Reinforcing flame retardancy, dimensional stability, and high strength of woods for structural applications through surface densification and chemical modification

The dimensional instability and flammability issues of wood hinder its application as a structural material in construction. In this study, we integrated wood surface densification technology with a chemical modification strategy to develop flame-retardant, high-strength, and dimensionally stable woods. The modified wood demonstrates a flexural strength of 193.98 MPa, surpassing that of the majority of both inorganic and organic materials. Additionally, after being immersed in water for 24 h, the composite material exhibits a rebound rate of merely 2.62 % and a water absorption rate of 3.16 %. Most significantly, the material's flame retardancy is substantially enhanced after treatment, resulting in negligible combustion when exposed to an open flame. The analyses reveal that surface densification chiefly improves the mechanical properties of wood. The introduction of ammonium dihydrogen phosphate (ADP) into cell walls enhances dimensional stability and flame retardancy, but it comes at the expense of mechanical performance. However, when epoxy polymer is introduced into the cell cavity, it effectively counteracts the adverse impact of ADP, thereby improving both the mechanical properties and dimensional stability of wood. This study effectively addressees the challenges of dimensional instability and flammability inherent in wood as a structural material in construction.