EFFECTS of CARBON BLACK On the Reversion BEHAVIOR of A Cured NATURAL Rubber Compound

The objective of this research was to evaluate the influence of four different types and five different loading levels of carbon black on the reversion behavior of natural rubber (NR) compounds. Carbon black, comprised of three furnace black (N330, N550 and N776) and one thermal black (N990), were each evaluated at loading levels from 10 to 50 phr in 10 phr increments. The reversion behavior of the unfilled NR compound was observed at 140 °C and higher, occurring to a greater extent as the curing temperature increased. After incorporating carbon black into the NR compound, it was found that the three furnace carbon blacks at only 10 phr caused reversion of the NR compound at a lower temperature (130 °C) and the reversion rate with all four carbon black filling types and loading levels increased with increasing curing temperatures. At 50 phr loading, when the curing temperature was 170 °C or higher, the NR filled with N330 had the lowest reversion resistance as indicated by the shortest plateau region and the highest reversion rate. Moreover, it was observed that N550 had the most pronounced effect on the reduction of the plateau region, except at a curing temperature of 130 °C. On the other hand, the NR compound filled with 50 phr of the thermal black, N990, had the greatest reversion resistance. At a curing temperature of 160 °C, for all carbon blacks, increasing the carbon black loading decreased the reversion resistance. The effect of carbon black on the cure characteristics is proposed to be the reason for the reduced reversion resistance. Carbon black type-concentration combinations with the fastest curing reactions yielded NR compounds with the lowest reversion resistance. The cure behavior depended not only on the surface area and structure of the carbon black but also its surface activity. After removal of the functional groups on N330, the ability to accelerate the curing reaction decreased, and the reversion resistance increased. Faster curing led to a slow desulfuration and so higher sulfur ranks in the networks. This is proposed to be the reason why N330, which gave the shortest cure time, yielded a filled NR compound with the lowest reversion resistance.