Polymer and Ion Concentration Effects on Gellan Gel Strength and Strain

Failure stresses and strains were measured in compressive, tensile and torsional modes on gellan gels at four polymer (0.6–1.8% w/v) and seven Ca ++ (1.5–60 mM) concentrations. Shear stresses at failure were equal in all three testing modes and proportional to gellan content. Low calcium gels increased linearly in strength with Ca ++ concentration until it reached a level of about 0.5 calcium ions per repeat tetrasaccharide unit of gellan gum polymer. Gel strength decreased linearly with Ca ++ at higher concentrations. Low calcium gels were extensible with failure strains decreasing as the logarithm of Ca ++ ; whereas high calcium gels were brittle and failed at a constant strain, the value of which was twice as high in compression and torsion as in tension.