3.2. Curing characteristics
Figs. 3–5 show the curing characteristics i.e., scorch time
(ts2), cure time (tc90) and torque variation (MH – ML) of
LENR-coated OPA filled NR composites, and compares them
to the raw OPA filled NR composites (control). The ts2 and
tc90 of the OPA filled NR composites showed a decrease
whilst the torque variation increased when the OPA loading
was increased for both raw OPA and LENR-coated OPAs. At
the same filler loading, the curing characteristics of LENRcoated
OPA filled NR composites were found to be lower
than that of raw OPA filled NR composites. This may be
attributed to the adjacent double bond by the oxirane
group from ENR, which was accelerated in the vulcanization
reaction [11,12]. Even although the addition of a
compatibilizer was expected to improve the torque variation
of composites; the LENR coating showed a contrasting
effect by lowering the torque variation of the OPA filled NR
composites. This was mainly caused by softening of the
composites due to the ratio of the rubber phase volume to
raw filler being increased when LENR-coated OPA was
added. This is clearly shown in Fig. 2, where the surface