Thermogelling behaviour of starches to be used in ceramic consolidation processes

Starch is one of the agents used as both consolidator/binder of the ceramic suspension and pore former at temperature for porous ceramic processing. In this work, the thermogelling behaviour of aqueous suspensions of different starches (potato, cassava, and corn) was studied by dynamic rheological testing and optical microscopy in order to optimize the thermal consolidation of ceramic green bodies prepared by the starch consolidation method. Viscoelastic properties (G′, G″, tan δ) as a function of the temperature (30–95 °C) were determined by non-isothermal rheological measurements (temperature sweep tests). In these tests, the influence of experimental variables on viscoelastic properties, such as the amount of Dolapix CE-64 as dispersant (0, 3, 4.5, and 6 wt%), the heating rate (1, 2, 5, and 10 °C/min) and the starch concentration (14 and 40 vol%) was analyzed. Swelling capacity and the analysis of volume-weighted granule size distributions (median volume granule diameters, distribution widths and arithmetic mean diameters) in aqueous suspension, as a function of the temperature, was also evaluated. In addition, the degree of disintegration of starch granules and the rheological stability of the gels were also studied by dynamic time sweep test. The obtained results are useful in order to establish the experimental variables to be used in the thermal consolidation step for the production of porous ceramics with controlled microstructures.