International.
Scientists at Amirkabir University of Technology studied the effect of bird droppings and tree gums on two polyurethane coatings for repainting.
For this purpose, gum arabic and pancreatin were used as simulators of tree gum and bird fall, respectively. These substances were applied on coatings exposed to UV radiation and moisture for different exposure times.
Several techniques were used to study the appearance of degraded coatings. Structural analysis of the samples was performed by FTIR spectroscopy. The surface free energy and thermomechanical characteristics of the refinish coatings were studied by measuring the contact angle and DMTA, respectively. All experiments were carried out before and after the degradation process.
Overall, it was revealed that while pancreatin degrades coatings chemically, gum arabic affects mechanically and chemically, leading to crumpling with deformations on the surface of the coating. It was also concluded that cross-linking density and surface free energy play a critical role in the degradation of car repair coatings. It was shown that the low cross-linking density and Tg of the polyurethane system created a dynamic system that can be post-cured during the experiment, leading to improved biological resistance.
