Shrinkage in relation to the TTT-Features of an epoxy adhesive

In the progress of curing of a thermoset adhesive the viscosity of the resin and hardener formulation changes as the chemical reaction increases the average length and the degree of crosslinking between the constituent oligomers. Gelation occurs once a continuous 3-dimensional network of polymer chains has been created. After vitrification the micro structure of the resin is fixed and further cure is affected by diffusion limitations. Under confined conditions in an adhesive joint, shrinkage stress occurring at an early state of the curing process is likely to cause defects due to local debonding and thus a reduction of strength and durability. Therefore mastering of the curing kinetics and the physico-chemical changes in the transition from the liquid to the solid state is essential to successfully process adhesives in demanding applications. This paper will discuss different criteria and experimental methods for the calorimetric and rheological analysis of the curing of a two component epoxy adhesive. D...