Catalytic Recycling of Thermoset Carbon Fiber-Reinforced Polymers

We present a one-step method for recycling carbon fiber reinforced polymers produced from prepreg using catalytic chemical solvolysis. This process involves employing Al­(NO3)3·9H2O as an efficient catalyst and dimethylacetamide (DMAc) as a solvent to successfully reclaim carbon fibers from epoxy amine-cured composites. Initially, DMAc infiltrates the compact structure of the cured epoxy, expanding the dimensions of the composite. Subsequently, the Lewis acid catalyst, with the assistance of the nitrate counterion, breaks the C–N bonds in the cured system, as discussed in a proposed mechanism, and releases the carbon fibers from the composite. Two catalysts, Al­(NO3)3·9H2O and Fe­(NO3)3·9H2O, were compared for their effectiveness in the recycling process. Both catalysts achieved a degradation ratio (DR) of approximately 100%, yet they influenced the carbon fiber properties differently. It was established that a 20% concentration of Al­(NO3)3·9H2O at 160 °C for 5 h resulted in nearly a 100% degradation ratio without causing surface damage to the fibers. The recycled carbon fiber exhibited mechanical and chemical properties comparable to the original ones. Furthermore, the recovered epoxy matrix was repurposed as a cohardener or cobinder for creating a new cured matrix system. The mechanical and thermal properties of the prepared cured-epoxy resin specimens were assessed through tensile and DSC tests. The recycled solvent demonstrated identical properties to the initial solvent, remaining suitable for reuse in the recycling process.