2015 Volume 71 Issue 7 Pages 224-231
This article concerns PBO fiber structure, especially a preferential orientation of the a‐axis of the PBO crystal in the fiber. It has been reported that the a‐axis of the PBO crystal aligns parallel to the radial direction on the round cross section for PBO AS and HM fibers. This observation was proved by selected‐area electron diffraction and micro‐focus X‐ray diffraction. An application of water vapor coagulation is carried out in this study. It is proved that the fiber so made shows a random orientation of the PBO crystal a‐axis on the cross section. This fact has never been reported on any scientific or engineering journals before as far as the authors have concerned and it becomes state‐of‐the‐art in this study. A mechanism to explain the presence and/or absence of such preference is proposed. The authors believe that the presence of this radial preferential orientation comes from a combination or a balance of polymer‐solvent interaction and the direction of diffusion for solvent from the center to the outside of the fiber.