## 1 Introduction  
Fused deposition modeling (FDM) or fused filament fabrication (FFF) technology is a method of creating three-dimensional (3D) objects by sequentially applying layers of molten plastic. This is the most popular 3D printing method in the world, which is used in millions of 3D printers--from simple models to industrial systems. FFF printers work with various types of plastic. The products created using this technology are suitable for product testing, prototyping and production of ready-to-use objects. Currently, FFF printing is actively developing in the field of printing using highly filled ceramics filaments with polymer binder. This method is one of the ways to obtain finished ceramic parts using additive technologies. The idea of the process is, firstly, to obtain a green body with a complex spatial configuration using the FFF method; then, the polymer binder is removed from the green body using a catalytic and/or thermal method; and finally, sintering of the green ceramic body is carried out. The advantages of this technology include its low cost compared to other additive printing methods; the disadvantages are the high porosity of finished products and limited accuracy [1]. The solution to these problems can be achieved by increasing the content of ceramic filler in the filament. The higher the content of the ceramic component, the lower the content of the polymer component, and thus, the porosity and shrinkage during sintering of the green body will be lower. A reduction in porosity indicates an increase in the density of the c ceramic piece, which influences the improvement in its mechanical properties. However, an increase in the filler concentration makes the filament brittle and harms the printing of green bodies [2; 3; 4; 5; 6; 7]. This occurs because the inclusion of solid particles in the polymeric matrix limits its molecular mobility and, in turn, increases its viscosity. For this reason, it is necessary to constantly ensure that the 3D printer nozzle is not clogged with ceramic filler and that the nozzle thread does not break or deform, as this would negatively affect the productivity and efficiency of the process. In addition, it must be ensured that the high solids content is well distributed together with the polymeric binder, since heterogeneity in the filament leads to the formation of pores and defects in the parts. Thus, in order to implement the use of filaments with a high ceramic content in 3D printing, it is necessary to determine the balance between the composition of the filler and the rheological properties of the filled ceramic polymer composition, as well as the flexibility of the thread obtained from it. For this purpose, it is necessary to modify the polymer component in order to reduce the viscosity, ensure the uniform distribution of the ceramic filler, increase the flexibility of the resulting filaments and preserve the fluidity of melted material during printing. Currently, there is no unambiguous scientific and technical solution to this problem. To impart the necessary rheological behavior, a large number of different technological additives, such as dispersants, binders, surfactants, thickeners, etc., are used. Each of these additives has a different effect on the viscoelastic behavior of thermoplastics and filaments made from them. Therefore, for each new filament composition, an individual selection of the necessary additives and their volume concentrations is required. Polyamide 12 (PA12) was selected as the backbone polymer. This thermoplastic has proven its worth even in FFF printing technology. Polyamide is resistant to abrasion and UV radiation; moreover, it has excellent flexibility. And one of the main advantages of this type of plastic is that it is not prone to coking at high temperatures, which is important during the further thermal debinding and sintering of ceramic. Alumina (Al\({}_{2}\)O\({}_{3}\)) was chosen as the ceramic filler.