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| - Suitable nonfibrous porous layers are blushed polymer layers composed of a cellulose ester such as cellulose acetate, cellulose acetate/butyrate or cellulose nitrate disclosed in U.S. Pat. Nos. 3,992,158 and 1,421,341, microporous membranes composed of polyamide such as 6-nylon or 6,6-nylon, polyethylene or polypropylene, microporous membranes composed of polysulfone disclosed in CA 106, 140219k (
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