Ultrafiltration hollow fiber membranes from poly(ether imide): preparation, morphologies and properties

Ultrafiltration hollow fiber membranes were prepared from poly(ether imide) (PEI) with a wet spinning method. Effects of N,N-dimethylacetamide (DMAc) as a solvent additive in internal coagulant and acetic acid as a nonsolvent additive in dope solution on the morphologies and performances of the membranes were investigated respectively. Scanning electron microscope (SEM) study indicated that the addition of DMAc into the internal coagulant changed the inner fiber surface from dense skin layer to porous structure. However, the pure water flux of the membrane decreased with the increase of DMAc content. On the other hand, the addition of acetic acid into casting solution promoted the spinodal demixing of the membrane-forming system and suppressed the macrovoid formation in the membrane. Nodular structure was formed in the fiber skin layer. With the increase of acetic acid ratio, the pure water flux of the membrane increased about four times, and the solute retention showed a slight decrease. The mechanical properties could also be improved slightly by this additive. The influences of PEI dope concentration on membrane morphologies and properties were also studied. It was found that tighter structure was formed for higher PEI concentration, in turn, the pure water flux of the membrane decreased from 23.4 l/(m2 h) 100 kPa for 17 wt.% PEI concentration to 7.2 l/(m2 h) 100 kPa for 25 wt.% PEI concentration. The thermal resistance of the PEI ultrafiltration membranes prepared in this work was examined using a hot water treatment up to 80 °C. No change was observed for the permeation performances of the membranes, while the study of mechanical properties showed that the elongation at break of the membrane decreased slightly.