(603a) Flow-Induced Crystallization in Materials Extrusion Additive Manufacturing

Semicrystalline polymers are often used in additive manufacturing (AM) processes due to the ease of processing in the melt state and the rapid, dramatic increase in mechanical properties during crystallization. Despite the benefits of AM, the uncertainty in the quality of the printed part makes more widespread implementation challenging. Much of the uncertainty in semicrystalline polymer AM stems from the complex relationship between processing conditions and the resulting semicrystalline microstructure. Here, we present a systematic study of printing conditions on the semicrystalline morphology of parts printed from poly(lactic acid) (PLA). The slow crystallization kinetics of PLA generate parts with low crystallinity, however a secondary annealing process at high temperatures (140 °C) generate a space-filled spherulitic texture, with smaller spherulites near the weld zone between the extruded layers. This spherulite size distribution is attributed to a higher nucleation density templated into the part by the temperature and deformation history of the printing process. We show that a combination of materials characterization and process line infrared thermography can be used in theoretical continuum modeling to predict the spatial variation in spherulite size.