3.4. Tear strength
The effect of filler loading on the tear strength of SMR
L/ENR 25 and SMR L/SBR is shown in Figs. 10 and
11, respectively. It can be seen that the dependence of
tear strength on filler loading is very similar to that of
tensile strength. For the reinforcing fillers, i.e. carbon
black and silica, tear strength increases with increasing
filler loading due to the increase in rubber–filler reinforcement as the filler loading is increased. However,
for calcium carbonate which is a non-reinforcing filler,
tear strength decreases gradually with increase in the
filler loading. This observation is associated with the
increasing dilution effect of calcium carbonate as the
filler loading is increased. For a fixed filler loading, the
carbon black-filled system indicates the highest tear
strength, followed by silica and calcium carbonate, a
finding which is similar to that observed for tensile
strength as discussed earlier. The larger surface area of
carbon black compared to silica enhances better rubber–
filler reinforcement in the former system. Conversely,
the non-reinforcement nature of calcium carbonate
accounts for the lowest tear strength obtained in this
study. The difference between reinforcing fillers (i.e. car-
bon black and silica) and non-reinforcing filler (calcium
carbonate) magnifies as the filler loading is increased,
indicating the significance of the effect of rubber–filler
reinforcement at higher loading of filler. Fig. 12 com-