Comparative study of surface modification of polyethylene by parallel-field and cross-field atmospheric pressure plasma jets

Abstract

Atmospheric pressure plasma jets (APPJs), which can be roughly classified as parallel-field APPJ and cross-field APPJ based on the direction of gas flow and electrical field, have been widely used for surface modification of polymers, but the modification difference between the two kinds of APPJ remains unknown. In this paper, the surface modification of polyethylene (PE) sheet by the two types of APPJ is comparatively studied. Results show that the two types of APPJ can improve the surface wettability of the PE sheet obviously through the comprehensive effect including plasma etching and inducing of hydrophilic groups. However, some differences are also observed. Compared with the cross-field APPJ, the etching effect induced by the parallel-field APPJ is more obvious under the same treatment condition. Additionally, the concentration of active species induced by the cross-field APPJ is higher than that of the parallel-field APPJ at the upstream region. By contrast, at the downstream region, the concentration of active substances induced by the parallel-field APPJ is higher. Finally, the bonding experiment shows that both plasma treatments can improve the bonding properties of PE surfaces, but the adhesion force improved by the parallel-field APPJ is always higher than that of the cross-field APPJ under the same parameters, which is attributed to the more remarkable etching effect that produces a large number of nano-grooves, thus increasing the contact area between UV glue and PE surfaces.