Abstract
Cellulose-based materials are a promising biomaterial
candidate for certain medical applications, such as
wound-care products. We studied the potential of
nanocellulose-based hydrogels for use as pastes in the 3D
printing of structures with special functionality for
medical applications. We used computational fluid
dynamics (CFD) to relate the rheological properties of
the paste and the printing parameters to the resolution
and quality of the printed specimen.
The considered printing paste was two times
microfluidized bleached kraft pulp pretreated with
TEMPO-mediated oxidation. Transient and steady-state
rheometry was carried out to obtain parameters for
rheological modelling, and capillary viscosimetry was
used to verify the limiting behavior at very high shear
rates. 3D printing experiments were carried out for
validation, to determine the dependency between operating
pressure and mass flow within the nozzle, as well as the
printing speed and line resolution at constant operating
pressure.
Different levels of rheological description were
considered for explaining the observed flow behavior.
These include models with both instantaneous and
history-dependent response to the flow conditions. We
implemented separate CFD models for the flow conditions
inside the printing head and during the deposition.
Volume of fluid method was used to describe the
interaction between the hydrogel and the surrounding air.
The calculations were performed with the open source CFD
package OpenFOAM.
The rheometry showed that, under steady-state conditions,
the nanocellulose hydrogel accurately follows power-law
fluid behavior. However, transient experiments indicated
that thixotropy plays a significant role in situations
with rapidly varying shear rates. The CFD analysis of the
printing head revealed that practical shear rates can
reach much higher values than ones considered in
conventional rheometry. The effect of thixotropy on the
flow was studied both inside the printing head and during
deposition. We demonstrated the feasibility of the models
to describe the main elements of the 3D printing process.
The models can be used to study the sensitivity of the
printing resolution and specimen quality on the material
properties and the printing parameters.
Original language | English |
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Publication status | Published - 2016 |
Event | NAFEMS Exploring the Design Freedom of Additive Manufacturing through Simulation - Helsinki, Finland Duration: 22 Nov 2016 → 23 Nov 2016 |
Seminar
Seminar | NAFEMS Exploring the Design Freedom of Additive Manufacturing through Simulation |
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Country/Territory | Finland |
City | Helsinki |
Period | 22/11/16 → 23/11/16 |
Keywords
- 3D printing
- nanocellulose
- hydrogel
- computational fluid dynamics
- ProperTune