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

Experimental Techniques and Materials used
is known to indicate the number of effective network chains per unit volume
of rubber. For a filled vulcanizate, it should reflect not only the effect of
chemical linkages but also the density of polymer– filler attachments.
Circular specimens of diameter 20 mm were punched out from the
vulcanized sheets. Specimens of known weight were immersed in the
solvents in different test bottles and kept at room temperature. Samples were
removed from the bottles at periodic intervals and the wet surfaces were
quickly dried using tissue paper and the weights of the specimen after
swelling were determined at regular intervals, until no further increase in
solvent uptake was detected.
The volume fraction of rubber, Vr, in the swollen network was then
calculated by the following equation 2.4 . 7, 8
Where,
Vr =
(D − FT) ρ
(D − FT) ρ + A ρ
−1
r
−1 −1
r o s
T = the weight of the test specimen
D = the weight of the deswollen test specimen
F = the weight fraction of insoluble components
………………………. (2.4)
Ao = the weight of the absorbed solvent corrected for the swelling
increment
ρr = density of the rubber
ρs = density of the solvent
1
Knowing the value of Vr, the total chemical crosslink density Mc was
2
calculated using Flory-Rehner equation. 9, 10
Cross link density =
[ n(1
− V ) + V + χV
2 ρVs(
V )
Where Vs = molar volume of the solvent
2]
r r
1/3
r
r
χ = rubber – solvent interaction parameter
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