Abstract
The influence of divalent (Ca 2+ and Mg 2+) and monovalent (Na + and K +) cations on the failure stresses and strains in gels formed with gellan polymer were investigated. Gellan gels containing 0.6-2.2% polymer and varying cation concentrations were tested using large compressive deformation until failure. Maximal true shear stresses and corresponding shear strains represented gel strength and extensibility. At small cation concentrations, the strength of gellan gels increased while the extensibility decreased with cation concentrations. The strongest gels were obtained at cation levels corresponding to 0.5 cations per carboxylate group in the repeat gellan unit for gels crosslinked with divalent cations and 10 to 30 cations per repeat gellan unit for gels with monovalent cations. At optimum cation levels, gellan gels with Ca 2+ were stronger than with Mg 2+, and gellan gels with K + were stronger than with Na +. Above the optimum cation levels, gellan gels became brittle, and the strength of the gels decreased with increasing cation concentrations.
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