Use of analytical techniques to reveal the influence of chemical structure of clearcoat on its biological degradation caused by bird-droppings

摘要

There are various biological materials which may repetitively deposit on a painted automotive body during its service life, causing possible local defects. This study is an attempt to reveal the mechanism of degradation caused by bird-droppings and to compare the performance of clearcoats having various resin/hardener ratios. Two different testing methods varying in aging conditions, of the effect of natural bird-droppings, were applied to two types of clearcoats. Variations in chemical structure were characterized by the aid of FTIR spectroscopy and DMTA analysis. Also, in order to establish an experimentally viable procedure to assess such an effect, synthetic countertype of bird-droppings (pancreatin) was used to simulate this natural phenomenon. The results revealed that a digestive enzyme (lipase) present in bird-droppings, can induce the hydrolysis reaction of coating polymer leading to a locally distributed etched surface. It was also found that the clearcoat containing higher ratios of melamine cross-linker had poorer performance against bird-droppings in spite of having a greater cross-linking density.