Preparation And Performance Study Of Hydrophilic Poly (Vinylidend Fluoride) Blend Membranes

PVDF membrane is widely used in the separation field for itsexcellent thermal-chemical stability and mechanical property. However,PVDF membrane is hydrophobic and easily polluted by oil, protein andother macromolecules. Blending is an efficient approach to improve thehydrophilic properties of membrane. PVA is a widely used water-solublepolymer. In this work, modified PVA (polyvinyl butyral(PVB) andcationic polyvinyl butyral (CPVB)) were blended with PVDF to fabricatemore hydrophilic PVDF membranes.Firstly, we mainly discussed the synthesis of CPVB using 3-chloro-2-hydroxypropyl trimethyl ammonium chloride (CTA) and n-butyraldehydeacetals as reagent, subsquently. The chemical structures of CPVB wereconfirmed by 1H-NMR spectra. The solubility of CPVB in varioussolvents was examined. The hydrophilic property of casting film ofCPVB was verified by contact angle tests. Visual method showed thatPVDF/PVB/DMAc and PVDF/CPVB/DMAc ternary system werepartially compatible.Secondly, the PVDF/PVB blend membranes were prepared by immerse precipitation method from PVDF/PVB/DMAc ternary system.The compatibility of PVDF/PVB and the effects of PVDF/PVB blendratio, additive, coagulation bath content and temperature on blendmembrane performance were studied. DSC showed that PVDF/PVBblend systems were incompatible blend. With PVB content increased, thewater flux of PVDF/PVB blend membrane increased from 5.4 L/m2.h to128L/m2.h. The highest water flux was obtained when ethanol/water(25/75) solution was used as coagulation bath. The water flux alsoincreased when coagulation bath temperatue increased.Thirdly , DSC method was used to determine the compatibility ofPVDF/CPVB blend system, and it was proved to be partially compatibleblend. The influencing factors of PVDF membrane structure andperformance are studied. CPVB can improve the hydrophilicity ofPVDF/CPVB blend membranes, which could be illuminated by thedecrease in dynamic contact angle and the significant increase of waterabsorpation ratio. The water flux of blend membrane reached 8100L/m2.has ethanol/water (25/75) solution was used as coagulation bath.