Eggshell Powder‐Based Eco‐Friendly Cellulose Nanofiber Aerogels With Excellent Thermal Insulation, Superior Flame Retardancy, and Exceptional Mechanical Durability

ABSTRACT Green flame‐retardant cellulose nanofiber‐based aerogels were synthesized by the incorporation of eggshell powder (ESP) via a simple mechanical mixing strategy. Various weight percentages of ESP powder (10%, 20%, and 30%) were mixed with 3 wt% of CNF suspension and then freeze‐dried. The ESP‐modified cellulose nanofiber‐based aerogels (ESP‐CNFA) were fabricated by combining 30 wt% ESP with a CNF suspension. The prepared aerogel demonstrated enhanced mechanical strength, outstanding flame retardancy, and extremely low thermal conductivity. The ESP‐modified cellulose nanofiber‐based aerogel (ESP‐CNFA) exhibited a LOI value of 32 and excellent flame‐retardant behavior in the vertical flammability test. The flame retardancy behavior of the ESP‐CNFA was analyzed by cone calorimetry test, which had a low peak heat release rate value of 22.8 kW/m 2 and a total heat release rate value of 5.7 MJ/m 2 . The low smoke production rate value of the ESP‐CNFA was highly desirable for fire safety applications in the current scenario. The low thermal conductivity of 31.7 mW/mK for the ESP‐CNFA demonstrated its effectiveness as an ideal green material for thermal insulation applications. The findings suggest that the ESP‐CNFA finds wide applications such as flame‐retardant materials in the packaging, building, automotive, and aerospace industries, without compromising their thermal insulation behavior.