The viscosities of supercooled liquid fructose and glucose are measured between a lower viscosity limit corresponding to 95°C and an upper limit of about 10 6 Pa.s. The glass transition temperature of fructose is estimated from the viscosity data using different extrapolation procedures. The Vogel‐Tamman‐Fulcher and power‐law equations gave estimates of 283K and 289K, respectively and the Williams‐Landel‐Ferry equation 286K. These values are in agreement with recent calorimetric determinations of the glass transition temperature.
Abstract This study compares treatments of the compaction and stress transmission data obtained for potato starch at different water contents in the range 5‐25% (wet weight basis) compacted in a cylindrical geometry. An increase in water content leads to a greater density for a given pressure, approaching zero porosity at the higher water contents. The limiting gradient of the Heckel plot, which is the reciprocal of a generalised deformation stress, falls with increasing water content due to a plasticisation mechanism. Electron microscopy of granules taken from the compacts revelas greater plastic deformation at the higher water contents. The ratio of transmitted to applied stresses shows irregular variation with water content and degree of compaction. At the higher water contents (> 17%) the stress ratio is however relatively independent of compacted height as predicted by the classical semiparticulate analysis.
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