Fabrication, Thermo-Mechanical, and Morphological Characterization of Hydroxyapatite-Reinforced Polyurethane...

Petrochemical costs, limited fossil fuel reserves, and concerns about greenhouse gas emissions have raised interest in developing renewable approaches for synthesizing biobased polyurethanes. This study aims to solve these problems by making nanocrystalline hydroxyapatite (HA) reinforcement from waste chicken eggshells and adding it to polyurethane synthesis through in situ polymerization. The novelty of the research lies in the utilization of HA as a reinforcement material and renewable resources for polyurethane production. The results confirm that HA was successfully added to the polyurethane backbone. Fourier transform infrared (FTIR) analysis confirmed that the NCO groups were changed to urethane linkages. TGA examination demonstrated that the samples exhibited thermal stability up to 457 °C with a mass loss of 61%, indicating enhanced thermal stability. DMA measurements showed improved mechanical properties of the synthesized polyurethanes, with storage modulus (E'), complex modulus (E*), and compliance complex (D*) values of 0.177, 22.522, and 0.660 MPa^-1, respectively. SEM analysis confirmed the homogeneous surface and well-dispersed HA reinforcement. Swelling characteristics revealed an optimum absorption of 30% H₂O, 35% CH₃OH, and 45% CCl₄. Polyurethane composites exhibited significant chemical resistance and hydrolytic stability in acidic and basic media. Additionally, the composites demonstrated efficient adsorption of methyl orange from wastewater, with the PUHCI series achieving a maximum adsorption capacity of 85.50 mg/g under optimal conditions of 0.030 g/mL dose, 45 °C temperature, 2.5 h contact time, and pH 6.0..