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Influence of lanthanum stearate

PolymerDegradationandStability94(2009)845–850

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PolymerDegradationandStability

journalhomepage:http://www.wenkuxiazai.com

Influence of lanthanum stearate

/locate/polydegstab

In?uenceoflanthanumstearateasaco-stabilizeronstabilizationef?ciencyofcalcium/zincstabilizerstopolyvinylchloride

LongFang,YihuSong,XiaonanZhu,QiangZheng*

DepartmentofPolymerScienceandEngineering,ZhejiangUniversity,KeyLaboratoryofMacromolecularSynthesisandFunctionalizationofMinistryofEducation,ZhedaRoad,Hangzhou310027,China

articleinfo

Articlehistory:

Received13November2008Receivedinrevisedform15January2009

Accepted19January2009

Availableonline7February2009Keywords:

Polyvinylchloride(PVC)Calcium/zincstabilizersLanthanumstearateCo-stabilizer

abstract

In?uenceoflanthanumstearate(LaSt3)asaco-stabilizeronstabilizationef?ciencyofcalciumstearate(Ca)/zincglutarate(Zn)stabilizerstopolyvinylchloride(PVC)at180??Cinairwasinvestigated.TheresultsshowedthatcombinationofLaSt3withCa/Znstabilizerspresentedanobviousimprovementofstabilizationef?ciencytoPVCcomparedwiththeCa/Znstabilizers.Moreover,additionofLaSt3totheCa/Znstabilizerscouldsigni?cantlyenhancestaticstabilitytimeofPVC.Incorporationof2phrLaSt3co-stabilizertoPVCcontaining3phrCa/Znstabilizersresultedinmarkedincreaseofonsetdegradationtemperatureandreductionsinaveragedegradationrateaswellasthedynamicstoragemodulus(G0)andlossmodulus(G00)at180??C.In?uenceofCa/ZnratioontensilestrengthofPVCintheabsenceorinthepresenceofLaSt3wasdiscussedindetail.AtlowCa/ZnratiosLaSt3hadanobviousimprovementinthetensilestrength,whileathighCa/Znratiosthiseffectbecameinconspicuous.

Ó2009PublishedbyElsevierLtd.

1.Introduction

Itiswellknownthatlowthermalstabilityofpolyvinylchloride(PVC)isamaindrawbackorlimitationforitsapplication.Properstabilizersmustbeincorporatedinordertorestrainthedegrada-tionofPVCduringthermalprocessing.Ingeneral,thestabilizersareclassi?edasleadsalts[1],organictin[2],soapsalts[3]andrareearthstabilizers[4].Stabilizersplaytheroleinstabilitymainlythroughabsorptionofhydrochloricacid(HCl)releasedfrompartialPVCdecompositionorsubstitutionoflabilesitesofpartiallydecomposedPVCmacromolecules[5].Applicationofleadsaltsandorganictinstabilizersarelimitedduetotheirtoxicity,eventheyhavehighef?ciencytostabilizePVC.Ontheotherhand,rareearthstabilizerandCa/Znstabilizersarerestrainedbecauseoftheirlowef?ciency.Exceptforexploringnewkindsofstabilizerssuchas(natural)polyols[6],saturatedpolyesters[7],esterthiols[8,9],andintercalatedhydrotalcite-likematerials[10],anovelnontoxiccomplexstabilizerswithhighef?ciencyhasattractedresearchers’interestforPVCprocessing.

Ca/Znstabilizershavesynergisticeffectandpresentfavorablestabilization[11–15].However,Ca/Znstabilizershavesomedisad-vantagesinlong-termstabilityduetotheirmarked‘‘zincburning’’effect.Hence,extrasubstancemustbeaddedsoastoimprovethe

*Correspondingauthor.Tel./fax:þ8657187952522.E-mailaddress:zhengqiang@http://www.wenkuxiazai.com(Q.

Influence of lanthanum stearate

Zheng).

0141-3910/$–seefrontmatterÓ2009PublishedbyElsevierLtd.doi:10.1016/j.polymdegradstab.2009.01.024

ef?ciencyofstabilization.Co-stabilizationofsomeadditiveswithCa/Znstabilizerssuchaspentaerythritolandorganotin[16],epoxidizedsun?oweroil[17],b-diketone[18],polyols[19],hydrotalcites[20],zeolites[21]andinorganicphosphates[22]hasbeenreported.However,nosatisfactorystabilizationexistsintheaboveauxiliarystabilizerssothattheef?ciencyofthecomplexstabilizersisnotsohigh.

Rareearthstabilizerhasexcellentlong-termstabilizationeffectandrareearthcompounds,suchastris(mono-i-octylphthalate)[23],stearates[24],citrates[25]andmalates[25]havebeenusedasPVCthermalstabilizersrecently.Theheat-stabilitytimeofPVCcontaining3phr(perhundredresin)lanthanumtris(mono-i-octylphthalate)isabout40minat190??C,beinglongerthanthatofCa/Zncomplexandcomparablewiththatofdibutyltindilaurate[23].Moreover,rareearthstearatesshowhigherstabilizingef?-ciencytorigidPVCascharacterizedbylongerincubationperiodandlowerrateofdehydrochlorinationascomparedwiththeindustrialthermalstabilizerscalciumstearate,zincstearate,butylstannummercaptide,phosphiteesters,b-diketoneandepoxidizedsun?oweroil[24].Ontheotherhand,rareearthcitratesexhibitstabilizationeffectsuperiortobasicleadsaltstabilizerswhilethestabilizationeffectofrareearthmalatesiscomparabletoorganictincompounds[25].Theextrastabilizationabilityofrareearthstabilizersmaybeattributedtotheirabilitytochangetheconfor-mationofPVC[26]andtorestraindehydrochlorination[27]soastobatethechainreactionandexchangethelabilefunctionalgroupsinthePVCbackbonechainsforothermorestablesubstitutesderived

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