Study On Polyvinylidene Fluoride (PVDF)/Polyvinyl Alcohol (PVA) Blend Membrane

On principle of polymer blend phase separation, PVDF/PVA flat membranes were prepared using phase inversion method. The compatibility of PVDF/PVA and the effects of PVDF/PS blend ratio, polymer concentration, additive, coagulation bath and after treatment on blend membranes performance were studied. On the basis of above work, hydrophilic PVDF/PVA hollow fiber membranes were prepared.PVDF/PVA blends showed incompatibility by the results of dynamic mechanical analysis (DMA), ultrared attenuated total reflection (FTIR-ATR) sampling technique, and optical microscope observation. So new interface microvoid structure was produced as a result of phase separation in PVDF/PVA. With PVA content increased, the pure water flux of PVDF/PVA blend membrane increased due probably to the new interface microvoid structure, and decreased with PVA content increased again, which reached the maximum when PVDF/PVA was 8/2 (wt/wt). The trends of rejection ratio and alcohol flux are contrary. PVA could improve the hydrophilicity of PVDF/PVA blend membranes, which could be illuminated by the decrease of contact angle. The phenomenon of del amination happened in casting bath, so the ultrared attenuated total reflection (FTIR-ATR) was different between surface and undersurface of PVDF/PVA blend membrane. The algebraic difference of contact angle between surface and undersurface reached the maximum when PVDF/PVA was 7/3 (wt/wt). The membrane thickness and rejection ratio increased whereas porosity and water flux decreased with polymer concentration increased. The blend membranes performance was the best when PEG600 concentration ratio was 6%. Temperature and composition of coagulation bath were much effective for porous structure and blend membranes performance. The blend membranes performance could be improved due to the compact porous structure by heat treatment, whereas alcohol treatment had no effect on porous structure. Top-quality PVDF/PVA blend membrane could be obtained through selecting proper preparation condition, blending was an efficient method to improve the PVDF membrane performance.The results of blend hollow fiber membranes were shown as follow. As PVA content increases, the finger-like pores became larger, the skin layer became thinner, and the interface microvoid was observed in membrane skin layer. Based on bursting pressure and tensile strengths results, we suggested that the mechanical properties of PVDF/PVA blend hollow fiber membranes were worse than that of PVDF membrane. PVA can improve the hydrophilicity of PVDF/PVA hollow fiber membranes, which could be illuminated by the decrease in contact angle, the increase in equilibrium water content (EWC) and the variety in dynamic moisture regain. The pure water flux increased while the rejection ratio decreased with PVA content increasing. Moreover, PVA can improve the anti-fouling property of PVDF/PVA hollow fiber membranes, which could be illuminated by the result of increase coefficient of resistance.