Guifang Wu¹, Han Kuilderd¹ and Sonja Salmon²

¹ Novozymes China, 14 Xinxi Lu, Shangdi Zone, Haidian District, Beijing 100085, China

² Novozymes North America Inc., PO Box 576, 77 Perry Chapel Church Road,
Franklinton NC 27525, USA

Abstract

Enzymes are applied during the preparation, after-dyeing and finishing stages of textile production to facilitate the removal of natural or applied impurities and help modify the physical properties of textiles. In this paper, shortened processes, for instance, simultaneous desizing and scouring with enzymes, catalase for excess hydrogen peroxide removal after bleaching and laccase applications on textiles are evaluated in comparison with conventional processes. It has been highlighted that enzyme technology supports the overall industry trend toward shorter process time, milder process conditions, as well as delievering cost-effective innovation, improving the quality of goods and providing compliance to environmental regulations.

Key words: Enzyme; Sustainable; Bio-scouring; Catalase; Laccase

1. Introduction

The aim of preparation for woven fabrics involves the following steps: singeing, desizing, alkali scouring, bleaching. The whole preparation is a long process and uses a large amount of harsh chemicals such as sodium hydroxide. Before amylase was introduced to textile desizing in 1952, oxidants were widely applied to remove size chemicals from woven fabric. Apart from their desizing effect, oxidants also damage the cellulose fibers and result in unexpected strength loss. The same negative impact on cellulose fibers from chemicals in traditional process is inevitable because a large quantity of sodium hydroxide and hydrogen peroxide is required to achieve the desirable dyeing properties. In addition, the long process consumes enormous amount of water and the heavy dosage of chemicals ends up with a high load of COD and BOD in effluent.

Nowadays enzymes are applied during the preparation, after-dyeing and finishing stages of textile production to facilitate the removal of natural or applied impurities and help modify the physical properties of textiles. Since the first commercial application of amylase, the efforts in research and development on enzymes have led to a couple of successful industrial practice with enzymes to replace harsh chemicals or improve the textile quality. This includes several well-established applications, such as cellulase for denim processing, laccase for denim bleaching, catalase for excess hydrogen peroxide removal after bleaching, pectate lyase for scouring of cotton, peroxidase for post-wash of reactive-dyed textiles, protease for silk and wool treatment, and so on.

This paper is to evaluate 3 applications of enzyme for textile processing in the respect how they are contributing to the environmentally sustainable growth of the whole society as well as the financially sustainable growth of textile producers.

2. Simultaneous desizing and scouring with enzymes Increasing your production capacity

Conventional scouring uses high concentrations of sodium hydroxide and surfactant to remove the waxes and hemicelluloses in the primary cell wall layer of cotton. In 1999 Novozymes introduced a commercial pectate lyase (PL) for bio-preparation of cotton fabric. With this PL it was shown that it is possible to reduce the residual pectin levels to low enough levels to ensure good wetting ability and dyeing properties. Initially PL was used solely for the processing of knitted goods, yarn and fiber where desizing is not required.

In 2005 Novozymes launched an amylase with broad working range of pH and temperature, which allows to combine desizing and scouring in one bath (CDB) so as to shorten the whole preparation process and save water and energy. This concept of simultaneous desizing and bioscouring has been tested in bulk production by several mills, which in all the cases turned out to be a more economic and environmentally friendly process than conventional processes. Our experience with a linen mill in China is shared as below:

1) Process conditions

2) Results of CDB treated fabric in comparison with the normal process

3) Advantages and benefits found by the mill

                   Flexible incubation time (2-48 h) without fabric damage

                   One pre-treatment recipe for all their production

                   Improved side-to-side and end-to-end uniformity of dyeing due to no residual alkali related

Problems.

                   Softer fabric handle and smoother appearance

                   Lower cost and lower effluent as they use caustic from mercerizing with roughly half the

strength

                   Effluent recycling is possible

                   Use less auxiliaries resulting in overall chemical cost saving of RMB0.05/yard

                   Time, water, and energy savings and reduced fabric shrinkage due to fewer process steps,

about 30% increase in production capacity

                   Improved operator working conditions

Due to major benefits achieved in cost savings and improved quality the mill has changed its entire production over to enzymatic preparation process.

3. Catalase for Bleach Clean-up Saving water and energy

Fabrics are often bleached with hydrogen peroxide prior to dyeing and finishing. Residual hydrogen peroxide must be removed to obtain the most efficient dyeing. Repeated water washes or chemical reducing agents have traditionally been used, and now it is common practice to apply catalase enzymes which decompose hydrogen peroxide to oxygen and water. Significant process savings are possible because the treatment is fast, mild, and dyeing can be carried out in the same liquor and equipment as the catalase treatment.

1)   Process conditions

2) Efficiency of H₂O₂ removal

2) Cost saving

(1000 kg of fabric, liquid ratio 10:1. Cost indication is based on China market)

4. Laccase for denim Staying ahead of fashion trend

Traditionally, chemical bleaching agents and mechanical treatment are applied to denim to create washed-down look, which result in fabric strength loss due to their less selectivity. Since laccase was introduced to the industry in 1996, enzymatic treatment has become another tool to create more fashion styles on denim.

1) Laccase for denim bleaching

It is well-known that laccase is able to decolorize indigo with assistance of a proper enhancer. Commercial laccase product from Novozymes enables to create unique shades of faded blue, which is distinctly different than traditionally bleached denim. Originally the laccase enzyme was developed for denim bleaching. The enzyme is also efficient for clean-up process to remove back staining.

Compared to conventional chemical oxidants, the enzymatic approach protects the fabric from further strength loss and reduces use of harsh chemicals and effluent load as well. In the meantime, the mild process becomes easier to control.

2) Laccase mediated dyeing process

In the fashion-driven denim segment, a new color can be applied to the denim to give a saturated or color-contrast finish, which is known as overdyeing. For such dyeing operations, direct dyes are generally used. The denim containing products are contacted with the direct dye in a bath containing 5-40g/L salt at 85-95^oC, pH7-8.5 for 0.5-2.5 hours.

In nature, laccase enzyme plays an important role in the oxidative biosynthesis of natural compounds, starting with simple aromatic organic compounds that are substrates for the enzyme. These laccase catalyzed oxidation reactions can lead to chemical bond formation in a way that extends the aromatic conjugation, leading to colored products. When this was applied on garment, a new process, enzyme mediated dyeing process (EMDP) was created. The EMDP is a one-bath treatment to produce color effects on textile materials by using laccase enzyme to catalyze the oxidative coupling of color-forming compounds. The color-forming compounds are an essential part of the concept. The range of colors and color properties generated depend on the particular compounds selected for the process.

Essential components in the EMDP include:

• Material (garment) to be dyed
• Color-forming base compound
• Oxygen
• Laccase enzyme

Other color modifier compounds or conventional garment processing auxiliaries can be included in the same bath according to actual demand.

The EMDP can be run in a typical washing machine with open-air and agitation. During the process, low molecular weight base compounds are circulated in the garment washing equipment, together with the load of garments. They are able to penetrate through the fabric load to give an even distribution due to their small size and corresponding high mobility. When laccase is added, the color-forming coupling reactions occur quickly in and around the fibers in the garment to give a range of color effects. The extent to which the produced color associates with or is physically entrapped within the fiber structure can provide many finishing options, ranging from bleach and fade resistance to quick wash-down and vintage fashion effects. Therefore, the EMDP is a versatile process for producing color during garment finishing. Process parameters can be controlled to give reproducible color effects, or can be flexed to give unique and individualized garments.

5. Future Perspective

For the textile industry as a whole, enzyme technology is obviously supporting the overall industry trend toward shorter process time, milder process conditions, as well as delivering cost-effective innovation, improving the quality of goods and providing compliance to environmental regulations.

In future practice, cost savings using enzyme technology is perceived as the key driver for mills and laundries to replace conventional processes with enzymatic preparation processes, while the increasing concerns on environmental protection from the global community will of course speed up the evolution of textile processing towards biocompatible enzyme technology. Novozymes feels it is able to contribute to both these factors with its present product range as well as leading the development of new and innovative products for the future.

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