The evolution of structure and properties of poly(p‐phenylene terephthalamide) during the hydrothermal aging

Abstract

The evolution of structure and properties of poly(p-phenylene terephthalamide) (PPTA) with different hydrothermal aging temperatures were systematically investigated. The cooperative change in tensile strength and reduced viscosity upon aging time indicated a direct chemical structure-property correlation. The linear relationship between tensile strength and reduced viscosity was explored. Wide angle X-ray diffraction measurements disclosed the crystal structure of aramid fibers was stable with aging time and temperature. Fiber exhibited skin and core structure in different ways. Cracks and microfilbrils were observed in the core after hydrothermal aging, while the structure was unchanged in the skin. Fourier transform infrared spectroscopy also proved that the chemical structure of the skin was not affected by degradation. The results elucidated the hydrolysis of amide function happened in amorphous or bundles between microfibrils in the core rather than in skin of the fiber. V C 2012 Wiley Periodicals, Inc. J Appl Polym Sci 126: 552-558, 2012

Hydrothermal aging mechanisms of aramid fibers via synchrotron small‐angle X‐ray scattering and dynamic thermal mechanical analysis

“…The difference in the surface morphologies of the untreated and aged fibers was small compared with the difference in their reduced viscosities (Table I). Thus, the surface morphology was not affected by hydrothermal aging; this was consistent with our previous scanning electron microscopy results 29. The skin–core structure is one of the unique structures in aramid fibers.…”

“…This behavior implied that the voids were derived from the interfaces of the amorphous region between the crystals and not from the bonding ties. It was proven by our WAXD results 29. The crystallinity was not affect by hydrothermal aging.…”

“…This finding was consistent with the results obtained for the as‐received fiber. In our previous work,29 no void was observed with field emission scanning electron microscopy. However, the aged fibers in this study exhibited 2D patterns that were different from those of the as‐received fibers.…”

Microstructural developments of poly (p-phenylene terephthalamide) fibers during heat treatment process: a review

“…The apparent crystal sizes of the (110) and (200) reflection planes -which are determined by the equatorial scan using Scherrer formula -are found to be sensitive to [39,43] …”

“…High temperature resistance and high modulus are joint properties of PPTA fibers because they both arise from the strong intermolecular forces in the fiber structure 130 . The hydrolysis of amide linkages happens between the microfibrils in the core rather than in the skin of the PPTA fiber 39 . During heat treatment processes the lattice distortion (crystalline perfection) is sensitive to the heating temperature, however, the orientation is more sensitive to the applied tension 89 .…”