Improving the perm-selectivity and anti-fouling property of UF membrane through the micro-phase separation of PSf-b-PEG block copolymers

Abstract

PSf-b-PEG block copolymers with different PEG contents were synthesized to fabricate the highly perm-selective and anti-fouling ultrafiltration (UF) membranes. PEG homopolymer was also blended into the polysulfone casting solutions to fabricate the control (PSf/PEG blend) membranes. The membrane pore structure, surface properties and separation performances of PSf-b-PEG block copolymer membranes and PSf/PEG blend membranes were investigated to identify the role of PEG block for the pore formation. Our results find that the higher PEG content in the PSf-b-PEG block copolymer and in the PSf/PEG blend system was favorable to form more pores and thinner top skin layer with the slightly larger pore size and the higher MWCO of the fabricated membranes. But under the same content, PEG in the block copolymer could help to generate more pores but with similar pore size than PEG in the blend system during the phase-inversion process, which is because of the micro-phase separation of PSf block and PEG block. The fabricated PSf-b-PEG21 (PSf-b-PEG having 21 wt% PEG) membrane had a high water permeation coefficient of 980.0 ± 33.0 LMH/bar and a high BSA rejection above 98%, succeeding the current perm-selectivity upper-bound of the reported polymeric UF membranes. Antifouling experiments confirmed that the PSf-b-PEG21 membrane exhibited a slow and less flux decline during the fouling stage, but a fast and high flux recovery after the backwash cleaning. Our work provides some insights on the relationship of PSf-b-PEG block copolymer composition and membrane structure-separation properties.