Effect of the amount of cork particles on the strength and glass transition temperature of a structural adhesive

The inclusion of particles (micro or nano) is a method to improve the mechanical properties, such as toughness, of structural adhesives. Structural adhesives are known for their high strength and stiffness but also for their low ductility and toughness. There are many processes described in the literature to increase the toughness, the use of rubber particles being one of the most common processes. In the present study, natural micro particles of cork were used with the objective to increase the ductility of a brittle epoxy adhesive. The idea is for the cork particles to act like a crack stopper. The influence of the amount of cork particles was studied. Particles of cork ranging in size from 125 to 250 µm were mixed in the epoxy adhesive Araldite 2020 from Huntsman. The amount of cork in the adhesive was varied between 0.5% and 5% in weight. This evaluation was made using tensile tests and it was evident that the failure strain was related to the amount of cork particles in the resin. The results concerning the single lap joints and the glass transition temperature confirm the increased ductility obtained in the tensile tests.