Solubilization of Chitosan in Strong Acid Medium

Abstract

This paper describes the equilibrium reaction of chitosan in the presence of a strong acid HCI; the degree of protonation is determined as a function of the initial concentration of acid in which chitosan is dispersed. The solubilization of chitosan is obtained for a minimum degree of protonation α = 0.5 at a stoichiometric ratio [HCl]/[Chit-NH2] ≈ 0.5–0.6. The degree of protonation is determined by potentiometry and conductimetry The conductivity of an acidic solution decreases in the presence of chitosan: it passe-through a minimum at a degree of protonation equal to approximately 1. Under the same conditions, the relative viscosity passes through a maximum corresponding to a degree of protonation of around 0.75; it then decreases because of an excess of highly dissociated acid. The salting out of chitosan is estimated at an acid concentration of larger than 1 M.