Rheological and Viscoelastic Properties of Chitosan Solutions Prepared with Different Chitosan or Acetic Acid Concentrations

Chitosan (Ch) is a partially crystalline biopolymer, insoluble in pure water but soluble in acid solutions. It has attracted interest from researchers to prepare solutions using different acid types and concentrations. This research aims to study both the effect of chitosan (Ch) or acetic acid (Ac) concentrations, at different temperatures, on rheological and viscoelastic properties of Ch solutions. To study the effect of Ch, solutions were prepared with 0.5-2.5 g Ch/100 g of solution and Ac = 1%, whereas to study the effect of Ac, the solutions were prepared with 2.0 g of Ch/100 g of solution and Ac = 0.2-1.0%. Overall, all analyzed solutions behaved as pseudoplastic fluid. The Ch strongly affected rheological properties, the consistency index (K) increased and the index flow behavior (n) decreased as a function of Ch. The activation energy, defined as the energy required for the molecule of a fluid to move freely, was low for Ch = 0.5%. The effect of Ac was less evident. Both K and n varied according to a positive and negative, respectively, parabolic model as a function of Ac. Moreover, all solutions, irrespective of Ch and Ac, behaved as diluted solutions, with G" > G'. The relaxation exponent (n") was always higher than 0.5, confirming that these systems behaved as a viscoelastic liquid. This n" increased with Ch, but it was insensitive to Ac, being slightly higher at 45 degrees C.