The formation and transition behaviors of the mesophase in poly(D-lactide)/poly(L-lactide) blends with low molecular weights

The poly(D-lactide)/poly(L-lactide) (PDLA/PLLA) blends with low molecular weights were cast from solution. After heating to above the melting temperature, followed by cooling at various rates, DSC, WAXD and FTIR studies revealed that a mesomorphic phase developed in the PDLA/PLLA 90/10 and 80/20 (or 10/90 and 20/80) specimens when the temperature window spanned from 80 degrees C to 110 degrees C. The mesophase melted and reorganized into crystallites after the temperature increased to similar to 130 degrees C. Although the formation and transition of the mesophase was observed at lower temperatures in partially crystallized specimens, the mesophase could exist steadily when the temperature did not exceed 100 degrees C. The content of the mesophase was proven to be strongly dependent on the cooling rate, the D/L weight ratio and the molecular weights in the blends. The formation of the mesophase could be explained by the fact that the crystallization of the PLA matrix was disturbed by the addition of small amount of enantiomeric PLA.