*3.2. Morphology and Structural Properties*

The SEM was applied to study the samples' surface morphology before and after landfills for up to two weeks, as shown in Figure 2. The SEM micrographs of the pure PLA sample show a flat and smooth surface. However, some scratches occurred on the PLA surface when UV irradiation up to 500 h was applied. It is clear that the polymer's structure was degraded under UV light radiation and so the degradation process in the soil environment would become much more intense. According to the SEM results of PES, starch seeds were relatively well distributed in the structure. After being exposed to UV light for 500 h, the PES sample's surface was affected negatively and the changes in the morphology are observable. As observed in the micrographs of PSEs, starch particles had acceptable distribution in the PLA phase, considering no emulsifier was used. PSE<sup>s</sup> became sensitive after UV exposure, with some bubbles formed on the surface leading to a destruction in the surface after the landfill period. The PSE<sup>3</sup> film micrograph before being treated with UV displayed a very smooth and uniform morphology with no pore or bubble on the surface. However, after exposure to UV light, the PSE<sup>3</sup> film was mostly degraded and displayed some pores in the range of 1.5 to 2 µm on the surface.

**Figure 2.** SEM micrographs of PLA film composites before and after degradation at 1.5 k× magnification.

After six weeks of landfilling, the SEM micrographs of samples showed progressive biodegradation for the PLA and starch samples (PSES, PSE<sup>3</sup> and PSE32), whereas PES experienced less degradation than them. The reason might be found in the type of bonds in the PES sample, which is single covalent bonds [57]. Therefore, microorganisms showed less tendency towards the PES sample. The addition of starch to the PLA ester groups caused the compound more prone to degradation [58]. In contrast, it is known that the addition of polar groups to PE makes it more resistant to biological degradation [59]. Comparing the SEM images of PSE<sup>3</sup> and PSE<sup>32</sup> indicates the effect of PEG solvent on forming the pores in the film structure. As can be seen, the use of ethanol as a solvent resulted in better PEG dispersion and smoother surface in PSE<sup>32</sup> [60]. It is important to notice that the UV irradiation caused a dramatic change in the films' surface like forming bubbles and irregularities, leading to a faster degradation rate when they had been landfilled. It can be seen that the surface of samples after landfill became porous and also cracks were formed rooting in the microorganisms' activity and their effect on the morphology. The degradation rate depends on different factors, among which the nature of microorganisms, soil humidity, pH, temperature and the physicochemical properties of the substrate can be enumerated [61]. The pure PLA sample did not experience a high degradation rate compared to the PLA/starch films. Therefore, it cannot be considered as a suitable biodegradable polymer. However, the addition of a biopolymer such as starch increased its biodegradability properties dramatically.
