Enhanced mechanical strength and performance of sulfonated polysulfone/Tröger's base polymer blend ultrafiltration membrane

Abstract

To improve the mechanical strength and separation performance of sulfonated polysulfone (SPSf) ultrafiltration membranes, Tröger's base (TB) polymer was blended into the casting solution. An acid-base crosslinking structure between the sulfonic acid groups of SPSf and tertiary amine groups in TB would contribute to their good compatibility and influence the membrane formation process, morphology and properties. The formation of acid-base pairs was confirmed by the existence of quaternary amine groups in the X-ray photoelectron spectra of SPSf/TB blend membranes. According to the pore structure analysis of ultrafiltration membranes, the blending of TB polymer into SPSf enhanced the surface and total porosities, and reduced the top layer thickness. In addition, the finger-like pores became more regular and vertically interconnected. The SPSf/TB blend membrane showed a higher water contact angle than SPSf membrane due to the addition of hydrophobic TB polymer and formation of acid-base crosslinking structure. The SPSf/TB blend membranes showed higher pure water fluxes (127.4–342.7 L m−2 h−1) than the SPSf membrane (51.6 L m−2 h−1). All membranes showed similar retention factor for bovine serum albumin (BSA), a model protein foulant. In static experiments, the amount of BSA adsorbed by the SPSf/TB blend membranes was much lower than that of the pristine SPSf membrane because the enhanced charge of the blend membranes (ζ = −72.46 ~ −79.17 mV) strengthened the electrostatic repulsion between membrane surface and BSA. The flux recovery ratio after three ultrafiltration cycles using SPSf/TB blend membranes was lower than that of SPSf membrane because pore blockage and irreversible pollution occurred more easily under a high flux, larger average pore size, and lower hydrophilicity. The introduction of TB polymer enhanced the mechanical strength of the ultrafiltration membrane due to the formation of acid-base crosslinking structure between TB polymer and SPSf.