MANUFACTURE OF TEXTILES # 31

Background:

During the weaving process the warp (chain) threads are exposed to considerable mechanical strain. In order to prevent breaking, they are usually reinforced by coating (sizing) with a gelatinous substance (size).

In the weaving of cotton blend fabrics, the size material most often contains starch in native or modified form, sometimes in combination with other polymers such as polyvinyl alcohol (PVA), polyacrylic acid (PAA) or carboxymethyl cellulose (CMC). Small amounts of fats or oils may be also added to the size, with the aim of lubricating the warp coat surface.

As a consequence of the sizing, the warp threads of the fabric are not able to absorb water or finishing agents to a sufficient degree. This means that first the size must be removed (desizing) before finishing. Some types may be removed in a simple scouring process (water soluble sizes). But in most cases chemical breakdown of the size polymer in a separate desizing treatment is necessary in order to obtain the desired quality of the final fabric [2]. Table 1 provides a comparison of the biodegradability of the various sizes used interms of their BOD and COD contributions.  

Table 1: Biodegradability of size raw materials

In the conventional process of desizing, the breakdown of the size polymer is carried out using oxidizing agents such as ammonium persulfate or hydrogen peroxide at high pH and temperature. The treatment reduces the tensile strength of the fabric and results in poor removal of some PVA-containing sizes.

The quantity of size is about 15 % of the yarn weight [4]. The material balance for the desizing process is presented in table 2.

Table 2 : In- and output desizing

The COD value can be from 3500 mg O2 /l to 23000 mg O2 /l [1].

Alternative eco-friendly desizing agents are available in the market in the form of enzymes. The present case study is an illustration of such an enzymatic desizing process that has been fully implemented in the Netherlands by a big finishing company KTV. This company is using the enzyme for more than 20 years.

Cleaner Production Principle:

Material substitution

Cleaner Production Application:

Complete removal of starch-containing size without fiber damage is best obtained by using enzymatic desizing agents. Formerly amylase derived from mold, pancreas or malt where used in desizing. Today liquid bacterial amylase preparations dominate.

The enzymatic desizing process can be divided into three stages :

Impregnation : Enzyme solution is absorbed by the fabric. This stage involves thorough wetting of fabric with enzyme solution at a temperature of 70C or higher with a liquid pick up of 1 liter per kg fabric. Under these conditions there is sufficient enzyme stability (temperature, pH, calcium ion level govern the stability). During this stage gelatinization of the size (starch) is to the highest possible extent.

Incubation     : The size is broken down by the enzyme. Long incubation time allows a low enzyme concentration.

After-wash      : The breakdown products from the size are removed from the fabric. The desizing process is not finished until the size breakdown products have been removed from the fabric. This is best obtained by a subsequent detergent wash (with NaOH) at the highest possible temperature.

Desizing could be done in:

The process conditions for each are provided in table 3.

Table 3 : Process conditions

There are three enzymes Aquazym 120l, Aquazym Ultra 250l and Termamyl 60l. In this table only data on the aquazym and the aquazym-ultra are presented.

The enzyme is commercial available at Novo Nordisk.

Environmental and Economic Benefits:

Constraints:

The use of the enzyme depends on the kind of size. If there are chemicals used in the size to which the enzyme is not resistant then it is impossible to use the enzyme.

Contacts:

Type of Source Material; Articles, interviews.

Citation

1. SPIN document, textielveredeling, march 1993.
2. Novo Nordisk enzymes for the textile industry, desizing, dec.1991
3. Dorthe Marcher et al.,paper presented at the seminar on Sizing, Italy, march 1993.
4. A. Klingenberg, Textielchemicalien, Stichting Natuur en Milieu, Utrecht, 1986.

Industry/Program Contact and Address

Not available. No permission is asked to or given by the contact.

 

Abstractor Name and Address

Annelies den Braber, TME, Institute for Applied Environmental Economics

Grote Marktstraat 24, 2511 BJ The Hague

Netherlands

Tel: +3170-3464422; Fax: +3170-3623469

Review Status:

This case study was submitted to UNEP IE by the Institute for Applied Environmental Economics (TME) of the Netherlands on the part of the UNEP IE working group on Biotechnology. The case study was edited for the ICPIC diskette in August 1995. Subsequently a technical review of the case study was carried out by Dr. Prasad Modak, Environmental Management Centre, Mumbai, India.

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