Scleroglucan gelation by in situ neutralization of the alkaline solution.

Scleroglucan gels were prepared by neutralization of aqueous alkaline solution of scleroglucan by in situ release of acid. Transition of scleroglucan chains in a disordered state to the triple-helical state result in cross-linking of the polysaccharide. The pH and the storage and loss moduli, G' and G' ', were determined as a function of time after initiating the pH reduction. Experiments were performed in the temperature range from 20 to 90 degrees C and in the polymer concentration range from C(p) = 10-200 mg/mL. The concentration dependence of the apparent plateau value of the storage modulus showed a lower critical concentration, C(p,0), in the range 12-15 mg/mL needed for gelation and a second power dependence of G' on concentration in the range 50-200 mg/mL. In situ pH reduction was achieved using formamide (methanoic acid) or ethyl acetate (ethyl ethanoate) which hydrolyze in alkaline solution, yielding carboxylic acids. The more rapid hydrolyses of ethyl acetate compared to formamide yielded a faster decrease of pH in solution and a more rapid increase of the storage modulus. The present gelation process of scleroglucan based on the in situ reduction of pH has advantages in applications where external control of the conditions is difficult to achieve.