TEXTİLE TERMİNOLOGY

Konuyu word belgesi olarak indir

Textile Fibres and Terminology

Textile Fibres

• 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.

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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 μm. 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.

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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).

• Wool – The most important of the fibres of animal origin is wool, the hair of

the sheep (Ovis ales). The characteristics of wool fibres differ depending on

the breed and general condition of the sheep.

Wool, the hair of various breeds of sheep, is a warm springy fibre. It’s scaly

structure led in the past to unwanted felting (matting of fibres) and shrinkage

in laundering but modern finishing treatments have now overcome these

difficulties; similarly, attack by the clothes moth is no longer a problem.

In the UK alone there are 34 main breeds of sheep and a further 43 rare

breeds and hybrids. When wool fibres have been processed it is not possible

to say with confidence from what breed of sheep or country they have

originated because wool fibres from several breeds have the same

microscopical appearance. There are four main types of wool fibre: fine,

coarse, outercoat and kemps. Each type has a characteristic scale pattern so

that it is possible to distinguish between types, although it is not possible to

assign a type to a breed of sheep.

Wool fibres are generally white, with the finer fibres having a circular cross

section and the coarse fibres being more irregular in contour. Kemp fibres are

usually chalky white in appearance, very coarse and brittle, with a long

tapering tip and a taper over a short distance to the root end.

An important aspect of the environmental impact of wool processing is the use

of pesticides on sheep. Although the problem has been minimised over recent

years with the introduction of tighter restrictions or even bans on the use of

some formulations, this is still a major concern since these toxic chemicals

make their way into rivers.

Another impact at this early stage which is maybe less obvious, is the

methane generated globally by the many hundreds of millions of sheep.

Methane is a powerful greenhouse gas and contributes to the effect of global

warming.

Again, as with cotton there is also the effect of transporting huge quantities of

textiles across the globe with the associated fuel usage and fume generation

problems.

The scouring of the raw wool, the next stage, is a process which produces a

liquid effluent with a very high organic load and solids content and varying

levels of pesticide contamination. The highly polluting nature of this waste and

the strict discharge consents associated with the process means that scourers

have to treat their effluent on-site.

Another environmental problem is that many of the dyestuffs available for

obtaining good dark shades on woollen fabric or yarn are mordant dyes

containing chromium. The discharge of chromium is strictly controlled and so

companies are being forced into using alternatives or consider on-site effluent

treatment.

In the carpet industry permethrin, another pesticide, is added to the yarn that

goes into making contract carpets, this is a quality requirement to protect the

wool from moth attack. The effluent from this process must therefore be

treated and continually monitored.