Extensional Stress-Induced Orientation and Crystallization can Regulate the Balance of Toughness and Stiffness of Polylactide Films: Interplay of Oriented Amorphous Chains and Crystallites

Polylactide (PLA) films with an excellent balance of toughness and stiffness were realized by extensional stress efficiently. For the relatively low extensional stress, gauche–gauche conformers that originated from the oriented amorphous chains lead to super-toughening behavior. Among higher extensional stress, strain-induced orientation and crystallization act as the driving force of reinforcement. This mechanism is evidenced by the pronounced enhancement in the elongation at break from 16.9 up to 294.9% accompanying the variation yield strength from 45.3 up to 135.5 MPa. The highest elongation at break results from the early stretching stages, whereas the highest yield strength is obtained from a high draw ratio. More impressively, PLA films show temperature-invariant super-ductility and reinforcement at low temperatures (0 and −20 °C). This work provides a preferable and scalable method to fabricate competitive PLA materials, expanding the practical application of sustainable polymers served at a wide temperature range or in harsh environments.