Preparation And Performance Study Of PVDF Modified Membrane By TIPS Method

Polyvinylidene fluoride(PVDF)membranes stand out in many separation membranes due to their high mechanical strength,high dielectric constant,and good thermal stability.However,in the ultrafiltration process,the PVDF membrane is easily fouled due to its high hydrophobicity,and the anti-pollution ability is low,resulting in limitation of the service life and use efficiency of the membrane.Therefore,modifying the PVDF membrane to improve the hydrophilicity of the membrane is the most important factor in further developing the PVDF ultrafiltration membrane.In this paper,different forms of ZnO and ionic liquids were used as additives.PVDF modified membranes were prepared by thermally induced phase separation(TIPS).The effects of the type and content of additives on the morphology and properties of the membranes were investigated.The details are as follows:Firstly,PVDF flat membranes were prepared by TIPS method.The effects of PVDF concentration,diluent ratio and coagulation bath temperature on the microstructure,hydrophilicity,mechanical properties,porosity and water permeability of the membrane were investigated.The study found that when the concentration of PVDF is 20%,the mass fraction of triethyl phosphate(TEP)is 27%,and the coagulation bath temperature is 60 °C,the overall performance of the membrane is optimal.Secondly,PVDF/ZnO hybrid membranes with different forms of nano-ZnO as additives were prepared by TIPS method.The effects of morphology of ZnO particles on the microstructure and properties of hybrid membranes were systematically investigated.Studies have shown that the addition of ZnO can improve the photocatalytic effect of the membrane.In the process of treating dye wastewater,the hybrid membrane can degrade the organic dye under the illumination for self-cleaning.At the same time,it was found that the PVDF hybrid membrane(ie P-ZnO membrane)doped with porous ZnO has the best overall performance.P-ZnO hybrid membrane has the lowest surface roughness,the highest hydrophilicity,the maximum pure water permeation flux,the highest OVA rejection,the largest FRR and the highest MB photocatalytic degradation rate under the same conditions of three kinds of ZnO particles.Next,the effect of the addition amount of ZnO on the structure and properties of the membrane was investigated by using porous ZnO as an additive.It is found that the hydrophilicity and water flux of the membrane increase with the increase of ZnO content,and the membrane water flux can reach 78.6 L·m-2·h-1,which is about 57.5% higher than that of pure PVDF membrane.At the same time,with the increase of ZnO content,the self-cleaning performance of the membrane is also enhanced,and the degradation rate of MB can reach 51%.Finally,the modified PVDF ultrafiltration membrane was prepared by using ionic liquid as additive.The effect of ionic liquid addition on membrane structure and properties was investigated.The results show that when the mass fraction of [Bmim]Cl is 0.25%-0.5%,the comprehensive performance of the modified membrane is the best.At this time,the hydrophilicity of the modified membrane is greatly improved,the water flux and rejection can be increased by 61.1% and 38.4% respectively,and the flux recovery rate can reach 86.4%.