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Practical Dyeing Volume 1 - Dye Selection and Dyehouse Support By James Park and John Shore 2004 Society of Dyers and C...

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Practical Dyeing Volume 1 - Dye Selection and Dyehouse Support By James Park and John Shore

2004 Society of Dyers and Colourists

Copyright © 2004 Society of Dyers and Colourists. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means without the prior permission of the copyright owners.

ISBN 0 901956 84 8

Contents Volume 1 – Dye Selection and Dyehouse Support Chapter 1 Globalisation of Textile Coloration and Related Industries

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Chapter 2 Impact of Dyeing And Finishing on the Environment

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Chapter 3 Services and Resources

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Chapter 4 Control, Automation and Robotics

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Chapter 5 Product Evaluation

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Chapter 6 Colour Communication, Colorimetry and Match Prediction

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Authors’ Preface The original idea of practical monographs was conceived in the 1970s as a result of an on-going debate as to what constituted a practical paper and the lack of such papers within the pages of the Journal of the Society of Dyers and Colourists. There is of course no absolute definition of a practical paper since this depends on the interests of the individual reader, location within the industry, topicality and, not least, the burning issues of the day. The Society of Dyers and Colourists attempted to rectify this lack of practical information by encouraging such papers for publication in the Journal, as well as initiating a series of practical monographs, authored by experts in various areas of textile coloration. Between the years 1981 and 1993, nine such monographs were published. Only two of these are still available: 1. Batchwise Dyeing of Woven Cellulosic Fabrics, by G W Madaras, G J Parish and J Shore (1993) 2. Instrumental Colour Formulation, by J Park (1993). For several reasons, not least the diminishing educational resources available for textile coloration, sources of practical, current information are increasingly required. This was the incentive behind the production of this practical e-book intended to assist practitioners occupying ‘hands-on’ positions at all levels within the industry. Copious recent references are included in each chapter. Two further e-books by the current authors will augment the information in this publication: 1. Dyeing Laboratory Practice, by J Park and J Shore (in preparation) 2. Dyehouse Management Practice, by J Park and J Shore (in preparation).

Chapter 1 Globalisation of Textile Coloration and Related Industries 1.1 Impact of the Oil Crisis on Global Fibres Production Although religious tradition [1] describes that, having eaten of the forbidden fruit of the tree of knowledge, man required some form of cover for reasons of modesty, it is more likely that primitive Homo sapiens required protection from the elements. In earliest times, skins and fur from animals gave some protection but skins in particular were inflexible and did not fit the body contours snugly. At some point in time, it was found that the long thin fibres from plants or animals could be twisted together and that the thread produced in this way could be interlaced to form more flexible clothing. The domestic origins of textile manufacture are lost in prehistory, but natural fibres are known to have served man’s needs for thousands of years. Recent archaeological evidence shows the imprint of woven materials on clay pots estimated to be 27000 years old, made long before settled farming and domestication of animals first began. More specific records suggest that woollen garment making began in Central Asia around 9000 BC, linen in Europe about 8000 BC and silk cultivation in China about 5000 BC [2]. Natural fibre processing remained a cottage industry until the industrial revolution in the second half of the eighteenth century. Man-made fibres were first produced at the end of the following century by regeneration of cellulose filaments from solution. Synthetic fibres began with the discovery of nylon in the 1930s, followed by polyester and acrylic fibres during the Second World War, although it was not until the 1950s that these completely new fibrous polymers achieved significant commercial use for civilian purposes. Today worldwide synthetic fibre production exceeds 28 megatons annually [3]. Establishment of the OPEC cartel by the major oil-exporting nations following the 1973 Yom Kippur war between Israel and neighbouring Arab states had a devastating immediate effect on the world’s chemical industries. The price of crude oil was increased at a stroke from US$ 3 to US$ 12 per barrel. Chemical companies were tightly squeezed by the discrepancy between the soaring costs of energy and raw materials and the declining selling prices for their finished products. New plants erected at great expense could not be filled as demand fell dramatically. These effects were aggravated further by the second oil crisis of 1979 following the fundamentalist revolution that deposed the Shah of Iran, when the oil price doubled again [4]. Operating costs had to be lowered by closing unprofitable units, laying off personnel and saving energy. World overcapacity in petrochemicals and polymers was even more serious and its effects extremely far-reaching. The 1980s saw strong growth in exports of cheap synthetic fibres, especially polyester, from Turkey, Mexico, Eastern Europe and the Asia Pacific region. Rationalisation measures were easier to organise in Japan than elsewhere because of the discipline that the trade ministry (MITI) was able to exert through a cartel that had been formed between firms producing petrochemicals. Between 1978 and 1982 a 17% cut in production of synthetic fibres was achieved, although this did not restrict the range of fibres manufactured by each producer. In Western Europe there was more regard for the principles of free competition. Bilateral arrangements between individual firms in the 1980-84 period led to the

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Practical Dyeing, Volume 1

closure of unprofitable units and increased specialisation by each producer. In the field of synthetic fibres, a European Community agreement allowed each company to specialise in certain polymer types while giving up production of unprofitable ones. Such efforts reduced the total capacity for synthetic fibres in Europe by almost a million tons. American companies were obliged to act alone during this period of global reorganisation because of anti-trust legislation. The multinational corporations tended to close down their chemical fibres and plastics subsidiaries in Europe and divert this production to their USA factories. Some petrochemicals capacity was taken over by smaller companies with lower overheads that could still operate profitably. Diversification into speciality products and cost-cutting measures allowed the reorganised major producers to survive and return to profitability in the mid-1980s after several difficult years. Strong growth in synthetic fibre capacity during the mid-1990s, particularly in the Far East, led to a sharp decline in prices, aggravating the restructuring amongst fibre producers. Chemical conglomerates in Western Europe and the USA began to develop into life science companies. Hoechst gave up fibre manufacture by selling its Trevira division. DuPont now regards life science as the apex of its business profile, although still remaining involved in synthetic fibres production [5]. World cotton prices rocketed by 60% in the early 1990s, following poor harvests in PR China and Pakistan, encouraging farmers around the world to grow more cotton. Cotton consumption boomed in the 1990s as environmental concerns grew and consumer fashion in developed countries shifted back towards natural fibres. Chinese cotton output peaked in the mid-1980s and had halved by the mid-1990s, mainly because of pesticide-resistant bollworm infestation. Cotton demand will continue to grow, as the expansion of textile and clothing exports to developed markets in Western Europe and North America will come from the largely cotton-based industries of the Indian subcontinent and the Pacific Rim [6]. Cotton and wool textiles can be regarded as biodegradable speciality products increasingly retained for finishing in growth-oriented regions and designed for export as luxury goods to the markets of industrialised nations. Synthetic textiles, on the other hand, are essentially standard products manufactured in high-tech oil-based factories by industrial economies for sale at low prices for mass consumption in developing countries [7]. The success of textile goods in the future will be dependent on life-cycle acceptability and utility from the initial raw materials through to ultimate disposal. It is widely perceived that natural fibres are environmentally benign. Whilst it is true that natural fibrous polymers are biodegradable, the negative effects of pesticides, fungicides and fertilisers used in their cultivation have often been overlooked. Synthetic fibres can take many years to be transformed into breakdown products that can be assimilated by the natural environment. Research is under way to dramatically accelerate that process by developing biodegradable fibre variants. It seems likely that synthetic fibres will only retain market share if they can be converted back to their raw materials at an acceptable cost, as in the interconversion of caprolactam and nylon 6, or can be rendered biodegradable. In the case of polyester, uncontaminated waste can either be remelted and reextruded, or alternatively converted back to the starting intermediates by methanolysis. Recycling technologies for nylon 6.6 are also well advanced and waste nylon carpets can be recycled. The conversion of acrylic and modacrylic


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copolymers back to the monomer units for recycling is not yet possible, however. Accordingly, these fibres are expected to continue to lose market share [2]. Table 1.1 indicates fibre production data worldwide in 1996 and 2001. These trends emphasise the growing importance of cotton and polyester fibres whether alone or in blends, these two fibres accounting for over 70% of world fibre production. Manufacture of synthetic fibres is now more than 50% of the total. It is estimated that by the year 2050, polyester consumption will have overtaken that of cotton. The earth’s population is currently growing at about 1.3% per annum but improved living standards for many people ensure a growth rate of 2% in the average consumption of textile goods per head. Many of the textile products that characterised the rapid growth of the synthetic fibres industry in the 1950s and 1960s have become mature commodities, providing only slow growth and low profit margins. Intense global cost pressure, higher consumer expectations, a highly diverse customer base and reduced spending on research have contributed to sluggish growth in the fibres business. Environmental concern favours products that exhibit properties such as biodegradability and recyclability. Future fibres must be manufactured by safe, energy-efficient and zero-pollution processes. Figure 1.1 ranks the level of structural sophistication in various natural or manmade materials, illustrating how future fibres will acquire higher value through precise solutions to complex requirements. Ultimately the capability to build up highly specialised materials is determined at the molecular level. At the base of the pyramid in Figure 1.1 are essentially simple materials of industrial value with properties defined largely by the composition and macromolecular sequence. At the next level are high-performance fibres such as cellulose, aramids and carbon fibre. In these, both molecular conformation and spatial features are important property determinants. Still higher in structural organisation are natural materials such as silk or leather, with properties that are enhanced by the participation of individual macromolecules in specialised lamellar or helical structural arrangements. At the apex of the pyramid are biocomposites of natural origin, probably the most sophisticated materials known. In addition to the features already mentioned, these cellular components of living organisms are arranged in interconnected patterns that allow for highly specialised properties and functionality. The refinement of recombinant DNA methodology has made it possible to manipulate and direct the specificity of the biosynthetic process in certain fibreforming polymers, notably proteins. By utilising structure and sequence information from naturally occurring macromolecules, it is possible to design similar polymers from modular building blocks, such as amino acids, each providing a specific end-use performance. Using this approach it has become possible to construct genetic templates that encode bioengineered analogues to spider and moth silks [8,9]. These templates are expressed from a host organism to provide polymers that can be processed into highly lustrous fibres suitable for textile applications. In 1997-98 there was a loss of financial confidence in some of the boom markets of the Asia Pacific region. Thailand, Malaysia, Indonesia and the Philippines suffered rapid devaluation of their currencies and high national debt, fuelled by excessive borrowings [10]. Intense global competition ensured that this monetary disorder worsened the already difficult trading conditions for European man-made fibre producers. The build-up of excess capacity for intermediates and fibres

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production depressed prices and led to attempts to export fibres overseas at dumped prices. Local selling prices in Asia fell to levels that did not cover production costs. European producers risked paying twice over during the crisis, as substantial contributors to IMF (International Monetary Fund) support programmes and later in lost jobs as a result of dumping of low-price fibres into European markets [11]. This economic crisis in the Asia Pacific region seriously affected wool prospects in Western Europe. Overproduction in Asia deepened the plight of wool producers at every stage. Combing plants had been constructed or expanded during more prosperous times in Asia, Australia and South Africa. Tops and other products from these plants were now offered in Europe at prices low enough to destabilise the market. The situation was particularly worrying in Japan, a leading market for high-quality woollens and worsteds, as well as the most important buyer of pure cashmeres. Slowdown of consumer demand in these sectors was also evident in the USA and Western Europe [12].

1.2 Diversification of Dye Manufacture Worldwide The oil crises of the 1970s presented dyemakers and dye users with acute difficulties because of the dependence of dyes and auxiliary products on petroleum-based intermediates. Energy costs accelerated at 20 to 30% per year, more than doubling throughout the period 1975 to 1981. Many of the American chemical companies withdrew from the dyes sector in the late 1970s because of lack of profitability [13]. Chemical plants in the USA were centred mainly on large-scale continuous processes and were reliant on imported intermediates that had risen dramatically in price. Sales were mainly restricted to the domestic market with no tradition of the export marketing of dyes. Dyemakers in Europe had traditionally dominated the market and were better placed to weather the storm. Inevitably, however, they had to slim down operations to counter the effects of world overcapacity. This resulted from the decline in the traditional export markets and the emergence of new producers of commodity dyes in Eastern Europe and the Far East. Established manufacturers in Europe and Japan had to rely much more on discovering new speciality products, but the costs of research and development were much increased by the need to meet increasingly strict requirements for hazard testing. Japan’s vigorous economic growth brought about problems of pollution in the 1970s. As a result the country took an initiative, ahead of the rest of the world, in applying strict environmental regulations. Dyemakers and dye users consumed much of their corporate resources in taking the required measures to meet the challenges of environmental protection. The oil crises of the 1970s caused dye consumption to decline substantially. An industry-wide rationalisation became essential and the top five Japanese dyemakers cooperated in establishing a system of concerted production of disperse dyes and basic dyes through a consignment arrangement between them [14]. Long and costly test programmes now have to be carried out on newly discovered dyes or chemicals before they can be marketed. Many familiar and longestablished fine chemicals would not necessarily be available if they had had to be subjected to the test procedures now enforced by legislation. Safety testing has become so time-consuming and costly that research and development costs increased fourfold during the 1980s, greatly limiting the number of new speciality products reaching the market-place. It now takes much longer to attain this point


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from the date of discovery, so that the patent protection remaining when the new product is launched gives the discovering firm a much shorter lead over its rivals. The impact of the oil crises on the structure of the dyemaking industry was less immediate and far-reaching than for fibres manufacture, because the pattern of production of dyes and their intermediates is such that rationalisation within or between companies is a more complex process that takes longer to resolve. Optimistic forecasts of growth in synthetic fibres had led to overcapacity in dyemaking plants, notably for disperse dyes, and reactive dyes failed to live up to early expectations that they would soon achieve a predominant position on cellulosic fibres. Non-traditional suppliers of dyes based in low-wage nations, notably in the Asia Pacific region, began to take a significant share of local demand for commodity dyes and pigments. Profits were mostly reinvested to expand production capacity, enabling these companies to target world exports as a new area for growth [15]. The recession of the 1990s resulted in decreased demand for dyes just as this new capacity came on stream, leading to overcapacity problems. These fluctuations in supply and demand created a chaotic market-place with an increasing number of aggressive suppliers competing for a variable but always limited demand. This situation initiated a new round of industry restructuring with alliances, joint ventures, acquisitions and closures being made to combat competition. Non-traditional suppliers now represent more than one-third of the textiles dyes business worldwide [16], as indicated in Table 1.2. The main centres of dye manufacture are Western Europe, the USA, Russia, Japan, India and P R China. Asian capacity is growing at the expense of Europe and America. Table 1.3 shows the distribution of dyemaking activity throughout the world in 1996 [17]. Total production capacity was estimated to be about 900 kilotons but total demand was running at only 650 to 680 kilotons, representing an overcapacity of about 30%. It is estimated that by 2006 the Asian textile industry will account for more than half of world dye consumption [10]. Demand in Europe and the Americas is static or slowly declining. P R China and India are expected to show the most active growth in textile dye usage. At the beginning of the 1990s there were six major European dyemakers, four Japanese and one in the USA. Ten years later, after considerable rationalisation, there remained only four European and two Japanese dye manufacturers [15]. Table 1.4 lists several reasons why in developed economies there are increasing demands for quality dyes and processes but a diminishing consumption of commodity products. Greater amounts of disposable income mean that there is more demand for all fibre types in quality textiles but low economic growth rates operate in the opposite direction. Environmental legislation is driving the development of products with improved ecological profiles. The growth in activity in the Asia Pacific markets in the early 1990s encouraged the German dyemaker BASF to transfer the headquarters of its dyes and chemicals business for textiles and leather to Singapore in 1996, not long before the economic crisis of 1997-98 in the region. The other major producer DyStar continued to consolidate its activities in Germany. Despite high local costs in terms of wages, taxes and environmental protection, as well as stringent operating conditions, major advantages were claimed to justify remaining in this traditional location. These included innovative customers in a high-quality market, well-trained and well-motivated personnel, together with opportunities for close collaboration with research institutes and progressive textile machinery makers

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[18]. Since then BASF and DyStar have merged to form the world’s largest dyemaking group. Table 1.5 indicates that the drive for industrialisation in the developing world creates the potential for greater competition between importers and local manufacture. The low labour costs make it easier for local dyemakers to compete successfully against the traditional suppliers. The lowering of tariff barriers allows easier access to other trading regions and increases the attractiveness of imported quality products. Industrialisation leads to improved educational opportunities, higher skill levels and the potential for higher quality production. Production capacity for dyes in India is estimated at 75-80 kilotons p.a., with most producers concentrated in Gujarat and Maharashtra. The 48 larger dyemaking plants account for 70% of this total and about half of their total production is destined for export. There are about 900 small-scale independent units also producing dyes for local usage. In the 1990s the Indian dye industry went through a difficult phase, owing to low growth in demand, low profitability and environmental restrictions [15]. India has adopted a relatively hardline policy regarding ecological impact, with closures of chemical plants and dyehouses that are unable to treat effluent to satisfactory standards. In 1997 P R China produced 255 kilotons p.a. of dyes, the vast majority of which were commodity products. Exports of dyes from China have risen from 95 kilotons in 1996 to 156 kilotons in 1999, almost all the increase being in disperse dye presscake. It is not surprising, therefore, that this remarkable surge in activity is seen as the major threat to the established dyemakers elsewhere [15]. During the 1990s about 5000 small-scale chemical units in China were closed down, either on pollution grounds or to facilitate consolidation of the industry into larger units [10]. Taiwan’s major capacity is in reactive and disperse dyes, estimated at over 20 kilotons in 1998. The leading Taiwanese producer, Everlight Chemical Industrial, has a growing international reputation for reactive dyes and has steadily increased capacity above its 1996 level of 11 kilotons. Everlight has been collaborating with BASF since 1998 on joint production of selected Procion dyes [15]. The main characteristics of the Brazilian dye industry are: 1. almost total dependence on imported intermediates 2. intense competition, resulting from the presence in Brazil of all the major producers worldwide 3. substantial overcapacity in the industry 4. approximately 33% of Brazilian dye consumption is imported 5. about 25% of local production is exported, mainly to other Latin American markets 6. lack of specialisation in specific dye classes or sophisticated products. The low prices offered by Asian producers of intermediates, mainly from India and PR China, make local Brazilian investment in capacity for these chemicals highly unlikely. Foreign trade plays a major role due to low import duties [19].


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1.3 Globalisation of Textile Manufacture and Processing Since 1970 the capacity of the UK textile industry has halved: bleaching has shrunk to 44%, dyeing to 56% and printing to 35% of their former size [20]. This trend is not untypical of the situation in the European Union generally. The UK industry is still mainly run on a commission basis. Typically the woven fabric is imported in the grey state by a textile merchant and sold to a textile garment manufacturer, who sends it to a dyer and finisher for wet processing. Developing countries are increasingly equipped to dye and finish their own woven fabric, putting a great deal of pressure on the remaining UK commission finishers, who are competing against low-wage operations carried out in state-of-the-art, highly automated finishing plants. The knitted fabric industry has suffered less from fabric imports but almost all yarn supplies are imported. Companies in this sector are increasingly plagued by imported made-up garments, however, such as Tshirts [20]. According to a 1990 world survey of the major importers and exporters of textiles and clothing [21], the combined output of the five leading Far East producers exceeded that of the five major European countries (Table 1.6). As globalisation evolves, the importance of the Asia Pacific region in the world textile market becomes more evident. This growing dominance stems from the fact that tropical and coastal Asia is the most densely populated region in the world. It has substantially lower costs of production, including labour, energy and raw materials. Initially, developing countries have low labour costs and by the late 1980s, there was a factor of 80 between the rates paid in developed countries and those of developing countries. This differential has been eroded with time as third world countries have developed. Once modern machinery with automation and robotics have been installed, processing costs decrease as a result of lower labour requirements. During the early 1980s there was a pronounced movement of the centre of the world’s textile industry from the highly industrialised nations towards the lowercost economies of the developing world. Textile production in countries such as Taiwan and South Korea expanded at an incredible rate. The shift of the textile centre to the Asia Pacific zone has profound implications for suppliers outside this region. For suppliers to be effective in penetrating the rapidly developing and exceptionally price-sensitive Asian market, they must be capable of selling products that offer real value for money. The globalisation of textile manufacture implies that suppliers must be able to operate internationally in a highly competitive economic environment [22]. International trade in textiles and clothing is governed by the multi-fibre arrangement (MFA), established in the early 1970s as an interim measure to control imports from low-cost developing markets during the restructuring of the mature textile producers. The treaty has been amended at intervals but the established industries in Europe and the USA claim that the developing nations have maintained their trade barriers and supported their industries to gain significant commercial advantages. After 2005 the world textile trade will operate without the MFA. Following a phased reduction in tariffs, duties and quotas, the global industry will operate as a free trade zone, inevitably resulting in further import penetration of the developed markets [23]. An interesting comparison of the cost structures for textile finishing in Germany and South East Asia has been made in the context of the global response of dye suppliers to these differences [24]. Striking variations are evident between South East Asia, Japan, Western Europe and the USA in terms of their approaches to

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effluent legislation and degree of concern about different types of contaminant or ecological hazard. Unduly sensational reports in the German media have been blamed for allegedly damaging the image of the local textile finishing industry, subsequently provoking the rash of ecolabels introduced to reassure customers. Nevertheless, the challenge posed by environmental issues is probably the most important problem facing the wet processing industry; it will shape the development of acceptable chemical technology and be a major driving force for change in processing methods [25]. The 1990s became the age of the healthconscious and discerning consumer who demands quality products that offer value for money. European consumers, in addition to desiring quality products at attractive prices, also require them to be innocuous. Safety legislation and its enforcement have compelled dyers to be cautious in introducing new processes and equipment. Environmental pressures and the growing popular interest in the materials used to manufacture clothing have persuaded suppliers of chemicals and equipment to design and develop processes and machinery that are less polluting and more energy-efficient. In the 1990s the textile finishing industries of such developing countries as Pakistan and Turkey have revolutionised their operations. Pakistan opened nine new factories in five years, with European technologists training the local workforce. Phenomenal growth trends are evident in P R China but the Chinese are facing intensified competition from other Asian producers, including Pakistan, Turkey, India and Indonesia. With a workforce estimated at 15 million and relatively low labour costs, the Chinese textile and clothing industry has become the biggest in the world. P R China, now incorporating the Hong Kong SAR, is already the dominating supplier of these products to the lucrative markets of Western Europe and the USA, accounting for more than 25% of world exports (Table 1.6). This huge country has tremendous potential for future growth. China forms a quarter of the world’s population but accounts for only 17% of world fibre consumption. The retailing sector is set for rapid expansion in the coastal cities and economic zones as incomes improve over forthcoming years. China may have to divert some output away from exports in an attempt to satisfy fast-rising domestic demand. Textile production in P R China exceeds 11 megatons p.a., an increase of about 50% over 1993 levels. The average growth rate has been above 5% p.a. throughout the two decades since 1980. During the 1980s textile material exports rose by 11% p.a. in volume terms, whilst made-up clothing exports shot up by an astonishing 70% from a low base [26]. However, China’s rapid expansion, coupled with a succession of poor cotton harvests, created serious raw material shortages in the mid-1990s. Many textile mills across China had to be closed, forcing the world’s largest fibre producer to import major quantities of raw cotton and synthetic fibres. There is increasing resistance in developed markets to growing incursions from Chinese imports of manufactured goods, including made-up garments. Overmanning and inefficiency will continue to be a drain on the industry, weakening the cost-competitiveness of Chinese textile and apparel exports in the face of rising competition from elsewhere. The capital needed to fully re-equip the Chinese industry is immense and depends on substantial foreign investment. Plagued by obsolete equipment, P R China has had to restrain growth in textile output in order to update selected mills and consolidate the organisational structure of the industry. Old plant has been scrapped and only the best and most vigorous enterprises supported. Transport, power supply, communications and


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distribution facilities have been overwhelmed by the mushroom growth of the economy. The southern provinces possess a more developed infrastructure with easier access to the important export market and distribution centre of the Hong Kong SAR. However, costs there are far higher than in the more remote inland provinces [26].

1.4 Definition of the Global Consumer The global consumer shares with other individuals elsewhere in the world certain characteristic traits, such as lifestyle preferences and reactions to purchasing stimuli, that are independent of traditional geographical markets. All consumers are subject to a myriad of influences on shopping behaviour and product choice. Some factors, such as energy, the environment and the increasingly rapid flow of information, cut across national frontiers. These pressures exert a considerable impact on the business environment but may not be recognised or articulated by the individual consumer. Factors that may be considered in defining different segments of a retail market include: age profiles, household patterns, earning power, lifestyles, work and leisure time requirements. Table 1.7 displays current changes in the demographic composition of the UK population profile, which is broadly similar to other developed countries in Western Europe. It clearly indicates an ageing pattern, with the over-35s (postwar baby-boomers) growing in numbers at the expense of teenagers to thirty-somethings (post-pill babies). Table 1.8 categorises the shopping population into the traditional socio-economic groups based essentially on a classification of professional and manual occupations. Table 1.9 indicates general trends of consumer expenditure on clothing in various categories of the UK population. Taking the broad-scale figures in these three tables it is clearly evident that an important target segment for this market would be garments for women (purchasing 55% of all clothing) aged 35 to 54 (most rapidly growing sector of the population) with occupations in groups C1 and C2 (more than 50% of working adults). This example is a simple analysis of broad-scale trends but by utilising more refined statistics in a similar way it is possible to derive much more precise target customer profiles [27]. The results of marketing surveys into the major factors that are influential in clothing purchase decisions made by the most active sector of the shopping population are indicated in Table 1.10. These factors apply, to a greater or lesser degree, in all of the world’s developed markets. Socio-cultural trends are active agents of change present throughout the developed world. Five of these are listed in Table 1.11 as specifically relevant to clothing, fabrics and fashion, reflecting certain facets of the individual consumer’s interaction with the environment [28].

1.5 Organisation of Textile Production in a Global Economy A global market is one in which the individual consumer has access to information about goods and services available from around the world. Markets are defined by the appeal of products to global consumers rather than restricted within traditional cultural or geographical boundaries. The relatively affluent consumers in the interlinked economies of Europe, North America and Japan share many characteristics: comparable income levels, well-educated, similar leisure and travel interests, access to the same sources of media-generated information.

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Worldwide product identity, high visibility of brandnames, a universal logo and shared promotional messages are features that contribute to the growth of a global business. Corporate value structures, management style and marketing strategies ignore political borders but respect cultural differences specific to each geographical region in the ‘borderless world’. Businesses operating in this trading situation must offer products that have global market appeal and be demonstrably committed to serving a global network of demanding customers [28]. Tailoring product ranges to meet the requirements of different sectors of the global market-place is expensive. Many exporting companies face a dilemma because they are not sufficiently capitalised to acquire the necessary manufacturing facilities and global marketing organisations required to remain competitive. The more they penetrate the global network, the more they must respond to the numerous local differences between market sectors. Therefore companies have to find new ways to exploit company strengths while keeping costs under control, tackling strategic opportunities without seriously depleting resources. In other words, to do more with less. Possible approaches to facilitate this include licensing agreements, franchises, company alliances, joint ventures, mergers and acquisitions [22]. The globalisation of the textile industry has resulted from the application of telecommunication systems to enable computerised analysis of sales data from retailing in any region of the world to be readily and instantly transferred to a textile manufacturing facility and its associated dyeing, printing and finishing services, so that supply and demand can be much more closely integrated. Similar communication links enable textile designers in different countries to collaborate simultaneously on design editing and modification using advanced computer-aided design (CAD) systems. To be successful in today’s economic environment, the retailer must have a clear picture of the consumer that is to be served. Much time, effort and resources are devoted to the analysis of market statistics in order to understand the purchasing profiles of today’s consumers. Larger retailers aim to cater for a range of different market sectors, whereas smaller and more specialised suppliers focus on a clearly defined market niche. Lively display layouts, making shopping precincts and retail outlets more exciting places to visit, together with the introduction of niche marketing areas within larger retail stores, have been important in stimulating market developments. Technology has revolutionised the consumer/retailer transaction. Electronic barcoding of individual garments and the development of electronic point of sale (EPOS) data capture through computerised checkout tills now allows the scheduling of deliveries of individual products on a daily basis. The more advanced retail organisations communicate directly with their suppliers using electronic data interchange (EDI) systems. This minimises the stock levels carried by the retail outlets and has a significant impact on the working capital needed to finance the business, minimising lost opportunities and price mark-downs, as well as allowing rapid and accurate monitoring of the sales pattern for newly introduced items. Delaying colouring and garment sizing instructions to a date as near as possible to the EPOS transaction increases the accuracy of demand forecasts, reduces lead times and further minimises mark-downs and lost opportunities. The early 1990s saw the onset of economic recession. Demand in developed markets declined and retailers challenged traditional sales patterns to retain


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market position. The historical approach towards seasonal buying, based on spring/summer and autumn/winter fashion collections, maintained by the leading fashion houses of Western Europe, has been significantly eroded. These have been replaced by four or sometimes six shade palettes in the year. The impact of this trend means that many more new shades have to be programmed into the production schedule [23]. The market-place is now highly reactive to new ideas and trends, irrespective of the calendar. Speed of response to sudden volatility in demand and the ability to influence fashion styles are critical to the retailer’s success [29]. These developments favour those suppliers who can offer flexibility of response and short lead times to supply fabric or garments. Recession conditions have seen the disposable income of the average consumer decrease, so that garment price levels play a more important role in the decision to purchase. Many retailers have been unable to raise the selling prices for core products over several years. In the ultra-competitive market-place, retailers must offer value for money and differentiate through quality, availability and customer service. The increased influence of retail organisations has put pressure on garment manufacturers and fabric producers, creating a highly competitive environment in which the overwhelming need to satisfy the retailer’s demands is paramount. The discerning consumer is swayed by marketing, reputation, style, availability and price. To survive, retailers must be able to offer the right product at the right time and at the right price. The textile chain consists of a sequence of various interlinked operations that follow a definite route; Figure 1.2 is a simplified representation of the relationships involved. The process begins traditionally about two years in advance with forecasts of the target season’s designs, fabrics, colours and finishes. Much later, merchandising decisions are taken to promote selected products and to define which garment styles, sizes and colourways will be manufactured. This stage is delayed as late as possible in order to minimise the risks of making wrong choices. This requirement means that the manufacturing and processing links in the chain are under constant pressure to reduce their lead times to the retailer. The provision of detailed EPOS information helps the retailer and suppliers to plan ahead and respond quickly to the market-place. For the retailer sales patterns act as the basis for re-order and price mark-down decisions. For the manufacturer and processor such data give vital information for production planning (PP) and materials requirements planning (MRP) decisions. The purpose of sharing this commercial information is to persuade suppliers to cooperate with the retailer towards shared objectives and to focus on the task of getting the correct assortment of goods on the sales floor when the customer is ready to buy. Typical American experience indicates that initial order lead times can be reduced by 30% or more. In-season re-orders can be programmed so that retail outlets can receive frequent consignments of best-selling lines. This ensures that the suppliers are making what the retailer knows his customer wants [31]. Each supplier link in the textile chain must evaluate its own and its competitors’ strengths and weaknesses, as well as devising a strategy to consolidate partnerships with other links in the chain. It is important for such partnerships to examine critical aspects of the service provided and to define specific measures that can be taken to generate a competitive advantage in the market-place. The driving force is the retailer’s commitment to the needs of the customer. Having established these operating relationships it is essential that these principles are

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carried through so that suppliers respond to the retailer and the customer in the most dynamic and cost-effective manner [29]. The textile marketing chain is long and complex. The traditional business environment was so full of variables and imponderables that failure to produce to specification frequently occurred and allowance for non-conformance was routinely accepted. However, the increasingly stiff competition in the global market-place has changed the climate in which industry has to operate. Enhanced customer choice between wider ranges of products and retail outlets has emphasised the need for the retailer, garment maker, fabric supplier and finisher to improve their financial performance. The industry can no longer tolerate the possibility of one link in the marketing process adversely affecting the efficiency and viability of the total supply chain as it attempts to fulfil the customer’s requirements. Total quality management (TQM) may be regarded as an ideal that is ultimately unattainable, but quality control measures should be established and continually refined so that effectiveness is seen to approach closer and closer to the optimum. The focus on TQM has provided an alternative means of defining the value of controlled production performance. Using what is now becoming a standard analytical technique, the cost of quality (the cost of conforming to the required standard of performance) is defined and expressed as a percentage of sales revenue. The key factors contributing to this measure are: 1. Preventive maintenance – calibration and procedures

costs

of

laboratory,

quality

management,

2. Shading additions and re-dyes – internal costs of non-conformance 3. Appraisal – goods inspection and quality control systems 4. Reprocessing – internal and external costs 5. Claims and debits – external costs of non-conformance 6. Consequential – lost opportunities for profit. It is quite common for quality costs to be as high as 25% of the sales revenue [32]. Quick response (QR) is a mode of operation by which manufacturing or service industry attempts to supply products or services to its customers in the precise quantities, variants and time frames that they require [31]. The objective is to do this on a continuing basis to achieve minimum lead times and avoid commercial risks, whilst retaining maximum competitiveness and flexibility. QR entails stricter disciplines and immediate communications but it will yield improved performance in terms of turnover and sales, combined with an increased level of service to the customer. Typically in America the initiative for QR projects started at the retail end of the textile supply chain. Major retail organisations have shown a willingness to adopt creative approaches to long-range planning, supplier selection, stock control and distribution, transportation and handling. The adoption of QR by the manufacturing sector thus becomes an instrument of survival and maintenance of competitive position. The full benefits of QR operation can only be realised if all links in the supply chain are committed and actively involved in the system. The most dynamic response performance has been achieved in the knitwear sector; a greater proportion of dyeing and finishing in garment form has


13

dramatically shortened lead times. Piece dyers have reorganised production schedules to ensure quicker response to market demands and progress has even been possible in yarn and loose stock dyeing. Continuous open-width dyeing was traditionally reserved for long runs per colour and semi-continuous methods (such as pad-batch) for batch sizes intermediate between exhaust and fully-continuous methods. The economic climate together with the need for quick response has eroded demand for continuous and semi-continuous dyeing and such plant may often run uneconomically because of short runs. It seems likely that small-batch QR production with focused marketing and dynamic response to fashion demands will enhance added value, leading to higher levels of profitability. The QR system targets the production of saleable merchandise that is actively demanded in the market-place. Stock inventory is not created until orders and reorders are placed, so that the inventory of finished goods is set up at the correct time. The concept of just-in-time (JIT) means having only the right products in the right place at the right time, with consistency of quality [31]. It is vital in these circumstances to be absolutely sure that the inventory set up is free from all defects. Thus TQM is an essential prerequisite for successful JIT. In the current economic climate the risks and consequential costs of carrying or creating excess or substandard stock in any sector of the supply chain immediately creates serious problems. In a complex market such as textiles and apparel, the problem of forecasting fluctuating demand brings dangers to the adoption of JIT that make close liaison between the various links of the supply chain not merely desirable but absolutely vital. Incorrect chemical pretreatment has been shown to be implicated in about 70% of all faults in finished fabrics [33]. The last two decades have seen major improvements in control systems to improve the reproducibility of dyeing by minimising deviations from standard conditions. Nevertheless, many factors must be taken into account if troublefree processing is to become routine. Changes in consumer lifestyle and the widespread use of central heating systems have favoured the growth in sportswear and leisure clothing, which now account for more of the apparel market than formal wear [34]. Greater problems in respect of soiling of sportswear and leisure garments dictate the use of dyes of higher fastness to washing, particularly where perborate-activated detergents may be used at lower laundering temperatures [21]. The concept of right-first-time (RFT) processing gained rapid acceptance in the 1980s, when it was originally termed blind dyeing. The RFT philosophy is intended to provide higher quality with quick response, as well as maximising productivity, process efficiency and profitability. To minimise fibre damage, high-quality textiles must be subjected to the shortest possible time of wet treatment compatible with achieving the target properties. The cost of non-conformance is a simple but effective measure of the losses incurred by the production of unacceptable goods that do not meet the required specification [33]. On average, a single shading addition can add 10 to 30% to the cost of an exhaust dyeing. If an unlevel or off-shade dyeing has to be stripped and re-dyed, the cost of processing increases by more than 100%, guaranteeing either financial loss or an uncompetitive quote if this degree of inefficiency is allowed for in the original price. Not only are shading additions and re-dyes bad for profit, they also interfere with productivity and cause delivery dates to be missed, resulting in loss of goodwill and future business.

14


In the dyehouse the total cost of production can be calculated by adding the cost of additional processes necessary to achieve the required performance to the standard cost for routine processing. Table 1.12 shows the cost of nonconformance calculated by means of computer modelling techniques for a typical knitgoods dyehouse operating on a commission basis. The blind dyeing process is the ideal that represents the processing cost, productivity and profitability for troublefree RFT production. If, after checking the shade, a small shading addition to the cooled dyebath is required, the total cost of production is increased by 10% but productivity is reduced by 20%. More importantly, the profit for this production batch is reduced by more than 50%. If a large shading addition is needed, calling for the exhaust dyebath to be drained, rinsed and re-set, then the impact on processing cost, productivity and profitability is even more dramatic. In this case a substantial loss of nearly 50% is incurred. The most costly scenario is to have to strip and re-dye a faulty dyeing. To recoup this loss it is necessary to dye another four RFT production batches, all of which must be problem-free. The figures in Table 1.12 are only part of the story since they do not allow for the reduction in revenue which occurs through loss of production when machines which should be processing the next batches are tied up with corrective treatments. These factors also have a bearing on the ‘designed capacity’ of the plant and impact on capital expenditure. By improving the capacity for RFT production, wasteful additional processing to achieve the required performance can be eliminated. For the knitgoods dyehouse model from which Table 1.12 was calculated, the average number of batches per machine per week represents the full capacity of the dyehouse when operating at 60% RFT production. Improving this figure will reduce the variable costs (excluding labour) and improve return on sales (ROS) as shown in Figure 1.3. For example, improving RFT production from 60 to 90% will increase the ROS from the original 100% to 130% and generate additional capacity accordingly. In order to obtain RFT production consistently, there are numerous factors that the dyer must take into account, as indicated in Table 1.13. Factors associated with the inherent constitution of the starting materials are best monitored by laboratory testing on a regular basis. Those factors arising from the requirements of the dyeing process and the associated colour control measures should be dealt with in a series of standard operating procedures (SOP) that need to be designed in accordance with the substrates, dye classes and dyeing methods currently operated within the dyehouse. The factors which can be controlled by SOP, plus dye purchasing, are matters of company policy and cannot be changed without senior management approval. Similar lists can be established for preparation, aftertreatment and finishing processes. The financial rewards from improved quality and efficiency include [32]: 1. Increased sales from RFT production 2. Increased productivity from the same equipment and time frame 3. Reduced working capital required because of lower stocks of material awaiting processing, shorter process routes and less strategic stocks of finished goods awaiting despatch because of quicker response to market trends 4. Reduced occurrence of shading and re-dyeing operations. This not only frees additional production capacity but ensures that production planning is much less disrupted by unforeseen delays. It is therefore easier to plan for on-time


15

deliveries with only short lead times, maximising the opportunities available to respond to fast-moving trends in the market-place 5. Cost savings generated by lower processing costs and reproducibility of guaranteed quality. In order to control a process effectively it is necessary to identify and measure all relevant process variables. Microprocessor control has been successfully established for: 1. Time/temperature profile of the dyeing cycle 2. Speed of fabric rope movement in jet machines 3. Dyeing machine speed/output 4. Product addition according to controlled profiles 5. Redox potential, pH and specific gravity can be controlled by on-line systems. The target set values together with predetermined tolerances are stored in the control system; providing that the process controller detects values within these acceptable limits, the processing cycle moves on to the next step. If the value detected lies outside the pre-set tolerance range, an alarm device calls for on-line attention so that corrective action can be taken. Systems are available to synchronise liquor circulation, fabric speed and process cycle in jet dyeing.

References [1]

Genesis, chapter 3, verse 7.

[2]

J P O’Brien and A P Aneja, Rev. Prog. Coloration, 29 (1999) 1.

[3]

J Rupp, Internat. Text. Bull., 48 No. 4 (Aug 2002) 28.

[4]

J Park and J Shore, JSDC, 115 (1999) 298.

[5]

H J Koslowski, Chem. Fibers Internat., 48 (1998) 174.

[6]

D Morris and A Stogdon, JSDC, 111 (1995) 341.

[7]

H K Rouette, Textilveredlung, 32 (1997) 108.

[8]

S R Fahnestock and S L Irwin, Appl. Microbiol. Biotechnol., 47 (1997) 23.

[9]

S R Fahnestock and L A Bedzyk, Appl. Microbiol. Biotechnol., 47 (1997) 33.

[10]

P Kelshaw, JSDC, 114 (1998) 35.

[11]

C Purvis, Chem. Fibers Internat., 48 (1998) 7.

[12]

Anon, Wool Record, 157 (April 1998) 1.

[13]

G N Mock, Rev. Prog. Coloration, 32 (2002) 80.

[14]

S Abeta and K Imada, Rev. Prog. Coloration, 20 (1990) 19.

[15]

P Bamfield, Rev. Prog. Coloration, 31 (2001) 1.

[16]

A X Rad, Dyer, 185 (Nov 2000) 12.

[17]

K V Srinivasan, Colourage Annual, 46 (1998) 79.

[18]

A X Rad, Melliand Textilber., 79 (1998) 530.

[19]

J Falzoni, Rev. Prog. Coloration, 25 (1995) 64.

[20]

C Smith, Rev. Prog. Coloration, 29 (1999) 37.

[21]

I Holme, Rev. Prog. Coloration, 22 (1992) 1.

[22]

K Cheuk, JSDC, 111 (1995) 135.

[23]

M J Bradbury, P S Collishaw and S Moorhouse, SDC Biennial Conf., Blackpool (Oct 2000).

[24]

W Reddig, Melliand Textilber., 78 (1997) 834.

[25]

I Holme, Textile Month, (Sept 1990) 55.

[26]

J Glasse, JSDC, 111 (1995) 98.

[27]

F Moore, JSDC, 111 (1995) 212.

16


[28]

D Siegel, JSDC, 113 (1997) 231.

[29]

M J Bradbury and J Kent, JSDC, 110 (1994) 173 and 222.

[30]

K Parton, JSDC, 110 (1994) 4.

[31]

J Hobson, JSDC, 107 (1991) 305.

[32]

P S Collishaw, D A S Phillips and M J Bradbury, JSDC, 109 (1993) 284.

[33]

W Prager and M J Blom, Text. Chem. Colorist, 11 (1979) 11.

[34]

P W Leadbetter and A T Leaver, 15th IFATCC Congress, Lucerne, (Jun 1990).


17

Table 1.1 Global production of various fibre types [3]

Fibre type Cotton Polyester Nylon Acrylic Wool Silk Other synthetics* Other cellulosics Total Global population (billions) Average consumption (kg/head)

Production (megatons) 1996 2001 20.03 18.73 19.24 13.30 3.73 3.93 2.58 2.62 1.36 1.49 0.086 0.071 3.16 1.96 2.63 2.87 44.97 52.81 5.77 6.16 7.79 8.57

Change +1.30 +5.94 -0.20 -0.04 -0.13 +0.015 +1.20 -0.24 +7.84 +0.39 +0.78

* Mainly polypropylene fibres

Table 1.2 Market share (%) of the global textile dyes industry held by various suppliers [16] Dye manufacturers DyStar Large non-traditional suppliers Ciba Small non-traditional suppliers Japanese dyemakers Clariant Small traditional suppliers Medium traditional suppliers

Market share (%) 23 22 15 14 9 8 5 4

Table 1.3 Production of dyes and pigments worldwide [17] Country Germany USA Russia and CIS Japan Switzerland UK India Other countries

Production (%) 22.4 18.0 11.3 9.3 8.3 8.2 6.6 11.1

Worldwide production in 1996 was about 700 kilotons

18


Table 1.4 Factors governing the pattern of dye consumption in developed countries [10] Factor Increased disposable income Fashion demands Low economic growth rate Focus on high-quality, high-value products Environmental legislation

Market impact Enhanced requirements for all fibre types Requirement for high-quality dyes and processes Depressed growth of standardquality goods Reduced demand for commodity dyes Boost in demand for environmentally safe products

Table 1.5 Factors governing growth of dyemaking in developing countries [10] Factor Increasing disposable income Political will to create an industrialised economy Low labour costs Lowering of tariff barriers Improving education and technical skills Greater access to developed export markets

Market impact Demand for textile goods increasing Rapid rise in local manufacture Local manufacture able to compete with importers Importing of quality products becomes more attractive Improving quality Growth in export-oriented producers

Table 1.6 Top ten world importers and exporters of textiles and clothing [21]

Country USA Germany Hong Kong UK France Japan Netherlands Italy Belgium Switzerland Total

Imports (US$ billion) 29 565 23 175 12 169 11 942 11 768 10 631 6 833 6 681 5 796 4 364 122 924

Country Hong Kong Italy Germany South Korea PR China Taiwan France Belgium Japan UK Total Asia Total Europe

Exports (US$ billion) 18 182 16 564 15 903 13 540 11 327 9 324 7 904 6 311 6 060 5 797 58 423 52 479


19

Table 1.7 UK population age profile 1992 to 2001 (millions) [27]

Age (years) 0-4 5-14 15-24 25-34 35-44 45-54 55-64 65+

1992 3.9 7.3 8.0 9.2 7.8 6.9 5.8 9.1

1996 4.0 7.6 7.3 9.3 8.0 7.6 5.8 9.5

2001 3.85 7.9 7.3 8.3 8.9 7.8 6.2 9.3

Change (%) 1992-2001 -1.3 +7.6 -9.6 -10.8 +12.4 +11.5 +6.5 +2.2

Table 1.8 Shopping population by socio-economic group [27] Group A B C1 C2 D E

Proportion of adult population (%) 3.1 15.7 25.6 26.0 17.0 12.6

Classification by occupation Upper professional Middle professional Lower professional Skilled manual Unskilled manual Subsistence level

Table 1.9 UK consumer expenditure on clothing (£ million) [27]

Category Womenswear Menswear Girlswear Boyswear Infantswear Total

Expenditure 1989 9 500 4 800 1 200 950 700 17 150

1994 9 700 4 500 1 400 1 000 650 17 250

Change (%) 1989-1994 +2.1 -6.7 +14.3 +5.0 -7.7 +0.6

20


Table 1.10 Results of surveys into influential factors in clothing purchase decisions by female customers aged 18 to 45 [28] Factor Fashion

Comment A constant factor, whatever other criteria are involved Great importance attached to all three of these factors, which greatly influence the decision to buy Many customers are prepared to pay more for clothes that they perceive to be of higher quality Three of every four customers want information on clothing that they are interested in purchasing

Fit, comfort and shape retention Price

Product information

Table 1.11 Socio-cultural trends relevant to clothing, fabrics and fashion [28] Experiencing with all the senses – a fundamental shift away from the dominance of the visual to savouring with all five senses. In fabric terms, texture and handle are becoming as important as colour and pattern Well-being – concern for the ‘total self’, both mental and physical. In clothing terms, this translates into expectations of comfort and visual appeal Personal appearance – dress is used as a means of self-expression and personal statement, but fashion and style have become more cross-cultural Networking – an interactive social dynamic in which individuals belong to several mobile and diverse groups, adapting clothing to the activities they are engaged in at various times Intelligent shopping – individuals are better informed about the value, quality and features of products in the market-place. The constitution of components of a product are as significant as its external appearance or function

Table 1.12 Cost of non-conformance to blind dyeing method (RFT=100) [33]. Process Blind dyeing Small addition Large addition Strip and re-dye

Cost 100 110 135 206

Productivity 100 80 64 48

Profit 100 48 -45 -375

Practical Dyeing, Volume 1 Table 1.13 Important factors influencing RFT production Starting materials Purity of water Dyeability of textile substrate Preparation of textile substrate Standardisation of dye supply Moisture content of dyes Dyeing process control Weighing of substrate batch to be dyed Weighing and dispensing of dyes Weighing and dispensing of chemicals Control of liquor ratio Control of pH Time / temperature profile Control of liquor flow Control of substrate movement (if relevant) Colour control Selection of dyes Behaviour of dyes in combination Accuracy of laboratory dyeing recipe Accuracy of transfer to bulk-scale recipe Batch to batch reproducibility in bulk-scale dyeing Method of colour assessment Determination of metamerism index

21

22


Figure 1.1 Architectural hierarchy of fibres and biocomposite materials [2] Increasing structural sophistication.

Bones, teeth, wood, shells, wool fibres

Quaternary – folding patterns multiple components in a composite structure.

Collagen, silk

Cellulose, aramids, carbon

Glass, polyester, nylon, ceramics

Tertiary – supermolecular helices, lamellae. Secondary – conformation.

Primary – composition and sequence.

Figure 1.2 Primary steps in the textile chain [30] Fashion forecasting

Merchandise ordering

Yarn manufacture

Re-ordering

Fabric manufacture

Garment manufacture

Retailing

Customer

Dyeing and finishing


23

Figure 1.3 Relationship between RFT production and return on sales [32]

150

Return on sales, %

140

130

120

110

60

70

80

RTF production, %

90

100

Chapter 2 Impact of Dyeing and Finishing on the Environment 2.1 Developments in Health and Safety Legislation Health and safety were almost never regarded as significant by the industrial entrepreneurs of the nineteenth century and earlier. Risks were taken with chemicals and equipment that would now be regarded as horrific. Accidents must have occurred with alarming frequency and there was no system in place to compensate the inevitable victims or even to record the events adequately so as to avoid future disasters. No doubt workers had to learn the hard way by practical experience how to treat moving machinery and corrosive chemicals with due respect, but this knowledge was of limited value to individuals forced to work hastily in dangerous surroundings. Early UK legislation under the Alkali Act (1863) created the world’s first national pollution control agency, the Alkali Inspectorate, to control atmospheric emissions of acidic gases primarily from factories producing caustic alkalis. More insidious, however, were the potential health risks resulting from longer-term exposure to toxic or carcinogenic chemicals. Operatives were expected to provide and wash their own working clothes. These must have become heavily contaminated with chemical stains, putting the worker’s family also at risk of exposure to hazardous vapours [1]. It was not until the 1940s that a causal connection was established between the high incidence of bladder cancer in employees of firms making or using dyes and their prolonged exposure to certain arylamine intermediates, following epidemiological studies of individuals who had spent their working lives in these industries. Following a period of unprecedented growth and optimism in the chemical industries worldwide during the 1950s and 1960s, a sociopolitical reaction set in during and after the oil crises of the 1970s. Public demand, often fuelled by media misinformation and speculation [2,3], became insistent that the manufacture and use of industrial chemicals should be more closely regulated and monitored. A series of tragic accidents occurred over this period, involving cyclohexane at Flixborough (UK), dioxins at Seveso (Italy), mercury compounds at Minamata (Japan), and methyl isocyanate at Bhopal (India). These were followed in 1986 by the Chernobyl (USSR) nuclear explosion that polluted much of Northern Europe and the Schweizerhalle (Switzerland) fire that polluted the Rhine basin in the heart of Europe, reinforcing this trend towards a political climate of reform and control. The UK Control of Pollution Act (1974) applied the first controls to the disposal of industrial wastes. The Environmental Protection Act (1990) was the first governmental commitment to protection of the environment and the Water Resources Act (1991) covered the disposal of effluent to controlled waters. This sweeping legislation was designed to impose financial constraints on the release of contaminated air or waters, according to the principle that the polluter must pay to clean up the polluted environment [4]. A major step forward in legislative protection against health risks in the working environment was the UK Health and Safety at Work Act (HSWA) in 1974. This placed a duty on employers to safeguard the health and safety of all personnel entering the workplace. The Control of Substances Hazardous to Health (COSHH) regulations provide a framework aimed at protecting workers against health risks

24


25

from hazardous substances. The main requirement of the Personal Protective Equipment (PPE) regulations is that gloves, nasal masks, eye protection and safety footwear must be used wherever there are relevant hazards to health and safety [5]. Much helpful advice and data have been published by the UK Health and Safety Executive (HSE). Possible hazards to the general public from traces of chemicals in the environment have been increasingly the subject of active debate in the media and elsewhere in recent years. Since 1992 a Textiles Group of the Institute for Health Protection of Consumers and Veterinary Medicine in Germany has focused on the issue of health risks from textiles. Topics that have been studied include allergic reactions caused by textile materials, carcinogenic and mutagenic substances present in dyeings and finishes, azo dyes capable of being reduced to form hazardous arylamines, dye carriers, flame retardants, traces of dioxins in textile fibres, assessment of exposure to textile contaminants and the toxicological investigation of colorants and auxiliaries in textiles [6]. 2.1.1 Risk evaluation and prevention Indispensable to the management of risk by reduction or avoidance is a knowledge of the risk and the controlling factors determining its magnitude. Risk in this context is a function of the potentially harmful effects arising from inherent toxicological properties of the chemical and the extent of its bioavailability to the organism exposed. Risk is also a function of degree of exposure and the probability of its occurrence. Obviously, the risk of experiencing harmful effects can be lowered by limiting the degree of exposure and this approach affords a means of improving safety [7]. Industry has a substantial interest in helping the risk assessment approach to operate. Failure to do so will encourage regulation based on hazard considerations alone. There is already a trend in favour of the precautionary principle and the introduction of various ‘black lists’. Such discriminatory actions undermine the agreed basis for chemicals control and warrant an unreserved rejection by the chemical industry [8]. Thus two components, exposure and hazard, must be evaluated together in determining the level of risk posed by a given colorant or other chemical. Risk management may therefore be regarded as a series of interdependent steps (Figure 2.1). The process of risk evaluation for personnel working with dyes and textile chemicals has been discussed in detail [9]. The more extensive the database covering the toxicological, physical, chemical and application properties of the product, the easier it is to evaluate the risks involved. Although exposure levels are just as important as hazard potential for the risk evaluation, the quality of the exposure data is often the weak point in the data available. Consequently, in many instances it is not possible to be fully confident of the reliability of the risk evaluation, which may tend to be in error on the side of over-estimation. Particular attention should be given to improving aspects of exposure assessment (occupational exposure, consumer exposure, environmental release) [10]. The widespread use of colorants creates a great diversity of exposure situations. The most serious exposure potential exists for operatives in colorant manufacture and those employees of dye user firms engaged in weighing and dispensing. Dust particles less than 7 µm in size can gain access into the lungs and pose the greatest problem. It is not feasible to market all colorants in liquid form and considerable efforts have been devoted to the development of low-dusting solid forms. The monitoring of amine excretion in the urine of individuals exposed to

26


arylamines, or dyes expected to be metabolised in the body to such amines, offers a possibility of checking the adequacy of safety precautions [7]. The conventional classification of organic colorants into broad chemical classes or application ranges is of limited help in hazard assessment. It is not possible to generalise about the toxicological properties of entire groups like these. Biological activity can vary dramatically in spite of close structural similarities. Nevertheless, an observed toxic effect can often be attributed to a specific structural feature within a narrow subclass of colorants or to a specific metabolite produced from them, as in the formation of benzidine from its parent disazo dyes. Organic colorants generally exhibit relatively low acute toxicity. This is especially true of organic pigments because of their extremely low bioavailability. Of major concern, however, are the potential carcinogenic and allergic effects of specific dyes and intermediates. As a basis for the determination of risk it must be assumed that the colorants are properly handled and applied. It is not appropriate to estimate risk primarily on the basis of exposure values obtained under improper working conditions, or where appropriate plant and equipment are not available. Ensuring satisfactory operating conditions and training of operatives to handle products correctly is essential nowadays for technological success as well as for health and safety requirements. In this way, exposure levels can be kept below the threshold of unacceptable risk. It is reasonable to accept that for practical purposes levels of exposure exist below which the risk becomes trivial [7]. The various measures to reduce risk are an integral part of risk management. A state of ‘zero risk’ cannot be reached, but efforts to maintain exposure levels below the threshold of unacceptability must be unremitting, in order to increase the margin of safety. An essential prerequisite for effective risk control is the provision of readily accessible hazard information on the computer disc, in safety data sheets and on warning labels. It is prudent to minimise exposure to all chemicals through good working practice. Respiratory protection by approved equipment must be worn wherever dusts or aerosols are being generated or disturbed. A constructive approach to reducing risk is the replacement of hazardous products by safer ones. This cannot be achieved quickly in most instances, because of the complex profile of technical and economic requirements that governs selection of a colorant for a specific purpose [11]. 2.1.2 Safety data sheets From 1974 onwards, the member companies of ETAD (Ecological and Toxicological Association of the Dyestuffs Manufacturing Industry) issued safety data sheets for all organic colorants in their selling ranges. Subsequently, various EU directives have enforced the provision of material safety data sheets (MSDS) for all hazardous substances and preparations. The standard 16-heading format covers the composition of the material in question, possible hazards, first aid and firefighting measures, steps to be taken in the event of unintentional release, handling and storage facilities, limitation of exposure using personal safety equipment, physical and chemical properties, stability and reactivity, toxicological and ecological data, disposal instructions, transportation information and regulations [12]. Ecological test data include biodegradability, BOD (biochemical oxygen demand), COD (chemical oxygen demand), DOC (dissolved organic carbon) and TOC (total organic carbon) [13].


27

When a potentially hazardous substance or preparation is first placed on the market the producer must make available the MSDS for that product to all organisations purchasing or receiving that material for their potential use or testing purposes. All supplying companies in the EU are responsible for issuing appropriate MSDS to their customers and these must be in the appropriate languages of the member states in which the recipient firms are situated. The EU format is recommended as an appropriate model for all countries outside the EU that do not mandate other specific MSDS formats. 2.1.3 Ecolabelling The current multitude and diversity of ecolabelling schemes (national or regional, non-governmental, privately sponsored and company labels) has led to the confusion of consumers and raised questions about potential trade distortion. Criteria have been applied by ETAD to the evaluation of ecolabelling schemes [10], which should preferably: 1. be risk-based rather than discriminatory 2. provide objective criteria of evaluation 3. be regional or international in scope 4. apply to consumer goods rather than specific dyes 5. require dye selection only if there is real environmental benefit. The main deficiency of existing schemes is that they focus on the exclusion of certain hazardous dyes, but do not take into account that it is the conditions of manufacture and use that are the most important determinants of environmental impact. For an ecolabelling system to be worthwhile, it should really take account of the full history of the product from material sourcing through manufacture, distribution, application and disposal. The EU Ecolabelling Scheme is a voluntary system for consumer products, designed to assist product selection and to encourage manufacture of products that are less damaging to the environment. Criteria for a specific product group are developed by applying a lifecycle assessment (LCA) to gauge their impact at every stage of a product’s life. The scheme applies across all member states of the EU and is intended eventually to replace existing national labelling initiatives. The Nordic Swan label is another important multinational ecolabelling scheme, designed to guarantee an objective standard for products that must satisfy strict requirements. It is administered in Norway, Sweden, Finland and Iceland; the green swan logo is based on the emblem of the Nordic Council. Important national ecolabelling programmes include Blue Angel in Germany (the world’s first in 1977), Eco-Mark in Japan and Green Seal in the USA. The two leading private textile ecolabels operating in Western Europe are GuT and Oeko-Tex. Prominent companies in the European carpet industry founded the Gemeinschaft umweltfreundlicher Teppichboden (Association of Eco-friendly Carpets!) in 1990, with the aim of optimising the production cycle of textile floor coverings. Approximately 75% of the carpets manufactured in Western Europe are produced under the control of GuT. In 1991 the Austrian Textile Research Institute and the Hohenstein Research Institute jointly established Oeko-Tex, the International Association for Research and Testing in Textile Ecology. The OekoTex Standard 100 contains detailed analytical procedures for specific substances

28


that are ecologically hazardous, stipulating individual limit values based on research data. The detailed features of these various ecolabelling schemes have been reviewed [14] and an analytical comparison of the EU Ecolabel, Nordic Swan, Eco-Mark and Green Seal systems gave rise to a set of eight criteria to be taken into account in any effective ecolabelling programme [15].

2.2 Colorants in Waste Waters The high visibility of water-soluble dyes released to the environment ensures that only extremely low concentrations in watercourses would not be noticed. A typical limit of visibility in a river would be as low as 0.1 to 1 mg/l. but this varies with the illumination, colour and clarity of the water. The human eye can detect a reactive dye at a concentration down to 0.005 mg/l in pure water, particularly in the red to violet sector [16]. There is considerable debate, however, about what level of environmental hazard is represented by visible colour in a watercourse. The view has been expressed that dyestuffs should not be regarded as water pollutants because at concentrations of the same order of magnitude as these visibility limits their harmful effects are negligible [17]. Nevertheless, even though this colour problem is mainly if not entirely an aesthetic one, the fact is that the general public will not tolerate coloured amenity water and the problem therefore has to be addressed and rectified [18-20]. It has been estimated that although about 450 kilotons of organic dyes are manufactured annually worldwide, some 9 kilotons (2%) are wasted in manufacture and another 41 kilotons (9%) wasted during application [21]. The extent to which dyes from various classes are lost in exhaust dyebaths and wash liquors has been assessed (Table 2.1). Such losses vary considerably, however, according to depth of shade, liquor ratio and application technique. On average for all classes of dyes, losses are typically 10% for a deep shade, 2% in a medium depth and negligible for a pastel dyeing [22]. Residual colour in treated waste liquors from disperse dyeing may be attributable to the presence of dispersing agents of the formaldehyde-naphthalenesulphonate type. These agents contribute colour in two ways. Not only do these chemicals absorb visible light to a limited extent they also undergo photochemical reactions on exposure of the contaminated waste liquors to sunlight, resulting in the formation of yellowish oxidation products [23]. The main consideration regarding the environmental impact of residual dyes is concerned with toxicity to aquatic organisms. This is normally expressed in terms of the LC50 value, which represents the concentration of the substance under test that is required to kill 50% of the organisms exposed. With the exception of a small minority (about 2%, mainly basic dyes), organic dyes generally show only low toxicity to fish (Table 2.2) and other organisms such as Daphnia magna. There is little or no published data for the effects of dyes on this freshwater invertebrate [22]. Bioaccumulation is also important, defined as the factor F = Ca/Ce, where Ca is the concentration of the pollutant in the fish species and Ce that for the general environment [24]. The partition coefficient (P) of the colorant in an noctanol/water mixture can be used as an indicator of bioaccumulation. If P is less than 1000 it can be predicted that F in fish will be less than 100, a level at which no problems are foreseen. More than 75 dyes investigated by ETAD gave F values


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of less than 100. Water-soluble dyes do not bioaccumulate and even those disperse dyes and pigments that give P values above 1000 still show no evidence of bioaccumulation in fish [22]. Algae form an important part of the aquatic ecosystem, with algal photosynthesis a critical source of oxygen. The adverse effects of dyes in inhibiting growth of green algae (Selenastrum capricornutum) do not parallel the effects on fish, so that no conclusions about the one can be drawn from the other. Nevertheless, those basic dyes that yield low LC50 values in fish toxicity tests also tend to inhibit algal growth at concentrations as low as 1 mg/l. In an investigation by the American Dye Manufacturers Institute (ADMI), among a series of 56 dyes tested, 15 inhibited algal growth and 13 of these were basic dyes. Investigations have been carried out by ETAD and ADMI to determine whether dyes have an adverse effect on waste water bacteria and hence whether dyes could have any deleterious effect on the operation of effluent treatment plants. ETAD developed a screening test, later adopted by the OECD, to detect the effect of dyes on the respiration rate of aerated sludge. Using this test, it was found that only 18 of the 202 dyes examined had an LC50 value of less than 100 mg/l and these were all basic dyes. Of the 30 basic dyes tested only 12 did not show an inhibitory effect at the test level of 100 mg/l. At this limit dyes are unlikely to adversely affect the bacteria in polluted water or soil. In view of the good to excellent fastness of most colorants, it is not surprising that they are not readily biodegradable. Biodegradability may be defined as the degree of decomposition of an organic contaminant after biological treatment under specified conditions [25]. With the brief retention times normally prevailing in effluent plants, there is practically no evidence of biodegradation of colorants under aerobic conditions. Bioelimination includes removal of the colorant by adsorption on the biomass as well as that undergoing biochemical decomposition. A large majority of dyes can be absorbed by the biomass to the extent of 4080%. High adsorption occurs with basic dyes, direct dyes, disperse dyes and most of the premetallised and milling acid dyes [26,27]. The only dye types that are not substantially absorbed during biological treatment are the highly soluble multisulphonated levelling acid dyes and virtually all reactive dyes, which share similar characteristics.

2.3 Reuse of Dyes Reuse of dyebaths was once common practice, especially when applying natural dyes by traditional methods. When synthetic dyes were introduced and standard methods of manufacture were developed, there was a greater justification and demand for reproducibility at the dyeing stage. The pressure of dwindling resources and the economic and environmental benefits of recycling effect chemicals where practicable have revived interest in the possibility of dyebath reuse. Instrumental colour matching can be adopted to measure the content of dyes in a partly exhausted dyebath and to provide an appropriate shading addition to adjust the concentrations back to their original levels. Recycling is worthy of consideration for vat dyebaths because the redox process is reversible and only the dye absorbed by the cellulosic fibres is oxidised at a later stage of processing [28]. One of the dyehouses in North Carolina has been successfully recycling indigo dyebaths for many years [29]. Sulphur dye effluent from traditional dyeing systems contains sulphides and thiosulphates as well as

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the residual unfixed dye. The discharge of sulphide liquors to drain is not normally permissible because of the toxicity of hydrogen sulphide vapour that would be released under acidic conditions. Stringent standards are required for consent and sulphide waste is normally separated from other effluent streams and treated by oxidation or precipitation. Reactive groups in dye molecules that fail to react with the substrate are hydrolysed during dyeing or discharge of the residual dyebath. Recycling is therefore not a viable option in the case of reactive dyeings [28]. Bioelimination (the sorptive removal of dyes during biological treatment of effluent) is also ineffective for reactive dyes, which show little adsorption in this way. This behaviour is independent of the degree of sulphonation or the ease of hydrolysis of the reactive dye molecules. There is no chemical change to direct dyes during orthodox application, so their exhaust dyebaths are eminently suitable for recycling. Membrane processes have been used successfully to remove direct dyes from dyehouse effluents. There are possible cost savings associated with reuse of the electrolyte, depending on the rejection properties of the membrane [28]. Considerable adsorption of direct dyes occurs during biological treatment of dyehouse waste liquors containing them. This effect is not dependent on the degree of sulphonation of the direct dye molecules [22]. Disperse dyes remain unchanged during orthodox application and their exhaust dyebaths are suitable for recycling. Such dyes were successfully removed from an effluent stream by a microfiltration membrane module on an industrial scale [30]. In this trial the permeate was reused but not the dyes, although other work has demonstrated that recycling of disperse dyes is possible [31]. Moderate to high adsorption of disperse dyes takes place during biological treatment of dyehouse effluent. Basic dyes do not undergo chemical change during dyeing, but the proportion remaining in the exhausted dyebath is low (typically 2-3%) and scarcely justifies isolation for reuse. Recycling of the process water, however, may allow recovery of the inorganic salts and other auxiliary chemicals present [28]. There is normally a high degree of sorptive removal of residual basic dyes during biological treatment of effluent. This is important, because basic dyes tend to exhibit toxicity to aquatic organisms. Acid dyes remain unchanged during dyeing and are highly suitable for reuse. Removal of acid dyes from dyehouse effluent has been achieved by membrane processing on an industrial scale. The process water and auxiliary chemicals are also suitable for recycling to the dyebath [28]. The sorptive removal of acid dyes during biological treatment of effluent varies with their degree of sulphonation. Levelling acid dyes of high solubility exhibit low sorption, whereas the more hydrophobic neutral-dyeing dyes are bioeliminated to a much greater extent [22]. Reuse of the permeate from a reverse-osmosis membrane process on dyebath effluent containing premetallised acid dyes has been achieved [30].

2.4 Arylamines from Azo Dyes In the debate about the toxic effects of dyes and chemicals, there is no doubt that carcinogenic effects are perceived by the general public as the most threatening. Chemicals remain a focus for this concern in spite of the weight of evidence that they make only a minor contribution to the incidence of cancer


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[3,6,32]. The generally accepted estimate of cancer causation, based on mortality statistics, indicates that only 4% of all cancer deaths are attributable to occupational exposure. Another 2% are considered to arise from environmental causes and 1% from other forms of exposure to industrial products. As by far the largest chemical class, it is perhaps not surprising that azo dyes have attracted most attention with regard to carcinogenicity. Some structurecarcinogenicity trends for azo dyes and their metabolites have been discussed with a view to attempting prediction of dye carcinogenicity [33,34]. If an azo dye is carcinogenic and is relatively stable in the hydroxyazo tautomeric form, the dye itself is likely to be the active carcinogen. In contrast, those dyes that exist predominantly in the ketohydrazone form are more readily reduced to metabolites. In this case, the pro-carcinogen is likely to be an arylamine and the ultimate carcinogenic potential can thus be deduced from the availability of a suitable active site on the metabolite. Azo pigments, because of their extreme insolubility and low bioavailability, are unlikely to be metabolised even if they exist preferentially in the hydrazone form [33]. Most water-soluble azo dyes do not form carcinogenic arylamines when reductively cleaved. In many cases, the reduction products are arylaminesulphonic acids, which have little or no carcinogenic potential. Anaerobic conditions, such as apply in digesting sewage sludge or when residual colorants are present in river sediments, favour biodegradative reactions. Under these circumstances the biodegradation of dye chromogens is a primary cause of colour removal. Dyes are quite readily absorbed by sludge, suspended solids or sedimental matter. With azo colorants these conditions render the azo group susceptible to reductive cleavage, giving rise to arylamines as breakdown products [35,36]. There is concern that arylamine metabolites formed under such anaerobic conditions could be desorbed later into the aquatic aerobic environment and thus represent a hazard. The arylamines, however, are generally susceptible to aerobic degradation. Aniline and its monosubstituted derivatives, such as anisidines, phenetidines and toluidines, are readily degraded. Diaminobiphenyls, including benzidine, dianisidines, tolidines and dichlorobenzidines, are more resistant but still inherently biodegradable [37]. A wider selection of arylamine metabolites from azo dyes, including arylaminesulphonic acids, gave broadly similar results [38]. Epidemiological studies first alerted the colorants industries to causal links between certain manufacturing operations and an increased risk of bladder cancer among workers [3,39,40]. Regulations were passed in the 1960s that placed a virtual ban on the importation and use of certain dye intermediates, such as benzidine and 2-naphthylamine, and certain processes, including auramine manufacture [41]. Most responsible colorant manufacturers in Europe, Japan and the USA ceased production of benzidine-based dyes in the early 1970s due to inability to ensure their safe handling in the dyehouse. However, owing to the attractive economic and technical merits of such dyes on leather and cellulosic fibres, manufacture continued in other parts of the world (for example: Latin America, India and the Asia Pacific region). The voluntary cessation of manufacture of benzidine and the dyes derived from it by major manufacturers in the developed economies created a series of research targets to find replacements with the corresponding technical properties. Alternative non-mutagenic diamines were sought [42] and found to yield dyes exhibiting satisfactory performance [43]. Unfortunately, these were almost always substantially less cost-effective than the analogous benzidine-based

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products they were intended to replace and which were still available commercially from non-traditional suppliers. Following the emergence in the early 1990s of conclusive evidence of animal carcinogenicity from CI Acid Red 114 derived from o-tolidine and CI Direct Blue 15 derived from o-dianisidine, several dyemakers ceased production of these and other dyes made from these two diamines. A thin-layer chromatographic method was developed to identify benzidine, o-tolidine, o-dianisidine and related non-sulphonated benzidine derivatives and optimised to separate benzidine from these analogous diamines [44]. In 1994 the German government issued an amended regulation concerning consumer goods involved in direct body contact, including clothing, shoes and bedlinen. This banned the use of azo colorants that could be reduced to give any of twenty specified arylamines. These amines have been classified by the German MAK organisation as substances that have been unequivocally proven to be carcinogenic. Following the German ban, the EU ecolabelling scheme adopted the same list of twenty arylamines and added two more that have been classified by the EU as category 2 carcinogens [45]. A full list of these specified amines is given in Table 2.3, including the actual names on the official list and some alternative systematic names. The German regulation embraced the concept that an azo dye capable of being cleaved to yield a carcinogenic arylamine is itself a carcinogen. A group of 278 azo dyes has been recognised as being carcinogenic according to this definition [9]. Most of these are derived from o-toluidine, benzidine and its symmetrically 3,3'-disubstituted derivatives o-dianisidine and otolidine (Table 2.4). When the implications of this unilateral ban by the German authorities began to be realised, it seems to have become a prime example of how not to enact legislation in such a commercially and technically complex area. Although the major dyemakers in Western Europe, Japan and the USA had already ceased manufacture of benzidine-derived azo dyes in the early 1970s, the 1994 ban had an immediate and substantial impact on certain sectors of the dye-using industries, notably cotton textiles and leather. The globalisation of trade in the 1990s ensured that there were many repercussions both inside and outside the EU. No risk analysis had been carried out and there was no consultation with interested parties outside Germany before the ban, is spite of notification procedures required by EU regulations [46]. Although the 1994 regulation specified consumer goods, suppliers were asked by German retailers to guarantee that all the materials supplied were free from the banned dyes. Thus companies higher up the supply chain became involved, if their goods containing such dyes were to be imported into Germany. A major stumbling-block initially was the lack of an official list of dyes to be banned. This left dye users uncertain about the availability of acceptable dyes from suppliers, especially colorant merchants who do not manufacture the products that they sell. Until 1996, there was no officially recognised test method to isolate and identify all the specified arylamines after extraction from textiles or leather. Analysis was sometimes undertaken by testing organisations lacking the necessary skills or expertise. It was not surprising, therefore, that spurious results (false positives) were sometimes obtained [46]. For example, 2-naphthylamine has been detected occasionally in dyes derived from 1-naphthylamine, owing to contamination of the intermediate [47].


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Benzidine may be formed by reduction of 4,4´-dinitrobiphenyl, which can arise by homolytic dediazoniation of the 4-nitrobenzenediazonium ion and dimerisation of the resulting 4-nitrophenyl radicals [47,48]. In a similar way, 4-aminobiphenyl can result from dediazoniation of the benzenediazonium ion and subsequent coupling of the resulting phenyl radical with aniline [47,49]. Hydrolysis of the amide linkage in CI Pigment Red 8 can release p-chloroaniline and decomposition of the non-azo dye CI Acid Blue 150, made from bromamine acid and benzidine, can regenerate benzidine [50]. It is also possible for 2-naphthylamine to be formed by desulphonation from water-soluble dyes derived from Tobias acid (2-naphthylamine-1-sulphonic acid) [50,51]. In 1996 an official German analytical method was published for the detection of banned amines in relation to cotton, viscose, wool and silk; a second method was introduced for leather [52]. The official procedure recommends reduction at 70°C with a sodium dithionite solution buffered to pH 6 with citrate [53]. More aggressive conditions are known to produce false positive results where the amine detected is an artefact of the test procedure, resulting from chemical reactions other than azo cleavage [47,50]. The thin-layer chromatographic separation depends on differences in rates of diffusion of the arylamines with various eluants on sorption layers of varying polarity [54,55].

2.5 Sensitisation and Acute Toxicity of Dyes Allergic contact dermatitis or skin sensitisation by dyes or other chemicals appears as a persistent irritating rash. The presence of certain dye stains on the skin has been known to accelerate the reddening effect of sunlight exposure (erythema). The causation of skin sensitisation by dyes, both in animal tests and in exposed workers or the general public, has been reviewed [56,57]. Cases of occupational skin sensitisation [58] attributable to dyes are uncommon [59], even in those workplaces where inadequate handling precautions have been taken. Occasionally, reports of organic pigments causing skin sensitisation have arisen but such cases appear to arise from the presence of soluble impurities. Typically, disperse dyes of the nitrophenylazo (e.g. CI Disperse Red 17) or aminoanthraquinone (e.g. CI Disperse Blue 3) types have been implicated in cases of contact dermatitis [60,61]. Circumstances common to such cases appear to be heavy depths of low fastness on nylon (rather than polyester) and occurring in articles of clothing that are in direct contact with the skin, often in areas that are likely to become moistened by perspiration. Hosiery, socks, blouses and close-fitting athletic or fashion wear, such as velvet leggings, are representative of the types of garment where this problem has arisen [40]. A list of nine such dyes that may be sensitising has been drawn up: CI Disperse Yellow 3, Orange 3, 37 and 76, Red 1 and Blue 1, 35, 106 and 124. Garments containing any of these dyes should carry a hazard warning label and for contact clothing such as hosiery they should not be used. The possible mechanism of sensitisation in the case of nitro-substituted azo dyes is thought to be the production of the quinonimine derivative by reduction and oxidation [59]. Sensitisation of the respiratory tract by inhaling dust particles from various chemicals has frequently been reported in industry. It is likely to result in symptoms of respiratory disease or distress when the sensitised individual is exposed to a specific allergen. Respiratory allergy is the clinical manifestation of this state, with bronchial asthma or allergic rhinitis (resembling hay fever) constituting typical disease symptoms. It is believed that relatively high exposure

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levels are important in the induction phase. There is also evidence that a predisposition to respiratory allergy may be caused by genetic or other factors. As there is no suitable animal test system for respiratory sensitisation, ETAD has provided guidance on the hazard labelling of reactive dyes in this context [62]. Instances of severe sensitisation to the dust from reactive dyes have been reported [63]. These prompted the UK Health and Safety Executive to initiate a study involving about 440 workers in 51 dyehouses who were in contact with reactive dye powders. About 15% of them showed work-related respiratory or nasal symptoms. In 21 individuals their allergic reactions could be attributed to contact with one or more specific reactive dyes [64]. Reactive dyes are capable of reaction with amino, hydroxy and thiol groups in proteins. Such a reaction seems to be the initial step of the sensitisation process. The reactive dye may react with human serum albumin (HSA) to form a dye-HSA conjugate, which behaves as an antigen. This in turn gives rise to specific antibodies and these, through the release of mediators such as histamine, produce the allergic symptoms [6,64]. Acute toxicity refers to effects that occur within a brief time after a short-term exposure, such as a simple oral administration. The generally low acute oral toxicity of colorants is well-established [65-67]. This is normally expressed in terms of the LD50 value, a statistically derived dose that is expected to cause death in 50% of treated animals (typically rats) when administered over a prescribed period in the test. In 1974 ETAD began a programme to generate a systematic toxicological database. More than 80% of commercial dyes have an LD50 value (rat, oral) greater than 5000 mg/kg. In response to an EEC Council Directive of 1979 regarding the labelling of dangerous substances, ETAD in 1986 decided to publish a list of twelve colorants that have been classified as toxic on the basis of their acute peroral LD50 values. These varied within the range 25 mg/kg (CI Basic Red 12) to 205 mg/kg (CI Basic Blue 81) and the list included six basic dyes, three azoic diazo components, two acid dyes and one direct dye. Although such data provide an essential basis for advice on safe handling procedures, long-established experience indicates that dyes, and even more so organic pigments, present few acute toxicological risks providing good practices are followed.

2.6 Heavy-Metal Contaminants in Dyes Much effort has been devoted to minimising the trace metal content of colorants and in effluents from dyemaking plants. Heavy metals are widely used as catalysts in the manufacture of dyes. Mercury is used when sulphonating anthraquinones, copper when reacting arylamines with bromoanthraquinone and dichromate as oxidant when making triphenylmethane dyes. Certain basic dyes and stabilised azoic diazo components (Fast Salts) are marketed in the form of tetrachlorozincate complex salts. Metal salts are used as reactants in dye synthesis, particularly for the ranges of premetallised acid, direct or reactive dyes, which usually contain copper, chromium, nickel or cobalt. Difficulties arising particularly from the presence of chromium residues in effluents from factories involved in the manufacture or use of premetallised dyes have stimulated research on dye complexes of iron (III), which is unlikely to give rise to significant pollution problems because of a much higher permitted level in effluent compared with that for chromium [68-70].


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The toxic effects of trace metals towards animals or aquatic life are highly dependent on the physical and chemical form of the contaminant [71]. For example, dissolved copper (II) or chromium (III) ions are highly toxic, whereas the same atoms coordinated within stable organic ligands such as dye molecules are not harmful. Unfortunately this is not widely acknowledged in setting limits for consent conditions, where the total metal content is often specified rather than the forms in which it is present. The permitted levels for trace metals in dyehouse effluents vary from one country to another and even between different areas in the same country [1,25]. When restrictions on the contamination of effluent by chromium residues were imposed in the 1970s, the initial reaction in the wool dyeing industry was to predict the rapid demise of chrome dyes. This expected decline did not materialise because of the outstanding fastness of chrome dyeings and the efforts made to minimise effluent pollution [1,21]. In 1996 member firms of the GuT carpet ecolabelling scheme introduced a voluntary ban against the use of metalcomplex dyes on certain nylon floorcoverings. Extension of this ban to all carpets made from nylon, wool or their blends has been predicted [72]. Ecolabelling schemes covering apparel and household textiles must also take account of the presence of premetallised dyes because of the obvious risk that extraction into perspiration or saliva can take place from dyeings of inadequate wet fastness [73]. The presence of residual unbound transition-metal ions on a dyed substrate is a potential health hazard. Various eco standards quote maximum permissible residual metal levels. These values are a measure of the amount of free ions extracted by a perspiration solution [74]. Histidine is an essential amino acid that is naturally present as a component of perspiration. It is recognised to play a part in the desorption of metal-complex dyes in perspiration fastness problems and in the fading of such dyes by the combined effects of perspiration and sunlight. Virtually all of the chrome dyes that remain of major commercial importance are simple monoazo structures. These products are easy to manufacture from lowcost intermediates, readily water-soluble and build up well to heavy depths. Owing to their relatively small molecular size they show good level-dyeing properties when applied to wool at pH 4 and the boil. The unique combination of level-dyeing behaviour and outstanding wet fastness offered by chrome dyes made them increasingly important in the 1970s, when shrink-resist wool knitwear suitable for laundering in household washing machines was introduced. Since then there has been a growing awareness of the environmental hazards associated with chromium compounds, especially the hexavalent chromium form [75]. Although 10 mg per day of chromium (III) in food is normal for good health, it is important to concede that chromium (VI) is highly toxic to mankind and aquatic life [76]. Chromium is more toxic in soft than in hard water and game fish are more susceptible than coarse fish, factors that are relevant in determining consents [22]. Typical limiting values in the UK regarding permissible amounts of chromium for discharge to effluent are 0.2-0.5 mg/l as the more potent chromium (VI) dichromate ion and 2-4 mg/l as the chromium (III) cation. Proposed ecological criteria for the EU ecolabel with respect to chromium baths are 0.5 mg/l for chromium (VI) and 5 mg/l for chromium (III) ions [77]. Legislation covering the release of chromium-containing effluents is becoming increasingly strict, especially in Germany, the UK and the USA [78]. Draft regulations indicate that no more than 0.1 mg/l total chromium will be tolerated in future [76].

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Originally the amounts of dichromate used in the traditional afterchrome process varied between about 25 and 50% of the total amount of chrome dye present, with the lower and upper limits set at 0.25% and 2.5% of the mass of wool. These quantities were well in excess of the stoichiometric amount required even for formation of the 1:1 complex. This approach resulted in excess dichromate remaining in the aftertreatment bath for discharge to effluent, as well as on the wool fibre where it contributed to further oxidative degradation. Users of chrome dyes are increasingly concerned with dyeing under mild conditions, typically at pH 4.5 and 85°C followed by chroming at pH 3.5-3.8 and 90°C to minimise wool damage [79,80]. Chroming in a fresh bath tends to give lower residual chromium content but does increase the processing costs. Every effort should be made to exhaust the dyebath as much as possible, because any residual mordant dye will complex with chromium (III) ions in the dye liquor. Apart from complicating effluent treatment, this raises the possibility of lower fastness resulting from deposition on the surface of the wool. Concern regarding exposure to chromium is not just related to effluent discharge. It is obvious that residual unbound chromium present on the fibre is also a potential hazard. The Oeko-Tex ecolabel specifies 1 ppm total chromium or cobalt on babywear and 2 ppm chromium or 4 ppm cobalt on other garments. These figures represent the amount of free metal extracted by a standard perspiration solution. In general, typical 1:2 metal-complex dyeings will satisfy these requirements in full depths, chrome dyeings only to medium depths and premetallised 1:1 complexes only in pale-depth dyeings.

2.7 Halogenated Colorants During the 1990s, several environmental agencies and activist groups argued that the banning of chlorine and all chlorinated organic chemicals will be necessary to protect the environment. The impact of such a comprehensive ban would be immense, particularly for those organic dyes and pigments that are predominantly dependent on chlorine-containing intermediates used in their manufacture. Approximately 40% of all organic pigments contain chloro substituents in the pigment structure itself, although this corresponds to only 0.02% of total chlorine usage. In the EU and Japan, controls on the discharge of absorbable organohalogen (AOX) compounds are becoming increasingly severe. Certain shrink-resist treatments and insect-proofing agents for wool, trichlorobenzene carriers for polyester dyeing and reactive dyes of the chloroheterocyclic types certainly fall into this category [81,82]. Interestingly, organofluorine compounds do not fall into the AOX classification since the fluoride ion liberated as soluble silver fluoride according to the test protocol is not detected. It seems likely, therefore, that reactive dyes containing vinylsulphone or fluoroheterocyclic groups will become more important [21]. Many direct, disperse and vat dye structures contain chloro-substituted aryl nuclei and some have trifluoromethyl substituents to enhance light fastness. It is to be hoped that rational evaluation of the available evidence will convince regulatory authorities that the mere presence of an inert chloro substituent in a molecule does not mean that it will pose an environmental risk [40].


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2.8 Natural Dyes In Germany during the 1970s there was a growing demand by supporters of the Green movement for greater use of natural dyes of vegetable origin to dye natural fibres such as wool, silk and cotton. This trend has been taken up enthusiastically in tropical countries with climates suitable for growing such dyeyielding plants [83,84], including woad [85], lac dye [86], lichens [87] and even tea plants [88]. Research has been carried out with a view to minimising the amounts of mordanting chemicals necessary to apply natural dyes [89-91], in order to offset criticism that such processes would be as polluting as the use of premetallised synthetic dyes. Contamination of effluent streams with residual heavy metals from mordanting [92,93] is by no means the only drawback of a return to the multi-stage coloration methods that prevailed before the discovery of synthetic dyes [94,95]. Natural dyes are tinctorially weaker and duller; variability of harvest, climate and location makes definition of a standardised product extremely difficult. They often give level-dyeing problems and show inferior fastness to light and washing compared with their synthetic counterparts. Only madder red and indigo blue are able to meet typical commercial standards of fastness. From the viewpoint of application, most natural dyes fall into the mordant class and require a variety of metal salts to assist in their fixation to natural fibres. There are also a few that can be regarded as vat, direct or acid dyes [96] but they serve only to supplement the limited colour gamut attainable by a two-stage mordant dyeing process. Reactive, disperse, basic and premetallised dyes are entirely absent, so that natural dyes are of zero interest for the dyeing of polyester, polyester/cotton, nylon or acrylic fibres. Calculations show that about 400 kg of cultivated dye plants are required to yield enough dye for dyeing the same depth as given by 1 kg of synthetic dye on cotton or wool, at a cost ratio of about 100:1. Vegetable dyes have to be isolated from leaf extracts and the large volume of residual biomass requires disposal [97]. Furthermore, if the present worldwide consumption of dyed cotton were coloured with natural vegetable dyes rather than synthetic ones, approximately 30% of the world’s agricultural land would be needed for their cultivation [92,94]. This is more than 13 times the area currently in use to grow the cotton and does not take into account what would be required if the other textile fibres, paper and leather were also to be coloured in the same way. The extraction of natural dyes from animal sources is just as wasteful of resources, time-consuming and by no means environmentally friendly. To obtain 1 kg of cochineal scarlet requires the harvesting of 150,000 insects reared on cactus plants. The living insects are swept off the leaves into bowls or cloths and executed by immersion in steam or hot water, then dried by prolonged exposure to sunlight. If production of the classical vat dye Tyrian purple were to be restored on a large scale, isolation of 1 kg of this colorant would demand the slaughter of about 10 million specimens of a Mediterranean mollusc (Murex brandaris). Vast quantities of these discarded shells that develop an obnoxious odour when exposed to the sun would become unsightly spoilheaps, extremely offensive to the coastal environment [72,94].

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2.9 Reducing Agents The most important reducing agent that is necessary for several key dyeing processes is sodium dithionite (Na2S2O4, sodium hydrosulphite, CI Reducing Agent 1). In conjunction with caustic soda, it is almost always the preferred reducing system for vat dyes and the most effective reduction clear for disperse dyeings on polyester. With sulphur dyes, however, the alkaline dithionite system is difficult to control and some of these dyes may be partly destroyed by overreduction. Nevertheless, it is effective with sulphurised vat dyes and the CI Solubilised Sulphur brands. There are serious potential environmental problems associated with sodium dithionite, since in effluent it produces sulphite and sulphate ions. Although the sulphite can be readily oxidised to sulphate, this does not alleviate the major problem, since high concentrations of sulphate can cause damage to unprotected concrete pipes and drainage chambers. Thus there are environmental reasons for seeking effective alternatives to dithionite, although in most instances their higher cost and greater stability to atmospheric oxidation makes them of particular interest for continuous dyeing and printing rather than for exhaust dyeing or reduction clearing. Certain derivatives of sodium dithionite are commercially significant, particularly sodium formaldehyde-sulphoxylate (HOCH2OSONa, sodium hydroxylmethanesulphinate, CI Reducing Agent 2) made by the reaction of sodium dithionite with formaldehyde. The corresponding product of reaction with acetaldehyde, sodium acetaldehyde-sulphoxylate (HOCH(CH3)OSONa, sodium hydroxylethanesulphinate), is less important but both of these agents have been used in vat printing, especially the flash-ageing process. They are much more stable than sodium dithionite at lower temperatures and can be used to prepare stable pad liquors and print pastes. At higher temperatures in steaming or flash ageing they are capable of bringing about rapid reduction of vat dyes. As vat dyes are invariably fixed under alkaline conditions, the sodium salts of sulphoxylic acid are preferred to the basic salts of zinc or calcium. These are HOCH2OSOZn(OH), zinc formaldehyde-sulphoxylate (CI Reducing Agent 6), and HOCH2OSOCa(OH), calcium formaldehyde-sulphoxylate (CI Reducing Agent 12), which are unstable under alkaline conditions. Sodium formaldehyde-sulphoxylate has been used occasionally in combination with sodium dithionite but other two-component systems based on formaldehydesulphoxylates have usually depended on an accelerator or catalyst system. For example, a process that has been adopted to some extent in bulk practice [98,99] comprises a strongly alkaline solution of sodium borohydride (NaBH4, sodium tetrahydroborate) together with a second reducing agent consisting of sodium formaldehyde-sulphoxylate and the catalyst sodium nickel cyanide, NaNi(CN)2. Various advantages have been claimed for this process, but there are misgivings regarding the environmental acceptability of sodium nickel cyanide [100]. Alternative accelerators used with sodium formaldehyde-sulphoxylate include sodium dimethylglyoxime, anthraquinone and various aminoanthraquinonesulphonic acids. Although sodium borohydride is itself a reducing agent, it generally reacts too slowly for use alone in vat dyeing systems; nor is there any evidence that it will act as a stabiliser for sodium dithionite [101], as has sometimes been suggested. Trisodium nitriloethanesulphinate, N(CH2CH2OSONa)3, has been proposed as a reducing agent for flash-age printing and batchwise package dyeing with vat dyes


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on cotton at high temperature [102]. This agent does not appear to have attained commercial application, however. Sodium formaldehyde-sulphoxylate is rarely, if ever, used for the application of sulphur dyes owing to handling difficulties, inadequate cost-effectiveness and poor efficiency [103]. The performance of this rather stable reducing agent in the reduction clearing of disperse dyeings on polyester is also unsatisfactory. In a detailed comparison with four other reducing systems, formaldehyde-sulphoxylate showed inadequate improvement of fastness ratings even when applied in the presence of anthraquinone as activator [104]. Thiourea dioxide (NH2.CSO2.NH2, formamidinesulphinic acid, CI Reducing Agent 11) is a powerful reducing agent for vat dyes. It gives lower concentrations of sulphite and sulphate anions in effluent than sodium dithionite, but shows certain practical disadvantages. In hot aqueous alkali sodium formamidinesulphinate decomposes to yield urea and the active reducing agent species sodium hydrogen sulphoxylate (HOSONa). Although thiourea dioxide is more stable than dithionic acid under acidic conditions, sodium formamidinesulphinate formed in alkaline media is more readily oxidised than sodium dithionite, thus negating the potential advantage of the higher stability in acid solution. Thiourea dioxide can cause over-reduction of indanthrone dyes. Experimental work has indicated the possibility of using thiourea dioxide in combination with other agents such as (a) sodium dithionite, formaldehyde and caustic soda, or (b) saturated aliphatic ketones, but commercial exploitation has not been evident. In a comparison of five reduction clearing systems for disperse dyeings on polyester, only thiourea dioxide gave results as good as sodium dithionite. It is three times as expensive for this purpose but causes only half the sulphur pollution of dithionite in effluent [104]. In a detailed evaluation of exhaust dyeing with sulphur dyes, thiourea dioxide gave colour yields and fastness ratings similar to those with sodium sulphide, although is some cases slightly different hues were observed. On balance, thiourea dioxide is much less hazardous to the environment than sodium sulphide; the major improvement is the decreased amount of oxidant required for chemical treatment of the effluent and a second advantage is the markedly lower sulphate ion content. Although thiourea dioxide is more expensive, calculations of processing costs must take into consideration the cost of treating waste liquors compared with those containing sulphide [105]. Hydroxyacetone (CH3COCH2OH, acetol) is a sulphur-free reducing agent originally introduced for vat dyeing that has also proved moderately successful with sulphur dyes. It requires strongly alkaline conditions at elevated temperatures because of its relatively sluggish reducing rate; the vapour is flammable and dyebaths have a penetrating odour characteristic of acetone. Hydroxyacetone is suitable for application in dyeing with indigo, vat or sulphur dyes, including the continuous dyeing of cotton yarn with sulphur dyes or indigo, as well as the exhaust dyeing of knitgoods with vat dyes that are difficult to reduce. Hydroxyacetone does not cause over-reduction of indanthrone vat dyes but does give different tones with carbazole vat dyes compared with conventional dithionite methods. Although colour yields are not quite as high as with dithionite, the advantages include biodegradability, lower COD values and decreased chemical usage. The effluent contains no sulphide, sulphite or sulphate, but hydroxyacetone does contribute to the dissolved organic carbon content. There are environmental benefits claimed for the use of mixtures of sodium dithionite and hydroxyacetone [106]. Organic complexes of iron have been investigated as alternatives to sodium dithionite in vat dyeing [107] and the reduction clearing of disperse-dyed

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polyester [104]. Iron (II) hydroxide Fe (OH)2 is a powerful reducing agent and this reducing power increases with higher alkalinity of the medium. Alkalinity results in precipitation, however, and an iron (II) complex must be formed in order to maintain a homogeneous solution. The selected complex must be reasonably stable but not so inert that the iron (II) ion cannot exert its reducing action. Complexes of iron (II) chloride with triethanolamine or gluconic acid (an oxidation product of glucose) are suitable, the acid complex being favoured on environmental grounds because it does not contain nitrogen or sulphur. It is advantageous to keep the gluconic acid concentration low to ensure a lower COD value in the effluent, but too low a concentration of iron (II) ions results in paler unlevel dyeings because of insufficient vatting of the pigment. The use of iron (II)-gluconic acid did not cause over-reduction of sensitive dyes even when dyeing was prolonged. With most dyes the colour yield was equal to that given by sodium dithionite [107]. Traditionally the most widely used reducing agents for sulphur dyeing have been sodium sulphide (Na2S) and sodium hydrosulphide (NaHS). Technically these are still the most widely preferred, not only for their effectiveness but also because they are relatively inexpensive. Environmental concerns are gradually curtailing the use of sulphides as reducing agents [108,109], although as late as 1995 some 90% of all sulphur dyes applied worldwide were still reduced by sulphides [103]. The environmental problems arising from sulphide usage include the toxicity of hydrogen sulphide, corrosion of the effluent drainage system, damage to the treatment plant and the often associated high pH and unpleasant odours. Sulphides cause no odour nuisance above pH 9 but at neutral or acidic pH values gaseous hydrogen sulphide is liberated. Neutralisation or acidification may occur in the dyehouse or during waste stream mixing. In some applications, particularly in jet and winch dyeing, there is a danger that dissolved sulphides may be prematurely oxidised by air. Antioxidants, added along with sulphur dyes and primary reducing agent, may be applied in order to minimise this problem. Polysulphides (such as Na2S2 or Na2S4) or sodium tetrathionite (Na2S4O6) have been widely used for this purpose and provide improved dyebath stability. However, polysulphides yield free sulphur on acidification and this can lead to acrid odours of sulphur dioxide on the dyed substrate. An alternative approach to sulphide dyebath stabilisation is to add a relatively more stable alkaline reducing agent such as sodium dithiodiglycolate (NaOOCCH2SSCH2COONa) [110]. Indeed, such compounds may be selected as primary reducing agents in conjunction with alkali. Although they do not give rise to environmentally undesirable inorganic sulphides in the effluent, their chemical stability results in high COD values, often causing more problems than those arising from sodium sulphide [111]. 2-Mercaptoethanol (HSCH2CH2OH) with alkali has been suggested as an alternative to sulphide methods [112], offering the advantages of no sulphides in the effluent and no odour from the dyebath, although the product itself can give off unpleasant and highly toxic fumes. This sulphur dyeing process is relatively costly with a tendency towards lower yields and a more restricted range of suitable dyes than when using traditional systems, so that it has not achieved significant commercial exploitation. The most promising alternative to sulphides, from an environmental point of view, is the reducing sugar glucose with sodium hydroxide or carbonate. This system does not satisfactorily reduce all sulphur dyes, however. It is reasonably effective with the CI Solubilised Sulphur brands [112], with which it may be used


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either alone or in conjunction with sodium polysulphide, usually resulting in increased dye yields. It can be used as a supplementary reducing agent with the CI Leuco Sulphur brands, thus giving a lower sulphide content in the dyebath, or together with sulphide or polysulphide in the reduction of the traditional waterinsoluble CI Sulphur brands. The glucose reducing system has a characteristic odour of burning sugar that many people consider preferable to the odour of an alkaline sulphide bath, although others find it excessively sweet and nauseous. Nevertheless, the versatility of glucose-based binary systems has been emphasised [103]. The glucose system is pH- and temperature-sensitive, becoming transformed into various decomposition products and gradually losing its reducing power. The intermediate by-products possess some reducing action but are not sufficiently stable. The binary dithionite/glucose system has a reduction potential only slightly lower than that of dithionite alone, even though the potential of glucose alone is much lower. The careful addition of glucose lowers the potential of sodium dithionite to the point where full colour yield is achieved without the risk of over-reduction. Dyeing tests have confirmed that although sodium dithionite alone is exceptionally concentration-sensitive, the addition of glucose gives a more stable system. Optimal colour yield and reproducibility are obtained even if dyeing temperature, time and chemical concentrations fluctuate slightly, within narrow limits. Similar results have been observed for other binary systems of glucose with hydroxyacetone or sodium formaldehyde-sulphoxylate as stabiliser.

2.10 Carriers Although polyester or cellulose triacetate fibres are usually dyed under pressure, their blends with wool are still dyed at or near the boil. Under these conditions a carrier must be used to ensure adequate exhaustion and build-up of disperse dyes within a commercial dyeing cycle. Even in high-temperature dyeing the usual maximum temperature (about 130°C for polyester and 120°C for triacetate) may be excessive, as when dyeing textured polyester fabrics that may suffer loss of crimp at 130°C. Smaller amounts of a suitable carrier may be added in these circumstances to promote migration and assist more rapid and complete exhaustion. Carrier compounds fall into four main classes: phenols, chloroalkyl compounds, aryl hydrocarbons and aryl esters. Typical examples in commercial use include biphenyl, trichlorobenzene, dichlorophenyl ethers, o-phenylphenol, Nalkylphthalimide, methylnaphthalene, methyl cresotinate, methyl salicylate, butyl benzoate, diethyl or diallyl phthalate. Mechanisms proposed for carrier action and ideal requirements of carrier chemicals have been comprehensively reviewed [113]. Over the last decade the use of carriers has declined markedly and continues to do so, essentially for health, safety and environmental reasons [114-117]. In some countries these products are now virtually banned. Nearly all carrier compounds exhibit some or all of the following hazards: toxicity, physiological irritancy or poor biodegradability (Table 2.5). Harmful effects from carrier dyeing can arise in three ways: 1. carrier that is volatilised during dyeing or subsequent heat setting becomes an atmospheric contaminant

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2. residual carrier in the fibre can be a health hazard, as well as causing an unpleasant odour on heating or during storage 3. residual carrier in the dyebath contributes to effluent pollution and may be environmentally harmful. Typical pollution loads for comparable high-temperature and carrier methods are given in Table 2.6. Carrier residues differ considerably in odour. A dry heat treatment of dyed polyester at 160-180°C after dyeing, to volatilise the residual carrier, is the most effective method of minimising problems of odour and anomalously low light fastness. The steam volatility of carrier chemicals and their toxicity to human and plant life need careful consideration. For example, o-phenylphenol has relatively low volatility in steam and traditionally has been preferred for use in machines open to the atmosphere. The chlorinated benzenes, on the other hand, are readily steam-volatile and are toxic, so should not be used in machines where volatilised carrier is likely to condense inside the roof of the machine, forming ‘carrier spots’ where they fall onto the fabric. Biphenyl is relatively non-toxic to river life but is not readily biodegradable; methylnaphthalene, also of low toxicity, is moderately biodegradable, but halogenated benzenes are both toxic and difficult to biodegrade.

2.11 Volatile Organic Compounds Carrier chemicals represent an important subclass of the large group of volatile organic compounds (VOCs). The toxicity of many aryl hydrocarbons and their chloro derivatives is well-established but they are often useful as specific low-cost solvents and extractants. They may be involved in a range of industrial syntheses and are often found in effluents from chemical plants. Appropriate waste water treatment is essential and it is advisable to separate such effluents into three streams: (a) aryl hydrocarbons, (b) chlorinated compounds, and (c) low concentrations of mixed contaminants. Each stream can be processed individually to avoid problems arising in subsequent biological treatment [118]. A 1997 EU Directive defined a VOC as any organic compound having a vapour pressure of at least 10 Pa at 20°C, or corresponding volatility at other operating temperatures in industry. A rapid technique for determining whether any given organic liquid should be characterised as a VOC has been described [119]. The 1990 Environmental Protection Act defined a VOC as any carbon compound that participates in atmospheric photochemical reactions. Carbon monoxide, carbon dioxide, carbonic acid, ammonium carbonate, metal carbonates and carbides are all excluded. A broader description of atmospheric contaminants is that of hazardous air pollutants (HAPs) and a programme of regulations (MACT standards) is being developed, based on maximum admissible control technology. The best source of information that signals the potential hazards of a solvent or other VOC is the SDS available from the product supplier (section 2.1.2). Precautions in handling, storage, transportation and disposal are provided. Recommended occupational exposure conditions are defined in terms of threshold limit values (TLVs). The prospect of fire hazard becomes important whenever the temperature of a solvent exceeds its flash point [120]. An EU commission proposal covering the use of VOCs does not significantly affect typical textile dyeing and finishing plants but textile coating and printing


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processes that exceed a defined threshold of VOC consumption are included within the legislation [4]. Only a few specific solvents are used in the formulation of aqueous-based coatings. They can be quantified individually and the total VOC content determined directly. A solid-phase micro-extraction technique with gaschromatographic analysis of the extract has been recommended [121]. The Environmental Protection Act obliges printers of paper and packaging materials to prevent the atmospheric release of solvents by: 1. reduction at source and eventual elimination or replacement of solvents 2. abatement of emissions using biological digestion, thermal oxidation or solvent recovery. Carbon adsorption systems for solvent recovery offer the most attractive solution for factories using only one or two solvents [122]. Dry-cleaning establishments and even spot removal using solvents, as frequently necessary in garment processing and finishing plants, are included in EU legislation covering VOCs [4]. Traditional dry-cleaning with perchloroethylene has been subjected to increasingly stringent limitations and research has been carried out to seek eco-friendly alternatives. More than 130 organic solvents were screened for this purpose and twelve of them were selected for further study. Excellent cleaning performance was achieved using ultrasound together with a relatively dilute aqueous solution of a propyl, n-butyl or t-butyl monoether of propylene glycol (ROCH2CH2CH2OH) [123].

2.12 Formaldehyde For decades the presence of formaldehyde in textiles and other consumer products has given rise to much controversial discussion. Consumer protection agencies have been extremely critical about the alleged health risks, whereas producers have claimed that it is relatively innocuous and readily detectable by its strong odour and eye irritation at tolerably low concentrations (0.01-0.1 ppm). However, workers exposed frequently to the vapour soon become acclimatised and can tolerate substantially higher levels (1-10 ppm). The present UK maximum atmospheric exposure limit in the working environment is 2.0 ppm. Formaldehyde vapour causes coughing and temporary shortness of breath. However, its aqueous solubility results in rapid absorption mainly in the upper airways, so that the irritant effect does not reach the lungs. It is a severe eye irritant, dissolving in the ocular fluids and causing inflammation. After more than a century of commercial exploitation and extensive use by the medical profession, there is still no evidence that exposure to formaldehyde has caused cancer in humans [124]. The main cause of allergic contact dermatitis from cotton and its blends with synthetic fibres is the presence of residual free formaldehyde and N-methylol reactant finishes capable of releasing formaldehyde [125]. Similar derivatives of formaldehyde are sometimes used as stabilising agents to minimise wool fibre damage in the dyeing of wool blends above the boil. Repeated contact of the skin with formaldehyde-treated textiles can result in dermatitis at concentrations as low as 2% by mass of the formaldehyde derivative on the textile material. The release of formaldehyde from resin-finished textiles into the atmosphere is governed by several factors, including: 1. choice of resin/catalyst system

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2. inadequate curing of the applied resin 3. omission of the washing stage after curing 4. extensive use of steam pressing and forming in garment manufacture 5. prolonged storage of finished fabrics or garments in confined spaces 6. efficiency of local ventilation system 7. atmospheric conditions of storage, high temperature and humidity favouring formaldehyde release. Regulations covering formaldehyde in textiles and clothing vary significantly between member nations of the EU but efforts are being made to seek harmonisation by carrying out a complete risk analysis. This is likely to include an obligation to warn the consumer to wash a garment before first use if there is a high level of free formaldehyde present [4]. Several test methods are available for determination of formaldehyde release from textiles. These vary in terms of ease of operation, consistency of test results and practical significance in relation to problems of (a) exposure to formaldehyde vapour in the working environment, and (b) the propensity for skin irritation from resin-treated textiles [124].

2.13 Biocidal Agents Formaldehyde is just one of a large group of biologically active compounds with a variety of applications in textile dyeing and finishing. It is not surprising that chemicals selected for their biocidal activity are the focus for particular concern with regard to their potential impact on the environment. The most far-reaching EU legislation for the aquatic environment is the Dangerous Substances Directive, which established the List I (Black list) and List II (Grey list) substances. List I covers products which should be eliminated on account of their toxicity, persistence and bioaccumulation. List II is for products with a less deleterious effect. Typical examples of substances that feature strongly in these lists are given in Table 2.7. All the Black-listed organic chemicals exemplified here are chlorinated structures, unlike those of the Grey list examples. In the UK the 1989 Water Act made specific reference to the discharge of prescribed substances (Red list in Table 2.8), consents for which are the responsibility of Her Majesty’s Inspectorate of Pollution (HMIP). Twelve of these substances also appear in List I of the EU Directive (Table 2.7). There are three major areas in the textile processing industry where biocidal agents are of practical interest: 1. insecticides used on wool and other animal fibres to prevent attack by moth and beetle larvae 2. bactericides used as preservatives to prevent biodegradation of natural polymers, such as thickening agents or starch sizes 3. bactericides applied to textile materials in order to inhibit bacterial activity during storage or end-use applications. Damage to wool garments during storage can occur when certain moths or beetles lay their eggs within the wool yarns and fibrous material is consumed by the larvae that emerge from these eggs. Any insecticide applied must be directly effective against these specific larvae. Since effective agents are not harmful to other insects that do not consume wool, it seems likely that such products operate only through the digestive tract of the larva. In addition to health and


45

safety requirements, fastness properties also need to be taken into account. Fastness demands on wool carpets are not so stringent as for machine-washable wool clothing. Environmental, as well as health and safety factors, have resulted in an almost total ban on the use of dieldrin, the first product to be used for this purpose. This hexachlorinated multicycloalkyl compound proved to be toxic to humans, animals, fish and birds, and was highly persistent in the environment. Similar factors coupled with the relatively small size of the market for insectproofing of wool are acting restrictively against several other well-established agents used for this purpose. In an excellent review of the subject [126], the important insect-proofing agents in commercial use are placed in two categories. The first category includes those compounds that were developed specifically as wool mothproofing agents, most of these being anionic multichlorinated aryl structures suitable for application to wool together with typical milling acid dyes. One of the best known is the tetrachloromonosulphonated compound sulcofenuron. This product is relatively costly but has very good fastness to washing and light. Sulcofenuron is one of the only three types of insect-resist agent permitted in the GuT ecolabelling scheme (section 2.1.3). Compounds in the second category were originally developed as pesticides for agricultural use. Most of these have pyrethroid structures, including permethrin and cyfluthrin which are the other two insect-resist agents permitted for the GuT label. These synthetic pyrethroids share certain structural features with their natural counterparts, the most important of which is pyrethrin I. Owing to the increasing costs of registration and ecotoxicological testing of new products in relation to only modest market demands, it is unlikely that novel agents designed specifically for wool could now be developed [126]. Any further advances in this field are likely to be spin-offs from agricultural pesticide development, although this research sector is also unfavourably affected by trends in favour of organic farming methods. Natural pyrethroids lack the photochemical and hydrolytic stability necessary for use as insect-resist agents for wool. The synthetic analogues possess satisfactory stability and exhibit the low mammalian toxicity and lack of bioaccumulation of the naturally occurring agents. Permethrin, however, is toxic to aquatic organisms and is therefore subject to increasingly severe discharge limits. There is some evidence that this agent is not fully effective against certain beetle larvae and mixtures of permethrin with other compounds are sometimes preferred [127]. Vinylsulphone fibre-reactive insect-resist agents have been described, in which the insecticidal feature is an organophosphorus group. The vinylsulphone group reacts with nucleophilic sites in wool keratin, conferring excellent wet fastness. An interesting aspect of these agents is that they do not act as insecticides on wool until they become activated by hydrolysis of an ester bond that links the reactive group to the biologically active portion of the molecule, when enzymatic wool digestion processes take place within the insect larva. A development reported more recently involves reduction of the cystine disulphide bonds in wool with thioglycolic acid to form nucleophilic thiol groups, followed by crosslinking of the wool keratin using bifunctional reactive dyes [128]. Although this approach conferred improved insect resistance there were adverse effects on physical characteristics of the wool such as tensile strength, shrinkage and stiffness, thus limiting the potential of the process for commercial use. To achieve the highest fastness ratings, insect-resist agents should be applied to wool from the dyebath. This may not always be possible, however, and

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alternatives include addition to the scouring bath or together with spinning lubricants [126]. Particular care is necessary in the choice and application level of these agents for fibre blends, since their partition behaviour between the component fibre types varies. Pyrethroids, for example, tend to partition in favour of nylon in wool/nylon blends [129]. It is not surprising, given their aquatic toxicity, that these agents are subjected to continual environmental scrutiny [130]. In order to comply with minimum discharge requirements, it is obviously helpful to be able to apply the minimum levels needed for adequate functionality. Bactericides are often added to microbially nutritious polymers, such as natural thickeners, dispersants and size polymers, in order to protect them against biodegradation during storage [131-133]. In the case of printing pastes, biological degradation on storage can lead to a significant loss of viscosity and rheological malfunction. Various biologically active compounds have been utilised as bactericides, but formaldehyde and certain phenol derivatives, such as cresols, chlorophenols or phenylphenols, have proved particularly suitable. These are added either by the supplier of the thickener concentrate, or by the printer during formulation of the stock thickener paste. The environmental implications of adding biocides to polymer formulations must always be borne in mind since, by definition, all effective biocides are more or less toxic. Thus addition of a biocide may render a normally biodegradable polymer less so. Hence biocides should be added at as low a concentration as possible, although the rate of microbial attack of the polymer increases with the humidity during storage. Sensitive thickening agents, however, can be protected by incorporating a suitable biocide, usually at less than 0.1% on the mass of thickener, which is just about sufficient for effectiveness [132]. Together with the thickener, this small amount of biocidal contaminant is washed out with copious volumes of water after print fixation, entering the effluent stream at such high dilution that it no longer has any bacteriological effectiveness. It has been suggested that suppliers of dispersants and polymer concentrates will cease to incorporate preservatives in their products [131]. The printer or warp sizer will then be responsible for using, in exactly the correct amount, a preservative that is just about tolerable under the conditions of application. Formaldehyde has been widely used for this purpose but is now ecologically undesirable. Phenolic compounds have also been popular and effective, but the nucleophilic OH group present can adversely affect the yield and hue of dyes containing highly reactive groups [133]. Commission textile processors need to be aware of the possible use of biocides by fabric suppliers, yarn spinners or cotton growers higher up the supply chain. Instances have arisen where cotton finishers in the UK have unknowingly discharged effluent containing pentachlorophenol (PCP) even though they have not been applying it in their fabric processing routines. This problem came to prominence in 1990 when it was revealed that overseas weavers of these imported fabrics had been adding PCP to their warp sizing baths as a preservative to avoid starch size degradation in hot climates. When the starch is removed during fabric desizing and scouring, the soluble sodium pentachlorophenate is also carried into the effluent stream. PCP can be difficult to treat in a conventional biological treatment plant because of its adverse effect on waste water bacteria. This stable compound is not degraded by bacterial action and is bioaccumulative, causing progressive damage to the aquatic environment [4]. Some imported cottons were found by analysis to contain PCP levels as high as 500 ppm. A typical jig load of fabric containing only


47

5 ppm of PCP can give rise to a level of 1.7 ppm in the effluent volume from that dyeing. This compares with a consent level of only 0.02 ppm of PCP in effluent after treatment and discharge [134]. Eventually elimination of PCP usage by the Asian weavers was achieved in the early 1990s by international negotiation but at the cost of greatly increased claims for fabric damaged by mildew during transit to Europe, an occurrence that was relatively rare before the ban on using PCP in sizing baths [4]. Biocidal chemicals have been applied to cotton for many years as rotproofing finishes for awnings, tents and geotextile materials. There is increasing incorporation of bactericidal agents in medical textiles, hosiery, underwear and sportswear, in order to prevent infection, promote healing or prevent the development of odours. A comprehensive index of antimicrobial chemicals is available [135]. Although this volume covers a variety of applications, there is a section devoted to ten agents suitable for textile treatment (Table 2.9). Only three of these are chlorinated structures. Poly(ethylene glycol) crosslinked with dimethyloldihydroxyethyleneurea (DMDHEU) has been reported to give fabrics with antibacterial properties suitable for nonwoven protective surgical apparel [136]. Triclosan kills a wide variety of bacteria that cause food poisoning, dysentery, cholera, pneumonia, tetanus, meningitis, tuberculosis and sore throats. It is also capable of inhibiting the development of bacterially generated odours and deactivates the yeasts responsible for mouth ulcers and athlete’s foot. This compound can be incorporated during fibre production to give durable antibacterial properties [137]. Despite the widespread use of Triclosan in toothpaste and acne creams, apparently it may cause allergic dermatitis in susceptible individuals, especially when used in products for foot treatment [135]. Poly(hexamethylenebiguanide) has been used for the sanitisation of swimming pools. On textiles, it has been incorporated into antibacterial fabrics ranging from medical products to odour-free socks [138,139]. This cationic polymer is mainly of interest on cotton and is applied as a solution of the hydrochloride by padding at neutral pH. The positively charged polymer exhibits high substantivity for the negatively charged fibre surface. Approximately 1% of the agent on the mass of the cotton is optimal for bacterial performance. No thermal curing treatment is necessary but a wet-on-wet padding with an anionic fixing agent can be given to enhance fastness of the antibacterial effect. This polymer has a long history of use as a bactericide, exhibits low toxicity, does not contribute to AOX values and is environmentally acceptable, being bioeliminated by adsorption on the biomass.

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U Sewekow, Textil Praxis, 45 (1990) 1195.

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B J McCarthy and B C Burdett, Rev. Prog. Coloration, 28 (1998) 61.

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T R Giridhar, Colourage, 45 (Jun 1998) 27.

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J H Pierce, JSDC, 110 (1994) 131.

[17]

W Beckmann and U Sewekow, Textil Praxis, 46 (1991) 346.

[18]

P Cooper, JSDC, 109 (1993) 97.

[19]

Colour in dyehouse effluent, Ed. P Cooper (Bradford: SDC, 1995).

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D M Lewis, Rev. Prog. Coloration, 29 (1999) 23. I G Laing, Rev. Prog. Coloration, 21 (1991) 56.

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A J Greaves, D A S Phillips and J A Taylor, JSDC, 115 (1999) 363.

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C Diaper, V M Correia and S J Judd, JSDC, 112 (1996) 273.

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J J Porter, Amer. Dyestuff Rep., 79 (Jun 1990) 21.

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C A Buckley, Water Sci Tech., 25 (1992) 203.

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K Hunger, Chimia, 48 (1994) 520.

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D Brown and B Hamburger, Chemosphere, 16 (1987) 1539.

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E A Clarke and D Steinle, Rev. Prog. Coloration, 25 (1995) 1.

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Carcinogenic substances regulations (London: HMSO, 1967).

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J S Bae and H S Freeman, AATCC Review, 1 (Sep 2001) 67.

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[44]

A Puntener, D Mausezahl and C Page, J. Soc. Leather Technol. Chem., 77 (1993) 1.

[45]

P A Turner, JSDC, 111 (1995) 53.

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K T W Alexander, JSDC, 112 (1996) 341.

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S W Oh, M N Kang, C W Cho and M W Lee, Dyes and Pigments, 33 (1997) 119.

[48]

C T Page and J Fennen, J. Soc. Leather Technol. Chem., 82 (1998) 75.

[49]

A Puntener, J Fennen and C T Page, J. Soc. Leather Technol. Chem., 80 (1996) 1.

[50]

U Sewekow and A Westerkamp, Melliand Textilber., 78 (1997) 56.

[51]

W B Achwal, Colourage, 44 (May 1997) 29.

[52]

A Hudson and P A Britten, Rev. Prog. Coloration, 30 (2000) 67.

[53]

A Geisberger, JSDC, 113 (1997) 197.

[54]

B Küster and U Wahl, Textilveredlung, 32 (May/Jun 1997) 121.

[55]

K Hübner, E Schmele and V Rossbach, Melliand Textilber., 78 (1997) 720.

[56]

F Klaschka, Melliand Textilber., 75 (1994) 193.

[57]

K L Hatch, Text. Chem. Colorist, 30 (Mar 1998) 22.

[58]

F Gallagher, JSDC, 113 (1997) 307.

[59]

V A Shenai, Colourage, 45 (Oct/Nov 1998) 62.

[60]

K D Wozniak, A Keil and D Müller, Textil Praxis, 45 (1990) 965.

[61]

P Elsner, Textilveredlung, 29 (1994) 98.

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H Motschi, JSDC, 116 (2000) 251.

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J M Wattie, JSDC, 103 (1987) 304.


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A Docker, J M Wattie, M D Topping, C M Luczynska, A J N Taylor, C A C Pickering, P Thomas and D Gompertz, Brit. J. Industrial Medicine, 44 (1987) 534.

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E A Clarke and R Anliker, The handbook of environmental chemistry, Vol. 3A, Ed. O Hutzinger (Berlin: Springer-Verlag, 1980) 181.

[66]

E A Clarke and R Anliker, Rev. Prog. Coloration, 14 (1984) 84.

[67]

R Anliker in Toxic hazard assessment of chemicals, Ed. M L Richardson (London: Royal Society

[68]

H S Freeman, L D Claxton and V S Houk, Text. Chem. Colorist, 27 (Feb 1995) 13.

[69]

J Sokolowska-Gajda, H S Freeman and A Reife, Dyes and Pigments, 30 (1996) 1.

[70]

J Sokolowska-Gajda, JSDC, 112 (1996) 364.

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[75]

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[76]

D M Lewis, JSDC, 113 (1997) 193.

[77]

L Benisek, Wool Record, 158 (Apr 1999) 42.

[78]

P A Duffield, R R D Holt and J R Smith, Melliand Textilber., 72 (1991) 938.

[79]

G Meier, JSDC, 95 (1979) 252.

[80]

A Hoyes, Wool Record, 151 (Apr 1992) 49.

[81]

B M Müller, Rev. Prog. Coloration, 22 (1992) 14.

[82]

W S Hickman, JSDC, 109 (1993) 32.

[83]

S I Ali, JSDC, 109 (1993) 13.

[84]

P M Chan, C W M Yuan and K W Yeung, Text. Asia, 28 (Oct 1997) 58: 29 (May 1998) 59.

[85]

M Ryder, Wool Record, 157 (May 1998) 41.

[86]

Eco-Fab, Colourage, 45 (May 1998) 79.

[87]

K D Casselman, Wool Record, 157 (Oct 1998) 57.

[88]

H T Deo and B K Desai, JSDC, 115 (1999) 224.

[89]

G Dalby, JSDC, 109 (1993) 9.

[90]

U Sewekow, Melliand Textilber, 76 (1995) 330.

[91]

H Bürger, Melliand Textilber., 76 (1995) 910.

[92]

B Glover, JSDC, 114 (1998) 4.

[93]

V A Shenai, Colourage, 45 (Jan 1998) 19.

[94]

B Glover and J H Pierce, JSDC, 109 (1993) 5.

[95]

B Glover, Text. Chem. Colorist, 27 (Apr 1995) 17.

[96]

D J Hill, Rev. Prog. Coloration, 27 (1997) 18.

[97]

G Horstmann, JSDC, 111 (1995) 182.

[98]

M M Cook, Amer. Dyestuff Rep., 68 (Mar 1979) 41.

[99]

G L Medding, Amer.Dyestuff Rep., 69 (Sep 1980) 30.

[100] L C Ellis, AATCC Nat. Tech. Conf. (Oct 1981) 266. [101] U Baumgarte and U Keuser, Melliand Textilber., 47 (1966) 286. [102] P Senner and J Schirm, Textil Praxis, 20 (1965) 1006. [103] M Hähnke and C Schuster, Melliand Textilber., 76 (1995) 414. [104] S Anders and W Schindler, Melliand Textilber., 78 (1997) 85. [105] W Czajkowski and J Misztal, Dyes and Pigments, 26 (1994) 77. [106] H Schlüter, Melliand Textilber., 76 (1995) 143. [107] B Semet and G E Grüninger, Melliand Textilber., 76 (1995) 161. [108] R A Guest and W E Wood, Rev. Prog. Coloration, 19 (1989) 63. [109] W Marx, Textilveredlung, 26 (1991) 74. [110] C Heid, Z. ges. Textilindustrie, 70 (1968) 626. [111] W E Wood, Rev. Prog. Coloration, 7 (1976) 80. [112] R Klein, JSDC, 98 (1982) 106. [113] A Murray and K Mortimer, Rev. Prog. Coloration, 2 (1971) 67.

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[114] D Fiebig and K König, Textil Praxis, 32 (1977) 694. [115] G Dürig, Textilveredlung, 11 (1976) 62. [116] P Richter, Textilveredlung, 13 (1978) 134. [117] R C D Kaushik, J K Sharma and J N Chakraborty, Colourage, 40 (Apr 1993) 33. [118] F Rey and V Oles, Textilveredlung, 32 (1997) 252. [119] C Nielsen, B Hogh and E Wallstrom, J. Oil Col. Chem. Assoc., 80 (1997) 467. [120] R L Stout, J. Coatings Technol., 70 (Oct 1998) 161. [121] A C Censullo, D R Jones and M T Wills, J. Coatings Technol., 69 (Jun 1997) 33. [122] B Mills, Professional Printer, 41 (Nov/Dec 1997) 10. [123] R E McCall, F M A Patel, G N Mock and P L Grady, AATCC Internat.Conf. and Exhib. (1997) 150. [124] M Hewson, JSDC, 110 (1994) 140. [125] M H Beck, Text. Horizons Internat., (Oct 1992) 96. [126] D M Lewis and T Shaw, Rev. Prog. Coloration, 17 (1987) 86. [127] J Barton, Dyer, 185 (Sep 2000) 14. [128] J L Burtness and B M Gatewood, AATCC Internat. Conf. and Exhib. (1995) 324. [129] R J Mayfield, JSDC, 101 (1985) 17. [130] J Haas, SDCNZ 13th Internat. Symp. (Oct 1992) 37. [131] F Bayerlein, Melliand Textilber., 70 (1989) 948. [132] W Tiedemann, P Hülsberg, P Horlacher and D Kinast, Textil Praxis, 47 (1992) 337. [133] F Gähr, G Schulz, C Leibold and J M Engel, Melliand Textilber., 77 (1996) 398. [134] A P Lockett, JSDC, 108 (1992) 474. [135] M Ash and I Ash, The index of antimicrobials (Aldershot: Gower, 1996). [136] R S Jinkins and K K Leonas, Text. Chem. Colorist, 26 (Dec 1994) 25. [137] J W McCurry, Text. World, 147 (Jan 1997) 52. [138] J D Payne and D W Kudner, AATCC Internat. Conf. and Exhib. (1995) 341; Amer. Dyestuff Rep., 85 (Jun 1996) 26. [139] J D Payne, Text. Chem Colorist, 28 (May 1996) 28; JSDC, 113 (1997) 48.


51

Table 2.1 Extent to which dyes are lost in exhaust dyeing and washing-off [22]

Dye class Reactive Sulphur Acid Direct Vat Disperse Metal-complex Basic

Proportion of applied dye lost in effluent (%) 20-50 30-40 7-20 5-20 5-20 1-20 2-5 2-3

Table 2.2 Fish toxicity of dyes in common use [22]

LC50 value (mg/l) 500

Proportion of tested dyes (%) 2 1 27 31 28

Table 2.3 List of specified arylamines classified as carcinogens [9] Name on official list o-Aminoazotoluene 4-Aminobiphenyl Benzidine p-Chloroaniline 4-Chloro-o-toluidine 3,3´-Dichlorobenzidine 3,3´-Dimethoxybenzidine 3,3´-Dimethylbenzidine 4-Methoxy-m-phenylenediamine 6-Methoxy-m-toluidine 4,4´-Methylene-bis(2-chloroaniline) 4,4´-Methylenedianiline 4,4´-Methylene-o-toluidine 4-Methyl-m-phenylenediamine 2-Naphthylamine 5-Nitro-o-toluidine 4,4´-Oxydianiline 4,4´-Thiodianiline o-Toluidine 2,4,5-Trimethylaniline

Alternative systematic name 2-Amino-4,4´-dimethylazobenzene 4,4´-Diaminobiphenyl 4-Chloroaniline 4-Chloro-2-methylaniline o-Dianisidine o-Tolidine 2,4-Diaminoanisole 2-Methoxy-5-methylaniline 4,4´-Diamino-3,3´-dichlorodiphenylmethane 4,4´-Diaminodiphenylmethane 4,4´-Diamino-3,3´-dimethyldiphenylmethane 2,4-Diaminotoluene 2-Aminonaphthalene 2-Methyl-5-nitroaniline 4,4´-Diaminodiphenyl ether 4,4´-Diaminodiphenyl thioether 2-Methylaniline

52


Table 2.4 Azo dyes that yield the specified arylamines on reduction [9]

Specified arylamines 4,4´-Diaminobiphenyl (benzidine) 3,3´-Dimethoxybenzidine (o-dianisidine) 3,3´-Dimethylbenzidine (o-tolidine) 2-Methylaniline (o-toluidine) Other arylamines Total

Number of azo dyes 59 80 51 51 37 278

Proportion (%) 22 29 18 18 13 100

Table 2.5 Chemical and biochemical oxygen demand data for various types of carrier chemical [116] Carrier type o-Phenylphenol N-Alkylphthalimide Arylcarbonate ester Methyl cresotinate Dichlorobenzene Trichlorobenzene

COD (mg/l) 1000-2000 1000-2100 900-1900 800-1700 500-1000 300-1000

BOD5 (mg/l) 200-800 100-200 700-800 200-800 0 0

Table 2.6 Chemical and biochemical oxygen demand data for high-temperature and carrier dyeing methods [117] Polyester dyeing method Carrier dyeing on the winch High-temperature jet dyeing

COD (mg/l) 1888-2043 584-722

BOD5 (mg/l) 189-200 165


53

Table 2.7 Important examples of dangerous substances in the Black and Grey lists [22] List 1 Cadmium Mercury Carbon tetrachloride Chloroform Dichloroethanes Trichloroethylene Perchloroethylene Hexachlorobutadiene Hexachlorobenzene Pentachlorophenol Monochlorobenzene Dichlorobenzenes Trichlorobenzenes DDT Aldrin Dieldrin Endrin Lindane

List II Arsenic Boron Chromium Copper Inorganic tin Iron Lead Nickel Vanadium Zinc Ammonia Sulphide Organotin compounds Benzene Toluene Xylenes

Table 2.8 Initial Red list of prescribed substances in the Water Act [22] Cadmium Mercury Dichloroethanes Hexachlorobutadiene Hexachlorobenzene Pentachlorophenol Trichlorobenzenes Polychlorobiphenyls Tributyltin compounds Triphenyltin compounds DDT

Aldrin Dieldrin Endrin Lindane Atrazine Azinphos-methyl Dichlorvos Endosulfan Fenitrothion Malathion Simazine Trifluralin

54


Table 2.9 Typical biocidal finishing agents applied to textile materials [135] Caprylhydroxyethylimidazoline Captan Dichlorophene Diiodomethyl-p-tolylsulphone Dimethylaminopropylricinoleamidobenzyl chloride Lauryl/stearyltrimethylammonium halide Myristylamine Sodium 2-mercaptobenzothiazole Triclosan Zinc pyrithone


55

Figure 2.1 Key steps for chemical risk management [10] Hazard assessment Risk evaluation

Exposure assessment

Risk prevention

Chapter 3 Services and Resources 3.1 Organisation and Stages for Coloration The application of colour to textile substrates not only increases significantly the added value of the product but is a major factor by which textile manufacturers and retailers can differentiate their products from those of their competitors. Thus the wet processing sector is an important component of the textile manufacturing chain that provides the design, colour, finish and performance characteristics of the finished product. Wet processing plants are established to apply colour at various stages of the manufacturing chain. The stages at which coloration can take place are illustrated in the flow diagram in Figure 3.1. These facilities may be part of a vertical organisation or they may be an independent company providing a commission service to a particular sector of the textile industry. The structure of the industry and the involvement of commission dyers vary in different sectors of the textile industry, as shown in Table 3.1. Traditionally, commission processors were located in close proximity to their major customer base but, as indicated in section 1.5, this is no longer necessarily the case as the textile manufacturing chain is increasingly organised on a global basis. Large textile manufacturing groups have conventionally carried out their wet processing within the group, with coloration being carried out at various possible stages throughout the processing sequence. In view of the infrastructure required, smaller manufacturing companies tend to rely on commission processors. Various factors, including problems with quality or quick response, sometimes encouraged the smaller manufacturers to establish in-house wet processing plants, although this can incur a significant cost penalty. The need for RFT and quick response production has already been emphasised and justified in section 1.5. To achieve such objectives, wet processing requires a significant infrastructure supported by adequate services and resources, the subjects of this chapter. The emphasis placed on these aspects often differs between vertical groups and commission dyers. In the current harsh economic climate, services and resources can be fertile areas for cost savings. Whilst some cost reductions are acceptable, others may significantly interfere with the attainment of RFT production and quick response. Despite the importance of services and resources, provision of them is often less than ideal. Reasons for this include the installation of wet processing in unsuitable buildings, the impact of technological change and the emergence of new legislation.

3.2 Water Supplies Although sporadic attempts have been made to develop solvent or solventassisted methods of dyeing, water remains the principal solvent used in textile processing. For this reason, dyeing and finishing plants were traditionally sited close to abundant supplies of water of suitable quality for textile processing. Water is no longer a cheap resource, however, and now this geographical factor seldom applies. Water quality may have changed for various reasons, such as construction of roads or housing estates where watercourses have been diverted, the incidence of acid rain or drainage of fertilisers from farmland.

56


57

Most of the world’s water is saline, only 2.7% being directly available for use. No less than 88% of this is needed for agriculture, 7% for industry and only 5% for human use. For more than 90% of the earth’s population, water is a limited resource with many regions having less than 10 l/day available. In contrast, the textile processing industry requires 50-150 l/kg of textile material processed [1]. Water for textile processing is usually obtained from one of three sources: 1. surface water from reservoirs or rivers (the quality of river water may vary greatly according to season and flow of water) 2. ground water from wells or boreholes 3. water from a public or municipal source in urban areas (this must be legally potable but it may not be suitable for textile wet processing). 3.2.1 Water Specification Several attempts have been made to establish a specification for water suitable for textile processing. Hardness salts give faults in scouring and dyeing, whilst high solids cause filtration problems in package dyeing of loose fibre, yarn or fabric. A typical specification for process water is given in Table 3.2 [2]. 3.2.2 Water Treatment The treatment of water supplies is usually carried out for the following reasons: 1. removal of solid matter by sedimentation and filtration 2. correction of the pH value 3. elimination of residual chlorine, if this has been added by the water authority 4. removal of hardness (calcium and magnesium ions) by softening processes 5. removal of heavy-metal ions (iron, manganese and copper). These treatments are based on simple neutralisation and precipitation reactions. Water containing suspended humic acids from peat requires treatment with an aluminium salt followed by removal of the coagulated impurities by settling. Chlorinated water can be treated with a reducing agent (sulphite or thiosulphate), before softening using zeolites or synthetic ion-exchange resins. Water for steam raising is softened using lime-soda precipitation containing polyphosphate conditioners. 3.2.3 Water Consumption Detailed surveys of water usage in the 1970s indicated that there were marked differences in water consumption (10-550 l/kg) between companies processing different substrates, as shown in Table 3.3, although use had been reduced over the preceding decade [3]. It has been estimated [3] that 50-60% of dyehouse water is used for processing, 25-35% for cooling and 5-10% for steam raising, although this varies with the process, equipment used and efficiency of processing. Water consumption according to fibre type and process is shown in Table 3.4. In an efficient package dyehouse processing synthetic-fibre yarns, process water requirements may be as low as 8 l/kg with cooling water consumption three times this amount. A similar relationship applies to jet dyeing of fabric [7].

58


Welbeck Fabric Dyers Ltd (UK) commission dyers and finishers process about 17.5 M metres p.a. of fabric entailing considerable costs for water and effluent services. Commencing with a thorough audit in 1995 the water usage was assessed in four areas: preparation, dyeing, finishing and non-metered uses. Preparation accounted for about 20% of the total water consumption. By fitting optimised valve settings, the annual usage in the first year was reduced by about 30% (34,000 m3), with incidental savings on water heating [8]. 3.2.4 Water Savings and Conservation Recurring water shortages and the increasing cost of water have encouraged development of measures to reduce water consumption, as listed in Table 3.5. Fluctuations in water requirements, especially the peaks and troughs associated with demands of production, can be alleviated by increasing the storage capacity for water. Since it is recognised that water quality is an important factor in achieving RFT production (Table 1.13), a treatment plant may be required if the water supply is not of adequate quality for textile processing. The costs of this treatment (including considerable capital expenditure) are incentives to minimise water consumption and to reuse water whenever possible, with or without treatment after use. Pressures have increased to improve the effluent quality, providing a further incentive to reuse effluents (section 3.3.2) especially if operating to a standard acceptable for disposal into a river. 3.2.5 Water Recycling Reuse of water from selected continuous preparation, washing and rinsing operations is not new. Counter-current washing has long been used in continuous preparation where rinse water is fed to the previous bath in the processing range. The use of standing baths has long been practised for dyes of relatively low substantivity, such as indigo and sulphur blacks dyed on cotton. The systematic reuse of dyebaths was adopted in the solvent-assisted dyeing of wool [9] to minimise the consumption of the costly solvent (benzyl alcohol). In aqueous dyeing systems successful dyebath reuse demands high exhaustion, dyebath auxiliaries that do not interfere with subsequent dyeings, and estimation of the concentrations of residual dyes, chemicals and auxiliaries. The reuse of dyebaths without intermediate treatment can give water savings up to 90%, depending on the number of times the bath is reused. Reproducibility, fastness and levelness were not impaired by the reuse of dyebaths without treatment when dyeing wool and wool/nylon carpet and handknitting yarns [10]. Substantial savings were obtained in chemicals (57-80%), water (27-62%), energy (20-43%) and effluent charges (11-58%). Similar results have been achieved with dyebath reuse in the dyeing of nylon pantihose with disperse dyes [11], jet dyeing of Nomex with disperse dyes [12], jet dyeing of polyester knitted fabrics with disperse dyes [13] and nonwoven microfibre nylon fabrics with 1:2 metal- complex dyes [14]. A major concern is the possible build-up of additives or impurities, which might interfere with dyeing behaviour. Control of dyebath pH becomes increasingly important and buffer systems will give stable and reproducible conditions [15]. Where water recycling is being implemented, one option is to segregate colourless wastes containing low levels of contamination from coloured wastes requiring treatment before reuse, providing the infrastructure costs of


59

implementation on existing sites do not mitigate against this option [16]. A procedure for the reuse of residual finish liquors has been described, based on the application of simple test methods for repeated assessment of the quality of the liquor after storage for various times up to six weeks. Test parameters include pH, electrical conductivity, specific COD, fluidity and visual examination. By comparing these results in relation to storage time, a profile of storage instability can be derived. Hence the residual degree of usefulness of a given batch of liquor can be predicted. Correlation between the residual usefulness defined in this way and the finish effects attainable can be demonstrated. To some extent it is possible to enhance this residual quality level in order to broaden the versatility of the reusable liquors [17]. 3.2.6 Hot Water Supply The availability of a hot water supply at about 50°C, suitable for preparing dyebaths and carrying out rinses, can assist in shortening processing cycles. A high grade of hot water can be obtained by discharging the liquors from polyester dyeings at top temperature through high-temperature drains and then through a heat exchanger. Dyebaths from other dyeing processes can be treated similarly, although too much low-grade hot water may be obtained if the flow rate through the cooling coils is not sufficiently low. Such low-grade hot water is often useful in continuous preparation plants. A level probe can be inserted in the hot water storage tank and a temperature probe in the cooling water return and these are coupled to a microprocessor. High-grade hot water, above a specified temperature, can then be returned directly to the hot water storage tank and heated further, if required, to the target temperature by a heating coil. Water significantly below the target temperature is returned to the cold water supply tank. Water between the specified and target temperatures can be run to waste, unless the hot water supply tank requires topping-up, when this water is added and heated.

3.3 Effluent Effluents from wet-processing plants are complex and their composition varies according to the range of processes carried out. Traditionally most textile effluents (about 90%) were discharged to water authority sewage works but larger companies often operated their own effluent treatment plant. This latter option is likely to increase, not only as effluent treatment charges increase but also as consent limits for discharge to sewer or watercourses become more stringent and cover a wider range of contaminants. Additionally, water recycling becomes a serious option if the costs of the raw water, pretreatment for wet processing and effluent treatment to enable discharge to a river or watercourse are taken into consideration. 3.3.1 Effluent Composition In establishing consent limits and, in the case of sewage plant operation, setting charges for effluent treatment, the important factors are volume, pH, suspended solids and the biological and chemical properties of the effluent that express the degree of pollution, as defined in Table 3.6.

60


Determination of COD is more reproducible than BOD. TOC determination may replace BOD and turbidity may replace suspended solids in discharge limits. Typical consent limits are shown in Table 3.7. Apart from the obligation to meet these limits, there may also be a restriction on the volume that can be accepted, especially peak loadings likely to be reached from time to time. Legislation has been introduced in which five processes and twenty-three chemicals (the so-called Red list) are prescribed processes and substances which require separate consideration as regards effluent. The prescribed chemicals include agents such as DDT, pentachlorophenol and dieldrin, the latter two having been widely adopted as mothproofing agents for wool (see also Table 2.8). Companies treating effluent use the so-called Mogden formula to calculate the total cost, although the component charges may vary between different treatment companies. The Mogden formula is explained in Figure 3.2. On average, effluent costs account for about 10% of total production costs in the textile industry [18]. A detailed comparison of water consumption and effluent pollution from various wet processes for cotton (Table 3.8) indicated that bleaching and washing-off require 75% of the water but contribute only 6% of the BOD and 8% of the pollution load. Conversely, desizing and scouring account for about 75% of the BOD and pollution load but use only 6% of the water [19]. However, the pollution load can be significantly decreased by oxidative desizing, which converts carbohydrate residues to carbon dioxide and water [20]. Coloration processes take a 10-20% share in all these distributions and this is also broadly true of the wool dyeing sector. The dyeing and finishing of synthetic-polymer fibres require just as much water, but the BOD is usually substantially lower, owing to the relatively low level of impurities present compared with natural fibres. The major classes of contaminants in textile effluents can be classified into five groups and even the most problematical can be isolated and treated individually [21]. There are advantages in separating effluents into individual streams for treatment according to their characteristics before combining them for discharge. Production-integrated methods of minimising contamination and quantity of waste liquors are now favoured, rather than the traditional reliance on end-of-pipe treatments to deal with the entire pollution load arising from the textile processing sequence. For example, useful by-products such as wool grease can be recovered and recycled. Treatment of concentrated dyebaths is more economical than end-of-pipe treatment of composite waste water [22]. Although the latter approach does not interfere with the choice and flexibility of the textile production pattern, it is the least attractive option economically [18]. 3.3.2 Effluent Treatment Methods Methods of effluent treatment may be classified into three main categories: physical, chemical and biological, as listed in Table 3.9. Primary stages of treatment are mainly physical and include screening, sedimentation, flotation and flocculation to remove fibrous debris, undissolved chemicals and particulate matter. Primary treatment does not significantly remove colour. Secondary stages are designed to eliminate the organic load and consist of a combination of physico-chemical separation and biological oxidation. Biological treatment does not remove sufficient colour, COD and electrolytes to be satisfactory on its own but is often the least costly method of treatment. Physico-chemical separation depends on the forces of chemisorption to extract the colloidal organic


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compounds from the liquid phase. Tertiary stages of treatment have become more important but they make a major contribution to treatment costs. This stage is important for the removal of colour and no one treatment will deal with the removal of all types of colour. Biological processes must be protected from shock loads of industrial pollutants, especially those containing toxic constituents. Preliminary stages include equalisation, neutralisation and disinfection. Major reasons for poor results from settling tanks include significant fluctuations in flow, temperature and composition of waste liquors which cause convection currents and stratification in the tanks and interfere with normal sedimentation. Balancing of flow and composition together with cooling or heat recovery is necessary. Disinfection with chlorine may protect the micro-organisms in the biological stage from toxic contamination. Industrial effluent treatment alternatives are indicated in Figure 3.3. As indicated above, there are many physical and chemical processes available for the treatment of textile effluents. The removal of colour has become a major issue over the last ten years and if treated water meets all acceptable quality standards, recycling becomes a serious consideration. Economic viability is the most important factor in selecting treatment for a dyehouse effluent to remove colour and achieve successful reuse in wet processing. The basic processes used by dyehouses to remove colour, although not necessarily to make it suitable for reuse, include those listed in Table 3.10 [23]. The possibility of water recycling has been extensively reviewed [16]. Aerobic activated sludge processes have been used either on the dyehouse site or at a local sewage treatment plant, to remove biodegradable chemicals measured as either BOD or COD. Effluent containing soluble anionic dyes, such as acid, reactive and direct dyes, is not decolorised by this process since dyes are only partially removed by adsorption on to activated sludge. The chromophoric systems in many dyes are stable to the mildly oxidising conditions in activated sludge and further specific colour removal processes are required before recycling. Oxidation using chlorine dioxide or ozone, coagulation/flocculation, membrane and adsorption processes have all been used in conjunction with activated sludge to meet regulatory consent conditions. Combinations of such processes do not necessarily give a treated water of sufficient consistency for recycling. Anaerobic biological treatments will remove the colour of azo dyes by reduction of the azo groups. A strong oxidant such as chlorine, sodium hypochlorite, chlorine dioxide or ozone may be effective in decolorising dyehouse effluents by destroying chromophoric systems. Catalytic oxidation, using hydrogen peroxide catalysed with iron (II) sulphate in acidic solution (Fenton’s reagent) produces a water quality suitable for recycling for specified applications. The removal of colloidal iron after settling is critical for recycling. This process destroys water-soluble dyes and reduces COD by oxidation of organic matter. Electrochemical variations of the process have been developed and alternative catalytic oxidation processes, such as photochemical systems using ultraviolet light, have been proposed to decolorise effluent. In a recent series of trials, effluents from six dyehouses containing acid, disperse or metal-complex dyes were treated on a pilot plant using various advanced oxidation processes based on hydrogen peroxide or ozone, with or without UV radiation. Decolorisation occurs more quickly than COD reduction under these conditions. The most effective lowering of COD, TOC and AOX requires

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UV/peroxide treatment in the presence of a trace level of iron (II) sulphate as free-radical initiator. The oxidation conditions may have to be varied according to the dye classes or chromogenic groups present. A combination of abiotic oxidation followed by a biological activated sludge process was shown to yield an effluent quality that would permit reuse of the waste water in commercial rinsing or washing processes [24]. Inorganic coagulants based on multivalent calcium, magnesium, aluminium or iron (II or III) salts that form voluminous precipitates with alkalis have long been used to partly remove soluble anionic dyes from coloured effluents. Anionic chemical auxiliaries may also be removed. Water-soluble polyelectrolyte flocculants facilitate separation of suspended flocs containing complexed dyes. A plant for this operation, together with the associated separation and sludge disposal facilities, occupies a large area. As in many physico-chemical dye removal processes, conditions established for optimum removal from one effluent may not be effective with another. To ensure flexibility and consistency, refining treatments may be necessary, particularly for recycling. Activated-carbon adsorbents and ion-exchange resins have been used for water purification, including colour removal. These media are expensive for highly coloured effluents but can be employed either as a principal colour removal method or as a refining treatment. Other adsorbents evaluated include lignite coke, chitin-containing polymers and acid-treated clays. Membrane processes, such as nanofiltration and reverse osmosis, are interesting when recycling is the objective. The effluent is passed through pores small enough to remove dissolved dyes. Pre-filtration is carried out to prevent blocking of the membranes and reverse osmosis will remove acid and reactive dyes of high solubility, whilst also removing salt. However, each effluent requires the selection of an optimum pore size, configuration, membrane type and operating pressure to produce the required water quality, especially if recycling is involved. The practical and economical feasibility of using membrane technology to recycle dye liquors has been assessed. Factors affecting the practicality of recycling dyes include: the dyeing process, classes of dyes used, effluent volume, frequency of use of specific dyes and the auxiliaries added to the dyebath. Similar considerations apply to the suitability for recycling of the process water associated with the dyeing process. Other relevant factors include the water quality attainable before recycling and the process stages for which this water is acceptable. To assess the economics of dyebath effluent reuse, water company treatment and supply charges as well as dye and chemical costs must be considered [25]. In a recent evaluation, dyebath effluents from several dyehouses representing various dyeing processes were treated in a nanofiltration test unit to compare membranes from different manufacturers. Membrane retention values in excess of 99% were attained with regard to residual colour from reactive, disperse, acid and metal-complex dyebaths. The COD and TOC loadings were thereby reduced by about 90%. Laboratory dyeing tests demonstrated that permeates and concentrates yielded by nanofiltration are reusable in the dyehouse. Nonrecyclable concentrates can be subjected to biological aftertreatment to meet the limit values for discharge to the municipal purification plant. The economics of nanofiltration recycling systems depend essentially on the point at which nanofiltration can be rationally integrated into the production process [26]. It is neither feasible nor desirable to attempt to deal with the total effluent flow in this way because of the large-area membranes needed to cope with such


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quantities. Emulsified polymeric materials with low stability to shear stress put severe limitations on this technique by rendering the membrane impermeable, especially washings containing a high content (>10%) of residual acrylic binder. With complex mixtures of contaminants ultrafiltration is applied first to separate out dispersed pigments and polymeric constituents, followed by reverse osmosis to remove dissolved substances such as dyes, salts and surfactants [27]. Available methods of removing colour from effluent were reviewed and descriptions were given of two full-sized treatment plants [23]. One of these is sited at a dyehouse processing about 180 tonnes of fabric per week with a weekly water consumption of 50,000 m3. The basic treatment consists of screening to remove coarse suspended solids, followed by a fine rotary screen to remove fibres and lint. The effluent is then pumped into a balancing tank, holding about 1200 m3, representing 3-4 hours of production. This tank, maintained at about 40°C, evens out the composition and protects the living organisms in the subsequent biological tanks from any shock treatment. Variable-speed pumps transfer the mixed effluent into the activated-sludge tanks. During a three-hour treatment at 40°C in the presence of air, injected through diffusers, the waste material is consumed to produce an increasing amount of biomass. The mixed liquor is then passed to a clarifier. The biomass is allowed to settle by gravity and the clear purified water is drawn off from the top. The settled sludge is pumped into a re-aeration tank, where the biomass completes the digestion of absorbed nutrients before it is contacted with fresh effluent. A cationic polymer is dosed into the coloured water, interacting with the anionic dyes to form an insoluble product. The coloured particles are treated with a flocculant in the presence of any suspended solids to produce large flocs in a reaction tank. These are separated from the clean liquid by dissolved air flotation, in which fine bubbles of air are released into a tank containing the suspension, lifting them to the surface to form a stable layer. The solids from this process are combined with the surplus sludge from the biological tanks for disposal. It is estimated that this plant to treat 50,000 m3 of effluent per week would now cost in excess of £ 3 million. The various methods of removing colour from effluent have been reviewed and an indication given of the capital and running costs involved [28]. Water to be recycled, especially for coloration processes, must at least meet the specification given in Table 3.2. A suggested general quality requirement for treated and recycled effluent to be used in scouring and washing-off processes is given in Table 3.11. Possibilities for recycling and descriptions of successful installations have been discussed [16]. A schematic diagram of a water treatment plant including reverse osmosis for removal of colour is shown in Figure 3.4 [29]. This plant is claimed to recycle 95% of the effluent input. The last twenty years have seen tremendous activity in the areas of water usage and effluent quality. The supply, consumption, recovery and disposal of water were reviewed [21] and many predictions have since become realities. The impact of legislation regarding effluent disposal was reviewed [30]. Many governments in the EU and elsewhere have tightened legislation over the years but have not always imposed this because of a lack of affordable treatment. Apparently this honeymoon period is now over [31] and legislation is likely to be vigorously enforced. There has obviously been a significant improvement in the quality of river water. By 2001, wildlife protection agencies in the UK were rejoicing that many attractive species, including otters, kingfishers and salmon, had returned to areas where they had not been seen for up to 30 years [32]. Some of this improvement

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is a direct result of the demise of the dyeing and finishing industry. However, those dyehouses still in business in Leicestershire now treat their discharge onsite and Severn Trent Water Authority (STWA) has been able to switch off all colour removal plants at its sewage treatment works [32]. The signs are ominous for other dyehouses in the SWTA region since the successes in Leicestershire will prompt action in other areas. Although many dyehouses now treat their effluent prior to discharge, very few actually recycle the treated effluent to achieve a major payback. Simple flocculation will meet the consent limits but the cost of chemicals and the increase in suspended solids contribute significant costs which cannot be passed on to the customer. Crossflow membranes provide the highest quality, allowing up to 95% of the treated water to be recycled. Costs of treating incoming water are decreased and energy savings achieved through heat recovery. Membrane filtration will reduce the COD, suspended solids and colour. Based on a model dyehouse working on three shifts for five days per week and producing 15m3 of effluent per hour, a saving in excess of £100,000 per year has been calculated. The Cognis Securyl EFW system allows water to be recycled with a demonstrated cost saving [33].

3.4 Steam Textile wet processes consume much energy, mostly supplied as steam. Steam heating can be supplied as low-, medium- or high-pressure steam, the latter being essential for the processing of synthetic-fibre materials at high temperature. A useful review of the properties of steam and its use, particularly in steamers used for various textile processes, has been given by Hickman [34]. 3.4.1 Boiler Plant Until the 1940s, coal-fired Lancashire boilers were used for steam raising. These were relatively cheap and easy to construct, simple to operate and did not require high-quality feed water or sophisticated water treatment. Fluctuating steam demands were not a problem since the boiler had good storage capacity for water and steam. A thermal efficiency of about 75% was obtained. This was acceptable while coal was cheap but these boilers required full-time stokers. The Lancashire boiler was replaced by the economic boiler fitted with a combustion chamber and tubes to allow two or three passes of the furnace gases and thereby give a larger heat-conducting surface. However, the steam and water capacity is reduced, so that the standard economic boiler is highly sensitive to fluctuations in steam demand. Lancashire boilers were designed to produce from 2000 to 5500 kg of steam per hour at a working pressure of 150 to 200 psi, whilst economic boilers have a capacity from 450 to 11000 kg per hour at a working pressure of 250 psi. As the temperature of the exit flue gases from either boiler type can be as high as 500°C, an economiser is usually fitted to recover some of this heat. An economiser is a multi-tubular heat exchanger and this is fitted in the gas stream between the boiler and the chimney. The hot gases pass around the outside of the tubes and feed water passes through the tubes. It is estimated that a saving of 1% in fuel costs is obtained for every 4.5°C increase in feed water temperature.


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Both types have been superseded in modern plants by so-called packaged boilers. These are basically modified economic boilers but, as the name implies, the boiler together with all the ancillary equipment (such as feed-water pump, forceddraught fan, oil heater and pump) are mounted on a common base so that the minimum of civil engineering work is required for their installation. Several such units can be installed to meet short- and long-term demands, such as seasonal requirements for space heating. A major advantage of packaged boilers is their ease of installation. Already mounted on a solid base, connections are readily made to the fuel, power and water supplies and also the steam system. Provision is required for disposal of ‘blow-down’ and the chimney, usually an integral part of the boiler, need be only as high as required by the local authority. Packaged systems are usually treble-pass ‘wetback’ boilers, in that the combustion chamber is completely enveloped in the boiler shell and surrounded by the boiler water, whereas in a conventional economic boiler the combustion chamber is outside the boiler shell. With so much heating surface in the packaged boiler, an economiser is not required but the boiler feed water should be preheated in the feed-water tank or hot well. Pre-heating in the hot water tank at atmospheric pressure is limited by the elevation of this tank above the feed-pump suction. The higher this tank, the higher the possible temperature of the feed water. The extensive heating surface in the boiler is achieved at the expense of water and steam storage capacity, so fluctuations in steam demand can still cause problems even with the relatively fast response of the boiler. Treatment of the feed water is necessary, since scale-forming salts in the feed water are rapidly precipitated on to the internal boiler surfaces. Closed-coil heating systems in dyeing machines are essential to minimise the consumption of boiler feed water and to prevent contamination of process liquors with water treatment chemicals. Since only the raw water or feed water requires treatment, it is advantageous to return the maximum condensate to the boiler from the processing plant. Start-up procedures for packaged boilers are relatively simple and modern units are highly controlled or automated so that the boiler plant will run unattended. To overcome the problem of fluctuating steam demand, the thermal storage boiler was developed. This is basically a large-sized economic boiler with a very high water capacity. In a modern plant, the alternative of using a steam accumulator is more popular. This is a large cylindrical vessel filled to about 75% capacity with cold water. Steam is fed from the boiler plant and injected into the water via a series of nozzles. When the water boils, steam is produced and as the temperature of the water continues to rise, the steam pressure rises until it equals that of the steam being supplied from the boilers. When the accumulator pressure equals the supply pressure, the accumulator is fully charged. Much sensible heat is now stored in the compressed water and steam can be drawn off to supply processes. As accumulator pressure starts to decrease, the sensible heat stored in the water is gradually converted into steam and this continues until the accumulator pressure reaches the process steam pressure. The accumulator has then been discharged. However, the accumulator would again produce steam if the process steam pressure is lowered. In practice, accumulators are not usually operated over the full pressure range, but over a narrower range to ensure that at the minimum there is a reasonable head of pressure on the process steam system and at the maximum the pressure is not too near the point of blowing-off. Control and reducing valves are fitted to regulate charge and discharge of steam. The accumulator is usually operated in parallel with the boiler plant supplying the process steam, so that when boiler steam production is

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greater than demand, the excess steam charges the accumulator. When demand exceeds boiler plant output, the accumulator increases supply by discharging. Packaged boilers are widely used in textile wet processing plants, whereas the highly efficient water-tube boilers are seldom installed. In these boilers the steam pressure and temperature are as high as possible and they are often used to supply power generation plant with high-pressure superheated steam. In textile wet processing plants, the working pressure of the boilers is usually four to six times the process steam pressure, the boiler producing steam in the range of 150 to 200 psi. This is controlled by reducing valves between the boilers and the process equipment to give an operating pressure of 25 to 40 psi. A revolutionary system of water heating was developed at the University of Florida during the energy crisis of 1974. This technology is now available in Europe under the name of Direct Contact Water Heating (DCWH). All indirect energy-transfer interfaces, such as gas/steel and steel/water, are eliminated by using the gas flame to impinge directly on the fresh water. Water is injected downwards into a cylinder and the gas flame injected upwards from the other end. DCWH can be guaranteed to yield a remarkable 99.7% thermal efficiency [35]. A high efficiency gas-fired steam generator has been developed which can be particularly useful as a satellite in-line heater for preparation and washing ranges [36]. Steam generation can be decentralised and the equipment can be incorporated into new machinery, making such units independent. Operating efficiencies are in excess of 80% and energy costs are reduced by at least 50%. 3.4.2 Properties of Steam To discuss the qualities of steam, it is necessary to understand some basic definitions and these are given in Table 3.12 [37]. 3.4.3 Fuels With the obsolescence of traditional coal-fired boilers, influenced by the increasing cost of imported coal, the demise of the UK coal industry and environmental considerations, boiler plants are now usually oil- or gas-fired. Dual firing is also possible, the method adopted depending on the economics of fuel supply at a given time. If natural gas is chosen, the gas supply industry usually insists on a contract that is liable to possible three-month periods of interruption since domestic users have first priority. This usually means that there must be storage capacity for a three-month supply of oil and these storage tanks need to be contained in an enclosed bund in case leakage or spillage occurs. Premium prices may be demanded for this oil since it is not on a regular contract supply basis. 3.4.4 Steam Distribution The essential link between steam-raising and processing plants is the steam distribution system. The benefits of efficient steam production can be lost through inefficient distribution. The steam main must be of the correct size for the volume and flow rate of steam to be distributed. Under-sizing of steam pipes will result in starvation at the processing equipment, whilst over-sizing will increase the initial capital cost and aggravate radiation losses. Pipe sizes are usually determined on the basis of the flow of steam required or on the pressure drop. Having assumed


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a given flow rate, the volume of steam is calculated on the basis of the crosssectional area of the pipes. For dry saturated steam, the flow rate required is usually between 24 and 36 m/s. Sizing of steam pipes on the basis of flow takes no account of the distance the steam has to travel. Due to frictional resistance in the pipes, uneven pressure variations can arise throughout the network of piping. This is unacceptable since it is important to have a constant steam pressure at the processing end of the pipework. With the requirement of this constant pressure, pipe sizes are best based on pressure drop. In this approach, the effective length of the pipe run should be known or estimated and account taken of restrictions such as curves, elbows, junctions, valves and expansion loops. The plant layout should be arranged to favour short lengths and straight pipe runs. Future requirements should also be considered. There are specialist companies to advise on and install the necessary pipework. Steam pipes are usually manufactured from hot- or cold-rolled seamless steel tube and lengths can be joined by screwed or welded couplings but preferably flanges with joints between are used. The thickness of the tube depends on working pressure and to a lesser extent on steam temperature. Standards are available in different countries regarding the various components required in a steam line. Valves are another important component of the distribution network and should be chosen with care. The parallel-slide valve is possibly the most useful since it offers little resistance to steam when fully open and does not leak when fully closed. This type of valve is not suitable as a control valve since opening to and closing from a partially open position will cause ‘hunting’ of the valve and considerable vibration in the steam line which can cause damage and leaks. Globe valves are suitable for controlling equipment and the size should be selected according to the amount of steam required. For equipment requiring a lower steam pressure than that supplied from the main distribution system, a reducing valve is fitted in a branch line from the main line and this enables a steady but lower pressure to be obtained. Valves may stick in the open position, so that it is important particularly with reducing valves to have an adequate safety valve. Steam mains and branch lines should be fitted with pressure gauges; steam meters and thermometers may also be useful. Allowances must be made for expansion when fitting a steam main, since a pipe carrying steam at 150 psi will expand by about 0.3% (1 cm in every 30 metres). The pipes must be supported and anchored. The supports should allow for free movement of the pipe in all directions and should be placed near junctions. Spacing of supports depends on other features of the building to enable rigid support to be obtained. Expansion is usually arranged via expansion bends or bellows. Provision must also be made for condensate drainage and return. Steam pipes usually slope slightly to allow this to occur. Water remaining in steam pipes causes ‘hammer’ due to the water being carried along the pipe with the steam. This is particularly dangerous at start-up since the flow of water can be rapid enough to fracture a valve. Steam is advantageously circulated within the processing plant by means of a ring main. Steam from the boiler plant is supplied in a single pipe into the processing buildings. A T-junction fitted at this point feeds the steam in both directions into a ring of pipework. The advantages of using a ring main include:

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1. the ability to use piping of smaller diameter with some reduction in capital cost 2. there is no machine at the end of the main which could be starved of steam 3. steam demands on a branch can be served in both directions, eliminating a pressure drop in that branch. Valves are fitted at various points in the ring main so that sections of the plant can be shut down for maintenance without affecting the rest of the plant. Machinery suppliers are able to quote steam requirements fairly accurately so that branch lines can be accurately sized. Connections to machinery should be made from the top of the main to provide steam as dry as possible and these connections are preferably fitted with a valve. Expansion and draining of branch lines are necessary and steam traps to discharge condensate should be fitted with strainers on the inlet side to remove dirt. Steam lines and condensate returns should be efficiently insulated to minimise heat loss, save fuel and lower running costs. Rigid sections of fibreglass or mineral wool, held in position by light-gauge steel and fixed with metal bands, are widely used.

3.5 Pipework As seen in previous sections, considerable pipework is required for each section of processing plant, particularly dyeing machines. Services requiring pipework include hot and cold water supply, steam line, condensate return, cooling-water supply and return, compressed air and pre-dissolved dyes and chemicals from the dispensary (sections 3.12 and 4.2). Effluent may flow into a common drain or through heat-exchangers to recover sensible heat. Pipework for all these services can be sited on a pipe bridge located at a high level above the machines. This allows ease of access and is much more convenient than sinking most of it in the floor. Pipework to convey supply water or recovered water to be reused should be made from corrosion-free material, preferably stainless steel, to prevent water contamination. Short, straight pipe runs are preferred wherever possible and this can be assisted by the appropriate positioning of the boiler, softening and recovery plants within the building complex. Dye-cycle times can be significantly decreased and dyeing machine utilisation increased if the inlet/outlet pipework allows rapid filling and draining of machines.

3.6 Electricity Supply Electricity is typically supplied from public generating sources at 11000 volts and an alternating frequency of 50 Hz. For industrial use, this is stepped down by transformers to 415 volts at the same frequency. The supply is normally threephase and neutral, giving 415 volts phase-to-phase and 240 volts phase-toneutral. There are significant differences throughout the world in voltage and frequency so that machinery suppliers need to fit motors and ancillary equipment to meet the local requirements. Although alternating-current and direct-current motors of different types are available, the selection of appropriate motors is normally made by the machine supplier. Where continuous dyeing and finishing processes are operated, it is crucial that driving motors have matched characteristics, such as starting response and acceleration ramp.


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Adequate switching arrangements are necessary so that lights and machinery can be switched off when not in use. The correct motor should be used for the equipment to be driven. Capacitors are usually installed in the supply so that the balance of capacitive-inductive-resistive loads (power factor) is close to unity, thereby saving cost. Few, if any, textile plants now generate their own electricity supply with the option of selling surplus power to the local electricity authority. However, where so-called ‘brown-outs’ (frequent interruptions to the electricity supply) are anticipated, it is worthwhile installing an oil-powered generator to start up and supply critical needs (such as dyeing machines) within seconds of a power failure occurring. Some large modern plants in developing countries have installed a dedicated power plant on-site in case national supplies become intermittent or unreliable.

3.7 Compressed Air Valves on processing equipment, whether automated or not, are actuated pneumatically. Compressed air is also required for lid seals on dyeing machines and for the pressure required on nip rollers. An adequate supply of clean, dry compressed air is generated by rotary oil-sealed compressors delivering about 10 cubic metres/minute and reduced to the required pressure at the valve according to requirements. Generators are usually automatically controlled and incorporate after-coolers, refrigerated air dryers and submicron filters to ensure that the supply is free from water, oil and dirt particles.

3.8 Heating, Ventilation and Air-Conditioning Traditional wet processing factories must have been the darkest (and wettest) of all of the satanic mills. Modern dyehouse buildings are likely to be windowless structures to conserve energy, with a high level of artificial illumination. Machines are totally enclosed as a further energy-saving measure to prevent the escape of steam and effluent is discharged into closed drains or pipework. Pleasant working conditions are therefore possible, with facilities for control of heating, cooling, ventilation and full air-conditioning. The atmosphere in wet processing areas is totally changed ten times per hour to provide fresh air of a suitable quality. Humidity control in the grey storage area may assist in achieving consistent results on dyed wool [38]. In both wet and dry areas fresh-air intakes, filter sections, automatic modulating damper boxes, heating batteries and centrifugal fan sets can be installed in the roof to save space. Air is usually distributed through galvanised sheet-metal ducting which terminates in adjustable aluminium air grilles. The automatic modulating damper box controls the amount of fresh air mixing with recirculated air. Switches on the damper motors operate extractor fans to balance the amounts of input and extract air. Heater battery outputs are automatically controlled by room thermostats which operate control valves in the heater pipework.

3.9 Buildings Modern textile wet processing machines and their ancillary equipment are unlikely to be housed satisfactorily in traditionally designed textile buildings nor, indeed,

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in modern conventional factory sheds erected on an industrial estate. The needs for copious water supply and effluent disposal are additional factors that complicate the selection of a suitable location. It is unfortunate that many modernised wet processing facilities have been located in existing unsuitable buildings, thereby detracting from their effectiveness. Custom-designed and -built facilities are the best option for a modern wet-processing plant, although probably difficult to justify in many cases (section 3.15). Good external roadways are needed to allow for tanker deliveries of commodity chemicals such as acids, alkalis, salts, detergents and bleaching agents. The delivery doorways should be large enough to provide easy access for complete machine items or modular units during installation. Many of the services discussed in this chapter will be supplied by specialist contractors, particularly with a greenfield site installation since the wet processing company is unlikely to have the manpower and expertise available. An installation of this kind together with the use of specialist services has been described [39]. Steel and reinforced concrete are the materials of choice for construction of a wet processing plant. The design is likely to be based on Portal steel-frame construction to give a wide clear-span area with the roof pitch, span and height being flexible to the requirements of each processing facility. Ancillary equipment can be slung and pipe bridges supported from girders beneath the gently sloping roof. Portal frame units can be separated by conventional brickwork whilst process control offices, laboratories and dispensaries can be built at a higher level within the building. Steelwork will usually be coated to minimise corrosion, although this problem is less likely with enclosed machines. Such buildings will have roof insulation and air-conditioning (section 3.8) to eliminate condensation and give a pleasant working environment. Although modern dyehouse floors can be kept virtually dry, they usually slope slightly to a drain (either in the centre or edge of the unit) to allow for cleaning up spillages. Floors, usually concreted up to 20 cm thick, must be of sufficient load-bearing capacity for equipment placed on them plus the movement of handling devices such as fork-lift trucks. Floors are usually sealed to repel water and chemicals. Easy-clean surfaces are advantageous for ceilings, walls and floors, whilst electrical supply equipment and lights must be protected from water and heat. Modern stenters and similar machines are usually fitted with independent exhaust equipment, including scrubbing, extraction and heat recovery. Dyehouses usually include areas for grey storage, preparation, dyeing, drying, finishing, final inspection and finished goods storage. Dimensional requirements of each Portal frame unit will be influenced by the processing sequences used, the textile materials to be handled and the sector of the industry. Plant layout is considered in section 3.10. Batchwise dyeing operations can benefit from a two- or three-tier design of building. In a Portal frame building, a three-tier design is useful for a packagedyeing plant for fibre or yarn where vertical kier/vertical spindle machines are used (section 13.5). The machines are positioned on the floor of the building (tier 1) and an operating platform is erected, usually in checker-plate, at the machine operating level (tier 2). The dispensary is built in a mezzanine (tier 3) from which dyes and chemicals can be fed by gravity to the dyeing machines. This gives easy access to pumps and services in tier 1. For package-dyeing machines such as horizontal kier types which can be placed directly on the floor and for fabricdyeing machines such as winches, jets and jigs, a two-tier installation is appropriate. In the three-tier configuration, the building height may be up to nine


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metres to allow for the headroom required by cranes for unloading the frames. However, this height leaves ample space for the ancillary areas mentioned above.

3.10 Plant Layout The plant layout should be such that work flow is unrestricted and bottlenecks are avoided. The various stages within the processing sequence must also be in balance. A traditional U-shaped arrangement can be useful. Siting of boiler and pipework is a key factor to give short, straight pipe runs. It is perhaps easier to design a dyehouse for batchwise operations [40] and possible layouts for fibre and yarn dyeing operations are given in later chapters (Figure 12.9 and Figure 13.15 respectively). Batchwise operations for fabric and garment dyeing could perhaps be based on similar concepts. In continuous dyeing and finishing plants, process stages can be close-coupled to give long machine runs without the need to break-out fabric between process stages. The length of the building is thus a key factor. The direction of fabric movement can only be altered at points where the fabric is wound onto A-frames for transit or storage. Potential layouts for preparation, dyeing and finishing of woven fabrics using 1960s technology have been given [41,42].

3.11 Handling Devices When package dyeing loose fibre, yarn or fabric, cranes are used to load and unload the carriers in which the substrate is contained. These need to be of a sufficient safe working load (SWL) to accommodate the total weight of carrier, substrate and water. The dyed material can then be transported by crane to the drying machine, usually a hydro-extractor, thereby minimising manual handling. Fabric rope-dyed by batchwise methods is run from the dyeing machine into trucks over an exit reel. Such fabric is then untwisted and dewatered, either continuously or by rotary hydro-extraction. Sufficient suitably designed trucks are required to accommodate the likely volume of work in progress. Fabrics from continuous or semi-continuous dyeing (section 16.9) are usually rolled as batches of large diameter, using A-frames with independent batching devices. After continuous processing in rope form the fabric is opened into full width using a scutcher (section 15.3) before drying in open width. Stenters are usually equipped with edge-uncurling devices and weft straighteners.

3.12 Dye And Chemical Dispensing Major factors in achieving reproducibility in dyeing are the weighing, measuring and dispensing of dyes and chemicals. Sumner [43] identified inaccurate weighing of dyes and measuring of chemicals as the two most important causes of offshade batches. The location, design, layout and equipping of the ‘drugroom’ or dispensary, therefore, are vital factors in the quality management of a dyeing operation. This facility also impacts on health and safety requirements, as discussed in section 2.1.1. Many advantages and savings can be gained by the selection of rationalised ranges of dyes, auxiliary products and chemicals, as discussed in section 5.8.1. In view of the demonstrated importance of these factors, it is surprising that they have been neglected in many dyehouses.

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It is standard practice to isolate the dispensary from the main production area of the dyehouse to avoid contamination of work in progress. The removal of all dye handling from dyeing machine operatives, moving the dispensary into a dedicated area and ensuring that only suitably trained personnel work there, probably achieves the greatest single step in improving accuracy. A saving in labour costs follows but these actions are also essential on health and safety grounds. Early dyestores were primitive ‘kitchens’. Even when dyes and chemicals are dissolved or dispersed manually, it is advantageous to locate the dispensary on an upper mezzanine of a two- or three-tier dyehouse, so that dye/chemical solutions/ dispersions can be gravity-fed to the process equipment. Where it is not possible to site the dyestore on an upper floor because of building restrictions, mobile dispensing tanks can provide a first step towards centralising dye and chemical handling. Dispensing to processing equipment sited on the same level is possible but requires the use of pressure pumps to transfer solutions or dispersions and this complicates cleaning procedures [44]. In an ideal design, a bulk storage area on the ground floor holds unopened containers of dyes and auxiliaries. A lift is provided for transferring these to the higher level dispensary when needed. On this upper mezzanine, a dry room with suitable storage devices is available for products in immediate use. Another dry room, equipped with a laminar-flow or down-draught extraction booth, is used for weighing. It is preferable to convey product containers to this second room for weighing in turn directly from a delivery container into a clean, dry, stainlesssteel bucket using a clean, dry scoop. A wet room is provided for dissolving or dispersing and dispensing from mechanically stirred mixing vessels. The floor in the dispensary should be chemically resistant and of sufficient weightbearing capacity to allow for the traffic of heavy containers. Walls and floors should allow for easy and regular cleaning. Suitable storage for dyes ranges from simple shelving to paternoster devices. The wide variations that exist in container design and size, often influenced by the physical properties of solid or liquid brands of dyes and auxiliaries, complicate the design of storage systems. The variability which can occur in the moisture content of disperse dyes caused by changes in ambient conditions has been studied [45] and the influence that such changes have on the colour of wool dyed with acid dyes has been measured instrumentally [38]. The simplest expedient is to keep containers tightly closed between weighings. Air-conditioning and ventilation should be considered in the dispensary, since recent work [38] indicates that this investment gives a short payback period through improved consistency in wool dyeing. Complete air changes should occur six times per hour, with simple ‘air-lock’ door systems (often photo-electrically controlled) under slightly negative pressure being provided at entrances to maintain the atmospheric conditions while preventing the escape of contamination. Extraction equipment with air-conditioning and ventilation in the dispensing area removes steam from mixing and dispensing tanks. Weighing of dyes, chemicals and auxiliaries is crucial. Repeatable and accurate weighing to within 1% of target is required. At least two balances are required, one to handle amounts in grams up to 1 kg and the other for 1 kg or more. To weigh small quantities for pastel dyeings and shading additions, dilute solutions of the dye can be used. The weighing operation raises serious concerns for health and safety since the disturbance of powders produces aerosols which can be inhaled by the weighing operative (section 2.5). Reactive dyes have been the main cause for concern


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[46]. Engineering solutions are the preferred approach to this problem with the installation of weighing booths and extraction cabinets. The selection of suitable physical forms, such as liquids, grains or non-dusting powders, also alleviates the problem. ‘Space-suiting’ including nasal masks, goggles, gauntlets and overalls that must be regularly laundered are provided individually for each operative. Standard operating procedures should be established for dissolving or dispersing and dispensing dyes. The modern dispensary is equipped with stainless-steel dispensing tanks, these being either conical or cylindrical in shape, the number required for each dyeing machine depending on the process details. Such tanks are usually equipped with the facilities listed in Table 3.13. Dyes, chemicals and auxiliaries are gravity-fed to the dyeing machine through stainless-steel or glass tubes. When dispensing from the mezzanine level, sufficient time must be given at the appropriate phases of the dyeing routine to allow homogenisation of the liquors and travel to the dyeing machine. The increasing use of ultra-low liquor ratio (ULLR) dyeing machines and centralised dispensing emphasises the need for dyes and chemicals of adequate solubility or dispersibility and stability properties. Large weights of salt and alkali associated with the dyeing of cellulosics are added at the dyeing machine level. The packaging, storage and handling of dyes and chemicals have been reviewed [47].

3.13 Laboratory Support The works or support laboratory must be the nerve centre of the modern coloration operation. The laboratory plays a major role in establishing the limits of accuracy required to obtain a high degree of reproducibility and in maintaining the SOP required in bulk processing to ensure that a high success rate of RFT production is achieved. The laboratory can therefore make a major financial contribution to the well-being and profitability of the company. Unenlightened management has often regarded the laboratory as a financial drain on the company and this should certainly not be the case. Exact simulation of production processes is neither possible nor necessary, but it is essential to establish reliable transfer of lab recipes into bulk-scale production. The penalties of achieving wrong-first-time (WFT) production have been summarised in Table 1.12. By taking these figures, it has been shown that the cost of jet dyeing a 300 kg batch of fabric WFT and having to give a single shading addition equates with the cost of between 3 and 25 laboratory dyeings or a 3 to 10 kg sample dyeing, depending on the substrate/dye combination. The cost of a single redyeing equates with the cost of between 25 and 85 laboratory dyeings [48]. The nature of work carried out in such laboratories, together with their design, organisation and equipping have been extensively discussed and working methods for the various activities have been given [49]. The laboratory is situated in close proximity to the dispensing and production facilities, one option being on a mezzanine floor above the production area.

3.14 Management Strategy for Success An important, and perhaps an increasingly scarce, resource is an efficient and effective management team to control the plant supported by the necessary labour force. The various aspects of dyehouse management have been discussed [40].

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Market research will be carried out continuously by the successful company. There are a number of management tools and techniques which can assist in this essential market research. Competitor profiling systematically analyses the competition to learn from their strengths and weaknesses. Customer retention (the duration of customer relationships) is a measure of customer satisfaction and reasons for loyalty or defection can be established. Customer satisfaction can be measured by asking customers to define the company’s performance. Strategic alliances can often be built between companies prepared to commit resources to achieve common objectives. Such alliances can be with customers, suppliers or even competitors and benefits can include entry into new markets, supplementing skills or sharing financial risks and commitments. Value chain analysis is used to identify potential sources of a company’s economic advantage in its industry. Process re-engineering, the redesign of a company’s core business, may be required to achieve dramatic improvements in productivity, turn-round time or quality. There are five major forces that impact on the long-term success of a business, as listed in Table 3.14. The successful company develops core competencies, based on the knowledge and skill of its workforce, to create a differentiable customer value. Total quality management (TQM) defines the performance requirements of products and services based on customer needs in order to meet these specifications with zero defects. Having established the market potential the production facility must conform to the TQM criteria and must be balanced between processes. Operation of the plant must be based on a well-defined business philosophy including the selection of appropriate customers and product lines. Management is about change, not preserving the status quo. Failure to change soon enough or radically enough can result in eventual extinction. It is perhaps worth discussing briefly some of the changes that impact on dyehouse management. The costs of dyes, chemicals, resources and labour are levelling out on a worldwide scale and modern technology is available to all. As automation and robotisation are adopted more widely, labour costs decrease considerably. A major criticism of the UK textile and coloration industries has been lack of investment. Developing countries are investing, often obtaining development bank funding to do so, but their workers may lack the training, education or attitude to achieve high efficiencies from modern plant. Investment in these countries is often confined to machinery and hardware. The need for adequate and appropriate procedures, people skills and software may be neglected. Undue deference to the status quo often exists. Any significant change (and consequent improvement) in current practice implies a criticism of established procedure and a ‘loss of face’ for senior individuals opposing the innovation. There is therefore little opportunity in such an environment to learn from previous mistakes. A company cannot readily or quickly launch major changes in products, processes, markets or customer base and thus requires well-defined long-term objectives. This corporate strategy includes the actions listed in Table 3.15. Capital expenditure may be required for the reasons shown in Table 3.16. The gradual replacement of equipment is the important sector for investment, since it can permit the production range to be expanded and enable the company to evaluate the latest machines and processes. This approach allows facilities and machines to be updated within the financial capabilities of the business. The


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company can thereby remain viable without the need for an abrupt and painful injection of large amounts of capital which have to be financed. When identifying outstanding companies, there are usually two important factors which lead to success: 1. qualifiers: those basics which a company must get right in order to survive 2. differentiators: those factors which give the company an edge over its competitors. In most cases the successful company has the attributes shown in Table 3.17. As regards strategy, most successful companies have formulated a clear statement of their goals and aspirations, have communicated these to everyone in the organisation so that they can ‘buy-in’ and have monitored and communicated the outcomes frequently. Such companies ensure that all employees act on the belief that customers want a product that is right for them and want it now. This approach secures business from the most exacting customers by adopting exacting standards, exploits special niches, gets products right-first-time and responds to external changes such as environmental concerns. Key strategies are listed in Table 3.18. A participative management style will build a dedicated and responsive workforce with high morale so that everyone identifies with the company’s objectives. In the production plant, especially where there is a significant technical input, the chief executive is unlikely to be a desk-bound manager and ‘management by walking about’ (MBWA), making regular contact with staff at all levels, is highly effective. Continuous management development is essential and the company must clarify its needs for management talent in the future. A SWOT (strengths, weaknesses, opportunities and threats) analysis defines those areas of competence and those in which efforts are required to achieve the desired level. Success depends on the company developing the attributes listed in Table 3.19. Empowerment is an important concept and requires the motivation listed in Table 3.20. All personnel should foster a climate of honesty and fairness in dealing with problem situations. Isolated incidents involving faulty production or breakdowns may be attributable to chance, but multiple events of a similar kind usually signal incompetence or inadequate training. It is vital to adopt a positive approach to teamwork in problem solving that has no need for witch-hunts or the blaming of individual operatives.

3.15 Economic Considerations As will be seen from this chapter and the volume 3 chapters, machinery and processing developments have been much concerned with cost savings and particularly the resources discussed in this chapter, including labour. The latter topic will be discussed further in section 4.4. Process optimisation is, in general, a fruitful means of cost reduction [50]. Feasibility studies are required before re-equipping an existing operation or a totally new facility is considered. If major changes have occurred in processing needs, building a new plant may be more economical than updating an existing one. However, it is more difficult to justify minor improvements on the basis of modest savings requiring prior capital expenditure.

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The possibility of building a new plant on a greenfield site is attractive since it allows the latest equipment to be installed throughout. A greenfield location may have other attractions, since many existing plants are on ‘island’ sites surrounded by other premises, including domestic accommodation. Ease of access and parking are often difficult, space for future development is seldom available and residents may not be sympathetic to new construction. Noise and odour restrictions, water availability and effluent disposal may make the current site unattractive. The disruption caused by building the new plant whilst maintaining production should not be underestimated. It has been previously noted that existing buildings may be unsuitable and the cost of modifying these may be prohibitive. The costs of repairs and maintenance for old buildings may also be high, so that a new building of the correct design and size in a new location may be a cost-effective option. Few feasibility studies have been published, not only because of their uniqueness to a given investment and company strategy but also because they are usually shrouded in secrecy (if not mystery). Two UK papers covered the economics of bleaching, dyeing and finishing of woven cotton in the late 1960s. In one [41], it was concluded that installation of the latest equipment in modern buildings could be justified if market conditions were favourable and specialised production was undertaken. In the other [42], it was argued that investment in modern equipment could be at least as successful in existing buildings. One difficulty can be the escalating cost of machinery, however, the equipment evaluated in these two papers having risen in cost by a factor of ten in the inflationary period 19551970. Two feasibility studies in the 1980s dealt with the establishment of yarn package dyehouses on greenfield sites, one being in the UK [51] and the other in the USA [52]. There was a surprising degree of agreement between these studies, both concluding that investment on a greenfield site was feasible for a new business but unlikely to be so for an existing operation due to poor market prices. This underlines the need to carry out feasibility studies for each option at a time as close as possible to construction. Many of these views expressed in the 1980s regarding automation would now be quite different.

3.16 Capital Investment – Quo Vadis? The economic considerations of capital investment are discussed in several of these chapters. It was shown that on a greenfield installation, 65% of the capital investment is required for the resources and services discussed in this chapter [49]. Although the actual capital required has probably increased by at least a factor of ten over the intervening years, the distribution has probably remained fairly consistent. It is appropriate to discuss the future of capital investment in this chapter. Major changes have occurred in the global textile industry over recent decades with developing countries, often already major agricultural producers, grasping textile production as a major industry. Technology and machinery are readily available for use by relatively low-cost labour, with there being a ready local market for the product. The governments of developed countries have often been unsympathetic to their textile industries. Nowhere is this more apparent than in the UK where few indigenous spinning and weaving firms have survived and knitters, dyers and finishers are dependent on imported yarns and fabrics. Much of the demise of what are considered in some quarters as ‘mature’, ‘smokestack’


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or ‘sundown’ industries has been blamed on the low cost of production in developing countries. These volumes should dispel this pejorative view, since the wet processing industry is in many respects a high-technology sector. It has been shown that there is a levelling-out of global wage rates and that it is feasible for a developed country to invest in spinning and weaving, based on current technology (open-end spinning and projectile weaving machines) [53]. From the year 2005, the global textile industry will operate without the restrictions of the multi-fibre arrangement (MFA) and the industry will thus become more competitive with free trade being established without tariffs, duty or quotas being imposed on textiles or garments. The successful company will need to exploit management technology, with the development of appropriate investment plans and production strategies. Success depends on the company possessing distinctive competencies in the areas listed in Table 3.21, that will lead to significant added value. The absence of these means that the company is never likely to be viable and should seek a better method of using shareholder’s capital elsewhere immediately. The results of piecemeal installations are often disappointing. New dyeing plants that have been installed without adequate support facilities and the necessary management philosophy are known to be achieving less than 50% RFT production. Many new investments are based on misleading calculations from preceding production, when high levels of RFT were not achieved and much reprocessing existed. As discussed in section 1.5, RFT production gives a significant increase in output, as a result of new work being produced, in addition to the elimination of corrections. Labour costs are levelling out and these will assume even less significance as modern, labour-saving machines are installed equipped with control equipment and robotics. It is believed that feasibility studies carried out similar to those described above would conclude that a modern building housing modern equipment together with control technology and robotics, where appropriate, would be viable provided the criteria listed in Table 3.22 are met. Needless to say, no such feasibility studies have been published and it takes a courageous and strong management to build, commission and run such a facility. Evidence confirms that the approach given in Table 3.22 is being followed for new facilities for niche products, for example, a package dyehouse to dye yarn for the automotive industry [54], although the financial performance of such developments remains an unknown quantity.

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W B Achwal, Colourage, 45 (Oct 1998) 36.

[2]

I Gailey, JSDC, 96 (1980) 600.

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W Dürig, Amer. Dyestuff Rep., 70 (Feb 1981) 26.

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S M Jaeckel, J Knight and P Pyle, JSDC, 92 (1976) 157.

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G Horstmann, Australasian Textiles, 6 (Jan/Feb 1993) 34.

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J Park, JSDC, 95 (1979) 400.

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Anon, Colourage, 45 (Aug 1998) 45.

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W Beal, K Dickinson and E Bellhouse, JSDC, 76 (1960) 333.

[10]

Water quality requirements and waste water recycling in the UK textile industry, Textile

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F L Cook, W C Tincher, W W Carr, L H Olson and M Averette, Text. Chem. Colorist, 12 (1980)

Research Council (1978). 1.

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[12]

W C Tincher, F L Cook and L A Barch, AATCC Nat. Tech. Conf., (1981) 271.

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F L Cook, R M Moore and G S Green, AATCC Internat. Conf. and Exhib., (1988), 184.

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J Koh, J Cho and J Kim, AATCC Review, 1 (2001) 27.

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J Koh, G Shim and J Kim, Color. Technol., 117 (2001) 337.

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J K Skelly, Rev. Prog. Coloration, 30 (2000) 21.

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R Teichmann. Textilveredlung, 32 (1997) 131.

[18]

W Köhn, Melliand Textilber., 79 (1998) 647; Textilveredlung, 33 (Sep/Oct 1998) 24.

[19]

W Dürig, IFATCC Symposium, Barcelona, (1975).

[20]

W S Hickman, JSDC, 109 (1993) 34.

[21]


[22]

W S Perkins, AATCC Internat. Conf. and Exhib., (1996) 354.

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Colour in dyehouse effluent, Ed. P Cooper (Bradford: SDC, 1995).

[24]

K H Gregor, Melliand Textilber., 73 (1992) 526; 79 (1998) 643.

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C Diaper, V M Correia and S J Judd, JSDC, 112 (1996) 273.

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T Schäfer, J Trauter and J Janitza, Textilveredlung, 32 (Mar/Apr 1997) 79.

[27]

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K Jeavons, Proc. textile ind. dyehouse water recovery and reuse conf., Huddersfield (May 1999)

[30]

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[33]

Anon, Dyer, 187 (Jan 2002) 21.

[34]

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[35]

W Dunlop, Dyer, 187 (May 2002) 25.

[36]

Nordsea Gas Technology Ltd., JSDC, 101 (1985) 381.

[37]

W Ronald in Engineering in textile coloration, Ed. C Duckworth (Bradford: SDC, 1983).

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V M Adamiak, J-H Dittrich, S Struckmeier and R D Reumann, Color. Technol., 117 (2001) 313.

[39]

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[40]

J Park and J Shore, Dyehouse management manual

[41]

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J M Bainbridge, A Burgess and G Milns, JSDC, 86 (1970) 345.

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(Bombay: Multi-Tech Publishing Co.,

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D Hildebrand and F Hoffmann, Text. Chem. Colorist, 25 (Apr 1993) 24.

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J Park and J Shore, Dyeing laboratory manual (Upperhulme: Roaches International Ltd. 1999).

[50]

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[51]

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P Lennox-Kerr, Textile World, 147 (Aug 1997) 85.


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Table 3.1 Vertical and horizontal organisation Stage for dyeing Fibre, tow and top Yarn

Fabric

Garments Totally vertical operation

Wet processing options Commission In-house by spinner Commission Merchant dyer (buys yarn and dyes for sale) In-house by spinner, knitter, weaver or carpet manufacturer Commission Knitter as part of knit, dye, cut, make-up, trim Weaver Commission By knitter or garment producer Fibre to finished fabrics or garments within one company

Table 3.2 Process water specification [2] Parameter Colour pH value Total hardness (ppm, CaCO3) Alkalinity to Methyl Orange (ppm, CaCO3) Iron (ppm) Manganese (ppm) Total dissolved solids (ppm) Suspended solids (ppm) Chloride (ppm) Sulphate (ppm)

Limits Hazen No. Clear 2-5 7.0–7.5 10–25 35–65 0.02-0.1 0.03 65–150 Nil 0–30 0–30

Table 3.3 Average water consumption by fibre type [3]

Fibre type Wool Cotton Synthetic-polymer

Consumption 1966 150–550 100–300 25–200

(l/kg) 1975 75–300 50–200 10–100

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Table 3.4 Water consumption by process [4-6]

Fibre type Cotton

Wool Synthetic-polymer Acrylic Wool Nylon Nylon Wool Cotton Cotton Cotton Cotton Cotton

Process Scouring Bleaching Jig dyeing Winch dyeing Hank dyeing Fabric dyeing Garment dyeing Sock dyeing Sock dyeing Hose dyeing Loose stock dyeing Continuous dyeing Yarn dyeing Printing Fabric dyeing Garment dyeing

Consumption (l/kg) 10-80 10–130 10-60 100–450 40-65 65–190 100-230 265–465 125–150 100-240 40-60 60-80 100-140 140–200 100–180 80–140

Reference [4]

[5]

[6]

Table 3.5 Measures to reduce water consumption Development of efficient standard operating procedures (SOP) Following SOP exactly, assisted by automation Installation of machines operating at low liquor ratios Operating at minimum liquor ratio by processing full machine loads Monitoring liquor levels, assisted by automation, to avoid overfilling Improved production scheduling to avoid unnecessary machine cleaning and downtime Replace direct heating by heat exchangers to avoid liquor volume increases Control rate of flow of cooling water through heat exchangers Return cooling water from closed-coil systems Use of water-soluble lubricants to eliminate separate scouring Combine processes or use one-bath methods whenever possible Avoid aftertreatment or excessive rinsing, especially overflow rinsing Allow drainage time between rinses Adopt counter-current rinsing methods in continuous processing Reuse relatively clean rinsing water for processes not requiring high-quality water Partial purification and bath reuse Total water purification and recycling


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Table 3.6 Definition of degree of pollution Factor Biochemical oxygen demand (BOD)

Chemical oxygen demand (COD) Total organic carbon (TOC) Dissolved organic carbon (DOC) Biodegradability

Bioelimination

Definition Atmospheric oxygen consumed by microorganisms during the biochemical decomposition of the contaminants, often during a five-day test Oxygen consumed when the contaminants are oxidised in a boiling aqueous acidic dichromate solution Total organic contaminants, both suspended and dissolved, expressed in terms of the carbon content of the effluent Organic carbon present in the dissolved phase after centrifuging or membrane filtration Degree of decomposition of an organic contaminant after biological treatment under specified conditions This includes the material removed by adsorption on the biomass as well as that which undergoes biochemical decomposition

Table 3.7 Effluent consent limits Parameter BOD (ppm) COD (ppm) Suspended solids (ppm) pH Temperature Toxic metals total (ppm) Toxic metals soluble (ppm) Ammonia as N (ppm) Colour – absorbance at 500 nm

Sewer 800 400 6 to 10 Not above 43°C 30(a) 10

(a) Sum of concentrations of Cr, Zn, Cu, Cd, Sn, Pb.

River 15 25 5 to 9 Not above 30°C 0.5(a) 10 0.05

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Table 3.8 Water usage and pollution loads in cotton finishing processes [19]

Process Desizing Scouring Bleaching Mercerising Dyeing Printing Wash-off Finishing

Water usage (l/kg) 20 4 180 7 30 25 110 5

Water usage (%) 5 1 46 2 8 7 30 1

Approx. BOD (mg/l) 4500 11000 1000 30 1000 1200 200 1500

BOD (%) 22 54 5 5 6 1 7

Pollution load (%) >50 10-25 3 6000 kg) to a colour necessary for viability High-quality basic dye liquids required Increased downgrading compared with ecru production Slow response to fluctuations in market demand Shorter runs (1000-6000 kg continuously) to a colour Dye cost 10% lower than gel dyeing Moderate flexibility to market demand Short runs ( P2

Area of contact y2

Figure 16.9 Typical pad-batch dyeing unit [6] Driven roller

Pad mangle

A-frame

Scray

Dye solution

Alkali solution

Mixing pump

Rotating batch

A-frame

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Figure 16.10 Entry and exit features of a vat dyeing steamer [20,46] Extraction pipe

Fabric exit

Fabric entry

Overflow pipe

Sampling point

Weir and water seal

Entry slot with heated lip

Figure 16.11 Counterflow washing in an eight-box range [20] Fabric exit

Fabric entry Cold water feed

Hot water overflow

Drain Cold water supply

Heat exchanger

Chapter 17 Garment Dyeing 17.1 Advantages and Technology of Garment Dyeing Garment dyeing has become an increasingly important sector of the dyeing and finishing industry in recent years [1]. However, dyeing in garment form as an alternative process route has been available for many years and has been an established tradition for certain articles particularly suited to this approach [2]. Ever since the formation of major retail organisations offering ranges of textile garments there have been commission dyers specialised in processing fullyfashioned garments of the highest quality. The global market-place now has a tremendous demand for quality leisurewear and casualwear goods varying greatly in colour and fashion details. As an alternative to dyeing fabric lengths (‘pieces’ traditionally about 100 yards long) that are subsequently cut to shape and made into garments, a significant proportion of the knitgoods wet processing industry is concerned with the dyeing and finishing of garments. Originally, garment dyeing was mainly concerned with underwear, sweaters, pullovers, socks, tights, pantihose and stockings knitted from ecru yarn. Table 14.1 gives an indication of the various knitgoods processed in this way. Originally, the fibre types processed were silk, mainly in the form of stockings, and wool. The need for wool products to survive garment dyeing without shrinking and felting gave the impetus required to develop shrink-resist treatments [3], leading ultimately to the standards of machine-washability which are currently expected of wool garments in terms of dimensional stability and fastness to washing. The processing of wool garments, including shrink-resist treatments, has been discussed in section 8.14. Many of the forces serving in the Second World War were thankful for socks, sweaters and headgear that had been shrink-resist treated and garment dyed, so this technology is not exactly new. The dyeing of knitted garments was extended to other fibres, particularly nylon and acrylic fibres, as these became commercially significant from about 1950 onwards. Elastomeric yarns are now a major feature of garments (section 14.3). The processing of these synthetic fibres had much in common with the technology already developed for the dyeing and finishing of wool garments. The successful processing of polyester garments had to await the development of hightemperature machines, especially the rotating-cylinder machines discussed in section 17.2.4. At that time the dyeing of cotton garments was largely limited to the work carried out by laundries and dry-cleaners to give such articles a new lease of life by over-dyeing. The advantages of garment dyeing include: 1. the capability to produce small batches in a range of colours, which would be uneconomical by other processing routes 2. reduction in coloured waste textile materials 3. many desirable effects required in knitgoods can only be obtained by garment dyeing and finishing 4. colour decisions can be left until late in the process, thereby responding quickly to changes in fashion and providing opportunities to re-order the most popular colours 5. long before it became a ‘buzz’ term, quick response was possible by what is a ‘fast track’ method of coloration late in the processing cycle (Figure 8.2).

165

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The problems associated with the dyeing of traditional garment types include [4]: 1. the knitted garment may contain panels from different knitted batches, giving rise to bulk variations and difficulties of penetration and levelness 2. inadequate yield, patchy dyeing and poor penetration of seams 3. the possibility that the garment dyeing method can be eroded by other techniques on the basis of cost, ease of dyeing blends, better colour continuity and higher fastness. The third problem has been overcome as the importance of ‘quick response’ was realised, facilitating changes in colour and fashion to meet current demands. Indeed, the success of garment dyeing has been assured by developing products not traditionally dyed in this form. These are complete garment assemblies made from woven fabrics and processes to simulate the ‘distressed look’ associated with worn denim. The dyeing of such woven garments is a much more difficult task than that of dyeing knitgoods, since the woven garments are dyed with ancillary components, such as buttons, zips, linings and trims of different fibres. The garment dyer has become a ‘fashion dyer’ and garment dyeing presents a greater challenge than conventional fibre blends. Extensibility and dimensional instability of fabrics are found to play a major role in poor tailoring performance and unattractive garment appearance [5]. Garments subjected to wet processing have to be designed specifically to allow for changes in dimensions and physical properties. Suitable selections of the various components are necessary if body fabric, trims, linings, buttons and sewing threads (all differing in composition) are to be dyed and matched satisfactorily. The selection of sewing threads and interlinings has been discussed in this context [6,7]. Cotton goods destined for garment dyeing are normally made up using unmercerised cotton threads to give inconspicuous solid-dyed seams. Conversely, subtly contrasting effects can be deliberately achieved using either mercerised cotton thread to show up darker against the unmercerised garment panels or polyester thread to remain undyed when the cotton panels are garment-dyed. Sewing tensions should be kept to a minimum in lock-stitch and chain-stitch operations, deliberately producing slacker stitches, to help avoid seam pucker resulting from shrinkage of threads during subsequent garment dyeing. Many cotton casualwear garment designs incorporate metal components such as zips, buttons or press-studs, which may pose specific problems in garment dyeing. Where metal components are present in the undyed garment, the selection of prepared fabric for making-up is recommended to avoid possible interaction with peroxy-based bleaching systems [8]. Catalytic decomposition of the bleaching agent by metal ions can lead to severe fabric degradation that shows up as dye-resist marks or strength losses, particularly in areas close to the metal components. Ferrous-based materials should be avoided, since corrosion from attack by electrolytes may be evident, as well as the risk of rust stains. Discoloration of garment dyeings may arise in the immediate vicinity of metal press-studs. These are made of brass, coppered, blackened with sodium sulphide and then polished. Many direct and reactive dyeings are sensitive to copper and will form complexes of markedly different hue by localised reaction with traces of copper from the studs. Sequestering agents such as EDTA may help to minimise these effects but do not provide a guarantee. The best option in these circumstances is to replace the offending press-studs with nickel-plated brass. The dyer of the goods is seldom made aware that press-studs will be incorporated


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in the finished garment. A mild detergent should be selected when laundering studded garments and perborate or other oxidants avoided. Where garments contain metallic components the manufacturer should give appropriate washing instructions on the label [9]. The dyeing of cotton garments has been a major growth area in the last twenty years, associated with the increasing popularity of casual-, sports- and leisurewear for which the relaxed appearance achieved by garment dyeing is fashionable. The comfort and aesthetic appeal of such garments favours the selection of cotton. A major advantage of dyeing in garment form is the much shortened lead time from fabric production to electronic point of sale (EPOS) compared with traditional routes. Thus garment dyeing gives quick response for the replenishment of orders based on EPOS information. Lead times can be eight weeks for traditional routes, compared with two weeks when garment dyeing is chosen for multi-component cut-and-sew garments. Lead times for fullyfashioned cotton garments can be reduced from sixteen weeks to two or three weeks by garment dyeing. Processing routes for these two fabric types are illustrated in Figure 17.1 and Figure 17.2 respectively [10]. Garment dyeing costs can be two or three times the cost of fabric dyeing, depending on batch sizes. The payback for garment dyeing comes from a reduction of up to 50% in inventory and mark-down costs. If these costs represent 10 to 15% of the value of the goods sold, garment dyeing has been calculated to have a payback period of two to three years [11]. Garment dyeing may be carried out by commission dyers either specialising in this activity or carrying out a range of dyeing services, by in-house dyeing operations or even by laundries. Garments handled belong to four categories [12]: 1. fully-fashioned garment dyeing by major commission dyers 2. cut-and-sew garments, both woven and knitted, dyed to high fastness standards 3. boutique-trade cotton goods of low fastness suitable for hand washing only 4. washing, desizing, bleaching or stone-washing of denim garments.

17.2 Garment Dyeing Machinery 17.2.1 Paddle Machines Traditionally, side-paddle or overhead-paddle machines have been used for dyeing garments in all their various forms, including shrink-resist wool and garments requiring milling in addition to dyeing. The side-paddle machine, as illustrated in Figure 17.3, consists of an oval stainless-steel vessel with a central island and a large paddle along one side of the machine to agitate the liquor. The liquor/garment interchange is relatively slow, since this is the only method of agitation. This machine gives satisfactory results with loosely-knitted fullyfashioned garments but thick constructions can give rise to problems of seam penetration. Dyes and chemicals are added to the machine through a hopper situated on the central island. Paddle speed is usually variable and heating is by either open or closed steam coils. The overhead-paddle machine, shown in Figure 17.4, is less versatile with a lower degree of agitation, often resulting in uneven distribution of dyes and chemicals.

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Socks, stockings and tights are usually loaded into mesh bags for dyeing in paddle machines. The paddle rotates at 5 to 10 rpm and paddle machines operate at a liquor ratio from 25:1 to 40:1. Traditional paddle machines seldom have sophisticated control systems and are labour-intensive in operation, particularly in unloading. The Italian company Flainox manufactures a modern side-paddle machine featuring control equipment and a gate in the side of the machine which can be opened to facilitate unloading of the garments into a truck, as shown in Figure 17.5. Machine sizes range from 4 to 150 kg of garments. 17.2.2 Rotary-Drum Machines The garments are contained in a perforated horizontal cylinder which rotates slowly in a vat of a slightly larger size. The drum is usually divided into four segments and has been widely used for dyeing stockings, pantihose and socks. Heating is by direct steam injection and the drum rotates at a speed of up to 5 rpm, with drum reversal about every 20 to 30 seconds. These machines, widely known as Smith drum machines, operate at a liquor ratio of 20:1. The lack of sufficient agitation is the main limiting factor. A typical machine is illustrated in Figure 17.6. 17.2.3 Toroid Machines In these machines, typified by the Pegg Toroid and its later version the Pegg Ktype, the garments circulate in the liquor in a toroidal path with the aid of an impeller situated below the perforated false bottom of the vessel, as illustrated in Figure 17.7. Movement of the goods depends completely on the pumped action of the liquor. High-temperature versions of this machine operating at 120 to 130°C were developed in the 1970s for dyeing fully-fashioned polyester or triacetate garments. The liquor ratio of such machines is about 30:1. 17.2.4 Rotating-Cylinder Combined Dyeing and Hydro-Extraction Machines The development of garment dyeing machines with markedly lower liquor ratios has given major savings in resources. This machine resembles an industrial version of a front-loading domestic washing machine. The principle of the machine is shown in Figure 17.8. Liquor ratios of 10:1 or lower are obtained and dyeing is carried out with the cage rotating at 3 to 35 rpm, with drum reversal every 20 to 30 seconds. Hydro-extraction is carried out at 500 rpm. The advantages of this machine type include the following [10,13]: 1. low liquor ratio with savings in resources 2. dry loading to hydro-extracted unloading 3. optional basket geometry of open, D- or Y-pocket configurations allowing one, two or three compartments 4. external liquor circulation 5. high-speed hydro-extraction 6. high-temperature capability 7. control systems for time/temperature, rotation profile and dispensing dyes and chemicals


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8. sophisticated design for heating and cooling with heat exchanger and heat recovery 9. variable rotation speed for the dyeing operation with drum reversal 10. in-line lint filter 11. tilting mechanism for ease of unloading. Despite the fact that garment dyeing accounts for only 6% of textiles production [13], there has been intensive development of rotating-cylinder dyeing and hydro-extraction machines, particularly in Italy. A machine of this type, the Flainox NRP, is illustrated in Figure 17.9. Such machines have control and dispensing systems and a capacity of 50 to 150 kg, operating at a liquor ratio of 8:1. In the Bellini Robotel, a liquor ratio of 3:1 is possible for the dyeing stage and 15:1 for washing-off. Dry-cleaning machines used for batchwise solvent processing were developed from industrial dry-cleaning equipment, operating on a similar principle and including solvent recovery. Solvent dyeing of polyester was of some practical interest in the 1970s but is no longer viable. However, full pieces knitted from yarn-dyed polyester can be solvent-scoured in such machines, followed by hydroextraction before unloading for stentering. The Sancowad (S) process [14] utilised aqueous foam application at liquor ratios as low as 2:1 to minimise the cost of resources. Densely foaming surfactants provided a foamed dyebath containing water-soluble dyes. This process was superseded by development of the modern rotating-cylinder dyeing machine. 17.2.5 Hosiery Dyeing Machines More recently, circulating-liquor machines such as the Bellini TCC have been used for dyeing stockings and tights [15]. This avoids creases, ladders and fabric abrasion, which are common problems with rotary machines, and this improvement in quality is further enhanced by boarding prior to dyeing. In the TCC machine, the hosiery is loaded into circular, perforated carriers, removed after dyeing and transferred directly to a rotary hydro-extraction unit, thereby saving handling. Cabinet machines, in which the hosiery is loaded on trays, have also been used to preserve the quality and appearance of the goods. The traditional process for dyeing and finishing nylon stockings was to heat set (pre-board), drum dye and finally set (post-board) the stockings in an autoclave, each stocking being mounted on metal formers (boards). This final operation was expensive and labour-intensive, so dye-boarders were developed [16] to combine the operations of dyeing and boarding. Presentation of the stockings on boards provided an ideal opportunity for dye liquor application by spraying from the roof of a pressure chamber. The complete process consisted of steam relaxation at atmospheric pressure, spraying with a two-minute dwell to allow the dye liquor to run down the former, discharge of the dye liquor, treatment in saturated steam and finally hot-air drying. The process was limited to the use of disperse dyes (see section 17.3). 17.2.6 Drying Hydro-extraction facilities are not an integral part of the dye-boarder, so the goods are hydro-extracted in a rotary centrifuge and then dried in a tumble dryer.

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Conveyor-type radio-frequency dryers can also be used for hosiery and garments after rotary hydro-extraction. 17.2.7 Automation As already mentioned, the handling of garments in conventional paddle machines is labour-intensive and rotary machines have as a minimum a tilting device to aid unloading. An automated system for garment handling has been described [17] in which the goods are dyed in tilting, open-pocket rotating machines which are sling-loaded from overhead rails. When dyeing and hydro-extraction is complete, the machine tilts forward and unloads the goods onto a transfer shuttle which takes the goods to a tumble dryer. When drying is complete, the goods are automatically unloaded from the opposite side of the drying machine onto a flatbed conveyor for transfer to the finishing operations.

17.3 Dye Application and Processing Garments and hosiery can be dyed successfully in all types of machinery described in the previous section but the automated, rotating-cylinder combined dyeing and hydro-extraction machine is finding most favour. Loading of the goods into mesh bags is often an integral part of the procedure to preserve the quality of the goods by preventing abrasion and creasing. The processing of wool materials in garment form has been discussed in section 8.14 and the methods described for handling and trimming are widely used for other fibre types. Differences in wrinkle-shedding behaviour between wool, cotton and synthetics have been discussed in terms of the thermomechanical characteristics of these various fibres [18]. Nylon garments are usually heat-set by a boarding-type process, before or after dyeing. This is basically for the prevention or removal of creases and to impart dimensional stability. Nylon hosiery, including tights, pantihose and stockings, was traditionally dyed with disperse dyes using a tertiary combination of lowenergy dyes. This dye selection effectively covered barre attributable to differences in the prior thermal history of the nylon and allowed the dye-boarding process to be introduced. Disperse dyes were satisfactory when only relatively pale mode shades were required. More stringent fastness demands and fashion requirements for dark or bright colours have meant that milling acid and 1:2 metal-complex dyes have virtually entirely replaced disperse dyes. Optimum results with the current selections are achieved using the widely popular rotatingcylinder machines with control systems. Acrylic garments are dyed with basic dyes taking all the precautions discussed in terms of dye selection, retarder concentration and time/temperature control (section 11.4). Dyeing machines with adequate control systems are necessary. Polyester can only be dyed satisfactorily in high-temperature versions of the Pegg Toroid or rotating-cylinder machines. Fibre blends are widely encountered in garment dyeing, especially in socks, where wool/nylon, wool/acrylic and nylon/cotton blends are popular. The dyeing of blends requires careful dye selection and appropriate dyeing techniques have been well documented [19].


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17.4 Cotton Garments The pressures of quick response have encouraged garment dyeing of knitted and woven goods, including multi-component designs incorporating woven or knitted panels (as compared in Figure 17.1 and Figure 17.2). The difference in lead time is significant by using garment dyeing routes for fully-fashioned garments. Knitted fabrics require less preparation than woven fabrics and are usually scoured or bleached/scoured, relaxed and dried using a conveyor dryer before delivery to the garment maker. Heavy-gauge knitwear is normally processed as a complete garment whereas fine-gauge knitwear is dyed as garment blanks and separate trims for subsequent finishing and trimming. Woven cotton fabrics are usually prepared continuously before delivery to garment manufacture by a sequence that will include singeing, desizing, scouring and/or bleaching and often mercerising. This is an added benefit towards quick response since it shortens processing time for the garment dyer. Alternatively, grey (unprepared) fabric can be delivered to the garment manufacturer, so that the garments have to be desized, scoured and/or bleached, depending on the brightness of shade required [20]. In this case an allowance should be made for shrinkage by cutting the components oversize. This approach precludes singeing and mercerising from being undertaken. Desizing in garment form is carried out by a fairly rapid (15 to 60 minutes), high-temperature (80 to 90°C) enzyme process and bleaching is carried out with hydrogen peroxide. During preparation, water-soluble or self-emulsifiable lubricants may be applied to assist in cut-andsew operations [10]. Alternatively, durable elastomers may be applied. The use of specialised chemicals in garment processing has been discussed [21]. For pale colours and when fastness requirements permit, knitted or woven garments can be dyed with direct dyes, using SDC Class A and B types to aid level dyeing and seam penetration. Widespread use is made of reactive dyes since these provide a wide gamut of colours, including bright shades, of high fastness properties. The monochlorotriazine reactive dyes are ideally suited for garment dyeing since their relatively low reactivity favours level dyeing, with high-temperature application assisting diffusion and migration. This is particularly the case if a migration technique is used where dyeing is carried out at a top temperature of 90 to 95°C, which aids seam penetration and levelness, before cooling to 80°C for alkaline fixation. Limited use is made of vat dyes if fastness to industrial laundering or chlorine is required. The hot pigmentation technique is generally used. The vat dyes are applied as dispersions under alkaline conditions at 60 to 80°C. After a levelling period, sodium dithionite is added to reduce the dyes to their leuco forms and penetration into the cotton fibres takes place. After overflow rinsing to pH 10, the leuco dyes are reoxidised to the pigment form and soaped to give optimum fastness [10]. As already mentioned, certain woven garments contain many ancillary components that must be selected with care. The dyeing of such assemblies is an extreme case of blend dyeing, often involving unusual combinations of components [19]. Since many of these components are present as small percentages of the total garment, they are dyed at what are effectively very long liquor ratios, giving rise to exhaustion and reproducibility problems. Cotton garments are preferably dyed in rotating-cylinder machines, in which the level of control equipment is satisfactory for the application of reactive dyes. After hydro-extraction, the garments are tumble-dried to give complete relaxation. Conveyor and RF dryers may also be used. Garments may be steam-trimmed to improve appearance.

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The term ‘biopolishing’ has been coined by the Danish firm Novo Nordisk, a leading company in the enzyme production sector, for enzyme finishing treatments of natural fibres in fabric or garment form. The objective of such processes is the elimination of surface pills formed during preparation and dyeing by the accumulation of fibrous debris and superficial microfibrils. The effectiveness of these treatments depends on the enzyme type and application conditions, including pH, temperature and treatment time; no mechanical action is necessary. The main characteristics imparted to the goods are: 1. improved appearance and freedom from pilling faults 2. cleaner, smoother surface, conferring a cooler feel 3. softer and more attractive handle 4. enhanced luminosity of coloured goods [22]. Cellulase enzyme preparations for this purpose contain three active ingredients: exo-cellulase, endo-cellulase and emulsin (β-D-glucosidase). These catalyse a controlled hydrolysis of the more accessible cellulose material to consolidate the superficial microfibrils, leaving the fibre surfaces smoother and conferring a more uniform appearance [23-25]. Enzyme preparations for the biopolishing of wool garments are based on alkaline proteases. These can be applied before or after dyeing depending on the finishing characteristics required [26].

17.5 Wet Processing of Denim Fabrics Denim jeans were originally introduced for gold miners during the California Gold Rush and were subsequently marketed as workwear with emphasis on their durability and practicality. Jeans eventually were discovered and appreciated as casual wear and thus became a fashion garment. Techniques were developed to enhance denim garments as a fashion item, including washing to eliminate the traditional stiffness of the fabric together with stone-washing, with or without chlorine, ice-washing with permanganate or cellulase enzyme washing. These techniques are carried out in rotary-drum machines of the Smith drum type because of its robustness. The warp yarns of denim garments are dyed continuously by repeated dipping into the leuco indigo dye liquor followed by air oxidation (section 13.9). The more times the dipping occurs, the darker the shade that is produced. Black sulphur dyes are also used either alone or in combination with indigo. The warp is sized to assist weaving and an undyed weft is inserted during the weaving process. After weaving and garment making, the garments are desized with an α-amylase enzyme and scoured with alkaline detergent. Additives may be included in the scouring bath to accelerate the washdown process. The garments are tumble washed for 20 to 60 minutes and a softener applied. Tumble drying and pressing complete the process. Garments may be processed inside out to minimise abrasion marks. This processing provides comfort and softness, compared with the firm finish of traditional unbroken workwear. Current fashion favours the ‘broken-in’ or ‘distressed’ worn and faded look. Stone-washing accelerates production of the washdown effect and gives the garments a scuffed appearance and softer handle by introducing abrasive stones into the wash liquor. Starch residues and some dyed surface fibrous material are removed by the abrading action of the stones and hot water. Natural or manmade stones are available but pumice and volcanic rock are the most widely


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used. As washing proceeds, the stones slowly disintegrate, reducing the severity of the process with time [27]. The stones abrade the fabric and eventually corrode the rotary-drum machine, which cannot be used for other processing. The process sequence is desize, stone-wash at 50 to 70°C for 30 to 90 minutes, apply softener, de-stone and tumble dry. By incorporating hypochlorite into the stone-washing procedure, the colour intensity of the indigo, or other chlorine-sensitive dye present, is reduced. Residual chlorine must be removed before drying to avoid fibre degradation and an anti-chlor is given using sodium bisulphite or hydrogen peroxide. The so-called ‘ice-wash’ process is carried out with stones impregnated with potassium permanganate. This oxidises the dye present in the surface of the yarns in the garment. Stones are soaked for one to two hours in potassium permanganate solutions (1.5 to 5.0%). The stones should be drained before use. The fabric is desized and scoured, then introduced slightly damp into a machine containing the stones. The ratio of stones to garments is usually 1:2 to 3:1. Treatment is for 10 to 30 minutes. Residual manganese dioxide must be removed from the garments. Many of the drawbacks of stone-wash finishing, with or without oxidant additions, can be avoided by controlled enzyme treatment under neutral or acidic conditions. Advantages of this approach [28,29] include: 1. process times can be reduced by 30 to 50% 2. garment loading of the machine can be increased by up to 50% 3. much less damage of the garments or the machine parts 4. labour-intensive removal of stone dust from the treated garments is eliminated 5. no problems associated with the disposal of oxidant-contaminated stones 6. avoidance of oxidants and stone dust ensures much less contamination of waste-waters. Acidic or neutral cellulase preparations are available. The different activities of such products have been evaluated. Acidic preparations have been recommended for rapid but relatively superficial treatments and neutral types to achieve more severe modifications of the denim [30]. Three types of cellulose-hydrolysing enzyme may be included in such preparations [31]: endo-cellulase, exo-cellulase and emulsin (β-D-glucosidase). The factors that determine the degree of effect obtained include the type and concentration of enzyme applied, temperature and time of treatment. The pH of the wash liquor must be carefully controlled and the dyebath pH in the warp dyeing process is also important because of its influence on the degree of penetration of indigo into the warp yarns [31]. The Retro Dye (T S Chemicals/Jeans Care/Denykem) system is claimed to replace completely the stone-wash finish using pumice stones. Treatment for 20 minutes at 5:1 liquor ratio with Bioprep TBS (cellulase enzyme preparation) and Lyoprep Extra (combined scour and anti-crease agent) is followed by a 3-minute rinse to ensure maximum removal of size polymer [32]. For a highly ‘distressed’ look, partial substitution of pumice stones with enzyme treatment can achieve the appearance required [28]. In this case, the ratio of stones to garments is typically 1:2 to 2:1. The ‘weathered’ or ‘distressed’ look for casual clothing can also be obtained by surface coloration of the garments with pigments. As pigments are nonsubstantive, the garments have to be pretreated with a polymer to provide sites for adsorption of the pigment particles [33,34]. Washing processes to achieve the

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desired effects are carried out as described above, before thermal treatment to cure the pigment binder system. A varied selection of analytical tests to determine the chemical parameters that indicate the response of cotton denim garments to stone-washing treatments, with or without the addition of enzymes or oxidising chemicals, has been described [35]. Indigo fading may be aggravated by incorrect application of silicone softeners in finishing, but selected agents from other classes may exert a slight protective effect [36]. The phenomenon of indigo fading on exposure to photochemical smog is often encountered. Owing to the pronounced ring dyeing that results from continuous dyeing of warp yarns with indigo, most of the dye present in blue denim is highly accessible to free-radical destruction by noxious gases. The yellowing of denim jeans that may occur in processing plants or during storage before retail has been attributed to exposure of the goods to oxidative gases (ozone or oxides of nitrogen), but it is suspected that by-products of the oxidation of indigo are implicated. Measures to minimise this yellowing in storage include [37]: 1. avoid silicone softeners that may enhance fading and photoyellowing 2. pack the jeans in BHT-free plastic film before storage 3. ensure that harmful gases are excluded from storage areas 4. ban the use in warehouses of vehicles powered by internal combustion engines. Subsequent yellowing of denim jeans has often been associated with the technique of ‘ice-washing’ in the presence of stones pretreated with potassium permanganate. Analytical studies have shown that although thorough rinsing markedly lowers the residual metal content of ice-washed denim, substantial amounts often remain [38]. Photoyellowing of the rinsed goods may persist and it is difficult to correlate this with the presence of specific trace metals [39]. Solutions of nitrous acid and oxalic acid were found to be the most effective media for rinsing out trace metal contaminants [38]. The presence of anthranilic acid and isatin as by-products of the oxidation of indigo has been confirmed in denim jeans after the ice-wash process. Both of these can contribute to yellowing faults if not adequately removed by hot water rinsing [40]. Metal-ion contaminants are capable of forming salts with anthranilic acid that are more difficult to wash out of the goods. Manganese dioxide is a brown product of limited aqueous solubility readily formed by the reduction of permanganate anions. Brownish oxides of iron (rust) may arise from abraded metal surfaces inside the machine or metallic accessories attached to the garments [41]. Tests with various agents of the aminopolycarboxylate type indicated that EDTA was the most efficient means of sequestering dissolved transition-metal ions during rinsing of ice-washed denim, at a cost of only 1% of the total cost of washing-off [42]. Photoyellowing has also been attributed to the retention of arylamine by-products of indigo oxidation by complexing with aluminium ions present in the cotton [38]. However, a rise in calcium content of denims as a result of washing also appeared to be linked with a yellowish discoloration [39]. Furthermore, the mineral vesuvianite from igneous rocks (the source of pumice) is a complex silicate of Ca, Mg, Fe and Al. In spite of the long history of indigo dyeing, it must be assumed that the jury is still out on the question of precisely which constituents are responsible for the yellowing phenomena observed in this context.


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17.6 Dry-Cleaning of Garments Chlorinated solvents, especially perchloroethylene and trichloroethylene, have been widely used in the traditional dry-cleaning of garments because of their low cost and useful technical performance, especially their non-flammable property. However, alternatives have been sought because of health and safety concerns, including possible carcinogenic hazards and the effects of AOX compounds on the environment. Several commercially available (but flammable) solvents (isooctane, limonene, isopropyl lactate and certain dibasic esters) were found to perform better than perchloroethylene in many but not all respects when applied as dry-cleaning solvents [43]. Aqueous-based alternatives to dry-cleaning have been evaluated in order to avoid the technical problems and costs of equipment and processing associated with dry-cleaning solvents. The Aquatex (John Linthwaite Associates, Ripponden) cleansing system is designed for microprocessor-controlled aqueous washing and drying in conjunction with non-hazardous detergents and finishing agents specifically formulated by Oils and Soaps (Bradford). This system is applicable to a wide range of appropriate goods, including suitings, evening wear, wedding dresses, delicate garment constructions, waxed textiles, suede, leather, curtains and duvets. Tests have confirmed that for all water-based stains aqueous cleansing shows higher degrees of stain removal from suede, leather and textile garments than conventional dry-cleaning with solvents [44]. The Drywash (Global Technologies LLC) process is an alternative dry-cleaning technique based on the application of supercritical carbon dioxide. It is claimed to be quicker, cleaner and superior in performance to existing commercial dry-cleaning, posing no threat to human health or the environment. Flammable solvents are avoided and the process does not generate hazardous liquid or solid wastes, or contribute to depletion of the ozone layer [45].

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Figure 17.1 Processing routes for multi-component cut-and-sew cotton garments Traditional route

Garment dyeing route

Woven

Knitted

Woven

Knitted

Continuous prepare

Batchwise prepare and dye

Continuous prepare

Batchwise prepare

Dye

Finish

Dry

Relax dry

Deliver to garment manufacturers

Finish

Deliver to garment manufacturers

Cut-and-sew

Cut-and-sew

Stock

Stock

Garment dye and finish

Retail sale

Retail sale

Lead time about eight weeks

Lead time about two weeks

Figure 17.2 Processing routes for fully-fashioned cotton garments Traditional route

Garment dyeing alternatives

Prepare yarn (hank/package)

Knit garment blanks

Yarn dye and dry

Make-up

Stock

Wind

Stock

Dye garment blanks and tumble dry

Knit garment blanks

Garment dye and tumble dry

Make-up and finish

Finish

Make-up

Finish

Stock

Lead time 12 to 16 weeks

Retail sale

Retail sale

Lead time 2-3 weeks

Lead time 5-6 weeks

178 Figure 17.3 Side-paddle garment dyeing machine

Figure 17.4 Cross-section of overhead-paddle machine


Practical Dyeing, Volume 3 Figure 17.5 Flainox side-paddle machine

Figure 17.6 Smith drum machine

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Figure 17.7 Pegg Toroid machine A B

C

E

A B C D E F

D

F

Water spray Liquor level Distributor Steam pipe Impeller Drive

Figure 17.8 Rotary-drum dyeing and hydro-extraction machine

C B D G A E F

A B C D E F G

Perforated drum (with Y-pocket) Machine controller Sampling port Liquor-level indicator In-line lint filter Heat exchanger Addition tanks

Practical Dyeing, Volume 3 Figure 17.9 Flainox NRP rotary-dyeing machine

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Chapter 18 Carpet Dyeing 18.1 Carpet Production The technology of carpet coloration generally resembles other textile sectors but it is often regarded as a separate industry, possibly since product specifications and properties have more in common with the furnishing fabrics sector. The carpet industry is a major consumer of dyes, although the sector accounts for only 5% of world fibre usage. Conversely, the carpet industry utilises a high proportion of certain fibre types, such as nylon and polypropylene. An indication of world production of carpets is given in Table 18.1. Over the period shown there has been a growth rate of about 4% per annum. Production is concentrated in North America (45%) and Western Europe (32%), where much of the consumption takes place. Contract end-uses account for 33 and 22% of carpet production in North America and Western Europe respectively.

18.2 Fibre Distribution The wear characteristics of a carpet are important and these properties are influenced by the fibre type, the composition of the blend, the yarn specification and the mass of carpet per unit area. The distribution of fibre usage is shown in Table 18.2. Nylon continues to dominate as the principal carpet fibre. Polypropylene has increased in importance and all other fibres have declined. Acrylic fibre consumption in carpets is negligible. Consumption of polyester, including carrierfree dyeable types, has declined steeply in the carpet sector. Wool’s share of the market is decreasing overall but it is still significant in woven constructions where blends such as wool/nylon are used, although these carpets are almost exclusively manufactured in the UK.

18.3 Carpet Production Methods Traditionally most carpets were woven but from the 1960s onwards tufting and other non-woven constructions became the major methods of manufacture [1], almost to the exclusion of weaving in the USA, as shown in Table 18.3. Nylon carpets are mainly tufted (90%), wool carpets mainly tufted (49%) or woven (47%), and polypropylene may be needlefelt (43%), tufted (38%) or woven (19%) [2]. Processing routes for both woven and tufted carpets are shown in Figure 18.1, together with the stages at which coloration can take place. Traditional dyeing of loose stock or yarn for woven carpets has given way mainly to piece dyeing and printing of tufted constructions, providing much improved economy and flexibility of production. Approximately 70% of tufted nylon carpeting is coloured in piece form and approximately half of this is dyed or printed continuously [2].

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18.4 Coloration Processes The distribution of production between the various coloration processes specified in Figure 18.1 is given in Table 18.4. Over the period shown, producer coloration and continuous piece dyeing have grown in importance whilst batchwise methods of carpet dyeing have declined, particularly in Western Europe. Carpet printing has declined significantly in North America. This topic will not be discussed further here, especially since it has been admirably discussed elsewhere [3]. The traditional methods for coloration of woven carpets include loose stock dyeing, especially for achieving exceptional levelness and fastness in solid shades for Wiltons, and hank dyeing, which is widely preferred for Axminsters since many small lots are required for the numerous colourways. Staple yarn for tufted carpets is traditionally dyed as loose stock, whereas filament yarn is producercoloured or space-dyed. Continuous dyeing and printing are important for tufted nylon carpets and package dyeing has been developed successfully for most types of yarn. Producer coloration of carpets has increased in importance from the late 1980s onwards. This can be associated with the emergence of polypropylene as the second most important fibre, but producer-coloured nylon, both masspigmented and chip-dyed, is also increasing in importance. Phosphorescent polypropylene or nylon carpet yarns have been produced by Afterglow Accent Yarns Inc of Chatsworth, Ga. Chips are moistened and coated with a finely divided zinc sulphide in powder form followed by melt spinning, resulting in the production of phosphorescent filament yarns [4]. Variations in the metering of pigment master-batches, in the texturing, heat setting and winding of bulked continuous filament yarns and in the tufting process itself, become visible as distinct longitudinal streaks in plain-coloured cut-pile carpets. By contrast multicoloured cut-pile, loop-pile and staple cut-pile carpets are less sensitive [5,6]. Nylon yarns are usually dyed with acid dyes under carefully controlled conditions. Polypropylene, on the other hand, is normally mass-coloured with pigments and streak problems can originate from inadequate control of pigment master-batches. The tufter as carpet producer often takes the largest share of responsibility for these faults but variations can arise in production of the pile yarn. Streaks in the dyed nylon yarn or carpeting may be associated with variability in polymer dyesite content and delustrant level. Further causes of shade streaking include crosssectional variations of individual filaments, bulk-related differences, crimp variability, fluctuations in yarn setting temperature, tension and moisture content of the yarn, tufting tension and cutting variations [7]. Texturing conditions for nylon 6.6 filament yarns were systematically varied and the resulting bulked yarns characterised for crimp, relative dyeability and propensity to form streaks in two-ply saxony carpets. The streak formation was highly correlated with crimp variations rather than dye uptake differences [8].

18.5 Fastness Requirements In common with automotive and furnishing fabrics, a high level of light fastness is required in finished carpets. Other properties of importance for carpets are fastness to wet and dry rubbing, shampooing and water (or sea-water). The application of stain-blocking agents demands the use of fast dyes. For contract end-uses, such as aircraft carpets, the dyes must be fast to the flame-retardant

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finishes applied. Carpets are usually given an elastomeric coating on the back of the carpet in the form of a latex (to lock the tufts into the backing fabric) or a foam (to give the carpet improved resilience). Dyeings must withstand these processes, whilst the presence of traces of copper or manganese in the dyed fibre may adversely effect the latex-curing process. The fading of dyed nylon carpet fibres is an oxidative degradation catalysed by UV radiation and sensitised by titanium dioxide if present as a delustrant. Ultramid UV (BASF) is a modified nylon 6 derivative containing a photostabiliser integrated into the polymer chain. This functions as a radical trap that suppresses essential steps in the degradative process. Ultramid UV heat-set carpet yarns are available as regular, deep-dye and basic-dyeable variants. Multicoloured Ultramid UV carpets exhibit markedly higher fastness to light than conventional differentialdyed nylon 6 carpets [9].

18.6 Dye Selection for Batchwise Application Dye selection and methods of application to wool or nylon have been discussed in Chapters 8 and 10. Increasing use has been made of acid donors that allow the pH to decrease gradually as dyeing proceeds. Monosulphonated levelling acid dyes can be applied with an anionic levelling agent at 80 to 85°C and a pH of 6.0 to 7.0, depending on the depth of shade. This low-temperature method and controlled pH gives good reproducibility and colour corrections are seldom necessary. Superior tuft definition is obtained and side-to-centre colour variations are eliminated. To save energy, various low-temperature dyeing methods are used, based on pH control and an appropriate dyeing assistant. Control of pH is essential in nylon dyeing and various buffer systems are available for this purpose (Table 18.5) [10,11]. Alternatively, acid donors may be used; these are usually esters of organic acids that hydrolyse to give a gradually decreasing pH as the process proceeds through the time/temperature profile. Initially, tufted carpeting was plain-dyed on winches, variety being obtained using textured or sculptured effects by varying the height of the pile during tufting. Tufting machine developments, including scroll pattern attachments, sliding needle bars and streak-breaking have improved the design and patterning potential. Colour contrast or shadow effects can be obtained using differentialdyeing nylon variants. This differential uptake is achieved by varying the number of amino end-groups in the nylon polymer, since this determines the dyeability with anionic dyes. The introduction of sulphonic acid groups into the polymer structure confers dyeability with basic dyes and resistance to anionic dyes [12]. A wide range of contrast effects can be obtained from the various yarns available (Table 18.6), with selected disperse dyes being used to provide a ground shade on all yarn types when required. To achieve a high degree of contrast, acid dyes should be selected that do not stain the basic-dyeable yarn under the preferred dyeing conditions at pH 6 and basic dyes that do not stain the deep-dyeing yarn. Slight staining of the normal yarn will always occur and thus acid dyes should be used for deep colours, so that only slight dulling arises from the basic dye stain on the normal yarn. Carpeting containing differential-dyeing nylon is given a combined scour-bleach to remove the sighting colours (applied to identify the various yarn components) and lignin impurities. After rinsing, the carpet is placed in a cold bath containing a nonionic dispersant and a weakly cationic levelling agent acidified to pH 6. The


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dispersant acts as an anti-precipitant to prevent interaction between the oppositely charged dyes and the levelling agent increases the contrast between the acid- and basic-dyeable yarns. The basic dye is added, followed by the acid dyes after a suitable running time. The temperature is raised to 95°C at 1.5°C per minute and dyeing continued for 45 to 60 minutes. Acid should not be added to increase exhaustion since this can seriously impair the migration properties of the dyes. Monosulphonated levelling acid dyes are preferred for plain colours in the Brückner Carp-O-Roll process and differential effects can also be obtained. Guidance on dye selection for winch dyeing of various forms of nylon carpet has been given [13]. Interest in polyester carpets has waned but disperse dyes are applied either by carrier-dyeing methods on the winch or in high-temperature jets as described earlier. Carrier selection is important since some give inadequate dye yields and light fastness, as well as posing environmental problems. The introduction of polyester fibres, such as Trevira 210 (Hoechst), which can be dyed at the boil without carrier, was a significant development that may yet result in a revival of polyester carpets [14]. Piece dyeing of wool carpets is generally carried out with levelling and 1:1 metalcomplex dyes [15] and has been discussed earlier. Acrylic carpets in piece form would suffer severe deformation that would be set into the carpet during winch dyeing. Blend dyeing is relatively unimportant in winch dyeing, although 50/50 polyester/nylon (using selected disperse dyes) and 80/20 wool/nylon (using levelling acid dyes) are encountered.

18.7 Dye Selection for Continuous Application Nylon carpets can be dyed continuously using metal-complex, milling or levelling acid dyes together with auxiliaries for levelling, wetting and prevention of frosting, antifoams and anti-precipitants. Monosulphonated levelling acid dyes give high colour yields and moderately good wet fastness. Intrinsically fast dyes, such as milling acid or metal-complex types, diffuse more slowly during steam fixation and may give lower wet fastness if penetration into the nylon is inadequate. Differential-dyeing carpets can also be dyed continuously.

18.8 Dye Application Processes 18.8.1 Loose Stock Dyeing Fibre dyeing methods have been widely used to produce yarns for both weaving and tufting of plain carpets, where a high standard of both levelness and fastness is required. Loose stock dyeing is also appropriate before spinning multicoloured yarns for tweed or heather-mixture effects. Fashion-oriented carpets based on traditional Berber styles and the Wooltweed concept [16] have been developed. Fibre dyeing, using either batchwise or continuous methods (sections 12.4 and 12.5), is appropriate when large weights of fibre per colour are required. In the batchwise method, large dyelots can be blind-dyed and the final colour obtained by dyeing correction lots. Continuous dyeing methods are available to give savings in labour, energy, water and effluent compared with conventional exhaust methods. A continuous range consists of padding, dye fixation, continuous back-

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washing and drying. In the Smith-Fastran EDF, a hydraulic ram was used to feed the padded fibre into the fixation unit under pressure and fixation was achieved by radio-frequency energy in 15 minutes. A production of 750 kg per hour could be achieved, whilst a radio-frequency dryer after back-washing gave a controlled moisture content. Fibre lubricants and softeners are applied after dyeing and these must be chosen with care, since they are unlikely to be removed by scouring in a later process if dry-spun yarns are used for tufting. Lubricants that give adverse soiling or static properties must not be used, whilst uneven application may result in stripiness on plain-dyed carpets. 18.8.2 Yarn Dyeing Hank dyeing has been widely used for the production of yarns for Axminster weaving. The designs in such carpets usually require many colours in relatively small dyelots. Other carpet styles (such as tufting) require large dyelots and, to achieve these, several hank-dyeing machines may be coupled together. A carpet hank dyehouse usually has a wide spread of machine sizes. Hank dyeing and the necessary machinery have been discussed in sections 13.2 and 13.4. The introduction of jumbo hanks and the use of RF drying have been of particular relevance to the carpet industry. Automatic handling devices for loading and unloading hanks from the dyeing machine have been developed and used in the carpet hank dyehouse to reduce labour costs; these are discussed in section 4.4. With yarns spun in oil, adequate scouring before dyeing is essential to minimise the risk of stripiness in the carpet as a result of differential soiling during wear. Uniform hydro-extraction is desirable before thermal drying on poles, since differential moisture content at this stage, leading to variations in yarn tension, may be another cause of stripy carpets. Hank dryers for carpet yarns have been designed so that they can be operated with a minimum of labour by having entry and exit points situated close together. Robotic handling of jumbo hanks, together with a squeezing unit to reduce moisture content to 50%, then unloading and packing after drying can be incorporated into a system such as that shown in Figure 18.2. The carpet industry has been slow to adopt yarn dyeing in package form, even allowing for the advantages of ‘quick response’ production which can be important in the contract sector. The high capital cost involved and the investment in jumbo hank technology have been two reasons for this but a few package-dyeing units have been installed, usually when traditional hank-dyeing facilities have reached the end of their useful life. The technology and advantages of package dyeing of carpet yarns have been well documented [17-19] and discussed in section 13.3. Savings in handling, including a reduction in winding processes, make a major contribution but improvements in carpet manufacture and planning are also possible. Jumbo packages can be processed and the preparation of packages to a suitable specification is important for the success of the process. Most, if not all, yarn types can be package-dyed and the method is extremely useful for dyeing singles yarn used in the production of marl or ‘stipple’ yarns, which are difficult to hank dye. Intermingled filament yarns containing differential-dyeing components can be dyed in package form ready for tufting. Package-dyeing machines are amenable to a high level of control and this can be allied to automation and robotics as discussed in Chapter 4.


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Continuous dyeing methods for yarn have been particularly successful in the carpet sector. Superba, well-known for its continuous relaxation equipment for yarn, developed a continuous yarn dyeing range, whilst Mageba has demonstrated that yarn can be processed on its narrow fabric ranges. The setting of twist in carpet yarns is necessary to give improved tuft definition in cut-pile carpets, to develop special pile textures, to improve carpet stability in piece dyeing or printing and to improve the appearance retention during wear. Setting can be carried out in hank form, either in hank-dyeing machines, in basket cages (using boiling water with or without the addition of chemicals), in autoclaves or in tape-scouring machines. Yarn setting can be carried out as an integral part of package dyeing. A continuous process for wool yarn was developed based on a four- or five-bath unit for package-to-package processing, designated the ANDAR/WRONZ Chemset process [20]. Handling is simplified, since the yarn from a package is scoured, set, insect-resist treated and back-wound on to a package ready for tufting. Chemical setting involves treatment in sodium bisulphite at pH 7.0, which permits cut-pile wool carpets to resist the mechanical action that can cause texture loss in winch dyeing [21]. 18.8.3 Batchwise Piece-Dyeing Methods Batchwise and continuous methods of piece dyeing are essentially restricted to the coloration of tufted carpets, particularly those manufactured from nylon, and are important application methods as indicated in Table 18.4. Traditionally, long runs were considered necessary for continuous dyeing. It was estimated that a carpet producer required per colourway the equivalent of the production capacity from six winches before continuous dyeing became viable. However, shorter runs are now the trend. Continuous methods can still be cost-effective in resources and labour because rapid-change applicators have reduced downtime, making the process more competitive. Carpet-tufting machines are highly productive and piece dyeing avoids many inventory problems that occur with fibre- or yarn-dyed materials. Filament yarns in loop-pile constructions are robust and versatile for piece dyeing, since fibre shedding does not occur and sculptured designs, typically based on multi-level tufting techniques, can be produced. However, the formation of ‘ladders’ can be a problem with loop-pile carpets. Staple yarns are used in cut-pile constructions and fibre shedding usually occurs in batchwise dyeing, although ladders are not a problem. Certain finishes for cut-pile carpets can only be obtained by piece dyeing. As indicated above, nylon is the principal fibre for tufted or woven piece dyeing. Carpets containing differential-dyeing nylon yarns are processed by batchwise or continuous methods. Polyester carpets are seldom piece-dyed, despite the development of high-temperature versions of the carpet winch. Not much wool carpeting has been dyed in piece form because of loss of tuft definition and felting. However, the chemically set yarn described above avoids these problems and details of wool carpet processing on the winch have been given [22], although reel speeds are reduced to 20 m/min. The batchwise dyeing of carpets is carried out on large stainless-steel winches similar in design to those used in other sectors of the industry, described in section 14.6.1. Machines for carpet dyeing need to be more robust in construction and more sophisticated in design. Pumps or impellers are fitted to aid liquor

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circulation, whilst scroll openers and centring devices are provided for open-width processing. A conventional carpet winch is illustrated in Figure 18.3. Discussion has arisen as to whether rope or open-width form gives the best results in batchwise carpet dyeing. Rope dyeing gives better levelling but causes more creasing, although it may be necessary for re-dyeing if unlevel dyeings are obtained. Carpet lengths of 100 to 200 metres in widths up to five metres (weighing up to 2500 kg) are normally processed and reel speeds are in the range of 60 to 100 m/min. Modern machines are fitted with automatic controllers and rates of temperature rise are adjusted to 1 or 2°C per rope revolution. External heat exchangers and automatic pH controllers with dosing systems [23] have been installed on some versions. An automated dispensary is necessary because of the large quantities of dye to be dispensed. The internal surfaces of the winch are regularly smoothed by buffing to prevent snagging and ladder formation. Because of the heavy weights involved, power-driven reels are necessary to unload the wet carpet into heavy-duty trucks, usually mechanically hauled to transport the carpet in the dyehouse. A recent development [24] is the NTM Obermaier Novacarp equipment for dyeing carpet in open-width at liquor ratios in the range 10:1 to 20:1, using troughs that follow the contour of the carpet package. Variable load sizes can be dyed at a constant liquor ratio and savings in water (30%), electricity (95%) and time (70%) compared with winch dyeing, have been claimed. The maximum fabric speed is about 120 m/min and the dyelot size 2000 metres2. The machine is illustrated in Figure 18.4. Jet dyeing machines, such as the Then Carpetflow, have been developed [25] for the high-temperature dyeing of polyester carpets but these machines can also be used for other tufted carpets in rope form. Cost reductions, as high as 70% compared with winch dyeing, have been claimed as a result of low liquor ratios (down to 12:1) and the consequent savings in water, effluent and energy. High quality in terms of level dyeing, reproducibility, development of bulk and freedom from running marks is claimed; by coupling jet tubes, batches of up to 2400 m2 can be dyed successfully. Nylon tufted carpet has been dyed by a cold pad-batch method using the Brückner Carp-O-Roll process. The method is claimed to favour sensitive fabrics, such as velours, where pile deformation could occur in winch or continuous dyeing. Differential-dyeing materials can be successfully processed but, as expected, variable pile-height material cannot be dyed successfully. The processing costs compare favourably with batchwise and continuous methods, especially due to the energy savings obtained. The carpet is pre-steamed before it passes to the dye applicator, where a metered dye supply is applied by a nozzle system to give a dye liquor uptake of 150 to 300%. 18.8.4 Continuous Piece-Dyeing Methods Continuous dyeing ranges involve considerable capital investment and are almost exclusively used to colour tufted nylon carpets. Since many sections of the range are common to both continuous dyeing and printing, it is not unusual for printing and dyeing for plain colours to be applicable in the same line [26]. A continuous dyeing range is illustrated schematically in Figure 18.5. The general trend towards shorter production runs requires flexible equipment capable of quick colour changes, short downtimes and minimum dye-liquor waste.


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Continuous dyeing of carpets is carried out before the latex coating or foam backing is applied and a typical unit will include the following sections: 1. dye-liquor preparation area (colour kitchen, usually housed away from the application unit) 2. carpet sewing-in 3. compensator and lint removal unit 4. pre-steamer or jet bulker 5. colour application unit 6. steamer 7. washing unit with vacuum extraction 8. chemical finish application 9. dryer. Colour applicators are based on a number of techniques, including the following [24]: 1. padding 2. dip-drain methods 3. curtain coating 4. Küsters Fluidyer 5. spray methods 6. foam application 7. hot dye-liquor techniques. Continuous dyeing ranges usually operate at speeds in the range 5 to 30 m/min but this depends on the weight per unit area of the carpet, which in turn will influence the efficiency and, therefore, the speed of the drying unit [26]. Carpet widths are typically 4 or 5 metres and considerable quantities of dye-liquor must be prepared. For example in continuous dyeing a 4-metre wide carpet weighing 1 kg/m2 and running at 10 m/min with a 300% pick-up will require 120 litres of dye-liquor per minute [2]. Colour kitchens and their ancillary equipment are discussed in section 3.12 and several companies can supply this equipment for continuous dyeing of carpeting. Liquid brands of dyes are an attractive option in view of the large volumes to be handled. For continuous dyeing, tanks for mixing and storing prepared thickener are required together with dissolving and mixing tanks for dyes and chemicals, with at least two dye-liquor storage tanks per colour station [2]. Automated dosing, recipe calculation, recipe storage and dye usage statistics are standard data. Carpet lengths must be sewn together efficiently and without skewing before loading into a J-box compensator of adequate size to give enough sewing time, particularly in high-speed machines. Hours of production time can be lost by inadequate stitching. Combined beater/vacuum devices are used to remove lint, which would give resist marks on finished carpet if allowed to remain on the surface. A short steaming treatment for 5 to 20 seconds is given to the carpet on the pre-steamer, using low-pressure steam at temperatures of 100 to 105°C. This gives a uniform moisture content, slight pre-bulking and removes creases which can give rise to uneven dye uptake. Alternatively a jet bulker is used to give a short vigorous continuous washing treatment to the carpet, using either cold water or hot water up to 70°C. Detergent may be added, but this is preferably avoided to prevent foaming. Jet bulking removes lubricants, sighting colours and

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creases to deliver a clean, uniform carpet. The carpet is passed over a vacuum slot to reduce the moisture content to 40 to 50%. The main problems with pad application for coloration are tailing and side-tocentre colour variations over the extensive width of the carpet. Swimming-roll padders, as developed by Küsters, assist in overcoming these problems [26]. Most conventional padders are used to pre-wet the carpet for subsequent dye application on a swimming-roll pad. Pick-up is in the range 80 to 120%, with padding at ambient temperature to minimise tailing. Dye retarding agents applied at a high pH may assist in minimising tailing effects. In dip-drain methods as developed by the BDA the carpet is impregnated with dye-liquor by passing under a roller in the colour trough. There is a slight squeezing action resulting in a liquor uptake of 400 to 800%, controlled by liquor viscosity and carpet speed. After impregnation, the carpet rises vertically about 4 m to the steamer entry and excess dye-liquor drains back down the carpet into the trough. High drying energy requirements arising from the high pick-up and large volume of dye-liquor necessary to fill the trough, together with dye wastage (about 20%) make this an expensive process. Curtain coating methods, as developed by Fleissner and Küsters, are aimed at giving a uniform application of dye-liquor by ensuring that a continuous film of dye-liquor falls evenly from a ‘weir’ reservoir applicator onto the carpet surface [26]. Liquor pick-up is 300% on to pre-wetted carpet, giving a total uptake of 400% and thus less liquor loss in the steamer. Since there is no exchange of liquor, there are no tailing problems associated with the actual applicators. The equipment allows for quick colour changes (about 20 minutes). By applying multiple dye streams, space-dyed or random-colour effects, such as the TAK [27] and Polychromatic systems [28] are possible. In the Küsters Fluidyer, liquor or aerated liquor is applied via a special distributor to a slot held in contact with the carpet pile by an inflated air bag [29]. Hot dyeliquors can be used and, with suitable ancillary equipment, quick colour changes are possible [30]. Dye uptake is adjustable over the range 50 to 400% for the production of either plain dyeings or ground shades for printing. Lower pick-up gives no liquor loss in the steamer and lower drying energy requirements. Dyeliquor is applied to dry carpet and since there is no liquor interchange there are no tailing problems. Spray application techniques are available at various levels of sophistication [31-33]. In the Otting version, oscillating sprays are mounted about 1 cm apart and deposit a liquor spray, the density of which is adjustable pneumatically, onto the carpet surface. The Millitron (Deering Milliken) [31], Chromotronic (P Zimmer) [32] and Titan [33] units were developed for jet printing. Depending on the effects required, pick-up can be varied from 50 to 400%. Foam application machines have been developed to reduce liquor uptake and thereby minimise energy, chemical and thickener costs [34] but frosting can be a problem at low pick-up levels. Certain applicators, including the Küsters Fluidyer and Otting spray, can be operated with hot dye-liquor to give superior solidity of shade with steaming times of only 1 to 2 minutes. Although there are no significant energy cost savings, a higher production rate can be obtained using a shorter steamer [35]. Festoon steamers are preferred for uniformity in solid colours and to achieve good contrast on differential-dyeing nylon [36]. Steaming times of 2 to 5 minutes for nylon and 4 to 10 minutes for wool are required. Cut-pile and wool-rich carpets generally need longer steaming times to achieve full penetration of dye [2]. At


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high liquor pick-up, it is preferable for the carpet to enter the steamer at the top to reduce liquor flowing back onto cold carpet, thereby avoiding problems of air pockets and steam losses. With lower pick-up, the carpet can enter at the bottom of the steamer; roof entry of the steam is a more efficient system, since air pockets are eliminated as the steam forces the air downwards [29]. Unfixed dye, auxiliaries and thickeners must be removed by washing before drying and finishing. This is essential to improve the wet fastness, handle and freedom from soiling. Modern washing systems require efficient spray/vacuum systems with variable slot widths [29]. Perforated-drum washing systems have been developed by Fleissner, as illustrated in Figure 18.6. Wool and wool-rich cut-pile carpets need a gentle action during passage through the washing stage to avoid excessive pile burst [2].

18.9 Finishing of Carpets Antistatic or antisoil finishes can be applied by spraying or padding between the washer and the dryer. Spraying is mostly preferred but gives limited penetration down the pile. Dip-and-nip padding methods give good penetration and a higher uptake, thus requiring a higher energy requirement in drying. Stain-blocking agents (section 10.4) can be applied in the dye-liquor prior to the steamer or before drying. Application conditions can be critical for optimum stain-blocking and to minimise subsequent yellowing [26]. The effluents from mothproofing treatments of wool, especially those based on permethrin, have adverse effects on the environment if discharged to drain (section 2.13). In a finishing process developed by WRONZ, the permethrin-based agent Eulan SPA (BAY) was sprayed onto carpeting as an improved alternative to application on loose wool or yarn, in order to minimise effluent pollution. Spray/vacuum systems for finish application are claimed to overcome some of the limitations of conventional spray or foam applicators and offer the advantage of requiring no further steaming to confer adequate fastness. A disadvantage, however, is the small volume of liquid effluent remaining to be treated and discharged. A further possibility is the dry carrier technique, in which the active agent is encapsulated in an inert dry powder (typically talc) as carrier medium. This approach has the advantage that no liquid effluent is formed but poststeaming is necessary to give adequate fastness [37]. In the foam application sector, the Autofoam Advanced Carpet Applicator (Datacolor International) system is claimed to solve the environmental problems associated with insect-resist treatments for wool carpets. Hitherto, mothproofing agents have been applied mainly in the scouring or dyeing stages. The closedloop system ensures that effluent pollution is eliminated and facilitates insectproofing. The automatic control system maintains the chemical composition, density and pressure of the foam applied to the carpet surface, so that the pile is thoroughly penetrated and the agent absorbed is evenly distributed at the required concentration. Carpets treated with permethrin-based mothproofers by this process are resistant to photodegradation and problems with carpet cleaning or effluent treatment are avoided [38]. Apart from insect-resist finishing, the Autofoam ACA system is suitable for the application of stain-blocking agents, pile appearance enhancers, softeners, antistats, flame-retardants and fluorochemical soil-repellents [39].

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After application and fixation of finishing chemicals, vacuum slot extraction removes most of the water and final drying is carried out on horizontal or drum dryers, which are at their most efficient when used in conjunction with heat exchangers and moisture-level indicators [40]. Over-drying is costly and can also cause thermochromic changes which complicate colour-matching procedures. Temperature and air velocity in the dryer should be uniform with upper limits on both, so that satisfactory handle and tuft definition are obtained. The fabric is then inspected over a suitable frame and any ladders in loop-pile carpet are repaired. A latex coating or foam backing is then applied continuously and finishing agents applied by spraying at the entry end of the range. Steaming and back-beating may be carried out to raise the pile and enhance the bulk. Shearing to remove surface fibres is carried out after (or in line with) the backing process, followed by final inspection. Modern shearing machines have two or four cutting cylinders with automatic machine control in which processing details are recorded, with seam and metal detectors being standard features. Infrared treatment is a viable alternative to gas-fired ovens and hot-air dryers for the curing of latex coatings. Bulk trials using the Hereaus Noblelight unit for this purpose resulted in a 40% increase in output and improvement in carpet quality because of more thorough curing of the latex [41].

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T L Dawson in Textile printing, Ed. L W C Miles (Bradford: SDC, 1994).

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P Lennox-Kerr, Internat. Carpet Bull., 255 (Jan 1995) 2.

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K Berhalter, Chem. Fibers Internat., 48 (1998) 65.

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K Berhalter and W Hoof, Melliand Textilber., 79 (1998) 764.

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M L Honeycutt, AATCC Internat. Conf. and Exhib., (Oct 1995) 107.

[8]

R W Miller and J H Southern, Text. Research J., 61 (1991) 61.

[9]

P M Bever, U Breiner, G Conzelmann and B S von Bernstorff, Chem. Fibers Internat., 50 (2000)

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P Charles and J Park, Dyer, 140 (1968) 371.

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T L Dawson, Dyer, 162 (Aug 1979) 19.

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J Shore, Blends dyeing (Bradford: SDC, 1998).

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J Park, JSDC, 109 (1993) 133.

[14]

H Beiertz, Chemiefasern, 42/94 (1992) 64.

[15]

M Stursa, Melliand Textilber., 70 (1991) 954.

[16]

J Park, Wool Record, 146 (Aug 1987) 23.

[17]

K Limbert, JSDC, 91 (1975) 299.

[18]

C Philpott, Dyer, 153 (1975) 298.

[19]

J Park, Dyer, 158 (1977) 481.

[20]

A J McKinnon, Wool Sci. Rev., 66 (Dec 1989) 31.

[21]

G H Crawshaw, Text. Chem. Colorist, 23 (Jun 1991) 13.

[22]

C T Page et al., Australian Text., 11 (Feb 1990) 52.

[23]

Ciba-Geigy Brochure, 9126 (1977).

[24]

P Owen, AATCC Review, 1 (Oct 2001) 20.

[25]

W Christ, Internat. Text. Bull., Dyeing/Printing/Finishing, 27 No.3 (1981).

[26]

A Keller, Internat. Carpet Yearbook, (1995) 27.

[27]

K Zimmerli, Amer. Dyestuff Rep., 68 (1979) 19.

[28]

T L Dawson, JSDC, 90 (1974) 235.

[29]

K Zimmerli, Amer. Dyestuff Rep., 75 (Jun 1986) 28.


[30]

D Ward, Dyer, 185 (Mar 2000) 15.

[31]

Deering Milliken, USP 3 696 779 (1974).

193

[32]

P Zimmer, Dyer, 156 (1976) 554.

[33]

Anon, Amer. Dyestuff Rep., 68 (1979) 39.

[34]

T L Dawson, JSDC, 97 (1981) 262.

[35]

J Hilden and J Diekmann, Internat. Text. Bull., Dyeing/Printing/Finishing, 32 No. 4 (1986) 11.

[36]

M A Herlant, Amer. Dyestuff Rep., 76 (Mar 1987) 27.

[37]

P E Ingham and C K Rowan, Textile Asia, 21 (Sep 1990) 112.

[38]

Anon, Internat. Carpet Bull., 246 (Feb 1994) 7; Wool Record, 153 (Mar 1994) 29; 154 ((Mar 1995) 25; Canadian Text. J., 111 (Dec1994/Jan 1995) 28.

[39]

J Greenwood, Internat. Carpet Yearbook, (1997) 21.

[40]

T L Dawson, JSDC, 98 (1982) 387.

[41]

Anon, Wool Record, 151 (Dec 1992) 15.

194


Table 18.1 World carpet production (m2 x 106)

Geographical area North America Western Europe Rest of the World Total

Year 1989 1130 940 630 2700

2000 1670 1220 890 3780

Table 18.2 Consumption (% by mass) of fibres in the carpet industry

Fibre Nylon Polypropylene Wool Polyester Other

Western Europe 1989 2000 41 53 32 40 15 5 6 2 6 -

North America 1989 2000 74 62 16 30 1 1 9 7 -

Table 18.3 Production of carpets by construction (%)

Construction Tufted Needlefelt Woven Others

Western Europe 1989 2000 66 57 22 25 10 12 2 6

North America 1989 2000 95 87 3 5 1 3 1 5

Table 18.4 Production (%) by various coloration methods

Coloration method Producer Batchwise Printing Continuous

Western Europe 1989 2000 31 45 32 8 23 25 14 22

North America 1989 2000 24 37 34 22 17 4 25 37


195

Table 18.5 Systems for pH control in nylon carpet dyeing

pH value 4.5 5.0 6.0 7.0 8.0

Agents and concentrations (g/l) required Disodium Sodium Sodium dihydrogen hydrogen phosphate acetate phosphate 0.5 1.0 1.5 0.25 0.6 1.2 0.04 1.8

Table 18.6 Nylon fibre variants for carpets Nylon type Extra deep Deep Normal (standard) Low Light basic Basic

Dye class used Acid Acid Acid Acid Basic Basic

Acetic acid (80%) 1.2 1.0

196


Figure 18.1 Processing routes and stages for coloration Tufted

Woven

Staple fibre

Fibre

Producer coloration

Loose stock dye

Spin

Continuous filament

Space or package yarn dye

Spin Tuft

Yarn dye Piece dye or print Weave

Figure 18.2 Minetti hank dryer for carpet yarns


197

Figure 18.3 Gaston County Super Beck

Figure 18.4 Obermaier Novacarp carpet dyeing equipment

Figure 18.5 Continuous carpet-dyeing range

Colour application

Steaming

Washing

198


Figure 18.6 Application of perforated-drum technology

Dye applicator

Steamer combination perforated drum/loop steamer

Perforated drum washing machine

Perforated drum dryer

Chapter 19 Closing Comments 19.1 An Expanding Market As a result of a continuing harsh economic climate in the textile industry of the developed world, it is readily overlooked that both household textiles and clothing manufacture are in fact growth areas as a result of both the increasing global population and the increasing value of disposable income available, particularly in developed countries. Between 1960 and 1998, textile manufacturing grew by an average of 2.1% per annum, the growth rate having peaked at 3.7% per annum in the 1960s. Total global fibre consumption grew from 15,153 kilotons in 1960 to 46,612 kilotons in 2000, an annual increase of 2.8% in fibre consumption over this period. These figures represent a somewhat lower average than that for worldwide manufacturing as a whole, which grew at an average of 4.2% per annum over the same period [1]. Although this continuing trend is good news for textile production, the main areas to benefit from this growth in dyes and textiles manufacture have been in developing countries, as discussed in Chapter 1. The reasons behind this have been listed in Tables 1.4 and 1.5 and discussed elsewhere [2]. They include the recognition by developing countries that textiles can be a sunrise industry if supported by an adequate labour supply and initially a captive local market demand that is eventually expanded into export.

19.2 A High-Tech Industry The preceding chapters have demonstrated that textile production in general and the dye manufacturing, textile dyeing and finishing sectors in particular are hightech operations. This technology is accessible to all countries, often made more readily available to developing countries as a means of entry for the marketing of relevant products. Developing countries, often with appropriate financial assistance, have been quick to invest in modern dyeing and finishing plants, including control equipment, automation and robotics. This has resulted in considerable reductions in the labour required, so that the low labour cost in developing countries is no longer the dominant issue that it was in the past. This sophisticated technology, including appropriate dye selection, the latest equipment and ancillary services and the refinement of application techniques leads to the capability to achieve virtually total RFT processing by blind dyeing techniques. This facilitates the establishment of ‘lights out’ operations by the use of robotics. By these means, major cost reductions, substantial savings and increases in profitability and productivity are attainable. RFT production is necessary to fulfil the ‘quick response’ demanded by the market.

19.3 Need for Investment To establish a successful dyeing and finishing operation by exploiting the latest equipment and techniques, it is necessary to initiate capital investment in the most suitable facilities. Developed countries have failed to encourage such investment whereas some developing countries have made major investments. The existing differences between these various countries will gradually be eroded,

199

200


as indicated above, and a ‘level playing field’ will eventually be reached. Developed countries will once more be able to compete on price as well as quality, but appropriate investment is required. Success may often depend on identifying ‘niche’ products for specialised markets. Such venture capital investment must be substantiated by feasibility studies which will include factors such as whether to upgrade existing facilities or to establish a greenfield operation. Alternative processing routes and equipment available for different routes or processes need to be evaluated. Health, safety and environmental issues must also be addressed. Investment in people, not least the education of young entrants into the industry, is of primary importance.

19.4 An Era of Change Fundamental changes have occurred in the textile industry, not least in the wet processing sector, over recent decades. These have effectively made many established practices and facilities obsolete, with the obvious need to replace these with modern buildings, plant and attitudes. The textile industry has evolved into retail-specified manufacturing demanding RFT production and quick response. This in turn has resulted in fashion changes throughout the year compared with the traditional two-season approach. This has enforced shorter runs per colour – a further factor to be considered in any feasibility study. Advances in colour communication, such as colour on screen and the use of the internet, as described in section 6.8, are likely to continue apace. Fibre usage is likely to evolve further; the forecast that polyester will take over from cotton as the prime fibre is already becoming firmer. The consumption of natural fibres, wool and cotton in particular, is likely to decline as land is turned to the production of alternative arable crops. Much of the cotton produced in future is likely to be genetically modified varieties. However, it is unlikely that there will be major developments in dyes, chemicals or fibres, not least because of escalating costs of R&D together with health, safety and environmental testing. These latter issues are likely to remain major concerns in the modern wetprocessing industry.

References [1]

Industrial Statistics Yearbook. New York, United Nations, published annually.

[2]

J. Park and J. Shore, Dyehouse management manual (Bombay: Multi-Tech Publishing Co., 2000).

200

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