DSC analysis of isothermal melt-crystallization, glass transition and melting behavior of poly(L-lactide) with different molecular weights

Isothermal melt-crystallization, glass transition and melting behavior Of pOly(L-lactide) (PLLA) with different molecular weights were investigated by using differential scanning calorimetry. Analysis by Avrami equation showed that crystallization was initiated by heterogeneous nucleation, followed by 3-dimensional growth. The maximum reciprocal half-time of crystallization (1/t(1/2)) was detected at 105 degrees C. Double endothermic peaks were observed around the glass transition for PLLA with intermediate crystallinities, indicating the coexistence of bulk-like and confined amorphous regions. Doublemelting behavior was analyzed and combined with the equilibrium melting temperature evaluation by non-linear Hoffman-Weeks extrapolation, from which a value of 207.6 degrees C was deduced for PLLA of infinite molecular weight. Lauritzen-Hoffman theory was employed to analyze the crystallization kinetics. Regime II-III transition was found to occur at 120 degrees C for PLLA of lower molecular weight. The crystal morphology was also examined by scanning electron microscopy through chemical etching method. (C) 2007 Elsevier Ltd. All rights reserved.