Pre-surface treatment of carbon fiber reinforced composites for enhancement of adhesion between coating and adherends

Abstract

One of the most important aspects in manufacturing an aerospace structure is its composite materials. Composite coatings are exposed to many environmental conditions, which can significantly affect them. In this research, three different surface treatments were introduced to examine their effects on the adhesion between the composite coating and the substrate. These treatments were plasma cleaning, ultraviolet (UV) radiation, and sanding. A cross-cut test was conducted on the composite panels to assess the adhesion of paint to the substrate after all three treatments. Coating performance analyses were also carried out using a Fourier transform infrared spectrometer, contact angle, and optical microscopic images. The first set of panels was treated for 4, 8, and 12 minutes with oxygen plasma, and the surface wettability was assessed by contact angle measurement. The second set of panels was treated with UV radiation for 2, 4 and, 8 days, and the surface wettability was also assessed using the contact angle test. A few samples were treated with sandpaper. Two coats of paint, including a primer and a top coat, were used, and the panels were exposed to UV radiation and immersed in water. It was found that untreated panels showed a much higher contact angle of 86°, whereas panels treated with plasma exhibited a 33° water contact angle. In the case of UV radiation, the contact angle of untreated panels was found to be 106°, whereas the contact angle of panels treated with UV radiation was reduced to 47°. Panels treated with sandpaper showed a contact angle of 24°, whereas panels without sandpaper treatment showed a contact angle of 73°. The cross-cut test showed considerable flaking of the coating along the edges and squares of panels that were not treated, and very small flakes along the edges and parts of the grid square on panels that were treated, thus confirming the enhancement of adhesion by plasma, UV, and sanding treatments.