Abstract: The slow crystallization rate and insufficient toughness of polylactic acid (PLA) limit its wide application. In this study, a series of poly(ε-caprolactone-b-D-lactide) (PCL-b-DLA) block copolymers with different segment ratios were designed and synthesized, and then blended with poly(L-lactic acid) (PLLA) as nucleation and toughening agents. The effects of copolymer segment composition and loading content on the crystallization behavior and mechanical properties of PLLA were systematically characterized by nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and tensile testing. The results show that the PDLA hard segments can form stereocomplex crystals with PLLA, significantly promoting heterogeneous nucleation, while the PCL soft segments absorb energy through plastic deformation, enhancing toughness. When the copolymer segment ratio was 5:5 and the loading content was 5%–10%, the crystallization rate of the blend system was significantly increased, the elongation at break reached approximately 10%, and the tensile strength remained at 55–60 MPa. Imbalanced segment ratios or excessive loading lead to decreased compatibility, weakening the toughening and nucleation effects. Through rational design of the soft/hard segment ratio of the block copolymer, this study achieves synergistic improvement in the crystallization performance and toughness of PLLA, providing a feasible strategy for the development of high-performance PLA materials.

Key words: Polylactic acid, Poly（ε-caprolactone）, Block copolymer, Nucleating agent, Stereocomplex crystal