Experimental and theoretic studies on sound transmission loss of laminated mica-filled poly(vinyl...

Experimental and Theoretic Studies on SoundTransmission Loss of Laminated Mica-FilledPoly(vinyl chloride) Composites

Xing Wang, Feng You, Feng Shun Zhang, Jiang Li, Shaoyun Guo

The State Key Laboratory of Polymer Materials Engineering, Polymer Research Institute of Sichuan University,Chengdu 610065, China

Received 24 November 2010; accepted 10 January 2011DOI 10.1002/app.34047Published online 23 May 2011 in Wiley Online Library (wileyonlinelibrary.com).

ABSTRACT: The effects of dioctyl phthalate and inor-ganic filler, mica, on the sound insulation property ofpoly(vinyl chloride) (PVC) were investigated in this work.The stiffness and mass laws, which are the common theo-retic tools to predict the soundproof properties of materi-als, were used to analyze the sound transmission loss(STL). The experimental results revealed that the stiffnessand mass laws can describe well the sound insulationproperty of PVC/mica composites. The stiffness and sur-face density are important factors influencing the improve-

ment of STL. With the increase of content of mica, STLand resonance frequency, fmn, of PVC/mica compositesincrease. Moreover, the change of STL in the stiffness-controlled region is more obvious than that in the mass-controlled region, because the addition of mica in PVCleads to a greater increase in the stiffness. VC 2011 Wiley Peri-odicals, Inc. J Appl Polym Sci 122: 1427–1433, 2011

Key words: sound transmission loss; stiffness; surfacedensity; PVC; mica

INTRODUCTION

With the development of modern industry and traf-fic system, noise pollution has become one of manyfactors that affect human health and environmentworldwide. Therefore, the techniques using soundabsorption and insulation materials to reduce ambi-ent noise have received much attention.1,2 Herein,the viscoelastic polymer materials show the greatpotential for insulating or damping the sound andvibration due to their unique combination of inher-ent damping, light-weight, and processable abilitycompared to metal and inorganic materials3–5

However, most polymer materials, which havelower modulus and surface density compared tometal and inorganic materials, cannot be solely usedto insulate sound because of their poor sound insu-lation performance. At present, the application ofpolymer material in the field of sound insulation hasbeen focused on structure designing of polymericand metal or inorganic materials, such as con-strained layer.6–8 Here, viscoelastic polymer materi-als are used as interlayer to increase sound transmis-

sion loss (STL) because of their unique mechanical,high damping properties, and low density. Yoonet al.9,10 studied damping properties and STL of aseries of polyurethane composites as damping layerand concluded that the damping loss is the key toenergy consuming when the wave of sound trans-mits through the polymer. Such a sandwich struc-ture, which separates the substrate layer, canweaken the sound transmission in the resonance andcoincidence regions. On the basis of above works,materials with multilayered structure have beendesigned.11–13 In these materials, the multilayeredinterfaces lead to the multiple reflection of acousticwaves, and the internal layers have multiform defor-mation, such as tension, compressing, and shearingthat can dissipate more acoustic energy.However, the layered structure designing of dif-

ferent materials brings some disadvantages: unstableinterface, high fabrication cost, and density. There-fore, improving the soundproof ability of singlepolymer by simple filling modification is attractingresearchers’ attention.14–17 Moreover, with the exten-sive applications of polymer materials in the con-struction, transportation, and other fields, a higherSTL of polymer material itself is also required.The acoustic insulation ability of single polymer

material mostly depended on the surface density,stiffness, and uniformity of material. In general, theaddition of inorganic filler in polymer can easilyincrease these properties. Lee et al.16 found that theprincipal factor, influencing the improvement ofsound insulations of ABS/CNT composites, was

Correspondence to: J. Li or S. Guo ([email protected] [email protected]).

Contract grant sponsor: National Natural ScienceFoundation of China; contract grant number: 50933004.

Contract grant sponsor: National Key Technology R andD Program; contract grant number: 2009BAG12A07-E02-1.

Journal of Applied Polymer Science, Vol. 122, 1427–1433 (2011)VC 2011 Wiley Periodicals, Inc.

enhancement of stiffness by CNT additives. More-over, consumption and reflection of sound energyalso have effect on STL of material. A kind of soundinsulation material based on the polymer containinghollow glass microspheres was also studied.17 Theresult showed that the dilatation vibration of themicrospheres plays a key role in the sound attenua-tion of the polymer composites in the quasi-staticregion.

Although the methods to improve the acousticinsulation ability of polymer have been reported, thetheoretic study on the acoustic insulation ability ofsingle polymer material is still scarce. The stiffnessand mass laws are the common theoretic tools topredict the soundproof properties of some buildingmaterials.18,19 In this work, the acoustic insulationability of poly(vinyl chloride) (PVC) with differentstiffness and surface density was investigated usingstiffness and mass-controlled laws. PVC was selectedas soundproof matrix material because of its wideuse as building and automotive material and itsgood compatibility with most filler. Mica, a platelikefiller, was filled into PVC to adjust its stiffness andsurface density. Mica has been reported to improvethe vibration damping property20 and gas barrierability21 of polymer composites due to its excellentmechanical, electrical insulation, and thermal prop-erties. However, there was rare report regarding theeffect of laminar mica on acoustic insulationproperty.

EXPERIMENTAL

Materials

PVC (SG-5) with a density of 1.20 g/cm3 wasobtained from Tianjin Dagu Chemical Factory,China. Crystallitic mica (1250 mush) with a densityof 1.92 g/cm3 was provided by Sichuan TianweiIndustry Co., China. Dioctyl phthalate (DOP) wasfrom Luoyang Jiarui Plastic Industrial Co., China.Other additives including lead salt stabilizer, poly-ethylene wax, and stearic acid were commercialproducts.

Sample preparation

PVC/mica composites were prepared by blendingPVC and mica with various proportions (0, 10, 20,30, 40, and 50 wt %) for a period of 8 min in a twinroll mixer at 160�C and followed by compressionmolding at 160�C and 15 MPa pressure for 5 min,then naturally cooled to room temperature underpressure. The sheets were then removed and die cutfor the appropriate tests. The contents of processingadditives (DOP, combined lead salt stabilizer, lubri-cant, and processing acid) were, respectively, 0–30,

5, 2, and 2 phr (parts per hundred parts ofPVC resin).

Measurements and characterization

STL is a key quantification of the effectiveness ofacoustical insulation for engineering applicationsand then simply defined as the transmission coeffi-cient (s) expressed in decibels (dB) according toEq. (1) below22:

STL ¼ 10� log101

s

� �(1)

A four microphone impedance tube was providedby BSWA Technology Co., Beijing for the measure-ment of STL, as shown in Figure 1. Two separatetubes with diameters of 60 and 30 mm were used tomeasure STL. The frequency ranges on the two tubeswere assumed to be 100 Hz to 2.5 KHz for largetube and 1.6 KHz to 6.3 KHz for the small tube perthe manufactures impedance testing specifications.An open-ended tube condition and a hard close-ended tube condition were used for both sizedtubes. The transfer function method was used tocalculate the STL.23 The dimensions of the specimenswere 30 and 60 mm in diameter and 1 mm in thick-ness. The results were measured as the average ofthree times.Tensile modulus of PVC and composites were

measured on an SANS CMT4104 Electronic Univer-sal Testing Machine (Shenzhen, China) with dumb-bell specimen dimensions of 25 � 6.5 � 1 mm3 anda crosshead speed of 5 mm/min (GB/T 1040–2006)at 23�C. The results were reported as the average offive samples.The bulk densities (qm) of the fabricated speci-

mens were obtained through measuring their massesand volumes, and the surface densities of unit area(q) were defined as the ratio of bulk density andthickness of specimens.

Figure 1 System connection of sound transmission losstesting. [Color figure can be viewed in the online issue,which is available at wileyonlinelibrary.com.]

1428 WANG ET AL.

Journal of Applied Polymer Science DOI 10.1002/app

Liquid nitrogen cryogenic fractured specimenswere used for scanning electron microscope (SEM)observation. After the fractured sections were sput-ter coated with gold, the morphology observationwas taken on a JSM-5900LV (Japan) SEM at an accel-erating voltage of 20 kV.

RESULTS AND DISCUSSION

Effect of DOP content on the STL of PVC

Figure 2 shows the dependence of STL of PVC with30 phr dioctyl phthalate (DOP) on the sound fre-quency. In this typical curve of STL versus soundfrequency (f), a lowest STL value appears at the res-onance frequency, fmm, which is determined by thephysical parameters and boundary conditions of thespecimen. Moreover, the curve can be divided intotwo zones according to sound frequency. In zone 1(f < fmn), STL decreases quickly with increasing fre-quency due to resonance effects. On the contrary,STL increases gradually with the increase of fre-quency in zone 2 (f > fmn).

Many researchers showed that besides the fre-quency, the stiffness and mass (or density) of materi-als can affect greatly the acoustic insulation abil-ity.16,24,25 In zone 1, the stiffness plays a critical rolein the sound insulation, and STL increases with theincreasing stiffness. In zone 2, STL of material com-plies with the mass law and increases with theincrease of the surface density of unit area of thepanel. Therefore, zones 1 and 2 are also referred toas stiffness-controlled and mass-controlled stages.

As an important processing additive, DOP cannotonly improve effectively processability of PVC butalso change its stiffness in a large scope. Accordingto the definition,25 the stiffness of materials, B, canbe expressed by the following equation

B ¼ 1

12� Eh3

1� l2(2)

where E, h, and l are elastic modulus, thickness,and Poisson ratio of materials, respectively.Figure 3 shows the quantitative relationship of

DOP content, stiffness, and surface density of unitarea of PVC. It can be found that the stiffness ofPVC obviously decreases with increasing DOP con-tent. When the content of DOP changes from 0 to30 phr, the stiffness reduces by 71%. According tothe above discussion, such a large decrease in thestiffness would lead to an obvious change of STL instiffness-controlled region.Figure 4 shows the effect of DOP content on STL

in the sound frequency range of 100–6300 Hz. It canbe clearly found that in zone 1, the curves of STLversus frequency move to the direction of lower fre-quency with the increase of DOP content in PVC.These changes mean that increasing DOP content

Figure 2 Typical STL versus frequency curve of PVCpanel with 30 phr DOP.

Figure 3 The stiffness and surface density of unit area ofPVC with different DOP content.

Figure 4 The STL versus frequency curves of PVC withdifferent DOP content.

EXPERIMENTAL AND THEORETIC STUDIES ON STL 1429


causes simultaneously the decrease of STL and fmn.However, in zone 2, the change of STL is indistinc-tive. This is attributed to the very small change ofthe surface density of materials with different DOPcontent, as shown in Figure 3.

STL of PVC/mica composites

The PVC composites containing different contentmica were prepared through melting blend. Toensure the processability, 30 phr DOP was incorpo-rated in composites. Laminar mica can be exfoliatedto form platelets in PVC matrix during melting proc-essing because of their good compatibility,26 asshown in Figure 5. Some works showed the effect ofthis plate morphology on the vibration damping ofspecimen.27 When the specimen is vibrating, theshear takes place in the damping layer between themica platelets, which increase the mechanical loss ofenergy being converted into heat. In this part, theeffects of mica on the physical properties and STL ofPVC were discussed.

Some works reported that the presence of micaplatelets restricts the mobility or deformability ofPVC molecules and consequently leads to an in-crease of elastic modulus.28–30 According to Eq. (1),the stiffness also increases with the addition of mica.Additionally, mica was used here as a kind of high-density filler in this work. Its introduction into PVCcan also increase the surface density of PVC compo-sites. Table I shows that the elastic modulus, stiff-ness, and surface density of unit area of samplesincrease with increasing the mica content from zeroto 50 wt %. The stiffness and surface density areimproved by 75 and 27%, respectively. The increase

in stiffness is much greater than that in surfacedensity.In the same way, the dependence of STL of PVC/

Mica composites on frequency can be divided intostiffness-controlled (zone 1) and mass-controlled(zone 2) regions as shown in Figure 6. In stiffness-controlled region, STL can be calculated approxi-mately by the following equation19:

STL ðstiffnessÞ ¼ 10 logpqfqc

� �2

1� fmn

f

� �2" #2

8<:

9=; (3)

where q is the density of air and c is acoustic speedin air.For single panel, the resonance frequency (fmn) can

be evaluated by Eq. (4).

fmn ¼ 0:45Cphm

a

� �2

þ n

b

� �2� �

(4)

where a, b are the dimensions of panel; m, n are inte-gers 1, 2 . . . and Cp is the speed of longitudinalwave in material, which can be calculated by Eq. (5).

Cp ¼ E

qm 1� l2ð Þ½ � (5)

In our experiment, the tested samples in imped-ance tube were cut to 60 and 30-mm diametercircular plate. So, the fmn can be calculated by thefollowing equation:

fmn ¼ 0:45Eh

qm 1� l2ð Þ½ �mffiffiffip

pr

� �2

þ nffiffiffip

pr

� �2" #

(6)

where r is the radius of panel.According to eqs. (3) and (6), STL in stiffness-con-

trolled region increases with the increase of the elas-tic modulus of material and decreases with theincrease of measured frequency. This result isconsistent with the above discussion.

Figure 5 SEM micrograph of mica-filled PVC.

TABLE IThe Effects of Mica Content on the Elastic Modulus,

Stiffness, and Surface Density of Unit Areaof PVC/Mica Composites

Content ofmica (wt %)

Elasticmodulus(MPa)

Stiffness ofunit area

(�107N/m2)

Surface densityof unit area(kg/m2)

0 721 6.85 1.2210 741 7.04 1.2820 820 7.8 1.3330 900 8.57 1.440 1173 11.2 1.4850 1260 12 1.56

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In mass-controlled region (zone 2), when soundwave impacts a specimen, the specimen vibratesaccording to the change of the atmospheric pressure.The vibration energy dissipates during the transmit-ting process from inside to outside of the specimenand increases according to the increase of the weightof the material.31 This relation is called the mass lawof sound insulation, that is, Eq. (7), by which STL inzone 2 can be calculated.

STL ðmassÞ ¼ 10 logpqfqc

� �2

¼ 20 logqþ 20 log f � 42

(7)

Figure 6 (a–f) Theoretic and experimental results of the STL for PVC/mica composites with different mica contents.

TABLE IIThe Experimental and Theoretic ResonanceFrequency (fmn) of PVC/Mica Composites

with Different Mica Contents

Content ofmica (wt %)

Experimental(Hz)

Theoretic(Hz)

0 500 53810 500 54020 630 56230 630 58640 710 72350 710 735



Thus, the theoretic STL and fmn values of PVCcomposites with different mica content in both stiff-ness-controlled and mass-controlled regions, whichare illustrated in Figure 6(a–f) and Table II, can beobtained according to eqs. (3), (6), and (7). At thesame time, the experimental values of STL and fmn

measured by impedance tube are also illustrated inFigure 6(a–f) and Table II. It can be found from Fig-ure 6(a–f) that, for all samples with different micacontent, the values of STL obtained through theo-retic calculation are very approximate to thoseobtained through experimental measurement. Thisindicates that the stiffness and mass laws candescribe well the acoustic insulation ability of PVC/mica composites and provide a reliable guidance forthe design and optimization of soundproof compos-ite with fillers. It is also noted from Figure 6(a–f)that the experimental values of PVC/mica compo-sites are slightly greater than the theoretic values.This difference may be attributed that the sounddamping by reflection or scattering would beincreased when the layered mica fillers act asanother wall for sound blocking. Moreover, whenthe fillers are dispersed in the wall of PVC, we cananticipate that the energy dissipation as heatthrough hysteresis can be increased, because thewall of PVC should move together with the massiveinorganic when it recovers its deformation causedby sound waves.32 So, relative to the matrix, thecomposites filled with mica have many contributionscoming from the frictional loss and the plateletstructure, which may increase the sound insulationcapacity.

The change of STL with frequency of all curves inFigure 6(a–f) shows the similar trend. In stiffness-controlled region (zone 1), the STL decreases quicklywith increasing sound frequency and reaches theminimum at fmn due to resonance results. And then,

the STL begins to increase with increasing of soundfrequency according to mass law when sound fre-quency is higher than fmn. Table II listed the experi-mental and theoretic fmn values of PVC/mica com-posites with different mica contents. It can be foundthat the experimental and theoretic values are rela-tively close. The differences may originate from therestraints on rotation of edges of the fixture duringthe measurement. The addition of mica affectsgreatly fmn, which increases with the increase of con-tent of mica due to the improvement of stiffness ofcomposites.For a more comprehensive comparison of the

acoustic insulation ability of PVC/mica compositeswith different mica contents, the average values ofSTL of PVC/mica composites in stiffness-controlledand mass-controlled regions were plotted in Figure7. It can be found that the average STL value in stiff-ness-controlled region increases obviously withincreasing mica content up to 40 wt % and then hasa small drop with the further increase of filler con-tent. The average STL value increases by 40% withthe addition of 40 wt % of mica in PVC, because thestiffness of composites increases greatly as shown inTable I. Therefore, in stiffness-controlled region, itmight be concluded that the increasing stiffnessplays a principal role in the improvement of theSTL of PVC/mica composites. However, with thefurther increase of the content of mica, the uniform-ity of composites becomes worse. This results in adecrease in STL.On the other hand, the average STL in mass-con-

trolled region also increases with increasing micacontent due to the increase of surface density ofcomposites. However, the maximum increase of STLis only 12.8%, because the surface densities of com-posites are not greatly improved with increasingmica content, as shown in Table I. Therefore, theaddition of mica leads to more significant change ofthe acoustic insulation ability in the stiffness-con-trolled region.

CONCLUSIONS

In this research, the STL of PVC with different DOPcontent was investigated. It is found that the STLdecreases with increasing of DOP content due to thereduction of stiffness. Moreover, various amounts ofmica were introduced into the PVC matrix toimprove the sound insulation property. The resultsshow that the STL value of PVC/mica is improvedobviously because of the introduction of mica, espe-cially in stiffness-controlled region. The increasedaverage STL can be a significant value in practicalnoise reduction. By the stiffness and mass laws, thesound insulation efficiency for soundproof compos-ite can be evaluated, and contribution of mica on

Figure 7 Average STL values of PVC compositeswith different mica contents in the frequency range of 100–6300 Hz.

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sound insulation is confirmed. It is demonstratedthat the increased stiffness and the unique structureof microconstrained layer as the addition of flakemica induce the improvement of acoustic attenua-tion. As a future work, the practical applications ofthe thin and light-weight sound insulation materialwill be developed.

APPENDIX

Parameters used in the article.

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TABLE

Symbols

s sound transmission coefficientqm bulk density of specimenq surface density of unit area of specimenq density of airf sound frequencyfmn resonance frequencyB stiffness of specimenE elastic modulush thickness of specimenl Poisson ratioc acoustic speed in aira, b dimensions of specimenm, n integers 1, 2. . .Cp speed of longitudinal wave in materialr radius of specimen in impedance tube



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