Manipulating membrane permeability and protein rejection of UV-modified polypropylene macroporous membrane

A three-step photo-induced graft polymerization of 2-hydroxylethyl acrylate (HEA) on the polypropylene macroporous membrane was carried out by using the chain transfer agent (CTA) benzyl dithiobenzoate (BDTB). Firstly, benzophenone was immobilized on the membrane surface; secondly, polyHEA (PHEA) was grafted on the membrane surface under UV irradiation in the presence of HEA and BDTB; thirdly, the PHEA grafted membranes with and without CTA moieties were respectively immersed in a thermostated water bath at 55 °C for the further grafting polymerization of HEA; in this step, PHEA was also grafted on the second-step modified membrane, with the grafted membrane containing CTA moieties served as macro-CTA and azodiisobutyronitrile (AIBN) as initiator. The degree of grafting (DG) of PHEA increased with UV irradiation time in the first step. In the second step, DG increased with UV irradiation time and monomer concentration, and with the decrease of CTA concentration. In the third step, DG continuously increased with reaction time under thermostated conditions without adding the free radical initiator; for the PHEA grafted membranes with CTA moieties on the grafting chain, DG was relatively higher than that for the PHEA grafted membranes without CTA moieties; also PHEA was grafted on the membrane surface by using the second-step modified membrane as the macro-CTA and AIBN as initiator, DG continued to increase with the reaction time. The pure water flux increased with the rise of DG up to 4.48 wt.%, then it decreased gradually, which shared the same trend with the water flux during the filtration of protein dispersion. The flux recovery ratio after water cleaning also increased with the rise of DG. But the rejection of protein dispersion followed the reversed trend of the pure water flux: it decreased down to 4.48 wt.% then increased with the rise of DG.