Diffusivity and solubility of organic vapors in modified polyethylene films. II. Diffusivity studies

Abstract

AbstractThe diffusion coefficient at zero concentration and the free volume parameters in Fujita's free volume theory were measured for benzene, hexane, and heptane in modified polyethylene films using an unsteady‐state absorption technique. Films were modified by gamma irradiation, solvent conditioning, and post‐ and preirradiation conditioning. Dc=0 was found to drop with irradiation, the drop being larger the larger the molecular size of the diffusing molecule. A relationship for the dependance of Dc=0 on the crosslink density is proposed. Solvent conditioning led to an increase in Dc=0 directly proportional to the swelling power of the conditioning agent and to the molecular size of the diffusant molecule. In most cases, combined treatment resulted in an increase in Dc=0, the extent of which was dependent upon the relative effect of the swellant and the irradiation dose. In all cases, postirradiation conditioning led to values of Dc=0 higher than those obtained by preirradiation conditioning. The fractional free volume of the polymer was found to decrease with irradiation, showing a marked drop at low doses when reaching a state where the dose was of small effect. Changes in f(0,T) with conditioning and with combined treatment followed the same general pattern as Dc=0. β(T) was unaffected by any kind of treatment studied. Bd changed in practically the same manner as f(0,T) but in the opposite direction. A method is proposed for the optimum choice of a membrane modification procedure based on solubility and diffusivity results.