HOLLOW FIBERS OF ACRYLONITRILE POLYMERS FOR ULTRAFILTER AND METHOD FOR PRODUCING THE SAME

摘要

A hollow fiber of acrylonitrile polymer for ultrafilter use, said acrylonitrile polymer containing at least 60 mol % of acrylonitrile units, having a structure consisting of (1) a reticulate porous region concentric with the central axis of the hollow fiber; the reticulate porous region including therewithin at least one succession of voids concentric with the central axis of the hollow fib??? and (2) a gradient-type porous region adjacent to the outer portion of the reticulate porous region or to each of the outer and inner portions of the reticulate porous region and concentric with the reticulate porous region and the central axis of the hollow fiber; the average sized of pores in a gradienttype porous region decreasing from about 5.mu.-1.mu. adjacent the reticulate porous region to about 0.1.mu.-several .ANG. at the surface of the hollow fiber, is prepared by dissolving, at a temperature in the range of -5.degree.C to 0.degree.C, an acrylonitrile polymer containing at least 60 mol% of acrylonitrile units in a nitric acid aqueous solution having a concentration in the range of 65-95% by weight to prepare a spinning solution, having a polymer concentration in the range of 2-40% by weight, extruding the resultant solution through spinnorettes having ? ring form orifices into an aqueous toagulation bath, having a concentration of nitric acid of 30% by weight or less, at a temperature of 4-50.degree.C and concomitantly feeding a liquid as an internal coagulant into the central part of the ring form orifices.