DSC analysis of isothermal melt-crystallization, glass transition and melting behavior of poly(l-lactide) with different molecular weights |
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Authors: | Yong He Yanfei Hu Jia Wei |
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Institution: | a Department of Materials Science, Fudan University, Shanghai 200433, China b Research Center on Artificial Biopolymers, Max Mousseron Institute on Biomolecules, UMR 5247, Faculty of Pharmacy, University Montpellier I, 34060 Montpellier, France |
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Abstract: | 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/t1/2) was detected at 105 °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. Double-melting behavior was analyzed and combined with the equilibrium melting temperature evaluation by non-linear Hoffman-Weeks extrapolation, from which a value of 207.6 °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 °C for PLLA of lower molecular weight. The crystal morphology was also examined by scanning electron microscopy through chemical etching method. |
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Keywords: | l-lactide)" target="_blank">Poly(l-lactide) Crystallization kinetics Glass transition Melting behavior Equilibrium melting temperature |
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