From agro-waste to functional biopolymers: High-lignin PLA composites plasticized with eugenyl acetate for circular economy-based materials

Polylactic acid (PLA) is one of the most widely used bioplastics; however, its inherent brittleness and the limited filler contents typically employed restrict both its performance and bio-based content. In this work, fully disintegrable under industrial composting conditions PLA biocomposites containing exceptionally high lignin contents (30-50 wt%) were successfully developed using eugenyl acetate (EAc) as a fully natural plasticizer and itaconic anhydride-grafted PLA (PLA-g-IA) as a compatibilizer. Eugenyl acetate induced a drastic reduction in the glass transition temperature and transformed PLA into a highly ductile material, achieving strain at break values exceeding 400%. The incorporation of lignin significantly increased stiffness, hardness, and char formation, while progressively reducing toughness at high loadings. Among the investigated formulations, the composite containing 30 wt% lignin exhibited the best balance between ductility, stiffness, and bio-based content, maintaining strain at break values more than 100% higher than neat PLA. Mechanical, thermomechanical, thermal, morphological, and surface analyses confirmed that the combined plasticization-compatibilization strategy enables stable processing and functional performance even at extreme lignin contents. All materials fully disintegrated under industrial composting conditions within six weeks, demonstrating that neither lignin nor eugenyl acetate compromise end-of-life circularity. These results establish a new pathway for designing high-bio-content, fully disintegrable PLA materials through synergistic natural modification strategies.