Fig. 4 displays the tear strength of various NR vulcanizates.
The gum exhibits the lowest tear strength while the
vulcanizates having equal amounts of fillers give similar
tear strength. Although, it is established that spherical
particles can blunt the crack tip more effectively than the
plate-shaped filler having high aspect ratio particles [14],
such a small amount of CB and silica (6 phr) used in this
experiment may not be sufficient to effectively blunt the
tear tip. However, the tear strength of CB- and silica-filled
NR vulcanizates markedly increases when they were
prepared to have similar hardness to that of clay-filled
vulcanizate. At similar hardness level, CB-filled sample
exhibits similar tear strength to that of silica-filled
vulcanizate, but much higher than that of the clay-filled
vulcanizate. The higher amount of fillers in CB- and
silica-filled vulcanizates may obstruct the tear path more
effectively than that for the clay-filled vulcanizate. It has
also been reported that if the clay platelets are aligned in
the perpendicular direction to the applied force, the stress
may be concentrated at the sharp edges of particles and
promote earlier failure compared to spherical fillers [14].