Structure and Properties of Polyethersulfone Membranes Based on Polyethersulfone-Nonsolvent-Solvent Systems

The effect of degree of saturation of casting solutions (alpha*-the ratio of the nonsolvent amount added to the polymer solution to the non-solvent amount which causes phase separation) and nonsolvent power on the structure and performance of membranes prepared from system "Polyethersulfone (PES)- non-solvent-solvent" have been studied. Nonsolvent power has been characterized in terms of precipitation number (PN), i.e., the amount of nonsolvent that leads to phase separation of 100 mL of a 1% PES solution. Glycerol (PN = 27.8 g/dL), polyethylene glycol 400 (PN > 1000 g/dL), and their mixtures have been used as a nonsolvent additive to the casting solution. It has been shown that membranes with a nice spongy structure are formed in the case of using casting solutions located near the binodal line. In this case, the membrane flux depends on the nonsolvent power: the higher the PN of the nonsolvent, the higher the membrane flux. The highest flux is exhibited by membranes prepared from casting solutions with a degree of saturation of alpha* = 0.52-0.81 depending on the PN of the nonsolvent. In this case, macrovoids are present in the structure of the supporting layer of the membranes; the size and shape of the macrovoids also depend on the PN of the nonsolvent: the higher the PN, the larger the macrovoid size in the membrane supporting layer. The results have made it possible to propose a new approach to obtaining PES membranes with a desired structure and properties.