Process-Structure-Property Relationships in 3D-Printed Epoxy Composites Produced via Material Extrusion Additive Manufacturing

Extrusion-based additive manufacturing (AM) technologies, such as direct ink writing (DIW), offer unique opportunities to create composite materials and novel multi-material architectures that are not feasible using other AM technologies. DIW is a novel 3D-printing approach in which viscoelastic inks, with favorable rheological properties, are extruded through fine nozzles and patterned in a filament form at room temperature.

Recent developments in DIW of polymer composites have led to expanding the range of materials used for printing, as well as introducing novel deposition strategies to control filler orientation and create improved functional/structural composite materials. Despite these substantial advancements, the successful and optimal utilization of any AM technology necessitates a deeper understanding of the process-structure-property relationships for each material system employed. To shed light onto the process-structure-property relationship in 3D-printed polymer composites, this dissertation focuses on understanding relationships between ink composition (i.e., filler morphology and loading), ink processing conditions, ink rheology, printing parameters (i.e., nozzle size and print speed), filler orientation/arrangements, and mechanical properties in 3D-printed epoxy-based composites produced via DIW.

In this work, printable epoxy-based composite inks have been developed for DIW utilizing filler materials with different morphologies, including nanoclay (NC) platelets, fumed-silica (FS) spheroidal nanoparticles, silicon carbide (SiC) whiskers and chopped-carbon-fibers (CFs). First, the rheological requirements for successful DIW are studied using an epoxy/NC system as a model material, and the effects of the deposition process on the arrangements of NC platelets and mechanical anisotropy in 3D-printed nanocomposites are investigated. Second, the impact of filler morphology and printing parameters on the extent of mechanical anisotropy and filler orientation in 3D-printed composites are explored. Third, the effects of the ink formulation and processing parameters on the evolution of fiber length distribution (FLD) and mechanical behavior of 3D-printed CF composites are investigated. Furthermore, the effects of printing parameters on mechanical anisotropy and fiber orientation distribution (FOD) in 3D-printed CF composites are explored.

Overall, this work provides a broad framework for enabling more rigorous engineering design of 3D-printed polymer composites via material extrusion AM, as well as guiding the optimal selection of processing/printing parameters that govern microstructure and performance in 3D-printed polymer composites.