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ChemicalIndustry&ChemicalEngineeringQuarterly16(4)373378(2010) CI&CEQ

373

OGBEMUDIA JOSEPHOGBEBOR1UZOMA NDUBUISI OKWU1FELIX EBHODAGHEOKIEIMEN2DANIEL OKUONGHAE21Rubber Technology Department,Rubber Research Institute ofNigeria, Benin City, Nigeria2University of Benin, Center forBiomaterials Research, Benin City,

NigeriaSCIENTIFIC PAPER

UDC 678:678.074

DOI 10.2298/CICEQ100110038O

PHYSICO-MECHANICAL PROPERTIES OFELASTOMERS BASED ON NATURAL RUBBERFILLED WITH SILICA AND CLAYElastomersbasedonnaturalrubber(NR)andsilicaandclayfillershavebeen

investigatedfor theirphysico-mechanical properties.Thevariousmixeswere

compoundedinaBanbury-Pullenlaboratorymillandvulcanizedusingtheeffi-

cientvulcanizationsystem.Theoscillatingdiscrheometer(ODR)wasusedfor

determinationofcurecharacteristics.Itwasestimatedthatreplacementofsi-

licawith clay upto30phr(50%replacement) increased thecompoundcure

ratewithareductioninabsolutetorquelevel(Tmax)ofthenaturalrubbermix.

Scorchtime(Ts2)wasobservedtobethehighestata30/30fillerratio.Hard-ness and tensile propertiesof obtained elastomericmaterials werestudied.

Theresultsshowadecreaseinparametersasthereplacementofsilicawith

naturalclay progresses.Therewasimprovement inelongationatbreakwith

theincreaseofclaycontent.Thereplacementofsilicafillerwithclayreduced

theabrasionproperties(mgloss/1000rev.)

Keywords: silica;clay;rubber;processingsafety;physico-mechanicalproperties.

Claysarederivedfromnaturaldepositsandare

essentially hydrated aluminium silicates, containing

certain groupsofhydrousmagnesium, iron,sodium,

calcium,potassium,andotherions[1]. Theyareinex-pensivenaturalmineralsandhavebeenusedasnon-

black fillerfor rubber and plastic toimproveproces-

sabilitybyreducingnerveinimprovingshapingopera-

tionsandensuringdimensionalstabilityinunvulcani-

zed stocks [2,3] formanyyears. Ithasalso recently

beenused infoundrysandmouldswhere itwas re-

portedtosubstantiallyimprovemechanicalproperties

[4].Theconsumptionofnonblackfillersintherubber

industryisknowntobeinmillionsoftonsperyear[5].

Silica,ontheotherhand,isprominentlyusedasfiller

inmanyrubberwaresduetoitsappreciableabilityto

reinforce the elastomerswhilemaintainingexcellent

abrasionresistance.But,itshighcostandheatbuild-

up problems which cause deterioration of material

propertieshavebeenofconcerntoitsusers[69].In

this study the clay and silicawereusedas fillers in

natural rubber compounds. The aim of the project

Correspondeningauthor:O.J.Ogbebor,RubberTechnologyDe-

partment,RubberResearchInstituteofNigeria,PMB1049,

300001BeninCity,Nigeria.E-mail:[email protected]:10January,2010

Paperrevised:22June,2010Paperaccepted:1July,2010

was to determine the influence of filler mass ratio,

silica/clay ratio on curingandmechanicalproperties

ofelastomersbasedonnaturalrubber.

EXPERIMENTALNaturalrubber(NR)wasobtainedfromtheRub-

ber Research InstituteofNigeria (RRIN) plantations

situated at Iyanomo, near Benin City, Nigeria. The

claywascollectedformadepositinEdoCentralSe-

natorialdistrictofNigeria.Airdried(495C),pulve-

rized and sieved throughmesh size 300 m. X-ray

diffraction (XRD) recorded from monochromatic X-

-rays(MD10minidiffractometer),withNi-filterCuK

radiation and automatic slit analyzed using Bragg-

-Wulf equation ( = 2dsin), where is the X-raywavelength,d isthe interlayer spacing,andisthe

angle of diffraction in combination with the Interna-

tionalCenterforDiffractionData(ICDD)identification

chartshowedamineralcomplexcomprisingofchon-

drodite, Mg3FeSiO4H2O, titanian, TiO4SiO4H2O

and kaesutite, NaCa2MgFe)4TiSi6Al2O22(OH)2,witha

1:1tetrahedrallattice[5].Somephysico-chemicalpro-

pertiesoftheclaysamplearegiveninTable1.For-

mulations of five types of compounds are given in

Table 2. The compounding ingredients (zinc oxide,

stearic acid,paraffinoil,silica, etc.)were purchased

fromBerkChemicalsUK.Silica(vulkasilS)havinga

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374

particlesizearound 30nm,and density2.00gcm-3

wasusedintheexperiments.

Table1.Physicochemicalcharacteristicofclay

Particlesizedistribution(PSA)a

Content,mass%

Clay 83

Sand 10

Silt 7

Colour Grayish-brown

Densityofclay,gcc-3 2.62

Densityofsilica,gcc-3 2.00

SiO2 38.48

Al2O3 12.46

Fe2O3 6.18

TiO2 1.85

MgO 14.67

CaO 12.05

Na2O 1.42

K2O 9.57

Lossonignition 13.5

pH 7.43aAccordingtotheUSDA[22]

MixingMixingofrubbercompoundswascarriedoutin

a laboratory two roll mill (Banbury-Pullen, model,

35100).Themillopeningwassetat1.4mm,andthe

initialtemperatureofthemillwassetat805C.Themixinginvolvedatwostageoperation.Inthefirststep

aninitialbandingofnaturalrubberonthefrontrollof

atworoll-mill,followedbycutsonbothsidesofthe

band, followed by adding the half content of fillers,

thenzincoxide,stearicacid,paraffinoilandwax,al-

lowedtomixproperlyfor5min.Thiswasfollowedby

the incorporation of the remaining ingredients and

6PPDforafurther3.5min.Inthefinalsteptheaddi-

tionofacceleratorandvulcanizingagents(CBSand

sulphur)for2.0minwasdoneafterthestockwasal-

lowedtocoolto70C.

Cure behavior determination and sample preparationThe aptitude to vulcanization of rubber com-

pounds was determined on Alpha Oscillating Disc

Rheometer (ODR 2000) using a 1 rotor oscillating

amplitudeandfrequency50Hz[10].Thecureratein-

dex(CRI)[11]andotherparametersofthecurewere

estimatedfromobtainedrheographs.Theelastomeric

sampleswereobtainedbycompressionmouldingat

140 C using electric heated hydraulically operated

press for various times extrapolated from the

rheographs.

Mechanical properties characterizationHardness

The hardness tests of the rubber vulcanizates

werecarriedoutinaccordancetoBS903(ISO7619),

with an international rubber hardness tester. Speci-

menswith a thickness of6mmwere tested at room

temperature. The reported values are basedon the

averageoffivemeasurements[12].

Tensileproperties

Dumbbell-shaped samples were cut from the

molded sheets, according to BS 903, Part A2 (DIN

53504). Tensile properties:M100,M200 and tensilestrength (TS)were determined at room temperature

onZwick/RoelltestingmachineZ005withcrosshead

speedof200mm/min[13].Abrasionresistancetest

Theabrasiontestwascarriedoutinaccordance

toBS903,PartA9,consistingofatrialrun,arunning-

Table2.Formulationforinvestigatingclay/silicafilledNRrubbercompounds(adoptedmodelformulationfromMalaysianNaturalRubbe

ProducersResearchAssociation(MRPRA)TechnicalbulletinsheetD105D117,formanufactureofgeneralmechanicalgoods,which

includevarietyofproductslikehose,conveyorbelts,rubberlinings,gasketseals,rubberrolls,rubberizedfabricsetc.)

Component Phr Phr Phr Phr Phr

1.NaturalRubber 100 100 100 100 100

2.Paraffinoil 10 10 10 10 10

3.Clay 0 20 30 40 60

4.Silicaa 60 40 30 20 0

5.ZincOxide 10 10 10 10 10

6.Stearicacid 2 2 2 2 2

7.6PPDb 1.5 1.5 1.5 1.5 1.5

8.Wax 1.5 1.5 1.5 1.5 1.5

9.CBSc 0.6 0.6 0.6 0.6 0.6

10.Sulphur 2.8 2.8 2.8 2.8 2.8a

Silica(vulkasilS);particlesize:30nm;b

N-(1,3-dimethylbutyl)N-phenyl-p-phenylenediamine;c

N-cyclohexyl-2-benzothiazolesulfenamide.(AllchemicalswerepurchasedfromBerkchemicalsUK,Ltd.)

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-inperiodandfive testruns.Absolutevalueofabra-

sion losswas themean value determined from the

fivetestrunsexpressedasmilligramsper1000revo-

lutionsoftheabrasivewheel[14].

RESULTS AND DISCUSSIONThe rheological properties during cross-linking

of the natural rubber filledwithmixcompositionsof

silicaandclayareshowninFigure1 andallestima-

teddataaregiveninTable3.Ithasbeenstatedthat

ODR is a convenient technique for the functional

evaluationoffillersfortheirreinforcingpotentials[15

17].Thesilicafilledcompoundhadthehighestmini-

mumtorque(ML=22.23dNm),MLforothercom-

pounds silica/clay loading, were at 40/20 phr (40%

replacement loading);13.98d Nm,30/30phr (50%

replacementloading);9.42dNm,20/40phr(60%re-

placementloading);7.89dNm,and0/60phr(100%

replacementloading);3.91dNm,respectively.Since

MLisameasureofeffectiveviscosityofunvulcanized

mix,theresultsshowthatthestiffnessaswellasthe

viscosityoftheuncuredcompoundisreducedasthe

clay content increases. This effect correlates the

hydrodynamicequation[15]:

f=u(1+2.5c+14.1c2) (1)

Figure1.Rheographsat140C(arc.1)ofvaryingfillermixcompositionsinphr;silica/clay60/0,silica/clay40/20,

silica/clay30/30,xsilica/clay20/40,silica/clay0/60.

Table3.Curecharacteristicsofnaturalclay/silicafilledNR(compoundmix:rubber,NR(100),paraffinoil10,Stearicacid2.0)rubbe

compounds;MLminimumtorque;MHmaximumtorque;CRIcurerateindex,100/(T90Ts2);ts1timeto1unitriseaboveML;ts2ti-

meto2unitriseaboveML;ts10timeto10unitsriseaboveML;t90timetomaximumcrosslinking

Cureproperties Mix1 Mix2 Mix3 Mix4 Mix5

Clay 0 20 30 40 60

Silica 60 40 30 20 0

ts1/min 3.19 3.05 6.53 3.44 3.55

ts2/min 3.50 3.51 7.49 4.18 4.13

t10/min 4.48 4.28 8.33 12.30 6.21

t50/min 16.53 21.21 13.03 12.30 6.21

t90/min 41.46 48.02 30.19 34.25 12.14

Absolutetorquelevel(T90+ML),Tmax 63.69 62.0 36.61 42.14 16.05

CRI 2.63 2.25 4.41 3.33 12.48

ML/kgcm 22.23 13.98 9.42 7.89 3.91

MH/kgcm 62.74 41.34 42.23 32.57 37.46

(MHML)/kgcm 40.51 27.36 32.81 24.68 33.55

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wheref andu are the viscositiesof the filledand

unfilled compounds,andc isthevolume fraction of

the fillers.FromEq.(1) itis obvious thatviscosity is

expected to increase with increase in filler loading

(volume fraction). However, viscosity is also depen-

dent on the silica/clay interactions and between the

elastomernetworkandfillers.

Scorch times (ts2 inTable 3) for samples with

various fillerratio ofsilicaand clay (60/0, 40/20,30/

/30,20/40and0/60)were3.50,3.51,7.49,4.18and

4.13min,respectively.Thehighestvaluewasobser-

vedat30/30phr(50%replacementloading).Thisisa

valuableassessmenttothecompoundingrecipeasit

givescompoundsprocessingsafety[18].Thisscorch

retardingeffectcanbeobservedastheclayfraction

increases in the mix formulation. Some acids sub-

stanceslikephthalicanhydride(at0.5-2.0phr),other

been N-nitrosodiphnylamine (at 1-5 phr) have been

usedasretarders[19]inNRmix.Silicaisknownto

exhibit a cure retardingeffect when incorporatedas

filler inmixes curedusing the efficientvulcanization

system[20].Theextentofvulcanizationismeasured

bymaximumtorque(MH).Ahighrheometrictorque,

which isameasureofcrosslinkingdegree,was ob-

servedforthecontrolmix(60phrsilica)withoutclay.

Replacement of silicawith clay up to 50% replace-

ment,i.e.30/30phrincreasedthecurerateofnatural

rubberaswellastheirMH.

ThevulcanizatepropertiesofNRfilledwithmixblendsofsilicaandclayusedinthisinvestigationare

showninFigures2-7.Theall-silica,0%clay(control

mix) exhibited the characteristic reinforcingproperty

ofsilicafillers.Ingeneral,therewasanobservedde-

crease intensilepropertiesastheclaygraduallyre-

placedsilicaincompounds.Hardness(Figure1)and

tensilestressproperties(Figures3-5)whichincluded

M100,M200,and tensile strength (TS) followed the

samesequenceof reduction.Therewasmarked re-

duction in hardness (from 24-54%) as replacement

progressedthrough40/20,30/30,20/40,and0/60phr

of silica/clay in the filler mix. The M100 showed areductionfrom11to74%,whileM200showedare-

ductionfrom20to86.4%andtensilestrength(TS)in-

dicated a reduction from 12.3 to 78.7% as the clay

increasedinthemix,respectively.Particlesizesoffil-

lersplaysignificantroleincouplingoffillertopolymer.

As theparticlesizeoffillersinapolymercompound

decreases, its resilience and strength decreases

while the abrasion is increased [21]. This also by

extensioncorroborates the effect on the abrasion in

mgloss/1000revolutions,Figure7,astheclayinthe

filler mix increases. However, there was improved

extensioninthemixesastheclayin the formulation

increases.AsitcanbeseenfromFigure6elongation

atbreakwere190,223,238,245and 350% for the

60/0 phr (100% silica loading), 40/20 phr (40%

replacement loading), 30/30 phr (50% replacement

loading), 20/40 phr (60% replacement loading) and

0/60phr(100%replacementloading),respectively.

0

10

20

30

40

50

60

70

80

60/0 40/20 30/30 20/40 0/60

silica/clay, phr

IRH

Figure2.ComparativevaluesforhardnessofNRvulcanizates

filledwithdifferentratiomixofsilicaandclay.

0

1

2

3

4

5

6

7

8

9

10

60/0 40/20 30/30 20/40 0/60

silica/clay, phr

M100,MPa

Figure3.ComparativevaluesforM100ofNRvulcanizatefilled

withdifferentratiomixofsilicaandclay.

0

1

2

3

4

5

6

7

8

9

10

60/0 40/20 30/30 20/40 0/60

silica/clay, phr

M200,

MPa

Figure4.ComparativevaluesforM200ofNRvulcanizatefilled

withdifferentratiomixofsilicaandclay.

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0

2

4

6

8

10

12

14

60/0 40/20 30/30 20/40 0/60

silica/clay, phr

TS,MP

a

Figure5.Comparativevaluesfortensilestrength,TSofNR

vulcanizatesfilledwithdifferentratiomixofsilicaandclay.

0

50

100

150

200

250

300

350

400

60/0 40/20 30/30 20/40 0/60

silica/clay, ph r

EB,

Figure6.ComparativevaluesforelongationatBreakEB(%)of

NRvulcanizatesfilledwithdifferentratiomixofsilicaandclay.

0

0.5

1

1.5

2

2.5

3

3.5

60/0 40/20 30/30 20/40 0/60

silica/clay, phr

mg.

loss/1000rev.

Figure7.Comparativevaluesforabrasion(mgloss/1000rev.)

ofNRvulcanizatefilledwithdifferentratiomixofsilicaandclay.

CONCLUSIONIn this study, elastomeric materials reinforced

withsilicaandclaymixeswerepreparedbychanging

filler ratio in natural rubber compound formulations.For the five fillermixesstudied, the fillerratio30/30

phr (50% clay replacement) exhibited the optimal

scorchtime(7.49min),aconditionindicativeforgood

processingsafety.Silicafillersareusedinalotofrub-

ber articles such as hose, cables, footwearuppers,

mechanicalgoodsandthereforetheuseofclaypar-

ticlestogetherwithsilicamayfindacceptabilityinrub-

berindustryinareasrequiringprocessingsafety.Acknowledgements

The financial assistance of the Management

under the leadership of Mrs. M.U.B. Mokwunye as

wellasthetechnicalassistanceofstaffoftheRubber

TechnologyDepartmentofRubberResearchInstitute

ofNigeriaisgratefullyacknowledged.

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[4] N.A.Ademoh,Int.J.Phys.Sci.3 (2008)240-244.[5] O.J.Ogbebor,F.E.Okieimen,U.N.Okwu,Inter.J.Chem.

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29-32.

[7] M.P.Wagner,Rubber Chem.Technol.49 (1976) 703-708.

[8] F.Bomo,J.C.Morawski,inProceedingsof131stRubberDivisionACSMeeting,Montreal,2001,pp.18-22.

[9] R.J.Young,P.A.Lovell,IntroductiontoPolymers,Chap-man&Hall,London,1997,pp.350-362.

[10] ISO 3417 (2000-E), Rubber Measurementof Vulcani-sationCharacteristicsDiscRheometer.

[11] A.A. Yehia, B. Stoll. Kaunts, Gummi Kuntz. 40 (1987)327-331.

[12] British Standards Institute, BS 903, Part A57: Deter-minationofHardness(ISO7619).

[13] British Standards Institute, BS 903; Part A2: Determi-nationofTensileStress-StrainProperties(DIN53504).

[14] British Standards Institute, BS 903; Part A9: Determi-nationofAbrasionResistance.

[15] Rubber TechnologyandManufacture, C.M.Blow (Ed).,Butterworths,London,1971,pp.188-193.

[16] A.C.Patel,J.T.Byers,Elastomerics114(1982)29-33.[17] Z.A.M. Ishak, A.A. Baker, Eur. Polym. J.3 (1995) 259-

265.

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[20] W.H.Waddel,L.R.Evans,J.R.Parker,inProceedingsof19

th Rubber DivisionMeeting,ACS, Chicago, IL, 1994,

pp.39-45.

[21] J.U.Iyasele,F.E.Okieimen,J.Chem.Soc.Nig.33(2008)162-165.

[22] A. Klute,G.S.Campbell,R.D.Jackson,M.M.Mortland,D.R.Nielsen,MethodsofSoilAnalysisPart1:ASA,Inc.,

Madison,1986,pp.307-450.

OGBEMUDIA JOSEPHOGBEBOR1UZOMA NDUBUISI OKWU1FELIX EBHODAGHE OKIEIMEN2DANIEL OKUONGHAE2

1Rubber Technology Department,Rubber Research Institute ofNigeria, Benin City, Nigeria2University of Benin, Center forBiomaterials Research, Benin City,NigeriaNAUNI RAD

FIZIKO-MEHANIKA SVOJSTVA MEAVINAPRIRODNOG KAUUKA, SILICIJUM-DIOKSIDA IPRIRODNE GLINEIspitivanesufiziko-mehanikasvojstvaelastomerabaziranimnaprirodnomkauukui

puniocimatipasilicijumdioksidaigline.UlaboratorijiBanbury-Pullenpripemljenesuraz-

liitemeavine kojesu podvrgnutevulkanizaciji. Karakterizacija vulkanizata je vrena

pomouoscilujuogdiskreometra(ODR).Utvrenojedazamenasilicijumdioksidagli-

nom do30 phr (50%zamene) poveavabrzinu vulkanizacijemeavine uzsmanjenje

stepenaobrtnogmomenta(Tmax)prirodnegume.Vremesuenja (Ts2)jenajveepri

odnosupunilaca30/30.Prouavanesu,takoe,tvrdoaisilazatezanjadobijenihelasto-

mera.Rezultatipokazujusmanjenjenavedenihparametarazamenomsilicijum-dioksida

prirodnomglinom.Postojiizvesnopoboljanjeuprekidnomistezanjusapoveanjemko-

liine gline. Zamena silicijumovog punioca prirodnom glinom smanjuje abrazivne

osobine(mggubitaka/1000rev.).

Kljunerei:silicijum-dioksid;glina;guma;bezbednaobrada;fiziko-mehanike

karakteristike.

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