Fuente: Journal of applied polymer Lugar: RESEARCH ARTICLE To address the issue of insufficient high-temperature thermal stability of char layers in traditional phosphorus-based flame-retardant epoxy resin (EP) and in response to the urgent demand for green and sustainable materials in modern industry, this study adopts a bio-based modification strategy to optimize the flame-retardant system. Silicon element is incorporated to enhance the structural integrity and thermal durability of char layers; a flexible-chain flame retardant derived from lignin-based vanillin is designed and synthesized, whereby the hydrogen bonding interactions between its phenolic hydroxyl groups and the EP matrix reinforce interfacial compatibility, while the flexible-chain structure mitigates the matrix embrittlement caused by inorganic silicon-containing flame retardants. The synergistic effect of multiple flame-retardant elements and vanillin enables the system to achieve condensed and gas-phase dual-phase flame retardancy, with both environmental friendliness and high flame retardancy taken into consideration.

ABSTRACT
To address the flammability and brittleness of epoxy resin (EP) while meeting green development demands, we developed SiVD, a lignin-derived vanillin-based halogen-free flexible-chain flame retardant. At 5 wt% SiVD, modified EP achieved a limiting oxygen index of 30.1% and UL-94 V-0 rating. Cone calorimetry revealed 24.4% and 28.3% reductions in peak heat release rate and total heat release versus pure EP, along with markedly suppressed smoke production, demonstrating excellent flame retardancy and smoke suppression. The flexible segments of SiVD effectively alleviate EP's inherent brittleness. Even at an ultra-low 1 wt% loading, impact strength reached 60.31 kJ/m2 (247.6% higher than pure EP), while tensile and flexural strengths remained comparable, truly realizing synergistic enhancement of flame retardancy and toughness. Mechanistic studies show a dual-mode flame-retardant action: in the condensed phase, SiVD promotes a dense protective char layer; in the gas phase, it quenches free radicals and releases inert diluents. For toughening, its flexible moieties absorb impact energy, and excellent interfacial compatibility with EP mitigates mechanical deterioration typically caused by conventional flame retardants. This work offers a novel strategy for developing eco-friendly, high-performance flame-retardant EP materials.