Bio-Based Pyrrole Compounds Containing Sulfur Atoms as Coupling Agents of Carbon Black with Unsaturated Elastomers

In this work, the hysteresis of elastomer composites suitable for tire compounds was reduced by using CB functionalized with pyrrole compounds containing sulfur-based functional groups reactive with the elastomer chains. CB was functionalized with bio-based pyrrole compounds: 2-(2,5-dimethyl-1H-pyrrol-1-yl)ethane-1-thiol (SHP) and 1,2-bis(2-(2,5-dimethyl-1H-pyr-rol-1-yl)ethyl)disulfide (SSP), bearing an -SH and an -SS- functional group, respectively. SHP and SSP were synthesized via a one-pot two-step synthesis, with yields higher than 70%, starting from biosourced chemicals as follows: 2,5-hexanedione from 2,5-dimethylfuran, cysteine and cysteamine. The functionalization of CB was carried out by mixing the CB with PyC and heating, with quantitative yields ranging from 92 to 97%. Thus, the whole functionalization process was characterized by a high carbon efficiency. The formation of the covalent bond between SHP, SSP and CB, in line with the prior art of such a functionalization technology, was proven by means of extraction and TGA analyses. The reactivity of the sulfur-based functional groups with unsaturated polymer chains was demonstrated by using squalene as the model compound. Poly(styrene-co-butadiene) from solution anionic polymerization and poly(1,4-cis-isoprene) from Hevea Brasiliensis were the elastomers employed for the preparation of the composites, which were crosslinked with a sulfur-based system. Pristine CB was partially replaced with CB/SHP (33%) and CB/SSP (33% and 66%). The PyC resulted in better curing efficiency, an increase in the dynamic rigidity of approximately 20% and a reduction in the hysteresis of approximately 10% at 70 degree celsius, as well as similar/better ultimate tensile properties. The best results were achieved with a 66% replacement of CB with CB/SSP. This new family of reactive carbon blacks paves the way for a new generation of 'green tires', reinforced by a CB reactive with the polymer chains, which provides high mechanical properties and low rolling resistance. Such a reactive CB eliminates the use of silica, and thus the ethanol emission resulting from the condensation of silane is used as a coupling agent. In addition, CB-based tires are characterized by a higher mileage, at a moment in which the reduction in tire wear has become a primary concern

Functionalization of graphene related materials with biosourced C-3 and C-6 building blocks. From synthesis to applications

The functionalization of sp2 carbon allotropes is one of the hot research topics in advanced research on materials. Nowadays, carbon nanotubes and graphene related materials are extensively studied due to their exceptional mechanical and electrical properties. They are capable of substantially improving the properties of polymeric materials. Their functionalization is a crucial step, for allowing an even dispersion in the matrix. In this research, the functionalization of graphene related materials was performed with biosourced C-3 and C-6 molecules. They were glycerol and galactaric acid derivatives: pyrrole compounds (PyC) and 2-pyrones. The reactions for their synthesis and for the carbon allotrope functionalization were green and characterized by high atom efficiency, with a yield up to 96%. Indeed, the reactions were carried out in the absence of solvents and catalysts and adducts were obtained by simply mixing, with the help of either thermal or mechanical energy. The developed functionalization methods were successful for: carbon black, carbon nanotubes, few layers graphene. The bulk structure of the carbon substrate was left substantially unaltered: functionalization occurred in peripheral positions, at the edges of the graphene layers. Functional groups of defined chemical structure were covalently bound to the carbon material and stable adducts, up to very high temperature, were formed. Reliable hypotheses for the functionalization mechanisms were elaborated. In Figure 1b the supposed domino reaction based on the pyrrole compound, with the Diels Alder cycloaddition as the last step is represented. Such functionalization technique was developed as a pervasive technology, which allowed to pursue a variety of applications: (i) decoration with metals to obtain catalysts for the selective deuteration of pharmaceutical molecules as well as antibacterial ingredients (ii) rubber compounds for dynamic-mechanical applications (tires) (iii) conductive inks