given in Table 1. The effect of vulcanization and incorporation of MA
on the resistivity of the blends were studied for NR85CS15 and
NR65CS35 blends. For these blends the resistivity increased by dynamic
vulcanization using DCP. The NR85CS15 blend vulcanized with DCP
shows highest resistivity value. The effect of incorporation of DCP and
MA on the resistivity values of the NR85CS15 blend sample is shown in
Figs. 2 and 3. It is seen from the figure that, the incorporation of these
into the blend increases the resistivity values. The vulcanized blend
shows a maximum enhancement in the electrical resistivity at room
temperature. The decrease in resistivity upon heating is also observed
from the figure. The MA modified blend also shows an increase in
resistivity. The temperature dependence of I–V characteristic curves
on NR85CS15 blend is shown in Fig. 4. The slope of the curve increased
with increase in temperature. This means that the volume resistivity
decreased with temperature.
The main function of an insulator is to insulate the current carrying
conductors from each other and from the ground, which requires
materials with very low dielectric constant. For rubber, the dielectric
constant increases with temperature due to change in intra and inter
molecular interactions. Therefore it is necessary to modify rubber to
thermally more stable by adding some ingredients or dynamic
vulcanization. The variation of dielectric constants of pure components
and the blends of NR/CS as a function of frequency is shown in
Fig. 5. It shows that the blend NR80CS20 exhibits the lower value; while
the chitosan exhibits the maximum value of dielectric constant. The
dielectric constant values of the blends decreased with increase in
frequency. The effect of blend composition on the dielectric constant
values is given in Table 2 for different frequencies. The table shows
that the dielectric constant of natural rubber is less at higher
frequencies. The blend NR85CS15 shows the least frequency dependent
and more stable. Above 20% chitosan in the blend, the dielectric
constant increased, which can be attributed to the change in overall
polarity of the system with the addition of chitosan.
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 compositions
compositions
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.