Study On Structure Control And Performance Of PSF Ultrafiltration Membrane Preparated By Solution Phase Inversion

The polymeric ultrafiltration membranes are easily compacted during the filtration applications under a relatively high pressure. In this work, polysulfone (PSF) ultrafiltration membranes with a density gradient of the sponge-like cross-section structure were prepared via the solution phase inversion process by controlling the properties of casting solution. These membranes have the good compressive strength and the high water flux.Firstly, in terms of effect of zero shear viscosity of the casting solution on the morphology and permeability of polysulfone ultrafiltration membranes, two systems were designed:the PSF/DMAC binary system and PSF/DMAC/PVP ternary system in which the viscosity was dominated by changing the concentration of PSF and the molecular weight of PVP, respectively. By measuring the viscosity and the cloud point of casting solutions, the phase-separation process, surface and cross morphologies, pore size and porosity and the water flux of membranes, it was found that the zero shear viscosity of casting solutions was one of the most important parameters for the morphology and permeability of polysulfone membranes.Secondly, in terms of fabrication of polysulfone ultrafiltration membranes of a density gradient cross section with a good compressive strength, three different kinds of systems including PSF/DMAC/PVP, PSF/DMAC/Ethanol ternary systems and PSF/DMAC/Ethanol/PVP quaternary system were used as casting solutions. By measuring the water flux, surface and cross morphology, the anti-pressure stability, the variation of the pore volumes between the fresh and pressurized membranes, it was found that the PSF ultrafiltration membrane with a density distribution structure possessing a good compressive strength and a relatively high water flux could be prepared by using PVP and ethanol together in PSF/DMAC/Ethanol/PVP solution.Lastly, in terms of influence of nano-sized SiO2-PAMPS fillers on the morphology and property of PSF ultrafiltration membranes, the different monomer ratios of SiO2-PAMPS nanoparticles were prepared by dispersion polymerization and then were used to fabricate the novel SiO2-PAMPS/PSF hybird ultrafitration membranes. By measuring the pure water flux, the porosity and the pore size, the surface and cross morphology, the stretching test, the compressive strength test and the water contact angles (before and after shaking) of membranes, it was found that the SiO2-PAMPS nanoparticles were excellently stable on the membrane surface. Meanwhile, the water flux, the mechanical property and the compressive strength of hybrid membranes were significantly improved. The hybrid membrane prepared by the PSF/DMAC/Ehanol/SiO2-PAMPS4 (the monomer mol ratio (MSiO2/MPAMPS) is 15.3:1, and the concentration of the nanoparticles is 0.3 wt%) casting solution had the water flux of 190 L/m2.h under 0.1 MPa, the tensile strength of 4.3 MPa, the breaking elongation of 20.5%, and the cross section of which was greatly stable even under the continuous operation with 0.5 MPa.