Enhancing Multifunctionality and Morphology Refinement in Poly(lactic Acid)/thermoplastic Starch Blends Using Nano-Lignin as a Compatibilizer

Abstract

ABSTRACT A multi-component system was developed using poly(lactic acid) (PLA), thermoplastic starch (TPS), and micro- and nano-lignin via melt mixing. This research addresses the challenge of compatibilization in immiscible polymer blends while also imparting multifunctional properties. Morphological analysis revealed that nano-lignin is a more effective compatibilizer than micro-lignin, achieving significant morphology refinement by reducing the TPS domain size from 15–25 µm in the blend to 4–10 µm in the nanocomposite (~60–75% reduction). Rheological characterization revealed improved elasticity, with a G′ slope decreasing from 0.37 in the blend to 0.09 in the nanocomposite, indicating improved interfacial adhesion. Nano-lignin also demonstrated effective nucleation, increasing PLA crystallinity from 6.7% in pure PLA to 34.1% in the nanocomposite. The nanocomposite also showed higher water contact angles (61.5°) than the blend (47°) and the micro-lignin-loaded blend (48.5°), with a significantly smaller change over time. Potent antioxidant properties were obtained for the blends loaded with both micro-lignin (70.3 ± 3.6%) and nano-lignin (84.2 ± 2.9%). The bacterial adhesion experiments revealed that the nano-lignin-loaded blend exhibited effective antibacterial activity (log reductions of 2.24 and 2.10 against S. aureus and E. coli, respectively). The results demonstrate the potential of PLA/TPS/nano-lignin systems for advanced materials applications that require multifunctional properties. GRAPHICAL ABSTRACT