Characterization of gellan gels using stress relaxation

Abstract

The effect of testing parameters on stress relaxation characteristics and the relationship between those characteristics and intrinsic gel properties were investigated. Gellan gels were tested in stress relaxation using different crosshead speeds (3–300 mm/min) to apply strain (3–20%) to specimens of 21 and 31 mm diameter with aspect ratios of 0.5, 1.0 and 1.5. Relaxation appeared to be associated with a release of hydraulic pressure in the gel matrix. The relaxation rate was inversely related to specimen diameter, but positively related to the pore sizes in the gel matrix. Increasing the applied strain resulted in larger initial stresses but slightly lower equilibrium stresses. The equilibrium stresses were positively related to the strength of the gels and, thus, to the degree of crosslinking in the polymer network. As long as the polymer networks were not permanently damaged during relaxation tests, the gel structure could be restored upon soaking in water.