In-situ constructuring boron-modified phenolic aerogels with enhanced mechanical performance and flame retardancy

Phenolic aerogels are widely used in aerospace applications owing to their inherent flame retardancy, which exceeds that of combustible organic aerogels. However, these materials remain susceptible to smoldering even after being removed from an open flame, due to oxygen diffusion through their porous carbon structure, sustaining internal exothermic reactions. To mitigate the effects of their smoldering combustion, this study focuses on boron modification of the surface of phenolic aerogels’s porous framework. The results show that the material's limiting oxygen index (LOI) increased from 26.9 % to 29.9 %, while its peak heat release rate (pkHRR) decreased by 20.07 % in cone calorimetry tests. Moreover, total smoke production (TSP) dropped by 69.72 %, demonstrating significantly improved flame retardant properties. The materials demonstrated excellent mechanical properties, with tensile, flexural, and compressive strengths of 14.70 MPa, 23.49 MPa, and 7.15 MPa, respectively. This study presents a novel approach to developing phenolic aerogel composites that combine high flame retardancy, superior mechanical performance, and effective thermal insulation, showing great potential for building fire protection and aerospace applications.