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Desizing is a textile process that is used as a pre-treatment in the manufacture of woven fabrics. Desizing involves removal of the warp glue (size) that has to be impregnated on the warp threads in order to protect them from mechanical abrasion during the weaving process. The adhesives currently used are starch products such as polyvinyl alcohol (PVA), polyacrylic acid (PAC), carboxymethylcellulose (CMC). Furthermore galaktomannan and polyester are used. Adhesive agents must be removed before dyeing and processing. The requirements are therefore that they should be:
- Easy to remove.
- Resistant to alkali.
- Easy to demonstrate in order to be able to control that the glue has been removed.
Starch adhesive are usually removed by adding enzymes that simply breaks down starch adhesives and make them water soluble. PVA, PAC and CMC are water soluble. PVA is somewhat sensitive to alkali and peroxide; these substances can change them and make them difficult to wash out. Certain adhesive PACs are thermally unstable and can become insoluble if heated. Imported raw fabrics already contain warp glue (size), while in Sweden you can make the decision yourself. This normally means that the choice of adhesive is not controlled from within Sweden. PVA and PAC-sensitive adhesive is often used in the synthetic material while the starch adhesive is mostly used on cellulosic fibres. In general there are often required higher amounts of starch and cellulose derivatives other than the synthetic glue (size) calculated as weight per cent of fibre materials.
Environmental Facts - desizing
Starch products are easily biodegradable. CMC, PVA, and PAC are partially biodegradable. Some observations suggest that some modified starch adhesives are persistent. Adhesive agents and their enzymatically degraded variants show no fish toxicity. The persistent adhesives end up in sewage treatment plants with other sewage sludge. In processing woven fabrics more than 50% of the sewers organics consists of adhesive agents. Most of the adhesive quantities are usually composed of starch adhesives that are easily biodegradable. In addition, it may also be degraded by desizing. Other solutions data has been found in the Tox Info Manual and also data from the adhesive manufacturers . Examples of adhesive that are commonly used are shown in the following points:
- Polyvinyl alcohol (PVA) is prepared from polyvinyl acetate to form acetic acid, which is easily biodegraded. According to earlier data, PVA is persistent, but more recent data from the manufacturers indicates that the substance is biodegradable. Various molecular weights may be the cause of these conflicting data and the adaptation of sludge organisms.
- Polyacrylic acid (PAC) is easily degradable in the aquatic environment but toxic to algae. Acrylic polymer is partially persistence, probably because of the degree of polymerization (molecular size) and the adaptation of sludge organisms.
- Carboxymethyl cellulose (CMC) is probably somewhat more difficult to degrade than cellulose, which is due to its degree of carboxylation.
- Polyester (PET) can be hydrolysed enzymatically. Both terephthalic acid and ethylene glycol is easily biodegradable in an aquatic environment.