Investigation of the Impacts of Dope Solution Viscosity on Membrane Morphological and Operational Characteristics

In non-solvent induced phase separation (NIPS), organic solvents are generally used to dissolve polymers. Organic solvents derived from petroleum sources, such as N-methyl-2-pyrrolidone (NMP) and dimethylacetamide (DMAc), have been traditionally used to fabricate polymeric membranes. These solvents are often volatile and/or hazardous, and regulatory pressure has been rising in Europe and China to stop the use of these. Therefore, using renewable solvents derived from biomass is of great interest in order to make membrane fabrication more sustainable. In this study, the viscosities of different dope solutions made by dissolving polysulfone (PSf) in DMAc and in NMP were measured as a function of polymer concentration and dope temperature. Morphological characteristics of membranes prepared using the tested dope solutions monitored included contact angle, zeta potential, surface roughness, surface pore size distribution and pure water permeability. Correlations between dope solution viscosity and membrane properties were analyzed to develop a mathematical model that could be extrapolated to provide information regarding casting dope viscosity to achieve desirable membrane properties when using new solvents and scaling up the membranes.