Elastic Modulus of the Crystalline Regions of Poly (p-phenylene terephthalamide) Single Fiber Using SPring-8 Synchrotron Radiation

The elastic modulus, El, of the crystalline regions of poly (p-phenylene terephthalamide) (PPTA) single fiber in the direction parallel to the chain axis was measured by X-ray diffraction using synchrotron radiation at beamline BL46XU of SPring-8. The El value of the PPTA single fiber was obtained as 156 GPa at room temperature from the initial slope of the stress–strain curve of the crystal lattice. However, the inclination of the stress–strain curve changed at a tensile stress of around 1000 MPa, which produced an El′ value of 199 GPa in a higher stress region. This indicates that the deformation mechanism in the crystal lattice at higher tensile stress was different from that in the initial stage of the tensile deformation. Stress hardening of PPTA was also observed macroscopically during the tensile deformation process. Stress hardening in the crystal lattice was found to directly affect macroscopic stress hardening of the PPTA fiber.