(201b) Carbon Nanotube Length Reduction from Planetary Ball Milling

Carbon nanotubes show great evidence as additives in polymer composites to boost desired mechanical and electrical properties. However, the cost of carbon nanotubes currently limits their viability in industry as more traditional carbon forms like carbon black and carbon fiber yield similar boosted properties with lower costs. One strategy to lower the cost of carbon nanotubes is to increase yield by increasing nanotube length grown on conventional supported catalysts to upwards of 1 mm, eliminating the need to separate carbon nanotube product from catalyst and support material. With this comes the challenge of dealing with very long carbon nanotubes which can cause a variety of processing issues when compounded into a polymer. In this study, both very long and more standard length commercial carbon nanotubes were broken in a planetary ball mill. The length reduction of these carbon nanotubes was quantified using SEM imaging and ImageJ/FIJI image processing software. The Burgio-Rojac model for planetary ball milling was used to correlate the single impact energy and cumulative energy of milling to carbon nanotube length. It was found that the single impact energy varied for each nanotube type, likely due to differences in nanotube diameter. It was also found that the length reduction of the nanotubes for increasing cumulative energies was independent of mass of nanotubes in the mill and initial packed density of the nanotubes. An exponential function that models the length reduction of nanotubes based on the cumulative energy of milling was developed.