The fracture surfaces of NR vulcanizates filled with
various fillers are illustrated in Fig. 6. As can be seen, thedispersion of various fillers in NR is not much different
when using 6 phr of filler. However, at the same hardness
level, S35 has the poorest filler dispersion because
the aggregate of silica can be readily observed in
Fig. 6(e). It has been also shown in the previous study
that filled rubber vulcanizate having poor silica dispersion
exhibits lower crack growth resistance despite its
lower modulus compared to other vulcanizates [12].