MODIFICATION OF FOOD CHARACTERISTICS WITH CELLULOSE HYDROCOLLOIDS II: The Modified Bingham Body ‐ A Useful Rheological Model*

Rheological measurements were made with the Weissenberg Rheogoniometer on a series of unctuous materials including butter, margarine, an ointment, and gels prepared from sodium carboxymethylcellulose of a low degree of substitution. In steady shear, these substances show a sharply peaked stress overshoot. The stress response to an imposed sinusoidal strain is almost a square wave. These responses may be qualitatively described by a modified Bingham body consisting of a viscous element of viscosity, ν, a yield element having a yield stress of s̀0, r at rest and s̀0, s when moving (s̀0, r≥s̀0, s), and an elastic element of modulus, G, connected in series. The response of this model for imposed steady and sinusoidal shear has been calculated in terms of the model parameters. The boundary condition equations for the imposed sinusoidal shear case cannot be solved in a closed form. Numerical solutions were obtained by computer for the full range of the parameters using a successive approximation technique. The predictions of this model are in good agreement with experimental results, and enable such results to be interpreted in terms of meaningful physical parameters.