Thermodynamic properties of dilute solutions of cellulose derivatives

Abstract

AbstractHeats and entropies of dilution of dilute solutions (concentration range 0.2–1.0 g./100 ml.) of cellulose acetate, ethyl cellulose, and cellulose nitrate, of similar degrees of substitution and polymerization, in a number of representative solvents, have been obtained from temperature coefficients of osmotic pressure. In some cases, degradation of polymer at the higher temperature used seems possible and an attempt is made to allow for this in the estimation of values of ΔH̄1 and ΔS̄1. Heats of dilution for the cellulose acetate and ethyl cellulose systems are generally endothermal, those for the cellulose nitrate systems being exothermal. Entropies of dilution are less than those obtained for comparable systems containing less polar and more flexible polymers. Those for the cellulose nitrate systems do not differ much from “ideal” values. The value of ΔH̄1/ϕ22, where ϕ2 is the volume fraction of polymer calculated from the density of the bare polymer, for each cellulose acetate system and most of the ethyl cellulose systems seems to be effectively independent of concentration. Values for the cellulose nitrate systems seems to be effectively independent of concentration. Values for the cellulose nitrate systems become less negative as the concentration increases. Values of ΔH̄1 for the cellulose acetate and ethyl cellulose systems are generally in the order to be expected from the solubility parameters of the solvents and polymers. ΔS̄1/ϕ22 may vary with concentration in a manner rather similar to that suggested by simpler lattice theories. These results are tentatively interpreted in terms of solvation of polymer and possible endothermal mixing of solvated polymer and solvent. Although values of the entropy contribution to the interaction parameter χ1 for the cellulose acetate and ethyl cellulose systems are not always inagreement with the predictions of simpler lattice theories it is possible, if solvation, segment size, and chain stiffness are allowed for, that the thermodynamic properties of dilute solutions of cellulose derivatives may be at least qualitatively interpreted in terms of such theories.