Multifunctional Integration of Latent-Heat Buffering, Nanoporous Insulation, and Metal–Organic Framework-Mediated Flame Retardancy in Cellulose Aerogels for High-Performance Thermal Management and Fire Safety

The integration of thermal insulation, transient thermal buffering, and fire safety in lightweight sustainable materials is highly desirable but remains challenging. Herein, a multifunctional phase-change cellulose aerogel (PCMA) was developed by incorporating a flame-retardant PWUiO-66 phase into a cellulose nanofiber framework via hydrothermal-assisted freeze-drying. The resulting aerogel exhibits a hierarchically porous structure with confined functional domains, enabling simultaneous suppression of heat transfer and enhanced fire resistance. Relative to pristine CNF, PCMA exhibits reduced thermal conductivity (0.710 m^–1·K^–1 and 0.164 m^–1·K^–1) and thermal diffusivity (0.700 (mm)²/s, 0.700 (mm)²/s), together with improved resistance to transient thermal shock. The confined phase-change domains provide heat-buffering capability by absorbing thermal energy during heating, while cone calorimetry reveals a substantial reduction in peak heat release rate from 69.4 to 30.8 kW·m^–2. Structural characterization shows that the incorporation of PWUiO-66 transforms the smooth fibrillar CNF network into a roughened and interconnected porous architecture, which improves thermal insulation and promotes the formation of a stable char barrier during combustion. These results indicate that the multifunctional performance of PCMA arises from the synergistic combination of hierarchical porous insulation, phase-change-assisted thermal buffering, and MOF-mediated flame-retardant stabilization. This work offers an effective strategy for designing cellulose-based aerogels for advanced thermal protection and fire-safe insulation applications.