silica has become along with carbon black, the most important filler in the rubber industry. The use of silica instead of carbon black in passenger car tire tread compounds leads to lower rolling resistance, equal wear resistance, and higher wet grip. To improve the compatibility of silica with the rubber it is necessary to modify the silica surface. For this purpose, bi-functional organo-silanes such as bis (triethoxysilylpropyl) tetrasulfide (TESPT), or bis(triethoxysilylpropyl) disulfide (TESPD) are commonly used.
Usually, the modification of the silica surface using silane coupling agents is performed during the mixing process. During this procedure two chemical reactions take place: i) bonding of the organosilane to the silica surface, and ii) reaction between the silane and the rubber. This mixing method exhibits some disadvantages, such as the need of an additional step to ensure the finalization of the reaction between the silane and the silica, and the generation of ethanol as a by-product of the silanization reaction.To overcome these disadvantages, one of the possible solutions could be the pre-silanization of the silica (i.e. surface modification of the silica in a chemical reactor).
In order to analyze the effect of the different silanization processes on the in-rubber properties, different compounds prepared using in-situ and ex-situ silanization were evaluated and compared in the present work. For this study, TESPD was used as coupling agent and hexadecyltrimethoxysilane as covering agent