Engineering Hierarchical Cellulose Aerogel Networks Toward Decoupled Heat Transfer and Enhanced Multi-Phase Fire Safety

Cellulose-based aerogels are promising sustainable thermal-insulation materials, but their practical application is often limited by insufficient mechanical robustness and intrinsic flammability. Herein, a multiscale network-engineering strategy is proposed to fabricate a cellulose-based composite aerogel integrating structural stability, thermal insulation, and fire safety. By synergistically introducing in situ generated aluminum trihydroxide (ATH) and microencapsulated APP@ATH–MEL into the cellulose scaffold, the flame-retardant components function not only as active fire-safety agents but also as structural regulators that promote the formation of a highly interconnected hierarchical framework. This regulated architecture enhances interfacial interactions, improves load-transfer efficiency, suppresses structural collapse during freeze-drying, and introduces tortuous pathways and abundant interfaces for heat-transfer regulation. As a result, the optimized composite aerogel exhibits a low thermal conductivity of 35 mW·m⁻¹·K⁻¹ together with improved compression resistance. Thermal analysis reveals a reduced mass-loss rate and increased char yield, while cone calorimetry confirms suppressed heat release, reduced gaseous emissions, and improved residue stability. The enhanced fire safety is attributed to a synergistic multi-phase mechanism involving endothermic shielding, gas-phase dilution, condensed-phase char formation, and inorganic-residue reinforcement, which collectively inhibit heat and mass transfer during combustion. This work provides an effective strategy for the design of lightweight, mechanically robust, and fire-safe cellulose-based composite aerogels for advanced thermal-insulation applications.