A Highly Toughened Poly(lactic acid)/Ethylene-co-Vinyl Acetate Blend with the Simultaneous Addition of Hydrophobic Nanoparticles and Compatibilizer

In recent years, due to environmental pollution and sustainability issues, plastic industries have been encouraged to use biodegradable polymers. Poly(lactic acid) (PLA) is one of the most well-known biodegradable polymers with the advantage of bio-based nature. However, the inherent brittleness of PLA is its main disadvantage. The blending technique is the most effective and practical method to overcome the brittleness of PLA.

A highly toughened PLA was prepared through physical melt-blending with ethylene-vinyl acetate (EVA) in the presence of hydrophobic nanosilica and SEBS-g-MA block copolymer compatibilizer. The morphology, thermal properties, mechanical properties, and linear rheology of the samples were investigated.

Transmission electron microscopy (TEM) images revealed that nanosilica is predominantly localized in the EVA droplets and at the interface of PLA and EVA. Some were also resided in the PLA matrix. Upon incorporating of nanoparticles, the interfacial strength improved and that the average droplet size was decreased. In the presence of compatibilizer, the morphology considerably changed: the dispersed spherical EVA phase turned into the cylindrical shape. Addition of copolymer and nanoparticles decreased the crystallization of PLA in the blends. Addition of 5 phr nanosilica considerably enhanced tensile toughness, elongation-at-break, and impact strength. On the other hand, the simultaneous addition of nanoparticles and compatibilizer dramatically improved the mechanical properties. For example, the elongation-at-break and impact strength of the compatibilized PLA/EVA blend containing 5 phr nanosilica were increased from 7% and 5.1 kJ/m2 to 141% and 71 kJ/m2 (compared to a neat blend), respectively. Finally, the microstructure of the blends was assessed through rheological measurements.