Rheological and mechanical characterization of wet agglomerates processed in low shear mixer

The mechanical and rheological characterization of structures processed by wet agglomeration is a way to study their structural organization. The aim of this study is to submit and discuss the results of mechanical and rheological characterization of wet agglomerates obtained by wetting cereal powder in low shear mixer. For various conditions of wetting, these properties are obtained thanks to shearing and compression tests led on a powder rheometer (FT4 – Freeman Technology, UK). The analysis of the mechanical and rheological properties of agglomerates obtained after wet agglomeration process has been carried out thanks to an approach based on soil science and granular media. This approach makes it possible to highlight the great influence of water content on the rheological behavior of the agglomerates bed bulk: its increase results in variations of the friction between grains together with variations in their cohesion. These variations are analyzed regarding the modifications in the population balance induced by the increase in water content. Uniaxial compression tests make it possible to calculate, through three compression models (Kawakita, Hackel and Adams), the agglomerates strength. It is shown that it evolves according to a decreasing power law when water content increases. These results are in accordance with the fractal description of the agglomeration process that support a decrease of the agglomerates solid volume fraction, and thus of their resistance, with water content.

► This study highlights the elasto-plastic behavior of wet food agglomerates.
► Mechanical properties of agglomerates bed bulk emerge from agglomerates structuring.
► Food agglomerates’ strength follow a decreasing power law with water content.
► These results reinforces the fact that wet agglomeration in low shear mixer follow a fractal process.