attributed to the smallest average particle size of 4.60 mm
and highest specified surface area. However, the incorporation
of OPA produces the highest cure rate indices over
silica and carbon black. This is owed to the mineralogical
composition in OPA where various metal elements accelerate
the curing rate of rubber compound. The higher ts2
and tc90 of OPA filled vulcanizates compared to carbon
black-filled vulcanizates may be attributed to low OPA
loading (1 phr) compared to carbon black loading (50 phr).