Morphological, structural, and tensile changes of polyurethane‐poly(3‐hydroxybutyrate) (PU‐PHB) elastomeric composites were evaluated after accelerated test in standard compost media. Size of PHB particles together with their uniform dispersion in the matrix were found to be key parameters for material's resistivity against degradation media. PU‐PHB composite films were synthesized by the “green” solvent free method, where commercially available PHB (PHB‐COM) and PHB produced by bacterium Cupriavidus necator H16 (PHB‐BUT) were both used in the amount of 1, 5, and 10 wt % in composites. Scanning electron microscopy revealed excellent dispersion of PHB‐COM microparticles in the PU matrix resulting in negligible weight losses of the material (max 0.7 wt %). On the contrary, PHB‐BUT particles were agglomerated which promoted partial degradation of the material (max 3.3 wt % loss) manifested by holes on the surface but without severe damage (e.g. fragmentation). Structural analysis confirmed lower crystallinity and less ordered crystalline phase of PHB after the degradation test, particularly in composites made of PHB‐BUT. Moreover, the materials were less stiff after the composting test, but beneficial with higher elongation at break. Such properties are favorable for the use of renewable PHB in the current industrial applications of PU elastomers.
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