Research On The Surface Modification And Optimization Of Polyvinylidene Fluoride (PVDF) Flat Sheet Membrane

Polyvinylidene fluoride(PVDF)is one of the most commomly used and well established polymer membrane materials,which has the advantages of high mechanical strength,good chemical stability,and long life cycle.However,as a typical non-hydrophilic material film,its membrane is easy to suffer membrane fouling in the actual applications,seriously affecting its performance and service life.Therefore,the preparation of high-throughput and strong anti-fouling PVDF matrix membranes by hydrophilic modification is of great importance for improving membrane system stability and reducing its operating costs.In this project,different proportions of PVDF,PVDF-co-CTFE and polyvinylpyrrolidone(PVP)were blended and the flat sheet membrane was firstly prepared by the immersion precipitation method.Then,tBMA monomer was grafted onto the active site of the PVDF-co-CTFE component on the blend membrane surface.Through a series of subsequent reactions,hydrophilic and oleophobic triblock copolymer(PVDF-co-CTFE)-PMAA-g-fPEG(AP)was formed on the membrane surface.The properties of prepared membranes with different composition of the membrane materials were investigated.It was found that the porous membrane structure of the base membrane by adding 5% wt PVP enhanced the surface grafting reaction.The higher the content of PVDF in the base membrane,the higher the mechanical strength and durability of the modified membrane will be;and the higher the content of PVDF-co-CTFE,the better the surface hydrophilicity and oleophobicity of the obtained membrane will be.The major factor that limited the greater hydrophilicity of the modification membrane surface was attributed to the uneven grafting and the insufficient graft density.When the blend ratio of PVDF and PVDF-co-CTFE was 6:4 and the amount of PVP added was 5 wt%,the modified membrane showed the best performance in the flux decay and flux recovery,and the oil rejection rate was up to 98.62%.,which demonstrated excellent oil fouling resistance and reusability.In order to further improve membrane surface properties in such as higher hydrophilicity in the above studies,PVDF-co-CTFE was subsequently used to synthesize AP through the same reaction mechanism,and then the AP was blended with PVDF,PVP and a new component: inorganic non-metallic additive Graphene Oxide(GO).Membranes were again prepared by the immersion precipitation method.The solvent selection,PVP addition amount,GO addition amount,and the effect of PVP,AP,GO interactions on themembrane structure and properties were investigated in the PVDF/AP/GO/PVP blend system.The study showed that GO component can be well dispersed with the use of DMAc as the membrane preparation solvent;the addition of 1.5 wt % PVP can not only provide a porous membrane structure but also ensure that the mechanical strength would not be too low to affect practical applications.The addition of AP obviously improved the hydrophobic performance.The addition of GO did not affect the overall finger pore structure but increased the membranes' sponge layer thickness,which is beneficial to the improvement of the mechanical strength;the hydrophilic property of the membrane was further improved by the addition of GO through its hydrophilic group and the interaction with PVP;with the GO addition amount of 0.20 wt%,the blend membrane showed the best filtration flux,flux recovery and rejection.Its oil rejection rate was up to 98.94%,showing outstanding anti-oil fouling performance.