Process for producing polyacrylonitrile reverse osmotic membranes

A process for producing a polyacrylonitrile reverse osmotic membrane which comprises the steps of dissolving an acrylonitrile polymer in formamide-containing dimethylformamide to prepare an acrylonitrile polymer solution for membrane formation;

• shaping the polymer solution into a membranous product of a desired form while maintaining the temperature of the polymer solution above its gellation temperature;
• removing the solvent from the membranous product by bringing one side of the membranous product into contact with an aqueous solution of a temperature lower than 15.degree. C. containing at least 10 weight % of a water-soluble solvent compatible with the mixed solvent, immediately or after bringing it once into contact with an inert atmosphere, and by bringing the other side of the membranous product into contact with an inert medium or an aqueous solution of a temperature higher than 0.degree. C. containing not more than 50 weight % of a water-soluble solvent compatible with the above-mentioned mixed solvent, immediately or after bringing it once into contact with an inert atmosphere;
• subjecting the thus-obtained solidified membrane to a heat treatment at a temperature between 50.degree. and 120.degree. C.;
• and then subjecting the membrane to a plasma treatment.