Structural and mechanical characterization of polyurethane-CaCO 3 composites synthesized at high calcium carbonate loading: An experimental and theoretical study

Abstract

Due to its exceptional biocompatibility, Polyurethane (PU) reinforced with calcium carbonate (CaCO₃) is a composite material with significant biomedical applications. However, much of the currently known mechanical and chemical information regarding composites has been obtained at low and moderate CaCO₃ content levels. This study employs experimental and theoretical tools to evaluate the structural, morphological, and mechanical properties of pristine polyurethane, and when doped with CaCO₃ at 25 and 50 wt.%. In the experiments the samples are characterized using X-ray diffraction (XRD), infrared spectrophotometry (FT-IR), scanning electron microscopy (SEM), and tensile and flexural mechanical tests, while theoretical calculations are performed to evaluate the carbonate-polymer interaction. The XRD and FT-IR results indicate that CaCO₃ is at the calcite phase and that PU-CaCO₃ materials exhibit a broadening of bands related to the NH₂ group. This result is explained using theoretical calculations that demonstrate a weak interaction between those molecules with the CaCO₃ surface, where the molecule-calcite interaction occurs primarily through the NH₂ molecular link. With respect to mechanical behaviour, the results show less fracture resistance and greater stiffness for the materials containing CaCO₃, compared to those containing only PU. These results are explained in terms of the stress concentration due to CaCO₃ within the polymer. Finally, the results detailed in this paper show that a high calcium carbonate loading is suitable for increasing the rigidity and decreasing the fracture toughness of the biomaterial, in association with a reduction of the plastic region.