Acoustic Performance of PLA and Hemp Fiber Biocomposites in Sandwich-Structured Sound Absorption Panels

Growing environmental concerns and the need for sustainable living have increased interest in eco-friendly materials for noise reduction, leading to research on natural and biodegradable alternatives to traditional synthetic sound absorbers. This study investigates the acoustic performance of sound-absorbing panels fabricated from nonwoven poly(lactic acid) (PLA) fibers blended with hemp fibers. The panels were produced with PLA-to-hemp fiber ratios of 100/0, 75/25, 50/50, 25/75, and 0/100 (by weight). Hemp fibers underwent alkali treatment (NaOH) to remove lignin and hemicellulose, which was confirmed by FTIR analysis, showing an increase in C=C stretching (1600–1740 cm⁻¹) of cellulose compounds and a reduction in C–C aromatic rings. Morphologic analysis revealed that alkali treatment smoothed the hemp fiber surface by removing wax and lignin, reducing the average fiber diameter from 23.31 to 18.39 µm. To enhance structural integrity and acoustic efficiency, sandwiched PLA/hemp woven fabrics were incorporated as outer layers. The impedance tube method demonstrated that PLA fibers exhibited higher sound absorption than hemp fibers. The sandwiched PLA/hemp (50/50, treated) configuration achieved the highest sound absorption coefficient, attributed to increased porosity and surface area, enhanced acoustic impedance matching, and improved airflow resistivity. These findings confirm the potential of PLA/hemp biocomposites as eco-friendly sound absorption materials, offering a sustainable alternative for acoustic applications.