Comparative Evaluation of Different Methods of Carboxylation of Carbon Nanotubes as a Modifier of Mechanical Properties of Heat-Resistant Polyimide Based Nanocomposites

This work is a comparative evaluation of process effectiveness of multiwall carbon nanotube carboxylation in a variety of chemically active media: in concentrated and dilute nitric acid, in a mixture of nitric and sulfuric acids, in hydrogen peroxide, and in potassium permanganate. The formation of carboxylic groups on the surface of nanotubes was controlled via IR-spectroscopy, and their concentrations were determined using thermogravimetry (TG). The kinetics of increasing the concentration of carboxylic groups in the process of treating nanotubes by various methods was investigated. Nanocomposite films were prepared as a result of introducing the carboxylated nanotubes into an aromatic polyimide. The relationship between mechanical properties of films and the method of carboxylation and duration of chemical treatment was investigated. Treatment in a mixture of nitric and sulfuric acids leads to the most intense carboxylation of nanotubes. But in this environment, as in hydrogen peroxide, there is a marked degradation of nanoparticle surface. Treatment in potassium permanganate proceeds under milder conditions, does not lead to significant generation of defects on the surface of the nanotubes, but requires an increase in process duration.