Steady and Dynamic Rheological Properties of Concentrated Chitosan Solutions at Different Concentrations and Temperatures.

The diverse properties and applications of chitosan materials require a broad spectrum of characterization techniques. In the meantime, due to chitosan's high gel-forming capability, the rheological properties of chitosan solutions vary significantly depending on their state, i.e., solution or gel. To elucidate the solution and gel-based characteristics of chitosan, the present study was conducted to thoroughly investigate its rheological characteristics at different concentrations (1.25%, 2.5%, and 4% w/v), using various steady and dynamic rheological measurements and different mathematical models. The results showed that the concentration of chitosan solutions strongly affects their rheological properties in terms of shear stress, viscosity, and various dynamic rheological characteristics, through strain, angular frequency, and temperature sweep tests. In this regard, an elastic behavior was observed for low concentrations of chitosan solutions at lower shear strains, while the higher concentrations and higher shear strains exhibited predominantly viscous behavior. In frequency sweep measurements, the 1.25% and 2.5% w/v chitosan solutions showed viscous-like behavior and the 4% w/v solution exhibited solid-like behavior with almost constant storage and loss modulus profiles over the studied frequency range. According to temperature sweep measurements, viscous-like behavior was dominant at lower temperatures, which resulted in elastic gel structures at higher temperatures. Investigating the recoverability of prepared solutions by cyclic strain measurements revealed that the higher-concentration solutions of chitosan possess the desired capability to recover their structure. The results of this study provide detailed rheological insights into chitosan solutions suitable for designing and developing various chitosan-based products for different applications.