Four kinds of natural rubber were used for specimens, the kinds A, B and C were cured with sulphur and the kind D was cured with peroxide. The kinds A, B and C had different initial densities of crosslinking.
The actual density, N0 for the four samples, was obtained by using the equation of f(0)=N0 RT (α-α-2) and by the swelling method using the equation of Flory-Rhener.
According to the results obtained already, both the scissions of main chains and crosslink sites occurred at the same time for A, B and C, but the only main-chain scission occurred for the sample D.
The Eq. (1) was obtained for the sample D because k=0 in the Eq. (3) of
[ft/f0={1-2k/M0·qm(t)}·e-x/M0·qm(t)+k/M0·qm(t)·e-2x/M0·qm(t)]
(ft/f0)D=e-xD/M0·qm(t) (1)
or
qm(t)=-N0, Dln(ft/f0)D (2)
As the Eq. (3) of [ft/f0={1-2k/M0·qm(t)}·e-x/M0·qm(t)+k/M0·qm(t)·e-2x/M0·qm(t)] is applicable to the samples of A, B and C, and qm (t) is equal to the four samples under the same condition, the Eq. (4) is established by substituting the Eq. (2) into the Eq. (3).
-N0, Dln(ft/f0)D=(ft/f0)A-(ft/f0)DN0, D/N0, A/(ft/f0)DN0, D/N0, A-2·M0/kA·1/(ft/f0)N0, D/N0, A (4)
Using the experimental data of (ft/f0)A, (ft/f0)D and the known value of N0, A, N0, D and M0, kA is calculated from the Eq. (4).
Similarly kB, kC and kD are obtained.