Transparent wood composites with phosphorylated cellulose for enhanced fire safety: A bioinspired solution for sustainable building materials

This study proposes a bioinspired char-forming architecture to develop fire-safe transparent wood. This is achieved by synergistically incorporating phosphorylated cellulose (PC) into wood aerogels. The incorporation of PC enhances the flame retardancy of polyurethane acrylate (PUA) composites. The PC was synthesized through phosphorous acid modification of microcrystalline cellulose and then uniformly distributed within delignified wood aerogels. These aerogels were subsequently impregnated with UV-curable PUA resin to produce transparent wood structures. The PC-modified wood exhibited excellent flame-retardant properties, including self-extinguishing behavior and the formation of continuous, thermally stable char layers during combustion. Structural and chemical characterizations using FTIR, XPS, SEM, and elemental mapping confirmed successful integration of PC into the wood matrix. Thermal analysis (TGA) and micro-scale combustion calorimetry showed a significant reduction in peak heat release rate (pHRR) (by 42 %) and an increase in char yield (up to 36 wt%). Phosphorylated cellulose-functionalized wood aerogels endowed PUA composites with 26 % lower pHRR and 25 % reduced total heat release (THR) via char-formation-dominated flame-retardant mechanisms. Importantly, the modified transparent wood retained high optical transmittance (∼50 %) and mechanical strength (∼30 MPa tensile strength), making it suitable for multifunctional applications. To better understand the flame-retardant mechanism, molecular dynamics simulations were conducted, demonstrating the barrier role of the char layer in suppressing the release of flammable gases.