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 of chemical degradation and evaluating this 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 mass via high-temperature size exclusion chromatography (HT-SEC) analysis. The decrease in the molar mass was further supported by the presence of carbon-centered free radicals in the polyethylene that was 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 has a synergistic effect with the thermo-oxidative degradation processes and contributes significantly to the decrease in their molar mass.

The construction of ballistic-resistant body armor is experiencing an increasing use of flexible unidirectional (UD) composite laminates that comprise multiple layers. Each UD layer contains hexagonally packed high-performance fibers with a very low modulus matrix (sometimes referred to as binder resins). Laminates are then made from orthogonal stacks of these layers, and these laminate-based armor packages offer significant performance advantages over standard woven materials. When designing any armor system, the long-term reliability of the armor materials is critical, particularly with regard to stability with exposure to temperature and humidity, as these are known causes of degradation in commonly used body armor materials. To better inform future armor designers, this work investigates the tensile behavior of an ultra-high molar mass polyethylene (UHMMPE) flexible UD laminate that was aged for at least 350 d at two accelerated conditions: 70 °C at 76% relative humidity (RH) and 70 °C in a desiccator. Tensile tests were performed at two different loading rates. The mechanical properties of the material after ageing demonstrated less than 10% degradation in tensile strength, indicating high reliability for armor made from this material.

The increasing amounts of discarded textiles represent a potentially valuable resource that could be reclaimed, for example, by chemical techniques. This work underscores the significance of utilizing chemical recycling techniques for multicomponent fabrics under mild reaction conditions to investigate the reusability of recovered components. We present a method for recovery of cotton, elastane, and nylon from polyester blends through mild alkaline hydrolysis supported with a phase-transfer catalyst. To juxtapose the impact of these various fibers on the depolymerization of the polyester component into terephthalic acid (TPA), consistent reaction conditions were maintained. The average TPA yield (by mass) was 93.9 ± 2.8% for pre-consumer materials and 89.5 ± 3.1% for post-consumer materials. This comparative analysis provides insights into factors contributing to the observed decrease in the TPA yield. Inimitable to this study, an analysis of the reuse potential of recovered cotton via tensile strength was performed. The average cotton recovery (by mass) was 95.9 ± 0.8%. Comprehensive material characterization of all recovered components was performed. This research paves the way for a deeper understanding of the potential contamination of TPA, the quality of recollected fibers, and what components of a mixed textile stream act as potential “disruptors” to recyclability.

Hyperbranched polymers are commonly used as surface and cure modifiers, along with nanoparticles, of epoxy resins used in medical and infrastructure applications; however, their impact on structure and performance of the epoxy resins is not fully understood. Here, a commercial epoxy-aromatic amine resin (EP-AA) system is blended with off-stoichiometric amounts of hyperbranched amine (HA), and the cure kinetics, structure, polymer dynamics, and mechanical properties of the different compositions are evaluated. Cure kinetic studies indicate that the curing of the hyperbranched amine is nearly complete prior to that of the aromatic amines. At its highest concentration (1% by mass), the hyperbranched amine is found to autocatalyze the epoxy and the aromatic amine cure, but the bulky HA groups slow the diffusion kinetics during the final stages of the cure process. This results in a heterogeneous, cocontinuous network structure consisting of unreacted secondary amines that increase the side-group/pendant contribution and increase the free volume within the polymer network. The restricted cooperative segmental mobility of the polymer network in the 1% by mass HA blend results in poor energy dissipative properties, as evidenced by reduced strength and strain to failure.

Herein, we describe the design, synthesis, and analysis of anhydrous fuel cell membranes that can operate at temperatures above 100 °C, in view of enhanced performance and stability. Traditional polymer electrolyte membrane fuel cells (PEMFCs) do not operate efficiently above 100 °C because water is used as a proton-conductive medium through the Grotthuss hopping mechanism. By substitution of water with heterocyclic amine monomers and use of ionizing radiation to graft them onto fluoropolymer films, proton-conductive network solid-state polymer electrolyte membranes (PEMs) were developed. PEMs were synthesized using indirect radiation grafting of the following heterocyclic amine monomers: 4-vinylpyridine and 5-vinylpyrimidine onto fluorocarbon substrates. The resulting PEMs have proton conductivities greater than 10^–2 S/cm above 100 °C and perform independent of humidity conditions. These PEMs also demonstrate a positive correlation of increased proton conductivity with increasing temperatures above 100 °C. The chemical properties and structures of the grafted monomers affect the proton-conductive mechanism and performance of the PEMs. The data generated through this research will further the development of anhydrous PEMs through radiation grafting to achieve higher proton conductivity, enhanced performance, and stability.