Study of rheological properties and printability criteria of alumina pastes for micro-extrusion process
GOURDONNAUD D. 1, BOURRET J. 1, PATELOUP V. 1, CHARTIER T. 1, PICTON L. 2, CHALEIX V. 3, BIENIA M. 1, GEFFROY P. 1
1 CNRS, Institute of Research for Ceramics (IRCER), UMR 7315, University of Limoges, European Ceramics Center, Limoges, France; 2 Laboratoire Polymères, Biopolymères, Surfaces (PBS), UMR CNRS 6270, Normandie University, UNIROUEN, Mont-Saint-Aignan, France; 3 Institut OmegaHealth, LABCiS – UR 22722, University of Limoges, Limoges, France
Additive manufacturing corresponds to a large family of shaping processes, enabling to build 3D ceramic parts with a layer-by-layer approach, by combining material and computer sciences. Among them, the micro-extrusion process consists of forcing a paste through a nozzle whose inner diameter is at the submillimeter range. The final quality of micro-extruded ceramic parts mainly depends on the rheological behavior of the paste strongly linked to the nature of the organic additives.
The most common organic additives come from the petrochemical industry and can potentially be harmful to the environment or operators' health. Hence, this work aims to develop an environmentally friendly alumina ceramic paste for the micro-extrusion process, in accordance with green chemistry requirements1. Alumina pastes have been prepared in an aqueous medium with both a natural dispersing agent and a binder. Particular attention was paid to the chemical interactions between additives, paste rheology and printability.
The physico-chemical characterizations of the organic additives used in this work (molar mass of polymer, etc..) have been made. The dispersing efficiency of ammonium lignosulfonate was compared to that of ammonium polymethacrylate. Moreover, to go more deeply, the use of polysaccharides gels as a natural binder has been studied. The influence of the formulation and of the order of constituent incorporation on the rheological properties, the plasticity, the cohesion or on the printability of alumina pastes has been examined.
Thus, according to the results, characterization of the viscoelastic properties of alumina pastes is necessary, but insufficient to distinguish two pastes with different behavior of printability. This confirms that the usual printability criteria of pastes reported in the literature for micro-extrusion process do not allow the prediction of the real behavior of pastes in working conditions of the micro-extrusion process.
Then, the correlations observed between the nature of organic additives and the printing quality of ceramic parts have highlighted the importance of the interactions between the constituents of the paste. This shows in particular that the cohesion of the organic matrix with the ceramic particles is one of the key parameters for the printability of pastes. Indeed, the internal cohesion of the paste depends mainly on both the space occupied by the polymers and on the strength of the physico-chemical interactions between the organic phase and ceramic particles. From a microscopic point of view, this cohesion manifests itself by the organization and mobility of the constituents in the paste under the high shear stresses during the extrusion. From a macroscopic point of view, it is clearly related to the migration of liquid phase during extrusion or to the elastic recovery after printing.
This study thus allows to identify other key parameters of printability, which lead to control and to improve the impression quality of micro-extruded ceramic parts. Therefore, it is likely possible to define new criteria, based on the characteristics of the network of polymer chains including the ceramic particles.
[1] C. Duran et al. "Eco-friendly processing and methods for ceramic materials -a review". Journal of the Ceramic Society of Japan, 116(1359):1175–1181, 2008.
