Experimental assessment and 2D-Modelling of the viscous sintering of superimposed filaments based on biopolymer

Abstract. Additive Manufacturing by Molten material Extrusion (AM-ME) of biocompatible and edible parts based on natural biopolymers, such as zein, a protein extracted from corn, opens prospects for applications in the pharmaceutical field. Cohesion between deposited layers requires filament spreading and diffusion of macromolecules at the interface. Viscous sintering has to be characterized and modelled in the case of zein, to better control its processing in the molten state. Sintering kinetics of polymer melts is generally assessed in an instrumented furnace and modelled using the Frenkel-Eshelby approach. It is based on the evaluation of the growth rate of the bonding neck between two circular parts, linked to the melt’s surface tension (Γ), the driving force, and viscosity (η). It was recently completed by the acquisition of 3D scans by dynamic X-ray tomography (5.2 μm pixel size, 1 scan/s) on the ANATOMIX beamline of Synchrotron SOLEIL, to follow the hot-melt sintering of 4 filaments (LFilament=5 mm, ∅Filament=2 mm) disposed in two layers. The analysis of the reconstructed volumes leads to assess the decreasing size of the central pore during sintering. 2D modelling is carried out by FEM combined to Level Set with COMSOL Multiphysics®. It requires a simplification of the geometry according to an axial symmetry and an adaptive time-stepping. At 120 °C, a typical temperature to process plasticized zein, simulated and experimental sintering are similar, with a decrease rate of the central pore at about 1%/s. Increasing sintering rates are obtained as the temperature and surface tension increase.