CHITOSAN CARBOXYLIC-ACID SALTS IN SOLUTION AND IN THE SOLID-STATE

When chitosan is associated to simple carboxylic acids, such as formic , acetic, etc., electrostatic interactions occur, resulting in a salt formation, to a greater or lesser degree. Fourier transform infra-red (FTir) spectroscopy and potentiometric techniques were used to charact erize the nature of such interactions, in aqueous solutions and in fil ms. The evolution of solid state samples during storage and upon dehyd ration was studied, by FTir spectroscopy and transmission X-ray diffra ction. Results showed that the carboxylic acid content of the films pr ogressively decreased in relation with the physicochemical parameters of the acids (pK(a), solubility, etc.). These results were compared wi th those obtained with a strong acid such as HCl or a complex carboxyl ic acid (lactic). In X-ray diffraction experiments, three crystalline structures of chitosan were found: a hydrated form, independent of the chemical nature of the salt, and two dehydrated forms depending on th e chemical structure of chitosan.