Research Of Modified Polysulfone Membrane Based On Cellulose Nanofibers/Sulfonated Polysulfone

In this research, the addition of sulfonated polysulfone(SPSf) and cellulose nanofibers(CNF) surface hydrophobic modification were used to increase the compatibility between CNF and polysulfone(PSf). CNF/PSf/SPSf membrane, methacryloxypropyltrimethoxy silane modified cellulose nanofibers(M-CNF)/PSf membrane and M-CNF/PSf/SPSf membrane were prepared by Loeb-Sourirajan (L-S) phase inversion process. The performance of the membranes and the rheological properties of three casting solutions were investigated. Through comparison, the M-CNF/PSf/SPSf membrane with the best comprehensive performance was chosen to applied in the ultrafiltration process of soybean protein solution, the optimum technological conditions of ultrafiltration process and membrane cleaning methods were investigated.The prepared CNF was in nanoscales, with a high length-diameter ratio and crystallinity. Several characterizations all showed that the compatibility between PSf and CNF was promoted by adding SPSf. The best addition amount of SPSf was 10% of the total content of PSf and SPSf. The pore structure of the membranes could be changed by the addition of CNF, also the performance of ultrafiltration, mechanical performance and antifouling performance could be improved through this way. When the addition of CNF was 0.3 wt%, the CNF/PSf/SPSf membrane showed the best pure water flux and mechanical performance, and the attenuation coefficient decreased from 51.4% to 31.3% compared with the PSf membrane.The surface of CNF was modified by methacryloxypropyltrimethoxy silane (MPS). The M-CNF basically maintained the original morphology of CNF, but the number of hydroxyl groups was decreased, oxygen-carbon ratio decreases from 0.63 to 0.54, and the crystallinity and thermal stability were decreased either. When the addition of MPS was 0.3 wt%, M-CNF and PSf showed the best compatibility. The pore structure of the membranes could be changed by the addition of M-CNF, also the performance of ultrafiltration, mechanical performance and antifouling performance could be improved through this way. The maximum tensile strength and breaking elongation of the M-CNF/PSf membrane were increased by 43.6% and 62.4% respectively compared with the PSf membrane.A variety of test results were all proved that good interactions formed among M-CNF, SPSf and PSf. Compared with the PSf membrane, the M-CNF/PSf/SPSf membrane showed the good performance in all aspects, the maximum of pure water flux reached 126.5L/m2h, the maximum tensile strength and breaking elongation were increased by 35.3% and 46.4% respectively, and the attenuation coefficient decreased from 51.4% to 33.1%.The three kinds of casting solutions were all belonged to pseudoplastic fluid. The viscosity of the casting solutions increased with the increase of the solute content and decreased with the increase of temperature. Non-newtonian fluid index decreased with the increase of the solute content.Using the optimal comprehensive performance of the M-CNF/PSf/SPSf membrane to investigate the optimum technological conditions of the ultrafiltration process of soybean protein solution. The soybean protein concentration was 1.2 g/L, the solution temperature was 50℃, operating pressure was 0.15 MPa, the pH value of soybean protein solution was 9. The 0.5% sodium dodecyl sulfate solution showed the most effective cleaning method of the polluted membranes. Two kinds of compound cleaning plans were designed, and plan B made the water flux recovery rate reached above 90%.