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Unlike carbon black, silica is polar and naturally not compatible with nonpolar hydrocarbon elastomers. This lack of interaction or compatibility between the filler and the elastomer typically causes lower properties compared with carbon black–filled compounds. A common approach to deal with this problem is to use silane coupling agents in the system to link the silica and the polymer chains via covalent bonds. An alternative is the introduction of polar functional groups or chemically reactive groups into the elastomer chains, which can improve the compatibility of elastomers with fillers such as silica. In this article, the effect of three functionalized SBRs, one backbone modified with carboxylate moieties, one modified with dithiol groups, and one partially Si-coupled, on the dynamic and mechanical properties of a silica-reinforced tire tread compound will be discussed and compared with a reference compound that contains unmodified s-SBR as the main polymer. The results show the significant potential of two of these modified SBRs to reduce the rolling resistance of tire treads made thereof, while no major change in wet grip occurs. Zinc oxide is known as the best activator for sulfur vulcanization. Zn ions combine with accelerators to form an active complex that catalyzes the vulcanization process. However, in silica-filled compounds, ZnO may interfere with the silanization process because of its alkaline nature, and it may compete with the silanes in reacting with the acidic –OH groups on the surface of silica particles. When functionalized SBRs with higher polarity are used in silica compounds, ZnO may interact with these moieties as well. To investigate the effect of ZnO on the properties of the silica-reinforced tread compound, a series of compounds have been prepared, in which the addition of ZnO in a later stage was compared with conventional mixing. The dynamic and mechanical properties of the final compounds are discussed.

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One of the important aspects in the development of new tire compounds is the correlation between the dynamic mechanical properties of the rubber, measured on a laboratory scale, and the actual tire performance. The measuring protocol for dynamic mechanical properties with high precision and good correlation with tire properties is therefore of main concern. To predict wet traction, the viscoelastic behavior of the rubber materials at high frequencies (in the MHz range) need to be known. Viscoelastic master curves derived from time-temperature superposition can be used to describe the properties of the materials over a wide frequency range. The construction of master curves for tread compounds filled with different amounts of silica is discussed. From the vertical shifts as a function of temperature, activation energies are derived that apparently are in the linear response region by fulfilling the Kramers-Kronig relations, and their values correspond to physical phenomena as the underlying principle. Strain sweep viscoelastic measurements, per definition outside the linear region, lead to much higher activation energies. Because the deformation strains employed for these strain sweep measurements are more realistic for wet traction or skidding phenomena, it is concluded that the value of the above measurements in the linear region to predict traction is only limited or a first but still important indication.

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