The Effect of Natural Tree Gum and Environmental Condition on the Degradation of a Typical Automotive Clear Coat

In this work the effects of natural gum and its simulated compound (Arabic gum) on an acrylic based clear coat applied on different basecoats were studied. The experiments were conducted at various aging processes to simulate the real outdoor conditions by the aid of different analytical techniques including optical microscopy, scanning electron microscopy, ATR-FTIR spectroscopy, DMTA and micro hardness measurements, by which the chemical and mechanical responses of the system were investigated. Results showed that, Arabic and natural gums, due to their sticky nature in the slurry state, can strongly attach to the clear coat surface and perform a significant stress during the drying process. It was shown that, this stress was responsible for the surface cracks produced by gums, indicating a physical degradation mechanism. However, it was revealed that, biological materials could also affect the clear coat chemically. In addition, different surface cracks produced by gums on the clear coat applied on silver and black basecoats were observed and attributed to their surface chemistry and mechanical properties differences. It was shown that different amounts of aluminum flakes existed in the basecoat layers of silver and black system can effectively influence the curing degree of the clear coats applied on the se systems. This leads to different cross-linking density, toughness and surface chemistries. Therefore, different interactions of clear coats and gums, as well as stress distribution and relaxation behaviors of these two systems were found effective in such degradations. Comparison of the mechanical properties and visual effects of gums on clear coats indicated a more severe degradation under the post aging, due to the greater effect of UV light.