Study of two types of styrene butadiene rubber in tire tread compounds

The ratio of vinyl butadiene and styrene groups in styrene butadiene rubber (SBR) structures is a crucial factor that affects the inherent rubber characteristics such as glass transition temperature, Tg, hysteresis, strength, etc. In this paper, two types of SBR (Krynol 1721 and Buna VSL 5025-1) which contain higher ratios of these two groups, were blended with natural rubber (SMR 5) and compared with a blend of general purpose SBR (Krynol 1712) and SMR 5. The results show that the blends with the two rubbers possess a markedly lower resilience (i.e. higher hysteresis) than that of the general purpose SBR. Besides resilience, other properties of the compounds, Mooney viscosity, scorch time, cure time, tensile strength, tear strength, and ageing resistance were also investigated. At a similar blending ratio of 50:50, blends with Krynol 1721 and Buna VSL 5025-1 show markedly lower rebound resilience while other mechanical properties are considered acceptable. This preliminary investigation indicates that the two rubbers are suitable for wet grip improvement. Subsequently, the ratio of Krynol 1721 and Buna VSL 5025-1 in the blends was varied from 30 to 70 phr. As the ratio of the rubbers is increased, a reduction in rebound resilience is also observed and the effect of Buna VSL 5025-1 is more pronounced than Krynol 1721. The result is consistent with the higher Tg of the former. Mooney viscosity, scorch time, cure time and ageing index (based on tensile strength) are increased but there is a slight drop in tensile strength and tear strength.