*3.5. Dynamic Mechanical Analysis*

DMA is a technique widely used to characterize a material's physical properties, such as its glass transition, but is also sensitive to other relaxation processes, making it particularly relevant to assess the impact the addition of the nanofiller has on these events. For example, the storage modulus (*E* 0 ) and loss tangent (*tan δ*) curves for pure PLLA, PVDF, and their binary and ternary nanocomposite blends, prepared by quenching from the melt state, are shown as a function of temperature (see Figures 11 and 12, respectively). It can be seen that between −70 to −20 and 40 to 70 ◦C, the *E* 0 of the blends decreased sharply as they passed through the glass transition regions of PVDF and PLLA, respectively. After this, in the temperature ranging from 80 to 140 ◦C, the *E* 0 of the blends rose slightly due to the PLLA component cold crystallizing (Figure 11a). Below the *T*<sup>g</sup> of PVDF as its composition increased in the blend, *E* 0 also improved according to the rule of mixtures. However, between the *T*<sup>g</sup> of the two polymers, *E* 0 was seen to decrease with increasing PVDF content, as at this point the PVDF had transitioned from a leathery to rubbery state. The *T*g and *E* 0 (at 25 ◦C) values for all the samples are presented in Table 3, where it is seen that with increasing PLLA content, *E* 0 increased due to it having a higher modulus than

PVDF at this temperature. The addition of the INT-WS<sup>2</sup> nanofiller to the samples resulted in them all having higher *E* 0 throughout the complete testing temperature range. This is related to the nanofillers' nucleating properties on the polymers and it enhancing their stiffness (Figure 11b), as can be seen, for example, comparing PLLA/PVDF (80/20) with the sample with 0.5 wt.% INT-WS2, where the room temperature modulus increased 27% from 2274 MPa. *Polymers* **2021**, *13*, x FOR PEER REVIEW 14 of 19

**Figure 10.** WAXS diffractograms of PLLA, PVDF, binary PLLA/PVDF, and ternary PLLA/PVDF/INT-WS<sup>2</sup> hybrid nanocomposites obtained at room temperature after dynamic crystallization from the melt. **Figure 10.** WAXS diffractograms of PLLA, PVDF, binary PLLA/PVDF, and ternary PLLA/PVDF/INT-WS<sup>2</sup> hybrid nanocomposites obtained at room temperature after dynamic crystallization from the melt.

*3.5. Dynamic Mechanical Analysis* **Table 3.** DMA parameters of different PLLA/PVDF/INT-WS<sup>2</sup> blend nanocomposites based on PLLA, PVDF, and INT-WS<sup>2</sup> .


content, as at this point the PVDF had transitioned from a leathery to rubbery state. The *T<sup>g</sup>* and *E′* (at 25 °C) values for all the samples are presented in Table 3, where it is seen that with increasing PLLA content, *E′* increased due to it having a higher modulus than PVDF at this temperature. The addition of the INT-WS<sup>2</sup> nanofiller to the samples resulted in them all having higher *E′* throughout the complete testing temperature range. This is related to the nanofillers' nucleating properties on the polymers and it enhancing their stiffness (Figure 11b), as can be seen, for example, comparing PLLA/PVDF (80/20) with the

from 2274 MPa.

**Figure 11.** Evolution of the storage modulus (*E′*) as a function of temperature for indicated (**a**) binary PLLA/PVDF and (**b**) ternary PLLA/PVDF/INT-WS<sup>2</sup> hybrid nanocomposites obtained in the tensile mode at 1 Hz; inset is the room temperature values of storage modulus (*E′*) obtained for all binary and ternary hybrid nanocomposites. **Figure 11.** Evolution of the storage modulus (*E* 0 ) as a function of temperature for indicated (**a**) binary PLLA/PVDF and (**b**) ternary PLLA/PVDF/INT-WS<sup>2</sup> hybrid nanocomposites obtained in the tensile mode at 1 Hz; inset is the room temperature values of storage modulus (*E* 0 ) obtained for all binary and ternary hybrid nanocomposites.

**Table 3.** DMA parameters of different PLLA/PVDF/INT-WS<sup>2</sup> blend nanocomposites based on PLLA, PVDF, and INT-WS2. **Material** *E′***<sup>25</sup> °C (GPa)** *Tg***, PVDF (°C)** *T***g, PLLA (°C)** PLLA 3127 - 55 80/20 2274 - 54 60/40 2055 −36 57 40/60 1985 −37 54 20/80 1776 −38 50 PVDF 1560 −37 - PLLA-INT 3640 - 54 From Figure 12a of the *tan δ* curves, it can be seen that the immiscible blends all presented individual *T*<sup>g</sup> transitions at temperatures characteristic of the pure PVDF and PLLA polymers, though in the case of PLLA, the *T*<sup>g</sup> peak decreased slightly and broadened, possibly related to its partial miscibility with PVDF at the interface between the two polymers or its nuclei at this location also increasing chain mobility. The mobility of the PLLA chain segments were improved with INT-WS<sup>2</sup> addition as can be seen with an increase in the *tan δ* peak of 60/40-INT (Figure 12b) compared to the same blend without nanofiller. The position (glass transition temperature) and height of the *tan δ* peak are associated with segmental mobility. The decrease in *T*<sup>g</sup> means the enhancement of chain segment mobility and the increase in the height of the *tan δ* peak reveals the rise in segmental mobility. Both the decrease in *T*<sup>g</sup> and the increase in the height of *tan δ* indicate that the blend nanocomposites had high mobility of chain segments.

> 80/20-INT 2886 −37 53 60/40-INT 2415 −35 53 40/60-INT 2293 −39 56

posites had high mobility of chain segments.

20/80-INT 2154 −37 - PVDF-INT 1923 −37 -

From Figure 12a of the *tan δ* curves, it can be seen that the immiscible blends all presented individual *T<sup>g</sup>* transitions at temperatures characteristic of the pure PVDF and PLLA polymers, though in the case of PLLA, the *T<sup>g</sup>* peak decreased slightly and broadened, possibly related to its partial miscibility with PVDF at the interface between the two polymers or its nuclei at this location also increasing chain mobility. The mobility of the PLLA chain segments were improved with INT-WS<sup>2</sup> addition as can be seen with an increase in the *tan δ* peak of 60/40-INT (Figure 12b) compared to the same blend without nanofiller. The position (glass transition temperature) and height of the *tan δ* peak are associated with segmental mobility. The decrease in *T<sup>g</sup>* means the enhancement of chain segment mobility and the increase in the height of the *tan δ* peak reveals the rise in segmental mobility. Both the decrease in *T<sup>g</sup>* and the increase in the height of *tan δ* indicate that the blend nanocom-

**Figure 12.** Evolution of the loss factor (*tan δ*) as a function of temperature for indicated (**a**) binary PLLA/PVDF and (**b**) ternary PLLA/PVDF/INT-WS<sup>2</sup> hybrid nanocomposites obtained in the tensile mode at 1 Hz. **Figure 12.** Evolution of the loss factor (*tan δ*) as a function of temperature for indicated (**a**) binary PLLA/PVDF and (**b**) ternary PLLA/PVDF/INT-WS<sup>2</sup> hybrid nanocomposites obtained in the tensile mode at 1 Hz.
