| With the development of human society, the demand for the beautiful environment and clean energy have been more and more urgent. Especially in China, the country blooms in recent decades and environmental issues have caused more and more bad consequences, including the pollution of drinking water. In the same time, due to the shortage of the fossil energy, it is necessary to develop the new energy sources, including lithium ion batteries. Poly (vinyl chloride) (PVC) and polypropylene (PP) membranes are widely adopted in the fields of water treatment and lithium ion batteries, respectively. Although they are different materials in different fields, they would face similar problems because of their intrinsic properties. (1) When PVC membranes are exposed in water containing organic substances and microorganism, the membranes tend to be fouled and cause the increasing resistance to water permeation, further leading to the reduced life of the membranes. (2) PP separators present the bad compatibility with liquid electrolyte, which cause the leakage of liquid electrolyte and further lead to the reduced charge/discharge performances. Therefore, it is necessary to modify the polymer membranes to achieve the higher performances. According to the previous discussion, this project is based on the basic theory and methods of polymer chemistry to introduce polar functional groups onto surfaces by traditional radical copolymerization, living radical polymerization, coupling reactions, etc., to strength the compatibility between the membranes and water or liquid electrolyte. The detail research contents and major conclusions are listed as follows.PVC blend membranes with amphiphilic copolymers are designed and prepared to study the effect of copolymer and coagulation bath on the structures and properties. In this work, the amphiphilic copolymer (P(MMA-r-PEGMA)) with different molecular weight and similar compositions were synthesized by traditional radical copolymerization technique using methyl methacrylate as the hydrophobic monomer and polyethylene glycol methacrylate as the hydrophilic monomer. Then PVC blend membranes were prepared by non-solvent induced phase separation (NIPS) process with different coagulation baths (water and ethanol). The structures and properties of two kinds of membranes were compared. By investigating the membrane formation kinetics in different coagulation baths, surface chemical compositions as well as the membrane structures, the effect of coagulation bath on the membranes were demonstrated. The X-ray photoelectron spectroscopy (XPS) characterization indicated the obvious surface segregation of PEG chains on the skin layer of blend membranes formed in different baths. And the lower molecular weight of copolymer would cause the higher segregation ratio. The static protein adsorption experiment and dynamic protein solution filtration process inferred that the membranes with larger surface roughness would cause the severe membrane fouling. Moreover, the surface PEGylation would improve the hemocompatibility of PVC membranes.The PVC blend membranes containing non-ionic PVC based copolymer are designed and prepared to study the effect of the compositions and dosage of copolymers on the structures and properties. Non-ionic amphiphilic copolymer PVC-g-PHEMA was synthesized by grafting hydrophilic monomer hydroxyethyl methylacrylate (HEMA) onto PVC backbones via ATRP process. A series of copolymer with the grafting degree from 0～127.8% were prepared by changing the reaction time. When the copolymer with the grafting degree of 53.4% was used as the additive, the surface hydrophilicity and antifouling property was obviously improved. And when the dosage was 10%, the water flux and BSA rejection were 113.6 L m-2 h-1 and 84.9%, respectively. However, the blend membranes were not formed well due to the bad compatibility of PVC and PHEMA segments, when the dosage was higher than 12.5%. Moreover, a novel and facile method named in situ ATRP modification method was provided for membrane modification. Comparatively, the membranes prepared from the new method possessed the similar hydrophilicity, permeability, separation and antifouling performances. Due to the simpler operation conditions, the new method is promising for the industrial production.The PVC copolymer containing tertiary amine groups is synthesized, and the structures and properties of membranes with positive charge are studied. PVC copolymer was synthesized by grafting dimethylaminoethyl methacrylate (DMA) onto PVC backbones via ATRP process. The grafting degree of the copolymers was regulated by changing the reaction time and the synthesis kinetics was also carefully investigated. And the reaction was proven to be "living"/controllable. Due to the hydrophilicity and positive charge, the copolymer membranes had the potential for dye separation. The water flux and Victoria Blue B rejection of the membrane with 31.1% of PDMA in copolymer were 26.0 Lm-2 h-1 (0.5 MPa) and 91.2%, respectively. The PVC membranes with positive charge were prepared by quarterization of PVC-g-PDMA followed by blend and blend followed by quarterization of PVC/PVC-g-PDMA membrane. The membranes showed the excellent antibacterial property as well as the effective separation and resistance to lysozyme.The PVC membranes with negative charge are designed and prepared to study the effect of the compositions and dosage of copolymers on the structures and properties. PVC-g-PMAA was synthesized by one-step ATRP process and one-step hydrolysis reaction. The copolymers with different grafting degree was changed by reaction time. The ultrafiltration membranes with negative charge were prepared by blend and NIPS method. It indicated that PMAA chains obviously segregated on the skin layer of the blend membranes and the membranes were endowed with negative charge. Compared with PVC pure membrane, the permeability of blend membranes were improved and BSA rejection was over 90%. Due to PMAA chains, PVC/PVC-g-PMAA blend membrane displayed pH sensitivity, which increased with the PMAA content in blend membrane. Owing to the negative charge as well as the hydrophilicity, the blend membranes effectively reduced BSA adsorption and improved the antifouling property, especially at neutral and alkaline environment.Basing on the surface modification technique, PEG and organic-inorganic hybrid layer are introduced onto PP separator for the higher performances. The surface modification process was based on the polydopamine coated PP separators.1) The PEG chains were bonded onto PP separators by the coupling agent (hexamethylene diisocyanate, HDI). The surface chemical compositions, morphology and structures, wettability as well as the electrochemical properties of separator-liquid electrolyte system were carefully investigated. When the grafting degree was 6.2%, the ionic conductivity was 0.99×10-3 S cm-1, which was higher than that of PP separator. At the same time, the charge/discharge performances of the cells were also improved.2) The organic-inorganic hybrid layer was incorporated onto PP separators by sol-gel process. The surface chemical compositions, thermal stability, wettability and ionic conductivity of separator-liquid electrolyte system were studied. It indicated that the thermal stability and wettability of the separators were obviously improved and the ionic conductivity was also promoted. |
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