Homogeneous silicone-modified boron-containing phenolic resins with outstanding ablation resistance

Conventional silicone-modified boron-containing phenolic resins (BPRs) suffer from mechanical denudation caused by phase separation between silicone and resin matrix, limiting their applicability in aerospace thermal protection systems. Despite efforts to reduce the scale of phase separation, micro-scale phase separation still exists due to the chemical incompatibility of silicone and BPR. In this work, a homogeneous silicone-modified BPR (BSiPR) was synthesized by an in-situ hybridization strategy, achieving improvements in flexural strength (53.9 %), tensile strength (38.7 %), and fracture toughness (48.2 %) compared to neat BPR. Specifically, the homogeneous structure BSiPR was obtained by selectively reacting to hydroxymethyl group with aminopropyltriethoxysilane (APTES). Benefiting from the homogeneous silicone nanophase structure, the carbon layer derived by BSiPR is more robust and ordered. The carbon layer adheres well to the surface of the carbon fiber under high velocity air flow, thus the carbon fiber reinforced BSiPR (CF/BSiPR) composites have excellent resistance to mechanical denudation. By resolving the phase separation challenge, this approach provides a scalable pathway for developing aerospace composites with simultaneous enhancements in chemical ablation resistance and mechanical denudation.