Dense,Self‐Formed Char Layer Enables a Fire‐Retardant Wood Structural Material

Wood is one of the most abundant, sustainable, and aesthetically pleasing structural materials and is commonly used in building and furniture construction. Unfortunately, the fire hazard of wood is a major safety concern for its practical applications. Herein, an effective and environmentally friendly method is demonstrated to substantially improve the fire‐retardant properties of wood materials by delignification and densification. The densification process eliminates the spaces between the cell walls, leading to a highly compact laminated structure that can block oxygen from infiltrating the material. In addition, an insulating wood char layer self‐formed during the burning process obstructs the transport of heat and oxygen diffusion. These synergistic effects contribute to the material's excellent fire‐retardant and self‐extinguished properties, including a 2.08‐fold enhancement in ignition time (t_ig) and 34.6% decrease in maximum heat release rate. Meanwhile, the densified wood shows a more than 82‐fold enhancement in compressive strength compared with natural wood after exposure to flame for 90 s, which could effectively prevent the collapse and destruction of wooden structures, and gain precious rescue time when a fire occurs. The facile top‐down chemical delignification and densification process enabling both substantially enhances fire‐retardant performance and mechanical robustness represents a promising direction toward fire‐retardant and high‐strength structural materials.