Sodium cellulose xanthate

The resultant yellow sodium cellulose xanthate is dispersed in an aqueous caustic soda solution, where some hydrolysis occurs. This process is referred to as ripening and the solution as viscose . When the hydrolysis has proceeded sufficiently the solution it transferred to a hopper from which it emerges through a small slit on to a roller immersed in a tank of 10-15% sulphuric acid and 10-20% sodium sulphate at 35-40°C. The viscose is coagulated and by completion of the hydrolysis the cellulose is regenerated. The foil is subsequently washed, bleached, plasticised with ethylene glycol or glycerol and then dried. 

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. ... 

Geometric effects coupled with diffusion and nucleation usually control the rates of all solids deposition phenomena. Such effects can be put to good use in the production of special products such as cellulose yarn (rayon), by the precipitation of cellulose in filament form as it emerges as sodium cellulose xanthate liquid from the spinnerets into a bath containing sulphuric acid, which extracts the sodium as sodium sulphate, and the carbon disulphide. In a similar manner, the fabrication of aromatic polyimide fibres is performed by dissolving the polymer in concentrated sulphuric acid and forcing the solution through spinnerets into water. 

Cellulose xanthate, or more exactly, sodium cellulose xanthate or sodium cellulose dithiocar-bonate, is obtained by mixing the aged soda cellulose with carbon disulfide in a vapor-tight xanthating chum. Based upon weight of cellulose, the amount of carbon disulfide used will be in the range of 30 percent for regular rayon to 50-60 percent for modified varieties. 

Viscose Silk.—III. From Cellulose Xanthate. We have referred to the solvent action of xanthic acid, which is the ethyl ether of di-thio-carbonic acid, viz., HS-CS-OC2H5. When sodium cellulose is dissolved in xanthic acid the cellulose is in the form of sodium cellulose xanthate. A solution properly prepared by treating cellulose with sodimn hydroxide and carbon di-sulphide in the presence of benzene or carbon tetra-chloride, in which polymerization of the cellulose compound is effected, is decomposed by forcing capillary streams of the solution into a solution of ammonium sulphate. The cellulose is thus obtained as in the other processes in the form of fine filaments of a hydrated cellulose possessing silk-like properties. Artificial silk of this type is known as viscose silk and is made in large quantities. In 1914 about 20,000,000 pounds of artificial silk were made, of which about 3,000,000 pounds were made in the United States. Most of this product was viscose silk. 

Water soluble derivatives of cellulose have also been made through the formation of sodium cellulose xanthate (Cell-O-CS Na ) ( 12) and copper amine complexes (that is, the cuprammonlum process) ( X3). Both these derivatives require regeneration of the Insoluble cellulose structure at the time of membrane formation. Strong salt and acid solutions are used to precipitate the soluble derivatives and simultaneously recover the cellulose structure. Residues of xanthate or cuprammonlum salt decomposition must subsequently be washed out of the resulting membrane. 

Carbon disulfide is widely used in production of rayon, carbon tetrachloride, rubber chemicals and cellulose film, and is a by-product of widely used dithiocarbamate pesticides. Chronic low level and long term exposure to CS2 can cause eye, ear, cardiovascular, nervous system and reproductive effects (Tan et al., 2001), (WHO Criteria 10, 1979), (Kaloyanova, 1981). There are scientific reports that the long term exposure to low concentrations of CS2 is related to endocrine disturbances as well (Lancranian I. et al., 1972) (Lyubomirova K. et al., 2006). Carbon disulfide is mostly used in viscose industry to yield sodium cellulose xanthate from alkali cellulose. (Tan et al., 2001). 

The first step in manufacture of cellulose is to treat the cellulose with caustic soda (NaOH) and allow it to oxidize until the degree of polymerization is down to 200 to 400. Treatment with CSj then yields sodium cellulose xanthate, which is dissolved in aqueous NaOH. This material, called viscose, is extruded through a small slit onto a roller immersed in a tank of weak sulfuric acid and sodium sulfate, which hydrolyzes the xanthate groups, regenerating the cellulose and yielding CSj and... 

Because of the strong intermolecular bonds, cellulose does not melt and does not dissolve readily in ordinarily available solvents chemists have resorted to the derivatization of cellulose to render it soluble and processable. Specifically, the viscose process was developed. It converted cellulose into sodium cellulose xanthate, which was soluble in a caustic solution, making it possible to wet-spin the polymer into a fiber or film. This technique was accepted worldwide and has prospered. The process, however, consists of multiple steps and causes pollution. As a result, end users have looked for alternate methods of processing cellulose. 

The pulp is first steeped in an aqueous solution of sodium hydroxide (17 18%), which causes the fibers to swell and converts the cellulose to sodium cellulosate, commonly called alkali cellulose or white crumb. After steeping, the swollen mass is pressed to obtain a precise ratio of alkali to cellulose and then shredded to provide adequate surface area for uniform reaction in subsequent process steps. The alkali cellulose is aged under controlled conditions of time and temperature to depolymerize the cellulose by oxidation to the desired DP prior to reacting with carbon disulfide to form sodium cellulose xanthate. The xanthate, which is a yellow to orange crumb, is dissolved in dilute sodium hydroxide to yield a viscous orange-colored solution called viscose. The solution is filtered, deaerated, and ripened to the desired coagulation point (called salt index) appropriate for spinning. 

The soluble derivative, sodium cellulose xanthate, is formed by reacting alkali cellulose with carbon disulfide. The reaction has been studied for both cellulose and simple model systems [151,152]. Xanthation is normally conducted by placing alkali cellulose crumb in a reactor, pulling a vacuum, and then introducing CS2. As the reaction proceeds, CS2 is consumed and the vacuum is regained. The extent of vacuum regain is used to follow the reaction. 

The aged crumbs, which contain about 30% cellulose, are then transferred to a jacketed, cooled, hexagonal shaped xanthation vessel. A vacuum is applied and about 10% CS2 added with great care, as it is an extremely flammable substance. The vessel is slowly rotated on its axis, churning the two components for about 3 h to form a deep orange, thick, viscous mass of sodium cellulose xanthate. 

Regenerated cellulose, cellulose acetate, acrylic and some other fibres are spun from solution, either by dry spinning, with evaporation of solvent, or by wet spinning into a coagulation bath. In viscose rayon, the solute is sodium cellulose xanthate, which is a chemical derivative of cellulose soluble in caustic soda, so that a chemical reaction is involved in fibre formation. 

C6Hio05)n+ nNaOH (CeHg040Na)n + nH20 Sodium cellulose, swelled cellulose (C6Hg040Na)n + nCS2 n (SC-0CeHg04)n Sodium cellulose xanthate... 

In wet spinning, the polymer solution is spun into a coagulant bath. An example is a 7% aqueous solution of sodium cellulose xanthate (viscose), which is spun into a dilute sulfuric acid bath, also containing sodium sulfate and zinc sulfate (160). The zinc ions form temporary ionic cross-links between the xanthate groups, holding the chains together while the sulfuric add, in turn. 

Sodium chitin xanthate-silk fibroin Sodium cellulose xanthate-silk fibroin Sodium /V-acetyl xanthate-sodium cellulose xanthate Sodium /V-aceylation salts-sodium cellulose xanthate... 

Microcrystalline chitosan gel/sodium alginate (2 1)-sodium cellulose xanthate... 

Hirano, et al. 59 Chitin-cellulose-silk fibroin Sodium chitin xanthate-sodium cellulose xanthate-silk fibroin aq. 5% NaOH aq. 10% H2SO4 and 40-43% (NHiIjSOi... 

Addition of carbon disulfide to alkali cellulose, followed by solution in a sodium hydroxide solution produces sodium cellulose xanthate, used in the viscose process. Extruded into a sulfuric acid bath as a film, the material known as cellophane is produced. Spun into a sulfuric acid bath, this material regenerates the cellulose as cellulose II. The product is known as rayon. 

The next step in the process is to turn the cellulose into a form in which it can subsequently be dissolved in water. Alkali cellulose is stirred with carbon disulphide in closed churns. At the end of churning it has been converted from a white to an orange colour. At this stage it is called sodium cellulose xanthate or simply xanthate . The xanthate is a... 

The resultant alkali cellulose is pressed to remove most of the excess NaOH solution and is shredded to increase the surface area and make the material easier to process. The shredded alkali cellulose is pre-aged with the presence of oxygen in the ambient air to reduce and control the cellulose molecular weight. After reaching the desired molecular weight, carbon disulfide (CS ) is added to the shredded alkali cellulose in a specially designed vessel called a Barette at 20-30°C for 1-3 hours to cany out the xanthation step, which leads to the formation of sodium cellulose xanthate. The following is the main reaction in the xanthation step ... 

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