Advances in the spatial & temporal characterization of structure development during extrusion 3D printing

Additive manufacturing (AM), or 3D printing, is used to rapidly process polymeric materials into complex geometries. Extrusion-based AM is one of the most popular techniques. Here, filaments are deposited onto a print bed by extrusion through a nozzle attached to a translating print head. While AM is widespread and relevant for a range of novel applications, its implementation has outpaced our fundamental understanding of the structure development that occurs during the printing process. Many complex rheological and thermodynamic processes compete against one another during printing, which leads to defects at the filament-filament interface such as void formation or undesirable anisotropy in the mechanical properties. Characterization and quantification of direct structure development is necessary to improve interfacial adhesion and optimize the ultimate material properties. Synchrotron X-ray scattering techniques provide a promising route to observe real-time structural evolution across a wide regime of length scales (angstrom to hundreds of nanometers), and time scales (sub-millisecond to 1000s of seconds) relevant to the AM process. Recent investigations using small angle (SAXS), wide angle (WAXS), and X-ray photon correlation spectroscopy (XPCS) are described. The measurement of multi-scale, non-equilibrium behavior in real printing operations could be used to expand upon the rheological behavior of various printing materials, and further understand the influence of complex flows that occur during 3D printing