Developing methods to assemble nanomaterials into macroscopic scaffolds is of critical significance at the current stage of nanotechnology. However, the complications of the fabrication methods impede the widespread usages of newly developed materials even with the superior properties in many cases. Here, we demonstrate the feasibility of a highly-efficient and potentially-continuous fiber-spinning method to produce high-performance carbon nanotube (CNT) fiber (CNTF). The processing time is <1 min from synthesis of CNTs to fabrication of highly densified and aligned CNTFs. CNTFs that are fabricated by the developed spinning method are ultra-lightweight, strong (specific tensile strength = 4.08 ± 0.25 Ntex
−1
), stiff (specific tensile modulus = 187.5 ± 7.4 Ntex
−1
), electrically conductive (2,270 S m
2
kg
−1
), and highly flexible (knot efficiency = 48 ± 15%), so they are suitable for various high-value fabric-based applications.
In this study, we have developed an efficient and scalable method for improving the mechanical properties of carbon nanotube (CNT) fibers. The mechanical properties of as-synthesized CNT fibers are primarily limited by their porous structures and the weak bonding between adjacent CNTs. These result in inefficient load transfer, leading to low tensile strength and modulus. In order to overcome these limitations, we have adopted chemical vapor infiltration (CVI) to efficiently fill the internal voids of the CNT fibers with carbon species which are thermally decomposed from gas phase hydrocarbon. Through the optimization of the processing time, temperature, and gas flow velocity, we have confirmed that carbon species formed by the thermal decomposition of acetylene (CH) gas successfully infiltrated into porous CNT fibers and densified them at relatively low temperatures (650-750 °C). As a result, after CVI processing of the as-synthesized CNT fibers under optimum conditions, the tensile strength and modulus increased from 0.6 GPa to 1.7 GPa and from 25 GPa to 127 GPa, respectively. The CVI technique, combined with the direct spinning of CNT fibers, can open up a route to the fast and scalable fabrication of high performance CNT/C composite fibers. In addition, the CVI technique is a platform technology that can be easily adapted into other nano-carbon based yarn-like fibers such as graphene fibers.
This study demonstrates that small amount of oxygen incorporated into carbon nanotubes (CNTs) during the purification process greatly increases their solubility in chlorosulfonic acid (CSA). Using as-purchased and unpurified CNT powders, the optimal purification process is established to significantly increase the solubility of CNTs in CSA, and spin CNT fibers with high mechanical strength (0.84 N tex ) and electrical conductivity (1.4 MS m ) from the CNT liquid crystal dope with high concentration of CNTs in CSA. The knowledge obtained here may guide development of a way to dissolve extremely long CNTs at high concentration and thereby to enable production of CNT fibers with ultimate properties.
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