High Mass Residual Silica/Polybenzoxazine Nanoporous Aerogels for High-Temperature Thermal Protection

High-performance thermal protection materials are urgently needed for thermal protection applications under extreme conditions. Organic aerogels are considered to be promising and efficient thermal protection materials, but their low mass residuals have been the main obstacles to limiting their development and application. Herein, by an in situ copolymerization of benzoxazine prepolymers and N,N-dimethylformamide (DMF)-soluble silica (SiO2) precursors, polybenzoxazine (PBO) with increased SiO2 contents was formed, leading to high mass residual SiO2/PBO (PBOS) aerogels with dual-network nanoporous structures. The dual-network nanoporous structures of the PBOS aerogels were obtained owing to the similar gelation and cross-linking rates of PBO and SiO2, facilitated by the introduction of ethanol and an increased gelation temperature. The resulting PBOS aerogels exhibited high mass residuals (75.96% Ar, an increase of approximately 26%; 52.23% air, an increase of approximately 30%), considerably higher than those of the existing silicon-modified PBO aerogels. The PBOS-4 aerogel demonstrated excellent high-temperature thermal insulation properties by maintaining a low back temperature of 59.9 °C when exposed to a 1200 °C butane flame for 600 s. Benefiting from the high mass residual and thermal stability, the quartz fiber-reinforced PBOS-4 (QF/PBOS-4) nanoporous aerogel composite exhibited outstanding ablation resistance under a 1500 °C oxyacetylene flame for 600 s, with linear and mass ablation rates of 0.8 μm s–1 and 0.67 mg s–1, respectively. This study presents a method for producing high-performance thermal protection materials suitable for aerospace applications. By addressing the inorganic–organic compatibility issues of low-density materials, this research enhances the potential use of PBO-based aerogel composites in both civil and military applications.