Microstructures And Performance Of PAN-Fe₃O₄ Ultrafiltration Membranes, And Effect Of An Orthogonal Magnetic Field

This dissertation introduces the principle of ultrafiltration, the classification and the manufacturing methods of ultrafiltration membrane, and, the facts influencing the microstructures and performance of ultrafiltration membrane. The reviews are also given for the applications of ultrafitration, the main problems existing in the application, the development trend of ultrafiltration, and, the research advance in the organo-mineral membranes. The orientation of material molecular in the ultrafiltration membrane has not been controlled at will according to the need of membrane microstructure. In order to solve this problem, novel PAN- Fe₃O₄ ogano-mineral ultrafiltration membranes were prepared under no magnetic field or an orthogonal magnetic field by the wet phase inversion process from suspentions. These suspentions consist of polyacrylonitrile (PAN), dimethyl sulfoxide (DMSO), ferrosoferric oxide (Fe₃O₄), polyvinylpyrrolidone (PVP) or polyethylene glycol (PEG). The heat resistance and the solvent resistance of PAN-Fe₃O₄ ultrafiltration membrane were investigated by the analysis of TGA, DSC and DMA, and, the dissolving experiments, respectively. The microstructures of PAN- Fe₃O₄ ultrafiltration membrane were investigated by the Atomic Force Microscope (AFM) and the Scanning Electronic Microscope (SEM or FESEM). The performance of membranes was also examined by the filtration tests of pure water, BSA (Bovine Serum Albumin) aqueous solution and pig blood aqueous solution in a cross-flow ultrafiltration equipment. The main achievements and results are as follows:The arrangement orientation of material mocular has an important effect on the microstructure and the performance of ultrafiltration membrane. When an orthogonal magnetic filed of 1500Gs was applied in the manufacturing process of membrane, the result indicates that the arrangement orientations of material Fe₃O₄ are consistent with the magnetic field. This result may give a new method to control the microstructure of ultrafiltration membrane.In the ultrafiltration of protein solution, the relative flux of membrane is generally 20-30%. The contrast tests of pig blood solution indicates that the flux and the relative flux of a PAN- Fe₃O₄ membrane prepared under an orthogonal field are higher than that of a corresponding PAN- Fe₃O₄ membrane prepared under no field. In addition, the stable relative fluxes of magnetized membranes are above 35%, even over 50% for individual membrane. The difference between magnetized membranes and non-magnetized membranes is very small for the rejections to pig blood proteins. At the same time, the fouling mechanism of membranes given in this thesis can give a reasonable explanation on the change of membrane performance. Our results show that the magnetization of membranes can effectively improve the anti-fouling ability of the PAN- Fe₃O₄ membrane. The obtained result may give insight to the development of new membranes with a good anti-fouling performance in the filtration of blood solution.No chemical bond was found between PAN and Fe₃O₄ in the membrane at room temperature. The addition of Fe₃O₄ can improve the temperatures of dehydrogenated reaction and decomposition of PAN but dot change the glassy transition temperature. The resistance against acid is stronger than the resistance to base for a PAN- Fe₃O₄ membrane. This membrane will lose the value in a solution with pH value of over 10. The resistance against acid for this membrane depends on the concentration and the oxidation of an acid.For the PAN- Fe₃O₄ membranes, a 1.1wt% addition of Fe₃O₄ can obviously reduce the mean pore size and increase the surface roughness. But the addition of Fe₃O₄ change from 1.1wt% to 4.3wt%, the roughness and the pore size of membrane gradually become small. In addition, the water flux and the rejection of membranes basically become high with the change of Fe₃O₄ addition amount form 0wt% to 4.3wt%.The Fe₃O₄ particles are well-distributed in the PAN- Fe₃O₄ membrane. The magnetic coercivity of the PAN- Fe₃O₄ membrane is 114Oe and don not change with the Fe₃O₄ content in a membrane. The remanent magnetizations of membranes are improved with the increase of Fe₃O₄ content. Membrane samples can reach the saturation of the magnetization when the external fields reach above 5400Oe.For the PAN- Fe₃O₄ membranes prepared under an orthogonal magnetic field, the addition of Fe₃O₄ can reduce the thickness of membrane skinlayer and result in a change of macro pores in sublayer from regular, and perpendicular to the membrane plane to irregular and oblique to the membrane plane. The pore size, the surface roughness, the pure water fluxe, and the flux of BSA solution first reduce and then increase with the increase of Fe₃O₄ addition amount in the membranes. The rejections gradually decline with the increase of Fe₃O₄ addition amount and change within 2%. Contrary to the common results, the membrane permeability and the anti-fouling performance appear to have no direct correlation to the roughness of membrane surface in our results.