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Materials 2017, 10(8), 871; doi:10.3390/ma10080871

Synchrotron Microtomography Reveals the Fine Three-Dimensional Porosity of Composite Polysaccharide Aerogels

1
Department of Food and Environmental Sciences, P.O. Box 66 (Agnes Sjöbergin katu 2), University of Helsinki, FI-0014 Helsinki, Finland
2
X-ray Tomography Group, Swiss Light Source, Paul Scherrer Institute, 5232 Villigen, Switzerland
3
ESRF—The European Synchrotron, CS40220, Grenoble CEDEX 9, 38043 Grenoble, France
*
Author to whom correspondence should be addressed.
Received: 31 May 2017 / Revised: 24 July 2017 / Accepted: 25 July 2017 / Published: 28 July 2017
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Abstract

This study investigates the impact of ice-templating conditions on the morphological features of composite polysaccharide aerogels in relation to their mechanical behavior and aims to get a better insight into the parameters governing these properties. We have prepared polysaccharide aerogels of guar galactomannan (GM) and tamarind seed xyloglucan (XG) by enzymatic oxidation with galactose oxidase (GaO) to form hydrogels, followed by conventional and unidirectional ice-templating (freezing) methods and lyophilization to form aerogels. Composite polysaccharide aerogels were prepared by incorporating nanofibrillated cellulose (NFC) into polysaccharide solutions prior to enzymatic oxidation and gel formation; such a cross linking technique enabled the homogeneous distribution of the NFC reinforcement into the gel matrix. We conducted phase-enhanced synchrotron X-ray microtomography (XMT) scans and visualized the internal microstructure of the aerogels in three-dimensional (3D) space. Volume-weighted pore-size and pore-wall thickness distributions were quantitatively measured and correlated to the aerogels’ mechanical properties regarding ice-templating conditions. Pore-size distribution and orientation depended on the ice-templating methods and the NFC reinforcement that significantly determined the mechanical and shape-recovery behavior of the aerogels. The results obtained will guide the design of the microporous structure of polysaccharide aerogels with optimal morphology and mechanical behavior for life-sciences applications. View Full-Text
Keywords: polysaccharide; nanofibrillated cellulose; ice-templating; synchrotron microtomography; image analysis polysaccharide; nanofibrillated cellulose; ice-templating; synchrotron microtomography; image analysis
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

Supplementary materials

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    Description: Supplementary data consist of 8 videos (Video S1 to Video S8) and word document file which contains supplementary figures (From Figure S1 to Figure S7). Video S1: Video (360° rotation) of 3D reconstructed structure of oxidized GM (GMox) aerogel prepared by conventional freezing (CF). Video S2: Video (360° rotation) of 3D reconstructed structure of oxidized GM (GMox) aerogel reinforced with 25% NFC (GMox-NFC), prepared by conventional freezing (CF). Video S3: Video (360° rotation) of 3D reconstructed of oxidized GM (GMox) aerogel prepared by unidirectional freezing (UF) using liquid nitrogen. Video S4: Video (360° rotation) of 3D reconstructed structure of oxidized GM (GMox) aerogel reinforced with 25% NFC (GMox-NFC), prepared by unidirectional freezing (UF) using liquid nitrogen. Video S5: Video (360° rotation) of 3D reconstructed structure of oxidized XG (XGox) aerogel prepared by conventional freezing (CF). Video S6: Video (360° rotation) of 3D reconstructed structure of oxidized XG (XGox) aerogel reinforced with 25% NFC (XGox-NFC), prepared by conventional freezing (CF). Video S7: Video (360° rotation) of 3D reconstructed structure of oxidized XG (XGox) aerogel prepared by unidirectional freezing (UF) using liquid nitrogen. Video S8: Video (360° rotation) of 3D reconstructed structure of oxidized XG (XGox) aerogel reinforced with 25% NFC (XGox-NFC), prepared by unidirectional freezing (UF) using liquid nitrogen. Figure S1: Segmented middle slice (s1080/2160) from Local thickness map of GMox (A) and GMox-NFC (B) prepared by conventional freezing (CF) method and unidirectional freezing (UF) method (C & D), respectively, for pore size distribution. Figure S2: Segmented middle slice (s1080/2160) from Local thickness map of XGox (A) and XGox-NFC (B) prepared by conventional freezing (CF) method and unidirectional freezing (UF) method (C & D), respectively, for pore size distribution. Figure S3: Volume weighted pore wall thickness distribution of GMox (A) and GMox reinforced with NFC (B) using conventional freezing (CF) method. Volume weighted pore wall thickness distribution of GMox (C) and GMox reinforced with NFC (D) prepared by unidirectional freezing (UF) method. Figure S4: Volume weighted pore wall thickness distribution of XGox (A) and XGox reinforced with NFC (B) using conventional freezing (CF) method. Volume weighted pore wall thickness distribution of XGox (C) and XGox reinforced with NFC (D) prepared by unidirectional freezing (UF) method. Figure S5: Segmented middle slice (s1080/2160) from Local thickness map of GMox (A) and GMox-NFC (B) prepared by conventional freezing (CF) method and unidirectional freezing (UF) method (C & D), respectively, for pore wall thickness distribution. Arrows indicate the observed buckling effect. Figure S6: Segmented middle slice (s1080/2160) from Local thickness map of XGox (A) and XGox-NFC (B) prepared by conventional freezing (CF) method and unidirectional freezing (UF) method (C & D), respectively, for pore wall thickness distribution. Arrows indicate the observed buckling effect. Figure S7: Cubical samples for aerogels after mechanical compression test. GM= guar galactomannan, XG=tamarind xyloglucan, ox=oxidized, NFC= nanofibrillated cellulose, CF=conventional freezing, UF=unidirectional freezing.

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Ghafar, A.; Parikka, K.; Haberthür, D.; Tenkanen, M.; Mikkonen, K.S.; Suuronen, J.-P. Synchrotron Microtomography Reveals the Fine Three-Dimensional Porosity of Composite Polysaccharide Aerogels. Materials 2017, 10, 871.

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