Surface functionalization of polypropylene using a cold atmospheric pressure plasma jet with gas water mixtures

This work presents a surface analytical study on polypropylene (PP), treated with a cold atmospheric pressure plasma jet (CAPPJ) system. A novel treatment approach to moisten the process gas is followed, enabling high concentrations of admixed water at atmospheric conditions. Experiments were carried out with a systematic increase of water admixtures in the process gas (air/N₂). Optical emission spectroscopy (OES) was used to determine chemical changes in the plasma. Contact angle measurements, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) were performed on PP samples directly after the plasma treatment and an additional subsequent washing step of the surface. The results show that water admixtures significantly change the chemistry and morphology of the treated surfaces. However, these changes heavily depend on the process gas (air or N₂). While in the case of N₂ process gas water admixtures influenced the chemistry of so called created low molecular weight oxidized material (LMWOM), the formation of LMWOM during the plasma treatment was quenched completely when water was admixed into air process gas instead.