The Research On Preparation Technology Of Poly (Vinylidene Fluoride) Microporous Membrane Via Thermally Induced Phase Separation

Thermally induced phase separation (TIPS) is a new method of preparation ofmicroporous membranes, it is composed of heat loss arising from the phase separation and theprinciple is relatively simple. Poly(vinylidene fluoride) has excellent chemical resistance. Notonly that, PVDF resin with high tensile strength and impact strength, in the organic material,it isa good material for asymmetric membrane. But it is easy to cause pollution, shorten the servicelife of the membrane, restricting its further development of the field of membrane separationbecause of the stronger hydrophobic. In this paper, PVDF flat micro porous membrane wasprepared via thermally induced phase separation and a variety of blends to improve thehydrophobic of the PVDF membrane. Based on the theory research of flat membrane,combining with hollow fiber membrane preparation process for the preparation of hydrophilicbetter micro porous hollow fiber membrane, hydrophilic micro porous membrane for therealization of PVDF industry to provide theory and practice basis.In the diluents selection, through a large number of solubility experiments, we select theDiethyl Phthalate (DMP), benzophenone (DPK), biphenyl carbonate (DPC) to study differentdiluents on the micro porous membrane, taking DMP as single diluents, researched polymerconcentration, and cooling conditions on the microscopic structure of the membrane. The studyfound that the microstructure formed by the different single diluents significantly is different,and not conducive to the preparation of high-performance micro porous membranes.Composite diluents can content compatibility by adjusting the mixing ratio. In this paperwe select DMP and DOP as composite diluents, through the research we found that with theDMP content increased, the crystallization temperature decreased, the spherulite structure ismore obvious.On the basis of the composite diluents, by blending PMMA, nanoscale TiO2andPMMA/TiO2, to improve the hydrophobic of the PVDF membrane. We found that the effect ofPMMA/TiO2blend modified is better. It formed a connective structure and more holes, thechange of contact angle is bigger, hydrophilic is better; when blending of PMMA, the effect ofPMMA addition on membrane structures is larger, system from spherulite structure to networkstructure, with the increase of adding amount, membrane hydrophilic constantly improved, when adding amount of PMMA is30%for polymer, membrane comprehensive modificationeffect is better; when blending nano TiO2, the effect of addition on membrane structure is small,still with spherulite structure; with the increase of adding amount, membrane hydrophilicconstantly improved, when the adding amount for polymer is3%, comprehensive effect isbetter.According to the modification results, determined the optimum preparation conditions offlat membrane, namely PMMA/TiO2blending modification, diluent content accounted for60%,DMP:DOP=1:1, PMMA:PVDF=3:7, TiO2nanometer add accounts for about2%-3%of thepolymer,20℃water bath cooling. basing on the flat membrane, to analyze the influencingfactors on the performance of the hollow fiber membrane spinning process, using theorthogonal experiment to determine the best membrane process of the hollow fibermicroporous membrane, preparation of hydrophilic PVDF hollow fiber membrane, for the nextstep the hydrophilic PVDF microporous film industry lay a good foundation. Contrast withunmodified PVDF microporous membrane, water flux of the hydrophilic membrane wassignificantly higher than the unmodified membrane, and resistance to pollution performance.