3.2. Peroxide vulcanized NBR
The physical properties of NBR composites cured by different
concentrations of DCP, namely, 0.5, 1 and 1.5 phr, are given in Table
3. The data have shown that the TS pass through a maximum
and then decrease with the increase of DCP content. While, Eb
diminishes with DCP concentration. Shore A hardness and M100
values increase with the increase of DCP indicating the increase
in cross-link density of the vulcanizates. It is thought that the increase
of DCP level leads to an increase in the number of CAC
bonds [15], and this is reflected in the values of Vr, Mc and crosslink
density. Decreasing the values of TS by increasing cross-link
density, can be explained by the fact that on using DCP the peroxide
radicals can act through abstraction and addition mechanisms.
The over-crosslinked domains (or clusters) may experience the
highest forces where the network strand will reach a critical force
and break [16].