High-molecular-weight poly(L-lactic acid) (PLLA) and poly(D-lactic acid) (PDLA) are blended at different ratios and their crystallization behavior was investigated. Solely homo-crystallites mixtures of PLLA and PDLA were synchronously and separately formed during isothermal crystallization in the temperature (T-c) range of 90-130 degrees C, irrespective of blending ratio, whereas in addition to homo-crystallites, stereo-complex crystallites were formed in the equimolar blends at T-c above 150 and 160 degrees C. Interestingly, in isothermal crystallization at T-c = 130 degrees C, the spherulite morphology of blends became disordered, the periodical extinction (periodical twisting of lamellae) in spherulites disappeared, and the radial growth rate of spherulite (G) of the blends was reduced by the synchronous and separate crystallization of PLLA and PDLA and the coexistence of PLLA and PDLA homo-crystallites. However, the interplane distance (d), the crystallinity (X-c), the transition crystallization temperature (T-c) from alpha'-form to alpha-form, the alternately stacked structure of the crystalline and amorphous layers, and the nucleation mechanism were not altered by the synchronous and separate crystallization of PLLA and PDLA and the coexistence of PLLA and PDLA homo-crystallites. The unchanged d, X-c, transition T-c, long period of stacked lamellae, and nucleation mechanism strongly suggest that the chiral selection of PLLA or PDLA segments on the growth sites of PLLA or PDLA homo-crystallites to some extent was performed during solvent evaporation and this effect remained even after melting. (C) 2011 Elsevier Ltd. All rights reserved.