A Study of Biological Degradation of an Automotive Clear Coat Using Different Analytical Techniques

Automotive coating systems experience a wide range of natural conditions which will influence their aesthetic and physical-mechanical properties during their service life. To name a few, exposure to sunlight, scratching by car wash brushes, deposition of biological and natural occurring substances are among the most important factors directly affecting the performance of the coatings. Bird droppings, tree and insect gums are common natural materials usually tending the coating to fail. The mechanism by which this failure occurs has not been clearly proved yet. Chemical alterations of the coating upon exposure to these degrading biological substances as well as mechanical effects they import have been reported in the literature. This study aims to investigate the effect of natural and simulated bird droppings (pancreatin) on the optical and physical-mechanical performance of a base coat/ clear coat automotive system. To this end, different analytical methods inclusive of AFM, SEM, Optical microscopy, DMTA and FT-IR were used to reveal the mechanism of degradation. Effects of biological materials on the optical attributes of the coatings such as gloss and DOI retention, *E and *L were also studied. The experiments were conducted at simulated o utdoor weathering conditions by the aid of a xenon cabinet and a climatic hot/cold cycle test. It has been shown that the above biological materials affect the coatings differently. Formation of etched areas and the occurrence of tiny holes and cracks were observed after the exposure leading to significant decrease in optical performance of the films. Attempts were also made to discuss these observations with respect to the results found by Tg and Vickers hardness easurements. FT-IR spectroscopy revealed that the degradation is a result of decomposition of the clear coat.

Keywords:

Biological degradation , Bird dropping , Pancreatin , Climatic cycle