On the stiffness of chitosan hydrochloride in acid-free aqueous solutions

Chitosan hydrochlorides (F-A = 0.226, i.e. DA = 22.6%) were randomly degraded by ultrasonication and characterized by viscosity measurements in aqueous acid-free solutions. It is shown that acid-free aqueous solutions of chitosan hydrochloride of variable ionic strengths (0.06 M less than or equal to mu less than or equal to 0.3 hi) are free of aggregation as evaluated by the values of the Huggins constants (0.31 less than or equal to k less than or equal to 0.63). These solutions were employed to study the solution properties of chitosan hydrochloride at different ionic strengths, which allowed the determination of its salt tolerance as well as its characteristic stiffness parameter. Following Smidsrod's approach chitosan hydrochloride gave a stiffness parameter B = 0.06, in agreement with the value reported by Rinaudo et al. It is suggested that the higher values of B reported for chitosan in the literature may be attributed to aggregation. (C) 2000 Elsevier Science Ltd. All rights reserved.