Tread formulation

Firestone and Shell started commercial production of cis-polyisoprene by the anionic process in the 1950 s but these plants are no longer in operation now. About the same time, Phillips started the manufacture of polybutadienes by the anionic route and ever since, there has been a steady growth in their use, particularly in the tire-tread as well as tire-carcass formulations. These solution polybutadienes, generally, have low vinyl contents but recently, Phillips has found some interesting applications for medium vinyl polybutadienes as well.14 Polybutadienes with 50-55 percent vinyl contents behave like emulsion polymerized SBR in tire tread formulations and exhibit very similar tread... 

Solution random copolymers prepared by the above procedures have performed well in tire-tread formulations. 22 They require about 20 percent less accelerator (see Table II) as compared to an emulsion SBR and give higher compounded Mooney, lower heat buildup, increased resilience and better retread abrasion index. 

Tire-Tread Formulations. The isobutylene polymers are notorious for their poor affinity toward carbon black relative to other elastomers that are rich in unsaturation. Yet reinforcement with carbon black is critical to use in these polymers in tire treads where a certain degree of abrasion resistance is required. It is expected that the Exxpro-phosphonium ionomers can interact with the carbon black(both regular and oxidized forms) surface and thereby localize them within the PIB phase as shown ... 

TABLE 9.31 Model Truck Tire Tread Formulation ... 

The authors collected the test data shown in Table X. From these data it can be noted that the number-average molecular weight, or of a commercial emulsion SBR such as IISRP 1500 or 1712 is typically 90,000 to 175,000. The primary molecular weight of a solution-polymerized polymer produced with an anionic lithium catalyst can, in contrast, be increased toward 250,000 without gelation. In addition, emulsion-polymerized SBR contains only about 92% rubber hydrocarbon as a result of the presence of residues from the production process solution polymers tend to be near 100% hydrocarbon. As a consequence, the authors concluded that the number-average molecular weight can be considered the key parameter of polymer macrostructure, particularly with respect to the hysteretic characteristics of a tread formulation. Hence the differences in macrostructure between emulsion- and solution-polymerized polymers will dictate many of their properties in a tire tread compound. 

Tread compounds can be based on either a single polymer or a blend of polymers. Natural rubber, emulsion SBR, solution SBR, BR, and isobutylene-based elastomers are used in such blends. The following tables illustrate tread formulations designed for specific applications ... 

In contrast to the ASME s existing ethical codes, the Goals put the rhetoric of public obligation before those of corporate and member interests. While the Goals echoed well-tread formulations of professionalism, its prose borrowed heavily from Paschkis T S Committee, making reference to deleterious second order effects of technology, mass layoffs, and technological imperialism. ... 

The action of accelerators is improved by the presence of activators in practice, a combination of zinc oxide and a fatty acid is nearly always used. Specifically, the activator increases the efficiency of the vulcanizing system so that, typically, only about 5 sulphur atoms are combined for each cross-link formed. As a consequence, the vulcanizate shows improved physical properties, aging characteristics and appearance (less sulphur bloom). The use of accelerator-activator systems is standard practice in rubber compounding and a typical basic tread formulation might be as follows ... 

Retrospective View of Vinyl-BR Properties In the 1950s, the Phillips Petroleum Company and the Firestone Tire and Rubber Company started commercial production of polybutadienes by organolithium polymerization for use in tyres. These solution BRs, having low vinyl contents (8-10%), were used in blends with emulsion SBR in tyre treads for balancing traction and wear performance properties. In the early 1970s when styrene monomer was in short supply, developments from Phillips Petroleum Company and EniChem (formerly the International Synthetic Rubber Company) showed that vinyl-BRs with 50-55% vinyl content behaved like emulsion polymerized SBR in tyre tread formulations and exhibited very similar tread wear and wet skid resistance. Tread compounds containing 45%-vinyl polybutadiene showed lower heat build-up and better blow-out resistance than E-SBR and blends of E-SBR with cw-BR. EniChem introduced trial quantities of a medium-vinyl butadiene rubber (MVBR) under the name Intolene 50 in 1973. 

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. 

Where great mechanical strength is not required, and thus carbon black not used, rubbers can be colored with pigments, just as plastics. A typical radial passenger-tire tread formulation is shown in Table 19.1. Notice that the additives (everything except SBR polymer and cw-polybutadiene) make up 122.25 parts per hundred parts polymer or more than half of the tire ... 

Diesters are also used in proprietary high performance BR/SBR tire-tread formulations at approximately 10 phr to reduce hysteresis, improve hot traction in racing tires, increase flex life and other requirements of track and street car and motorcycle tires. 

A typical radial passenger-tire tread formulation is shown in Table 21.1. Notice that the final compound is less than 45% polymer. 

Chandra and Pillai [28] used a low-molecular-weight recycled rubber as a processing aid in a number of tyre tread formulations and compared its performance with other commercial process aids. This process aid (Ecoreen T) is shown to function as well as or even better than depolymerised NR or similar process aids. The same workers also reported on the use of new products with low viscosity that are produced by blending low-molecular-weight virgin polymers with recycled butyl rubber [29]. When these products... 

Since low c/5-polyisoprene is limited to approximately 20 % inclusion in natural rubber compounds due to the fall-off in physical properties, interest in this type of polymer has been specifically for processing reasons. Tyre performance has been shown to be unimpaired in tread formulations containing this level of both Cariflex IR 305 and IR 500 polymers. 

The use of high c/ -polyisoprene is not limited to tread formulations and it is used to significantly greater advantage in other tyre components. 

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