Comparison between isothermal cold and melt crystallization of polylactide/clay nanocomposites.

The isothermal cold and melt crystallization behavior of intercalated polylactide (PLA)/clay nanocomposites (PLACNs) were studied using differential scanning calorimetry (DSC), polarized optical microscope (POM), X-ray diffractometer (XRD) and Fourier Transform Infra-Red Spectrometer (FT-IR). The results show that the degree of crystallinity of PLA matrix decreases monotonously with increasing clay loadings for both the cold and melt crystallization. The cold crystallized sample shows a double melting behavior and lower melting temperature compared to that of melt-crystallized sample, especially in the presence of clay. The crystallization kinetics was then analyzed by the Avrami and Lauritzen-Hoffman methods for further comparison between these two crystallization behaviors. The results reveal that PLA and its nanocomposites present higher activation energy in melt crystallization than that in cold crystallization due to the reptation of entire polymer chains. The addition of clay facilitates the overall kinetics of melt crystallization, which is attributed to both the nucleation effect of clay and enhanced diffusion of PLA chains. However, for cold crystallization, only very small amounts of clay can slightly increase the kinetics, while larger amounts impede the process. The presence of clay leads to a diffusion-controlled growth of nucleation of PLA matrix in the cold crystallization process and, the hindrance effect of clay hence becomes the dominant factor gradually with increasing clay loadings in the case of high-rate nucleation.