Study On The Preparation And Blend Modification Of Polyethersulfone Hollow-Fibre Membrane

Polyethersulfone (PES) hollow fiber membranes were prepared basing on the phase separation behavior of PES dope by phase inversion method. Moreover, the sulfonated PES (SPES) was blended with PES to improve the hydrophilicity of PES membranes.With the addition of DMAc into the internal coagulant, micropores were formed in the inner surface of the hollow fiber, and the finger-like macrovoid was suppressed in the cross section of the hollow fiber according to the scanning electron microscopy (SEM) observation. With higher PES concentration, the membrane structure became denser, and a membrane with higher retention and lower pure water flux was obtained. While PES content were 20wt%, the obtained membrane had the better combination performances. Increasing the extrusion rate, the wall thickness and pure water flux increased. The maximum pore size and retention decreased, and the sponge-like structure near the outer surface changed to a finger-like structure with dense skin layer. With the increase of air gap distance, the inner and outer diameter decreased gradually. The finger-like structure near the outer surface changed to a sponge-like structure, and pure water flux and retention was improved. Lifting the temperature of coagulation bath caused the decreasing of the inner and outer diameter and increasing of the maximum pore size and pure water flux. When the air gap distance was 10 cm, the pore size at the outer surface of hollow fiber increased with increasing the temperature of coagulation bath. With the temperature of coagulation bath at 40℃ and 50℃, the micropores formed at the outer surface, and w the finger-like structure near the outer surface changed to a sponge-like structure. However, the phenomena did not appeared in the same conditions if adopting air gap distance as 0 cm. When small molecules were used as additives in casting solution, it was found that LiNO₃ and acetic acid were superior to ethanol and acetone in improving the performance of the membranes. Further studies on using acetic acid as additives in casting solution and varying theinternal coagulant composition, it was found that the minimum content of DMAc in coagulation bath must be less than 20%wt for the formation of micropores in inner surface.SPES was blend with PES to prepare ultrafiltration hollow fiber membranes to improve their hydrophilicity. With the addition of SPES into PES solution, spinodal phase separation occurred and the formation of the finger-like macrovoid was suppressed. In this case, adding DMAc and ethanol into the outer coagulant enlarged the dimensions, and increased the pure water flux of the obtained membranes. But the retention decreased gradually, and the finger-like structure near the outer surface changed to a sponge-like structure as well.