Surface Modification Of Aromatic Polyamide Reverse Osmosis Membrane By Grafting 3-allyl-5, 5-dimethylhydantoin

Aromatic polyamide composite reverse osmosis (RO) membrane is susceptible to chlorination and biofouling, which shortens membrane life and limits the further application of RO technology. In this work, ADMH-grafted membrane and AAc-ADMH grafted membrane were prepared by free-radical graft polymerization of two functional monomers, hydantoin derivative 3-allyl-5,5-dimethylhydantion (ADMH) and hydrophilic acrylic acid (AAc). Thus, we successfully realized the surface modification of aromatic polyamide composite RO membranes to improve both chlorine resistance and antimicrobial performance of the membranes.After graft polymerization with ADMH, the composite membrane had better hydrophilic property. All the ADMH-grafted membranes showed lower water fluxes but generally higher salt rejection than the unmodified ones within the experimental orafn bgoet.h A tfhtee ru fnrmeeo cdhiflioerdin aen tdr eAatDmMenHts- g(r2a0f0te0d pmpmem?hb rcahnleosr indee carte apsHed 4; )t,h teh es awlta rteejre fcltuioxness of the ADMH-grafted membranes also decreased, but the decreases were generally smaller than those of the unmodified ones. By considering the changes in membrane permselectivity and chlorine resistance after surface modification with ADMH, the optimum polymerization conditions were determined. Moreover, after free chlorine treatments, the ADMH-grafted membranes obtained higher reduction rates of E. coli. and showed higher antibacterial properties than the unmodified ones.After graft polymerization with AAc-ADMH, the membrane surface contact angles decreased, and the surface"peak"structures increased and had some bulges. With the increasing mass fraction ratio of [AAc]/[ADMH] in the monomer mixtures, the salt rejections of the AAc-ADMH grafted membranes increased, but the water cflhulxoersin ien carte paHse d4 )f,i rtshte a wnda ttehre fnl udxeecsr eoafs ethde. AAfAtecr- AfrDeeM cHhl ogrrianfet etdre matemmebnrtsa n(e2s0 0in0c prepamse?dh and salt rejections decreased; the increases of water fluxes and the decreases of salt rejections enhanced as the mass fraction ratio of [AAc]/[ADMH] in the monomer mixtures increased. Within the experimental range, we determined the [AAc]/[ADMH] mass fraction ration 1:2 as the the optimal grafting condition to prepare the ADMH-AAc grafted membranes. The results showed that compared with the unmodified membranes, the AAc-ADMH grafted membranes prepared under the optimal grafting conditions showed low water fluxes but high salt rejections. After free chlorine treatments, the AAc-ADMH grafted membranes had smaller reductions in water fluxes and salt rejections and showed higher chlorine resistances than the unmodified ones. Moreover, free chlorine treatments also endowed the AAc-ADMH grafted membranes with good sterilization functions.The membrane permselectivities of the ADMH and AAc-ADMH grafted membranes prepared under the respective optimum conditions were compared. The results showed that the AAc-ADMH grafted membranes had higher water fluxes but lower salt rejections than the ADMH-grafted ones. After treated with 2000 ppm ? h chlorine at pH 4.0, the AAc-ADMH grafted membranes had higher reductions in salt rejection but lower reductions in water fluxes than the ADMH-grafted ones. After treated with the same chlorine conditions, the antibacterial properties of the AAc-ADMH grafted membranes were lower than the ADMH-grafted membranes. This suggested that the addition of AAc segments to the ADMH chain blocks can improved the water fluxes of the ADMH-grafted membranes before and after chlorination, but at the cost of salt rejections and antimicrobial performance of the grafted membranes.