Controlled functionalization of sp2 carbon allotropes for the reinforcement of diene elastomers

To achieve important mechanical properties, natural and synthetic rubbers need reinforcing fillers. sp2 carbon allotropes are indeed relevant reinforcing fillers for rubber compounds. Carbon black has been used for over a century and nanofillers such as graphene, graphene related materials and carbon nanotubes are dramatically increasing their importance. Ultimate distribution and dispersion of the carbon fillers in the rubber compounds has to be obtained. To achieve this goal, carbon allotropes should be used as such or should they be functionalized? In this work, controlled functionalization of sp2 carbon allotropes was performed. In particular, the aim was to introduce, on carbon allotropes, oxygenated functional groups, without altering the graphitic structure of the substrate. Methods developed are presented. They were based on reaction of carbon materials with hydrogen peroxide, potassium hydroxide and a derivative of 2-amino-1,3- propandiol, better known as serinol. All the reactions were inspired to the basic principle of sustainable chemistry, with the aim to avoid the use of solvents and catalysts. Research performed with the serinol derivative is in particular discussed. The Paal-Knorr reaction of serinol with 2,5-hexanedione was performed, obtaining 2- (2,5-dimethyl-1H-pyrrol-1-yl)-1,3-propanediol, named as serinolpyrrole (SP). The aromatic ring in SP was exploited to form stable adducts with the carbon allotropes. Hypothesis on the mechanism for the adduct formation is presented. Rubber compounds, based either only on carbon black or on carbon black and silica as the filler systems, were prepared and sulphur-based crosslinking behavior and dynamic-mechanical properties were investigated.