SERDP 2016 Project-of-the-Year Award for Weapons Systems and Platforms
Carbon fiber polymer composites are important structural materials for weapon systems and aerospace platforms. They provide remarkable strength, reduced susceptibility to corrosion, and significant weight reductions compared to aluminum, which allow for enhanced warfighter capability, reduced fuel usage, and enhanced resistance to corrosion, thereby greatly reducing lifecycle costs.
Most thermosetting resins are synthesized from phenols that are generated from unsustainable petroleum sources by multi-step routes that are energy and solvent intensive. Further, many of the precursors to conventional thermosetting resins have estrogenic effects and toxicity issues. To address these environmental challenges while increasing the availability of sustainable, domestic sources for high temperature materials, Dr. Benjamin Harvey and his team from the Naval Air Warfare Center developed new methods to efficiently convert bio-based feedstocks to polyphenols and thermosetting resins that in many cases outperform petroleum based materials.
New thermosetting polymers have been prepared from vanillin and creosol, two molecules that can both be readily derived from lignin. In addition, a liquid, highly processable monomer has been derived from anethole, a significant component of pine resin and the essential oil of star anise. Another avenue of research has focused on the conversion of eugenol, the main component of clove oil, into thermosetting polymers, polycarbonates, and homogenous network structures.
As a key example of the remarkable properties afforded by these bio-based materials, a hydrophobic polymer has been synthesized from pine resin that exhibits one of the lowest water uptakes ever measured for this class of materials and thermomechanical properties that are unaffected by exposure to boiling water for four days. This remarkable material has obvious applications for use in maritime environments.
In one of the most exciting and innovative facets of this work, biosynthetic phenols are being used as precursors to thermosetting polymers. In collaboration with industrial partners, the phenols are generated from biomass sugars via fermentation with metabolically engineered organisms. A key example of this technology is the development of a thermosetting resin from the trisphenol resveratrol. The derivative polymer has the following attributes:
Polymer composites prepared from resveratrol are of significant interest for missile cases, high temperature structural components, and fire resistant coatings.
Several of the resins developed through this project have been incorporated into both flat panel laminates as well as bulk molding compounds (BMCs) that can be fabricated into virtually any shape. Bio-based BMCs have been used to fabricate composite polar bosses (rocket case connectors) that are roughly half the weight of conventional aluminum polar bosses. The simple and efficient BMC fabrication process is expected to greatly reduce the cost and lead time of these components.
In addition to the remarkable material properties of the bio-based polymer composites, initial computational studies predict that many of the bio-based polyphenols will not bind to the estrogen receptor site making them safer to use for both thermosetting and thermoplastic polymer applications. Further, studies have shown that some of the bio-based thermosetting resins can be partially recycled by pyrolysis under humid conditions.
Over FY16, the scope of this project was extended to include work on a new class of bio-based thermosetting phthalonitriles in collaboration with the Naval Research Laboratory under their SERDP-funded effort. To date 8 new bio-based phthalonitrile resins have been prepared. These thermally stable and highly processable materials have potential applications as replacements for high temperature polyimides.
For this important work, Dr. Harvey and his project team received the 2016 SERDP Project-of-the-Year Award for Weapons Systems and Platforms for their project titled Cyanate Ester Composite Resins Derived from Renewable Polyphenol Sources.