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 (), 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.
Highlights
Poly(L-lactic acid) (PLLA), a semi-crystalline polymer, has attracted a lot of attention due to its biodegradation, recyclability, being producible from renewable resource, and nontoxicity to the human body and the environment [1,2,3,4]
The degradation of PLLA is closely related to polymer morphology, crystal structure, and thereby the crystallization history
Since the crystallinity and microstructure of PLLA are determined by its thermal history and crystallization process, it is important to establish an in-depth understanding of the process–structure–properties relationship in order to obtain a material with controlled structures and desired properties
Summary
Poly(L-lactic acid) (PLLA), a semi-crystalline polymer, has attracted a lot of attention due to its biodegradation, recyclability, being producible from renewable resource, and nontoxicity to the human body and the environment [1,2,3,4]. The excellent biodegradable and biocompatible properties of PLLA enabled its wide application in biomedical field as well as other industrial sectors such as homeware, packaging, etc. In tissue engineering applications in particular, the growth kinetics of cells and tissues can be remarkably improved using PLLA substrates designed with appropriate degradation rates. The degradation of PLLA is closely related to polymer morphology, crystal structure, and thereby the crystallization history. Much research effort has been devoted to increasing the crystallinity of PLLA, as this will lead to improved material mechanical properties such as the elastic modulus and strength. Since the crystallinity and microstructure of PLLA are determined by its thermal history and crystallization process, it is important to establish an in-depth understanding of the process–structure–properties relationship in order to obtain a material with controlled structures and desired properties
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