Pretreatment Temperature Optimization and Mechanical Properties Improvement: 500°C Resistant Carbon Fiber‐Reinforced Polyimide Composite Material

ABSTRACT To address the severe degradation of mechanical properties of carbon fiber‐reinforced polyimide (PI) composites subjected to high temperatures (500°C), a systematic study was conducted to investigate the regulatory mechanism of imidization pretreatment temperature on the microstructure and high‐temperature properties of the composites. By combining characterization techniques such as infrared spectroscopy and dynamic mechanical thermal analysis, the authors revealed the dynamic effects of different pretreatment temperatures (80°C, 130°C, and 180°C) on the degree of imidization, pore evolution, and molecular chain relaxation. The study demonstrated that a stepwise imidization process (80°C, 130°C, and 180°C) achieved a 93% degree of imidization in the resin matrix. Furthermore, the resulting PI composite exhibited an interfacial shear strength of 106 MPa (a 47% increase compared to conventional processes) and a flexural strength of 1221 MPa at 500°C, retaining 71% of its ambient temperature flexural strength. Furthermore, the composite achieved a glass transition temperature ( T _g ) of 500°C. This study proposed an imidization pretreatment strategy, which improved the high‐temperature stability of the composite material by optimizing the imidization pretreatment temperature, and developed PI/CF composite materials that can withstand a 500°C service environment, providing theoretical support and technical paths for the development of a new generation of ultrahigh temperature polymer‐based composite materials.