Fused Filament Fabrication (FFF), or Material Thermal Extrusion (MTE), is a complementary technology to Ceramic Injection Moulding (CIM), by which parts are manufactured layer by layer by depositing extruded material (powder + polymers) through a nozzle similar to those used in plastic filament printers. This technology is an indirect additive manufacturing process since once the green part is printed, debinding and sintering processes are needed to obtain the final metal/ceramic parts. FFF is a simple and cheap technique, useful for multimaterial fabrication, since the co-printing of filaments leads to tackle the challenge of ceramic-ceramic composites printing.

In AM of ceramics by FFF, alternative thermoplastic polymers have been recently proposed as substitutes of the CIM polymeric matrices in FFF process. Bioresources and biodegradable polymers such as PolyLacti acid (PLA), combined with other thermoplastics or celluloses, reinforce the cero-carbon footprint and cero-waste feature of the sintering post-process. The design of the polymer matrix determines the printing parameters and filament properties, as well as the printed parts and sintered microstructures, while the use of the colloidal technology for phases mixing of the composite widening the scope of the FFF in ceramics. Inorganic charges up to 50 vol.% and an extremely uniform dispersion of powders within the thermoplastic matrix, are key in the indirect printing of 100% ceramic materials. The dispersion and stabilization of inorganic particles (different in morphology and size) in a colloidal suspension allows the homogeneous mixing of phases, leading to the uniform distribution of the thermoplastic structurer among ceramic particles in granules, filaments and 3D printed parts. Moreover, this colloidal approach improves anchorage of inorganic particles to the polymeric matrix, and consequently printing conditions, comparing with the traditional fusion route used for mixing composites. The use of the Colloidal Feedstock provides a continuous printing using filaments or granules. Its characterization in terms of thermal rheology provides the accurate conditions for the printing of high inorganic charged composites and hence for indirect printing of ceramic pieces with micro/nanostructures for different applications.

The authors want to acknowledge the financial support from the Spanish Government (Agencia Estatal de Investigación) through the projects PID2019–106631GB-C42 and TED2021-129920B-C41 (AEI/10.13039/501100011033).