Influence of hollow glass microspheres on 1K epoxy structural adhesive for the automotive industry

In this study a close to reality one component (1K) structural epoxy adhesive is introduced. The physical properties have been investigated by means of gravimetric water uptake, bulk tensile tests, and lap shear tests. The influence of two different types of hollow glass microspheres (HGM) on the ageing behaviour has been observed via accelerated ageing tests followed by lap shear tests of galvanized steel. Results show that the formulation described outperforms very brittle and basic systems consisting of bisphenol A diglycidyl ether (DGEBA) and dicyandiamide (DICY) in terms of ductility. The addition of HGM resulted in higher water absorption suggesting that water gathers as a liquid in the HGM. Further, the addition of HGM led to an increase of the cohesion failure percentage on unaged lap shear specimens without significantly influencing the tensile shear strength and the addition of the bigger HGM observed led to a change in fracture mechanism from substrate-near cohesion failure to cohesion failure. The results of this study on the long-term durability of bonded steel joints indicate that the addition of HGM into the adhesive system has no significant effect on the ageing behaviour in two of three corrosion tests. It can be concluded that the incorporation of HGM is a possible solution not only reducing the amount of chemicals required for automotive adhesive production, but also promoting lightweight construction because of the decreased density of the adhesive system.