AGING OF CARBON-FIBER-REINFORCED BISMALEIMIDE-MATRIX COMPOSITES IN OXIDATIVE CONDITIONS

The effect of oxidation with increasing time at 250-degrees-C (up to 2 500 h) was studied on two series of composites consisting of a bismale imide matrix reinforced with PAN-based high-tensile carbon fibers (siz ed and unsized). An extensive study at the microstructural and nanostr uctural scales (optical microscopy, SEM and TEM) has permitted us to d etermine the geometry and intensity of the oxidation. The matrix is fi rst increasingly etched and then destroyed. From this point the fibers themselves are attacked. Perforations perpendicular to and channels p arallel to the fiber axis develop. Correspondingly the major weight lo ss occurs as the matrix is oxidized, whereas the specific surface incr eases as the fibers are attacked. Sizing favors matrix attack. Whether sized or not, the fibers have a strong adhesion to the matrix.