Investigation of the effect of using recycled polypropylene waste on the sound absorption coefficient of micro-perforated panels as a green absorber

The use of sound absorbers as fillers behind micro-perforated panels can enhance sound absorption coefficients while offering a sustainable approach to reducing plastic waste. This study aimed to investigate the effect of polypropylene waste, as a recycled material, on the sound absorption coefficient of micro-perforated panels and propose an eco-friendly solution. After preparing the required equipment, composites were manufactured based on experimental runs as single-layer and double-layer panels with varying densities. The micro-perforated panels were made from plexiglass with pore diameters of 0.7 mm, a thickness of 1 mm, and a porosity of 1%. Polypropylene waste was used as a filler behind the micro-perforated panels to evaluate its impact on the sound absorption coefficient. The sound absorption coefficients of the samples were measured according to the ISO 10534-2 standard using the impedance tube apparatus (BSWA, Model SW360). Data design and analysis were performed using Design Expert software (version 11) and SPSS24. After conducting the experiments, variance analysis models were employed to describe relationships between the investigated parameters and response variables to predict optimal conditions. The evaluation of sound absorption coefficients of micro-perforated panels revealed that coefficients at high and medium frequencies were significantly higher than at low frequencies. For single-layer panels, the highest sound absorption coefficient at high frequencies was observed with a thickness of 1.5 cm and a density of 250 kg/m³ (0.8759), while the highest coefficient at medium frequencies corresponded to a thickness of 2.5 cm and a density of 200 kg/m³ (0.7512). For double-layer panels, higher sound absorption coefficients were noted at lower densities and a thickness of 2 cm, with superior performance at high frequencies. Using sound-absorbing materials behind micro-perforated panels and increasing thickness improved sound absorption coefficients, whereas increasing density had a negative effect. Single-layer panels generally performed better than double-layer ones. Furthermore, the incorporation of polypropylene waste enhanced the sound absorption properties of the panels, and the optimized panel with polypropylene waste was recommended for further investigation. The use of recycled polypropylene in micro-perforated panels enhances noise reduction while promoting sustainability, with applications in buildings, transportation, and industrial noise control.