Muchlisinalahuddin
Polyurethane foams, while widely used for acoustic insulation, exhibit limited effectiveness at low frequencies and are typically derived from non-renewable sources. This study addresses both limitations by fabricating polyurethane composites reinforced with nanocellulose extracted from oil palm empty fruit bunches, an abundant agricultural waste. We prepared nanocellulose through alkali and bleaching treatments followed by mechanical grinding, then incorporated it into a polyurethane matrix at weight ratios of 3%, 5%, 10%, and 20%. Sound absorption coefficients were measured using a Brüel and Kjær impedance tube following ASTM E1050-2 across a frequency range of 1600 to 6000 Hz. The control polyurethane showed absorption coefficients below 0.3 at low frequencies, improving to approximately 0.75 near 4000 Hz. The addition of nanocellulose systematically shifted peak absorption toward higher frequencies and increased maximum coefficients. The 10% nanocellulose composite achieved the highest peak absorption coefficient of 0.78 at approximately 3500 Hz, representing a significant improvement over the control. The 5% formulation provided a well-balanced absorption profile across mid-to-high frequencies with coefficients exceeding 0.7 above 3000 Hz. However, the 20% composite exhibited a more gradual increase in absorption, indicating fiber agglomeration and reduced pore connectivity at higher loadings. Performance remained limited below 1000 Hz for all formulations. These results demonstrate that nanocellulose from oil palm empty fruit bunches can effectively enhance the mid-to-high frequency sound absorption of polyurethane composites. This work contributes to the development of sustainable acoustic materials while valorizing agricultural waste, offering a viable pathway for noise control applications where high-frequency attenuation is required.