Creep-recovery-creep tests to determine the yield stress of fluid gels containing gellan gum and Na+

• Creep-recovery-creep tests as a method to determine the yield stress are assessed.
• LA-gellan gum fluid gels with Na+ is the system selected to apply the method.
• Unstable results are observed near the yield stress, the value assigned being 3.6 Pa.
• Flow curve derived from the tests illustrated a very shear thinning behaviour.

In this work, combined creep-recovery-creep tests were designed to determine the yield stress and the inception of non-linear time-dependent rheological behaviour for fluid gels containing 0.2 wt% gellan gum and 0.22 M Na+ as promoting cation of the gel formation. Experiments were performed from 3 Pa up to 6 Pa and samples were allowed to relax for the required equilibration time to avoid the effects of shear history. The response of these tests at the smaller stresses studied (below critical shear stress of 3.6 Pa) was controlled by non-linear viscoelasticity. Subsequently, a slight increase in shear stress above the critical shear stress by just 0.1 Pa resulted in a dramatic change in the creep flow properties. This made it possible to determine a practical yield stress and the onset of thixotropic properties. In addition, it was possible to determine the shear rate dependence of viscosity from the creep-recovery-creep tests, which illustrated the very shear thinning behaviour of these fluid gels.

Figure optionsDownload as PowerPoint slide