*3.3. Mechanical Properties*

Typical stress–strain curves for bare PBS, bare PBAT, PBS/PBAT/TPRH, and PBS/PBAT/TPS composites are shown in Figure 3. Bare PBS, bare PBAT, and commercial PBAT are highly elastic polymers with high elongation at break. With the introduction of 40% TPRH or TPS, a significant change for both tensile strength and elongation at break was observed compared to bare PBS and bare PBAT. Table 3 represents the tensile data obtained from TPRH composites and TPS composites at a different ratio. For the testing, both TPRH and TPS (as filler materials) were fixed at 40% by weight. The tensile strength, Young's modulus, and elongation at break of bare PBAT were found to be 38.99 MPa, 16.1 MPa, and 1421.9%, respectively. The bare PBS possessed lower tensile strength (30.63 MPa), lower elongation at break (547.45%), and higher Young's modulus (166.23 MPa) when compared with PBAT. The higher incorporation of PBS caused an increment in tensile strength and Young's modulus, but decrement in elongation at break. The increment of Young's modulus and decrement in elongation at break is because of PBS, which has a lower elongation at break (547.45%) and higher Young's modulus 166.23 MPa. The TPRH36/24 and TPS36/24 were prepared using a PBAT:PBS ratio of 36:24. Both the composites with more incorporation of PBS exhibited better tensile strength and Young's modulus, but lower elongation at break when compared with TPRH48/12 and TPS48/12, which is consistent with the work of Boonprasertpoh et al. [29]. This shows that when both polymers (PBS and PBAT) were at a comparable amount, the co-continuous phase occured. This was confirmed with SEM morphology, which is elaborated in the later section. Furthermore, the DSC result shows that TPRH36/24 and TPS36/24 have higher relative crystallinity than TPRH48/12 and TPS48/12, supporting PBS contribution towards a crystallization process. This subsequently affects the tensile strength of the polymer matrix.

*Polymers* **2021**, *13*, x 8 of 20

**Figure 2. Figure 2.**  The mechanism between maleic anhydride, DCP, PBS, PBAT, and TPRH/TPS. The mechanism between maleic anhydride, DCP, PBS, PBAT, and TPRH/TPS.

subsequently affects the tensile strength of the polymer matrix.

*3.3. Mechanical Properties* 

Typical stress–strain curves for bare PBS, bare PBAT, PBS/PBAT/TPRH, and PBS/PBAT/TPS composites are shown in Figure 3. Bare PBS, bare PBAT, and commercial PBAT are highly elastic polymers with high elongation at break. With the introduction of 40% TPRH or TPS, a significant change for both tensile strength and elongation at break was observed compared to bare PBS and bare PBAT. Table 3 represents the tensile data obtained from TPRH composites and TPS composites at a different ratio. For the testing, both TPRH and TPS (as filler materials) were fixed at 40% by weight. The tensile strength, Young's modulus, and elongation at break of bare PBAT were found to be 38.99 MPa, 16.1 MPa, and 1421.9%, respectively. The bare PBS possessed lower tensile strength (30.63 MPa), lower elongation at break (547.45%), and higher Young's modulus (166.23 MPa) when compared with PBAT. The higher incorporation of PBS caused an increment in tensile strength and Young's modulus, but decrement in elongation at break. The increment of Young's modulus and decrement in elongation at break is because of PBS, which has a lower elongation at break (547.45%) and higher Young's modulus 166.23 MPa. The TPRH36/24 and TPS36/24 were prepared using a PBAT:PBS ratio of 36:24. Both the composites with more incorporation of PBS exhibited better tensile strength and Young's modulus, but lower elongation at break when compared with TPRH48/12 and TPS48/12, which is consistent with the work of Boonprasertpoh et al. [29]. This shows that when both polymers (PBS and PBAT) were at a comparable amount, the co-continuous phase occured. This was confirmed with SEM morphology, which is elaborated in the later section. Furthermore, the DSC result shows that TPRH36/24 and TPS36/24 have higher relative crystallinity than TPRH48/12 and TPS48/12, supporting PBS contribution towards a crystallization process. This

**Figure 3.** Stress–strain curves of PBS/PBAT/TPRH and PBS/PBAT/TPS composites. **Figure 3.** Stress–strain curves of PBS/PBAT/TPRH and PBS/PBAT/TPS composites.


**Table 3.** Tensile strength, Young's modulus, and elongation at break for PBS/PBAT/TPS and PBS/PBAT/TPRH composites.

Table 3 reveals that both TPRH and TPS composites showed lower tensile strength, elongation at break, but higher Young's modulus when compared with bare PBS and PBAT. This result was in agreement with the study of Hardinnawirda and Aisha [45], who claimed that when the rice husk loading exceeds 15 wt%, the tensile strength shows a remarkable decrement. Incorporation of 40% TPS or TPRH caused linear decrement in the tensile strength and elongation at break of PBS/PBAT matrix, which was same as the results of Garalde et al. [46]. The decrement of tensile strength was due to the stiffness of TPS or TPRH, causing the steric hindrance effect ascribed to cross-linked aromatic structures of PBS and PBAT. The presence of filler material caused reinforcing effects on the properties of the composites, thus reducing the mobility of polymer chains. The improved Young's modulus compared to bare PBAT was due to the enhanced interaction between the carbonyl group of PBS/PBAT matrix and OH groups of TPRH or TPS. The enhanced interaction allows efficient stress transfer from semi-crystalline TPRH to PBS/PBAT [46].

PBAT/PBS/TPRH composite blends with 40% filler prepared in this work, attained remarkable mechanical properties when compared to reported work by Sabetzadeh and his colleagues with just 15% loading of starch filler [47]. The tensile strength and elongation at break of the 15% filler in LDPE were reported to be between 9–12 MPa and 260–360%, respectively [47]. The PBAT/PBS/TPRH composites prepared in this work exhibited better

tensile strength and Young's modulus but lower elongation at break than commercial PBAT. For the injection molding process, tensile strength, Young's modulus, and elongation at break required are 11.70 MPa [29], 78.13 MPa [29] and 9% [48]. Thus, all the samples prepared in this work are applicable for the injection molding process as they possess the required mechanical properties.
