The rubber–filler interaction of OPA filled natural rubber
compounds at various low loading of OPA is illustrated in
Fig. 5. It can be seen that the Qf/Qg value decreased up to
1 phr loading of OPA, but on further increase in OPA loading
it increased. This result indicates that the rubber-filler
interaction is strongest when 1 phr of OPA was added to
the natural rubber matrix, which agrees with the tensile
properties shown in Table 3