Rheology and crystallization behavior of asymmetric PLLA/PDLA blends based on linear PLLA and PDLA with different structures

In this study, several asymmetric poly(L-lactide)/poly(D-lactide) (PLLA/PDLA) blends were prepared by adding small amounts of PDLA with different structures into linear PLLA matrix. The effect of PDLA on rheological behavior, crystallization behavior, nucleation efficiency and spherulite growth of PLLA was investigated. Rheological results indicated that PLLA/PDLA blends showed solid-like viscoelastic behavior at low temperature (<200°C), and the cross-linking density of PLLA/PDLA melt at 180°C followed the order: PLLA/6PDLA > PLLA/L-PDLA > PLLA/3PDLA > PLLA/4PDLA. No-isotherm and isotherm crystallization results indicated that the crystallization capacity of PLLA/PDLA blends was strongly related to the PDLA structure, crystallization temperature and thermal treatment temperature. Furthermore, the dimension of crystal growth during isotherm crystallization presented the obvious dependent on the PDLA structure. The nucleation efficiency of sc-crystallites in the blends and spherulite density during isothermal crystallization were also studied. Nucleation efficiency of sc-crystallites in the PLLA/S-PDLA blends showed the obvious dependent on thermal treatment temperature with respect to PLLA/L-PDLA, and nucleation efficiency sc-crystallites in the PLLA/S-PDLA blends first decreased and then increased as the thermal treatment temperature increased. Spherulite density of PLLA/PDLA blends was also related to thermal treatment temperature and the PDLA structure. This study has discussed the temperature dependence of the stereocomplex networks between PLLA and PDLA with different structure, and then its consequential influence on rheology and crystallization capacity of PLLA, which would provide the theoretical direction for PLA processing.