Fibers and yarns based on carbon nanotubes (CNT) are emerging as a possible improvement over more traditional high strength carbon fibers used as reinforcement elements in composite materials. This is driven by a desire to translate the exceptional mechanical properties of individual CNT shells to achieve high performance macroscopic fibers and yarns. One of the central limitations in this approach is the weak shear interactions between adjacent CNT shells and tubes within macroscopic fibers and yarns. Furthermore, the multiple levels of interaction, e.g., between tubes within a multi-walled CNT or between bundles within a fiber, compound the problem. One promising direction to overcome this limitation is the introduction of strong and stiff cross-linking bonds between adjacent carbon shells. A great deal of research has been devoted to studying such cross-linking by the irradiation of CNT based materials using either high energy particles, such as electrons, to directly covalently cross-link CNTs, or electromagnetic irradiation, such as gamma rays to strengthen polymer cross-links between CNT shells and tubes. Here we review recent progress in the field of irradiation-induced cross-linking at multiple levels in CNT based fibers with a focus on mechanical property improvements.
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