Abstract: A method for forming a microporous sheet of fluorocarbon polymer (e.g., polytetrafluoroethylene). An aqueous dispersion of polytetrafluoroethylene which includes a dissolved water-soluble, crystallizable metallic organic salt, preferably sodium benzoate, is formed into a sheet. Water is evaporated from an exposed surface of the sheet to grow crystals of the organic salt dispersed throughout the sheet. Then, the sheet is sintered. After cooling, the salt crystals are leached from the sheet by dissolution in water to leave a porous structure suitable for such uses as a filtration membrane or as a separation barrier in batteries or electrolytic cells.

Abstract: A microporous filter having pleated filter cartridge is provided with inlet and bypass ports for establishing tangential flow across outside boundary of cartridge inlet side resulting in slow clogging operation.