Abstract: Polyimide fiber (PI_f) based fabric is widely used as a reinforcement in polymer matrix composites for aerospace and automotive applications due to its high specific strength and environmental stability. However, the inadequate flame resistance and high-temperature mechanical properties of polymer matrices limit their performance in fire-prone environments. To address the demand for flame retardancy and mechanical reliability, here we employ ZnO ceramic instead of polymer matrix to prepare continuous PI_f reinforced ceramic matrix composites by using the cold sintering process. The dispersibility of ZnO powder is first optimized by surface modification with a silane coupling agent, which also enhances the flexural strength of cold-sintered ZnO ceramic. After slurry impregnation, the ZnO powder-filled 3D PI_f felt is then densified by cold sintering at a temperature as low as 220 °C. While the ceramic matrix provides the composite with excellent flame retardancy, the polymer fiber improves the thermal shock resistance, which together allow the composite to maintain structural integrity against a 1000 °C flame. Moreover, the composite exhibits extraordinary mechanical reliability and strength with a Weibull modulus of 13.7 and retention of initial strength after 10,000 fatigue cycles at 80 % of fracture stress. The effective load distribution provided by the random PI_f fabric structure, along with the high elongation at break of the PI_f, enables significant energy absorption during crack propagation even under impact damage. This novel ceramic matrix composite expands the application potential of superior performance polymer fibers and establishes a foundation for the development of lightweight, flame-retardant, and mechanically robust materials.

Key words: Polyimide fibers, Ceramic matrix composites, Fatigue resistance, Flame retardancy, Cold sintering process