Phase transitions in cellulose solutions. The kinetics of precipitation of cellulose from diluted cadoxen solutions

Solutions of cellulose (degree of polymerization: 296 ± 16) in tris(ethylenediamine)cadmium(II)hydroxide-ethylenediamine-water (cadoxen), 1.015% (weight per volume) were diluted 1:1.5 with water. The ensuing isothermal precipitations were followed dilatometrically at temperatures ranging from 27.50 to 48.45°C. The precipitation data were characterized by a positive temperature coefficient. They generally conformed to a one-dimensional nucleation rate law; the Avrami exponents were close to unity. Alternatively, they fit a first-order reaction rate expression with respect to cellulose concentration. The low crystallinity of the precipitated cellulose leads to the interpretation of the kinetics in terms of the dissociation of a cellulose-cadoxen complex, rather than phase separation, as the rate-determining step. The nucleation rate law suggests a one-dimensional nonrandom cooperative chemical process, while the first-order rate law suggests a random process.