research article reinforcement of multiwalled carbon

Research ArticleReinforcement of Multiwalled Carbon Nanotube inNitrile Rubber In Comparison with Carbon Black ConductiveCarbon Black and Precipitated Silica

Atip Boonbumrung1 Pongdhorn Sae-oui2 and Chakrit Sirisinha13

1Department of Chemistry Faculty of Science Mahidol University Bangkok 10400 Thailand2MTEC National Science and Technology Development Agency Pathumthani 12120 Thailand3Rubber TechnologyResearchCentre (RTEC) Faculty of ScienceMahidolUniversity SalayaCampusNakhonPathom73170Thailand

Correspondence should be addressed to Chakrit Sirisinha chakritsirmahidolacth

Received 7 September 2015 Accepted 10 January 2016

Academic Editor Claude Estournes

Copyright copy 2016 Atip Boonbumrung et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

The properties of nitrile rubber (NBR) reinforced by multiwalled carbon nanotube (MWCNT) conductive carbon black (CCB)carbon black (CB) and precipitated silica (PSi) were investigated via viscoelastic behavior bound rubber content electricalproperties cross-link density andmechanical propertiesThe filler content was varied from 0 to 15 phrMWCNT shows the greatestmagnitude of reinforcement considered in terms of tensile strength modulus hardness and abrasion resistance followed by CCBCB and PSi The MWCNT filled system also exhibits extremely high levels of filler network and trapped rubber even at relativelylow loading (5 phr) leading to high electrical properties and poor dynamic mechanical properties Although CCB possesses thehighest specific surface area it gives lower level of filler network than MWCNT and also gives the highest elongation at breakamong all fillers Both CB and PSi show comparable degree of reinforcement which is considerably lower than CCB andMWCNT

1 Introduction

NBR is used in numerous applications where high resistanceto hydrocarbon oil is required such as fuel hoses o-ringsgaskets and industrial rolls Unfortunately NBR is not crys-tallizable under high strain and therefore the reinforcingfillers such as carbon black (CB) and precipitated silica(PSi) are generally incorporated to yield sufficiently highmechanical properties As a drawback the incorporationof reinforcing fillers typically causes processability problemsdue to high bulk viscosity of rubber compounds Addition-ally the high loading of reinforcing fillers could give negativeresults in some vulcanizate properties such as compressionset and hysteresis loss (or heat build-up) As a consequencenovel reinforcing fillers with relatively high specific surfacearea andor aspect ratio have been introduced for examplenanoclay and carbon nanotubes (CNT)With the uses of suchfillers the filler loading required for any given properties

could be markedly decreased while good dynamic mechan-ical properties of the rubber could still be preserved Bythis means a balance of processability static and dynamicmechanical properties is possible As one can expect thedifficulty in mixing is the major limitation for the utilizationof the nanofillers [1] CNT has gained much attention in thepast 2 decades due to its extremely high mechanical strengthand electrical conductivity and therefore is attractive to beused in a wide range of polymer composites [2ndash6] It has beenreported that at a given modulus of composites the requiredfiller loading could be reduced remarkably by substituting theconventional fillers such as CB and PSi with CNT [7ndash9] Theuses of CNT as reinforcing fillers have been reported in bothplastic and elastomeric matrices [10ndash16]

Although comparison of reinforcement magnitudebetween CNT and other fillers has been reported to someextent most of works have been focused on nonpolar rubberssuch as NR [17ndash19] EPDM [17] and SBR [20] Consequently

Hindawi Publishing CorporationJournal of NanomaterialsVolume 2016 Article ID 6391572 8 pageshttpdxdoiorg10115520166391572

2 Journal of Nanomaterials

Table 1 Physical characteristics of fillers

Filler Mean primary particle size (nm) BET specific surface area (m2g) DBPA (mL100 g) Density (gcm3)MWCNT 95 (outer diameter) 286 mdash 2CCB 30 1103 420 mdashCB 20ndash30 111 114 2PSi 10ndash30 135 mdash 205

Table 2 Compounding recipe

Ingredient Content (phr)NBR 100Filler (MWCNT CCB CB and PSi) 0 5 10 and 15Stearic acid 05DCP 2

such comparison in polar rubbers including nitrile rubberis of interest This study aims to compare the reinforcementefficiency of MWCNT with other conventional reinforcingfillers (ie CB PSi and CCB) in peroxide cured NBR byinvestigating viscoelastic behavior mechanical propertieselectrical properties bound rubber content and cross-linkdensity of the rubber filled with these fillers

2 Experimental

21 Materials Nitrile rubber (NBR N230SL) (acryloni-trile content of 35 and density 098 gcm3) was suppliedby JSR (Japan) Multiwalled carbon nanotubes (MWCNTNANOCYLTM NC7000) were manufactured by NANOCYL(Belgium) All other materials were supplied by suppliers ormanufacturers in Thailand Conductive carbon black (CCBPrintex XE2-B) was supplied by JJ-Degussa Huls (Thailand)Carbon black (CB N220) was manufactured byThai CarbonBlack PCL Precipitated silica (PSi Tokusilreg 233) was pur-chased from Tokuyama Siam Silica Co Ltd Details of fillercharacteristics have been reported elsewhere as tabulated inTable 1 [19 21ndash27] Commercial grade stearic acid and 98active dicumyl peroxide (DCP) were supplied by ChemminCo Ltd and Petchthai Chemical Co Ltd respectively

22 Composite Preparation NBR compounds were preparedaccording to the formulation given in Table 2 by two-rollmill at room temperature NBR was initially masticated for1 minute and then stearic acid was added followed by thefiller (MWCNT CCB CB or PSi) DCP was added at 15thminute of the mixing cycle The mixing was continued foranother 5 minutes A curing process of rubber compoundswas conducted using a hot-press at 160∘C with respect to theoptimum cure time (119905

11988890) as predetermined from the moving

die rheometer (MDR MD+Alpha Technologies USA)

23 Characterization Bound rubber content (BRC) a mea-sure of rubber-filler interaction was measured by immersingapproximately 02 g of rubber compounds in 100mL acetonefor 7 days at room temperature The insoluble fraction was

then filtered and dried at 60∘C until a constant weight wasobtained The calculation of BRC is illustrated in [28]

BRC () =[119908119891119892minus 119908119905(119898119891 (119898119891+ 119898119903))]

119908119905[119898119903 (119898119891+ 119898119903)]

times 100 (1)

where 119908119891119892

is the weight of filler and gel after being dried119908119905is the specimen weight before solvent immersion and119898119891and 119898

119903are filler and rubber fractions in the compound

respectivelyViscoelastic behavior of the cured samples was measured

using a dynamic mechanical analyzer (Gabo Qualimetermodel Eplexor 25N Germany) Strain sweep tests wereperformed under tension mode with dynamic strain rangeof 001ndash10 frequency at 5Hz and static strain of 10 at25∘C To determine the dynamic mechanical properties asa function of temperature the test specimen was deformedsinusoidally at static and dynamic strain of 1 and 01respectively frequency of 10Hz with a heating rate of2∘Cmin

Volume resistivity of the rubber was investigated bya Hall Effect Measurement System (Bridge Technologiesmodel HMS 3000 USA) A conductive paste was applied onthe specimen surface prior to testing in order to improvereliability of the test results

Hardness test was performed using a Shore A durom-eter (Wallace model H17A UK) as per ISO 7619-1 Tensileproperties weremeasured using a universal mechanical tester(Instron model 5566 USA) based on ISO 37 (die type 1)Heat build-up of theNBR vulcanizates was determined by theGoodrich flexometer (BF Goodrich Model II USA) understatic load of 245N at 100∘C frequency of 30Hz and dynamicdeformation of 445mm The volume loss or abrasion loss ofthe vulcanizates was determined using DIN abrasion tester(Zwick abrasion tester model 6120 Germany) according toISO 4649

Swelling test was used to determine the cross-link densityof the NBR vulcanizates using the Flory-Rehner equation[29] The test specimens with dimensions of approximately1 times 1 times 02 cm3 were immersed in 100mL acetone for 7 daysThe weights of the test specimens before and after immersionwere used to calculate the cross-link density as illustrated in

119899 = minus1

2119881119904

(ln (1 minus 119881

119903) + 119881119903+ 1205941198812

119903

11988113

119903 minus (1198811199032)

) (2)

where 119899 is the number of cross-links per unit volume(molecm3)119881

119904is the molar volume of acetone (734mLmol)

[30] 119881119903is the volume fraction of rubber in swollen gel ()

and 120594 is the NBR-acetone interaction parameter (0349) [31]

Journal of Nanomaterials 3

0

5

10

15

20

25

30

35

0 1 10Strain ()

Unfilled5MWCNT

10MWCNT15MWCNT

E998400

(MPa

)

(a)

Unfilled

0

2

4

6

8

10

12

0 1 10Strain ()

5CCB10CCB15CCB

E998400

(MPa

)

(b)

Unfilled

0

1

2

3

4

5

6

7

8

9

10

0 1 10Strain ()

5CB10CB15CB

E998400

(MPa

)

(c)

Unfilled

0

1

2

3

4

5

6

7

8

9

10

0 1 10Strain ()

5PSi10PSi15PSi

E998400

(MPa

)

(d)

Figure 1 Strain sweep results of the NBR vulcanizates filled with different fillers (a) MWCNT (b) CCB (c) CB and (d) PSi

The calculation of 119881119903is exhibited in [32]

119881119903=

1198981119889119904

1198981(119889119904minus 119889119903) + 1198982119889119903

(3)

where 1198981is the weight of rubber before swelling 119898

2is the

weight of rubber after swelling 119889119903is the density of NBR

(098 gcm3) and 119889119904is the density of acetone (079 gcm3)

[30]

3 Results and Discussion

The influences of filler type and loading on storage modulusas a function of strain are shown in Figure 1 Theoreticallythere are four main factors governing 1198641015840 (i) filler-fillerinteraction (ii) filler-rubber interaction (iii) hydrodynamiceffect and (iv) rubber network The magnitude of filler-fillerinteraction can be determined from the decrease in 1198641015840 with


0 5 10 15Filler loading (phr)

PSiCB

CCBMWCNT

1E + 10

1E + 09

1E + 08

1E + 07

1E + 06

1E + 05

1E + 04

1E + 03

1E + 02

1E + 01

1E + 00

Volu

me r

esist

ivity

(Ωcm

)

Figure 2 Electrical volume resistivity of the NBR vulcanizates filledwith different fillers

increasing strain Obviously for theMWCNT filled system aformation of transient filler network could be observed evenat relatively low filler loading (5 phr) and the magnitude oftransient filler network is much more pronounced at higherloadings as evidenced by the higher 1198641015840 at low strain In theCCB filled system the formation of transient filler networkbegins at 10 phr However at any given filler loading themagnitude of filler network of the CCB filled system isconsiderably lower than that of the MWCNT filled systemFor the CB and PSi filled systems the magnitude of transientfiller network is negligible throughout the filler loading rangestudiedThe filler network formations found in theMWCNTand CCB filled systems are evidenced by electrical volumeresistivity results as shown in Figure 2 It is generally acceptedthat the formation of filler network gives a sharp drop inelectrical resistivity because when filler network is formedthe connected carbon black network is capable of carryingelectrons leading to a dramatic change of conductivity [3334] This point is widely known as a percolation thresholdObviously the sharp drop of electrical volume resistivity isfound when MWCNT and CCB are incorporated at 5 and10 phr respectively Due to the absence of filler networkthe resistivity of the CB system is relatively unchanged eventhough the CB is incorporated up to 15 phr Since PSi is notelectrically conductive predicting the level of PSi networkformation is not possible using the measurement of electricalvolume resistivity The electrical volume resistivity of the PSifilled system is therefore relatively high and comparable tothat of the unfilled system

It could also be observed fromFigure 3 that at sufficientlyhigh strain (10) where the filler network is believed to befully destroyed the MWCNT filled system still possesses thehighest 1198641015840 followed by the CCB PSi and CB filled systemsrespectively To explain the high magnitude of high-strain1198641015840 found in the MWCNT and CCB filled systems there are

three factors to be considered The hydrodynamic effect astypically caused by a dilution of deformable polymeric phasewith an undeformable filler phase is not very crucial and

PSiCB

CCBMWCNT

0

2

4

6

8

10

12

14

0 2 4 6 8 10 12 14Filler loading (phr)

E998400

(MPa

)

Figure 3 1198641015840 at 10 strain of the NBR vulcanizates filled withdifferent fillers

PSiCB

CCBMWCNT

0

2

4

6

8

10

12

14

0 5 10 15

BRC

()

Filler loading (phr)

Figure 4 Bound rubber content (BRC) of the NBR compoundsfilled with different fillers

could be neglected because all fillers employed herein havecomparable densityTherefore the dominant factors affectingthe high-strain 1198641015840 are (i) rubber-filler interaction and (ii)rubber network Figure 4 shows the BRC results of the filled-NBR compounds Apparently the CCB and MWCNT filledsystems exhibit significantly higher BRC than the CB andPSi filled systems At 5 phr MWCNT yields the highest BRCdespite the inert surfaces of MWCNT [35]The unexpectedlyhigh BRC found at 5 phr ofMWCNT is believed to arise fromthe rubber trapped in MWCNT agglomerates and networkAlthough the BRC of the MWCNT filled system tends toincrease continuously with increasing MWCNT loading itis obvious that at 10 phr and above the system incorporatedwith CCB gives higher BRC than that incorporated withMWCNT The explanation is given by the higher fillerstructure and specific surface area of the CCB [22] Inaddition at sufficiently high loading (ge10 phr) where networkof CCB is formed the rubber trapped in CCB network couldalso contribute to the high BRC Although the CCB system


PSiCB

CCBMWCNT


1E minus 3

9E minus 4

8E minus 4

7E minus 4

6E minus 4

5E minus 4

4E minus 4

3E minus 4

2E minus 4

1E minus 4

0E + 0

Cros

s-lin

k de

nsity

(mol

cm

3)

Figure 5 Cross-link density of the NBR vulcanizates filled withvarious fillers

demonstrates the highest BRC and thus the rubber-fillerinteraction at 10 phr or higher the high-strain 1198641015840 of thissystem is still lower than that of the MWCNT filled systemat any filler loading (see Figure 1) This finding could be dueto the highest cross-link density of theMWCNT filled systemas evidenced by the cross-link density results calculated fromthe Flory-Rehner equation (Figure 5) However it must benoted that the calculated cross-link density in this workincludes not only the actual cross-link density of rubbernetwork but also the trapped and bound rubbers

Regardless of the filler type the cross-link densityincreases with increasing filler loadingThe results are under-standable as the magnitudes of trapped rubber and boundrubber increase with increasing filler loading At any givenloading the MWCNT filled system represents the highestcross-link density followed by the CCB PSi and CB filledsystems respectively The explanation is given to the greatestamount of trapped rubber in MWCNT network It could bealso observed that cross-link density of the MWCNT systemas calculated from the Flory-Rehner equation is unexpectedlyhigh particularly at high MWCNT loadings This is probablydue to the high extent of MWCNT network which is capableof resisting the solvent swelling of the rubber matrix

Figure 6 shows the temperature-dependent tan 120575 of theNBR vulcanizates The damping peak (tan 120575max) of all vul-canizates is found at the temperature of approximately minus9∘Cregardless of filler type and loading However the tan 120575maxand relative tan 120575 area (as tabulated in Table 3) decrease withincreasing filler loading due to the dilution effect particularlyin the MWCNT filled system containing the relatively highmagnitude of trapped rubber followed by CCB PSi and CBfilled systems respectively Some authors have reported therelationship between tan 120575max of unfilled and filled rubber asshown in [36 37]

tan 120575119898119891=tan 120575119898119906

1 + 120573120601 (4)

where tan 120575119898119891

and tan 120575119898119906

represent maximum tan 120575 of filledand unfilled systems respectively 120573 is a phenomenological

Table 3 Summary of dynamic viscoelastic response

Loading (phr) MWCNT CCB CB PSi

tan 120575max

0 154 154 154 1545 112 138 150 15110 088 119 144 14015 07 099 138 132

Relative tan 120575 area

0 100 100 100 1005 080 094 099 10010 066 085 097 09515 055 074 094 093

120573120601lowast

0 0 0 0 05 038 012 003 00210 075 029 007 01015 120 056 012 017

lowastCalculated from (4)

interaction parameter determining the interfacial interactionof filler and matrix 120601 is an effective volume fraction offiller the 120573120601 values as illustrated in Table 3 demonstrate thecombination of interfacial interaction strength and effectivevolume fraction As expected the MWCNT filled systemshows the highest 120573120601 value which is considerably higherthan those of the CCB CB and PSi However due to thepoor interaction between MWCNT and rubber as a resultof inert surfaces of MWCNT the 120573120601 value is dominatedby the effective volume fraction The 120573120601 values of the CCBfilled system are higher than those of the CB and PSi filledsystems because the CCB possesses higher specific surfacearea and structure Also at the temperature range of 20ndash70∘Cthe MWCNT filled system shows the highest tan 120575 despiteits highest cross-link density The poor interfacial interactionand the highmagnitude ofMWCNT network are responsiblefor such highest magnitude of energy dissipation On theother hand the tan 120575 values of the CB and PSi filled systemsare comparable and relatively low compared with that of theMWCNT filled systemThis is mainly attributed to the lowerspecific surface area and lower level of filler network of CBand PSi

Table 4 shows mechanical properties of the NBR vul-canizates Regardless of the filler type most mechanicalproperties such as tensile strengthmodulus and hardness arecontinuously improved with increasing filler loading Alsothe degree of reinforcement depends greatly on the fillercharacteristics that is MWCNT gives the highest level ofreinforcement followed by CCB whereas both PSi and CBshow the lowest level of reinforcementGreater reinforcementof MWCNT over other conventional reinforcing fillers isin agreement with previous work [10 18 38] Compared tothe unfilled system the abrasion loss of the filled systemsdecreases with increasing filler loading mainly attributed tothe dilution effect and the increased cross-link density andthus modulus and hardness At any given filler loading bothCCB and MWCNT filled systems possess markedly greaterabrasion resistance than the CB and PSi filled systems Thisis the consequence of the greater magnitudes of moduluscross-link density and hardness as discussed earlier The


10 30 50 70

Unfilled5PSi5CB

5CCB5MWCNT

minus50 minus30 minus10

Temperature (∘C)

0

02

04

06

08

1

12

14

16

18

15PSi15CB

15CCB15MWCNT

10 30 50 70

Unfilled


Temperature (∘C)

0

02

04

06

08

1

12

14

16

18

10PSi10CB

10CCB10MWCNT

10 30 50 70

Unfilled


Temperature (∘C)

0

02

04

06

08

1

12

14

16

18

tan 120575

tan 120575

tan 120575

(a)

Unfilled5PSi5CB

5CCB5MWCNT

20 30 40 50 60 70Temperature (∘C)

0

005

01

015

02

025

03

20 30 40 50 60 70Temperature (∘C)

0

005

01

015

02

025

03

10PSi10CB

10CCB10MWCNT

Unfilled

20 30 40 50 60 70Temperature (∘C)

0

005

01

015

02

025

03

15PSi15CB

15CCB15MWCNT

Unfilled

tan 120575

tan 120575

tan 120575

(b)

Figure 6 tan 120575 values of the NBR vulcanizates filled with different fillers (a) temperature range of minus50ndash70∘C (b) enlarged temperature rangeof 20ndash70∘C


Table 4 Mechanical properties of NBR vulcanizates

Properties Loading (phr) MWCNT CCB CB PSi

Tensile strength (MPa)

0 29 plusmn 037 29 plusmn 04 29 plusmn 04 29 plusmn 045 86 plusmn 01 43 plusmn 01 41 plusmn 02 36 plusmn 0410 129 plusmn 04 91 plusmn 02 53 plusmn 05 38 plusmn 0215 177 plusmn 05 146 plusmn 06 85 plusmn 15 53 plusmn 03

Elongation at break ()


Modulus at 100 (MPa)


Hardness (Shore A)


Heat build-up (∘C)


Abrasion loss (mm3)


heat build-up test results also agree well with the tan 120575results as discussed previously that is the heat build-upincreases consistentlywith increasing filler loadingAt a givenfiller loading the MWCNT filled system shows the highesttemperature rise due to its relatively high magnitude of fillernetwork and poor filler-rubber interfacial interaction [2238 39] However except for the MWCNT filled system theelongation at break appears to increase with increasing fillerloading Such increase is believed to be due to the slippageof un-cross-linked rubber molecules around filler particleswhich increases the specimen volume under high extension[40]

4 Conclusions

MWCNT shows the greatest reinforcing efficiency as evi-denced by the sharp increases in tensile strength 100modulus hardness and abrasion resistance of the NBRvulcanizates The presence of MWCNT also leads to thesignificant reduction of volume resistivity even at very lowfiller loading (5 phr) However due to its poor interfacialinteraction and highmagnitude of filler network the additionof MWCNT results in poor dynamic mechanical propertiesand thus highmagnitudes of tan 120575 and heat build-up Despiteits highest specific surface area the reinforcing efficiency ofCCB is slightly inferior to that of MWCNT However CCBstill gives higher reinforcement than CB and PSi

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The authors gratefully acknowledge the financial supportof the Center of Excellence for Innovation in Chemistry(PERCH-CIC) Sincere appreciation is also extended to theRubber Technology Research Centre (RTEC) Mahidol Uni-versity and National Metal andMaterials Technology Center(MTEC) for supporting the materials and test equipment

References

[1] S Thomas and R Stephen Rubber Nanocomposites JohnWileyamp Sons New York NY USA 2010

[2] R H Baughman A A Zakhidov and W A de Heer ldquoCarbonnanotubesmdashthe route toward applicationsrdquo Science vol 297 no5582 pp 787ndash792 2002

[3] J N Coleman U Khan W J Blau and Y K Gunrsquoko ldquoSmallbut strong a review of the mechanical properties of carbonnanotube-polymer compositesrdquoCarbon vol 44 no 9 pp 1624ndash1652 2006

[4] V N Popov ldquoCarbon nanotubes properties and applicationrdquoMaterials Science and Engineering R Reports vol 43 no 3 pp61ndash102 2004


[5] S Iijima ldquoHelicalmicrotubules of graphitic carbonrdquoNature vol354 no 6348 pp 56ndash58 1991

[6] S Rooj A Das K W Stockelhuber D-Y Wang V Galiatsatosand G Heinrich ldquoUnderstanding the reinforcing behavior ofexpanded clay particles in natural rubber compoundsrdquo SoftMatter vol 9 no 14 pp 3798ndash3808 2013

[7] M A L Manchado L Valentini J Biagiotti and J MKenny ldquoThermal and mechanical properties of single-walledcarbon nanotubes-polypropylene composites prepared by meltprocessingrdquo Carbon vol 43 no 7 pp 1499ndash1505 2005

[8] R Andrews and M C Weisenberger ldquoCarbon nanotube poly-mer compositesrdquo Current Opinion in Solid State and MaterialsScience vol 8 no 1 pp 31ndash37 2004

[9] L Bokobza ldquoMultiwall carbon nanotube elastomeric compos-ites a reviewrdquo Polymer vol 48 no 17 pp 4907ndash4920 2007

[10] M A Lopez-Manchado J Biagiotti L Valentini and J MKenny ldquoDynamic mechanical and Raman spectroscopy studieson interaction between single-walled carbon nanotubes andnatural rubberrdquo Journal of Applied Polymer Science vol 92 no5 pp 3394ndash3400 2004

[11] L D Perez M A Zuluaga T Kyu J E Mark and B LLopez ldquoPreparation characterization and physical propertiesof multiwall carbon nanotubeelastomer compositesrdquo PolymerEngineering and Science vol 49 no 5 pp 866ndash874 2009

[12] P Potschke T D Fornes and D R Paul ldquoRheological behaviorof multiwalled carbon nanotubepolycarbonate compositesrdquoPolymer vol 43 no 11 pp 3247ndash3255 2002

[13] DQian E CDickey RAndrews andT Rantell ldquoLoad transferand deformation mechanisms in carbon nanotube-polystyrenecompositesrdquo Applied Physics Letters vol 76 no 20 pp 2868ndash2870 2000

[14] M S P Shaffer and A H Windle ldquoFabrication and charac-terization of carbon nanotubepoly(vinyl alcohol) compositesrdquoAdvanced Materials vol 11 no 11 pp 937ndash941 1999

[15] L Vaisman E Wachtel H D Wagner and G MaromldquoPolymer-nanoinclusion interactions in carbon nanotube basedpolyacrylonitrile extruded and electrospun fibersrdquoPolymer vol48 no 23 pp 6843ndash6854 2007

[16] P Verge S Peeterbroeck L Bonnaud and PDubois ldquoInvestiga-tion on the dispersion of carbon nanotubes in nitrile butadienerubber role of polymer-to-filler grafting reactionrdquo CompositesScience and Technology vol 70 no 10 pp 1453ndash1459 2010

[17] H Lorenz J Fritzsche A Das et al ldquoAdvanced elastomer nano-composites based on CNT-hybrid filler systemsrdquo CompositesScience and Technology vol 69 no 13 pp 2135ndash2143 2009

[18] L Bokobza and M Kolodziej ldquoOn the use of carbon nanotubesas reinforcing fillers for elastomericmaterialsrdquo Polymer Interna-tional vol 55 no 9 pp 1090ndash1098 2006

[19] P Thaptong C Sirisinha U Thepsuwan and P Sae-OuildquoProperties of natural rubber reinforced by carbon black-basedhybrid fillersrdquo PolymermdashPlastics Technology and Engineeringvol 53 no 8 pp 818ndash823 2014

[20] L Bokobza and C Belin ldquoEffect of strain on the propertiesof a styrene-butadiene rubber filled with multiwall carbonnanotubesrdquo Journal of Applied Polymer Science vol 105 no 4pp 2054ndash2061 2007

[21] A Schroder M Kluppel R H Schuster and J HeidbergldquoSurface energy distribution of carbon black measured by staticgas adsorptionrdquo Carbon vol 40 no 2 pp 207ndash210 2002

[22] S A NanocylNanocylTM

NC7000 Series-Product Datasheet-ThinMulti-Walled Carbon Nanotubes Nanocyl S A SambrevilleBelgium 2009

[23] M M Saatchi and A Shojaei ldquoMechanical performance ofstyrene-butadiene-rubber filled with carbon nanoparticles pre-pared by mechanical mixingrdquo Materials Science and Engineer-ing A vol 528 no 24 pp 7161ndash7172 2011

[24] J B Donnet Carbon Black Science and Technology CRC PressNew York NY USA 1993

[25] H S Katz and J Mileski Handbook of Fillers for PlasticsSpringer Science amp Business Media 1987

[26] B P Grady Carbon Nanotubes-Polymer Composites Manufac-ture Properties and Application John Wiley amp Sons 2011

[27] N Hewitt and P Ciullo Compounding Precipitated Silica inElastomers Theory and Practice William Andrew 2007

[28] S S Choi ldquoDifference in bound rubber formation of silicaand carbon black with styrene-butadiene rubberrdquo Polymers forAdvanced Technologies vol 13 no 6 pp 466ndash474 2002

[29] P J Flory and J Rehner ldquoStatistical mechanics of crossminuslinkedpolymer networks II SwellingrdquoThe Journal of Chemical Physicsvol 11 no 11 pp 521ndash526 1943

[30] R L Myers The 100 Most Important Chemical Compounds AReference Guide Greenwood Press 2007

[31] B C Guo F Chen W W Chen Y D Lei and D MJia ldquoReinforcement of nitrile rubber by in situ formed zincdisorbaterdquo Express Polymer Letters vol 4 no 9 pp 529ndash5382010

[32] M Barlkani and C Hepburn ldquoDetermination of crosslinkdensity by swelling in the castable polyurethane elastomerbased on 14mdashcyclohexane diisocyanate and para-phenylenediisocyanaterdquo Iranian Journal of Polymer Science amp Technologyvol 1 no 1 pp 1ndash5 1992

[33] I Balberg N Binenbaum and N Wagner ldquoPercolation thresh-olds in the three-dimensional sticks systemrdquo Physical ReviewLetters vol 52 no 17 pp 1465ndash1468 1984

[34] D Stauffer Introduction to PercolationTheory Taylor amp FrancisAbingdon UK 1992

[35] K A Wepasnick B A Smith J L Bitter and D Howard Fair-brother ldquoChemical and structural characterization of carbonnanotube surfacesrdquoAnalytical and Bioanalytical Chemistry vol396 no 3 pp 1003ndash1014 2010

[36] L Qu G Yu X Xie L Wang J Li and Q Zhao ldquoEffectof silane coupling agent on filler and rubber interaction ofsilica reinforced solution styrene butadiene rubberrdquo PolymerComposites vol 34 no 10 pp 1575ndash1582 2013

[37] K D Ziegel and A Romanov ldquoModulus reinforcement inelastomer composites I Inorganic fillersrdquo Journal of AppliedPolymer Science vol 17 no 4 pp 1119ndash1131 1973

[38] P Sae-Oui UThepsuwan PThaptong and C Sirisinha ldquoCom-parison of reinforcing efficiency of carbon black conductivecarbon black and carbon nanotube in natural rubberrdquoAdvancesin Polymer Technology vol 33 no 4 2014

[39] C Nah J Y Lim B H Cho C K Hong and A N GentldquoReinforcing rubber with carbon nanotubesrdquo Journal of AppliedPolymer Science vol 118 no 3 pp 1574ndash1581 2010

[40] Y Fukahori ldquoNew progress in the theory and model of carbonblack reinforcement of elastomersrdquo Journal of Applied PolymerScience vol 95 no 1 pp 60ndash67 2005

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Table 1 Physical characteristics of fillers

Filler Mean primary particle size (nm) BET specific surface area (m2g) DBPA (mL100 g) Density (gcm3)MWCNT 95 (outer diameter) 286 mdash 2CCB 30 1103 420 mdashCB 20ndash30 111 114 2PSi 10ndash30 135 mdash 205

Table 2 Compounding recipe

Ingredient Content (phr)NBR 100Filler (MWCNT CCB CB and PSi) 0 5 10 and 15Stearic acid 05DCP 2

such comparison in polar rubbers including nitrile rubberis of interest This study aims to compare the reinforcementefficiency of MWCNT with other conventional reinforcingfillers (ie CB PSi and CCB) in peroxide cured NBR byinvestigating viscoelastic behavior mechanical propertieselectrical properties bound rubber content and cross-linkdensity of the rubber filled with these fillers

2 Experimental

21 Materials Nitrile rubber (NBR N230SL) (acryloni-trile content of 35 and density 098 gcm3) was suppliedby JSR (Japan) Multiwalled carbon nanotubes (MWCNTNANOCYLTM NC7000) were manufactured by NANOCYL(Belgium) All other materials were supplied by suppliers ormanufacturers in Thailand Conductive carbon black (CCBPrintex XE2-B) was supplied by JJ-Degussa Huls (Thailand)Carbon black (CB N220) was manufactured byThai CarbonBlack PCL Precipitated silica (PSi Tokusilreg 233) was pur-chased from Tokuyama Siam Silica Co Ltd Details of fillercharacteristics have been reported elsewhere as tabulated inTable 1 [19 21ndash27] Commercial grade stearic acid and 98active dicumyl peroxide (DCP) were supplied by ChemminCo Ltd and Petchthai Chemical Co Ltd respectively

22 Composite Preparation NBR compounds were preparedaccording to the formulation given in Table 2 by two-rollmill at room temperature NBR was initially masticated for1 minute and then stearic acid was added followed by thefiller (MWCNT CCB CB or PSi) DCP was added at 15thminute of the mixing cycle The mixing was continued foranother 5 minutes A curing process of rubber compoundswas conducted using a hot-press at 160∘C with respect to theoptimum cure time (119905

11988890) as predetermined from the moving

die rheometer (MDR MD+Alpha Technologies USA)

23 Characterization Bound rubber content (BRC) a mea-sure of rubber-filler interaction was measured by immersingapproximately 02 g of rubber compounds in 100mL acetonefor 7 days at room temperature The insoluble fraction was

then filtered and dried at 60∘C until a constant weight wasobtained The calculation of BRC is illustrated in [28]

BRC () =[119908119891119892minus 119908119905(119898119891 (119898119891+ 119898119903))]

119908119905[119898119903 (119898119891+ 119898119903)]

times 100 (1)

where 119908119891119892

is the weight of filler and gel after being dried119908119905is the specimen weight before solvent immersion and119898119891and 119898

119903are filler and rubber fractions in the compound

respectivelyViscoelastic behavior of the cured samples was measured

using a dynamic mechanical analyzer (Gabo Qualimetermodel Eplexor 25N Germany) Strain sweep tests wereperformed under tension mode with dynamic strain rangeof 001ndash10 frequency at 5Hz and static strain of 10 at25∘C To determine the dynamic mechanical properties asa function of temperature the test specimen was deformedsinusoidally at static and dynamic strain of 1 and 01respectively frequency of 10Hz with a heating rate of2∘Cmin

Volume resistivity of the rubber was investigated bya Hall Effect Measurement System (Bridge Technologiesmodel HMS 3000 USA) A conductive paste was applied onthe specimen surface prior to testing in order to improvereliability of the test results

Hardness test was performed using a Shore A durom-eter (Wallace model H17A UK) as per ISO 7619-1 Tensileproperties weremeasured using a universal mechanical tester(Instron model 5566 USA) based on ISO 37 (die type 1)Heat build-up of theNBR vulcanizates was determined by theGoodrich flexometer (BF Goodrich Model II USA) understatic load of 245N at 100∘C frequency of 30Hz and dynamicdeformation of 445mm The volume loss or abrasion loss ofthe vulcanizates was determined using DIN abrasion tester(Zwick abrasion tester model 6120 Germany) according toISO 4649

Swelling test was used to determine the cross-link densityof the NBR vulcanizates using the Flory-Rehner equation[29] The test specimens with dimensions of approximately1 times 1 times 02 cm3 were immersed in 100mL acetone for 7 daysThe weights of the test specimens before and after immersionwere used to calculate the cross-link density as illustrated in

119899 = minus1

2119881119904

(ln (1 minus 119881

119903) + 119881119903+ 1205941198812

119903

11988113

119903 minus (1198811199032)

) (2)

where 119899 is the number of cross-links per unit volume(molecm3)119881

119904is the molar volume of acetone (734mLmol)

[30] 119881119903is the volume fraction of rubber in swollen gel ()

and 120594 is the NBR-acetone interaction parameter (0349) [31]


0

5

10

15

20

25

30

35

0 1 10Strain ()

Unfilled5MWCNT

10MWCNT15MWCNT

E998400

(MPa

)

(a)

Unfilled

0

2

4

6

8

10

12

0 1 10Strain ()

5CCB10CCB15CCB

E998400

(MPa

)

(b)

Unfilled

0

1

2

3

4

5

6

7

8

9

10

0 1 10Strain ()

5CB10CB15CB

E998400

(MPa

)

(c)

Unfilled

0

1

2

3

4

5

6

7

8

9

10

0 1 10Strain ()

5PSi10PSi15PSi

E998400

(MPa

)

(d)



119881119903=

1198981119889119904

1198981(119889119904minus 119889119903) + 1198982119889119903

(3)


2is the



[30]





PSiCB

CCBMWCNT

1E + 10

1E + 09

1E + 08

1E + 07

1E + 06

1E + 05

1E + 04

1E + 03

1E + 02

1E + 01

1E + 00

Volu

me r

esist

ivity

(Ωcm

)





PSiCB

CCBMWCNT

0

2

4

6

8

10

12

14


E998400

(MPa

)


PSiCB

CCBMWCNT

0

2

4

6

8

10

12

14

0 5 10 15

BRC

()





PSiCB

CCBMWCNT


1E minus 3

9E minus 4

8E minus 4

7E minus 4

6E minus 4

5E minus 4

4E minus 4

3E minus 4

2E minus 4

1E minus 4

0E + 0

Cros

s-lin

k de

nsity

(mol

cm

3)





tan 120575119898119891=tan 120575119898119906

1 + 120573120601 (4)

where tan 120575119898119891

and tan 120575119898119906




tan 120575max

0 154 154 154 1545 112 138 150 15110 088 119 144 14015 07 099 138 132


0 100 100 100 1005 080 094 099 10010 066 085 097 09515 055 074 094 093

120573120601lowast

0 0 0 0 05 038 012 003 00210 075 029 007 01015 120 056 012 017





10 30 50 70

Unfilled5PSi5CB

5CCB5MWCNT


Temperature (∘C)

0

02

04

06

08

1

12

14

16

18

15PSi15CB

15CCB15MWCNT

10 30 50 70

Unfilled


Temperature (∘C)

0

02

04

06

08

1

12

14

16

18

10PSi10CB

10CCB10MWCNT

10 30 50 70

Unfilled


Temperature (∘C)

0

02

04

06

08

1

12

14

16

18

tan 120575

tan 120575

tan 120575

(a)

Unfilled5PSi5CB

5CCB5MWCNT

20 30 40 50 60 70Temperature (∘C)

0

005

01

015

02

025

03

20 30 40 50 60 70Temperature (∘C)

0

005

01

015

02

025

03

10PSi10CB

10CCB10MWCNT

Unfilled

20 30 40 50 60 70Temperature (∘C)

0

005

01

015

02

025

03

15PSi15CB

15CCB15MWCNT

Unfilled

tan 120575

tan 120575

tan 120575

(b)











Hardness (Shore A)




Abrasion loss (mm3)



4 Conclusions




Acknowledgments


References


















































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




0

5

10

15

20

25

30

35

0 1 10Strain ()

Unfilled5MWCNT

10MWCNT15MWCNT

E998400

(MPa

)

(a)

Unfilled

0

2

4

6

8

10

12

0 1 10Strain ()

5CCB10CCB15CCB

E998400

(MPa

)

(b)

Unfilled

0

1

2

3

4

5

6

7

8

9

10

0 1 10Strain ()

5CB10CB15CB

E998400

(MPa

)

(c)

Unfilled

0

1

2

3

4

5

6

7

8

9

10

0 1 10Strain ()

5PSi10PSi15PSi

E998400

(MPa

)

(d)



119881119903=

1198981119889119904

1198981(119889119904minus 119889119903) + 1198982119889119903

(3)


2is the



[30]





PSiCB

CCBMWCNT

1E + 10

1E + 09

1E + 08

1E + 07

1E + 06

1E + 05

1E + 04

1E + 03

1E + 02

1E + 01

1E + 00

Volu

me r

esist

ivity

(Ωcm

)





PSiCB

CCBMWCNT

0

2

4

6

8

10

12

14


E998400

(MPa

)


PSiCB

CCBMWCNT

0

2

4

6

8

10

12

14

0 5 10 15

BRC

()





PSiCB

CCBMWCNT


1E minus 3

9E minus 4

8E minus 4

7E minus 4

6E minus 4

5E minus 4

4E minus 4

3E minus 4

2E minus 4

1E minus 4

0E + 0

Cros

s-lin

k de

nsity

(mol

cm

3)





tan 120575119898119891=tan 120575119898119906

1 + 120573120601 (4)

where tan 120575119898119891

and tan 120575119898119906




tan 120575max

0 154 154 154 1545 112 138 150 15110 088 119 144 14015 07 099 138 132


0 100 100 100 1005 080 094 099 10010 066 085 097 09515 055 074 094 093

120573120601lowast

0 0 0 0 05 038 012 003 00210 075 029 007 01015 120 056 012 017





10 30 50 70

Unfilled5PSi5CB

5CCB5MWCNT


Temperature (∘C)

0

02

04

06

08

1

12

14

16

18

15PSi15CB

15CCB15MWCNT

10 30 50 70

Unfilled


Temperature (∘C)

0

02

04

06

08

1

12

14

16

18

10PSi10CB

10CCB10MWCNT

10 30 50 70

Unfilled


Temperature (∘C)

0

02

04

06

08

1

12

14

16

18

tan 120575

tan 120575

tan 120575

(a)

Unfilled5PSi5CB

5CCB5MWCNT

20 30 40 50 60 70Temperature (∘C)

0

005

01

015

02

025

03

20 30 40 50 60 70Temperature (∘C)

0

005

01

015

02

025

03

10PSi10CB

10CCB10MWCNT

Unfilled

20 30 40 50 60 70Temperature (∘C)

0

005

01

015

02

025

03

15PSi15CB

15CCB15MWCNT

Unfilled

tan 120575

tan 120575

tan 120575

(b)











Hardness (Shore A)




Abrasion loss (mm3)



4 Conclusions




Acknowledgments


References


















































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials





PSiCB

CCBMWCNT

1E + 10

1E + 09

1E + 08

1E + 07

1E + 06

1E + 05

1E + 04

1E + 03

1E + 02

1E + 01

1E + 00

Volu

me r

esist

ivity

(Ωcm

)





PSiCB

CCBMWCNT

0

2

4

6

8

10

12

14


E998400

(MPa

)


PSiCB

CCBMWCNT

0

2

4

6

8

10

12

14

0 5 10 15

BRC

()





PSiCB

CCBMWCNT


1E minus 3

9E minus 4

8E minus 4

7E minus 4

6E minus 4

5E minus 4

4E minus 4

3E minus 4

2E minus 4

1E minus 4

0E + 0

Cros

s-lin

k de

nsity

(mol

cm

3)





tan 120575119898119891=tan 120575119898119906

1 + 120573120601 (4)

where tan 120575119898119891

and tan 120575119898119906




tan 120575max

0 154 154 154 1545 112 138 150 15110 088 119 144 14015 07 099 138 132


0 100 100 100 1005 080 094 099 10010 066 085 097 09515 055 074 094 093

120573120601lowast

0 0 0 0 05 038 012 003 00210 075 029 007 01015 120 056 012 017





10 30 50 70

Unfilled5PSi5CB

5CCB5MWCNT


Temperature (∘C)

0

02

04

06

08

1

12

14

16

18

15PSi15CB

15CCB15MWCNT

10 30 50 70

Unfilled


Temperature (∘C)

0

02

04

06

08

1

12

14

16

18

10PSi10CB

10CCB10MWCNT

10 30 50 70

Unfilled


Temperature (∘C)

0

02

04

06

08

1

12

14

16

18

tan 120575

tan 120575

tan 120575

(a)

Unfilled5PSi5CB

5CCB5MWCNT

20 30 40 50 60 70Temperature (∘C)

0

005

01

015

02

025

03

20 30 40 50 60 70Temperature (∘C)

0

005

01

015

02

025

03

10PSi10CB

10CCB10MWCNT

Unfilled

20 30 40 50 60 70Temperature (∘C)

0

005

01

015

02

025

03

15PSi15CB

15CCB15MWCNT

Unfilled

tan 120575

tan 120575

tan 120575

(b)











Hardness (Shore A)




Abrasion loss (mm3)



4 Conclusions




Acknowledgments


References


















































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




PSiCB

CCBMWCNT


1E minus 3

9E minus 4

8E minus 4

7E minus 4

6E minus 4

5E minus 4

4E minus 4

3E minus 4

2E minus 4

1E minus 4

0E + 0

Cros

s-lin

k de

nsity

(mol

cm

3)





tan 120575119898119891=tan 120575119898119906

1 + 120573120601 (4)

where tan 120575119898119891

and tan 120575119898119906




tan 120575max

0 154 154 154 1545 112 138 150 15110 088 119 144 14015 07 099 138 132


0 100 100 100 1005 080 094 099 10010 066 085 097 09515 055 074 094 093

120573120601lowast

0 0 0 0 05 038 012 003 00210 075 029 007 01015 120 056 012 017





10 30 50 70

Unfilled5PSi5CB

5CCB5MWCNT


Temperature (∘C)

0

02

04

06

08

1

12

14

16

18

15PSi15CB

15CCB15MWCNT

10 30 50 70

Unfilled


Temperature (∘C)

0

02

04

06

08

1

12

14

16

18

10PSi10CB

10CCB10MWCNT

10 30 50 70

Unfilled


Temperature (∘C)

0

02

04

06

08

1

12

14

16

18

tan 120575

tan 120575

tan 120575

(a)

Unfilled5PSi5CB

5CCB5MWCNT

20 30 40 50 60 70Temperature (∘C)

0

005

01

015

02

025

03

20 30 40 50 60 70Temperature (∘C)

0

005

01

015

02

025

03

10PSi10CB

10CCB10MWCNT

Unfilled

20 30 40 50 60 70Temperature (∘C)

0

005

01

015

02

025

03

15PSi15CB

15CCB15MWCNT

Unfilled

tan 120575

tan 120575

tan 120575

(b)











Hardness (Shore A)




Abrasion loss (mm3)



4 Conclusions




Acknowledgments


References


















































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




10 30 50 70

Unfilled5PSi5CB

5CCB5MWCNT


Temperature (∘C)

0

02

04

06

08

1

12

14

16

18

15PSi15CB

15CCB15MWCNT

10 30 50 70

Unfilled


Temperature (∘C)

0

02

04

06

08

1

12

14

16

18

10PSi10CB

10CCB10MWCNT

10 30 50 70

Unfilled


Temperature (∘C)

0

02

04

06

08

1

12

14

16

18

tan 120575

tan 120575

tan 120575

(a)

Unfilled5PSi5CB

5CCB5MWCNT

20 30 40 50 60 70Temperature (∘C)

0

005

01

015

02

025

03

20 30 40 50 60 70Temperature (∘C)

0

005

01

015

02

025

03

10PSi10CB

10CCB10MWCNT

Unfilled

20 30 40 50 60 70Temperature (∘C)

0

005

01

015

02

025

03

15PSi15CB

15CCB15MWCNT

Unfilled

tan 120575

tan 120575

tan 120575

(b)











Hardness (Shore A)




Abrasion loss (mm3)



4 Conclusions




Acknowledgments


References


















































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials












Hardness (Shore A)




Abrasion loss (mm3)



4 Conclusions




Acknowledgments


References


















































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials
















































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



research article reinforcement of multiwalled carbon

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