Cold atmospheric pressure plasma treatment for adhesion improvement on polypropylene surfaces

Abstract Cold atmospheric pressure plasma from a plasma jet was used to improve the adhesion properties of polypropylene (PP). Differences in adhesion were at first observed for either air or N2 as process gas, tested on a PP-acrylic pressure sensitive adhesive (PSA) model system. For a deeper understanding changes in the surface chemistry and topography on PP after plasma jet treatment, using several different O2/N2 mixtures, were investigated in a comprehensive surface analytical study. Independent of the gas composition a majority of plasma induced polar groups exist as water soluble low molecular weight oxidized material (LMWOM), located within the first few nanometers. Consequently, the observed changes in the surface chemistry for various process gas compositions are mainly attributed to differences in the formed LMWOM. However, these chemical changes indicated also differences in the interaction mechanism of plasma reactive species with the polymer surface and therefore, in the resulting plasma-polymer etching process. Hence, significant changes in the topography have been observed for different process gas compositions, which could be reliably correlated with the obtained adhesion results.