Allyl-functional epoxy/BMI co-curing for single-layer carbon fiber composites with enhanced mechanical, thermal, and EMI shielding properties

Ultrathin carbon fiber composites with high electromagnetic interference (EMI) shielding effectiveness are attractive for lightweight multifunctional applications. Herein, single-layer T800 carbon fiber fabric composites were prepared using four epoxy-based curing systems (ED, EBD, AD, and ABD) to investigate the effect of allyl-functional epoxy/BMI co-curing on network structure, interfacial characteristics, thermomechanical behavior, tensile properties, thermal stability, electrical conductivity, and EMI shielding performance. The results show that the allyl-functional epoxy/BMI co-curing strategy promotes the formation of a more integrated crosslinked network and a stronger fiber/matrix interphase. Consequently, ABD/T800 exhibits the best comprehensive performance, including higher storage modulus retention, elevated glass transition temperature, improved thermal stability, and enhanced tensile strength. In particular, ABD/T800 achieves an excellent X-band EMI shielding effectiveness of 80–89 dB at an ultrathin thickness of ∼0.3 mm. S-parameter analysis indicates that the shielding behavior is mainly governed by surface reflection and suppression of electromagnetic-wave transmission, while internal attenuation only provides a secondary contribution after wave entry into the laminate. The superior shielding performance of ABD/T800 is mainly attributed to the continuous conductive carbon-fiber framework, relatively high electrical conductivity, and optimized co-cured matrix/interphase structure. This work demonstrates an effective curing-network design strategy for the development of lightweight, mechanically robust, thermally stable, and high-performance EMI shielding carbon fiber composites.