Effect of propionic acid in the casting solution on the characteristics of phase inversion polysulfone membranes

Polysulfone (PSF) membranes were prepared from homogeneous polymer solutions. The cast solution films were coagulated by immersion in the nonsolvent water bath or by exposure at 75% relative humidity. The precipitation rate of the cast solution film was enhanced with the addition of nonsolvent (propionic acid, PA) in the casting solution. When the cast film was solidified by the immersion precipitation, the addition of PA resulted in the increase of membrane permeability. On the contrary, even though PA was added in the casting solution, the membranes prepared by vapor exposure did not show an improvement of water permeate flux. From the characterization of the formed membranes, it was found that the number of the polymer aggregates or of the nucleation sites is increased by the addition of PA. The overall results indicated that in the specific concentration of 15 wt% PSF solution, the PA added in the casting solution works as a significant "demixing enhancer" in the phase inversion process.