Degradation of low gloss polyurethane aircraft coatings under UV and prohesion alternating exposures

In this work, scanning electron microscopy (SEM)/energy dispersive X-ray analysis (EDX), atomic force microscopy (AFM), and electrochemical impedance spectroscopy (EIS) were used to study the accelerated weathering coating degradation that occurred in two low gloss polyurethane aircraft coating systems. One was epoxy primer with a traditional matte polyurethane topcoat and the other was the epoxy primer with a fluorinated polyurethane topcoat. The coated panels were exposed in a QUV chamber and a Prohesion chamber alternately. It was found that the primer with the matte topcoat system could not stop water penetration effectively, and the coating system was destroyed after 25 weeks. In contrast, the primer with the fluorinated polyurethane topcoat system formed a good barrier of water on the substrate, and the coating system was still functional after 2 years of exposure. Adhesion tests showed that the loss of coating adhesion caused the eventual failure of the low gloss coatings. (C) 2003 Elsevier Science Ltd. All rights reserved.