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Residual alignment and its effect on weld strength in material-extrusion 3D-printing of polylactic acid

Costanzo, Andrea; Spotorno, Roberto; Candal, Mar�a Virginia; Fern�ndez, Mar�a Mercedes; M�ller, Alejandro J; Graham, Richard S.; Cavallo, Dario; McIlroy, Claire

Residual alignment and its effect on weld strength in material-extrusion 3D-printing of polylactic acid Thumbnail


Authors

Andrea Costanzo

Roberto Spotorno

Mar�a Virginia Candal

Mar�a Mercedes Fern�ndez

Alejandro J M�ller

RICHARD GRAHAM richard.graham@nottingham.ac.uk
Professor of Applied Mathematics

Dario Cavallo

Claire McIlroy



Abstract

© 2020 Elsevier B.V. Gaining a molecular understanding of material extrusion (MatEx) 3D printing is crucial to predicting and controlling part properties. Here we report the direct observation of distinct birefringence localised to the weld regions between the printed filaments, indicating the presence of molecular orientation that is absent from the bulk of the filament. The value of birefringence at the weld increases at higher prints speeds and lower nozzle temperatures, and is found to be detrimental to the weld strength measured by tensile testing perpendicular to the print direction. We employ a molecularly-aware non-isothermal model of the MatEx flow and cooling process to predict the degree of alignment trapped in the weld at the glass transition. We find that the predicted residual alignment factor, A¯, is linearly related to the extent of birefringence, Δn. Thus, by combining experiments and molecular modelling, we show that weld strength is not limited by inter-diffusion, as commonly expected, but instead by the configuration of the entangled polymer network. We adapt the classic molecular interpretation of glassy polymer fracture to explain how the measured weld strength decreases with increasing print speed and decreasing nozzle temperature.

Journal Article Type Article
Acceptance Date Jun 22, 2020
Online Publication Date Jun 30, 2020
Publication Date Dec 1, 2020
Deposit Date Jun 29, 2020
Publicly Available Date Jul 1, 2021
Journal Additive Manufacturing
Print ISSN 2214-7810
Electronic ISSN 2214-8604
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 36
Article Number 101415
DOI https://doi.org/10.1016/j.addma.2020.101415
Keywords Material Extrusion; Birefringence; Molecular Orientation; Weld Strength; Polylactic acid
Public URL https://nottingham-repository.worktribe.com/output/4738436
Publisher URL https://www.sciencedirect.com/science/article/pii/S2214860420307879
Additional Information This article is maintained by: Elsevier; Article Title: Residual alignment and its effect on weld strength in material-extrusion 3D-printing of polylactic acid; Journal Title: Additive Manufacturing; CrossRef DOI link to publisher maintained version: https://doi.org/10.1016/j.addma.2020.101415; Content Type: article; Copyright: © 2020 Elsevier B.V. All rights reserved.

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