OXYGEN NITROGEN SEPARATION BY POLYBUTADIENE/POLYCARBONATE COMPOSITE MEMBRANES MODIFIED BY ETHYLENEDIAMINE PLASMA/

The surface of a polybutadiene/polycarbonate composite membrane was mo dified by ethylenediamine (EA) plasma. It was found that the O-2/N-2 s electivity increased after plasma treatment while the gas permeability decreased, Three phenomena, surface cross-linking, grafting and etchi ng, are often accompanied by plasma treatment, which may affect the me mbrane permeability and selectivity. It was found that the surface cro ss linking was responsible for the decrease of permeability and the af finity of EA toward oxygen was responsible for the increase of selecti vity. When examining the performance of membranes treated at various p lasma powers, surprisingly, it was found that the membrane treated at 70 W, which owned lesser overall EA content than the one treated at 50 W, had a higher O-2/N-2 selectivity and a higher O-2 permeability. Th e increase of permeability may be due to surface etching. The increase of selectivity was a mystery. After XPS analysis, it was found that a lthough the overall nitrogen content was lower, the surface N/C ratio of the 70 W EA plasma treated membrane was slightly higher than that o f the 50 W one. This result may explain why the membrane treated at 70 W possessed a higher O-2/N-2 selectivity than the one treated at 50 W . If this is true, it implies that a high nitrogen-containing thin top layer is all that is required for a high O-2 selectivity. (C) 1998 El sevier Science B.V.