ setting after pressure decatising, for improved tailorability. Continuous steam setting. This machinery is similar in design to that previously described, but rather than pre-wetting the fabric to create steam in situ, the fabric is continuously steamed as it passes around the cylinder. This type of machinery is claimed to be suitable for fabric preparation for pressure decatising or afterwards, for handle variation (by varying steam pressures and wrapper tensions) and consistency of finish.

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Continuous pressurised machines. Machines are available to continuously decatise fabric, using saturated steam under pressure. The decatising cylinder is covered with a permeable blanket. The fabric passes around the cylinder and is sandwiched by a continuous permeable belt. Fabric transport is at minimum tension. Steaming conditions are variable, with decatising up to 3 bar steam pressure (up to 135 °C) claimed. Effective seals at input and output prevent steam loss and entry of air. High levels of set and uniform treatment are claimed. 11.1.9.3 Batchwise decatising at atmospheric pressure Batch machines for decatising at atmospheric pressure remain available in the industry. The fabric is rolled in a wrapper fabric onto a perforated drum and steam is passed through, in to out or out to in. Air is suctioned through the roll to cool it before doffing the fabric. Developments in this area include the use of ‘improved’ chemical setting products. After impregnation, the fabric is interleaved with a special wrapper and wound onto the perforated cylinder, followed by steaming and cooling. Enhanced setting compared to non-chemical batch decatising is claimed.

11.1.10 Conditioning It is important for wool and wool blend fabrics to be correctly conditioned. Mention has already been made of the need to avoid over-drying fabrics on the tenter. Over-dry fabrics recover moisture slowly, particularly in hot countries. Generally, 12–15% moisture regain (residual moisture on dry wool) is the basic requirement for an all-wool fabric, prior to operations such as pressing and decatising. Various types of conditioning machines are available. Steam shrinkage machinery (as discussed in Section 11.1.8) provides the possibility of shock cooling, usually after steaming (but sometimes before) to provide a dewing effect. Spray systems are widely established, usually located in bars prior to pressing or decatising operations. New developments in conditioning machinery include passing fabric through a mist of micro droplets of moisture. A spinning brush in contact with a rotating cylinder partially immersed in water creates the droplets. A heating battery causes partial evaporation, aiding moisture penetration into the fabric. Another system passes the fabric around a large diameter drum in a saturated atmosphere, using airflow through the fabric to distribute the moisture. With this type of machine, deeper penetration conditioning is claimed. Both of these systems offer controlled conditioning to required regain levels.

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Radio frequency (RF) drying systems are also finding application. RF drying at temperatures of 40–60 °C is claimed to control moisture evenly across and throughout the fabric.

11.1.11 Summary of machine developments Many improvements in machinery designs have been highlighted in this section on the finishing of woven fabrics. Improved reliability of processing has been an important target. All modern textile finishing equipment has a high degree of automation and microprocessor control of operating parameters. This is important to help reduce operator error, for data storage and for reproducibility of fabric finish, batch-to-batch. Versatility of equipment is important for wool, due to the short-run nature of the business and the variety of wool fabrics produced. Batch processing operations are important in this respect; batch scouring/milling and pressure decatising in particular allow a wide variety of finishes to be produced. Environmental and cost/energy savings are also important considerations. Open-width scouring machines are designed to use minimum water and chemicals and to reduce effluent. Rinsing liquors are often recycled. Heat-recovery units are normally fitted to tenters as standard, diverting recovered heat to operations such as scouring. Scrubbing or alternative systems are available to reduce emissions. Attention has been drawn to progress in minimising processing tensions, beneficial for lightweight fabrics and elastane-containing fabrics. Machinery is often modular in construction, allowing companies to build lines as appropriate, a typical example being open-width scouring lines. Individual processes are often linked, e.g. open-width scouring and crabbing; raising and shearing; steam relaxation and decatising; streamlining finishing procedures. The variety of finishing machines available is such that they cannot be adequately illustrated in this short review. Illustrations of many machines are, however, available in Reference 1.

11.1.12 Machine-washable woven fabrics Wool products shrink on washing due to the presence of overlapping scales on the fibre surface (see Sections 4.4.5 and 7.5.3). When subjected to mechanical action, scales on adjacent fibres that are opposed, create a ratchet action and cause the fibres to move. This phenomenon, known as felting, continues until the fibre assembly is completely entangled.

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The chemistry of shrinkproofing processes is given in detail in Section 7.5. Many developments have been aimed at producing machine-washable wool products, and attention has largely been focused on wool knitwear. The main process that has been used is the chlorine/Hercosett process that is applied to wool tops. Chlorine/Hercosett-treated yarns can also be used in the manufacture of woven products. A further additive may sometimes be required to improve the washed appearance and ease of ironing. However, many manufacturers prefer treatments that can be applied entirely during fabric finishing. Economic considerations often favour this route: for example, it is not necessary to hold stocks of the more expensive treated yarns as well as standard untreated versions, and a fabric can be treated in response to an order for a machine-washable quality. The most common treatment is the application of a bisulphite adduct of a polyurethane resin to the fabric in open width, using a pad mangle. The fabric is then dried at a sufficiently high temperature to cure the resin. The anti-felt mechanism in this case is different to that for the knitwear route in that the resin forms points of adhesion (‘spot welds’) between the fibres and yarns, inhibiting relative movement during washing. When using this system, a slight excess of resin over that required to achieve shrink resistance is usually applied to ensure complete effectiveness and to develop a firm handle. The handle can be further modified by wet processing. Other processes that have been developed include one based on pretreatment with permonosulphuric acid followed by application of an alternative resin. This gives a softer handling fabric that is preferred for certain products. Whilst the above techniques are capable of meeting the requirement for machine washability, other easy care aspects may have to be considered, notably the requirement for minimum ironing and, in the case of trousers, a permanent crease. It is possible to impart a permanent crease by application of a chemical reducing agent to the pleat line and pressing the garment. However, alternative resin-based treatments are becoming more common for imparting both minimum iron and crease-retention properties. Based on such developments, pure wool products such as easy-care skirts, trousers, jackets and even suits are becoming available in the marketplace.

11.1.13 Examples of basic finishing procedures Product variety in woollen and worsted fabrics may be enhanced greatly by combining finishing processes in different sequences as well as by changing the parameters of the individual processes. The possible variations are enormous: a few examples of processing routines follow:

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i) All wool worsted, plain weave, colour woven, clear finish: (Crab) – open width scour – (crab) – dewater – (scutch) – dry – shear – relax/press – pressure decatise ii) All wool worsted, 2/2 twill, colour woven flannel: Crab – rope scour – mill – rescour – (crab) – dewater – scutch – dry – shear – relax/press – pressure decatise – continuous decatise iii) Blend of 55% polyester (low pill)/45% wool, colour woven: (Crab) – open width scour – (crab) – dry – heat set (170 °C, 30 sec.) – rope scour/soften – dewater – scutch – dry – shear – relax/press – pressure decatise – continuous decatise. iv) Melton, stock dyed woollen spun: Mill in grease – scour – carbonise in open width, 5° Beaumé sulphuric acid – dry and bake – dry mill – neutralise and rinse – tenter – shear – press/relax – pressure decatise – finish relax. v) Velour, woollen spun piece dyed: Mill in grease – scour – dye – (dry) – carbonise in open width, 5° Beaumé sulphuric acid – dry and bake – dry mill – neutralise and rinse – raise wet on double-action machine – tenter – shear – raise dry on teasel machine – shear – relax – decatise finish.

11.2

Finishing of knitted fabrics

Many colour knitted fabrics simply require steam-relaxation as a final finishing process, followed by decatising if a further press finish is required. However, wet finishing is used to ensure full relaxation and where improved handle and cleanliness are required.

11.2.1 Wet finishing Wet processing procedures normally involve processing the tubular fabric in rope form in a winch, rope scour or softflow/overflow dyeing machine. Knitted structures can easily stretch and distort during wet finishing and it is important to minimise wet processing tensions, for example, by avoiding long lifts and drag. Relaxation zones with the fabric plaited allow for recovery of extension. If fabrics are stretched excessively and then set, e.g. by dyeing, it may be difficult to rectify dimensions. Fabrics that are prone to distortion or cockling during wet finishing may require crabbing or an initial anti-cockle treatment. This involves treating the fabric in hot or boiling water, depending whether colour knitted or ecru for piece dyeing. For example, colour knitted fabrics are treated for 5–6 minutes at 70–80 °C; ecru fabrics 5–6 minutes at the boil. Reductive anticockle setting procedures are also used if a high level of setting is required.

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To prevent creasing it is important that fabrics are slowly cooled after the setting process. Winch scouring is traditionally used for a clear finish. Softflow/overflow machines that are suitable for dyeing wool fabrics are also used for scouring knitted fabrics because of the gentle action and low tensions applied. For more development of bulk and finish, rope scouring is used. Nip pressure should be just sufficient to grip the fabric and avoid slippage, and low enough not to crease or damage the fabric. Rubber rollers are often used to provide adequate grip and control at low pressures. Scouring is carried out at 40–45 °C for 30–45 minutes, using 1% (owf) synthetic detergent (and pH 8.5–9.0, depending on colour fastness), followed by rinsing for a similar period, gradually cooling to cold to avoid creasing. To protect the surface, it is good practice to process the fabric face in. After wet processing, excess moisture can be removed by hydroextractor if the fabric is not susceptible to creasing, or by mangle. After extraction, the fabric is plaited and straightened in tubular form, with the slitting mark aligned in the middle.A slitting machine then slits and plaits the fabric for drying in open width. Machines that will automatically untwist, dewater and plait with minimal tension are available.

11.2.2 Drying Slit fabric is usually dried on a tenter frame. Wool fabrics should be dried as near to relaxed dimensions as possible, as excessive stretching may lead to problems of relaxation shrinkage. It is important that tenters have effective overfeed, to facilitate removal of any length processing tensions applied during wet finishing. It may be necessary to extend width dimensions to allow for adequate overfeed. Extending the width by up to 10% is acceptable, providing some form of post relaxation process is available to remove excess width. Tenters designed specifically for knitted fabrics often have supporting beds and may incorporate clips or tapes to hold the fabric on the pins. Scroll rollers are necessary to open curling edges. Drying machines for tubular knits include continuous drying types, where the fabric (after dewatering and plaiting) is overfed onto a moving brattice. The fabric is lightly held by a top brattice that is adjustable in height, and is dried and relaxed by a flow of hot air. Some such machines also handle slit fabrics in open width.

11.2.3 Relaxation shrinkage To remove any relaxation shrinkage remaining after drying, a steam relaxation table is most effective. The fabric is overfed onto a moving belt and

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steamed at minimum tension. Vibration promotes relaxation, and some machines incorporate ironing zones to impart a press finish. In the absence of this type of equipment, relaxation shrinkage can be reduced at the tenter by using a steam box at the tenter entry, or by repeated wetting and drying with overfeed. Rewetting fabrics on a pad mangle with minimum length tension and storing for a short while to allow relaxation is sometimes practised prior to tenter drying. Storage times should be minimal to avoid creasing.

11.2.4 Final finish Fabrics requiring a further pressed effect are normally decatised, using either batch or continuous machinery. It is important to ensure minimum processing tensions.

11.2.5 Summary for knitted fabrics The key to successful finishing of knitted fabrics is to minimise operating tensions, particularly during wet finishing. Careful handling between operations is also important. Relaxation shrinkage can then be minimised during final finishing.

11.3

Finishing of knitwear

Pure wool knitwear may be made from worsted-spun or woollen-spun yarns. The two basic types are generally associated with different finishing procedures.

11.3.1 Worsted spun knitwear Worsted-spun articles generally require a smooth, clear finish with good stitch clarity and definition. When fabrics are knitted from dry spun yarns or yarns with low oil content, it is usually sufficient to simply steam-relax the garments (usually on frames). Steaming releases yarn or knitting tensions and reduces the potential for relaxation shrinkage. However, if further relaxation is required or if the knitwear requires scouring, wet finishing is used. Wet finishing should be carried out as gently as possible to maintain a clear finish. To minimise facing up, the knitwear is usually turned inside out. The goods are processed partly made up, e.g. as body and sleeve, with no neck trims. Trims are finished in mesh bags. During wet finishing, worsted-spun knitwear can exhibit cockling, due to release of localised tensions causing distortion of the knitted loop. Cock-

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ling can also be a problem along the interface between the top of the welt and the body of the knitwear panel. To overcome this problem, anticockling procedures are used. Several procedures are available, depending upon the severity of the problem and whether the knitwear is ecru or knitted from dyed yarns. Basically, the knitwear is treated by immersing in hot or boiling water for a predetermined time. Reducing agents are often added to improve setting. After anti-cockle treatment, the fabric may be scoured. For both the anticockle treatment and scour procedures, machinery with gentle action should be used, e.g. side paddle type having a gentle paddle action. Scouring is carried out at 40 °C, using 1% on the weight of wool (oww) synthetic detergent followed by rinsing. In some countries, garment dyeing is practised. After scouring, the garment is chlorinated to prevent it felting or shrinking during the dyeing cycle. After dyeing, a softener may be applied, or a resin plus softener to produce a machine-washable product. Light hydroextraction is followed by intermittent tumble/rest drying at 70–80 °C. Procedures are selected to minimise creasing and to retain a clear surface finish. Steam pressing completes the finishing procedure.

11.3.2 Woollen-spun knitwear Woollen-spun knitwear, when delivered to the finishing department, can contain high levels of spinning lubricant (as much as 8–9%), has a harsh handle and a generally ‘flat’ appearance. Scouring removes oil and dirt. Milling is applied to soften and bulk the hand, provide some consolidation of the structure and subdue the stitch structure of the knitwear. To achieve such finishes, rotary washing drums are generally used. Scouring normally uses an intermittent cycle of wash/rest to allow sufficient scouring time for oil removal, without excessive development of milled finish at this stage. Processing conditions are 40 °C with 3–4% (oww) synthetic detergent, preferably at pH 8.5–9.0, depending on colour fastness. Several baths may be required, depending on the level of oil present. After scouring, the knitwear is thoroughly rinsed. Milling follows, using similar detergent concentrations but with continuous cycling of the machine for the time required to give the desired finish, followed by rinsing. Softeners may be added to the final rinse. Alternatively, special detergent/ softening preparations are available for scouring and milling. The finished knitwear is hydroextracted and tumble dried, followed by steam press finishing. Modern drum machines have compartment drums, incorporate hydroextraction and have automatic and programmable control of finishing cycles. Tilting mechanisms allow for easy unloading.

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11.3.3 Easy-care knitwear Wool can be treated to give machine-wash performance, either at the fibre stage (prior to spinning and knitting) or during wet finishing of the garment. The basic principle is similar in both cases in that an oxidising agent, typically chlorine, is applied which modifies the fibre scales and which imparts a degree of shrink resistance in its own right. A resin is subsequently applied which covers the scales, thereby producing machine-washable wool. Of the various processes, the largest production is by the chlorine/Hercosett process, which is applied at the fibre stage to worsted tops, and also to loose wool, for woollen spun garments. Total Easy Care knitwear has been introduced to the market. This is both machine washable and dryable by tumbling. Such performance is achieved by selection of the physical parameters of the yarn and the knitted structure, coupled with careful attention to the chemical treatment conditions and wet finishing conditions that ensure full garment relaxation.

Reference 1 Rouette H-K and Kittan G, Wool Fabric Finishing, Ilkley, UK, Wool Development International, 1991.

12 Overview of global dynamics in the wool textile industry P D F KILDUFF

12.1

Introduction

Over the last 40 years the textile and apparel industries have witnessed an unprecedented period of change, affecting the nature of their products, processes, markets and competition. Whole new applications and industry sectors to service them have emerged, while others have slipped into decline and a few have even disappeared. The wool textile industry has not been immune to this dynamic, and some changes have not been favourable to the industry. In particular, competition from new fibres and textile products, combined with shifting consumer preferences has, overall, negatively impacted demand for the products of the wool textile industry. This has particularly been the case during the 1990s, when wool textile production and capacity suffered an unprecedented world-wide decline. Nevertheless, wool textile manufacturing remains a significant element of world textile activity. Despite the problems of recent years, it is likely to see a return to growth over the coming decade underpinned by product innovation and more favourable shifts in consumer needs. This chapter provides an overview of the pattern of change in the wool textile industry, world-wide, and outlines the economic forces shaping demand for and supply of wool textiles. As a starting point, it is appropriate to consider the overall dynamics of the international textile and apparel industries in order to establish a context for the patterns of change in the wool textile industry.

12.2

Overview of trends in world textiles

Textile manufacturing represents a relatively mature and therefore, low growth activity compared with manufacturing as a whole. Whereas the value of world manufacturing output as a whole grew at an annual average rate of 4.2%, in real terms, between 1960 and 1998, textile manufacturing grew at just 2.1% per annum.1 333

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Table 12.1 Growth of world mill fibre consumption 1960–2000 [Source: ICAC] Million kg

Annual growth (%)

1960

15 153

1960s

3.7

1970

21 741

1970s

3.1

1980

29 580

1980s

2.5

1990

37 882

1990s

2.1

2000

46 612

1960–2000

2.8

A more frequently used proxy for textile activity is mill fibre consumption. Overall, world consumption of fibre by the textile industry grew from around 15.2 billion kilograms in 1960 to approximately 46.6 billion in 2000, representing an annual growth rate of 2.8% over the whole period. However, growth has progressively slowed during each decade, a trend also reflected in the value of industry output. From a rate of 3.1% per annum in the 1960s, growth of mill fibre consumption fell to 2.1% per annum during the 1990s (see Table 12.1). Within the overall global growth trend of the textile industry, and of the apparel industry also, there has been a slow shift in the geographic distribution of production. As basic pillars of industrial development, the textile and apparel industries have been close to the forefront of the internationalisation process that has seen a move from the discrete national industries of 50 years ago towards a globally integrated industry.2 During this time, international trade in textiles and apparel has grown at a rate approximately twice that of global output. In the process, the dominant position of the industrialised nations in manufacturing has been eroded by developing countries, mainly in Asia. A number of developing nations have become major net exporters of apparel, though some are large net importers of textiles. By contrast, most of the industrialised nations have become large net importers of both textiles and apparel.3 The extent of relocation has varied between products. The most striking shift has been in the production of apparel and of cotton textile manufacturing. Diffusion has been slower in the higher value, and more capital and skill intensive sectors of textile production. This has included wool textiles. As a result of these changes, there has been a shift in the emphasis of textile and apparel manufacturing in the industrialised nations towards man-made fibre based products, home furnishings and technical textiles.2 Although production has been migrating to lower cost centres in developing countries, final consumption of textiles and apparel has remained heavily concentrated in the industrialised nations. In 2000, these were esti-

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mated to account for over 40% of final fibre consumption, although they contained less than 15% of the global population.4 This skewed consumption position reflects the global economic imbalance between rich and poor nations. Around three-quarters of global GDP was generated by the industrialised nations in 2000.5 Nevertheless, there has been a gradual shift in final consumption towards developing countries. An important characteristic of globalisation in textiles and apparel has been the more rapid integration within geographic regions of the globe, as expressed by intra-regional trade flows. This regionalisation process has progressed furthest within Western Europe. However, during the 1990s, it proceeded most rapidly within Asia, within the Americas and between Eastern Europe, North Africa and Western Europe.3 This trend is associated with the creation of regional trading blocs (such as the EU, NAFTA in North America, MERCOSUR in South America and ASEAN in South East Asia) that promote freer trade and investment within their affiliations than with external trading partners. To some extent it also reflects a desire by manufacturers and retailers to develop production sources in adjacent low-cost countries that can offer shorter manufacturing lead times than more distant suppliers.2 Another key feature of international trade in textiles and apparel is the extent to which it is concentrated. Although there has been a steady stream of nations establishing export-oriented textile and apparel industries since the 1950s, trade is still dominated by a relatively small number of large exporting and importing nations.3

12.3

Factors shaping global integration in textiles

The principal factors that have shaped and continue to reshape the global textile (and apparel) industries include government policies, changing consumer requirements, technological change; and the competitive strategies of textile manufacturers and companies in related sectors. Governments have played a key role in globalisation through their support for trade and economic liberalisation. The progressive reduction of tariffs on fibres, textiles and apparel over the last 50 years has provided the key catalyst for the global integration of the textile and apparel industries. However, markets in developing countries have remained difficult to reach, and international tensions resulting from the speed of change and the uneven distribution of benefits have resulted in a burgeoning array of trade barriers. These have been a factor in a slowing of trade growth in the 1990s.2 Government policies have also been important with respect to industrial targeting and protection. On the one hand, governments in developing countries have encouraged the growth of new capacity. In the industrialised

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nations, on the other hand, government support programs and trade protection has slowed the shake-out of less-competitive operations. Also important has been the role of international institutions, such as the World Bank and the United Nations. These have provided assistance for the establishment of textile and apparel export industries in the least developed countries.2 Liberalised trade and improved international communications in the form of multi-national media (especially films, television and the Internet), and low travel and communications costs are another force driving globalisation. These are accelerating the diffusion of new ideas and tastes between nations. The result has been a convergence of lifestyles towards an industrialised, urban, consumer and casual lifestyle model, and the creation of international market segments.2 The ability to identify and exploit these trends have been behind the success of global brands such as Benetton, Polo Ralph Lauren, Nike and Burberry, and of global products, such as jeans, suits and certain sportswear items. On the supply side, new information technologies (IT) and management systems such as ISO 9000 have enabled improved long-distance supply capabilities. Equally important, through standardisation, they have provided a more transparent marketplace by creating new benchmark capabilities that suppliers and customers can adopt to guarantee performance.2 Companies in adjacent sectors have also played an important role in promoting globalisation in textiles. In pursuit of global positions in their own markets, chemicals and equipment manufacturers, who develop many of the new fibre, finishing and process technologies for the textile and apparel industries, have ensured that new products or technologies have diffused rapidly. Similarly, large apparel companies, trading houses and retailers have actively sought-out new sources of supply and lowered entry barriers into international markets by sub-contracting the manufacture of their own merchandise. In many cases, they have provided technical assistance to help new suppliers bring their manufacturing capabilities up to international standards.2 Finally, textile manufacturers themselves have responded to internationalisation of their markets and migration of their apparel customer base by expanding their business abroad. Similarly, faced with pressures to cut costs in order to remain competitive, many companies have internationalised their supply chains through a combination of foreign direct investment, subcontracting and out-sourcing.2

Overview of global dynamics in the wool textile industry

12.4

337

Overview of trends in wool textile production and trade

12.4.1 Introduction Data on the wool textile industry is poor relative to other sectors of the industry. Information on wool textile production for many producing nations is either not available or is incomplete. There are also significant variations between nations on definitions and the design of the industry sample from which data is drawn. The data that is presented here has been compiled by the International Wool Textile Organisation (IWTO). It is the most authoritative source available and provides an overview of the global dynamics in the industry. However, particular care should be taken in using this data.

12.4.2 Mill fibre consumption Against the background of expanding fibre consumption by the textile industry between 1960 and 2000, consumption of wool stagnated. Between the 1960s and early 80s, wool consumption by the textile industry fluctuated around 1500 million kilograms. Subsequently, wool consumption experienced a strong upswing, reaching a peak of 1904 million kilograms in 1988. With the recession in the early 1990s, however, consumption fell sharply and has since stabilised again around 1500 million kilograms. By contrast, synthetic fibres experienced spectacular growth, increasing from 702 million kilograms in 1960 to 23 160 million in 2000. Over the same period, consumption of cotton advanced steadily from 10 356 million kilograms to 19 604 million, in the process retaining its place as the single most important fibre (see Fig. 12.1). As a result of these trends, the share of wool in total fibre consumption fell, in volume terms, from 9.9% in 1960 to 3.2% in 2000. In this respect, it has become little more than a marginal fibre. However, this does not fully reflect the fortunes of the wool textile industry as, in parallel with other sectors of the industry, there has been a significant shift towards man-made fibres. An IWTO estimate from a sample of leading producer nations suggests that man-made fibres accounted for around two-thirds of fibre consumption by the wool textile industry in 1999, compared with less than 50% in 1974. In the early 1960s, the figure was less than 20%.

12.4.3 Trends in output of the wool textile industry Production data provides a direct indication of how the 1990s were a traumatic decade for the wool textile industry. The data available for top, yarn

338

Wool: Science and technology 25,000

Million Kilograms

20,000

15,000

10,000

5,000

0 60 63 64 66 68 70 73 74 76 78 80 83 84 86 88 90 93 94 96 98 00 9 1 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 20 Cotton

Wool

Man-made Cellulosic

Synthetic

12.1 World mill fibre consumption of the principle fibre types: 1960–2000. [From ICAC.]

and fabric production suggests that world output fell significantly between 1989 and 1999, although there are no reliable aggregate figures available (see Tables 12.2–12.4). Within this overall picture, there was a shift of production from traditional centres in Europe, the US and Japan to developing nations and, to a lesser extent, towards wool producing countries such as Australia and Argentina. In common with other areas of textile and apparel activity, Eastern Europe and the former Soviet Union experienced a collapse in wool textile production during the 1990s. Within Western Europe, the traditional locus of wool textile manufacturing, there was a shift to newer centres of production, notably Turkey, Spain and Portugal, although these have also been adversely impacted by competition from Asia. Also, in contrast to the French, German and British wool textile industries, all of which experienced a steady decline over many years, the Italian wool textile industry showed remarkable resilience up until the late 1990s, when it too encountered a sharp downturn. In Asia, the principal growth centres have been China and India. However, Chinese production also showed a sharp contraction after 1994. Despite problems in the data noted above, differences are evident between the top, yarn and fabric production sectors of the industry.Top production, as a highly capital and skill intensive business, has remained more

Overview of global dynamics in the wool textile industry

339

Table 12.2 World production of wool/hair tops (including carded sliver) in million kg [Source: IWTO Wool Statistics, various years] 1989 Americas

Asia & Australasia

Argentina

8.6

Brazil

9.5

6.5

19.7 4.9

32.0

30.9

14.3

Uruguay

NA

46.8

36.3

Australia (b, c)

23.4

44.9

53.6

China

93.3

223.0

163.0

India

13.5

18.0

Israel

3.3

2.6

Japan

78.0

34.9

Korea (South)

15.9

13.6

New Zealand (a)

NA

1.7

1.8

Taiwan

12.5

21.3

24.2

0.0

4.0

20.1

1.5

Belgium

24.8 NA 16.9 NA

NA 0.0

France

72.0

61.2

36.8

Germany

41.4

42.3

17.1

Hungary

1.6

Italy (b)

59.8

56.5

57.3

Poland

9.5

3.8

1.7

Portugal

5.6

3.1

3.0

15.3

13.6

11.0

0.9

0.1

0.0

Turkey

23.8

23.5

10.6

UK

38.7

32.9

15.3

2.5

2.0

1.6

19.2

21.8

13.7

Spain Switzerland

Africa

NA

1999

USA (b)

Thailand (a) Europe

1995

Egypt (c ) South Africa

NA

1.6

a) Exports. b) Includes small quantities of tops of man-made fibres (Australia and USA) or of non-wool natural fibres (Italy viz 226 in 1995; 160 in 1996; 135 in 1997; 155 in 1998). c) Seasonal year ending year shown. (Australia 30 June) NA = not available.

concentrated in fewer nations. Yarn production has shown the most rapid shift away from industrialised nations to developing countries, while fabric production has migrated more slowly, owing to the high level of skill required in fabric finishing.

Table 12.3 Total yarn production (woollen and worsted) by the wool textile industry in million kg, 1989–1999 [Source: IWTO Wool Statistics, various years]

Western Europe

Eastern Europe

Asia & Australasia

Africa

Americas

Austria Belgium Denmark Finland France Germany Greece (d) Irish Republic Italy Netherlands Norway Portugal Spain Switzerland Turkey UK Bulgaria Croatia Czech Republic Hungary (e) Poland Romania Yugoslavia Russian Federation Australia (c) China (b) Hong Kong India Israel Japan New Zealand Pakistan (c) South Korea Syria Taiwan Algeria Egypt (c) South Africa USA

1989

1995

1999

5.4 97.6 3.5 1.0 70.1 46.0 9.3 NA 534.3 3.1 2.3 31.5 84.2 NA 161.5 140.0 NA NA NA NA 77.2 NA NA NA 20.1 250.0 6.9 63.4 NA 219.5 20.6 NA 227.6 NA 16.9 NA 19.0 41.7 612.9

4.1 54.3 1.0 1.1 43.1 39.6 7.6 10.9 540.5 NA 3.4 NA 69.1 3.7 208.0 108.3 13.5 3.3 16.7 0.6 34.4 31.6 6.8 42.7 23.1 513.8 NA 81.0 1.0 123.0 20.6 5.5 (g) 120.4 1.6 14.0 NA NA 28.8 532.9

NA 41.0 0.4 NA 30.8 25.4 NA NA 454.5 NA 2.5 (a) NA 71.0 2.5 153.6 87.4 6.2 0.4 9.8 0.6 18.2 14.5 4.7 28.6 17.7 368.4 NA 95.0 NA 78.4 24.9 5.3 (h) 111.0 NA NA 1.8 2.1 23.8 443.2

a) 1998 data. b) Knitting (hand & machine) yarns only; of which worsted types 153.4 million kilograms and woollen 129.1 million kilograms in 1991. c) Seasonal year ended year shown (Australia 30 June). d) New, official series; previously a trade estimate. e) Wool predominant only. f) 1996 data. g) 1998 data. NA = not available.

Table 12.4 Total fabric production (woollen and worsted) by the wool textile industry in million square metres, 1989–1999 [Source: IWTO Wool Statistics, various years]

Western Europe

Eastern Europe

Asia

Africa North America

South America

Austria (a) Belgium Denmark (f) France (a) Germany (e) Italy Netherlands Rep. of Ireland (a) Spain Turkey UK (d) Bulgaria Czech Republic Hungary Poland Romania (h) Slovak Republic Yugoslavia Former USSR Australia (b) China (j) India (j,k) Japan (c) South Korea Taiwan Egypt (b,a) South Africa Canada Cuba USA (e,g) Uruguay

1989

1994

1999

NA NA NA 112.3 128.1 573.4 4.4 NA 69.7 91.2 93.1 NA 87.7 29.0 143.1 141.0 NA 100.4 715.0 9.4 279.6 96.8 510.3 101.2 14.9 23.5 33.8 NA NA 143.6 7.8

5.1 6.2 0.8 73.8 90.1 611.4 NA 1.2 72.7 103.3 81.4 20.1 39.3 3.3 49.1 41.5 9.6 14.6 111.0 8.2 653.9 102.8 408.5 95.4 6.9 NA 26.2 10.6 NA 149.3 9.5

10.5 (i) NA 0.9 84.2 86.1 474.8 NA NA 99.4 136.7 55.9 7.0 20.1 0.1 (i) 34.7 12.5 4.4 6.9 73.5 6.3 278.5 111.9 277.5 NA NA 3.4 17.2 10.4 120.0 64.7 NA

a) Apparel only. b) Year ended 30 September of year shown (Egypt), 30 June (Australia). c) Estimated from the statistics of the dyeing and finishing sector which reflect more accurately production of fabrics of wool and other fibres by the wooltextile industry. Previous series covered national production of wool predominant grey fabrics – viz.; 249.3 in 1995; 248.6 in 1996; 247.9 in 1997; 212.9 in 1998; 199.0 in 1999. d) Deliveries/shipments. e) Comprises only fabrics containing by weight 50% or more of virgin or reprocessed wool (Germany) 36% (United States). f) Excluding blankets. g) Excluding woven felts. h) Including some carpets. i) New series. j) Million linear metres. k) Includes approximately 12 million linear metres of shoddy fabrics in 1994 and 1999.

342

Wool: Science and technology

12.4.4 Trends in wool textile trade Overall, trade in wool textiles mirrored the decline in global production during the 1990s, with some recovery becoming evident at the end of the decade (see Tables 12.5 and 12.6). Within the aggregate picture, traditional centres in Europe, the US and Japan have continued to be major exporters, though in most cases their export surplus shrank considerably during the 1990s. East European nations and developing countries in Asia, Latin America and North Africa figure prominently as large net importers of wool type fabrics. This reflects the growth of apparel manufacturing which has migrated from nearby industrialised nations. A few early movers among these nations, notably Turkey, have moved to a position of self-sufficiency in wool textiles, towards which many of the others are striving. Strikingly, India has played only a relatively minor role in trade. This partly reflects restrictions on imports and, on the export side, the limited international competitiveness of Indian mills in terms of quality and service.

12.5

Factors behind the declining importance of wool and wool textiles

12.5.1 Overview The principal problems affecting demand for the industry’s products have related to increased inter-fibre competition with the rise of synthetics; competition from alternative yarn and fabric forming technologies; the shift in consumer expenditures in favour of lighter weight and casual products; and constraints on fibre supply.

12.5.2 Inter-fibre competition In the 1960s, the market penetration of synthetic fibres was assisted by a combination of factors. These included the novelty of the new fibres, which made them fashionable; their superior properties in terms of strength, wear resistance and ease of care; the relative stability of their prices, which removed many of the uncertainties traditionally facing textile firms owing to price fluctuations in natural fibres; the possibility they offered textile firms for lowering production costs; and the intensive promotional efforts of man-made fibre producers to create consumer awareness and preference for their products. Subsequent expansion was encouraged, in part, by technical advances that both broadened the range of fibres and widened the application of individual fibre types by modifying their characteristics to suit specific end-uses. It was also stimulated by falling fibre prices, arising from cost reductions through learning, process innovations, increasing scale

W Europe

S America

N America

USA (b)

Irish Republic (c)

4 424

211

2 213

334

1 027

1 383

Greece

Iceland

6 049 22 510

8 838

France

684

2 008

23 208

767

Finland

Germany

1 698

0

6 662

0

7 577

1 195 1 876

1 995 1 558

Denmark

Cyprus (d)

Belgium

Austria

Peru (d)

14

1 0

Chile (d)

Colombia (d)

0

55

20

296

74

1 155

1999

281

Brazil

27

9 501

Mexico

Argentina (d)

923

Canada

1996

Exports

3 490

64

1 061

20 099

8 246

479

3 401

66

6 091

3 043

9

20

174

81

121

5 297

99

1 481

1996

Imports

3 242

43

3 977

19 446

6 774

355

3 801

47

12 259

2 783

30

58

41

339

289

7 278

39

1 239

1999

592

934

147

322

3 109

-1 029

291

-2 950

3 064

-725

329

-47 -1 793

-1 703 288

-5 597 -66

-907 1 486

1 165

-20 1 986

-27 -58

-173

-1 485

-284

-269

-94 200

35 -6 982

-90 -4 796

-84

1999

-558

1996

Balance

Table 12.5 Aggregate trade in yarns (woollen and worsted) by the wool textile industry in thousand kg, 1996 and 1999 [Source: IWTO Wool Statistics, various years]

Overview of global dynamics in the wool textile industry 343

Asia & Pacific

E Europe

Table 12.5 (cont.)

3 861 2 227

Portugal

Spain

36 176

Hong Kong (b)

NA 42 298

China

Bangladesh (d)

712 470

Former Yugoslavia (d)

Australia (a)

32 776

47 413

59

762

1 104

824

66

1 316

46

Former Soviet Union (d)

Romania (d)

437 5 765

181 2 630

Hungary

Poland (d)

45

17 381

2 180

1 218

3 129

71

19 440

522

4 481

85

1 977

3 928

855

588

34 473

1999

1 989

Czech Republic

Bulgaria (d)

UK

Turkey

Switzerland

79

878

Norway

Sweden

916

33 694

Netherlands

Italy

1996

Exports

42 574

54 626

NA

4 451

1 003

388

1 481

963

888

738

336

18 357

5 311

2 364

986

2 726

3 430

1 116

4 762

15 943

1996

Imports

39 162

36 046

791

6 893

890

1 501

1 031

1 031

922

887

474

12 758

9 616

1 837

1 111

2 815

5 132

1 032

5 077

16 064

1999

-732 11 367 -6 386

NA -6 398

214 -6 131

-291 -3 981 -12 328

-677

-965 928

-1 435

-485 4 734

1 667

-707

-429 2 242

1 251

4 623 -265

-7 436

-4 789 1 083

-619

-838 -1 026

-907 2 117

-1 204

-177 431

-4 489 -238 -499

18 409

-3 846

1999

17 751

1996

Balance

344 Wool: Science and technology

a) b) c) d)

1 671

45 155

Tunisia (d)

20

255

805

648

Morocco (d)

Mauritius

1

0

0 65

Egypt (d)

4 937

Algeria (d)

9 831

24

1

129

4 831

4 900

324

1 015

413

1 251

311

285

195

NA

748

26

421

145

677

637

5 010

2 809

13 380

851

748

Year ending 30 June of year shown (Australia and New Zealand); 31 March (India). Exports include re-exports. Includes small quantities of yarn classified as neither woollen nor worsted. Estimated from the trade returns of trading partners and possibly incomplete.

Africa

Taiwan

NA

1

Thailand (d)

0

Saudi Arabia (d)

Syria (d)

0

29 NA

6 069

New Zealand (a)

Pakistan (d)

6 672

Malaysia

Philippines (d)

9 575

5 193

Macao (d)

3 957

3 013

South Korea

909

0

1 397

19

Jordan (d)

112

6 318

Japan

42

4 464

Israel (d)

India (a,d)

578

1 399

815

1 457

400

36

266

2 269

294

60

867

39

673

398

6 614

14 341

12 109

536

814

-598

NA

-860

-652 NA

-603 -368

-36 -399

-285 -246

4 671

9 636

NA

-59 -270

-26 -747

-39 -738

-116 NA

8 902

4 433

-1 714

5 392

6 035

183

-10 384

-11 200

-11 983 204

-702 -536

-832

5 740

-706

4 140

Overview of global dynamics in the wool textile industry 345

W Europe

S America

N America

8 032

Greece

Netherlands

Italy

5 478

72 948

770

27 003

7 660

Germany

France

733

Denmark

5 407

68 713

1 119

22 397

1 926 1 244

2 044

Belgium

1 143

1 902

1 329

2 123

Austria

Uruguay

0

1

77

58

Colombia (c)

Guatemala (c)

245 3 292

504 3 383

0

2 655

1 599

Chile

7

709

1 326

3 035

35 842

33 631 1 700

31 181

25 585

1999

Brazil

Argentina

Mexico (c)

Canada

(000s kilograms)

India (c,e)

China

USA (d)

(000s square metres)

1996

Exports

3 562

5 196

1 910

20 325

8 417

1 207

2 030

3 032

11

317

244

5 082

456

360

454

5 304

471

61 664

9 595

1996

Imports

3 736

4 654

2 841

16 860

8 378

1 062

1 506

1 589

215

668

622

5 012

563

310

1 920

5 010

567

65 930

16 127

1999

1 916

1 671

64 059

-1 722 67 752

-1 140

-346 5 537

-757 6 678

420 182

14

-446 -474

1 687

2 112

-545 -667

-186 -317 -1 703

-318 -1 720

48 -1 699

735 -310

255

-3 411 -353

-3 978

2 468

-30 088

-28 033 1 229

15 054

1999

15 990

1996

Balance

Table 12.6 Aggregate trade in woven fabrics (woollen and worsted) by the wool textile industry in thousand square metres (a) and thousand kg, 1996 and 1999 [Source: IWTO Wool Statistics, various years]

346 Wool: Science and technology

1

Tunisia

8

110

583

Taiwan

Morocco (b)

4 (e)

46

4 240

11 202

Thailand (c)

Syria (b)

South Korea

Japan

617

Indonesia (c)

Israel (c)

4

Bangladesh (c)

911

Former Soviet Union

63

Slovakia 519

476

Former Yugoslavia (c)

2 130

Romania

82

2 549

482

Poland (b)

Hungary

Czech Republic

Bulgaria (c)

2 552

9

289

483

56

0

5 943

11 839

927

43

2

1 611

270

147

197

1 374

270

2 495

510

9 480

4 619

995

3 826

3 921

3 098

3

2 290

1 777

1 182

3 707

5 545

541

360

66

5 316

5 879

1 538

5 568

7 843

3 195

2 458

971

7 898

4 719

1 420

3 104

3 830

3 088

3 585

820

1 140

302

2 123

3 406

445

1 071

531

8 182

5 087

1 759

8 455

6 686

3 352

2 444

2 286

8 229

4 768

1 307

4 632

-8 258 -1 612 -4 817 -6 571 -529 -1 028

-5 092 -1 475 -5 360 -4 405 -62 -359

-3 079

-3 090

-337

-1 707

-3 296

-1 773 107

-302 -1 084

-1 136

3 820

8 433 533

5 657

482

-5 312

-5 713

76

51 -3 082

91 -3 113

-1 776

-489

-149 1 251

-312

-401 -2 146 5 355

-806

-1 278

18

-2 329

Data for India, China and the US is available only on the basis of area. Excluding blankets. Partly estimated. Including the following quantities of pile fabrics (in tonnes): imports 451 in 1996; 504 in 1997; 682 in 1998; 655 in 1999; exports 197 in 1996; 347 in 1997; – in 1998; 2236 in 1999. e) Year ending 31 March of year shown.

a) b) c) d)

Africa

Asia & Pacific

E Europe

Switzerland

Turkey 13 253

1 019 2 573

Spain

United Kingdom

1 592 3 122

Portugal

Overview of global dynamics in the wool textile industry 347

348

Wool: Science and technology

economies in production, and intensifying price competition between producers.6 In the 1970s and 80s the process of rapid market penetration achieved by synthetics in consumer textile applications subsided. This partly reflected the high penetration already achieved and the greater difficulty of further displacing natural fibres. However, there was also a shift in consumer preferences in favour of natural fibres. This was largely based on their greater aesthetic appeal in terms of handle and appearance, but it was also encouraged by the more concerted efforts of natural fibre marketing and research organisations, such as the International Wool Secretariat (IWS) and Cotton Incorporated, to develop easy-care finishes and to promote their products. In the case of cotton, an additional factor was a substantial fall in fibre prices relative to man-made fibres as a result of expanding production and improved agricultural productivity.6–9 In the 1990s, however, expanding production of low cost man-made fibres in Asia, and the development of a new generation of man-made fibres with sophisticated technical and aesthetic properties, has again negatively impacted consumption of natural fibres, particularly wool, as noted previously.7–9

12.5.3 Competition from alternative yarns and fabrics Although the wool textile industry readily adapted its products to include man-made fibres in pure form or in blends, the growing availability of synthetic fibres in the 1950s stimulated the development of alternative low-cost fibre to fabric production routes, such as warp and circular knitting, carpet tufting and non-wovens. These new sectors and sub-sectors of production competed, in part, with traditional wool woven textile products in woven upholstery, carpets and blankets, and in woven and knitted outerwear. This substitution was often on the basis of lower costs but also on their technical or aesthetic suitability for a specific purpose. In knitwear, worsted spun yarns were displaced, in part, by texturised polyester filament yarns. In carpets, traditional wool woven carpets were displaced by tufted carpets, often using nylon filament yarns. In blankets, woven products faced competition from non-woven fabrics.6

12.5.4 Market changes Demand for wool textile products has benefited from the increasing importance that consumers have attached to the aesthetic and comfort properties of their clothing and surroundings. However, shifting consumer tastes and lifestyles have negatively impacted upon demand for wool textiles. Improved home heating, increased use of private transport, a shift in atti-

Overview of global dynamics in the wool textile industry

349

tudes within society to greater informality and an increasing amount of time devoted to active sport and leisure has tended to favour lighter-weight casual attire at the expense of stiffer, heavier and more formal apparel.6,10 Although wool textile manufacturers have responded by introducing finer yarns and lighter-weight fabrics, this trend has benefited short staple and filament fabrics at the expense of long staple products. In home textiles, there has been a shift to the use of quilts and duvets at the expense of blankets. Demand for hand-knitting yarns has been hit by busy lifestyles, growing consumer affluence and the falling real cost of knitwear in the shops. In recent years, there has been a shift in discretionary expenditures to non-apparel items, such as mobile telephones.4 Compounding this situation, wool has had problems stemming from its mature image and its association with winter and heavy outerwear products. Due to neglect by wool producers, textile manufacturers and fashion companies, the younger generation are largely ignorant of wool’s qualities.11–14

12.5.5 Constraints on fibre supply Other factors impacting demand for wool have been production-side constraints.15–18 Wool fibre production has been constrained by competition for pasture from other crops, and by environmental issues regarding sheep grazing and wool processing. However, it has also been impacted by a relatively complacent growing industry – which has not matched the productivity growth and innovation shown by the man-made fibre industry and by many other branches of agriculture, including cotton. This underachievement is often ascribed to the guaranteed price system that was maintained by governments in producing nations, notably the Australian Wool Commission. This ensured that farmers obtained a minimum return. In 1990, during the downswing of an international recession, demand for wool collapsed causing the guaranteed price system to be abandoned and resulting in a sharp drop in wool prices that rippled through the textile industry in the form of stock write-downs. Many wool farmers were ruined and pasture was diversified into other, more lucrative products. The sharp fall in fibre prices also undermined confidence among wool textile manufacturers.

12.6

Patterns of industry development and adjustment

12.6.1 Introduction In combination, the long-term globalisation of the wool textile industry together with its declining fortunes during the 1990s, has resulted in

350

Wool: Science and technology

significant upheavals across the industry. This section considers the dynamics of change in the wool textile industries both of the industrialised and of developing nations, with specific reference to the leading producer/ consumer countries.

12.6.2 Adjustment in the industrialised nations Although the international diffusion of wool textile production has proceeded more slowly than in other sectors of the industry, since the mid 1980s the expansion of production in developing nations has placed an increasing squeeze on traditional manufacturing centres in Europe, the US and Japan.19–21 Strong capacity expansion in Asia up to 1997 resulted in overproduction, with product coming into international markets at weak prices, undermining existing pricing structures. The ensuing economic crises in Asia, Russia and Latin America compounded these problems by temporarily removing export demand. This particularly hit the European industries. At the same time, companies were struggling to cope with volatile raw materials costs; with increasing investment requirements as a result of the growing costs of new technology, and of environmental, health and safety regulations; and with a reluctance on the part of apparel and retail customers to accept price increases. The poor conditions seriously hurt industry profitability, particularly that of companies which focused on volume markets.4,22–27 The pattern of adaptation to international competition across the industrialised nations has been similar.4,6,10,14,22–27 As imports from developing countries have grown, commodity products and businesses have been abandoned. There has been a shift up-market with products that are more innovative and sophisticated in terms of fashion and technical properties. This has included an emphasis on differentiating the product offer from those of competitors through branding, quality of service and close relationships with customers.While most downsizing has occurred in apparel-related areas of production, there has been an increased emphasis on contract furnishing applications. These markets have been less exposed to the full force of international competition, due to the more technical nature of the purchase decision and the importance of technical innovation. The internationalisation of marketing and production activities has been another important theme. As competition has intensified in their domestic markets, companies have expanded their international presence. The internationalisation of manufacturing operations has been spurred by the need to improve cost competitiveness. An increasing number of companies have abandoned domestic production in favour of manufacturing in developing countries, sub-contracting or sourcing. Another important factor influenc-

Overview of global dynamics in the wool textile industry

351

ing this migration, however, has been the tendency for production to be drawn closer either to the fibre source, in the case of early stage processing, or to apparel manufacturing in the developing countries. This migration pattern has been influenced by the need to satisfy cost and speed requirements, and also by local government incentives.4,6,10,14,22–27 These strategic shifts have been accompanied by extensive rationalisation of the traditional industries in Europe, Japan and the USA. This has involved cost reduction and downsizing measures and a wave of consolidation. Many mills, especially those concentrating on volume markets, have been closed. In wool combing, and in dyeing and finishing, increased investment requirements have favoured larger operations and caused many smaller businesses to close. Often, specific markets have become dominated by a handful of domestic players. Generally, however, many of the large, diversified groups have given way, through downsizing and de-integration, to small and medium-sized businesses that are more tightly focused around a specific product market or process technology. Typically, these employ flexible operations that serve specialist, often high quality, niches. Many are engaged in the focused marketing of innovative yarns or fabrics. A feature of these businesses is close co-operation with customers and suppliers, rapid product development and, in some cases, co-branding with leading apparel and retail brands.4,6,10,14,22–27 In Western Europe, there has been extensive consolidation, especially in top making, where production has become concentrated in the hands of a few major companies. Asian companies have entered the market through acquisitions, as some indigenous players have downsized or left the industry. In Eastern Europe and the former Soviet Union weak domestic demand, inefficient work practices, old equipment and low capacity utilisation caused considerable upheavals during the 1990s. Increasingly, however, Eastern Europe has benefited from the migration of wool textile production out of Western Europe.28,29 Of all the major European wool textile industries, the Italian industry has proven the most resilient.19,20,23,30,31 Although the woollen sector of Prato has proved more sensitive to international pressures than the worsted sector in Biella, Italy retains a vertically integrated wool textile industry. This contrasts with most other European nations where some activities have virtually disappeared as companies have opted for offshore sourcing. The Italian industry has benefited from the sophistication of the Italian market and their close association with innovative Italian fashion designers that have gained world recognition. Many Italian mills come under family control and focus on a single activity in the production chain with a narrow product range. These companies are highly flexible and innovative. They collaborate closely with suppliers and customers to develop new styles and improve quality. Faced with shrinking demand in the late 1990s, the industry has

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focused on generating improvements to quality and service, and on lowering breakeven points to permit even smaller batch sizes. Historically, the German textile complex, from machinery and chemicals through to finished products, has been extremely strong.24,26,32 However, the industry has unravelled during the 1990s under the burden of high production costs and the loss of offshore processing advantages for German textiles as former East European countries have gained free trade status with the EU. Besides the high wage labour and strong currency, Germany’s extremely strict environmental constraints have especially hurt wool textile processing in that country. As elsewhere, the combined result of cost and competitive pressures has been widespread unprofitability, causing extensive rationalisation and downsizing, and many company failures. This has prompted a search for more cost-effective manufacturing locations resulting in a migration of capacity to Portugal, Eastern Europe, Asia and South Africa. German design, manufacturing and marketing skills have remained undiminished, and the ability of German firms to orchestrate international supply chains is well established. This advantage is reinforced by the central location of Germany in Europe. At home, the response of German fibre, textile and clothing companies has been to drive production to ever-higher levels of efficiency and to emphasise new technology and product innovation. German manufacturing has become increasingly confined to specialist, high value/high technology products, and there has been increasing emphasis on technical textile markets as a growth opportunity. During the 1990s, much of the French wool textile industry, including many of the larger groups, was in severe financial difficulties as a result of shrinking markets and growing competition. Under-investment in modernisation, due to an inability to raise investment capital, eroded the industry’s longer-term competitiveness. Subsequent assistance from the French government helped to rectify this situation but not before extensive loss of capacity. The more competitive industry that has emerged comprises mainly small specialist business but retains a few major vertical groups. The output mix of the industry has shifted towards higher quality, luxury products associated with the French fashion industry and technical fabrics. Larger companies have been active in relocating production abroad and some have made selective acquisitions of European rivals to build dominant market positions in the EU.33,34 The traditional leading position of the UK in wool textiles receded rapidly from the 1960s. The industry proved too conservative and too production oriented in responding to international competition and market changes in terms of fashion and segmentation. UK companies were unable to compete with the greater creativity and flexibility of their Italian counterparts, both in lower cost and in more fashionable cloths. The growth of low cost imports from Turkey and Asia compounded this situation. Only at

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the very top end, and in certain specialist niches, has the UK retained a leading position. The outcome has been a long steady attrition, in which many of the larger companies have been broken-up, closed or changed ownership (in some cases several times). Much production has migrated offshore.6,27,35 Turkey emerged rapidly as a major producer of wool textiles and related apparel during the 1980s. Much of this production was for the West European market. Since 1995, the industry has been disrupted significantly by two major earthquakes, by exposure to the Russian financial crisis and by low cost imports from the Far East.36 The Japanese wool textile industry long held a dominant position in Asia but, since the mid 1980s, production has dropped precipitously.22,25,37 This followed an escalation in the value of the Yen and the rapid growth of manufacturing capacity and exports from developing Asia. The initial development of wool textile production in South East Asia was largely associated with Japanese foreign investments that date back to the 1960s. These were motivated predominantly by the need to preserve established markets, as local governments erected trade barriers to Japanese exports. They were also, in part, motivated by the opportunities, afforded through lower labour costs, to export to third countries. Much of this investment was tied closely to the strategies of the major trading houses, with their financial strength and their extensive international sourcing, marketing and distribution capabilities. Some investments extended to Latin America and Europe. As basic textile production migrated offshore, at home, Japanese companies invested heavily in upgrading products and process technologies. During the 1990s, however, investment in mainland Asia accelerated, particularly in China. A feature of this new expansion was increased involvement of trading companies in wool textile manufacturing. The domestic industry was further undermined by the weak Japanese economy and by escalating competition in Asia, culminating in the Asian economic crisis starting in 1997. Extensive rationalisation and loss of capacity has followed. Increasingly, Japanese production is focused on luxury and higher technology synthetic products. Up to the mid-1990s, the US wool textile industry continued to grow, assisted by a higher level of tariff protection than was afforded to its counterparts within the industrialised nations. Following the creation of NAFTA, however, Mexico expanded rapidly as a major supplier of wool apparel to the US.Although this benefited US wool fabric exports, it quickly led to the growth of Mexican production. The US industry was further affected by a loophole in the NAFTA agreement that permitted Canadian men’s and boys tailored garments to be made from non-NAFTA fabric. Growing imports and falling prices squeezed industry profitability, encouraging a number of larger US companies to invest in Mexican operations. The situation was compounded by a slow-down in apparel demand after

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1998 and by an acceleration of apparel imports from Asia at the expense of Mexican and Caribbean suppliers. The outcome was a sharp drop in output, resulting in bankruptcies and mill closures. Smaller, more flexible operations manufacturing high quality products and servicing specialist niches have fared best in this environment.4,10,38–42

12.6.3 Patterns of evolution in developing countries In the developing nations, the rapid expansion of apparel production has encouraged the growth of textile and man-made fibre industries, including wool textiles. The creation of large export apparel industries has brought about a need for large quantities of fabric to service their requirements. In the early stages of industry development, limitations in the textile capacity and technical skills of developing nations obliged them to import much of their fabric needs for export apparel, typically from the industrialised nations. However, local capacity has often expanded quickly to substitute for these imports, encouraged by low manufacturing costs, local government policy and the need for faster response in the supply chain. As noted already, it has usually been assisted by equipment suppliers and international consultants, and by inward investments of established manufacturers in the industrialised nations. Yarn production has usually expanded more quickly due to the greater technical skills required in wool weaving and finishing. As domestic industries have expanded, they have often diversified and upgraded their product range. In the process, they have changed from an import substitution role to an export industry. Finally, some of the more sophisticated companies have begun to develop strong marketing and design capabilities, and to embark on foreign direct investments of their own. In other developing nations this has typically taken the form of greenfield investments, but in industrialised nations it has typically been pursued through acquisitions.4,43 China witnessed a rapid build-up of wool textile capacity and output up to the mid 1990s. However, much of this focused on basic heavy-weight fabrics and darker colours, with little emphasis on high-quality products. Poor management, especially in state-owned companies, lacked an understanding of market requirements, resulting in over production, slow adaptation to market changes, falling prices and high stock levels. In addition, the industry suffered from low productivity and poor quality due to obsolete equipment, over-manning and inadequate technical skills. Subsequently, the industry has been subject to severe rationalisation and upgrading with the encouragement of the Chinese government. Obsolete equipment has been scrapped and large numbers of workers have been made redundant. Heavy investments have been made in new technology and in technical, design and marketing skills, as Chinese companies

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have sought to shift into higher quality segments with more fashionable merchandise.44–48 In Sections 1.14–1.16, wool promotion strategies of the principal wool grower countries are briefly described, notably the New Zealand Fernleaf brand as distinct from various programmes under the Woolmark umbrella. Although India has a long established tradition in wool textiles, the Indian wool textile industry has made only a modest impact on international markets. This is partly a legacy of the policy of ‘swadeshi’, or selfreliance, under which India largely sealed itself off from the world economy through a series of import and export controls. In this cocoon it fell behind as other Asian countries achieved economic take-off by exposing themselves to the dynamics of international competition. Despite extensive reform during the 1990s, an array of bureaucratic controls continue to constrain production and international trade. Government policy has been preoccupied with protecting employment in the rural handloom industry and not with encouraging a competitive manufacturing industry capable of taking its place in international markets. Despite these obstacles, modernisation of the wool textile industry has accelerated, assisted by an inflow of foreign investment. A vibrant industry comprising a multitude of small businesses and larger export-oriented firms has begun to emerge.49

12.7

Outlook for the wool textile industry

12.7.1 The outlook for consumption Today, the emphasis of wool fibre and textile marketing has switched from quantity to quality. Product and process innovation has extended the appeal and applications of wool. The development of softer, lighter-weight fabrics, based on finer yarns and fibres, innovative blends with other natural and man-made fibres, and new finishing techniques, has improved the technical performance range and trans-seasonal appeal of wool textiles. New developments have extended the application of wool textiles to include a wider range of casual and sportswear items. Another area of technical development has been so-called single-stage processing, involving the production of fabric directly from scoured, dyed fibre in the form of felts or non-woven products. This has seen applications in blankets, building insulation, agrotextiles, industrial felts and performance sportswear, among others.50–53 In parallel, new efforts have been made to promote consumer awareness of wool and to position it as a quality item for formalwear and smart casualwear through new sub-brands of the Woolmark. However, there is an uphill struggle to achieve consumer recognition on a par with cotton and branded man-made fibres, especially among younger consumers. Furthermore, wool promotion and development has lost additional ground

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as a result of reduced support from wool growers and the fragmentation of the former technical development and marketing body that represented the leading grower nations, the IWS, into nationally organised institutions.54–57 In future, market trends may favour a shift back to the products of the wool textile industry. This includes the prospect of a general fashion swing back towards smarter, more tailored apparel at work. Also, the ageing of populations and increasing consumer affluence in the industrialised nations is expected to support positive demand for wool, both in apparel and furnishings. In addition, apparel and furnishings markets are expanding quickly in developing nations, due to their higher economic and population growth rates. The growing middle class consumers in these nations, especially in China, are looking for higher grade products.4,47,48,58

12.7.2 The outlook for production The pace of globalisation in the wool textile industry is likely to accelerate, despite difficulties in implementing trade agreements made under the Uruguay Round of the General Agreement on Tariffs and Trade (GATT). This is exemplified by China’s acceptance for entry into the new World Trade Organisation (WTO) by the US and EU and by the extensions of free trade agreements between the European Union and Mexico and between the US and sub-Saharan Africa.4 Trade liberalisation and improving international communications will underpin a continued intensification of competition and migration to low cost production locations close to large apparel manufacturing centres. The pace of upgrading in developing nations will accelerate as partnerships between local textile manufacturers, and their raw materials and equipment suppliers, will enable them to better exploit new technologies. Competition will also escalate in the upper market segments, as leading companies in the developing nations upgrade their creative design and marketing capabilities to close the gap with those in Europe, Japan and the US. The result will be a further shake-out of companies and capacity, both in industrialised nations and in the less competitive developing countries. China is expected to be the biggest winner after quotas expire. Overall, China’s accession to the WTO should see its wool textile and apparel exports expand more rapidly, though anti-surge provisions in bilaterals agreed with WTO trading partners will act as a constraint.4 Also, as noted previously, the emphasis in the Chinese textile and apparel industries in recent years has been on upgrading quality rather than expanding volume. In the traditional centres of production in industrialised nations, an increasingly specialist industry will survive, focusing on market niches with luxury or highly sophisticated products.

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References 1 ‘Industrial Statistics Yearbook’, New York, United Nations, Vol 1, various years. 2 Kilduff P D F, ‘A hitch-hikers guide to the global textile and apparel industries’ in Gupta, S (Ed.) Smart Textiles Their Production and Marketing Strategies, New Delhi, NIFT, November 2000, 1–29. 3 See, for example, International Trade Statistics, Geneva, World Trade Organisation, 2000, 148–161 and earlier years in this publication series. 4 Kilduff P D F and Priestland C, Strategic Transformation in the US Textile and Apparel Industries: A Study of Business Dynamics with Forecasts up to 2010, Raleigh, the Textile and Apparel Business Intelligence Consortium, North Carolina State University, May 2001, 5.8–5.10. 5 World Development Indicators, Washington, World Bank Group, 2000, http://www.worldbank.org/data/wdi2001/index.htm. 6 Kilduff P D F, Corporate Responses to Recessionary Conditions in the UK Textile Industry Since 1979, PhD thesis, Leeds, University of Leeds, 1989, pp 61–62. 7 Borland V S, ‘Natural resources’, America’s Textile Industries, 2000, 29, (6), K/A66–K/A70. 8 Anon., ‘An urgent need to increase wool consumption’, Wool Record, 1999, 158, (3654), 25. 9 Mackie G, ‘Natural selection’, Textile Horizons, 1999, November, 8–11. 10 Yasuda H, An Analysis of the Responses of the US Textile and Apparel Industries to Changes in the Business Environment Between 1960 and 1992, PhD Thesis, Leeds, University of Leeds, September 1994, 106–112, 186. 11 Anon., ‘Japanese demand outstrips supply of SRS wool’, Wool Record, 1999, 158, (3655), 37. 12 Anon., ‘Growing fears that wool could become a minority fibre’, Wool Record, 1999, 158, (3654), 31. 13 ‘Global research highlights the way ahead for wool’, Wool Record, 1999, 158, (3660), 37. 14 Belleli T, ‘The economical situation of the wool textile industry’, Industrie Textile, 1997, (1284), 27–28. 15 Anon., ‘World Wool Supply to 2002’, Textile Asia, 29, (1), 65–69. 16 Anon., ‘Wool output heads for a 40 year low’, Wool Record, 1999, 158, (3659), 13. 17 White B, ‘Wool at the crossroads?’, ITMF Annual Conference Report, 1998, ‘The changing textile face of Asia’, 64–72. 18 Anon., The Times-News, 30/ 9/ 2000. 19 Anon., ‘Mr Giancarlo Lombardi’s views on textile situation’, Wool Record, 1999, 158, (3654), 21. 20 Anon., ‘A difficult year for Italian wool textile mills’, Wool Record, 1999, 158, (3654), 19. 21 Anon., ‘Asian dream becomes a nightmare’, Wool Record, 1998, 157, (3642), 1. 22 Graham J F and Kilduff P D F, The Japanese Textile and Clothing Industry: A Strategic Perspective, Leeds, The Textile Intelligence Centre, University of Leeds, February 1993, 4–6. 23 Graham J F and Kilduff P D F, An Analysis of the Textile Industry in the Biella Region of Italy, Leeds, The Textile Intelligence Centre, University of Leeds, May 1993, 5–20.

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24 Graham J F and Kilduff P D F, Current Developments in the German Textile and Clothing Industries, Leeds, The Textile Intelligence Centre, University of Leeds, April 1994, 32–47. 25 Graham J F and Kilduff P D F, The Japanese Textile and Clothing Industries: Recent Developments, Leeds, The Textile Intelligence Centre, University of Leeds, October 1995, 13, 15. 26 Kilduff P D F, Graham J F, Hart D and McNab J, An Analysis of Current Developments in the German Man-made Fibre, Textile and Clothing Industries, Leeds, The Textile Intelligence Centre, University of Leeds, April 1996, 3.14– 3.26. 27 Kilduff P D F, Brooke P and Graham J F, A Review of the Competitive Dynamics of the UK Textile and Apparel Industries, Leeds, The Textile Intelligence Centre, University of Leeds, January 1997, 2.2–2.5, 4.5, 7.1–7.2. 28 Graham J F and Kilduff P D F, Textiles and Clothing in Czechoslovakia, Hungary and Poland: An Analysis of Change and Competitor Activity, Leeds, The Textile Intelligence Centre, University of Leeds, September 1992, 9–12, 17–18. 29 Graham J F and Kilduff P D F, Current Developments in the Textile and Clothing Industries of Eastern Europe and the CIS, Leeds, The Textile Intelligence Centre, University of Leeds, January 1996, 6.1–6.7, 9.2–9.3. 30 Anon., ‘The usual light, the usual shade’, Rivista-della-Tecnologie-Tessili, 1999, (2), 28–40. 31 Anon., ‘Cautious optimism’, Wool Record, 2000, 159, (3671), 56–57. 32 Anon., ‘Wool goes back to nature’, Wool Record, 1999, 158, (3652), 39. 33 Graham J F and Kilduff P D F, Chargeurs: An Analysis of Their Textile Involvement, Leeds, The Textile Intelligence Centre, University of Leeds, May 1993, 3–5, 10–12. 34 Anon., ‘Not always gold that glitters’, Wool Record, 2000, 159, (3671), 81 35 Borland V S, ‘Tradition and Innovation’, America’s Textile Industries, 2000, 29 (1), K/A60–K/A65. 36 Private communication. 37 Anon., ‘Japanese weaving industry reaches a critical stage’, Wool Record, 1996, 155, (3623), 65 38 Anon., ‘Italy main source of men’s-wear imports’, Wool Record, 1999, 158, (3658), 35. 39 Anon., ‘Decade of growth for wool in the United States’, Wool Record, 1999, (3658), 33. 40 Anon., ‘US industry develops and markets healthy products’, Wool Record, 1998, 157, (3639), 18. 41 Spilhaus K, ‘Textile firms rise to new challenges’, Wool Record, 1996, 155, (3618), 19. 42 Fisher G, ‘New England’s woollen mills are at full production’, Wool Record, 1997, 156, (3633), 17. 43 Kilduff P D F, McNab J, Brooke P and Graham J F, An Analysis of International Strategic Market Opportunities for UK Textile and Clothing Businesses, Leeds, The Textile Intelligence Centre, University of Leeds, October 1996. 44 Graham J F and Kilduff P D F, ‘Textiles and Clothing in China: Current Developments and Future Prospects’, London, Financial Times Management Reports, October 1994.

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45 Jiang H H, An Analysis of the Evolution of the Chinese Textile and Clothing Industries, Distribution System and Markets since 1979, PhD thesis, Leeds, University of Leeds, 1998. 46 Anon., Asia Pulse, 20/ 12/ 2000. 47 Anon., ‘Dawn of a new era as wool industry prepares for high grade output’, Wool Record, 1997, 156, (3638), 55. 48 Anon., ‘China to overhaul cotton industry and upgrade woollen sector’, Wool Record, 1998, (3641), 39 49 Graham J F and Kilduff P D F, ‘Textiles and Clothing in India: Current Developments and Future Prospects’, London, Financial Times Management Reports, December 1994. 50 Anon., ‘Innovations in the quest to make wool more competitive’, Wool Record, 1999, 158, (3651), 33 51 Carnaby G, ‘Nonwovens as a radical new future for wool’, Wool Record, 157, (3645), 39 52 Anon., ‘Wool nappies booming in the USA’, Medical Textiles, 1999, December, p5 53 Anon., ‘New technologies offer significant market potential’, Wool Record, 1999, (3657), 43. 54 Liddle J, ‘Mission to inform’, Wool Record, 1999, (3657), 17. 55 Anon., ‘The vexed issue of wool marketing’, Wool Record, 2000, (3664), 1. 56 Anon., ‘Putting wool back on the shelves’, Wool Record, 2000, (3667), 1. 57 Anon., ‘Storms ahead so someone must take the tiller’, Wool Record, 2000, (3668), 1 58 Peter P, ‘Ageing of America’, Wool Record, 1998, 157, (3639), 19.

Index

A-layer, 70 abrasion resistance, 260 absorption of water, 80– 4 acid cracking, 47, 50–1 acid hydrolysis, 141–2 acid levelling dyes, 243–4 acid milling dyes, 245 acids, absorbed by wool, 135–7 aerobic/anaerobic treatments, 52 afterchrome dyestuffs, 242, 243 ageing, 104–5 air quality, 303 air-jet weaving, 275 airflow method, 14 ‘airless’ drying, 42 alcohol destabilisation, 51–2 alizarin, 239 alkalis, 137–9, 142–3 Allwörden membrane, 70 aluminium, 149, 228 amide groups, 142 amino acids, 61, 130 analysis, 141–2 and formaldehyde, 153–5 oxidation of, 143–4 in wool, 62, 63–4, 65, 131, 133 ANDAR scouring, 30–1, 39 anthraquinone, 239 antistatic treatment, 224–5, 303 artificial fibres, 1, 337, 342–8 Ashenhurst, Thomas, 272 auctions, 10–11, 12 Australian Wool industry, 1, 2, 3, 7 autolevellers, 178–9 automatic winding, 265

360

Axminster weaving, 292–4 azo dyes, 255–6 backwashing, 173–4 baking, 41 barré, 287 batch crabbing, 315 batch scouring machines, 317 batt, 306 beam warping, 268 beating, 41 beetles, 217 benchmarks, 1, 336 bicomponent spinning, 201–2 Biochemical Oxygen Demand (BOD), 50 blankets, 349 bleaching, 41, 145, 215–16, 237 blending, 23–4, 183, 186, 293–4 blends, 240, 251, 298 for felts, 305 bonding, 301–2, 310–11 bound yarn, 201–2 break load, 97–9, 100 Brierley (setting theory), 272–3 brightness index, 15–16 British Wool Marketing Board, 8 Brussels weaving, 294 bulk testing, 16 burr beaters (carding), 165 carbohydrates, 67 carbonising, 22, 39–41, 182, 232, 246, 319–20 carcinogens, 255–6

Index carder, 185–6 carding, 163–9 actions, 164–6 feeding, 184–5 quality of, 166–8 in semi-worsted processing, 180–1 speeds, 168 in woollen processing, 184–8 carding wools, 182 carpets, 125–6, 180, 290–304 and antistatic treatment, 224, 225, 303 and colour fastness, 252 deterioration of, 303–4 hand knotting, 291 and insect-resist treatments, 219 performance features, 302–4 and photodegradation, 227–8 physical behaviour, 125 and polymer grafting, 231 shading, 125, 303–4 tufting, 290, 291 wear, 126, 303 weaving, 291, 292–7 wools, 3, 7, 13, 14 cell membrane complex, 67, 107, 116–17 cellulosic materials, 251 central wool facility, 9–10 Cerifil spinning system, 205 Chapman model (fibril-matrix composite), 108–14 Chemical Oxygen Demand (COD), 50 chemically bonded fabrics, 310–11 China, 1, 353, 354–5, 356 chlorine and antistatic treatment, 224 and oxidation, 145 and shrinkproofing, 220–1, 222, 223 chlorine/Hercosett process, 327, 332 chromium, 243, 245–6 and environment, 254, 255 circular knitting machines, 279–82 ‘Clip Cone’ system, 262 cochineal, 239 cockling, 285, 308, 330–1 colour, 15–16, 271 fastness, 252

361

reversion, 216–17 stability, 226–7 combing, 161–3, 171–3 brushes, 172 quality, 173 rectilinear comb, 171, 172 compact (condensed) spinning, 200, 201 complete garment, 279, 288 computer blend selection, 18 computer control, 277–8, 326 Condensers (carding), 188 conditioning, 325–6 consumer awareness, 355 consumers, health and safety, 253 contaminants, 21–2, 37–8 see also scouring continuous crabbing, 316 conveyor dryer, 42–4 copper, 148–9 Core Bulk Test, 16, 18 core sampling, 6, 12 cortex, 67, 69, 70–2, 114–16 Cott Opener, 28 cotton, 290, 334, 337, 348 ‘Cotton machines’ (‘Cottons Patent’), 276 Cotton, William, 276 crabbing, 314–16 see also setting creases, 145, 233, 327 creep, 90, 92, 93 crimp, 95, 114–16, 174, 195 Crompton, Samuel, 190 crossbred wool, 3, 13 crosslinking, 61, 62, 107, 130, 151–6 and damage repair, 151–2 and dialdehydes, 155 and formaldehyde, 152–3 tests for, 152 crushing of vegetable matter, 41 CSIRO, 2, 7, 84 cut and sew knitwear, 288 cut-pile carpets, 299 cuticle cells, 67–70 cutis, 70 Cyclic Openers, 28 cylinder crabbing machines, 316 cysteine, 217

362

Index

cystine (CYS), 61, 107, 130 and insect-resist, 217 and metals, 148, 149 oxidation of, 143–4 reacts with alkalis, 138, 142–3 reductive cleavage, 145–6 dark fibre contamination, 16 de Smet scouring process, 45 decatising, 323–5, 330 batchwise decatising, 323, 325 continuous pressurised machines, 325 continuus steam setting, 324 pressing/decatising machines, 324 pressure decatising, 323– 4 Delay Factor, 186–7 design, 259, 270–3, 279 desuinting, 34 detergent, 33–4, 317 dialdehydes, 155 diazonium salts, 151 dichloroisocyanuric acid (DCCA), 221 dieldrin, 218 dielectric constant, 118–19, 120 dimers, 73–6, 77 direct selling, 7 directional frictional effect (DFE), 105–6, 220 dirt, 21, 22 discolouration, 132 disposal, 253 doffing (carding), 188 double jersey machines, 281–2 double-rove spinning, 198–9 doubling (spinning preparation), 178 doublings (fully fashioned knitwear), 276 drawing, 177–80, 181 drawing-in (warp threads), 268–70 drum openers, 26–7 drying, 40–1, 42–5, 320–1, 329 Drysdale sheep, 7, 14 Duhamel process (scouring), 35 dumping, 9–10 durability, 303 Duralite carpets, 297, 298 dusting of wool, 25–9 dyeing, 139–41, 237–57 dyebath ionic strength, 137, 138

and shrink-resist process, 241 stages in production process, 240–1 for tufted carpets, 298–9 uptake chemistry, 140–1 variations in substrate, 249 and wool morphology, 139–40 and yellowing, 216–17 dyes classification of, 242–7 commercial forms, 247–8 natural, 238–9 Dylan treatments, 222 East Europe, 351, 352 easycare properties, 240, 326–7, 332 eco labels, 253 effective fineness, 196 effluent, 36, 49–55, 253, 255 components, 49–50 primary treatments, 50 secondary treatments, 50–3 tertiary treatments, 53–4 total treatments, 54–5 elastic recovery, 86–8, 89 elasticity, 260 electrical resistance, 119–21 electronic control, 188 ‘emission protection ordinance’, 253 energy conservation, 56, 326 environmental concerns, 6, 21, 252–6, 326 and dyeing, 238 in Germany, 253, 352 and insect resist treatments, 218–19 and scouring, 36 and shrinkproofing, 223 enzymic hydrolysis, 143 epicuticle, 69 esterification, 151 European wool industry, 351 evaporation, 53 fabric cockling, 285, 308, 330–1 density, 285 design, 270–3 faults, 285–7 mechanics of, 123–5 production, 339, 341

Index quality, 284–7 spirality, 285, 287 structure, 271–3, 282–4 face-to-face weaving, 296–7 ‘fancy’ twisting, 262 farm management, 6 fast acid dyes, 244–5 Fearnought, 29, 183 feed in carding, 184–5 feed-hoppers, 26 felting, 122, 125, 155, 219, 326 and fibre morphology, 219–20 felts, 300–1, 304–7 quality indicators of, 306–7 uses of, 305 Fernmark brand, 19 Feughelman, Max, 84 fibre bending behaviour, 92–7 breakage, 101, 116, 166, 167, 169 in combing and carding, 173, 186 consumption, 334 diameter, 13–14, 195 failure in, 101, 116 friction, 105–6, 107, 117–18, 220 length, 14–15, 167, 195 morphology, 60–79 opening, 186 properties when processing, 190–2, 197 protection in dyeing, 256 separation, 186 strength, 97–101, 116–17 torsional properties, 95, 98, 99 in yarn cross-section, 195 see also wool fibril-matrix composite, 108–14 free-energy diagram, 108–9 finishing, 314–32 of knitted fabrics, 328–30 of woven fabrics, 314–28 see also individual finishing procedures e.g. milling, carbonising flame-retardant properties, 225–6, 302, 308 flat knitting machines (‘flatbeds’ or ‘V-beds’), 277–9, 288 flat-woven carpets, 297–8 fleece fabrics, 281

363

Fleissner suction drum scouring bowl, 30 floating fibres, 178 flokati rugs, 295 flow patterns, 10, 11 flyer roving frame, 180 folding, 206–7 follicle, 74 formaldehyde, 152–5 France, 352 friction of wool, 105–6, 107, 117–18, 220 friezé texture (tufted carpet), 299 fully fashioned knitwear, 276–7, 288 garment manufacture, 287–8 gauge, 286, 288 circular knitting, 280, 281 flat knitting, 277 fully fashioned knitwear, 276 genomics, 76 gilling finisher, 175 preparer (intermediate), 169–71, 173 globalisation, 335–6, 349–55, 356 and developing countries, 354–5 and industrialised nations, 350–4 and migration patterns, 350–1 glutaraldehyde, 155 governments and globalisation, 335–6 grab sampling, 12 gripper-jacquard system (Axminster weaving), 292 guaranteed price system, 349 hand knotting, 291 hard water, 35 Hauteur, 168, 171, 175–7 health and safety, 218, 253 heat of sorption, 82–4 herringbone effect, 271 hydroentanglement, 309–10 hydrogen bonds, 62, 107, 110, 315 hydrolysis, 141–3 hydrophilic groups, 82 impurities, 21–2 India, 291, 342, 355 insect-resist treatments, 41, 217–19 integral knitting, 279

364

Index

interlock fabric, 283– 4 Intermediate feed, 187 intermediate filament (IF), 106, 108, 115, 116 International Wool Secretariat (IWS), 3, 18, 348 International Wool Textile Organisation (IWTO), 2, 9, 11, 337 intersectors (gilling), 170 iodination, 150 irregularity index (I), 196 Italy, 351–2 IWTO Draft Test Method, 15 Japan, 54, 353 kapok, 312 keratin associated proteins (KAP), 60, 67, 72, 74 keratin-intermediate filaments (KIF), 60, 67, 72, 74 keratins, 60, 75, 106–7 amino acid composition, 131 degradation of, 227 keto acids, 216 knitted fabrics, 328–30 knitting, 275–89 and carpet manufacture, 302 circular knitting machines, 279–82 flat knitting machines, 277–9 fully fashioned, 276–7 yarns, 180, 264, 349 knitwear, 275–289, 330–2 lagooning systems, 53–4 landfill disposal, 54 lanolin, 47, 48, 62 laser-scanning devices, 14, 16, 18 ‘length after carding’ test, 15, 17, 192 levelling auxiliaries, 249, 250 levelness, 243–4, 248–51 and machinery, 249–50 lifestyle changes, 239–40, 336, 348–9 lipids, 62–7, 70 and dyeing, 139 Lo-Flo process (scouring), 36–7 load-extension properties, 84–6 London Shrinkage process, 322

loss factor, 118–19, 120 lubrication, 208 in gilling, 170 in woollen carding, 183–4 Lycra, 201, 240 machine washability, 326–7, 332 macrofibrils, 67, 71, 72, 115 man-made fibres, 1, 337, 342–8 manual winding, 265 manufacture of wool products, 258–89 marketing, 18–20 matrix stress, 110–12 mechanical properties of wool, 84–106 medullation, 18 mercury, 147–8 Merino wool, 2, 3 and cleaning, 34–35 and dark fibres, 177 fibre diameter, 13 and niche marketing, 20 metal complex dyestuffs, 245–7 metal ions, 35 metal-wool reactions, 147–50 18- methyl eicosanoic acid (18-MEA), 67, 69, 70 Mexico, 353 microfibrils, 67, 71, 72, 115 milano fabric, 284 milling, 318, 319 mineral salts, 67 moisture absorption, 80–4 and crimp, 116 in gilling, 170 removal, 40 mordant dyes and mordants, 239, 243, 254 Morel rollers, 165–6 moths, 217 mule spinning, 190, 191 multi-purpose finishes, 229–30 NAFTA, 353 Near Infra Red Analysis (NIRA), 17–18, 56 needled and needlepunched fabrics, 125, 307–9 floorcoverings, 308

Index in horticulture, 309 and waste trade, 308 Nepal, 291 neps, 166, 168, 171, 174, 181 neutralisation of acid, 41 New Zealand, 1, 2, 3, 10 and carpet wool, 290–1 and wool colour, 15 ninhydrin, 150 noil, 168, 171, 173, 174, 182 nonwoven materials, 307 nucleic acid, 67 nylon, 251–2, 290, 300, 348

polypeptides, 60, 61 polyurethane elastomeric fibre, 251 polyurethane resin, 327 potassium permanganate, 221–2 pre-carding, 182–3 preheating, 24–5 pressed felts see felts pressing, 322–3 process control, 55–6, 250 projectile weaving, 273 proteins, 61, 65, 72, 74 degradation, 137 structure, 72

on-line colour monitoring, 17 open-width scouring machines, 318–19 opening of wool, 25–9 Optalyser (wool grading), 177 ortho-cortex, 114–16 oxidation, 143–5, 215, 224

quality control, 55–6, 151, 188 dyeing, 238

packages, 266 pairing twist, 203 Parafil, 262 patterns, 270–2, 279, 298, 300 peptidyl shift, 232 peracetic/ammonia test, 144 Peralta rollers, 186 Perendale sheep, 20 performic acid/ammonia test, 152 permethrin, 218 permonosulphuric acid, 222, 327 pH control, 250–1 pharmaceutical and cosmetic industries, 48 photobleaching, 132–4, 226–7 photochemical damage, 131–5, 226–7 photostabilisers, 226–8 photoyellowing, 134, 226–7 pile, 303, 321 plain weave, 270 pleats, 145, 233 Plyfil spinning system, 206 plying, 206–7 pollution, 49, 150 polyester, 251, 348 polymers grafting, 230–1 and shrinkproofing, 222, 223–4

radiation, 131 raising, 321 rake systems (scour bowls), 30 rapier weaving, 273–5 flexible rapier machinery, 274–5 rigid rapier machinery, 274 ‘ratchet mechanism’, 220 reactive dyestuffs, 247 recombing, 174, 209 recovery behaviour (elastic), 86–8 reduction, 145–6, 215 regularity, 259 relaxation, 322, 329–30 rib fabric, 283 ring spinning, 189, 192–7 and yarn properties, 197 ring twisting, 261 Roberts, Richard, 190 rollers (drafting), 177–8 root tip differences, 249 Rovingtex (slubbings), 188 rubber elasticity curve, 110, 111 rubbing-frame, 179–80 Russia, 1, 351 safety, 218, 253, 302–3 sampling and testing, 2, 3, 8, 9 methods, 11–18 Sandolan MF dyes, 244 scale masking, 222 scales, 117–18, 122, 219–20, 326 Scotch feed, 187

365

366

Index

scour bowl design, 29–32, 36 Scour Waste Integrated Management System (SWIMS), 51 Scoured Wool Cleaners, 28–9 scouring, 9, 21–41, 316–19 aqueous jet, 29–30 and bleaching, 216 by solvents, 45–6 and carbonising, 232 chemistry of, 33–5, 39–41 development of, 35–9 and effluent treatment, 50 and energy conservation, 56 and insect-resist treatments, 219 methods reviewed, 22–3 and photoprotection, 227 process control/quality assurance, 55–6 and testing, 17–18 scouring train, 29–32 scribbler (carding), 185 ‘scutching’, 318 sectional warping, 267–8 self-twist spinning, 202–4 semi-worsted processing, 162, 180–1 sett (fabric structure), 271–3 setting (in fibres), 104–5, 122, 232–3, 314–15 explained, 112–14, 233 and twist, 266 shearing (of fibres), 321–2 shearing (of sheep), 5 sheep husbandry, 1–3 Short Wool Processor, 28 shrinkproofing, 219–24, 240 and dyeing, 241 silver, 148 singeing, 322 single jersey, 281, 282–3 machines, 280–1 Sirolan CF, 51 Siroscour, 34, 37–9 Siroset, 233 Sirospun, 198–9, 260–1 sisal look, 297, 300 sizing, 260 skin, 70 sleep, 311–12 sliver formation, 160

slubbings, 160, 188 Solospun, 200–1, 260–1 solvent carbonising, 320 solvent scouring, 45–6 South Africa, 2, 8, 22 specific heat of wool, 102 spin-twist, 198–9 spinning, 189, 192–206 preparation for, 160, 177–80 splicing, 208 spool-gripper system (Axminster weaving), 292 spraying devices, 170 squeeze rollers (scouring), 32–3 stainblocking, 228–9 staining tests, 151 standardisation, 1, 336 static electricity, 121–2, 224–5, 303 steaming, 208 stenter, 320–1, 329 stitch density, 285 stitch distortion, 285 stratum corneum, 70, 76–7 stress relaxation, 89, 90, 91 stress-strain curves, 85–8, 89, 95, 99 and alcohols, 86 at different humidities, 114 and fibril-matrix composite, 109–10, 111, 113 for rovings, 123, 124 and setting, 104–5, 112–14, 115 and thermal properties, 102–4 structural mechanics of wool, 106–18 STRUTO fabrics, 310–11 substrate and levelness, 248–9 suction drum dryer, 42, 43 suint, 21, 22 sulphitolysis, 146–7 sulphonated dyes, 246 sulphur, 61, 62, 65, 70 sulphuric acid, 40, 41, 50–1 Sulzer Brothers (projectile weaving), 273 sunlight, 131, 132, 226–8 super-fine wool, 13 supercontraction, 103, 105, 109–10 superheated water crabbing machines, 316 surfactants, 224

Index swelling behaviour of wool, 82 Syntans (stainblocking), 229 Synthappret (polymer treatment), 223– 4 synthetic fibres, 1, 337, 342–8 tanning, 155 tear ratio (combing), 173 tensile curves, 94, 96 tensile fracture, 99–101 tenter, 320–1, 329 terry loop, 281 test houses, 7–8 testing and photodegradation, 228 for shrinkproofing, 224 and staining, 229 textiles consumption, 334–6 globalisation, 333–6, 350–6 production patterns, 356 production rationalisation, 351 regional trading blocks, 335 texture, 298 thermal properties, 102–4 thermally bonded fabrics, 310–11 top dyeing, 208–9 finishing, 175 production, 338–9 properties, 175–7 Topmaker software, 177 torsional properties, 95 ‘Total Carding Power’, 181 Total Easy Care knitwear, 332 Treotek spinning system, 205 1,1,2 trichloroethylene (TCE), 46 Tritec, 262, 263 TRP (aromatic acid), 134, 135, 141, 142 tufting, 260, 290, 291, 298–300 Turkey, 291, 342, 353 twist, 95, 96, 98, 99, 179 and crimp, 115, 116 setting, 266 and spinning, 189, 194, 201, 202–4 and stress-strain curve, 122–3 twisted self-twist, 203 twisting, 206–7, 258–64 machinery, 261–4

367

need for, 259–61 and quality, 260 and weaving, 260 and yarn structure, 264 two-for-one twisting, 206–7, 261–2 two-phase model, 108, 109 two-stage twisting, 262 two-strand spinning (twin-spun), 198–9 ultrafiltration/microfiltration, 52–3 Unidryer, 44–5 United Kingdom, 8, 352–3 upholstery, 180, 227–8 vegetable matter (VM), 22 and carbonising, 39–40, 232, 319–20 and carding, 163, 169 and combing, 171 test, 17 velour, 298 Very High Speed Carding (VHSC), 168 visco-elasticity, 114 warp knitting, 275–6 warp preparation, 266–9 warp yarns, 269 Wascator (shrinkproof testing), 224 waste fibres, 182, 307–8 water in hydroentanglement, 310 quality, 35 in wool processing, 253–5 waxing, 208 see also lubrication weave density, 271–3 weaving, 269–75 and design, 270–3 machinery, 273–5 and twisting, 260 warp preparation for, 266–9 yarns, 264, 269 web, 306 weft yarns, 269 wet finishing, 328–9, 330 Wilton carpets, 294, 295 winding, 207–8, 264–6 wireloom weaving, 294–5

368

Index

wool acid/base behaviour, 135–9 analysis of, 141–3 brokers, 6 chemical composition, 61–7, 131 chemical reactions, 130–59 classification of, 5 consumption, 337 declining importance of, 342–9 defined, 60 degradation, 131–2 electrical properties, 118–22 exporters, 8–9 harvesting, 5 imports and exports, 342, 343–7 manufacture of products, 258–89 mechanical processing, 160–1 mechanical properties, 84–106 oxidation, 143–5, 215, 224 packaging, 10 physical properties, 80–129 production, 3–5, 337–42 promotion, 18–19 reacts with metals, 147–50 structure, 67–76, 80, 81 thermal properties, 102–4 trade, 1, 333–59 see also fibre wool damage assessment, 142 woolgrease, 21–2, 46–8, 62 recovery, 46–7, 48 uses, 48

woolgrowers, 5–6 woollen processing, 162, 181–92, 331 Woolmark, 3, 19, 355 woolscouring see scouring Wooltech system, 46 worsted processing, 161–80, 330 wrap (hollow spindle) spinning, 204–5 wrinkling, 104 WRONZ comprehensive scouring system, 36 yarn and fibre properties, 197 fibres in cross-section, 195 formation, 160 irregularity, 196, 285 jointing, 265–6 packages, 266 physical properties, 122–3 production, 160–214, 339, 340 steaming, 208 structure, 264 tension, 194 weaving characteristics, 269 yellow wool components, 134–5 yellowing, 132, 225–6 in dyebath, 216 yellowness measurements, 15–16 Zirpro process, 225–6, 229, 230