Circular composite materials: Biomass-based furan epoxies with high-performance and closed-loop recyclability

Epoxy thermosets based on diglycidyl ether of bisphenol A (DGEBA) are widely used for high-performance commercial composites. This study explores renewable, recyclable alternatives using furfural-derived diepoxies (diol- and diacid-based) as replacements in anhydride-cured epoxy systems reinforced with glass or flax fibers for the first time. The biobased furan epoxies, synthesized in higher scale, demonstrate superior mechanical properties compared to DGEBA. Notably, the glass fiber reinforced composites with the diacid-derived epoxy resin achieve a significantly higher Young's modulus, 24.0 GPa (tensile) and 28.5 GPa (flexural), versus DGEBA's 15.9 and 21.0 GPa, respectively. It also shows highly enhanced tensile (357 MPa) and flexural (779 MPa) strengths, outperforming DGEBA (296 and 613 MPa). Charpy impact tests on unnotched specimens confirm improved toughness (156 vs. DGEBA's 146 kJ/m2). Furthermore, the composites produced from the diacid-based bioepoxy resin exhibit closed-loop chemical recyclability due to furan ester bonds which are capable to undergo methanolysis with catalytic K2CO3 under mild conditions providing reusable furan monomer in good yields and high purity. Therefore, this work presents a conceptually new and a promising strategy to develop high-performance composites with enhanced sustainability and recyclability, utilizing furfural-based diepoxy featuring an inherently solvolytically degradable chemical structure.