*3.1. Biodegradation*

The biodegradation process of the synthesized bio-composites is represented by Figures 2a–c, 3a–d, 4a–d, 5a–d and 6. The weight loss of the bio-composite films was estimated after 7, 15, and 30 days. Linear biodegradation was observed in the bio-composite samples, which indicated obedience to pseudo-zero-order kinetics in reaction rates and constant, as well as independent rates of biodegradation [35]. From the figures, it can also be seen that the bio-composite films had a slower degradation initially. However, after 30 days the degradation was enhanced. The results also suggest that the addition of fenugreek slowed the degradation process of the starch-based bio-composite films. A sample with a lower percentage of fenugreek was obtained with maximum degradation among all synthesized bio-composite films. Ecologically-friendly and biodegradable properties were proved by the outcomes demonstrated.

**Figure 2.** Prepared samples for soil biodegradation test (**a**) 5% fenugreek, (**b**) 10% fenugreek, and (**c**) 15% fenugreek.

**Figure 3.** 5% fenugreek containing bio-composite degradation sample on (**a**) Day 1, (**b**) Day 7, (**c**) Day 15, and (**d**) Day 30.

**Figure 4.** 10% fenugreek containing bio-composite degradation sample on (**a**) Day 1, (**b**) Day 7, (**c**) Day 15, and (**d**) Day 30.

**Figure 5.** 15% fenugreek containing bio-composite degradation sample on (**a**) Day 1, (**b**) Day 7, (**c**) Day 15, and (**d**) Day 30.

**Figure 6.** Biodegradibility comparison of the synthesized bio-composites at different percentages of fenugreek.

#### *3.2. Tensile Strength*

Figure 7a–c shows the tensile behavior of the developed bio-composites. Table 4 shows the comparison of tensile strength, tensile strain, and the Young's modulus of the prepared samples. An increase in the percentage of fenugreek decreased both the tensile strength and the tensile strain of the bio-composites, up to a certain level. Maximum stress development was reflected in the tensile strength of the film during the tensile testing [36]. The higher concentration of fenugreek decreased tensile strength and increased flexibility [37]. The presence of 15% of fenugreek exhibited the lowest tensile strength of 1.357 N/mm2, due to the increased water presence in the matrix of the film, provided by the hygroscopic nature of fenugreek. The disarrangement of the polymer network was caused by the fenugreek present in the film, which worked to decrease the tensile strength and increase the film's flexibility [38]. Lower concentration percentages of fenugreek were distributed properly in the matrix, resulting in higher mechanical strength. However, minimum tensile strain was obtained after the addition of 10% of fenugreek. Tensile strain slightly increased after that percentage.

**Table 4.** Comparison of tensile strength, tensile strain and Young's modulus of the prepared samples.


**Figure 7.** Tensile behavior of the bio-composite samples at various ratios of fenugreek (**a**) 5%, (**b**) 10%, and (**c**) 15%.

#### *3.3. Scanning Electron Microscopy*

The microstructure of the developed bio-composites is seen in Figures 8a–d, 9a–d and 10a–d. Defects such as voids, cracks, and micropores are seen in SEM images, and result in more porous and irregular surfaces. The samples containing a higher percentage of fenugreek show more micropores, due to the cohesion between the tamarind starch and fenugreek. Voids and micropores may affect the modulus of elasticity and tensile strength of the bio-composite samples [39,40]. The biodegradation process of the bio-composite samples may be accelerated in the soil, due to the interaction between micropores and microorganisms [41]. Impurities are seen with globular-like fibers on the surface in higher magnification images, because potency is provided to the biomass by the non-cellulosic contained in the natural biomass [42].

**Figure 8.** SEM images of 5% fenugreek bio-composite at (**a**) 500 μm (**b**) 200 μm (**c**) 100 μm (**d**) 50 μm.

**Figure 9.** SEM images of 10% fenugreek bio-composite at (**a**) 500 μm (**b**) 200 μm (**c**) 100 μm (**d**) 50 μm.

**Figure 10.** SEM images of 15% fenugreek bio-composite at (**a**) 500 μm (**b**) 200 μm (**c**) 100 μm (**d**) 50 μm.
