Scorch time, cure time and minimum torque of
NR compounds filled with silica/CB hybrid filler are
depicted in Figs. 1–3, respectively. It should be
noted that the total hybrid filler content in each
vulcanizate is 50 phr and the amount of silica ranges
from 0 to 50 phr. The results show that scorch time
and cure time of the vulcanizates increase with
increasing silica content up to 30 phr and then they
slightly decrease when silica content is further
increased. These results are consistent with the
previous work showing an increase in scorch
protection of the compound with increasing silica
surface area [8]. This is due to the adsorption of
accelerator by silanol groups on the silica surface.
Although it is well established that the use of
coupling agent (Si-69) would reduce the adsorption
of accelerator on the silica surface, the amount of