Change of chemical composition and hydrogen bonding behavior due to chlorination of crosslinked polyamide membranes

Abstract

The effect of membrane exposure to hypochlorite oxidant on property changes (chemical composition and hydrogen bonding behavior) of four FilmTec® thin film composite crosslinked polyamide membranes has been investigated. Crosslinking densities of the membranes were about 25-35%, with about 3-4 chlorines bound to the repeating unit of the polyamide membranes. This was equivalent to ~ 39% of all nitrogens being chlorinated in the polyamide membranes assuming the amide nitrogen is the dominant reaction site with chlorine. FTIR spectra showed the amide I band (C=O stretching peak at 1663 cm -1) of polyamide membranes shifted to higher wave-numbers and the peak intensity of the amide II band (N-H bending peak at 1541 cm -1) decreased after chlorination. The peak shift and decrease of peak intensity resulted from breakage of hydrogen bonds between C=O and N - H groups within the polymers. The XPS and FTIR analytical analysis showed that there is no difference in the chlorine attack of polyamide membranes of higher or lower crosslinking density, and that the chlorination breaks and weakens hydrogen bonding. © 2008 Wiley Periodicals, Inc.