Catalytic disconnection of C–O bonds in epoxy resins and composites

Abstract

Fibre-reinforced epoxy composites are well established in regard to load-bearing applications in the aerospace, automotive and wind power industries, owing to their light weight and high durability. These composites are based on thermoset resins embedding glass or carbon fibres1. In lieu of viable recycling strategies, end-of-use composite-based structures such as wind turbine blades are commonly landfilled1–4. Because of the negative environmental impact of plastic waste5,6, the need for circular economies of plastics has become more pressing7,8. However, recycling thermoset plastics is no trivial matter1–4. Here we report a transition-metal-catalysed protocol for recovery of the polymer building block bisphenol A and intact fibres from epoxy composites. A Ru-catalysed, dehydrogenation/bond, cleavage/reduction cascade disconnects the C(alkyl)–O bonds of the most common linkages of the polymer. 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. Our results demonstrate that chemical recycling approaches for thermoset epoxy resins and composites are achievable.

A strategic approach to wind turbine blade recycling: Using life cycle assessment to enable data driven decision making

“…Recovery of usable matrix polymers from analogous composite structures has been demonstrated using chemical based recycling process for alternative "recyclable epoxy" systems (e.g., Recyclamine [12]) and standard epoxy systems using targeted catalsyed decomposition [13]. The former requires the use of specific epoxy hardener systems during WTB production and there is currently a lack of published data to conduct independent LCA for the latter, therefore these recycling solutions have not been considered in this analysis.…”

Epoxy Thermosets Designed for Chemical Recycling

“…Ahrens et al have recently made a significant advancement in the field by utilizing ruthenium catalysis to efficiently cleave CÀ O bonds in amine-cured epoxy networks, resulting in the moderate-yield recovery of bisphenol A (BPA). [33] Furthermore, the use of a costly and toxic ruthenium catalyst is a disadvantage in this study.…”

Base-Mediated Depolymerization of Amine-Cured Epoxy Resins

“…A relatively new contribution employs a homogeneous Ru-based catalyst. 18 Work to date has primarily focused on recycling carbon fiber, including assessment of postrecovery mechanical properties of the fibers. However, the epoxy portion of these composites also represents a substantial amount of unrecovered carbon, encouraging opportunities to recover epoxy monomers while still maintaining carbon fiber strength and alignment.…”