Rayon cuprammonium, viscose

What is regenerated cellulose Explain what is chardonnet silk, cuprammonium rayon, and viscose rayon, and how they are prepared. 

Rayon Not a process but the generic name for regenerated cellulose fibers made by the Viscose and related processes. See Cross-Bevan-Beadle, Cuprammonium, Viscose, Lyocell. 

Cotton Cuprammonium rayon Regular viscose rayon High-tenacity viscose rayon Saponified acetate rayon Cellulose acetate (secon- dary) Cellulose tri- acetate... 

Asahi Chemical Industries (ACl, Japan) are now the leading producers of cuprammonium rayon. In 1990 they made 28,000 t/yr of filament and spunbond nonwoven from cotton ceUulose (65). Their continuing success with a process which has suffered intense competition from the cheaper viscose and synthetic fibers owes much to their developments of high speed spinning technology and of efficient copper recovery systems. Bemberg SpA in Italy, the only other producer of cuprammonium textile fibers, was making about 2000 t of filament yam in 1990. 

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. 

Today rayon is made by either the viscose or the cuprammonium process. The latter process is based on Schweitzer s discovery in 1857 that it is possible to dissolve cellulose in cuprammonium hydroxide, the soln being due to the formation of a Cu cellulose complex. The mfg procedure involves processing the cuprammonium soln by filtration and deaeration prior to pumping it thru holes in a spinneret into si alkaline w which coagulates the Cu-cellulose soln into rayon filaments. The filaments are then stretched to the desired fineness (Ref 11). The viscose process is the most widely used because of its great versatility and low cost operation. 

Viscose rayon is but one variety of rayon, a more general term for derivatized or reconstituted cellulose. Other rayons include fiber prepared from collodion, cellulose acetate, and cellulose fiber regenerated from a cellulose-copper ammonium solution cuprammonium rayon) (Kauffman 1993). 

In the original process, the cellulose nitrate itself was used as the fiber (hence its satirical description as mother-in-law silk ). The regenerating agent is ammonium hydrosulfide. The basic process was first demonstrated by J.W. Swan in London in 1885 but commercialized by Count L.M.H.B. de Chardonnet ( Father of the rayon industry ) in France in 1891 and operated there until 1934. The last working factory, in Brazil, burned down in 1949. The other processes for making rayon fibers by regenerating cellulose ( viscose, cuprammonium) gave superior products. See also Rayon. 

Highly degraded cellulosic materials, such as viscose rayon, D.P. 250 to 350, may be dispersed in 8-12 % caustic at low temperatures. Upon increasing the temperature in a stepwise manner, the dispersed material may be fractionally precipitated. " This method of fractionation is of particular interest since viscosity data indicate that the state of dispersion of degraded cellulosic materials in caustic solution and in cuprammonium solution is similar. "... 

The fractionation of cellulosic materials dispersed in cuprammonium solution has usually been accompanied by an amount of degradation sufficient to render the results questionable. However, Battista and Sisson, " using acetone and n-propyl alcohol as precipitants, were able to resolve viscose rayon yam (D.P. 490) dispersed in cuprammonium solution into fractions varying in average degree of polymerization from 535 to 142, and from 615 to 132, respectively. 

The first large scale application of ion exchange to effluent treatment was in the recovery of water, ammonia, and basic copper sulfate from the waste streams encountered in the cuprammonium rayon process. Originally a phenolic type condensation resin was employed, but more recently carboxylic acid acrylic-based exchangers have been introduced. A similar process exists for zinc recovery from the spinning acids of viscose rayon plants, except that in this operation a sulfonic acid resin is employed. 

A 0-5 per cent solution of a regenerated cellulose has a fluidity of about 40, which is approaching the limit of accuracy of measurement. It is therefore usual to work with a 2 per cent solution which brings fluidities into the range of 7-5 to 35,- and normally well-bleached regenerated cellulose rayon should have a fluidity of 11 to 12. For mixtures of cotton and viscose or other chemically similar rayons, the weights of fibre required per 100 ml of cuprammonium solution are given in Table 3.2. 

Cuprammonium rayon is made from scoured and bleached cotton linters or purified wood pulp with a high a cellulose content. The cellulose is washed and then pressed until it contains about 50 per cent of water. In this state, it is placed in a mechanical mixer together with cuprammonium solution and agitated until completely dissolved, whilst the temperature is maintained at 5° C (41 °F). The solution is then diluted to about 10 per cent concentration. After filtration and exposure to vacuum to remove air bubbles and dissolved gases, the solution is allowed to ripen in enclosed vessels until it is the desired viscosity. In modem practice copper carbonate is mixed intimately with the cellulose in a shredding machine and the resultant mass is then broken up and stirred for some hours with aqueous ammonia and caustic soda, when it passes into solution. 

Establishments primarily engaged in manufacturing cellulosic fibers (including cellulose acetate and regenerated cellulose such as rayon by the viscose or cuprammonium process) in the form of monofilament, yarn, staple, or tow suitable for further manufacturing on spindles, looms, knitting machines, or other textile processing equipment. 

In 1920, the Tubize Company built a plant to produce the yarn in the United States. By 1934, however, other types of superior rayon had been developed, so the nitrocellulose plant was sold to a company in Brazil. Several incidents of explosions and fires caused by the incompletely denitrated cellulose resulted in setbacks to the Chardonnet silk process, but, fortunately, the simultaneous development of cuprammonium and viscose solutions for spinning rayon rapidly replaced the more dangerous nitrocellulose fibers. 

The name rayon was officially adopted in 1924 by the National Retail Dry Goods Association. Prior to this, the fiber was called artificial silk, wood-silk, or viscose silk. On October 26, 1937, the Federal Trade Commission (FTC) officially defined rayon as a textile fiber or yarn produced chemically from cellulose or with a cellulose base. This definition covered cuprammonium and viscose rayon as well as acetate fiber. To avoid confusion in the trade, FTC rules were adopted on December 11, 1951, which defined rayon as man-made textile fibers and filaments composed of regenerated cellulose. A separate definition was adopted for acetate, man-made textile fibers and filaments composed of cellulose acetate. ... 

The properties of cuprammonium rayon are sufficiently different from those of viscose rayon that today it is produced as a specialty fiber for several applications. Apart from its use as a substitute for silk in scarves, ties, fine dresses, and linings, the use of hollow cuprammonium fibers for hemodialysis in artificial kidneys has become important. 

Continuous-filament (regular) rayon is produced by either the cuprammonium or viscose process. Both are supplied as yarn having a high sheen resembling silk. End uses include those applications where durability and dimensional stability are not particularly important. Cuprammonium fibers can be spun in finer deniers than viscose fibers, and they find a market for ladies shawls, scarves, blouses, coat linings, etc. The amount of cuprammonium fiber produced is quite small relative to viscose rayon. 

Rayon manufactured by different processes varies both chemically and physically. Most rayon is made by the viscose process, where the cellulose is treated with caustic soda and then with carbon disulfide to form cellulose xanthate, which is dissolved in a weak caustic solution to form the viscose. With the cuprammonium process, the cellulose is digested in an ammonia solution of copper sulfate and the solution is forced through the spinnerets into dilute acid for hardening. 

The acetate rayons are more resistant than the viscose or cuprammonium. Fiber 40 (FMC Corp.) is a type of rayon called Avril, made by a special pulping process that decreases the tendency to shrink when the fiber is wet. Avlin Fabray (Steamess Technical Textiles Co.) is a thin, lightweight, porous, nonwoven fabric of rayon fiber used for throw-away garments. 

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