Abstract
Previously, it was concluded that poly(p-phenylene terephthalamide) (PPT) fibers comprises a number of pillar-shaped micro-fibrills consisting of extended molecular chains. One of the basis for this notion was the fact that the birefringence calculated for the perfectly uniaxial orientation was less, or at least not greater, than the observed for real PPT fibers. In order to clarify this point, the effect from the interference fringe was taken into account and referred to the result of the electron diffraction measurement. The relation between the fine structure and the mechanical properties of PPT fibers was also studied in the light of the S-S hysteresis behavior, the elongation of fiber period and the structural deformations.
The following results were obtained:
(1) Assuming that the orientation of the b-axes of crystals of a PPT is radial in the sheath and random in the core, the calculated and observed birefringence became agreeable.
(2) The high tenacity and the high modulus of PPT fibers are considered due to the extended chain structure.
(3) The remarkable tendency of fibrillization on structural deformation of this fiber, not seen for other synthetic fibers, is also considered to relate to the pillar-shaped micro-fibrill structure. This may lead to poorer fatigue resistance compared with other synthetic fibers, when used as a reinforcement material in rubber.
