Fabrication of Strong and Thermally Insulated Sodium Alginate Aerogels via a Salt-Regulated Freeze-Casting Strategy

Traditional petroleum-based aerogels are more suitable for thermal insulation than inorganic aerogels due to their high mechanical flexibility and low mechanical brittleness. However, petroleum-based aerogels have limitations in terms of biodegradability and thermal insulation. Sodium alginate (SA), a marine-derived polysaccharide material, is an eco-friendly material suitable for producing aerogels with outstanding thermal insulation and biodegradability. However, the widespread application of SA aerogels has been limited by their mechanical brittleness. To overcome this limitation, a salt-regulated freeze-casting strategy was employed to fabricate mechanically robust SA aerogels with an anisotropic structure and enhanced thermal insulation performance. By systematically varying the SA concentration (1.5–4.5 wt %) and NaCl concentration (0.0–0.1 M), the anisotropic aerogels that achieve an optimal balance between mechanical strength and thermal insulation performance were successfully engineered. The optimized aerogel, fabricated with an SA concentration of 4.5 wt % and a NaCl concentration of 0.075 M (4.5 wt %-0.075 M), demonstrates a compressive modulus of 6.88 MPa that is 14.3 times higher than commercial polystyrene foam, an axial thermal conductivity of 0.0362 W/(m·K), and good flame retardancy. Therefore, this strategy paves the way for designing SA aerogels with high mechanical strength and good thermal insulation performance.