Property improvement of CNT spun yarns and their composites through pressing, stretching and tensioning

Untwisted multi-walled carbon nanotube (CNT) yarn was spun from vertically aligned CNT arrays by solid-state drawing CNT webs through a ceramic die. CNT yarn-reinforced epoxy composites were developed using a resin drop method. Waviness and poor packing of CNTs in the untwisted spun yarns have limited the mechanical properties of the yarns and their composites. Therefore, pressing along with sliding was applied to create thin-twisted yarns with dense packing of the CNTs. Besides, stretching and tensioning techniques were applied to the twisted yarns to reduce twist angle as well as waviness of the CNTs and their bundles. Stretching and tensioning of the press-slid yarns under constant loads of 0.15, 0.25, 0.35 N enhanced the mechanical properties of the yarns significantly. Moreover, stretching and tensioning of the press-slid CNT yarns increased the mechanical properties of the yarn composites considerably. However, tensioning of the press-slid yarns is more effective than their stretching.