Facile and sustainable functionalization of carbon black, as filler for rubber composites

Carbon black (CB) is one of the ten most important chemicals in the world and plays a fundamental role in rubber composites, promoting not only the substantial improvement of mechanical properties but also faster vulcanization and electrical conductivity. The research here reported was aimed at the controlled modification of the chemical nature of carbon black, introducing functional groups onto its surface, without altering the bulk structure. A facile functionalization method was developed, using pyrrole compounds (PyC) prepared through the Paal-Knorr reaction of a primary amine with 2,5-hexanedione. The functionalization of carbon black was obtained by make it react with PyC at a temperature of 180°C for 4 hours,avoiding the use of any solvent or catalyst. Stable dispersions of CB-PyC adducts were prepared in solvents with different solubility parameters. Qualitative results of dispersion tests were used to calculate the Hansen spheres for CB-PyC adducts. Rubber composites were prepared with the so-formed CB-PyC adducts. This work paves the way for the facile and sustainable modification of the solubility parameters of sp2 carbon allotropes and for the predictive assessment of their compatibility with different environments.