Rayon from cellulose nitrate

The principal chemical iadustry based on wood is pulp and paper. In 1995, 114.5 x 10 metric tons of wood were converted iato - 60 x 10 metric tons of fiber products ranging from newsptint to pure cellulose ia the United States (1,76). Pure cellulose is the raw material for a number of products, eg, rayon, cellulose acetate film base, cellulose nitrate explosives, cellophane, celluloid, carboxymethylceUulose, and chemically modified ceUulosic material. 

There was significant interest in developing commercial processes based on phenolic resins in the 1890-1910 era. By this time, cellulose nitrate, vulcanized rubber, and viscose rayon had all found places in commerce [24]. Smith patented processes for manufacture of commercially useful molded articles from phenolic in 1899-1900 [2,25-28]. His products were made with phenol, paraldehyde (2,4,6-trimethyl-1,3,5-trioxane) or parafonnaldehyde, and additives in the presence of HCl at elevated temperatures. 

Since bacterial cellulose from all suitable carbohydrate substrates i8 identical with natural cellulose, its industrial importance20 is obvious. Relatively large amounts of bacterial cellulose were produced in Germany during the first World War. More recently products similar to parchment, mercerized cotton, cellulose nitrate,21 acetate14 and viscose rayons have been produced from bacterial cellulose. 

Cellulose acetate has replaced cellulose nitrate in many products, for example, in safety-type photographic films. When a solution of cellulose acetate in acetone is passed through the fine holes of a spinneret and the solvent evaporates, solid filaments are produced. Acetate rayon is prepared from threads of these filaments. Some applications and solvents of commercial cellulose acetate grades are summarized in Table 9-5. 

Artificial silk was first produced from cotton waste in the early 1900s. Three Englishmen are credited with discovering how to produce viscose (rayon) from a cellulose solution using wood and woody materials. During World War I, this process was used to make guncotton (by nitrating the cellulose) and other explosives. The rayon was also used as artificial silk. Special dyes, now known as acid dyes, had to be developed to color this product. 

The early history of polymers is really the conversion of natural polymers into useful materials. Examples include the vulcanization of rubber (Goodyear, 1839), celluloid (which is plasticized cellulose nitrate—Hyatt, 1868), and cellulose-derived fibres, e.g. cuprammonia rayon (Despeisses, 1890) and viscose rayon (Cross, Bevan and Beadle, 1892). The first truly synthetic polymer, that is, one made from laboratory chemicals, was Bakelite (Bakeland, 1907). This was made from phenol and formaldehyde. Bakeland probably did not know the chemical structure of the Bakelite, but he did realize that organic chemicals containing multiple functionality yielded insoluble materials. The various phenol-formaldehyde resins (PF), e.g. Bakelite and novolacs, were thus obtained in an empirical manner. 

Uses of pulp 95% of all pulps are paper pulps , used for paper and board production, from the rest, the dissolving pulps , chemicals are made like viscose (cord rayon, modal fibers, cellulose guts, cellulose films, acetyl cellulose) or cellulose derivatives (cellulose ethers, cellulose nitrates, methyl cellulose, carboxy cellulose). The requirements concerning quality differ considerably from one application to the other. 

Viscose rayon is produced by extruding a solution of cellulose xanthate, produced from "soda cellulose and carbon disulfide, into dilute acid, which breaks down the cellulose xanthate and reprecipitates the cellulose in a form suitable for spinning. Acetate rayon is produced by extruding a solution of cellulose acetate the organic solvent is eillowed to evaporate to leave a fiber of cellulose acetate. Cellulose acetate is also used in plastics and paints manufacture. Cellulose nitrate (nitrocellulose, guncotton) is used as a propellant. Ethers of cellulose are used as protective colloids (see p. 221) and as detergents. 

The chemical industry s interest in polymers dates back to the 19th century. In those days it was a case of synthetically modifying natural polymers with chemical reagents to either improve their properties or produce new materials with desirable characteristics. Notable examples were nitration of cellulose giving the explosive nitrocellulose, production of regenerated cellulose (rayon or artificial silk) via its xanthate derivative, and vulcanization of rubber by heating with sulphur. Manufacture of acetylated cellulose (cellulose acetate or acetate rayon) developed rapidly from 1914 onwards with its use both as a semi-synthetic fibre and as a thermoplastic material for extrusion as a film. 

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