A highly fire-safe wood hybrid based on delignification and multi-component co-impregnation strategies

Natural wood is a pervasive sustainable structural material with efficiency, aesthetically pleasing, usefulness, and durability, which is widely used in building construction. However, the fire safety of wood is unsatisfactory for many advanced engineering structures and applications. To address this issue, a highly fire-safe wood hybrid was developed, inspired by transparent wood, through partial delignification and co-impregnation with multi-component flame retardants. The results showed that partial removal of lignin from wood (∼5 wt%) significantly increased the loading of flame retardants from 70 wt% to 133 wt%. Furthermore, it provided exceptional self-extinguishing and fire retardancy to the wood hybrid. The vertical burning test revealed that the wood hybrid did not self-propagate when directly exposed to an open flame and rapidly self-extinguished when removed from the igniting flame. Notably, it did not ignite at an external heat flux of 50 kW/m 2 (cone calorimetry experiment), and the recorded peak heat release rate was reduced by more than 85 % compared to the original wood. It is demonstrated that the co-impregnation of guanidine phosphate and boric acid modifies the thermal decomposition pathway of wood hybrid during burning, allowing the wood to form homogeneous and dense char residues. These carbonaceous structures were embedded with phosphate and borophosphate species, which provide the char residues with improved resistance to oxidation and higher thermal stability, preventing heat and oxygen from infiltrating the underlying wood. In summary, this work provides a facile delignification and co-impregnation strategy that greatly improves the fire retardancy of wood and represents a promising approach toward highly fire-safe structural materials.