Fundamentals and Practices in Colouration of Textiles, Second Edition

561 Pages·2014·27.89 MB·English

by  Chakraborty, J. N

Fundamentals and Practices in
Colouration of Textiles
Fundamentals
and Practices in
Colouration of Textiles
Second Edition
J N Chakraborty
WOODHEAD PUBLISHING INDIA PVT LTD
New Delhi
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First published 2010, Second edition published 2014
© Woodhead Publishing India Pvt. Ltd., 2014
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Preface
Colouration of textiles is an art and less complicated than actually thought;
just needs due attention to ascertain look, quality and consistency in product.
Each textile is coloured with specific colourants through its own technology.
Thorough realization of basics of colouration is the basic need to achieve that.
This book is an attempt to explain basics of colouration with a match in practi-
cal application precisely but in detail. Effective technical excellence can be
achieved in dye houses only if the dyer has adequate skill to run the shop-floor
with a grip over it. It is common in all dye houses to face typical new prob-
lems on every new day, which adds on to the daily experience; and certain part
of dyed textile comes out as faulty dyeing. Fundamental knowledge is a tool
to reduce these faults, save money and makes the dyer capable of handling
critical situations in dyeing. With implementation of ISO, tremendous pres-
sure has been felt to produce quality products and to remain in rhythm with
highly competitive global market.
It was realized since long to have a text book in chemical processing
of textiles, which can cater needs of industries, academicians, and to shape
potential technicians. To materialize it, dye and chemical manufacturer’s rec-
ommendations have been introduced to make the book practically healthy.
However to limit its volume, textile fibres of prime importance only have
been focused in detail. This is purely a text book; references supported at
places are to help readers to know more if they desire so. Chapters have been
made precise and compact; even a small chapter covers related area with full
depth.
Any suggestion from its readers to upgrade and to make it more meaning-
ful and reader friendly will be duly acknowledged.
J N Chakraborty
June, 2009
Acknowledgement
The book ‘Fundamentals and Practices in Colouration of Textiles’ covers a
large spectrum in colouration; basically nurtured and shaped by researchers
throughout the world. Author is thankful to them for their sincere contribution
to script this book.
Author duly acknowledges with thanks the permission extended by
international leading textile organizations, viz. Society of Dyers & Colour-
ists (SDC, Bradford), American Association of Textile Chemists and Color-
ists (AATCC, USA), Melliand Textilberichte GmbH, The Textile Institute
(Manchester), Indian Institute of Technology (IIT, Delhi), Ahmedabad Tex-
tile Industries Research Association (ATIRA, India), Northern India Textile
Research Association (NITRA, India) to reproduce required texts, figures and
tables from their published journals and books.
Author also expresses thanks to publishers of Indian Journal of Fibre &
Textile Research (Delhi), B I Publications (Delhi), Colour Publications Pvt Ltd
(Mumbai), The Indian Textile Journal (Mumbai), Prentice Hall of India Ltd
(Delhi), Sevak Publications (Mumbai), The Textile Research Journal (USA),
for their kind permission to reproduce some material from their publications.
Author duly acknowledges permission extended by globally reputed
manufacturers of dyes, chemicals and apparatus, viz. Atlas (USA), Atul Ltd
(India), Dystar (Germany), ICI (UK), Jaysynth Dyechem Ltd (Mumbai) to
incorporate their technical recommendations in this book to make it practi-
cally so meaningful. However, Figure 21.1 was originally reproduced from
ICI manual; when communicated, ICI confirmed that the technology was sold
to Croda, but personalities in Croda could not find the same within their right.
On further communication to ICI, they observed silence. The technology of
indigo dyeing was originally developed by BASF (Germany) and was later
transferred to DyStar.
Some reproductions have been made from the book ‘Dyeing & Chemical
Technology of Textile Fibres’ by E R Trotman, sixth edition, which was pub-
lished by B I Publications Delhi, 1994; however the publisher has intimated
Acknowledgement xxi
that it has the right of reprint and not the copyright, which was with Charles
Griffin Co. Ltd, UK. Trying best, author could not find contact details of the
Charles Griffin Co. Ltd. Author also sent letters and e-mails to ITS Publishing
(International Textile bulletin, Switzerland), Verlag Konradin Verlag Robert
Kohlhammer GmbH (Textile Praxis International, Stuttgart), Oliver & Boyd
(UK), Thomas Nelson & Sons Ltd (UK) but in vain. Author draws attention of
these publishers to communicate him to include their names in its forthcom-
ing edition.
This book was composed throughout a long period, during which author
had misplaced a very few research papers after inclusion of specific table or
figure and could not recollect the source. Author requests various publishers,
researchers and manufacturers to please communicate him with proof to make
required correction in the next edition of this book.
Author extends thanks to Woodhead Publishing India for their interest to
publish this book and to others who had helped in preparing manuscript of
this book.
J N Chakraborty
June, 2009
Preface to the second edition
The second edition of the book ‘Fundamentals and Practices in Colouration in
Textiles’ is now being released with an in-depth vision on few of the chapters.
In its maiden version, only the basic technology involved in chemical process-
ing of textiles was explained. It was realized to put more depth to few of the
chapters in the second edition. At the same time, four new chapters, viz. Dye-
ing with Natural Dyes, Differential Coloured Effect in Dyeing, Enzymatic
Dyeing of Textiles, and Synthesis of Dye Intermediates, are being introduced
to make the book useful for a large spectrum of readers.
Because of the environmental pollution caused by synthetic dyes, natural
dyes are getting preference in colouration in spite of possessing few inherent
drawbacks and under debate on their eco-friendliness. The chapter highlights
classification, structure, colour index specification as well as various aspects
of dyeing with natural dyes.
Dyeing does not necessarily imply production of levelled mono-coloured
shades. A large number of designed mono-coloured shades could be produced
by manipulating dyeing technology; even multi-coloured effects can also be
easily developed on textiles. This is essential to stay in the modern day textile
and apparel market and to enhance colour appeal.
Application of toxic chemicals substantially increases waste water load
and kills aquatics; this could be reduced drastically if enzymes are introduced
to substitute these toxic chemicals. Even, enzymes can increase dye uptake
thus reducing draining out of unused colour at the end of dyeing, or alternately
reducing requirement of dye for a given shade.
Dyestuffs are not directly synthesized rather manufactured from dye
intermediates because synthesis of a single intermediate can help to manufac-
ture a number of dyes. The new chapter summarizes synthesis of few impor-
tant intermediates.
It is expected that this new edition will be more informative and helpful
for its readers.
J N Chakraborty
January, 2014
1
Introduction to colouration of textiles
Abstract: Dyeing is a process of thorough colouration of textiles, and its
success lies on the type and extent of pretreatment imparted to develop good
absorbency as well as whiteness. Various influencing factors during dyeing,
such as pH, form of textile, type of fibre, formulation of dyeing recipe, prepa-
ration of dye solution, liquor ratio, selection of machinery, etc., also, play a
crucial role in development of levelled shades with least effort and cost. Right
programming of the dyeing schedule and scientific approaches for recipe for-
mulation as well as addition, if required, are the other keys to avail maximum
utilization of machineries, workforce, power and finally delivery of the prod-
uct to the market at the right time. This chapter highlights these basic concepts
for effective implementation of technology of dyeing.
Key words: pretreatment, absorbency, dyeing, surface dye strength
1.1 Importance of pretreatment
Textiles are dyed in three different forms, viz. fibre, yarn and fabric (knitted/
woven), and the methods include either of exhaust/batch or padding. Thor-
ough colouration in exhaust method involves a sequential mechanism, e.g.
migration of dye from bath to fibre surface, adsorption of dye on the surface
of fibre and diffusion of dye inside followed by fixation. It is essential to con-
firm complete absence of impurities in fibre to ensure formation of levelled
shades. If impurities are hydrophilic in nature, an efficient wash prior to dye-
ing removes these impurities and facilitates effective deposition of dye on
surface of the fibre (the first step). Absence of impurities inside fibre keeps
fibre pores clean to give a passage to dye, so that it can migrate inside. In fact,
the impurities are mostly hydrophobic in nature and hinder surface deposi-
tion, adsorption and diffusion, which finally results in an uneven dull light
shade with very poor wash and rubbing fastness in spite of higher concentra-
tion of dye. If dyeing technique is changed to padding, affinity of dye does
not play crucial role as dye is forcibly placed on textile avoiding the problem
2 Fundamentals and Practices in Colouration of Textiles
associated with the first two steps, i.e., migration of dye from bath to fibre
and surface deposition, but presence of impurities at the interior will suppress
adsorption as well as diffusion both, which is irrespective of dyeing method,
because presence of impurities is bound to resist formation of levelled and
fast shades. Further, a pale shade can only be formed on a good white ground,
but since different textiles possess their own inherent colours they require
prior bleaching. This has necessitated pretreatment of all textiles to acquire
required absorbency and whiteness prior to dyeing.
1.2 Types of impurities
Impurities, present in various textiles, are of two types: natural and added.
Natural fibres like cotton, wool, silk, etc., are grown under natural conditions,
during which these fibres acquire natural impurities like dirt, dust, minerals,
fatty matters, etc. Manmade fibres, such as polyester, nylon, acrylic, etc., are
industry made and do not possess natural impurities but acquire impurities,
such as machine oil, grease, etc., during various processes; impurities that are
externally added like spin finish are called added impurity. All natural fibres
also collect little added impurity during mechanical processing imparted and
obviously retain collectively more impurity requiring a drastic pretreatment
for effective removal to develop a wetting time around 5 s. As a routine test,
a drop of water is allowed to fall on scoured cotton to disappear inside within
this time possessing good absorbency. Manmade fibres retain little added
impurity and a mild pretreatment is adequate.
1.3 Types of pretreatment
The pretreatment process is not same for all fibres due to difference in their
properties, variation in composition and percent and type of impurity content.
Cotton is singed first to remove protruding fibres, which otherwise hinder
formation of brilliant shade due to enhanced scattering of light. Cotton warp
is sized to protect it from damage during weaving but requires its subsequent
removal to allow diffusion of chemicals and dyes. Presence of natural as well
as added impurities, which are hydrophobic in nature, impairs absorbency,
and the wettability remains too poor to exercise any successful dyeing. This
necessitates scouring of cotton with an aim to improve absorbency with least
fibre damage – purely a purification process. Scoured cotton is bleached to
make it whiter – essential to build-up brilliant shades – and finally bleached
cotton is mercerised to improve its lustre and chemical reactivity or dyeabil-
ity. If cotton is to be marketed as full bleach where absorbency is of least
Introduction to colouration of textiles 3
importance, thorough scouring may be avoided but double bleach is to be
introduced instead.
Wool retains grease, stain, suint, etc., which are hardened during singeing
and pose problem in removal during scouring. Wool is carbonised first with
acid to eliminate cellulosic impurities, such as leaves, grasses, etc., followed
by removal of stain with the help of a solvent; either singeing and/or crop-
ping are imparted to burn or cut protruding fibres, respectively (Peters, 1967;
Karmakar, 1999). If cropping is to be imparted and not singeing, then that
may be done at any stage before dyeing. However, fabric may get distorted
during cropping and hence singeing is preferred (Sule, 1981). Woollen yarn
is preferred in knitting and is not sized. Fabric structure is stabilised through
crabbing or blowing to avoid distortion followed by mild scouring to remove
impurities at 55–60°C; H O bleaching is imparted for required whiteness.
2 2
Silk is composed of sericin and fibroin; sericin forms the outer layer as
protective coating while fibroin remains at the interior and is the fibrous part.
Silk yarn is made of filaments and do not require sizing, hence singeing and
desizing both are omitted. A well-controlled degumming with very mild alka-
line soap at boil is imparted to remove sericin effectively and to make the fibre
highly absorbent. Degumming of silk with boiled-off liquor which comes
from the spent bath from previous degumming process is the most efficient
method of degumming. Bleaching is done with H O at 70°C.
2 2
Manmade fibres, such as polyester, nylon and acrylic retain mainly added
impurities. Thermoplastic fibres, like polyester and nylon, are not singed at
the initial stages as protruding fibres may melt to form molten beads which
traps impurities as well as leads to sizing of materials inside and also cause
hinderance in its removal during subsequent treatments. The beads formed
accept more dye causing specky dyeing. It is better to start pretreatment with
desizing; singeing may be imparted in post-colouration stages. Both, polyes-
ter and nylon fibres are scoured in mild alkali followed by chlorite bleaching
(NaClO ); presence of chlorine in sodium chlorite reduces elastomeric nature
2
of nylon, and a peracetic acid bleach is the most preferred option. Polyester
is preferably dry heat set for structural stabilization while nylon is steam set.
Acrylic, on the other hand, is not sized, as its main use is knitting; mild scour-
ing, chlorite bleaching and stabilization by autoclaving at 105°C with steam to
develop bulkiness completes its pretreatment. However, a modified sequence
comes into effect when different textiles are blended: the sequence of pretreat-
ment depends on share of component fibres in that blend, impurity content
of component fibres, whether any of the components were previously passed
through any pretreatments and treatment of one component should not have
negative effect on another.