TESPT compounds

FIGURE 35.13 Typical fingerprint of a masterbatch mixing process of a solution-based styrene-butadiene rubber (S-SBR)/Silica/TESPT tread compound on a GK 320E (Harburg Freudenberger) with PES5 rotors. 

The compositions of the pure S-SBR compounds are given in Table 6. In the recipe containing TESPT, the amount of sulfur was adjusted to compensate for the presence of sulfur contained in TESPT, to represent equimolar quantities in all cases. For the compounding ingredients, see Table 1. 

Combining silanes with silica led to high-performing silica-filled rubber compounds. Organofunctional silanes with polysulfane groups such as bis-(3-(triethoxysilyl)propyl)tetrasulfane (TESPT) and bis-(3-(triethoxysilyl)propyl)disulfane (TESPD) (Fig. 12) are utilized to improve dispersability of silica in the rubber matrix. 

OC2Hs)3Si, S2, ., i(OC2H5)3 Fig. 12. Tetrasulfane TESPT (above) and disulfane TESPD (below) silanes used in tire compounds. 

Even though the final performances of the cured rubber compounds are very important, the process stability is also of great importance in manufacturing and cannot be neglected when choosing the silane structure. Figure 13 shows strain/modulus curves of three silica-filled rubber compounds using TESPT, TESPD, and mercaptopropyitriethoxysilane, respectively. 

The hydrophilic nature of silica also affects the cure characteristics of rubber compounds, the properties of vulcanized rubber and also the compatibility with non-polar rubber such as natural rubber (NR). Silica retards the vulcanization as it reacts with zinc-accelerator-sulfur complex. These drawbacks can be overcome through the use of silane coupling agents. The most common silane coupling agent used is bis(3-triethoxysilylpropyl) tetrasulfide (TESPT). A silane... 

This method allows the sol-gel siliea NR latex eompound to be moulded into the desired shape. TESPT was eo-mixed with TEOS and eoneentrated NR latex. Ammonia which functioned as base catalyst was added into the concentrated NR latex. The silica-TESPT-NR latex compound was then subjected to heat to complete the sol-gel silica conversion process. The dried sol-gel silica-NR mixture was compounded as per normal mixing procedure. A good dispersion of silica particles of the size between 100 and 500 nm was achieved. Using the two-level factorial design, it was concluded that the mechanical properties, i.e. tensile properties and tear strength, were significantly affected by the TEOS loading. It was also found that the amount of ammonia present in the concentrated latex, i.e. 0.7% (w/w) was sufficient to convert TEOS into silica. 

TESPT remained the industry standard coupling agent for sulfur cured rubber into the 1990s. With the development of HDS came expanded applications for silica-based compounds, particularly in high performance passenger tire treads which needed a combination of tread wear, low rolling resistance, and good wet traction (73). This combination of performance attributes can be simultaneously optimized to unique levels with silica. Recipes with 50-100 phr silica were now permissible and desirable. 

Today, for the hydrated precipitated silica to be effective in reducing the rolling resistance in a tire tread, it must be used with an organosilane. The most common organosilane used today as a rubber compounding ingredient for use with silica is TESPT (bis-[3-(triethoxysilyl)propyl] tetrasulfide). 

TESPT is used to improve the compatibility of silica with carbon-based elastomer formulations. When silica is used in a rubber compound without TESPT or some other silane, the rubber generates more heat in cured dynamic applications. For example, in tread formulations, without TESPT, the silica-loaded treads will have higher rolling resistance and impart poorer fuel economy. 

TESPT, an organosilane, is usually preferred to the older mercaptosilanes, such as MPTMS (mercaptopropyltrimethoxysilane) or MPTES (3-mercaptopropyltriethoxysi-lane), because the mercaptosilanes have a very objectionable odor. However, some MPTES is used by the footwear industry because such stocks are faster curing than TESPT, allowing the compounder to reduce the amount of accelerator, such as TMTM, and increase productivity. 

The use of TESPT as a coupling agent in silica-rubber tyre tread compounds to enhance filler-matrix compatibility is studied under certain mixing conditions. This paper aims to show the effects of variations in the mixing time and temperature on the dynamic mechanical properties of silica-filled tyre tread compounds. The leaetions described lead to different results at different temperatures and the influence of the presence of zinc oxide during mixing is also taken into consideration. 33 refs. 

COMPARATIVE STUDIES ON EFFECTS OF TESPT AND TESPD TREATED SILICA COMPOUNDS ON PROCESSING AND SILICA DISPERSION DURING MIXING IN NATURAL RUBBER... 

When added to a conventional accelerator/sulphur compound of NR containing 60 pphr precipitated amorphous white silica, the bifunctional organosilane bis(3-triethoxysilylpropyl)tetrasulphane (TESPT) had a profound effect on the viscosity and cure properties. The Mooney viscosity decreased when 7 pphr silane/60 pphr silica was mixed with the compound. The scorch time shortened when 3 pphr silane/60 pphr silica was added to the mix and the optimum cure time was also reduced when 7 pphr silane/60 pphr silica was introduced into the rabber. The rate of cure of the mix accelerated with 7 pphr silane/60 pphr silica. 11 refs. 

NR was Standard Indonesian Rubber (SIR-10), carbon black was NllO (Cabot) and silica was Ultrasil VN3 Sp (Degussa). The coupling agent was bis-(3[triethoxysilyl]-propyl)-tetrasulphane (TESPT) (Si 69, Degussa) [9]. The compound formulation is given in Table 12.1 and the composition of fillers is given in Table 12.2. 

Compound 4 at the dump temperature of 150 °C and 160 °C clearly shows that the higher temperature results in the higher torque, i.e., the generation of an increased amount of the long-relaxation-time component. Also, the order in the curves of compounds 1, 2 and 3 indicates that with more TESPT present the torque level became higher. However, the order is reversed between the curves of compounds 3 and 4 (dump temperature 150 °C). Overall these results indicate gel and long branch formation caused by the reaction between NR and TESPT. 

Eigures 12.18a and 12.8b are the scans obtained for silica and TESPT together in the proportions given by the compound formulation. The reactions were completed when heated up to 250 °C, as there was no reaction seen in the second scan. 

---