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.
|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||NAFEMS Exploring the Design Freedom of Additive Manufacturing through Simulation|
|Period||22/11/16 → 23/11/16|
- 3D printing
- computational fluid dynamics