Functionalized carbon black for elastomeric composites with low dissipation of energy

The most important application of elastomeric composites, tire compounds, relies on the following dynamic-mechanical properties: dynamic rigidity and hysteresis. For car tires, hysteresis is tuned as a function of temperature: high at low temperature and low at medium-high temperature, to promote traction on wet roads and low energy dissipation (rolling resistance), respectively. To obtain these properties, amorphous precipitated silica is used as reinforcing filler. The strengths of silica are: nano dimensions and the possibility of incorporating and establishing chemical bonds with the elastomers’ chains. Carbon black (CB), which is also largely used in tire compounds, does not have functional groups able to promote chemical bonds with the rubber matrix. It would be highly desirable to functionalize the surface of carbon black with such functional groups: a CB with a cradle to gate LCA comparable if not even better than silica’s LCA could be used in replacement of silica in tire compounds. In this work, a pyrrole compound (PyC) was used for functionalizing CB by applying the so-called “pyrrole methodology”. The selected PyC contained a thiol group which was expected to react with the sulphur-based crosslinking system, thus forming chemical bonds with the rubber chains. 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. These findings seem to confirm the formation of the expected rubber-filler chemical bond and are even comparable to those of silicabased rubber composites. The results here reported pave the way to CB-based rubber composites with a low environmental impact.