Dynamic mechanical properties of short banana fiber
reinforced polyester composites are greatly dependent
on the volume fraction of the fiber. The dynamic modulus
shows a decrease with incorporation of fiber below
the glass transition temperature and has a positive effect
on the modulus at temperatures above Tg. The maximum
improvement in properties is observed for composites
with 40% fiber loading, which is chosen as the
critical fiber loading. Increase of frequency shifts the Tg
to higher temperatures supporting the good fiber/matrix
interaction, which is clear from the SEM.
At the maximum possible fiber loading in this study i.e.
40% loading, the loss modulus peak gets broadened
emphasizing the improved fiber/matrix adhesion. Moreover,
an additional peak occurs at high fiber loading in
the tan  curves, due to the interlayer effect. Addition of
fiber lowers the tan  peak height, which again points to
the improved fiber/matrix adhesion. The glass transition
temperature is shifted positively on the addition of fiber.
Cole–Cole plots show an imperfect semicircle showing
the heterogeneity of the system as well as the good
interfacial adhesion at high fiber loading. Activation
energies calculated for the different systems show the
highest value for 40% loading. Use of master curve and
the relationship of the shift factors are useful in predicting
the long-term behavior of the composite.