Can Tg be used as a service temperature indicator for the selection of a structural adhesive?

Abstract

In order to contribute to the ongoing discussion on the reliability of epoxy (EP) and polyurethane (PUR) adhesives for load bearing structures, a study was conducted at LNEC where several structural adhesives were subjected to several temperature regimes and subsequently assessed, namely to compare their glass transition temperature (Tg) with strength and stiffness decrease with increasing service temperature. The results showed that the PUR and EP adhesives display significantly different viscoelastic responses over the temperature ranges attained normally in service. Thus temperature-induced creep is a risk factor that needs to be considered cautiously when approving novel adhesive types for structural applications. The study of the specific components and formulations of the various adhesives studied, showed that the resultant strength and temperature stability varied greatly. Because of that, careful adhesive selection, considering its glass transition temperature, thermal performance and possibly a post-cure procedure, should be made.