Gelation mechanism of deacetylated rhamsan gum

Abstract

Non-Newtonian behaviour and dynamic viscoelasticity of deacetylated rhamsan gum in aqueous solution were measured with a rheogoniometer. The flow curves, at 25 °C, of deacetylated rhamsan gum showed Newtonian behaviour at concentrations below 0.2%, but plastic behaviour above 0.3%. The yield value of the last named solutions was estimated to be 8.0 and 11.0 Pa at 0.3 and 0.5%, respectively. The elastic modulus increased with an increase in concentration and gelation occurred at a concentration above 0.3%. The elastic modulus for a solution of 0.3% decreased a little with increase in temperature up to 30 °C, then it showed a constant value with increase in temperature. However, when the temperature reached 50 °C, which was estimated to be a transition temperature, the elastic modulus decreased rapidly with further increase in temperature. The elastic modulus of the deacetylated rhamsan (0.2%) increased with addition of CaCl 2 (6.8 mM) and gelation occurred at low temperature (0 °C). The elastic modulus showed a little high value in the presence of urea (4.0 M). Possible gelation mechanism of the deacetylated rhamsan was proposed.