The cure characteristics of the studied
materials, expressed in terms of optimum cure time,
t
90
, were compiled and are shown in Figure 2. It can
be seen that rich ENR had a significantly shorter
optimum cure time, compared to rich NR. The
optimum cure time decreased with an increase in the
ENR content. The shorter cure time observed in rich
ENR was due to the limited availability of crosslink
sites obtained from an acid-catalyzed epoxy ringopening
reaction
by
sulfoxide
and
sulfenic
acid
from
oxidation
of the sulphur during the vulcanization
process (Poh, Chen, & Ding, 1996; Lee et al., 1997),
which might have led to ether crosslinks
vulcanization by sulphur alone was faster and more
efficient for ENR than for NR since isolated double
bonds reacted more rapidly than contiguous double
bonds (Gelling & Morrison, 1985; Ooi, Ismail, &