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 the understanding of: (i) the influence of aromatic oil on the dynamics of the individual phases in S-SBR/BR blends, and (ii) the preference of  the specific oil in either phase.

S-SBR/BR (50/50 and 70/30 wt-ratio) blends with varying concentrations of aromatic oil were studied. Conventional techniques for the determination of T_g (glass transition temperature or α-relaxation process), such as Differential Scanning Calorimetry and Dynamic Mechanical Analysis were of limited use for fulfilling the aim. Therefore, Broadband Dielectric Spectroscopy, 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 BR and S-SBR phases, respectively. The distinct effective T_g’s (T_g^eff) of the S-SBR and BR phases varied with the amount of aromatic oil added. T_g^eff of the BR phase was close to the T_g of virgin BR, whereas T_g^eff of the S-SBR phase was close to the blend average T_g. This is in accordance with the model for phase dynamics of miscible blends by Lodge and McLeish (2000). With this study novel insight into the dynamic heterogeneity of traditional S-SBR/BR blends is obtained.