An all-natural wood-inspired cellulose nanofiber composite aerogel for superior thermal insulation and flame retardancy.

Nanocellulose aerogels with low thermal conductivity, lightweight, and abundant pore structures are widely used in thermal insulation materials. However, the growing need for environmental protection places new, stringent demands on the sustainability of aerogels. Herein, an all-natural aerogel with an oriented porous structure, excellent flame retardancy, and low thermal conductivity was prepared, which included bamboo cellulose nanofiber (CNF) framework, sodium alginate (SA) cross-linking, and sodium-based montmorillonite (Na-MMT) for thermal insulation and flame retardancy. The resulting aerogel with a channel structure similar to that of natural wood contributes to low thermal conductivity (21.1 mW/(m·K)) and excellent mechanical properties. The deposition of Na-MMT and CaCl endowed the aerogel with excellent flame retardancy (an ultimate oxygen index of 90 %, a peak heat release rate as low as 19.34 kW/m, and a total smoke production rate as low as 0.122 m), enhanced compressive strength (208.5 kPa) and elastic modulus (261.1 kPa). Finally, its all-natural raw materials make aerogel extremely biodegradable and sustainable, thus reducing the damage of waste materials to the natural environment. This natural wood-like aerogel has outstanding flame retardancy, low thermal conductivity, and excellent mechanical properties, and can be used as an important green building material.