Surface Hydrophilization And Antifouling Properties Of Microporous Polypropylene Membrane

Microporous polypropylene membrane (MPPM) is a promising polymeric membrane material, which has been widely used due to its high stability, well-controlled pores and low cost. However, the intrinsically high hydrophobicity limits its separation efficiency in aqueous solution, and easily causes hydrophobic interactions between the membrane surface and protein or bacteria which mediate membrane biofouling including protein fouling and bacterial fouling. Thus, it is of great importance to enhance the surface hydrophilicity of MPPM and improve the antifouling ability. In this thesis, various surface hydrophilization strategies for MPPM were developed to construct antifouling surface, which is capable of resisting protein adsorption, bacterial adhesion or killing bacteria. Furthermore, the antibacterial mechanism was explored in detail. Our specific studies are concentrated on the following aspects:A facile and effective method combining interfacial crosslinking with pretreatment by dielectric barrier discharge plasma at atmospheric pressure was developed for the surface hydrophilization of MPPM. The modified MPPM was characterized by FESEM, FT-IR/ATR, XPS, and the measurement of water contact angle and water flux. It is found that the surface hydrophilicity was considerably enhanced, which can be attributed to the introduction of a stable and quaternized layer. Results of protein filtration indicate that the modified MPPM can resist the adsorption of positively charged proteins, while facilitate the adsorption of negatively charged proteins, exhibiting a selective antifouling property.Combining physical entrapping and covalent immobilization of benzophenone, sulfobetaine methacrylate (SBMA) was successfully grafted on MPPM by UV-induced graft polymerization to further enhance the antifouling properties. It is found that the SBMA-grafted MPPM possesses high hydrophilicity and strong resistance to the adsorption of bovine serum albumin and lysozyme. Besides, the modified MPPM with an optimal grafting density can completely inhibit the adhesion of Gram-negative E. coli,P. fluorescens and Gram-positive S. aureus, demonstrating excellent anti-adhesive performance for bacteria.A polycation-immobilized surface was constructed on MPPM using the UV-induced grafting of N,N-dimethylaminoethyl methacrylate (DMAEMA) and subsequent quaternization or quaternization-crosslinking. The antibacterial performance of surface-immobilized polycation and its mechanism were explored in detail. It is found that non-crosslinked polycations exhibit strong antibacterial performance for both E. coli and S. aureus, which is enhanced with increasing the surface density of positive charge or contact time. Nevertheless, the crosslinked ones can not kill bacteria at all regardless of charge density and contact time.To further explore the antibacterial mechanism of surface-immobilized polycation, we prepared electrospun ultrafine fibrous membranes of poly(DMAEMA-co-alkyl methacrylate) with ultrahigh density of surface positive charge. The effects of crosslinked structure and hydrophobic alkyl chains on the antibacterial activity were investigated. For the non-crosslinked fibrous membrane with shorter alkyl chain, stronger antibacterial performance was observed. However, the crosslinked fibrous membrane can only attract bacteria by electrostatic interaction but cannot kill them in all cases. Based on these results, we propose that the chain flexibility is the prerequisite for the antibacterial performance of surface-immobilized polycations.