Silica-filled tire tread compounds: an investigation into the viscoelastic properties of the rubber compounds and their relation to tire performance

Abstract

With increasing the global concern for fossil fuel consumption, automotive industry moves toward more efficient vehicles. Tires are of great importance in this respect, as the tire compound material in contact with the road surface and under the cyclic deformation dissipates energy due to its viscoelastic nature. On the other hand the friction between the road and the tire surface is required for a safe drive. These two contrary characteristics of the tire need a compromise to deliver a secure and efficient ride. Regarding the environmental issues, since July 1st, 2012, all the tire manufacturers in Europe are obliged to provide an efficiency label for their tires indicating three characteristics which includes fuel efficiency (related to Rolling Resistance (RR) performance) and safety (related to Wet Skid (WS) performance). Present thesis deals with these two important aspects of the tire; RR and WS, investigating on a green tire tread material. Loss factor (tanδ) is a determining parameter in analyzing the tire tread material performance. It has been accepted that the tanδ value of a tread compound measured at a temperature around 60°C and a frequency of 10Hz can be representative of the Rolling Resistance performance of a tire made thereof. However for Wet Skid performance the situation is a bit different. In order to predict Wet Skid, the viscoelastic properties of the rubber materials at high frequencies, in the megahertz (MHz) range, should be measured which is not feasible with the current laboratory facilities. Nonetheless Viscoelastic master curves derived from time-temperature superposition (TTS) can be used to describe the properties of the tread materials over a wide frequency range. Part of this thesis deals with different dynamic mechanical measuring methods and the analysis afterwards to receive a reliable viscoelastic mastercurve and defines the interpretations of the results. With the introduction of silica technology in passenger car tire tread applications, the filler-polymer interactions have become of key importance. Besides the silane coupling agents and control of the silanization process, a polymer functionality can play an essential role in the polymer-filler interactions. The aim is to reduce the hydrophobic characteristics of the hydrocarbon polymers and make them more compatible with hydrophilic silica, thereby giving better silica dispersion and better polymer-filler interactions. Second part of the thesis deals with employing the new generation of Styrene-Butadiene Rubbers which are functionalized either in the backbone or at the chain-end. The dynamic mechanical measurements on the tread compounds made from these rubbers reveal the significant potential of these modified SBRs to reduce RR of tire treads made thereof, while no major change in WS occurs.