Effect of molecular weight on the nucleation efficiency of poly(lactic acid) crystalline phases

Effect of molecular weight on the nucleation efficiency of poly(lactic acid) crystalline phases PLA is well known to exhibit a low degree of crystallinity and slow crystallization kinetics. It is also a polymorphic material with two slightly different crystalline phases named α and α’. This work aimed at investigating the effect of PLA crystalline phases on the kinetics of crystallization, by means of a simple, telling and expedient technique, known as self-nucleation. To achieve this purpose, PLA samples were first crystallized at various temperatures to change the mix in the α and α’ phases. The samples were then partially melted by increasing the temperature near the melting temperature and then crystallized again upon cooling to examine the effect of the α and α’ crystal remnants on the non-isothermal crystallization behavior. A double crystallization peak was clearly evidenced for self-nucleated PLA samples indicative of the different crystallization efficiency of the two PLA phases using a specific thermal protocol. Thermal analysis, XRD and optical microscopy were combined to examine the effect of cooling rate and holding time at a given partial melting temperature on the ratio between the two observed crystallization peaks. Moreover, effect of molecular weight of PLA on the crystallization kinetics and the self-nucleation of PLA was investigated. The self-nucleation experiments revealed that the low and high-molecular weight PLA exhibited the highest non-isothermal crystallization temperature, Tcmax, equal to 160 °C for the samples isothermally crystallized in the range of temperature between 80 and 130 °C. Although for the high-molecular weight PLA Tcmax was a function of the original crystalline phase as well as the phase transition mechanism, for the low-molecular weight PLA, it was constant regardless of what the initial crystalline phase was. Based on crystallization and melting enthalpies, the proportion of the α and α’ phases was quantified using deconvolution analysis. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Polymer Research Springer Journals

Effect of molecular weight on the nucleation efficiency of poly(lactic acid) crystalline phases

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Publisher
Springer Netherlands
Copyright
Copyright © 2017 by Springer Science+Business Media B.V.
Subject
Chemistry; Polymer Sciences; Industrial Chemistry/Chemical Engineering; Characterization and Evaluation of Materials
ISSN
1022-9760
eISSN
1572-8935
D.O.I.
10.1007/s10965-017-1337-x
Publisher site
See Article on Publisher Site

Abstract

PLA is well known to exhibit a low degree of crystallinity and slow crystallization kinetics. It is also a polymorphic material with two slightly different crystalline phases named α and α’. This work aimed at investigating the effect of PLA crystalline phases on the kinetics of crystallization, by means of a simple, telling and expedient technique, known as self-nucleation. To achieve this purpose, PLA samples were first crystallized at various temperatures to change the mix in the α and α’ phases. The samples were then partially melted by increasing the temperature near the melting temperature and then crystallized again upon cooling to examine the effect of the α and α’ crystal remnants on the non-isothermal crystallization behavior. A double crystallization peak was clearly evidenced for self-nucleated PLA samples indicative of the different crystallization efficiency of the two PLA phases using a specific thermal protocol. Thermal analysis, XRD and optical microscopy were combined to examine the effect of cooling rate and holding time at a given partial melting temperature on the ratio between the two observed crystallization peaks. Moreover, effect of molecular weight of PLA on the crystallization kinetics and the self-nucleation of PLA was investigated. The self-nucleation experiments revealed that the low and high-molecular weight PLA exhibited the highest non-isothermal crystallization temperature, Tcmax, equal to 160 °C for the samples isothermally crystallized in the range of temperature between 80 and 130 °C. Although for the high-molecular weight PLA Tcmax was a function of the original crystalline phase as well as the phase transition mechanism, for the low-molecular weight PLA, it was constant regardless of what the initial crystalline phase was. Based on crystallization and melting enthalpies, the proportion of the α and α’ phases was quantified using deconvolution analysis.

Journal

Journal of Polymer ResearchSpringer Journals

Published: Oct 12, 2017

References

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