Low-temperature hydrothermal synthesis of ultra-high-strength phenolic aerogel composites based on a physicochemical double-crosslinked network

Conventional methods for preparing phenolic aerogels often suffer from poor mechanical properties, high production costs, and complex fabrication processes. Herein, this study reports the preparation of an ultra-high strength carbon fiber needled felt-reinforced phenolic aerogel (NCF/PRA) composite via a low-temperature (< 100 °C) hydrothermal synthesis combined with ambient pressure drying. Using the silane coupling agent KH-560 as a curing agent, the interfacial bonding strength of the material was enhanced through crosslinking reactions during polymerization. Simultaneously, a physico-chemically dual-crosslinked polymer network was formed, endowing the PRA with high mechanical strength. The as-prepared NCF/PRA composite exhibits ultra-light weight, efficient thermal insulation, good load-bearing capacity, and allows for the fabrication of large-sized samples. It achieves a specific strength as high as 110.61 MPa/(g/cm³). The outstanding thermal insulating capability of the 30 mm thick NCF/PRA composite was directly demonstrated by a mere 57.83 °C on the backside, recorded under severe ablation testing (3.62 MW/m², 2300 °C, 30 s). By presenting a unique method to engineer robust, cost-efficient, and environmentally benign PR aerogel composites, this research underscores their promising candidacy for future thermal protection systems.