Effect of alignment and packing density on the stress relaxation process of carbon nanotube fibers spun from floating catalyst chemical vapor deposition method

In this study, we investigate the effects of the alignment and compaction of carbon nanotube (CNT) bundles on the time-dependent behaviors and relaxation process of the CNT fibers spun from floating catalyst chemical vapor deposition method. The long-term mechanical behavior of the CNT fibers shows a strong time-dependency in relaxation process that evidences a noticeable viscose force due to weak interfaces between their CNT bundles. The CNT fibers with higher alignment and compaction exhibit stronger CNT-CNT interfaces, resulting in better inter-tube load transfer efficiency, more difficult CNT bundles slippage, and higher elastic behavior. More importantly, among different viscoelastic models used to simulate the relaxation behavior of the CNT fibers, fractional order viscoelastic model is found to provide the highest accuracy at the entire tested time scale, indicating that the relaxation process of the CNT fibers follows the Mittag-Leffler function. This work suggests that the relaxation process of the CNT fibers spun from the floating catalyst method is a long-term process which occurs in multiscale structure at multi-time scales.