Permselective membrane and process for manufacturing thereof

A method for preparing by solvent phase inversion spinning a hollow fiber membrane suitable for dialysis, the membrane comprising at least one hydrophobic polymer and at least one hydrophilic polymer, an outer surface of the membrane having pores having sizes in the range of 0.5-3 μm, the density of said pores on the outer surface being in the range of 10,000 to 150,000 pores per mm2, the method comprising:

• dissolving said at least one hydrophobic polymer and said at least one hydrophilic polymer in at least one solvent to form a polymer solution,
• extruding said formed polymer solution through an outer ring slit of a nozzle with two concentric openings,
• extruding a center fluid through the inner opening of the nozzle, and
• washing said membrane, wherein the polymer solution coming out through the outer slit opening is, on the outside of the precipitating fiber, exposed to a humid steam/air mixture comprising a solvent in a content of between 0.5 and 5% by weight related to the water content,
• the polymer solution consisting of 10-20% by weight of the at least one hydrophobic polymer, 3-11% by weight of the at least one hydrophilic polymer, 66-86% by weight solvent, and 1-5% by weight suitable additives.

A method for preparing by solvent phase inversion spinning a hollow fiber membrane suitable for dialysis, the membrane comprising at least one hydrophobic polymer and at least one hydrophilic polymer, an outer surface of the membrane having pores having sizes in the range of 0.5-3 the density of said pores on the outer surface being in the range of 10,000 to 150,000 pores per mm2, the method comprising:

• dissolving said at least one hydrophobic polymer and said at least one hydrophilic polymer in at least one solvent to form a polymer solution,
• extruding said formed polymer solution through an outer ring slit of a nozzle with two concentric openings,
• extruding a center fluid through the inner opening of the nozzle, and
• washing said membrane, wherein the polymer solution coming out through the outer slit opening is, on the outside of the precipitating fiber, exposed to a humid steam/air mixture comprising a solvent in a content of between 0.5 and 10% by weight related to the water content,
• said center fluid including a part of said at least one hydrophilic polymer.

A method for preparing by solvent phase inversion spinning a hollow fiber membrane suitable for dialysis, the membrane comprising at least one hydrophobic polymer and at least one hydrophilic polymer, an outer surface of the membrane having pores having sizes in the range of 0.5-3 μm, the density of said pores on the outer surface being in the range of 10,000 to 150,000 pores per mm2, the method comprising:

• dissolving said at least one hydrophobic polymer and said at least one hydrophilic polymer in at least one solvent to form a polymer solution,
• extruding said formed polymer solution through an outer ring slit of a nozzle with two concentric openings,
• extruding a center fluid through the inner opening of the nozzle, and
• washing said membrane, wherein the polymer solution coming out through the outer slit opening is, on the outside of the precipitating fiber, exposed to a humid steam/air mixture comprising a solvent in a content of between 0.5 and 10% by weight related to the water content,
• said center fluid consisting of 45-70% by weight precipitation medium, 30-55% by weight solvent, and less than or equal to 5% by weight said at least one hydrophilic polymer.