  Although individual carbon nanotubes (CNTs) are superior as constituents to
polymer chains, the mechanical and thermal properties of CNT fibers (CNTFs)
remain inferior to commercial synthetic fibers due to the lack of synthesis
methods to embed CNTs effectively in superstructures. The application of
conventional techniques for mechanical enhancement resulted in a mild
improvement of target properties while achieving parity at best on others. In
this work, a Double-Drawing technique is developed to deform continuously grown
CNTFs and rearrange the constituent CNTs in both mesoscale and nanoscale
morphology. Consequently, the mechanical and thermal properties of the
resulting CNTFs can be jointly improved, and simultaneously reach their highest
performances with specific strength (tenacity) $\rm\sim3.30\,N\,tex^{-1}$, work
of rupture $\rm\sim70\,J\,g^{-1}$, and thermal conductivity
$\rm\sim354\,W\,m^{-1}\,K^{-1}$, despite starting from commercial
low-crystallinity materials ($I{\rm_G}:I{\rm_D}\sim5$). The processed CNTFs are
more versatile than comparable carbon fiber, Zylon, Dyneema, and Kevlar.
Furthermore, based on evidence of load transfer efficiency on individual CNTs
measured with In-Situ Stretching Raman, we find the main contributors to
property enhancements are (1) the increased proportion of load-bearing CNT
bundles and (2) the extension of effective length of tubes attached on these
bundles.
