Modelling flow-enhanced crystallisation during fused filament fabrication of semi-crystalline polymer melts

McIlroy, C.; Graham, R.S.

Abstract

Achieving better control in fused filament fabrication (FFF) relies on a molecular understanding of how thermoplastic printing materials behave during the printing process. For semi-crystalline polymers, the ultimate crystal morphology and how it develops during cooling is crucial to determining part properties. Here crystallisation kinetics are added to a previously-developed model, which contains a molecularly-aware constitutive equation to describe polymer stretch and orientation during typical non-isothermal FFF ow, and conditions under which ow-enhanced nucleation occurs due to residual stretch are revealed. Flow-enhanced nucleation leads to accelerated crystallisation times at the surface of a deposited filament, whilst the bulk of the filament is governed by slower quiescent kinetics. The predicted time to 10% crystallinity, t10, is in quantitative agreement with in-situ Raman spectroscopy measurements of polycaprolactone (PCL). The model highlights important features not captured by a single measurement of t10. In particular, the crystal morphology varies cross-sectionally, with smaller spherulites forming in an outer skin layer, explaining features observed in full transient crystallisation measurements. Finally, exploitation of ow-enhanced crystallisation is proposed as a mechanism to increase weld strength at the interface between deposited filaments.

Citation

McIlroy, C., & Graham, R. (2018). Modelling flow-enhanced crystallisation during fused filament fabrication of semi-crystalline polymer melts. Additive Manufacturing, 24, 323-340. https://doi.org/10.1016/j.addma.2018.10.018

• Journal Article Type: Article
• Acceptance Date: Oct 6, 2018
• Online Publication Date: Oct 10, 2018
• Publication Date: 2018-12
• Deposit Date: Oct 8, 2018
• Publicly Available Date: Oct 11, 2019
• Journal: Additive Manufacturing
• Print ISSN: 2214-8604
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 24
• Pages: 323-340
• DOI: https://doi.org/10.1016/j.addma.2018.10.018
• Keywords: Fused filament fabrication; semi-crystalline polymer melt; flow-enhanced crystallisation; polycaprolactone
• Public URL: https://nottingham-repository.worktribe.com/output/1150698
• Publisher URL: https://www.sciencedirect.com/science/article/pii/S2214860418305554