Cotton fibre processing
Cotton fibres may be classified roughly into three large groups, based on staple length (average length of the fibres making up a sample or bale of cotton) and appearance. The first group includes the fine, lustrous fibres with staple length ranging from about 2.5 to 6.5 cm (about 1 to 2.5 inches) and includes types of the highest quality—such as Sea Island, Egyptian, and pima cottons. Least plentiful and most difficult to grow, long-staple cottons are costly and are used mainly for fine fabrics, yarns, and hosiery. The second group contains the standard medium-staple cotton, such as American Upland, with staple length from about 1.3 to 3.3 cm (0.5 to 1.3 inches). The third group includes the short-staple, coarse cottons, ranging from about 1 to 2.5 cm (0.5 to 1 inch) in length, used to make carpets and blankets, coarse and inexpensive fabrics, and blends with other fibres.
Most of the seeds (cottonseed) are separated from the fibres by a mechanical process called ginning. Ginned cotton is shipped in bales to a textile mill for yarn manufacturing. A traditional and still common processing method is ring spinning, by which the mass of cotton may be subjected to opening and cleaning, picking, carding, combing, drawing, roving, and spinning. The cotton bale is opened, and its fibres are raked mechanically to remove foreign matter (e.g., soil and seeds). A picker (picking machine) then wraps the fibres into a lap. A card (carding) machine brushes the loose fibres into rows that are joined as a soft sheet, or web, and forms them into loose untwisted rope known as card sliver. For higher-quality yarn, card sliver is put through a combing machine, which straightens the staple further and removes unwanted short lengths, or noils. In the drawing (drafting) stage, a series of variable-speed rollers attenuates and reduces the sliver to firm uniform strands of usable size. Thinner strands are produced by the roving (slubbing) process, in which the sliver is converted to roving by being pulled and slightly twisted. Finally, the roving is transferred to a spinning frame, where it is drawn further, twisted on a ring spinner, and wound on a bobbin as yarn.
Faster production methods include rotor spinning (a type of open-end spinning), in which fibres are detached from the card sliver and twisted, within a rotor, as they are joined to the end of the yarn. For the production of cotton blends, air-jet spinning may be used; in this high-speed method, air currents wrap loose fibres around a straight sliver core. Blends (composites) are made during yarn processing by joining drawn cotton with other staple fibres, such as polyester or casein.
No one knows exactly how old cotton is. Scientists searching caves in Mexico found bits of cotton bolls and pieces of cotton cloth that proved to be at least 7,000 years old. They also found that the cotton itself was much like that grown in America today.
In the Indus River Valley in Pakistan, cotton was being grown, spun and woven into cloth 3,000 years BC. At about the same time, natives of Egypt’s Nile valley were making and wearing cotton clothing.
Arab merchants brought cotton cloth to Europe about 800 A.D. When Columbus discovered America in 1492, he found cotton growing in the Bahama Islands. By 1500, cotton was known generally throughout the world.
Cotton seed are believed to have been planted in Florida in 1556 and in Virginia in 1607. By 1616, colonists were growing cotton along the James River in Virginia.
Cotton was first spun by machinery in England in 1730. The industrial revolution in England and the invention of the cotton gin in the U.S. paved the way for the important place cotton holds in the world today.
Eli Whitney, a native of Massachusetts, secured a patent on the cotton gin in 1793, though patent office records indicate that the first cotton gin may have been built by a machinist named Noah Homes two years before Whitney’s patent was filed. The gin, short for engine, could do the work 10 times faster than by hand.
The gin made it possible to supply large quantities of cotton fiber to the fast-growing textile industry. Within 10 years, the value of the U.S. cotton crop rose from $150,000 to more than $8 million.