Polydiene-Carbon Black Oil Compounds

This is one of the most important classes of industrial polymer compounds. They are used in pneumatic automobile and truck tires. There are distinct rubber compounds for the 1) tire tread, 2) carcass (which contains reinforcing belts and fabrics), 3) sidewalls, 4) liners, etc. These compounds generally involve the following components [3,4]  

The polydiene rubber-carbon black compoimd is one of the simplest in terms of component interaction. The major components are polymers, carbon black, and oil. The elastomer compounds are miscible or nearly so. The hydrocarbon oils dissolve roughly equally in the amorphous rubbery polydienes. The various polydiene elastomers and oils are almost as one phase. It appears they dissolve in each other at elevated temperatures and form a cross-Hnked structure together while miscible [7,8]. One problem is that the oils can distribute themselves differently among the various elastomers (Section 6.4). 

Carbon black is nonpolar and its particles are small enough to lead to significant interparticle van der Waals forces and associated agglomeration. Much of this is overcome by mastication during the mixing processes. There are, however, no small amphiphilic molecules needed to break up agglomerated as in the case of calcium carbonates. The shear viscosity of the polymer plus oil plus filler system is 

Small polar and amphiphilic molecules are, however, present to aid in the eventual vulcanization process as accelerators. These include zinc oxide and stearic acid, which probably react to form zinc stearate. 

It is well established as shown by Ahn and White [9] that such small molecules in polyolefin matrices migrate to steel walls of dies and induce slippage. This is also the case in carbon black compounds [ 10,11 ]. Zinc stearate or stearic acid can migrate to steel walls and induce sKp. 

---

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. 

---