Characterization of aqueous solutions of mixture of chitosan and agar

Abstract

The influence of temperature on pH and dynamic viscosity of pure chitosan and mixture of chitosan/agar (cs/ag) solutions was studied over a temperature range of 20oC to 50oC. It was found that the pH of chitosan/agar ratio of 60/40 is the highest affected solution by temperature while all the solutions showed similar effect by temperature in terms of viscosity at a constant shear rate. Results also showed that the temperature dependence of pure chitosan solution and chitosan/agar mixtures can be described using Arhenius equation. Apparent activation energies were found to be 15.41, 16.52, 15.21 and 15.46 kJ mol-1 for chitosan/agar proportions of 100/0, 80/20, 60/40 and 50/50 respectively. Relatively high activation energy at 50/50 composition can be attributed to the co-continuous morphology of the blend at the particular composition. The effect of the presence of agar in chitosan solutions on the viscosity as a function of shear rate was also examined at room temperature. Generally, results showed two regions of flow profiles; low shear rate and high shear rate regions. At low shear rate region, the shear rate dependant viscosity decreased dramatically suggesting shear thinning behavior. However, the shear-rate dependant viscosity was found to be nearly independent of shear rate at high shear rates. In addition, lower shear thinning and higher viscosities were observed when the concentration of agar was increased.