Effect of Aromatic Oil on Phase Dynamics of S-SBR/BR Blends for Passenger Car Tire Treads

Even though S-SBR/BR blends are commonly used for passenger car tire treads, little is known about the phase dynamics arising from the local morphological heterogeneities. The present study aims at developing the understanding of: (i) the influence of aromatic oil on the dynamics of the individual phases in S-SBR/BR (50/50) blend, and (ii) the partition of the aromatic oil in either phase. S-SBR/BR (50/50) blends with varying concentrations of aromatic oil (0/10/20 phr) were studied. Conventional techniques for the determination of Tg (glass transition temperature or α-relaxation process), such as Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA) were of limited use for fulfilling the goal of the present study. Therefore, Broadband Dielectric Spectroscopy (BDS), a more sensitive technique to study the α-relaxation process was employed. It was possible to de-convolute the dielectric loss (ε") peak of the vulcanized blends into two super-positioned relaxation processes, α' and α (in increasing order of frequency), which were attributed to the S-SBR and BR phases, respectively. The distinct effective Tg’s (Tgeff) of the S-SBR and BR phases varied with the amount of aromatic oil added. Tgeff of the BR phase was close to the Tg of virgin BR, whereas Tgeff of the S-SBR phase was close to the blend average Tg. This is in accordance with the model for phase dynamics of miscible blends by Lodge and McLeish (2000). With this a deeper insight into the dynamic heterogeneity of traditional S-SBR/BR (50/50) blends is obtained.