Research Of Solution Blending In Modification Of PVDF Membrane

The technology of membrane wastewater treatment is one of the hottest technologies in the water treatment currently, but its development is seriously obstructed because of its shortcomings, such as lower output, easier to be polluted, higher price and so on. This article prepared a new polymer membrane-PVB/PVDF blended membrane, which is lower price, big water flux, high intension and not easier to be polluted.The research mentality and the main content of this paper are as follows:1. The miscibility of PVB/PVDF blending system was investigated by method of shear viscosity, intrinsic viscosity, polarized optical microscopy and Fourier transform infrared spectrophotometer (FTIR). The curve of the viscosity-constitute of the PVB/PVDF blending system was nonlinear, which indicated that PVB and PVDF were partly miscible. Then the quantitatively research for the compatibility of the blending system was discussed by intrinsic viscosity method, and the results showed that when the blending ratios were 9:1,8:2,7:3,3:7,2:8 and 1:9, the blending system was compatible. The conclusions from polarized optical microscopy and FTIR agreed with the result of intrinsic viscosity.2. The permeability and mechanical properties of the blending membrane were investigated with the changes of the polymer concentration and blending ratio in the casting solution, and the best blending ratio and the suitable polymer concentration were confirmed. The results showed that the optimum blending ratio of the casting solution is7:3, and with the conditions of that the polymer concentration of the casting solution was 23%, the blending membrane would have the best performance.3. Determine the induced phase separation factors of the blendjng system in different conditions, and study the influence of the different phase separation mechanisms on the morphology and performance of the blending membrane. Phase separation can be induced by mutual diffusion between the solvent and non-solvent, diffusion induced phase separation (DIPS). Also is induced by that dissolving ability is decrease due to the reduced temperature or adding additives, thermally induced phase separation (TIPS). Still is owing to both the two mechanisms. Through observing the structure of the membrane which made under two phase separation mechanisms, the results showed that it was enormous implications of different phase separation mechanisms on membrane's structure. When the membranes made by the mechanisms pure TIPS, the cross section of PVB/PVDF blended membranes was composed by spongy-like structure; the membranes'cross-sectional structure, which were made by DIPS/TIPS, were mainly made up by finger-like structure, only few spongy-like structure. The membrane performance test showed that the water flux of the blending membrane which was made by the method of TIPS/DIPS was much better than the membrane's which was made by the method of DIPS. On the contrary, breaking strength of the blending membrane which was made by the method of TIPS/DIPS was smaller.4. The suitable coagulation bath temperature was found by investigating the influence of different coagulation bath temperatures on blending membrane's structure and mechanical properties. Observing membranes'structure which were made from different coagulation bath temperatures, it was found that the higher coagulation bath temperature was, the finger-like structures became fewer, which lead to the decrease of membrane's water flux. When the coagulation bath temperature reached 90℃, the finger-like structure disappeared, and membrane's structure was the typical spongy structure, small and well-distributed. By comparing of permeability and mechanical properties of the blending membranes which were made from different coagulation bath temperature, it was found that membrane's water flux decreased and tensile strength increased when the coagulation bath temperature rose. Water flux of blend membrane, which was made in bath temperature of 5℃, was the largest one of all membranes. when coagulation bath temperature rose, the pure water flux decreased sharply, while the film fracture strength changed very slowly. So the best coagulation bath temperature was 5℃.5. This paper investigated the influence of inorganic small molecules additives of a series of PEG and PVP (K30) on blending membrane's mechanical properties by test means of membrane performance testing and scanning electrometry microscopy (SEM). The results showed that compared with membranes which were added with the series of PEG, membrane's water flux and mechanical property, added with PVP (K30), were increased greatly and this membrane was flat and not curled. So PVP (K30) was picked as the best additive to improve performance of PVB/PVDF blending membrane. Meanwhile, the study results showed that membrane's water flux was increased at first, and then it was decreased with the increase of concentration of PVP K30.The tensile strength was increased all the time. Because of concentration of polymers was high, the tensile strength of PVB/PVDF blending membrane was big enough and had reached 327.92N/cm2 when the concentration of PVP (K30) was 5%, which we chose as the best use level finally.