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Studies on Ethylene Propylene Diene Rubber andThermoplastic Polyurethane Blends: The Effect ofMaleationR. Dhamodharan a , Pralay Maiti b & Ganga Radhakrishnan aa Polymer Division, Central Leather Research Institute , Adyar, Chennai, Indiab School of Materials Science and Technology, Institute of Technology, Banaras HinduUniversity , Varanasi, IndiaPublished online: 28 Oct 2008.

To cite this article: R. Dhamodharan , Pralay Maiti & Ganga Radhakrishnan (2008) Studies on Ethylene Propylene DieneRubber and Thermoplastic Polyurethane Blends: The Effect of Maleation, Polymer-Plastics Technology and Engineering, 47:11,1081-1089, DOI: 10.1080/03602550802355792

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Studies on Ethylene Propylene Diene Rubber andThermoplastic Polyurethane Blends: The Effect of Maleation

R. Dhamodharan1, Pralay Maiti2, and Ganga Radhakrishnan1

1Polymer Division, Central Leather Research Institute, Adyar, Chennai, India2School of Materials Science and Technology, Institute of Technology, Banaras Hindu University,Varanasi, India

Blends of maleated ethylene propylene diene rubber (EPDM)and thermoplastic polyurethane (TPU) have been studied to under-stand the effect of the maleation level of EPDM on the compati-bility and morphology of the blends. Blends with differentmaleation levels on EPDM (0.25, 0.50, and 0.75 wt%) were com-pared for mechanical, thermal, and other properties. The appear-ance of single Tg for 0.5% and 0.75% confirms that a maleationlevel of more than 0.5 wt% is required for EPDM blends withTPU. However, best mechanical properties are obtained for 0.5%maleated EPDM and TPU blends. Aging, filler reinforcement,and weather resistance measurements were also studied for theblends of varying maleation levels.

Keywords Compatability of blends; Maleated EPDM; Polymerblends and alloys; Thermoplastic polyurethanes;Weather resistance

INTRODUCTION

It has long been the demand and practice of industry toblend dissimilar polymers to improve the properties ofeach. Blending now has emerged as a major tool to obtainnew polymeric materials with desirable properties. Rubberand plastic blends have been produced as rubber tough-ened plastics or as thermoplastic elastomer (TPE)[1–3].Since the 1980s, new developments of polymer blendsand alloys of thermoplastic species have been sharplyincreasing, and the main reason for this is to produce poly-meric materials at lower cost. Blending also provides mate-rials with an unusual combination of mechanical, thermal,chemical, and morphological properties[4–6].

The most difficult task is the development of materialswith a full set of desired properties. This has been achievedby selecting blend components in such a way that the prin-cipal advantage of the first polymer will compensate fordeficiencies of the second one and vice versa[7,8]. In recent

years, elastomeric rubber and plastic blends have becometechnologically interesting for use as thermoplastic elasto-mers[9]. These materials exhibit some of the physicalproperties of elastomers at lower temperatures and are pro-cessable at elevated temperatures. Polymer blends generallyexhibit poor mechanical properties due to incompatibilityand phase separation. Several studies have been reportedto minimize phase separation and increase interfacialadhesion. One such versatile approach is the addition ofa compatibilizing agent[10,11]. Blending TPU with EPDMfor improving mechanical properties and the function ofmaleated EPDM in improving the compatibility of EPDMwith TPU has been reported in our previous work[12].

The aim of the present work is to vary the maleation levelof ethylene propylene diene rubber and to study its compati-bility with polyurethane rubber. Three different maleationlevels (0.25, 0.50, and 0.75 wt%) of EPDM were blendedwith polyurethane. Improvements in the mechanical proper-ties of EPDM have been studied. Compatibility of theblends has been studied by using DSC (Differential Scan-ning Calorimeter). Morphological studies were observedby using SEM (Scanning Electron Microscope). The resultswere compared for compatibility and mechanical propertiesfor choosing the right maleation level. Improvement in theaging properties of the blends was studied. Weather resist-ance tests were done using an Ozone chamber.

EXPERIMENTAL

Materials

EPDM used in this study is Esprene 505 A, manufac-tured by Sumitomo Chemicals, Japan. It is a terpolymerwith ethylidene norbornene (ENB). The Mooney viscosityof the polymer ML (1þ 4) @ 100�C is 52 and the specificgravity is 0.86 gm=cc. Polyurethane used in this study isMillathane 66 (Ester type), manufactured by TSE Indus-tries, Japan. It is an ester type TPU with Mooney viscosityML (1þ 4) @ 100�C at 50 and a specific gravity of

Address correspondence to R. Dhamodharan, PolymerDivision, Central Leather Research Institute, Adyar, Chennai –600020, India. E-mail: dhamodharan_raja@yahoo.co.in

Polymer-Plastics Technology and Engineering, 47: 1081–1089, 2008

Copyright # Taylor & Francis Group, LLC

ISSN: 0360-2559 print/1525-6111 online

DOI: 10.1080/03602550802355792

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1.15 gm=cc. Maleated EPDM used in this study is obtainedfrom Pluss polymers, India. 0.25, 0.50, and 0.75 wt%maleated EPDM were used for this study. The Mooneyviscosities (ML (1þ 4) @ 100�C) of 0.25 wt% maleatedEPDM henceforth labeled as 0.25 mEPDM; 0.5 wt%maleated EPDM as 0.5 mEPDM), and 0.75 wt% maleatedEPDM as 0.75 mEPDM are 107.5, 126.6, and 135.5,respectively.

Blends Preparation

Blends were prepared in a two roll open mill. Two partsof dicumyl peroxide (40% active on EPDM carrier) wasalso mixed with the blends. Tensile slabs were preparedin an electrically heated compression molding press at180�C for 5 min. Table 1 given below indicates the variousblends prepared for this study.

Tensile Test

A tensile test was performed in ZWICK (Zwicki, 2.5 ton)tensile testing M=C at a pull rate of 500 mm=min. Thetensile test was performed at 25�C and at a relative humidityof 65%. The shape of the dumbbell was type die C as perASTM D 412. Tensile strength was calculated from theloads recorded and an original cross-sectional area of thespecimen.

SEM Analysis

HITACHI SEM was employed to observe and recordthe fracture surface of all blends. Moulded slabs in theform of thin strips were immersed in liquid N2 for 5 minand then fractured. The fractured surfaces were thencoated with a thin layer of 10–20 nm of gold=palladiumalloy. The coating was carried out by placing the specimenin a high vacuum evaporator and then vaporizing the metalheld in a heated tungsten basket.

DSC Study

The glass transition temperature (Tg) measurements ofthe blends were done with DSC Dupont 910 DifferentialScanning Calorimeter. The analysis was carried out insealed aluminium pans and the amount of the samplewas 8–10 mg. The heating rate was fixed at 10�C=min. Tg

considered in this study corresponds to the midpoint oftransition in heat flux vs. temperature plot. DSC wasperformed from �100�C to þ150�C under N2 atmospherewith the gas flow rate of 40 ml=min.

TGA Analysis

Thermogravimetric analusis (TGA) was performedusing a Dupont 951 Thermo gravimetric analyzer. Thesample weight was 8–10 mg and the heating rate wasfixed at 20�C=min. Analysis was performed from 30�Cto þ 600�C in a N2 atmosphere with a gas flow rate of40 ml=min.

Swelling Experiments

TPU is a polar rubber and it resists nonpolar rubbersolvents like toluene etc. EPDM is a nonpolar rubberand it resists polar solvents like DMF. Swelling studieswere done for the blends in toluene and in DMF at 25�Cfor 4 h. EPDM swells in toluene and TPU swells inDMF. Swelling studies of the blends will help us under-stand the nature of polarity of the blends in terms of swell-ing characteristics in toluene and DMF. The volumechange (%) is calculated by measuring the volume of thesamples before and after the test using the Archimedesprinciple. About 5 gm of sample was swollen in 100 ml ofthe solvent for 4 h at 25�C for the test.

Hardness Tests

Hardness is resistance to indentation. Hardness testswere performed in Wallace micro hardness meter as perBS 903, part A26. The hardness meter works on the prin-ciple of forcing an indentor into the material and measur-ing how far the indentor penetrates into the sample. Thetests were performed at a room temperature of 25�C. Hard-ness was measured on a 2 mm thick slab on IRHD scale.

Flexing Resistance Tests

Flexing resistance tests were performed in a Ross Flex-ometer as per BS5131. The test is intended for comparingthe resistance of rubbers to the formation of growth ofcracks. The test is performed at �5�C. After 1000 cyclesof flexing, crack development was measured.

Aging Tests

For the satisfactory performance of the polymers andtheir blends in service, it is not only the mechanical proper-ties which are important, but also the aging properties.

TABLE 1Recipe of blends prepared

EPDM(0.25%maleated)

EPDM(0.75%

maleated) TPU

DICUMYLperoxide

(40% active)

0 0 100 220 0 80 250 0 50 280 0 20 2

100 0 0 20 20 80 20 50 50 20 80 20 20 100 0 2

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Aging studies are done at high temperature. Blends, whichare miscible at lower temperature, become immiscible athigh temperature, resulting in a larger reduction in tensilestrength. Aging studies were done at 120�C, for 24 h inhot air ovens. Tensile strength was recorded before andafter ageing tests.

Filler Reinforcement Studies

Fillers are added in any polymer to improve the mech-anical properties and to reduce cost. To study the fillerimpact on the blends, 20 PHR (parts per hundred rubber)silica was added to the blends. Mixing was done in atwo-roll mill. Slabs were prepared in electrically a heatedcompression moulding press at 180�C for 5 min. Tensilestrength was measured in the dumbbells. A hardness testwas also performed.

Weather Resistance Studies

Ozone in the atmosphere affects rubber and causescracks and loss of mechanical strength. Ozone exposurecuts the polymer chains exposed at the surface andinitiates the growth of cracking. Natural flexing of thecracks exposes more surfaces for the ozone to attack.Ozone resistance test for the blends was performed in aSATRA–HAMPDEN ozone equipment model 903, asper ASTM D 1149. The test temperature was 40�C andthe relative humidity was 50%. The ozone concentrationwas 100 pphm (parts per hundred million). The durationof the test was 72 h. After the test, the samples wereobserved for crack growth using a 7-magnification glass.

RESULTS AND DISCUSSION

Stress-strain curves of TPU with 0.25 mEPDM blendsare shown in Fig. 1. Twenty percent incorporation ofTPU in mEPDM (maleated EPDM) increases both theelongation at break and tensile strength. With the furtheraddition of TPU, the tensile strength increases but elonga-tion at the break decreases for 50 wt% TPU. Further.addition of TPU in 0.25 mEPDM decreases elongation atthe break, but tensile strength increases as compared topure 0.25mEPDM and decreases with respect to 50 wt%TPU blends. Figure 2 exhibit the stress-strain curve of0.75 mEPDM=TPU blends of varying compositions. Boththe strength and elongation at break decreases with theaddition of TPU, presumably due to the higher percentageof maleation level. Figure 3 shows the change in tensilestrength with the incorporation of TPU in mEPDM.Results of tensile strength of unmodified EPDM andTPU blend and 0.5 mEPDM and TPU blend are takenfrom our previous work[12] and shown in Fig. 3. As seenfrom Fig. 3, tensile strength of the blend increases withincorporation of TPU up to a certain level for each blend

and then drops. For 0.25 mEPDM and TPU blend, tensilestrength increases up to 50% of TPU addition and thendrops. For 0.5 mEPDM and TPU blend also, tensilestrength increases up to 50% of TPU addition and thendrops. For 0.75 mEPDM and TPU blend, tensile strengthof the blend drops with the incorporation of TPU forany composition. Hence, tensile strength of the blendincreases with an increase in the maleation level up to0.5 wt% and then drops. The increase in tensile strengthup to 0.5 wt% maleation level indicates improvement inmiscibility of blends and intermeshing morphology.

FIG. 1. Stress strain curves of 0.25 mEPDM and TPU blends.

FIG. 2. Stress strain curves 0.75 mEPDM and TPU blends.

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Elongation at break is expressed in terms of wt% ofTPU in Fig. 4 Results indicate that elongation at breakincreases with the incorporation of TPU up to a certainlevel for each blend and then drops. For 0.25 mEPDMand TPU blend, elongation increases upto 20% of TPUand then drops. For 0.5 mEPDM and TPU blend, theincrease in elongation at break is up to 20% of TPU andthen drops. For 0.75 mEPDM and TPU blend, the elonga-tion drops with the TPU addition for almost all composi-tions. When the results of the mechanical properties(tensile strength and elongation) are analyzed together, itis inferred that up to 20% of TPU incorporation inmaleated EPDM tensile strength and elongation at breakincrease and the maximum in tensile strength and elonga-tion at break occurs for 0.5 mEPDM and TPU blend upto50 wt% of the TPU component.

Morphology of the blends was studied by using scan-ning electron microscopy (SEM). Figure 5(a) shows theSEM images of EPDM at 80% and TPU 20%. Phase sepa-rated morphology of two components is seen in the picture.Figure 5(b) shows the SEM image of 0.25 mEPDM 80%and a TPU 20% blend. In this picture also, phase separ-ation or noncontinuous domains are clearly observed.Figure 5(c) shows a SEM image of 0.5 mEPDM 80% andTPU 20%. Intermeshing morphology is evident. Compar-ing to other SEM images, clear, continuous morphology

has been observed. This observation is in agreement withthe mechanical properties. Figure 5(d) shows the SEMimage of 0.75 mEPDM 80% and TPU20%, which showsvery little extent of phase separation that affects the mech-anical property as described earlier. Where there is phaseseparation in SEM morphology, the corresponding mech-anical properties (strength and elongation at break) arelowered somehow. So, there is a direct correspondencebetween morphology and mechanical properties.

DSC measurements were made to study the glass tran-sition temperature of the blends to understand the phasebehavior. Incompatible blends exhibit two distinct glasstransition peaks, and a single Tg is expected from compat-ible blends. Figure 6(a) shows DSC measurements of0.25 mEPDM and TPU blends. For all the blend compo-sition, we can see two transitions (Tg) which indicateincompatibility. For 0.25 mEPDM 80% and TPU20%,glass transitions are seen at �40�C and at �20�C. Figure6b shows DSC measurement for 0.75 mEPDM and TPUblends. Results of glass transitions of unmodified EPDM80% and TPU 20% blend and 0.5 mEPDM 80% andTPU 20% blend are taken from our previous paper[12],and compared with the results of 0.25% and 0.75% malea-tion levels of EPDM 80% and TPU 20% blend. Results areshown in Fig. 6(c). As seen in the figure, clear, single transi-tions are seen for 0.5% and 0.75 mEPDM 80% and TPU20% blend. Two transitions are seen for unmodified and0.25 mEPDM and TPU blend. Figure 6(d) shows theDSC measurements done on TPU80% and EPDM 20%blends of different maleation levels. All the blend compo-sition shows two transitions and hence, indicates theirFIG. 4. Elongation at break of blends against wt% of TPU.

FIG. 5. SEM images of (a) EPDM 80% and TPU 20%; (b)

0.25 mEPDM 80% and TPU 20%; (c) 0.5 mEPDM 80% and TPU 20%

and (d) 0.75 mEPDM 80% and TPU 20%.

FIG. 3. Tensile strength of blends against wt% of TPU.

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FIG. 7. TGA curves of (a) 0.25 mEPDM 80% and TPU 20%; (b) 0.75 mEPDM 80% and TPU 20%; and (c) compiled TGA curves of EPDM 80%

and TPU 20% blends.

FIG. 6. (a) DSC curves of 0.25 mEPDM 80% and TPU 20%; (b) DSC curves of 0.75 mEPDM 80% and TPU 20%; (c) Compiled DSC curves of

EPDM 80% and TPU 20% blends; and (d) Compiled DSC curves of EPDM 20% and TPU 80% blends.

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incompatibility. These findings are in agreement with themechanical property results.

Figure 7 shows TGA measurements done on0.25 mEPDM and TPU blends. The heat resistance ofTPU is enhanced with the incorporation of maleatedEPDM. As the EPDM content is increased, the degradati-on temperature shifts from less than 300�C to around500�C. A similar trend is observed with 0.75 mEPDMand the TPU blend, which is also shown in Fig. 7(b).Figure 7(c) shows the compilation of thermograms ofTPU 20% and EPDM 80% of different maleation levels.It is clear that with an increasing maleation level of EPDM,the degradation temperature of the blend increases. Swell-ing tests were conducted with toluene and DMF at 25�C for4 h of TPU with EPDM and 0.5 mEPDM blends. Resultsare shown in Fig. 8(a) and (b). It indicates that the solvent

resistance of EPDM improves with the addition of TPU.On the other hand, swelling resistance of TPU in DMFimproves with the incorporation of EPDM. So, solventresistance of both the components increases in the presenceof each other.

Hardness measurements were done for TPU withEPDM and 0.5 mEPDM blends. Results are shown inTables 2 and 3 It indicates that hardness of the blends iscomparable to that of pure polymers. Flexing resistancetests were performed at �5�C for TPU with EPDM and0.5 mEPDM blends. Crack development was monitoredafter 1000 cycles. Results are shown in Tables 4 and 5Results indicate that crack development is greater inTPU with unmodified EPDM blends as compared tomEPDM. This could be due to inhomogenity=homogeneityeneity or the state of the dispersion of the blends. In theTPU 20% and 0.5 mEPDM 80% blend, the crack develop-ment is lower. This could be due to an intermeshingmorphology of the blends.

For the TPU=EPDM and TPU=0.5 mEPDM blends,aging was done at 120�C for 24 h in hot air ovens. Tensilestrength was recorded before and after the aging tests.Tensile strength of fresh and aged pure polymers andblends are compared and shown in Figs. 9(a) and (b).For the unmodified EPDM and TPU blend systems, theretention of tensile strength after aging was only 28–45%of the fresh blend systems. This poor retention was dueto the immiscibility of the blend resulting in a phase separ-ation of the individual polymers. For the 0.5 mEPDM andTPU blend systems, the retention of tensile strength afterageing was 85–92% of the fresh blends. The increase intensile strength retention after aging for the 0.5 mEPDM=

FIG. 8. Swelling behavior of (a) TPU with unmodified EPDM blends

and (b) TPU with 0.5 mEPDM blends.

TABLE 2Hardness of TPU with unmodified EPDM blends

Sample identification Hardness (IRHD)

EPDM 100% 53TPU 100% 55TPU80%:EPDM 20% 54TPU 50%:EPDM 50% 53TPU20%:EPDM 80% 53

TABLE 3Hardness of TPU with 0.5% maleated EPDM blends

Sample identification Hardness (IRHD)

0.5MEPDM 100% 56TPU 100% 55TPU80%:0.5MEPDM 20% 55TPU 50%:0.5MEPDM 50% 56TPU20%:0.5MEPDM 80% 56

TABLE 4Flexing resistance of TPU with unmodified EPDM blends

Sample identification Flexing resistance (mm=Kc)

EPDM 100% 0.0067TPU 100% 0.0033TPU80%:EPDM 20% 0.0085TPU 50%:EPDM 50% 0.0082TPU20%:EPDM 80% 0.0074

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TPU blend as compared to the unmodified EPDM=TPUblends confirms miscibility, and also indicates that theseblends are suited for high temperature application.

To study the filler impact on EPDM and TPU blend,precipitated silica was mixed with unmodifiedEPDM=TPU blends and 0.5 mEPDM=TPU blends.Twenty PHR (parts per hundred rubber) silica was added

FIG. 9. Tensile strength comparison of (a) fresh and aged blends (b)

fresh and aged TPU=0.5 mEPDM blends. Reinforced blend systems for

TPU with EPDM blend systems and (b) hardness comparison of nonrein-

forced with silica reinforced blend systems for TPU=EPDM blend systems.

TABLE 5Flexing resistance of TPU with 0.5% maleated

EPDM blends

Sample identification Flexing resistance (mm=Kc)

0.5 mEPDM 100% 0.0058TPU 100% 0.0033TPU80%:0.5MEPDM 20% 0.0040TPU 50%:0.5MEPDM 50% 0.0050TPU20%:0.5MEPDM 80% 0.0055

FIG. 10. Tensile strength comparison of non-reinforced with (a) silica

reinforced blend systems for TPU with EPDM blend systems and (b)

hardness comparison of non-reinforced with silica reinforced blend

systems for TPU/EPDM blend systems.

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to the blends. Mixing was done in a two-roll mill. Slabswere prepared in an electrically-heated compressionmoulding press at 180�C for 5 min. Tensile strength wasmeasured for the dumbbell shaped samples. Hardnessmeasurements were also performed. Tensile strength andhardness results are shown in Figs. 10(a) and (b) forTPU=EPDM blends. For TPU=0.5 mEPDM blends,results are shown in Figs. 11(a) and (b). Results indicate

that the addition of silica increases tensile strength andhardness substantially in the unmodified blend systems.As seen from the results, tensile strength increases by80% in an unmodified EPDM 80%=TPU 20% blend withthe reinforcement of silica, when compared with the tensilestrength on nonreinforced systems. For TPU=0.5 mEPDMblends system, tensile strength increases by 83% with thereinforcement of silica when compared with the tensilestrength of nonreinforced systems.

Weather resistance (Ozone) tests were performed onTPU 20%=EPDM 80% blend system and TPU20%=0.5 mEPDM blend systems. The ozone concentrationwas 100 pphm (parts per hundred million). The duration ofthe test was 72 h. For better visual examination of thetested sample, 20 phr carbon black was added to the blendsamples. After carbon black addition, the sheets weremolded. Dumbbell-shaped specimens were cut from thesheets. Twenty percent stretching was given to the dumb-bells in the test fixture while performing the ozone test.After 72 h of test in the ozone chamber, dumbbells wereexamined for cracks using a 7-magnification glass. Theresults show that in the TPU 20%=EPDM 80% blend sys-tem, minute cracks were seen. No cracks were seen in theTPU 20%=0.5 mEPDM 80% blend system.

CONCLUSION

From our findings, we conclude that the blend of TPU20% and 0.5 wt% maleated EPDM 80% is the most com-patible blend, because it possesses good mechanical proper-ties and combines the properties of TPU and EPDM: goodflexing resistance, better aging resistance, and good ozoneresistance. The above properties of the blend make itideally suited for footwear application. This blend canalso find application in places where optimum resistancetowards polar and nonpolar solvents are required, asthe blend has improved resistance towards toluene andmoderate resistance towards DMF.

ACKNOWLEDGEMENTS

The authors express sincere thanks to the Director ofCLRI for granting permission to conduct this researchwork. We thank all suppliers of raw materials used in thestudy. We also thank Management of Brakes India Ltd.for the support extended for this research work.

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