Effects of Time and Temperature on the Reaction of Tespt Silane Coupling Agent During Mixing with Silica Filler and Tire Rubber

Abstract

The addition of a coupling agent to silica-rubber compounds enhances the filler-matrix compatibility. Under certain mixing conditions the surface of the filler may be only partly activated, which may have an adverse effect on the properties in the final product. Some coupling agents may also act as sulfur donor. The dump temperature employed during mixing and the length of time the compound is exposed to that temperature govern the reaction mechanisms of the coupling agent and determine whether the agent leads to the formation of a silica-rubber bond or acts as a curing agent. A temperature of at least 130 °C is necessary to ensure that the reaction between the coupling agent and the silica proceeds, whereas the coupling agent starts to react with the rubber or to donate sulfur, resulting in scorching, at temperatures above 160 °C. An increase in the 300% modulus and/or G' at 100% strain above 150 °C is an indication of scorching caused by the sulfur in the coupling agent. No scorching is observed when a coupling agent without sulfur is used. Another important parameter is the mixing time. It was observed that the coupling agent must be mixed with the silica for at least 10 minutes at 150 °C to obtain a sufficient degree of coupling.

Optimization of Mixing Conditions for Silica-Reinforced Natural Rubber Tire Tread Compounds

“…In order to explain the difference in change of Mooney viscosities with dump temperature of silica-filled NR compounds in comparison with previous experience with SBR compounds, 10 two additional compounds were prepared. These compounds were composed of rubber with only TESPT and DPG at amounts of 5.0 and 1.5 phr, respectively.…”

“…High temperatures improve the silanization rate due to the temperature dependence of the reaction 5 and reduction of sterical hindrance of the silylpropyl groups of the coupling agent by increased thermal mobility. 9 Based on a study with SBR/BR compounds, 10 the dump temperature should be in the range of 145 o C to 155 o C to achieve good silanization and to avoid pre-crosslinking. Furthermore, a mixing time of at least 10 minutes is needed for the silanization reaction during the first mixing step.…”

Silane grafted natural rubber and its compatibilization effect on silica-reinforced rubber tire compounds

“…To complete the reaction between silica and, for example, bis-(3-triethoxysilylpropyl)tetrasulfide (TESPT) silane during mixing, the discharge temperature of a silicafilled Styrene-Butadiene Rubber (SBR) compound should be above 130°C. But at a temperature above 160°C the silane starts to react with the elastomer to form premature crosslinks [3]. For silica-filled NR compounds with TESPT as coupling agent, a discharge temperature is recommended in the range of 135-150°C while a higher temperature leads to degradation of the NR [4].…”

Using a sulfur-bearing silane to improve rubber formulations for potential use in industrial rubber articles

“…TESPT has a fast cure kinetics and ability to form disulfidic rubber-to-filler bonds [12,15]. This silane possesses tetrasulfane and ethoxy groups (Scheme 1).…”