REGENERATED CELLULOSICS

Originally, the word rayon was appHed to any ceUulose-based man-made fiber, and therefore included the cellulose acetate fibers. However, the definition of rayon was clarified in 1951 and includes textiles fibers and filaments composed of regenerated cellulose and excludes acetate. In Europe the fibers are now generally known as viscose the term viscose rayon is used whenever confusion between the fiber and the cellulose xanthate solution (also called viscose) is possible. 

AH synthetic fibers are produced as continuous filaments, either as yams or tows. Yams are fine enough to be woven or knitted direcdy, but caimot be intimately blended with other fibers on the principal conversion systems used for cotton or wool. For these processes, staple fibers, made by cutting the much larger tows into short lengths, are needed. Tows can also be stretch broken into sHvers or tops, which can then be drawn out and twisted into spun-yams. 

The first successhil attempt to make textile fibers from plant cellulose can be traced to George Audemars (1). In 1855 he dissolved the nitrated form of cellulose in ether and alcohol and discovered that fibers were formed as the dope was drawn into the air. These soft strong nitrocellulose fibers could be woven into fabrics but had a serious drawback they were explosive, nitrated cellulose being the basis of gun-cotton (see Cellulose esters, inorganic esters). 

Sir Joseph Swan, as a result of his quest for carbon fiber for lamp filaments (2), learned how to denitrate nitrocellulose using ammonium sulfide. In 1885 he exhibited the first textiles made from this new artificial sHk, but with carbon fiber being his main theme he failed to foUow up on the textile possibihties. Meanwhile Count Hilaire de Chardoimet (3) was researching the nitrocellulose route and had perfected his first fibers and textiles in time for the Paris Exhibition in 1889. There he got the necessary financial backing for the first Chardoimet silk factory in Besancon in 1890. His process involved treating mulberry leaves with nitric and sulfuric acids to form cellulose nitrate which could be dissolved in ether and alcohol. This collodion solution could be extmded through holes in a spinneret into warm air where solvent evaporation led to the formation of soHd cellulose nitrate filaments. 

Although this first route was simple in concept, it proved slow in operation, difficult to scale up safely, and relatively uneconomical compared with the other routes. Denitration of the fibers, necessary to allow safe use wherever the fabrics may risk ignition, spoiled their strength and appearance. Nevertheless, Chardoimet earned and truly deserved his reputation as the Eather of Rayon. His process was operated commercially until 1949 when the last factory, bought from the Tubize Co. in the United States in 1934 by a Bra2iUan company, burned down. 

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