Modification of the surface properties of a polypropylene (PP) film using an air dielectric barrier discharge plasma

Modification of the surface properties of a polypropylene (PP) film using an air dielectric barrier discharge has been studied using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and contact angle measurement. The atmospheric pressure air discharge is found to modify the PP surface in both morphology and composition, as expressed in the following outcomes: the spherulitic features of the surface of the pristine PP film change into randomly-shaped surface protrusions, with the surface roughness increasing as the processing time is extended; heavily oxidized carbon species are found on the plasma-processed surface and the contact angle is also reduced dramatically from 93.7° for the untreated surface to 53.8° post-treatment. After long-term storage in ambient air, the much lowered surface contact angle of the processed PP film is found to in part recover. Effective plasma-induced chemical etching appears to equilibrate after 25% of the surface carbon is oxidized. The CH3 functionalities in the PP are believed to be oxidized preferentially by the air discharge plasma.