The Study Of Antifouling And High Flux Cellulose Acetate Ultrafiltration Membranes

As a green and energy-efficient separation technology, ultrafiltration exhibits a vast prospect of application in separation, purification and condensation,while membrane fouling still constitutes a bottleneck of its development.Major approaches, such as developing novel hydrophilic membrane materials and hydrophilic modification of membrane materials have been carried out for fouling reduction. In this dissertation, cellulose acetate(CA) membranes were prepared via the phase inversion process, and Poly(vinylpyrrolidone)-b-poly(methylmethacrylate)-b-Poly(vinylpyrrolidone)(PVP-b-PMM A-b-PVP)、Cellulose nano whisker(CNW) and N-phthaloyl chitosan(NPHCs) were added to fabricate modified CA membranes. The morphology, permeation performance, antifouling property, hydrophilicity, mechanical property as well as thermal propertyof the modified membranes were discussed in detail.PVP-b-PMMA-b-PVP modified CA ultrafiltration membranes with anti-fouling property were prepared via immersion precipitation phase inversion method. The effects of PVP-b-PMMA-b-PVPon the structure and properties of the modified membranes were investigated. Compared to CA membrane, the CA/PVP-b-PMMA-b-PVP membranes had higher porosity, pure water flux and permeation, but they showed the lower protein rejection. The surface morphology of the modified membranes was examined, the results indicated that they had rough surface. The surface hydrophilicity of the modified membranes was improved due to the enrichment of PVP chains on the membrane surface, which was confirmed by the pure water flux recovery ratio and contact angle measurement. In addition, the modified membranes exhibited better anti-fouling ability to protein compare with CA membrane.Cellulose nano whisker(CNW) was blended with CA ultrafiltration membrane and the blended membranes were characterized. The water content、pure water flux and membrane hydrophilicity of modified CA/CNW ultrafiltration membrane increased with an increase of CNW content in the casting solution. The surface roughness and surface pore size of CA/CNW membrane increased by the addition of CNW, and the sponged pore structure increased. However, the pore size and surface roughness of the membranes with CNW presented the trend of decrease after the first increases with the increase of adding amount of CNW. The pure water flux of CA ultrafiltration membrane increased from 34.84 L?m-2 h-1 to 233.45 L?m-2 h-1, while maintaining high protein entrapment rate. The hydrophilic of blend membranes enhancement, while the water flux recovery rate increased from 56.00 % to 96.73%, which effectively improved the anti-fouling ability of CA ultrafiltration membrane. At the same time, the mechanical properties and thermal stability of blend membranes improved.N-phthaloyl chitosan(NPHCs), which could be dissolved in various organic solvents, is synthesized for the modification of CA ultrafiltration membrane. The pore size, porosity, pure water flux of CA membranes increased with an increase of NPHCs concentration in the casting solution. The significant effect of hydrophilicity of NPHCs and PEG600 on the fouling of CA/NPHCs blend membranes by protein was also discussed. It was found that CA/NPHCs blend membranes had outstanding antifouling properties. Thus, the modified chitosan proved to play an important role in the improvement of UF membrane performance.