The increase in the number of polar functional groups
increases intermolecular interactions and reduces chain
mobility. The increased Tg values reported above and
shown in Figs. 5 and 6 restrict molecular chain movement
and also affect the flow and rigidity of the materials. This
study measured rubber plasticity which is one of the properties
commonly used to evaluate the processability of
rubbers in industry. The results are given in Table 4 and
show that the plasticity of NR is lower than that of the
ENR30, the NR-g-PMMA and the E(NR-g-PMMA)s, respectively.
The NR has the lowest plasticity value indicates that
it is softer and flows more easily than the modified NRs.
The NR-g-PMMA with 6 mol% of grafted PMMA shows a
remarkable increase of plasticity due to the presence of
hard PMMA thermoplastic. The epoxidation of the graft
copolymer further increases the plasticity values only
when the epoxide content is raised to 30 mol%. At this
level, the plasticity of the epoxidized graft copolymer is
higher than that of the epoxidized natural rubber due to
the effect on the rigidity of the grafted PMMA in combination
with the epoxide groups on the NR chains.