Fig 1

The development history of high-performance fibers."

Fig 2

Wet spinning of CNT fibers. (a) Wet spinning of CNT/PVA composite fiber 12; (b) wet spinning by CNT-fuming sulfuric acid solution 24; (c) wet spinning by CNT-chlorosulfonic acid liquid crystal dope 25."

Fig 3

Dry spinning of CNT fibers from CNT forests. (a) The first report of "dry-drawing" approach 13; (b) introducing twist during dry-spinning from CNT forests 32; (c) CNT fibers obtained by dry spinning from ultralong CNT forests 33, 34."

Fig 4

Floating catalyst CVD direct spinning of CNT fibers. (a) Schematic diagram of the synthesis and spinning set-up, (b) a photograph showing a layered CNT sock formed in the gas flow, (c–e) photographs taken at typical stages of the spinning process 41."

Fig 5

The typical works of CNT fibers by FCCVD direct spinning process. (a) The first report of CNT fiber by FCCVD 45; (b) the first report of continuous spinning of CNT fibers by FCCVD 14; (c) small batch spinning of CNT fibers by FCCVD 41; (d) high strength CNT film (9.6 GPa) by FCCVD 16."

Fig 6

Simplified models of the assembly structure of CNT fibers and their tensile fracture 55."

Fig 7

Effects of the CNT structure on the mechanical performance of CNT fibers. (a) Effect of catalyst content on the wall number of CNT and the strength of fiber 67; (b) HRTEM image of a CNT bundle with collapsed double-wall CNTs greater than 5 nm 69; (c) tensile strength versus aspect ratio for CNT fibers by wet spinning 72; (d) specific strength distribution of CNT fibers for different gauge lengths 63."

Fig 8

Mechanical enhancement of CNT fibers by stretching treatment. (a) Schematic of multi-step stretching of CNT/BMI composite fiber, (b) typical stress-strain curves for CNT/BMI composite fibers prepared by different stretching methods 86; (c) schematic representation of fast stretching and densification processes of CNT fibers using chlorosulfonic acid, (d) stress-strain curves of stretched CNT fibers 89."

Fig 9

Mechanical enhancement of CNT fibers by densification treatment. (a) A schematic of the system for rolling CNT fiber, (b) SEM image of the CNT fiber after rolling 47; (c) schematic of the diamond wire drawing dies used to align and densify CNT fibers, (d, e) microphotographs of CNT fibers after being pulled through diamond dies 98."

Fig 10

Mechanical enhancement of CNT fibers by promoting inter-tube interaction. (a) Setup for applying incandescent tension annealing process to CNT fibers and the cross-section SEM images before and after treatment, (b) comparison of specific strength and specific modulus of CNT fibers after incandescent annealing under different applied stresses 107; (c) a schematic illustration of the reinforcement of the CNT fibers by mussel-mimetic, catechol-containing adhesives, (d) SEM image of treated CNT fiber 115; (e) schematic and TEM images of a CNT fiber, (f) a PDA-CNT fiber and (g) a py-PDA-CNT fiber 116."

Table 1

Summary of the efficient enhancement methods for mechanical property of CNTFs."

Fig 11

A simplified model of carrier transport in CNT fibers 140."

Fig 12

Electrical conductivity enhancement of CNT fibers by inter-tube conductive material filling. (a) Schematic depict for synthesis of PIS-cross linked CNT fiber by aryl radical coupling reaction 158; (b) schematic diagram of continuously produced hybrid CNT/graphene yarn 159; (c) schematic illustrations of the preparation process of the Py-PDA/CNT/C composite fiber 160."

Fig 13

Electrical conductivity enhancement of CNT fibers by doping. (a) Elemental mapping of iodine for I2 doped CNT fiber, (b) comparison in specific conductivity among raw, doped CNT fibers and several metals 170; (c) schematic illustration for the fabrication of highly conductive and macroscopic CNT sheets, including mechanical stretching, chemical doping, and dip-coating processes 149."

Fig 14

Electrical conductivity enhancement of CNT fibers by compositing with metal. (a) Schematic representation of various steps for CNT-Cu composite fabrication, (b) variation of resistivity with current density for CNT-Cu composite, (c) comparison of specific conductivity of CNT-Cu with different metals 184; (d–f) morphologies and Cu element mapping of CNT/Al-Cu composite fibers 112."

Table 2

Summary of the efficient enhancement methods for conductivity of CNTFs."