Comparative actions of a low pressure oxygen plasma and an atmospheric pressure glow discharge on the surface modification of polypropylene

We compared the action of low pressure oxygen plasma (LPOP) on the surface modification of polypropylene (PP) with that of atmospheric pressure glow discharge (APGD) with liquid electrolyte cathode. Both water and 0.05 M KCl aqueous solution were used as liquid cathodes in APGD system. The surface properties of PP were characterized by contact angle measurement followed by surface free energy calculation, Fourier Transform Infrared by Attenuated Total Reflectance (FTIR/ATR) and Atomic Force Microscopy (AFM). It was found that the actions of two processes were qualitatively the same. After treating PP surface with both methods, we commonly observed OH-groups, CO groups in ester, ketone and carboxyl groups, CO groups in unsaturated ketones and aldehydes. Both modification processes were also able to improve surface free energy and surface smoothing. In spite of some common features, however, the kinetic regularities of two processes were different. Characteristic time to reach stationary state in LPOP was always shorter than in APGD. Etching rates were higher in LPOP. Besides, the depth profile of oxygen-containing groups was somewhat different as well as surface morphology.