Theoretically, the torque difference (MHdML) represents
the shear dynamic modulus, which is indirectly
related to the total crosslink density of a rubber compound
[10,13–15]. The total crosslink density is contributed by the
sulphide crosslinks and physical crosslinks [16,17]. The
addition of up to 5.0 phr of ALK into the silica-filled NR
compounds increased the torque difference (MHdML) of
the silica-filled NR vulcanisates. This is clearly attributed to
the action of the ALK, not only as a secondary accelerator,
but also as filler dispersant. The ALK accelerated the
sulphur reaction and enhanced the state of the sulphide
crosslink. The ALK increased the degree of silica dispersion
and formed the additional physical crosslinks by silica–NR
attachments (which will be seen in FTIR result).