Swelling and absorption by cellulose acetate in binary solvent‐hexane mixtures

Abstract

AbstractPreferential absorption and swelling by cellulose acetate in binary solvent‐type liquid/hexane mixtures has been studied at 25°C. Secondary cellulose acetate, of acetic acid yield 53.7%, was used in fibrous form and as film. Triacetate, prepared by nondegradative acetylation of the secondary, was also used. Factors affecting preferential absorption by the fibrous secondary acetate seem to include the activity of the solvent‐type liquid and its chemical type, the swelling power of the mixture, and steric effects. Preferential absorption of ketones and esters other than methyl formate appears to be independent of both acetyl content and structure. Absorption of methyl formate, acetic acid, and heterocyclic bases by the triacetate is less, at all concentrations, than by the secondary acetate. At low concentrations cresols and chlorinated hydrocarbons are absorbed to a smaller extent by the triacetate but at higher concentrations the reverse is the case, such variations in absorption being ascribed to steric effects and to the elimination of hydroxyl groups on complete esterification. Absorption by the secondary acetate films also suggests steric effects. Comparison of the measured weight of films with that estimated from the change in composition of the mixture following absorption, assuming no hexane to be absorbed, Suggests that this assumption is true at low concentrations. At higher concentrations, leading to high degrees of swelling or to gelatinization, the mixture seems to be imbided. There is no general relationship between swelling and the δ value of the solvent‐type liquid but δ values for the mixtures just causing complete solution of the acetates are not very different when the mixtures involve solvents of similar chemicals type.