Characterization of Silica Modified with Silanes Using Thermogravimetric Analysis Combined with Infrared Detection

The introduction of tire labelling and legislation in Japan, Europe, Korea and elsewhere is increasing the demand for tires with both reduced rolling resistance and increased wet grip. This can be accomplished using tire treads reinforced with silica, provided that the silica is strongly bound to the rubber. In the case of rubbers such as styrene-butadiene rubber (SBR) and butadiene rubber (BR), this can be achieved by coupling the hydrophilic silica to the hydrocarbon rubber using an alkoxysilane.

In this study, the silica surface has been modified by reaction with a wide range of coupling and non-coupling silanes, normalizing the silane loadings to the standard 8% w/w TESPT (triethoxysilylpropyl tetrasulfide), to have the same number of silane groups available for silanization. The chemistry and extent of these silanizations were elucidated using thermogravimetric analysis combined with infrared detection (TGA-IR). The silane grafting efficiencies were typically 50-60%, but higher in the case of the smaller silanes, MTMS (methyltrimethoxysilane) and MTES (methyltriethoxysilane), and rather lower in the case of the bulkier DTSPM (di-(tridecyloxypentaethyleneoxy)ethoxysilylpropyl mercaptan). However, the silica surface coverage increases with increasing size of the silane. In the TGA, ethoxy and methoxy groups are displaced from the grafted silanes at lower temperatures (up to about 450°C), and other groups generally at higher temperatures. The influence of these modified silicas in reinforcing SBR/BR tire tread compounds will be discussed.