Textile Enzymes

The textile industry has been quick to adopt new textile enzymes. Enzymes for textile applications was first developed for stonewashing jeans in 1987, it was only a matter of a few years before almost everybody in the denim finishing industry had heard of them, tried them and started to use them. AETL was quick to introduce the same way back in 1991. We begin this section by covering this industry.

Before cotton yarn or fabric can be dyed, it goes through a number of processes in a textile mill. One important step is scouring - the complete or partial removal of the non-cellulosic components of native cotton such as waxes, pectins, hemicelluloses and mineral salts as well as impurities such as machinery and size lubricants. Scouring gives a fabric with a high and even wettability that can be bleached and dyed successfully. Today, highly alkaline chemicals such as sodium hydroxide are used for scouring. These chemicals not only remove the impurities but also attack the cellulose, leading to a reduction in strength and loss of weight of the fabric. Furthermore, the resulting wastewater has a high COD (chemical oxygen demand), BOD (biological oxygen demand) and salt content.

In 2004, AETL introduced Addscour that reduces environmental impact and, in most cases, works out more economical to use. Unlike other commercial bioscouring enzymes available based on alkaline pectinase, Addscour is effective for batch and continous process and can be used for scouring of knit and woven fabrics and garments. The effectivity comes because of right enzymes blended in Addscour over years of research. The new process is called Bio-Preparation. It has been welcomed because rinsing water can be reduced by more than half compared with traditional processes. This is especially advantageous since hot rinsing water is used, meaning that considerable amounts of energy can be saved. Quality improves too. The enzymatic treatment leaves the cellulose structure almost intact, so it reduces weight loss and strength loss. Bio-Scouring has a number of potential advantages over traditionally prepared textiles. It reduces total water consumption by around 25%, the treated yarn/fabrics retain their strength properties, and the weight loss is much less than for processing in traditional ways. Bio-Scouring also gives softer cotton textiles.

Enzymes like heat stable amylase, fungal amylase are used for desizing woven fabrics because of their highly efficient and specific way of desizing without harming the yarn. As an example, desizing on a jigger is a simple method where the fabric from one roll is processed in a bath and re-wound on another roll. First, the sized fabric is washed in hot water (80-95°C) to gelatinise the starch. The desizing liquor is then adjusted to pH 5.5-7.5 and a temperature of 60-80°C depending on the enzyme. The fabric then goes through an impregnation stage before the amylase is added. Degraded starch in the form of dextrins is then removed by washing at 90-95°C for two minutes. The jigger process is a batch process. By contrast, in modern continuous high-speed processes, the reaction time for the enzyme may be as short as 15 seconds. Desizing on pad rolls is continuous in terms of the passage of the fabric. However, a holding time of 2-16 hours at 20-60°C is required using low-temperature alpha-amylases before the size is removed in washing chambers. With high-temperature amylases, desizing reactions can be performed in steam chambers at 95-100°C or even higher temperatures to allow a fully continuous process.

AETL offers products like series of Rapidenz HT as heat stable amylase and Rapidenz Cool as ambient temperature amylase.

Abrasion Yarn the abrasive action of lightweight pumice stones on the garment surface, which removes some of the dye. However, too much abrasion can damage the fabric, particularly hems and waistbands. This is why denim finishers today use acid, hybrid or neutral cellulases to accelerate the abrasion by loosening the indigo dye on the denim. Since a small dose of enzyme can replace several kilograms of stones, the use of fewer stones results in less damage to garments, less wear on machines, and less pumice dust in the working environment. Productivity can also be increased through laundry machines containing fewer stones but more garments. With a stone-free process, the need for the removal of dust and small stones from the finished garment is reduced. There is also no sediment in the wastewater, which can otherwise block drains. Denim garments are dyed with indigo, which adheres to the surface of the yarn. The cellulase molecule binds to an exposed fibril (bundles of fibrils make up a fibre) on the surface of the yarn and hydrolyses it, but leaving the interior part of the cotton fibre intact. When the cellulases partly hydrolyse the surface of the fibre, the indigo is partly removed and light areas are created.

Neutral cellulases or Neutrastone Series designed by AETL acting at pH 6-8, acid cellulases (Denicell Series) acting at pH 4-6 and hybrid cellulases (Addcool Series) acting at pH 5 - 6.5 are used for the abrasion of denim. There are a number of cellulases available, each with its own special properties. These can be used either alone or in combination in order to obtain a specific look. Application research in this area is focused on preventing or enhancing backstaining depending on the style required. Backstaining is defined as the redeposition of released indigo onto the garments. This effect is very important in denim finishing. Backstaining at low pH values (pH 4-6) is relatively high, whereas it is significantly lower in the towards neutral pH range. Neutral cellulases are therefore often used when the objective is minimal backstaining. Hybrid cellulases are effective tool to save energy cost as processing can be done at ambient or room temperature conditions.

Backstaining is not the cause of worry now a days due to availability of effective anti backstaining agents based on chemicals. AETL is one of the first companies to introduce backstaining removing enzyme (Stain Clear Series), unlike chemical agents which are used to prevent backstaining. Products are based on blends of different proteases, lipase and endolase.

Enzymes have opened up new possibilities in denim finishing by increasing the variety of finishes available. For example, it is now possible to fade denim to a greater degree without running the risk of damaging the garment. This can be effectively done by using enzymes like Laccase or peroxidase replacing bleaching chemicals like hydrogen peroxide or hypochlorite. Peroxidases introduced by AETL as Ecowash BB are further advantageous over Laccase as it has to be used in neutral pH 6 - 7 and temperature 50 - 55 0C. The denim industry is driven by fashion trends. The various cellulases available for modifying the surface of denim give fashion designers a pallet of possibilities for creating new shades and finishes. The combination of new looks, lower costs, shorter treatment times and less solid waste has made abrasion with enzymes the most widely used fading process today. Incidentally, since the denim fabric is always sized, the complete process also includes desizing of the denim garment.

Cotton and other natural and man-made cellulosic fibres can be improved by an enzymatic treatment called Bio-Polishing. The main advantage of Bio-Polishing is the prevention of pilling. Cellulases hydrolyse the microfibrils (hairs or fuzz) protruding from the surface of yarn because they are most susceptible to enzymatic attack. This weakens the microfibrils, which tend to break off from the main body of the fibre and leave a smoother yarn surface. A ball of fuzz is called a 'pill' in the textile trade. These pills can present a serious quality problem since they result in an unattractive, knotty fabric appearance. After Bio-Polishing, the fabric shows a much lower pilling tendency. Other benefits of removing fuzz are a softer, smoother feel and superior colour brightness. Unlike conventional softeners, which tend to be washed out and often result in a greasy feel, the softness-enhancing effects of Bio-Polishing are washproof and non-greasy. AETL's Sebrite series is much effective to impart pill proof biopolishing on woven and knit cotton fabric and garments. Sebrite also gives high color retention.

For cotton fabrics, the use of Bio-Polishing is optional for upgrading the fabric. However, Bio-Polishing is almost essential for the new polynosic fibre lyocell (the leading make is known by the trade name Tencel®). Lyocell is made from wood pulp and is characterised by a tendency to fibrillate easily when wet. In simple terms, fibrils on the surface of the fibre peel up. If they are not removed, finished garments made with lyocell will end up covered in pills. This is the reason why lyocell fabric is treated with cellulases during finishing. Cellulases also enhance the attractive, silky appearance of lyocell. Lyocell was invented in 1991 by Courtaulds Fibres (now Acordis, part of Akzo Nobel) and at the time was the first new man-made fibre for 30 years. Addcool series is best suitable for biopolishing of lyocell as it works at pH 5.5 - 6.0 and temperature 30 - 45 0C, causing less damage to fabric and high quality finish.

The Bio-Polishing of cotton and other fibres based on cellulose came first, but in 1995 enzymes were also introduced for the Bio-Polishing of wool. Wool is made of protein and so this treatment features a protease that modifies the wool fibres. 'Facing up' is the trade term for the ruffling up of the surface of wool garments by abrasive action during dyeing. Enzymatic treatment reduces facing up, which significantly improves the pilling performance of garments and increases softness. Proteases or Sebrite WDE of AETL are also used to treat silk. Threads of raw silk must be degummed to remove sericin, a proteinaceous substance that covers the silk fibre. Traditionally, degumming is performed in an alkaline solution containing soap. This is a harsh treatment because the fibre itself, the fibrin, is also attacked. However, the use of proteolytic enzymes is a better method because they remove the sericin without attacking the fibrin. Tests with high concentrations of enzymes show that there is no fibre damage and the silk threads are stronger than with traditional treatments.