Revealing filler morphology in 3D-printed thermoset nanocomposites by scanning microbeam X-ray scattering

Room temperature direct-ink-write printing of epoxy-nanoclay-carbon fiber composites produces parts with high stiffness and strength. Establishing clear relationships between print parameters, filler orientation, and properties is difficult, in part owing to challenges in characterization. Here, we perform scanning microbeam X-ray scattering with 5 micrometer spatial resolution on cross-sections of printed parts with (a) epoxy-nanoclay composite and (b) epoxy-nanoclay-carbon fiber reinforced composite. The nanoclay morphology is directly visualized, illuminating the road geometry with far greater clarity than other techniques. Near the boundary of each road, the nanoclay platelets are preferentially oriented coplanar with the road boundary. Shear alignment within the nozzle during extrusion, and road-to-road shear upon deposition are two proposed factors leading to this orientation. In the sample containing carbon fiber, wide angle X-ray diffraction enables the mapping and visualization of the fibers directly onto the road geometry. The carbon fiber does not significantly affect the nanoclay morphology. Finally, from the small angle X-ray scattering map, we qualitatively reproduce a polarized optical microscope image, revealing that optical microscopy is capable of visualizing the large-scale road structure in these epoxy-nanoclay systems.