Sound Absorption Characteristics of Polyurethane Composites with Nanocellulose from Oil Palm Empty Fruit Bunches

Abstract

This study explores the sound absorption behavior of polyurethane-based composites reinforced with nanocellulose derived from oil palm empty fruit bunches. Nanocellulose was synthesized through chemical and mechanical processes and incorporated into the polyurethane matrix at weight ratios of 3%, 5%, 10%, and 20%. Test specimens were prepared with standardized dimensions and evaluated using a four-microphone impedance tube system following ASTM E2611-19 to determine the frequency-dependent acoustic response across the 125–5000 Hz range. The results demonstrated a clear improvement in sound absorption in the mid-to-high frequency bands (1000–4000 Hz) as nanocellulose content increased, with peak absorption coefficients (α) exceeding 0.7 at frequencies above 3000 Hz for 5% and 10% formulations. This enhancement is attributed to increased tortuosity, airflow resistivity, and complex internal structures formed by the nanocellulose fibers. However, performance in the low-frequency range (100–1000 Hz) remained limited across all compositions, and excessive filler loading (20%) led to diminishing returns due to particle agglomeration and reduced pore connectivity. These findings suggest that oil palm empty fruit bunch nanocellulose holds substantial potential as a sustainable acoustic reinforcement material, particularly for high-frequency applications. Further structural optimization is recommended to expand its applicability for broadband noise control.