A thermo-chemo-mechanical model for material extrusion of frontally polymerizing thermoset polymers

The material extrusion of thermoset polymers that undergo frontal polymerization produces three-dimensional structures with complex freestanding shapes without the use of sacrificial support material. In this technique, a gelled monomeric ink is extruded from a nozzle and undergoes rapid curing by a self-energized reaction front. Between extrusion and complete curing, the material experiences large deformations, viscous dissipation, rapid heating, and solidification. A mathematical model for these processes is developed in the current study to guide the selection of process parameters for achieving defect-free prints and high dimensional stability. A thermo-chemo-mechanical theory is presented to model the extruded viscoelastic filament and its transition to a fully cured thermoset polymer. Additionally, a computational model is developed to simulate the 3D printing of common structures. Numerical examples are included for linear and curvilinear extrusions to illustrate the role of printing parameters like the extrusion, front, and printer head velocities. Comparisons with experiments, including some new experiments, for archetypal geometries demonstrate the utility of the model in the identification of process parameters for defect-free prints.