Formation of Stereocomplex Crystal and Its Effect on the Morphology and Property of PDLA/PLLA Blends

Stereocomplex-polylactic acid (SC-PLA) is obtained in poly(d-lactic) acid/poly(l-lactic) acid (PDLA/PLLA) blends under adjusting processing conditions. It is found that the degree of crystallinity of overall SC-PLA is up to 43.7% in PDLA/PLLA blends of 1:1 mass ratio. Formation of stereocomplex (SC) crystals forces molecular chains in the blends to be more closely arranged and further enhances interaction between molecular chains, thus forming a physical cross-linking network in the SC crystals, resulting in the blends having a special microstructure. The mechanism of formation of the SC crystal physical cross-linking network is elucidated by dielectric spectroscopy, and the relationships between homocomplex (HC) crystals, SC crystals, and amorphous regions in the blends are also analyzed. Interestingly, mechanical properties of the blends are significantly improved due to formation of an SC crystal cross-linking network.