Effects of nucleating agents on the morphologies and performances of poly(vinylidene fluoride) microporous membranes via thermally induced phase separation

The effects of nucleating agents on the morphology and performance of poly(vinylidene fluoride) (PVDF) microporous membranes via thermally induced phase separation were investigated. The nucleating agents studied were dicyclohexyl benzene amide (TMB‐5), 2,2‐methylene bis(4,6‐tertiary butyl phenol) sodium phosphate (TMP‐1), and 1,3 : 2,4‐di‐p‐methylbenzylidene sorbitol (DM–LO). Light transmittance experiments and differential scanning calorimetry (DSC) were performed to obtain phase diagrams of PVDF/tributyl citrate/di(2‐ethylhexyl) phthalate/nucleating agent doped solutions. The morphology and performance of the prepared PVDF microporous membranes were characterized with scanning electron microscopy and microfiltration experiments. The results show that the thermodynamics of liquid–liquid phase separation were not affected by the addition of the nucleating agents, but solid–liquid phase separation was influenced. The system with 0.3 wt % TMB‐5 had the fastest crystallization rate and a better nucleation ability. The PVDF microporous membranes had a partly closed, lacy bicontinuous structure with TMP‐1 and DM–LO, whereas the membrane with 0.3 wt % TMB‐5 had an interconnected bicontinuous structure. The pore size distribution became narrower with the addition of nucleating agent. With 0.3 wt % TMB‐5, the membrane had the minimum mean pore size (0.095 μm), a porosity of 80.3%, and a pure water flux of 270 L·m^?2·h^?1; these values were higher than those of the pure PVDF membrane. The performances of the membranes decreased with additions of TMB‐5 of greater than 0.3 wt %. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013