Natural rubber tread base

S. Bandyopadhyay, S. Dasgupta, N. Mandal, S.L. Agrawal, S.K. Mandot, R. Mukhopadhyay, A.S. Deuri, and S.C. Ameta, Use of recycled tire material in natural rubber based tire tread cap compound Part I (with ground cmmh rubber). Progress in Rubber, Plastics and Recycling Technology, 21(4), 299, 2005. 

Blends of elastomers are routinely used to improve processability of unvulcanized rubbers and mechanical properties of vulcanizates like automobile tires. Thus, cis-1,4-polybutdiene improves the wear resistance of natural rubber or SBR tire treads. Such blends consist of micron-sized domains. Blending is facilitated if the elastomers have similar solubility parameters and viscosities. If the vulcanizing formulation cures all components at about the same rate the cross-linked networks will be interpenetrated. Many phenolic-based adhesives are blends with other polymers. The phenolic resins grow in molecular weight and cross-link, and may react with the other polymers if these have the appropriate functionalities. As a result, the cured adhesive is likely to contain interpenetrating networks. 

As compared to natural rubber, epoxidized grades of natural rubber show improved reinforcement with silica without any coupling agent. Radial tyre tread prepared using formulations based on natural rubber with epoxide... 

Natural rubber and polybutadiene blends tend to be used in tire sidewalls, which undergo flexing, and in tire treads, which have a lug pattern and contain high-stress zones at the base of the tread blocks. 

The elastomers and elastomer blends used in tire compounds, and particularly tread compounds, are thus equally important to the structural design parameters of the tire (Table 4.7). A properly designed tread compound will ensure the tire can meet its performance targets. Tread compounding materials fall into one of five general categories polymers, fillers, protectants, vulcanization system, and various special purpose additives. Elastomers for tread compounds are typically natural rubber (NR), styrene-butadiene rubber (SBR), polybutadiene (BR), and in some instances isobutylene based polymers for winter and special performance tires. 

Polybutadiene/natural rubber blends tend to find application in truck tire tread compounds and side valls. Polybutadiene is also blended vith SBR in treads. Here blend ratios tend to be optimized for factors such as vear resistance, traction requirements, rolling resistance, and damage resistance. Empirical guidelines for determining blend ratios are based on the vork of Nordsiek and co vorkers revie ved earlier [4]. Briefiy... 

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 ... 

Other patents include Ternary Blend of Polyisoprene, Epoxidized Natural Rubber and Chlorosulfonated Polyethylene to Goodyear Tire Rubber, U.S. Patent 5,736,593, April 7, 1998, and Truck Tire With Cap/Base Construction Tread to Goodyear Tire Rubber, U.S. Patent... 

Although the consumption of polymer is small, an important use of natural rubber is in off-the-road tires, such as earthmover tires and aircraft tires. Earth-mover treads can be compounded with natural rubber to have excellent tear resistance and to reduce torn treads and chunkouts. In aircraft tires, the natural tread absorbs well the blow in landing. Natural rubber is little used in retreads although frequently used in the cushion gum, the thin rubber compound layer that joins the tread to the tread base in retreading. 

A natural rubber rich undertread layer can enhance the adhesion between belt or cap-ply and tread whilst a thicker subtread compound may be included to offer some additional benefits of low hysteresis for car tyres and low heat generation for truck tyres within the bulk of a thick section. The cure system needs better flexibility and low heat generation. Typically the cure system will be based on CV/SEV. A general composition for a tyre tread base is depicted in Table 41. 

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