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Structural Hierarchy and Polymorphic Transformation in Shear-Induced Shish-Kebab of Stereocomplex Poly(Lactic Acid)
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
2016 (English)In: Macromolecular rapid communications, ISSN 1022-1336, E-ISSN 1521-3927, Vol. 37, no 9, 745-751 p.Article in journal (Refereed) PublishedText
Abstract [en]

The realization of hierarchical shish-kebab structures for stereocomplex poly(lactic acid) (PLA) is achieved by the application of a shear flow (100 s-1 for 1 s) mimicking what can be expected during polymer processing. Compared to the normal shearing scenarios, this transient and strong shear flow enables the creation of dense shish precursors in time- and energy-saving manner. The distribution of crystal form associated with the hierarchical structure is revealed by 2D Fourier transform infrared spectroscopy imaging, creating a unique visualization for both spatial resolution and polymorphism identification. Interestingly, in the shear stereocomplex chains are preferentially extended and crystallized as stable central cores with weak temperature dependence, whereas the development of lateral kebabs is defined by the distinct relation to the crystallization temperature. Below the melting point of homocrystals, both homo and stereocomplex crystallization are engaged in lamellar packing. Above that, exclusive stereocomplex crystals are organized into ordered lamellae. Combining the direct observations at multiscale, the ordered alignment of stereocomplex chains is recognized as the molecular origin of fibrillar extended chain bundles that constitute the central row-nuclei. The proposed hypothesis affords elucidation of shish-kebab formation and unique polymorphism in sheared stereocomplex PLA, which generates opportunities for engendering hierarchically structured PLA with improved performance. A transient and strong shear mimicking the typical melt processing scenario is used to create compact shish-kebab superstructures for stereocomplex poly(lactic acid). The highly oriented fibrillar extended chains are found to constitute the central shish, while 2D Fourier transform infrared spectroscopy imaging offered a direct visualization for determination of polymorphic transition that is associated with spatial hierarchy.

Place, publisher, year, edition, pages
Wiley-VCH Verlagsgesellschaft, 2016. Vol. 37, no 9, 745-751 p.
Keyword [en]
crystal structures, polymorphism, stereocomplex poly(lactic acid), transient shear flow, Chains, Complexation, Crystal structure, Energy conservation, Fourier transform infrared spectroscopy, High density polyethylenes, Lactic acid, Temperature distribution, Crystallization temperature, Hierarchical structures, Poly lactic acid, Polymorphic transformation, Shish kebab structures, Structural hierarchies, Temperature dependence, Shear flow
National Category
Physical Chemistry
URN: urn:nbn:se:kth:diva-188226DOI: 10.1002/marc.201500736ISI: 000375683300002ScopusID: 2-s2.0-84960969258OAI: diva2:935935

QC 20160613

Available from: 2016-06-13 Created: 2016-06-09 Last updated: 2016-06-15Bibliographically approved

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Hakkarainen, Minna
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