Методические указания и контрольные задания для судентов-заочников
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S I L KSilk, the only natural animal fibre that does not grow from the skin as a protective covering, is extruded as a long continuous filament by the silkworm. Silk filaments are extruded by the silkworms in spinning their cocoons. The spinning begins by the insect making first an outer network and then winding the silk in a continuous thread around its body. The operation of spinning occupies about five days, during which time the insect usually produces from 2,000 to 3,000 feet of silk. Within 10 - 12 days after completion of the cocoon, the enclosed insect is ready to emerge. After moistening one end of the cocoon with enzymes that partially dissolve the fibres the moth pushes aside the filaments and emerges from the cocoon, lays its eggs and dies. In performing this operation the insect cuts the silk filament making it unsuitable for application. When microscopically examined, silk is seen to consist of two blended strands. These are produced by special glands which extend nearly the whole length of the body. The silk filament being so fine makes it necessary to reel together several filaments in order to obtain a thread of sufficient size. This is done in large factories called filatures. Here the cocoons are placed in basins of hot water near the boiling temperature. The hot water softens the gum which covers the silk filament and sets the fibre free. After the end of the silk fibre being found the cocoons are reeled off into hanks. A single cocoon of good quality may furnish from 400 to 800 yards of reelable filament. Silk that has been reeled is known as raw silk. The damaged cocoons and the parts of each cocoon which cannot be reeled are known as waste silk. Waste silks are combed and spun into spun silk. Owing to the outstanding properties (high strength, lustre, elasticity and beauty) silk can be successfully used for the production of different kinds of clothes and for industrial purposes. THE HISTORY OF MAN-MADE FIBRESThe first person to visualize the possibility of making an artificial fibre by a process similar to the spinning of the silkworm was Robert Hooke, an English scientist. He included a discussion of the subject in his book "Micrographia", published in 1665, no concrete developments along these lines having occurred, however, until the middle of the 19th century. In 1842 an English silkweaver, Louis Schwabe, exhibited a machine for making artificial filaments. This machine used nozzles with fine holesthrough which the liquid was forced in order to form filaments, this being the principle of spinnerets used today. Schwabe spun his filaments of glass, but was not satisfied with the product and appealed to British scientists to discover a better material from which to manufacture filaments. A further development preparing the way for man-made fibres was the discovery of nitrocellulose by C.F.Schonbein, a Swiss chemist, in 1846. In 1855 Audemars of Lausanne took matters a liuttle further.He obtained nitrocellulose from mulberry twigs and dissolved it in a mixture of ether and alcohol with caoutchouc. From the mass that resulted he drew, with a steel needle, threads that solidified in air, and finally wound them on a spool. This process is described in British Patent 283 of 1855. But it was too early then for the process to be developed practically. The development of man-made fibres as a textile really began with the work of Count Hilaire de Chardonnet (1839-1924) who is often called the "father of the rayon industry", rayon being a man-made fibre based on cellulose. He produced his first fibre by what became to be known as nitrocellulose method in 1884. The development of rayon represented the first big break fromnature in the production of fibres. Rayon being based on naturally occurring fibrous material (cellulose), the fibre cannot be considered as true man-made fibre.Rayons are made by alteration of natural fibrous substance (cellulose). Further research became centred in producing fibrous material that cannot be found in nature. It was discovered that chemically fibrous material was composed of long-chain molecules. These were eventually synthesized from simple materials (coal,water and air). A well-known example of synthetic fibres is nylon. It originated in the laboratories of E.I. du Pont de Nemours & Co.in 1927. It was first introduced to the public in 1938 as bristles in tooth brushes. In 1939 hosiery knitted of nylon yarn was produced in limited scale. In 1940 nylon hosiery was offered to the public on a national scale. The emergence of synthetic fibres means that it is now possible to produce entirely new fibres with desired combinations of properties. |
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