Improving macroscopic physical and mechanical properties of thick layers of aligned multiwall carbon nanotubes by annealing treatment

In this work we present a systematic study of the effects of high temperature treatments on the macroscopic physical and mechanical properties of millimeters thick layers of self-standing vertically aligned multi wall carbon nanotubes (MWCNTs). Annealing treatments were carried out on pristine MWCNT chunks in argon gas, in the temperature range of 1500-2200 °C. The analysis showed a change in most of the physical properties as an effect of the graphitization process. Raman results showed a monotonic increase in the crystallite size as the annealing temperature increases due to the lattice defect removal kinetic. Improvement in thermal stability exhibited by thermo-gravimetric analysis in oxidative environment witness a significant reduction in defectiveness. X-ray diffraction confirmed a higher degree of ordering after the annealing process and indicated no significant re-arrangement of the interlayer spacing between the graphene shells. Loading tests showed, beside a negligible change of maximum load, an increase in elastic modulus proportional to the annealing temperature