Slippage-inhibiting effect of interfacial cross-linking of nanotubes by defluorination on the mechanical properties of free-standing multi-walled carbon nanotube yarns: Comparison with individual multi-walled carbon nanotubes

Carbon nanotube yarns (CNTYs) spun only by twisting have a low mechanical strength due to the slippage of individual CNTs. This hinders the practical applications of CNTYs. Here, we studied the slippage-inhibiting effect of the interfacial cross-linking of the nanotubes by defluorination on the mechanical properties of free-standing MWCNTYs and compared with the fracture tensile strength of the individual defluorinated MWCNTs. The mechanical properties of defluorinated MWCNTYs increased with increasing annealing temperature, and MWCNTYs defluorinated at 800 °C under a pressure of 76 Pa (p-deF₈₀₀-MWCNTYs) exhibited an average specific fracture strength of 0.69 N/tex and an average specific fracture stiffness of 103.2 N/tex, with high flexibility. As the fracture tensile strength of individual defluorinated MWCNTs was low, the high strength of the p-deF₈₀₀-MWCNTYs was attributed to the cross-linking of the active carbon atoms in the outer nanotubes with those of the adjacent nanotubes through sp²C and sp³C bonds, which led to the transfer of load to the yarns. Thus, the results of our study highlight the importance of good balance between the defects of CNTs and cross-linking between CNTs.