PURPOSE: To enhance the permselectivity to an org. liq. from its aq. soln. by heat-treating a porous membrane contg. a polyvinylidene fluoride-based polymer at ≥35°C to form the aq. volatile org. liq. soln.-concentrating membrane.
CONSTITUTION: A soln. consisting of a polyvinylidene fluoride-based polymer, its solvent and an org. solvent having higher volatility than the solvent is cast over the surface of a solid, etc., in fixed thickness. The solvents are vaporized for a fixed time, and then the solvent is substituted for a solidifying solvent to obtain a sheet-shaped porous membrane. The porous membrane of the polyvinylidene fluoride-based polymer is heat-treated at a temp. higher than 35°C or appropriately higher than 50°C and lower than the m.p. of the polymer to obtain an aq. volatile org. liq. soln-concentrating membrane. The polyvinylidene fluoride content of the membrane is appropriately controlled to at least 50wt.%.
FUJII YOSHINARI
IWATANI HIDETSUGU
