Sustainable development of bioepoxy composites reinforced with recycled rigid polyurethane foam for mechanical, thermal, acoustic, and electromagnetic applications in a circular economy approach.

The accumulation of polyurethane (PU) waste presents a critical environmental challenge due to the inefficiencies of traditional disposal methods like landfilling and incineration. This study introduces a sustainable approach by repurposing 99.89% pure rigid polyurethane foam granules (~ 150 µm) as fillers (5 wt.%) in bio-epoxy composites, complemented with 99.89% pure vermiculite particles (~ 10 µm) at varying concentrations (2-10 wt.%). Comprehensive characterization techniques, including high-resolution scanning electron microscopy (HR-SEM) and Fourier transform infrared spectroscopy (FTIR), were employed to evaluate the composites' mechanical, thermal, electrical, acoustic, and electromagnetic interference (EMI) shielding properties. The study specifically measured EMI shielding effectiveness in the frequency range of 8-12 GHz. Among the formulations, sample S5 exhibited superior mechanical performance, with tensile strength (10.47 N/mm2), impact strength (0.006 kJ/cm2), and flexural strength (46.80 N/mm2). EMI analysis revealed a dielectric constant of 1.111 and shielding effectiveness of -35.24 dB, while sample S3 achieved optimal acoustic absorption (NRC 0.295). Thermal assessments showed the lowest thermal conductivity (0.141 W/mK) and a reduced burning rate (6.8 mm/min) for S5. These results highlight the viability of recycled PU foam-based composites in minimizing plastic waste and advancing net-zero carbon emission goals. Potential applications include battery enclosures, engine bay insulation, and cabin soundproofing in electric vehicles. This work establishes the novelty of integrating recycled materials into bio-epoxy matrices to address environmental challenges and create high-performance composites.