Effects of Material and Treatment Parameters on Noise-Control Performance of Compressed Three-Layered Multifiber Needle-Punched Nonwovens Nazire Deniz Yilmaz, 1 Stephen Michielsen, 2 Pamela Banks-Lee, 2 Nancy B. Powell 2 1 Department of Textile Engineering, Pamukkale University, Denizli 20020, Turkey 2 College of Textiles, North Carolina State University, Raleigh, North Carolina 27695 Received 6 September 2010; accepted 19 April 2011 DOI 10.1002/app.34712 Published online 23 August 2011 in Wiley Online Library (wileyonlinelibrary.com). ABSTRACT: The effects of material and treatment pa- rameters on airflow resistivity and normal-incidence sound absorption coefficient (NAC) of compressed three- layer nonwoven composites have been studied. Material parameters included fiber size and porosity, and treatment factors included applied pressure and duration of com- pression. Fibers used included poly(lactic acid) (PLA), polypropylene (PP), glassfiber, and hemp. Three-layered nonwoven composites were classified based on material content and fiber blend. LHL and PGP were sandwiched structures consisting of PLA/Hemp/PLA and PP/glass- fiber/PP layers, respectively. PGI consisted of three layers of an intimate blend of PP and glassfiber. Statistical mod- els were developed to predict air flow resistivity from ma- terial parameters and the change in air flow resistivity from compression parameters. Independent variables in the first model were porosity and fiber size and, in the lat- ter model, were compressibility, pressure, and initial mate- rial parameters. An increase in air flow resistivity was found with increased compression. No significant effect of compression duration was detected. Two additional statis- tical models were developed for the prediction of sound absorption coefficient based on material and treatment pa- rameters. The independent variables of the first model were air flow resistivity, thickness, and frequency, and those of the second model were compressibility, initial thickness, and initial density of the composite, diameter and density of the fiber, compression pressure, and fre- quency. A decrease in sound absorption coefficient was detected with increasing compression, while no effect of duration was detected. V C 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123: 2095–2106, 2012 Key words: sound absorption; compression; nonwoven; layered composites; biodegradable INTRODUCTION There is an ever increasing demand for better living and working environments. 1 To meet this demand, noise reduction is a must; as noise has negative effects on physiological and psychological human health, besides deteriorating working and learning efficiencies. 2 This situation makes noise control engineering more important and more complicated, taking diversified life styles into consideration. 1 Noise control can be achieved by three means. Pri- mary methods include alterations at noise and vibra- tion sources. Secondary methods include modifica- tions along the sound propagation path, and tertiary methods deal with sound receivers. Primary meth- ods are constrained by technical and economical parameters; while tertiary methods necessitate that each receiving person is treated individually. This makes the secondary methods, which include the uses of sound barrier and absorbers, relatively prac- tical and cost-efficient. 2,3 Sound absorbers are porous materials that can be classified into three groups: cellular materials like foams, granular materials like woodchip panels, and fibrous materials like nonwoven stuctures. 3 Sound dissipation occurs in the tortuous pore channels of porous materials due to viscosity and heat conduc- tivity of the medium. 4,5 Among fibrous materials, nonwovens are promis- ing materials for noise reduction applications. Com- pared to foams, nonwovens are advantageous in that they absorb more sound over a broader frequency range. 6 Also, nonwovens can be recycled and may have more environmentally friendly manufacturing methods compared to polyurethane foams. 7 In studying acoustic properties of porous materi- als, acoustic impedance, Z, is a very important mate- rial characteristic. Acoustical impedance, defined by eq. (1), is the ratio between the sound pressure, p, and the particle vibration velocity, v x 1,3 : Correspondence to: N. D. Yilmaz (ndyilmaz@pau.edu.tr). Contract grant sponsor: Scholarship for Doctoral Research and Education at North Carolina State University from Turkish Council of Higher Education (to N.D.Y.). Journal of Applied Polymer Science, Vol. 123, 2095–2106 (2012) V C 2011 Wiley Periodicals, Inc.