Comparative study on the adhesive properties of different epoxy resins

Adhesive properties of different epoxy resins have been evaluated in terms of the lap shear strength using aluminium adherends. Its durability in various humid environments has also been analysed. The fracture mechanisms were determined by ESEM observations. Despite fact that fracture seems macroscopically adhesive, it was found that there is an important participation of cohesive fracture mechanisms. Also, it has been demonstrated that the extension of these micro-cohesive mechanisms is directly correlated with the adhesive strength. Studied epoxy formulations are based on the two different crosslinking mechanisms, addition reaction and homopolymerisation. Curing behaviour and TTg reached were studied by DSC. Conventional curing process was carried out with different amine hardeners, while the homopolymerisation reaction was initiated by imidazoles. The results indicate that epoxy/amine systems present a higher adhesive strength than homopolymerised resins. Nevertheless, the hydrothermal ageing causes more damage to epoxy/amine networks. This observation has been associated with the lower water uptake tendency of homopolymerised resins due to its lower hydroxyl group concentration. A new epoxy formulation based on the use of polyaminesiloxane as a hardener has been analysed. This system presents relatively good adhesive resistance, high value of TTg and low water absorption compared with other aliphatic amine/epoxy resins.