Study On Modification Of PVDF Porous Membrane Prepared By Phase Inversion

As one of the most popular material for microporous membranes,poly(vinylidene fluoride) (PVDF) has earned lots of attention due to its comparative molding properties,thermal and chemical stability,porous-controllability,et al.Whereas,inconvenience is in existence that PVDF membranes are inclined to be fouled by proteins and so there yields high driving force for water to permeat across membrane matrix.It is urgent to find effective methods to improve the hydrophilicity of PVDF membranes.In this thesis,flat PVDFmembranes were prepared by phase inversion method.The effects of preparation conditions on the structure and properties of PVDF membranes were studied.It was found that with the increasing of PVDF concentration in casting solution,the average pore size and water flux of membrane decreased gradually.With the increasing of DMAc content in solvent,the finger-like structure inside the membrane changed to sponge-like structure,while the pore size and contact angle both increased gradually.By rising temperature of coagulation the porosity of obtained membrane became higher.The hydrophilic substance PVP used as effective addictive the pore-inducing agent,while the add of TiO2 would increased the tensile strength and strength at break.After the microporous membranes modified with cross-linked HPAE,the PVDF blending membrane presented the interpenetrating polymer network structure.However,only the un-crosslinked HPAE can formed microvoid,with the degree of crosslinking increased,pores on surface and water flux would decreased.As a result,a proper degree of crosslinking can improve the hydrophilicity of PVDF membranes.The blend membranes containing higher concentration of HPAE showed lower static protein adsorption.During the preparation of a series of PVDF/PMMA blending membranes and PVDF/ polyether modified silicone oil blending membranes,the different contents of PMMA(polyether modified silicone oil) were introduced to the PVDF/DMAc system and their effects on membrane properties are investigated.In the PVDF/PMMA blending membranes,the increase of PMMA lead to the higher porosity,larger average pore diameter and water flux.The low concentration of PMMA improved the hydrophilicity of PVDF membranes.During the formation of membranes,the migration of PMMA to the top surface of the membrane improved the hydrophilicity.In the PVDF/ polyether modified silicone oil blending membranes,the data showed its modification effect was not as distinct as PVDF/PMMA blending membranes.Furthermore,the introduction of polyether modified silicone oil into membrane system increased the PVDF mechanical properties and hydrophilicity because of its good extending ability in PVDF matrix.