PRODUCTION OF POLYETHERSULFONE HOLLOW-FIBER ULTRAFILTRATION MEMBRANES.2. EFFECTS OF FIBER EXTRUSION PRESSURE (EP) AND PVP CONCENTRATION INTHE SPINNING SOLUTION

The dimensional and UF performance characteristics of hollow fiber mem branes produced by the solution spinning technique using three polymer solutions (C3, C4, and C5) were studied experimentally. The polymer ( polyethersulfone, PES)/solvent (1-methyl-2-pyrrolidone, NMP)/additive (polyvinyl pyrrolidone, PVP) concentration (wt%) used were 20/65/15, 2 0/60/20, and 25/63/12, respectively, for C3, C4, and C5 solutions, and their corresponding viscosities were 9222, 22,809, and 29,286 cP. The extrusion pressures (EP) used in fiber production were 5 to 15, 20 to 40, and 20 to 60 psig, respectively, for C3, C4, and C5 solutions; th e internal coagulant water flow rate (WFR) used were 7.5 and 10 mL/min for C3 fibers, and 5 mL/min for C4 and C5 fibers; and the length of a ir gap (LAG) was held constant at 80 cm in the production of all the f ibers. An increase in EP always tended to increase OD, while ID decrea sed, increased, or remained constant depending on the WFR used. An inc rease in PVP concentration in the fiber spinning solution contributed to greater fiber swelling effects. Nascent fiber velocity (NFV) tended to increase with an increase in EP, but it decreased considerably wit h an increase in PVP concentration in the fiber spinning solution and the consequent increase in solution viscosity. Both fiber dimensions a nd skin layer morphology were found to be governed by the combined eff ects of desolvation, fiber swelling, and fiber stretching during fiber production.