Green Tire Tread Compounds Based on Silica-reinforced Epoxidized Natural Rubber (ENR): Comparison of the Role of Water in the Cure of ENR, sSBR/BR, NR and BR

As concerns grow regarding climate change and the cost and long-term availability of oil supplies, there is an increasing desire for products such as tires to be manufactured in part or entirely from renewable materials, as well as for the energy consumption and carbon footprint over the life cycle of the tire to be minimized.  This can be achieved in tire treads by using the renewable polymer, epoxidized natural rubber (ENR-25, with 25% epoxidation), reinforced with silica.  In addition to providing lower rolling resistance, and hence reduced fuel consumption, silica-filled ENR tire treads also deliver enhanced wet traction, when compared with treads based on silane-coupled silica-filled synthetic rubbers (solution SBR/BR blends).  The unique interaction of ENR with silica is a crucial factor.

The cure behavior of silica-reinforced ENR-25, NR, cis- BR and solution SBR/BR has been compared with and without added water or ethanol, and in the presence and absence of the sulfur cure system.  The cure behavior of silica-reinforced ENR-25 is radically changed when water is present in the compound.  The torque rise is earlier, faster and much larger, and there is also a significant shoulder before the main cure, with a steep rise in torque from the start of the cure, associated with the development of a silica network.  Similar effects may be seen in the cure behavior of the other rubbers, but their extent and the role of water of varies.  These differences are thought to reflect the differences in rubber-silica interaction and silica dispersion in ENR, NR, BR and sSBR/BR.