Currently, several principles of 3D printing are known and have been gradually developed and improved. The most commonly used is the FFF (Fused Filament Fabrication) or FDM (Fused Deposition Modeling) method. The principle of this method is that the filament is fed into the nozzle and the resulting melt is applied on the pad in repeated thin layers until a three-dimensional object of desired shapes and dimensions is created.
The materials used for filaments are predominantly polymeric materials differing in their mechanical and thermal properties (e.g. acrylonitrile butadiene styrene, polylactic acid, polyethylene terephthalate and others). In addition to polymeric materials, the filaments can also contain various additives (wood flour, ceramic particles, graphene, etc.) which serve to improve the mechanical properties or the appearance of the material. Their disadvantage is that they significantly affect the rheological properties of the melt or have abrasive properties on the nozzles which can lead to their wear and more frequent replacement.
Recently, a team of inventors from the Polymer research institute and established Slovak company active in 3D printing managed to use recycled polyethylene terephthalate glycol as the polymer matrix of the material for 3D printing, which has in comparison with polyethylene terephthalate a higher impact resistance and clarity. The institute was established in 1953 in order to carry out fundamental and applied research and new developments in the field of civil engineering and architecture.
Due to the fact that it is a recycled material, its price is several times lower than the price of non-recycled polyethylene terephthalate. Furthermore, this fact did not reflect in the properties of the resulting 3D object. For the purposes of improving the mechanical properties (static and dynamic) and reducing the weight of the final product, carbon fibers in a suitable ratio with expanded graphite have been mixed into this polymer matrix. Expanded graphite, that has lubricating effects, also reduces the abrasive properties of carbon fibers, improves the rheological properties of the polymer melt with carbon fibers and adds fine roughness to filaments, resulting in an easier feed into the nozzle. Thanks to the high thermal conductivity of the expanded graphite it is not necessary to change the temperature parameters of the processing
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