Effect of flavonoid monomer and epoxy value: Toward making bio-based epoxy resin with intrinsically highly flame retardant and smoke suppression

The flammability, high-density smoke, and sustainable development of epoxy resin (EP) have significantly restricted its advanced applications in safety within the engineering field. Herein, we proposed an innovative approach to fabricate a series of bio-based EPs with similar flavonoid units and varied epoxy values using natural compounds (daidzein, naringenin, quercetin) to challenge the fire-safety and smoke suppression of general EPs. Owing to the effect of epoxy values and the contribution of flavonoid units, the cured EPs have outstanding thermal stability and remarkable cross-linking density as confirmed by thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). Consequently, the char residue of all bio-based EPs with flavonoid units after burning was obviously increased, and the flame retardancy was improved considerably to UL-94 V-0 rating with above 32 % for LOI value. Especially, the cured quercetin epoxy monomer (QEP) enabled the EP to exhibit an impressive flame retardant and smoke suppression performance compared to DGEBA/DDS. The total heat release (THR), total smoke production (TSP), and peak smoke production rate (pSPR) respectively decreased nearly 76.1 %, 81.4 % and 48 % compared to that of DGEBA/DDS. This work presents a modular design strategy for flame-retardant bio-based EPs, providing a new feasible approach for developing novel engineering-safe EPs.