In this study, we prepared short-carbon-fiber (CF)-reinforced poly(lactic acid) (PLA)-thermoplastic polyurethane (TPU) blends by melt blending. The effects of the initial fiber length and content on the morphologies and thermal, rheological, and mechanical properties of the composites were systematically investigated. We found that the mechanical properties of the composites were almost unaffected by the fiber initial length. However, with increasing fiber content, the stiffness and toughness values of the blends were both enhanced because of the formation of a TPU-mediated CF network. With the incorporation of 20 wt % CFs into the PLA-TPU blends, the tensile strength was increased by 70.7%, the flexural modulus was increased by 184%, and the impact strength was increased by 50.4%. Compared with that of the neat PLA, the impact strength of the CF-reinforced composites increased up to 1.92 times. For the performance in three-dimensional printing, excellent mechanical properties and a good-quality appearance were simultaneously obtained when we printed the composites with a thin layer thickness. Our results provide insight into the relationship among the CFs, phase structure, and performance, as we achieved a good stiffness-toughness balance in the PLA-TPU-CF ternary composites.

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