Synthesis and viscoelastic characterization of sulfonated chitosan solutions

In this study, sulfonated chitosan (SCS) with a water-soluble property was synthesized and rheologically characterized. The Maxwell Model can accurately describe a regular chitosan (CS) solution. The G′, G″ crossover shifted toward lower frequencies as the CS concentration increased, revealing an increase of relaxation time. A frequency–concentration superposition master curve of CS solution was therefore plotted and well fitted by the experiment result. However, a modified Maxwell Model, which captures the occurrence of the quasi-plateau region of G′ in the low-frequency range, representing the initially falsely connected structure between the sulfonic acid groups and the protonated ammonium groups, was proposed for the SCS solution. The crossover of G′ and G″ was found to be independent of the SCS concentration, indicating its lower molecular weight yields a high overlap concentration, Ce. The rheological properties of SCS solutions can be affected as the following factors are increased in the order of declining effect; pH level > temperature > salt concentration.