Highly graphitized carbon fiber prepared from poly (p-phenylene-benzo-bis-oxazole) fiber

Abstract

Commercially available PBO (poly (p-phenylene-benzo-bis-oxazole)) fibers were carbonized and heat-treated at 3000°C without mechanical treatements. The structure and texture of the 3000°C-treated PBO fibers were investigated by SEM observations and XRD and magnetoresistance measurements. The SEM images of the carbon fibers reveal carbon layers extending clearly along the fiber axis. Two types of textures in the cross sections were found. One is a radial texture and another is that like a palm-leaf fan spreading the carbon layers from a point near the periphery of the cross section. Average misorientation angle of carbon layers along the fiber axis was evaluated to be ±2° from the 002 X-ray diffraction. The interlayer spacing d002 and lattice constant along a-axis ao were 0.3355nm and 0.2461nm, respectively, and the crystallite sizes Lc and La exceeded 100nm. The average crystallite transverse magnetoresistance (Δρ/ρ) cr, and magnetoresistance anisotropy ratios rTL and γTL measured at 77K and in a magnetic field of 1T for the single filaments were 46%, and 0.007 and 0.68, respectively. The 3000°C-treated PBO fiber, therefore, can be characterized as a highly graphitized and highly oriented carbon fiber.