Tensile strength of pressure-agglomerated potato starch determined via diametral compression test: Discrete element method simulations and experiments

Abstract

Starch is important excipient and binder in agglomerates, tablets, capsules, briquettes, and pellet formulations for food, pharmaceutical, biomass, coal/biomass fuel, and metallurgy applications. The aim of this study was to compare the results of determination of the tensile strength of cylindrical starch agglomerates via a diametral compression test using a macro-approach following Hertz's solution, with those obtained via the micro-approach using the discrete element method (DEM). Potato starch with moisture contents of 12% and 17% was compacted in a cylindrical die 10 mm in diameter with a displacement velocity of 0.02 mm s−1 and compressed to 38, 76, 115, and 153 MPa. The tensile strength was measured in the diametral compression test with a deformation rate of 0.033 mm s−1. EDEM software was used to perform numerical simulations. The components of the stress tensor in the agglomerate were determined in the representative volume element with the shape of a cuboid (0.25 × 0.25 × 1 mm3). DEM simulations using the linear elastic–plastic model with linear adhesion exhibited good agreement with the experimental results. With the agglomerate deformation, the curvature of the compressive-force chains—in the shape of two arches combined with the tension-force chains—increased. At failure, the crack was initiated in the vicinity of the agglomerate centre and propagated towards the loading platens, damaging the connections between the compressive-force chains. Hertz's formula correctly described the tensile strength of the agglomerates for an adhesive stiffness-to-plastic stiffness ratio higher than 0.04.