The influence of the short-term ultraviolet radiation on the structure and properties of poly(p-phenylene terephthalaramide) fibers

The influence of the short-term (<20 h) ultraviolet (UV) radiation (at 60 +/- 3 degrees C with a relative humidity of 50 +/- 1 RH%) on the integrated performance of poly(p-phenylene terephthalaramide) fibers was comprehensively studied, and the mechanism behind the influence was intensively discussed by detecting the overall changes in both chemical and morphological structures. Results demonstrate that the short-term UV radiation has different effect on the core part from the surface part of PPTA fibers. Specifically, the short-term UV radiation slightly decreases the crystalline index without changing the chemical structure of the core part of PPTA fibers; while that introduces a large amount of oxygen atoms on the surfaces of UV-KF fibers, and induces a distinctive increase in the surface roughness of fibers even the irradiation time is only 1 h. These structural changes make UV-KF fibers show decreased contact angle and improved wettability while remaining the outstanding glass transition temperature. All parameters of tensile properties including tenacity, break extension, energy to break and modulus almost linearly decrease as the irradiation time extends; however, these parameters almost level off when the irradiation time is longer than 3 h. After irradiated for 18 h, the tenacity, break extension, energy to break of UV-KF fiber is 88%, 90%, and 86% of the corresponding value of original fiber, respectively. (C) 2012 Elsevier B.V. All rights reserved.