Micro-extrusion of ceramic pastes based on eco-friendly additives – MECERAMECO

The MECERAMECO JCJC project aims then to develop, at the the Institute of Research for Ceramics (IRCER), the micro-extrusion process with an innovative approach linked to respect for the principles of green chemistry.
Micro-extrusion is a shaping process, which is used to make, from a paste, geometrically 3D complex ceramic parts at the milimetric scale. This technique has a wide range of potential applications in various domains: health, energy ... Moreover, it has great flexibility because parts can be made “on demand” from modelling in a Computer Aided Design format without requiring machining or of the development of dedicated tools for machining. In comparison with micro-injection or micro-machining, micro-extrusion presents some advantages. It is a way to move towards the manufacture of complex objects at a millimetric scale with a high productivity (reduced time for drying) and low cost (no molds and no diamond tools required).
The success of micro-extrusion depends strongly on the rheological behavior of the paste and consequently on its composition containing both the ceramic powder and the additives (solvent, dispersant, binder, plasticizer). Usually, these additives come from the petrochemical industry and could have a negative impact on the environment and on the operator’s health. French, European or even international legislations on the use of organic substances at the industrial level are becoming more and more restrictive, which often results in significant additional costs, with the upgrading of industrial installations or new ecological taxes for the recycling of waste. In order to develop materials respecting the principles of green chemistry, special attention should be paid to water-based solvents and to bio-based eco-friendly additives. Studies have already been carried out in this direction and should be exploited. For example, pastes or suspensions based on cellulose derivatives are reported in the literature. That is why, in IRCER, studies have started to explore the use of cellulose derivatives and go further by replacing them, for example, by binder based on non-chemically transformed products such as psyllium.

These preliminary studies are encouraging and should be continued. This project then has two main objectives. The first concerns the development of eco-friendly bio-sourced concentrated (> 45% vol) ceramic pastes (oxides or non-oxides) that are innovative and ready-to-use. Their rheological behavior must be adapted to the micro-extrusion process and ensure sufficient cohesion of the green ceramic part. From a fundamental point of view, the interactions between polymers and ceramic raw materials will be studied in order to optimize paste formulations. The relationship between the rheological properties of pastes, including plasticity and cohesion, and their extrudability through nozzles with a diameter of between 1 mm and 100 µm will be examined in order to establish printability criteria. The second objective is to develop, at IRCER, a digital chain specifically dedicated to the production of ceramic parts. To the opposite of the fabrication of metallic or plastic products by additive manufacturing, no software specialized on the micro-extrusion of ceramic parts, which would be able to compute the manufacturing program directly from a CAD model, is available on the market. Therefore, the only viable solution is to use and to adapt elements of digital chain already existing for other prototyping processes. The work carried out on this last point should make it possible to extrude any object from a numerical model in a quasi-automatic manner, by setting the different parameters of the digital chain, such as path computation, depending on the extrudability characteristics of the developed pastes and the desired final structural and microstructural properties.