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pH-Dependent Gelation of a Stiff Anionic Polysaccharide in the Presence of Metal Ions

Cross-linking of polysaccharides by metal ions provides polymer gels highly required by industrial applications. In this article, we study the rheological properties and microstructure of solutions of a stiff anionic polysaccharide xanthan cross-linked by chromium (III) ions, and we demonstrate that...

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Autores principales: Shibaev, Andrey V., Muravlev, Dmitry A., Muravleva, Aleksandra K., Matveev, Vladimir V., Chalykh, Anatoly E., Philippova, Olga E.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: MDPI 2020
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7240365/
https://www.ncbi.nlm.nih.gov/pubmed/32290178
http://dx.doi.org/10.3390/polym12040868
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author Shibaev, Andrey V.
Muravlev, Dmitry A.
Muravleva, Aleksandra K.
Matveev, Vladimir V.
Chalykh, Anatoly E.
Philippova, Olga E.
author_facet Shibaev, Andrey V.
Muravlev, Dmitry A.
Muravleva, Aleksandra K.
Matveev, Vladimir V.
Chalykh, Anatoly E.
Philippova, Olga E.
author_sort Shibaev, Andrey V.
collection PubMed
description Cross-linking of polysaccharides by metal ions provides polymer gels highly required by industrial applications. In this article, we study the rheological properties and microstructure of solutions of a stiff anionic polysaccharide xanthan cross-linked by chromium (III) ions, and we demonstrate that their properties are highly sensitive to the preparation pH. Stable gels are obtained in a wide range of pH from 2.4 to 7.8. The maximum elastic modulus is observed for the gels made at pH 6.3, and by freeze-fracture transmission electron microscopy it is shown that they are characterized by the most dense network structure. However, out of this pH interval, no gelation is observed. At low pH (< 2.4) it is due to high protonation of carboxylic groups of xanthan preventing their interaction with chromium ions, and to the disappearance of oligomeric ions, which are effective in cross-linking. At high pH (> 7.8) the absence of gelation is caused by the transformation of reactive chromium ions into insoluble chromium hydroxide. At the same time, for the gels initially formed at pH 6.3, subsequent change of pH to strongly acidic (1.4) or basic (8.9) medium does not affect appreciably their properties, meaning that chromium cross-links are stable once they are formed. These observations open a reliable route to produce polysaccharide gels with required mechanical properties in a wide pH range where they initially cannot be prepared. It is also shown that the increase of pH to 6.3 of the initially ungelled solution prepared at pH 1.5 results in gelation. This effect offers a facile way for delayed gelation of polysaccharides, which is especially required by oil industry.
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spelling pubmed-72403652020-06-02 pH-Dependent Gelation of a Stiff Anionic Polysaccharide in the Presence of Metal Ions Shibaev, Andrey V. Muravlev, Dmitry A. Muravleva, Aleksandra K. Matveev, Vladimir V. Chalykh, Anatoly E. Philippova, Olga E. Polymers (Basel) Article Cross-linking of polysaccharides by metal ions provides polymer gels highly required by industrial applications. In this article, we study the rheological properties and microstructure of solutions of a stiff anionic polysaccharide xanthan cross-linked by chromium (III) ions, and we demonstrate that their properties are highly sensitive to the preparation pH. Stable gels are obtained in a wide range of pH from 2.4 to 7.8. The maximum elastic modulus is observed for the gels made at pH 6.3, and by freeze-fracture transmission electron microscopy it is shown that they are characterized by the most dense network structure. However, out of this pH interval, no gelation is observed. At low pH (< 2.4) it is due to high protonation of carboxylic groups of xanthan preventing their interaction with chromium ions, and to the disappearance of oligomeric ions, which are effective in cross-linking. At high pH (> 7.8) the absence of gelation is caused by the transformation of reactive chromium ions into insoluble chromium hydroxide. At the same time, for the gels initially formed at pH 6.3, subsequent change of pH to strongly acidic (1.4) or basic (8.9) medium does not affect appreciably their properties, meaning that chromium cross-links are stable once they are formed. These observations open a reliable route to produce polysaccharide gels with required mechanical properties in a wide pH range where they initially cannot be prepared. It is also shown that the increase of pH to 6.3 of the initially ungelled solution prepared at pH 1.5 results in gelation. This effect offers a facile way for delayed gelation of polysaccharides, which is especially required by oil industry. MDPI 2020-04-10 /pmc/articles/PMC7240365/ /pubmed/32290178 http://dx.doi.org/10.3390/polym12040868 Text en © 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
spellingShingle Article
Shibaev, Andrey V.
Muravlev, Dmitry A.
Muravleva, Aleksandra K.
Matveev, Vladimir V.
Chalykh, Anatoly E.
Philippova, Olga E.
pH-Dependent Gelation of a Stiff Anionic Polysaccharide in the Presence of Metal Ions
title pH-Dependent Gelation of a Stiff Anionic Polysaccharide in the Presence of Metal Ions
title_full pH-Dependent Gelation of a Stiff Anionic Polysaccharide in the Presence of Metal Ions
title_fullStr pH-Dependent Gelation of a Stiff Anionic Polysaccharide in the Presence of Metal Ions
title_full_unstemmed pH-Dependent Gelation of a Stiff Anionic Polysaccharide in the Presence of Metal Ions
title_short pH-Dependent Gelation of a Stiff Anionic Polysaccharide in the Presence of Metal Ions
title_sort ph-dependent gelation of a stiff anionic polysaccharide in the presence of metal ions
topic Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7240365/
https://www.ncbi.nlm.nih.gov/pubmed/32290178
http://dx.doi.org/10.3390/polym12040868
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