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Combining Modeling and Measurements to Predict Crystal Morphology in Material Extrusion

McIlroy, Claire; Seppala, Jonathan E.; Kotula, Anthony P.

Authors

Claire McIlroy

Jonathan E. Seppala

Anthony P. Kotula

Abstract

Semicrystalline polymer melts are commonly used in material extrusion (MatEx) for 3D printing. Although flows have a profound effect on polymer crystallization, the relationship between typical MatEx deformation rates and printed-part crystal morphology is yet to be understood. Here, MatEx is used to print a wall of polylactic acid filaments. The linear rheology and quiescent crystallization kinetics are characterized, infrared imaging is used to measure temperature variations during the MatEx process, and optical microscopy is employed to determine the resulting crystal morphology before and after a postprinting thermal annealing process. Our flow-enhanced crystallization model demonstrates that MatEx-induced polymer stretch leads to a higher nucleation density and greater space filling in the weld regions between deposited filaments. Consequently, after annealing, the weld regions feature smaller spherulites than the filament center, as shown by optical microscopy. Finally, flow-induced crystallization is proposed as a method to improve weld toughness.

Publication Date Jun 19, 2019
Publisher American Chemical Society
Pages 85-113
Series Title ACS Symposium Series
Series Number 1315
Book Title Polymer-Based Additive Manufacturing: Recent Developments
Chapter Number 6
ISBN 9780841234260
Institution Citation McIlroy, C., Seppala, J. E., & Kotula, A. P. (2019). Combining Modeling and Measurements to Predict Crystal Morphology in Material Extrusion. In Polymer-Based Additive Manufacturing: Recent Developments, 85-113. American Chemical Society. doi:10.1021/bk-2019-1315.ch006
DOI https://doi.org/10.1021/bk-2019-1315.ch006

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