The diffusion of gases and vapors in rigid PVC

Gravimetric sorption rate measurements have been carried out for (CO2, H2), and ten C1-C6 organic vapors at low concentrations (≤ 0.2%) in PVC films and uniform-particle powders at 30°C. The dominant transport process in all cases appears to be Fickian diffusion. A distinguishable contribution of relaxation-controlled swelling was observed for the more soluble vapors, such as acetone and benzene. A significant contribution of surface adsorption to the total sorption process was detected only for the n-alkanes, among the penetrants studied. Diffusion coefficients, determined from half-sorption times and polymer dimensions, range from 4 × 10 −8 cm2/sec for H2O to 1.5 × 10 −15 cm2/sec for n-hexane. Diffusivities determined in this study, in combination with those for gases reported by Tikhomorov, et al. (Makromol. Chem. 118 177 (1968)), define a continuous curve, covering more than nine orders of magnitude, when plotted as a function of the molar volume constant, b, of the van der Waals equation of state for gases and vapors.