Preparation, flame retardancy, and hydrophobicity of phytate ammonium/silica sol modified wood: Inspired by plant cuticles

Wood is widely utilized in furniture manufacturing and architectural decoration; however, its inherent flammability poses significant fire safety risks. Addressing the shortcomings of traditional phosphorus-nitrogen flame retardants, such as high hygroscopicity and weak char formation, this study draws inspiration from the structure of plant epidermis. A hybrid ammonium phytate (PA)/SiO₂ system featuring a dual-protection mechanism, comprising an “outer hydrophobic barrier and an inner inorganic skeleton,” was constructed via the sol-gel method. Experimental results indicate that the modified wood exhibits excellent water resistance, achieving a water contact angle of 136° and a significantly reduced water absorption rate. The limiting oxygen index (LOI) went up by more than 170%, the peak heat release rate (pHRR) went down by 37% with a 30-second delay, and the total heat release (THR) went down by 22.6%. Thermal stability was also notably enhanced, with the char residue yield increasing by over 75% and the maximum weight loss rate decreasing by approximately 66%. Mechanistically, PA promotes the dehydration and carbonization of wood, functioning synergistically with the SiO₂ skeleton to construct a dense and stable organic-inorganic composite char layer that enhances thermal insulation, oxygen shielding, and crack resistance. Simultaneously, the outer barrier composed of a Si–O–Si network and a long-chain hydrophobic layer reduces surface energy and retards the transport of moisture, heat, and combustible volatiles, thereby achieving a synergistic improvement in both flame retardancy and durable moisture resistance.