Equilibrium Melting Temperature of Polymorphic Poly(l-lactide) and Its Supercooling Dependence on Growth Kinetics
School of Materials Science and Engineering, East China Jiaotong University, Nanchang 330013, China
School of Mechanical and Aerospace Engineering, Queen’s University Belfast, Belfast BT9 5AH, UK
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
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 (
), 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
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
= 196.4 °C as estimated by the nonlinear extrapolation method.
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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.
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(11):625.
Zhang, Ri-Chao; Sun, Dan; Lu, Ai; Zhong, Meiling; Xiong, Guangyao; Wan, Yizao. 2017. "Equilibrium Melting Temperature of Polymorphic Poly(l-lactide) and Its Supercooling Dependence on Growth Kinetics." Polymers 9, no. 11: 625.
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