Research Article

164

Received: 3 December 2008, Revised: 14 January 2009, Accepted: 17 January 2009, Published online in Wiley InterScience: 26 February 2009

(www.interscience.wiley.com) DOI: 10.1002/pat.1411

Anti-vibration and vibration isolatorperformance of poly(styrene-butadiene-styrene)/ester-type polyurethanethermoplastic elastomers

Jyh-Horng Wua*, Chia-Hao Lia, Hsien-Tang Chiub**, Zhi-Jian Shongb

and Peir-An Tsaic

This investigation presents novel thermoplastic elas

Polym. Adv

tomers (TPEs) based on poly(styrene-butadiene-styrene) (SBS)and ester-type polyurethane (TPU-EX) materials were prepared with varying compositions. A series of investigationswere conducted on the relationships between mechanical properties, dynamic mechanical properties, anti-vibrationand vibration isolator properties given, and the different compositions. The experimental results show incompat-ibilities between SBS and TPU-EX. SBS mechanical properties, dynamic mechanical properties, anti-vibration andvibration isolator properties are improved with an increase in the amount of TPU-EX, suggesting that the blending ofSBS with TPU-EX was consistent with the compound rule. Based on the obtained results, the viscoelasticity of SBSmaterials, their capacity to isolate vibration, and their anti-vibration performance can be adjusted by controlling theproportion of TPU-EX. Copyright � 2009 John Wiley & Sons, Ltd.

Keywords: thermoplastic elastomers; SBS; polyurethane; anti-vibration

* Correspondence to: J.-H. Wu, Nano-Powder and Thin Film Technology Center,Industrial Technology Research Institute, Tainan, Taiwan.E-mail: george6916@yahoo.com.tw

** Correspondence to: H.-T. Chiu, Graduate school of Polymer Engineering,National Taiwan University of Science and Technology, Taipei, Taiwan.E-mail: hchiu@mail.ntust.edu.tw

a J.-H. Wu, C.-H. Li

Nano-Powder and Thin Film Technology Center, Industrial Technology

Research Institute, Tainan, Taiwan

b H.-T. Chiu, Z.-J. Shong

Graduate school of Polymer Engineering, National Taiwan University of

Science and Technology, Taipei, Taiwan

c P.-A. Tsai

General Education Center, Jen-Teh Junior College of Medicine, Nursing and

Management, Miaoli, Taiwan

INTRODUCTION

Blending is the process of mixing two or more polymers indifferent proportions to yield particular performance.[1–3] One ofthe primary advantages of blending is its simplicity, as it requirescommon equipment and technology[4,5], and its variouscomponents have predictable physical and chemical properties,facilitating the predication of the properties of the mixture.Rubber is extensively applied as an anti-vibration material in

machinery, transportation, and construction. With advances inhigh technology fields, the demand for anti-vibration equipmenthas increased rapidly—particularly in the areas of aeronauticsand precision instruments. However, as more people arebecoming environmentally conscientious, Thermoplastic elasto-mers (TPEs) have replaced vulcanized rubber because of theirfavorable mechanical properties and recyclability.[6] Oneadvantage of such elastomers is that they can be processedby conventional thermoplastic processes such as extrusion,injection molding, and others. TPEs have properties similar tothose of vulcanized rubber, such as softness, flexibility,extensibility, and resilience.Poly(styrene-butadiene-styrene) (SBS) TPE has mechanical

characteristics that are similar in many respects to those ofconventional vulcanized rubber, but with the advantages of low-temperature flexibility, chemical stability, and electrical insula-tion.[6] This material is commonly adopted in plastic blends,footwear, and other adhesive applications. Thermoplasticpolyurethane (TPU) is easily processed with good elongation,excellent damping properties, and high abrasion resistance.[6–9]

. Technol. 2010, 21 164–169 Copyright �

The main areas of application of TPU are in the automotive, shoe,wire, and cable industries.SBS and ester-type polyurethane (TPU-EX) can be blended to

produce novel TPEs materials, but this synthetic route has notbeen reported. The main goal of this investigation is to evaluateSBS and TPU-EX prepared in various proportions by meltblending. In experiments on mechanical properties, dynamicmechanical analysis (DMA), hysteresis, and dynamic propertieswere tested to evaluate the anti-vibration and vibration isolationperformances of SBS/TPU-EX TPEs.

2009 John Wiley & Sons, Ltd.

Table 1. Compositions of SBS/TPU-EX thermoplastic elasto-mers

Sample

Materials (wt%)

SBS TPU-EX

SBS 100 —SEX7525 75 25SEX5050 50 50SEX2575 25 75TPU-EX — 100

Figure 1. A typical hystersis damping curve.

Figure 2. The state of load–displacement curve.

PERFORMANCE OF THERMOPLASTIC ELASTOMERS

1

EXPERIMENTAL

Materials

The polymers utilized were SBS radial copolymer (grade: TPE475)(LCY Chemical Industry Inc, Taiwan) with a styrene content of40%. The ester type TPU (grade: EX-85A) was manufactured byCoating Chemical Industry Inc, Taiwan.

Sample preparation

The SBS containing TPU-EX (as shown in Table 1) were preparedby melt blending pellets of both components in a twin-screwextruder (Werner and Pflederer, Model-ZSK 26 MEGAcompoun-der). Extrusion was performed at a screw rotation rate of 500 rpmand temperature of 170–1908C. The extruded thread was thenpelletized. These blended pellets were then injected into 2mmthick molds.

Mechanical properties measurements

Mechanical properties were measured using a Universal TensileTester with a tension velocity of 500mm/min based on ASTMD412C specifications. The Shore hardness test was determined bya Shore A durometer from ASTM D2240.

Dynamic mechanical properties analysis

Composites were trimmed to 30mm� 6mm� 2mm. DMA(model no. Q800) with a temperature increase rate of 5 8C/minwithin the range of �90–1308C under a frequency of 1 Hz wasused for temperature scanning.

Determination of compression stiffness

The material testing system (type: MTS–810) is utilized to testcompression stiffness of the experiment piece with a dimensionof 45� 0.5mm� 45� 0.5mm� 12� 0.5mm under a defor-mation range of 1mm. Calculation of the compression stiffness(Ks) is as follows:

Ks ¼F

X(1)

Where F is the compression force and X is the compressiondisplacement.

Determination of compression hysteresis

Themeasurement was carried out using amaterial testing system(MTS-810) at a frequency of 1 Hz and displacement of 1mm. Theloss of energy in each cycle, DW, was calculated from the

Polym. Adv. Technol. 2010, 21 164–169 Copyright � 2009 John

hysteresis loop, and the damping constant, b, was calculatedfrom DW as shown below:[10]

DW ¼ pKsbX2 (2)

The calculated b was then converted into the hysteresisdamping curve, where X is the displacement of the part in jthcycle, similar to Fig. 1, where:[10]

XjXjþ0:5

¼ffiffiffiffiffiffiffiffiffiffiffiffiffiffi2þ pb

2� pb

s(3)

Xjþ0:5

Xjþ1¼

ffiffiffiffiffiffiffiffiffiffiffiffiffiffi2þ pb

2� pb

s(4)

Testing methods for dynamic properties of vibrationisolation

SRIS 3503-1990[11] non-resonance testingmethod was employed,in which the specimens were placed in the material testingsystem (MTS-810), and subjected to vibration at a frequency of1 Hz and displacement of 1mm. Figure 2 is the loading–displacement graph under sine wave loading. The horizontal axisrepresents displacement while the vertical axis representsloading. The energy loss of the nanocomposites DW is the area

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Figure 4. The hardness and compression stiffness of SBS/TPU-EX ther-

moplastic elastomers. This figure is available in color online at www.interscience.wiley.com/journal/pat

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surrounded by the loading–displacement curve, where P is theload, X the displacement, jk�j the absolute resilience modulus, dthe phase angular, k1 the storage modulus, k2 the loss modulus, cthe damping coefficient, v the angular frequency, Ks thecompression stiffness, and R is the dynamic ratio calculatedusing the equations below: [11]

k�j j ¼ Po=Xo ¼ BC

AB(5)

sin d ¼ ð2pÞ � ðDW

WÞ (6)

k1 ¼ k�j j cos d (7)

k2 ¼ k�j j sin d (8)

c ¼ k2v

(9)

R ¼ k�j jKs

(10)

RESULTS AND DISCUSSION

Physical properties of SBS/TPU-EX thermoplastic elastomers

Figure 3 presents the mechanical properties of the SBS/TPU-EXTPEs. The elongation at break of SBS exceeds that of TPU-EX. Thetensile stress and tensile modulus of SBS are lower than those ofTPU-EX. Finally, the tensile stress and modulus of the SBS/TPU-EXTPEs increase with the proportion of TPU-EX, and the elongationdecreases. Figure 4 shows the hardness and stiffness propertiesof SBS/TPU-EX TPEs. The hardness and stiffness of SBS are lowerthan those of TPU-EX. The hardness and stiffness values of SBS/

Figure 3. The elongation at break, tensile stress and modulus of SBS/TPU-EX thermoplastic elastomers. This figure is available in color online at

www.interscience.wiley.com/journal/pat

www.interscience.wiley.com/journal/pat Copyright � 2009

TPU-EX TPEs increase with the TPU-EX ratio. Overall, this trend canbe attributed to the softness of the polymer chain structure ofSBS, and stiffness of the polymer chain structure of TPU-EX. Theabove results indicate that SBS/TPU-EX composite systemsexploit the properties of one component to offset the weaknessof the other in mechanical performance.

Dynamic mechanical properties of SBS/TPU-EXthermoplastic elastomerTPEs

The storagemodulus as a function of temperature for SBS/TPU-EXTPEs is shown in Fig. 5. It reveals a glassy region of SBS at lowtemperature: the chain conformation is frozen into a rigidnetwork, yielding a high storage modulus and low loss. As thetemperature increases, the polymer chain begins tomove, rapidlyreducing the storagemodulus and causing high loss. In particular,polymers in the transition region from the glassy state to therubbery state have great potential for damping vibration. Thepolymer chain of TPU-EX is stiff, and so its storage modulusexceeds that of SBS. More polymer chains move at higher

Figure 5. Variation of storage modulus with temperature of SBS/TPU-EXthermoplastic elastomers. This figure is available in color online at

www.interscience.wiley.com/journal/pat

John Wiley & Sons, Ltd. Polym. Adv. Technol. 2010, 21 164–169

Figure 6. The temperature dependence of tan d at 1 Hz for SBS/TPU-EX

thermoplastic elastomers. This figure is available in color online atwww.interscience.wiley.com/journal/pat

Figure 8. The hysteresis loops of SBS/TPU-EX thermoplastic elastomers.

(The compression loading was 350 kg, f¼ 1Hz, displacement¼ 1mm).This figure is available in color online at www.interscience.wiley.com/

journal/pat

PERFORMANCE OF THERMOPLASTIC ELASTOMERS

temperatures (high damping regions). Also, the storage modulusvalues of SBS increase (glassy region, T<�908C) with the TPU-EXcontent. Second, the curves of both TPEs at TPU-EX 50 and75wt% have three regions—glassy, transition, and secondarytransition. In the transition region, the storage modulus of SBS/TPU-EX TPEs increases with TPU-EX content.Figures 6 presents the temperature dependence of the tan d at

1 Hz for SBS/TPU-EX TPEs. These curves show that SBS has two tand peaks—the low glass transition temperature (Tg1) of the SBSbutadiene block �72.38C, and the high glass transitiontemperature (Tg2) of the SBS styrene block 102.18C. The glasstransition temperature (Tg) of the TPU-EX polymer is around�8.18C. Three tan d peaks were obtained from SBS blended withTPU-EX, and the tan d peaks differed slightly from those of pureSBS and TPU-EX. The materials in the two phases areincompatible. Additionally, the tan d peak values of SBS/TPU-EXTPEs increase and decrease as the TPU-EX content increases. Thedamping capacity of a polymer is given by the tan d values atthe ambient temperature. These effects are clearly visible in themagnified region of tan d values at 258C, presented in Fig. 7,indicating that the TPEs of SBS/TPU-EX depend on the TPU-EXcontent, and have better damping characteristics than SBS atambient temperatures.

Figure 7. Variation of tan d as a function of TPU-EX content for SBS/

TPU-EX at 258C.

Polym. Adv. Technol. 2010, 21 164–169 Copyright � 2009 John

1

Hysteresis of SBS/TPU-EX thermoplastic elastomers

Under alternating stress, hysteresis occurs when the rate ofdeformation is less than the rate of variation of stress variation. Inthis case, since the absorbed and released energies are notbalanced in each cycle, the stretching and recoil curve form aclosed loop, which is known as a hysteresis loop. The area withinthe loop represents the energy loss. For elastomer materials, alarger hysteresis loop means higher damping, which moreeffectively reduces vibration.[12] The damping constants may bederived from the area surrounded by hysteresis loops. Based onthe theory of free vibration, the vibration-isolating capacity ofmaterials can be evaluated from the damping constant and thehysteresis damping characteristics.[10]

Figures 8 and 9 present the hysteresis loop and vibration-damping curve of SBS/TPU-EX TPEs under compressive vibrationat 258C at 1 Hz with a displacement of 1mm. Figure 10 shows theenergy loss over a cycle (DW) and the damping constants (b)obtained from the hysteresis loops. DW indicates that theanti-vibration property of SBS is improved as the amount ofTPU-EX is increased. Therefore, the material is assumed tobecome better able to transform its kinetics to those of thermaldissipation upon the application of an external force. Simul-taneously, adding TPU-EX increases stiff, and improves theanti-vibration performance of the SBS/TPU-EX system. However, ahigher damping constant of TPU-EX indicates faster energydissipation at particular amplitudes, which becomes stable withless vibration. When TPU-EX is blended with SBS, theexperimental results were obtained that indicated similartendencies of b as were revealed by the DW results. Therefore,the TPU-EX content plays important roles in the design ofmaterials to isolate vibration , and determines their anti-vibrationperformance.

Dynamic vibration isolation and anti-vibration properties ofSBS/TPU-EX thermoplastic elastomers

The relationship between the dynamic ratio and the tan d

obtained may be exploited to evaluate the isolation of vibrationand the anti-vibration capacity of elastomer materials. Table 2presents the dynamic test results for SBS/TPU-EX TPEs under

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Figure 9. The hysteresis damping curves of SBS/TPU-EX thermoplastic elastomers.

Figure 10. The hysteresis loops (DW) and damping constants (b) of SBS/

TPU-EX thermoplastic elastomers.

Table 2. The dynamic properties of anti-vibration perform-ance of SBS/TPU-EX thermoplastic elastomers

Sample jk�j d k1 k2 c R

SBS 218.28 10.09 215.54 34.49 5.489 1.38SEX7525 255.01 9.64 252.08 38.47 6.123 1.34SEX5050 283.56 8.25 281.18 36.64 5.831 1.11SEX2575 387.61 9.56 383.24 57.99 9.231 1.06TPU-EX 520.21 10.87 512.64 88.39 14.071 0.95

Figure 11. The loading dynamic ratio and tan d of SBS/TPU-EX thermo-

plastic elastomers.

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loading by 350 kg at 258C and, 1 Hz, with a displacement of 1mm.A lower dynamic ratio (R) indicates better vibration isolation, anda higher damping or loss factor (tan d), favoring shock absorption.Figure 11 shows the relationship between R and tan d; the figureindicates that the dynamic ratio of SBS exceeded that of TPU-EX.Additionally, the dynamic ratio of the SBS decreased as theTPU-EX content increased. Restated, the blending of SBS withTPU-EX exhibits favorable vibration isolation, indicating thatthe TPU-EX is the source of vibration isolation performance inSBS/TPU-EX TPEs. TPU-EX effectively converts the mechanicalenergy to heat energy. Also, the anti-vibration performance ofSBS/TPU-EX TPEs improves as the TPU-EX content is increased.

www.interscience.wiley.com/journal/pat Copyright � 2009 John Wiley & Sons, Ltd. Polym. Adv. Technol. 2010, 21 164–169

PERFORMANCE OF THERMOPLASTIC ELASTOMERS

Based on the above mentioned, the viscoelasticity of SBSmaterials, their capacity to isolate vibration, and their anti-vibration performance can be adjusted by controlling theproportion of TPU-EX.

CONCLUSIONS

In this investigation, SBS and TPU-EX materials were combined toform novel TPEs. Based on the above discussion, DMA curvesshow that SBS/TPU-EX has three tan d peaks, suggesting that thematerials systems are incompatible. The mechanical properties,dynamic mechanical properties, and anti-vibration performanceof SBS/TPU-EX TPEs are improved as the TPU-EX content isincreased. Therefore, different compositions can be used tocontrol the final characteristics of SBS/TPU-EX TPEs.

Polym. Adv. Technol. 2010, 21 164–169 Copyright � 2009 John

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