Thermoreversible Association and Gelation of Methylcellulose in Aqueous Solutions

Abstract

Methylcellulose is an associative polymer. Aqueous solutions of methylcellulose show the interesting thermoreversible gelation behavior that they gel upon heating and return to a liquid upon cooling. Thermally induced hydrophobic association and dissociation of methylcellulose in water explain the mechanism of thermoreversible gelation. The thermal analysis proves that the association of methylcellulose molecules in water is thermorevesible but the dissociation occurs at much lower temperatures than those for the association. The viscoelastic properties of methylcellulose aqueous solutions correlate excellently with the micro thermal results. The evolution of the gel elasticity G e at a given gelling temperature (65 to 75°C) could be approximately expressed by G e ∼ c 2.56. At the same concentration, increasing of molecular weight of methylcellulose increases the heat absorbed during the sol-gel transition as well as G e. While the addition of salts does not change the patterns of gelation and degelation of methylcellulose, the salts could shift the sol-gel transition to lower or higher temperatures from a salt-free methylcellulose solution, depending on the salt type.