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Composites of poly(<span style="font-variant: small-caps;">l</span>-lactic acid) (PLLA) reinforced by adding inorganic nanotubes of tungsten disulfide (INT&#8211;WS₂) were prepared by solvent casting. In addition to the pristine nanotubes, PLLA nanocomposites containing surface modified nanotubes were studied as well. Several surface-active agents, including polyethylene imine (PEI), were studied in this context. In addition, other biocompatible polymers, like poly <span style="font-variant: small-caps;">d</span>,<span style="font-variant: small-caps;">l</span>-lactic acid (PDLLA) and others were considered in combination with the INT&#8211;WS₂. The nanotubes were added to the polymer in different proportions up to 3 wt %. The dispersion of the nanotubes in the nanocomposites were analyzed by several techniques, including X-ray tomography microscopy (Micro-XCT). Moreover, high-temperature rheological measurements of the molten polymer were conducted. In contrast to other nanoparticles, which lead to a considerable increase of the viscosity of the molten polymer, the WS₂ nanotubes did not affect the viscosity significantly. They did not affect the complex viscosity of the molten PLLA phase, either. The mechanical and tribological properties of the nanocomposites were found to improve considerably by adding the nanotubes. A direct correlation was observed between the dispersion of the nanotubes in the polymer matrix and its mechanical properties.