Nanoporous Polybenzoxazine Aerogels for Thermally Insulating and Self-Extinguishing Materials in Aerospace Applications

Phenolic-based aerogel composites possess particular characteristics, such as low thermal conductivity, light weight, and superior ablative properties, in near-space vehicles. However, their machinability and flammability require further improvement, hampering their application for high-performance thermal protection systems in the aerospace field. Here, we prepare nanoporous polybenzoxazine (PBO) aerogels with outstanding thermally insulating and self-extinguishing properties by an effective-cost ambient pressure drying (APD) approach rather than a conventional high-pressure supercritical drying pattern. The PBO aerogels are prepared by adopting different exchange solvents of tert-butyl alcohol, ethanol, and n-hexane. The results obtained indicate that PBO aerogels (with n-hexane as the exchange solvent) by APD have an optimal three-dimensional nanoporous network structure, a pore size distribution in the range 20–140 nm, an obvious self-extinguishing property (extinguished itself instantly despite exposure to a 1200 °C flame), superior thermal insulation (the cold surface temperature of the sample reached only 36.4 °C after 400 s despite its opposite surface existing at a 65.8 °C atmosphere), and excellent machinable properties (easy-to-form special-shaped sample). PBO aerogels are a great potential candidate material system for thermal protection systems in aerospace applications in the future.