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

• Published in: Polymer (Guilford) 2001-06, Vol.42 (13), p.5925-5935
• Main Authors: Rao, Y, Waddon, A.J, Farris, R.J
• Format: Article
• Language: English
• Subjects: Applied sciences; Exact sciences and technology; Fibers and threads; Forms of application and semi-finished materials; Poly(p-phenylene terephthalamide) Kevlar® fibers; Polymer industry, paints, wood; Structure and properties; Technology of polymers; Wide-angle X-ray diffraction
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/S0032-3861(00)00906-X

The evolution of the mechanical properties and structure of poly(p-phenylene terephthalamide) (PPTA) fibers with different post-treatment methods involving heat, tension, hydrostatic pressure, and different environments was systematically investigated. Wide-angle X-ray diffraction measurements reveal that the crystal structure of PPTA fiber is not stable and changes upon post-treatment. The cooperative changes in the modulus and two structure parameters — the misorientation angle and the paracrystalline parameter upon treatment — indicate a direct structure–property correlation. After studying free-length annealing and heat-tensioning of fibers, several structure parameters — the c-dimension of lattice constants, the paracrystalline parameter, the intensity ratio between (110) and (200), and the orientation angle — were found to be affected greatly by the tension applied during heat stretching; while other structure parameters such as apparent crystal sizes, equatorial crystallinity and a, b dimensions of the lattice constant are insensitive to the applied tension but determined by the applied temperature and time. A sudden change in the crystal structure at 400°C suggests a α-relaxation in the crystalline region, which is supported by the DMTA and TMA measurements.