Preparation Of Polyvinylidene Fluoride Film By TIPS And NIPS Method And Its Properties

The hydrophobic PVDF were selected as membrane material to prepare PVDF membranes. The effects of different preparation methods, O-MWNTs and PVDF concentration and different additives on structure and performances of PVDF membranes were exploerd in detailed. The paper mainly includes three aspects.First,the multi-wall carbon nano-tubes(MWNTs) have rapidly become the research focus of chemistry, physics and material science because of its excellent properties.To enhance the dispersity of MWNTs, O-MWNTs were prepared by using a simple and feasible two stages approach before incorporate into the polymer matrix. Then, TIPS was adopted to prepare PVDF/O-MWNTs membranes. The results demonstrate that the PVDF/O-MWNTs membranes with bi-continuous structure were successfully prepared via TIPS and the structure is neat and denser. The O-MWNTs and PVDF concentration mainly determine the morphologies and performances of the resultant PVDF/O-MWNTs membranes. With the increase of O-MWNTs and PVDF contents, the membrane morphologies change to be denser. Also, the BSA rejections and the surface hydrophilicity of the resultant membranes are evidently improved. The BSA rejection reaches more than 90.0% with appropriate O-MWNTs concentration. Meanwhile, Pure water flux significantly declines with the addition of O-MWNTs. The mechanical properties of the resultant PVDF/O-MWNTs membranes are significantly improved with appropriate amounts of O-MWNTs.Second, the effects of different kind additives(PEG 200 and PVP K30)on membranes were explored. PEG 200 worked as an auxiliary to enhance the dispersion of O-MWNTs. The PVP K30 was used to prepare porous membrane structures. The results show that PEG 200 can make the spong-like structure of membranes become thicker. Adding PVP K30 as porogen could induce the formation of finger-like structure and macrovoids. PVP K30 enhances the permeation performance of PVDF/PFSA membranes while PEG can not for its denser surface layer. PVDF mainly show β form and the addition of O-MWNTs can also improve the hydrophilcity and permeation performance of PVDF/PFSA membranes. The mechanism properties can also enhanced with proper amount of O-MWNTs.Last,on the basis of the previous two sections, C-TIPS were proposed to prepare PVDF/PFSA charged membranes. Effects of casting temperature and PFSA content on the morphologies, permeation performances, electro kinetic properties, crystalline form, and contact angles of the resultant PVDF membranes were investigated in detail. The results show that the all membranes have asymmetric structure with macro-voids in the cross sections. Much higher casting temperature leads to the formation of thicker top skin layer and thus a decrease in permeation flux. Adding PFSA in dope solutions can improve the surface hydrophilicity, porosity and apparent zeta potential(ζapp) in absolute value, and promote the permeation flux of the resultant PVDF membranes. The crystal forms of PVDF membranes are mainly β phase, and the crystallinity slightly increases with the increase of casting temperature.