Fibers, Synthetic
Uses for synthetic fibers range from nylon stockings and clothing to cables and tire reinforcement. Synthetic fibers are made from polymers that are either melted into a solution by heat or dissolved by a solvent. The solution is then passed through a metal plate with fine holes, called spinnerets. This process forms the polymers into strands. The fibers are then either cooled or passed through a jet of air to allow the solvent to evaporate. Most fibers at this point are subjected to cold drawing, a strengthening technique developed by Wallace Carothers' team in its search for artificial silk. After drawing, the fibers are washed, dried, dyed, and woven.
The first patent for synthetic fiber was granted to George Audemars in 1855. A related patent was granted to Sir Joseph Swan (1828-1914) in 1880. Both of these men produced fibers from cellulose, which, unfortunately, were not very strong.Hilaire Comte de Chardonnet later found that by denitrating the fibers he could strengthen them until they were as durable as silk. Edward John Bevan (1856-1921) and Charles F. Cross developed the industrial production process for this material, which he called rayon. In the modern production process, rayon is prepared by subjecting a solution of cellulose to chemical reaction, aging, or solution ripening; followed by filtration and removal of air, spinning the fiber, combining the filaments into yarn, and finishing (bleaching, washing, oiling, and drying). Strength is achieved by orienting rayon molecules when they are made. Hydroxyl groups in the cellulose molecule cause rayon to absorb water; in the dry state the fibers are hydrogen bonded, and dry rayon retains its strength even at high temperatures.
Acrylonitrile, which was produced by Charles Moureau (1863-1929) in 1893, is used in the production of nitrile rubber, acrylic fibers, insecticides, and plastics. The fibers formed by acrylonitrile are unstable at their melting point, so melt extrusion is impractical. Solution spinning was not possible for many years because no appropriate solvent had been found. Today cold drawing is used to strengthen the fibers by orienting the molecules and allowing hydrogen bonding to occur. The fibers are then dried and woven into a fabric that resembles soft wool, which is used for sails, cords, blankets, and clothing.
Nylon 66 is a polyamide based on hexamethylene diamine and adipic acid. Nylon 6 is based on caprolactam. Nylon was developed by DuPont Company researchers as a substitute for silk. Carothers and his team of assistants had been researching long chain polyesters and polyamides. In 1938 they had almost given up hope on finding a suitable fiber when two members of the team discovered cold drawing. Nylon is used in clothing, laces, toothbrushes, sails, fish nets, and carpets. It is resistant to alkalis, molds, solvents, and moths; but damaged by strong acids, phenol, bleaches, and heat above 338°F (170°C).
John R. Whinfield and J. Dickson continued Carother's research and made a polyester with terephthalic acid in 1941. The fiber was christened Terylene and marketed as Dacron in the U.S. by the DuPont Company. Acrilan, produced by the Chemstrand Corporation, is an acrylic fiber used in fabrics and may be blended with wool or cotton to form clothing, carpeting, linens, draperies, and upholstery. Fabrics made from Acrilan resist mildew, moths, and wrinkling. They also tend to dry quickly. Dacron polyester is resistant to weak acids and alkalis, solvents, oils, mildew, and moths; it is damaged by phenol, and heat above 338°F (170°)C.
Orlon, which is an acrylic fiber containing at least 85% acrylonitrile units, is a class of synthetic fibers first produced commercially by the DuPont Company in 1950. The fibers vary in size, texture, and ability to hold dyes. They can be woven or knitted, usually into bulky garments. Orlon is made by dissolving acrylonitrile in an organic solvent, then filtering the solvent and dry-spinning the fibers, and finally drawing the fibers. Orlon is used in upholstery and carpets. It is resistant to dilute acids and alkalis, solvents, insects, mildew, and weather; it is damaged by alkalis and acids, heat (above 356°F [180°C]), acetone, an d ketones.
Vinyon filaments and fibers were developed by the Carbide and Carbon Chemicals Corporation, which licensed American Viscose Corporation to produce them in 1939. The fiber is a copolymer of 88 % vinyl chloride and 12 % vinyl acetate. It was the first plastic fiber produced on a large scale in the United States. The fibers are stretched in a process similar to cold drawing. The stretching increases the strength of the fibers but lowers its elasticity. The fiber does not take dyes and becomes sticky if heated to over 149°F (65°C). At 167°F (75°C), garments made of the fiber will shrink. Further research led to the development of a fiber Vinyon N, which is a copolymer of vinyl chloride with acrylonitrile. For fibers, the copolymer ranges from fifty-six to sixty percent copolymerized vinyl chloride. It was patented in 1947.
Kevlar is a polyamide fiber developed by Stephanie Kwolek of DuPont in 1965. Kevlar is a polyamide in which at least 85 wt% of the amide linkages are directly attached to two aromatic rings. Its molecular structure of alternating aromatic rings and amide groups crosslinked by hydrogen bonding makes it incredibly strong. Kevlar's lightweight and high strength make it very marketable. It is commonly used to make bulletproof vests, heavy duty conveyor belts, and composite structures; and to reinforce radial tires.
Other important synthetic fibers based on high polymers (i.e., macromolecules) include acetate (consisting of esters of cellulose, but not regenerated cellulose); spandex (segmented polyurethanes); vinyls and vinylidenes (copolymers of vinyl chloride, and vinylidene chloride or vinyl acetate); fluorocarbons (long chain molecules with bonds saturated by fluorine); olefins (at least 85 wt% ethylene, propylene or other olefin other than amorphous rubber olefins); vinal (at least 50 wt% of vinyl alcohol units in a long polymer chain); and azlon (any regenerated naturally occurring protein).
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