Structure-controllable Fabrication And Surface Modification Of Poly(Ether Sulfone) And Poly(Phthalazinone Ether Sulfone Ketone) Porous Membranes

In the preparation of polyethersulfone (PES) and poly(phthalazinone ether sulfone ketone) (PPESK) membranes by phase inversion process, it often is difficult to control the membrane structure due to the diversity of membrane-forming parameters, and thus the membrane reproducibility is poor. In this thesis, on basis of the investigation of the cooperative action of thermodynamics and kinetics during membrane formation, the effects of membrane-forming conditions on membrane structure and properties were studied. In addition, to improve the hydrophilicity and anti-fouling ability of PES porous membrane, the surface modification was performed by corona-induced graft polymerization of acrylate acid (AAc). The influences of the grafting of poly(acrylate acid) (PAAc) on membrane structure and properties were investigated. Furthermore, a blending method in a single-step was adopted in order to simplify the hydrophilic modification of PES and PPESK membranes. A superhigh molecular weight poly(styrene-alt-Mnaleic anhydride) copolymer (SMA) and poly(phthalazinone ether sulfone ketone)-graft-poly(ethylene glycol) copolymers (PPESK-g-PEGs) were synthesized and used as additives for PES and PPESK membranes, respectively. The enrichment of the additives on membrane surfaces and their effects on membrane properties were studied.The thermodynamic state and membrane-forming kinetics for PES membrane -forming system were studied via the cloud point determination using nephelometer and light transmission experiments. The influences of the main factors including solvent/nonsolvent pair, polymer concentration, additives and coagulation bath composition on membrane structure and properties were investigated. The order of solubility for PES in different solvents is DMSO < DMF < DMAc < NMP, and the affinity of solvents with H₂O: DMAc < NMP < DMF < DMSO. When using pure H₂O as coagulation bath, instantaneous de-mixing occurs in the membrane-forming systems using all these investigated solvents. The order of de-mixing rate is NMP < DMAc < DMF < DMSO, and the developing degree of membrane sub-layer: DMSO < DMF < DMAc < NMP, and water permeation flux of membrane: DMF < DMAc 2 and strongly depends on corona parameters and graft polymerization conditions. The GY increases with corona power and treatment time. In the meantime, the GY also ascends with the increase of AAc solution concentration, reaction temperature and reaction time. The membrane morphology analysis and water contact angle measurements showed that the graft polymerization occurred not only on the membrane surfaces, but also on the pore walls of the cells inside the membranes, indicating that corona discharge penetrated through the whole membrane. The water fluxes for the modified PES membranes are bigger than that of the origin membrane due to a lower resistance of water permeation through membraneafter the introduction of hydrophilic PAAc graft chains. But excessive PAAc graft chains result in the fill and coverage of membrane pores, and thus a reduced flux. The grafting of hydrophilic and charged PAAc chains weakens the interaction between membrane and protein, and thus enhances the fouling resistance of PES membrane.Superhigh molecular weight SMA was used as additive in the preparation of PES phase inversion membrane and the influences of SMA concentration on membrane structure and properties were investigated. Two glass transfer temperatures (T_g) were observed in the DSC curve of PES/SMA blend, which shifted toward each other compared to the T_g of pure components. This phenomenon indicates that PES and SMA are partially miscible. Abundant carboxylic groups but not anhydride groups were detected on the blend membrane surfaces, suggesting that anhydride groups had hydrolyzed into carboxylic groups due to using hot H₂O as coagulation bath. XPS analysis confirmed that the hydrolyzed SMA chains preferentially segregated to membrane-coagulant interface during membrane formation. An amount of 10 wt.% SMA-added generates a 39.1 wt.% of surface coverage. The addition and surface enrichment of SMA endows PES membranes with significantly enhanced hydrophilicity, permeability and fouling resistance, and the mechanical strength of membrane is well maintained. On the same conditions for membrane preparation, the modifying efficiencies of SMA-g-PEG graft copolymers to PES membrane are better than SMA does.The thermodynamics and kinetics for PPESK membrane-forming system were also studied via cloud point determination and light transmission experiments. The influences of main factors including casting temperature, polymer concentration, additives and coagulation bath composition on membrane structure and properties were investigated. It is found that the system at a higher temperature becomes thermo -dynamically more stable, but phase separation rate and membrane structure have not big changes at different temperatures. With the increase of PPESK concentration in casting solution, the system tends to delayed de-mixing and the obtained membrane has a dense skin layer and sponge-like sub-layer. The addition of PVP causes the system more unstable and a higher viscosity for casting solution. The trade-offbetween thermodynamic enhancement and kinetic hindrance during phase inversion results in that the flux of PPESK membrane initially increases, then decreases with the increase of PVP amount. When a small amount of solvent is added into the coagulation bath, the system tends to delayed de-mixing and an asymmetrical membrane with a smaller pore size of skin layer is obtained. A symmetrical sponge -like microfiltration membrane is formed when the concentration of solvent in the coagulation bath is relatively high.Amphiphilic PPESK-g-PEG graft copolymers were synthesized via Williamson ether reaction of chloromethylated PPESK (CMPPESK) with a sodium alkoxide of methoxyl PEG The resulting copolymers can be swelled by water but is insoluble in water. PPESK-g-PEGs were miscible with PPESK resin and used as additive in the preparation of PPESK ultrafiltration membrane by immersion precipitation. XPS analysis confirmed the enrichment of the additives on membrane surfaces. The increase of casting temperature is advantageous to the surface segregation of the hydrophilic additives and has only a little impact on membrane structure. A low amount of solvent in coagulation bath also promotes the surface segregation of PPESK-g-PEGs, but excessive solvent in coagulation bath is disadvantageous to the surface segregation. The addition and surface enrichment of PPESK-g-PEGs contributed PPESK membrane with significantly improved hydrophilicity and anti-fouling ability.