Comparison of the surface characteristics of polypropylene films treated by Ar and mixed gas (Ar/O 2) atmospheric pressure plasma

In an attempt to modify the hydrophobic surface properties of polypropylene (PP) films, this study examined the optimum process parameters of atmospheric pressure plasma (APP) using Ar gas. Under optimized conditions, the effects of a mixed gas (Ar/O 2) plasma treatment on the surface-free energy of a PP film were investigated as a function of the O 2 content. The polar contribution of the surface-free energy of the PP film increased with increasing O 2 content in the gas mixture. However, slightly more oxygen-containing polar functional groups such as CO, C O, and COO were introduced on the PP film surface by the Ar gas only rather than by the Ar/O 2 gas mixture. In addition, AFM analysis showed that the Ar plasma treatment of the PP film produced the smoothest surface as a result of the relatively homogeneous etching process. The Ar plasma treatment is slightly more effective in improving the wettability of a PP film than the Ar/O 2 plasma treatment but the polar contribution of the surface-free energy of the PP film increases with increasing O 2 content in the gas mixture.