Silicotungstic Acid-Intercalated ZnAl-LDHs Nanosheets-supported CNF Aerogels for Enhanced Thermal Insulation and Flame retardant

Lightweight, heat-insulating, and high-temperature-resistant materials are essential for the safety of spacecraft and precision equipment. Nanocellulose (CNFs), with their high specific surface area, low thermal expansion coefficient, and high strength, hold promising prospects for lightweight and thermally insulating aerospace materials. However, the inherent flammability and high brittleness of CNFs severely limit their widespread use in high-temperature fields. To address these issues, this study successfully synthesized [SiW ₁₂ O ₄₀ ] ⁴⁻ -intercalated ZnAl-SiW ₁₂ O ₄₀ -LDHs and incorporated them into CNFs with boric acid (BA) to prepare SiW-LDHs+BA/CNFs aerogels. The CNFs served as the support backbone for the assembled ZnAl-SiW ₁₂ O ₄₀ -LDHs, while BA enhanced the flame-retardant behavior and mechanical stability. Results showed that LDHs could be uniformly distributed within the porous network of CNFs aerogels. When the mass fractions of ZnAl-SiW ₁₂ O ₄₀ -LDHs and BA were 50.0% and 2.0% of CNFs, respectively, the 50.0SiW-LDHs+BA/CNFs aerogel exhibited excellent thermal insulation and flame-retardant performance. The thermal conductivity decreased to 0.038 W/(m·K) and the t _250°C (time required for the central temperature on the backside of the aerogel to reach 250 °C from room temperature) was 2237.6 s, 1082.6 s longer than that of pristine CNFs aerogel. Specifically, the 50.0SiW-LDHs+BA/CNFs aerogel did not ignite during the 70 s of exposure flame. The compressive strength and specific modulus after the impact of the 50.0SiW-LDHs+BA/CNFs aerogel were increased by a maximum of 255.0% and 118.0% compared to of pristine CNFs. The flame-retardant mechanism was deduced based on the analysis of the morphology and chemical composition of the combustion residues. Given its excellent thermal insulation and flame-retardant performance, the SiW-LDHs+BA/CNFs aerogel shows great potential for application in aerospace and high-temperature thermal protection fields.