Adhesion of carbon black to elastomers

Measurements are described of the strength of adhesion of lightly-crosslinked elastomer sheets, either with clean contacting surfaces or with one or both surfaces coated with layers of carbon black particles. The strength of self-adhesion showed large differences that correlated with the glass temperature, thus indicating that a major factor in self-adhesion is viscous energy dissipation. A lesser but still marked effect of the elastic modulus was observed, the more highly crosslinked sheets showing lower self-adhesion. When layers of carbon black particles were interposed, the measured strength of adhesion was increased in all cases, becoming about twice as high for elastomers with low self-adhesion, and showing a somewhat smaller increase for elastomers with high self-adhesion. After correcting for incomplete coverage of the surface, the actual strength of adhesion to carbon black is inferred to be about four times higher. Similar levels of bonding to carbon black were found for several hydrocarbon elastomers, although the increase in adhesion was most evident for those with low levels of self-adhesion - polybutadiene and natural rubber in the present study. Thus, no specific effect of elastomer surface chemistry was found. Instead, adhesion to carbon black appeared to be governed by simple wetting considerations.