Influence of twist angle and diameter on yarn densification and mechanical-electrical properties of multi-ply carbon nanotube yarns

Owing to their limited thickness, carbon nanotube (CNT) yarns are unsuitable for direct use in most industrial applications. We proposed a multi-ply spinning process that extracts a large number of spinnable CNT arrays to fabricate thick bundles of CNT yarn with comparable apparent densities. The twist angle and diameter of the CNT yarn were determined by the number of turns per meter and the number of CNT arrays. The twist angle exhibited a distinct correlation with the mechanical properties of the yarn. The relationship between the twist angle and tensile strength tended to be inversely proportional, with an ideal level observed at 24°, resulting in a tensile strength of 650 MPa. Yarns with low twist angles exhibited increased strength until they eventually broke without breaking into smaller fragments after the application of tensile strain. In contrast, the yarns with high twist angles exhibited a steady decrease in strength due to fragmentation, resulting in the fibers breaking several times. The relationships between the twist angle, diameter, and electrical characteristics of the yarns were examined. For CNT yarns with comparable apparent densities and diameters, the twist angle had minimal impact on the resistance. Conversely, for CNT yarns with similar twist angles, an increase in the diameter resulted in a reduction in the resistivity. This reduction occurred because the substantial thickness created a more extensive network than the interlayer resistance among the CNTs.