*3.5. Morphology Analysis*

Figure 5 shows the surface morphology of TPRH and TPS with irregular (Figure 5a) and spherical (Figure 5b) shape, respectively. The TPS granules with spherical shape caused a reduction in the contact area of the polymer matrix when compared with the irregular shape of TPRH [52]. For bare polymers of PBS (Figure 6a) and PBAT (Figure 6b), smooth surface morphology was observed while with filler loading, a rough surface was observed as shown in Figure 6c–f. When 40% of TPRH was added into PBAT/PBS matrix, the TPRH particles dispersed homogeneously in the PBAT/PBS matrix, as shown in Figure 6c,e. Some voids in the interfacial boundary were observed in TPRH48/12 due to the pull out of the rice husk particle from the PBAT/PBS matrix. This is caused by the difference in polarity between the hydrophilic rice husk and the hydrophobic PBAT. Fewer filler pullouts with good fibers-matrix adhesion were observed in TPRH36/24 (Figure 6e) as compared to TPRH48/12 (Figure 6c). For TPS blends, a similar trend was observed in TPS48/12 (Figure 6d), which showed a higher filler pullout than the TPS36/24 (Figure 6f). The SEM morphology of TPRH36/24 and TPS36/24 exhibited the co-continuous phase as PBS and PBAT are at a comparable amount. Hence, this explains the less pull out circumstances and better tensile strength in TPRH36/24 and TPS36/24 in comparison to TPRH48/12 and TPS48/12.

comparison to TPRH48/12 and TPS48/12.

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

the extent of crystallinity [51].

*3.5. Morphology Analysis* 

**Figure 5.** Surface morphology of (**a**) irregular TPRH granules and (**b**) spherical TPS granules. **Figure 5.** Surface morphology of (**a**) irregular TPRH granules and (**b**) spherical TPS granules.

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

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

Figure 5 shows the surface morphology of TPRH and TPS with irregular (Figure 5a) and spherical (Figure 5b) shape, respectively. The TPS granules with spherical shape caused a reduction in the contact area of the polymer matrix when compared with the irregular shape of TPRH [52]. For bare polymers of PBS (Figure 6a) and PBAT (Figure 6b), smooth surface morphology was observed while with filler loading, a rough surface was observed as shown in Figure 6c–f. When 40% of TPRH was added into PBAT/PBS matrix, the TPRH particles dispersed homogeneously in the PBAT/PBS matrix, as shown in Figure 6c,e. Some voids in the interfacial boundary were observed in TPRH48/12 due to the pull out of the rice husk particle from the PBAT/PBS matrix. This is caused by the difference in polarity between the hydrophilic rice husk and the hydrophobic PBAT. Fewer filler pullouts with good fibers-matrix adhesion were observed in TPRH36/24 (Figure 6e) as compared to TPRH48/12 (Figure 6c). For TPS blends, a similar trend was observed in TPS48/12 (Figure 6d), which showed a higher filler pullout than the TPS36/24 (Figure 6f). The SEM morphology of TPRH36/24 and TPS36/24 exhibited the co-continuous phase as PBS and PBAT are at a comparable amount. Hence, this explains the less pull out circumstances and better tensile strength in TPRH36/24 and TPS36/24 in

using rice husk waste to substitute starch in the polymer matrix.

**Figure 6.** Fractured morphology of (**a**) PBS, (**b**) PBAT, (**c**) TPRH48/12, (**d**) TPS48/12, (**e**) TPRH36/24, and (**f**) TPS36/24. **Figure 6.** Fractured morphology of (**a**) PBS, (**b**) PBAT, (**c**) TPRH48/12, (**d**) TPS48/12, (**e**) TPRH36/24, and (**f**) TPS36/24.

#### *3.6. Water Absorption*  The water absorption of the bare PBS, PBAT, and PBS/PBAT blends are shown in *3.6. Water Absorption*

Figure 7. All polymers undergo three stages during the water absorption which are absorption, saturation, and swelling. The water absorption of PBAT and PBS film increased slightly and achieved saturation of around 0.35% after 10 days of immersion in water. The low water absorption capacity was due to PBAT and PBS being hydrophobic polymers with the presence of acyl groups [31]. However, at the initial stage (day 3), it was obvious that PBS, having higher crystallinity, possessed a water absorption capacity The water absorption of the bare PBS, PBAT, and PBS/PBAT blends are shown in Figure 7. All polymers undergo three stages during the water absorption which are absorption, saturation, and swelling. The water absorption of PBAT and PBS film increased slightly and achieved saturation of around 0.35% after 10 days of immersion in water.

of 0 wt%, while PBAT had a capacity of 0.39%, which indicated that the degree of crystallinity is an important factor for water absorption of the polymer. Besides this, PBS The low water absorption capacity was due to PBAT and PBS being hydrophobic polymers with the presence of acyl groups [31]. However, at the initial stage (day 3), it was obvious that PBS, having higher crystallinity, possessed a water absorption capacity of 0 wt%, while PBAT had a capacity of 0.39%, which indicated that the degree of crystallinity is an important factor for water absorption of the polymer. Besides this, PBS with a high degree of crystallinity was less prone to water absorption as compared to PBAT due to the smaller amorphous region accessible for water intake.

*Polymers* **2021**, *13*, x 14 of 20

**Figure 7.** Water absorption of bare PBS, bare PBAT, and PBS/PBAT blends with immersion times. The PBS/PBAT/TPRH composites showed a larger water absorption capacity than **Figure 7.** Water absorption of bare PBS, bare PBAT, and PBS/PBAT blends with immersion times.

bare PBAT and PBS. The water absorption rose tremendously in the first 24 h, and reached the saturation limit after 24 h of immersion. The TPRH48/12 and TPRH36/24 showed water absorption capacity at 11.78 and 9.24%, respectively after 24 h. The composite TPRH36/24 possessed a lower water absorption capacity than TPRH48/12 due to the intrinsic nature of PBS with high crystallinity. Moreover, the water absorption capacity of PBS/PBAT/TPRH was also found to be more than PBS/PBAT/TPS, which is an attribute to the lumen and cell wall of rice husk that provide more room for the water absorption [18]. Besides, the hydrophilic nature of rice husk that favors the intermolecular hydrogen bonding enhanced the water absorption of the film. The swelling in composites occured due to the presence of internal stresses that prevents polymer matrix from absorbing water [53]. The swelling effect was observed for both TPRH and TPS blends after 3 days of immersion, which in agreement with the work was reported by Muthuraj et al. [54]. Nevertheless, TPRH36/24 and TPRH48/12 The PBS/PBAT/TPRH composites showed a larger water absorption capacity than bare PBAT and PBS. The water absorption rose tremendously in the first 24 h, and reached the saturation limit after 24 h of immersion. The TPRH48/12 and TPRH36/24 showed water absorption capacity at 11.78 and 9.24%, respectively after 24 h. The composite TPRH36/24 possessed a lower water absorption capacity than TPRH48/12 due to the intrinsic nature of PBS with high crystallinity. Moreover, the water absorption capacity of PBS/PBAT/TPRH was also found to be more than PBS/PBAT/TPS, which is an attribute to the lumen and cell wall of rice husk that provide more room for the water absorption [18]. Besides, the hydrophilic nature of rice husk that favors the intermolecular hydrogen bonding enhanced the water absorption of the film.

showed lower water absorption capacity (5.17 and 8.68%) than the reported LDPE by Sabezadeh et al. [47] with 11% absorption capacity at day 15. Water absorption characteristics influence the water vapor barrier properties of a material. Thus, the results indicated that the fabricated polymer in this work has good water vapor barrier property, which would extend the shelf life of the food. *3.7. Soil Burial Test*  The entire composites showed a smoother surface before the degradation process. The mass change in the PBS/PBAT blended composites as a function of degradation time is shown in Table 5. The macroscopic appearance of biodegradation in PBS/PBS blended composites at different burying time is shown in Figure 8. Matting of the sample surface The swelling in composites occured due to the presence of internal stresses that prevents polymer matrix from absorbing water [53]. The swelling effect was observed for both TPRH and TPS blends after 3 days of immersion, which in agreement with the work was reported by Muthuraj et al. [54]. Nevertheless, TPRH36/24 and TPRH48/12 showed lower water absorption capacity (5.17 and 8.68%) than the reported LDPE by Sabezadeh et al. [47] with 11% absorption capacity at day 15. Water absorption characteristics influence the water vapor barrier properties of a material. Thus, the results indicated that the fabricated polymer in this work has good water vapor barrier property, which would extend the shelf life of the food.

> and color change was noticeable after the degradation process. The mass loss percentage increased with increasing burying time for the entire samples, which affirmed the
