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Rheology and gelation of deacylated gellan polysaccharide with Na+ as the sole counterion

  • E. R. MorrisEmail author
  • R. K. Richardson
  • L. E. Whittaker
Conference paper
Part of the Progress in Colloid and Polymer Science book series (PROGCOLLOID, volume 114)

Abstract

The effect of NaCl on the formation, melting, and mechanical properties of Na+ gellan gels can be divided into five regions of rheological response.
  1. 1.

    Small additions of salt, up to a total Na+ concentration of about 25 mM, have virtually no effect on the rheological properties of the ordered polymer at low temperature; the solutions remain fluid on cooling, and give mechanical spectra similar to those of entangled polysaccharide coils.

     
  2. 2.

    Slightly higher concentrations (about 40 mM Na+) induce formation of “weak gels” (i.e. solutions that remain pourable but give gel-like mechanical spectra). Network formation is attributed to Na+ ions promoting helix-helix aggregation by binding to carboxyl groups of the polymer and thus reducing charge density, and by suppressing residual electrostatic repulsion by nonspecific charge screening.

     
  3. 3.

    Na+ concentrations in the approximate range 100–300 mM give true, self-supporting, gels whose strength and setting point (T o) increase with increasing concentration of salt and which melt in two steps, attributed to dissociation of unassociated helices and cation-mediated aggregates, respectively.

     
  4. 4.

    To continues to increase with Na+ concentration over the range 300–750 mM, but the gel strength falls, suggesting destabilisation of the network structure by association of helices into a progressively smaller number of progressively larger aggregates.

     
  5. 5.

    At NaCl concentrations above about 750 mM, T o drops sharply. It is tentatively suggested that this reduction in the stability of the helix structure is of lyotropic origin.

     

Key words

Gellan polysaccharide Gelation Rheology Coil-helix transition Helix—helix transition 

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Copyright information

© Springer-Verlag 1999

Authors and Affiliations

  • E. R. Morris
    • 1
    Email author
  • R. K. Richardson
    • 1
  • L. E. Whittaker
    • 1
  1. 1.Silsoe College SilsoeCranfield UniversityBedfordUK

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