Sound Absorption Performances

One increasingly important property for interior components in automotive applications, where natural fiber-reinforced composites have performance advantages, is the acoustic absorption. Natural fiber-reinforced composite materials in an interior component have an open cell structure. It will therefore contribute to sound absorption and may result in a reduced need for absorbers. Multilayer components further offer many possibilities to tailoring the acoustic absorption of the system. 

Vcp is the inner porosity of coir fiber, Vi is the volume of other constituent, Vtotal is the volume of coir fiber, Wi is the weight fraction of other constituent, Ptotal is the density of coir fiber, and Pi is the density of other constituent. 

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Unfinished Products. Unfinished fiber glass products are available in the form of boards, blankets, and batts in various thicknesses and densities. These products are used by fabricators who apply finishes to make products suitable for ceilings, walls, open-plan office screens, etc. They also are used for sound absorption behind decorative and protective facings such as perforated or expanded metal and wood grilles. Thicker materials have better low frequency performance than thinner materials. Low frequency performance can be improved by spacing the material away from a sound-reflecting surface rather than applying the material directly to the surface. 

The sound absorption tests, performed according to the ISO Standard No. 354, showed that the absorption capacity of the panels would fall in the range of comparable systems. 

Partly due to their porous structures, plant fibers present high thermal, electrical and acoustical insulation performance and they can be incorporated in biocomposites produced for these causes [49]. Huda and Yang [7] measured the sound absorption capacity of corn husk and jute reinforced PP composites. They found their noise reduction is comparable, and higher sound absorption was achieved when the corn husks xmder-went enzyme treatment before composite manufacturing process. It should be considered that moisture absortion substantially deteriorates heat and electrical insulation performance [71]. 

Horizontal panels a complex multi-layered sandwich involving woven glass fabric in an epoxy RTM system, and inner layers of glass mat around a foamed PUR layer. This ensures high rigidity at low weight, with far better fracture performance than could be achieved with simpler (and cheaper ) systems such as SMC, plus excellent sound absorption. 

Nonwoven fabric properties and performance include nonwoven fabric mechanical properties (tensile, compression, bending, and stiffness) gaseous and liquid permeability, water vapour transmission rate (WVTR), liquid barrier properties, sound absorption properties, and dielectric properties. 

Natural fibre-based composites also offer good mechanical performance, good formability, high sound absorption, and material cost savings. 

Most textiles that are used for acoustic purposes show open porosity due to many interconnected pores or voids inside. The acoustic performance of a porous textile is mainly determined by its (air) flow resistivity, which is an intrinsic property of the textile and is a measure of how easily air can enter and pass through a porous textile material (Cox and D Antonio, 2009). Flow resistivity, also known as static flow resistivity, is related to acoustical properties and plays a critical role in the calculation of many intrinsic acoustic properties of porous textiles, such as the characteristic impedance, the propagation constant, and the sound absorption coefficient. In the S.l. Unit system, flow resistivity is quoted in units of Nsm" and is defined as the unit-thickness specific flow resistance o (Morfey, 2001),... 

Although absorption plus chemical reaction sounds more complex than physical absorption or desorption, the absorption of oxygen in sulfite solutions is often used to characterize the performance of bubble columns or stirred reactors. With a 0.2-1.0 N solution of sodium sulfite and a small amount of copper sulfate as catalyst (10 M), the rate of oxidation is independent of sulfite concentration, and the oxygen absorption rate is constant until nearly all the sulfite has reacted ... 

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