Preparation And Investigation Of The Porous Polyvinylidene Fluoride(PVDF) Membrane Grafting With Ionic Liquid

Poly(vinylidene fluoride)(PVDF)is widely used in the fabrication of porous microfiltration or ultrafiltration membranes due to its excellent mechanical property,chemical resistance,thermal stability and processability.However,PVDF membranes show a strong nonspecific adsorption for microorganisms,cells and proteins and suffer from so called “biofouling” when encountering living system mainly due to its hydrophobicity,which intensively limiting its application.Hydrophilic modification that can effectively improve the anti-fouling ability of PVDF membrane has been an important project in the studies of PVDF membrane.Room temperature ionic liquid(IL),an organic salt with special structure,has been greatly used as a multifunctional addition agent in polymer modification research.Our previous studies have demonstrated that PVDF and IL are thermodynamically compatible and the PVDF/IL composites exhibit excellent mechanical properties,antibacterial properties and low dielectric loss.In this paper,PVDF was modified by copolymerization of hydrophilic ionic liquid,1-vinyl-3-butylimidazolium chloride([VBIm][Cl]),through electron beam irradiation grafting technology.Then the PVDF-g-IL porous membranes were prepared via immersion precipitation phase inversion method and electrospinning technique.The effects of IL grafting ratio on the structure and properties of PVDF-g-IL porous membranes were researched.The main research contents and conclusions are listed in the following:(1)The copolymerization modification of PVDF using ionic liquidThrough electron beam radiation grafting technology,the PVDF-g-IL composite was obtained by the immobilization of IL on PVDF molecular chain.Wherein,the cations of IL were fixated while the anions were still free.FT-IR results proved the successful grafting of IL onto the PVDF molecular chain.(2)Study on the structure and properties of the porous PVDF-g-IL membranesThe porous PVDF-g-IL membranes were prepared by immersion precipitation phase transformation process,and its chemical composition,morphology,contact angle and water flux were analyzed.The results of XPS concluded that the grafted ionic liquid moiety tended to accumulate and distribute on the surface of the membrane during the process of membrane formation.Through the SEM,one could be clearly observed that the PVDF-g-IL membranes have more inter-connective pores on the finger-like hole walls,forming hierarchical pore structure.The results of the contact angle indicated that the introduction of IL was beneficial to the improvement of hydrophilicity and wetting ability for PVDF-g-IL membranes.The water flux results showed that the water flux of the PVDF-g-IL porous membrane significantly increased,compared with the pure PVDF porous film.(3)Study on the structure and properties of the porous PVDF-g-IL membranesTaking bovine serum protein(BSA)as the pollution model,the results of static BSA adsorption tests and the dynamic permeability tests showed that the addition of IL was beneficial to improve the abilities of antifouling for the PVDF-g-IL porous membranes.The results of antibacterial tests showed that the PVDF-g-IL membranes exhibited excellent antibacterial properties against either E.coli or S.aureus while the pure PVDF membrane was poor.The studies on blood compatibility,including the hemolysis,blood platelet adhesion,thromboelastography test and cytocompatibility,indicated that the PVDF-g-IL membranes with a low IL grafting ratio showed a good biocompatibility.(4)Study on the adsorption behavior of the porous PVDF-g-IL membranesThe PVDF-g-IL porous membrane was applied to the adsorption of thymol blue(TB),an anionic dye.And the kinetic model and isotherm model of the adsorption process were also calculated.The results showed that PVDF-g-IL porous membrane was a highly effective adsorbent.And the adsorption behavior of PVDF-g-IL membrane was influenced by the p H,concentration and temperature of TB solution.What's more,the adsorption process followed the pseudo second-order kinetic model and had a better fitting with Langmuir isotherm model.It demonstrated that the adsorption site on PVDF-g-IL membrane surface was homogeneous and the TB molecules were adsorbed on the membrane surface by monolayer.The particle diffusion model showed that the adsorption of TB molecule by PVDF-g-IL membrane was affected by multiple diffusion processes,among which the diffusion process to the membrane surface was more important than that in the pores.(5)The study on multifunction PVDF-g-IL materialOn the basis of the above studies,more functions were explored for the material of PVDF-g-IL.The porous PVDF-g-IL membrane had excellent separation efficiency for both oil-in-water and water-in-oil system.In addition,the PVDF-g-IL hollow fiber membrane could effectively intercept the methyl orange molecules.And the study found that the PVDF-g-IL nanofiber film that prepared by electrostatic spinning due to the good properties of spinnability was an excellent adsorbent for the heavy metal ions.