- Program Areas
- Installation Energy and Water
- Environmental Restoration
- Munitions Response
- Resource Conservation and Resiliency
- Weapons Systems and Platforms
Recycling of Composites and Prepregs by Oxidative Catalysis
Dr. Steven Nutt | University of Southern California
Polymer composites are widely used across the defense services because of their high performance and light weight relative to conventional metal alloys. Most of the polymer matrices involved are thermoset epoxies, which undergo an irreversible cure reaction, converting them from viscous liquids to stiff, glassy solids. The irreversibility of this curing impedes the productive reuse of scrap and recycling of end-of-life fibre-reinforced plastic (FRP) composites and constitutes a growing obstacle to more wide-spread use. Amplifying the problem is the inefficiency of FRP manufacturing methods: generally, 20% to 30% of purchased material (prepreg) becomes production waste, and no standard approaches exist for reusing production waste or recycling end-of-life FRP composite products. At present, most composite waste is sent to landfills, often with attendant haz-mat disposal fees. The widespread use of composites in defense applications has led to an urgent need for new strategies for the recycling of scrap and end-of-life composites. Moreover, developing catalytic reactions that will gracefully deconstruct cured FRP matrices will require the development of technology to enable catalysts and reagents to move and react within the complex solid-phase composite architecture. The project team have recently invented methods to enable such catalytic depolymerization of common thermoset polymers used in composites manufacturing, and the long-term goal remains to apply these catalytic methods to the cleavage of FRP matrix linkages in a way that enables the recovery of useful small-molecule monomers and preserves the length and order of composite fibers. Realizing this goal requires solving the problem of selective polymer cleavage using only sustainable reagents, and understanding the transport of catalysts, reagents, and products through the assembled composite material environment. Having shown the first catalytic oxidation capable of realizing this objective, the project team are now poised to develop the discovery into useful applied technology.
Three decades of efforts in FRP composite recycling have not resulted in a tenable solution to the deconstruction and recycling of these materials. Prior work in this field has focused on physical processes: mechanical grinding, pyrolysis, and solvolysis. All of these approaches have major drawbacks – waste products, fiber damage, unscalable, etc. The time is right for a different approach, one that exploits new chemistry for the disassembly of the FRP polymers widely used in the Department of Defense (DoD). Just as cure chemistry is integral to the success of FRP manufacturing and performance, an ingenious invention is needed to reverse it. Such an approach requires expertise in both composites engineering and in homogeneous catalysis, which the team brings to the problem. The recent results indicate that oxidative catalysis can address this need. Developing catalytic reactions that will gracefully deconstruct cured carbon fiber reinforced polymer (CFRP) matrices has required basic understanding of how catalysts and reagents move and react within the complex composite architecture. In this project the team will transform these discoveries to usable technology for catalytic deconstruction of composite materials.
The proposed project will develop a new chemical solution for FRP recycling, including both production waste and end-of-service-life scrap. A sustainable FRP recycling solution will increase overall efficiency of manufacturing, recovering high-value constituent materials and returning them to service, reducing costs and adverse environmental impact. The results and insights gained from these rigorous studies will advance the knowledge and understanding on chemical recycling of FRPs and provide a pathway towards improved recycling of both fibers and polymers harvested from current-generation composites.