Modification Of Polyethersulfone Ultrafiltration Membrane With Zwitterionic Groups

Polyethersulfone (PES) membrane has many desirable properties including chemical intertnessm, favorable mechanical strength and low cost. However, in many cases, the nonspecific protein adsorption on the membrane surface and in the membrane pores due to the inherent hydrophobic characteristics of PES often causes serious membrane fouling and thus rapid decline of permeation flux. In order to ensure the wide applications of the PES membrane, zwitterionic groups were introduced to PES membrane to resist fouling by improving its protein adsorption-resistant property. In this thesis, two kinds of zwitterionic groups, including Soybean phosphatidylcholine (SPC) and N, N-dimethyl-N-methacryloxyethyl- N-(3-sulfopropyl) (DMMSA) were used to modify the PES membrane.PES/SPC blend membranes were prepared by simple blending of PES and SPC. The surface of PES/SPC blend membranes was characterized by X-ray photoelectron spectroscopy (XPS). XPS data revealed that the phosphorylcholine (PC) groups were concentrated at the surface by changing the composition of coagulation bath. Addition of N,N-dimethylformamide (DMF) in coagulation bath could prolong coagulation time and facilitate the migration of SPC from polymer bulk to membrane surface. BSA adsorption amount decreased from 56.2 g/cm2 for SPC-free PES membrane to 2.4 g/cm2 for PES/SPC blend membrane.The fouling-resistant property of the blend membranes was improved considerably with the increase of SPC content.PES ultrafiltration membranes were modified by photolysis using ultraviolet light and grafted hydrophilic monomers, DMMSA, onto the membrane surface to create more hydrophilic and lower fouling membrane surfaces. The surface of PES/DMMSA grafted membranes was characterized by XPS. XPS data revealed that the content of sulfobetaine groups on the surface reached satruration after irradiated 4h or the DMMSA concentration upon 4.8 wt% in solution. The results of SEM suggest that pore damage must happen when the membrane was irradiated 4h. Although the fouling-resistant property of the PES/DMMSA membranes was improved considerably, compared with the method of blend, graft can introduce more decreaes of flux due to reaction between DMMSA and PES which blocked membrane pores to some extent.