Cellulose is soluble only in unusual and complex solvent systems. The subject has been

reviewed [128-131]. Solvents for cellulose are central to the rayon and cellulose film

industries, but are also necessary for solubilizing cotton for the determination of molecular

weight and degree of polymerization (DP) by chromatographic methods. These solvents fall

into several categories. The solvents discussed do not include processes where cellulose is

converted to a derivative that is subsequently dissolved in another medium. For example,

cellulose acetate is soluble in acetone, but this is not a solution of cellulose. However, the

viscose process that forms a cellulose xanthate derivative, from which cellulose is readily

regenerated, is generally considered to use a cellulose solution because solvation and

derivatization occur simultaneously. The viscose process is the most important method

for making cellulose solutions for industrial use [132]. Alkali cellulose (pulp swollen in

NaOH) is pressed and aged to reduce molecular weight. Xanthation (a reaction with CS2)

takes place in a vessel that contains an inert atmosphere (CS2-air mixtures are explosive).

The orange xanthate is subsequently dissolved in aqueous alkali to make the spinning dope.

The dope is pumped through spinnerets in which there are from 14 to 40,000 holes. The

spun dope is converted back to cellulose by the sulfuric acid in the coagulating bath.

Another system with simultaneous derivitization and dissolution uses dimethyl sulfoxide

and formaldehyde [133].