Sustainable Sound Absorber from Nonwoven Fabric of Natural Biduri Fibers (Calotropis gigantea) with Polyester Binder

In recent years, the research on sound-absorbing material has been directed to sustainable materials such as kenaf fiber and coconut coir fiber. Herein, this study offers the acoustic absorption performance of a novel natural fiber that is biduri fiber (Calotropis gigantea). Biduri fiber is a cellulose fiber that has a low density and a hollow structure along the fiber; hence, it has potential for sound absorption. Biduri fibers were thermally bonded with polyester fibers into nonwoven fabric. The sound absorption coefficient was measured using an impedance tube system, according to International Organization for Standardization (ISO) 10534-2:1998. The nonwoven fabric effectively absorbed high-frequency sound (2000–5000 Hz). The absorption coefficient reached 0.95 at 1600 Hz for nonwoven fabric with 95 wt.% of biduri fibers, a density of 25.9 kg m−3, and a thickness of 15–21 mm, which was better than glass wool and several natural fibers. Nonwoven fabrics with a thickness of 15–21 mm and ≥80 wt.% of biduri fibers met Indonesian National Standard 8443:2017 for high- and low-frequency sound silencers. Using the approximate relationship of the absorption coefficient between normal and random incidence sound, it was found that those nonwoven fabrics were categorized as class B sound-absorbing material according to ISO 11654:1997.