Additional information to finishing of cotton and bast fibres

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1. DESCRIPTION OF TECHNIQUES, METHODS AND EQUIPMENT


Mills finishing woven fabric consisting mainly of CO and/or CV

Woven fabric consisting mainly of cotton and cotton blends is finished on semi-continuous/continuous lines or in discontinuous mode mainly depending on the size of the lot. Pretreatment operations such as desizing, scouring and bleaching are very often combined in one single step in continuous lines. Pretreatment of viscose usually requires alkali treatment and washing only, providing that the sizing agents are water-soluble, which is normally the case.


Process sequenz for the finishing of woven fabric.jpg


In addition to the processes mentioned in Figure 2.44, further treatments may be exceptionally applied, such as pretreatment with liquid ammonia (carried out at a very few sites in Europe only).


2. NEW TECHNOLOGIES


a) Changes in the process


1.) Plasma treatment

2.) Enzyme catalysed finishing treatment:

Main enzymatic processes already in use or currently emerging in the textile sector for cotton:


Enzyme catalysed finishing treatment.jpg


3.) Reduction of water consumption

Water consumption often goes along with energy consumption in textile industry, because water is heated up in a large scale for the process baths.

The following specific water consumption levels are considered achievable using certain measures:

  • finishing of woven fabric consisting mainly of cellulosic fibres ……50 – 100 l/kg
  • finishing of woven fibres consisting mainly of cellulosic fibres (including vat/or reactive printing) ………………………………………………………………… < 200 l/kg

For information on water reduction measures see “Finishing” in general.


4.) Formaldehyde-free or formaldehyde-poor finishing agents

Easy-care finishing is mainly carried out on cellulosic fibres and their blends in order to increase the crease recovery and/or dimensional stability of the fabrics.

Easy-care finishing agents are mainly compounds synthesized from urea, melamine, cyclic urea derivates and formaldehyde. Cross-linking agents (reactive groups) are composed of free or etherificated N-methylol groups.


Chemical structure1.jpg


Chemical structure2.jpg


Formaldehyde-based cross-linking agents may release free formaldehyde. Formaldehyde is thought to be carcinogen and is a threat to the workforce (formaldehyde can also be released for example, during cutting operations). The presence of free formaldehyde or partly hydrolysable formaldehyde on the finished fabric also represents a potential risk for the final consumer. The European Eco-label scheme sets a threshold of 30 ppm for production that come into direct contact with the skin.

Low-formaldehyde or even formaldehyde-free products are an alternative.


Overview of formaldeyhde.jpg


Main achieved environmental benefits

With low-formaldehyde or formaldehyde-free products, a reduction of formaldehyde emissions in finishing is achieved. Formaldehyde residues on the textile can be minimised (<75 mg/kg textile, or even lower than 30 ppm for consumer requirement). With optimised catalysts, curing temperature and therefore energy consumption can be reduced.

Operational data

A typical recipe for low-formaldehyde finishing of cotton (woven fabric) is:

  • 40 – 60 g/l cross-linking agent
  • 12 – 20 g/l catalyst
  • liquor pick-up: 70%
  • drying and condensation (150°C, 3min)

A typical recipe for a formaldehyde-free finishing of cotton is:

  • 80 – 120 g/l cross-linking agent (integrated catalyst)
  • liquor pick-up: 80%
  • acidifying with acetic acid
  • drying and condensation (130°C. 1min)

Cross-linking compounds are often applied in combination with wetting agents, softeners, products which increase rip-resistance etc.

Source: BAT in textile industry, 2003


b) Changes in the heat supply system

No information is available.

c) Changes in the energy distribution system

No information is available.


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