Investigating the acoustic performance of sustainable composites utilizing recycled polypropylene and denim shoddy: fabrication, characterization, and theoretical Modelling

Addressing the urgent need for sustainable materials, this study investigates the development of eco-friendly composites using Recycled Polypropylene (RPP) and Denim Shoddy (DS) for sound insulation. Two configurations were fabricated through compression molding: one with only RPP and the other incorporating a DS interlayer, repurposing waste materials such as post-consumer cosmetic containers and denim textile waste. The investigation evaluated the composites' density and sound transmission loss (STL). Theoretical calculations of STL in diffuse fields across various angles assessed the composites' real-world applicability. Incorporating a DS interlayer significantly improved sound insulation properties, with the composite exhibiting a higher density of 916 kg/m³ compared to 891 kg/m³ for Neat RPP. STL measurements showed that the composite achieved approximately average STL of 39.0 dB under normal incidence and 30.8 dB in the diffuse field, compared to 37.7 dB and 30.6 dB for Neat RPP, indicating a positive correlation between increased density and enhanced sound insulation. These findings highlight the potential of using recycled and waste materials for eco-friendly, sound-insulating material. The developed materials show promising applications in highway noise barriers, generator insulation, and office cabin partitions. This research contributes to sustainable materials science by demonstrating innovative sound-insulating composites' environmental and practical benefits.