Microdispersion of silica in tire tread compounds based on epoxidized natural rubber

There is an increasing desire for products to be manufactured in part or entirely from renewable materials and for the energy consumption over the life cycle of products to be minimized.  In the case of tire treads, silica-reinforced epoxidized natural rubber (ENR-25, with 25% epoxidation) can meet this challenge, as it uses a renewable polymer, providing low rolling resistance, as well as enhanced wet grip.

A new technique has been developed to evaluate silica microdispersion in tire tread vulcanizates.  The vulcanizates were swollen in styrene, the styrene polymerized and ultrathin sections examined by transmission electron microscopy (TEM).  Image analysis of the micrographs provides a distribution of silica particle sizes, varying in cross-sectional area from about 200 nm² up to about 40,000 nm².  The dispersed silica aggregate size distributions in silica-filled ENR-25 vulcanizates were compared with the distributions in silica-filled solution SBR/BR tread vulcanizates, with and without silane included.  The silica microdispersion in the ENR-silica vulcanizates was found to be better than in the silane-coupled SBR/BR-silica vulcanizate, which in turn was better than in the SBR/BR-silica vulcanizate without silane added.  Indeed, aggregates that appear to be reduced to as few as one to three fundamental silica particles are visible.  The enhanced microdispersion is expected to benefit tire tread properties.