Polysulphone/montmorillonite nanocomposite membranes: Effect of clay addition and polysulphone molecular weight on the membrane properties

Polysulphone (PSf)/sodium montmorillonite clay (MMT) nanocomposite membranes were prepared via a congruence of the wet-phase inversion and the solution dispersion techniques, and a thermodynamic study, as well as an investigation of its morphological properties, hydrophilicity and membrane performance, were performed with respect to the PSf molecular weight and MMT content. An increase in both of these parameters contributed to a dislocation of the binodal curve to lower non-solvent contents. Exposure to 80% relative humidity of water vapour prior to immersion produced cylindrical defects in the surface and closed-cell morphology, whereas the membranes prepared by immediate immersion exhibited dense surfaces. In addition, there was competition between the thermodynamics and kinetics of the membrane formation. As the MMT content and PSf molecular weight increased, the membrane porosity increased due to a delayed liquid–liquid phase. The contributions from the acid–base interactions improved in the membranes with a higher PSf molecular weight. The membranes prepared by exposure to 80% relative humidity of water vapour exhibited high permeability values due to defects, and the membranes prepared by immediate immersion exhibited reduced permeabilities as the PSf molecular weight and clay content increased. Finally, these membranes, which have higher clay contents and PSf molecular weight, exhibited higher rejection values and were more selective to solute passage.