Uniaxial compression and stress relaxation tests on alginate gels

The rheological behavior of alginate gels was analyzed using uniaxial compression and stress relaxation tests. The engineering compressive stress (sigma(E))-deformation (epsilon(E)) curves were found to be concave upward and independent of the crosshead speed (V-l) for V-l greater than or equal to 120 mm/min. By considering all the stress (sigma(E))-time (t) data for t greater than 10 times the average loading period, the viscoelastic response of these gels was described by means of a 3-element Maxwell body characterized by a relaxation time of 300 s. Such gels exhibited an apparent linear viscoelastic solid behavior for epsilon(E) less than or equal to 8% and a nonlinear one for larger deformations. However, for epsilon(E) > 32 % their solid viscoelastic behavior tended to a liquid one. Empirical models allowed the viscoelastic properties, as well permanent deformation, of these gels to be quantitatively described as functions of the deformation applied and/or loading rate.