Study On Preparation And Mechanism Of Nano Cellulose/Polyethersulfone Composite Membrane Material

The object of this paper was to improve hydrophilic and anti-fouling properties of membrane materials and to widen the application of membrane materials. The nano cellulose was blended with polyethersulfone casting solution using ultrasonic treatment. The nano cellulose/polyethersulfone composite membrane was prepared by phase inversion immersion process. It was investigated that the effects of preparation factors on pore structure, ultrafiltration property and mechanical performance of composite membrane. According to orthogonal test, the optimal factors of preparation process of composite membrane were obtained, as follows:the mass ratio of nano cellulose was 1%; the mass ratio of polyethersulfone was 18%; the mass ratio of polyvinylpyrrolidone K30 was 0.3%; the solvent was N, N-dimethylethanolamine; the coagulation bath was water; and the temperature of coagulation bath was 30℃.The effect of nano cellulose on performances of composite membrane was studied by testing various properties. These results showed that the molecular weight cutoff was 4.27×104 Da. The hydrophilic property and anti-fouling property of composite membrane were improved, which was attributed to the existence of nano cellulose. The composite membrane was characterized by fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA) The surface layer, support layer and cross section of composite membrane were observed by atomic force microscopy (AFM) and scanning electron microscopy (SEM), respectively. The asymmetric membrane structure was observed which was composed of surface layer and porous support layer. And composite membrane had more loosen finger-like pore structure.The viscosity and phase structure of blending casting solution were tested by viscosity measurement and fluorescence microscope. It was indicated that the blending casting solution was partly compatible system. In the thermodynamics and dynamics process of blending casting solution, the effect of nano cellulose was analyzed using phase diagram and coagulation rate constant. The results were illustrated that the thermodynamics performance of phase equilibrium and component of phase point were changed by adding to nano cellulose. In the preparament process of composite membrane, the coagulation rate constants of all stages were increased, due to the addition of nano cellulose. The nano cellulose accelerated the blending casting solution to solidify the composite membrane, which controlled the pore structure of composite membrane and improved the performance of composite membrane.The optimal factors of ultrafiltration process of milk solution were discussed, as follows:the operating press was 0.1 Mpa; the concentration of milk protein solution was 1 g/L; the temperature and pH value of milk solution were 40℃and 11, respectively. It was measured that the ultrafiltration property of composite membrane in different working pressures with milk solutions in different concentrations. The math model of the ultrafiltration, which was suitable for purification of milk protein solution, was set up. The five cleaning methods were used to clean the fouling composite membrane. The order of cleaning methods'effect was ultrasonic cleaning>alkalis cleaning>oxidation cleaning> acid cleaning>water back flushing.