A bio-sourced molecule as carbon black coupling agent in rubber compounds with low hysteresis

The prime application of rubber composites is represented by tire compounds. To achieve the desired tire performances an equilibrium between dynamic rigidity and hysteresis must be acquired. Amorphous precipitated silica is the preferred reinforcing filler to have low energy dissipations and thus low fuel consumption. Indeed, silica is characterized by nano dimensions and by the possibility of establishing chemical bonds with rubber chains allowing the achievement of high hysteresis at low temperatures, to promote wet traction, and low hysteresis at medium-high temperatures, for low fuel consumption. Carbon black (CB) is the main filler for tire compounds, but it does not have functional groups able to promote chemical bonds with the rubber matrix, though it would be highly desirable. In this work, a pyrrole compound (PyC) containing a thiol group, and which can be synthesized starting from bio-based building blocks was used to functionalize CB by the socalled “pyrrole methodology”. The thiol group was expected to react with the sulphurbased crosslinking system and/or with rubber chains, thus forming strong bonds with the rubber matrix. Results The synthesis of the PyC and the functionalization reaction were characterized by high atom efficiency. A poly(styrene-co-butadiene) copolymer from anionic solution polymerization was used as the main rubber for the compound preparation. The crosslinked composite material filled with functionalized CB revealed substantial improvements with respect to the composite with pristine CB, in particular: high rigidity and low hysteresis at high temperature. Composite properties were even comparable to those of silica-based rubber composites. The formation of the expected rubber-filler chemical bond via the thiol group of the selected PyC was confirmed studying such functionalizing agent in a squalene-based model compound. The results here reported pave the way to CB-based rubber composites with a low environmental impact.