At the start of the research, the dispersion of filler particles in the composites was assessed. Figure shows SEM images taken on cross-sections of rectangular composite specimens used for the impact test measurements. Images 'a' and 'b' show the morphology of PBS-DLS composites with the addition of 10% and 20% by weight of nano-hydroxyapatite, respectively. As can be seen from the figure, the nanoparticles have a strong tendency to agglomerate. This tendency was already evident on the pre-process powder (Figure ). The problem of agglomeration of HAp nanoparticles in PBS-based composites has already been noted by Wenmin Guo . Insufficient dispersion of the filler can affect the functional properties of the materials. The situation is different in the case of coPBS_10%µHAp and coPBS_20%µHAp composites. The microparticles do not show a clear tendency to agglomerate as in the pre-process powder (Figure ). Figure shows the elongated shape of some HAp particles can be seen. However, there are only few of these, because during the process of filling the injection mould, the particles orient themselves parallel to the flow direction of the material, i.e. along the jet direction. Therefore, when viewed in section, the image shows whiskers from the 'base'. A more detailed analysis of the particle size in the composites was supported by particle size distribution studies.