VISCOELASTIC PROPERTIES OF CA2-GELLAN AND NA+-GELLAN GUM AQUEOUS-SOLUTIONS()

Viscoelastic properties of gellan gum aqueous solutions under forces o f the order of 10(-6)-10(-8)N and displacements of 10(-3)-10(-4) m wer e studied using a magnetic rheometer constructed in our laboratory. Th e concentration of Ca2+ in the gellan gum has a strong effect upon the mechanical behaviors of the solutions: (i) solutions of Specimen 1 (C a2+ 0.5 wt%, C-p=1.15%) showed negative thixotropy; (ii) abrupt decrea se in viscosity was observed in the narrow temperature range (+/-1 deg rees C) for the solution of Specimen 2 (Ca2+ 0.1 wt%, C-p=1-3 wt%) and Specimen 3 (Ca2+ <0.01%, C-p=2-3%), while rigidity was almost constan t in the same temperature range; (iii) the solution of Specimen 3 show s unstable mechanical behavior, and this may be attributed to the inho mogeneity of the order of similar to 10(-4) m in solution. A small amo unt of Ca2+, as in the case of Specimen 2, removes this inhomogeneity from gellan gum aqueous solutions. Copyright (C) 1996 Elsevier Science Ltd