Overcoming Strength-Ductility Trade-off in Fully Biodegradable Polylactic Acid/Elastomer Composites: Synergistic in Situ Topological Fibrillation and Supercritical CO 2 -Induced Nanocrystals

Polylactic acid (PLA) is one of the most widely studied biodegradable polymers, yet its adoption in high-performance applications remains limited by its intrinsic brittleness, low toughness, and poor thermal resistance. Considerable efforts have been devoted to overcoming these shortcomings, but achieving simultaneous improvements in strength, ductility, and heat resistance without sacrificing biodegradability remains a critical challenge. Here, we show a scalable strategy that integrates in situ fibrillation of poly(butylene adipate- co -terephthalate) (PBAT) with supercritical CO 2 -induced nanocrystals to overcome these limitations. The fibrillated PBAT phase provides a high surface-area morphology that enhances interfacial interactions and heterogeneous nucleation, while nanoscale nanocrystals formed under ambient scCO 2 promote ductile deformation by enabling chain mobility that contrasts the brittleness typically induced by thermal annealing. The prepared PLA/PBAT composites exhibit superior tensile performance (71.0 MPa strength and 21.8% elongation), significantly elevated Vicat softening temperature (∼155 °C), and accelerated alkaline hydrolysis, thereby coupling great mechanical robustness with environmental degradability. This multiscale structural design not only surpasses traditional trade-offs in biodegradable polymers but also advances the development of biobased plastics that combine high functionality with a closed-loop sustainable lifecycle.