The role of material composition in the construction of viscoelastic master curves: silica-filler networks effects

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 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. In order 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. In this paper, 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 which apparently are in the linear response region by fulfilling the Kramers-Kronig relations, and their values correspond to physical phenomenon 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.