Structuration of wheat powder by wet agglomeration: Case of size association mechanism

The wet agglomeration of powder results from the combined action of mechanical energy and the addition of a wetting liquid binder. The wet agglomeration process is induced by successive contacts and/or collisions between native particles and nuclei/agglomerates. The aim of this work is to identify the phenomenological law that leads to the association mechanism occurring during the wet agglomeration of durum wheat semolina in a low shear mixer. This work is based on the study of the distribution of properties of the structures formed during the process. A twin study of the water content and solid volume fraction distributions of structures appearing in the bulk for each experimental wetting highlights the growth regime of an agglomerate. In this regime, a decrease in solid volume fraction associated with an increase in median diameter is observed. This leads to the fractal growth of structures. Despite this, the agglomerates progressively saturate, pore network filling occurring faster than volume expansion. Analysis of the standard deviations of the hydro-textural parameters (water contents and solid volume fractions) highlights their dependence on the diameters of agglomerates. This suggests that wet agglomeration preferentially occurs between structures of the same size and texture. This pattern of association is in accordance with the fractal structuration previously highlighted in low shear mixers under the same wetting and mixing conditions. (C) 2013 Elsevier B.V. All rights reserved.