Combined effects of microwaves, electron beams and polyfunctional monomers on rubber vulcanization

43-3-26 Journal of Microwave Power & Electromagnetic Energy ONLINE Vol.43,No.,2009

Elena Manaila1*, Diana Martin1, Daniela Zuga Stelescu2, Gabriela Craciun1, Daniel Ighigeanu1 and Constantin Matei1

1National Institute for Lasers, Plasma and Radiation Physics, Bucharest, Romania2National R&D Institute for Textile and Leather, Bucharest, Romania

* [email protected] Thispaperpresentscomparativeresultsobtainedbyconventionalvulcanizationwithbenzoylperoxide(CV-BP),separateelectronbeamvulcanization(EB-V)andsimultaneouselectronbeamandmicrowavevulcanization(EB+MW-V)appliedtotwokindofrubbersamples:EVA(ethylenevinylacetate)rubber-sample(EVA-sample)andEPDM(ethylene-propyleneterpolymer)rubber–sample(EPDM-sample).TheEVA-samplescontain61,54%EVAElvax260,30.77%carbonblack,1.85%TAC(triallylcyanurate)polyfunctionalmonomerand5.84%filler(zincoxide,stearicacid,polyetylen glycol and antioxydant). The EPDM-samples contain 61.54% EPDM Nordel 4760,30.77%carbonblack,1.85%TMPT(trimethylopropanetrimethacrylate)polyfunctionalmonomerand5.84%filler(zincoxide,stearicacid,polyetylenglycolandantioxydant).Therubbersamplesdesignedfordifferentvulcanizationmethodswereobtainedfromrawrubbermixtures,ascompressedsheetsof2mminthepolyethylenefoilstominimizeoxidation.ForEBandEB+MWtreatmentsthesheetswerecutinrectangularshape0.15x0.15m2.ThephysicalpropertiesofsamplesobtainedbyCV-BP,EV-VandEB+MW-Vmethodswereevaluatedbymeasuringthetearingstrength,residualelongation,elongationatbreak, tensilestrength,300%modulus,100%modulus,elasticityandhardness.TheobtainedresultsdemonstrateanimprovementofrubberseveralpropertiesobtainedbyEBandEB+MWprocessingascomparedtoclassicalprocedureusingbenzoylperoxide.

Submission Date: 15September2008 Acceptance Date:17 April2009

Publication Date:31August2009

Combined effeCts of miCrowaves, eleCtron beams and PolyfunCtional monomers on

rubber vulCanization

Keywords: Metallicglass,microwaveheating,magneticfieldmaximum

INTRODUCTION

Thegeneralpracticeintherubbervulcanizationindustryistouseconventionalperoxidecuringsystems and vulcanization agents, althoughit was found in 1940 that polymers can becrosslinkedbyelectronbeam(EB)technologies[Makuuchi, 1995; Holl, 1995; Basfar, 1995;

Anelli,1995].Peroxidevulcanizationmustbeperformedathightemperaturesunderanoxygen-depletedatmosphere,thuscreatinganundesirableproduct surface. An alternative vulcanizationmethod isEBvulcanization [Jinhua,2001].EBvulcanization has demonstrated extremelypositive results compared to the conventionalcuringsystemsuchas:nopolymerdegradationdue to high temperature as EB cross-linkingoccurs at room temperature, no oxidativedegeneration in polymers as observed inclassicalcross-linking,directcross-linkingbyGuest Editor:Dr.AnishUpadhyaya,IndianInstituteof

Technology,Kanpur,India

International Microwave Power Institute 43-3-27

C-C linkage by EB, extremely strong bonds,high degree of cross-linking, extremely shortcuring cycles, very high productivity, perfectfor thin products, and lower material waste[MGB Rubber Company, 2007]. The majorobstacle in EB crosslinking of rubbers is therequirementofhighirradiationdosestoachievethedesiredcrosslinkdensityindifferentrubberstructures[Yasin,2005].Lowirradiationdosesare required for the process efficiency and a high doseratemustbeusedtogivelargeproductioncapacities.Thus,forindustrialscaleprocessing,the problem of reducing the electrical energyconsumptionaswellastheEBcostisespeciallyimportant.Reportedpaperssuggestthatappropriatepolyfunctional monomers (PFMs) in polymermatrix[Yunshu,1998;Majumder,2000;Jinhua,2001;Yasin, 2002;Yasin, 2003; Hung, 2004;Yasin,2005;Vijayabaskar,2005]andmicrowave(MW)additionalenergy[Martin,2002]toEBirradiation could be used to obtain desiredrubberphysicalpropertiesatlowerirradiationdoses.Theapplicationofmicrowavesinawiderange of areas, including rubber processing,utilizesclassicalinteractionofelectromagneticradiationwithmattersuchasdielectricheatinginsolidsandliquids.Theadvantagesofusingmicrowaves and microwave systems can besummarizedasfollows:rapidenergy transfer,volumetric and selective heating, very highheating rate, convenient and clean heating,fast to switch on and off, clean environment,free from products of combustion, compactequipment, and the microwave systemcools rapidly when the field is switched off. Microwave rubber vulcanization has beenstudiedsince1969andindustrialappliedsince1971 [Ottner, 1969; Meisel, 1971].The maindisadvantage of MW is restriction to polarmixtures.Manyrubbermixturesarenon-polardielectrics,buttheadditionofcarbonblackorotherchemicaladditivesareusedforobtainingpolar rubber compounds for MW processing[Ottner, 1969; Meisel, 1971; Catala, 1998].The principal advantages of MW technologiesover other rubber vulcanization methods are

summarized as follows [Hills, 1971; Morton,1987; Metaxas, 1982; Parodi, 1996; Parodi,2001]:muchfasteranddeeperheatingofrubberitems and much lower specific consumption (with respect to all classical vulcanizationmethods),superiorworkingsafety(overmoltennitrate salt-baths, molten metal baths, andoverheated steamunderpressure), absenceofanyenvironmentalimpactrisksandecologicalissues(ascomparedtomoltensalt-baths),highermanufacturingthroughputrates(withrespecttoall classical vulcanization methods), minimizedplantmaintenancecosts (as compared tomoltensalt-bathsandvulcanizationbyoverheatedsteamunderpressure),absenceofrubberpigmentordyediscolorationphenomena(with respect tovulcanizationbyoverheatedsteamandmoltensalt-baths), negligible process start-up times(as compared to all classical vulcanizationmethods). ThemaingoalofthispaperwastocombinetheadvantagesofEBirradiation,MWheatingandPFMsadditioninrubbermixturesinordertoreducetherequiredelectronbeamdoselevelandtoimprovetherubberproperties.Thereisno previous work in the literature examiningthe effect of simultaneous EB and MW inrubber processing with the exception of ourwork[Martin,2002].

EXPERIMENTAL INSTALLATIONS

An experimental installation that permitsseparate, successive or simultaneous EB andMWirradiation,EI-EB+MW,wascarriedoutfor comparative studies testing the effects ofdifferent irradiation modes, different rubbersample compositions and different EB andMWdosesonthevulcanizationdegreesoftheprocessed rubber samples. The EI-EB+MWconsistsmainlyofthefollowingunits: • An accelerated electron beam source(EBS) of 1.8 MeV and 10.8 kW maximumoutputpower; •Amicrowavesource(MWS)of2.45GHzand1700Wmaximumoutputpower;


•Amultimoderectangularcavity(MRC)of0.612mx0.612mx0.367minnerdimensions,usedasvulcanizationchamber. The MWS and MRC units were carriedoutintheNationalInstituteforLasers,Plasmaand Radiation Physics, Electron AcceleratorsLaboratory in Romania. As EBS is used anelectronacceleratorILU-6MbuiltattheInstituteof Nuclear Physics-Novosibirsk in Russia. Itis placed at Electrical Project and ResearchInstitute from Bucharest, Romania.The ILU-6M electron beam source is a resonator-typeaccelerator, operating at 115±5 MHz. Thisaccelerator generates electronbeampulses of0.375 ms duration, up to 0.32 A for currentpeak intensity and 0.006A for mean currentintensity.Themaximumcross-sectionalsizeofthescannedEBattheILU-6Mvacuumwindowexitis1.1mx0.0656m. ThescannedEBoftheILU-6MacceleratorisintroducedperpendiculartotheMRCupper-endplates througha100μmthickaluminumfoil of 0.55 m x 0.15 m. Figure 1 shows thephotographoftheMRCunderILU-6Mscanner.The MRC can be used without conveyor, instatic regime, or with an internal conveyorpassing through MRC by changing its lateralwalls.Also,MRCcanbeplacedonanexternalconveyor in order to pass under the ILU-6MscannerasshowninFigure1. The MW power is also coupled with theMRCupperendplatebytwoslottedwaveguidesused as MW radiating antenna. Each slottedwaveguide is coupled with a MW injectionsystem (MWIS) of 2.45 GHz and adjustableoutput power up to 850 W. The slottedwaveguide system provides good microwaveenergy transfer and uniformity over a largearea [Leprince, 1992]. The radiating antennaconsisting of several inclined series slots cutin the broad wall of a WR430 rectangularwaveguide, propagating the dominant mode,have theadvantageof simplicityof structure,manufacturing ease and adaptability ofconfiguration to meet different radiation pattern requirements. All slots are spaced λg/2 away

fromadjacentslotsinthesamewaveguide.TheWR430waveguidewasselectedbecauseithasthe shortest guide wavelength (λg)at theusedfrequency (2.45 GHz), which allows for theradiatingslotstobeplacedascloseaspossible.A slot cut in the broad wall of a waveguidein a transverse direction to the current linesproduces a significant perturbation to the current sheet with the result that the internalfield is coupled to space. All slots were covered with gas insulated thin Teflon foils. With a multiple slotted waveguide feeding the samecavity, the opportunity exists to distributethe microwave power so as to give a betterexcitationofmodesandabetteruniformityofheatingthancanbeachievedwithasinglefeedatahigherpowerlevel.Thepowerisfedintooneendoftheslottedwaveguideandtheotherwaveguideendisconnectedtoamovableshortcircuit (MSC) for MRC impedance matchingtotheMWinjectionsystem. The photograph of MRC under MWworking tests following theadjustmentof theslotted waveguide movable short circuit forimpedance matching is shown in Figure 2.

Figure 1. The MRC under ILU-6M scanner.


DuringMWtestseachMWISconsistedofthefollowingcomponents:a2.45GHzmagnetronof850Wmaximumoutputpower,amagnetroncontrolledpowersupply(MCPS),arectangularwaveguide launcher to fit to WR430 waveguide, aferritecirculatorandadualdirectionalcouplerfor forward and reflected power monitoring. After MSC adjustment the maximum reflected power was 5% from forward power.A betterimpedance matching can be obtained by theadditionaluse,besidethemovableshortcircuitoftheslottedwaveguides,ofathree-stubtunerintroducedbetweentheMWISoutputendandtheslottedwaveguideinputasseeninFigure2.ApolyethylenetubewithcirculatingwaterwasplacedintoMRCtoabsorbtheexcessenergywhen working with small samples or poormicrowave absorbing samples. MicrowavesaregeneratedbyMCPSas10mspulsesat50Hzrepetitionrate.TheconventionaloperationmodeofmagnetronssuppliedbyanL.C.singlephasehalf wave doubler (L.C.HWD) was properlymodified in order to permit the MW power adjustment. The main power units consistingofahighvoltagediode(HVD),ahighvoltagecapacitor (HVC) and a high voltage anodetransformer(HVAT)aresimilartotheunitsused

for the conventional magnetron energizationsystem. The difference consists in the use ofa separate transformer for the filament supply (HVFT)andofanA.C.variatoraddedtotheHVATprimarycircuit.Moredetailsaregiveninthereference[Martin,2001]. The MRC final operative configuration used insideEI-EB+MWforrubbervulcanizationisshown in Figure 3. In this configuration each MWISconsistsonlyofamagnetron,aMCPSand a rectangular waveguide launcher to fit the WR430slottedwaveguide. Therubbersampleswereobtainedfromrawrubbermixtures,ascompressedsheetsof2mminthepolyethylenefoilstominimizeoxidation.For radiation treatments the sheets were cutintoa rectangular shapewith thedimensions,0.15x0.15m2.Thetreatmentwasperformedwith layers of three sandwiched sheets usingtheILU-6Macceleratorof1.8MeVenergythatimposes the useful penetration of irradiatedmaterial.Figure4showsthephotographoftherawrubbersamplesinsideMRC. TheEBeffectsarerelatedtotheabsorbeddose(D),expressedinGrayorJkg-1andabsorbeddoserate(D*),expressedinGys-1orJkg-1s-1.TheMWeffects are related to SAR (Specific Absorption

Figure 2. The MRC under MW working tests following the adjustment of slotted waveguide movable short circuit for impedance matching.


Rate,expressedinW.kg-1)whichisequivalentto D* and SA (Specific Absorption, expressed inJ.kg-1)thatisequivalenttoD.SARvalueswereusedforMWirradiation,preventingthesamples’ final temperature during MW+EB irradiationfromrisingabove60-70ºC.TherawrubbersampleswereirradiatedbyseparateEBorcombinedEB+MWprocessingbyrepeatedlypassingMRConaconveyorundertheILU-6Mscanner. The single pass dose with conveyorunder the ILU-6Mscanner isadjustable from12.5kGyto50kGy.

MATERIALS AND SAMPLE PREPARATION

Twokindsofrubbersampleswereused: • EVA-samples, based on EVA (ethylenevinylacetate)rubber,containing61.54%EVAElvax 260,30.77%carbonblack,1.85%TAC(triallylcyanurate) polyfunctional monomerand 5.84% filler (5 phr zinc oxide, 0.5 phr stearicacid,3phrpolyetylenglycoland1phrantioxydant); •EPDM-samples,basedonEPDM(ethylene-propyleneterpolymer)rubber,containing61.54%EPDM Nordel 4760, 30.77% carbon black,1.85%TMPT(trimethylopropanetrimethacrylate)polyfunctional monomer and 5.84% filler (5 phr zincoxide,0.5phrstearicacid,3phrpolyetylenglycoland1phrantioxydant).

Platesof150mm×150mm×2mmwereobtainedinalaboratoryelectricalpressat170ºC.Theresultedplatesweresubjectedtothefollowingvulcanizationmethods: •Conventionalvulcanizationwithbenzoylperoxide (CV-BP) at 160ºC and 150 MPa byusinganelectricalhydraulicpresser; • Separate EB vulcanization (EB-V) byusingEI-EB+MWinstallation; •SimutaneousEBandMWvulcanization(EB+MW-V)byusingEI-EB+MWinstallation.The physical properties (PP) of samplesobtained by CV-BP, EV-V and EB+MW-Vmethods were evaluated by measuring thetearing strength (TeaS), residual elongation(REL) (REL is a measure of ductility ofplastics;itistheelongationofaplasticspecimenmeasured1minuteafterruptureinatensiletest)elongation at break, tensile strength (TenS),300% modulus (300%M), 100% modulus(100%M), elasticity (EL) and hardness (Har).ThesePPofsamplesweremeasuredaccordingto the international standards as follows: SRISO34-1/2000fortearingstrengthwithtestingspeed460mm/min,SRISO37/1997forresidualelongation,elongationatbreak,tensilestrength,300% modulus, 100% modulus and elasticitywith testing speed 460 mm/min and SR ISO7619/2001 for hardness. For each test wereused 5 samples. Standard errors were in therangeof4-7%.

Figure 3. The MRC final operative configu-ration used inside EI-EB+MW.

Figure 4. Photograph of the raw rubber samples inside MRC.


Figure 5. The CV-BP, EB-V and EB+MW-V effect on EVA and EPDM tearing strength.

Figure 6. The CV-BP, EB-V and EB+MW-V effect on EVA and EPDM residual elongation.

Figure 7. The CV-BP, EB-V and EB+MW-V effect on EVA and EPDM elongation at break.

Figure 8. The CV-BP, EB-V and EB+MW-V effect on EVA and EPDM tensile strength.


RESULTS AND DISCUSSIONThe experiments were performed at thefollowing radiation parameters: D = 60 kGy,SAR = 2 kW/kg and SA = 360 kJ/kg. Theresults are presented in Figures 5–12. TheseresultsdemonstratethatmajorpartofphysicalparametersofsamplesprocessedbyEB-VandEB+MW-V methods exhibited better valuesthan those obtained by CV-BP method. Twoparameters,residualelongationforEVA(Figure6) and tensile strength for EPDM (Figure 8),exhibit the most significantly improvement by

Figure 11. The CV-BP, EB-V and EB+MW-V effect on EVA and EPDM elasticity.

Figure 9. The CV-BP, EB-V and EB+MW-V effect on EVA and EPDM 300% modulus.

Figure 10. The CV-BP, EB-V and EB+MW-V effect on EVA and EPDM 100% modulus.

Figure 12. The CV-BP, EB-V and EB+MW-V effect on EVA and EPDM on EVA hardness.

EB+MW-V method compared to EB-V andCV-BP methods. The comparable values forthese parameters can be obtained by separateEBirradiationonlyby increasingEBdosebyafactorat leastof1.5.It isveryimportanttonotethat theimprovementofacertainrubberphysical parameter for a given rubber typedepends strongly on sample composition,EB absorbed dose, MW absorbed dose andespeciallyonSARlevelinthecaseofadditionaluseofMWirradiation.Thatis,foreachrubberphysical parameter improvement there is acertainrubbercomposition,acertainD,SAand


SARvaluethatisdifferentofthoserequiredforotherrubberphysicalparameters.Theserubberprocessingmodesarestillunderexperimentalstudies.

CONCLUSIONS

The general conclusion from this study isthat combined EB and MW irradiation is aviable andpromisingmethod in thematerial-processing field in view of the reduction of power consumption, the improvement of thetreatedmaterialpropertiesandofthetreatmentprocesscostreduction.Ourfutureobjectiveistocontinuethisresearchwiththestudyoftheeffectsofrubbernature,rubbercomposition,especiallypolyfunctional monomer concentration, EBabsorbed dose level, MW absorbed dose leveland MW absorbed dose rate (SAR) on therubbervulcanizationdegreesobtainedbyEB-VandEB+MW-Vmethods.REFERENCES

Makuuchi,K.,Yoshii,F.andGunewardena,J.A.(1995)“Radiation vulcanization of NR latex with lowenergy electron beams” Rad. Phys. and Chem.46(46),pp.979-982.

Holl,P.,J., (1995)“Twoidealapplicationsfor the lowenergyelectronbeamaccelerator:vulcanizationofpressure-sensitiveadhesivesandcontrolledthrough-curingof coatingsonparquet”Rad.Phys.Chem.,46(46),953-958.

Basfar,A.A.andSilverman,J.,(1995)“Improvedozoneresistance of styrene-butadiene rubber cured by acombinationofsulfurandionizingradiation”Rad.Phys.Chem.,46(46),pp.941-944.

Anelli, P., Baccaro, S., Carenza, M., and Palma, G.(1995)“Radiationgraftingofhydrophilicmonomersontoethylene-propylenerubber”Rad.Phys.Chem.,Volume46(46),pp.1031-1035.

MGM Rubber Company-Research and Development,Electron Beam Radiation Technology for Curing(2007),http://www.mgmrc.com/ebeam-trech.htm.

Jinhua,W.,Yoshii,F.andMakuuchi,K.(2001)“RadiationVulcanization of ethylene-propylene rubber with

polyfunctional monomers” Rad. Phys. and Chem.60(1-2),pp.139-142.

Yasin,T.,Ahmed,S.,Yoshii,F.,andMakuuchi,K.,(2002)“Radiationvulcanizationofacrylonitrile-butadienerubber with polufunctional monomers” React.Funct.Polum.53.,pp.173-181.

Yasin, T., Ahmed, S.,Yoshii, F., and Makuuchi, K.,(2003)“Effectofacrylonitrilecontentonphysicalpropertiesofelectronbeamirradiatedacrylonirtile-butadienerubber”React.Funct.Polym.57,pp.113-118.

Yasin,T.,Ahmed,S.,Ahmed,M.,andYoshii,F.(2005)“Effectofconcentrationofpolyfunctionalmonomerson physical properties of acrylonitrile-butadienerubberunder-electronbeamirradiation”Rad.Phys.andChem.73(3),pp.155-158.

Majumder,P.S.andBhowmick,A.K.(2000)“StructureProperty relationship of electronbeam- modified EPDM rubber” J.Appl. Polym. Sci. 77, pp. 323-337.

Vijayabaskar,V.andBhowmick,A.K.(2005)“Electronbeam modification of nitrile rubber in the presence of polyfunctional monomer” J.Appl. Polym. Sci.95,pp.435.

Hung, H. D., Ho, S. S. and Serguei, P. (2004)“Crosslinking and degradation of polypropyleneby electron beam irradiation in the presence oftrifunctional monomers” Rad. Phys. and Chem.69(3),pp.239-244.

Yunshu,X.,YibeiF.,Yoshii,F.,andMakuuchi,K.(1998)“Sensitizingeffectofpolyfunctionalmonomersonradiation crosslinking of polychloroprene” Rad.Phys.andChem.53(6),pp.669-672.

Martin, D., Ighigeanu, D., Mateescu, E., Craciun,G. and Ighigeanu, A. (2002) “Vulcanization ofrubber mixtures by simultaneous electron beamandmicrowaveirradiation”Rad.Phys.andChem.65(1),pp.63-65.

Ottner, C. (1969) “Le comportament d’elastomereset de melanges dans un champ electrique ahyperfrequence”Rev.Gen.Caoutch.Plast.,46(12),pp.1453-1454.

Meisel,N.(1971)“Vulcanisationencontinud’elastomeresextrudesenbaindeselouparhyperfrequences”Rev.Gen.Caoutch.Plast.,48,pp.397-401.

Catala, J.M.,HernandezD.S.andEliasde losReyes


(1998) “Rubber vulcanisation for the footwearindustry using microwave energy in a pressure-aidedcavity”Proc. Internat.Conf.OnMicrowaveChemistry,Prague,CzechRepublic,September6-11,p.OR30.

Hills,D.A.(1971)“HeattransferandVulcanizationofRubber”Elsevier,London.

Morton,M.(Ed.)(1987)“RubberTehnology”,3rded.,VanNostrand-Reinhold,NewYork.

Metaxas, A.C. and Meredith R. J. (1982) “IndustrialMicrowaveheating”,2nded.,Peregrinus,London.

Parodi,F.(1996)“PhysicsandChemistryofMicrowaveProcessing”, in Comprehensive Polymer Science,2ndsuppl.,Pergamon(ElsevierSci.Publ.),Oxford,UK,chapter19.

Parodi, F. (2001) “Microwave Processing of PlasicMaterials, Resins and Rubbers”, Proceedings ofthe ASSOTEC workshop “Microwave heating inIndustrial Processes” (ASSOTECV, Milan, Italy,October18,2001),p.23(inItalian).

Leprince,P.andMarec,J.(1992)“Microwaveexcitationtechnology”inPlasmaTechnology,M.CapitelliandG.BorkeEds.,PlenumPress,NewYork,pp.167-183.

Martin, D., Jianu, A. and Ighigeanu, D. (2001) “AMethodforthe2.45GHzMagnetronOutputPowerControl”IEEETransactionsonMicrowaveTheoryandTechniques49(3),pp.542-544.

Combined effects of microwaves, electron beams and polyfunctional monomers on rubber vulcanization

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