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Resil's Application Research Centre (ARC) answers some of the frequently asked questions relating to enzyme applications

1. How Can Enzymes be Denatured Post-cycle?

Enzymes need to be denatured after the desired effect is achieved. If left behind, the enzymes lead to detrimental effects like loss in tear strength. For example, after a cellulase wash in bio-polishing or in denim fading, it is essential to denature cellulase as it will cause strength loss if left on the material. Primarily, there are two methods to denature enzymes:
l Hot treatment at 800C for 15 to 20 minutes or
l Raising the pH to about 10 to 11.

2. How can the problem of backstaining in enzyme processing be avoided?

'Backstaining' is a term normally associated with denim washing. The denim garment's appeal is in its pre-washed, faded appearance and a softer hand-feel. To give a washed- down effect and worn look, denim garments/fabrics are first desized, followed by treatment with fading enzymes.
During these two steps, more in case of the latter, the indigo dyes bleed from the denim warp yarns, which tend to resettle on the garment or fabric. This phenomenon is called 'backstaining'. It comes in the way of achieving the desired colour contrast after denim washing, and hence it is essential to reduce it.

One of the steps that can be taken to minimise backstaining is to add products into the desize bath to minimise resettlement of the released indigo dye. Since denim is usually desized with amylase enzymes, which are not compatible with anionic dispersants, polymeric dye scavengers are added into the bath.

In cases where denim is faded with cellulase enzymes, backstaining is severe. Two types of cellulase enzymes - acid cellulase and neutral cellulase - are used in denim fading. Acid cellulase has an optimum pH of 5.0 to 5.5 and neutral cellulase, 6.5 to 7.0.

It has been found that at pH 7.0, there is minmal or no backstaining. Any lower, and the backstaining is higher. Also, at pH 7.0 to 7.5, neutral enzymes still retain 90 per cent of their activity, while at pH 6.0, the colour removal effect of acid enzyme is reduced to less than40 per cent. It is clear that the neutral cellulase's optimum pH coincides with the pH at which little or no backstaining occurs.

This comparison of the pH dependence of acid and neutral cellulases and backstaining helps establish that neutral cellulases are more effective in minimising backstaining.

At times, it has been noticed that hard water comprising ferrous ions tends to lead to more backstaining. In case the water is hard and has metal ion content, it is recommended to use chelating and sequestering agents to reduce the amount of backstaining.

Yet another method to minimise backstaining is to use non-ionic surfactants and dispersing agents that help hold the indigo dye in the bath. Another important factor, which at times is overlooked, is the rinsing/clean-up cycle. Two to three rinses of about two seconds each at high water levels help in taking out the loose indigo. Even a scour cycle after the enzyme wash helps in pulling out the loose indigo. At times, processors have also found that a little quantity of Sodium Hypo Chlorite in the clean-up cycle helps in loosening the indigo dye.

3. How can streak marks be prevented from forming?

'Streaking' is a term used to describe the effect of enzymes within folds that occur in a denim garment during initial wetting. In subsequent processing steps like desizing and fading, the enzymes used act differently in these creases, depending on whether the folds are directed outward or inward. In the case of folds directed outwards, the enzymes act strongly towards the projected area of the fold, resulting in high colour removal, and thus leading to the formation of white streaks. In the case of fold directed inwards, the enzymes have a milder effect: the area remains protected from the abrasion activity and experiences low colour removal. In consequence, we get darker streaks.

Streaks can be avoided or minimised through several processes:
l Firstly, trousers need to be piped out before being loaded into the washing machine.
l The garment needs to be loaded lengthwise, with the denim leg parallel to the washing drum's axis of rotation. This reduces random distortion and helps prevent streaks.
l Desizing is an important step in denim washing, since inefficient or non-uniform size removal can actually introduce streaks. Desizing with just a regular amylase enzyme may not help. It is necessary to combine the desizing agent with a good quality lubricant.
l During denim fading also, it is advisable to add a good quality lubricant to minimise the chance of streaking.
l It is safer to maintain the load size at about 50 to 60 per cent of the rated machine capacity. Heavier loads do not allow the garments to move well in the wash wheel, allowing unevenness in shade and crease marks to appear in the final garment. Exceptions to this would include special cases of unusual garments such as fleece-lined jackets or extraordinary weight denim, either light or heavy, where the load may be adjusted accordingly.
l Historically, water has been maintained at higher than normal levels for laundry. However, many fabrics are now available that respond to medium or low water levels, and these fabrics actually tend to streak with high water levels.
l The total running time of the desizing process needs to be at a minimum to limit undesired abrasion and excessive colour loss. This process can be aided by including the soak time, allowing the garments to completely wet out and become more flexible before starting the agitation, thus reducing the streaks.
l Whenever possible, the wash wheel should not run while the water is filling or draining.
l First adding non-ionic lubricants and wetting agents to the water and then loading the garments helps in minimising streaks.
l Extra precautions like pre-removal of hard creases and pre-breaking of the sizing films, help in reducing the risk of streak marks.

4. Should garments be washed inside out or outside in while desizing?

Denim garments, particularly those made from heavy denim, are often turned inside out before desizing, because this reduces the tendency to generate abrasion or crack marks on the finished garment.

5. How can one check whether a garment has been desized effectively?

Ideally, after desizing, residual size should not be more than 1% owm. It is always a good practice to check the presence of starch by the iodine spotting method. A drop of dilute iodine solution (I2 in KI) is placed on the fabric and the colour change observed. A dark violet colour indicates excessive starch and if so, the garments must be re-desized. The lower the intensity of colour, the better the efficiency of desizing.

6. How can one achieve minimum strength loss in the cellulase enzyme wash process?

In the cellulase enzyme wash process, particularly in the biopolishing of cotton, there is a weight loss of 1 to 5 per cent and strength loss of about 5 to 15 per cent. High strength loss can be avoided by maintaining the exact time required for processing. For example, all biopolishing enzymes traditionally take 40 to 45 minutes to provide good biopolishing effects. It is advisable to check the degree of biopolishing of the lot within 30 to 35 minutes. If the desired biopolishing is achieved, then the process can be terminated and the strength of the material saved. Most importantly, over-dosing of enzymes must be avoided.

7. How can one achieve less fraying in denim washing?

'Fraying' usually occurs during stone washing of denim garments. The garments are run in a machine along with stones for a considerable period of time. This prolonged beating action on the garments results in fraying. This process can be replaced with a good quality, environment friendly, and cost-effective fading cellulase enzyme. This will eliminate the severe beating action and process time, which in turn, reduces fraying.