Important Property

 

Viscosity

 

Gum arabic imparts the lowest viscosity to water of then normal, unhydrolyzed industrial gums, A comparison of its solution viscosity with tragacacanth karaya, ghatti, and corn fiber gums is shown in figure 1. Gum arabic mixes well with other industrial gums, and at high concentrations has suspending, stabilizing, and emulsifying properties. Gum arabic solutions exhibit Newtonian viscosity at concentrations up to 40%; but at higher concentrations, they acquire pseudoplastic character. Normally, gum arabic solutions are of pH about 4.5-5.5, which is near pH 6, where maximum viscosity is displayed. Solution viscosity decreases with age, following a zero rate order.

 

 

This decrease is commonly due to hydrolysis; but gum arabic solutions are affected, as are solutions of other gums, by ultraviolet radiation and other glycosidic bond-breaking phenomena. Viscosity rises with increases in pH to about 6 then gradually falls to about pH 12 , where it again levels off. However, a more or less broad maximum viscosity is displayed over the range pH 2-10. As expected, when the pH is lowered to 3 or less, the ionization of the carboxyl groups is repressed, and the polymer tends to gel and lose solubility.