Favorable formation of stereocomplex crystals in poly(l-lactide)/poly(d-lactide) blends by selective nucleation.

An aryl amide derivative (TMB-5) was used to nucleate the poly( l -lactide)/poly( d -lactide) (PLLA/PDLA) blend for the first time. The effect of TMB-5 nucleating agent on the crystallization behavior of PLLA/PDLA blend was systematically investigated. The selective nucleation of stereocomplex (sc) crystals by incorporation of TMB-5 was realized under appropriate crystallization conditions. During the cooling process, various morphology of TMB-5 due to its partial or complete dissolution in the PLLA/PDLA blend melt was observed. Furthermore, an sc crystals layer on the lateral surface of TMB-5 was found. Upon cooling a PLLA/PDLA blend from 260 °C at rates between 2 and 100 °C/min, 0.5 wt% addition of TMB-5 induced a single melting peak of sc crystals and no homocrystallization was observed in the subsequent DSC heating scan. The melting temperature of the sc crystals was found to decrease in the presence of TMB-5 from 230 to ca. 200 °C, which is still 20 °C higher than that of PLLA homopolymer. The results suggest that the supramolecular structure of the nucleating agent plays an important role in the crystallization of the PLLA/PDLA blend. The difference in solubility and recrystallization ability of TMB-5 in polymer melt results in the variation of crystallization behavior of PLLA/PDLA blend, which is correlated with the concentration of TMB-5 and crystallization conditions including the final melting temperature, annealing time and cooling rate. [ABSTRACT FROM AUTHOR]