Polydiene-Rubber-Silica Compounds

A newer generation of tires includes silica particles. These have been called green tires Green tires are welcomed in market because of their better gas mileage and traction, and lower rolling resistance than pure carbon black tires. These generally involve the components  

The polymer components play the same role as they do in rubber-carbon black compounds (Section 8.3.1). The replacement of much of the carbon black with silica, however, makes the total compound quite different. 

Silica particles are polar and porous (Section 1.4.6). The silica particles show not only significant interparticle van der Waals forces, but also strong polar and dipole bonds. This results in much higher viscosities than in carbon black compounds (Eq. 8.3) and more complex rheological properties generally. Silica compounds are hard to process and silica agglomerates are difficult to disperse in rubber matrices [ 12]. The surface of silica is hydrophilic, which is incompatible with oleophilic rubber matrices. There has been much research on breakup of silica agglomerates [13 to 20]. 

The interaction silica and silane would seem more complex than the polydiene-carbon black oil compounds. Many of the problems with rubber-silica tire compounds can be related to those of rubber-carbon black compounds. 

---