Changes In Sound Absorption Capability And Air .

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J. Korean Wood Sci. Technol. 2018, 46(2): 149 154pISSN: 1017-0715 eISSN: 9Original ArticleChanges in Sound Absorption Capability and Air Permeabilityof Malas (Homalium foetidum) Specimens after High1Temperature Heat Treatment2324Chun-Won Kang Chengyuan Li Eun-Suk Jang Sang-Sik Jang Ho-Yang Kang4†ABSTRACT1)The changes in sound absorption capability and air permeability of Malas wood after high temperature heat treatmentwere investigated. The average air permeability of Malas in longitudinal direction after heated under the temperatureof 190 during 3 hours was about 23.48 darcys and that of control was about 3.11 darcys. The noise reduction coefficientsof Malas specimens were 17% for treatment and 10% for control. The means of sound absorption coefficient of specimensin the frequency range of 50 6,400 Hz were 42% for treatment and 17% for control, respectively.Keywords: heat treatment, air permeability, sound absorption coefficient, Malas1. INTRODUCTIONproper sound absorption capability of wood wasnecessary for good acoustic environment. It wasSolid wood thermal modification has been widelyrecognized that the sound absorption capability of woodstudied over the years (Hill, 2006). In general, thermalwas influenced by airflow resistivity or air permeabilitymodificationwaterthat varied according to the sound incident surfaceabsorption, thus increasing dimensional stability andstructure and pore characteristics (kang et al., 2012;reducedhygroscopicityanddecay resistance. However, the information on changeskang et al., 2008; kang et al., 2010; kang et al., 2011;in sound absorption property and permeability of woodwassilieff, 1996).after high temperature heating treatment was scare.Therefore, the purpose of this study was to evaluateMalas wood has been used as interior or exterioreffect of high temperature heating treatment on thematerials because of its good hardness, resistance tosound absorption property and permeability of malasweathering and relatively good elastic properties. Inwood which was one of widely used wood in southeastthe case of the wood used as interior materials, theAsia.1Date Received January 29, 2018, Date Accepted March 8, 2018A part of this paper was presented at the conference of 9th International symposium of IWoRS in Baly, Indonesia,September 20172 Department of Housing Environmental Design, and Research Institute of Human Ecology, Chonbuk National University,Jeonju 54896, Republic of Korea3 Department of Wood Science and Engineering, Beihua University, China4 Department of Bio-based Materials, Chungnam National University, Daejeon 34134, Republic of Korea† Corresponding author: Ho-Yang Kang(e-mail:, ORCID: 0000-0002-0544-0721)- 149 -

Chun-Won Kang Chengyuan Li Eun-Suk Jang Sang-Sik Jang Ho-Yang Kang2. MATERIALS and METHODS2.1. Specimen PreparationMalas (Homalium foetidum) lumbers imported fromPapua New Guinea were used in this study. The greenmalas lumbers with 120 mm in width, 30 mm in thickness and 1800 mm in length were heated under thetemperature of 190 for 3 hours. From green malasand heat treated malas, five cylindrical log cross sectionswith 28.9 mm in diameter and 10 mm in thickness wereprepared. The total quantity of 10 pieces log cross sections were oven dried under the temperature of 100 .The average moisture content (MC) of control and heattreated specimens were 6.08% and 4.12%, respectively.The average specific gravity of control and heat treated33specimens were 0.76 g/cm and 0.65 g/cm , respectively.Fig. 1. Diagram Of Sample Chamber.measuring until all pores was empty as the pressure2.2. Gas Permeability and Pore SizeMeasurementbeing increasing. The pressure and flow rate of thegas through the dried specimen were measured althoughThe permeability of specimens was measured bymembrane pore size analyzer (Porous Material Incorporated, CFP-1200AEL) according to capillary flow porometry as precious research (kang et al., 2017). Theprinciple of this method was described in ASTMthe liquid in all pores was not existence. The gas permeability and pore structure of wood specimen were evaluated from the results. The gas permeability of woodspecimen was calculated according to Equations (1)and (2).316-03. The pore structure and permeability were eval-v - (k / ) (dp/dx) ·················· (1)uated using liquid and gas flow as a function and thepressure difference. When a wood specimen was soakedwhere, v flow rate, k permeability, viscosity,in the wet solution, the specimen with different diameterp pressure, x locationof holes was easily wet because the solution had theF vA - (kA/ ) (dp/dx) ··········· (2)low surface tension of 15.9 N/m. After thoroughlysoaked specimen was put into sample chamber, thechamber was sealed as shown in Fig. 1, and then non-re-where, F flow, A cross sectional areasactive nitrogen gas was circulated. The bubble pointwas first measured at the pore with largest diameterinside which the pressure was the minimum value com-2.3. Sound Absorption Rate Measurementpared to other pores, that is, at the place to overcomeThe sound absorption rate of specimen was measuredthe capillary action of the fluid from gas pressure, asby two microphone transfer function method usingthe solution was forcing out. After that, the flow wasimpedance tube (B&K company, kit type 4706), pulse- 150 -

Changes in Sound Absorption Capability and Air Permeability of Malas (Homalium foetidum)Specimens after High Temperature Heat Treatmentanalysis equipment and a spectrum analyzer (B&K3. RESULTS and DISCUSSIONcompany), as precious research (kang et al., 2012). Inthis study, the variation of sound absorption rate wasmeasured as change of frequency in the range of3.1. Change of Pore Structure andPermeability of Specimen50 6,400 Hz. During measurement, temperature, relativeCapillary flow porometry estimates the constrictedhumidity and atmospheric pressure were 25 , 52%pore diameter of a porous material, which is the smallestand 1008.0 hPa for control specimens and 24.6 , 48%pore diameter of one flow pathway. This constrictedand 1008.0 hPa for treated specimens, respectively.pore may be enlarged by heat treatment as shown inMoreover, the velocity of sound, air density and acousticFig. 2. The pore size distribution as a function of average3impedance were 346.15 m/s, 1.176 kg/m and 407.0 Pa/pore diameter by CFP represent that the pore diameter(m/s) for control specimens and 345.92 m/s, 1.177 kg/m3enlarged and the number of permeable pores in treatedand 407.2 Pa/(m/s) for treated specimens, respectively.wood increased, as compared to control wood.Fig. 2. Typical plots of pore size distribution as a function of average porediameter of 10 mm thick malas wood (top: control, bottom: heat treated).- 151 -

Chun-Won Kang Chengyuan Li Eun-Suk Jang Sang-Sik Jang Ho-Yang KangFig. 3. Typical plots of air flow rate in longitudinal direction vs. pressure for10 mm thick malas wood (top: control, bottom: heat treated).The change of permeability for control and treatedspecimens is presented in Fig. 3. Average permeability3.2. Change of Sound Absorption Rateof Specimenof control specimens was 3.11 darcy while that of treatedThe sound absorption rates of specimens in thespecimens was 23.48 darcy, which is about 8 timesfrequency range of 50 6,400 Hz are shown in Fig. 4.higher than that of control specimens. This trend couldAs showed in Fig. 4, the sound absorption rates ofbe attributed to the flow passageway inside wood aftertreated specimens showed higher values than those oftreatment being more and larger than before treatment.control specimens in almost all frequency range. The- 152 -

Changes in Sound Absorption Capability and Air Permeability of Malas (Homalium foetidum)Specimens after High Temperature Heat TreatmentFig. 4. Relationship between sound absorption coefficient and frequency for 10 mmthick malas wood (top : control, bottom : heat treated).difference in sound absorption rates between treatedto the inclusions inside wood such as gum, carbohydrate,and control specimens became larger with increasingetc. being melted and discomposed out during treatment.of frequency beginning from 1 kHz, reached 2 timesIt can be inferred that the sound absorption rate ofin frequency range of nearby 2 kHz and nearby 6 kHz.treated specimens was significantly increased becauseIt indicates that the sound absorption rate of treatedthe flow of the air as the medium transferring the energyspecimens is increasing with increasing of frequency,of sound wave was increased due to improvedwhich is a typical characteristic of porous soundpermeability during heat treatment.absorber. This trend could be accounted for there beingThe NRC (noise reduction coefficient, mean valuemore pores and larger flow passageway in wood dueof sound absorption coefficient at the frequency of 250,- 153 -

Chun-Won Kang Chengyuan Li Eun-Suk Jang Sang-Sik Jang Ho-Yang Kang500, 1,000 and 2,000 Hz) showed a value of 0.17 forHill, C.A.S. 2006. Wood modification—chemical, thermaltreated specimens and 0.10 for control specimens, whichand other processes. John Wiley and Sons Ltd.,Chichester.indicated that the NRC of treated specimens is improvedby 70 percent compared to that of control specimens.Kang, C.-W., Choi, I.-G., Gwak, K.-S., Yeo, H.-M.,It is advised that to apply the heated malas wood asLee, N.-H., Kang, H.-Y. 2012. Changes of soundenvironmentally friendly sound absorption materials isabsorption capability of wood by organosolvpossible.pretreatment. Journal of the Korean Wood Scienceand Technology 40(4): 237-243.Kang, C.-W., Kang, W., Chung, W.-Y., Matsumura,4. CONCLUSIONJ., Oda, K. 2008. Changes in anatomical features,air permeability and sound absorption capabilityIn order to evaluate changes in sound absorptionof wood induced by delignification and permeability, the sound absorption rateJournal of the Faculty of Agriculture, Kyushuand permeability of heated malas wood were measuredbefore and after heat treatment in this study. The resultsof this study were as follows:University 53(2): 479-483.Kang, C.-W., Kim, G.-C., Park, H.-J., Lee, N.–H., Kang,W., Matsumura, J. 2010. Changes in permeability1. The sound absorption rate of treated specimensand sound absorption capability of yellow poplarshowed high value in almost all frequency range. Thuswood by steam explosion treatment. Journal of themalas wood after heat treatment was could be consideredFaculty of Agriculture, Kyushu University 55(2):as sound-absorbing materials because its mean valueof sound absorption rate in the frequency range of50 6400 Hz was over 40%.327-332.Kang, C.-W., Lee, Y.-H., Kang, H.-Y., Kang, W., Xu,H.-R., Chung, W.-Y. 2011. Radial variation of2. The permeability of heated malas wood wassound absorption capability in the cross sectionalincreased by about 8 times compared to that of control.surface of yellow poplar wood. Journal of the Korean3. The pore diameter of heated malas wood wasenlarged compared to that of control.Wood Science and Technology 39(4): 326-332Kang, C.-W., Oh, S.-W., Lee, T.-B., Kang, W.,Matsumura, J. 2012. Sound absorption capabilityACKNOWLEDGMENTand mechanical properties of a composite rice hulland sawdust board. J Wood Sci 8: 273-278.This research was supported by Basic ScienceKang, C.-W., Park, H.-J., Jun, S.-S. 2012. SoundResearch Program through the National Researchabsorption capability and bending strength ofFoundation of Korea (NRF) funded by the Ministrymiscanthus particle based board. Journal of theof Science and ICT (NRF-2017R1A2B4012538).Korean Wood Science and Technology 40(1):38-43.REFERENCESKang, H.-Y., Lee, W.-H., Jang, S.-S., Kang, C.-W. 2017.Polyethylene glycol treatment of Han-ok roundwood components to prevent surface checking.ASTM 316-03 2011. Standard test methods for poreBioresources 12(2): 4229-4238.size characteristics of membrain filters by bubblepoint and mean flow pore test. American societyWassilieff, C. 1996. Sound absorption of wood–basedmaterials. Applied acoustics 48(4): 339-356.for testing and materials.- 154 -

The means of sound absorption coefficient of specimens in the frequency range of 50 6,400 Hz were 42% for treatment and 17% for control, respectively. Keywords: heat treatment, air permeability, sound absorption coefficient, Malas

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