Plasma Treatment of Crosslinked Polyethylene Tubes for Improved Adhesion of Water-based Paints

Cold plasmas fed trichloromethane-argon mixtures were used to treat cross-linked polyethylene (PE) to improve the adhesion of water-based paint. The effects of the plasma treatment undertaken at different percentages of CHCl3 in the plasma feed, C-Cl, were investigated using Infrared Spectroscopy in Diffuse Reflection (DR) mode, Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS), X-ray Photoelectron Spectroscopy (XPS), goniometry for surface contact angle measurements, profilometry for roughness measurements, and paint adhesion tests. All the treatments modify the surfaces by introducing chlorine. Oxygen is present in the bulk and on the surfaces of the treated and untreated material. The treatments do not alter the bulk, but tend to increase the surface roughness and contact angle. When CHCl3 is present in the plasma subsequent paint adhesion is improved from a very poor classification of 4 to an excellent classification of 0 (assessed according to the appropriate Brazilian standards (BS EN ISO 2409:2007 and BS 3900-E6:2007A)). Surface roughness is not increased at low C-Cl but improved paint adhesion occurs for all C-Cl > 0. Although the causes of the improved paint adhesion with the plasma treatment are unclear, they may be related to the plasma activation of unsaturated carbon and oxygen functionalities.