Zirconium chelated hybrid phenolic resin with enhanced thermal and ablation resistance properties for thermal insulation composites

To enhance the ablation resistance of phenolic-based composites, Zr⁴⁺ was coordinated with Ph-O^- of phenolic resin (PR) to obtain the Zr chelated hybrid PR (ZrPR), which reduces the Ph-OH content of PR and provides metal-organic chelated point for the cured system, ensuring higher thermal stability of PR. The initial decomposition temperature and thermal residual rate at 1000°C of ZrPR was increased from 305.0°C to 57.6% to 405.2°C and 65.5%. Carbon fiber (CF) reinforced ZrPR (CF/ZrPR) composites had flexural and interlaminar shear strengths of 496.0 and 34.0 MPa, 20.2 and 33.3% greater than unmodified composites (CF/PR). Thermal conductivity, linear and mass ablation rate of CF/ZrPR composites were 1.198 W/(m·k), 0.023 mm/s and 0.0607 g/s, respectively, which were 16.7, 50.0 and 10.6% lower than CF/PR composites. The surface ceramic layer with ZrO₂ and ZrC phase composition formed from ZrPR in extreme heat can produce an insulating effect to shield the inner material from catastrophic ablation. This research might lead to the development of new and more practical ablation resistant composites for aerospace applications.