• Cotton – Cotton fibres are the seed hairs of the plant Gossypium. They are usually off-white in colour although some varieties have been bred to incorporate a natural colour. Each fibre is formed by the elongation of a single cell from the surface of the seed. The word cotton is derived from it’s Arabic name pronounced kutan, qutn or qutan depending on the dialect.

Under a microscope , a cotton fibre appears as a very fine, regular fibre, looking like a twisted ribbon or a collapsed and twisted tube. These twists are called convolutions.

Almost half of the world’s requirements for textile fibres are met by cotton. It is grown in many parts of the world where a hot dry climate is to be found, the main producers being USA, the former USSR, China, India, Egypt, Africa and South America.

Cotton consists typically of between 88 to 96% cellulose with the rest being protein, pectic substances (congealed gum-like carbohydrates), ash and wax. After scouring and bleaching, cotton is then about 99% cellulose. The fibres are weakened and destroyed by acids but are resistant to alkalis.

The fibre length varies with the type and quality, within the range 10 to 65mm; the fibre diameter ranges from 11 to 22 ¼m. Cotton is a relatively strong fibre with a strength of 25 to 35 cN/tex and a breaking elongation of 7 to 9%. It is stronger when wet. Cotton also absorbs moisture readily, which makes cotton clothes comfortable to wear in warm weather (water retention of 50%, moisture regain of 7%).

Cotton fibre burns readily and is not inherently resistant to oxidising agents, and biodegradation, as well as acids. Despite these shortcomings cotton has a good wear life. Its properties can also be readily modified by chemical finishes which provide enhanced performance, e.g. crease resistance and flame resistance.

It is used in both 100% form and in blends with other fibres for household textiles and apparel. Synthetic fibres have largely replaced its use in industrial textiles.

The environmental impact of the cotton manufacturing process starts in the field with the fertilisers and insecticides used in the growing of the cotton plant. These have a direct impact on the land and the local flora and fauna. The US alone spends about 500 million dollars a year on pesticides for protection against the bollworm and other harmful bugs. These pesticides also have an effect on people living in the viscinity of cotton fields. Nausea, diarrhoea and throat irritation being the most common complaints. It is also interesting to note that the gas leak at Bhopal , India which killed over 3,000 people came from a pesticide used in the spraying of cotton crops.

The ginning or separation of the seed from the fibre is a dusty process that has serious health implications on cotton workers in developing countries, where the separation is carried out using traditional methods. The fibre is then packaged and transported across the globe. The production of natural fibres is conducted in many separate locations, transportation of the cotton bales has therefore a significant impact on the environment.

The spinning process introduces another set of significant impacts, producing more dust, noise and waste fibre and is also a relatively large consumer of electricity (as much as 2½ tonnes of oil per tonne of yarn). Relative humidity in the processing plant must also be controlled to minimise breakages, another consumer of energy. Weaving creates a similar set of impacts plus the added effect of using size and biocides has to be considered on the aqueous environment. Sizes are either natural, like starches or synthetic such as polyvinyl alcohol. The new sizes make weaving on the faster modern machinery a lot easier, but they have the drawback of being harder to biodegrade from the waste water.

Cotton preparation, that is singeing, desizing, scouring, bleaching and mercerising impacts on both the air and water. Singeing produces a dusty odorous emission, whilst the other preparative processes are the major contributors to BOD/COD in a textile effluent. There is also the problem of pentachlorophenol (pcp) on imported fabric which is washed out during preparation. This is an eco-toxic rot-proofing chemical with a very low discharge consent (maximum allowable concentration).

Cotton is by far the most popular fibre in use today, at least in terms of volume of production. The most widely used class of dyestuff on cotton are reactive dyes, which unfortunately are also the most poorly exhausted, producing a more coloured effluent. Colour consents on discharges have therefore been enforced in certain areas where there are significant numbers of cotton dyers.

The main pollution problem associated with cotton finishing processes is that of formaldehyde emissions from resin and other finishes. Low formaldehyde formulations have improved over the past few years but not far enough to eliminate the need for abatement on many stenters.

Attempts have been made to reduce the impact of cotton growing by eliminating pesticide use and by growing coloured strains of cotton so that the preparation and dyeing of the cotton is minimised. The bollworm can be eliminated by imposing a three month fallow period at the end of the growing season, and certain short fibre coloured cottons used by Indians in Central America have been cross bred with long fibre strains by a company in the US called Foxfibre. However, the amount of organic cotton grown in the US is still only a tiny fraction of the global output ( by the mid-1990’s, 80 cotton growing countries were producing about 85 million bales of cotton).


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