Using ultra-thin interlaminar carbon nanotube sheets to enhance the mechanical and electrical properties of carbon fiber reinforced polymer composites

A major shortcoming of carbon fiber reinforced polymer composites (CFRP) is their interlaminar performance. This study provides an inexpensive and readily scalable solution to this problem by incorporating ultra-thin sheets of carbon nanotubes (CNT) between the plies (laminates) of CFRPs. To this end, dry carbon fiber fabrics are first sandwiched between CNT sheets. The fabrics are then stacked and infused with epoxy to form a CFRP with interlaminar CNT sheets. Contrary to the typical approach where microns-long CNTs are distributed randomly within a CFRP for reinforcement, this study uses similar to 100 nm thick CNT sheets consisting of aligned and ultra-long (0.3 mm) nanotubes. Despite their negligible weight fraction of only 0.016%, the interlaminar CNT sheets enhanced the CFRP's flexural strength by 49%, interlaminar shear strength by 30%, and mode I fracture toughness by 30%. X-ray micro-tomography revealed that samples with interlaminar CNTs are significantly resistant to delamination and crack propagation. Moreover, the in-plane electrical conductivity of these composites increased commensurate with the weight fraction of CNTs, providing a maximum enhancement of 278% over the reference sample for 0.048 wt% of CNT sheets. This study reveals that for almost no change in weight and thickness, interlaminar CNT sheets can enhance the electrical conductivity and interlaminar performance of CFRPs.