Modelling Of Coupling Between Specific Energy And Viscosity During Twin Screw Extrusion Of Starchy Products
Résumé
Starchy products are commonly transformed by twin screw extrusion, either for the manufacturing of food products (extrusion cooking of snacks or breakfast cereals, for example) or for the production of bio-based materials (bioplastics). During the extrusion process, starch is submitted to high shear rates and stresses which lead to a modification of its basic structure. As many properties of the extruded starch are directly connected to the molecular weight and its distribution, it is very important to be able to predict the changes experienced during the extrusion process. In order to model the transformation of starch during twin screw extrusion process, it is thus necessary to take into account the strong coupling between viscosity and thermomechanical treatment. It is the purpose of the present work. We have used the software Ludovic0, which was developed ten years ago to calculate the flow of a polymer along a twin screw extruder. We have assumed that the degradation reaction (viscosity decrease) was linked to the specific energy received during the flow. We have compared extrusion cases with and without viscosity/energy coupling and we show that it is important to take it into account in order to correctly predict the parameters of the extrusion process (torque, energy, product temperature...) and the starch transformation.