Role of Water in Dielectric Properties of Starch Membranes - Natural Polymers, Biopolymers, Biomaterials, and Their Composites, Blends, and IPNs - page 296

The variation of the dielectric loss (ε'') as a function of frequency for various
temperatures for starch in 0% humidity is shown in Figure 6a and 6b. Two relaxations
are observed one at temperatures -100-0°C and another at -20-100°C. Here at -20°C,
the beginning of the presence of the second relaxation can be observed. The values of
the dielectric loss are found to be highest for starch in 75% humidity. The values for
dielectric loss at 60 and 80°C are nearly the same, while that for 100°C is found to
be lesser. This indicates the evaporation of the water from the sample. It is nearly the
same as that at 20°C this indicates that relaxations are very much dependent upon the
availability of water in the local environment of the starch molecules.

Figure 6a Figure 6b

relaxation Frequencies
The relaxation frequencies were determined by estimating the frequency maxima from
the dielectric loss spectra. The relaxation frequencies for starch with different water
contents is shown in Figure 7. At low temperatures (-100-0°C), it was observed that
dry starch, starch in 51% humidity and starch in 75% humidity had nearly the same
values. They also showed an Arrhenius behavior. At low temperatures, the relaxation
frequencies increased with increase in temperature as the water content increased. The
effect was found to be more at higher temperatures (0-100°C). It was observed that
the relaxation frequencies were highest for samples with 75% humidity. This indicates
that the presence of water facilitates the response of the molecules to the applied field.
It is also observed that for starch with 51 and 75% humidity, the frequencies increases
with increasing temperatures and then decreases after attaining a peak at ~80°C. This
indicates the stiffening of the membranes due to evaporation of water. The activation
energies can be calculated using the Arrhenius relation. It is found that the activa-
tion energy for dry starch and starch in 51 and 75% humidity is ~46 kJ mol -1 . This is
indicative of presence of bound water. The corresponding dielectric strength values
were found to be low (<10) indicating that it is a local relaxation process. At higher
temperatures, it was observed that the activation energies were ~86 kJ mol -1 . Also, the
dielectric strength values for water containing starch was found to be ~15-20 indicative