CARBOXYLATION OF SCLEROGLUCAN FOR CONTROLLED CROSS-LINKING BY HEAVY-METAL IONS

Samples of carboxylated scleroglucan, sclerox, with a degree of carboxylation in the side-chains varying from 10 to 50% were made in order to investigate the potential of using carboxylation as a means to control subsequent gelation by heavy metal ions. The storage and loss moduli of aqueous solutions of sclerox samples as a function of time were determined at T = 20 degrees C and 30 degrees C after addition of trivalent chromium ions. The theological characterization showed a transition from a viscoelastic liquid to a gel with a characteristic time depending on the chromium concentration and the degree of carboxylation. For 20% carboxylation, the rate of change in the storage modulus could be controlled within nearly three orders of magnitude from 10(-3) to 1 Pa min(-1), using total chromium concentrations ranging from 0.3 to 6 mM. This rate was decreased by a factor of 2-5 by reducing the degree of carboxylation to 10%. The present study indicates that carboxylation of scleroglucan can be used to control the rate of gelation mediated by heavy metal ion complexation. This finding suggests that extension of the application range of this polysaccharide from an efficient viscosifer for polymer flooding to profile modification of high temperature oil reservoirs is attainable.