Sulfonated Polyethersulfone as a New Platform for Thin Film Composite Membranes

Membrane based separations are widely in many technically and commercially relevant processes, including sea and brackish water desalination and treatment. Current drawbacks from membrane-based processes are fouling propensity and low water fluxes. One solution to remediate these issues is the use of intrinsically hydrophilic support layers in composite membranes. The hydrophilic nature of the substrates will facilitate increased water transport across the membrane and provide anti-fouling characteristics. This study investigated the use of sulfonated polyethersulfone (SPES) as a new material for thin film composite membranes. Four degrees of sulfonation were examined. Asymmetric membranes were cast with polymer loadings between 12-20 % by weight using n-methyl-2-pyrrolidone (NMP) as the solvent and precipitated in water. Membranes films were characterized using a variety of techniques to analyze the physical, chemical and thermal properties. Select polymers were interfacially polymerized using m-phenylenediamine (MPD) and 1,3,5-benzenetricarbonyltrichloride (TMC) to create a polyamide layer on top of the membrane supports. The thin-film composite membranes were tested in both reverse osmosis (RO) and forward osmosis (FO) systems. The sulfonated polymers on average performed just as well or better than the unmodified polyethersulfone (PES) polymer in RO applications. With respect to the FO testing, wetting negatively affected the performance of the SPES. The base PES exhibited much greater fluxes and wetting than the SPES. It was determined that sulfonated polymers are a promising new material for thin film composite membranes, particularly for RO applications.