| abstract |
Hollow fibers of acrylonitrile polymers having waterpermeability greater than 0.2 ml/cm2.min.atm and useful as an inexpensive superior ultrafilter, comprising 1. A POROUS LAYER OR LAYERS EXISTING ON THE OUTER OR/AND INNER SIDES OF SAID HOLLOW FIBERS, THE AVERAGE SIZES OF PORES CONTAINED IN SAID POROUS LAYER OR LAYERS AND EXISTING ON EACH OF ASSUMPTIVE CYLINDRICAL SURFACES CONCENTRIC WITH THE CENTRAL AXIS OF SAID HOLLOW FIBERS, HAVING SUCH A GRADIENT THAT THE AVERAGE SIZES OF PORES CONTAINED IN THE POROUS LAYER EXISTING ON THE OUTER SIDE BECOME SMALLER TOWARD THE OUTER SURFACE OF SAID HOLLOW FIBERS WHILE THE AVERAGE SIZES OF PORES CONTAINED IN THE POROUS LAYER EXISTING ON THE INNER SIDE BECOME SMALLER TOWARD THE INNER SURFACE OF SAID HOLLOW FIBERS, AND 2. A RETICULATE POROUS LAYER ADJACENT TO SAID POROUS LAYER OR LAYERS (1) AND CONTAINING THEREIN AT LEAST ONE SUCCESSION OF VOIDS HAVING DIAMETERS OF AT LEAST 10 - 50 Mu , ARE PREPARED BY DISSOLVING AN ACRYLONITRILE POLYMER IN AN AQUEOUS SOLUTION OF NITRIC ACID OF 65 - 95% BY WEIGHT CONCENTRATION AND EXTRUDING THE RESULTING SPINNING SOLUTION THROUGH A DIE FOR HOLLOW FIBERS, INTO A COAGULATION BATH CONTAINING WATER OR AN AQUEOUS SOLUTION OF NITRIC ACID OF 30% BY WEIGHT OR LESS CONCENTRATION. |