Silica-Reinforced Epoxidised Natural Rubber Tire Treads – Performance and Durability

Concerns regarding climate change and public health have compelled governments to reduce the environmental impact of transport.  Many countries are introducing tire labeling and legislation targeting rolling resistance, wet grip and noise.  The proposed US tire label also includes wear performance.  Implementation of tire labeling is enabling buyers to choose better tires.  The tire industry is responding to these demands and is developing the next generation of green tires.  Current passenger tire tread technology is primarily petroleum-based; however, the long-term availability of fossil-fuel supplies is limited.  Thus a further step to minimize the environmental impact and carbon footprint of tires over their life cycle is to use sustainable materials not derived from fossil-fuels.  Sumitomo Rubber Industries used epoxidized natural rubber (ENR) reinforced with silica in their route to a greener fossil-fuel free tire (the ENASAVE 100).  At 25 mol% epoxidation ENR has a glass transition temperature (T_g) most suitable for tread applications.  Silica-filled ENR-25 tread compounds deliver lower rolling resistance, hence reduced fuel consumption, and enhanced wet and ice traction compared to benchmark premium passenger or truck treads.  Optimization of wear performance to extend product durability is a current focus of research.  However, correlation between laboratory abrasion and on-the-road tire wear is notoriously poor.  TARRC have used light microscopy and TEM to ascertain a mechanistic insight into tread wear, using results from wear studies on-the-road and laboratory abrasion.