Influence of dielectric barrier discharge atmosphere on polylactic acid (PLA) surface modification

In this work, polylactic acid (PLA) surfaces are exposed to a medium pressure dielectric barrier discharge (DBD). PLA surface transformations are realized with DBDs in different atmospheres (air, helium, helium/air mixtures) and are compared to study the influence of discharge atmosphere on the PLA surface modification. A first part of the paper is dedicated to the discharge characterization using current–voltage waveforms and optical emission spectra, while the second part containing contact angle and XPS results focusses on the surface modification effect. Results show that the discharge gas significantly influences the final PLA surface composition: the helium DBD leads to a high nitrogen incorporation on the PLA surface, while the air discharge results in a high oxygen incorporation. Moreover, the addition of a very small amount of air in helium is sufficient to completely change the chemistry on the PLA surface: nitrogen incorporation is hindered by the presence of oxygen containing plasma species, thereby proving the extreme reactivity of these plasma species. When more oxygen is added to the surface than nitrogen, the minimum contact angle value is limited to 59°. However, when the surface chemistry is essentially related to nitrogen grafting, the PLA wettability becomes higher (lowest contact angle value equal to 36°).