Isothermal Crystallization Process of Poly(L-lactic acid)/Poly(D-lactic acid) Blends after Rapid Cooling from the Melt

We observed the crystallization process in poly(L-lactic acid) (PLLA) and poly(D-lactic acid) (PDLA) blends using in situ simultaneous small-and wide-angle X-ray scattering measurements with a high-speed temperature control cell. In situ X-ray scattering measurements revealed that density fluctuations larger than the long spacing periods grew during crystallization above 130 degrees C. In particular, the time evolution of the density fluctuations has a strong dependence on the crystallization temperature. The density fluctuations will promote the crystal nucleation and growth processes of the stereocomplex and increase with increasing crystallization temperature, which is strongly correlated with the complexation of PLLA and PDLA chains. On the other hand, below 120 degrees C, the kinetics of stereocomplex formation might be hindered by the decreased mobility, and no density fluctuations were observed in the case of homo crystal growth of PLLA or PDLA.