Environmental ageing on GFRP pultruded joints: Comparison between different adhesives

In this paper, a series of mechanical tests were performed on GFRP (glass fibre-reinforced polymers) specimens, adhesively bonded in single-lap and butt joints, in both un-aged and aged conditions. Six different types of adhesives were compared: two epoxy, one acrylic, one methacrylate and two polyurethane adhesives. Two ageing conditions were investigated, i.e. temperature/moisture changes and UV exposure. Both environmental exposures had a slight effect on the load carrying capacity of the joints, while they remarkably increased their elongation, with a stiffness decrease of about 70 90%. For some adhesives, the load carrying capacity was improved because of the completion of the polymerization process caused by the high or slightly high temperatures. For all joints, in both exposures a great stiffness decrease occurred: it was ascribed to the reaching of adhesives Tg during cycles of combined high and low temperatures and to the polymer bonds dissociation during UV radiation. Both before and after the two ageing treatments, the highest load carrying capacity was recorded by the epoxy adhesives that, on the contrary, showed the highest joint elongations. The two polyurethane adhesives always recorded similar ultimate loads, but one of them presented lower deformations, also showing the best compatibility with pultruded laminates.