amor christina

rawmaterials

adhesionaDHesiVes&alaNts4/201118

Bio-badpolyesterpolyolsforreactivePURhotmelts

Thearchforbio-bad

SabineThüner,GabrieleBrenner,

Dr. ChristinaDiehlThedevelopmentoftailoredhy-

droxylgroup-badpolyesterpoly-

olsalreadyhadamajoreffecton

thetechnologyofone-componentmois-

ture-curinghotmeltadhesivesveral

hen,theamorphous,liq-

uid,andcrystallinecopolyesters,which

canbecombinedaccordingtoabuilding

blockconcept,haveallowedspecificfor-

mulationsofreactivePURhotmelts

(RHM)formanyapplicationsintheadhe-

analy-

sisconfirmrapidandsignificantgrowth

inthepast:globaldemandforpolyester

polyolsgrewbyanaverageof5.4%peran-

numbetween2005and2008/1/.

Theone-componentPURhotmelts

badonpolyesterpolyolsareveryre-

sistanttohightemperatures,havehigh

finalstrengths,lowprocessingtempera-

tures,andabroadadhesionspectrumon

ghini-

tialstrengthsalsoenablerapidfurther

processing-theadvantagesareobvious:

shortcycletimestranslateintoenergyef-

ficiencyandhighlevelsofproductivity.

Greenpolicyshift

Whileinthepastconventionalpolyester

polyolswerealmostallbadonpetro-

chemicalmonomerbuildingblocks(Fig-

ure1),forveralyearstheR&Ddepart-

mentsofthepolymerdesignershave

beenfacingnewchallenges.

Demandfortheincreaduofre-

newablerawmaterialsinthechemical

industryhasincreadconstantlysince

theadoptionoftheKyotoProtocolin1997

andnowextendswellbeyondsimplyde-

irechemical

industryhasbeenundergoingagreen

policyshiftformanyyearsandiscontin-

uouslystrengtheningitsprofitablesus-

ceefficiencyis

regardedasoneofthegrowthdriversof

confirmed,forexam-

ple,inananalysiscarriedoutbymanage-

mentconsultantFrost&Sullivan/2/in

2008,accordingtowhichsalesintheglo-

balmarketforchemicalsfromrenewable

rawmaterialswillgrowby28%between

2007and2015(Figure2).

Renewablerawmaterialsaredefined

asagriculturalandforestryproducts

thatareudbyhumanstogenerate

heat,electricityorfuel,ortomanufac-

dtopet-

rochemicalsubstances,renewableraw

materialsarenotfiniteandthushelpto

providesustainableresources.

Identifyingbio-badmonomers

Thechallengesofmaterialubeginwith

ro-

chemical-badaromaticandaliphaticdi-

esters,dicarboxylicacids,anddiolsudto

producepolyesterpolyolsaregenerallynot

-

quently,theycannotsimplybereplaced,

whichmeansthatinnovative,bio-bad

Figure1:Conventionalpolyesterpolyolscomparedtobio-badones

adhesionaDHesiVes&alaNts4/201119

rawmaterials

monomershavetobeidentifiedandtested

accordingtotheirsuitabilityforpolyester

nfocusoftherearch

isthebasicsuitabilityofbio-baddicarbo-

xylicacidsordiols,forexample,fromsor-

ghum,corn,orcastoroil:istheresufficient

reactivityinthepolycondensationreaction

andaretheyincorporatedinthepolyester?

Dotheyhavesufficientstabilityunderthe

harshreactionconditionsofmeltpolym-

erizationsothatdecompositionorother

condaryreactionscanbeexcluded?

Iftheelementaryrequirementsare

fulfilled,basicallymanynovelmono-

mersaresuitable,which,insomecas

arenotevenaccessibleviapetrochemi-

uldenableaccesstoinnova-

tivepolyestersfortheformulationof

example,long-chainlinearmonomers

thatcouldberecoveredfromfatsand

oilsarerecommendedforsynthesizing

high-crystallinepolyesterswithin-

creadinitialstrength.

Twoobjectivesshouldbepursuedinthe

developmentofbio-badpolyesterpolyols:

●Theactionspectrumoftheadhesive

formulatorsmustnotberestricted;in

otherwords,adivercombinationof

amorphous,liquid,andcrystalline

polyestersbadonthebuilding

blockconceptmustalsobepossible

withthebio-badtypes.

●Ahighshareofbio-badmonomers

inthepolyesterisdesirable;themin-

imumcontentshouldbe30%by

weight.

Whenthepolyesterhasbeendeveloped

onthebasisofbio-badmonomers,v-

alsofulfilltherequirementsprofilethat

isneededforreactivePURhotmelts?In

otherwords,doesthepolyesterhavethe

desirednecessaryphysicalproperties,

especiallyregardingmeltingpointand

glasstransitiontemperature?The

propertiescanbetspecificallyby-

lectingtherightmonomersandalso

throughtherelativecompositionofthe

icular,viscosity,melt-

ingpointandglasstransitiontempera-

tureesntiallydeterminetheproperty

profileoftheformulatedPURhotmelts.

Bio-polyester:statusquo

Thefirstbio-badpolyesterpolyolsthat

fulfilltherequirementshavebeende-

velopedandmarketedunderthebrand

Figure2:marketanalysis„Chemicalsfromrenewablerawmaterials2007–FC2015

Figure4:Propertiesofreactivehotmeltsbadonbio-badpolyesterpolyols

Figure3:Characteristicsofbio-badpolyestertypes

rawmaterials

adhesionaDHesiVes&alaNts4/201120

veformula-

torscancurrentlybeprovidedwithsix

differentbio-polyesters-twoamor-

phous,twoliquid,andtwocrystalline

evesufficientcross-link

densityand,atthesametime,good,

manageableviscosities,anOHvalueof

3containsan

overviewofthepropertiesofthebio-

badpolyestertypes.

Inmodelexperimentsthepolyester

polyolswerecombinedwitheachother

intermsofabuildingblocksystemin

manydifferentmixingratiosandthe

physicalandadhesivepropertiesofthe

-

ingonthelectionandthemixingratio

ofamorphous,liquid,orcrystalline

typesthepropertiesofthereactivehot

melts(RHMs)canbetailoredusing

knownmethods.

RHMformulationswithbio-

polyesters

Ananalysisoftheimportantproperties

ofhotmelts,suchasviscosity,opentime,

ttingbehavior,initialstrength,andco-

hesionprovidethefirstinformationin

thedevelopmentofguideformulations.

Themanufactureofmoisture-curinghot

meltadhesivesinthemeltisdonebycon-

vertingthepolyolsandmixturesofthem

withpure4,4’-diphenylmethanediisocy-

anate(MDI)inanOH/NCOratioof1/2.2.

Todeterminetheopentime,paper

stripsareappliedtotheadhesivefilm

atdefinedintervalsandarethenpulled

offagainassoonasthesurfaceistack-

ntimeisthepointintime

whenthelastremovedpaperstripex-

ttingtimethe

pointintimewhentwoT-shapedbond-

ed2-cmwidebeechwoodsubstrates

canbeloadedwitha500-gweightis

determined.

Initially,thepropertiesofreactive

hotmeltsweredeterminedonthebasis

Figure4shows,theamorphouspolyes-

tershaveshorteropentimesandtting

times,whiletheliquidtypesallowfor-

mulationofhighlyflexibleadhesives.

Thecrystallineproductscontrolthet-

tingbehaviorandincreacohesionof

theadhesive.

InotherexperimentstheRHMprop-

ertiesofbinaryandternarypolyolmix-

turesoflectedpolyestertypeswere

nRHM1,whichis

badonpolyesterK1,theadditionof

theliquidpolyesterF1prolongsthe

opentimeandthettingtimeofreac-

therhand,

theRHMformulations3and4,badon

ternarymixturesofA2,F1,andK1,ex-

hibitlongopentimesandarelatively

eadditionof

anamorphoustypetherelativelylong

opentimeremainsbutthettingtime

tenthettingtime

evenmoreandtoincreatheinitial

strengthforapplicationssuchasprofile

wrappingthehighercrystallinepolyes-

terK2(formulationsRHM5andRHM6)

issuitable(Figure5).

Adhesionrequirements

Apartfromthephysicalpropertiesofa

formulation,naturallytheadhesive

mustalsofulfilladhesionrequirements.

TernarymixtureRHM3exhibitedespe-

ciallygoodadhesionpropertiesonmany

differentsubstratesafterbeingcured

for7daysat20°Cand65%relativehu-

midity(Figure6).

Theversatilityoftheadhesionspec-

trumisveryimportant,sincereactive

hotmeltsprocesdwithstandard

equipment(suchasrollerapplication

systems)areudinjoiningtechniques

he

focusinthewoodworkingindustryison

edgebanding,profilewrapping,andflat

lamination,intheautomotiveindustry

hotmeltadhesivesareudmainlyin

carinteriorstoadheremanydifferent

reasofapplication

forreactivePURhotmeltsarebook

spines,sandwichbondinginthecon-

structionindustry(Figure7)andbond-

inginthetextileindustry,suchas

breathablemembranes.

Figure5:CharacteristicsofconversionproductswithmDi

adhesionaDHesiVes&alaNts4/201121

rawmaterials

Shorterttingtimeforflat

lamination

Withconsiderationofusingbio-bad

polyesterpolyolsinreactivePURhot

melts,theRHM3formulationproduced

especiallypositiveresultsintheflatlam-

inationofwoodenmaterials(Figure8).

Inmanycas,reactivehotmeltad-

hesivesformulatedexclusivelywith

conventionalpolyesterpolyolsdonot

fulfilltherequirementsprofileforflat

laminationasregardsverylongopen

timestoensuresufficientlylonghan-

dlingtimesincombinationwithagood

initialstrengthandrelativelyshortt-

uitablecombination

oftheinnovativebio-polyestersitisnow

possibletoformulatereactivehotmelts

withthedesiredimprovedproperties.

Theideaof“greenchemistry”is-

peciallyobviousinthelaminationof

woodensurfaces,sinceecologicalsus-

tainabilitytakesplaceintheformofa

three-levelcascade:

nergy-efficientreactivehot

melt(RHM)

atingtheRHMonthebasisof

bio-badpolyesterpolyols

gontherenewablematerial,

wood.

Otherapplicationsarefollowing:first

decorativematerialsbadonrenewa-

blerawmaterialsareavailablewithin

theautomotiveindustry.

Outlook

Apartfromthemanydifferentactivities

fromrearchersanddevelopersinthe

industry,veralinstitutesarealso

workingintensivelyinthefieldof

“chemistryfromrenewablerawmateri-

als”.Inclocollaborationbetween

companiesandinstitutes,rearchis

beingcarriedoutintonewsolutionsfor

thesustainableuofresources.

Inspiteofthefirstsuccesswith

bio-badpolyesterstoformulatere-

activePUhotmelts,development

workinthisfieldisstillinitsinfancy.

Continuousmonitoringofthemarket

withthefocusonnew,commercially

availablerawmaterialsisarequire-

mentforcompleterawmaterial

screeningtodiscoverbio-badmono-

fromthesustainablereplacementof

petrochemicalmonomersanotherfo-

cusisontheuofnovelmonomers

whichareonlyavailablefromrenew-

wayitwillbe

possibletosynthesizepolyesterpoly-

olsthatarenotonlybio-badbut

thatalsohaveimprovedpropertypro-

willenablenewfieldsofapplication

tobeopenedup.¢

Figure6:

adhesion

properties

Figure7:sandwichBonding

andflatlamination/3/

Figure8:ttingbehaviorof

reactivehotmeltswithlongopen

time

SabineThüner(r@evonik.

com)isMarketingManagerHotMeltsat

EvonikIndustriesAGinMarl,Germany.

GabrieleBrenner(r@evonik.

com)managesAppliedTechnologyReac-

tiveHotMelts,inaDiehl

(@)managesIn-

novationManagementAdhesivePolyesters.

/1/2009,ChemicalEconomicsHand-

book-SRIConsulting:PolyesterPolyols,p.6

/2/2008,Frost&Sullivan:Strategic

AnalysisoftheWorldwideMarketfor

BiorenewableChemicals,p.4-9/4-10

/3/Evonikinternal

Theauthors

References