Mechanistic insights into enhanced fire and smoke resistance in surface densified wood: a chemical-free thermophysical approach

Wood is a sustainable material, but its inherent flammability and smoke emissions limit its practical applications. This study proposes a thermo-physical strategy to enhance fire safety by fabricating surface densified wood (SDW). SDW were fabricated via hydrothermal pretreatment (20–80 °C) followed by thermo-densification, yielding samples with varying compression ratios (10–30 %; e.g., SDW 20 -30 %) and deformation stabilities (e.g., SDW 80 -30 %). Cone calorimetry revealed that the densified-surface-layer effectively suppressed heat and smoke release by promoting early char formation, which acted as a thermal and mass transfer barrier. SDW 20 -30 % showed 20 % and 70 % reductions in total heat release (THR) and total smoke production (TSP) within the first 360 s. Further improvements were achieved with enhanced densified-surface-layer’s stability: compared to SDW 20 -30 %, SDW 80 -30 % exhibited 32 %, 14 %, and 22 % reductions in CO yield, THR, and TSP, respectively, and delayed peak heat release rate by 73 s. Correlation analysis indicated that densified-surface-layer’s deformation stability contributed more significantly to fire hazard mitigation than densification degree. Thermal and chemical analyses confirmed increased crystallinity and compositional evolution in the densified-surface-layer, leading to improved thermal resistance. These findings demonstrate a chemical-free approach to improving wood fire safety and offer insights into the development of safer bio-based materials.