STUDIES OF PAN-BASED CARBON-FIBER SURFACES - THEIR INFLUENCE ON INTERFACIAL BONDING WITH PMR-15 POLYIMIDE AND COMPOSITE THERMOOXIDATIVE STABILITY

Atomic force microscopy has been used to study the surfaces of PAN-bas ed carbon fibers to gain a better understanding of their interactions with PMR-15 polyimide. Topographic images, average roughness, excess a rea, and fractal dimension were obtained. The polar nature of the surf aces was characterized as percent weighted dipole moment (% WDM) and i nterlaminar shear strength (ILSS) was measured for the composites. The loss of ILSS and mass under aging at 316 degrees C wets measured. The re is a linear correlation between the inverse of % WDM and initial IL SS indicating a limiting value of the latter of about 170 Mpa for this system. Further increases of the ILSS by dipolar bonding require an i ncrease of polar components in the matrix. Fiber/matrix dipolar intera ctions govern the thermooxidative stability. By inhibiting the develop ment of cracks along the fiber matrix interface, they slow the loss of ILSS and mass. Previous(1) correlations of roughness with % WDM and I LSS do not extend to additional types of fibers. Other surface paramet ers also correlate for some types of fibers, but not for others. Corre lations of surface morphology with ILSS might be obtained at dimension al scales below 25 nm. However correlations might not exist because of differences among fiber manufacturing and surface treatment.