Modification of polylactic acid (PLA) surfaces by argon DBD plasma jet treatment and x–ray irradiation

We investigated the influence of argon DBD plasma jet treatment on the surface chemical composition of polylactic acid (PLA). The surface has been analyzed by x-ray photoelectron spectroscopy (XPS) as well as by means of atomic force microscopy (AFM) and water contact angle measurements (WCA). Since existing studies on the XPS analysis of plasma-treated PLA do not explicitly address potential radiation-induced changes due to XPS, the x-ray-induced degradation of PLA was also investigated in this work. The degradation study has shown, that PLA undergoes a pronounced degradation, which is characterized by a decomposition of oxygen containing groups. The investigations on the argon plasma jet treatment of PLA have shown that, despite the inevitable presence of oxygen impurities in the process gas, on balance oxygen is removed from the PLA surface. This result differs significantly from the argon plasma treatment of PLA with planar DBD setups which has been reported to result in oxygen incorporation rather than oxygen removal. Interestingly, an increase in wettability is observed although oxygen and thus polar groups are removed. The plasma treatment is furthermore accompanied by an increase in surface roughness which might explain the increased wettability.