Method to produce a polytetra-fluoroethylene diaphragm

A method to form an electrolyte permeable diaphragm for an electrolytic cell for producing chlorine and an alkali metal hydroxide comprising:

• (a) combining about 1 to about 50 parts by weight polytetrafluoroethylene powder having an average particle size of about 100 to about 1,000 microns diameter with about 50 to about 98 parts by weight of a solid pore-forming powder having an average particle size of about 0.1 to about 100 microns diameter, and about 10 to about 1,000 parts by weight of a nonaqueous liquid capable of wetting the polytetrafluoroethylene and incapable of dissolving substantial amounts of the pore-forming powder;
• (b) mixing the combination with a shearing means sufficiently to reduce the average particle sizes of the polytetrafluoroethylene to leas than about 50 microns diameter;
• (c) removing a portion of the liquid from the mixture of step (b) until the mixture has a liquid to solid weight ratio of about 0.05 to about 1;
• (d) rolling the compressed mixture a plurality of times to form a sheet;
• (e) heating the sheet sufficiently to sinter the sheet material;
• and
• (f) removing at least a portion of the solid pore-forming powder from the sintered sheet by contacting the sheet with a liquid medium to produce a porous polytetrafluoroethylene sheet with a thickness of from about 5 to about 100 mils, an average pore size of from about 0.1 to about 100 microns, a gas permeability of from about 1 to about 100 seconds, a liquid permeability factor of from about 1 to about 60, and a tensile strength of from about 100 to about 1000 pounds per square inch.