COTTON

COTTON

Post 330 ⇒   by Gautam Shah 

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Cotton is the most widely used natural fiber, belonging to a cellulosic group. It is obtained as the seed hair of the cotton plant. Cotton is classified into three categories depending on the length of its fibers. Short staple fibers (9-19 mm) are used for filling in mattresses and spinning ropes and threads for floor spreads, etc. Intermediate-staple fibers (20- 32 mm) are used for weaving medium course fabrics like jeans, etc. and utility clothes such as bed sheets. Long staple fibers (more than 32 mm) are used for weaving fine fabrics like Sarees and Dhotis (both Indian wears), Lawn, Cambric, inner garments, knitwear, etc. Length of a cotton fiber is 1000 to 3000 times its diameter. Very short cotton fibers that stick to the seeds are called cotton linters, and these are not spun into yarn for weaving, but used in pressed cotton felt for bedding and upholstery, and in the production of paper and rayon. Cotton linters are treated with Nitric acid to produce ‘Gun Cotton’, used in explosives as raw material and for production of Nitro Cellulose or NC lacquers.

Cotton balls on Plant

Cotton fibers, at microscopic level, are ribbon like flat, and have a natural twist which helps the spinning and makes a strong thread. Cotton fibers have micro hairiness which traps air and moisture providing a warmth and capacity to absorb perspiration. The trapped air and the moisture absorption, together keep the body cool and comfortable. The hairy textures of the fiber are enhanced by brushing or teasing, and thereby increase the texture and capacity to trap air. Too much teasing can make break the fiber and make it weak. Teased fibers make a fabric dull and with poor wear-tear characteristics. Short staple and teased fibers make good mopes and cleaning or wiping clothes. Very Long staple cottons are now grown now as Hybrid varieties. These can be spun to very fine yarn and ultimately very fine quality fabrics. These fibers are also mixed with the rayon and polyesters or co-spun with synthetics filaments. Cotton fibers get easily creased, which can be flattened by ironing, calendering or chemical treatments.

Cotton Traders in Bombay -covered hand deals

Cotton fiber is easy to grow, separate, spin, weave, dye and print. Earliest use of Cotton has been traced to nearly 5000 BC. Cotton was grown in Indus valley area. Cotton cultivation was more common in tropical areas. Cotton grows into balls, which open out and swell when weather turns warm. The cotton balls are de-seeded in press called Gin. The fibers are separated, carded and combed to align them before spinning. Several spun yarns, are often spun again to form threads. The threads are used for sewing, knitting work crochet, rope making and for use as warp (long direction yarn in a woven fabric compared with weft).

Warp yarn beams for weaving

Cotton fibers are covered with a natural wax like substance. The wax gets removed on repeated washing, hot water soaking or with alkali treatment. The natural wax gives some water repellence, an ideal quality for mattress fill-in cottons. The natural wax containing cotton fabric (unwashed or treated) is called a Grey Cotton Textile. The grey fabric is of natural off-white shade whereas the washed or treated fabric is whiter or variously called bleached fabric. The grey fabric is preferred by designers for tapestry or curtains. In the first case due to its moisture and stain resistance, and in the second case due to its capacity to filter the sunlight to warm shade. Bleached or washed cotton fabrics absorb dyes or print colours well.

Carding or separation of Cotton fibers

Yarn spinning

Weaving Loom

Cotton fabrics tend to shrink substantially, when soaked or washed for the first time. This is due to the relaxation of natural curls in the fibers. Fabrics for apparel making, dyeing and printing are pre-washed or adequately shrunk beforehand to stabilize the structure.

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