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Phase Transformation Behavior of Polylactide Probed by Small Angle Light Scattering and Calorimetry
Author(s) -
Schmidt Nico,
KeukerBaumann Susanne,
Meyer Jörg,
Huber Klaus
Publication year - 2019
Publication title -
journal of polymer science part b: polymer physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.65
H-Index - 145
eISSN - 1099-0488
pISSN - 0887-6266
DOI - 10.1002/polb.24892
Subject(s) - differential scanning calorimetry , materials science , crystallinity , recrystallization (geology) , spherulite (polymer physics) , crystallization , isothermal process , composite material , thermodynamics , polymer , paleontology , physics , biology
Small angle light scattering (SALS) and differential scanning calorimetry DSC have been applied to investigate the melting of spherulites isothermally crystallized polylactide. At an isothermal crystallization temperature high enough, pure α ‐phase crystals are formed. Exposed to a temperature gradient, the crystals first melt and then recrystallize before they finally melt. With decreasing crystallization temperature, an increasing fraction of polylactide is crystallizing in the less stable α ′ ‐phase. α ′ ‐crystals also melt upon increasing the temperature but recrystallize to the more stable α ‐phase. A constant spherulite size is revealed by SALS for both processes, the α / α and α ′ / α melt‐recrystallization, until completion of the final melting, thereby supporting integrity of the spherulites throughout the entire processes. Joint DSC and SALS experiments demonstrate that the depolarized scattering invariant correlates with the heat flow recorded by DSC and thus offer an alternative measure for the degree of crystallinity. The following mechanism is identified for both processes: initial melting and recrystallization overlay each other. Crystallinity is not fully recovered upon recrystallization because only part of the original lamellae survives the melt‐recrystallization, though with an increased thickness. While lamellae are melting and reforming or simply transforming their phase, the spherulites survive the process until final melting. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57 , 1483–1495

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