Study of the ageing behaviour of polymer films treated with a dielectric barrier discharge in air, helium and argon at medium pressure.
Résumé
Plasma treatment of polymers is gaining more and more popularity as a surface modification technique, since it offers numerous advantages over the conventional chem. processes. Plasma surface treatment is an environmentally benign, fast and versatile technol. However, it has one major disadvantage: the induced modification of the surface is not permanent, since the surface tends to recover to the untreated state. This ageing effect is due to the reorientation of induced polar chem. groups into the bulk of the material. In this paper, the ageing of polypropylene (PP) and polyethylene terephthalate (PET) films, treated with a dielec. barrier discharge operating at medium pressure (5.0 kPa) in air, helium and argon, is studied. This study is performed using contact angle measurements and XPS. Results show that the working gas used during plasma treatment has a significant influence on the ageing behavior of both PP and PET films. The air-, helium- and argon-plasma treated PP films have a loss in treatment efficiency of 47%, 35% and 25% resp., while the air-, helium- and argon-plasma treated PET films have a loss in treatment efficiency of 39%, 34% and 29% resp. These results can be explained by the different crosslinking degrees of the polymer films after plasma treatment. Increasing the crosslinking degree will hinder the movement of the polymer chains and reduce the ageing effect.