Figure 9 - SEM/EDX-BSE electron images showing the homogeneous distribution of organo montmorillonites (Bofe and Chocolate) in PLA biocomposites, using Si as a trace element, via casting and extrusion methods. 1- Casting: (a and b) PLA/Bofe clay; (c and d) PLA/Chocolate clay. 2- Extrusion: (e and f) PLA/Bofe clay; (g and h) PLA/Chocolate clay 3.5 Mechanical properties The mechanical behavior of PLA biocomposites processed by casting and extrusion is shown in Figure 10. Samples obtained by casting (Figure 10a) revealed that PLA/Organo Chocolate samples exhibited lower strength compared to PLA and PLA/Organo Bofe samples (p < 0.05), likely due to excessive clay content, which may have acted as a stress concentrator, reducing the overall strength of the composite [Lima ET AL., 2019]. This suggests that the clay content in PLA/Organo Chocolate samples may have been above the optimal threshold, leading to a decrease in mechanical performance. For extruded samples (Figure 10b), tensile tests revealed that incorporating both organoclays into PLA reduced elongation at break and strength, while increasing modulus [Lima ET AL., 2021]. The addition of organoclay led to a stiffer composite, characterized by increased modulus and decreased elongation at break, indicating a more brittle material. The introduction of Chocolate organoclay into PLA nanocomposites proved more effective than Bofe organoclay, yielding a 13% increase in elastic modulus. This outcome was anticipated, as incorporating rigid fillers like clays typically enhances composite stiffness by restricting chain movement under tension. However, the presence of micrometric agglomerates of surface-modified clays may have acted as stress concentrators, contributing to reduced nanocomposite strength. Furthermore, the absence of a compatibilizing agent likely resulted in weak interfacial adhesion between the modified clay and PLA, exacerbating the strength reduction. The organoclays exhibited distinct effects on PLA morphology: Bofe organoclay primarily influenced the amorphous phase, whereas Chocolate organoclay impacted crystalline domains. As clays serve as substrates for PLA chain adhesion, Chocolate clay samples displayed higher crystallinity (Xc), yielding enhanced strength. In contrast, Bofe clay restricted chain mobility, decreasing elongation and increasing modulus.
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