Rayon viscose

Purified bleached wood pulp or sheets of cellulose are steeped in an alkali solu- 

Viscose and modified viscose are composed of cellulose and like cotton they are polymer of anhydroglucose unit. The significant physical differences between various regenerated cellulose and cotton polymers are listed in Table 1.14. HWM viscose rayon may appear nearly round in cross-section. Viscose polymers are very amorphous and have high moisture absorption capacity of 11 to 16%. Vis- 

Significant Physical Differences Between Rayon and Cotton 

Polymer Approx, no. of cellobiose units Approx. Approx, polymer polymer length (mm) thickness (nm) Approx, degree of polymesisation 

The sheets are shredded and the white crumbs are aged, which implies depolymerization to a molecular weight which is suitable for textile applications or tire cord. The material is then treated in closed equipment (batchwise or continuous) with carbon disulfide in order to xanthate the cellulose [Eq. (8)]. 

Byproducts give an orange-yellow color yellow crumbs are formed. The degree of xanthation (of cellulose) is low fewer than 0.5 hydroxyl groups need be derivat-ized to accomplish dissolution in dilute alkali. The polymer concentration for a textile yarn would be around 9% and the alkali concentration 5-6%. Eor a tire cord the polymer/alkali ratio is lower, both concentrations being 7%, for example. The 

The spinning bath for viscose contains sulfuric acid (at about 10% concentration) for the decomposition of the xanthate and neutralization of the alkali. Sodium sulfate is formed anyway, but is also dissolved in large quantities (about 20%) in the spinning bath to control the coagulation process. A further addition is zinc sulfate ( 3%), again to control coagulation. 

The spinning solutions - caustic plus acid - are highly corrosive. The spinnerets are made of gold/platinum, round, with diameters of a few centimeters only. The capillaries are small (50-75 gm) and close to each other ( 1 mm). The number of holes must be large because the standard filament titer of rayon yarns is around 1.7 dtex. The freshly spun filaments are very weak and a tube is often placed around the spinning bundle. 

Drawing is always carried out in a combined process, in most cases at least partly before the complete decomposition of the xanthate groups. Draw ratios may be low for rayon staple fiber. Tire cord is drawn to an elongation of 12-13% and a tenacity of about 500 mN tex. Note that these are conditioned values in a wet state the high-modulus character is lost the tenacity becomes lower (400 mN tex ) and the elongation much higher (25%). 

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Rayon. Viscose rayon is obtained by reacting the hydroxy groups of cellulose with carbon disulfide in the presence of alkali to give xanthates. When this solution is poured (spun) into an acid medium, the reaction is reversed and the cellulose is regenerated (coagulated). 

The cellulose molecule contains three hydroxyl groups which can react and leave the chain backbone intact. These alcohol groups can be esterified with acetic anhydride to form cellulose acetate. This polymer is spun into the fiber acetate rayon. Similarly, the alcohol groups in cellulose react with CS2 in the presence of strong base to produce cellulose xanthates. When extruded into fibers, this material is called viscose rayon, and when extruded into sheets, cellophane. In both the acetate and xanthate formation, some chain degradation also occurs, so the resulting polymer chains are shorter than those in the starting cellulose. 

Viscose-polyamide Viscose rayon Viscose rayon plants Viscosities Viscosity... 

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. 

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. 

Bulky Rayons. Unlike the thermoplastic synthetic fibers, viscose rayon cannot be bulked by mechanical crimping processes. Crimpers impart crimp to a regenerated cellulose fiber but it is not a permanent crimp and will not survive wetting out. 

Neste patented an industrial route to a cellulose carbamate pulp (90) which was stable enough to be shipped into rayon plants for dissolution as if it were xanthate. The carbamate solution could be spun into sulfuric acid or sodium carbonate solutions, to give fibers which when completely regenerated had similar properties to viscose rayon. When incompletely regenerated they were sufficientiy self-bonding for use in papermaking. The process was said to be cheaper than the viscose route and to have a lower environmental impact (91). It has not been commercialized, so no confirmation of its potential is yet available. 

C. R. Woodings and A. 1. Bartholomew, "The Manufacture, Piopeities and Uses of Inflated Viscose Rayon Fibres," 23rdMan-Made Fibres Congress, Dombim, Austria, 1984. 

C. R. Woodings, "The Development of Viscose Rayon foi Nonwoven Appheations," TAPPI Nonwovens Fibres Seminar 1979, pp. 15—28. 

A. G. Wilkes, "Galaxy-A New Viscose Rayon Fibre foi Nonwovens," Proceedings of the INDA-TEC 89 Conference, 1989. 

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

Cyclic Neopentyl Thiophosphoric Anhydride. This soHd additive, Sandoflam 5060, has been commercialhed in Europe by Sando2 for use in viscose rayon (91,92). It has the following stmcture [4090-50-1] ... 

It is generally accepted that, all other things being equal, the lower the secondary creep, the better the fiber is in terms of wear, shape retention, and crease resistance. This does not mean that glass, which has no secondary creep, is better in abrasion resistance than high tenacity viscose rayon, which has secondary creep, because the respective energy absorption capacities of these two materials, exclusive of secondary creep, are not equal. Nor does it mean that fibers that exhibit secondary creep are of no value. For fabrics to meet the requirements of wear, crease resistance, and shape retention, the load and extension yield points should not be exceeded during use. 

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... 

Kumar, K., Saxena, R. K., Kothari, R., Suri, D. K., Kaushik, N. K. and Bohra, J. N., Correlation between adsorption and x -ray diffraction studies on viscose rayon-based activated carbon cloth. Carbon, 1997, 35(12), 1842 1844. 

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. 

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). 

It is desired to synthesize a REAMEN for treating the gaseous wastes (Ri and Ra) of a viscose rayon plant. Three MSAs are available to select from. These MSAs are caustic soda, S], (a process stream already existing in the plant with mi = 5.0 kmol/m ), diethanolamine, Sa, (with m2 = 2.0 kmol/m ) and activated carbon, S3. The unit costs for S2 and S3 including stream makeup and subsequent regeneration are 64.9 /m and 169.4 /ro, respectively. Stream data ate given in Table 8.7. 

Most of the above can be made into plastic films - primarily used for wrapping. Film properties vary widely from permeable for food to impermeable to preserve dryness. Paper, treated or untreated, has been used for many years as a covering film, but has low strength when wet and is difficult to make transparent. In the 1920s, the transparency of cellophane revolutionized wrap. It is regenerated cellulose, like viscose rayon, except it is extruded in sheet instead of fiber, unfortunately it is sensitive to water and humidity. 

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). 

When ethanol is replaced by cellulose, sodium cellulose xanthate is obtained this dissolves in aqueous alkali to give a viscous solution (viscose) from which either viscose rayon or cellophane can be obtained by adding acid to regenerate the (reconstituted) cellulose. Trithiocarbonates (CS3 "), dithiocarbonates (COS2 "), xanthates (CS2OR ), difhiocarbamates (CS2NR2 ) and 1,2-dithiolates have an extensive coordination chemistry which has been reviewed. ... 

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). 

Viskose-kiinstseide, /. viscose rayon, -ver-fahren, n. viscose process. 

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). 

Recycling Zinc in Viscose Rayon Plants by Two-Stage Precipitation... 

Over 22.7 million kg (50 million lb) of zinc sulfate are used annually in the U.S. for the manufacture of approximately 454 million kg (one billion lb) of viscose rayon. Zinc is used as a regeneration retardant in the acid spinning bath. Because it is not consumed in any of the viscose reactions, these 22.7 million kg (50 million lb) of zinc represent process losses, through dragout by the filaments to the subsequent wash streams, filter backwashing, splashes, leaks, and the washing of equipment.14... 

There are ten viscose rayon manufacturing plants in the U.S., all of which are believed to use zinc sulfate in their spinning bath. This process greatly enhances the economics of removing this source of zinc pollution, allowing neutralization of the acid stream and recovery of the zinc while generating a good profit for industrial yarns and at a moderate cost for textile yams. 

This technology, with only small modifications to conform to local plant conditions, could have immediate application in any viscose rayon plant with soluble zinc in the plant wastestream. The techniques of initially precipitating the impurities, which would prohibit zinc recycle as well as the use of a sludge recirculation process to obtain a dense sludge, are excellent examples of good process engineering being applied to a waste problem. 

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