Preparation and characterization of PVDF–SiO2 composite hollow fiber UF membrane by sol–gel method

Organic–inorganic polyvinylidene fluoride (PVDF)–silica (SiO2) composite hollow fiber ultrafiltration (UF) membranes were prepared by the combination of a tetraethoxysilane (TEOS) sol–gel process with a wet-spinning method. The membrane formation mechanisms were investigated in terms of viscosity, precipitation kinetics and morphology. Results showed the dope viscosity increased with the increment of TEOS concentration in dope. The addition of TEOS accelerated the precipitation of the dope. SEM pictures showed the cross-section morphology of PVDF composite membranes changed from finger-like macrovoids to sponge-like structure with increasing SiO2 content. The mechanical, thermal stabilities and permeation property of PVDF–SiO2 composite membranes were further examined. At lower TEOS concentration, the hydrolyzed SiO2 particles, which were homogeneously dispersed in PVDF matrix, acted as the physical crosslinking points, and led to an improvement of mechanical and thermal properties. While at higher TEOS concentration, SiO2 formed network, which restricted the movement of PVDF and led to the decrease of the mechanical and thermal stabilities. Moreover, XRD and FTIR results revealed that the crystal structure of PVDF underwent a transition from α-phase to β-phase due to the addition of TEOS. The contact angle and UF experimental results of PVDF–SiO2 composite membranes showed an improvement of hydrophilicity and permeability. The PVDF–SiO2 membrane prepared from the dope with 3 wt.% TEOS concentration had the best UF performance and antifouling property.