Highly Filled Coextruded Dual-Layer Polymer/Ceramic Filament for Material Extrusion Additive Manufacturing

Highly filled composite feedstock in material extrusion (MatEx) additive manufacturing (AM) can enhance the properties of 3D printed parts. However, key challenges remain for highly filled composite filaments: (a) filament brittleness, (b) nozzle clogging, (c) rough surface finish, and (d) inconsistent mechanical performance due to shear-induced filler migration, agglomeration, and interference of interdiffusion with the polymer chain. In this study, we demonstrate that a highly filled core–shell dual-layer (DL) filament, with an acrylonitrile–butadiene–styrene (ABS)/calcium carbonate (CaCO3) composite core and a virgin ABS shell, is a feasible solution to overcome the limitations and maximize the advantages of composite filaments. First, we designed a coextrusion die with the two-dimensional (2D) finite element method (FEM) flow simulation to minimize interfacial flow instabilities and predict the interfacial position. The simulated interface agrees well with the experimentally measured values. Using the designed die, the highly filled core–shell DL filaments of up to approximately 30 wt % (12 vol %) were fabricated with precise diameters and adequate deviations. The parts printed using the filaments can enhance the tensile strength (22.3 MPa), anisotropy (32% deviation with respect to print directions), and visual gloss in comparison with an equivalent highly filled monolayer (ML) filament (15.3 MPa tensile strength and 80% anisotropy) under the same printing conditions. The fractured surface and cross-sectional optical view of the printed parts of DLand ML filaments elucidated the structural and rheological benefits of DL filaments in terms of interlaminar bond formation.