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 (σ_E)-deformation (?_E curves were found to be concave upward and independent of the crosshead speed (V_t for V_t≥ 120 mm/min. By considering all the stress (σ_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 ?_E≤ 8% and a nonlinear one for larger deformations. However, for ?_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.