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 d ivalent ion type and polymer concentration. Failure strength and defor mation were measured in compression and related to concentrations of g ellan and bound cations in gel matrices. Insufficient cations formed w eak, extensible gels. Maximum gel strength was achieved at 0.5 divalen t 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 th e same polymer concentration. Excessive cations weakened the gels. Twi ce as much reduction in gel strength resulted from additional Ca++ as compared to the same additional amount of Mg++. Differences between st rengths of the gels may be attributable to polymer cofigurations at ju nction zones in relation to cation size.