Application of Enzyme in Textile Wet Processing/Dyeing Industry

Enzyme is a living organism. In previous article, we have discussed about enzymes in details. Now we will explain uses of enzyme in textile wet processing. Humankind has used enzymes for thousands of years to carry out important chemical reactions for making products such as cheese, beer, and wine. Bread and yogurt also owe their flavor and texture to a range of enzyme producing organisms that were domesticated many years ago.

Uses of enzyme in wet processing
With the increasingly important requirement for textile manufacturers to reduce pollution in textile production, the use of enzymes in the chemical processing of fibers and textiles is rapidly gaining wider recognition because of their non-toxic and eco-friendly characteristics. They can be safely used in a wide selection of textile processes such as de-sizing, scouring, bleaching, dyeing and finishing, where the alternatives are very harsh chemicals whose disposal into the environment causes many problems.

Textile processing with enzymes aims to provide the textile technologist with an understanding of enzymes and their use with textile materials and in process engineering. It covers all the relevant aspects of textile processing with enzymes, from the chemical constitution and properties of textile materials as potential substrates for enzymes, to the processing of these materials; from basic biochemistry and enzymology to the industrial application of these biocatalysts.

Uses of Enzyme:
In different process of textile wet processing enzyme are widely used, the important sectors are highlighted below:

1. Desizing
2. Scouring
3. Bleaching
4. Garment Washing
5. Dyeing
6. Finishing

Desizing: Previously, in order to remove the size, textiles were treated with acid, alkali or oxidising agents, or soaked in water for several days so that naturally occurring microorganisms could break down the starch. However, both of these methods were difficult to control and sometimes damaged or discoloured the material. But by using enzymes, which are specific for starch, the size can be removed without damaging the fibers.

It represented great progress, therefore, when crude enzyme extracts in the form of malt extract, or later, in the form of pancreas extract, were first used to carry out desizing. Bacterial amylase derived from Bacillus subtilis was used for desizing as early as 1917. Amylase is a hydrolytic enzyme which catalyses the breakdown of dietary starch to short chain sugars, dextrose and maltose.

Scouring: Scouring (the process of removing natural waxes, pectins, fats and other impurities from the surface of fibers), which gives a fabric a high and even wet ability so that it can be bleached and dyed successfully. Today, highly alkaline chemicals (such as caustic soda) are used for scouring. These chemicals not only remove the non-cellulosic impurities from the cotton, but also attack the cellulose leading to heavy strength loss and weight loss in the fabric. Furthermore, using these hazardous chemicals result in high COD (chemical oxygen demand) and BOD (biological oxygen demand) in the waste water. Recently a new enzymatic scouring process known as ‘Bio-Scouring’ is being used in textile wet-processing with which all non-cellulosic components from native cotton are completely or partially removed. After this Bio-Scouring process, the cotton has an intact cellulose structure, with lower weight loss and strength loss. The fabric gives better wetting and penetration properties, making the subsequent bleach process easy and giving much better dye uptake.

Bleaching: When bleaching cotton, a lot of chemicals, energy and water are part of the process. The company Huntsman has developed a wetter/stabilizer that maximizes the wetting and detergency of the bleaching process and a one-bath caustic neutralizer and peroxide remover in order to shorten the bleaching cycle, reduce energy and water required and deliver more consistent bleaching results. They have developed surfactants that are environmentally friendly (in that they do not contain Alkylphenol ethoxylates), and the system is both Oeko-Tex and GOTS approved. After fabric or yarn bleaching, residues of hydrogen peroxide are left in the bath, and need to be completely removed prior to the dyeingprocess, using a step called bleach cleanup. The traditional method is to neutralize the bleach with a reducing agent, but the dose has to be controlled precisely. Incomplete peroxide removal results in poor dyeing with distinct change of color shade and intensity, as well as patchy, inconsistent dye distribution. Enzymes used for bleach clean-up ensure that residual hydrogen peroxide from the bleaching process is removed efficiently – a small dose of catalase breaks hydrogen peroxide into water and oxygen. This results in cleaner waste water and reduced water consumption.

Garment Washing: Enzymes have been used increasingly in the textile washing industry since the late 1980s. Many of the enzymes developed in the last 20 years are able to replace chemicals used by mills. Different types of washing such as enzyme wash, stone enzyme wash etc enzyme are used largely. The first major breakthrough was when enzymes were introduced for stone washing jeans in 1987 – because more than one billion pairs of denim jeans require some sort of pre-wash treatment every year. Within a few years, the majority of denim finishing laundries had switched from pumice stones to enzymes.

Dyeing: Today, enzymes are used to treat and modify fibers, particularly during textile processing and in caring for textiles afterwards. They are used to enhance the preparation of cotton for weaving, reduce impurities, minimize “pulls” in fabric, or as pre-treatment before dying to reduce rinsing time and improve color quality.

Finishing: Uses of enzyme in finishing section are classified in

a. Bio-finishing
b. Denim finishing

a. Bio-finishing: Biofinishing or biopolishing (removing fiber fuzz and pills from fabric surface) – enzymatic biofinishing yields a cleaner surface, softer handfeel, reduces pilling and increases luster;

b. Denim finishing: In the traditional stonewashing process, the blue denim was faded by the abrasive action of pumice stones on the garment surface. Nowadays, denim finishers are using a special cellulase. Cellulase works by loosening the indigo dye on the denim in a process known as ‘Bio-Stonewashing’. A small dose of enzyme can replace several kilograms of pumice stones. The use of less pumice stones results in less damage to garment, machine and less pumice dust in the laundry environment; in addition, it’s possible to fade denim without risk of damaging the garment.

About the Editor-in-Chief:

Mazharul Islam Kiron is a textile consultant and researcher on online business promotion. He is working with one European textile machinery company as a country agent. He is also a contributor of Wikipedia.

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