Research On Chitosan Hydrophilic Modification Of Fe₃O₄-FVDF Ultrafiltration Membrane

Good chemical stability, temperature tolerance, low prices and so on makes poly vinylidene fluoride（PVDF） widely used for ultrafiltration membrane. Membrane is easy to be fouled because of its strong hydrophobicity, which limits the application of PVDF ultrafiltration membrane. So in recent years the hydrophilicicy modification of PVDF ultrafiltration membrane raises widely attention, especially applying inorganic filler. But the modification effect of inorganic fillers is limited. In this paper, PVDF was taken as base material and Fe₃O₄ modified by chitosan（CS） was added into PVDF to prepare hybrid ultrafiltration membrane. Such research has not yet been reported. The embedding method and coprecipitation method were adopted to coat CS to the surface of Fe₃O₄ to improve the hydrophilicity of Fe₃O₄. Then the modified Fe₃O₄ was added in the casting solution of PVDF to prepare hybrid membrane by the phase inversion method. At the same time the membrane formation environment was controlled by magnetic field, hoping to improve the hydrophilicity of PVDF ultrafiltration membrane. At last the modified Fe₃O₄, CS-Fe₃O₄-PVDF hybrid membrane were tested. The influence of Fe₃O₄ content and magnetic field on the properties of CS-Fe₃O₄-PVDF hybrid membrane were investigated respectively.Embedding method was used to coat CS to Fe₃O₄ to prepare modified Fe₃O₄. Then Fe₃O₄ and modified Fe₃O₄ were added into the PVDF casting solution respectively. In the absence of magnetic field Fe₃O₄-PVDF hybrid membrane and CS-Fe₃O₄-PVDF hybrid membrane were obtained by phase inversion method. Then the membrane were used for bovine serum albumin（BSA） ultrafiltration experiment. Infrared spectra（FTIR）, particle size, scanning electron microscope（SEM） and contact angle were applied to test the characteristic of modified particles and the hybrid membranes. The results show that the CS is coated to the surface of Fe₃O₄; In addition, the BSA ultrafiltration experiment shows that the modified Fe₃O₄-PVDF hybrid membrane has stronger resistance to fouling than pure Fe₃O₄-PVDF hybrid membrane. When the content of Fe₃O₄ in casting solution is 60 wt%, the membrane has the lagest initial flux of 440 L/ m2h-1, when the content of Fe₃O₄ is 30 wt% the membrane has the lagest initial intercept rate of 58%. The absolute anti-fouling parameters shows that when the content of Fe₃O₄ is 60 wt%, the anti-fouling of the membrane is better; Relatively anti-fouling parameters shows that when the content of Fe₃O₄ is 30 wt% the anti-fouling of the membrane is better, and the contact angle is 80 °.Then Fe₃O₄ modified by coprecipitation method was added to the PVDF casting membrane liquid. The CS-Fe₃O₄-PVDF magnetized membrane and CS-Fe₃O₄-PVDF unmagnetized membrane were get when there was or no magnetic field respectively. Then membranes were used for BSA ultrafiltration experiment. The properties of modified Fe₃O₄ particles, CS-Fe₃O₄-PVDF magnetized and unmagnetized membrane were characterized by FTIR, SEM and contact angle. The results show that the CS is coated to the surface of Fe₃O₄. The content of CS on the modified Fe₃O₄ is 45.0 wt% obtained by quality standard. In addition, BSA ultrafiltration experiments show that when the content of Fe₃O₄ is 30 wt%, unmagnetized membrane has the lagest initial flux of 120 L/ m2h-1; When the content Fe₃O₄ is 10 wt%, the unmagnetized membrane has the lagest initial intercept rate of 100%. Absolute anti-fouling and relatively anti-fouling parameters show that when the content of Fe₃O₄ is 10 wt%, anti-fouling of the membrane is best. Compared with unmagnetized membrane, the permeability of magnetized membrane is better with the contact angle of 67°, flux attenuation coefficient of 0.15. The magnetic field has no obvious effect on anti-fouling of membrane. Keyword Chitosan, FeO, Coating, Poly vinylidene fluoride, Hydrophilicity,...