Sound Absorption Characteristics of Areca Husk Fiber Reinforced Flexible Pu Foam Composites

Abstract

In recent years, sound pollution has affected the quality of human life. Sound quality enhancement is the primary concern of automobiles, aviation, industries, and commercial and residential places. Currently, it focuses on utilizing eco-friendly, sustainable, biodegradable, and recyclable materials to control unwanted sound and improve sound quality. Most materials presently used for sound absorption (SA) applications are rock wool, glass wool, plastics, melamine foams, and synthetic fibers. Furthermore, synthetic fibers are highly toxic and adversely affect human health and the environment. These fibers are derived from petrochemical products and have issues with decomposition. Need for replacement of these materials motivated the researchers to explore developing economical and environmentally sustainable green products for sound-absorbing materials. Materials such as flexible fibrous foams, porous structures, perforated panels, granular membranes, and natural fiber composites are recommended for SA applications. Fibers extracted from plant wastes can be used for SA applications in vehicles due to their lightweight and porosity. Natural fillers or fibers-reinforced composite materials have many advantages, such as being biodegradable, inexpensive, widely available, lightweight, low cost, easy to process, economical, eco-friendly, and suitable for SA over a broad frequency region. Areca (betel nut) fruit shell husk consists of a significant amount of natural fiber known as areca fiber (AF), which covers the outside of the fruit. The fruit of the areca palm tree (areca catechu linnaeus) is a species of palm belonging to the palmecea family. The SA capability of raw areca fibers bundle (RAFB) as a function of the density and thickness of the test specimen is analyzed. Experimental results obtained using the impedance tube approach reveal that an increase in the specimen bulk density and thickness remarkably improves the SA capability of RAFB. Similarly, air volume behind the sample enhances the SA in the lower frequency range. Theoretical results predicted using the Johnson–Champoux–Allard (JCA) model matches well with the experimental predictions. The ability of the RAFB to absorb sound is demonstrated to be equivalent to other commercially available natural and artificial fibers by comparing the results available in the literature. The effect of unprocessed raw areca fiber (AF) particle reinforcement on the SA behavior of polyurethane (PU) foam composites is investigated. Influences of fiber weight percentage and graded distribution of fiber with varying fiber weight percentage on the SA coefficient (SAC) of the composite foams are examined through the impedance tube approach. Morphological studies are carried out with the help of FESEM images to investigate the acoustic energy dissipation mechanism of PU foam and its composites. The composite foam's SA capability is enhanced by increased fiber weight percentage, graded distribution of fiber wt.%, varying sample thickness, and air cavity length. In general, PU-AF composite specimens show a peak SA value of 0.95 around 450 Hz, which is not the case for other natural fiber results in the literature. Theoretical results predicted using the JCA model agree with the experimental results. The effect of filling unprocessed areca fiber (AF) particles reinforced polyurethane (PU) foam in the cavities of 3D-printed hexagonal and square honeycomb core cells is studied. Influences of unit cell size and graded cell size distributions on the SA coefficient are analyzed. The findings demonstrate that larger unit cell size and graded cell size distributions significantly enhance the SA capacity. The samples exhibited notable peak SA values of 0.94 at 650 Hz and 0.90 at 470 Hz for hexagonal and square cores, respectively, which found to be higher than the values reported in the literature.