Enzymes, such as cellulases, catalase, and laccase, are commonly used in the textile industry. These enzymes remove the starch, degrade excess hydrogen peroxide, bleach textiles, and degrade lignin. Because of the highly specific, efficient, non-toxic, and eco-friendly characteristics, the use of enzymes in the textile industry is rapidly growing. The most recent commercial advance is the application of cellulases for denim finishing and lactases for the decolorization of textile effluents and textile bleaching. Furthermore, using enzymes reduces process times, energy and water savings, improves product quality, and potential process integration.
Properties of enzymes used in textiles
Firstly, the enzyme accelerates the reaction by lowering the activation energy and remains intact at the end by acting as a catalyst. Secondly, enzymes operate under milder conditions. Enzymes can be used in catalytic concentrations at low temperatures and at pH values near neutral. Thirdly, enzymes are the best alternative to toxic, hazardous, and polluting chemicals. Fourthly, enzymes act only on specific substrates; for example, enzymes used in desizing do not affect cellulose; hence there is no loss of strength of cotton. Fifthly, enzymes are easy to control because their activity depends upon optimum conditions. Sixthly, enzymes are biodegradable. At the end of the reaction in which enzymes are used, we can drain the remaining solution because enzymes are biodegradable and do not produce toxic waste on degradation; hence there is no pollution.
Enzymes used in textile processing
1）Enzymatic desizing
Amylases remove starch-based sizes for improved and uniform wet processing in the textile industry. An amylase enzyme can be used for desizing processes at low-temperature (30-60ºC), and the optimum pH is 5.5-6.5. The advantage of these enzymes is that they are specific for starch, removing it without damaging the support fabric.
2）Enzymatic Scouring
Scouring is the removal of non-cellulosic material present on the surface of the cotton. In general, cellulase and pectinase are combined and used for Bioscouring. In this, pectinase destroys the cotton cuticle structure by digesting the pectin and removing the connection between the cuticle and the body of cotton fiber. In contrast, cellulase can destroy cuticle structure by digesting the primary wall cellulose immediately under the cuticle of cotton.
3）Enzymatic Bleaching
The purpose of cotton bleaching is to decolorize natural pigments and to confer a pure white appearance to the fibers. Mainly flavonoids are responsible for the color of cotton. The most common industrial bleaching agent is hydrogen peroxide. Conventional preparation of cotton requires high amounts of alkaline chemicals; consequently, vast quantities of rinse water are generated. However, radical reactions of bleaching agents with the fiber can decrease the degree of polymerization and, thus, to severe damage. Therefore, the replacement of hydrogen peroxide by an enzymatic bleaching system would lead to better product quality due to less fiber damage and substantial savings on washing water needed for the removal of hydrogen peroxide. An alternative to this process is to use a combination of suitable enzyme systems. Amyloglucosidases, pectinases, and glucose oxidases are selected that are compatible concerning their active pH and temperature range.
4）Biopolishing
Biopolishing is a finishing process that improves fabric quality by mainly reducing cellulosic fiber’s fuzziness and pilling properties. The process’s objective is to eliminate the microfibrils of cotton through the action of the cellulase enzyme. The biopolishing treatment brings the fabric a cleaner surface, a cooler feel, luster, and a softer feel.