Rayon production

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

Common names have been given to sodium sulfate as a result of manufacturiag methods. In rayon production, by-product sodium sulfate is separated from a slurry by filtration where a 7—10-cm cake forms over the filter media. Thus rayon cake was the term coiaed for this cake. Similarly, salt cake, chrome cake, phenol cake, and other sodium sulfate cakes were named. Historically, sulfate cakes were low purity, but demand for higher purity and controlled particle size has forced manufacturers either to produce higher quaUty or go out of busiaess. Sodium sulfate is mined commercially from three types of mineral evaporites thenardite, mirabilite, and high sulfate brine deposits (see Chemicals FROMBRINe). 

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). 

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. 

For rayon production, a controlled cleavage of the cellulose molecule is required to reduce the viscosity of the cellulose xanthate so that it can be forced through fine spinnerets. A similar reduction of viscosity is required for cellulose which will be sprayed as a lacquer. This cleavage is brought about by the air oxidation of alkali cellulose, and the process is speeded by the addition of a few parts per million of a transition metal compound which functions as an oxidation catalyst. 

During the preparation of viscose rayon, cellulose is dissolved in a bath containing sodium hydroxide and later reprecipitated as rayon using a solution of sulfuric acid. Name the salt that is a by-product of this process. Rayon production is, in fact, a significant commercial source for this salt. 

Among the fibers, all except acrylics and rayon have shown significant growth in production in the 1994-2003 period (Table 21.2). Rayon production in the U.S.A. has declined about 70% since 1984. The American proportion of the world output of modified cellulosic and noncellulosic fibers production is about 3 and 13%, respectively. The preparative details of several of the more important condensation polymers are discussed in the following sections. 

The relationship between electric impulse transmission and visual stimuli was examined in a group of 21 patients with chronic carbon disulfide exposure in a rayon production plant for 20-36 years and control groups of 25 or 36 healthy unexposed males (Sikora et al. 1990). A significant correlation was observed in latency and amplitude of response. The correlations suggest cerebral dysfunction of the visual pathway and diminished ability to transform visual information to motor reaction at the level of the cortical association center. The study was limited by the lack of quantification of exposure levels and the variability in responses in the exposed group. 

In a rayon production factory, exposure to carbon disulfide was measured by personal air sampling and the excretion of TTCA in urine (Meuling et al. 1990). Based on the personal air-sampling, the TWA exposure level for carbon disulfide was 12.6 mg/m3 (4 ppm). The study authors established a calculated biological limit value of 0.77 mg TTCA/g creatinine (0.57 mmol/mol creatinine) to correspond with 95% confidence, to a TWA air concentration lower than the threshold limit value (TLV) of 30 mg/m3. 

Table 1 summarizes some representative solvents or solvent systems for cellulose. The xanthate system has been used for a longtime to make viscose rayon and sponge. However, rayon production, where H2S is released to varying amounts during the recovery system of spent solvent, is shrinking because of environmental issues. On the other hand, cellulose is soluble in aqueous NaOH alone under limited conditions. Microcrystalline cellulose with DP 200—300 is soluble in 6—9% NaOH by freezing and defrosting procedures. Pretreatments of cellulose such as steam explosion are necessary for complete dissolution in the aqueous NaOH for normal bleached wood pulp and cotton linters with DP of more than 500. ... 

Alkaline metal Cu(N 143)4(01-1)2 (cuoxam) Cuprammonium rayon production system... 

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]. 

The expansion of rayon production in undeveloped countries, such as Taiwan, Indonesia, and South America, where new rayon plants have been constructed, has in many cases incorporated the newer technology. Typical of this would be the continuous belt xanthator... 

Continuous-filament textile rayon, produced from viscose, while representing only a fraction of the world s total rayon production, is still an important article of commerce. Although its strength is on the low side, especially when wet, its other aesthetic properties make it unique for certain specialty end uses. Of special appeal is lightweight, sheer, richly colored textiles that are both comfortable and attractive. Coat hnings are a major market. 

The characteristics and properties of HWM rayon have been described by Goldenberg [281]. The HWM fiber production is increasing worldwide, mainly by conversion of regular rayon production lines but in some cases by new plants or spinning lines built specifically for the purpose. 

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