Co-gel strategy for preparing hierarchically porous silica/polyimide nanocomposite aerogel with thermal insulation and flame retardancy

Many porous materials are used as thermally insulating materials to reduce heat loss; most of those materials have low heat stability, inferior mechanical properties, and inflammability. In this work, an efficient thermally insulating and flame-retardant silica/polyimide (SiO2/PI) nanocomposite aerogel with hierarchically porous structures was fabricated by a "co-gel" strategy. The co-gel process is to in situ generate a homogeneous nanocomposite gel using water-soluble polyimide (PAC) and silica precursors. Subsequently, the complex gel underwent freeze-drying and the imidization process. The target nanocomposite aerogel with a binary network structure in which the polyimide and silica particles were interspersed was acquired. The as-prepared SiO2/PI nanocomposite aerogels also exhibited highly hydrophobic properties (water contact angle of 120-127 degrees), allowing it to resist moisture, which is an important property of thermal insulation materials. The as-prepared SiO2/PI-3 nanocomposite aerogel possessed excellent mechanical property with compressive moduli of 1.96 MPa and specific modulus of 52.7 m(2) s(-2). Compared to most polymer-based aerogel and aerogel-like materials, the as-prepared SiO2/PI nanocomposite aerogels exhibited excellent flame resistances with low fire growth rate (0.2-0.6 W s(-1)) and excellent thermal insulation properties with low thermal conductivities that varied from 31.1 mW m(-1) K-1 to 58.5 mW m(-1) K-1 between 25 degrees C and 300 degrees C. This nanocomposite aerogel has very broad application prospects in the areas of thermal insulation in which fire safety is required.