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Polymers 2017, 9(11), 625; https://doi.org/10.3390/polym9110625

Equilibrium Melting Temperature of Polymorphic Poly(l-lactide) and Its Supercooling Dependence on Growth Kinetics

1
School of Materials Science and Engineering, East China Jiaotong University, Nanchang 330013, China
2
School of Mechanical and Aerospace Engineering, Queen’s University Belfast, Belfast BT9 5AH, UK
3
Institute of Chemical Materials, China Academy of Engineering Physics, Mianyang 621900, Sichuan, China
*
Author to whom correspondence should be addressed.
Received: 19 October 2017 / Revised: 8 November 2017 / Accepted: 14 November 2017 / Published: 16 November 2017
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Abstract

In this study, the isothermal crystallization process of poly(l-lactide) (PLLA) has been investigated using in situ XRD, differential scanning calorimetry (DSC), and polarized optical microscopy (POM). Linear and nonlinear extrapolation methods have been deployed to estimate the equilibrium melting temperature ( T m 0 ), which is used for analyzing the supercooling dependence of the PLLA spherulitic growth rate (G). A double-melting behavior observed for PLLA under crystallization Tc < 120 °C has been attributed to the formation of both α′ and α crystals. The T m 0 values of both α′ and α crystals have been evaluated using the linear method (172.8 °C) and nonlinear method (196.4 °C), with the nonlinear estimate being 23.6 °C higher. A discontinuity in the temperature dependence of spherulite growth rate is observed around 128.3 °C. Regime II–III transition is found to occur at 128.3 °C when T m 0 = 196.4 °C as estimated by the nonlinear extrapolation method. View Full-Text
Keywords: poly(l-lactide); equilibrium melting temperature; nonlinear extrapolation method; polymorphism; regime transition poly(l-lactide); equilibrium melting temperature; nonlinear extrapolation method; polymorphism; regime transition
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Zhang, R.-C.; Sun, D.; Lu, A.; Zhong, M.; Xiong, G.; Wan, Y. Equilibrium Melting Temperature of Polymorphic Poly(l-lactide) and Its Supercooling Dependence on Growth Kinetics. Polymers 2017, 9, 625.

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