An evaluation of an automotive clear coat performance exposed to bird droppings under different testing approaches

Abstract

In this study, the effects of two types of biological materials, i.e. natural bird droppings and pancreatin, on properties of an automotive acrylic melamine clear coat were studied. In addition, two different testing approaches including pre-aging and post-aging were utilized to investigate the biological resistance. To this end, effects of these biological materials on clear coat surface properties and appearance were investigated by different techniques including digital camera, SEM, AFM, optical microscopy and a gloss meter. In addition the mechanical properties of clear coats were evaluated by micro Vickers measurement and DMTA analysis. For further investigation FTIR analysis was utilized to have a more understanding of the failure mechanism. Results showed that the biological materials have an extremely vital effect on the appearance of the coatings. Decreasing of t g and hardness of the films made by pancreatin and bird droppings were observed and were attributed to the chemical alterations as proved by FTIR analysis. It was also found that the biological degradation occurred on the samples experienced the post-aged testing method was more severe than the samples exposed to pre-aged testing. On the other hands, although bird droppings and pancreatin revealed a same failure mechanism, the effect of the former was more severe. In addition, it has been shown that the enzymatic structure of biological materials is responsible for the catalyzing the hydrolytic degradation of clear coat at neutral pH. Therefore, the biological degradation mechanism may be regarded as an enzymatically induced hydrolytic cleavage.