Mechanically Twisting of Multi-Membrane Carbon Nanotube Yarn and The Enhancement of Its Mechanical Properties

The direct CVD-spun multi-membrane carbon nanotube yarn is mechanically twisted to engineer its structures and to enhance its mechanical properties. Homogenously twisted CNT yarns with a dense cross-section are achieved with different degrees of twisting. The mechanical twisting remarkably increases the tensile strength and modulus of the yarn as the result of radial compressive stress. At a twisting degree of 70 r/cm, the tensile strength of the yarn increases by two folds and the modulus by ten folds of those of the as-spun yarn. The corresponding twisting angle is 32 °, and the critical twisting coefficient is 32 texr/cm. As the result of the increases in strength and modulus, the mean fractural toughness of the yarn is increased by two times. The Poisson ratio of the twisted yarn is decreased to 0.17 ~ 0.20 from that of the as-spun fibers (0.25 ~ 0.27), as the result of twisting induced yarn densification. This study demonstrates the possibility to engineer the structures of the CNT membrane yarn and to enhance their mechanical performance via the mechanical twisting.