Ultrahigh-Strength polylactic acid blend films formed by interfacial compatibilization and kinetically controlled biaxial orientation

Abstract Biaxially oriented polylactic acid (PLA) films suffer from inherent strength limitations due to melt fracture at high stretch ratios and uncontrolled crystallization. This study overcomes these barriers by leveraging our previously developed epoxidized soybean oil (ESBO)-compatibilized blend of PLA and poly(3-hydroxybutyrate- co -4-hydroxybutyrate) (P(3HB- co -4HB)), designated as PPE, to enable rheology-guided high-rate biaxial stretching. ESBO compatibilization reduces melt viscosity by 80% and enhances interfacial shear modulus to 0.66 GPa, allowing stable processing at unprecedented 6 × 6 stretch ratios-doubling the practical limit of conventional PLA films. Critically, coupling low stretching temperature (85 °C) with ultrahigh strain rate (600%·s − 1 ) suppresses grain growth and forces crystal transition, achieving record 65.7% crystallinity. Consequently, the 6 × 6-oriented PPE film delivers 176 MPa tensile strength with 38% ductility, ranking among the highest reported for PLA-based biaxially oriented films. Mechanistically, high-rate stretching induces “kinetic freezing” of nanoscale phases, while strain hardening and α-crystal alignment create oriented entanglement networks that enable simultaneous strength/toughness. This work demonstrates that while chemical compatibilization provides essential interfacial stabilization, the decisive performance leap in sustainable polymers is predominantly driven by rheology-controlled stretching kinetics during processing, which governs hierarchical structural outcomes. Graphical Abstract