Hydration of a natural polyelectrolyte xanthan gum: Comparison with non-ionic carbohydrates

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Hydration of a natural polyelectrolyte xanthan gum: Comparison with non-ionic carbohydrates

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Publication Article, peer reviewed scientific
Title Hydration of a natural polyelectrolyte xanthan gum: Comparison with non-ionic carbohydrates
Author(s) Kocherbitov, Vitaly ; Ulvenlund, Stefan ; Briggner, Lars-Erik ; Kober, Maria ; Arnebrant, Thomas
Date 2010
English abstract
In dilute solutions, polyelectrolytes exhibit more hydrophilic properties than non-charged polymers do. However, extension of this statement on almost dry systems is questionable. In this study we present sorption calorimetric data on hydration of a natural carbohydrate polyelectrolyte xanthan gum and make comparison with analogous data of three types of cellulose which is a non-charged carbohydrate polymer. An analysis of the sorption isotherm shows that at given relative humidities xanthan gum absorbs greater amount of water than non-charged cellulose does. Nonetheless, the enthalpies of hydration of xanthan gum and of all three considered types of cellulose at zero water content are equal to −18 kJ/mol. Thus, entropy of hydration plays an important role in water sorption behaviour of xanthan gum. The apparent absence of an ion effect on polymer–water interactions can be explained by solvation of ions by OH-groups of the dry xanthan gum. Ab initio calculations presented here show that solvation of an ionic group of xanthan gum by a carbohydrate hydroxyl is as strong as hydration of the same group by water. The exothermic heat effect of hydration arises from the loss of the mobility of water on the rigid glassy environment of the polymer. For the first time, the glass transition temperature of dry xanthan gum is reported to be 60 °C.
DOI http://dx.doi.org/10.1016/j.carbpol.2010.04.055 (link to publisher's fulltext)
Publisher Elsevier
Host/Issue Carbohydrate Polymers;2
Volume 82
ISSN 0144-8617
Pages 284-290
Language eng (iso)
Subject(s) xanthan gum
hydration
sorption calorimetry
Sciences
Research Subject Categories::NATURAL SCIENCES::Chemistry::Physical chemistry::Biophysical chemistry
Research Subject Categories::NATURAL SCIENCES::Chemistry::Physical chemistry::Surface and colloid chemistry
Research Subject Categories::NATURAL SCIENCES::Chemistry::Organic chemistry::Polymer chemistry
Research Subject Categories::NATURAL SCIENCES::Chemistry::Organic chemistry::Pharmaceutical chemistry
Handle http://hdl.handle.net/2043/10750 (link to this page)

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