Mechanical Properties of Gellan Gels in Relation to Divalent Cations

Mechanical behavior of gels formed with gellan polymer crosslinked by calcium and magnesium ions was studied to determine the influence of divalent ion type and polymer concentration. Failure strength and deformation were measured in compression and related to concentrations of gellan and bound cations in gel matrices. Insufficient cations formed weak, extensible gels. Maximum gel strength was achieved at 0.5 divalent cations/repeat tetrasaccharide unit, assumed to be the condition for maximal numbers of complete junction zones. At optimum cation levels gels with Ca ++ were about 1.2 times stronger than gels with Mg ++ at the same polymer concentration. Excessive cations weakened the gels. Twice as much reduction in gel strength resulted from additional Ca ++ as compared to the same additional amount of Mg ++ . Differences between strengths of the gels may be attributable to polymer configurations at junction zones in relation to cation size.