Correlation between Cohesive Energy Density, Fractional Free Volume, and Gas Transport Properties of Poly(ethylene-co-vinyl acetate) Materials

Abstract

The transport properties of the poly(ethylene-co-vinyl acetate) (EVA) materials to He, N2, O2, and CO2 are correlated with two polymer molecular structure parameters, that is, cohesive energy density (CED) and fractional free volume (FFV), determined by the group contribution method. In our preceding paper, the attempt was made to approximate EVA permeability using a linear function of 1/FFV as predicted by the free volume theory. However, the deviations from this relationship appeared to be significant. In this paper, it is shown that permeation of gas molecules is controlled not only by free volume but also by the polymer cohesive energy. Moreover, the behavior of CO2 was found to differ significantly from that of other gases. In this instance, the correlation is much better when diffusivity instead of permeability is taken into account in a modified transport model.