Hierarchical Composites with Carbon Nanotube Grafted Carbon Fibers: A Critical Assessment

Carbon fiber reinforced polymer (CFRP) composites are engineered, synthetic materials of choice for an extensive range of applications, primarily in aerospace, automotive, wind turbine, and sports industries. Identifying viable technological pathways for increasing the range of properties that CFRPs currently offer might considerably widen the scope of their use. Hierarchical composites are made up of ‘fuzzy fibers’ or fibers that have been grafted with multiwalled carbon nanotubes. Apart from the important distinction that hierarchical composites use fuzzy fibers as reinforcement, they are similar to conventional CFRP composites in terms of manufacturing processes and resin system. Fuzzy fibers are synthesised through a variety of processes but the processing route involving high temperature chemical vapour deposition (CVD) is the most popular. We assess the possibility of using hierarchical composites synthesised via the CVD route as a replacement for conventional composites in situations that demand multi-functionality. This is motivated by the fact that improvements in Mode I and II fracture toughness and interlaminar shear strength without any loss of overall strength and stiffness is widely reported for hierarchical composites. Additionally, improvements in electrical properties, shielding to electromagnetic waves and thermal conductivity are also reported. We highlight the process-property relations in hierachical composites, attempt to identify the key process parameters and highlight the range of mechanical, thermal and electrical properties that have been obtained in our laboratory and by others. Finally, we attempt to identify area where hierarchical composites are most likely to find use as a versatile material.