*3.4. Thermal Behavior*

Table 4 summarizes the melting point, enthalpy of melting at 100% crystallinity, and crystallinity of the compounded blends. Figure 4 shows that all samples possessed endothermic peaks. The bare PBAT displayed a broad peak at 121.68 ◦C, while bare PBS exhibited a sharp peak at 114.04 ◦C. The direct proof of polymer miscibility was obtained by observing the change in the melting point (Tm) of both polymers in the blends. One melting point endotherm was observed for TPRH48/12, TPS48/12, TPRH36/24, and TPS36/24. This scenario indicated that PBS and PBAT were miscible. The T<sup>m</sup> of rice husk and starch was absent because the melting point was beyond 200 ◦C [49,50]. The melting point of corn starch and rice husk is 256 ◦C–258 ◦C [50] and 1440 ◦C, respectively [49].

The bare PBS with a high degree of crystallinity (64.03%) was less susceptible to water absorption because of smaller gaps present between the polymer chains. It was evident from the test results that the addition of filler material slightly reduced the melting point of PBS/PBAT blends. The composites TPRH48/12, TPS48/12, TPRH36/24, and TPS36/24 showed a lower degree of crystallization than PBS. This was due to fillers in polymer matrix reduces the mobility of polymer chains, thus causing the steric hindrance effect ascribed to the cross-linked aromatic structure, leading to a reduction in the extent of crystallinity [51].

Relatively, the composites TPRH36/24 and TPS36/24 exhibited a higher degree of crystallization than TPRH48/12 and TPS48/12. This was due to the high amount of PBS, which possesses higher crystallinity. This phenomenon was consistent with the results of the tensile test, whereby TPRH36/24 and TPS36/24 yield higher tensile strength, as shown in Table 3. However, there was no significant difference found in crystallinity between PBS/PBAT/TPRH blends and PBS/PBAT/TPS blends, indicating the potential of using rice husk waste to substitute starch in the polymer matrix.


**Table 4.** Thermal properties of bare PBAT, bare PBS, PBAT/PBS/RH blends, and PBAT/PBS/TPS blends.

blends.

**Table 4.** Thermal properties of bare PBAT, bare PBS, PBAT/PBS/RH blends, and PBAT/PBS/TPS

PBS 114.04 70.62 64.03 PBAT 121.68 9.76 8.56 TPRH48/12 110.29 8.49 15.52 TPS48/12 111.27 7.92 14.47 TPRH36/24 111.38 14.78 36.01 TPS36/24 111.72 17.69 43.10 Commercial PBAT 119.77 1.4 1.75

**Enthalpy of Melting of 100% Crystalline, ∆Hm100 (J/g)** 

**Xc (%)** 

**Code Tm (°C)** 

**Figure 4.** Second-heating Differential Scanning Calorimetry curves of (**a**) PBS, (**b**) PBAT, (**c**) TPRH48/12, (**d**) TPS48/12, (**e**) TPRH36/24, (**f**) TPS36/24, and (**g**) commercial PBAT. **Figure 4.** Second-heating Differential Scanning Calorimetry curves of (**a**) PBS, (**b**) PBAT, (**c**) TPRH48/12, (**d**) TPS48/12, (**e**) TPRH36/24, (**f**) TPS36/24, and (**g**) commercial PBAT.
