High strength carbon nanotube fibers

Carbon nanotube (CNT) fibers have attracted significant attention as next-generation lightweight structural materials owing to their excellent mass-specific mechanical properties and multifunctional potential. However, the exceptional intrinsic strength of individual CNTs is not readily translated into macroscopic fibers, because their mechanical performance is strongly governed by hierarchical internal structures such as CNT alignment, packing density, bundle connectivity, inter-tube contact, and defect distribution. Therefore, understanding the relationship between internal fiber structure and tensile properties is essential for developing high-strength CNT fibers.

In this study, CNT fibers were continuously fabricated using a floating catalyst chemical vapor deposition process. The synthesis conditions were controlled to regulate the formation and assembly of CNT networks during fiber spinning. By adjusting the carbon source supply, catalyst composition, and reaction environment, the morphology, continuity, and axial orientation of the as-spun fibers were tailored. These synthesis-driven structural features were then used to investigate how the initial fiber architecture affects the efficiency of subsequent post-treatment processes.

In CNT fibers, load transfer between neighboring CNTs and CNT bundles is mainly governed by weak van der Waals interactions, which limits the utilization of the intrinsic strength of CNTs at the macroscopic scale. To overcome this limitation, post-treatment strategies introducing additional interfacial interactions, such as polymer-mediated bonding and covalent crosslinking, were explored to reinforce inter-tube and inter-bundle junctions. However, the strengthening effect of these treatments depends strongly on the pre-existing internal structure of the fiber. Factors such as packing density, pore distribution, bundle size, and CNT alignment determine the accessibility of polymers or reactive species into the fiber interior and their ability to form effective load-transfer pathways.

Thus, this study emphasizes that post-treatment should be designed based on the internal structural characteristics of CNT fibers rather than applied as a universal strengthening method. By correlating structural analysis with tensile testing, the influence of fiber architecture on interfacial reinforcement and mechanical enhancement was systematically examined. This structure-guided approach provides insight into the design of lightweight, high-strength CNT fibers for advanced structural and multifunctional applications.