7. Differential scanning calorimetry
A nonisothermal DSC of PHBV and its composites with talc and
wood fiber was carried out. Fig. 6, illustrates the thermograms of
PHBV, PHBV/talc (60/40 wt.%) composite and its hybrid composites
with 20 wt.% talc and wood fiber each. Further details of the melting
temperature (Tm), melt crystallization temperature (Tc), cold
crystallization enthalpy ðDHcÞ, enthalpy of melting or crystallization
(DHf) and degree crystallinity (Xc) are provided in Table 5.
The melting point of PHBV decreases a little by 2 C in presence
of talc but there is no significant change in the enthalpy of crystallization
(DHf) or degree of crystallinity (Xc) value. The biomodal
endothermic peaks observed in case of PHBV melting region due
to heterogeneous crystal morphology headed towards the homogenization
of the spherulite growth in the presence of talc which resulted
in the slight drop of Tm. DHc and DHf of PHBV did not change
in presence of either filler, which negated any change in net crystallization.
Tc increased to 107 C from 103 C in presence of talc
thereby indicating the increase in crystallization rate of PHBV during
the cooling stage. The surface of talc acted as nucleating sites
that allowed the PHBV nucleation growth at a higher temperature
than the neat PHBV. The increased crystallinity rate is another indication
of the interfacial interaction between the talc surface and
PHBV molecular chains. Xc was not effected by any significant factor
on the addition of either talc or both wood fiber and talc. Xc was
calculated using, Xcð%Þ ¼ DHf
DHf ow 100. DHf was enthalpy of crystallization
of PHBV and DHf o was enthalpy of crystallization at
100% crystallinity of PHBV (109 J/g) [29,30]. w, the weight fraction
of PHBV in composite.