Madoka Hirashima

DSC and rheological studies on aqueous dispersions of curdlan

Abstract Differential scanning calorimetry (DSC) and dynamic viscoelastic measurements of aqueous dispersions of curdlan were performed to clarify the gelation mechanism. Second run DSC heating curves for aqueous dispersions of curdlan showed a single endothermic peak for dispersions heated to temperatures lower than 53°C, and splits into two peaks for dispersions heated to temperatures higher than 53°C, indicating that the structural disorders of at least two different energies are involved. Dispersions heated at temperatures higher than 120°C did not show any endothermic peak in the second run DSC heating curves indicating that structures formed at temperatures higher than 120°C are stable and thermo-irreversible. Mechanical spectra of the aqueous dispersions of curdlan showed solid-like behaviour both at 40 and 70°C although the mechanical loss tangent for the dispersion heated to a higher temperature was much smaller. All these results are consistent with previous findings that gels formed at higher temperatures are thermo-irreversible, and that gels formed at lower temperatures are thermo-reversible.

RHEOLOGICAL AND DSC STUDIES OF AQUEOUS DISPERSIONS AND GELS OF CURDLAN

Mechanical spectra of aqueous dispersions of curdlan showed solid-like behaviour both at 40°, and at 70°, and the mechanical loss tangent for the dispersions decreased with increasing temperature. 2% dispersions heated at temperatures higher than 120° did not show any endothermic peak in the second DSC run heating curves, indicating that structures formed at higher temperatures than 120° are stable and thermo-irreversible. However, 2% dispersions prepared by heating in the temperature range from 55 to 115° were thermo-reversible. Stress-strain curves for cylindrical gels of curdlan prepared at 90° were determined.