Porous resin-bonded recycled denim composite as an efficient sound-absorbing material

Abstract

Recently, a growing interest has been focused on utilizing alternative recycled sound-absorbing construction materials. This study investigates phenolic resin-bonded recycled denim as a potential replacement to synthetic sound absorbers. To this end, the discarded denim was collected from municipal waste sorting plants and shredded to back down into fiber form. Solid novolac resin and fibers were fed to the air-laid machine. The hybrid structures were then introduced to an oven to cure the resin and form an integrated flexible structure. Nonwoven composites at different bulk densities (61–102 kg/m3) and resin contents (10–35%) were produced. The sound absorption coefficient (SAC) of composite samples was determined using the impedance tube method. The relationship between SAC versus frequency was modeled using a logarithmic regression and the phenomenological model of Johnson-Champoux-Allard (JCA). Additionally, the noise reduction coefficient (NRC) values of the samples were compared with those of some commercially available glass wool nonwovens of the same physical properties. The results showed that the mechanism of sound absorption for samples is viscosity resistance, in which SAC at low frequencies is low, however at high frequencies is quite significant. The results of the statistical analysis confirmed that both the bulk density and resin content have a significant effect on the SAC. It was found that SAC rises with increasing the areal density and bulk density, and this raise is more pronounced at higher bulk densities. It was also observed that for samples of the same bulk density, SAC increases with increasing the resin content. The results indicated that resin-bonded recycled denim composites could successfully compete with commercial glass wool samples for noise control, apart from being environmentally friendly and economically viable.