Enzyme Washing of Textiles: Cellulase and Biopolishing

What enzyme washing is

Enzyme washing is an industrial wet process in which selected enzymes are used to modify cotton and other cellulosic materials, or to clear residues left by earlier steps. In a garment laundry it is the usual way to give denim a worn, faded look without relying only on pumice. In a fabric dyehouse the same family of enzymes is used to remove starch size, to help scour cotton, to destroy leftover hydrogen peroxide, and to biopolish knits and wovens so the surface is cleaner and less prone to pilling.

That is a wider field than the denim wash alone. The garment route that uses cellulase in place of, or together with, stones is described in Stone Washing of Jeans. This article covers the enzymes themselves, biopolishing of fabric, and how a cellulase treatment is actually run and stopped. It is not a domestic laundry cycle, and a household “enzyme detergent” is not the same thing as a mill or laundry process.

Enzymes are proteins that speed particular chemical reactions. Each type acts on a narrow substrate: amylase on starch, cellulase on cellulose, catalase on hydrogen peroxide, and so on. They work under relatively mild conditions of temperature and pH, and they can be inactivated once the effect has been reached. They are not harmless because they are biological. Used carelessly, a cellulase will keep attacking the fibre, and the cloth will lose mass and strength.

The main textile enzymes

The enzymes most often met in cotton processing are:

• Amylase, to hydrolyse starch size (desizing).
• Pectinase, often the main agent in a bioscour, to loosen pectin and help remove other natural impurities from cotton.
• Catalase, to destroy residual hydrogen peroxide after bleaching, before dyeing.
• Cellulase, to hydrolyse surface cellulose: this is the enzyme used for biopolishing and for denim wash-down.
• Laccase, used in some denim routes as an enzymatic way to reduce indigo, as an alternative to a conventional bleach.

A protease may appear in laundry or wool processes, because it acts on protein, but it is not a cellulase substitute and it can damage protein fibres if it is left active. The supplier’s product is a formulated mixture, not a pure protein in a bottle, and the method on the technical sheet is part of the process, not optional reading.

The figure is a schematic drawn for this article. The upper row names the main textile enzymes and the job each one is used for. That row is not a process sequence: a given batch may use only one of them. The lower row is a typical cellulase treatment cycle, from loading through inactivation to the rinse. It replaces a promotional graphic labelled “Garment Wash Chemicals” that was on the original post.

Amylase desizing

Most woven cotton is sized in the warp, often with starch, so that the yarn can survive weaving. That size has to come off before a level dye or a clean garment wash can be expected. Alpha-amylase hydrolyses the starch so that it can be rinsed away, and it is the usual first wet step for starch-sized woven fabric and for denim garments entering a wash laundry.

The conditions depend on the enzyme type (some are made for hotter baths than others) and on whether a detergent or wetting agent is used with it. After desizing, the goods are rinsed. Incomplete desize leaves a patchy surface that later cellulase work and dyeing will show up, so the step is worth checking rather than assuming it is finished because the time has elapsed.

Bioscouring and catalase

A conventional cotton scour uses alkali, detergent and heat to remove waxes, pectins and other impurities. A bioscour uses pectinase, sometimes with other enzymes such as lipase, to attack the pectin network so that impurities can be removed at milder alkalinity and, often, with less weight loss than a hard caustic boil. It does not automatically replace every scour, and the cleanliness still has to be judged by absorbency and by the later dye result, not by the name of the process. Preparation of this kind sits in the wider field of textile finishing and of wet processing in textile manufacturing.

Catalase has a different job. After a hydrogen peroxide bleach, leftover peroxide will interfere with many dyeing processes. Catalase decomposes that residual peroxide quickly under mild conditions, so the bath can be dropped or reused and dyeing can follow without a long, hot chemical kill. It does not bleach the fibre, and it does not replace the bleach.

Cellulase for biopolishing

Biopolishing is a cellulase treatment aimed at the fabric surface rather than at a faded denim look. Loose fibre ends and microfibrils on cotton, and on some other cellulosics, are hydrolysed and then removed by mechanical action. The cloth looks cleaner, pills less in later wear and washing, and often feels smoother. The effect is widely used on cotton knits, where pilling is a common complaint, and it can also be applied to wovens.

The treatment may be given in a jet or overflow machine on fabric, or in a rotary garment washer on made-up goods. Because the enzyme is attacking cellulose, some loss of mass and tensile strength is inherent. A short, well-controlled cycle on a suitable cellulase can clean the surface without taking the cloth below its specification. An over-long cycle, an overdose, or extra mechanical action on a light fabric will thin the material, weaken seams and, in the worst cases, open holes at high-abrasion points.

Dyes and finishes affect the result. A film-forming pigment binder, or a wrinkle-resistant resin finish, can limit the enzyme’s access to the fibre, so biopolishing is normally done before such a finish, not after it. Some dyes, including certain reactives, can also slow the enzyme; the trial should be made on the actual dyed quality, not only on greige fabric.

Cellulase for denim and enzyme-washed garments

On indigo denim the same surface attack is used to release dye and soften the hand. Indigo is typically concentrated at the surface of a ring-dyed cotton warp, as described in Vat Dyes for Cotton, so when surface fibre is removed the paler core and the undyed weft begin to show. That is why an enzyme wash can mimic a stone-wash fade.

The denim method — acid against neutral cellulase, backstaining, combined stone and enzyme cycles, and what comes after the wash — is covered in Stone Washing of Jeans and is not repeated here. Two points still belong in this article. First, standard acid cellulases are often more aggressive and can give more wash-down, but they also tend to cause more backstaining; modified-acid and neutral types are often chosen when contrast must be kept and redeposited indigo kept down. Second, the mechanical action of the drum is part of the process. The enzyme does not replace abrasion; it works with it. Load size, liquor ratio and machine type therefore change the look as much as the recipe does.

How a cellulase treatment is run

A practical cycle has a few controlled steps.

The goods are loaded and wetted out, and they are desized first if starch size is still present. The bath is then set to the pH and temperature recommended for the chosen cellulase, often with a buffer so that the pH does not drift. Published ranges are typically about pH 4.0–6.5 for standard acid cellulases and about pH 5.5–8.0 for neutral types, with a working temperature commonly in the region of 45–60 °C. Those figures are starting points, not a substitute for the supplier’s method.

The enzyme is added and the machine is run for long enough to give the effect, with enough mechanical action for loose fibre to be removed. Fabric in a low-action machine may need a more aggressive cellulase, or more time, than the same quality in a high-action jet or a rotary garment washer. Process times are often between about half an hour and two hours, with lighter fabrics towards the shorter end. Strongly ionic auxiliaries can suppress activity; non-ionic wetting agents are usually the safer companions. The liquor ratio matters because it changes both concentration and mechanical action; many fabric operations run in the region of 10:1, but the machine and the quality decide what is uniform.

When the effect has been reached the enzyme must be inactivated. That is typically done by raising the temperature, by raising the pH (making the bath more alkaline), or by a strong ionic change, and then rinsing. If this step is skipped, residual cellulase can continue to work in later holds, rinses or even in a poorly controlled drying stage, and the cloth will go on losing strength. After inactivation the goods are rinsed, neutralised if the pH was shifted, and usually softened, then dried and inspected.

The trial is approved against the required shade, surface, handle and strength, not only against a target cycle time.

Strength, shade and quality

The original version of this post said that enzyme washing “will not compromise the strength of the fabric.” That is not true of cellulase on cotton. Some surface-fibre loss is the mechanism of the finish. The question is whether the remaining cloth still meets the specification.

Checks that belong with the trial include tensile and tear strength, pilling, abrasion, mass per unit area, and shade or contrast, using the methods outlined in Fabric Testing: Names and Equipment. Denim should also be judged for backstaining and for weak points at pockets, belt loops and hems. A clean biopolished knit should be judged after domestic washing, because that is when pilling appears, not only off the machine.

FAQ

Is enzyme washing the same as stone washing?

No. Stone washing, in the original sense, abrades denim with pumice. Enzyme washing uses cellulase to attack surface cotton, which also releases indigo and softens the hand. The two are often combined on jeans, but enzyme washing also includes fabric biopolishing and other enzyme steps that have nothing to do with a stone-wash look. The denim comparison is in Stone Washing of Jeans.

What is an enzyme-washed fabric?

In apparel language it usually means a cotton or denim article that has been treated with cellulase to soften it and, on denim, to fade it. In the dyehouse the same words are sometimes used more loosely for any goods that have had an enzyme step, so it is better to say whether the treatment was a desize, a bioscour, a catalase kill or a cellulase biopolish.

Will enzyme washing weaken the cloth?

It can. Cellulase removes cellulose, so some loss of mass and strength is expected. A controlled biopolish or denim wash stays within the fabric’s specification. Over-processing, or leaving the enzyme active after the cycle, is what takes the cloth too far.

Do I have to deactivate the enzyme?

Yes, once the effect has been reached. Raising the temperature and/or the pH, followed by a thorough rinse, is the usual method. An enzyme left active will continue to attack the fibre.

Can enzymes replace every harsh chemical in preparation and washing?

No. They can replace or reduce some of them — starch desizing, part of scouring, residual peroxide, and some of the mechanical stone or bleach load on denim — but bleaching, dyeing and many finishes still use conventional chemistry. The comparison should be made on the actual route, not on the word “enzyme”.

Is a household enzyme detergent the same process?

No. Laundry detergents may contain enzymes to help with stains, but they are not a substitute for a controlled mill or garment-laundry treatment, and they are not used to biopolish or to wash down denim in the industrial sense.

References

• Cotton Incorporated, Enzyme Technology for Cotton Products (ISP-1003): the main enzyme types used on cotton, how cellulases are grouped by pH, the roles of mechanical action, temperature, time and liquor ratio, and the need to inactivate the enzyme and to manage strength loss and backstaining.
• Cotton Incorporated, Garment Washing Techniques for Cotton Apparel (TRI-3005): garment-wash routes for cotton, including alpha-amylase desizing and the use of cellulase, with or without stones, for wash-down.
• CottonWorks, Denim Finishing: enzyme washing as an alternative or addition to stone washing, and the control of backstaining.