Lightweight Nitrogen-Doped Phenolic Aerogels with Flame-Retardant and Thermal-Insulation Properties

The inherent flammability of phenolic aerogels has imposed significant limitations on its utilization. In order to unlock the potential of phenolic aerogels as insulation and flame-retardant materials, we fabricate a series of melamine-phenolic aerogels (MPAs) based on a copolymerization reaction of melamine and phenolics in a sol–gel process. By varying the quantity of melamine, the microstructures and the corresponding thermal properties of MPAs are investigated. The results indicate that MPAs possess ultralow thermal conductivity of 0.036–0.038 W/(m·K) and a density of 0.34–0.40 g/cm3. In addition, melamine greatly increases the flame retardancy of phenolic aerogels. A modified phenolic aerogel containing 40 wt % melamine has a limiting oxygen index (LOI) value of 32.7%. The measured maximum heat release rate values of MPAs decrease with the increase of melamine portions in samples, ranging from 138 to 74 kW/m2 in the cone calorimeter testing experiment. Furthermore, TG-MS-FTIR technology is used to analyze the gas emission during thermal decomposition, and the structure evolution of the solid phase is studied for a better understanding of the flame-retardant mechanism. This research is intended to present phenolic-based aerogel materials with outstanding overall performance and explore their potential for large-scale production in the future.