Simultaneous improvements in conversion and properties of molecularly controlled CNT fibres

TL;DR

This study demonstrates a scalable method to produce CNT fibres with simultaneously high conversion rates and enhanced mechanical and electrical properties by optimizing synthesis conditions and molecular composition.

Contribution

It introduces a parametric approach to improve both conversion and properties of CNT fibres during direct spinning from FCCVD, surpassing previous limitations.

Findings

Tensile strength of 2.1 N/tex achieved

Electrical conductivity increased to 3 x 10^5 S/m

High-temperature synthesis with toluene and optimized S/C ratio enhances properties

Abstract

Fibres of ultralong and aligned carbon nanotubes (CNT) have axial properties above reference engineering materials, proving to be exceptional materials for application in structural composites, energy storage and other devices. For CNT fibres produced by direct spinning from floating catalyst chemical vapor deposition (FCCVD), a scaled-up method, the challenge is to simultaneously achieve high process conversion and high-performance properties. This work presents a parametric study of the CNT fibre spinning process by establishing the relation between synthesis conditions, molecular composition (i.e. CNT type), fibre mechanical and electrical properties, and conversion. It demonstrates tensile properties (strength 2.1 N/tex, modulus 107 N/tex) above some carbon fibres, combined with carbon conversion about 5%, significantly above literature on similar materials. The combined improvement in conversion and properties is obtained by conducing the reaction at high temperature (1300 {\deg}C), using toluene as a carbon source, and through adjustment of the promotor to carbon ratio (S/C) to favor formation of few-layer, collapsed CNTs that maximize packing at relatively high conversions. Lower S/C ratios produce low-defect single-wall CNT, but weaker fibres. An increase in electrical conductivity to 3 x 10^5 S/m is also observed, with the data suggesting a correlation with longitudinal modulus.