Study On The Preparation And Performance Of PVC/PVB Blending Ultra-filtration Membranes

As a kind of membrane material, due to its poor membrane-forming property andits hydro-phobicity, Polyvinyl chloride (PVC) material must be modified to apply tothe manufacture of water treatment membranes. In this paper, for the process of PVCmembrane application, polyvinyl butyral(PVB), was introduced as a kind ofhydrophilic polymer, and blended to modify PVC. Compatibility of PVC/PVBblends, as well as the process of PVC/PVB blends ultra-filtration(UF) membrane, wasstudied. On this basis, PVC/PVB blends nine-channel UF membrane was developed,and its preparation process had been optimized. Innovation and engineeringapplications of this paper was reflected in the following main aspects:In this paper, for the first time, through theoretical and experimental methods,such as mixing enthalpy values, Florry-huggins interaction parameter, and dilutesolution viscosity method (referred to as the DSV method), the compatibility of PVC/PVB polymers were predicted and analysised, and the results were revealed:theoretically, the PVC/PVB blend system is fully compatible, and when the PVC/PVB blend ratio is greater than3/7, using PVC as the first component is superior tousing PVB on the compatibility of the blend system. Results of DSV pilot test showedthat: compatibility of PVC and PVB is favorable, which relates to factors such as theblend ratio, concentration and temperature, and increased as the polymerconcentration increasing within the experimental range. The compatibility of thesystem is best at45℃.In the preparation of DMAc-PVC/PVB blend flat UF membrane, influence ofrelevant parameters in the casting, evaporation and gelation process on the dynamicviscosity, gelling property, and the kinetic mass transfer process of the castingsolution, as well as on the microstructure, porosity, retention rate and water flux of theflat ultrafiltration membrane. The results showed that:1) Phase separation mechanismof DMAc-PVC/PVB system, as well as DMAc-PVC/PVB-Additive system, is adelayed phase separation, and the influence of process parameters above on thedemixing time t1of gelation is little, the parameters impact on the structure andperformance of the membrane mainly by impacting the liquid-liquid phase separationtime(ie, phase separation rate) t2. Overall, impact of kinetics mass transfer takesadvantage over the impact of the thermo-dynamic phase separation process, and thestructure and performance of the membrane depends primarily on the dynamic masstransfer process.2) The conditions of flat UFmembrane preparation was optimized, and the parameters was obtained as following: wt%(PVC+PVB)=18%, PVC/PVB=7/3, PEG600for additive, and the wt%(the PEG600)=5%; the casting temperatureand scraping temperature as40℃,ambient temperature as25℃, ambient humidityas70~75%, evaporation time as10s, the composition of gelation bath is aqueoussolution of DMAc, and DMAc volume content as30%, temperature of gelation bathas about40℃. Water flux up to120L/m2hr, and rejection rate to bovine serumalbumin(BSA) up to90%, could be thus attained.In this paper, the PVC/PVB blends nine-channel UF membrane wassuccessfully developed through the design of nine-channel spinneret and explorationof the preparation conditions, and the optimization process and results of thenine-channel hollow membrane was mainly discussed. Set casting temperature as40℃, extrusion pressure of casting solution as0.2MPa, air humidity as70%; the coreliquid as aqueous solution of DMAc, with volume content of DMAc of30%, atemperature of40℃, and fluid flow of6ml/min, using water as gelation bath, and40℃as bath temperature as well as the temperature of spinning tank, and the windingspeed just do not produce stretch to the membrane, in such experimental conditions,the uniform experiment of five factors and five levels was designed, using a uniformexperimental design method, and factors as following: the concentration of polymerblends (X1), mass percentage of PVC in PVC/PVB blends (X2), additive PEG600concentration (X3), the casting temperature (X4) and evaporation time (X5).Throughthe regression analysis, model equations to describe the quantitative relationshipbetween membrane performance and various influencing factors was thus obtained.The optimal experimental program within the experimental range was determinedthrough grid method,by Matlab programming, using water flux as the optimizationobjective, and the rejection rate as limiting variable. The conclusions obtained asfollowing: the water flux of the regression equation J=2789.609-258.995X1+6.179the X11+0.184X35-0.013X45, and rejection rate of the regression equation R=71.328-2.771X5+0.009the X12+0.116X15,-0.003X44+0.296X4, is theappropriate model to characterize the relationship between membrane performanceand its influencing factors, as well as the optimization of process parameters. Throughthe optimized calculation, using regression equation of water flux as the objectivefunction, regression equation of rejection rate as the constraint function, the optimalcombinations of process parameters for the could be obtained as following: thepolymer concentration wt%=17%, PVC/of PVB=9/1, PEG600as additive, with aconcentration of wt%=9%, both the casting temperature and the spinning temperatureas40℃, dry spinning process as14.3cm; finally obtained water flux of188.67L/m2hr, rejection rate on BSA as80.74%.