It can be seen in Fig. 8 that heat build-up of the vulcanizates
containing a small amount of filler is not much
different from that of the gum. However, it should be noted
that the clay-filled sample shows slightly higher heat buildup
than CB-filled and silica-filled vulcanizates when using
equal amounts of filler. When higher amounts of CB or silica
is added to prepare vulcanizates with similar hardness to
that of C6, CB-filled sample (CB14) exhibits the same heat
build-up value as that of C6, while heat build-up of silicafilled
sample (S35) increases considerably. The possible
explanation is also given as the combined effects of the
poor silica dispersion and lower crosslink density of silicafilled
sample when a high amount of silica is loaded. Heat
build-up of a vulcanizate is reported to increase with
decreasing crosslink density [13].