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. carbon 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 compares the tear strength between SMR L/ENR 25 and
SMR L/SBR at 40 phr of filler loading. As in the case
of tensile strength, SMR L/ENR 25 shows higher tear
strength than SMR L/SBR blend for all filler systems
investigated, an observation which confirms our previous
belief that strain-induced crystallization of SMR L and
ENR 25 contributes to the mutual rubber reinforcement
in the blend [1]. On the contrary, the non-crystallizable
SBR does not reinforce SMR L in SMR L/SBR blends
as shown by the lower tear strength compared with the
SMR L/ENR 25 system.
4. Conclusion
From this study, the following conclusions can be
drawn:
1. Tensile strength, M300 and tear strength of SMR
L/ENR 25 and SMR L/SBR blends show an increas-
ing trend with an increase in carbon black and silica
loading. This observation is associated with the rein-
forcing nature of the fillers where better rubber–filler
interaction is observed in the case of carbon black
However, for the calcium carbonate-filled blends, it
exhibits a decreasing trend with filler loading due to
the smaller surface area of the filler and hence weaker
rubber–filler interaction.
2. Elongation at break of the blends increases steadily with an increase in calcium carbonate loading, an
observation which is attributed to the non-reinforcing
nature of the filler. The dilution effect of the filler
becomes more significant as the filler loading is
increased. On the contrary, elongation at break for the
carbon black and silica-filled blends decreases gradually with filler loading due to the increase in rubber filler interaction as the filler content is increased.
3. For a fixed loading of filler, SMR L/ENR 25 blend
exhibits higher tensile strength, M300 and tear
strength but lower elongation at break compared to
SMR L/SBR blend. This finding is ascribed to the
better rubber–filler interaction and mutual rubber
reinforcement between SMR L and ENR 25—both of
which are strain-induced crystallizable rubbers—in
the former blend.