Fabrication and multifunctional properties of polyimide based hierarchical composites with in situ grown carbon nanotubes

Polyimide (PI) based hierarchical composites reinforced with carbon nanotubes (CNTs) directly grown on the surface of carbon fabric were prepared. The growth morphology and other characteristics of the CNTs were analyzed by detailed techniques, which proved the growth of CNTs on the surface of carbon fiber (CF). The CNT–CF/PI composites with a growth time of 40 min showed an increase of 33% in flexural strength, 42% in flexural modulus, 17 °C in the temperature at 5 wt% of weight loss, 27 °C in glass transition temperature and five orders of magnitude in through-thickness electrical conductivity as compared to those of conventional carbon fabric reinforced polyimide composites. The significant improvement of the comprehensive properties of the hierarchical composites can be attributed to the stiffer CNTs-reinforced matrix, the enhanced fiber–matrix interfacial adhesion and/or the strong synergetic effect between the nano and micro-scale fillers. The enhancement mechanism of the hierarchical composites on various different scales was also discussed in detail. It is believed that the present study can provide broad application potential in polyimide-based polymer composites and other types of high performance thermoplastic systems.