*Katerina Polaskova^1,3, Alp Ozkan², Petr Jelinek^1,3, Milos Klima¹, Zdenka Jenikova⁴, Francois Reniers², Lenka Zajickova^1,3
1Masaryk University, Brno, Czech Republic; ²Universite Libre de Bruxelles, Bruxelles, Belgium; ³Brno University of Technology, Brno, Czech Republic; ⁴Czech Technical University in Prague, Prague, Czech Republic
Non-thermal atmospheric pressure plasma discharges represent a promising technology for the modification of polymer adhesive properties. As working conditions of different discharges can differ significantly so does their effect on modified surfaces. In this work, we compare the effects of four different atmospheric pressure plasma jets on polypropylene (PP) slips. The three industrial jets utilize air as their working gas. The home-built RF plasma slit jet uses Ar. Optical emission spectroscopy was used to study the gas chemistry and for the calculation of the rotational gas temperatures. While spectra of all discharges contained OH, N₂ optical bands of different intensities, pronounced O and N atomic lines were observed only in the spectra of jets based on the gliding arc principle. In some cases, a continuous emission of NO2+ molecule was also observed. The chemistry of PP surfaces was assessed by water contact angle (WCA) and X-ray photoelectron spectroscopy (XPS). The changes in surface morphology were observed by a confocal microscope. Results from XPS and tensile strength measurements revealed that the presence of nitrogen-containing groups is beneficial for a stronger bond between PP and the epoxy adhesive. A direct correlation between low WCA and high tensile strength was not observed.