Viscosity Behavior of Chitosan and N,N,N‐Trimethylchitosan Chloride Salts in Acid‐Free Aqueous Solution

Abstract

The viscosity behavior of the chloride salts of chitosan () an N,N,N‐trimethylchitosan () was studied at 25°C. The dependence of the intrinsic viscosity ([η]) on the ionic strength (μ) was investigated by using acid‐free aqueous solutions of NaCl (0.06 M≤[NaCl]≤0.3 M). The linear dependence of the intrinsic viscosity on the reciprocal of the square‐root of the ionic strength (μ−1/2) and the decrease of the salt tolerance parameter (S) with decreasing molecular weight were observed in both cases. The method proposed by Smidsrød was employed to estimate the chain stiffness of the polyelectrolytes resulting in B≅0.11 for both polymers. Taking into consideration that the average degree of acetylation of N,N,N‐trimethylchitosan is lower than that of chitosan and that most of the hydroxyl groups of the former polymer is also methylated, it is suggested that the content of acetamido groups is not the most important factor for the stiffness of chitosan.