Structural Characterization of Heterogeneities in Highly Loaded Particle Composites Fabricated via Direct Ink Writing*

Additive manufacturing (AM) via pneumatic direct ink write (DIW) extrusion offers the ability to print tailored highly solids loaded polymer composites. The AM process inherently introduces heterogeneities such as particle aggregation, porosity, periodicity, and anisotropy across several length scales. Heterogeneities such as these can be difficult to predict and their effect on material properties is not yet well understood. Therefore, this work investigates the influence of processing parameters, polymer binder, and the ratio of volume fractions of solids with a bimodal size distribution on structural heterogeneity. Two polymer binders are investigated: bisphenol A glycidyl methacrylate (BisGMA)/triethylene glycol dimethacrylate (TEGDMA) and 55k Polyvinylpyrrolidone (PVP). Silica beads of two diameters, 10 μm and 170 μm, are mixed with a binder (at ratios of 15:85, 35:65, 65:36, and 85:15 by volume) to give a total solids loading of 61.4% by volume. Non-destructive imaging is performed via X-ray micro computed tomography. By quantitatively characterizing the microstructure from these images, heterogeneities will be investigated and connected to processing and material parameters.