Catalytic Disconnection of C–O Bonds in Epoxy Resins and Composites

Abstract

Fiber-reinforced epoxy composites are well established for load bearing applications in the aerospace, automotive and wind power industries, due to their light weight and high durability. These composites are based on thermoset resins, consisting of σ bond-based linkages and aromatic backbones, embedding glass or carbon fibers1. In lieu of viable recycling strategies, end-of-use composite-based structures such as wind turbine blades are commonly landfilled1-4. Due to the negative environmental impact of plastic waste5,6, the need for circular economies of plastics has become pressing7,8. However, recycling thermoset plastics is not trivial1-4. Here, we report a transition metal catalysed protocol for recovering the base chemical bisphenol A and fibers from thermoset epoxy resins. Our approach is based on disconnecting C(alkyl)–O bonds of the most common linkages of the polymer, using a ruthenium-catalysed dehydrogenation-bond cleavage-reduction cascade. We showcase the application of this methodology to relevant unmodified amine-cured epoxy resins as well as commercial composites, including the shell of a wind turbine blade. The high quality of the recovered fibers was confirmed using X-ray micro-computed tomography. Our results demonstrate that chemical recycling approaches for thermoset epoxy resins and composites are achievable. We anticipate that this study is a starting point for developing methodologies that hold the potential for establishing a circular economy for unmodified epoxy-based materials.