- 1 Varieties of Cotton Fibre
- 2 Production Of Cotton Fibre
- 3 Recent Developments in Cotton Fibre
- 4 Application of Cotton Fibre
- 5 Important Properties of Cotton fibres
- 6 Did You Know?
Cotton fibre, the purest form of cellulose found in nature is the seed hair of the plants of the genus Gossypium.
Archeologists found that it was grown and used for textile purposes in the Indus Valley well before 2100 B.C., and in Mexico by 3500 B.C.
Cotton fibre has been of service to mankind for so long that its versatility is almost unlimited and new uses are constantly being discovered.
Cotton fibre is called as KING OF fibreS in the textile world.”
Cotton is usually off-white in color although some varieties have been bred to incorporate a natural color.
Each fibre is formed by the elongation of a single cell from the surface of the seed. The word cotton is derived from its 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 the USA, the former USSR, China, India, Egypt, Africa, and South America.
Varieties of Cotton Fibre
Different kinds and types of cotton are grown in various parts of the world.
Variation among cotton fibres occurs because of growth conditions including such factors as soil, climate, fertilizers, and pests. The quality of the cotton fibre is based on its color, staple length, fineness, and strength.
Usually, longer fibres are finer and stronger. The particular kind of cotton is often identified by the name the country or geographical area where it is produced.
Though many species of cotton are grown commercially, they may be conveniently divided into three types.
There are three basic classes of cotton
These are the top quality types with a staple length of between 30 and 65mm.
They are the finest, strongest, softest and most expensive cotton and are used for the finest types of fabrics and sewing threads.
Some well known long-staple cottons are Sea Island and Egyptian.
The long-staple kinds of cotton are 29 mm or longer and are grown in the high-altitude areas of the Southwest.
The cotton grown in the San Joaquin Valley of California has a staple length from 28-29 mm and is stronger than the other Upland kinds.
American Pima cotton is grown in Arizona, Texas, New Mexico, and California. Total U.S. production for 2000 was 389,100 bales.
Pima S-7 remained the leading variety in Pima-growing regions accounting for about38% of planted acreage.
Other varieties include Phytogen 57 (30%), HTO (20%), White Pima (2%) Pima S6 (8%), and Conquistador (15%).
The average staple length of the 2000 crop was 45.8 (1.3 in.); micronaire averaged 4.1; 81% was Grade 2 and better.
Egyptian cotton fibres are light brown, fine strong and 32-38 mm in length. They are used in the same application as American Pima.
These form the largest class comprising more than 50% of cotton and are dominated by the American types. The staple length ranges from about 20 to 30mm. These are not as good as the long-staple type but are cheaper and more abundant.
These are lower grade cotton, with a staple length of less than 20mm. They are coarser, and harsher than medium-staple cotton and are used in the lower quality fabric.
Major Cotton producers at the present time are China, the USA, India, Pakistan, Uzbekistan; other countries producing small but not insignificant quantities include Brazil, Turkey, Mexico, Egypt, and Sudan.
At present, the four largest exporters of cotton in the world are the USA, Uzbekistan, Franc-zone Africa, and Australia.
American Upland cotton fibres are fairly white, strong, and dull and range in staple length from 22-32 mm. The Upland cotton is usually categorized as short-staple, medium-staple and long- a staple.
The short staple is less than 25 mm and is produced in Oklahoma and central and West Texas. The medium- staple cotton are 25-28 mm in length are produced in the Southeast, the Mississippi Valley, and the low valleys of Arizona and California.
Production Of Cotton Fibre
Cotton requires about two hundred days of continuous warm weather with adequate moisture and sunlight, frost is harmful to the plant.
Usually in March or April selected cotton-seeds are planted. The flowers in cotton plants appear in June or July and the cotton is usually ripe for gathering between August and October.
The seasons may differ in the different places of the world. As the flower withers, it is succeeded by a closed pod. This contains seeds which are wrapped up in young actively-growing hairs. Each cottonseed may produce as many as 20,000 fibres.
When the seeds are nearly ripe the pod burst open and the cotton hairs project, forming a white fluffy mass called a cotton ball.
During this period, the plant is subject to attack by many insects. Insecticides are sprayed to protect the plants at this stage.
The fibres are now exposed to the sun when they complete their ripening, and the cell gradually dries up, leaving the cotton in a fit state for harvesting.
The ripe bolls having matured fibres are picked by machines in developed countries and by hand in developing countries.
Mechanical picking, a faster and cost-effective method of harvesting, has some disadvantages as machine picks the immature bolls, as well as leaves, stem fragments with the matured bolls.
On the other hand higher grade of cotton is obtained by a selective and good hand picking. An expert picker can easily trace out the matured bolls and does not pick leaves or stem fragments with it.
This method is slower and the most expensive in developed countries but better for developing countries.
After the crop has been gathered the fibres are separated from the seeds by a process known as ginning. Gins may be classified into two types
- the saw gin and
- the roller gin.
A saw gin consists of a series of circular saws having specially shaped teeth and used mainly for short and medium staple cotton.
Modern gins have 80-120 saws mounted on a long, horizontal shaft at suitable intervals. Seed cotton is fed through a hopper and the saws operate against it as the fibres known as lints become separated from the seed.
In a roller gin, a knife jerks the seed from the fibre while the latter is pulled away between a roller and a fixed knife. McCarthy gin is a special type of roller gin.
Roller ginning which is often preferred for longer fibres is a slower and more costly process.
Cotton linters are the short, fuzzy hair-like fibres that remain on the seeds after ginning has been done. The cotton linters are removed by a second ginning process.
They are used in the manufacture of viscose rayon and acetates, plastics, shatterproof glass, photographic film and for other purposes
After ginning, the lints are compressed into rectangular bales, which are covered with jute or polypropylene bagging and bound with iron bands.
The bales generally weigh about 480 or 500 pounds each. These bales are then sent to the yarn manufacturing mills.
The assessment of cotton is carried out traditionally by the cotton classes, who depend upon the personal skill and long experience judging cotton quality by inspection and feel. The assessment is based on
(1) the staple length,
(2) the color and
(3) the amount of impurity in the cotton.
The classes work usually by a hand- examination of the cotton. Staple length is judged by taking a sample and pulling it to display a filmy web of fibre.
Recent Developments in Cotton Fibre
At present, there is a growing interest in naturally colored cotton and organic cotton because of the public’s rising interest in environmental issues.
Naturally colored cotton is usually shorter, weaker and finer than regular upland cotton while the fibre properties of organic cotton are in the normal range for conventional cotton.
Lower yields and increased processing waste due to poorer fibre quality are offset by a premium in market price. However, the production and supply of these specialty cotton is limited.
Recently, a genetically engineered pest-resistant cotton was developed in Australia. This cotton variety protects cotton plants from the boll caterpillar which has developed powerful resistance to chemicals.
Organic Cotton Fibre
Attempts have been made to reduce the impact of cotton growing by eliminating pesticide use and by growing colored strains of cotton so that the preparation and dyeing of the cotton is minimized.
The bollworm can be eliminated by imposing a three-month fallow period at the end of the growing season, and certain short fibre colored cotton used by Indians in Central America have been crossbred 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.
Application of Cotton Fibre
The wide range of wearing apparel like blouses, shirts, dresses, children wear, active wear, jackets, skirts, pants, sweaters, hosiery, neckwear.
Curtains, draperies, bedspreads, comforters, throws, sheets towels, table cloths, table mats, napkins.
Important Properties of Cotton fibres
Chemical Properties Of Cotton Fibre
- Effects of Acids
Cotton fibre gets Disintegrated by hot dilute acids or cold concentrated acids and it is Unaffected by cold weak acids.
- Effects of Alkalis
Swelling (mercerization) in caustic, but no damage to the cotton fibre
- Effect of Organic Solvents
Cotton is resistant to most common industrial and household solvents
- Effects of Other Chemicals
Bleached by hypochlorites and peroxides; oxidizes into oxy-cellulose. Cotton swells and disintegrates in cuprammonium hydroxide.
- Effect of Heat
Highly resistant to thermal deformation and degradation, an onset of decomposition in air (TGA) 5500F. Safe hot-plate (ironing) temperature 4250F yellows after 5 hours at 248 F.
Physical Properties of Cotton Fibre
- Breaking Tenacity (gf/tex) (gf/den)
Standard – 27-44gf/tex Standard -3.0-4.9 gf/den
Wet 28-57 gf/tex Wet 3.3-6.7 gf/tex
- Sunlight and Mildew Resistance
Excellent resistance to sunlight. Fabrics subjected to excessive mildew are laundered to minimize residual effects.
- Specific Gravity
Cellulosic polymer – 1.54
Cotton fibre- 1.27
- Moisture Regain
7% (under standard conditions).
- Moisture Absorbency
24-27% at 95% Relative Humidity.
- Breaking Elongation
standard breaking elongation- 3-9.5%
- Elastic Recovery
74% recovery after 2% elongation.
45%recovery after 5% elongation.
Upon ignition, fibre leaves fine gray ash and no bead.
Longitudinal appearance is flat and ribbon-like with convolutions.
Dissolves in 80% cold sulfuric acid.
- Average Toughness
- Dyes Used
Direct, vat, azoic, mordant, pigment, sulfur, reactive, etc.
- Tensile Strength (psi)
- Average Stiffness