Cellulose, alkali regenerated

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). 

Among the best-known nonderivatizing solvent systems is a combination between copper, alkali, and ammonia termed Schweizer s reagent. Solutions of cuprammonium hydroxide have been used for both analytical and industrial cellulose dissolution. Regenerated fibers with silk-like appearance and dialysis membrane have been (and partially continue to be) industrial products on the basis of cellulose dissolution in cuprammonium hydroxide. The success of this solvent is based on the ability of copper and ammonia to complex with the glycol functionality of cellulose as shown inO Fig. 11. Because of the potential side reactions (oxidation and crosslinking, Norman compound formation), alternatives to both ammonia as well as copper have been developed. Cuen and cadoxen are related formulations based on the use of ethylene diamine and cadmium, respectively. The various combinations of alkali, ammonia. 

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... 

Qi, H., Cai, J., Zhang, L., Kuga, S. Properties of films composed of cellulose nanowhiskers and a cellulose matrix regenerated from alkali/urea solution. Biomacromolecules 10, 1597-1602 (2009)... 

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. ... 

Fixation in 6-12 hours with a mixture of sodium hydroxide and trisodium orthophosphate, a metering device being necessary. This method is recommended for regenerated cellulosic fibres. This formulation contains the same total amount of alkali as method (1) with the same bath stability, but may be preferred where some buffering capacity is required and sodium silicate is undesirable. 

By introduction into cellulose of about 0.5 equivalent of methyl or ethyl groups a product is readily obtained which can be dissolved in alkali of 4-10%. The ether may be regenerated from this solution by... 

By the action of relatively small quantities of sodium chloroacetate on alkali cellulose, carboxymethyl ethers are obtained which give smooth solution in dilute alkali but which can be regenerated to give threads or films of high tensile strength. These products are relatively hygroscopic. The substances are soluble in the form of their sodium salts and form insoluble salts with many metals.8... 

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... 

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. 

This is an Sn2 reaction, which is proportional to the concentration of the epoxide and alkali cellulose, but since the base is regenerated, it is first order in epoxide. 

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 (alkali cellulose [9081-58-7]) 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). 

Regeneration of cellulose-based columns is most reliably achieved by using the acid/alkali precycling procedure described (see Note 13). 

The cellulose anion formed attacks the positive carbon atom in acrylonitrile to form a resonance-stabilized intermediate anion, which then adds a proton from water to form the product under simultaneous liberation of a hydroxyl ion. All the reaction steps are reversible and because of the regeneration of hydroxyl ions no alkali is consumed. However, the process is accompanied with the consumption of acrylonitrile in several side reactions, such as formation of 3,3 -oxydipropionitrile ... 

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