Synergistic Dual-Polymer-Assisted Assembly of Ultralow-Aspect-Ratio MWCNTs into Continuous Fibers for Viscoelastic Interfacial Densification

Effectively transferring the excellent properties of carbon nanotubes (CNTs) at the microscopic scale to one-dimensional macroscopic materials has always been a cross-scale assembly challenge that researchers urgently need to address. In this paper, we present a synergistic dual-polymer-assisted acid spinning and viscoelastic interfacial densification technique, successfully assembling commercially available large-diameter, short-length, low aspect ratio, but easily mass-produced and cost-effective multiwalled carbon nanotubes (MWCNTs) into macroscopic functional fibers with continuous stacking structures, substantial mechanical strength, and good electrical conductivity. These "low-quality" MWCNTs, when processed into fibers using conventional nanomaterial assembly techniques, typically produce samples that are fragile and prone to breakage, with mechanical properties even failing to meet the minimum strength requirements for careful manual collection. We achieved breakthroughs through the following multiple synergistic actions: (1) utilizing the acid-soluble aromatic polyamide polymer Kevlar to assist in the uniform dispersion of MWCNTs in concentrated sulfuric acid (CSA); (2) using Kevlar as a "welding agent" to enhance the MWCNT stacking structure; (3) introducing the water-soluble polymer poly(vinyl alcohol) (PVA) to slow down the CSA-water exchange rate and reduce fiber surface disturbances; (4) inhibiting the gelation/solidification rate to extend the assembly and orientation time of MWCNTs; and (5) filling the pores left after the removal of CSA and water. Ultimately, we successfully prepared dual-polymer-doped CNT fibers (DP-CNTFs) with continuous mechanical collection strength for subsequent densification treatment. Taking advantage of the thermoplastic properties of PVA, we employed polytetrafluoroethylene as a viscoelastic interfacial layer to perform hot-press densification and defect repair on DP-CNTF, further enhancing its mechanical strength by 147.80% and electrical conductivity by over 770%. This technique not only overcomes the practical application bottleneck of continuously assembling and post-treating low-quality MWCNTs but also demonstrates its superiority in large-scale production and performance enhancement, providing a novel pathway for the industrialization of MWCNTs and their fibers.