Surface modification of commercial aromatic polyamide reverse osmosis membranes by graft polymerization of 3-allyl-5,5-dimethylhydantoin

A commercially available aromatic polyamide reverse osmosis (RO) membrane was chemically modified to improve its chlorine resistance and anti-biofouling property. The raw RO membranes were modified by free-radical graft polymerization of 3-allyl-5,5-dimethylhydantoin (ADMH) using 2,2′-azobis(isobutyramidine) dihydrochloride as an initiator. Attenuated total reflective Fourier transform infrared spectra (ATR-FTIR) verified the successful graft of ADMH on the raw membrane surfaces. It was shown that two new FTIR adsorption bands at 1770 and 1714 cm−1 corresponding to two carbonyl groups in hydantoin ring appeared after graft polymerization, and the intensities of these two bands increased with increasing grafting time. Based on X-ray photoelectron spectroscopy (XPS), contact angle, and streaming potential measurements, graft polymerization increased the nitrogen and oxygen atom contents, improved surface hydrophilicity, and reduced surface charges of the raw membranes. The water fluxes of the ADMH-grafted membranes were higher than that of the raw membranes; however, the salt rejections decreased slightly. The chlorine resistances of the ADMH-grafted membranes were significantly improved by showing slight changes in water fluxes and salt rejections after chlorine treatments as compared with those of the raw membranes. Furthermore, the chlorinated ADMH-grafted membranes demonstrated obvious sterilization effects on Escherchia coli and substantial preventions against microbial fouling.