Non-toxic degradation of anhydride-cured epoxy thermoset using a deep eutectic solvent

Abstract

Anhydride-cured epoxy thermosets, unparalleled in electrical insulation, mechanical strength and chemical stability, serve as indispensable materials in electrical engineering. Efficient degradation of epoxy resins is a critical key to sustainable resource utilization from decommissioned electrical equipment and to the green transformation of the electrical industry. However, existing degradation approaches often involve toxic catalysts and result in environmental pollution. We propose a non-toxic and efficient transesterification strategy employing a deep eutectic solvent (DES) composed of potassium carbonate (K₂CO₃) and ethylene glycol (EG). Compared to traditional organic base catalysis, inorganic K₂CO₃ offers advantages of non-toxicity, cost-effectiveness and sustainability. By leveraging the formation of activated carbonates as intermediates, the DES system can specifically cleave ester bonds, allowing for efficient degradation. Anhydride-cured epoxy thermosets are nearly completely degraded in DES containing 0.12 g mL⁻¹ K₂CO₃ after 3 hours at 180 °C under ambient pressure. In addition, the method facilitates the non-destructive and complete extraction of carbon fibers from the cured epoxy thermoset matrix. Catalysts can be partially recovered through a straightforward separation technique. Our work presents a non-toxic and genuinely green strategy for sustainable degradation and recycling of anhydride-cured epoxy resins, establishing a versatile platform that can be extended to diverse classes of thermosetting epoxy composites.