Morphological studies of poly-p-phenylenebenzobisoxazole (PBO) fibers on the process that determines the direction of the crystal a-axis along the radius direction during the formation of fiber structures

This article concerns preferential orientations of the crystal a-axis for the standard type PBO AS and high modulus type HM fibers. The degree of radial preferential orientation of the crystal a-axis along the fiber radius direction was analyzed based on a newly-proposed 3D two-phase model. The result was compared with the previously analyzed three PBO fibers made through water vapor, hot water and non-aqueous coagulation processes. The proposed model fitted well the measured micro-focus X-ray scattering patterns of the (200) crystal plane as a function of the position of the fiber on which the source beam was focused. The crystal orientation of the c-axis was strictly estimated from the three equatorial diffractions based on Wilchinsky's generalized model. [Display omitted] •Preferential orientation of the a-axis of the PBO crystal in the fibers was analyzed.•Molecular orientation of PBO fibers was estimated strictly.•Fiber modulus should be related to molecular orientation not to preferential orientation.