Carbon nanotube fibers (CNTFs) offer exceptional intrinsic properties but are often limited by assembly defects and inefficient intertube load transfer. Here, we report a wet-spinning strategy enabled by poly(p-phenylene-2,6-benzobisoxazole) nanofibers and chains (PBOs)-reinforced intertube interactions to fabricate mechanically robust PBO/carbon nanotube (CNT) composite fibers (PCNTFs). By optimizing the PBOs content, highly aligned and densely packed CNT networks are formed and stabilized by a hydrogen-bonding interfacial architecture. Comprehensive structural characterization reveals maximized nanotube orientation, minimized void volume, and strengthened interfacial interactions at the optimal composition. As a result, the PCNTFs achieve a high tensile strength of 3.52 GPa, a Young’s modulus of 306 GPa, and a toughness of 71.5 MJ/m³, representing a 2.7-fold enhancement in toughness compared with pristine CNTFs. In situ Raman spectroscopy, stress–relaxation analysis, and fracture morphology observations further confirm the critical role of hydrogen-bonding-mediated interfacial interactions in governing efficient stress transfer and energy dissipation. Moreover, the optimized fibers exhibit a high specific penetration energy of 1.39 MJ/kg under high-speed impact, exceeding that of conventional impact-resistant fibers. This work establishes a scalable interfacial design strategy for CNT-based fibers with simultaneously high strength and toughness and provides a feasible pathway toward next-generation fibers for structural and multifunctional applications.

Floating catalysis chemical vapor deposition (FCCVD) direct spinning process is an attractive method for fabrication of carbon nanotube fibers (CNTFs). However, the intrinsic structural defects, such as entanglement of the constituent carbon nanotubes (CNTs) and inter-tube gaps within the FCCVD CNTFs, hinder the enhancement of mechanical/electrical properties and the realization of practical applications of CNTFs. Therefore, achieving a comprehensive reassembly of CNTFs with both high alignment and dense packing is particularly crucial. Herein, an efficient reinforcing strategy for FCCVD CNTFs was developed, involving chlorosulfonic acid-assisted wet stretching for CNT realigning and mechanical rolling for densification. To reveal the intrinsic relationship between the microstructure and the mechanical/electrical properties of CNTFs, the microstructure evolution of the CNTFs was characterized by cross-sectional scanning electron microscopy (SEM), wide angle X-ray scattering (WAXS), polarized Raman spectroscopy and Brunauer–Emmett–Teller (BET) analysis. The results demonstrate that this strategy can improve the CNT alignment and eliminate the inter-tube voids in the CNTFs, which will lead to the decrease of mean distance between CNTs and increase of inter-tube contact area, resulting in the enhanced inter-tube van der Waals interactions. These microstructural evolutions are beneficial to the load transfer and electron transport between CNTs, and are the main cause of the significant enhancement of mechanical and electrical properties of the CNTFs. Specifically, the tensile strength, elastic modulus and electrical conductivity of the high-performance CNTFs are 7.67 GPa, 230 GPa and 4.36 × 10⁶ S/m, respectively. It paves the way for further applications of CNTFs in high-end functional composites.