Unlocking the potential of lignin-activated in-situ char formation for fire-resistant foams

Fire-retardant foams, known for their lightweight, porous and excellent insulating properties, are widely used in sustainable, energy-efficient architecture, particularly high-rise buildings. Inspired by the unique seed-dispersal mechanism of Cistus , this study presents a novel design strategy that leverages the in situ melting of surface-exposed uncondensed lignin to achieve superior flame retardancy. This biomimetic approach enables the rapid formation of an thin renewable char layer (2 mm) within 15 min through the unique bonding and carbonization characteristics of lignin in lignocellulosic biomass. A novel layered flame-retardant polyvinyl alcohol (PVA) foam is developed by incorporating vanillic acid-treated eucalyptus (EF) into ammonium polyphosphate (APP). The foam exhibited exceptional fire-resistant properties, including sustained thermal insulation (2 h at 220 ℃), remarkably high limiting oxygen index (LOI, 51.00 %), ultralow peak heat release rate (pHRR, 24.01 kW m −2 ), and minimal total smoke production (TSP, 0.5 m 2 m −2 ). Notably, the thin heat-insulating char layer maintained stability for 60 min at 400 ℃. This study presents new opportunities for the advanced utilization of wood fibers in sustainable materials.