Enhancing Mechanical Properties of Poly(lactic acid) via Synergistic Effects of Chain Extension and Uniaxial Hot Stretching

Uniaxial hot stretching of poly(lactic acid) (PLA) has been demonstrated to substantially enhance its toughness while maintaining high strength. Building on this concept, we demonstrated the synergistic regulation of PLA molecular chains through chain extension and uniaxial hot stretching, providing an effective approach for enhancing the mechanical properties of PLA. The results indicated that an appropriate amount of chain extender (e.g., 1.5 wt %) promoted the formation of localized cross-linked structures. During uniaxial hot stretching, these structures significantly reduced the regularity of PLA molecular chains and refined the crystalline size, resulting in uniformly distributed, small crystallites. This microstructural optimization increased the strength of PLA to 144.6 ± 2.5 MPa with 1.5 wt % chain extender and effectively prevented brittle fracture caused by stress concentration at grain boundaries, achieving a balance between strength and toughness. The combination of chain extension and uniaxial hot stretching presents an effective strategy to substantially enhance the mechanical and thermal properties of PLA. The findings of this study provide a theoretical foundation and technical support for the development of high-performance PLA materials, with broad application prospects in sustainable packaging, biomedicine, and structural components.