SYNTHETIC FIBRES. The commercial production of synthetic textile fibres has been a development dating from about 189o. The first in the field, and by far the most important today, is rayon, but within the decade of the 193os many other types of synthetic fibres have been developed. All of these man-made fibres are produced either in the form of filament yarn (con tinuous parallel strands, similar to silk) or as staple fibre (short, uniform-length fibres to be spun into yarn in the same manner as cotton or wool). The following classification includes the great majority of the synthetic fibres known in 1940: Rayon.—All synthetic fibres made from a cellulose base are known as rayon. This includes yarn composed of chemical corn pounds of cellulose (cellulose acetate or ethyl cellulose rayon), as well as yarn of regenerated cellulose (viscose, cuprammonium, and nitrocellulose rayon). A full discussion is given in the follow ing section on rayon.
Natural Protein-Base Fibres.—One large group of synthetic fibres is made from a natural protein base (compared with the cellulose base of rayon). Commercial production of fibres in this group has been primarily of the type made from milk casein. Italy has led in the development and production of casein-base textiles during the past several years, but they were also manu factured commercially (194o) in Germany, Great Britain, Bel gium, and Holland.
These casein-base fibres have a chemical composition almost identical with wool, with the exception of a lower sulphur con tent. The fibres may be very fine and soft, or a harsh texture similar to coarser wools may be produced by modifications in the manufacturing process. The dyeing reactions of casein-base fibres are the same as those of wool, which is a great advantage in blending these two fibres. Casein-base fibres are usually manu factured in staple fibre form, rather than in continuous filaments, and are used principally in combination with wool. The lack of resiliency in casein fibre, as compared with wool, and its low wet strength make blending with wool desirable.
Also in this category of protein-base synthetic fibres is "re generated silk," which is made in Japan and Germany by dissolv ing silk noil or waste silk and spinning filaments from this solution.
Various other protein-base fibres have been reported, although they are not as yet commercially important. Protein from the
soybean is being converted into a textile fibre in both Japan and the United States, while experiments are also being conducted in the United States on the production of a synthetic fibre from zein, a corn protein. Fish protein and waste animal skin, leather, and muscle tissue have been utilized for fibre production in Ger many and Japan, the fibres made from muscle tissue being used principally for surgical purposes.
Synthetic Protein-like Fibres.—Another group of fibres are those made from coal, water, and air. The generic name of nylon has been given to this group, which is described as synthetic fibre-forming polymeric amides having a protein-like chemical structure.
Nylon was developed in the United States and was put into commercial production in 1939. Unusual strength and elasticity are claimed. Up to 1940 this yarn was used for hosiery and knit gloves, fish lines, surgical sutures, and, in the form of single large filaments, as bristles for tooth-brushes, etc. Other outlets will undoubtedly be developed as nylon comes into full commer cial production.
Synthetic Resin Fibres.—A second group of completely synthe tic fibres (no natural vegetable or animal base) are the vinyl and amyl resins developed in the United States and Germany.
Commercial production of the vinyl type of resin fibre was be gun in the United States in 1939. In 194o this fibre was being used mainly for filter cloths and similar industrial purposes where its low water absorption and resistance to chemicals is a partic ular advantage. Other qualities of this yarn, such as high wet strength, fire resistance, resistance to mildew, and elasticity, make it suitable for many specialized uses, including fish nets and lines, sails, tents, hosiery, fireproof draperies, etc., as well as ordinary textile purposes. The thermoplastic quality of this vinyl resin fibre has suggested its use with wool to give a fabric which will hold a crease, and its use in run-resistant knit goods. This same quality causes fabrics of this yarn to shrink when heated above a certain temperature. Thus these fabrics must not be washed in very hot water nor ironed with a hot iron.