Difference in Preferential Orientations of Crystal Planes and Crystal Sizes along the Radial Direction of Poly-p-Phenylenebenzobisoxazole (PBO) Fibers

This article describes the orientation of the crystal b-axis of poly-p-phenylenebenzobisoxazole (PBO) fibers, preferentially in a direction perpendicular to the fiber axis. Although the preferential orientation of the a-axis (i.e. the (200) crystal plane) in the various PBO fibers has already been reported, but to the best of our knowledge, there is a limited number of reports about the preferential orientation of the crystal b-axis of PBO. In order to estimate the degree of preferential orientation of different crystal planes, X-ray diffraction intensities of (010) and (210) for PBO were measured along the radial direction of the fiber and analyzed with an extended two-phase model and a micro-focus X-ray diffraction technique. The degree of preferential orientations of the crystal b-axis (i.e. the (010) crystal plane) was successfully estimated. Also, the positional dependence of apparent crystal size along the equator has been elucidated.