The role of surface pretreatment and surface analysis in the bondability of carbon fiber-polyimide matrix composites

The effect of surface pretreatment on the physical and chemical properties of carbon fiber-polyimide matrix composite surfaces was evaluated. Eight pretreatments were studied: methanol wash, gritblast, sulfuric acid soak, ammonia plasma, argon plasma, argon plasma followed by ammonia plasma, nitrogen plasma, and oxygen plasma. The pretreated surfaces were chemically characterized through the use of XPS (X-ray photoelectron spectroscopy), ISS (ion scattering spectroscopy), and PAS-FTIR (photoacoustic Fourier transform infrared spectroscopy). Surface fluorocarbon contamination was appreciably reduced with gritblasting, argon plasma and oxygen plasma pretreatments. Specific functional groups were incorporated into the composite surfaces through the choice of gases used in the pretreatment. Physical changes were determined through the use of HR-SEM (high resolution scanning electron microscopy). With the exception of the macroroughening produced by gritblasting and the pitting produced by long exposure times in the oxygen plasma, no signlficant differences in the topography of the pretreated composites were observed. The wettability of the pretreated composite surfaces increased, as demonstrated with contact angle measurements, due to a combination of a decrease in the fluorocarbon contamination and an increase in the surface functionality present.