Viscose rayon production

C. M. Deeley, "Viscose Rayon Production," JSJotes for the Associateship of the Textile Institute Examination Eectures, Sept. 14,1959. 

Fi ire 8.7 Simplified flowsheet for viscose rayon production (from El-Halwagi and Srinivas, Synthesis of reactive mass-exchange networks, Chem. Eng. Set., 47(8), p. 2116, Copyright 1992, with kind permission from Elsevier Science Ltd., The Boulevard, Langford Lane, Kidlington 0X5 1GB, UK). 

Concentrations of hydrogen sulphide in the work place vary widely with the shale oil industry and viscose rayon production industry reporting maximum exposure concentrations per day of 15-20 ppm. However, massive accidental exposure to hydrogen sulphide due to equipment failure has been the principal hazard in industry. Since hydrogen sulphide is heavier than air, accumulation to lethal concentrations in low lying or enclosed areas can occur... 

Diffusion dialysis was initially applied in viscose rayon production to recover caustic soda using parchment paper as a membrane. Today the largest industrial utilization of diffusion dialysis is to recover acids or alkalis from waste acids and alkalis using anion or cation exchange membranes. Figure 6.28 shows the principle of diffusion dialysis for acid recovery from waste acid solution. The process and membrane performance are evaluated on the basis of the flux of acids or alkalis (dialysis coefficient) and the ratio of the flux of metal salt to that of acids or alkalis (separation coefficient). The total dialysis coefficient [molh-1 m 2 (moll-1)], Uo, is defined by... 

A horizontal spinning machine, as is used in viscose rayon production, was first adopted. However, there is an essential difference in the coagulation mechanism of PVA and viscose solutions. In the case of viscose rayon, hydrolysis of cellulose-xanthogenate to regenerated... 

Several attempts at viscose rayon production were made by companies in the United States with the patent rights from Cross and Bevan, Steam, and Topham. None of these efforts were successful at producing fiber, and most of their viscose production went into sheets (films) and molded forms. Well-known American names were involved in these early struggles—A.D. Little, Daniel C. Spruance, Willard Saulsbury, Carleton Ellis, and T.S. Harrison [108]. 

Its early commercial success owed much to the flammabUity disadvantages of the Chardoimet process, but competition from the viscose process led to its decline for aU but the finest filament products. The process is stiU used, most notably by Asahi in Japan where sales of artificial sHk and medical disposable fabrics provide a worthwhile income. However, its relatively high cost, associated with the cotton fiber starting point, prevented it from reaching the large scale of manufacture achieved by the viscose rayon process. 

Commencing in the late 1930s, new developments to make very strong yams allowed the viscose rayon to replace cotton as the fiber of choice for longer life pneumatic tires. The pace of this line of development increased during World War II, and by the 1960s a significant part of the production of viscose yam was for tires and industrial appHcations. 

From 1910 onward waste filament yam had been chopped into short lengths suitable for use on the machinery designed to process cotton and wool staples into spun yams. In the 1930s new plants were built specifically to supply the staple fiber markets. During World War II the production of staple matched that of filament, and by 1950, staple viscose was the most important product. The new spun-yam oudets spawned a series of viscose developments aimed at matching the characteristics of wool and cotton more closely. Viscose rayon was, after all, silk-like. Compared with wool it lacked bulk, residence, and abrasion resistance. Compared to cotton, it was weaker, tended to shrink and crease more easily, and had a rather lean, limp hand. 

CeUulose is subsequendy regenerated from the viscose solution in sulfuric acid and carbon disulfide is Hberated. These are the basic steps in manufacturing viscose rayon. The production of regenerated ceUulose is estimated to account for mote than 75% of the total carbon disulfide consumption woddwide... 

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. 

World production in 1991 was about 1 million tonnes the principal industrial uses being in the manufacture of viscose rayon (35-50%), cellophane films (15%) (see below), and CCI4 (15 30%) depending on country. Indeed the CCI4 application dropped to zero in USA in 1991 because of environmental concerns (p. 304). 

Other uses of HCI are legion and range from the purification of fine silica for the ceramics industry, and the refining of oils, fats and waxes, to the manufacture of chloroprene mbbers, PVC plastics, industrial solvents and organic intermediates, the production of viscose rayon yam and staple fibre, and the wet processing of textiles (where hydrochloric acid is used as a sour to neutralize residual alkali and remove metallic and other impurities). 

Cellulose may be solubilised by treatment with sodium hydroxide and carbon disulfide. It can be regenerated by acidification of the solution. This is the basis of the production of regenerated cellulose fibre, so-called viscose rayon , which is a major textile fibre. The technique is also used for the production of continuous cellulose-derived film, so-called cellophane (from cellulose and diaphane , the latter being French for transparent). 

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. 

This term was originally intended to denote all kinds of man-made textile fibres, but is now applied only to cellulose types. Viscose rayon (regenerated from a solution of cellulose xanthate in sodium hydroxide) accounts for the greater part of world rayon production. Acetate rayon and cuprammonium rayon are relatively unimportant. 

Salts of the series of xanthic acids of the general formula ROCSSH. Certain xanthates such as ZIX are ultra accelerators for mbber. Cellulose xanthate is the intermediate product in the manufacture of viscose. See Viscose Rayon. Xanthogen Sulphide... 

Approximately 73% of all North American sodium sulfate is obtained directly from natural salt sources in Searles Lake, California and in Texas, Mexico, and Canada. Miscellaneous methods of manufacture account for smaller percentages. This includes 5% as a by-product in the production of viscose rayon, where sulfuric acid and sodium hydroxide are used to degrade the cellulose. Sodium dichromate manufacture gives another 6% of sodium sulfate as a by-product. 

The cuprammonia process, the viscose process, and the acetate process have been employed for the production of rayon. Cuprammonia and viscose rayons have similar chemical and physical properties. Both are easily dyed and lose their strength when wet because of a disruption of hydrogen bonding this wet strength is improved through chemical treatment of the rayon fabrics. Acetate rayon is readily softened in the ironing process and loses its luster in boiling water. 

The first application of the ferrous ion-hydrogen peroxide initiation for polymerizing vinyl monomers on and into cellulose fibers has been reported by Landeias and Whewell (41) in three successive papers. They are apparently the first who applied the "anchored catalyst technique, which other people have termed "in situ polymerization to cellulose grafting. The authors internally deposited methyl methacrylate, acrylonitrile, styrene, methyl vinyl ketone and methacrylamide in amounts between 10 and 80%. No attempt had been made to determine if actual grafting had occurred. In 1961 Richards (42) studied this question in great detail. Products obtained by polymerization of acrylonitrile and of styrene in viscose rayon were acetylated. Fractionation of... 

The production of aldehyde groups through periodate oxidation and subsequent formation of oxime groups is being used as a basis for an anionic initiation of grafting with titanium chloride as catalyst according to a process claimed by Asahi Chemical Industries Company (135). With this method styrene was grafted onto viscose rayon. Also bi- and tri-valent vanadium salts can be used as initiators. 

It is produced from a liquid solution in a process similar to that by which viscose rayon is made. The final product consists of long fibers with the lowest density of all commonly used reinforcements. Aramid s rigidity and strength are intermediate between those of glass and carhon. 

Sodium sulfate is also obtained as a by-product in the production of viscose rayon. Sulfuric acid and sodium hydroxide are used to degrade the cellulose to rayon in a fiber-spinning bath. 

Ca is a constant having the value of approximately 8 GPa for viscose-rayon yam. De Vries also investigated some other synthetic fibres his values for the constant Ca were found to be proportional to EjSO, so that the product CaS SO is a constant ... 

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