MORPHOLOGICAL-STUDY ON POLY-P-PHENYLENEBENZOBISOXAZOLE (PBO) FIBER

Morphological survey on new PBO fiber (Zylon(R)) was conducted by X-ra y and transmission electron microscopic studies. Crystal size, orienta tion of the crystal, fibrils, microvoids, and fine structure were disc ussed. It was found that the molecule in the fiber showed high orienta tion (more than 0.99 in Hermann's orientation function for heat-treate d fiber) and relatively small crystal sizes in the longitudinal (160 A ngstrom) and the transverse (110 Angstrom) directions. Crystal modulus estimated by extrapolation to perfect orientation on the plot of the fiber modulus as a function of fiber orientation (Northolt's method) s hows discrepancy from the crystal modulus directly obtained by X-ray s cattering. This discrepancy means that the Northolt's model is insuffi cient to describe the Young's modulus of PBO fiber. Microvoids elongat ed to the fiber direction were examined by small-angle X-ray scatterin g and transmission electron microscopic methods. The diameter of the m icrovoids was 20 Angstrom to 30 Angstrom and the fiber had a very thin microvoids-free layer (0.2 mu m). Preferential orientation of the a-a xis of crystal in the fiber was also confirmed. Summarizing these resu lts, a structure model of the PBO fiber was proposed. (C) 1998 John Wi ley & Sons, Inc.