## 4 Conclusions  
The addition of 0.10 vol.%, 0.25 vol.% and 0.50 vol.% of graphene oxide to the highly filled polymer composition with alumina resulted in a notable decline in the viscous and viscoelastic properties of the material. It was observed that the lowest concentrations of graphene oxide resulted in the most significant reduction in viscous and viscoelastic properties. The extruded filaments containing 0.10 and 0.25 vol.% GO were visually more flexible than those without GO. The tensile testing of all filaments revealed that graphene oxide effectively absorbed part of the load, thereby increasing the strength values to 11.72 MPa at 0.50 vol.% in comparison to 9.74 MPa at 0 vol.% GO. Furthermore, it is notable that the incorporation of 0.10 and 0.25 vol.% graphene oxide not only enhances the strength of filaments but also endows them with enhanced flexibility, as evidenced by an increase  
Figure 10: Microstructure (**A**,**B**) and distribution maps of aluminum (**C**) and oxygen (**D**) of the sintered sample printed from 0.10% GO/Al2O3 filament. in the relative elongation from 3.9 \(\pm\) 0.9% to 16.4 \(\pm\) 2.8%. The sample with the lowest graphene oxide concentration showed the highest plasticity. Throughout the 3D printing process using the FFF method, a decrease in shrinkage and warping of green bodies was observed in comparison to 0 vol.% GO filament. This indicates that graphene oxide has a positive effect on reducing the coefficient of thermal expansion of highly ceramic-filled polyamide 12. The possibility of obtaining ceramic products from the produced filaments was demonstrated. Complex gear-shaped samples were printed from a filament containing 0.10 vol.% GO, which were then subjected to the debinding and sintering procedures. The resulting ceramic samples retained their complex shape and exhibited a density of 94% of the theoretical value, a hardness of 14 \(\pm\) 0.8 GPa and a shrinkage of 22 \(\pm\) 0.8% (plane) and 23 \(\pm\) 0.6% (\(z\)-axis). The obtained values were lower than those reported in studies on similar topics [2; 5; 45; 46; 47; 48; 49], where density ranged from 95 to 99% of the theoretical values; the average shrinkage was 20-23%; and hardness ranged from 16 to 24 GPa. However, it should be noted that the amount of ceramic used in this study was lower than that used in the cited sources, where the aluminum oxide content was \(\geq\)78 wt.%. The present study demonstrated that a small amount of graphene oxide, at concentrations of 0.10 and 0.25 vol.%, can serve as a versatile additive, enhancing the rheological and mechanical properties of highly ceramic-filled polyamide 12. Additionally, it improved the 3D printability of the material, which ultimately facilitated the production of a ceramic product with a complex shape using the FFF method. The results achieved may contribute to fabrication of filaments with higher ceramic concentrations and enhance 3D printability of the feedstock, which will allow the manufacturing of denser ceramic products. Furthermore, the positive outcomes of this work can also be applied to different highly filled polymer compositions to improve their rheological properties in ceramic injection molding processes. As part of the planned further research, the objective is to maximize the concentration of the ceramic filler while maintaining the required rheological and mechanical characteristics of the filament. The intention is to leave graphene oxide as a reinforcing additive to alumina ceramic using vacuum furnaces or furnaces with a protective atmosphere during the debinding stage. This would result in an increase in the density and strength of the ceramic products produced using the FFF method in the future. Conceptualization, E.K. ; methodology, E.K. ; software, N.W.S.P. and A.S.; validation, E.K., N.W.S.P. and A.V.G. ; formal analysis, E.K. and A.S.; investigation, E.K. ; resources, S.N.G. and A.S.; data curation, A.V.G., N.W.S.P. and A.S.; writing--original draft preparation, E.K. ; writing--review and editing, A.S., N.W.S.P. and E.K.