Oxygen/nitrogen separation by plasma chlorinated polybutadiene/polycarbonate composite membrane

The surface of a polybutadiene (PB)/polycarbonate (PC) composite membrane was plasma-modified by CHCl₃ to enhance its oxygen/nitrogen selectivity. The selectivity of the composite membrane was significantly improved after plasma chlorination. The degree of chlorination on the surface of this composite membrane surface was controlled by the supplied power for plasma and the plasma treating time. The chlorination was verified by infrared spectroscopy (FTIR-ATR) and ESCA analysis. The CHCl₃ plasma treated membrane had an oxygen/nitrogen selectivity of 7.5 and a gas permeation flux of 0.3 GPU. The selectivity enhancement was attributed mostly to the alteration of the physical structure on the membrane surface rather than the chemical effect introduced by chlorine. It was found that the surface hydrophilicity of the plasma treated membrane increased after long period of storage. Surface swelling by water vapor may be the reason for the selectivity degeneration.