Effects of Thermal Aging on Molar Mass of Ultra-High Molar Mass Polyethylene Fibers
Zois Tsinas, Sara Orski, Viviana Bentley, Lorelis Gonzalez-Lopez, Mohamad Al-Sheikhly, Amanda L. Forster
Ultra-high molar mass polyethylene (UHMMPE) is commonly used for ballistic-resistant body armor applications due to the superior strength of the fibers fabricated from this material combined with its low density. However, polymeric materials are susceptible to thermally-induced degradation during storage and use, which can reduce the high strength of these fibers, and thus negatively impact their ballistic resistance. The objective of this work is to advance the field of lightweight and soft UHMMPE inserts used in various types of ballistic resistant-body armor, via elucidating the mechanisms and evaluating the chemical degradation, as well as the corresponding physical changes of the UHMMPE fibers upon thermal aging. This is the first comprehensive study on thermally-aged UHMMPE fibers that measures their decrease in the average molar mas via high temperature high-temperature size exclusive chromatography (HT-SEC) analysis. The decrease in the molar mass data were further supported by the presence of carbon-centered free radicals in the polyethylene detected using electron paramagnetic resonance (EPR) spectroscopy. These carbon-centered radicals result from a cascade of thermo-oxidative reactions that ultimately induce C-C ruptures along the backbone of the polymer. Changes in the crystalline morphology of the UHMMPE fibers were also observed through wide-angle X-ray diffraction (WAXS), showing an increase in the amorphous regions, which promotes oxygen diffusion into the material, specifically through these areas. This increase in the amorphous fraction of the highly oriented polyethylene fibers have a synergistic effect with the thermo-oxidative degradation processes and contributes significantly to the decrease in their molar mass.
, Orski, S.
, Bentley, V.
, Gonzalez-Lopez, L.
, Al-Sheikhly, M.
and Forster, A.
Effects of Thermal Aging on Molar Mass of Ultra-High Molar Mass Polyethylene Fibers, Polymers, [online], https://doi.org/10.3390/polym14071324, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=933200
(Accessed September 30, 2023)