Basic Principles Of Textile Coloration

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Basic Principles ofTextile ColorationArthur D BroadbentProfessor, Université de Sherbrooke, Département de génie chimique, Faculté de génie,Sherbrooke, QC, J1K 2R1, Canada2001Society of Dyers and ColouristsiiiPrelims.p65327/07/01, 10:06

Copyright 2001 Society of Dyers and Colourists. All rights reserved. No part of thispublication may be reproduced, stored in a retrieval system or transmitted in any formor by any means without the prior permission of the copyright owners.Published by the Society of Dyers and Colourists, PO Box 244, Perkin House, 82Grattan Road, Bradford, West Yorkshire BD1 2JB, England, on behalf of the Dyers’Company Publications Trust.This book was produced under the auspices of the Dyers’ Company Publications Trust.The Trust was instituted by the Worshipful Company of Dyers of the City of Londonin 1971 to encourage the publication of textbooks and other aids to learning in the scienceand technology of colour and coloration and related fields. The Society of Dyers andColourists acts as trustee to the fund, its Textbooks Committee being the Trust’stechnical subcommittee.Typeset by the Society of Dyers and Colourists and printed by Thanet Press Ltd, Kent.ISBN 0 901956 76 7ivPrelims.p65427/07/01, 10:06

ContentsPrefacexiiiCHAPTER polymers50Synthetic fibresSynthetic fibres 50Nylon fibres 51Polyesters 58Acrylic fibres 65Other synthetic fibres 68References 69vPrelims.p6520Polymer structure 34Molecular organisation in fibres 40Intermolecular forces 42Thermal properties of polymers 45References 49CHAPTER and textiles: properties and processingProperties of fibres 20Production and properties of yarns 22Fabric manufacture 25Preparation for dyeing 29Dyeing and finishing 32References 33CHAPTER background 1Modern textiles 10Colour, dyes and dyeing 13References 19CHAPTER introduction to textiles, dyes and dyeing527/07/01, 10:06

CHAPTER 70Cotton 70Cellulose 74Cotton processing 80Other vegetable fibres 90References 91CHAPTER fibres130Water treatmentWater quality for the dyehouse 130Water hardness 132Water softening 138Boiler water 144Dyehouse effluent and its treatment 146References 151viPrelims.p6592Introduction 107Structure of wool fibres 107Physical and chemical properties of wool 116Wool processing 122Speciality animal fibres 128References 129CHAPTER made fibres based on celluloseThe first regenerated cellulose fibres 92Viscose fibre 93Cellulose acetates 102References 106CHAPTER cellulosic fibres627/07/01, 10:06

CHAPTER theoryDyeing equilibria 197Dyeing kinetics 207Aggregation of dyes 213Conclusion 214References 214CHAPTER 1212.112.212.312.412.512.6174An introduction to dyes and dyeingDyes 174Dyeing methods 177Dyebath and fabric preparation 179Terms used in direct exhaust dyeing 180Continuous dyeing 190References 196CHAPTER 1111.111.211.311.4215Dyeing machineryBasic features of batch dyeing machines 215Dyeing machines for loose fibre and sliver 216Machines for dyeing yarn 218Machines for dyeing fabric 223Dyeing machines for specific articles 233Continuous dyeing equipment 234References 239viiPrelims.p65152Impurities in textile fibres 153Surface activity of detergents 155Synthetic surfactants 164Other applications of surfactants 172References 173CHAPTER 1010.110.210.310.410.5Auxiliary chemicals for wet processing and dyeing727/07/01, 10:06

CHAPTER .1213.13General description of acid dyes 240Classification of acid dyes 241The application of acid dyes in dyeing wool 243Mechanism of wool dyeing 248Problems of dyeing wool level 251Special wool dyeing processes 255Mordant dyes for wool 257Pre-metallised metal-complex dyes 264Dyeing nylon with acid dyes 268Dyeing nylon with metallised dyes 280Light and ozone fading of acid dyed nylon 282Nylon carpet dyeing 283Dyeing modified nylons 285References 286CHAPTER 1414.114.214.314.414.514.614.7Dyeing cellulosic fibres with direct dyes307Disperse dyesIntroduction to disperse dyes 307Chemical constitutions of disperse dyes 309Disperse dye dispersions 310Fastness properties of disperse dyes 313Dyeing cellulose acetate fibres 314Dyeing nylon with disperse dyes 317Dyeing polyester with disperse dyes 319Dyeing of other synthetic fibres 330References 331viiiPrelims.p65287Introduction 287Chemical constitutions of direct dyes 288Dyeing properties of direct dyes 289The effects of variations in dyeing conditions 296The aftertreatment of dyeings with direct dyes 300Dyeing different types of cellulosic fibres 303The origins of substantivity for cellulose 304References 306CHAPTER 1515.115.215.315.415.515.615.715.8240Acid, metallised and mordant dyes827/07/01, 10:06

CHAPTER 1616.116.216.316.416.516.6The development of reactive dyes 332Reactive dyes for cotton 333Batch dyeing of cotton with reactive dyes 339Bifunctional reactive dyes 347Continuous dyeing processes for cotton 348Reactive dyes for wool 353References 357CHAPTER .1217.1317.14358Vat dyesIntroduction 358Chemical constitution of quinone vat dyes 358The reduction of quinone vat dyes 360The substantivity and dyeing characteristics ofvat dyes for cellulosic fibres 366Dyeing cotton with leuco vat dyes 369Oxidation and soaping after dyeing 372Pre-pigmentation dyeing methods 373Fastness properties of vat dyes 376Dyeing with indigo and indigoid vat dyes 376Solubilised vat dyes 378Sulphur dyes 379Batch dyeing procedures with sulphur dyes 382Continuous dyeing with sulphur dyes 386Environmental concerns 386References 387CHAPTER 1818.118.218.318.418.5332Reactive dyes388Cationic dyesIntroduction 388Chemical structures of cationic dyes 389Preparation for dyeing acrylic fibres 389Dyeing acrylic fibres with cationic dyes 391Dyeing modified polyesters and nylons 397References 397ixPrelims.p65927/07/01, 10:06

CHAPTER 1919.119.219.319.419.5Introduction 398Azoic dyes 399Application of azoic dyes 404Fastness properties of azoid dyeings on cotton 407Other types of ingrain dye 408Reference 410CHAPTER 2020.120.220.320.420.520.6427Colour measurementFactors influencing colour perception 427Light sources and illuminants 428Reflection or transmission of light by an object 431Human colour vision 436Characterisation of the CIE standard observers 438Determination of the tristimulus values of a colour 446The Munsell colour system 457Visual uniformity of colour spaces 459References 464CHAPTER 2222.122.222.3411Union dyeingFibre blends 411Union dyeing 412Dyeing cotton/polyester blends 413Dyeing wool/polyester blends 423Dyeing cotton/nylon blends 423Dyeing nylon and polyester variants 425Reference 426CHAPTER 2121.121.221.321.421.521.621.721.8398Dyes synthesised in the fibreColour differences and colorant formulationColour difference equations 465Shade sorting 473Colorant formulation 477References 492xPrelims.p651027/07/01, 10:06465

CHAPTER ction 493Flat screen printing 494Rotary screen printing 498Engraved roller printing 502Printing styles 504Pigment printing 509Printing with soluble dyes 512Transfer printing 515Carpet printing 518Thickeners 520References 526CHAPTER 2424.124.224.324.424.5527Testing of dyes and dyeingsSpectrophotometric analysis of dye solutions 527The evaluation of the colour yield of dyes 530Fastness properties of dyeings and their assessment 531Identification of dyes on the fibre 540Separation of dyes by chromatographic techniques 541References 549CHAPTER 2525.125.225.325.425.5493Printing550Textile finishingIntroduction 550Mechanical finishing methods 551Thermal finishing processes 553Chemical finishing of fabrics from cellulosic fibres 554Other types of finishing chemicals 567Reference 568xiPrelims.p651127/07/01, 10:06

PrefaceAround 1993–94 I became interested in writing a textbook on textile dyeing andrelated topics along the lines of E R Trotman’s Dyeing and chemical technology oftextile fibres, the sixth edition of which was published in 1984. This led to asabbatical leave in the Department of Colour Chemistry at the University of Leedsduring 1994–95 that allowed completion of the planning and some initial writingof this work. My original idea was to produce a book dealing with the basicprinciples of textile dyeing and related subjects. In teaching these subjects, I hadfound that the available multi-author books, published mainly by the Society ofDyers and Colourists, were often too advanced for students, and I thought that asingle book serving as an introduction to these works might be useful.I remember reading around that time that such an undertaking is partly egodriven. Over the past six years, any ideas of fame or fortune rapidly dissipated. Theconstant effort required of a single author to produce a 25 chapter book, inaddition to full-time professional work, was only sustained because of my love forthe subject and of my fascination with how dyeing takes place. The latter wasreinforced on reading once again Tom Vickerstaff’s classic book Physical chemistryof dyeing. I began to realise that, despite all the wonderful technology available fortextile dyeing, we really understand so very little of the fundamentals. I firmlybelieve that the optimum choice, use, control and adaptation of modern dyeingtechnology can only be achieved through a sound understanding of basicprinciples. This book is the fruit of my efforts to provide that understanding. It isdesigned for readers who have completed studies in chemistry and mathematics upto pre-university level. Because of the wide range of topics included, some subjectsonly receive superficial coverage. Those that are presented in more detailobviously reflect my personal bias. I am solely responsible for any limitations ofcontent or detail, as well as the invariable errors required by Murphy’s law.At the end of each chapter are a limited number of references. Some of theseare cited in the chapter text, the latter ones are usually general reading references.The interested reader will find more detailed information and references in thebooks published by the Society of Dyers and Colourists and in technicalperiodicals. In addition, several of the colorant structures shown in the book areidentified by their Colour Index Generic Name. It is worth noting that in theColour Index itself many of these structures appear as sodium salts and not in thefree acid forms shown in these pages.xiiiPrelims.p651327/07/01, 10:06

My thanks to Prof. David Lewis and the staff of the Department of ColourChemistry at Leeds for their kind hospitality during my 1994–95 leave. Thephotographs of fibre cross-sections were kindly provided by Tom Micka of DuPontFibers (Figure 4.2) and by Doug Tierce of Acordis Fibers (Figure 6.2). TheAmerican Association of Textile Chemists and Colorists (AATCC) kindly allowedreproduction of Figure 4.6. I would also like to acknowledge Greentex Inc.(Montréal), Regent Ltd. (Montréal), C A Kennedy Inc. (Montréal), Then GmbH(Germany), Macart Textiles Ltd. (UK) and MCS SpA (Italy) for dyeing machineillustrations.The completion of this book is the result of the dedicated work of the editorialstaff of the SDC, in particular Paul Dinsdale and Carol Davies, who all have mysincere gratitude.ARTHUR D BROADBENTxivPrelims.p651427/07/01, 10:06

1CHAPTER 1An introduction to textiles, dyes anddyeingThe manufacture of textiles is a major global industry. It provides vast quantitiesof materials for clothing and furnishings, and for a variety of other end-uses. Thisbook deals specifically with textile coloration. It begins by introducing this subjectalong with some technical terms and concepts related to dyes, fibres and dyeing.At this stage, mastery of all the new ideas is not necessary. They will beencountered again throughout the book.Several examples of the molecular structures of dyes will be presented in thischapter so that the reader gains some familiarity with the variations in molecularsize, shape and ionic character. Do not be intimidated by these. In due course, therelationship between the key features of the molecular structure of a dye and itsdyeing properties will be more evident.1.1 HISTORICAL BACKGROUND1.1.1 Natural dyes and fibresThe production of fabrics and their coloration precedes recorded history. Severalcultures had established dyeing technologies before 3000 BC. These ancientartisans transformed the available natural fibres – linen, cotton, wool and silk –into fabrics, at first by hand, and later using simple mechanical devices. Shortfibres were first carded or combed, to lay them parallel to one another. Drawingout of a band of combed fibres by pulling, with gradual twisting, produced yarn.Finally, yarns were interlaced to form a woven fabric. The techniques used hardlychanged until the Industrial Revolution, when they became fully mechanised.Although finely ground, coloured minerals, dispersed in water, were used inpaints over 30 000 years ago, they easily washed off any material coloured withthem. Natural dyes were extracted from plant and animal sources with water,sometimes under conditions involving fermentation. Fabric was dyed by soaking itin the aqueous extract and drying. These dyes had only a limited range of dullcolours and the dyeings invariably had poor fastness to washing and sunlight. Thefastness of a dyeing is a measure of its resistance to fading, or colour change, on1chpt1Pages.p65127/07/01, 10:07

2AN INTRODUCTION TO TEXTILES, DYES AND DYEINGexposure to a given agency or treatment. Most natural dyes also lackedsubstantivity for fibres such as wool and cotton. Substantivity implies someattraction of the dye for the fibre, so that the dye in the solution graduallybecomes depleted as it is absorbed by the fibres.The poor substantivity and fastness properties of natural dyes often improved ifthe fabric was first treated with a solution containing a salt of, for example, iron,copper or tin. The conditions used favoured combination of the metal ions withthe particular fibre, or their precipitation inside it. These metal salts were calledmordants. When the pre-mordanted fabric was soaked in a bath of a suitablenatural dye, the dye penetrated into the fibres and reacted with the metal ionspresent. This reaction decreased the water solubility of the dye so the colour wasless likely to bleed out on washing. The word ‘mordant’ originated from the Frenchverb mordre meaning ‘to bite’. In Chapter 13, we shall see that the idea of the dyebiting the mordant, to form a stable dye–metal complex, is a useful description. Inmodern dyeing procedures, the dye reacts with the mordant in the fibre in aseparate process after dyeing, or the metal is incorporated into the dyestuff duringits manufacture.A few natural dyes gave better quality dyeings of cotton or wool, but involvedlong and difficult processes. For example, the colorant extracted from madder root,from the plant Rubia tinctorium, dyed cotton pre-mordanted with aluminium andcalcium salts to give the famous Turkey Red. Using an iron mordant, the samecolorant gave a purplish-black.Indigo, extracted from leaves of the plant Indigofera tinctoria, and Tyrian Purplefrom Mediterranean sea snails of the genera Murex and Purpura, are waterinsoluble pigments called vat dyes. These do not require mordants. During thetime of the Roman Empire, wool cloth dyed with Tyrian Purple was so highlyprized that only the ruling class wore garments made with it. For dyeing withIndigo, a water-soluble, reduced form of the dye was first obtained by extractionand fermentation. The process became known as vatting, from the name of thevessels used – hence the term ‘vat dye’. The soluble, reduced form of the dye iscalled a leuco derivative. Leuco Indigo has substantivity for wool and cotton fibres.After dyeing, air oxidation of the pale yellow leuco dye, absorbed in the fibres,regenerates the dark blue, insoluble pigment trapped inside them. Because of this,the fastness to washing is very good in comparison to most natural dyes. Scheme1.1 outlines the essential steps in vat dyeing.chpt1Pages.p65227/07/01, 10:07

HISTORICAL BACKGROUNDInsoluble vatdye pigment inaqueoussuspensionreductionSolubleleucocompoundin solutionLeucocompoundabsorbed inthe fibresoxidation3Insolublevat dyepigment heldin the fibresScheme The development of synthetic dyes and fibresIn 1856, William H Perkin reacted aniline with acidic potassium dichromatesolution in an attempt to prepare the anti-malarial drug quinine. From the dark,tarry reaction mixture, he isolated a purple, water-soluble compound that dyedboth wool and silk directly when immersed in its solution. No mordant wasrequired. Perkin established a factory for the large-scale production of aniline andfor the manufacture of this dye, later called Mauveine. He not only discovered thefirst major synthetic dye, but founded the modern chemical industry.Mauveine (proposed structure 1, Figure 1.1) is a cationic dye since each of itsmolecules has a positive ionic charge. The methyl groups in the structure ofMauveine arose from the use of aniline contaminated with toluidenes(aminotoluenes). Such cationic dyes are often called basic dyes since many, likeMauveine, have free amino groups capable of salt formation with acids.H3CNCH3HNNNH2CH31Figure 1.1 Proposed structure of MauveineMauveine has some substantivity for wool and silk. Such protein fibres containboth amino and carboxylic acid groups. In a neutral dyebath, the amino groups(NH2) in the wool are neutral but the carboxylic acid groups (CO2H) dissociategiving negatively charged carboxylate anions (CO2–), associated with positivelycharged sodium cations (Na ). Under these conditions, dyeing with a cationic dyechpt1Pages.p65327/07/01, 10:07

4AN INTRODUCTION TO TEXTILES, DYES AND DYEING(Dye ) involves a process of cation exchange in which the more substantive dyecation replaces the sodium ion associated with the carboxylate group in the woolor silk (Scheme 1.2).H2N WoolCO2 Na Dye (aq)H2N Wool CO2 Dye Na (aq)Scheme 1.2Perkin even developed a method for dyeing cotton with Mauveine using tannicacid as a mordant. This polycarboxylic acid was precipitated inside the cottonfibres as a tin salt. The mordanted cotton, immersed in a solution of Mauveine,absorbed the cationic dye (positively charged), which combined with the anioniccarboxylate groups of the tannic acid (negatively charged) inside the fibres.Perkin’s achievements are all the more impressive when we consider the limitedscientific information available in 1856. This was a period of heated debate overDalton’s atomic theory; the formation of organic compounds was still believed torequire a living organism, and Kekulé had not yet proposed the hexagonalstructure of benzene (1865).Two years after the isolation of Mauveine, Peter Greiss discovered thediazotisation reaction of primary aromatic amines, which produces diazonium ions,and later, in 1864, their coupling reaction with phenols or aromatic amines to giveazo compounds. Primary aromatic amines such as aniline (C6H5NH2) are oftendiazotised by treatment with sodium nitrite (NaNO2) in acidic aqueous solution attemperatures around 0–5 C (Scheme 1.3). The diazonium cation produced(C6H5N2 ) will couple with a phenol in alkaline solution (in a similar way to thereaction shown in Figure 1.2), or with an aromatic amine in weakly acidicsolution, to form an azo compound. This coupling reaction is an electrophilicaromatic substitution, like nitration or chlorination, with the diazonium ion as theelectrophile. Today, over half of all commercial dyes contain the azo group(–N N–) and many thousands of azo compounds are known. Diazotisation andcoupling are therefore two very significant reactions.C6H5 NH2 NaNO2 2HClC6H5 N2 Cl NaCl 2H2OScheme 1.3Each molecul

15.4 Fastness properties of disperse dyes 313 15.5 Dyeing cellulose acetate fibres 314 15.6 Dyeing nylon with disperse dyes 317 15.7 Dyeing polyester with disperse dyes 319 15.8 Dyeing of other synthetic fibres 330 References 331 Prelims.p65 8 27/07/01, 10:06

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