Super-Strong Carbon Nanotube Fibers Achieved by Engineering Gas Flow and Postsynthesis Treatment

Carbon nanotube fibers (CNTFs) are directly spun from a floating-catalyst chemical vapor deposition apparatus using gas-phase carbon and an iron nanocatalyst. The essential synthesis and post-treatment factors that affect the strength of CNTFs are investigated to obtain CNTFs with greater strength than those of any previously reported high-performance fibers. The key factors optimized included the degree of rotational flow inside the reactor, the ratio of the starting materials, and the postsynthesis treatment conditions. The formation of rotational gas flow inside the reactor was confirmed by computational fluid dynamics simulations, and the feed ratio of the starting materials was optimized through response surface methodology. In addition, a reproducible and highly efficient postsynthesis treatment method was established. Pristine CNTFs with a high specific strength (SS) (average 2.2 N/tex, max. 2.3 N/tex) were synthesized through decreased rotational flow and optimization of the CNTF synthesis conditions. To improve the SS of the CNTFs further, we adopted an acid wet-stretching method that included washing and heat treatment. This drastically increased the SS of the CNTFs (average 5.5 N/tex, max. 6.4 N/tex) because of the decrease in the volume of the pores between the CNT bundles.