Transport of liquids in structurally modified polyethylene

Abstract

AbstractCast linear polyethylene films subjected to dry and solvent annealing display markedly different sorption and difusion barrier properties than do untreated films. The subsequent sorption of liquid o‐ and p‐xylene and cis‐ and trans‐acetylene dichloride per unit volume of amorphous polymer increases as the annealing temperature and/or treating solvent concentration increases. Integral diffusivities calculated from sorption and steady‐state permeation rates show a monotonic increase with sorption per unit volume of amorphous polymer. The concentration dependence, however, is less marked than observed in similar systems at low permeant activity. Apparently the above treatment reduces the effective crosslinking imposed by the crystallites on the amorphous polymer chains through disentangling and incorporating some of these chains into crystallites. Thus the polymer is capable of a greater degree of swelling when brought into contact with a compatible liquid in a spite of a higher degree of crystallinity. The low concentration dependence of the diffusivities is probably due to heterogeneous distribution of excess permeant in a treated film. If the excess permeant were preferentially sorbed in regions of low polymer concentration then the above observations could be explained. Long‐duration, osmotic stress‐induced swelling and recrystallization have been cited to account for time‐dependent permeation rates in treated and untreated films.