Polyurethane foam is an outstanding material for various applications. It is manufactured by propelling liquid isocyanate-polyol mixture to form foams in the presence of a blowing agent. This paper ...comprises an experimental study on acoustic properties improvement of rigid polyurethane closed-cell foam, by incorporating various quantities of textile waste into the matrix. In order to obtain a homogenous, easy to handle material, an optimal percent of 10-50% textile waste was used. The sound absorption coefficient of the composite materials was measured using an impedance tube. The composite materials obtained have better sound absorption properties compared to rigid polyurethane foam. The noise reduction coefficient (NRC) of the composite material with 40% textile waste and 60% rigid polyurethane foam is twice as high as the 100% rigid polyurethane material.
•Studied effectiveness of steam explosion on wood cell walls.•Two different porous wood cell walls have studied.•Steam exploded wood shows better air permeability.•Steam exploded wood shows better ...sound absorption coefficient.•Correlated by ATIR-FTIR, XRD, FE-SEM and EDAX.
Steam explosion is a useful method to soften and dimensionally stabilizing wood. The effects of steam explosion at low pressure (6 bar) on wood cell walls are characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), capillary flow porometry and two-microphone transfer function. The average sound absorption coefficient (SAC) of treated Chinaberry samples on the cross-sectional surface exhibited significant improvement of 79% relative to control specimens over a wide frequency range of 250–6400 Hz. Whereas, a little increment SAC of 5% was observed in the case of Ginkgo wood. Color of steam-exploded woods became black due to chemical reactions in wood cell walls during the steam explosion. The air permeability, SAC and color change are correlated with the results of FTIR and XRD. These results suggest that steam explosion could be used to manufacture wood-based sound absorption board to control the acoustical housing environment.
This paper aims to investigate the acoustic properties of porous polycarbonate material (PPM) fabricated by additive manufacturing, and the feasibility to tailor artificial porous sound absorbing ...material is studied. Four PPM samples with different perforation angles were printed by using a 3D printer. Polycarbonate material was used, and the samples were printed with 25.4 micrometre layer resolution. Their sound absorption coefficient was experimentally measured using the two-microphone impedance tube method. It was found that with increased the perforation angle and constant porosity, the sound absorption was decreased. The results indicated that by adjusting the perforation angle and the airgap behind the sample, significant sound absorption can be achieved in the low frequencies where conventional porous materials may not be that effective. The results obtained in this paper provide a new approach for the fabrication of new porous sound absorbing materials.
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•Porous polycarbonate material (PPM) samples are fabricated by additive manufacturing.•Acoustic sound absorption properties of PPM samples are investigated.•Effects of perforation angle on sound absorption coefficient for PPM samples are presented.•Acoustic performances of PPM samples with airgap are discussed.
•Nanofiber membrane improved the sound absorption performance of composite structures at low frequency.•The average sound absorption coefficients of bi-layer and three-layer composites reached 0.56 ...in 100–1000 Hz.•Lamination sequence and layer thickness affected the sound absorption performance.•The noise of different frequency bands can be absorbed by adjusting different thickness combinations.
Aiming at the problem of poor low-frequency sound absorption performance of traditional fiber sound-absorbing materials, this work prepared nanofiber membrane-based multi-layer composites by lamination for sound absorption and noise reduction. By laminating polyvinyl butyral (PVB) nanofiber membrane with polyester (PET) fiber felt and polyurethane (TPU) film, bi-layer and three-layer composites structure sound-absorbing materials were manufactured, and the effect of lamination sequence and thickness of each layer on their sound absorption performance were investigated. The results testified that the composite structures have excellent sound absorption performance in low-frequency range while the nanofiber membrane was placed at the sound-facing surface. When the thickness of PVB was 2 mm, and the thickness of PET was 10 mm, the average sound absorption coefficient of PVB-PET structure composite reached 0.5646 in the low-frequency range. Notably, the frequency and peak of the first resonance sound absorption peak were 396 Hz and 0.8529, respectively, which can meet the needs of sound absorption and noise reduction. Another layer of TPU film was compounded on the backside of this structure, and the sound absorption peak was further transferred to the low-frequency range. The frequency and peak of the first resonance sound absorption peak of the three-layer composite structure material were 300 Hz and 0.7772, respectively. Compared to 10 mm thick PET fiber felts, the average sound absorption coefficients of both bi-layer and three-layer composite materials were improved by more than 200 % in the range of 100–1000 Hz. Additionally, the results of response surface optimization illuminated that the sound absorption of different frequency bands can be targeted through reasonable selection and optimization of structural parameters.
Grass has a high leaf density and requires minimum space to grow. This experiment was designed to determine the sound absorption behaviour of six grass species (Zoysia matrella (L) Merr., ...Stenotaphrum dimidiatum(L.) Brongn, Panicum repens (L.), Eleusine indica (L.) Gaertn., Axonopus compressus (Sw) P. Beauv, and Ischaemum sp.) for their possible use as noise screens. The sound absorption of each morphological leaf structure was studied. For Sound Absorption Coefficients (SAC) (α) studies, the reverberation room method under ISO 345:2003 standards was followed. A B&K dodecahedron Omni-directional speaker, power amplifier, and 2250L handheld analyser were used for reverberation time and RT60 measurements. Microscopic images of grass leaves were analysed using ImageJ software. This study revealed that grasses with the highest and lowest SAC for higher noise frequencies (> 1500 Hz) are S. dimidiatum Brongn and A. compressus, respectively. The SAC of S. dimidiatum Brongn positively correlated with noise frequency. In general, the correlation of SAC (α) with noise frequency (f) is in the form of log10α = a1log10f + b1 where a1 and b1 are grass type-dependent constants. The morphological parameters like total leaf area, total sample area, plant height, and sample dry weight strongly correlated with the SAC. But leaf thickness, length, width, surface area, and the weight of the sample poorly correlated with SAC in the frequency range.
Compared to the traditional synthetic fibrous materials, natural fibres represent sustainable solution to be used either in building construction and noise control engineering and acoustic ...treatments. Natural fibres are mainly employed in the building industry for their hygrothermal properties, however the possibility to also use them for acoustic purposes would greatly increase their appeal to the market. While synthetic fibres have been studied for almost fifty years, the knowledge of natural fibres is still limited and needs to be expanded. Natural fibres are affected by a large variability of the physical properties, which consequently causes great uncertainty in numerical modelling and difficulties during the design process of acoustics treatments. This study highlights the possibility to enhance the acoustic performance of hemp fibrous materials through the manufacturing process, investigating how each treatments affects the material’s physical characteristics and its sound absorption coefficient. Moreover, a simplified model to evaluate the acoustic performance of hemp fibrous materials as a function of their density is proposed, in order to provide a practical tool to investigate and compare different solutions. The physical parameters numerically evaluated for a varying compression rate have been compared with the experimental results, measured at each stage of the production process on samples with a different density and thickness. The global reliability of the proposed approach is finally investigated by comparing the experimental sound absorption for normal incidence with the results obtained from the Johnson-Champoux-Allard model.
This study intends to explore the potential of areca nut leaf sheath (ALS) fibers as an efficient sound absorber. The ALS fibers were characterized to investigate their physical properties closely ...associated with their performance as an efficient sound absorber. ALS fibers were processed into non-woven form and were characterized for their acoustical characteristics. The sound absorption coefficient was measured on samples of different thicknesses as per ASTM E1050. The experimentally measured sound absorption coefficients were compared with the theoretically estimated ones, using the empirical models of Delany-Bazley, Miki, Garai-Pompoli, and Allard. The predicted and experimental results were compared in different frequency zones and for different thicknesses. The accuracy of empirical models was evaluated by analyzing the root mean squared error of sound absorption coefficients. The optimum thickness was identified by analyzing the noise reduction coefficient. A linear and a logarithmic objective function was framed with sound absorption coefficients sampled at 10 Hz, and in 1/12th octave band to further improve the accuracy of the empirical models by inverse acoustical characterization. Inverse acoustical characterization was performed using genetic algorithm on the results of optimum thickness. The inverse acoustical characteristics were used in the most accurate empirical model to estimate the characteristic impedance and complex wavenumber. This characteristic impedance and complex wavenumber were used to study the effect of air–gap behind the ALS sound absorbers. A maximum noise reduction coefficient of 0.78 on a 54 mm thick sample was reported in the presence of a 50 mm air–gap. An effective sound absorber from natural sources was the outcome of the present study.
Introduction: In recent years tend to use of natural fibers has increased in making sound absorbers. Fiber-based natural materials have low density, low production costs, and are biodegradable. ...Material and Methods: In this study, the effect of nanoclay and the behavior of the nanocomposite specimens containing tea waste, polypropylene, and nanoclay in the sound absorption coefficient are investigated. Results: The results showed the sound absorption coefficient increases by increasing the tea waste weight percent of the polypropylene. 60% increase in tea waste has a special role in the absorption of sound waves at a frequency of 1000 Hz and 2500 to 6300 Hz frequency range as the TW60 N5 sample has the sound absorption coefficient 0.94 and 0.84 in 1000 and 6300 Hz frequencies, respectively. Comparison of the sound absorption coefficient of composite and nanocomposite showed that sound absorptions increase by adding nanoclay to the 5%, at frequencies above 2000 Hz. Conclusion: Tea waste-based sound absorbers can be used in noise control due to the high acoustic absorption and no harmful effects on human health.
•Introduce a novel approach to transform agricultural waste into functional construction materials.•Offers an in-depth analysis of the structural, thermal, and acoustic properties of the developed ...panels.•Utilizing rice straw, we address the issue of air pollution in regions with intensive agricultural activities, contributing to cleaner air and healthier living environments.
To address the pressing need for sustainable building materials, this study introduced an innovative and eco-friendly approach to manufacturing thermal-acoustic panels, utilizing agricultural waste with rice straw as the primary material. Paper pulp (PP) and Persea kurzii (PK) were used as non-chemical binders at ratios of 50:50, 60:40, 70:30, and 80:20. After mixing, all the samples were subjected to heat-free hydraulic compression at 5 bars to evaluate their physical, mechanical, thermal, and acoustic properties. Increasing the proportion of the binder directly impacted panel density and flexural strength while also inversely affecting porosity. The PK binder had a low thermal conductivity value of 0.040 W/mK, proving it was a good thermal insulator with a high sound absorption coefficient, especially at higher frequencies. The RSPP-4 panel had the highest noise reduction coefficient (0.51) and absorbed low frequencies, suggesting its potential for noise reduction. Microscopic analysis provided further insight into panel surface characteristics. PP exhibited a smooth surface with a continuous fiber weave that did not obscure the pores, while PK consisted of particles. The correlation between surface characteristics and acoustic performance, especially at high frequencies, underscored the intricate balance between material properties. Research results can be applied in the construction industry to develop sustainable building materials that offer superior thermal and acoustic properties. These thermal-acoustic panels can effectively utilize agricultural waste and show potential as environmentally friendly construction materials to enhance indoor comfort and acoustics in various building environments.
A technique is proposed that uses a multi-scale approach to calculate transport properties of compressed felts using only image analysis and numerical calculations. From the image analysis fiber ...diameter distribution and fiber orientation are determined. From a known porosity and the latter two characteristics, two representative elementary volumes (REV) are constructed: one based on the volume-weighted average diameter and one on an inverse volume-weighted average diameter. Numerical calculations on the former showed that it correctly estimates viscous and thermal permeabilities, while the latter correctly estimates tortuosity and viscous and thermal characteristic lengths. From these calculations, micro-macro analytical expressions are developed to estimate the transport properties of polydisperse composite felts based solely on open porosity, fiber diameter polydispersity, and fiber orientation. Good agreements are obtained between analytical predictions and measurements of transport properties. The predicted transport properties are also used in the Johnson–Champoux–Allard–Lafarge (JCAL) equivalent fluid model to predict the sound absorption coefficient of the felts. Excellent agreements are obtained with impedance tube measurements.
•Investigating transversely isotropic polydisperse fibrous media.•Modeling fiber microstructures for transport and sound absorbing properties.•Two microscale models established using volume and inverse-volume-weighted diameters.•Semi-analytical model predicts accurately for a wide range of porosities.
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