Abstract

Disclosed are hydrophilic polyolefinic microporous materials and a method for the preparation thereof. Such materials are prepared by impregnating a normally hydrophobic polyolefinic microporous substrate material with a solution of a nonionic alkylphenoxy poly(ethyleneoxy) ethanol surfactant having an HLB of from about 10 to 15 in a solvent system comprising from about 55 to about 65 volume percent methanol or acetone and from about 35 to about 45 volume percent water. It has been discovered that polyolefinic microporous materials rendered hydrophilic by this technique not only wet rapidly, but in addition may be multiply re-wet with aqueous solutions, such as aqueous alkali solutions, with excellent retention of their hydrophilic properties. The hydrophilic polyolefinic microporous materials of this invention find particular application as battery separators and as membranes for use in various chemical, medical and biotechnical processes.