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Denim garment processing: The eco-friendly way

The domestic readymade garment sector is booming, and garment processing has emerged as one of the important production routes towards meeting quick changing demands of the fashion market. In this article we look at processing of denim garments.

Advantages of garment processing

• Increases the opportunities available for differentiation of the end product.
• Offers option to retailer, which are not available in piece good finishing.
• Gives opportunity to impart unique looks and finishes that cannot be achieved in fabric form.
• It allows to hold colour and finishes until the last minute and enables you to shorten the time to market.

The spread of denim culture, all over the world brought with it a trend of fast changing fashions. One after another, several washes were introduced such as stone wash, acid wash, moonwash, monkey wash, show wash, frosted wash, white wash, mud wash, etc. Over the last 6-8 years, India has probably seen the most dramatic and exciting changes in the washing of denim garments.

Desizing: Traditional desizing is performed by using acid or oxidative desizing agents which is associated with many drawbacks and limitations. Due to uncontrolled and non-specific reaction, the cellulose material gets damaged and looses strength. With the introduction of enzyme based desizing process, the limitation and drawbacks of traditional desizing process can be overcome. The enzymatic desizing process is performed by using alphaamylase enzyme.

Advantages of enzymatic desizing over traditional desizing

1. Due to very specific reaction of enzyme, there is no adverse effect on cellulose, therefore better strength retention.

2. Saving of water as multiple washing is not required to remove the residual chemicals after desizing.

3. Process time of desizing can be reduced.

4. Neutralisation is not required because same processing conditions are required in next process therefore zero salt formation in ETP.

5. Saving of energy as desizing takes place at moderate temperature.

6. Feel of fabric is much softer and less hairiness on the fabric.

7. No adverse effect on other bath auxiliaries due to mild process condition.

8. No adverse effect on Lycra or polyester containing fabric.

9. Handling of chemical is safe and easy.

10. No adverse effect on machinery.

Stonewash Effect:

In traditional washing process, volcanic rocks or pumice stones are added to the garments during washing as abradant. Due to ring dyeing and heavy abrasion fading is more apparent but less uniform.

The degree of colour fading depends on the garment to stone ratio, washing time, size of stones, material to liquor ratio and load of garments. Normally after desizing, stone wash process starts with pumice stone addition in rotary drum type garment washer. Process time varies from 60-120 mins.

Stone wash effect is one of the oldest but highly demanded washing effects. Stone wash process gives “used” look or “vintage” on the garments, because of varying degree of abrasion in the area such as waistband, pocket, seam and body.

There are many limitations and drawbacks associated with stone washing process, which can be overcome by using new enzyme based washing technology. This technology also helps to conserve water, time, energy and environment.

Enzyme Wash

• Cellulase enzymes are natural proteins which are used in denim garment processing to get stone wash look on to the denim garments without using stones or by reducing the use of pumice stone.
• Cellulase attacks primarily on the surface of the cellulose fibre, leaving the interior of the fibre as it is, by removing the indigo present in the surface layer of fibre.

Cellulase enzyme is classified into two classes:

• Acid Cellulase: It works best in the pH range of 4.5-5.5 and exhibit optimum activity at 50.
• Neutral cellulase: It works best at pH 6 however its activity is not adversely affected in the range of ph 6-8 and show maximum activity at 55 C.

Advantage of enzyme washing

• Soft handle and attractive clean appearance is obtained without severe damage to the surface of yarn.
• Inexpensive, low-grade fabric quality can be finished to a top quality product by the removal of hairiness fluff and pills, etc.
• Simple process handling and minimum effluent problem.
• Better feel to touch and increased gloss or luster.
• Prevents tendency of pilling after relatively short period of wear.
• Can be applied on cellulose and its blend.
• Due to mild condition of treatment process is less corrosive.
• Fancy colour-flenced surface can be obtained without or a partial use of stone.
• More reproducible effect can be obtained.
• It allows more loading of the garment into machines.
• Environmental friendly treatment.
• Less damage to seam edges and badges.
• Wear and tear of equipment is minimum due to absence of stone.
• Use of softener can be avoided or minimised.
• Easy handling of floor and severs as messy sludge of stones does not interfere.
• Due to absence of stone, labour intensive operation of stone removal is not required.
• Homogenous abrasion of the garments.
• Puckering effect can also be obtained.
• Problem of pumice powder contamination on garment is not there.

Denim bleaching

In this process, a strong oxidative bleaching agent such as sodium hypochlorite or KMnO4 is added during the washing with or without stone addition. Discoloration is usually more apparent depending on the strength of the bleach liquor quantity, temperature and treatment time.

Limitations

• Process is difficult to control i.e. difficult to reach the same level of bleaching in repeated runs. When desired level of bleaching reached the time span available to stop the bleaching is very narrow. Due to harshness of chemical, it may cause damage to cellulose resulting in severe strength losses and/or breaks or pinholes at the seam, pocket, etc.
• Harmful to human health and causes corrosion to stainless steel.
• Required antichlor treatment.
• Problem of yellowing is very frequent due to residual chlorine.
• Chlorinated organic substances occur as abundant products in bleaching, and pass into the effluent where they cause severe environmental pollution.

3-E Bleaching concept for denim

Intensive research is underway for the development of sodium hypochlorite bleaching alternative eg, glucose bleaching, bleaching with sulphinic acid derivatives, and recently with laccase (enzyme).

Laccase enzyme belongs to the oxidoreductase group. Laccase’s oxidative effect is complex, it does not work independently. A mediator is necessary and a chemical mediator is employed between enzyme and indigo.

Advantages

• New Laccase based bleaching technique only affects the indigo and natural raw white of weft yarn is retained, giving the woven fabric a darker shade, which is not implicitly achieved with hypochlorite bleaching.
• The product is so specialised on indigo that it does not attack any other dyes.
• Laccases open up the door to bleach Lycra containing denim without loosing the strength of the fabric. In case of hypochlorite bleaching Lycra containing product affects adversely by loosing the tear and tensile strength.
• Finally the process is based on enzyme so no risk of environmental pollution and harmful effluent discharge.

Limitations

• Expensive, compared to traditional process.
• Heavy faded look is difficult to achieve.

Enzymatic anti-backstaining agent-protease:

The use of an engineered oxidatively stable alkaline protease that can tolerate a range of operating temperature and pH conditions offers flexible and alternative processes for backstaining clean-up, improved contrast of denim finishes, and reduced residual cellulase of fabric.

It is claimed that significant reduction in backstaining can be achieved at much lower temperature than conventional process by using small amount of protease either at the end of the cellulase washing step or during the rinsing step. By adding the protease at the end of the cellulase wash step, one rinse step is eliminated offering savings in time and energy. This process at lower temperature also claims to achieve a significant reduction of residual cellulase.

Selection of denim fabric

The right selection of fabric can help minimise the cost of treatment and to solve environment related issues.

Different colour depth fabric: To cut processing time, effluent load, minimum damage to fabric and minimum use of chemical, there are different depth of indigo on denim. For example, in case of ice wash where we remove more than half the dye during washing, one can use lighter shade fabric which will help to cut the process time, chemical consumption, effluent load. It will help garment processor to process garment more economically and with minimum faults.

Flat look denim: Different chemicals and processes are used to get flatter look on the denim garments. To meet this requirement special denim fabric has been developed which offers flat look after washing.

Quick wash denim: Quick wash denim fabric is dyed with modified technique of dyeing, so that during wash cycle, indigo dye can be removed quickly, giving washed look at shorter washing cycle. This results in more economical washes i.e. low water consumption, less usage of chemicals, less time and retaining fabric strength.

Tinted denim: With increase in demand of tinted/ overdyed look on garment, garment processor is using an additional process of tinting/ overdyeing, which is time consuming. It consumes large quantity of water and chemicals. It is also associated with the risk of patches and unevenness on garments. Now the denim fabric is also available in tinted form which saves processors time and risk.

Grainy look denim: Different chemicals and processes are used to get grain look on the denim garments. To meet this requirement special denim fabric has been developed which gives grainy look after processing of denim garment.

Soft feel denim: To meet such requirement, different varieties of denim fabric are available, which are having inherent softness. These fabrics require minimum application of softener at the garment stage.

New developments towards economical and ecological denim processing

Use of laser technology

It is a computer controlled process for denim fading. This technique enables patterns to be created such as lines and/or dots, images, text or even pictures. In one version of this concept, a mask is used to give the desired shape that is to be applied on the fabric. The laser projects through a lens system, which expands the beam. This beam is passed through the shaped mask that comprises an aperture of the desired shape and is then deflected by a mirror to strike the textile substrate. The duration of exposure determines the final effect on the fabric.

The novelty of this system is that

• It is water free fading of denim.
• It is an ecological and economical process.
• It can create local abrasion and fabric breaks, used look effect, moustache with excellent reproducibility and higher productivity.
• Being an automatic system, chances of human error are slim.
• The design is electronically translated on the fabric, thus avoiding the need for photolites of serigraphy cleaning.

The machine is very simple and compact, therefore requires very low maintenance and cleaning, extremely safe and reliable.

Sand blasting

Sand blasting technique is based on blasting an abrasive material in granular, powdered or other form through a nozzle at very high speed and pressure onto specific areas of the garment surface to be treated to give the desired distressed/ abraded/used look.

Advantages of sand blasting process

- It is purely mechanical process, not using any chemicals.
- It is a water free process therefore no drying required.
- Variety of distressed or abraded looks possible.
- Any number of designs could be created by special techniques.

Mechanical abrasion

- To give worn out effect, abraded look or used look, some mechanical processes have been developed. These are based on mechanical abrasion by which the indigo can be removed. Some of these processes are sueding, raising, emeresing, peaching and brushing.

Advantages of these processes:

- Control on the abrasion
- Different look on the garment can be achieved.
- All are dry process.
- Economical, ecological and environmental friendly.

Ozone fading

By using this technique, the garment can be bleached. Bleaching of denim garment is done in washing machine with ozone dissolved in water. Denim garments can also be bleached or faded by using ozone gas in closed chamber. The advantages associated with this process are:

- Colour removal is possible without losing strength.
- This method is very simple and environmentally friendly because after laundering, ozonized water can easily be deozonized by UV radiation.

Waterjet fading

Hydrojet treatment has been developed for patterning and/or enhancing the surface finish, texture, durability, and other characteristics of denim garment. Hydroject treatment generally involves exposing one or both surfaces of the garment through hydrojet nozzles.

The degree of colour washout, clarity of patterns, and softness of the resulting fabric are related to the type of dye in the fabric and the amount and manner of fluid impact energy applied to the fabric. Particularly good results are obtained with blue indigo dyed denim.

As this process is not involved with any chemical, it is pollution free. By using water recycling system, the technique can be used as economical and environmental friendly denim processing. Color washout of dye in the striped areas produces a faded effect without blurring, loss of fabric strength or durability, or excessive warp shrinkage.

Spray techniques

This technique is based on spraying the chemicals or pigments to get different effect on the garments. This can be done by using robotic spraying gun or by manual spray and followed by curing of the garment.

- It a water free process therefore zero effluent discharge.
- Less time consuming
- Different designs are possible
- Easy to use
- No adverse effect on fabric strength.

Single bath stone washing and tinting technique

Tinting of denim garment is usually done after the stone wash process. In this, garment has been lightly coloured in order to give the final denim appearance a slight shift. This is not true over dyeing but merely gives the impression of a change in overall colour of the fabric. This process consumes large quantity of water and chemical. To make this process economical and ecologically friendly, some novel colour based enzymes have been introduced in the market. By using this new technique, tinting and stone washing effect can be achieved in a single bath.

- Less process time to achieve tinted look.
- No extra chemical required therefore making process more economical.
- Less water consumption.
- Less energy consumption.
- Less chance of patches or unevenness

Alternate of pumice stone

To overcome the shortcoming of pumice stones, synthetic stones have been developed. These are made of abrasive material such as silicate, plastic, rubber or Portland cement.

The advantage of using such type of products are:

- All major problems associated with the use of volcanic grade pumice stone can be overcome.

- Durability of such product is much higher and can be used repeatedly from 50-300 cycle depending upon type of synthetic stone.

- Reproducibility of washing is manageable.

- As stone discharge of the process is very less, therefore making process is economical and ecological.

- Less damage of machine and garments.

Waste water solution

As the municipal discharge criteria are restrictive and cost of water high, producers will need to reuse the waste water. Many techniques are readily available for a processor to treat waste water. The basic limitation of a garment processor is the higher installation cost associated with such techniques.

Technocrats need to realise that they have to develop simple and cost-effective garment processing technologies, that aim at conservation of energy, water, time, and are environment-friendly.