The evolution of structure and properties in poly(p-phenylene terephthalamide) fibers

The evolution of the mechanical properties and structure of poly(p-phenylen e terephthalamide) (PPTA) fibers with different post-treatment methods invo lving heat, tension, hydrostatic pressure, and different environments was s ystematically investigated. Wide-angle X-ray diffraction measurements revea l that the crystal structure of PPTA fiber is not stable and changes upon p ost-treatment. The cooperative changes in the modulus and two structure par ameters - the misorientation angle and the paracrystalline parameter upon t reatment indicate a direct structure-property correlation. After studying f ree-length annealing and heat-tensioning of fibers, several structure param eters - the c-dimension of lattice constants, the paracrystalline parameter , the intensity ratio between(110) and (200), and the orientation angle - w ere found to be affected greatly by the tension applied during heat stretch ing; while other structure parameters such as apparent crystal sizes, equat orial crystallinity and a, b dimensions of the lattice constant are insensi tive to the applied tension but determined by the applied temperature and t ime. A sudden change in the crystal structure at 400 degreesC suggests a al pha -relaxation in the crystalline region, which is supported by the DMTR a nd TMA measurements. (C) 2001 Elsevier Science Ltd. All rights reserved.