| Poly (vinyl chloride)(PVC) is an outstanding membrane material due to its physical and chemical stability, rich sources and low cost. In this study, asymmetric PVC flat/hollow fiber ultrafiltration (UF) membrane were prepared by non-solvent induced phase separation (NIPS) method and studied by a series of characterizations to investigate the relationships among the forming process, microstructure and performance of the membrane.Firstly, the precipitation ability of polyethylene glycol400(PEG400), polyethylene glycol200(PEG200), diethylene glycol (DEG) and glycerol in PVC/N,N-dimethyl acetamide (DMAc), PVC/1-methyl-2-pyrrolidone (NMP) and PVC/N,N-dimethyl formamide (DMF) solutions were studied as well as the effects of polymer concentration, concentration and molecular weights of PEG. triethyl phosphate (TEP) concentration on the microstructure and performance. The results showed that the larger interaction parameters of PVC/non-solvent or the smaller ratio of carbon atom to hydroxyl atom of the non-solvent, the stronger precipitation ability of non-solvent to PVC solutions.Glycerol showed the strongest precipitation ability to PVC solution while PEG400showed the weakest precipitation ability. Besides, the pure water fluxes of the membranes were very low, which was18L/(m2·h·bar) at16%PVC concentration. The tenacity, as well as the pure water fluxes, of the membranes were improved when adding TEP to the casting solutions. It was also found that pure water fluxes of PVC membranes could be adjusted by adding various amounts of PEG400to the casting solutions, which increased with molecular weight of PEG.Secondly, PVC flat UF membranes were prepared in different coagulation baths by NIPS using DMAc as solvent, poly (vinylidene chloride-acrylonitrile-methyl methacrylate)(VAH) and poly (vinyl chloride-vinyl acetate-maleic anhydride)(HVAMA) as additives. The results showed that the hydrophilic and pure water fluxes of PVC membranes were improved greatly by adding VAH to the casting solutions, while the microstructures remained unchange. But HVAMA had little effect on the permeability of the membranes. As increasing coagulation temperature, the rate of exchange between the solvent and non-solvent increased and the dense cortex was formed with large network and gathered hole. As a result, both the pure water flux and rejection decreased. Moreover, increasing the concentration of DMAc in the coagulation bath decreased the precipitation rate in immersion precipitation and thus the cross-section of PVC membranes changed from fingerlike structures to spongeous structures, and the pure water fluxes decreased.Lastly, PVC hollow fiber UF membranes were prepared by different bore liquids by dry-wet spinning using DMAc as solvent, VAH as additives. Also, the effects of polytetrafluoroethylene (PTFE) and polytetrahydrofuran (PTMG) on PVC membranes were studied. The results showed that the cross-sections of the hollow fiber membranes changed from double-fingerlike structures to single-fingerlike structures, and the pure water flux decreased first, and then increased with the increase of the DMAc concentration in bore liquid. The minimal flux and the maximal flux occurred at the DMAc concentration of75%and95%respectively. The pure water fluxes and microstructures of PVC hollow fiber membranes were improved by adding PTFE and PTMG separately to casting solution. At8%PTFE and10%PTMG, the PVC hollow fiber membranes exhibited the best comprehensive performances while the flux was71.5L/(m2·h·bar). |
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