Study On Hydrophilic Modification Of PVDF Membrane

Poly(vinylidene fluoride)(PVDF)has received great attention as a membrane material with regard to its outstanding properties,i.e high mechanical strength,chemical stability,thermal stability,resistance to ultraviolet radiation,corrosion resistance,oxidation resistance,excellent resistance to chlorine and organic solvents,as compared with other polymeric materials.Besides,PVDF is a excellent biocompatible material,it will have a good prospect application in blood purification area.PVDF as hydrophobic membrane material inevitably led to following problem:The surface energy is low and wetting property is poor,which makes separation process needs larger drive force.The hydrophobic PVDF membrane is susceptible to fouling while treating aqueous solution containing natural organic matters,e.g.proteins.Proteins are prone to be easily absorbed onto the membrane surface or block the surface pores,decreasing the permeability and the final separation performance,depressing the lifetime of the membranes and subsequently causing more operation costs of the replacement and maintenance of the membrane component.When PVDF membrane is used in bio medicine area,proteins absorbing the surface of PVDF membrane speed up accumulation of antibiotic debris,which results in a number of biological reactions,such as thrombosis and biological reactions.Therefore it is very significant to improve the hydrophilicity of PVDF membranes to enhance the lifetime and reduce the operation cost of the PVDF membrane component.In this thesis,we use additives(NSA)and inorganic nano-particle to improve the hydrophilicity of PVDF membranes with scan electric microscope(SEM),atomic force microscope(AFM),contact angle test(CA),water flux test and BSA rejection test,and mechanical property test,etc.The specific research results of this paper are described as follows:1.The effect of different PVDF/NSA/dimethylacetamide(DMAC)systems was discussed to show their influence on structure and properties of PVDF membrane,especially the PVDF/Methanol/DMAC system.The results show that the suitable mass ratio of methanol and polymer,and coagulation bath temperature(CBT)facilitate the formation of spherulite structure.Besides,PVDF/Ethanol/DMAC system,PVDF/Glycerol/DMAC system,PVDF/Butanol/DMAC system,PVDF/Pentanol/DMAC system,PVDF/Hexanol/DMAC system,are all finger-like structure.Due to the higher tensile strength,Ethanol was chosen to be the non-solvent additive to prepare membranes of next chapter.2.We use PVDF/Ethanol/DMAC systems,blending with inorganic nano-particles of alumina(Al2O3),lithium magnesium silicate(Laponite),magnesium aluminum silicate(Veegum).It's found that by adding Nano-Al2O3 and decreasing CBT,the structure of PVDF membrane is changed from finger-like structure to sponge-like structure.And by adding nanoparticles lithium magnesium silicate(Laponite),magnesium aluminum silicate(Veegum),membrane structure and performance have no apparent change.With this good condition,PVDF-Al2O3 hollow fiber UF membranes were successfully spun by wet-spinning method.3.The method of blending SiO2 sol-gel and double layer membrane is used to prepare PVDF membrane.The PVDF membrane own sponge-like structure by blending SiO2 sol-gel,but need to improve mechanical strength.With the method of double layer membrane,we prepare the membrane what we want.