PVDF Ultrafiltration Membrane Polar Crystal Form Control And Anti-pollution Behavior Research

Among various membrane materials,polyvinylidene fluoride?PVDF?has attracted a lot of attentions due to its distinguished physicochemical properties.However,as a result of the hydrophobic nature,the current PVDF UF membranes suffer from serious fouling,which was seriously hindered its development in water purification process.Although the antifouling modification of polyvinylidene fluoride?PVDF?membrane has attracted much attentions recently,the role of PVDF polymorphism on membrane fouling resistance have rarely been mentioned.In this study,we report a new strategy to tailor the polymorphs and pore structure of the PVDF membranes,simultaneously,via incorporating the in-situ blending of Pluronic F127?F127?with a sodium chloride?Na Cl?coagulation bath?CB?.Then,the effect of PVDF polymorphs on membrane fouling behavior was also investigated.Firstly,the Na Cl CBs were utilized to create ion-dipole interactions between Na⁺and PVDF molecule chains,and to promote the formation of polar?-PVDF phase during phase inversion process.When cooperated with the Na Cl CBs,due to the intensified copolymer-polymer interactions,blending amphipathic F127 was demonstrated more effective in manipulating the membrane morphology compared with blending hydrophilic additives.The prepared membrane possessed a highly porous surface with narrowed size distribution,resulting in a great enhancement for both the permeability and selectivity.Secondly,two PVDF membranes with similar pore structure but distinct polymorphs were prepared,and their fouling behavior was systematically compared by using humic acid?HA?,bovine serum albumin?BSA?,dextran?DEX?and their mixture?SSW?as the typical organic foulants.A remarkable correlation between PVDF polymorph,membrane surface chemistry and fouling resistance was observed,demonstrating the exceptional ability of?-PVDF phase?i.e.,?-PVDF membrane?in fouling mitigations when compared to?-PVDF phase?i.e.,?-PVDF membrane?.Meanwhile,interaction forces between foulant-coated particle probes,simulating foulant molecules,and each membrane surface were measured by AFM and theoretical calculated depended on surface energy components.It is clearly shown that the enhanced fouling resistance of ?-PVDF membrane was mainly driven by the reduced adhesion tendency of foulants,which could further attribute to the strong electron donor monopolarity of?-PVDF phase(?^AB-=25.3 m J/m²)compared to?-PVDF phase(?^AB-=3.3 m J/m²).Finally,for each SSW-fouled membrane,depth profiling of the external fouling layer and composition of the extracted internal foulants were carefully investigated by variable angle FTIR and UV-vis spectrometer,respectively,suggesting the strong relationship between membrane fouling behavior and membrane-foulant and foulant-foulant interactions.