Waterborne vegetable oil epoxy coatings

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ProgressinOrganicCoatings

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Waterbornevegetableoilepoxycoatings:Preparationandcharacterization

MohammadYaseenShah,SharifAhmad∗

MaterialsResearchLab.,DepartmentofChemistry,JamiaMilliaIslamia,NewDelhi110025,India

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abstract

Articlehistory:

Received15January2012

Receivedinrevisedform27April2012Accepted3May2012

Available online 2 June 2012

Keywords:WaterborneVegetableoilCoatings

Theutilizationofrenewableresourcessuchasvegetableoils[VO]forthedevelopmentofenvironmentfriendlywaterborne[WB]materialsisencouragedworldwide.ThepreparationofWBmaterialsfromVOisachallengingtaskduetotheirhydrophobicnature.ThepresentworkdescribesthesynthesisofWBepoxyfromVO[WBOE].WBOEwascharacterizedforitsstructuralandphysico-chemicalattributes.Thecuredmaterialwassubjectedtophysico-mechanical,chemicalresistancetests,andthermalanalyses.ThecoatingsofWBOEshowedgoodphysico-mechanical,chemicalresistanceaswellasthermalstabilityandmayfindapplicationaseco-friendlyWBcoatingswithsafeusageupto220◦C.

© 2012 Elsevier B.V. All rights reserved.

1.Introduction

Environmentalconcerns,limitedfossilresourcesandeco-nomiccompetitivenesshavemotivatedacademicandindustrialresearcherstowardstheenhanceduseofrenewablefeedstockfortheproductionofenvironmentfriendlymaterials.Inthiscon-text,theutilizationofrenewableresourcessuchasvegetableoils[VO]isanecessarysteptowardssustainabledevelopment.VOsuchasLinseed,Soybean,Castor,CashewnutShellLiquid,Tung,Fish,Nahar,Rubberseedoilsarebeingusedforthepreparationofalkyds[1],epoxies[2–4],polyols[5,6]andpolyurethanes[7–11].VOderivativesasvalueaddedpolymers/monomersfindenhancedapplicationsasenvironmentfriendlywithlowVOC,solventless,highsolids,hyperbranchedorwaterborne[WB]coatingmateri-alsthatofferimprovedperformanceandreduction/eliminationintheuseofvolatileorganicsolventsincoatingsproducedthere-from.Thedevelopmentofwaterborne[WB]materialsfromVOisthemostchallengingtaskduethehydrophobicnatureofVOchains.VObasedWBcoatingmaterialsaregenerallynon-toxic,non-flammable,odorlessandeco-friendly.Besidesthese,abundantavailabilityofwaterassolventandrenewablenatureofVOareadditionaladvantages[12].Theapproachoffersasignificantoppor-tunitytoreducethedependencyonpetroleumbasedrawmaterialsincludingsolvents,andprovidessustainableandgreensolutionstothecoatingsindustry.Aigbodionetal.reportedtheprepara-tionofWBcoatingsfrommaleinatedandfumarisedRubberseedoil[13,14].Polyurethanedispersions[PUD]fromFishandLinseedoilhaveshowngoodcoatingpropertiesasreportedbyNimbalkarand

Athawale.FishoilPUDexhibitedgoodimpactresistance,adhesionandflexibility[15].SoybeanalkydemulsionsmodifiedwithTungoilpreparedbyWangetal.haveshowngoodhydrolyticstabilityandfilmgloss[16].SeveralotherworkershavealsopreparedVOderivedWBalkyds[12,13],PUD[11,17]andWBoil-acrylates[18].EpoxieshavebeenpreparedfromLinseed,Rapeseed,Olive,Corn,andSunfloweroils.However,limitedattentionhasbeenpaidtothesynthesisandcharacterizationofWBepoxiesfromVO[2].Inthisarticle,wedescribethepreparationofWBepoxy[WBOE]fromLinseedoil[LSO].WBOEwascharacterizedforitsstructureandphysico-chemicalproperties.WBOEwasthenreactedwithphthalicanhydride[PA]andtheirreactionproduct[WBOE-PA]wasfinallycuredwithWBphenol–formaldehyde[PF]toobtainWBcoatings[WBOE–PA–PF].Physico-mechanical,chemicalresistanceandther-malbehaviourofthecoatingswerealsoinvestigated.

2.Experimental

2.1.Materials

LSOwaspurchasedfromPioneer(Delhi,India),glacialaceticacid,hydrogenperoxide(30%),sulphuricacid,diethanolamine[DEA],phenol,formaldehyde(37%),phthalicanhydride[PA],ethanolanddiethyletherwereobtainedfromMerck(India),orthophosphoricacidandtriethylamine[TEA]weresuppliedbyS.D.FineChem.Ltd.(Mumbai,India).

2.2.PreparationofLSOepoxy(LSOE)andwatersolublephenol–formaldehyde(PF)

∗Correspondingauthor.Tel.:+919891290510.

E-mailaddresses:muntaziryaseen@gmail.com(M.Y.Shah),sharifahmadjmi@yahoo.co.in(S.Ahmad).

LSOE[19]andwatersolublephenol–formaldehyde(PF)[20]werepreparedbymethodsreportedelsewhere.

0300-9440/$–seefrontmatter© 2012 Elsevier B.V. All rights reserved.http://dx.doi.org/10.1016/j.porgcoat.2012.05.001

M.Y.Shah,S.Ahmad/ProgressinOrganicCoatings75 (2012) 248–252

249

Table1

PhysicochemicalanalysesofLSO,LSOEandWBOE.

Characteristics

LSO

LSOE

WBOEEpoxyequivalent–241480.6Hydroxylvalue(%)–

11.7617.87Refractiveindex1.4781.4821.489Specificgravity

0.959

1.0469

1.300

2.3.PreparationofWBoilepoxyfromLSOE(WBOE)

LSOE(0.1mole)wastakeninathree-neckedroundbottomflaskfittedwiththermometerandmagneticstirrer.DEA(0.1mole)wasaddeddropwiseintothereactionflaskwithcontinuousstirringat50◦Cfor10–15minandthetemperaturewasraisedgraduallyto80◦C.Nosolventwasusedduringthereaction.Theprogressofthereactionwasmonitoredbyepoxyequivalent[EE]andthinlayerchromatography[TLC].OnachievingthedesiredEE,thereactionwasterminated.Thefinalproduct(WBOE)wasfoundtobehighlyviscous,reddishbrownincolorandsolubleinasolventblendofwater:ethanol[50v:50v].

2.4.PreparationofWBOE-PA

Asolventblendofwater:ethanol[50v:50v]wasaddedtothereactionflaskcontainingWBOE.PAwasaddedtothissolutioninthepresenceof1–2dropsoforthophosphoricacidandthetemperaturewasraisedto150±5◦Cundervigorousstirring.Theprogressofthereactionwasmonitoredbythedeterminationofacidvalue(AV)atregularintervalsoftime.ThereactionwasstoppedafterachievingthedesiredAV;finallyyellowishbrownWBOE-PAwasobtained.

2.5.Characterization

FTIRspectraweretakenonSHIMAZDUspectrometermodelIRAFFINITY-1,FTIR-8400SusinganNaClcell.PhysicochemicalpropertieslikeAV(ASTMD5555-61),EE(ASTMD1652),hydroxylvalue[HV](ASTMD1957-86),specificgravity[SG](ASTMD792)andrefractiveindex[RI](ASTMD1747),giveninTable1,weredeterminedbystandardASTMMethods.Thermo-gravimetricanal-ysis(TGA)wasperformedonEXSTARTG/DTA6000from40◦Cto700◦Cinnitrogenatmosphereat20◦C/minheatingrate.Solubilityofthematerialwasassessedasprovidedinproceedingsections.

Forthepreparationandtestingofcoatings,WBOE-PAandPFweremixedinabeakerindifferentratios.Therecipesofthreedif-ferentratiosofcoatingmaterialsthatwerepreparedfromWBOE,PAandPFaregiveninTable2.WBOE–PA–PF-1,WBOE–PA–PF-2andWBOE–PA–PF-3,insolventblendofwater:ethanol(50v/50v)using40wt%solidcontent,wereappliedbybrush,oncommer-ciallyavailablemildsteel[MS]stripsof20mm×10mm×1mmsizeforchemicalresistanceand70mm×25mm×1mmsizeforphysico-mechanicalproperties.CoatingsofWBOE–PA–PF-1,WBOE–PA–PF-2andWBOE–PA–PF-3becamedrytotouchwithin10–15minbystovingat90◦C,inanoven.Afteradditional30minatroomtemperature,thecoatingsbecamedrytohard.Physico-mechanicalpropertiessuchasscratchhardness(BS3900),impactresistance(IS:101part5/sec3,1988),andbendtest(ASTMD3281-84)ofcoatingswereevaluated.Glosswasmeasuredat45◦byGlossmeterModelRSPT20(DigitalInstruments,SantaBarbara).

Table2

Formulationofthreedifferentratiosofcoatingmaterial.

Sample

WBOE(g)

PA(g)

PF(g)

WBOE–PA–PF-160.54WBOE–PA–PF-250.55WBOE–PA–PF-3

4

0.5

6

Thethicknessesofthesecoatings,determinedbyElcometer(Model345ElcometerInstrument,Manchester,UK),werefoundtobeinbetween100and110␮m.Chemical/corrosionresistancetestswereperformedinacid(3.5wt%HCl),alkali(3.5wt%NaOH),andtapwaterbyplacingthemin3-in.diameterporcelaindishesintheaforementionedmedia.Corrosiontestswerealsocarriedoutin3.5%NaClinsidesaltmistchamber.Periodicexaminationofthesesampleswasconducteduntilthecoatingsshowedvisualevidenceoflossingloss,deterioration,discolorationorweightloss.

3.Resultsanddiscussion

Fig.1explainsthepreparationofLSOE,WBOE,WBOE–PAandWBOE–PA–PFfromLSO.LSOEispreparedbyepoxidationandhydrationreactiontakingplaceatunsaturationonVOvia(insitu)epoxidationbyperacid[21,22].LSOEhassomehydroxylsinsertedonitsbackboneduetooxiraneringopeningbywateroracid(Table1)[21–23].TheoxiraneringsandhydroxylspresentinLSOEbackboneserveascrosslinkingsitesduringchemicalreactions.ThesefunctionalgroupsinLSOEreactwithDEA,formingWBOE.TheamideaswellashydroxylgroupsintroducesufficientpolarityinWBOE,assistinginitssolubilityinwater:ethanolblend[50v:50v].

3.1.Spectralanalysis

TheformationofLSOEfromLSOwasconfirmedbyspectralanal-ysisasalsoreportedpreviously[21,22].

FTIRspectrumofWBOE[Fig.2A(b)]showedreductioninintensityofabsorptionbandsat822cm−1(COCoxiranestr)andformationofbandsat1051cm−1(COCetherstr)relativetoLSOE[Fig.2A(a)][20,21]duetotheconsumptionofoxiraneringsbyreactionwithDEA(Fig.2A).ThepresenceofcharacteristicabsorptionbandsforoxiraneringinWBOEconfirmsthatsomeoxi-raneringsmoreorlessremainintactinWBOE,whichmayfurtherserveascrosslinkingsitesduringreactionwithPA.InWBOE-PA,disappearanceofbandsat822cm−1(COCoxiranestr)anddecreaseinintensityofbandat3400–3300cm−1areobservedduetochemicalreactionofresidualoxiraneringsand–OHgroupsofWBOEwithanhydrideringofPA.1HNMRspectraofLSOE[21]andWBOE[Fig.2(B)]alsorevealthepresenceofcharacteristicabsorptionbands.

3.2.Physicochemicalanalysis

Besidesspectralanalysis,theformationofWBOEfromLSOEisalsosupportedbyincreaseinthevaluesofEE,SG,RIandHV(Table1).TheincreaseinEEandHVinWBOErelativetoLSOEindicatestheformationofhydroxylgroupsbytheconsumptionofoxiraneringsofLSOE.

3.3.SolubilityofLSO,LSOE,WBOE,WBOE-PAandWBOE–PA–PFinwater:ethanolblend[50v:50v]

ThesolubilityofLSO,LSOE,WBOE,WBOE-PAandWBOE–PA–PFwasassessedin50v/50vwater:ethanolblend.Fig.3showshowthesolubilitytrendisimprovingstepwisefromLSOtoformVObasedWBmaterialwhichmayfindapplicationincoatings.LSObeingimmisciblewiththeblendclearlyformsaseparateupperlayer.LSOEisalsoinsolubleandduetoitshigherSGrelativetoLSO,itsettlesatthebottomthusformingthelowerlayer.However,WBOEandWBOE-PAwhendissolvedintheblendformedclearandtrans-parentsolutionsevenatroomtemperature(28–30◦C).ItcanbecomprehendedthatthepresenceofamideandhydroxylgroupsinWBOEfacilitatesitssolubilityinwater:ethanolblend[50:50(v/v)].

250M.Y.Shah,S.Ahmad/ProgressinOrganicCoatings75 (2012) 248–252

Fig.1.PreparationofwaterbornecoatingmaterialfromLSO.

3.4.Physico-mechanicalstudies

Itwasobservedthatcoatingsloadedwith<40wt%ofPFfailedtodry(attemperature90◦C)possiblyduetoincompletecuringoftheWBOE-PAwhilethecompositionswith>60wt%werefoundtobebrittle,duetoexcessivecrosslinkingbetweenWBOE-PAandPF.Hence40–60wt%ofPFwasconsideredastheoptimumcom-positiontoprepareWBOE–PA–PFcoatingswhichwereobtainedashard,transparentandglossycoatings,bycuringat90◦C(Fig.4).

Table3showsphysico-mechanicalpropertiesofdifferentratiosofcuredWBOE–PA–PFcoatings.AdecreaseinscratchhardnessvaluewasfoundfromWBOE–PA–PF-1toWBOE–PA–PF-3.Thecoatingswerefoundtopasstheimpactstrengthaswellasbendtestonloadingofupto50wt%PFwhichmaybeduetooptimumcontentofpolargroupsleadingtohardness,adhesionandflexibil-itytocoatings.AthigherPFamount,theperformancedeteriorates,attributedtobrittlenessofcoatings.Thusthecoatingscuredwith40–50wt%PFcanservegoodpurpose.

remainedcompletelyunaffected(nolossinweight,glossoradhe-sion)in3.5wt%NaCl(saltmistchamber)foraperiodof30daysandafterthisperiodcoatingsofWBOE–PA–PF-1andWBOE–PA–PF-2startedshowingsignsofcorrosionatedgesalongwithweightloss,duetopenetrationofcorrosivemediaintothecoatings.However,thecoatingsofWBOE–PA–PF-3beingwell-adherent(thepres-enceofpendantpolargroupsprovidesadhesionattheinterfaceofcoatingandmetalsurface)remainedunaffectednotallowingthecorrosivemediatopenetratethroughthem.

ThecoatingsofWBOE–PA–PF-1showedslightlossinglosswhilethoseofWBOE–PA–PF-2andWBOE–PA–PF-3remainedunaffectedintapwaterand3.5wt%HClfor25and20days,respectively.

WBOE–PA–PF-1coatingsshowedslightlossinglossafter8h,startedtodetachafter10handfilmswerecompletelyremovedfromthesubstrateafter24hin3.5wt%NaOH.CoatingsofWBOE-PA-PF-2showedslightlossinglossafter10handlostadhesionafter30h.However,coatingsofWBOE-PA-PF-3remainedunaffectedfor24h.Slightlossinglossbecameevidentandthecoatingsdetachedfromsubstratecompletelyafter70h.

3.5.Chemical/corrosionresistance

3.6.Thermalanalysis

Tostudytheircorrosionresistancebehaviour,suchaschangesintheirweight,adhesionandoverallappearance,coatedpanelsweresubjectedtoexposureinvariouschemicalmedialiketapwater,NaCl,HClandNaOH.Itwasobservedthatthecoatedpanels

TGAthermograms(Fig.5)ofWBOE–PA–PFshowedsimilardegradationcurvesaccreditedtotheirsimilarstructure.However,theyexhibiteddifferenttemperaturesofdegradationattributed

Table3

Physico-mechanicalanalysesofWBOE–PA–PF-1,WBOE–PA–PF-2andWBOE–PA–PF-3.

Characteristics

Scratchhardness(kg)

Impactresistance(150lb/in.)Bendtest1/8inchGlossat45◦

WBOE–PA–PF-1

WBOE–PA–PF-2

WBOE–PA–PF-33.5FailFail52

4.5PassPass58

4PassPass56

M.Y.Shah,S.Ahmad/ProgressinOrganicCoatings75 (2012) 248–252

251

Fig.2.(A)FTIRspectraofLSOE(a)andWBOE(b).(B)1HNMRspectraofWBOE.

Fig.3.Photographshowingsolubilityof(1)LSO,(2)LSOE,(3)WBOE,(4)WBOE-PAand(5)WBOE–PA–PFin50v:50vwater:ethanolblend.

Fig.4.Photographofcoatings.

Fig.5.TGAthermogramsofWBOE–PA–PF-1,WBOE–PA–PF-2andWBOE–PA–PF-3.

252M.Y.Shah,S.Ahmad/ProgressinOrganicCoatings75 (2012) 248–252

tothedifferenceintheratioofWBOE-PAandPF.3–5wt%losswasobservedbelow230◦Cattributedtothetrappedwaterorwatercondensedduetoreactionbetweenresidualhydroxylandcarboxylicgroups.Beyond230◦Cthefirstdegradationcontinuedupto440◦Cincurring40wt%loss.10wt%losswasobservedat257–268◦C,50wt%losswasnoticedat450◦C,478◦Cand570◦C,inWBOE–PA–PF-1,WBOE–PA–PF-2andWBOE–PA–PF-3,respec-tively.Thehighestdegradationtemperaturesofthethreeratiosrangedfrom450◦Cto460◦C.Thusthesecoatingscanbeusedsafelyupto220◦C.

4.Conclusion

VObasedWBepoxywaspreparedthroughsimpleonesteproute.Nocomplexderivatizationsteps,modifiersortoxicvolatileorganicsolventswereusedatanystepeitherduringsynthesisorcoatingformulation.WBOEcanactasaneco-friendlymate-rialforthepreparationofrenewableresourcebasedpolymericcoatings.WBOE–PA–PFshowedgoodscratchhardness,impactresistance,flexibilityandthermalstabilityofthecoatings.Thecoatingsremainedintactinaqueous,acidicandsaltmediawhichshowedtheirhighadherencetothesubstrate.However,thesesys-temscouldnotexhibitgoodalkaliresistanceperformancewhichcanpresumablybeattributedtoVOesterandetherlinkages.Theselinkagesaremostsusceptibletoattackbyalkali.Thus,whatstillremainunsoughtareverygoodalkaliresistanceofcoatingsand100%solubilityofthecoatingmaterialinwater.

Acknowledgement

MohammadYaseenShahacknowledgestheUniversityGrantsCommission,Indiafortheawardofthenon-netfellowshipduringtheresearchwork.

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