Cellulose xanthation

Carbon disulphide is an excellent solvent for fats, oils, rubber, sulphur, bromine and iodine, and is used industrially as a solvent for extraction. It is also used in the production of viscose silk, when added to wood cellulose impregnated with sodium hydroxide solution, a viscous solution of cellulose xanthate is formed, and this can be extruded through a fine nozzle into acid, which decomposes the xanthate to give a glossy thread of cellulose. 

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. 

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. 

Filtration of viscose is not a straightforward chemical engineering process. The solution of cellulose xanthate contains some easy-to-deal-with undissolved pulp fibers, but also some gel-like material which is retarded rather than removed by the filters. The viscose is unstable and tends to form more gel as it ages. Its flow characteristics make the material close to the walls of any vessel or pipe move more slowly, get older, and gel more than the mainstream viscose. So while filtration can hold back gels arising from incomplete mixing, new gels can form in the pipework after the filters. 

The next significant strength improvement followed the 1950 Du Pont (19) discovery of monoamine and quaternary ammonium modifiers, which, when added to the viscose, prolonged the life of the ziac cellulose xanthate gel, and enabled even higher stretch levels to be used. Modifiers have proliferated siace they were first patented and the Hst now iacludes many poly(alkylene oxide) derivatives (20), polyhydroxypolyamines (21—23), and dithiocarbamates (24). 

Several cellulose esters (qv) are prepared commercially. Cellulose xanthate [9032-37-5] is made by reaction of cellulose swollen in 8.5—12% sodium hydroxide solution (alkaU cellulose [9081-58-7J) with carbon disulfide and is soluble in the alkaline solution in which it is made. When such a solution, termed viscose, is introduced into an acid bath, the cellulose xanthate decomposes to regenerate cellulose as rayon fibers or cellophane sheets (see Fibers, REGENERATED CELLULOSICS). 

Reaction of alkali cellulose with carbon disulphide to produce a cellulose xanthate which forms a lyophilic sol with caustic soda. This may be extruded into a coagulating bath containing sulphate ions which hydrolyses the xanthate back to cellulose. This process is known as the viscose process and is that used in the manufacture of rayon. 

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. ... 

The xanthate method [62] is considered as one of the most promising methods for industrial chemical modification. The principal involved in the xanthate method of grafting is that cellulosic xanthate either ferrated or in acidic conditions reacts with hydrogen peroxide to produce macroradicals. The following reaction mechanism has been proposed ... 

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. 

That type of rayon which is regenerated from viscose, a syrupy liquid consisting mainly of a solution of cellulose xanthate in dilute sodium hydroxide. 

Salts of the series of xanthic acids of the general formula ROCSSH. Certain xanthates such as ZIX are ultra accelerators for mbber. Cellulose xanthate is the intermediate product in the manufacture of viscose. See Viscose Rayon. Xanthogen Sulphide... 

Viscose Also known as the Cross-Bevan-Beadle process. A process for making regenerated cellulose fibers. The product has been known by the generic name rayon since 1924. Cellulose, from cotton or wood, is first reacted with sodium hydroxide ( mercerization), yielding alkali cellulose. This is dissolved in carbon disulfide, yielding cellulose xanthate, which is dissolved in sodium hydroxide solution. Injection of this solution (known as viscose... 

Carbon dioxide supply, for the molten carbonate fuel cell, 72 220 Carbon dioxide ternary systems, phase behavior of, 24 4—5 Carbon diselenide, 22 75t Carbon disulfide, 4 822-842 23 567, 568, 621. See also CS2 in cellulose xanthation, 77 254 chemical reactions, 4 824—828 diffusion coefficient in air at 0° C, 7 70t economic aspects, 4 834-835 electrostatic properties of, 7 621t handling, shipment, and storage, 4 833-834... 

Cellulose triesters, moisture properties of selected, 5 416t Cellulose trinitrate, 5 396 Cellulose valerate(s), 5 419 moisture properties, 5 416t Cellulose x, 5 373, 378-379 8 21 Cellulose xanthate, 4 716 5 383 20 559 Cellulosic-acrylic fibers, dyeing, 9 201-202 Cellulosic fiber blends, dyeing, 9 199-202 Cellulosic fiber—nylon blends, dyeing, 9 202 Cellulosic fibers, 18 96... 

In 1891, British chemistry Cross and Bevan discovered that wood pulp when treated with sodium hydroxide solution and carbon disulphide, gets converted into cellulose xanthate. When cellulose xanthate is dissolved in caustic soda solution it gives a viscous solution that could be spun to form fibres called Viscose Rayon. Rayon is produced in large scale today in many countries including India. Rayon (also know as viscose) is in fact regenerated cellulose. 

A method of grafting vinyl monomers to substrates of cellulose xanthate was invented by Faessinger and Conte-. The initiation is a reaction of ferrated (12) or acidic (13) cellulose xanthate with hydrogen peroxide according to the following scheme (HO-OH and Fe + give HO- radicals) ... 

Metal Ion Initiation on Cellulose Xanthate. Vinyl monomers can be grafted to cellulose at high rates by reaction with cellulose xanthate using v5+, Fe + and Cr + as redox initiators l. 

Treatment of cellulose with a mixture of sodium hydroxide (NaOH) and carbon disulfide (CS2) yields cellulose xanthate. The action of acid on cellulose xanthate produces rayon or cellophane. 

Cellulose is sometimes used in its original or native form as fibers for textile and paper, but is often modified through dissolving and reprecipitation or through chemical reaction. The xanthate viscose process, which is used for the production of rayon and cellophane, is the most widely used regeneration process. The cellulose obtained by the removal of lignin from wood pulp is converted to alkali cellulose. The addition of carbon disulfide to the latter produces cellulose xanthate. 

In the cellulose-regenerating process, sodium hydroxide is initially added such that approximately one hydrogen, believed to be predominately a mixture of the hydroxyl groups on carbons 2 and 3, is replaced by the sodium ion. This is followed by treatment with carbon disulfide forming cellulose xanthate, which is eventually rechanged back again, regenerated, to cellulose. This sequence is depicted in structure 9.6. 

Cellulose.> Sodium salt. > Cellulose xanthate ---> Regenerated... 

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