Design and Characterization of Functionalized S-SBR for Eco-tires with Low Rolling Resistance and High Wear Resistance

Rolling resistance of tires has attracted much attention in the eco-tire industry because of its strong relation to fuel efficiency. The key technology to reduce the rolling resistance of tires is to improve dispersion of fillers, e.g. silica, in tread compounds. In this regards, several solution-styrene butadiene rubbers (S-SBR) with functional moiety at chain end have been developed to achieve improvement of the interaction with silica fillers. Recent market trends also suggest a need for high wear resistance even in eco-tire treads. To improve these properties, there is a growing requirement to further modify S-SBR.

Asahi-Kasei’s S-SBR provides significant improvement of rolling resistance as well as wear resistance of tire tread compounds due to its unique functionalization and high molecular weight technologies. To improve rolling resistance, our recent development of S-SBR for eco-tire tread compounds focuses on the functionalization of both chain ends. The technology of introducing functional moieties which have good interaction with silica into both chain ends of the S-SBR enables very low hysteresis loss due to improvement of silica dispersion as well as fixing free chain ends on the surface of silica in the compound. The fixation of free chain ends reduces energy loss because it prevents the chain to move during tire rolling.

To enhance wear resistance, we have developed a polymerization technology to produce S-SBR with high molecular weight. It is well known that the molecular weight of S-SBR strongly relates to wear resistance because tear strength is enhanced by increasing molecular weight. However, there were major difficulties in the manufacturing process to produce these high molecular weight polymers due to its high viscosity. Asahi Kasei has developed a very high molecular weight S-SBR by introducing branching structure in the polymer chain which enables to decrease the polymer viscosity without sacrificing processability.

We will present our S-SBR grades and development strategy, the latest generation of functionalization technology, and the mechanism of such performance improvements.