conditioning period, the swollen specimens were taken out
and weighed again. The specimens were then dried in an
oven at 70 C until constant weight was obtained. The
crosslink density was measured by applying the Flory
Rehner equation [8,9] as given in Equations (1)–(3) below:
Mc ¼
rpVsV1=3
r
lnð1 VrÞ þ Vr þ cV2
r
(1)
Vr ¼ 1
1 þ Qm
(2)
Vc ¼ 1
2Mc
(3)
where,Mc is the molecular weight between crosslinks, rp is
the density of the NR (0.92 g cm3), Vs is the molar volume
of the toluene (106.4 cm3/mol), Vr is the volume fraction of
the swollen rubber, Qm is the swelling mass of the OPA
filled NR vulcanizates in the toluene, c is the interaction
parameter between the rubber network and the toluene
(c ¼ 0.393) and Vc is the degree of crosslink density.