Application Research Of Solution Blending In Modification Of PVC Membrane

Membrane separation technology as a new technology industry is widely used in many application fields. But the popularization and development of the membrane technology is seriously hampered because of large quantity of materials handled, easy to polluted and use expensive,etc in membrane separation process. Therefore, development and selection of membrane materials and membrane manufacture craft research appears to be more important. Polyvinyl chloride(PVC) as the quantity of industrial production after polyethylene (PE), the second-largest synthetic resin with cheap, chemical stability,high mechanical strength and good resistance to microbial erosion etc, and is worth popularizing of the membrane material. But researches show that PVC film performance is poor, the hydrophilicity and toughness is not enough, so need to be carried on the modification.Currently the modification methods of membrane materials include graft copolymerization, inserting section copolymerization, blending and plasma surface radiation etc. Among of these, solution blending is the most simple and feasible method. It will combination of some composition which have good compatibility but with different properties, and play the role of mutual compensation, which will make the blending membrane with cheap and good comprehensive performance. Polyvinylidene fluoride (PVDF) with the chemical stability, excellent film-forming properties and good toughness, but the price is too expensive; Polymethyl methacrylate(PMMA) with good hydrophilic, the chemical stability and the price cheap, but its brittleness is big in preparation of membrane. Therefore blending PVDF, PMMA with PVC, not only can improve film-forming property of PVC but also improve its toughness and hydrophilic, thus the permeability good preparation, mechanical property good PVC film. So this study is to use the method of solution blending which blends PVDF, PMMA with PVC to modify the PVC membrane. This paper mainly carries out the following respects of content:First of all, the compatibility of the blending system is studied. The qualitative research for the compatibility of the blending system is discussed by determinating the relationship between the shearing viscosity of PVC/PVDF/PMMA blending system and blending ratio. The results show that the blending system of PVC/PVDF/PMMA is part of the compatibility. Then the quantitatively research for the compatibility of the blending system is discussed by intrinsic viscosity method, and the results show that when the blending ratios are 8:1:1,7:2:1,6:3:1,7:1:2, 6:1:3 and 5:1:4 the blending system is compatible.Then, the permeability and mechanical properties of the blending membrane are 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 are confirmed. The results show that the optimum blending ratio of the casting solution is 6:1:3, and with the conditions of that the polymer concentration of the casting solution is 16%and the temperature of the casting solution is room temperature, the blending membrane will have the best performance.The third is to determine the induced phase separation factors of the blending 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. Experimental results show that when the polymer concentration is constant the induced phase separation factors of the casting solution will be changed, while adding additives polyethylene glycol (PEG) with three molecular weight in different quality concentration. When the quality percentage of PEG200, PEG400 and PEG600 are less than 15%,18%and 20%, the PVC/PVDF/PMMA blending solution can only filmed by DIPS. While the quality percentage is higher than 15%,18%and 20%, the phase separation mechanisms of the blending system can be combination DIPS with TIPS, also can be the TIPS. Through observing the structure of the membrane which made under three phase separation mechanisms, the results show that it is enormous implications of different phase separation mechanisms on membrane's structure. When the membranes made by the mechanisms pure DIPS or its combination with TIPS, the cross-sectional structure will be asymmetric with finger-like maro-void; while the membrane morphology changed from finger-like maro-void to spongy structure. The membrane performance test show that, the water flux and porosity of the blending membrane are obviously improved by combination DIPS with TIPS, but the retention is decrease. The rentation and breaking strength are increase significantly by DIPS, but the water flux is reduce.Finally, this paper investigates the influence of inorganic small molecules additives of Al2O3,TiO2 and SiCO2 on blending membrane's mechanical properties. The effects of inorganic small molecules additives are discussed by test means of membrane performance testing and scanning electrometry microscopy (SEM) etc. The results show that adding five kinds of small molecules don't change the film forming mechanism, and all of them can significantly improve the permeability flux and hydrophilcity. Comparision the membranes mixed with nanometer SiO2, TiO2 and gel SiO2, TiO2, adding nanometer SiO2 and gel TiO2 can effectively increase the membrane's water flux, and mixed gel SiO2 can improve the mechanical property.