Morphology and Acoustical Properties of Sago Pith Waste Reinforced Polyester Composites

Indonesia generates abundant sago pith waste (SPW) because the country is the world's largest producer of sago starch. Although many efforts and studies have been devoted to processing this waste, SPW has not been utilized properly, and a large amount of SPW remains unprocessed and thrown away. On the other hand, increasing noise levels have become a problem in Indonesia due to the rapid industrialization in recent years. In this study, SPW is tested for use as a sound-absorbing material by first converting it into composite materials. The composites were manufactured by using unsaturated polyester resin mixed with SPW particles in three different volume fractions: 20% SPW, 30% SPW, and 40% SPW. SEM micrographs were performed to observe the morphology of the SPW particles and the composites. SEM micrographs revealed honeycomb structures of the SPW, and the average diameter of dried sago starch particles was observed to be around 5 μm. Further SEM examination on the composite specimens only found pores and holes previously occupied by sago starch particles, while the honeycomb structures were difficult to find except for the specimens with 40% SPW. The acoustics tests of all composite specimens were conducted using a set of impedance tubes between 0 and 6000 Hz. The plot lines of the coefficient of sound absorption are complex, and the SPW volume fraction that produces the best coefficient is affected by the sound frequency. However, the composite specimen with 30% SPW appears to have the best overall sound absorption properties.