| Membrane separation technology is considered to be a new environmental protection and low carbon industry and is widely applied in many fields. But in the membrane separation practical process, the popularization and development of membrane technology are restricted due to its disadvantages, such as big consumption, high price and easily polluted. So the development of new membrane materials and quest of new technology research appear more important. PVDF is a kind of new-style membrane material, which has many strong points, such as moderate price, chemical stability, high mechanical strength, easy to form, microbial erosion resistance, etc. So its appearance caused a sensation of academia and industry. Through further study found PVDF needs to be modified because of its insufficient, for instance big polarity, poor solubility, poor hydrophilic and low mechanical strength.The modification technology is mainly divided into physical modification and chemical modification. Physical modification includes blend modification and plasma processing. Chemical modification includes grafting copolymerization, inserting period of copolymerization, etc. Among the above modification methods solution blending is simple and easy to operate. It will combine two or more polymers with different chemical properties and good compatibility together. The polymers have mutual compensation effect and blend membranes with low cost and excellent comprehensive performance can be prepared. PVDF has resistance performance of acid and alkali, high mechanical strength, good chemical stability and strong rheological properties. But PVDF has poor hydrophilic, easy to crystal, low glass transition temperature, and poor selectively separate. Polyether imide (PEI) possesses good hydrophilic, separation selectivity, not easy to crystal and high glass transition temperature etc characteristics. We can not only improve the membrane formation performance of PVDF membrane but also improve its toughness and hydrophilic through blending PVDF and PEI. The blend PVDF/PEI membrane with excellent permeability and mechanical performance can be prepared. So this topic will blend PVDF and PEI using solution blend method, add into appropriate additive and prepare the modification separation membrane. The articie contents are as follows:1. Compatibility of the PVDF/PEI blend system was researched using ocular estimate. The results show that when the blending ratio is9.5:0.5,9:1,8.5:1.5,8:2and7.5:2.5, the system is compatible. From the phasecontrast mincroscope photos, we can see that PVDF/PEI blend system is part compatibility system.2. PVDF/PEI blending dense solution prepared by using DMAc as solvent was measured by using HAAKE RS150rheometer. The rheological curves of the blend solution with different blend ratio and the temperature of the blend solution on the rheological properties were studied. The results show that the apparent viscosity of the solution and the shear rate is linear correlation. When the blend ratio of PVDF:PEI is9:1, the change of zero viscosity is biggest and flow activation energy and non-Newtonian flow index of the blend solutions reach extremum.3. Pure water flux and rejection ratio of BSA solution were measured to ensure the optimal blend ratio of PVDF and PEI. It can be seen that the suitable conditions for preparing PVDF/PEI membranes are as followed:the blend ratio of PVDF/PEI is9:1, the mass fraction of casting solution is15wt%and the temperature is25℃.4. With the suitable blend ratio, the structure and performance of the membranes with different type and content of alcohol. From the experiment and SEM photos we can see that when the polymer concentration is unchanging, the result of added glycol fraction is best. Through changing the mass fraction of glycol the best adding capacity can be obtained.Through the above experiments, the suitable conditions are as followed the blend ratio of PVDF/PEI is9:1, the mass fraction of solid phase is18wt%, appropriate additive PVP and the mass fraction of glycol is5%. In this circumstance, the PVDF/PEI blend hollow fiber membranes with best performance can be prepared. |
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