Influence of chemical and plasma treatments on the adhesive properties of PTFE with an epoxy resin

Abstract

Poly(tetrafluoroethylene) (PTFE) films and fibres were surface modified by different methods (chemical and plasma treatments) to improve their wetting and adhesion properties. Both chemical and, to a lesser extent, ammonia and hydrogen plasma treatments have been shown to greatly enhance the adhesion between PTFE and an epoxy resin. In the last case (ammonia and hydrogen plasma treatments), the adhesion increase has been reiated to the degree of defluorination rather than to the presence of polar functions at the surface. In the case of the chemical treatment, in addition to the defluorination, the incorporation of a large amount of oxygen moieties can play an important role in adhesive properties. In all cases the failure zones, observed by X-ray photoelectron spectroscopy after pull-off tests, are characteristic of a cohesive failure. The differences between the chemical and the plasma treatments have been attributed to the modified depth, which is more important in the former case. Fibre wettability is enhanced by a previous ammonia plasma treatment making easier the formation of an epoxy microdroplet for microbond tests. For ammonia-plasma-treated PTFE fibres the ultimate load increases; this cannot be attributed to a debonding process since either the droplet or the fibre breaks.