Thin film composite (TFC) reverse osmosis (RO) membranes play a significant role in addressing rapidly expanding global needs for potable water. A well-known problem of TFC membranes is their sensitivity to oxidizing agents such as chlorine, which are used to disinfect the feed water or remove fouling from the membrane surface. Many studies on the chemical and performance degradation of these membranes have been carried out, but the fundamental physical properties of the functional polyamide barrier layer (PBL) and their stability after chlorine treatment remain largely unknown. This is mostly due to the lack of suitable techniques for accurately probing the ultrathin (<200 nm) PBL, which is insoluble due to crosslinking. In this study we report changes in the glass transition temperature (Tg) of the PBL of a commercial RO membrane as a function of chlorine treatment in which concentration and pH were systematically varied. The results indicate a monotonic decrease of Tg with increasing exposure time at a given chlorine concentration. Further, both the degree and the rate of Tg decrease vary significantly with both the chlorine concentration and pH value of the aqueous chlorine solution. Moreover, this change in PBL Tg shows direct correlation with the salt rejection of the membrane, but the magnitude of the correlation is specific to chlorine concentration and pH.
Citation: Journal of Membrane Science
Pub Type: Journals
Thin film composite membrane, Chlorine degradation, Polyamide barrier layer, Glass transition temperature