Table 3 shows that the dielectric constant of blend after
vulcanization is more stable. The added dicumyl peroxide undergoes
cross-linking reaction in the rubber phase and the cross-links formed
at the interface decreases the free volume. The cross-linked structure
will avoid increase in free volume resulting in stable dielectric
properties. The effect of vulcanization on the dielectric constant for
the blend with 10% of chitosan is shown in Fig. 6. The dielectric
constant decreases by vulcanization and it is more stable than pure
blend at lower frequencies. The vulcanized NR90CS10 blend is more
stable than MA compatibilized NR90CS10 and the vulcanized blend is
frequency independent at lower frequencies.
In electrical applications, it is desirable to keep the electrical losses
to a minimum. Electrical losses indicate the inefficiency of an
insulator. Dissipation factor is a measure of the alternating current
electrical energy, which is converted to heat. This heat rises the
temperature and accelerates deterioration of the polymeric materials.
The loss factor values with frequency for the various blend compositionscompositions
is given in Table 4. The dielectric loss decreases by the
vulcanization and compatibilization of the blend (Fig. 7).
AC conductivity (σac) values are obtained from the formula,
σac = f⋅ε1⋅tanδ = 1:8 × 1010ðSiemens = cmÞ;
where f is the frequency of measurement.
Fig. 8 gives a typical plot of AC conductivity as a function of
frequency for pure natural rubber, chitosan and blends of these two
systems. Natural rubber and chitosan shows non-linearity in AC
conductivity but the blends show a linear behavior. Fig. 9 shows the
AC conductivity curves for pure and modified NR90CS10 blends as a
function of frequency. The vulcanized material sample shows more
insulative compared to pure and MA treated blends
Dielectric constant at different frequencies (Hz)