Surface modification of polyurethane membranes using RF-plasma treatment with polymerizable and non-polymerizable gases

Low-powered gas plasmas containing oxygen, nitrogen or acrylic acid (AA) monomer (vapour) were used to modify and introduce specific functionalities on the surface of polyurethane membranes (PUs). Plasma treated films were characterized by X-ray photoelectron spectroscopy (XPS), while the hydrophilicity of the surfaces were examined by contact angle measurements. Pervaporation data (PV) were obtained for untreated and treated PUs. The results showed that plasma treatment processes increase in all cases on the polar nature of the PUs studied. HR-XPS results demonstrated that O2 treated PUs incorporated functionalities containing oxygen, while N2 plasma incorporated nitrogen at the PUs surface. AA plasma treatment resulted in the incorporation of carbonyl groups directly at the PUs surface. The pervaporation results showed that AA plasma polymerization treated PUs had much higher selectivity for the separation of methanol from methyl-t-butyl ether (MTBE) than untreated and O2, N2 treated PUs. In the case of AA treatment it was found that a thin film, with similar chemical properties to the poly (acrylic acid), was formed on top of the PU membrane increasing the PV efficiency for the separation of the mixture.