Hydrophilic Modification Of Poly(Vinylidene Fluoride) Membranes And Their Anti-fouling Performances

Polyvinylidene fluoride（PVDF）is a semi-crystalline polymer with strong C-F bonds,so it has high mechanical strength,excellent chemical and thermal stability,and good aging resistance.However,due to the hydrophobic nature of the PVDF polymer,PVDF membranes are susceptible to fouling when treating solutions containing hydrophobic macromolecules such as proteins,which are easily absorbed on the membrane surface to block the pores.Membrane fouling could dramatically reduce the permeability of the membrane,deteriorate the separation performance and shorten the lifetime of the membrane.In order to effectively alleviate membrane pollution problems,PVDF membranes with significantly improved hydrophilicity and anti-fouling performance were prepared by surface modification and in-situ synthesis in this paper,and the structure and properties of the membranes were detected by various characterization methods.The corresponding research results are as following:1.Biomass rhamnolipids were first used onto the surface of PVDF membrane for chemical grafting modification,the resulting modified membrane had excellent hydrophilic and anti-fouling properties.In this work,we first configured the PVDF casting solution,then prepared the pristine PVDF membrane by NIPS,and finally obtained the hydroxylated modified PVDF membrane by alkali treatment.As an amphiphilic surfactant,rhamnolipid has a carboxyl group on its long hydrophobic chain,which was bonded to the hydroxyl group on the alkali-treated PVDF membrane by esterification reaction,thereby making rhamnolipids’hydrophilic end exposed onto the membrane upper surface.The grafting results of rhamnolipids on the membrane were confirmed by FT-IR and thermogravimetric characterization.SEM images of the membrane surface and cross-section and surface AFM images showed that the membrane surface is smoother,but the density and diameter of membrane pores significantly decreased.The water contact angle results showed that the hydrophilic properties of the PVDF modified membrane are greatly improved.The filtration tests showed that the pure water flux of PVDF modified membrane decreased,but the rejection rate was unaffected,and the anti-fouling performance was greatly improved.The antifouling analysis showed that the result was mainly caused by the reduction of the irreversible fouling rate.Studies have shown that the hydrophilic properties and antifouling properties of the PVDF-Rha membranes have been greatly improved.2.In-situ synthesis of iron and manganese hydroxide in PVDF membrane,and the hydrophilicity and anti-fouling properties of the modified membrane obtained are effectively improved.In this work,anhydrous FeCl₃ and MnCl₂ was blended into PVDF polymer solution,and then phase inversion was carried out in NaOH solution to produce the corresponding iron and manganese hydroxide nanoparticles.The products formed in PVDF membrane were confirmed by FT-IR and thermogravimetric characterization.The water contact angle tests proved that the hydrophilicity of the modified membranes was greatly improved.Compared with the pristine membrane,SEM and AFM images revealed the results of in-situ synthesis of iron,manganese hydroxide nanoparticles in the modified membrane and the decrease of surface roughness.Filtration tests indicated that the pure water flux of the modified membrane decreased.The analysis of BSA solution filtration test of PVDF-0 membrane and PVDF-Fe membrane showed that the improvement of anti-protein contamination performance of PVDF-Fe membrane was the result of the combined effect of reduced irreversible fouling rate and increased reversible fouling rate.In summary,based on PVDF membrane materials,we have adopted two different modification methods,but both obtained modified membranes with hydrophilicity and anti-fouling properties.This paper provides new solutions and cognitive insights for PVDF membrane fouling in practical applications.