QF/PI@CNTs Composites via Prepreg-Hot Pressing Strategy for Full X-Band Microwave Absorption at Elevated Temperatures

Fiber-reinforced thermosetting polyimide-based composites have broad application prospects in the aerospace field, which makes it particularly important to optimize their preparation process and improve their electromagnetic (EM) wave absorption performance. In this study, quartz fiber/polyimide@carbon nanotubes (QF/PI@CNTs) prepregs with uniform resin distribution and controllable content were prepared through in-situ polymerization combined with a film-coating method. These prepregs were subsequently laminated and molded by vacuum hot-pressing to obtain composites integrating EM absorption and high-load bearing capability. The QF/PI@CNTs composite at a low filler ratio (3 wt% CNTs), by constructing a stable three-dimensional conductive network and inducing multi-scale interfacial polarization effects, demonstrated excellent EM wave absorption. Specifically, the QF/PI@C-3 composite achieved full-frequency absorption across the entire X-band from 25 °C (2.98 mm) to 300 °C (2.01mm), while maintaining an effective absorption bandwidth (EAB) covering 88% of the X-band at 400 °C (1.78mm). The minimum reflection loss (RL min ) improved from -26.42 dB at 25 °C to -70.35 dB at 100 °C, and remained -29.17 dB at 200 °C. Moreover, the composite also has a relatively high thermal decomposition temperature (T d5% =557 °C) and flexural strength (501.8 ± 22.9 MPa). This research provides feasible insights for the design of structural integrated materials with high-temperature EM absorption capability.