Preparation And Properties Of PVDF Hydrophilic Ultrafiltration Membrane

Polyvinylidene fluoride（PVDF）membranes are widely used,particularly in the field of water resources.However,the surface energy of the PVDF membrane is very low,leading to its poor hydrophilic performance,high driving pressure,and easy adhesion to organic pollutants such as proteins,which can cut down the membrane’s operating cycle and rise the costs of operating.Therefore,The hydrophilic modification of PVDF membrane is aimed at boosting hydrophilicity,which is an valid method to solve the above problems and has great significance.In this paper,the hydrophilic monomers hydroxyethyl methacrylate（HEMA）and acrylic acid（AA）were grafted on polyvinylidene fluoride（PVDF）by free radical polymerization to prepare PVDF-g-PHEMA and PVDF-g-PAA.After blending and doping,PVDF was prepared by phase inversion method.The influence of different graft monomers and surface treatments on the morphology and performance of the membranes were explored.The specific methods were as follows:（1）PVDF powder was defluorinated by alkali treatment and oxidized to obtain O-PVDF.The monomer HEMA was grafted by free radical polymerization to prepare polymer PVDF-g-PHEMA,which was blended with PVDF matrix to fabricate hydrophilic PVDF ultrafiltration membranes.PVDF ultrafiltration modified membranes were successfully prepared in one step.The effects of different oxidation time,grafting time,monomer concentration and mixing ratio on the morphology and properties of PVDF modified membranes were discussed.It turned out that the blended film had gradually changed from dense,smooth and non-porous to more surface pores.Compared with the customary membrane,the water contact angle of PVDF modified membranes decreased from 103°to 45.6°.The pure water flux of PVDF modified membrane increased,and the rejection rate of bovine serum protein BSA increased to 96%,which was relative to the original membrane.After BSA molecular simulation pollution,the flux recovery rate of the modified membranes were 1.7 times that of the unmodified membrane.（2）PVDF powder was defluorinated by alkali treatment and oxidized to gain O-PVDF.The monomer AA was grafted by free radical polymerization to prepare for polymer PVDF-g-PAA,which was blended with PVDF matrix to prepare hydrophilic PVDF ultrafiltration membranes.The relationship between the grafting time,monomer concentration and blend ratio and the structure and properties of PVDF modified membranes were systematically discussed.Results display the blend film had gradually changed from dense,smooth and non-porous to more surface pores.Referring to the unmodified PVDF membrane,the water contact Angle of the modified membranes weres only 33°and the water flux was about 17.8 times that of the original membrane.The rejection rate of BSA reached 95.10%.The flux recovery rate of the modified BSA membranes after being fouled was up to 97.64%.（3）The PVDF-CaCO₃ hydrophilic ultrafiltration membrane was prepared by utilizing the hydrophilic PVDF ultrafiltration membranes as template membrane and mineralizing a layer of calcium carbonate nanoparticles on the surface by means of solution impregnation method.The relationship between the infiltration concentration and time and the structure and performance of The PVDF-CaCO₃ hydrophilic ultrafiltration membrane was systematically investigated.under the optimal circumstances,using the unmodified membranes as a reference,the water contact angle of The PVDF-CaCO₃ hydrophilic ultrafiltration membrane was only 5°,the pure water flux increases from 320 L/（m²·h）to 878.6 L/（m²·h）,which were about 2.7 times higher.After BSA pollution,it had a higher recovery rate,as high as 98.24%,and had excellent anti-pollution performance.The surface of the composite membrane was enriched with PAA chains and calcium carbonate.Quality to ease the frequency of membranes cleaning,which saved the cost of water treatment.