Like many polymers, Polyethylene Terephthalate (PET) has excellent bulk physical and chemical properties but exhibit poor adhesion abilities. Therefore, in order to improve the deposition of a subsequent layer onto such compounds, a pretreatment of the surface is usually performed. Plasma treatments have a lot of advantages compared with other methods used to treat and modify such polymers like chemical, thermal or mechanical processes. Indeed the modifications only affect the top layer of the material without changing the bulk properties and it is environmental friendly (solvent free). It is well known that plasma treatment improves the wettability and the hydrophilicity of polymers by surface oxydation, creating at the interface new oxygen-based functionalities such as hydroxyl or carboxylic acid groups.

In this work, plasma treatment was performed on Polyethylene terephthalate (PET) using a Dielectric Barrier Discharge in Helium/ Oxygen and Argon/Oxygen mixtures at atmospheric pressure, and containing various concentration of water vapour. The experimental set up uses a roll-to-roll system, the film passing through electrodes at varying speeds (0.01m/min and 0.1m/min which correspond to film exposure times of 0.1 and 10 seconds respectively).

The goal of this work is to evaluate the influence of water vapour injection into the discharge on the polymer functionnalisation. It is shown that water changes the plasma characteristics, and strongly modifies the oxidative properties of the plasma. The influence of the water vapour partial pressure, the gap between electrodes and the power of the discharges are emphasized in order to optimize the surface wettability.

Chemical and physical changes on the polymer surface plasma treated are observed using X-ray Photoelectron Spectroscopy (XPS), Water Contact Angle and Atomic Force Microscopy (AFM) measurements.