The crystallization and phase transition behaviors of asymmetric PLLA/PDLA blends: From the amorphous state

The phase transition behaviors of melt-quenched asymmetric poly( l -lactide acid)/poly( d -lactide acid) (PLLA/PDLA) blends are investigated by the in-situ wide angle X-ray diffraction. Results indicate that the crystal structures and their transition of PLLA/PDLA specimens depend on the composition, molecular weight, and temperature. In the specimens with lower molecular weights (∼9 kg/mol), the poly(lactic acid) homocrystallites (HC), mesophase, and stereocomplex crystallites (SC) develop in specific blends. As the content of PDLA increases, the formation temperature of HC increases to a fixed value, while that temperature for SC reduces to a constant value, and the formation temperature of mesophase does not vary with composition. For the specimens with moderate molecular weights (∼30 kg/mol), the HC, modified HC, and SC develop in specific composition, the formation temperatures of both the HC are constant, and the formation of SC reduces to a fixed temperature. In the blends with molecular weight of ∼65 kg/mol, HC and SC develop, and the formation of HC does not vary, but that temperature for SC reduces slightly as more PDLA incorporated. After melting of HC, another enhancement of SC is observed in all the PLLA/PDLA specimens. The unique crystallization phenomena for these PLLA/PDLA specimens are analyzed.