Advancing Direct-Spun Carbon Nanotube Textiles, From Field Alignment to Innovative Applications

Abstract

The physical properties of carbon nanotubes (CNTs) are extraordinary and surpass most state-of-the-art bulk materials. However, three decades since their discovery, CNT technology commercially thrives as additives to plastics, paints, or battery electrodes rather than standalone macroscopic products. The main reason for this shortcoming is the inability to transfer the CNTs' superb nanoscale properties into macroscopic materials. To realize the CNTs' full potential so this material can be widely adopted, efficient and inexpensive methods must be developed to narrow the gap between nanoscale and bulk properties. Novel applications must also be developed to harness current CNT textiles' multifunctional capabilities rather than striving for the superiority of an individual physical property. CNT alignment within a textile has been proven to be a critical contributor to narrow the nano to the macro gap. To facilitate this need, a setup was designed to apply an AC electric field to continuously align the CNTs in situ during the CNT bundling phase in a floating catalyst CVD reactor. The resulting bulk CNT textiles demonstrated an increase in the specific electrical and tensile properties (up to 90 and 460%, respectively) without modifying the quantity or quality of the CNTs, as verified by thermogravimetric analysis and Raman spectroscopy, respectively. The enhanced properties were correlated to the degree of CNT alignment within the textile as quantified by small-angle X-ray scattering and scanning electron microscopy image analysis. The first application that was developed taking advantage of the direct-spun CNT textile's multifunctionality involved the design and production of active air filters using ultra-thin carbon nanotube electrically conductive membranes, mechanically supported by a porous polyester backing. Filtration efficiencies were measured up to 99.999%, while ultra-thin materials with low areal density (0.1 g m-2) exhibited pressure drops comparable to commercial High-Efficiency Particulate Air (HEPA) filters. These electrically conductive filters were designed to be actively self-sanitized by thermal flashes via resistive heating to temperatures above 80°C within milliseconds to seconds. The second application involved the development of a high-efficiency standalone electromagnetic interference shielding material (ESM) made of a direct-spun nonwoven CNT mat. The electrically conductive textile (~50×103 S m-1) was post-treated by chemical oxidation or thin copper metallization, increasing the conductivity by ~10 and ~1000 times, respectively, thus increasing its attenuation efficiency. The mats were tested for shielding effectiveness (SE) in an ultra-wide bandwidth of 30 kHz to 70 GHz. Maximal SE of >120 dB was measured for a 30 g m-2 CNTM (<100 μm thickness) at 70 GHz. SE normalized by thickness (SE/t) reached a value of >20,000 dB cm-1 for an HCl oxidized CNT mat. Both attenuation values are the highest values for non-metal-based ESMs. The textiles were also successfully utilized as ESMs integrated into waveguide gaskets or battery enclosures, outperforming their commercial counterparts.