Synthesis of a tetra-functional bio-based epoxy monomer for high-performance flame-retardant thermosets and non-destructively recyclable carbon fiber composites

The development of high-performance bio-based epoxy resins with superior heat resistance, mechanical and flame-retardant properties represent a critical pathway toward addressing advanced manufacturing demands and promoting sustainable development. Concurrently, efficient recycling technologies for carbon fiber (CF) from carbon fiber reinforced polymer (CFRP) waste are urgently needed. In this study, a divanillin-derived tetra-functional bio-based epoxy monomer (ADP-EP) containing imine bonds was synthesized and cross-linked with 4,4-diaminodiphenylmethane (DDM) and nadic methyl anhydride (NMA) to form two distinct cross-linked networks. The ADP-EP/DDM system exhibited exceptional heat resistance and mechanical properties, with a glass transition temperature ( T g ) of 259.3 ℃ and tensile strength of 100.2 MPa, significantly exceeding those of the conventional DGEBA/DDM system (180 ℃, 65.6 MPa). Microscale combustion calorimetry (MCC) revealed low flammability, with heat release capacity (HRC), peak heat release rate (PHRR), and total heat release (THR) reduced by 78.7 %, 79.2 %, and 48.2 %, respectively, compared to the DGEBA/DDM control. Moreover, the ADP-EP/DDM achieved a V0 rating in the vertical burning test (UL-94), confirming its intrinsic flame retardancy. Interestingly, incorporating ADP-EP into the anhydride-cured system enhanced heat resistance, with the D 5 A 5 /NMA system (5:5 DGEBA/ADP-EP molar ratio) demonstrating a T g of 189.1 ℃ while maintaining high tensile strength (75.2 MPa). Notably, the synergistic effect of dynamic imine and ester bonds enabled efficient degradation of the D 5 A 5 /NMA network under mild conditions (160 ℃ in 2-aminoethanol), achieving complete decomposition within 34 min. This approach effectively overcame the degradation challenges of high-temperature-resistant materials and enabled non-destructive recycling of CF from CFRP composites (CF-D 5 A 5 /NMA). The study provides innovative concepts for designing bio-based epoxy resins with high performance and degradability, offering significant scientific value and application potential in aerospace and sustainable composite materials.