Table 3 shows the curing characteristics of gum vulcanizates
and vulcanizates filled with oil palm ash, silica and
carbon black. The results show that each vulcanizates
exhibited different cure characteristics due to different
properties of the fillers. The cure characteristics depend on
filler related parameters such as particle size, surface area,
surface reactivity, moisture content (polarity) and metal
ions [10]. It was obviously seen that the silica-filled vulcanizates
show the highest ts2 and tc90. It is well accepted that
silica containing hydroxyl groups (–OH) [7] which absorbs
the curative agents and thus reduces the active sulphurating
agent. As a consequence, increases in scorch and cure
times of the rubber compound occurred when silica was
added. The carbon black-filled vulcanizates exhibited
lowest scorch time (ts2) and cure time (tc90), which may be