Thermally resistant structural adhesive based on a phenolic resin/PEEK/SiO₂ composite system, offering a balanced combination of strength, toughness, and thermal stability

The rapid advancement of hypersonic vehicles presents unprecedented challenges to thermal protection systems (TPS). During flight, these vehicles endure extreme high-temperature conditions, making their structural integrity highly dependent on high-temperature adhesives to ensure robust bonding of the vehicle's airframe. Phenolic resin (PF) stands out for its exceptional high-temperature resistance. However, traditional phenolic adhesives suffer from inherent brittleness and pose a risk of catastrophic failure under rapid thermal shock, rendering them inadequate for hypersonic flight missions. Therefore, we propose an innovative strategy to prepare a composite adhesive by embedding surface-activated polyetheretherketone (MPEEK) and nano-silica (nano-SiO₂) into a PF matrix. This material exhibits outstanding lap shear strength (23.82 MPa), with lap shear strength and work of debonding increasing by 9.11% and 80.02%, compared to conventional PF adhesives. This performance leap stems from a synergistic mechanism: PEEK microdomains promote plastic energy dissipation to inhibit crack propagation, while the nano-SiO₂ network reinforces the matrix through crack pinning. The resulting organic-inorganic hybrid network structure exhibits exceptional stability at high temperatures, maintaining an adhesive strength of 6.43 MPa even at 400 °C. Additionally, the feasibility of utilizing the adhesive system as a potential sprayable high-emissivity coating material was evaluated. The coating demonstrated an emissivity as high as 89.79% in the mid-infrared band (3-25 μm), indicating its capability to efficiently convert internal heat within the substrate into radiant energy and dissipate it outward. This dual-functionality paradigm provides a critical material reference framework for ensuring the mechanical reliability and thermal safety of hypersonic vehicle structures operating in extreme environments.