Studies on the use of nano zinc oxide and modified silica in NR, CR ...

Use of nano zinc oxide in natural rubber
vulcanizates with lower dosage of ZnO(p) and ZnO(s) are comparable with
N-5 vulcanizate with higher dosage of ZnO(c).
4.3.4 Swelling studies
Swelling studies in toluene
Table 4.9 shows the crosslink density of the filled vulcanizates.
Table 4.9 Crosslink density of NR vulcanizates
Vulcanizates Crosslink density × 10 -5 mol/g
N-5 4.62
N-6 5.40
N-7 4.89
Crosslink densities were calculated using Flory-Rehner equation. 16 It
is found that the crosslink densities of N-6 and N-7 vulcanizates are slightly
higher than that of N-5 vulcanizate. The high value of crosslink density
confirms the presence of higher crosslink in vulcanizates with ZnO(p) and
ZnO(s) compared to vulcanizate with conventional ZnO.
Swelling resistance in other solvents
The swelling resistance of the gum and filled vulcanizates were
studied by swelling a cut sample in various solvents for constant weight. The
swelling index is given in the Table 4.10. The swelling index values of all
filled vulcanizates are lesser than that of all gum vulcanizates. When the
forces that hold the macromolecules together are increased through cross
links, the high polymer will not dissolve any longer, but will swell to a
smaller or larger extent. With increasing cross linking, swelling becomes less.
The swelling index values of ZnO(p) and ZnO(s) composites are comparable
to that of conventional zinc oxide composites.
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