Balance between strength and toughness for fully bio-based composites achieved by oriented design of filler

Polylactic acid (PLA), a green and sustainable polymer, has shown promise as an alternative to conventional plastics, yet its practical utilization remains constrained by inherent brittleness and poor ductility. Here, we report flexible and twistable PLA composites engineered through the incorporation of tailored bio-based copolymer filler. At filler loadings of only 10 wt%, the composites achieve a tensile elongation at break of 159.60 % and a toughness of 52.40 kJ/m 3 , representing 14-fold and 13.3-fold enhancements over pristine PLA, respectively. Notably, the tensile strength remains high at 52.19 MPa, demonstrating an exceptional balance between strength and toughness. Mechanistic studies reveal favorable interfacial compatibility between the filler and PLA matrix, with energy dissipation occurring via synergistic mechanisms including matrix cavitation, crazing, and shear yielding. The composites exhibit remarkable room-temperature deformability, sustaining extensive bending and torsional strains. These findings advance the development of robust yet adaptable bioplastics, offering new opportunities for eco-friendly electronic devices and sustainable packaging materials.