Eco-friendly sodium alginate-based composite foam for thermal insulation and flame retardancy

Eco-friendly thermal insulation materials with better flame retardancy are of great significance in reducing energy consumption, minimizing fire hazards and protecting the environment. In this study, an eco-friendly mica/sodium alginate composite foam (SAM foam) was prepared by using sodium alginate and mica powder through the freeze-drying method and crosslinked by Ca²⁺. Additionally, to enhance the water resistance of SAM foam, the foam was hydrophobically modified with perfluorooctyltriethoxysilane (MSAM foam). The prepared SAM foam exhibits a porous structure with high porosity of 95.39 %, and low thermal conductivity (0.0438 W m^-1 K^-1), which endows it with good thermal insulation performance. More importantly, the incorporation of mica powder not only strengthened the mechanical properties of the SAM foam but also significantly enhanced its flame retardancy. Specifically, the foam exhibits a peak heat release rate of 13.8 kW m^-2, which is substantially lower than that of reported majority of flame-retardant polymeric materials. Furthermore, the limiting oxygen index (LOI) test results demonstrate that the SAM foam is non-flammable under the test conditions. Combined with its enhanced mechanical properties and a simple, potentially scalable fabrication process, the SAM foam may hold great potential for various applications, such as building insulation, packaging, and electronic device protection.