Composite materials consisting of an organic resin and fiber support are widely used throughout the Department of Defense (DoD), and the adoption of these materials in place of metal and ceramic components is accelerating. Composites provide a number of performance advantages over conventional materials, including a significant reduction in weight leading to reduced fuel usage and greater range for tactical vehicles, particularly aircraft. Although increased use of composites provides several environmental advantages, these benefits are offset by their nonsustainable derivation from petroleum products.
The objective of this project is to demonstrate the large-scale synthesis of high performance cyanate ester resins from sustainable and renewable polyphenols utilizing methods with low environmental impact. The resins will be used to fabricate flat panels and full-scale composite parts that will be sufficiently tested and characterized to allow for a future demonstration project.
Bis-Cyanate esters will first be prepared in multigram quantities from vanillin derivatives, guaiacol, eugenol, anethole, resorcylic acids, resveratrol, and salicylic acid. All of the resins will be thoroughly characterized using nuclear magnetic resonance (NMR) spectroscopy, elemental analysis, and when warranted, single crystal X-ray diffraction. The physical and processing properties of these cyanate esters will then be assessed using rheometry, thermal gravimetric analysis, differential scanning calorimetry, thermomechanical analysis, and Fourier transform infrared (FTIR) spectroscopy. This initial screening process will determine the suitability of various resins for use in high performance composites. In particular, resins with low melting points that exhibit mild and robust cure and produce thermosets with high glass transition temperatures (>~200 °C) will be targeted. Resins will also be evaluated on their ability to be scaled up to multikilogram quantities, the availability of precursor phenols from sustainable and renewable sources, and the ability to synthesize these materials using environmentally favorable methods. In accord with the latter, collaborations with performers in an Office of Naval Research (ONR) sponsored biosynthesis program will be leveraged to integrate developing technologies that have the potential to efficiently produce phenolic starting materials from waste cellulose. After the completion of the resin evaluation, three or four candidates will be scaled up to 0.5 kilograms/resin. Further scale-up will continue with concomitant development of composite formulations and the preparation of molds and tooling to allow for fabrication of small composite test articles. These test articles will be tested and evaluated to determine the suitability of these composites for use in DoD applications. Based on this testing, composites will be down-selected or modified, and the appropriate resins will be scaled up to multikilogram scales. Developmental test articles (polar bosses) will then be fabricated and tested. The synthesis, production, fabrication, maintenance, and decommissioning life cycle will be fully optimized in preparation for transition to a demonstration project.
Cyanate esters represent a next generation material with superior thermal stability, fire resistance, moisture resistance, and health and safety characteristics compared to epoxy resins. Increased availability of cyanate esters will not only spur the replacement of epoxy resins with a less toxic alternative, but will also make composite materials in general a more attractive option for DoD applications that require high performance thermosetting resins. Thus, the effort needed to eventually qualify and manufacture these non-petroleum-based resins will not only result in new materials that exhibit desirable environmental impact characteristics, but will also enable a significant expansion in the overall use of lightweight, fuel-saving polymer composite structures throughout DoD and in numerous civilian applications. (Anticipated Project Completion - 2016)