Table 4. It is starkly apparent that G0 increases consistently
with the filled vulcanizates when compared to gum NR
vulcanizates, especially at low temperature. G0 indicates
stored elastic energy in materials [14] thus, these results
justify that stored elastic properties were enhanced with
the filler filling of gum NR vulcanizates. At a very low
temperature, i.e. 110 C, the silica-filled vulcanizates
showed the lowest G0 when compared to OPA and carbon
black-filled vulcanizates. This could be due to the high
moisture absorption capacity of silica lending to the weak
filler/matrix interaction thus resulting in lower G0 [15].
Above the 90 C region, the ranking of fillers corresponding
to the G0 is: carbon black > silica > OPA, which
agrees with the maximum torque, M100 and M300 data as
discussed earlier.
As seen from Fig. 8 and Table 4, the tan d value shows a
marked decrease in the presence of filler that corresponds
with the trend: carbon black < silica < OPA. This can be a
consequence of fillers carrying greater stress hence less
energy dissipation occurs in the filler-filled vulcanizates.
Also, the tan d shows the amount of matrix material that is
capable of relaxation, depending on the filler content and
the restriction of chain mobility within the interphase of
NR matrix and reinforcing filler [16], thus resulting in the
tan d value for OPA being higher than silica-filled vulcanizates.
The Tg of gum NR vulcanizates (78 C) was
increased when filled with silica (73 C) and carbon black
(71 C). The positive shift toward higher temperature may
be linked to strong filler-rubber interaction. However,
Fig