In 2006, I made about 156 predictions. One of the predictions was that carbon nanotube fiber would be inexpensive and with over 50GPa tensile strength around 2014-2018.
Relative to 2006, there is inexpensive carbon nanotubes. Macroscopic carbon nanotube bundles were created in 2018 at Tsinghua university in China and they have 80 Gigapascals of tensile strength.
The work was done at Tsinghua University and other facilities in Beijing. Researchers were Yunxiang Bai, Rufan Zhang, Xuan Ye, Zhenxing Zhu, Huanhuan Xie, Boyuan Shen, Dali Cai, Bofei Liu, Chenxi Zhang, Zhao Jia, Shenli Zhang, Xide Li & Fei Wei.
A synchronous tightening and relaxing (STR) strategy further improves the alignment of the carbon nanotubes to increase the strength.
Superstrong fibers are in great demand in many high-end fields such as sports equipment, ballistic armour, aeronautics, astronautics and even space elevators. In 2005, the US National Aeronautics and Space Administration (NASA) launched a ‘Strong Tether Challenge’, aiming to find a tether with a specific strength up to 7.5GPa cm3 per gram for the dream of making space elevators. Unfortunately, there is still no winner for this challenge. The specific strength of existing fibres such as steel wire ropes (about 0.05–0.33 GPa cm3 per gram), carbon fibres (about 0.5–3.5GPa cm3 per gram) and polymer fibers (about 0.28–4.14GPa cm3 per gram) is far lower than 7.5GPa cm3 per gram). Carbon nanotubes, with inherent tensile strength higher than 100GPa and Young’s modulus over 1TPa, are considered one of the strongest known materials.
Generally, there are three types of CNT:
vertically aligned CNT (VACNT) arrays
ultralong horizontally aligned CNT (HACNT) arrays (‘ultralong CNTs’ for short).
Almost all the reported CNT fibers are fabricated using agglomerated CNTs or VACNT arrays with lengths less than a few hundred micrometres and with plenty of structural defects and impurities, giving those CNT fibers a tensile strength ranging from about 0.5 to 8.8GPa which is much lower than that of single CNTs.
Ultralong CNTs should have great advantages in fabricating fibers because of their macroscale lengths (ranging from centimeters to decimeters), neat surface, perfect structures and super-parallel alignments. But because the production of ultralong CNTs is extremely low, there have been no reports of fibers fabricated using ultralong CNTs, so the question of whether ultralong CNTBs possess equivalent strength to single CNTs has remained open.