Influence of carbon black on reversion behavior and thermal aging property of natural rubber

Abstract

The objective of this research was to evaluate the influence of the presence of carbon black on reversion behavior and thermal aging properties of natural rubber (NR) vulcanizates regarding to carbon black type and loading. There were four different carbon blacks used here including N330, N550, N774 and N990. The preliminary study on the reversion behavior of the gum NR compound found that the reversion was initially observed at 140℃ and the reversion occurred much more at higher curing temperatures. Moreover, thermal aging of the gum NR compound caused the increased modulus but the decreased elongation at break and tensile strength. After incorporating carbon black into the NR matrix, it was found that for all carbon blacks but N990 the presence of carbon black even only 10 phr caused reversion of the NR compound at lower temperatures. The reversion of the carbon black filled NR compounds also increased with increasing curing temperatures. At 50 phr loading when curing temperature was not less than 160℃, the NR compound filled with N330 had lowest reversion resistance indicating by shortest plateau region and highest reversion rate. On the other hand, the NR compound filled with 50 ohr N990 had the greatest reversion. At curing temperature of 160℃, for all blacks, increasing carbon black loading decreased reversion. It was also found here that thermal aging properties of the NR vulcanizates were influenced by the presence of carbon black and strongly governed by carbon black type. N330 had highest effect on the reduction of thermal resistance. And the reduction of thermal resistance by N330 depended on N330 loading. The higher the loading of N330 had the lower the thermal resistance. Effect of carbon black on the cure characteristic was proposed here to be a reason of the reduction of reversion and thermal aging resistance. Carbon black which had greatest effect on accelerating curing reaction led to the lowest reversion and thermal aging resistance. The cure behavior depended not only on the surface area and structure of carbon black but also the surface activity of carbon black After removal all functional groups on N330, the ability to accelerate cure reaction of N330 decreased, and the reversion and thermal resistance were now increased. Faster curing led to slow desulfuration which caused the higher sulfur ranks in the networks. This was proposed to be the reason why N330 giving fastest cure resulted NR with lowest reversion and thermal aging resistance. The XANES results also supported this. XANES spectra of the overcured NR vulcanizate filled with N330 shifted to higher energy. This was because high decomposition of polysulfidic linkages and. Then leaving network with high mono and disulfidic linkages responding to X-ray at higher energy.