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Effect of PVP Additive on PVDF/TPU Blend Hollow Fibre Membranes by Phase Inversion.

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Asymmetric blend hollow fibre membranes were made from a new casting dope containing poly(vinylidene fluoride) (PVDF)/thermoplastic polyurethane (TPU)I N,N-dimethylacetamide (DMAc )/polyvinylpyrrolidone (PVP). The separation property, microstructure, crystalline phase of membranes, and membrane strength were characterized by bovine serum albumin (BSA) retention experiments, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy-attenuated total reflection (FTIR-ATR), differential scanning calorimetry (DSC) and tensile testing, respectively. PVP at low concentration (<:::3 wt%) was a significant demixing enhancer which thermodynamically controlled the phase inversion process, improved flux, reduced a-form crystal structure, and decreased crystallinity of PVDF in membranes. At high concentration of PVP (>3 wt %) due to viscosity buildup, kinetic hindrance overwhelmed the thermodynamic factor which suppressed the formation of macrovoids, reduction of flux, and increase in crystallinity of PVDF in membranes.

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