Low-temperature adhesive curing in timber engineering: About the relationship between curing kinetics and mechanical properties

Adhesive bonding plays a pivotal role in timber engineering, enhancing structural integrity, sustainability, and aesthetic appeal, while also addressing environmental concerns. The assessment of strength in adhesively bonded timber joints involves cohesive strength, adhesive strength, and substrate failure, all of which are crucial considerations for designing dependable timber structures. A comprehensive investigation was carried out with the aim of improving adhesive bonding for construction by revealing the relationship between curing progress and mechanical adhesive properties. For that, dynamic DSC measurements, kinetic modelling, tensile tests to determine the cohesive and adhesive strength, as well as tests for the evaluation of stiffness and hardness were performed using a two-component polyurethane adhesive. The investigation yielded valuable insights, particularly regarding the time- and temperature-dependent development of the curing degree and the aforementioned material properties. Additionally, the correlation between the curing degree and the respective material properties could be determined, showing that cohesion and stiffness built up occurs quite similar while the build-up of adhesive strength correlates well with hardness. It was thus concluded that Shore D hardness might represent a practical indicator for monitoring the progress of curing at low temperatures, which is a suitable means of improving adhesive applications in the construction industry.