SORPTION OF ORGANIC VAPORS IN POLYETHYLENE

The solubilities of a series of aromatic vapors in semicrystalline polyethylene were obtained by a modified gravimetric sorption technique with a flow system capable of a wide range of temperatures and activities. The experimental data were fitted well by a theoretical model. This model takes into account the free energy contributions in the penetrant-polymer system from combinatorial-entropy, free-volume, interactional-enthalpy, and elastic factors. Both UNIFAC group contribution and solubility parameter methods were used to calculate the interactional effects. In semicrystalline polyethylene, the elastic contributions due to the inhibition of chain deformations in amorphous regions from crystalline domains were very significant in determining the temperature dependence of the solubilities. Unlike molten polyethylene, the effects of the number of methyl substituents and the chain length of an alkyl substituent in the benzene ring on solubilities were found to be insignificant for semicrystalline polyethylene. The elastic factor, which is absent in molten polyethylene, decreased the solubilities more significantly for the bulkier penetrants, resulting in the insignificant effects observed for semicrystalline polyethylene.