Thixotropy of Systems with Shear Thinning and Plastic Flow Behavior

Abstract

The definition of the thixotropy is a decrease in viscosity with time in shear and a subsequent recovery of viscosity after the shear deformation is removed. We used therefore start-up experiments with constant shear rates and can speak consequently of shear stress instead of viscosity. The shear stress increases sharply at the beginning of the stress growth experiment, passes an overshoot and begins to decrease up to the steady state shear stress. We can assume that a stress growth curve with an overshoot points out to thixotropic behavior. After the steady state shear stress is reached, the shear deformation is stopped, and the stress relaxation begins. It is to be expected that the shear stress will recover after the stress relaxation. Systems with shear thinning and plastic flow behavior were examined. The thixotropy is discussed in relation to the flow behavior. Stress growth experiments were performed with shear rates from the first Newtonian region and from the shear thinning region of the systems with shear thinning flow behavior. Stress start-up experiments were carrying out with shear rates from the first and second yield stress regions and from the transition section of a system with plastic flow behavior.

Effect of functional lipids on the quality of walnut butter prepared from defatted walnut meal by ball mill grinding

“…Thixotropy could reflect the phenomenon that the structure was disrupted and the viscosity of the system decreases when shear was applied to a system. After the removal of shear, the sample could gradually and reversibly return to the initial stress and viscosity, which was typical for non-Newtonian fluids (Hadjistamov, 2019). The thixotropic behavior was related to the "untangling-entanglement" process of protein molecules and the alignment of molecular protein chains in the shear direction (Benchabane and Bekkour, 2008).…”