ABSTRACT
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].
