Integrally skinned PSf-based SRNF‐membranes prepared via phase inversion—Part B: Influence of low molecular weight additives

• Presence of additives is required to synthesize SRNF membranes from PSf.
• Additive volatility does not seem to be a factor determining membrane performance.
• Using additives always increased viscosities of the casting solutions.
• The postulated link between macrovoids and high S/NS affinity is not confirmed.
• NMP and DMAc-based casting solutions led to the creation of macrovoids.

This paper is Part B of a two-paper series aiming at a better understanding of membrane formation via phase inversion process by means of immersion precipitation for hydrophobic, integrally skinned membranes. Four different polysulfone (PSf)/solvent systems, namely PSf/N-methyl-2-pyrrolidone (NMP), PSf/N,N-dimethylacetamide (DMAc), PSf/methyl sulfoxide (DMSO) and PSf/N,N-dimethylformamide (DMF), were used as base solutions to synthesize solvent resistant nanofiltration (SRNF) flat sheet membranes. The role of low molecular weight (MW) additives was studied with respect to performance of these SRNF membranes. In addition, their influence on the phase inversion process by means of immersion precipitation was studied fundamentally via viscosity and cloudpoint measurements to understand the role of the low MW additive in the formation process of integrally skinned SRNF‐membranes. The compositions of the membrane casting solutions were changed using different types of low MW additives in varied concentrations. They included: 1,4-dioxane (DIO), diethylene glycol diethyl ether (DGDE), dimethyl phthalate (DMPH), poly(ethylene glycol) dimethyl ether 250 (PEG-DME250), 2-propanol (IPA), acetone (AC), 2-butanol (BUT), γ-butyrolactone (γ-BUT), acetic acid (AA) and glycerol (GLY). The performance of the synthesized membranes was tested in SRNF by measuring iso-propanol (IPA) permeances and rejections of Rose Bengal (RB) in a high-throughput fashion. Performances were linked to membrane morphologies, as observed in scanning electron microscopy (SEM).