The Effects of Filler to Elastomer Adhesion
The effects of filler to elastomer adhesion can be illustrated by comparing the effect of a typical reinforcing carbon black before and after a process known as graphiti- zation. There is a strong natural adhesion between elastomers and the surface of conventional carbon blacks, but this can be removed by the graphitization process, which involves treating the carbon black at high temperature under an inert atmosphere. The results of such a comparison are presented in Table 4. The graphitization procedure used had only a minor effect on the physical properties of the carbon black (specific surface area and oil absorption) and no significant effect on dispersion in the elastomer.
As shown in the table, the main effect was an almost complete removal of bound rubber. Bound rubber is a test carried out on compounded but uncured elastomer and measures the amount of polymer “insolubilized” in a good solvent for the elastomer, after mixing with the filler. This is used as a measure of filler/elastomer interaction and indicates that graphitization has destroyed this. All of the reported compound properties have been changed by the graphitization, but by differing amounts. The biggest effects are seen to be on high extension modulus, abrasion loss, and hysteresis.