Construction and Performance Study of Phosphorus‐Free, Low‐Smoke, High‐Char‐Forming Fully Bio‐Based Flame‐Retardant Epoxy Resin

ABSTRACT

Traditional epoxy resins rely on non‐renewable petroleum resources and suffer from flammability, limiting their safe applications. This study reports a fully bio‐based intrinsically flame‐retardant epoxy resin (DVAEP) synthesized from vanillin (VAN) and epichlorohydrin (ECH) via a two‐step process. After curing with DDM, a dual‐crosslinked network was formed, and the structure was confirmed by FTIR and ¹ H NMR. DVAEP exhibits slightly higher crosslinking density than conventional bisphenol A epoxy resin (EP), while its glass transition temperature is lower due to the Schiff base structure. Benefiting from the high char‐forming ability of the biphenyl structure, DVAEP/DDM achieves a V‐0 rating in the UL‐94 test, a limiting oxygen index of 36.7%, 55% char residue at 800°C, and a 67.8% reduction in total smoke release compared to EP. The flame‐retardant mechanism is attributed to a condensed‐phase effect, where a dense graphitized char layer forms during combustion to inhibit heat and mass transfer. Mechanically, the flexural modulus reaches 3015 MPa, a 28.8% improvement over EP. This work provides a promising strategy for developing bio‐based intrinsic flame‐retardant epoxy resins with high flame retardancy, low smoke emission, and high rigidity.