Spatially-resolved chemical and mechanical examination of adhesive mixing efficiency with ATR-IR and Martens hardness

Abstract In this work, a new combined approach to investigate the quality of mixed and cured 2-component epoxy adhesives will be proposed. The spatially-resolved attenuated total reflectance fourier transform infrared spectroscopy (ATR-FTIR) on a microscale and Martens hardness were used to investigate the chemical and mechanical properties respectively the performance of mixed 2-component epoxy adhesives. Therefore, the measurement principle was proved on samples with different proportion of the adhesive hardener. The results show that the difference in hardener proportion has a significant effect on the measurable epoxy concentration and the Martens hardness. In a second step the testing methods were applied to differently mixed adhesive samples to investigate the mixing homogeneity. The mixing methods used were hand mixing, a static mixer, an asymmetrical dual centrifuge and a novel mixing method based on power ultrasound. With a spatially-resolved representation of the ATR-FTIR and Martens hardness test results it is possible to distinguish between different mixed samples and to analyze the mixing quality. It was shown that the resolution and the sensitivity of the ATR-FTIR spectroscopy and the Martens hardness method allow to evaluate the mixing homogeneity of the used 2-component epoxy adhesives. Furthermore, the correlation of the non-destructive ATR-FTIR and hardness test results with destructive lap shear test of adhesive joints was investigated. By this, it was shown, that also the mechanical properties of adhesive joints are affected by the proportion of hardener and the used mixing method and correspond with the ATR-FTIR spectroscopy and Martens hardness.