6. Dynamic-mechanical analysis
6.1. Storage modulus
Fig. 3, illustrates the storage modulus (E) of the PHBV and its
reinforced composites. As observed E, the elastic component of
the complex quantity increased by 75% at 20 wt.% talc loading
with supplementary increase of 120% at additional 20 wt.% wood
fiber loading, with respect to neat PHBV. This enhancement was
below the glass transition temperature (Tg) of PHBV. The increase
was by 103% and 208%, respectively above the Tg in the rubbery
stage with the similar loading trend of talc and wood fiber in PHBV,
suggesting that the fillers were posing restriction to the free rotation
of the molecular chains above Tg. The relative increment of E in
rubbery stage was higher than that in the glassy stage for the reason
that Poisson’s ratio in glassy polymer is less than 0.5 and the
thermal stress induced due to the mismatch of the coefficient of
linear thermal expansion of filler and matrix reduces the modulus
of polymer near the filler particles [27]. The platelet shape of the
talc particulates has also played a role in the increment of the modulus,
when compared to the increase in the rod like shape of wood
fiber filler [27]. The loss modulus (E) accounts for the viscous component
of the complex modulus or the out of phase component
with the applied strain, this generally increases with the addition
of filler. Talc at 20 wt.% in PHBV increase its Tg by 8 C as observed
from the shift of the E peak. (Fig. 4) Appearance of the two distinct
peaks in case of hybrid composite with 20 wt.% of talc and wood
fiber each in PHBV have resulted due to two distinct phases of
wood fiber and PHBV. The weak interface of wood fiber and PHBV,
which is not observed in case of the talc and PHBV may have contributed
to this.