3.3. Dynamical mechanical properties
Fig. 6depicts the temperature dependence of the storage modulus (E
0
) for pure PLA and its blends. As can be seen, the storage
modulus remain almost the same at temperatures below glass
transition temperature (Tg) but drop abruptly atTg
for all samples.
Upon heating in the range of 90–110C, the storage modulus increase for all blends due to cold crystallization while keep almost
the same for pure PLA (see the interpolative picture in Fig. 6). It
indicates that the incorporation of PBAT promote the crystallization of PLA matrix.
Notably, the influence of PBAT and TBT onE
0
hinges largely on
the temperature range. As can be seen, theE
0 belowTgfor all blends
is lower than that of pure PLA. The E
0
values fall sharply with the
incorporation of PBAT due to the lower modulus of PBAT against
PLA. However, the incorporation of TBT improves significantly the dynamical properties and theE
0
increases with the increasing
TBT concentration. This results are in agreement with that of tensile strength as discussed above. Conversely, all blends display
greaterE
0
values than PLA above cold crystallization temperature.
This phenomenon should be ascribed to the cold crystallization
process in which the PBAT acts as the heterogeneous nucleating
agent. As reported in other works, the addition of PBS also accelerated the cold crystallization of PLA[7,17]. Shibata et al. [7] observed that the temperature where the storage modulus started
to increase due to crystallization of PLLA component shifted to a
lower temperature region by addition of PBS, which indicating that
the addition of PBS enhances the cold crystallization of PLLA. Another previous work by Yokohara and Yamaguchi[17] demonstrated that the enhancement of storage modulus due to the cold
crystallization of PLA was shifted to lower temperature by blending PBS, this phenomenon indicated that PBS accelerated the cold
crystallization of PLA.