Residual alignment and its effect on weld strength in material-extrusion 3D-printing of polylactic acid
Costanzo, Andrea; Spotorno, Roberto; Candal, María Virginia; Fernández, María Mercedes; Müller, Alejandro J; Graham, Richard; Cavallo, Dario; McIlroy, Claire
María Virginia Candal
María Mercedes Fernández
Alejandro J Müller
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, ∆n. 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|
|Peer Reviewed||Peer Reviewed|
|APA6 Citation||Costanzo, A., Spotorno, R., Candal, M. V., Fernández, M. M., Müller, A. J., Graham, R., …McIlroy, C. (in press). Residual alignment and its effect on weld strength in material-extrusion 3D-printing of polylactic acid. Additive Manufacturing,|
|Keywords||Material Extrusion; Birefringence; Molecular Orientation; Weld Strength; Polylactic acid|
This file is under embargo due to copyright reasons.
You might also like
PolySTRAND Model of Flow-Induced Nucleation in Polymers
Nonlinear shear of entangled polymers from nonequilibrium molecular dynamics
Characterising droplet breakup rates of shear-thinning dispersed phase in microreactors