Increasing Permeability of Polymer Membranes by Irradiation in the Fully Swollen State

Abstract

THE permeability of polyolefin film may be made selective towards a particular solvent by annealing the film below its dissolution temperature in that solvent. For example^1,2, a selectivity towards p-xylene in a mixture of o, m and p-xylenes has been conferred on a polyolefin membrane in this way. Michaels and co-workers³ have extended this to other solvents and were able to increase permeability as much as fifteen-fold relative to untreated membranes, but with reduced selectivity toward the permeants. These enhanced permeabilities were, however, not permanent. We demonstrate here⁴ that when solvent annealing of a polyethylene film is followed by cobalt-60γ-irradiation—while the film is still in contact with the annealing solvent—permeabilities are greatly increased. The enhancement produced by a combination of irradiation and annealing, however, is not only greater than that caused by annealing alone, but is far more permanent.