Improved alignment and stress transfer in CNT fibre fabrics studied by in situ X-ray and Raman during wet-drawing

Abstract

Translating the superlative mechanical properties of nanocarbons to the scale of structural components requires assembling them into highly aligned networks with uniform internal stress transfer. Continuous, non-woven fabrics are produced by winding multiple filaments of carbon nanotube fibres (CNTF) directly spun from the gas phase. The CNTF fabrics are drawn by stretching in regular solvents, which increases specific tensile strength to 1.2 GPa/SG and modulus to 44 GPa/SG, reaching ∼70% the strength and ∼50% modulus of the single filament. Tensile measurements of misaligned CNTF fabrics soaked in solvents show an increased strain-to-break, a large drop in tensile force, and shear-induced local deformation, analogous to a polymer wet-drawing process. In-situ small-angle X-ray scattering during wet-drawing shows a progressive and transient increase in porosity, attributed to the separation of adjacent bundles “wedged” by the ingress of solvent when the fabric is under load. Wet-drawing increases degree of alignment, reaching Herman's orientation parameter values <P2> = 0.54 and a narrower distribution of local alignment. Maps of the downshift of 2D Raman band during tensile deformation confirm a more homogeneous spatial distribution of local moduli after wet-drawing CNTF fabrics, evidencing more cooperative loading and stress transfer. Tensile mechanical properties of fabrics aligned after wet-drawing can be successfully described by the uniform stress transfer model.