Modelling Thermoplastic Filaments’ Sintering by Level Set Method

The viscous sintering kinetics of thermoplastic polymers is generally studied by monitoring the evolution of the bonding neck between two particles (spherical, or cylindrical) and using a refined Frenkel-Eshelby’s model. Recently, we showed that the entire contour of sintering filaments could be modelled by lemniscates as figure-eight shape curves to assess bonding abilities of a 3D-printable plasticized biopolymer. Using COMSOL Multiphysics® software, we set up a 2D finite element model of thermoplastic filaments’ viscous sintering with flow front tracking by the level set method. This leads to contrasted images of the two phases, i.e. air and polymer, allowing the prediction of the shape of the interface corresponding to the filaments’ contour. An image analysis procedure is applied to the simulated sequences and the ones acquired during sintering trials of extruded filaments based on zein, a corn protein plasticized by 20w% glycerol. This method is based on the assessment of the coordinates of sintered filaments’ edge pixels and their fitting by lemniscates of Booth. We show that the 2D FEM approach combined with level set method allows simulating the hot melt viscous sintering of a 3D-printable thermoplastic biopolymer as a two-phase flow. Furthermore, the image analysis is successfully applied to simulated and experimental sequences, thanks to the monitoring of the filaments’ contour, to assess their bonding kinetics and check its modelling.