FT-IR and temperature-programmed desorption (TPD) study of the adsorption of probe molecules used to model epoxy resin adhesion to chromium, iron and stainless steel substrates

In this study, we investigated the reactivity of chromium, iron, and surface-treated 304L stainless steels (SS) toward molecules representing model epoxy resins. These molecules were ammonia (a basic probe molecule also representative of the hardener amine group), 1,2-epoxybutane (for epoxy groups) and 2(methylamino)ethanol (for the beta-amino alcohol resulting from the reaction of epoxy with amine). These molecules were analyzed in the adsorbed state by either FT-IR or temperature-programmed desorption (TPD). Surface analysis showed that the top surface of the treated 304L samples only contains chromium and iron as metallic elements. The chromium/iron ratio can be varied within a wide range according to the SS surface treatment used. When increasing the SS surface chromium enrichment, we show a simultaneous increase of (i) both density and strength of surface acid sites, (ii) the amount of beta-amino alcohol adsorbed. In addition, there is a marked improvement of the epoxy resin/304L bond strength when the SS surface is more chomium-enriched.