After Treatments

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After/post treatments are done to give fabric its final characteristics of appearance, function and tactile (touch). Another word for finishing is "appretur". An after-treatment may be a combination of mechanical, thermal and chemical treatments done to the fabric. For example: cutting of the loops, roughening to obtain a hairy surface, calendaring, embossing, these are often combined with chemicals to gain a permanent surface structure. The fabric may also be chemically treated to provide various protection functions.
Illustration: After/post Treatment

Examples of post-treatments

Mechanical processing Mechanical processing involves various kinds of pressures to mechanically alter the fabric used to gain changes in appearance or to reduce shrinkage when washed. Often the finishing of the fabric means that it is pushed together mechanically. Along with the addition of moisture and chemicals, and subsequent heat treatment, it means that shrinking during wash becomes significant. A purely mechanical action has virtually no environmental impact other than in respect of any noise and fiber dust when cutting and buffing. The effect of chemical additives are discussed under Chemical preparation.

Thermal processing including drying

The drying and curing of different finishes the chemicals are volatile and / or water distillable may evaporate into the air. Heat treatment is almost always used in the form of drying after one or more wet treatments. Moreover, the heat treatment is most commonly a way to fix the synthetic products to achieve dimensional stability (thermal fixation). Thermal fixing may result in volatile components such as spinning oils that may go with the drying air. Above all, the environmental disturbances occur in fixation of unwashed textiles (spinning lubricants depart when the air instead of ending up in the wash water).

Chemical preparation

The most common method for finishing is impregnated with various chemicals in aqueous solutions with subsequent dewatering and drying. The most important measure for energy-efficient processes is to ensure that the chemicals reach the fiber surface and get them to build up. In all wet impregnation there is a "pore volume or internal bath" of impregnating liquid that fills the capillaries in the fabric and contains a substance that will not stick to the fabric. To reduce this internal bath there is a range of methods for impregnation that has been invented. These methods are sometimes called "Minimum application" or abbreviated as MA. Surplus chemicals not only mean a higher consumption of chemicals, that also ends up in the drain, but they can also sometimes bring a deterioration of product properties. ICC (International Institute for Cotton) has in many studies shown that excess chemicals from the resin treatment of the inner bath resulted in harts-deposits in the fabric, thereby weakening the strength. By decreasing the internal bath with so-called MA technology one can (see below) obtain better strength for the garment while maintaining wrinkle treatment.


Minimum Application, MA

There are basically two ways to reduce the inner bath in impregnation, either by adding a limited time for bathing to the fabric, or by impregnating the fabric and then removing the inner bath by high dewatering. A so-called "Minimum Applications", MA, can be accomplished by using a so-called "Licker Roll", ie. a roller, which is partially dipped in the impregnation bath and transferring a predetermined amount to the fabric. In this way one can predict the bath amount on cotton to up to 40% calculated on the weight of the fabric. This is not possible to achieve in conventional impregnation if the product is to be impregnated. Different MA-technicians with textured rollers and various constructions for bath transfers are used especially in the post-treatments. In order for these techniques to be applied smoothly the treatment should not be uneven, it requires that the fabric suction is almost perfect.

A recent MA technology used to some extent is the spray technique. It means that a given amount of bath is to be sprayed onto the fabric with the help of ingenious centrifugal spinners. The usual technique: first dip the fabric in the impregnating bath, then drain, has improved recently. The decompressing rolls has changed so that pressing has become smoother (S-roll from Küster) and the roll surface has changed to improve dewatering.

Vacuum suction

Another technique that has been tested is vacuum suction. The excess liquid is sucked through a column from the fabric after dipping. Uneven woven edges can cause problems and with the edge not properly sealed the vacuum varied and dewatering was uneven. Increasing in usage of the technique has been substantial since the problems with edge seal has been solved by using a flexible tube. The equipment works best on normal fabrics that are not too sparse and that can improve dewatering significantly.

There are three main uses for vacuum suction:

  • At pre-treatments: The equipment delivers an effective output of the various washing and rinsing liquids including an efficient dewatering.
  • In continuous dyeing and finishing: Surplus chemicals in the inner bath can be reduced and returned to the impregnation bath. In addition, the penetration is better.
  • The wet-on-wet impregnation (successive impregnations without drying). This way requires as efficient dewatering as possible before moving on to the next treatment.

Today, vacuuming is used in all these areas, except for dying. Several trials are in effect that show interesting results, especially when it comes to getting an effective dye penetration compared to today's foulard-dyes. When vacuuming excess liquid is returned to the impregnating bath, as well as the foulard-dying. In addition, fiber debris and other contaminants, which sometimes cause problems with normal foulard-dying, are filtered out. When returning excess fluid to the impregnating bath, the concentration in the recirculating bath are controlled. Firstly, the impregnated chemical may have been adsorbed, secondly, the vacuum stage may create some dehydration. Most treatment chemicals have low selectivity and the risk is small that the bath composition is changed but the dying has both selective absorption and some filtering effects of dissolved substances that may change the color-bath. Also, foulard-dying presses dye-solution to the impregnation box. Here, it is known that selective absorption change concentrations, but the reversal is evenly distributed over the entire fabric and a "steady state" is achieved relatively quickly.

All continuous dyeing and finishing processes require dewatering and these processes are effective in reducing the excess chemicals. Furthermore, it is important that if it is possible to run several treatments in the same bath. This is to avoid unnecessary washing and drying and to automate the processes as far as possible in order to optimize. Today, however, these efforts are being replaced by more, shorter, production runs.

Finishing in discontinuous processes are generally more costly than continuous processes. The main reason is the high bath ratios and little opportunity for dewatering between the processes. The most common discontinuous apparatuses, jet, beam, X-roll, and Jigger “kuff”-devices, normally has no dewatering possibilities. The fabric must instead be removed from the apparatus and centrifuged, which is tedious and time consuming. It is common that after treatment it is made in the same apparatus. In some cases it can be done in the same bath, such as with color fixation and anti-static treatment.

Protective and functional treatments

In order to produce fabrics with various protection functions they can be based either on a fiber material that haves particular characteristics already during manufacture or it can subsequently provide the material properties through preparation. The latter method is most common.

Fire and flame

The use of flame treatment is regulated by the provisions of building codes or other provisions for fire safety, such as for clothes for work where they can be exposed to fire and heat. Even for upholstery and curtains there is a need to provide flame treatment. In principle, all fibers of organic origin can be ignited at high temperatures, but the most important is to prevent local fires from spreading. Frequently used textile fibers, such as cotton, can have fire retardant properties by various treatments. The most common way to provide fire protection on standard textile fibers is by impregnation with chemicals which contain nitrogen and phosphorus or a combination of halogenated hydrocarbons and antimony. Phosphorus-nitrogen compounds can be wash-resistant to cellulose fibers and is also available in flame-washable polyester fibers. Halogenated hydrocarbons and antimony usually provides poor wash ability and are therefore used mainly in materials that are not going to be washed. Another relatively frequent treatment for fire protection of wool fiber and its protein is to use salts from metals such as titanium and zirconium. There are also synthetic high temperature fibers to choose as an alternative to chemical treatment.
Some flame retardants release hydrogen cyanide when set afire and can be deadlier than carbon monoxide.1 Flame retardant chemicals can be toxic, and some are suspected carcinogens.2 In the European Union the use of certain flame retardants are banned or restricted.3

Innovation opportunities

• Investigate non-toxic flame retardant applications.
• Investigate the use of halogen-free flame retardants, such as from InnoSense LLC: www.innosense.us.
• Investigate using polyester as an alternative to textiles with a flame retardant coating. Polyester is inherently flame retardant.

Water, oil and stain repellency

A fabric can be made water and oil repellent by a polymer coat put on the fabric. This makes the fabric completely sealed which can cause comfort problems since the body's evaporation and perspiration cannot be vented. The fibrous material can also be made water and oil repellent by the fiber surfaces that have low surface energy that is not wetted by water or oil. Since ancient times, there have been treatments with waxes, metal soaps and paraffin. These treatments will repel water, but they have not been able to resist oils. Silicone can provide water repellency and in some cases oil repellency. The treatments with waxes, paraffin, metal soaps and silicones had limited wash-resistant functions. Fluorocarbons are becoming increasingly common in use to provide water, oil and stain repellency, fluorocarbons have good wash fastness if you follow the special washing instructions.

Water repellents

DWR (durable water repellent) is a coating added to fabrics at the factory. Durable water repellents (DWRs) are applied to garments and products to allow for breathability and water repellency. Common factory-applied treatments are fluorochemicals. Certain DWRs are known to have persistent, bioaccumulative and toxicological effects on the environment. The durable water repellent coatings used in the fashion and textile industry are currently not bio-based or biodegradable. Water repellent coatings also inhibit recyclability.

Innovation opportunities

• Investigate non-fluorochemical coatings, such as silicones, polyurethane (PU) and waxes. Although these coatings are recyclable on their own, they inhibit recyclability when applied to a dissimilar base layer. These coatings have the potential for recyclability if applied to a similar base layer.4
• Work with manufacturers to create bio-based or biodegradable water repellent finishes.
• Investigate recyclable waterproofing agents. Sympatex is made of completely safe polyether/ester, a combination of polyester and polyether molecules that is reportedly recyclable if applied to a similar base layer (i.e. polyester). Sympatex contains zero fluorochemicals.5
• Investigate durable water repellents from alternative, renewable non-toxic resources, such as castor oil.

Stain repellents

Stain repellent finishes are used to provide stain, soil and grease release and repellency to fabrics. Fluorochemicals are the most employed repellents used for textiles. The largest concern for chemicals used for soil and stain repellent finishes is perfluorooctanoic acid (PFOA), which is used in the manufacture of stain repellent finishes for textiles. PFOA is also produced indirectly through the gradual breakdown of fluorochemicals.6 PFOA is very persistent in the environment and has been found at very low levels both in the environment and in the blood of the general U.S. population.7 Recycling of textiles with stain repellent finishes is also very difficult. Flurochemicals are currently being phased out by major industrial users.8

Innovation opportunities

• Investigate short chain fluorocarbons that do not degrade into PFOA.
• Investigate stain resistant finishes that do not involve the use of PFOA, such as finishes from DuPont.

Antimicrobials

Antimicrobials are used in application such as socks, shoes and activewear to prevent odour caused by the breakdown of sweat. The use of organotins is often employed for antimicrobials on textiles. The organotins compound tributyltin (TBT) persists in the environment and builds up in the body. TBT is listed as a “priority hazardous substance” under European Union regulations and requires measures to be taken to eliminate its use.9 Organotins are highly toxic to aquatic species, are persistent, moderately bioaccumulative. A recent report conducted by Greenpeace revealed organotins detected in several activewear products.9

Innovation opportunities

• Investigate non-toxic biodegradable alternatives to organotins.
• UV curing of chitosan as an antimicrobial finishing for textiles is a still in development, and could provide a bio-derived, non-toxic, biodegradable alternative to organotins.10
• Experiment with natural fibres that intrinsically repel odours, such as wool.

Antistatic Treatment

Synthetic and blended fabrics are antistatic treated to reduce the problem of static charge in the manufacturing and use. Usually added substances are quaternary ammonium or acid amides and ethoxylates which increase the conductivity of the fiber surfaces. The treatment is done either by its own final impregnation or in addition to the normal end of the treatment. Wash resistance of antistatic treated products varies.

Mold protection

Need for mold protection is greatest on natural fibers since they are easier to be attacked by mildew and rot than synthetic fibers. It is not allowed to perform mold protection on textile products in Sweden. Even though, goods with this type of impregnation still reaches the country through imports.

Environmental Facts - protective treatment agent

Of the chemicals used in flame retardant treatment there has recently been paid special attention to brominated biphenyls and biphenyl. It is found that they accumulate in aquatic organisms. These flame retardants have been removed in manufacturing in Sweden. Although the brominated compound hexabromcyclododekan (HBCD) have been shown to be stored in the environment. It has been found in fish from Viskan (river in southwest Sweden) (study by the Environmental Protection Agency 1995/96). For this reason the Swedish textile industry sharply reduced emissions of this substance. Conclusions indicate that the substance can be classed as bio accumulative and very toxic to aquatic organisms. Also the use of other halogenated flame retardants have been severely restricted and the same applies to retardant fibers. These are produced by copolymerization between vinyl chloride (mod acrylic). Chlorinated paraffin are toxic to aquatic organisms and bio accumulating. Chlorinated paraffin with a high degree of chlorination is also persistent, i.e. Non-degradable. Antimony compounds are hazardous and can be contaminated with lead and arsenic. Phosphates (Propane and Pyrovatex) are not toxic but are persistent and can be potentially bio accumulative. In addition, they can cause malfunctions if they are placed in water-cleaning and treatment plants. Melamine, used in conjunction with the phosphates to achieve wash-resistant flame retardants, has low acute toxicity to aquatic organisms and low biodegradability.

Flame treatment is the treatment which requires the most weight added in order to function. It is not uncommon to add 20-30% based on fabric weight to ensure that the flame treatment meets the requirements. There are today many attempts to minimize the chemicals. When performing water and oil repellent treatments environmental risks may arise from emulsifiers and preservatives in wax emulsions and heavy metals in the metal soaps. Straight-chain paraffin is persistent. Silicones are persistent and bio accumulative. There are few environmental data for silicones and perfluorinated polymeric compounds (fluorocarbons). It is likely that it is persistent. Compared with other water and oil repellent treatments, the amount that must to be used in the perfluorinated polymers is rather small, typically, the amount of fluoropolymers is substantially less than 1% by the dry weight of the fabric.

In textile industry treatment the fluorine polymers are bound reactively to the fibers, and since no after wash is done, the emissions are rather small if the residual baths are utilized. Antistatic agents based on quaternary ammonium compounds have bacteriostatic action and are broken down, even though it proceeds slowly. These compounds are adsorbed strongly to sewerage sludge, which reduces their environmental hazard. In the newer plasticizers, such as fatty acid amides and aminoetoxylates, no environmental data was found. Probably they increases the nitrogen content of wastewater. The use of rot treatment is banned in Sweden because of its environmental properties. Abroad, however, these substances are still used. Textile products treated with rot treatments are still sold in Sweden, which means that the Swedish textile industry have a competitive disadvantage for certain product groups where rot treatments are required.

Treatment for the appearance and feel

In order to maintain the appearance (smoothness) and the dimensions of the textile material which swells in water, ie. mainly cellulose fibers, they are treated with reactive chemicals. These treatments are sometimes called resin treatments as polymeric resin is formed during the treatment. The primary purpose of the treatment is to create cross-links in the fibrous material to prevent wrinkling and contraction, as well as render the protective treatment (flame-resistant finish and water and oil repellency treatment) wash-resistant. A disadvantage of these treatments is that while they fix the shape and dimension of the fabric also makes the fabric rigid. This has a negative effect on the touch and tears and the durability. To counteract this stiffening the processing recipes often contain plasticizers. Plasticizers are also used on goods that are not resin-treated and then have the task of changing the grip and feel of the fabric. These treatments are not wash-resistant unless used in conjunction with the reactive resins or if they themselves are reactive.

Another important issue is the appearance of purity - especially on white fabrics where every little smudge is visible and remaining traces of dirt are visible even after washing. To make the fabric resistant to dirt, the same type of treatment is used as for water and oil-repellent treatment. These treatments means that dirt often get stuck in the form of aqueous or oily film on the fibers and cannot wet the fibers so it will instead “purl off”. This is where the expression stain repellent has its origin. There are also treatments that will facilitate the cleaning of laundry. This makes the fiber materials more easily can release dirt. Treatment is done with substances that make the fiber surfaces hydrophilic and easier to wet (soil loosening). Examples of such substances are carboxymethylcellulose (CMC), polyacrylic acid or ethoxylates.

Environmental Facts - treatment for appearance and feel

For wrinkle and dimensional stability treatments todays mostly used ones are cyclic urea without or with formaldehyde. Recently, the content of free formaldehyde is reduced by the health and allergy reasons. There is ideas of formaldehyde-free and formaldehyde poor substances. Although melamine formaldehyde compounds are used for these treatments (see Environmental facts protection treatments). The urea’s and melamine’s acute toxicity to aquatic organisms are strongly dependent on the amount of free formaldehyde and glyoxal (cyclic urea). Both aldehydes are readily biodegradable. No information was found regarding the degradability of partially reacted urea and melamine. In the case when softener is used it is often the same, describing the anti-static agent under the heading Environmental Facts - protective treatment agent ,page 46. For soil-repellent treatment agent refers to substances for water and oil repellency, since they are similar. Regarding soil release treatments they are essentially hydrophilic and readily soluble in water. Polyacrylic acid with a low degree of polymerization is easily degradable in aquatic environments, while CMC and ethoxylates are said to be more persistent. Allergic rash of textiles due to formaldehyde was for about 25 years ago are quite common but are now very uncommon.

Sources

Textile Environmental Handbook

  1. https://www.environmentalhealthnews.org/ehs/news/2012/burning-irony
  2. https://www.eis.uva.es/~macromol/curso07-08/ignifugos/Giulanca%20C.%20tesoro.pdf
  3. https://www.efsa.europa.eu/en/topics/topic/bfr.htm
  4. https://www.dowcorning.com/content/discover/discoverchem/how-si-degrades.aspx
  5. https://www.sympatex.com/en/membrane/224/ecology
  6. https://www.sciencedaily.com/releases/2005/09/050920002527.htm
  7. https://www.epa.gov/oppt/pfoa/pubs/faq.html#concerns
  8. https://www2.dupont.com/PFOA2/en_US/QandA/index.html
  9. https://www.greenpeace.org/eastasia/publications/reports/toxics/2014/little-story-monsters-closet/
  10. https://www.ncbi.nlm.nih.gov/pubmed/22905533
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