The Improvementof The Polyethersulfone (PES) Ultrafiltration Membrane’s Structure And Hydrophilicity

This paper takes the Polyethersulfone (PES) ultrafiltration membrane as the research object.As the PES itself has a strong hydrophobicity, the polyethersulfone ultrafiltrationmembrane often shows a poor anti-pollution and short service life. In this paper, we develop thetopic around the membrane structure control in the process of the immersion precipitation phaseinversion and the membranes’ hydrophilicity improvement. In this thesis, on basis of theinvestigation of the casting solution composition and coagulation bath composition duringmembrane formation, the effects of membrane-forming conditions (such as thepolymer concentration, the additive concentration and the coagulation bath composition) onmembrane structure and properties were studied, which provides theoretical guidance for makinga good permeability, good anti-pollution and hydrophilic membrane.This paper investigated the effects mechanism and degree of parameters on membranestructure. The mixed additives made from organic addictive PVP and inorganic addictive LiCl,which was used modified PES membranes in the process of blending modification. We usedsingle factor experiment and orthogonal experiment to studied the effect mechanism of eachcomponent and the inter action between each composition. And the optimal ratio of castingsolution and coagulation bath eventually were determined. The main content of the thesis can bedivided into three blocks: the single factor analysis of each influencing factor, the mechanismanalysis in the membranes’ formation process and the orthogonal analysis of multiplefactors. First of all, the effect mechanism of additives were explored. Second, the effect andmechanism is analysis by the experimental data in the single factor experiment. Finally, theoptimal level of the casting and coagulation solution was concluded by orthogonal method.The main factors influences including polymer concentration, additives and coagulationbath composition on membrane structure and properties were studied via the viscosity measurement. At the same time, we also did many test, such as water flux test, determination ofcontact Angle and moisture content, pore diameter test, intercept molecular weight test, pollutionindex test and the scanning electron microscope (SEM) test. The results show that: the effectorder of the experimental factors on viscosity was as follows: PVP concentration>PESconcentration>LiCl concentration; the effect order on the membrane pore size was as follows:PES concentration> coagulation bath ratio>LiCl concentration> PVP concentration; the effectorder on flux was as follows: PES concentration> coagulation bath ratio> LiCl concentration>PVP concentration; the effect order on contact angle of the membrane was as follows: PESconcentration> coagulation bath ratio> LiCl concentration> PVP concentration; the effectorder on interception rate of the membrane was as follows: PES concentration> coagulation bathratio>PVP concentration> LiCl concentration; the effect order on the membrane pollution indexwas as follows: PVP concentration> LiCl concentration> PES concentration> coagulation bathratio. The big difference between the viscosity of casting solution directly affected the membranestructure, with the viscosity increase, the finger-like macrovoids suppressed.PES concentrationmainly through affecting the viscosity of casting solution to influence the membrane structureand properties. With the increase of PES concentration in casting solution, the membraneexhibited a more dense surface, a thicker surface layer, and the finger-like structure is inhibited.The addition of PVP could increase the number of membrane pore, and benefit the developmentof the finger-like macrovoids, but it also has inhibitory effect on macropores generated. Theaddition of LiCl was main used to increase the number of pores on the surface of the membrane,while its influence on membrane pore size is limited. If you want to control the size of pores, itcan mainly by controlling the DMAc/H2O ratio in the coagulation solution and the PESconcentration. The addiction of PVP and LiCl in the casting solution had a great influence on themembrane anti-pollution, it can improve the pollution resistance ability of membrane, thus itwould increase the service life of membrane. When PES concentration in casting solution was19wt.%, PVP concentration was5wt.%, LiCl addition amount was1wt.%, DMAc/H2O was60/40,the comprehensive performance of membrane was better.