Cuprammonium solution rayon

Dissolution of the cellulose in cuprammonium solution followed by acid coagulation of extruded fibre ( cuprammonium rayon —no longer of commercial importance). In this case the acid converts the cuprammonium complex back into cellulose. 

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. 

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. 

The complete solubility of cellulose in cuprammonium solutions, discovered in 1857 by Schweizer, led to the development of the rayon industry, but, as in the case of alkali cellulose, the regenerated polymer is chemically the same as the precursor. Regeneration via cellulose xanthate solutions, invented by Cross... 

Although rayon swells in water, it is not attacked hy common organic solvents. It does dissolve in cuprammonium solutions. 

Schweizer s reagent The dark blue solution obtained by dissolving Cu(OH)2 in concentrated ammonia solution. Used as a solvent for cellulose, the cellulose is precipitated on acidification. Used in the cuprammonium process for the manufacture of rayon. 

The presence of free sulphuric acid in rayon-spinning baths limits application of the austenitic steels, but they are used for acetylation of cellulose in the acetate process. They are also used for dissolving and spinning solutions in the cuprammonium processes. 

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. 

Physical or physico-chemical capability (Table 1), including mechanical strength, permeation, or sieving characteristics, is another important requirement of biomaterials. Cuprammonium rayon, for instance, maintains its dominant position as the most popular material for hemodialysis (artificial kidney). Thanks to its good mechanical strength, cuprarayon can be fabricated into much thinner membranes than synthetic polymer membranes as a consequence, much better clearance of low-molecular-weight solutes is achieved. 

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). 

The manufacture of cuprammonium rayon is based upon Schweitzer s discovery that cellulose is dissolved by a solution of copper hydroxide in ammonia. Attempts to utilize this discovery for the preparation of fibres were made by Depaissis, but Pauly, in 1897, was the first to work the process on a commercial scale. His venture did not survive and it was left in abeyance until Bemberg took it up again in 1919 and succeeded because he introduced the method of stretch spinning, based on earlier work by Thiele. 

In 1937, Schweizer [91] discovered that cellulosic fibers such as cotton and hemp readily dissolve in copper hydroxide and ammonium hydroxide solutions. His system is recognized as the Schweizer reagent. The Bemberg Rayon Industry later utilized this solvent for the industrial production of cuprammonium fibers (or cuprammonium rayon) and developed the Bemberg process or cuprammonium process [92]. Kamide and Nishiyama [93] have recently published an excellent review on the history and science of cuprammonium technology. 

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. 

In another process, cellulose is dissolved in ammoniacal cupric hydroxide (Cu(NH3>4(OH)2). The solution is then spun as a fiber into a dilute sulfuric acid solution to regenerate the cellulose. The product is called Cuprammonium rayon. The material may still be manufactured on a limited scale. 

Schwoizer s reagont A solution made by dissoiving copper( 11) hydroxide in concentrated ammonia soiution. It has a deep blue colour and is used as a solvent for cellulose in the cuprammonium process for making rayon. When the cellulose solution is forced through spinnarets into an acid bath, fibres of ceiiuiose are reformed. 

Cuprammonium rayon n. A regenerated cellulose formed by dissolving cotton or wood-pulp linters in a solution of ammonia and copper oxide (from sulfate), then extruding the solution through spinnerets into warm water, where the filaments... 

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. 

A second process for producing regenerated cellulose fibre was introduced in 1897 in Germany. In this method, cellulose is treated with an ammoniacal solution of cupric hydroxide (Cu(NH3)4(OH)2) to form a soluble complex. The solution is then spun into dilute sulphuric acid to regenerate the cellulose. This process is relatively expensive because of the need to recover copper. However, the product, called cuprammonium rayon, is still made on a limited scale because of its pleasing appearance and feel. 

Natural polymers can be made into hbers through dissolution of the polymer in an appropriate solvent and then extmsion of the polymer solution into a coagulation bath. As an example, cellulose can be made into viscose rayon fibers, cuprammonium rayon, cellulose acetate and triacetate fibers, lyocell, and modal fibers depending on the processes used to make the fibers. Other natural polymers such as mbber, chitosan, alginic acid, and protein can also be made into fibers in an appropriate fiber-forming process. 

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