Controlled gelation of xanthan by trivalent chronic ions

Addition of trivalent chromic ions to xanthan solutions gives rise to gel formation. The dynamic shear storage and loss moduli (0.01 – 10 rad/s) of xanthan solutions with polymer concentrations ranging from 1 to 7 mg/ml and Cr³⁺ concentrations ranging from 0 to 50 m have been studied. It is found that the rate of gel formation is strongly dependent on the Cr³⁺ concentration, but to a much smaller extent on the xanthan concentration. The gelation time is less than 1 h for 50 m Cr³⁺ and about 40 h for 2 m Cr³⁺. It is found that the minimum Cr³⁺ concentration needed to give gelation of 1–7 mg/ml xanthan is 1–2 m .