Methodology for optimization of the curing cycle of paste adhesives

This contribution, carried out in the frame of the European Joint Technology Initiative ‘Clean Sky’, presents the results of a research program investigating the influence of fast curing on the quality of epoxy based paste adhesives. Today, the curing of paste adhesives is typically carried out following the supplier's recommendations. In order to reduce cycle time, save costs and energy resources, paste adhesives could be cured at higher temperature. To ensure a bonded joint quality with maximum mechanical performance, the limitation of this temperature increase is studied. This study shows the effects of the use of high temperatures in the curing process, which can lead to a degradation of the adhesive system due to the increase of void content, decreasing the mechanical performance in the paste adhesive as well as in the bonded joint. The goal of this research is to find fast and robust processing of paste adhesives and to develop a methodology to determine the maximum curing temperature possible. Different properties of the adhesive are investigated, including different thermal analysis techniques, optical and mechanical testing of the pure adhesive. Additionally, state of the art qualification of paste adhesives, single lap shear testing, is considered. In this study, a novel method to control the quality of the cured paste adhesives is defined based on the analysis of the pure cured paste adhesive, not influenced by the adherent quality, by measuring the void content and its effects on the bonded joint.