Influence of residence time on performances of PVDF membranes prepared via free radical polymerization



Poly(vinylidene fluoride) (PVDF) membranes were prepared with various residence times using water–ethanol (50 : 50, mass ratio) and pure ethanol coagulants as first coagulant, respectively. The physical properties of PVDF solution after free radical polymerization were investigated by dynamic light scattering (DLS), scanning electron microscopy (SEM), viscosity, precipitation kinetics, and surface tension. Resultant PVDF membranes were characterized by SEM, contact angle, mechanical properties, and filtration properties. The results showed that the longer residence time in the first coagulant contributed to the filtration properties improvement. Contact angles of the top-surfaces and bottom-surfaces of membranes decreased as residence time increasing in the first coagulant, and the top-surface showed better hydrophilicity than that of the bottom-surface. The pore size distributions of PVDF membranes showed that the dominating demixing process of the casting solution in water–ethanol coagulant was 5 s, and in that of ethanol was 10–15 s. Additionally, the short-time delay demixing process in water–ethanol first coagulant resulted in a thin dense layer near the top surface, and the longer time delay demixing process in that of ethanol contributed to the shift of the inter-globules to the cellular morphology in the case of the residence time increasing. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014, 131, 39987.