Preparation And Characterizations Of Poly(Vinyl Butyral) Flat Membrane Via Thermally Induced Phase Separation

At present,water pollution and water shortage have become an urgent problem for human survival.How to deal with water pollution has become a central issue.As one of the measures to solve water pollution,water treatment technology has developed rapidly.The field of water treatment has become one of the most widely used fields of industrial textiles.The traditional textile filter materials used for water treatment have low filtration efficiency,but many new fiber membrane materials have excellent separation efficiency.However,the fiber membrane materials such as polysulfone and polytetrafluoroethylene,inherently hydrophobicity lead to poor anti-pollution ability,which greatly limits the application.Although the hydrophilic modification of the surface improves the hydrophilicity of the membrane,it is generally poor in stability.Polyvinyl butyral(PVB)has a certain hydrophilicity due to its hydroxyl group in the molecule,and has excellent anti-pollution performance,and is a popular material for membrane separation technology.Compared with the traditional membrane-forming method,the thermally induced phase separation method(TIPS)has the characteristics of fast phase separation and uniform membrane pore size,and is one of the popular methods for preparing membranes.Therefore,in this paper,the polymer PVB was used as the raw material,caprolactam(CPL)was selected as the single diluent,CPL and polyethylene glycol 200 were used as the mixed diluent,and the hydrophilic PVB flat membrane was prepared by TIPS method.The application of membranes in the field of membrane separation provides scientific evidence and experience.Firstly,PVB flat membranes were prepared by TIPS method using PVB as polymer and caprolactam(CPL)as diluent.The effects of polymer concentration and cooling rate on the microporous structure,pore size,porosity,contact angle,water flux,rejection,anti-pollution performance and mechanical properties of the membrane were studied.The results show that the membrane structure obtained was formed with finger-like macrovoid well-connected bicontinuous honeycomb pores.As the PVB concentration increased,the pore size,porosity,contact angle and water flux of the membranes decreased significantly,and the membrane rejection and mechanical properties were significantly improved.As the cooling rate increased,the proportion of honeycomb structure in the pores of the membrane increased,the pore size,porosity,contact angle and water flux of the membrane decreased significantly,and the membrane rejection and mechanical properties are slightly improved.When the PVB concentration was 20wt%,the water bath temperature was 0℃,and the temperature of the casting solution was 170℃,the flat membrane could get the best comprehensive performace with 0.0859μm of the mean pore size,73.590 of the contact angle,179.6L·m-2·h-1 of the water flux,62.27%of the BSA rejection rate,3.58MPa of the breaking strength and 10.08%of the elongation.It can be seen from the experimental results in Chapter 2 that the dynamic antifouling performance,BSA rejection rate and mechanical strength of the PVB membranes prepared by using only CPL as a diluent are not significant,and the practical application in the membrane separation technology is of little significance.Therefore,in the third chapter,polyethylene glycol 200(PEG200)and CPL were selected as mixed diluents.The effects of CPL/PEG200 weight ratio,PVB concentration and cooling rate on the morphology and properties of the films were systematically investigated.It was found that when PEG200 was added to the casting solution,the proportion of honeycomb pores in the pores of the membrane increased.When the weight ratio of CPL/PEG200 was 4/6,the membrane pores were all honeycomb structure.On this basis,the effects of polymer concentration and cooling rate on membrane pore structure,contact angle,water flux,rejection,anti-pollution performance and mechanical properties were discussed.As the concentration of PVB increased,the pore structure of the membrane was completely honeycomb structure,the pore size,the contact angle and the water flux decreased,the rejection rate and the mechanical properties increased.The flat membrane could get the best comprehensive performace with weight ratio of CPL/PEG200 was 4/6,the PVB concentration was 20wt%,the water bath temperature was 0℃,and the casting liquid temperature was 170℃.In this case,the mean pore size of the membrane was 0.0502μm,the contact angle was 83.12°,and the water flux of the membrane was 141.02L·m-2·h-1 the BSA rejection rate was 94.89%,the breaking strength was 11.7 MPa,and the elongation at break was 26.7%.