Preliminary study of the sound absorption of composite panels composed by natural fibers and polyurethane at low frequencies

Bittencourt, C.C.S. Mechanical Engineering Departament, Pontifícia Universidade Católica do Paraná, Curitiba, PR, Brazil, claudia.bittencourt@pucpr.edu.br

Mansur, A. C. M. Mechanical Engineering Departament, Pontifícia Universidade Católica do Paraná, Curitiba, PR, Brazil

Silva, R. IPT – Technology Research Institute, São Paulo, SP, Brazil

Lima, K. F. IPT – Technology Research Institute, São Paulo, SP, Brazil

Abstract

Naturally sourced materials are becoming a valid alternative to traditional synthetic materials for applications in acoustic control in environments. In this paper, a preliminary study of the sound absorption of two types of composite panels made of natural fibers and polyurethane is presented. The natural fibers used are coconut husk fiber and sugar cane bagasse, both from agricultural waste, very common in Brazil. Polyurethane is a bicomponent formed by isocyanate and polyol obtained from castor oil. The samples were formed by two layers, one of fiber and the other of polyurethane, with approximately 17.0 mm thickness, 6 mm of fiber and 11 mm of polyurethane. The sound absorption of these composites was evaluated with the impedance tube and the results were compared with samples composed only of fibers and same thickness. The results are promising and showed that the samples of composite sugarcane fiber have better performance and an average gain of 0.3 in sound absorption between the frequencies of 700 and 1200 Hz, when compared only with fiber. In addition, they showed an absorption peak of 0.6 at 1000 Hz. However, the coconut husk samples showed an absorption peak of 0.57 at 790 Hz. Finally, a comparison between the samples with and without PU was carried out. The results show the sugar cane samples with PU have a higher performance for the frequency above 600 Hz.

Keywords:

natural fibers

impedance tube

sound absorption.

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