Studies of PAN-based carbon fiber surfaces : Their influence on interfacial bonding with PMR-15 polyimide and composite thermo-oxidative stability

Atomic force microscopy has been used to study the surfaces ofPAN-based carbon fibers to gain a better understanding of their interactions with PMR-15 polyimide. Topographic images, average roughness, excess area, and fractal dimension were obtained. The polar nature of the surfaces was characterized as percent weighted dipole moment (% WDM) and interlaminar shear strength (ILSS) was measured for the composites. The loss of ILSS and mass under aging at 316°C was measured. There is a linear correlation between the inverse of % WDM and initial ILSS indicating a limiting value of the latter of about 170 Mpa for this system. Further increases ofthe ILSS by dipolar bonding require an increase of polar components in the matrix. Fiber/matrix dipolar interactions govern the thermo-oxidative stability. By inhibiting the development of cracks along the fiber matrix interface, they slow the loss of ILSS and mass. Previous l correlations of roughness with % WDM and ILSS do not extend to additional types of fibers. Other surface parameters also correlate for some types of fibers, but not for others. Correlations of surface morphology with ILSS might be obtained at dimensional scales below 25 nm. However, correlations might not exist because of differences among fiber manufacturing and surface treatment.