Ceramics-Silikáty 52, (4) 250 - 259 (2008)

In this work rotational viscometry is applied to characterize the flow behavior of starch-containing suspensions at room temperature and oscillatory shear rheometry to characterize viscoelastic behavior in dependence of the temperature. It is shown that the relative viscosity of starch suspensions in sugar solution exhibits a strongly nonlinear increase and the starch type with smallest granules, i.e. rice starch, exhibits the steepest increase of the relative viscosity with concentration. The flow curves of ceramic suspensions with corn starch exhibit characteristic differences, dependent on the ceramic powder: zirconia suspensions exhibit shear-thinning behavior even for high starch contents, while suspensions containing alumina exhibit shear-thickening behavior for significantly lower starch contents. The results of oscillatory rheometry show, that the temperature of the transition of the purely viscous suspensions with 20 vol.% starch in water to viscoelastic gels (gelatinized starch) is approx. 62°C for suspensions of potato and wheat, 68°C for rice and 71°C for corn starch suspensions. At 80°C gelatinized potato starch exhibits the highest gel strength or rigidity (storage modulus 39 kPa), while gelatinized rice starch is the weakest (approx. 9 kPa) and corn and wheat starch gels are intermediate (approx. 12 and 25 kPa, respectively). Starch-containing ceramic suspensions behave in a viscoelastic manner at room temperature and upon heating transform into purely elastic solids, with a strength (rigidity, characterized via the storage modulus) of more than 1 MPa.