Understanding the multiple functions of styrene-co-maleic anhydride in fabricating polyvinylidene fluoride hollow fiber membrane via coupled phase inversion process and its effect on surface infiltration behavior and membrane permeability

Polyvinylidene fluoride/styrene-co-maleic anhydride (SMA) hollow fiber membranes were prepared via coupled phase inversion (thermally induced phase separation-nonsolvent induced phase separation) process. The multiple functions of SMA, such as surface enrichment, non-diluent, dispersion, pore-former, hydrophilicity and surface infiltration behavior, were discussed. The membrane formation mechanisms about surface deposition of SMA for the outer surface and pore-former of micelle for the matrix were proposed. The membrane microstructure for the matrix changed from the spherulite to the interconnected cellular pores enclosed by the stackage of small size spherulite and the porosity of the membrane increased from 57.22% to 74.62% with the addition of SMA. Interestingly, the continuous SMA deposition layer as thin as 50~160 nm can be fabricated by this coupled phase separation process, which in turn not only decreased the thickness of outer skin-layer and the pore size, but also enriched the SMA content on outer surface markedly, improved the hydrophilicity, flux and the anti-fouling performance. Finally, based on the traditional hydration layer (HL) notion, the anti-fouling mechanism of the membrane was further developed from the point of “building-foundation” relationship via the surface infiltration of SMA. The purpose of this manuscript is to offer a simple and effective way to regulate the membrane microstructure, introduce functional group and propose a revised anti-fouling mechanism.