In recent years, silica has become one of the most important fillers used in tire tread compounds due to its contribution to a better environment. Silica is capable of not only reducing the rolling resistance but also improving the wet skid resistance of tires, compared to carbon black as a filler. However, silica-filled compounds provide many difficulties during rubber processing, because of the polarity difference between silica and polymer. To overcome these polarity differences a bi-functional silane coupling agent is generally used. A typical silane coupling agent is bis-(triethoxysilylpropyl)tetrasulfide (TESPT). The silane chemistry during rubber processing is very complicated. Basically, from a processing point of view, two coupling reactions take place via TESPT. The first reaction is a coupling reaction between the TESPT molecule and the silica surface, the so-called silanization reaction. For this reaction hydrolysis of TESPT is required. The second reaction is silane-rubber coupling, supposed to happen only during the vulcanization stage. However, it is well known that TESPT acts as a sulfur donor during rubber processing. Therefore, premature crosslinking or scorch may take place at excess temperatures in the mixing stage already. All these reactions can take place simultaneously during silica rubber processing, and therefore the reinforcing mechanism of silica is much more complicated than that of carbon black. Diphenylguanidine (DPG) greatly contributes to the physical properties of silica filled rubber. DPG acts as a secondary accelerator but also as silanization accelerator. In addition, DPG is capable of interacting with the silica surface. Therefore, DPG also affects the reinforcement effect of silica in rubber. DPG is subject to toxic concerns and has a negative influence on rubber-metal adhesion. Therefore, in the future DPG-alternatives will be required. The first objective of the present thesis was to understand the reinforcing mechanism of different types of silica in rubber. Especially, the focus was on the bound rubber layer between silica and polymer, which significantly contributes to the physical properties of silica filled rubber. The second objective was to unravel the role of DPG played in silica-reinforced tire rubbers and the search for less toxic or environmentally friendly alternatives.
|Award date||8 May 2009|
|Place of Publication||Enschede|
|Publication status||Published - 8 May 2009|