Increased Tensile Strength of Carbon Nanotube Yarns and Sheets through Chemical Modification and Electron Beam Irradiation

Abstract

The inherent strength of individual carbon nanotubes (CNTs) offers considerable opportunity for the development of advanced, lightweight composite structures. Recent work in the fabrication and application of CNT forms such as yarns and sheets has addressed early nanocomposite limitations with respect to nanotube dispersion and loading and has pushed the technology toward structural composite applications. However, the high tensile strength of an individual CNT has not directly translated into that of sheets and yarns, where the bulk material strength is limited by intertube electrostatic attractions and slippage. The focus of this work was to assess postprocessing of CNT sheets and yarns to improve the macro-scale strength of these material forms. Both small-molecule functionalization and electron-beam irradiation were evaluated as means to enhance the tensile strength and Young's modulus of the bulk CNT materials. Mechanical testing revealed a 57% increase in tensile strength of CNT sheets upon functionalization compared with unfunctionalized sheets, while an additional 48% increase in tensile strength was observed when functionalized sheets were irradiated. Similarly, small-molecule functionalization increased tensile strength of yarn by up to 25%, whereas irradiation of the functionalized yarns pushed the tensile strength to 88% beyond that of the baseline yarn.

Aligned carbon nanotube–epoxy composites: the effect of nanotube organization on strength, stiffness, and toughness

“…However, at the same time, an approach to enhance their packing density may have sense, as it was shown above that even the simple densification by acetone spraying may increase the tensile strength and stiffness of the as-spun materials. Some reported treatments, such as UV [39] or electron-beam irradiation [40], twisting, and infiltration with polymeric compounds [41][42][43][44] appear to affect lateral interactions between nanotube bundles, as well as molecular level couplings between nanotubes and polymer chains [43], thus amplifying the mechanical performance of CNT fibres or yarns [44] (supplementary materials, S10). Remembering the hierarchical structure of the CNT fibres, upon polymer infiltration, a fibre itself can be regarded as a nanostructural composite [13,43] with 50-70 % of a fibre occluded with a polymer depending on the fibre's internal porosity.…”

Single-step process to improve the mechanical properties of carbon nanotube yarn

“…Covalent bonding among the tubes can be obtained via simultaneous functionalization and crosslinking [19]. Possible strategies for enhancing the friction between CNTs include modifying CNT surfaces through physical processes (e.g., condensing the tubes under high pressure) [16], chemical processes [20–22], chemical treatment followed by irradiation [23] and radiation processes only [24–26]. …”

Mechanical Strength Improvements of Carbon Nanotube Threads through Epoxy Cross-Linking

“…Covalent bond formation between CNTs is an approach that have potential to increase the mechanical strength of the assembly [22,23], as well as improve other physical properties [24]. Multiple cross-linking chemistries have been attempted but few of them have been focused on the mechanical strength improvements [22,23,25,26,27]; therefore, the search for an ideal reaction that will crosslink CNTs within the fiber continues. Here, we report a six-fold increase of the mechanical strength of the CNT threads after covalent cross-linking.…”