Introduction: 3D printing is a rapidly evolving advanced technology for the production of three-dimensional solid objects, gaining increasing importance in industry and the medical field. Its main advantage lies in the ability to produce cost-effective and functional parts with various properties. The most commonly used 3D printing technology is fused deposition modeling (FDM). The quality of 3D-printed products is significantly influenced by printing parameters and the materials used. Among the most commonly employed materials for FDM are polylactic acid (PLA), acrylonitrile butadiene styrene (ABS), polyethylene terephthalate (PET), thermoplastic polyurethane (TPU), and composite materials, which are versatile, lightweight, and flexible. An example of such composite materials is polymer composites reinforced with carbon fibers. Purpose: The aim is to investigate and analyze the impact of different carbon fiber contents on the mechanical properties of 3D-printed polymer composites based on thermoplastic polyurethane (TPU) and to compare the mechanical properties of samples prepared using two different technologies: 3D printing and conventional injection molding. Methods: Different carbon fiber contents (10 wt.%, 15 wt.%, and 20 wt.%) were compounded into the TPU matrix using a twin-screw co-rotating extruder. Filaments for 3D printing were prepared from the composite materials using a single-screw extruder. Test specimens for mechanical property evaluation were produced by injection molding and FDM 3D printing. The specimens were characterized through tensile testing and Shore A hardness measurements. Results: The highest measured Shore A hardness was 90 for TPU+CF20, while the lowest value of 80 was observed for pure TPU in the 3D-printed specimens. Tensile strength and Young’s modulus increased with higher carbon fiber content. TPU+CF20 exhibited the highest tensile strength and Young’s modulus, while the lowest values were found in unreinforced TPU, except in the case of injection-molded specimens, where the unreinforced TPU demonstrated the highest tensile strength. In contrast, elongation at break decreased with increasing carbon fiber content: TPU exhibited the highest elongation at break, while TPU+CF20 showed the lowest values in both 3D-printed and injection-molded specimens. Discussion and conclusion: We found that the carbon fiber content significantly affects on the mechanical properties of TPU-based 3D printed composite samples. Higher carbon fiber content led to increased tensile strength, Young’s modulus, and hardness. However, higher fiber content resulted in reduced elongation and elasticity of the material.
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