Study On Inorganic Particles/Poly(Vinylidene Fluoride) Composite Membrane

Based on the principle of polymer blend phase separation and the way of washing-out additive to form the micro-voids, PEG as additive, CaCO₃ as the dispersed phase, CaCO₃/PVDF composite flat membrane and CaCO₃/PVDF composite hollow fiber membrane were produced with the method of Loeb-Sourirakan phase transition. And adding diluent, the inorganic particle NM as the dispersed phase, the PVDF hollow fiber membrane was produced in low spinning temperature with the method of melt-spinning.The formation of the interfacial micro-voids and the regulation of the interfacial micro-voids on the non-interfacial micro-voids which were formed by PEG were researched. Further the effect of the content of the CaCO₃ and PEG, the coagulant bath temperature, molecular weight of the PEG and the particle size of the CaCO₃ to the structure and properties of the composite flat membrane were studied.First, the water flux and the retention rate of the CaCO₂/PVDF composite flat membrane were tested. And the results showed that the water flux firstly increased, then reduced, and finally increased again with the addition of CaCO₃ when the content of PEG was 0. After adding PEG, the water flux increased obviously. And the water flux increased with the addition of PEG. The microstructure of the membrane was observed. The results showed that the interfacial micro-voids were formed because of the bad compatibility between CaCO₃ and PVDF. And after washing out of the PEG, the non-interfacial micro-voids were formed, also it can increase the size of interfacial micro-voids. Then the CaCO₃/PVDF composite flat membrane possessed interfacial and non-interfacial micro-voids. Also the size of the micro-voids was bigger and the connectivity of the micro-voids was increased as the increasing of the molecular weight and the content of PEG. The coagulant bath temperature had the extremely remarkable influence to the forming and the water flux of the CaCO₃/PVDF composite flat membrane. When the coagulant bath temperature was 60℃, the forming of the flat membrane was quicker in the coagulant bath, shrunk fiercely, formed many folds, and the water flux is lower; When the coagulant bath temperature was 10℃, the forming of the flat membrane was slower, the coarsening time was long, the flat membrane was smooth, then the water flux increased highly. Also, the porosity, the water flux and the retention rate of the CaCO₃/PVDF composite hollow fiber membrane were tested. The results showed that the porosity and the hydrophilicity were increased because of the addition of CaCO₃. And the water flux of the hollow fiber membrane was increased on the basis of keeping or increasing the retention rate. The water flux of the CaCO₃(nm)/PVDF composite hollow fiber membrane was 1.7 times of the CaCO₃(nm)/PVDF composite hollow fiber membrane. The strength of the composite hollow fiber membrane was increased. And the microstructure of the composite hollow fiber membrane was observed. The results showed that the number of the big size micro-voids was reduced and the microstructure became compacter because of the addition of CaCO₃.The PVDF hollow fiber membrane was produced with the method of melt-spinning. The results showed that the spinning temperature was reduced because of the addition of the diluent. And the coupling agent is favorable to the spinning of NM/PVDF hollow fiber membrane. The water flux of the PVDF hollow fiber membrane washing with the NaOH solution is higher than the membrane washing with the water. But the flexibility and resistance to pressure of the PVDF hollow fiber membrane became worse.