Performance improvement of continuous carbon nanotube fibers by acid treatment

Continuous CNT fibers have been directly fabricated in a speed of 50 m/h–400 m/h, based on an improved chemical vapor deposition method. As-prepared fibers are further post-treated by acid. According to the SEM images and Raman spectra, the acid treatment results in the compaction and surface modification of the CNTs in fibers, which are beneficial for the electron and load transfer. Compared to the HNO₃ treatment, HClSO₃ or H₂SO₄ treatment is more effective for the improvement of the fibers' properties. After HClSO₃ treatment for 2 h, the fibers' strength and electrical conductivity reach up to ∼ 2 GPa and ∼ 4.3 MS/m, which are promoted by ∼ 200% and almost one order of magnitude than those without acid treatment, respectively. The load-bearing status of the CNT fibers are analyzed based on the downshifts of the G ^′ band and the strain transfer factor of the fibers under tension. The results reveal that acid treatment could greatly enhance the load transfer and inter-bundle strength. With the HClSO₃ treatment, the strain transfer factor is enhanced from ∼ 3.9% to ∼ 53.6%. (paper)