Melting behavior of poly(L-lactic acid): Effects of crystallization temperature and

Effects of crystallization temperature and time on the melting behavior Of poly(L-lactic acid) were studied with differential scanning calorimetry (DSC). The isothermal crystallization was performed at various temperatures (T(c)s), and DSC ruching curves for the isothermally crystallized samples were obtained at 10 K min(-1). When T-c was lower than T-d (similar to 135 degrees C), the double melting peaks appeared. The melting behavior, especially T-c dependence of the melting temperature (T-m), discretely changed at T-b (= 113 degrees C), in accordance with the discrete change of the crystallization behavior at T-b, which was previously reported. When T-c was higher than T-d, a single melting peak appeared. In addition, T-c dependence of dT(m)/dT(c) discretely changed at T-d. That is, the melting behavior, especially T-c dependence of T-m and dT(m)/dT(c), are different in three temperature regions of T-c divided by T-b and T-d: Regions I (T-c <= T-b), II (T-b <= T-c <= T-d), and III (T-d <= T-c). The effect of crystallization time on the melting behavior, melting temperature and heat of fusion in each temperature region of T-c is also discussed. (c) 2007 Elsevier Ltd. All rights reserved.