Abstract: A selectively permeable hollow fiber membrane for blood dialysis consisting substantially of a cellulose derivative, which has at least a dense layer on the innermost side and a porous layer of greater void percentage on the outside, and a process for producing the selectively permeable hollow fiber membrane consisting substantially of a cellulose derivative, which comprises extruding a spinning solution containing a polymer consisting substantially of a cellulose derivative dissolved in an organic solvent, from an annular slit into a filamentous form, while simultaneously introducing a core material solution with a water content of at least 50 wt % into the extruded filamentous body, and then immersing the filamentous body into a coagulating solution after passing it through a gas.

Abstract: A process for the preparation of a porous hollow filament composed mainly of an organic polymer, which comprises separately feeding a powder of the organic polymer and a liquid additive to a feed zone of twin-screw extruder, mixing the polymer with the additive in a kneading zone of the extruder to form a substantially liquid mixture, further kneading and compressing the liquid in a kneading and compressing zone of the extruder, feeding the liquid to an extruding zone of the extruder, and extruding the liquid from the extruding zone.