Production of Polyethersulfone Hollow Fiber Ultrafiltration Membranes. II. Effects of Fiber Extrusion Pressure (EP) and PVP Concentration in the Spinning Solution

Abstract

The dimensional and UF performance characteristics of hollow fiber membranes 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, 20/60/20, 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; the 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 air gap (LAG) was held constant at 80 cm in the production of all the fibers. An increase in EP always tended to increase OD, while ID decreased, increased, or remained constant depending on the WFR used. An increase 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 with an increase in PVP concentration in the fiber spinning solution and the consequent increase in solution viscosity. Both fiber dimensions and skin layer morphology were found to be governed by the combined effects of desolvation, fiber swelling, and fiber stretching during fiber production.