The thermal degradation of NR and the chemically
modified NRs was analyzed by TGA under nitrogen atmosphere.
The TGA and DTG curves are shown in Figs. 7 and
8, respectively. The initial temperature of weight loss (Ti),
the temperature at peak of the 1st derivative weight loss
(Tp) and the final temperature of weight loss (Tf) are shown
in Table 3. It can be seen from Fig. 7 that the thermal degradation
of NR, NR-g-PMMA and E(NR-g-PMMA)s with 10–
30 mol% epoxide is a one-step reaction. The 1st derivative
peak temperatures (Tp) indicate the point where the
weight loss changes at the greatest rate. The Tps of the
E(NR-g-PMMA) are higher than those of the NR-g-PMMA
and NR, respectively. In addition, increasing the epoxide
contents in the E(NR-g-PMMA)s increases both the Tp and
Tf. This is due to the increased polarity and hence intermolecular
interactions. Moreover, the increase in the number
of epoxide groups results in a decrease of reactive unsaturated
backbone and so less susceptibility to degradation.
Fig. 7b shows that the peak height of the DTG curves of the epoxidized graft copolymers is lower than that of the
graft copolymer and virgin NR, respectively. Also the peak
height of the E(NR-g-PMMA) decreases with increasing
epoxide contents. This indicates a lower degradation rate
of the epoxidized graft copolymers. Fig. 8 shows a comparison
of the E(NR-g-PMMA) with the ENR containing an
epoxide content of about 30 mol%. The presence of the
grafted PMMA enhances the thermal stability of the material,
as can be observed from a shift of the decomposition
temperatures in both the TGA and DTG curves.