Controlled oxidation of MWCNTs at low temperature

Carbon nanotubes (CNTs) are an allotropic form of carbon, extremely interesting for their electrical and mechanical properties[1]. Used as reinforcement in different matrices, CNTs present many problems due to their agglomeration and non-wetting surface, that can be solved by chemical functionalization[2]. In particular, when dispersion in common solvents or matrices is considered, it is necessary to have polar functional groups on the surface. Since oxygen-containing groups are easy to graft on the CNTs surface, oxidation seems to be the best way to guarantee improved surface polarity. Oxidation through acid attack has been extensively studied in literature[3], since this changes the CNTs hydrophilicity and improves their dispersion in various solvents. However, the use of acids creates numerous drawbacks such as a heavy damaging of the CNTs structure due to the aggressive environment present during the oxidation reaction. This work originates from the need to find an oxidation method able to preserve the nanotubes structure while functionalizing the surface, in order to be able to disperse them in solvents or matrices but keeping the whole advantage given from the properties of the single CNTs. The idea was to perform a very simple oxidation of carbon nanotubes (CNTs) by thermal treatment at a specific temperature in controlled atmosphere. The conditions were chosen through a thermal gravimetric analysis (TGA) screening in a low oxygen (1-5%) atmosphere. The very initial phase of the thermal degradation starts between 350 C and 450 C, hence, the thermal degradation of CNTs was tested at lower temperatures with an isothermal treatment. By choosing the right temperature, time and amount of oxygen, it was possible to perform a precise and non-destructive oxidation of the CNTs, as demonstrated by several characterization techniques. This process enable the production of oxidized CNTs, which can be easily dispersed in aqueous solutions, without damaging the structure of the nanotubes.