Surface hydrophilization of microporous polypropylene membrane by the interfacial crosslinking of polyethylenimine

Abstract

To endow microporous polypropylene membrane (MPPM) with durable surface hydrophilicity, a facile interfacial crosslinking approach was developed, combined with a pretreatment by dielectric barrier discharge (DBD) plasma at atmospheric pressure. The commercially available polyethylenimine (PEI) was coated on MPPM firstly and was sequentially crosslinked with p-xylylene dichloride and quaternized with iodomethane to form a permanently positively charged layer. The physical and chemical changes of the membrane surface were characterized by tensile test, FT-IR/ATR, XPS, and FESEM. The surface hydrophilicity of the modified MPPMs was evaluated by water contact angle and pure water flux measurements. Besides, the influence of surface charge on protein filtration involving flux decline and protein transmission was also investigated in detail. It is found that the optimal time of DBD plasma treatment is ∼30 s. Mass gain for the MPPMs during the interfacial crosslinking can be controlled conveniently by adjusting the PEI concentration from 1.0 to 15 g/L. The surface hydrophilicity can be significantly enhanced and is durable, characterized by the sharp decrease of water contact angle, the double increase of pure water flux and the stability test. The results of protein filtration suggest that the obtained highly hydrophilic and charged membrane surface is resistant to protein fouling. Furthermore, almost 100% of protein transmission indicates that the microfiltration characteristic of MPPMs is unchanged.