Sustainable ambient-dried cellulose xerogels enabled by bio-based ammonium phytate as a dual-functional crosslinker...

The development of sustainable, high-performance thermal insulators is crucial to reducing building energy consumption, which accounts for nearly 40% of global energy use. Cellulose-based porous materials have attracted considerable interest for this purpose owing to their renewability and inherently low thermal conductivity. However, the intrinsic flammability of cellulose and the structural collapse commonly encountered during conventional drying or flame-retardant modification processes make it difficult to simultaneously achieve high flame retardancy, low thermal conductivity, and sustainable fabrication in cellulose-based porous insulators. Herein, we report an ambient-drying strategy to fabricate cellulose/ammonium phytate (AP) composite xerogels for bio-based fire-retardant thermal-insulation application. In this design, bio-based AP serves dual roles as a crosslinking agent and a phosphorus-nitrogen synergistic flame retardant. The optimized xerogels exhibit a thermal conductivity of 45 mW m^-1 K^-1 and outstanding flame retardancy, with a high limiting oxygen index of 95% and a 95.2% reduction in peak heat release rate compared with pure cellulose xerogels. This work provides a practical pathway toward sustainable, fire-safe thermal insulation materials derived entirely from renewable resources.