The permeability of strained polymer films

The permeabilities of vulcanized rubber, polyethylene and polypropylene to various gases and vapors have been determined as a function of strain. No changes in the permeability constants were found in the case of rubber. Both polyethylene and polypropylene showed increasing permeability constants with increasing strain but with polyethylene there was a levelling off above a certain level of strain. The results are interpreted in terms of increases in the free volume with straining leading to increases in the diffusivities. A theoretical treatment of the effect of strain on the solubilities of penetrants in crosslinked polymers is presented and shown to lead to only small effects with moderate degrees of crosslinking and straining.