ADHESION PROPERTIES OF PLASMA-TREATED CARBON PEEK COMPOSITES

Carbon/PEEK composites have been treated by plasma to improve adhesion with conventional epoxy adhesives. Oxidizing (oxygen, air) and inert (nitrogen, argon) mixtures have been used, and the effects of treatment time and radio frequency power investigated. Plasma treatments resulted in the introduction of oxygen- and, in some cases, nitrogen-containing functionalities at the surface of the composite, as observed by X-ray photoelectron spectroscopy, and in increased wettability. Hydrophobic recovery occurred during ageing, but to a very limited extent that was reduced with increasing treatment time. While untreated samples showed no pull strength and adhesive failure, plasma-treated samples reached high pull strengths and cohesive failure even at very short treatment times (< 30 s). Pull strength values were relatively insensitive to the nature of the treatment gas and plasma parameters; furthermore, ageing did not affect adhesion but in some cases improved it. These effects suggest the occurrence of plasma-induced cross-linking of the surface layer.