Preparation And Properties Of PVB And PVDF Hollow Fiber Ultrafiltration Membranes

Recovery of perfluorosulfonic acid resin (PFSA) were conducted by regenerationand dissolution of the derteriorated perfluoro-ion-exchange membrane (PFIEM) inchlor-alkali industry. Moreover, the recovered PFSA was reused to preparare hollowfiber ultrafiltration membranes.Firstly, the charged poly(vinylidene fluoride)(PVDF) and poly(vinyl butyral)(PVB) hollow fiber ultrafiltration membranes were fabricated with PFSA as additiveby wet-spinning method. Evolution of the precipitation kinetics, morphologies,permeation performances, elecrokinetics and mechanical properties of the as-spunPVDF and PVB membranes were investigated with the PFSA content and bore liquid.The results illustrate that both the PVDF/PFSA/N-methyl-2-pyrrolidone (NMP) andthe PVB/PFSA/NMP dopes experience an instantaneous demixing mechanism and theprecipitation rate increases with the addition of PFSA. The less distance of Hansensolubility parameters (δs-p) between polymer and bore liquids, the higher hydraulicpermeability (Jw) the associated membrane has. Streaming potential (E)measurements verify that the absolute apparent zeta potential (ζapp) values of thePVDF and PVB membranes increase as the PFSA content increases. The mechanicalproperties of the PVDF and PVB membranes also increase when the PFSA contentincreases.Secondly, taking the PVDF charged membrane for example, the effect of PFSAcontent, electrolyte concentration, the species and valences of ions on measurement ofE, ζ and charged density (σ) was studied with the measuring media of salt solution atdifferent concentration and salt content. The results show that E, ζ and σ values allincrease with the PFSA content increases within a certain range. Both︱E︱and︱ζ︱values of the UF membranes decrease with the increase of the concentration ofelectrolyte solutions,︱E︱value increases with the increase of the operationpressure, while︱ζ︱decreses with the increase of the operation pressure.︱σ︱value of the UF membranes increases with the increase of the concentration of theelectrolyte solutions and the PFSA content, while decreasing with the increase of the operating pressure. It is shown that measurement of the membrane potential ispreferred for the study electrical capacities of UF membranes.Thirdly, the thermal stability, auti-fouling property and chemical stability ofPVDF charged membranes were also investigated. It was found that the PVDFcharged membanre had remarkable stability to acids, but poor stability to diluteNaOH solution or alkaline solutions. General speaking, the fabricated PVDF/PFSAblend membranes have stable chemical and thermal performance as well as goodmechanical property.Finally, effect of polyvinylpyrrolidones (PVPs) molecular weight (Mw) on thecoagulation process, morphology and propert of the PVB membranes was researchedwith PVP Mw and bore liquid. The results illustrate that the PVB/PVP/NMP dopeshave an instantaneous demixing mechanism and the demixing rate declines with therise of PVP Mw. The PVB membranes containing PVP with lower Mw have higherJw. The fibers with higher Mw have higher mechanical properties. In view of all thevarious factors, it can be concluded that the fibers with PVP K25(Mw=24000) asadditive have the best comprehensive performances.