Abstract
A composite material is one of the most vital attributes in the manufacturing of aerospace and wind turbine structures. In order to protect composite surfaces against environmental influences (e.g., ultraviolet [UV] light, moisture, oxygen, and pollutants), protective coatings are typically employed; however, these coatings tend to degrade during service and fail prior to the life expectancy as the result of debonding, buckling, cracking, and blistering of coating materials. In the present study, unidirectional and woven pre-impregnated (pre-preg) carbon fiber-reinforced composites (CFRCs) were prepared in a vacuum oven, and then a number of different surface treatment processes-oxygen plasma (0, 4, 8, and 12 min), UV light (0, 2, 4, and 8 days) and fine sandpapering (1500 mesh)-were applied on the CFRC panels. Two coats of primer and a topcoat were subsequently introduced to the surfaces of treated composite panels. The coatings were analyzed via Fourier transform infrared spectrometry (FTIR), optical microscopy, water contact angle (WCA), and cross-cut tests before and after water soaking/immersion and extensive UV light exposure tests. It was determined that plasma treatment, UV exposure, and sandpapering drastically reduced the WCA values (e.g., from 106 degrees to 33 degrees) of the composite panels prior to the coating process. The study showed that the surfaces are highly functionalized during these treatments, which in turn create strong bonds between the composite and the primed surfaces. The cross-cut and optical microscopy studies showed that the coating surfaces were severely damaged through flaking, deboning, and delaminating during the water immersion and UV exposure tests; however, the surface-treated composite panels were substantially less damaged. This study confirms that the surface treatment of composite panels is critically important for a longer service time of the composites in aerospace, wind turbine, and other industrial applications.