Fabrication of ultrafiltration membranes from non-toxic solvent dimethylsulfoxide: Benchmarking of commercially available acrylonitrile co-polymers

In recent years, increased attention is given to sustainability and environmental safety of existing processes and materials. The membrane separation is considered as attractive alternative to conventional separation processes due to its greater energy efficiency and smaller carbon footprint. However, most organic solvents used for the production of polymeric membranes (DMF, DMAA, NMP), are hazardous and toxic; thus, non-toxic solvents like dimethylsulfoxide (DMSO) are considered nowadays as a perspective alternative to this solvents. The systematic study of the application of DMSO as "green" solvent for the fabrication of ultrafiltration membranes from the commercial polymer was carried out. Acrylonitrile homopolymer and six co-polymers of various composition and molecular weight were screened. It was revealed that the viscosity of the polymeric solution plays a major role in the resulting morphology and the performance of the membranes obtained. Regardless of the polymer origin and solvent nature, the studied membranes possessed finger-like porous structure if the viscosity of casting solution was lower than 42 Pa∙s, and the sponge-like porous structure at the viscosity greater than 78 Pa∙s. Analysis of the filtration data revealed that the replacement of traditional solvent DMF by non-toxic DMSO allowed obtaining the membranes with better overall performance in terms of pure water flux and rejection. The use of DMSO allowed to decrease the concentration of poly(acrylonitrile-co-itaconic acid) from 15 to 12 wt% in the spinning solution to achieve the same viscosity; and the resulting hollow fiber membrane demonstrated higher water flux and rejection compared to the one prepared from DMF.