Flexible and transparent bio-based composites of Poly(lactic acid) and microfibrillated cellulose (MC): Mechanical, thermal, optical, thermomechanical properties and morphological evolution

Eco-composites reduce environmental impact, promote sustainability, and add value to renewable resources. This study investigated the development of sustainable composites based on poly (lactic acid) (PLA)/microfibrillated cellulose (MC), with and without the addition of epoxidized soybean oil (ESO) as a plasticizer. MC contents of 1, 3, and 5 phr (parts per hundred resin) were evaluated, while ESO was used at 5 phr. The composites were processed using extrusion and injection molding. The addition of MC to PLA resulted in agglomerates and low interfacial adhesion, limiting the mechanical properties. FTIR analysis showed that ESO interacted with PLA, promoting internal plasticization and improving interfacial adhesion with MC, which contributed to the formation of impact strength and flexible composites, as well as with optical transparency. Morphological analysis by optical microscopy and SEM indicated that ESO facilitated better distribution and dispersion of MC in the PLA matrix. The PLA/ESO/MC (5 phr) composite showed increases of 58.1% in impact strength and 467.1% in elongation at break, compared to PLA. Moreover, the composite maintained high stiffness and transparency in the range of 64–80% (400 to 800 nm). These results are promising for sustainable applications such as packaging, contributing to advances in green engineering.