Flow behaviour, linear viscoelasticity and surface properties of chitosan aqueous solutions

A study of rheological properties of chitosan solutions was carried out in terms of polymer concentration (0.05–2.5 wt%) and temperature (5–25 °C). The chitosan solutions studied exhibited Newtonian behaviour at concentrations lower than 0.25 wt%. Above this value, the rest of the systems showed shear-thinning behaviour. The viscoelastic properties of chitosan solutions above 0.25 wt% were characterized by oscillatory shear measurements under small-deformation conditions and the results showed fluid-like viscoelastic behaviour. Time-concentration and time-temperature superposition methods were carried out to obtain an overall master curve; where the rheological properties of chitosan solution at a specific temperature or concentration can be predicted over a broad time scale. The fact that the activation energy for steady shear flow was higher than for oscillatory shear promoted deviations from the Cox–Merz rule, when temperature was decreased at the highest chitosan concentration studied In addition, their dynamic surface tension behaviour and surface viscoelastic properties were explored. The time-dependent decrease in surface tension along with the limiting elasticity of the interface seems to indicate that commercial chitosan may play the role of an emulsifier as well as a stabiliser of O/W emulsions.