Long term stability of UHMWPE fibers

Abstract

The performance of ultra-high molecular weight polyethylene (UHMWPE) fibers for ballistic protection is predicated on the development of a highly aligned molecular structure that allows the polymer to exhibit a superior strength in the axial direction of the fiber. Body armor manufacturers have exploited the inherent strength of these materials to develop body armor that continues to defeat ever-increasing ballistic threats. However, even an ideal molecular structure will be subjected to degradation during use, which can reduce the high strength of these fibers, and impact their ability to protect the wearer. In this work, the long term stability of UHMWPE fibers is investigated by exposing yarns to temperatures of 43, 65, 90, and 115 °C for periods of time up to 81 weeks, and monitoring the tensile strength of the yarns. The activation energy for this aging mechanism was calculated to be approximately 140 kJ/mol. Changes in the oxidation index of this material due to aging were also studied using Fourier Transform Infrared Spectroscopy (FTIR), and these changes are compared with changes in tensile strength. The effect of aging on the morphology of the fibers is also studied using thermal analysis and X-ray diffraction (XRD) methods.