In-Situ synthesis of a self-developed phosphorus-nitrogen flame retardant in wood for superior and durable fire safety

Wood, as a sustainable and renewable bio-based material, possesses substantial potential for construction applications. However, its inherent flammability remains a major limitation. This study resolves this challenge through the in-situ synthesis of a novel phosphorus-nitrogen flame retardant (TAM) within wood via a two-step impregnation strategy using amino trimethylene phosphonic acid (ATMP), 1,3,5-tris(2-hydroxyethyl) isocyanurate (THEIC), and melamine (MEL) as precursors. The 1 %TAM-modified wood demonstrated markedly improved fire safety, achieving a limiting oxygen index of 34.2 %, along with significant reductions in total heat release (39.4 %) and total smoke production (51.2 %) compared with pristine wood. These enhancements are attributed to the formation of a dense and continuous char layer that effectively impedes heat and mass transfer. In addition, the in-situ-formed TAM network endowed the modified wood with excellent leaching resistance, maintaining 94.8 % mass retention after 14 days. Especially, it was found that the introduction of THEIC into TAM system significantly enhanced flame retardant effect. This study presents a practical approach for developing durable and high-performance fire-safe wood, supporting the advancement of sustainable bio-materials for industrial applications. • A novel P–N flame retardant (TAM) was synthesized in situ within wood using ATMP, THEIC and melamine. • THEIC served as a key char-forming promoter, enabling superior flame retardancy at an ultralow loading (1 wt%). • The TAM-treated wood achieved a high LOI of 34.2 %, with 39.4 % reduction in THR and 51.2 % reduction in TSP. • The formed water-insoluble network endowed outstanding leaching resistance (94.8 % mass retention after 14 days). • TAM promoted a dense, graphitized char layer that provided exceptional thermal shielding and pyrolysis inhibition.