Thermodynamic properties of solutions of cellulose acetate and cellulose nitrate

Abstract

Abstract Vapor pressure lowerings of solutions containing 10–50 wt.‐% of a secondary cellulose acetate and of a cellulose nitrate of similar degree of substitution in representative solvents have been measured over a range of temperature. Solvent activities and free energies, heats and entropies of dilution are obtained. At low polymer concentrations the cellulose acetate systems are endothermal but become exothermal at higher concentrations. Entropies of dilution show a somewhat similar variation with concentration when acetone, methyl acetate, and dioxane are used as solvents for the cellulose acetate, but with pyridine as solvent entropies are positive and increase with increasing polymer concentration. The systems cellulose nitrate‐acetone and cellulose nitrate‐methyl acetate are exothermal at all concentrations, but entropies of dilution are positive and increase with concentration from values not far from ideal to relatively large ones. An attempt is made to interpret these results in terms of solvation and chain stiffness. Values of the polymer‐solvent interaction parameter χ 1 are obtained by use of polymer volume fractions calculated from the densities of the dry polymers. As the volume fraction of polymer increases in the cellulose acetate systems, χ 1 would appear initially to fall from values characteristic of dilute solutions and then to increase. In the cellulose nitrate systems, χ 1 falls from small positive to relatively large negative values. Values of the heat χ h and entropy χ s contributions to χ 1 are also obtained. It is pointed out that it may be more logical to express polymer volume fraction in terms of solvated polymer and that this might lead to values of χ 1 , χ h , and χ s more in keeping with theories of polymersolvent interaction.