Improved Crystallization and Mechanical Performance of Poly(L‐Lactic Acid) via Incorporation of Biodegradable Polyurethane: Role of the Prepolymer Molecular Weight and Stereocomplex Crystallization

In this study, poly(lactic acid)‐based polyurethanes (PLA‐based PUs) made from poly( d ‐lactic acid) (PDLA) with molecular weights of 2, 5, and 10 kg/mol were melt‐blended with poly( l ‐lactic acid) (PLLA) to enhance its toughness without any additional compatibilizers. The properties of the PLLA/PU blends were systematically investigated considering the M n, PDLA . The results showed that too low or too high M n, PDLA was unfavorable to the original toughness of PLA‐based PU and its corresponding toughness of blends owing to their ratio of hard/soft segments, while its tensile strength remained high (> 45 MPa) regardless of M n, PDLA . Given this optimal M n, PDLA of 5 kg/mol, the PLLA/PU blends without and with stereocomplex (SC) crystallites exhibited an elongation at break of 138.3% and 282.5%, respectively, while the latter was 48 times greater than that of neat PLLA. Due to the presence of SC crystallites, the blends showed a fast crystallization rate, which crystallized within 1.2 min, whereas neat PLLA required 53.7 min. The presence of SC crystals increased complex viscosity, which further rose with increasing M n, PDLA due to the higher extent of SC crystallization. This work may provide a strategy for developing PLA‐based materials with enhanced toughness.