Various surface pretreatments of carbon fiber-polyimide matrix composites have been studied by XPS, ISS, PAS FTIR (photoacoustic Fourier transform infrared spectroscopy) and higbresolution SEM. Reduction of fluorocarbons from release cloth contamination and increase in carbowxygen-containing functional groups was observed on the surface of composite samples treated in an oxygen plasma. These plasma-treated samples also showed differences in surface topograpby, but no change in the photoacoustic infrared spectra when compared to a methanol-washed sample.
The single lap shear test and the wedge test were used to evaluate the effect of surface pretreatment on the strength and durability of adhesively bonded composite joints. Both types of joints were placed in three different environments: (1) room temperature, desiccator, lo00 h; (2) 204 "C, lo00 h; (3) immersion in boiling water for 3 days for the single lap shear test and until failure for the wedge test. The failure surfaces were analyzed using XPS to determine the locus of failure. An oxygen plasma was found to be the best pretreatment. The improvement in adhesive bonding following exposure to an oxygen plasma in comparison to the other surface pretreatments was attributed to several factoreduction in fluorocarbon contamination and an increase in oxygen surface functionality. This increased surface functionality and decrease in fluorocarbon contamination caused better wetting of the composite surface and also may lead to covalent bonding at the composite/primer interface.
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