CHEMICAL POLLUTION IN TEXTILE
Toxic chemicals in clothing:
  • PFAS (or PFCs) are synthetic chemicals found in some clothing, accessories and footwear, most commonly used for waterproof, stain and grease-repellant membranes, coatings and finishes
  • Long-chain PFAS such as PFOA and PFOS (C8) are already globally banned due to known cancer risks, and short-chain PFAS (C6), developed as safer alternatives, are now also in question
  • Called ‘forever chemicals’ because they exist beyond a product’s lifetime, PFAS can take hundreds of years to degenerate, creating the risk of seeping into landfill, waterways, humans and other animal species. This is why they’re increasingly identified as toxic to human health and nature
  • Stable, water-insoluble PTFE or PFCec-free chemicals, free of ‘PFCs of environmental concern’, are available, although they are slated to be less toxic and their long-term effects are still unknown
  • According to Statista, the global value of PFA management in waste disposal is forecast to rise from US $1.8bn in 2022 to $2.9bn by 2031, driven mainly by increasing legislation. Legislators will likely look to brands and retailers to pay more for that cost in the future
Fabric treatment processes
Solutions toward Chemical Pollution in Textile

Fabric treatment processes include Starting material, Finishing categories, Mechanical finishing, Chemical treatments, Other finishes, Colouration, Pollution aspects, Drying and shipping.

Starting Material

Modern standards in textile use seldom, if ever, allow a fabric to be sold to the ultimate consumer exactly as it appears immediately after being manufactured. This greige state, as it is known technically, is unacceptable for various reasons and further treatments are required to bring fabrics to the point where they can be used. In modern mills, the foremost aim is to minimise the financial costs of finishing (and all other operations), so it is common for a plan to be drawn up to control the entire train. Arang and Fernandez1 describe a computer program aimed at management, with applicability throughout the entire factory and with emphasis on environmental protection. The treatments carried out after manufacture may be broadly classified as either finishing or colouring. It is also not uncommon for a fabric to need washing before attempting any other processing. Washing, either in detergent or merely in water, has already been discussed at the fibre stage, but may be used at various stages in the manufacture and should be considered as having the same potential means of bringing about environmental damage wherever it takes place.

Finishing categories

Once a clean fabric is available, the finishing treatment can begin. The type of finishing selected depends on the fibre content of the fabric and the end use to which it will be put. Finishing is usually divided into two types, mechanical and chemical. These can be distinguished by considering the way in which they are carried out. Usually, it is assumed that a treatment is mechanical if it only involves the use of some kind of mechanical action, but it is often accepted that the use of heat and moisture may also be a part of mechanical finishing. Examples of this category of finishes commonly adopted include calendering, beetling, fulling, decating, brushing, raising, shearing, moiré, shrink-proofing and steaming.

Wool and synthetic-fibre fabrics are often considered to be the ones needing least finishing, because of their ability to be produced with many of the desirable features already incorporated. Wool cloths, though, are frequently given a range of both mechanical and chemical finishes, the mechanical ones of most interest being principally aimed at changing thermal insulation characteristics. Fulling is akin to felting and is achieved by subjecting the cloth to heat, moisture and agitation. Its purpose is to close up the tightness of the weave, so that the fabric retains heat better and is less likely to permit air to pass through and cause wind chill. As in felting, environmental costs result from machinery and energy factors, as well as from the discarded wash liquors (* W-3) (see Table 1.1 for an explanation of codes).

  • Brushing, raising and shearing
  • Moiré
  • Mechanical shrink-proofing
Mechanical Finishing

Brushing, raising and shearing are usually considered together; Korner2 explains the objectives and principles of the processes, together with discussion of the factors influencing them and the requirements for their successful operation. Brushing is, as its name implies, the passage of the fabric over a surface that brushes the fibres to lift them slightly out of the bed of the fabric. In this way, the amount of air enclosed is increased and, because trapped air holds heat well, so is the thermal insulation. Raising takes the process one step further, lifting the fibres still more by brushing them so roughly that the actual weave pattern is obscured. This not only increases insulating capability still further, but can conceal a sleazy cloth to some extent, so an open weave, with its inherently lower strength, can be disguised as a better one. Unfortunately, one side effect of this degree of raising can be an even greater reduction in strength, as the integrity of the fabric cohesion may be disturbed, thus shortening the life expectancy of the fabric. In such cases, there is another kind of environmental cost, that of the premature scrapping of the fabric, to add to the familiar ones of machinery and power consumption. There may also be a cost associated with the breakage of individual fibres, producing a certain amount of waste that cannot be reclaimed for any really valuable or useful practical purpose in view of the extremely short lengths of the fibre segments removed.

After raising, the appearance of the fabric tends to be rather ragged, because of the rough treatment it has received. For this reason, shearing is then carried out. This is a means of cutting off some of the fibres, so that they are all at a uniform height above the fabric surface, by passing the cloth through blades resembling those of a cylinder lawn mower. The side effect, which is a large quantity of waste fibre, is obvious and produces an inevitable environmental cost.

In moiré finishing, in which a fake watermark is embedded into a synthetic fabric in an attempt to make it look like a silk, heat and pressure operations take place, with one portion of the fabric being forced to run counter to another by passage around suitably arranged cylinders, so that a frictional effect is produced that marks both of the contacting sections of the cloth. Decating, calendering and beetling can also be considered in the same category. Each of these treatments involves the application of pressure, with or without heat and/or moisture, to a fabric. The purpose and the fibre types to which the respective finish is applied are different, but the basic principles (and the ecological effects) are the same in each case. Machinery and energy factors are present once more and, when steam is used, some waste heat is evident when it is allowed to escape onto the cloth.

Shrink-proofing as a mechanical finish uses the overfeed principle, in which damp fabric is pushed onto the pin frame of a tenter then subjected to sideways tensile stress while drying occurs. Energy losses are high, as described later, but the resultant fabric tends to be stronger and is less likely to be discarded. The fabric is also unlikely to be thrown away as waste prematurely, as it would be in the absence of shrink-proofing when a garment made from it might no longer fit after washing.

Chemical Treatments
  • Chemical shrink-proofing
  • Water resistance
  • Durability
  • Membranes
  • Coatings

 

Chemical treatments associated with shrink-proofing are normally used in modern plants and can be considered as the first example of a chemical finishing process. The mode of operation of such a process is to fill the interstices between the yarns of a fabric with a reagent that blocks the spaces so that the yarns cannot move into a closer juxtaposition. The process adopted may vary, either using impregnation with various resins, or by cross-linking with (for instance) dialdehyde, glyoxal and urea–formaldehyde. In both of these types of treatment, waste effluent of one or more of these chemicals (* W-3) is inevitable, and its subsequent discarding into the water environment will, just as inevitably, create a pollution problem. Xu et al.3 apply durable press to cotton in a one-step (and hence less polluting) method and compare the outcome to the more usual two-step process. They test results by crease recovery angle and strength measurements, finding that the two-step technique is better for crease recovery, but not as good for strength retention because of the longer curing times needed. These will, naturally, also increase environmental costs, offsetting to some extent the benefits imparted by this modification of the processing train. Optimum conditions for the two-step treat- ment are quoted as 4.3% citric acid and then 1.7% butane-tetracarboxylic acid. Cheng et al.4 attempt to improve the easy-care finishing of silk by using a multifunctional epoxide that reacts with the tyrosine in the silk to reduce the chemical activity of the fibre. Little or no change in wetting properties is evident, but the rate of hydrolysis in alkaline solution is very much lower after treatment. An anonymous writer5 reports the production of washable wool by easy-care finishing using oxidative or cross-linking techniques, noting that the process reduces shrinkage from about 30% to about 2%.

A similar end result occurs in the various methods used to provide water resistance. The type of reagent involved depends on the degree of resistance needed, whether merely for protection against light showers, or against heavy storms, or to prevent all aqueous liquid entry in, say, a garment for protection against chemical or biological warfare reagents. In addition, there is considerable interest in the development of finishes that are resistant to liquid water, but allow moisture vapour to pass through. This treatment compensates to a considerable extent for the main disadvantage of traditional storm-resistant fabrics, the tendency for the people wearing them to be wetter from their own perspiration than they would be from the actual rain being kept off their bodies.

The types of chemical used (and the resulting effect on the environment) vary, but are typified by insoluble metallic compounds, paraffin or waxes, bituminous materials, linseed or other drying oils and combinations of all these substances. Application in each case is usually achieved by padding, or passage through pressure rollers under or near the surface of the treatment liquid. Again, the inevitable machinery and energy factors must be accepted, but there is also the added problem of disposal of the chemical reagents. Paraffin and similar waxes are relatively harmless and can usually be reused easily, but some metallic compounds, oils and bituminous materials may be highly toxic (* W-3) and should only be released after considerable dilution. Even then, all of them are harmful in some degree and should be regarded as undesirable. In this context generally, the industry has begun to sound warnings. Expresses concern about the effects of pollution on the environment and Soljacic et propose that a system for eco- acceptable finishing ought to be developed. Gulrajani8 feels that the Indian chemical finishing system is already environmentally sound, but is antiquated. Mathew9 suggests that the use of ultrasound in all applicable wet processing steps, such as the preparation of sizes, emulsions, dye dispersions and thickeners for printing, would be beneficial to the planet’s well-being because it can reduce the amount of reagent needed. Duschek10 describes the mode of action of fluorocarbon polymers and the ability, by using a new technique, to apply such a finish in a low- emission manner (about 90% lower) to maintain emissions well below legislative standards and with no thermal after-treatment.

How well the rest of the industry follows strictures for ecological responsibility is not too encouraging, as we will shortly see, but all the chemical finishes currently in vogue will be considered here first. In an unusual approach, Barton11 reports the

possibility of ‘intelligent fabrics’ being developed. These would have fragrances, moisture, antibacterial finishes or thermal modifications incorporated into their structure to provide continuing effects. Until they are commercially realisable beyond the relatively few underwear applications presently available, the industry has to rely on more familiar techniques.

Moisture vapour permeability, in conjunction with liquid water resistance, is currently ardently sought as a kind of ‘philosophers’ stone’ in textile science. The elusive ability to allow complete moisture comfort with the total exclusion of all liquid water and the total capability of perspiration moisture to escape, has not yet been developed. The principle on which a successful technique can be expected to operate is a simple one, the fact that there is a significant difference between the molecular sizes of liquid and vapour aggregates of water. Unfortunately, we do not yet have the ability to control the size of fabric apertures to the necessary degree of accuracy. The methods of approach currently in vogue include hydrophobic finishes, coatings, and laminations of microporous films or membranes. More details of the latter two are provided by Fung.

Hydrophobic finishes tend to suffer from a serious defect, in that the finish slowly disappears during extended use. Thus, a raincoat which gives adequate protection against showers when bought may, after a few laundering or dry cleaning treat- ments, be less than satisfactory and leave the unfortunate wearer soaked. In terms of environmental damage, the application of the water-resistant finishing agent, usually consisting of a reagent similar to those mentioned above in connection with liquid water resistance, is a problem both at the manufacturing stage, when the surplus chemicals are flushed into the drain (* W-3), and after use if the garment is thrown away prematurely because it is no longer of any value for its intended purpose. The type of finish will be governed by the degree of water resistance required, but all of those currently in use tend to be slowly lost with time and this approach is not now regarded as having any real future.

Because of this, other solutions have been attempted. One of the earliest of these was the traditional oilskin often used by seamen and cyclists. This consists of a topcoat made from a fabric of cotton which has been saturated with an oil (usually linseed or some related substance) and heated to bake, and hence polymerise, the oil. The actual extraction of the oil, as with all oils, carries the environmental cost mentioned already, and the baking process is likely to produce toxic gaseous by- products (* A-2) as a result of the high temperatures needed for polymerisation. The garment, too, is usually not completely satisfactory, as anyone who has cycled in one will attest. The inside of the oilskin after pedalling strenuously up a steep hill leaves the cvclist in a sad state of drenched discomfort from perspiration that stays with him, entrapped by the impermeability of the oilskin, for the remainder of the journey.

The next type of solution to be discussed is the membrane, specifically described in a waterproof and breathable application by Bajaj;13 the technique is most familiarly typified for the general public by Gore-tex products. In these, a thin membrane of microporous material of polytetrafluoroethylene (PTFE) is sand- wiched between two layers of fabric, usually polyester, to reinforce the fragile membrane and prevent it from shredding. The production step involves making PTFE and polyester fabrics, accompanied by all the usual difficulties in polymer manufacture, and in producing an adhesive substance to hold the layers together. The adhesive will impose an environmental cost, as will the subsequent process of applying it by machinery. The approach is not completely satisfactory, as the excellent barrier performance preventing water ingress is not accompanied by a total capability to allow perspiration to escape. In addition, the fabric itself can suffer from delamination, leading to premature rejection. The author has experienced both of these drawbacks, having used such a fabric and redesigned the construction of the sandwich material to minimise the latter problem, in a design for the surgical operating theatre gowns illustrated in Fig. 13.2. As always, prematurely discarding a product is an added load on the ecological equilibrium, so the use of this type of material in water-resistant garments is not to be recommended unreservedly.

A compromise between the techniques of using a microporous membrane and a finish is the adoption of coatings. In these, a microporous material is applied to the external surface of a fabric (usually polyester again) and is adsorbed directly onto the fibres. This method of production still depends on manufacture of the poly- meric materials, but does not involve any separate adhesive, any separate application process or any risk of delamination. It has been shown to be more satisfactory from the ecological perspective. Steps are in progress to bring about further technical improvements to allow it to compete adequately on the basis of performance and financial factors. Kubin14 traces the development of coating technology and provides detailed information on recipes, process operation and properties im- parted for a range of types.

A wide range of other finishes should also be considered. These may be categorised in the areas of treatment designed to modify the nature, appearance or feel of the surface for aesthetic reasons, those designed to lengthen the life of the fabric and those intended to provide enhanced consumer satisfaction. The first type includes softening, stiffening and antistatic finishes, while the second may be exemplified by abrasion resistant or antimicrobial finishes. The third category has become of much greater importance and includes such attributes as a built-in resistance to creasing, flame, oil and stains. It can be deduced that there is likely to be some form of crossover between advantages imparted by the three types.

Softening and antistatic treatments both use the same type of reagents, such as quaternary ammonium compounds, to achieve their effect. These substances are manufactured in a process that has the customary environmental costs of chemical agent production. Application is seldom, if ever, completely perfect and quantities of the reagents are washed (* W-3) into the discard stream from the plant, affecting the local water purity. An anonymous author15 stresses the enormous need for softeners and discusses problems of sewability, yellowing and shearing stability that can arise from softener use.

Stiffeners, such as starch or vinyl compounds, need to be produced, either by extraction from cellulosic plant sources or by a chemical reaction and again are to some degree discarded in the waste stream (* W-3). A related type of finish is that of mercerisation, the process by which cotton is made more lustrous and stronger by short-term immersion in concentrated sodium hydroxide. The alkali is poten- tially an environmentally harmful agent if discarded into water or onto land (* W-3, L-2), so alternatives would be useful. Min and Huang16 provide details of a one-step process that includes desizing, scouring and bleaching as well as mer- cerising, but find that poorer dyeing results are produced by its application. Figure 7.1 shows the graph they derive for their cotton fabrics relating dye concentration (a) to dyeing time (t) on logarithmic axes. The colour level after a given time, but not the slope of the curve, is influenced by temperature, as may be seen in the diagram. Rathi,17 using enzymes, and Ramaswamy et al.,18 with simultaneous bleaching, also provide suggestions for mercerising, but imply no loss of proper- ties as a consequence of the action. Figure 7.2 shows bar charts derived by the latter authors indicating the effects of bleaching and mercerising on dye uptake.

Abrasion resistance is imparted by the application of some form of lubricating agent to the surface of the fabric. The substance chosen may be an oil, wax or a thermoplastic resin, with results and side effects comparable to those mentioned above in connection with these types of finishing agent. In extending fabric life by enhanced biological resistance, some consideration must be given to the hazards likely to be encountered by the fabric in use. There may, for instance, be a risk of insect damage, especially if wool fibres are present. If the fabric is likely to come into contact with the ground, or is to be used in a damp place, then the chances of rotting may be of concern. If it is to suffer long periods of exposure to the elements, especially where bright sunlight is present, then degradation by ultraviolet radiation is a possibility. Finishes have been designed for all of these and are frequently applied in the modern textile industry.

Resistance to biological agents, ranging in size from insects down to the smallest bacteria, can be introduced into textiles in the finishing process. Insect resistance is incorporated into a fabric by germicides (such as metallic salts), resins or organic mercury compounds, with the optimum substance toxic to the specific insect or mildew, and so on, being chosen to minimise damage in comparison with that suffered by an unprotected fabric. The most usual example of a harmful insect is the wool moth, which can degrade large quantities of fabrics by making holes in them. The moth operates by feeding on the disulphide links in the protein of the wool and has traditionally been combated by the use of dieldrin. This substance has been designated as harmful to humans because of its toxic and carcinogenic nature and is now banned in many countries. More recent techniques rely on less effective (in the opinion of many experts) substances, such as fluorides, compounds of antimony or chromium, dyestuffs (mitins or eulans) or formaldehyde to protect the wool.

All of these compounds, from dieldrin to its modern substitutes, constitute a load on the ability of the planet to renew itself in a healthy manner. The chemical agents (especially the more modern ones, which must be used in far higher concentrations than dieldrin) can produce adverse effects in many species and are toxic to humans. Other insects, such as carpet beetles, are dealt with in a similar manner, with comparable results. The protection of textiles against insect damage is not without effect on the world around us, and the extended life of garments made from susceptible fibres (allowing them to be kept for longer periods instead of being thrown away as a load on the environment) should be weighed against the risks of danger or harm to the various affected species of the planet. An exactly similar argument also applies to rotproofing agents, such as metallic salts, condensation resins or cellulose acetate, which function in the same way to prevent damage by microbiological agents, such as moulds or mildew that are present in soil or damp locations. These treatment substances, which operate either by preventing contact between cloth and the harmful agent or by inhibiting microbiological growth, also create hazards to planetary species when they are discarded (* W-3). Efforts are made to minimise the amount of all of these reagents sent to waste, but the best processing conditions, unfortunately, can still bring about appreciable risk of damage from effluent chemicals. These smaller-scale undesirable biological entities have aroused interest because, if they cannot be removed, they can either destroy the fabric or can make it unacceptable, both of which lead to environmental stress as a result of premature discard. In general, the same types of chemical reagent have been used in the past to deal with problems on this scale as have been adopted for controlling larger pests.

Ultraviolet resistance is imparted to fabrics by protecting them with an agent that absorbs radiation in the relevant portion of the electromagnetic spectrum. Instead of attacking the chemical structure of the fibres, the incident radiation uses its energy to bring about an increase in the vibration of specific bonds in the absorbent molecule, thus allowing the fabric to survive unscathed. Once more, these substances (including amines, sulphonated or benzoyl compounds and other complex organic reagents) are unsafe if released into the water system and impose difficulties on ecological protection capabilities.

Flame resistance is a topic that has occupied the attention of textile scientists for several decades. It is an inevitable end result of exposure to an open fire that a material which, like many textiles, contains a large amount of carbon in its molecule, may well burst into flame. If it does, the person wearing the material is likely to suffer burns, while others in the vicinity may be overcome by the fumes emitted or may be trapped in a building because they are unable to see through the smoke evolved. The methods adopted by the industry as far as possible to counteract these risks are, unfortunately, somewhat suspect. The principle involved, as a result of legislation enacted in many countries, is one of preventing ignition or, more often, slowing down the rate of spread of any flame occurring. The first of these approaches, though apparently unimpeachable, is seen to be flawed on practical examination. The finishing agent used, usually a compound of phosphorus, nitrogen and/or a halogen, may (as is normally the case for most finishes of any kind) be removed by extended care procedures, such as washing or dry cleaning. Thus, after a period of use, an article thought to be resistant to ignition can in fact burn and a false sense of security may be engendered in the owner.

Finishes designed to slow down the rate of spread of flame, in the same chemical categories, suffer from the same defect, but are also dangerous from another, more important, perspective. If, say, a cotton fabric ignites, it burns quickly and there is little time for intense heat to be produced in any one location. If it has been treated to slow down the rate of flame spread, the hot flame remains in contact with the

fabric for a longer period of time, so heat buildup can occur in a small area. The resultant damage to an arm covered by the cotton will be more severe and can include third degree, rather than superficial, burns that will leave permanent scars at least and may well damage the arm so badly that a skin graft is necessary. If, alternatively, the flame spread rate reduction is achieved by blending with a (less rapidly consumed) synthetic fibre fabric, this fibre can melt and stick to the skin, causing even greater problems.

Both categories of finish are inherently undesirable in the ecological sense. The reagents themselves are harmful when discharged into the waste water stream (* W-3), and may also cause skin reactions in some people. Disposal of the garments after prolonged use will allow leaching of any residual finish to take place, with further harm resulting once it reaches the underground water table. The end products of the combustion reaction if burning does take place are more dangerous for a treated fabric than for an untreated one, since there is an additional evolution of harmful chemicals such as hydrogen cyanide, halogen compounds or oxides of nitrogen, as well as a higher concentration of carbon monoxide as a result of incomplete combustion induced by the presence of the finish (* A-2). In addition, smoke density increases significantly in the presence of flame-retardant finishes, a factor that not only increases danger from a fire by preventing people from seeing an escape route (* A-3) but also adds to the pollution resulting from the combustion.

Other Finishes
  • Softening and antistatic treatments
  • Stiffeners
  • Microbiological-resistant treatments
  • Ultraviolet resistance
  • Easy-care finishes
  • Flame resistance

 

Shrink-proofing as a mechanical finish uses the overfeed principle, in which damp fabric is pushed onto the pin frame of a tenter then subjected to sideways tensile stress while drying occurs. Energy losses are high, as described later, but the resultant fabric tends to be stronger and is less likely to be discarded. The fabric is also unlikely to be thrown away as waste prematurely, as it would be in the absence of shrink-proofing when a garment made from it might no longer fit after washing.

The use of natural dyes, as opposed to synthetic ones, is often touted as a means of reducing environmental damage. Bhattacharyya and Acharekar, for instance, feel that the dyeing of jute with natural dyes to eco-specifications is now commercially feasible. There are, according to one author, benefits in lowered energy use, water consumption and allergenic effects, accompanied by easier biodegradation, though the problems of availability and colourfastness are noted. More serious concerns are voiced by Achwal, who points out that colour variation in natural dyeing can be so great that redyeing is needed, thus increasing the use of energy and water, with a consequent increase in both financial and ecological cost. Other writers add the observation that the necessary amount of dyes required would denude nature to an unacceptable extent, thus offsetting any possible advantages.

For all these reasons, recent work has tended to seek new means of adopting synthetic dyeing techniques with lower planetary loading, a matter of increasing importance according to one writer, who notes that the initial cost is high enough to discourage many manufacturers. However, the long-term savings in water, dyestuff, energy and waste treatment costs are appreciable. A crucial change in dye chemistry is being sought by several authors, mainly as a result of the harmful effects of certain dyestuffs, while a second approach suggested is the use of plasma treatments (low-temperature electrical gas discharges, such as those that can be achieved with a corona glow) to accelerate dyeing, increase brightness or improve penetration and hence fastness. The former paper, shows the effects of plasma treatment on the dyeing rate (for various natural dyes) associated with the use of oxygen, ammonia and carbon tetrafluoride sources. It can be seen that there is virtually no change between treatments as a result. Similar plasma treatments have been used to increase fibre quality in wool combing (with less waste water), or to modify wool surfaces in other applications, and thus are worth examining as a technique for improving dyeing.

Colouration
  • Dyeing with natural dyes
  • Synthetic dyes
Pollution Aspects
  • Acid and cationic dyes
  • Relative hazards
  • Supercritical dyeing
  • Plasma treatments

 

 

The discharge of pollution from colouration processes occurs in two critical ways. First, when the dye is applied to the fabric (or to some other fibre assembly if dyeing is carried out at an earlier stage of the production), the colouring agent is not all picked up by the fibres. There are inevitably some residual amounts of dyestuff that cannot be adsorbed and, although efforts are currently made to recycle them (as detailed in Chapter 13 and the Appendix), there are large quantities that cannot be reused, either because the particular shade is no longer applicable for the next fabric batch, or because the dilution is too great to make recovery economically viable. It is possible to distinguish to some extent between the different types of dye used, in order to allow some estimate of the relative harmful effects of each one to be made and a comparison of the chemistry of various dye types is of value in this exercise.

The simplest dye types are probably the acid and cationic (or basic) ones. These are applied directly to the fabric and are obtainable in a wide range of colours. However, they tend to have poor fastness, bringing about premature rejection of the dyed product (and hence early pollution) and many of them are carcinogenic or otherwise toxic (* W-3). More recently, substantive direct dyeing has been introduced with the aim of increasing fastness and hence reducing waste, a beneficial step from the ecological as well as financial point of view. Azoic dyes generally need low temperatures (for which energy is expended) and use toxic (* W-3) chemicals for their production. Mordant dyes, which depend on an auxiliary compound to provide fastness to light and washing, suffer from the fact that most mordants are heavy metals (notably chromium) that can bring about serious environmental problems once the excess reagent is discarded. Recognising this drawback, Parton35 suggests that alternative dye types should be sought and recommends reactive dyes with an increased range of colours without the chromium effluent. These combine chemically with the fibre, tending to be exhausted reasonably effectively. Disperse dyes, used in colouration of synthetic fibres, tend not to be as wasteful as are some other types, because the dye is insoluble in water but soluble in the fibres, so is less of a problem to extract once the process is complete. Sulphur dyes, also insoluble in water, can similarly be removed from waste liquors slightly more easily than most other types. Thus, both of these provide a means of reducing pollution. Vat dyes are applied as a colourless precursor and need the presence of oxygen to develop their colour; they may therefore be more difficult to control (since the precise depth of shade cannot be seen until dyeing is complete), with the resulting possibility of increased chances of rejection of the dyed goods. Finally, solution dyeing, in which the colour is developed by solubility of the dyestuff directly inside a synthetic fibre, is possibly even more easily prevented from polluting the water supply.

In all cases it must be remembered that the actual chemicals from which the dyes are made may be harmful in varying amounts, so that the escape of a small quantity of an efficiently applied dye type may be more dangerous than the leakage of a larger quantity of one that cannot be controlled as well. The human factor, too, should not be ignored. If the technologist carrying out the dyeing operation makes a miscalculation or fails to follow instructions properly, even the most efficient dyeing process can lead to disastrous production of large quantities of dangerous waste material. Shukla36 derives a list of the chemicals used in textile auxiliary treatment in 1997, noting that there is a shift towards environmental concerns in the selection of chemical agents used. His list incorporates not only dyeing and printing auxiliaries, but also those used in softening, flame resistance, oil repellency, antifoaming agents and fibre-protective substances of various types. Efforts to reduce the emission of harmful agents are in evidence, as found in material also included in summarised form in Section 5 of the Appendix.

Other approaches are being sought. Lennox-Kerr37 discusses new developments in dyeing with supercritical fluids, especially in attempts to reduce the current high cost that makes the process not economically viable. The theory behind this approach is that, if a substance that is normally a gas at room temperature is subjected to extremely high pressure, it can be liquefied. In this state, if it happens to be a suitable solvent, it can dissolve the chemical in question (a dyestuff in this case) and, when pressure is released, the liquid will evaporate, leaving the dissolved substance behind in the position to which it has been carried (i.e. the interior of a fibre in this example) while in solution. Lennox-Kerr notes that, in place of the most commonly used supercritical fluid, carbon dioxide, others like alkanes, ammonia, carbon monoxide and nitrous oxide, should be or are being tried and gives a summary of the process. Kawahara et al.38 examine the behaviour of a new type of polyester, made by a high-speed spinning technique, during supercritical dyeing with carbon dioxide. In comparison with conventionally produced fibres, the new polyester (which has comparatively large crystallites and low birefringence) is superior to the conventional one in dye uptake at low temperatures, but not very different at higher ones. The reason deduced for this behaviour is that fibre swelling in the supercritical fluid needs to reach a certain level, after which the dye diffusion is promoted and the larger crystallites mean that the new fibre reaches that level at a lower temperature.

Özdogan use plasma polymerisation to increase the dyeability of cotton in low temperature media. The treatment introduces to the anionic surface a cationic phase, and the resulting enhanced dyeability reduces water consumption, pollution and amount of dye needed. The authors suggest that there may be a benefit from developing modified dyestuffs to take advantage of the new technique when commercial applications are in progress.

In turning to printing, we should note first that virtually all printing processes use the same reagents as do dyeing treatments. Thus, the identical potential for harm exists in printing and the same relative risks for each type of dye used are also present. There are, though, added problems involved in printing and, in partial compensation, some minor benefits too.

In turning to printing, we should note first that virtually all printing processes use the same reagents as do dyeing treatments. Thus, the identical potential for harm exists in printing and the same relative risks for each type of dye used are also present. There are, though, added problems involved in printing and, in partial compensation, some minor benefits too.

In resist printing, a protective coating is first applied to the surface to prevent contact or attachment between the dye and the fabric in that region. The resist paste is applied in exactly the same manner as a printing paste, using chemical agents that block either the physical access of print paste to the fabric or the ability to form a chemical bond between fabric and colouring agent. Substances used (in addition to thickeners, which are needed to restrict movement away from the area that is to be prevented from becoming coloured, in the same way as direct methods) include paraffin and various resins. Each of these, but especially the latter, can be responsible for environmental risks after the excess is discarded. Once the resist paste is in place, the fabric is piece-dyed. The problems involved in the step exactly match those used in piece-dyeing itself.

In discharge printing, the order of operation is essentially reversed. The fabric is piece-dyed initially, then a discharge agent (one that destroys the colour of the dyestuff) is applied to selected areas to create a pattern of a white zone on a coloured one. The latter two methods are both used as a means of obtaining a richer colour in the dyed areas, since piece-dyeing gives a much greater intensity of shade than does printing. From the environmental perspective, the processes combine the worst aspects of printing and dyeing, because the disadvantages of using paste are supplemented by those of piece-dyeing, and the need to add extra reagents in the form of the resist or discharge agents compounds the problem still further.

Flock printing consists of the application of short dyed fibres to the surface of a fabric, either over the entire surface or in specific areas, with permanent attachment to the fabric being achieved by the use of a resin or other type of glue. Again, the ecological aspects of dyeing (of the fibres) have to be considered, in addition to those of the fixing agent when excess amounts are discarded to the environment.

Printing
  • Principles
  • Direct methods
  • Resist printing
  • Discharge printing
  • Flock printing
  • Heat-transfer printing

 

 

Drying and shipping

One further process needs to be considered, fabric drying. Again, it is not strictly a finishing treatment, but virtually all of the fabrics undergoing a finishing stage. need to be dried at least once, and often more times, at some point in manufacture. The process is considered in Chapter 11, but is mentioned here because it is so important in finishing.

The fabric has to be packed for shipment. This step, which is essential for protection from the elements, needs some form of outer coating, such as kraft paper or plastic, that has to be manufactured, with the usual environmental cost. In modern factories, it also involves the use of machinery, incorporating its costs. Finally, the matter of transportation should be considered. As before, this may be necessary during all parts of the production train, but the shipping of finished cloth is probably the largest single use of the operation.

These then, are the harmful effects on the planet associated with the manufacture of textile fabrics. Unfortunately, the problem does not end here. After the finished articles are passed on to the consumer, there are still more costs incurred as a consequence of their use. These will be the subject of the next chapter.

Solutions
  • Fibre and yarn: choosing Certifications and guidelines,
    source GOTS- and BCI-certified cotton, hemp, linen, nettle, FSC-certified lyocell and bio-based biodegradable synthetics. Taipei supplier Ocean Plastics developed a blend of cotton, pineapple fibre and biodegradable polyester, while Hemetex (HK) uses a thermo-regulating coconut blend base. The Toxic Substances Control Act regulates new and existing chemicals and their risks, finding ways to prevent or reduce pollution before it enters the environment.
  • Construction and finish: use compact drills, herringbones, twills and canvas weights for bottoms, chambrays and poplins for tops and ensure functionality and durability. Tie-dyes, painterly warps and discharge methods allow for colour variation. Take Eco-Accountability by incorporating natural dyeing methods.
  • Zero Discharge of Hazardous Chemicals (ZDHC) Certification: uses 100% regenerative cotton, with the dyeing process meeting ZDHC certification for a low-impact finishing option. UL Solutions partners with ADEC Innovations, the technology provider behind the supply chain software as a service (SaaS) platform CleanChain, to enhance chemical management across global supply chains in alignment with the Zero Discharge of Hazardous Chemicals (ZDHC) initiative for the apparel, footwear and accessories industry. With this partnership, CleanChain platform seamlessly integrates into UL Solutions services, offering a cohesive and data-driven solution for chemical management across the entire supply chain providing greater visibility into chemical inventories, managing chemicals hazardous to human health and the environment, and driving continuous improvement in sustainability performance. The bundled solution includes official ZDHC trainings for the value chain, wastewater testing and reporting, MRSL certification and monthly ZDHC Performance InCheck reports generation.
  • Commit to non-fluorinated chemicals: plan to swap out PFAS/PFCs completely in the long term. Start by transitioning into safer alternatives that meet criteria for a ‘polymer of low concern’
  • Use viable, earth-friendly biotech solutions: the consumer’s first concern will be health and wellbeing, but seize the opportunity to sell the sustainable innovation as an additional value add. Use viable, earth-friendly biotech solutions to reduce reliance on fossil fuels and look for low-carbon, recyclable and safely degradable alternatives
  • Bio-chemical assisted eco-friendly processing of wool: Wool Processing with biochemical is expected to change the concept of wool processing from high energy consuming and pollution oriented one to a bio-chemical process with advantages such as reduction in temperature, energy, water and reduction in effluent load etc.