Hollow fiber membrane for plasma separation

A hollow fiber membrane for plasma separation comprising a porous hollow polymer fiber defining a volume part of at least 70% by volume pores, said porous hollow polymer fiber displaying an inner fiber diameter from about 100 to 550 micron and a wall thickness from about 15 to 300 micron and being a polymer selected from the group consisting of a polyolefin, a copolymer polyolefin, a halogen containing polyolefin and polyethylene sulfide, said volume part displaying a filtration factor for separation of marcomolecules from biological cells in a liquid mixture containing both, said filtration factor for proteins of human blood, being in the molecular weight range of from about 60,000 to 3,000,000, of at least about 0.7, said porous hollow polymer fiber being produced by a method comprising preparing a homogeneous mixture from at least two components where one component is a fusible polymer present in the mixture in amounts from about 10 to 30 percent by weight and where a solvent component is a first liquid inert relative to the polymer and present in the mixture in amounts of from about 70 to 90 percent by weight and where said components form a binary system having in the liquid state a region of complete miscibility and a miscibility gap;

• extruding the mixture at a temperature above the segregation temperature of the mixture through a hollow fiber nozzle into a spinning tube containing a second liquid inert to the polymer and having a temperature in the spinning tube below said segregation temperature;
• moving the fiber and the second inert spinning liquid in the same direction and with about the same or only slightly different linear speed through the spinning tube;
• and removing the fiber under low tension from the spinning tube.