Liquid Detergents (Surfactant Science Series)

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LiquidDetergents

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SURFACTANTSCIENCESERIES CONSULTINGEDITORS MARTINJ.SCHICK Consultant FREDERICKM.FOWKES (19151990) NewYork,NewYork 1.NonionicSurfactants,editedbyMartinJ.Schick(seealsoVolumes19, 23,and60) 2.SolventPropertiesofSurfactantSolutions,editedbyKozoShinoda(see Volume55) 3.SurfactantBiodegradation,R.D.Swisher(seeVolume18) 4.CationicSurfactants,editedbyEricJungermann(seealsoVolumes34, 37,and53) 5.Detergency:TheoryandTestMethods(inthreeparts),editedbyW.G. CutlerandR.C.Davis(seealsoVolume20) 6.EmulsionsandEmulsionTechnology(inthreeparts),editedbyKennethJ. Lissant 7.AnionicSurfactants(intwoparts),editedbyWarnerM.Linfield(see Volume56) 8.AnionicSurfactants:ChemicalAnalysis,editedbyJohnCross(outofprint) 9.StabilizationofColloidalDispersionsbyPolymerAdsorption,TatsuoSato andRichardRuch(outofprint) 10.AnionicSurfactants:Biochemistry,Toxicology,Dermatology,editedby ChristianGloxhuber(seeVolume43) 11.AnionicSurfactants:PhysicalChemistryofSurfactantAction,editedbyE. H.LucassenReynders(outofprint) 12.AmphotericSurfactants,editedbyB.R.BluesteinandCliffordL.Hilton (seeVolume59) 13.Demulsification:IndustrialApplications,KennethJ.Lissant(outofprint) 14.SurfactantsinTextileProcessing,ArvedDatyner 15.ElectricalPhenomenaatInterfaces:Fundamentals,Measurements,and Applications,editedbyAyaoKitaharaandAkiraWatanabe 16.SurfactantsinCosmetics,editedbyMartinM.Rieger(outofprint) 17.InterfacialPhenomena:EquilibriumandDynamicEffects,ClarenceA. MillerandP.Neogi 18.SurfactantBiodegradation:SecondEdition,RevisedandExpanded,R.D. Swisher 19.NonionicSurfactants:ChemicalAnalysis,editedbyJohnCross

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20.Detergency:TheoryandTechnology,editedbyW.GaleCutlerandErik Kissa 21.InterfacialPhenomenainApolarMedia,editedbyHansFriedrichEicke andGeoffreyD.Parfitt 22.SurfactantSolutions:NewMethodsofInvestigation,editedbyRaoul Zana 23.NonionicSurfactants:PhysicalChemistry,editedbyMartinJ.Schick 24.MicroemulsionSystems,editedbyHenriL.RosanoandMarcClausse 25.BiosurfactantsandBiotechnology,editedbyNaimKosaric,W.L. Cairns,andNeilC.C.Gray 26.SurfactantsinEmergingTechnologies,editedbyMiltonJ.Rosen 27.ReagentsinMineralTechnology,editedbyP.SomasundaranandBrij M.Moudgil 28.SurfactantsinChemical/ProcessEngineering,editedbyDarshT.Wasan, MartinE.Ginn,andDineshO.Shah 29.ThinLiquidFilms,editedbyI.B.Ivanov 30.MicroemulsionsandRelatedSystems:Formulation,Solvency,andPhysical Properties,editedbyMauriceBourrelandRobertS.Schechter 31.CrystallizationandPolymorphismofFatsandFattyAcids,editedby NissimGartiandKiyotakaSato 32.InterfacialPhenomenainCoalTechnology,editedbyGregoryD. BotsarisandYuliM.Glazman 33.SurfactantBasedSeparationProcesses,editedbyJohnF.Scamehorn andJeffreyH.Harwell 34.CationicSurfactants:OrganicChemistry,editedbyJamesM.Richmond 35.AlkyleneOxidesandTheirPolymers,F.E.Bailey,Jr.,andJosephV. Koleske 36.InterfacialPhenomenainPetroleumRecovery,editedbyNormanR. Morrow 37.CationicSurfactants:PhysicalChemistry,editedbyDonnN.Rubingh andPaulM.Holland 38.KineticsandCatalysisinMicroheterogeneousSystems,editedbyM. GrätzelandK.Kalyanasundaram 39.InterfacialPhenomenainBiologicalSystems,editedbyMaxBender 40.AnalysisofSurfactants,ThomasM.Schmitt 41.LightScatteringbyLiquidSurfacesandComplementaryTechniques, editedbyDominiqueLangevin 42.PolymericSurfactants,IrjaPiirma 43.AnionicSurfactants:Biochemistry,Toxicology,Dermatology.Second Edition,RevisedandExpanded,editedbyChristianGloxhuberandKlaus Künstler 44.OrganizedSolutions:SurfactantsinScienceandTechnology,editedby StigE.FribergandBjörnLindman 45.Defoaming:TheoryandIndustrialApplications,editedbyP.R.Garrett 46.MixedSurfactantSystems,editedbyKeizoOginoandMasahikoAbe 47.CoagulationandFlocculation:TheoryandApplications,editedby BohuslavDobiáš

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48.Biosurfactants:Production•Properties•Applications,editedbyNaim Kosaric 49.Wettability,editedbyJohnC.Berg 50.FluorinatedSurfactants:Synthesis•Properties•Applications,ErikKissa 51.SurfaceandColloidChemistryinAdvancedCeramicsProcessing,edited byRobertJ.PughandLennartBergström 52.TechnologicalApplicationsofDispersions,editedbyRobertB.McKay 53.CationicSurfactants:AnalyticalandBiologicalEvaluation,editedbyJohn CrossandEdwardJ.Singer 54.SurfactantsinAgrochemicals,TharwatF.Tadros 55.SolubilizationinSurfactantAggregates,editedbySherrilD.Christian andJohnF.Scamehorn 56.AnionicSurfactants:OrganicChemistry,editedbyHelmutW.Stache 57.Foams:Theory,Measurements,andApplications,editedbyRobertK. Prud'hommeandSaadA.Khan 58.ThePreparationofDispersionsinLiquids,H.N.Stein 59.AmphotericSurfactants:SecondEdition,editedbyEricG.Lomax 60.NonionicSurfactants:PolyoxyalkyleneBlockCopolymers,editedby VaughnM.Nace 61.EmulsionsandEmulsionStability,editedbyJohanSjöblom 62.Vesicles,editedbyMortonRosoff 63.AppliedSurfaceThermodynamics,editedbyA.W.NeumannandJanK. Spelt 64.SurfactantsinSolution,editedbyArunK.ChattopadhyayandK.L. Mittal 65.DetergentsintheEnvironment,editedbyMilanJohannSchwuger 66.IndustrialApplicationsofMicroemulsions,editedbyConxitaSolansand HironobuKunieda 67.LiquidDetergents,editedbyKuoYannLai ADDITIONALVOLUMESINPREPARATION SurfactantsinCosmetics:SecondEdition,RevisedandExpanded,editedby MartinM.RiegerandLindaRhein PowderedDetergents,editedbyMichaelS.Showell EnzymesinDetergency,editedbyJanH.vanEe,OnnoMisset,andErikJ. Baas

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LiquidDetergents editedby KuoYannLai ColgatePalmoliveCompany NewYork,NewYork

M ARCELDEKKER,INC. N EWYORK•BASEL

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LibraryofCongressCataloginginPublicationData Liquiddetergents/editedbyKuoYannLai. p.cm.—(Surfactantscienceseries;v.67) Includesindex. ISBN0824793919(hardcover:alk.paper) 1.Detergents.I.Lai,KuoYann.II.Series. TP992.5.L561996 668'.14—dc20 9644787 CIP Thepublisheroffersdiscountsonthisbookwhenorderedinbulkquantities. Formoreinformation,writetoSpecialSales/ProfessionalMarketingatthe addressbelow. Thisbookisprintedonacidfreepaper. Copyright©1997byMarcelDekker,Inc.AllRightsReserved. Neitherthisbooknoranypartmaybereproducedortransmittedinanyform orbyanymeans,electronicormechanical,includingphotocopying, microfilming,andrecording,orbyanyinformationstorageandretrievalsystem, withoutpermissioninwritingfromthepublisher. MarcelDekker,Inc. 270MadisonAvenue,NewYork,NewYork10016 Currentprinting(lastdigit): 1098765432 PRINTEDINTHEUNITEDSTATESOFAMERICA

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Preface Liquiddetergentsplayveryimportantrolesinourdailylivesforpersonalcare, householdsurfacecare,andfabriccare.Weusetheseproductsjustabout everydayfromwashingourhands,hair,dishes,clothestocleaningvarious surfacesinourhomes.Inthelastthreedecades,liquiddetergentshavegained anincreasingpopularitylargelyduetotheconveniencetheyofferoverother forms.Duringthisperiod,therehavebeensignificantadvancesinbothscience andtechnologyinthisarea.Numerouspapershavebeenpublishedin professionaljournalsandtrademagazines,thousandsofpatentshavebeen granted,andlargenumberofnewproductshavebeenintroducedtothe marketplace.Theobjectiveofthisvolumeistoprovideacomprehensive reviewoftheseadvances. Thisisthefirstbookspecificallydevotedtothereviewanddiscussionofliquid detergents.Itisintendedprimarilyforscientistsandengineersworkinginthe detergentindustryandthedetergentrawmaterialsindustryaroundtheworld. Researchersinotherindustries—suchasthoseinthepetroleumindustrywho areinvolvedinenhancedoilrecoveryandthoseintextileprocessing—aswell asthoseinacademiawillalsousefulinformationinthisvolume. ConsistentwiththeoverallaimoftheSurfactantScienceSeries,thisvolume coversboththeoreticalandappliedaspectsofliquiddetergents.Therearea totalof14chapters.Chapter1givesaconciseaccountofthepast,present, andfutureofliquiddetergents.Therestofthevolumeisstructuredintotwo parts—theoriesandapplications.Chapters2–6presentanindepthdiscussion oftheoriesofcommonimportancetomostliquiddetergentsystemsincluding hydrotropy,phaseequilibria,rheology,polymericstabilizers,andnonaqueous surfactantsystems.Chapters7–13coverthetechnologicalaspectsofliquid detergentsinvariouspracticalapplicationsfromlightandheavydutyliquid

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detergents,liquidautomaticdishwasherdetergents,liquidsoaps,shampoos andconditioners,andfabricsoftenerstospecialtyliquidhouseholdsurface cleaners.Chapter14focusesonthemanufacturingaspectsofliquiddetergents. Itishopedthatthisvolumewillnotonlyserveasahandyreferenceto researchersbutalsostimulatemanynewinnovationsinthedetergentfield. IwanttotakethisopportunitytoexpressmysincerethankstoColgate PalmoliveCompanyforpermittingmetoundertakethisprojectandtothe leadershipteamatit*GlobalTechnologyDivisionfortheirstrongsupport. Specialthanksalsogotoallthecontributorsofthisbooknotonlyforsharing theirexpertiseandextensiveexperiencebutalsoforpatientlyenduringthe unavoidabledelaysofamultiauthoredbook. IwouldalsoliketoexpressmygratitudetoDr.MartinSchick,theconsulting editorofthisseries,forhisvaluablesuggestions,encouragementandpatience; andtothepublisher,MarcelDekkerInc.,inparticular,Ms.AnitaLekhwani, AssociateAcquisitionsEditor,andMr.JosephStubenrauch,Production Editor,fortheirpatienceandinvaluablehelp. Finally,Iwanttothankmywife,Jane,andmychildren,Melody,Amy,and Peterfortheirenduranceandsupportinthelastseveralyears.Itwaswiththeir loveandunderstandingthatIwasabletodevotenumerouseveningsand weekendstocompletethistask. KUOYANNLAI

Contents Preface Contributors 1.LiquidDetergents:AnOverview ArnoCahn 2.Hydrotropy StigE.FribergandChrisBrancewicz 3.PhaseEquilibria GuyBroze 4.RheologyofLiquidDetergents R.S.Rounds 5.PolymericStabilizersforLiquidDetergents MadukkaraiK.NagarajanandHalAmbuter 6.NonaqueousSurfactantSystems MarieSjöbergandTorbjörnWärnheim 7.LightDutyLiquidDetergents KuoYannLai,ElizabethF.K.McCandlish,andHarryAszman 8.HeavyDutyLiquidDetergents AmitSachdevandSanthanKrishnan 9.LiquidAutomaticDishwasherDetergents PhilipA.Gorlin,KuoYannLai,andNagarajDixit

10.ShampoosandConditioners ClarenceR.Robbins 11.LiquidSoaps RichardE.Reever 12.FabricSofteners AlainJacquesandCharlesJ.Schramm,Jr. 13.SpecialtyLiquidHouseholdSurfaceCleaners KarenWisniewski 14.ManufactureofLiquidDetergents R.S.Rounds Index

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Contributors HalAmbuterSpecialtyChemicalDivision—ProductDevelopment,The BFGoodrichCompany,Brecksville,Ohio HarryAszmanResearchandDevelopment,GlobalTechnology,Colgate PalmoliveCompany,Piscataway,NewJersey ChrisBrancewiczDepartmentofChemistryandCenterforAdvanced MaterialsProcessing,ClarksonUniversity,Potsdam,NewYork GuyBrozeAdvancedTechnologyDepartment,ColgatePalmoliveResearch andDevelopment,Inc.,Milmort,Belgium ArnoCahnArnoCahnConsultingServices,Inc.,PearlRiver,NewYork NagarajDixitResearchandDevelopment,GlobalTechnology,Colgate PalmoliveCompany,Piscataway,NewJersey StigE.FribergDepartmentofChemistryandCenterforAdvancedMaterials Processing,ClarksonUniversity,Potsdam,NewYork PhilipA.GorlinResearchandDevelopment,GlobalTechnology,Colgate PalmoliveCompany,Piscataway,NewJersey AlainJacquesFabricCare,ColgatePalmoliveResearchandDevelopment, Inc.,Milmort,Belgium SanthanKrishnanResearchandDevelopment,GlobalTechnology,Colgate PalmoliveCompany,Piscataway,NewJersey

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KuoYannLaiGlobalMaterialsandSourcing(AsiaPacificDivision),Global Technology,ColgatePalmoliveCompany,NewYork,NewYork ElizabethF.K.McCandlishResearchandDevelopment,Global Technology,ColgatePalmoliveCompany,Piscataway,NewJersey MadukkaraiK.NagarajanSpecialtyChemicalDivision—Product Development,TheBFGoodrichCompany,Brecksville,Ohio RichardE.ReeverRichardReeverandAssociates,Inc.,Minnetonka, Minnesota ClarenceR.RobbinsResearchandDevelopment,GlobalTechnology, ColgatePalmoliveCompany,Piscataway,NewJersey R.S.RoundsFluidDynamics,Inc.,Piscataway,NewJersey AmitSachdevResearchandDevelopment,GlobalTechnology,Colgate PalmoliveCompany,Piscataway,NewJersey CharlesJ.Schramm,Jr.ResearchandDevelopment,GlobalTechnology, ColgatePalmoliveCompany,Piscataway,NewJersey MarieSjöbergInstituteforSurfaceChemistry,Stockholm,Sweden TorbjörnWärnheim*InstituteforSurfaceChemistry,Stockholm,Sweden KarenWisniewskiResearchandDevelopment,GlobalTechnology, ColgatePalmoliveCompany,Piscataway,NewJersey *Currentaffiliation:Pharmacia&Upjohn,Stockholm,Sweden

1 LiquidDetergents:AnOverview ARNOCAHN ArnoCahnConsultingServices,Inc.,PearlRiver,NewYork I.Introduction II.LightDutyLiquids III.HeavyDutyLiquids IV.LiquidAutomaticDishwasherDetergents V.ShampoosandConditioners VI.LiquidSoaps VII.FabricSofteners VIII.SpecialtyLiquids IX.ManufactureandRawMaterials References

I.Introduction Liquiddetergentsareconvenienceproducts.Comparedwithpowdereddetergen dissolvemorerapidly,particularlyincoldwater,theygeneratelessdust,andthey dose.Itisnotsurprising,therefore,thatliquidformsofhouseholdcleaningprodu developedbymanufacturers. Withtheexceptionoffabricsoftenersandshampoos,thesolidformofcleaningp precededtheliquidform.Thisistrueofmanualandautomaticdishwashing,laund generalpersonalwashingproducts.Asaresult,

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thetechnicalhistoryofliquiddetergentsistoalargeextentoneofemulatingthe performancefeaturesofthepowdermodels. Allotherfactors—soil,waterhardness,andtemperature—beingequal, cleaningperformanceisafunctionoftheconcentrationandtypeoftheactive ingredientsthataredeliveredintothecleaningbath.Almostbydefinition,the liquidforminvolvesadilutionoftheactiveingredients,thatis,agivenvolume ofapowdereddetergentcangenerallydelivermoreactiveingredientsthanan equalvolumeofaliquiddetergent.Thetasktoprovideperformanceequality withpowdersisthereforenotinsignificant.Itismadeevenmoredifficultwhen inorganicsaltsareusedtoprovidecertainspecificperformancefeatures.These saltsoftenposeproblemsofsolubilityandcompatibilitywiththeorganic surfactantsoftheformulation.Finally,formulationproblemsaremostsevere whentheactivecomponentislessstableinanaqueousenvironmentthanina solidmatrix. Theseconsiderationsapplyprincipallytotheheavydutyliquids,thelargestof theliquiddetergentcategories,buttheyalsocomeintoplaywithliquid automaticdishwasherdetergents. Thesituationisdifferentforproductsdesignedforlightduty,handdishwashing andforsofteningfabrics.Theseliquidsaregenerallysuperiorinperformanceto theirpowderedcounterpartstotheextentthattheseexistedinthefirstplace. Thisisalsotrueofshampooformulations,forwhichthereisnocommonsolid equivalent. Thischaptergivesanessentiallyhistoricaloverviewofthevariouscategories. Historically,soapbasedshampoosandtheliquidpotassiumoleate formulationsfoundinwashroomdispenserswereprobablytheearliest commercialliquiddetergents. II.LightDutyLiquids Onatrulycommercialscale,theageofliquiddetergentscanbesaidtohave beguninthelate1940swhenthefirstliquiddetergentformanualdishwashing wasintroduced.Thisliquidconsistedessentiallyofanonionicsurfactant: alkylphenolethoxylate.Inuse,itproducedonlyamoderateamountoffoamin thedishpan. Thisprovedtobeaseriousdetriment.Tobesuccessful,consumerproduct innovationsmustshowalargemeasureofsimilaritytotheconventional productstheyareintendedtodisplace.Inthiscase,copiousfoamwasthe essentialperformanceattributethatneededtobeasclosetothatwhichcould begeneratedfrompowdersandsoapchips. Therequirementforcopiousfoamlevelshasatechnicalbasisandismorethan amereemotionalreactiontoavisualphenomenon.Withsoapbasedproducts, theappearanceofapermanentfoamsignaledthatallhardwaterionshad

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beenremovedbyprecipitationascalciumandmagnesiumcarboxylatesand thatexcesssoapwasnowavailabletoactasasurfactant. Thefoamingrequirementsforlightdutyliquidsweremetbythenextseriesof productintroductionsintheearly1950s.Theseformulationswerebasedon highfoaminganionicsurfactants.Theywerecapableofmaintainingadequate levelsoffoamthroughoutthedishwashingprocessandpossessedsufficient emulsifyingpowertohandletheloadofgreaseinthedishpantoproduce “squeakyclean”dishware. Inpractice,thiswasaccomplishedbyamixtureofanionicsurfactants— alkylbenzenesulfonate,alcoholethersulfate,andalcoholsulfates—sometimes incombinationwithnonionicsurfactants.Tomaintainfoamstability, alkanolamideswereincorporated.Insomeproducts,alkanolamideswere subsequentlyreplacedbylongchainamineoxides. Theformulationoflightdutyliquidsovercameasecondmajortechnicalhurdle inherentintheformulationofallliquiddetergents:tomaintainhom*ogeneityin thepresenceofsignificantlevels,about30%ormore,ofmoderatelysoluble organicsurfactants.Couplingagentsorhydrotropeswereintroducedforthis purpose,specificallytheshortchainalkylbenzenesulfonates,suchasxylene, cumeneandtoluenesulfonates,aswellasethanol. Lightdutyliquidshavemaintainedasignificantmarketvolumetothisday.This issomewhatsurprisingbecausetheprimaryfunctionoftheseproductsisto washdishes.Innewerhomesandapartments,thisfunctionhasbeentaken overbyautomaticdishwashingmachinesandthespecialdetergentsdeveloped foruseinthesemachines.Bothhaveexpandedgreatlysincetheirintroduction inthelate1950s.Somepartofthepersistenceoflightdutyliquidsisnodoubt aresultoftheiruseasfinefabricdetergentsforwashingdelicatelaundryitems byhand. Overtheyears,minoradditiveshavebeenincorporatedintolightdutyliquid formulations,principallytosupportmarketingclaimsforspecialperformance features.Foraperiodoftimeinthe1960s,antimicrobialswereincorporated intosomeproductsdesignedtopreventsecondaryinfectionsofbrokenskin duringdishwashing.Afteranabsenceofsome30years,antimicrobialsare againappearinginlightdutyliquids.Theirreturnisnodoubtconnectedwith increasingawarenessofthepossiblepresenceofbacteriainfoods,especially inchicken.Othercommercialproductscontainedproteinasaskinbenefit agent. Improvingtheconditionofskinasaresultofexposuretolightdutyliquid solutionsprovedtobetechnicallyverydifficult.Exposuretimesarerelatively short,about20minutes,threetimesadayunderthebestofcirc*mstances,and useconcentrationsarelow,about0.15%.Thecombinationoflowuselevels andshortexposuretimesmakesitdifficulttoovercometheadverseeffectsof skinexposuretootherinimicalinfluences,suchasdryairinheatedhomesand stronghouseholdchemicals.

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Generallyspeaking,lightdutyliquidcompositionsarerelativelynonirritatingto skin.Mildnesstoskincouldthereforebeclaimedbytheseproductswith reasonablejustification.Duringthe1960sand1970s,thecosmeticimagewas furtherenhancedbyopacifyinglightdutyliquidsandconferringuponthema lotionlikeappearance.Inmorerecentyears,dishwashingefficacy—effective emulsificationofgrease—combinedwithpersistentfoam,hasbeenthemain objectiveoftechnicalproductimprovement. Inlinewithcleaningefficacy,solidparticleshavealsobeenincorporatedinto somelightdutyliquidformulationswiththeobjectiveofraisingthe effectivenessoftheproductsinremovingsolidcakedonsoilfromdishes. III.HeavyDutyLiquids Oncelightdutyliquidproductshadestablishedanattractivemarketposition, thedevelopmentofheavydutyliquidscouldnotbefarbehind.Here,too,the requirementofsimilaritytotheexistingproductshadtobemet,inthiscase powderedlaundrydetergents.Thepowderedlaundrydetergentsofthe1950s werecharacterizedbythepresenceofhighlevelsofbuilder,specifically pentasodiumtripolyphosphate(STPP),andrelativelylowlevels,about15%, ofsurfactants.Informulatingaheavydutyliquid,therefore,themajortechnical objectivewastofindwaysofstablyincorporatingmaximumlevelsofbuilder salts. Thefirstcommerciallyimportantheavydutyliquidwasintroducedintothe U.S.marketin1958.Theproductwasbuiltwithtetrapotassium pyrophosphate,whichismoresolublethanSTPP.Evenso,inthepresenceof asurfactantsystemofsodiumalkylbenzenesulfonateandamixtureof alkanolamides,theformulationcouldtolerateonly15–20%oftetrapotassium pyrophosphate. Incorporationofanantiredepositionagent,anotheringredientpresentin laundrypowders,provedtobeanothermajortechnicalhurdle. Antiredepositionagents,generallycarbohydratederivatives,suchas carboxymethylcellulose,hadbeenintroducedintolaundrypowderstoprevent greyingafteranumberofrepeatwashcycles. Inoneproduct,thepatentedsolutiontothisproblemconsistedofbalancing twoantiredepositionagentsofdifferentspecificgravitysuchthatthetendency ofonetoriseinthefinishedproductwascounterbalancedbythetendencyof thesecondagenttosettleoutoftheproduct[1]. Eventhoughthefirstmajorcommercialheavydutyliquidcompositionwas formulatedwithabuildersystem,theconcentrationsofbuildersandsurfactants itdeliveredintothewashingsolutionwerelowerthanthoseprovidedbythe conventionaldetergentpowders.Asaliquid,however,theproductpossessed auniqueconvenienceinuse,particularlyforfullstrengthapplicationtospecific soiledareasofgarments.Conveniencewasaccompaniedbyeffectiveness,

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becausetheconcentrationofindividualingredientsintheneatformapproached thatofanonaqueoussystem. Thisisillustratedbythefollowingconsideration.Recommendedwashing productusedirectionsleadtowashingsolutionswithaconcentrationofabout 0.15%ofthetotalproduct.Atasurfactantlevelofabout15%intheproduct, thefinalconcentrationofsurfactantinthewashliquorisabout0.0225%.The efficacyofsurfactantinprovidingobservablecleaningatsuchlow concentrationatteststothepoweroftheinterfacialphenomenathatunderlie theactionofsurfactants. Bycontrast,aheavydutyliquidcontaining20%surfactant,appliedfull strength,leadstoasurfactantconcentrationof20%,somethreeordersof magnitudelargerthanintheearliercase.Atthese—almostnonaqueous— concentrations,solutionphenomena,suchasthoseoperatinginnonaqueous drycleaning,arelikelytoberesponsibleforcleaningefficacy.Thepopularity ofheavydutyliquidsforpretreatingstainswasthusbasednotonlyon conveniencebutalsoonrealperformance. Inthemid1960s,thebranchedchainsurfactantswerereplacedbymore biodegradableanalogsinalllaundryproducts.Inheavydutyliquids,sodium alkylbenzenesulfonate,derivedfromanalkylbenzenewithatetrapropyleneside chain,wasreplacedbyitsstraightchainanalog,referredtoassodiumlinear alkylbenzenesulfonate(LAS). Theconversiontomorebiodegradablesurfactantswaspromptedbythe appearanceoffoamsonriver.Theappearanceofexcessivealgalgrowthon stagnantlakespromptedasecondenvironmentaldevelopmentthatprovedto bebeneficialtotheexpansionofheavydutyliquids:thereductionor eliminationofthesodiumtripolyphosphatebuilderfromlaundrydetergents. Restrictionsontheuseofphosphateinlaundrydetergentswereimposedbya numberofstatesandsmalleradministrativeagenciesbeginningin1970. Becausenototallyequivalentphosphatesubstitutewasimmediatelyavailable, theperformanceofheavydutylaundrypowderswasadverselyaffected.As thewholewashperformancedifferentialbetweenpowdersandliquids narrowed,theusageofheavydutyliquidsforthewholewashexpanded, markedlysoinareaswherephosphatehadbeenbanned. Inthefirstnonphosphateversionofthecommercialproduct,phosphatewas replacedbyNTA(trisodiumnitrilotriacetate),apowerfulbuilder,comparable tothecondensedphosphatesinitsefficacyinsequesteringcalciumionsinthe washingsolution.Becauseofreportsofadverseteratogeniceffectsin laboratoryexperiments,thisbuilderwaswithdrawnfromthemarketlatein 1971.Itwasreplacedbysodiumcitrate,anenvironmentallymoreacceptable butinherentlylesspowerfulcalciumsequestrant.Atthesametime,surfactant levelswereincreasedbyafactorofabout3.Whathadhappenedinpractice (ifnotintheory)wasthathigherlevelsofsurfactantshadbeenintroducedto compensate

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forthelossinthebuildingcontributiontowashingefficacyprovidedearlierby phosphate. The1970ssawtheintroductionofseveralheavydutyliquidsthatcarriedthis substitutiontoitsultimate,beingtotallyunbuiltandconsistingsolelyof surfactantsatlevelsrangingfrom35%toabout50%.Thesecompositions weredistinguishedfromlightdutyliquidsbythepresenceofsurfactantswith longerhydrophobesand,ofcourse,bythepresenceoflaundryauxilaries,such asfluorescentwhitenersandantiredepositionagents.Withtheexceptionofa fewproductsbasedonsurfactantsonly,mostheavydutyliquidsare formulatedwithamixtureofanionicandnonionicsurfactants,withanionics predominating. ThesteadyexpansionofphosphatebansacrosstheUnitedStates, accompaniedbyanexpandingperceptionoftheconvenienceandefficacyof heavydutyliquids,ledtoanexpansionofthisproductcategoryinthetwo decadesbeginning1970.Thisexpansionwasfuelednotonlybythepublicity thatnormallyaccompaniestheintroductionofnewbrandsbutalsobysome significantproductimprovements.Thefirstofthesetoappearlateintheearly 1980swastheincorporationofproteolyticand,later,amylolyticenzymes.In liquiddetergents,withtheirrelativelyhighlevelofwater,proteolyticenzymes mustbestabilizedtopreventdegradationduringstorage[2,3]. Enzymesmakeasignificantanddemonstrablecontributiontowashingefficacy, notonlyintheremovalofenzymespecificstains,suchasgrassandblood,by proteinases,butalsoinanincreaseinthelevelofgeneralcleanliness.Thelatter effectistheresultoftheabilityofaproteolyticenzymetoactupon proteinaceouscomponentsofthematrixthatbindssoiltofabric. EnzymeshadbeenusedindetergentpowdersintheUnitedStatesandEurope asearlyas1960.TheyweresubsequentlywithdrawnintheUnitedStates,but notinEurope,whentherawproteinaseofthetimeprovedtohaveanadverse effectonthehealthofplantworkers.Improvementsintheenzymes,specifically encapsulation,eliminatedtheirdustinessandmadeitpossibletousethese materialsindetergentplantswithoutadversehealtheffects. Thesecondproductinnovationwastheincorporationofafabricsoftening ingredient.Again,apowderedversionofa“softergent”thathadbeenonthe marketforsometimeservedasthemodelproduct.Inthepowder,the mutuallyantagonisticanionicsurfactantsandcationicsofteningingredients couldbekeptapartsothattheywouldnotneutralizetheirindividualbenefitsin thewashcycle.Inaliquid,thisprovedtobeunattainable.Asaresult,the choiceofsurfactantsinliquidsoftergentswasrestrictedtononionics. Althoughtheincorporationofenzymesandfabricsoftenersstrengthenedthe marketpositionofheavydutyliquids,itdidnotsolvethebasicproblemof limitedgeneraldetergencyperformanceinnormalwashing.Asnotedearlier, heavydutyliquidscameclosetotheperformanceofthefirstnonphosphate laundrypowders.Withtime,however,theperformanceofnonphosphate laundry

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powdersimprovedasnewsurfactantsystemsandnewnonphosphatebuilders, notablyzeoliteincombinationwithpolycarboxylatepolymers,were introduced. Thelastdecadesawapartialconversionofsomemajorbrandsfromunbuiltto builtcompositions.Thefirstoftheseproductsemployedabuildersystem consistingofsodiumcitrateincombinationwithpotassiumlaurate[2].Inthe mostrecentversions,potassiumlauratehasbeenreplacedbyasmallmolecule etherpolycarboxylatesequestrant,amixtureofsodiumtartratemonosuccinate andsodiumtartratedisuccinate[3].Inthesebuiltproducts,thestabilizationof enzymesistechnicallymoredifficultthaninunbuiltsystems.Acombinationof lowmolecularweightfattyacids,lowmolecularweightalcohols,andverylow levelsoffreecalciumionsprovedtobethesolutiontothisproblem. Attheheightoftheirpopularity,heavydutyliquidsaccountedfor40–45%of theheavydutylaundryproductscategoryintheUnitedStates.Not unexpectedly,themarketshareofheavydutyliquidshasdeclinedsomewhat asnewdevelopmentsinlaundrypowders,notablytheintroductionofa bleachingfunctionandofconcentrated,higherdensitydetergentpowders,has reinvigoratedthisproductcategory. Iftheemulationoftheperformanceoflaundrypowdersistocontinueinthe future,andthereisnoreasontodoubtthistrend,theincorporationofastain removalandbleachingfunctionintoheavydutyliquidsshouldbethenext technicalimprovementintheseproducts.Indeed,thefirstproductclaiminga bleachingingredienthasmadeitsappearanceatthiswriting. Inlaundrypowders,effectivebleachinghasbeenattainedinthelastdecadeby incorporatingacombinationofsodiumperborateandanactivator.InEurope, sodiumperboratehasbeenusedformanydecadesasamajor(about20%) ingredientoflaundrydetergents.Attemperaturesnear100°C,sodium perboratealoneprovideseffectivebleaching.Aswashingtemperatureshave decreasedoverthepast15years,aneedhasarisenforanactivatorthatreacts withsodiumperboratetoformunstableperoxyintermediates,whichinturncan effectbleachingatthelowertemperatures. Topreventprematurereactionwiththeoxygensource,usuallysodium perborate,theactivatorscaneasilybeencapsulatedinpowdereddetergent products.Inanaqueousenvironment,thisistechnicallymuchmoredifficult. Oneapproachtowardtheincorporationofactivatedperborateintoheavyduty liquidsistoremovetheaqueousenvironmentandformulatenonaqueous systems[5].Toattainproducthom*ogeneity,theseformulationsrequire significantlevels,about20%,oforganicsolvents,suchaspropyleneglycol and/orethanol.Nonaqueoussystemshavebeenpatentedextensively, particularlyinEurope,butsofarhavenotbeenreflectedinmajornewproduct introductions. Nonaqueousliquidscouldbeconsidered“superconcentrated”andassuchare intunewiththerecenttrendtoconcentratedlaundrypowders.However,the

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needfororganicsolventscombinedwiththehighlevelofsurfactantspresentin theseformulationsrepresentsaburdenontheenvironmentandaddstothe costofsuchproducts.InEurope,specificallyinGermany,dischargeintothe environmentisaseriousproblemthatislikelytoinhibitexpansionofboth aqueousandnonaqueousheavydutyliquids. Suchsuperconcentrated,nonaqueousheavydutyliquidshavenotmadean appearanceinthemarketplace,but“concentrated”productshavebeen introduced,inconsonancewithageneraltrendtowardcompactioninitiatedby theintroductionofcompactorconcentrateddetergentpowders.Twotechnical approachestowardmoreconcentratedproductshavebeenfollowed.Thefirst, originatinginEurope,resultsinanopaqueproductcontainingrelativelyhigh levelsofbuildersaltsinsuspension.Astablesuspensionisachievedbysalting outthesurfactantsystembyanexcessofelectrolyte(whichincludesthebuilder salts)toformlamellarorspheruliticsurfactantaggregatesthatarecapableof suspendingbuilderinexcessofitssolubilityintheformulation.Therelatively highbuilderlevelscontributetoimprovedwholewashperformance,especially intheEuropeanliquids,whichcontainsodiumtripolyphosphateasthebuilder [4]. Asecondapproachtowardcompactionyieldsclear,isotropicliquidsthat appeartobepreferredbyU.S.consumers.Technically,thisinvolvesadifficult balancingactbecauseconventionalhydrotropingagents,suchascumeneor xylenesulfonates,maylosetheirefficacyinasystemenrichedinorganic components.Asthesystembecomesmoreorganicinnature,higherlevelsof solvents,suchasethanol,arerequiredincombinationwithneutralizationof acidicfunctionalities(LASorcitricacid)withalkanolamines,suchasmono andtriethanolamine.Ingeneral,thephasestabilityofthesystembecomesmore sensitivetochangesinactivelevelsbecausethestableoperatingregionofthe phasediagramisnarrowedrelativetomoredilutesystems. IV.LiquidAutomaticDishwasherDetergents Thedevelopmentofliquidautomaticdishwashingdetergentscontinuedthe patternofemulatingthecompositionofsolidproductsinaliquidform.Liquid automaticdishwashingdetergentswerefirstintroducedin1986atatimewhen themarketpenetrationofheavydutyliquidlaundrydetergentswasona pronouncedupswing,withoutanupperlimitinsight.Aliquidversionofthe automaticdishwashingdetergentpowdersthereforeappearedtobeattractive andtimely. Theseliquiddetergentproductsaresuspensionsratherthantruesolutions. Nonetheless,thetechnicalproblemsofformulatingthickbutflowable suspensionsareconsiderable.Again,theprimarytaskwastoincorporateas muchof

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theimportantingredients—principallybuildersinthiscase—aspossible.Even approachingthelevelsofsodiumtripolyphosphateandsodiumcarbonate presentinthepowderedversionsgivesrisetoaverythicksuspensionthatcan becoaxedoutofthecontaineronlywithconsiderabledifficulty.Makingthe suspensionthixotropicbyincorporationoftheappropriateclaymaterialsand, optionally,polycarboxylatepolymersprovidesasolutiontotheflowproblem [6].Beforeusebytheconsumer,theproductmustbeshakentoreduce viscosityandpromoteflow. Anothermajortechnicalproblemistheinadequatestabilityinanaqueous environmentofchlorinatedisocyanurates,theorganicchlorinesourceusedin powders.Sodiumhypochloritesatisfiesthestabilityrequirementsbut,onthe otherhand,reactswiththesurfactanttypesusedinpowderformulations.The specificationofsurfactantsforuseinliquidautomaticdishwashingproducts thereforeincludesnotonlytheuniversalrequirementoflowfoamlevels(and ideallythecapabilityofdestroyingthefoamsgeneratedduringthedishwashing processbyproteinaceoussoil)butalsostabilitytosodiumhypochlorite.Toa largeextent,theserequirementshavebeenmetbythealkyldiphenyloxide disulfonatesurfactants. Insomecommercialliquidautomaticdishwashingformulations,thesurfactantis omittedaltogether.Inpractice,thisisapossiblesolutionbecausedetergencyin hardsurfacecleaning,suchasdishwashing,isaccomplishedprimarilybythe phosphatebuilder.However,intheabsenceofsurfactantthereislittle defoamingofnaturalsoilsandnocontributiontothe“sheeting”ofwaterjust beforedrying.Suchsheetingminimizestheformationofwaterspotsondishes thathavegonethroughthedishwashingprocess. V.ShampoosandConditioners Shampoosareliquiddetergentsdesignedtocleanaparticularsubstrate,thatis, hairandscalp.Theybearsomeresemblancetohanddishwashingliquidsinthat theyareessentiallyunbuiltsurfactantsolutions. Estheticproperties,suchasappearance(clearorpearlescent),viscosity,and fragrance,areperhapsmoreimportantinthisproductgroupthaninanyother productcategorydiscussedinthisbook.Developmentandmaintenanceofan adequatefoamlevelisatonceaperformancepropertyandalsoaesthetic propertyinthatitisnoticedandevaluatedbytheuser. Shampoosalmostalwayscontainadditiveswithactivityinareasotherthan cleaningandfoaming,designedtoprovidespecificperformanceattributesthat confersuchpropertiesasluster,manageabilitytohair,andeliminationof dandruff. Theconcentrationinuseofshampoosisestimatedasnear8%.Thisisanorder ofmagnitudegreaterthantheuseconcentrationsoflaundryanddishwashing

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liquids.Mildnesstoskinandlowirritationtoeyesarethereforeimportant requirementsforshampoos. Salts,generallysodiumbutalsotriethanolammonium,oflongchainalcohol sulfatesandalcoholethersulfatesarethemostwidelyusedsurfactantsin shampooformulations.Alkanolamidesactasviscosityregulatorsaswellas foamstabilizers. Themostgeneralbenefitsassociatedwiththeuseofconditionersisareduction instaticchargeonhairandhenceagreatereaseofcombing,thatis,improved manageability.Cationic,quaternarysurfactantsandcationicpolymersprovide thesebenefitsasaresultofelectrostaticadsorptiononhair.Inanalogywith “softergents,”themutualantagonismofthecationicconditionersandthe anionicsurfactantsthatprovidetheprimaryshampoofunctionofremovingoily soilpresentsaprobleminthedevelopmentofconditioningshampoos.Some anionicsurfactants,notablycarboxylatednonionics,havebeenfoundtobe moretoleranttowardcationicsurfactantsthanthealcoholsulfatesoralcohol ethersulfates. Thehistoryofshampoosislong,beginningwellbeforethedaysofsynthetic surfactants.Theadventofthelattergreatlyexpandedoptionsforthe formulatorandatthesameimprovedtheestheticsoftheproducts. VI.LiquidSoaps Liquidsoapsisthepopulardescriptiongiventothisproductcategory.This definitionistechnicallynotquiteaccurate.Theseproductsmaycontainsome fattyacidsalts,buttheyarepredominantlysolutionsof(synthetic)surfactants ratherthanofsoap. Apartfromthepotassiumoleatesolutionsmentionedearlier,thehistoryof liquidsoapsisrelativelyshort.Itoffersarelativelyrepresentativeillustrationof thedevelopmentofaproductcategoryorsubcategoryintheU.S.market.The firstliquidsoapwasfirstintroducedbyasmallishU.S.companyinthelate 1970s.TheproductprovedtobesufficientlyattractivetoU.S.consumersto captureasignificantmarketshareinthepersonalwashingcategory.Inshort order,manycompetitivebrandswereintroducedthatsaturatedthefieldand,it seemed,stuntedthegrowthofthecategory.Inthemostrecentstage,thefield reducedtofewer,largerbrandsandthecategoryhasreachedarelativelyfirm levelfromwhichslowandsteadygrowthcanbeanticipated. Liquidsoapscanbestoredanddispensedwiththeconveniencecharacteristic ofallliquids.Beyondthesegenericattractions,theypossessanesthetic advantageoverconventionalpersonalwashingbarsinthatduringuse,and particularlyduringoccasionaluse,theyarenotsubjecttothevisualand physicaldeteriorationinappearanceofpersonalwashingbars.Storedinan aqueous

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matrix(residualwaterfromwashing),barstendtosloughandcracktovarious degrees.Thecracks,inturn,cancollectsoil,whichleadstoalessthan attractiveappearance. Liquidsoapscanbeconsideredsuccessorstothepotassiumoleatesolutions notedearlier.Presentdayproducts,however,areformulatedprincipallywith nonsoapsurfactants,including olefinsulfonate,alkylsulfates,andalkylether sulfates.Someproducts,however,stilldependonpotassiumsaltsoffattyacids astheprincipalconstituent. Asinotherpersonalproducts,specialtysurfactantsalsofindapplicationin liquidsoapformulations.Theseincludealkylphosphateesters,sarcosinates, andsulfosuccinates.Asexpectedfromconsumerproductsthatcontactskin,a numberofspecialtyingredientscanbefoundinproductsmakingspecific marketingclaims.Theseingredientsincludeglycerin,aloevera,and antimicrobialphenolics.Smalllevelsofcalciumsequestrants,suchasEDTA, andsodiumcitrate,arealsopresent. VII.FabricSofteners Fabricsoftenersorconditioners,asthenameimplies,areproductsthatconfer softnesstowashedtextilegoods.TheyfirstmadetheirappearanceintheU.S. marketinthe1950s.Themajoractiveingredientinfabricsoftening compositionsisacationicsurfactant,adi(longchain)alkyldimethylammonium halideormethosulfate.Thepositivechargeonthenitrogenatom,combined withthehighmolecularmassassociatedwiththelongalkylchains,ensured adsorptionofthecompoundonthesubstrateandasoftfeeloftheconditioned fabric. Incontrasttomostotherliquiddetergentcategories,fabricsoftenersarenot truesolutions.Thelongchainquaternarysaltsdonotdissolvetoforman isotropicsolution. Cottonistheprimarytargetsubstrateforfabricsofteners.Onrepeated washing,thefinestructureofcottonatthesurfaceofthefabricbecomes dendritic,thatis,manyfinespikesofcottonfibersareformedthatprotrude fromthesurfaceofthetextile.Electrostaticrepulsionholdsthesespikesin place,butinthepresenceofthecationicsofteningagent,theyaresmoothed out.Syntheticfabrics,suchaspolyesterandnylon,arenotsubjecttothis phenomenon.Muchofthe“softening”withthesesubstratesisprovidedbythe mechanicalflexingactioninthedrier.However,themechanicalactioncausesa buildupofstaticelectricityonsyntheticfabrics,whichcanresultinconsiderable sparkingwhengarmentsmadeofsyntheticfibersarewithdrawnfromaclothes drier.Fortunately,theagentsthatconfersofteningtocottonfibersalsoreduce thebuildupofstaticchargesonsynthetics.

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Inaconventionalfabricsoftenerformulation,thelevelofthequaternary surfactantisabout5%.Lowconcentrationsof“levelingagents”canalsobe present.Thesematerials,oftennonionicsurfactants,assistinuniformdeposition ofthesofteningquaternary.Inaddition,abufferingsystemisusedtoassurean acidicpH.Finally,asolvent,suchasisopropanol,presentatlevelsofabout 10–15%,assuresaviscosityrangesuitableforeasydispensingfromthebottle. Asanadditivetoimproveeaseofironingandtoreducethewrinkling tendenciesofthetreatedtextile,siliconederivatives,suchaspolydimethyl siloxanes,havebeenincorporatedintoliquidfabricsoftenercompositions[7]. Asanalternativesofteningquaternary,imidazoliniumcompoundshavebeen introducedwithaclaimofsuperiorrewetperformance.Thiscanbeauseful performancefeaturebecausewithcontinuingusageandbuildupofcationicson thesubstrate,thewaterabsorptionofthesubstratecanbeadverselyaffected. Theuseofanionicdetergentsinthemainwashcanmitigatethisphenomenon becausetheanionicsurfactantcancombinewiththecationicfabricsoftenerto formacombinationthatisremovedaspartoftheoilonthefabric. Sincethelate1970s,concentratedfabricsoftenerproductshavebeen marketedintheUnitedStatesandinEurope.Intheseproducts,the concentrationofthesofteningcationicisaboutthreetimesashighasinthe conventionalproducts. Inthemostrecentpast,theenvironmentalacceptabilityofthedialkyldimethyl ammoniumquaternaryhasbeenquestioned,particularlyinWesternEurope.In response,thenatureofthealkylgrouphasbeenmodifiedandamoderately extensivepatentliteraturehasarisencoveringthesemodifications.Forthemost part,thepatentedstructuresincludeanesterlinkage,generallyatthethird carbonatom,whichmakesforamorerapidbiologicalbreakdownofthe parentcompound[8]. Theliquidfabricsoftenersjustdescribedarealsoreferredtoasrinsecycle softeners.Thereasonisthattheseproductsareaddedtotherinsecycleofthe washwhennoorverylittleofanyanionicresiduefromthedetergentusedin themainwashcanbeexpectedtobepresent.Asinalltextiletreatments,fabric softeningandconditioningareinherentlymoreeffectivewhentheyarecarried outinaliquidbath,thatis,whenarinsecyclesoftenerisemployed.Addinga producttotherinsecyclesoftenerrepresentsameasureofinconvenienceto theuser.Beforespecialportsfortheautomaticadditionofrinsecyclebecame awidespreadfeatureofwashingmachines,theuseofarinsecyclesoftener usuallyrequiredanappropriatelytimedsecondtriptothewashingmachine. Itisnotsurprising,therefore,thatalternativemeansofsofteningproductswere soughtanddeveloped.Here,however,theusualsituationwasreversed,inthat nowgreaterconveniencerestedwith“solid”products,thatis,flexiblesheets treatedwithafabricsofteningcompositionsthatperformedtheirsoftening

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andstaticreducingfunctionsintheclothesdrierratherthaninthewashing machine. Softergents,mentionedearlierinconnectionwithheavydutyliquids,canbe viewedasrepresentingtheultimateinconvenience.Theseproductsrequireno additionaleffortbeyondlaundering.Asnoted,thisconvenienceisboughtat somecostinboththewashingandsofteningperformance. VIII.SpecialtyLiquids Inadditiontothemajorliquiddetergentcategoriesdiscussedearlier,several morespecializedliquidproductcategorieshavebeenmarketedforanumber ofyears.Intermsoffunction,character,andformulationingredients,thisisthe mostfragmentedgroupofproductsconsideredhere. Thelargestgroupcomprisesthe“general”hardsurfacecleaners.Inaddition, thereisalargevarietyofspecialtieswithinspecialtyliquids,suchaswindow cleaners,bathroomcleaners,andtoiletbowlcleaners. Themajorcategoryofgeneralhardsurfacecleanershasevolvedintotwo principaltypes:allpurposecleanersandsolventcleaners.Allpurposeliquids areessentiallydiluteversionsofheavydutyliquids.Again,asolidproductthat requireddissolutionbeforeusewasthemodelfortheliquidcleaners.Early versionsoftheliquidcleanerswerebasedonlowlevelsoftetrapyrophosphate builderandsurfactantand,additionally,auxiliaries,suchasalkanolamideanda sufficientamountofhydrotrope,tokeepthecompositionhom*ogeneous.For sanitizingproducts,theauxiliariesincludecompoundswithantimicrobial efficacy,suchaspineoilorantimicrobialcationics.Withtheadventof phosphatebans,sodiumcitratehasemergedasthemostcommonphosphate replacementintheseproducts. Forincreasedefficacyinremovingparticulatesoiladheringtothesubstrate, somegeneralpurposecleanersincorporateasoftabrasive,suchascalcium carbonate.Theresultingproductsaremilkysuspensionswithabout40–50% ofsuspendedcalciumcarbonate[9].Keepingthesecompositions hom*ogeneousthroughextendedstorageisatechnicalchallenge.Oneapproach tosolvingthisproblemistoprovide“structure”totheliquidmedium. Surfactantspresentasalamellarphasearecapableofstructuringliquids.Most recently,acompositioncontainingbothsoftabrasiveandbleachhasbeen introduced[10]. Thesehardsurfacecleanershavenotescapedtherecenttrendtoward compaction.Here,theapproachtoward“ultra”productsisbasedontheuse ofshorterchainsurfactantsthatcombinethesoilpenetrationefficacyof solventswiththegreaseemulsificationoftraditionalsurfactants.These surfactantsarealsosaidtorequirenobuildersbecausetheirperformanceisnot affectedbywaterhardness.

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Solventcleanersaregenerallyfreeofbuildersaltsanddependfortheirefficacy onsolventtypecompounds,suchasglycolethers.Solventcleanersareless effectiveonparticulatesoil,suchasmudtrackedintothehousefromthe outside,buttargettheirefficacyagainstoilysoils,particularlyonoilysoilon modernplasticsurfaces. Windowcleaningproductsconstituteaspecialtywithinthesolventcleaner category.Becauseanyresidueleftonglassafterdryingleadstostreakingoran otherwiseundesirableappearance,theseproductsarehighlydiluteaqueous solutionscontainingextremelylowsurfactantlevels—mostoftennonionic surfactants—andacombinationofglycolethersandisopropylalcoholasthe solventsystem. Bathroomcleaners,sometimesreferredtoastubtileandsinkcleaners, represent“subspecialty”liquidsthatmustbeeffectiveagainstacombinationof sebumsoildepositedfromskindetritusduringbathingorshoweringandthe hardnessdepositsderivingfromhardwateritselforfromitsinteractionwith soap,thatis,calciumsaltsoffattyacids.Onesubsetinthisgroupdependson acidsforremovingthiscombination.Theacidscontainedintheproductsrange fromthestronghydrochloricandphosphoricacidstomoderatelystrong organicacids,suchasglycollicacid.Otherproductsareformulatedatabasic pH,incorporatingancalciumsequestrants,suchasthesodiumsaltof ethylenediaminetetraaceticacid(EDTA),surfactants,and,inthecaseof productswithdisinfectingaction,antimicrobialquaternaries. Likebathroomcleaners,toiletbowlcleanersareformulatedtoremovemineral deposits,principallyironsalts,thatformanunsightlydepositatthewaterlevel. Again,acidsranginginstrengthfromhydrochlorictocitricarefoundinthese products. Anothersubsegmentofthespecialtyliquidsisthatofthedraincleaners.These arestronglybasicproductsbasedoncombinationsofsodiumhydroxideand sodiumhypochlorite. IX.ManufactureandRawMaterials Inprinciple,themanufactureofliquidsissimple,involvingonlytheformulation ofa*generallyaqueoussolutionorsuspension.Forlightandheavydutyliquids, whichcontainsodiumsaltsofsurfactantacids,neutralizationcanbecarriedout insitu,thatis,asafirststepinthemixingprocess.Theheatofneutralization mustbedissipatedbeforeadditionofthemoretemperaturesensitive ingredients,suchasthefragrance.Heatmustalsobedissipatedinthe productionofproductsthatrequireheatinputtosolubilizeindividual ingredients. Therawmaterialsfortheliquidhouseholdproductsdiscussedinthisbookare relativelyfewinnumber,includingthe“workhorse”surfactants,builders,

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hydrotropes,andasmallnumberofspecialfunctioningredients.Cost constraintsonthefinishedproductsareoneoftheimportantlimitingfactors. Thesituationisdifferentforthepersonalliquiddetergentsandliquidsoapsand especiallysoforshampoosandconditioners.Costconstraintsarerelaxed,and therangeofperformanceclaimsbasedonspecificanduniqueingredientsis nowverymuchexpanded.Althoughthevarietyoftheessentialsurfactantsis stillmanageable,thenumberofspecialtysurfactantsandspecialfunction ingredientsisverymuchgreater. Adetaileddiscussionoftheseingredientsisbeyondthescopeofthischapter. Detailsofthecharacteristics,properties,andmanufactureoftherawmaterials canbefoundinotherreferenceworks[11]. Inthefollowing,therawmaterialsfoundinliquiddetergentcompositionsare listedtoprovideaconvenientsummaryforfurtherreference.Forthelarge scalecategoriesoflightandheavydutyliquids,forautomaticdishwasher detergents,andforfabricsofteners,thelistisfairlycomplete.Forspecialty liquids,shampoosandconditioners,andtoalesserextentforliquidsoaps,only limitedexamplesofspecialfunctionalingredientshavebeenselected. I.Lightdutyliquids A.Surfactants 1.Alkylbenzenesulfonate(linearalkylatesulfonate,LAS)salts 2.Alkylethersulfatesalts 3.Alkylsulfatesalts 4.Betaines 5.Alkylpolyglycosides B.Foamstabilizers 1.Fattyacidalkanolamides(monoanddi) 2.Alkyldimethylamineoxides C.Hydrotropes 1.Shortchainalkylbenzenesulfonates(xylenesulfonatesalts) 2.Ethanol II.Heavydutyliquids A.Surfactants 1.Alkylbenzenesulfonatesalts 2.Alkylethersulfatesalts 3.Alkylsulfatesalts

A.Surfactants 1.Alkylbenzenesulfonatesalts 2.Alkylethersulfatesalts 3.Alkylsulfatesalts 4.Alcoholethoxylates 5.Nmethylglucamides

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B.Builders 1.Sodiumcitrate 2.Sodiumsaltsoftartratemonoanddisuccinatemixture C.Hydrotropes 1.Saltsofshortchainalkylbenzenesulfonates(xylenesulfonate, cumenesulfonate,toluenesulfonate) 2.Ethanol D.Bases:Alkanolamines E.Otherspecialfunctionalingredients 1.Enzymes(proteinase,amylase,lipase):stainremover 2.Borax(cleaningaid) 3.Sodiumformate,calciumchloride(enzymestabilizingsystem) 4.Hydrogenperoxide(bleach) 5.Propyleneglycol(solvent) III.Liquidautomaticdishwasherdetergents A.Surfactants 1.Alkyldiphenyloxidedisulfonatesalts 2.Hydroxyfattyacidsalts B.Builders: 1.Pentasodiumtripolyphosphate 2.Tetrasodiumpyrophosphate 3.Sodiumcarbonate 4.Sodiumsilicate C.Bases:Sodiumandpotassiumhydroxide D.Otherspecialfunctionalingredients 1.Sodiumhypochlorite(bleach) 2.Clay(smectite,bentonite):viscosityregulator,suspendingagent 3.Polyacrylatesodiumsalts(viscosityregulator) 4.Monostearylacidphosphate(sudsdepressant) IV.Shampoosandconditioners

2.Clay(smectite,bentonite):viscosityregulator,suspendingagent 3.Polyacrylatesodiumsalts(viscosityregulator) 4.Monostearylacidphosphate(sudsdepressant) IV.Shampoosandconditioners A.Surfactants 1.Alkylsulfatesalts 2.Alkylethersulfatesalts 3.Acylaminopropylbetaines 4. Olefinsulfonatesalts B.Foamstabilizers/viscosityregulators:Fattyacidalkanolamides

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C.Otherspecialfunctionalingredients 1.Polyquaternium7(cationicconditioner) 2.Glycolmonostearate(opacifier) 3.Aloevera(lusterpromoter) 4.Jojoba(lusterpromoter) 5.Derivativesofhydrolyzedkeratin(skinandhairconditioner) V.LiquidSoaps A.Surfactants 1.Alcoholsulfatesalts 2.Alkylethersulfatesalts 3. Olefinsulfonatesalts 4.Fattyacidsalts B.Sequestrants 1.EDTA 2.Sodiumcitrate C.Foamstabilizers/viscosityregulators:Fattyacidalkanolamides D.Otherspecialfunctionalingredients 1.Phenolicantimicrobials 2.Glycerin VI.Fabricconditioners A.Surfactants 1.Dialkyldimethylammoniumhalideormethosulfatesalts 2.Monoalkyltrimethylammoniumhalidesalts 3.Alkylimidazoliniumsalts 4.Alcoholethoxylates 5.Alkyl(ethyleneoxide/propyleneoxide)nonionics B.Solvents 1.Isopropanol 2.Ethanol C.Otherspecialfunctionalingredients:Polydimethylsiloxanes(levelingagent)

B.Solvents 1.Isopropanol 2.Ethanol C.Otherspecialfunctionalingredients:Polydimethylsiloxanes(levelingagent) VII.Specialtyliquids A.Surfactants 1.Alkylbenzenesulfonatesalts 2.Alcoholsulfatesalts

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3.Alkanesulfonatesalts 4.Alkylethersulfatesalts 5.Alkylphenolethoxylates 6.Alcoholethoxylates B.Builders/sequestrants 1.Sodiumcarbonate 2.Sodiumsesquicarbonate 3.Sodiumcitrate 4.EDTA C.Acids/alkalis 1.Hydrochloricacid 2.Phosphoricacid 3.Glycollicacid 4.Sodiumhydroxide 5.Sodiummetasilicate 6.Alkanolamines D.Hydrotropes:Shortchainalkylbenzenesulfonatesalts(toluene,cumene) E.Bases:Alkanolamines F.Otherspecialfunctionalingredients 1.Pineoil(disinfectant) 2.Benzalkoniumcationics(antimicrobials) 3.Sodiumhypochlorite(bleach) 4.Calciumcarbonate(softabrasive) 5.Alumina(suspendingaid) 6.Alkylglycolethers(solvents) 7.Isopropanol(solvent) References 1.I.ReichandH.Dallenbach,U.S.Patent2,994,665toLeverBrothers Company(1963). 2.J.C.LettonandM.J.Yunker,U.S.Patent4,318,818totheProcter&

References 1.I.ReichandH.Dallenbach,U.S.Patent2,994,665toLeverBrothers Company(1963). 2.J.C.LettonandM.J.Yunker,U.S.Patent4,318,818totheProcter& GambleCompany(1982). 3.R.D.Bush,D.S.Connor,S.W.Heinzman,andL.N.Mackey,U.S. Patent4,663,071totheProcter&GambleCompany(1987). 4.B.J.Akred,E.T.Messenger,andW.T.Nicholson,BritishPatent 2,153,839AtoAlbright&WilsonLimited(1985). 5.G.Broze,D.Bastin,andL.Laitem,U.S.Patent4,749,512toColgate PalmoliveCompany(1988). 6.M.JulemontandM.Marchai,BritishPatent2,116,119AtoColgate PalmoliveCompany(1982).

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7.R.J.Dumbrell,J.P.Charles,I.M.Leclerq,R.M.A.deBakker,P.C.E. Goffinet,B.A.Brown,R.E.Atkinson,andF.E.Hardy,BritishPatent 1,549,180totheProcter&GambleCompany(1979). 8.J.C.Letton,U.S.Patent4,228,042totheProcter&GambleCompany (1980). 9.U.S.Patent4,129,527,F.P.Clark,R.C.Johnson,andJ.Topolewskito theCloroxCompany(1978). 10.C.K.Choy,F.I.Keen,A.Garabedian,andC.J.Spurgeon,U.S.Patent 4,695,394totheCloroxCompany(1987). 11.G.Barker,inSurfactantsinCosmetics(M.M.Rieger,ed.),Marcel Dekker,NewYork,1985.

2 Hydrotropy STIGE.FRIBERGandCHRISBRANCEWICZ DepartmentofChemistryandCenterforAdvancedMaterialsProcessing,Clarks Potsdam,NewYork I.Introduction II.HistoricalReview III.Fundamentals IV.CleaningandWashing V.Summary References

I.Introduction Liquiddetergentconcentratescommonlycontainhydrotropestoavoidexcessive theformulationandtoimprovetheirdetergency.Bothfunctionsrelyonthefunda propertiesofhydrotropes. Inthischapter,historicalknowledgeaboutthefunctionofhydrotropicmoleculesi reviewed,followedbyadescriptionofhydrotropicactioninliquiddetergentsusi commercialhydrotropewithanunusualstructure. II.HistoricalReview Theterm“hydrotropy”wascoinedin1916byNeuberg[1,2],whofoundthataq solutionsofcertainsaltspossessedtheabilitytoenhancethesolubilityinwaterof otherwisewaterinsolublesubstances.Hefoundthatthealkalimetalsaltsofbenz salicylicacid,benzenesulfonicacidandits

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manyderivatives,naphthoicacid,andvariousotherhydroaromaticacids displayedhydrotropicactivity.Inhisstudy,Neuberginvestigatedalarge numberoforganicsolutes,suchascarbohydrates,alcohols,aldehydes, ketones,hydrocarbons,esters,ethers,lipids,fats,andoils. Thesecondphaseorperiodofactivitystarted30yearslater,withanemphasis onchemicalengineeringandindustrialapplications.McKee[3]showedthat concentratedaqueoussolutionsofverysolubleneutralsaltsoforganicacids, suchassodiumbenzoate(NaB),salicylate(NaS),benzenesulfonate(NaBS), ptoluenesulfonate(NaPTS),xylenesulfonate(NaXS),cumenesulfonate (NaCS),andcymenesulfonate(NaCyS),increasedthesolubilityofawide varietyoforganicandsomeinorganiccompoundsinwater.Henotedthatmost hydrotropicsolutionsprecipitatedthesolubilizedsoluteondilutionwithwater andshowedthatthispermitseasyrecoveryofthehydrotropeforfurtheruse. Lumb[4]studiedtheternaryphasediagramsofsystemsconsistingofwater octanolpotassiumalkanoatesand,basedontheirsimilarities,postulatedthat thehydrotropyexhibitedbytheloweralkanoates(e.g.,butyrate)and surfactantsolubilizationwereessentiallythesamephenomenon.Ontheother hand,LichtandWieneroftheUniversityofCincinnati[5]agreedwithMcKee [3].Theyattributedtheincreaseinsolubilitytoa“saltingin”effectratherthan byasimilarityinstructuretosurfactants. Thefinalcomparisonwithsurfactantphaseequilibriawasmadetwodecades laterwhenLawrence[6],FribergandRydhag[7],andPearsonandSmith[8] presentedphasediagramsforhydrotropes.Thesephasediagrams demonstratedhydrotropicsolubilizationasanextensionofsurfactant solubilizationintolessorderedsystems. Inmoderntimes,hydrotropeshavefoundmanyapplications.Theiruseincludes thepharmaceuticalfield,withsolubilizationofdrugs,specificallytemazepam[9] andthecoronaryvasodilatornifedipine[10].Hydrotropeshaveshown promiseinenhancingtheactionofdrugswithsuchcombinationsas theophyllinewithinsulin[11]andhavebeenutilizedtoimprovetransdermal deliverysystems[12]. Inchemicalengineering,theoriginalMcGee[3]approachwasrecently continuedinsuchprocessesascatalysisandextraction[13,14].Itisalsoused inthepaperandpulpindustry[15–19]. Theapplicationinliquiddetergentsisadirectconsequenceofthefundamentals ofhydrotropicsolubilization.Hence,inthischapterwefirstdescribe hydrotropicactioningeneral,followedbyatreatmentofanunusual hydrotropicagentinthecontextofdetergency. III.Fundamentals Therearetwoessentialfeaturesofhydrotropesolubilization:comparatively largeconcentrationsofhydrotropearerequiredtoinitiatesolubilization,andthe

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maximumamountsolubilizedintotheaqueoushydrotropesolutionislarge comparedwithwhatisfoundinanaqueousmicellarsolutionofasurfactant. ThesetwocharacteristicsareillustratedinFig.1[7].Thedashedlineshows thestronglyenhancedsolubilityofoctanoicacidinasodiumxylenesulfonate solutionatconcentrationsinexcessof20%byweightofthehydrotrope.The contrastbetweenasolubilityoflessthan1%forconcentrationsat15%ofthe hydrotropeandtherapidincreasetomorethan30%byweightofoctanoic acidathigherconcentrationsillustratesthetypicalpropertiesofhydrotrope mediated

Fig.1 Thesolubilityofoctanoicacidintoanaqueoussolutionofa hydrotropesodiumxylenesulfonate,dashedline,requires highconcentrationsofthehydrotropetoinitiatesolubilization (~20%),butthesolubilizationincreasessteeplytolargevaluesfor smallincreasesinhydrotropeconcentrationsabovethose values.Thesurfactant(sodiumoctanoate),ontheotherhand (solidline),requireslowerconcentrationstostartthe solubilization(~5%)butthemaximumsolubilizationislimited.

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solubilization.Thecontrastbetweenthevaluesforthedashedandsolidlines illustratesthedistinctionofhydrotropesolubilizationfromthatbyasurfactant, inthiscasesodiumoctanoate.Thesolubilizationoftheoctanoicacidwiththe surfactantisinitiatedatamuchlowerconcentrationthanwiththehydrotrope, butthemaximumamountoftheacidsolubilizedremainsatamodestlevelof lessthan8%. Thecomparisonwithsurfactantsolubilizationoffersanimmediateexplanation forthehighconcentrationofhydrotroperequiredtoinitiatethesolubilization.It hasbeenwellknownformanyyears[20]thatasurfactantwithashorter hydrocarbonchainhasanincreasedvalueofthecriticalmicellization concentration(CMC).TheCMCistheconcentrationatwhichsolubilization begins. Hence,thehighhydrotropeconcentrationforinitialsolubilization(Fig.1)is reasonableandexpectedbecausethephenylgroupisanalogoustoonlythree tofourcarbonsinastraightchain.Theveryhighhydrotropeconcentrationfor initialassociationofthemoleculesandtheaccompanyingsolubilizationare givenarationalexplanation. Themuchhighervaluesofsolubilizedmaterialforthehydrotropein comparisonwiththevaluesforthesurfactant(Fig.1)areunderstoodfirstafter amorecompletephasediagramisconsideredforthetwocompounds.Figure 2revealstheessentialfeaturesofthetwosolubilizedmechanisms.Increased amountsofoctanoicacidinthesurfactantwatersolutiongiverisetoseveral phases,fourofwhichareillustratedinFig.2.AreaainFigure2consistsofan aqueoussolutionofnormalmicelles,thestructureofwhichisshowninFig.3a. Athighersurfactantconcentrationsaliquidcrystallinephasecontaining cylindricalsurfactantassociationsstackedinaclosepackedhexagonalarrayis formed.ThisregionislabeledareadinFig.2,anditsstructureisshowninFig. 3d. Atincreasingconcentrationsofoctanoicacid,alamellarliquidcrystalis formed,asshowninFig.2,regionc.Thisphasehasastructureof“infinite” bilayersofsurfactantinterlacedwithlayersofwater,asshowninFig.3c. Afurtherincreaseinthecontentofthesolubilizateresultsintheformationofan octanoicacidsolutionofinversemicelles,whichcontainwatersolubilizedin theircores.ThisregionisshownasareabinFig.2,andthestructureofan inversemicelleisdepictedinFig.3b.Theessentialfeatureofthephase diagramisthepresenceofthelamellarliquidcrystalregion,whichseparates thenormalmicellarsolution(Fig.3a)fromthesolutionofinvertedmicelles(Fig. 3b). Thisisinstrongcontrasttotheconditionswithhydrotrope(Fig.2)forwhich onlyonesolubilityregion(Fig.2)ofsignificanceisfoundwithincreasing

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Fig.2 Whenwaterandoctanoicacid(solidlines)arecombinedwith sodiumoctanoate,fourphasesareobtained:aandbare micellarsolutions(Fig.3aandb),andcanddareliquid crystals(Fig.3candd).Thecombinationwithahydrotrope sodiumxylenesulfonate,dashedline,givesasingleareaof anisotropicsolution(e).

Fig.3 Theamphiphileorganizationinanormalmicelle(a), inaninversemicelle(b),inalamellarliquidcrystal (c),andinaliquidcrystalofhexagonallypacked amphiphilecylinders(d).

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amountsofoctanoicacid.Asshownbythedashedline,acontinuousisotropic liquidphasereachesfromtheaqueouscornerto80%octanoicacidwithout interruption. Withthisinformation,thereasonforthe“anomalously”highsolubilizationby thehydrotropeisobvious.Itssolubilityregionisnotinterruptedbythe formationofaliquidcrystal;theshiftfromwatercontinuoustooctanoicacid continuoussolutionnowtakesplacewithoutaphasetransition. Itisessentialtorealizethatthephasechangeswhenoctanoicacidisaddedto thewatersodiumoctanoatecombinationarenotaquestionofsolubility.The octanoicacidiscertainlysolubleintheliquidcrystallinephase,regionc(Fig.2) andinfinitelysoinitsownsolution,regionb(Fig.2).Thedifferentphases foundinthesurfactantsystemareonlyamatterofmolecularorganizationofthe systemcomponents,notoftheirmutualsolubility. Thesimilaritybetweenthesolubilizationactionofsurfactantandhydrotrope (Fig.4)isnowimmediatelyevident.Thesurfactantandhydrotropesolubility regionsareanalogouswiththesurfactantrequiringlowerconcentrations becauseofitsgreaterhydrophobiccharacter.Hence,thedifferencebetween regionsinFig.2isnotadistinctioninsolubility;numerousphasesinthe surfactantsysteminFig.2arearesultofpackingrestrictionsimposedbythe lengthofthehydrocarbonchains.Thetransitionbetweennormalandinverse micellesrequiresalamellarpackingfortwohydrocarbonschainsofeight carbonseach.AsthestructuresinFig.5suggest,acombinationofthebulky hydrotropeandthelonghydrocarbonchainofasolubilizatedoesnotstabilizea lamellarpacking,andthetransitionfromnormaltoinverseassociation structurestakesplaceviadisorderedaggregates,asshowninFig.4b. IV.CleaningandWashing Theseprocessesaremainlyconcernedwiththeremovalof“oilydirt,” dependingtoahighdegreeonthecomplexphaseequilibriaencounteredinthe surfactantwater“oilydirt”system[21]. Twotreatmentshavebeenpublished[22,23]ontheactionofanontraditional hydrotropestructureinsuchsystems.Insteadoftheusualbulkymolecule(Fig. 5),thiscompound[24]isadicarboxylicacidofconsiderablechainlength(Fig. 6). Thefundamentalphenomenahavebeeninvestigatedoftheactionofthis hydrotropeinaliquidcleaner.Insuchanapplication,thehydrotropefunctions intheformulationconcentratebypreventinggelation.Inaddition,underthe diluteconditionsinthewashingprocess,thehydrotropefacilitatestheremoval ofoilydirtfromthefabric.Inthefollowingsectionthesetwofunctionsare relatedtothephaseequilibriaofwateramphiphilesystems. Theformulaforthedicarboxylicacid(Fig.6)hasahydrophiliclipophilic balancesimilartothatofoctanoicacid,buttheinfluenceofthetwoacidson

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Fig.4 Thetotalsolubilityregioninthesurfactantsystem(a)issimilar tothatofthehydrotrope(b);theonlydifferenceisthatthe changefromnormaltoinverseassociationstructurestakesplace viaanorderedlamellarliquidcrystal(aphaseseparation)in thesurfactantcase(a),andinthehydrotropesystemthe transitiontakesplaceoverdisorderedaggregateswithinthe solution(b).

amphiphilicassociationstructuresisentirelydifferent,ascanbeseeninFig.7 [25].Theoctanoicacidcausestheformationofaliquidcrystalwhenaddedto asolutionofwaterinhexylamine.Thesizeofthelamellarliquidcrystalline regionislarge(Fig.7a).Additionofthedicarboxylicacid,ontheotherhand, givesnoliquidcrystal,anditmaybeconcludedthatit*actionincon

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Fig.5 Thereasonforthedifferenceintransitionstructures,Fig.4,isthatthe carboxylicacidandthesurfactant(octanoicacidandsodiumoctanoate) areofsimilarchainlengthandalamellarpackingiseasily stabilized.Thedifferenceinstructureinthehydrotropeandfatty acidcombination(sodiumxylenesulfonateandoctanoicacid),on theotherhand,resultsinadisorderedstructure.

centratedsystemsissimilartothatofthecommonshortchainhydrotropes despiteitslonghydrocarbonchain(Fig.7b). ActivityindilutesystemswasinvestigatedusingamodelsystemfromUnilever [26]inwhichoctanolmimickstheoilydirt.Alamellarliquidcrystalwas presentatlowconcentrationoftheoilydirt[23],intheabsenceofthe hydrotrope(Fig.8).Afteradditionofthehydrotrope,theamountofmodeloily dirtsolubilizedwithoutliquidcrystalformationwasgreatlyenhanced.Clearly, thishydrotropefunctionsnotonlyasadestabilizerofliquidcrystalsinthe formulationconcentratebutalsoasadestabilizerofliquidcrystalsunderthe diluteconditionsofthewashingprocess.

Fig.6 Thedicarboxylicacidhydrotropehasanelongatedstructure.

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Fig.7 Thecombinationofwaterandhexylaminewithoctanoic acid(a)givesahugeareaofalamellarliquidcrystal (LC);thecombinationwiththedicarboxylicacidinFig.6 resultsinanisotropicliquidsolutiononly(b).

Themolecularmechanismbehindthedestabilizationofliquidcrystalswas clarifiedlater[27].Thespecificdisorderingbroughtforwardbythehydrotrope inthewatersurfactantoilydirtliquidcrystalwasfirstdetermined,followedby aninvestigationintotheconformationofthediacidmoleculeitself[22]. Theorderofthehydrocarbonchainsinaliquidcrystalisdirectlyobtainedfrom nuclearmagneticresonance(NMR)spectrausingamphiphileswithdeuteriated chains.EachmethylenegroupandtheterminalmethylgroupgiveaNMR signaldoublet,andthedifferenceinfrequencybetweenthetwosignalsis proportionaltotheorderparameter[27].Usingalamellarliquidcrystalmodel systemof“oilydirt,”surfactant,andwater,theinfluenceofthehydro

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Fig.8 Thesolubilizationofamodelcompoundforoilydirtwassmall inasurfactantsolutionatconcentrationsbelowtheCMC ()becauseoftheformationofaliquidcrystal.A combinationofhydrotropeandsurfactantgavean increasedsolubilization(—)causedbythehydrotrope destabilizationoftheliquidcrystal.

tropeonthestructurecouldbedirectlydeterminedusingNMR.Additionof thehydrotropemoleculeresultedinanarrowingofthedifferencebetweenthe NMRsignalsduetoadisorderingoftheliquidcrystal,asshowninFig.9[26]. Itwasassumedthatthiswastheprimaryfactorinthedestabilizationofthe liquidcrystal. Next,thediacidconformationwasdeterminedafteritwasaddedtotheoily dirtliquidcrystallinephase.Figure10showstwopossibilitiesforthe conformationofthehydrotropeintheliquidcrystal. Inoneformofthediacid(Fig.10b),bothpolargroupsarelocatedatthe interfacebetweentheamphiphilepolargroupsandthewater;theother possibilityisthatonlytheterminalcarboxylicgroupisfoundatthissite(Fig. 10a). Thetwoconformationsresultindifferentinterlayerspacing(Fig.10),anda determinationofthisdimensionwasusedtodistinguishbetweenthetwo alternatives.Lowanglexraydiffractiongivestheinterlayerspacingdirectly fromthemaximainthediffractionpattern. Interpretationoftheresultsisstraightforward;ifadditionofthediacidtoa lamellarliquidcrystalmodeldirtsystemdidnotincreasetheinterlayerspacing, theconformationinFig.10biscorrect;ifanincreasetookplace,thenFig.10a woulddescribethestructuralorganizationofthediacidmolecule. Theinterlayerspacingwiththediacidaddedwasveryclosetothehostliquid crystal(Fig.11),andthefirstconformation(Fig.10b)isobviouslytheone encounteredintheliquidcrystal.Asacomparison,theadditionofoleicacid withonepolargrouplocatedattheinterface,gavetheexpectedincreasein interlayerspacing,asshowninFig.11.Destabilizationofthelamellarliquid

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Fig.9 Additionofahydrotrope,Fig.6,toalamellarliquid crystalgaveareductionoftheorderparameterof thesurfactanthydrocarbonchain( );additionofa surfactantgavenochangeinorder( ).

Fig.10 Ahydrotrope,Fig.6,conformationwithonlyonepolargroupatthe water/amphiphileinterface(left)resultsinanenhancedinterlayerspacing d comparedwiththevalued foraconformationwithbothpolar 1

groupsattheinterface(right).

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Fig.11 Thelowanglexrayvaluesforinterlayerspacinginalamellarliquidcrystal (×)wasunchangedwiththeadditionofahydrotrope( ),Fig.6.Addition ofalongchaincompound,oleicacid,gavetheexpectedincrease( ).

crystallinephaseisnotonlyaffectedbythediacid;itappearstobeageneral propertysharedbyotherhydrotropes,suchasalkanols,shortchain quaternaryammoniumsalts,xylenesulfonates,andglycols,asshownby PearsonandSmith[8]andDarwishetal.[28]. Insomecases,theoilydirtislesspolarthanthemodelsystembyKielmanand VanSteen[26];forlesspolarfattyoilstheconceptofhydrotropicbreakdown ofaliquidcrystalisalsouseful[29]. V.Summary Thefunctionofhydrotropesinthedetergencyisdiscussedagainsttheir interactionwithlyotropicliquidcrystals.Themainactivityofthehydrotropeas apartofaliquiddetergentistoavoidgelationinbothconcentratedanddilute surfactantsystems. Thisabilityisdirectlyrelatedtoadetergent'sphaseequilibriawithhydrophobic amphiphiles.Thesephaseequilibriaillustrateandexplainthetwobasic characteristicsofhydrotropes:thatis,theirhighassociationconcentrationand theirpronouncedsolubilizingpower.

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References 1.C.Neuberg,Biochem.Z.,76:107(1916). 2.C.Neuberg,J.Chem.Soc.,110(II):555(1916). 3.R.H.McKee,Ind.Eng.Chem.Ind.Ed.,38:382(1946). 4.E.C.Lumb,Trans.FaradaySoc.,47:1049(1951). 5.W.LichtandL.D.Wiener,Ind.Eng.Chem.,41:1528(1949). 6.A.S.C.Lawrence,Nature(London),183:1491(1959). 7.S.E.FribergandL.Rydhag,Tenside,7:80(1970). 8.J.T.PearsonandJ.M.Smith,J.Pharm.Pharmacol.,26:123(1974). 9.A.D.Woolfson,D.F.McCaffer,andA.P.Launchbu,Int.J.Pharm., 34:17(1986). 10.N.K.Jain,W.Patel,andL.N.Taneja,Pharmazie,43:254(1988). 11.T.Nishihata,J.H.Rytting,andT.Higuchi,J.Pharm.Sci.,70:71(1981). 12.D.W.Osborne,ColloidsSurf.,30:13(1988). 13.V.G.GaikarandM.M.Sharma,SolventExtr.IonExch.,4:839(1986). 14.A.Mahapatra,V.G.Gaikar,andM.M.Sharma,Sep.Sci.Technol., 429:23(1988). 15.G.E.StyanandA.E.Bramhall,PulpPuu.Can.,80:725(1979). 16.D.E.Bland,Res.Rev.Aust.CSIROChem.Technol.,27(1976). 17.P.J.Nelson,Appita,31:437(1978). 18.D.E.Bland,J.Skicko,andM.Menshun,Appita,31:374(1978). 19.E.L.SpringerandL.L.Zoch,Pap.6:815(1979). 20.K.Shinoda,ColloidalSurfactants,AcademicPress,NewYork,(1963), pp.9–15. 21.K.H.RaneyandC.A.Miller,J.Coll.I.Sc.,119:539(1987). 22.T.FlaimandS.E.Friberg,J.Coll.I.Sc.,97:26(1984). 23.J.M.CoxandS.E.Friberg,J.Am.OilChem.Soc.,58:743(1981). 24.B.F.Ward,Jr.,C.G.Force,A.M.Bills,andF.E.Woodward,J.Am. OilChem.Soc.,52:219(1975). 25.T.Flaim,S.E.Friberg,C.G.Force,andA.Bell,TensideDetergents, 20:177(1983). 26.H.S.KielmanandP.J.F.VanSteen,FaradayDisc.,191(1979).

24.B.F.Ward,Jr.,C.G.Force,A.M.Bills,andF.E.Woodward,J.Am. OilChem.Soc.,52:219(1975). 25.T.Flaim,S.E.Friberg,C.G.Force,andA.Bell,TensideDetergents, 20:177(1983). 26.H.S.KielmanandP.J.F.VanSteen,FaradayDisc.,191(1979). 27.S.E.Friberg,S.B.Rananavare,andD.W.Osborne,J.Coll.I.Sc., 109:487(1986). 28.I.A.Darwish,A.T.Florence,G.M.Ghaly,andA.M.Saleh,J.Pharm. Pharmacol.,40:25(1988). 29.S.E.FribergandL.Rydhag,J.Amer.OilChem.Soc.,48:113(1971).

3 PhaseEquilibria GUYBROZE AdvancedTechnologyDepartment,ColgatePalmoliveResearchandDevelopm Milmort,Belgium I.Introduction II.WhatisaPhaseDiagram? A.Twocomponentphasediagrams B.Threecomponentphasediagrams C.Recordingphasediagrams III.PhaseDiagramsforIonicSurfactantContainingSystems A.Ionicsurfactant:water B.Ionicsurfactant,water,andorganicmaterialternarysystems C.Ionicsurfactant,water,protondonatingmaterial,andhydrocarbon quaternarysystems IV.PhaseDiagramsforNonionicSurfactantContainingSystems A.Nonionicsurfactantandoil B.Nonionicsurfactantandwater C.Nonionicsurfactant,water,andoil D.Effectsofsystemparametersonphasebehavior References

I.Introduction Allliquiddetergentscontainatleastonesurfactantinthepresenceofothermateri electrolytes,oilymaterials,andotherimpurities.Unlikeacademicresearch,thefo workwithindustrialgraderawmaterials

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containingsignificantamountsofmolecules,thepropertiesofwhichdifferfrom thoseofthemainproduct.Theunderstandingofhowagivenpropertyofa*give “pure”systemisaffectedby“impurities”isaccordinglyofessentialpractical importance.Understandingtheprinciplesbywhichagivenproductbehaves (asisorunderuseconditions)allowsustoreplacecounterproductivetrial anderrorbymoreefficientmethodswithabroaderrangeofpotential applications. II.WhatIsaPhaseDiagram? Aphasediagramisagraphicrepresentationofthephasebehaviorofasystem studied.Thesolidliquidvaporbehaviorofasinglecompoundasafunctionof temperatureandpressurecanberepresentedbyaphasediagram.Phase diagramsusuallyinvolvemorethanonecomponent.Theyareveryusefultools forformulation,becausetheyallowtheformulatortodefinenotonlythe acceptablecompositionofaproductbutalsotheorderofadditionofthe differentrawmaterials. A.TwoComponentPhaseDiagrams 1.TemperatureandComposition Whetheragivenproportionoftwo(liquid)compoundswillmixisdefinedby thermodynamics.Although,inregularsystems,theentropyofmixingisalways positiveandaccordinglyfavorabletomixing,theenthalpyofmixingcanbe positiveornegativedependingontheenergyofformationoftheheterocontacts attheexpenseofthehom*ocontacts. Anexothermicmixtureusuallyleadstomixinginallproportions.Ifthemixingis endothermic,thenumberofcoexistingphasesandtheircompositiondependon temperature.Increasingtemperatureusuallyresultsinanincreaseinthemutual solubilitiesofthetwocompounds,eventuallyleadingtocompletemiscibility aboveacriticaltemperature,theupperconsolutetemperature(UCT).Note thatsomeabnormalsystemscanalsopresentalowerconsolutetemperature (LCT).BothUCTandLCTarethermodynamiccriticalpoints.Atacritical point,thecompositionsofthetwophasesinequilibriumbecomeidentical. Figure1isaschematicrepresentationofatwocomponentphasediagram characterizedbyUCT.TheleftaxiscorrespondstopureA,andtherightaxis correspondstopureB.theabscissacorrespondstodifferentAB compositions.Itisverycommontoexpressthecompositionsinweight fractions,althoughnotcompulsory.Molefractionsorvolumefractionscanalso beused.Thecentral,shadedareacorrespondstothetwophasedomain.The clearzonearounditissinglephase.

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Fig.1 Phasediagramoftwosubstancesthatare onlypartlymiscibleatlowtemperature andbecomefullymiscibleabovethe “upperconsulatetemperature.”

2.TieLinesandLeverRule Whenamixtureseparatesintwophases,itisimportanttoknowthe compositionsandtheamountsofthetwophasesinequilibrium.Atielinelinks thetwocompositionsinequilibrium.Thismeansthatanycompositionlocated onthesametielinewillseparateintwophases,thecompositionsofwhichare definedbythepointsofcontactofthetielinewiththephaseboundary. Therelativeamountsofthetwophasesisdeterminedaccordingtothelever rule(Figure2).Ifthecompositionsareexpressedinweightfractions,the weightfractionofphaseAisCB/ABandtheweightfractionofphaseBis AC/AB. B.ThreeComponentPhaseDiagrams Practicalsystemsinvolvemorethantwocomponents.Athreecomponent systemcanberepresentedinanequilateraltriangle(Figure3).Acornerofthe trianglerepresentsapurecomponent,asiderepresentsbinarymixturesofthe componentsrepresentedbytheadjacentcorners,andanypointinthetriangle representsoneandonlyonetricomponentcomposition.

Fig.2 Leverrule,allowingquantificationoftheproportionofthetwo coexistingphasesinatwophasedomainofaphasediagram.

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Fig.3 Methodofdeterminingthecomposition ofathreeingredientmixture.

TheweightfractionofcomponentAinthecompositionrepresentedbyPinthe triangleisgivenbytheratioofthelengthsofthesegmentsperpendiculartothe sidesPa/(P b+Pb+Pc). Similarly,theamountofBisgivenbyPb/(P a+Pb+ Pc) andtheamountofCbyPc/(P a+Pb+Pc). Ofcourse,suchaphasediagramisisothermal.Theeffectoftemperatureona threecomponentphasediagramcanbevisualizedinthreedimensions,with temperatureattheelevationaxis.Thephasediagramlookslikeatriangular prism,witheveryhorizontalslicecorrespondingtoonetemperature. 1.FieldsandDensities Thereisanimportantdifferenceamongthethermodynamicfunctionsofstateas farasphaseequilibriaareconcerned.Somethermodynamicfunctionsofstate, suchastemperatureandpressure,havethesamevalueinallthephasesofa systematequilibrium.Theyareactuallytheforcesdrivingasystemtoits equilibrium.Suchfunctionsarereferredtoasfields [1]. Theotherthermodynamicfunctionsofstategenerallypresentdifferentvaluesin thedifferentphasesofasystematequilibrium.Typicalexamplesarethe volumesofthephasesandtheircomposition.Suchfunctionsaredensities. Athermodynamicexpressionoffunctionsofstatecanbeexpressedasasum offieldvariablesmultipliedbytheirconjugateddensity.Forexample, G=U+PVTS+ ini whereUistheinternalenergy,PVistheproductofthefieldvariablepressure andthedensityvariablevolume,TSistheproductofthefieldvariable temperatureandthedensityvariableentropy;and iniistheproductofthe fieldvariablechemicalpotentialofiandthedensityvariablenumberofmoles ofi.

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Thechemicalpotentialsarethefieldfunctionsconjugatedwiththe concentrations. 2.PhaseRule Foramulticomponentsystem,thephaserule[2]allowsustoknowthenumber ofindependentvariablesnecessarytodefinecompletely(fromacompositional pointofview)asystem.Thisnumberiscalledthenumberofdegreesof freedomorthevarianceofthesystem.Thevarianceƒisgivenbytherelation ƒ=C +2 whereCisthenumberofchemicallyindependentingredientsinthesystem, isthenumberofcoexistingphasesattheequilibrium,andthelasttermtakes careoftemperatureandpressure. Forisobarsystems,suchasallsystemsunderatmosphericpressure,thelast termshouldbe1.Similarly,isobarandisothermsystemshave0asthelast term. Adirectimplicationofthephaseruleisthatathreecomponentsysteminone phaseatatmosphericpressureandat25°Chasavarianceequalto2.This meansthattwodimensionsarenecessarytodescribesuchasystem.Another implicationisthatsuchasystemcouldshowamaximumofthreecoexisting phases. Asystembasedonfivecomponentswillneed,accordingtothephaserule,a fourdimensionhyperspacetobecompletelydescribed.Torepresentsucha system,somevariablesareusuallygrouped.Theaccuracyofthe representationis,ofcourse,imperfect. Amoreaccurateprocedureistosetavariabletoaconstantvalue.Thisis impossiblewithacompositionbecauseitisadensityandisdifferentineachof thecoexistingphases.Thephaseruledeterminesthenumberofindependent variablesasystemneedstoberepresentedbutdoesnotintroduceany restrictiononthechoiceoftheindependentvariables.Itisaccordinglymuch bettertofixafieldvariabletoreduceasystemofonedimension.Insteadof usingconcentrations(densityvariables),arepresentationasafunctionofthe chemicalpotentialsiseasiertoreadandismoreaccurate.Theproblemisthat, inpractice,itisverycomplicatedtoworkatdefinedchemicalpotentials. 3.TieLinesandCriticalPoints LetusconsidertwoliquidsAandBthatarenotverysolubleineachother. AdditionofliquidCincreasesthemiscibilityofBinAandofAinB.Cbehaves likeincreasingtemperatureinthebinaryphasediagram.Themajordifferenceis thatthetielinesarenolongerparalleltothebaseline,andthecriticalendpoint isnolongeratthemaximumofthemiscibilitygap(Figure4).ThisisbecauseC doesnotpartitionevenlybetweenthetwocoexistingphases.

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Fig.4 AWinsorIIternaryphasediagram.

Inthepresentcase,itgoespreferablyinB.Thecriticalendpointislocated neartheAcorner.Anisothermalcriticalendpointisusuallyreferredtoasa plaitpoint. 4.ThreePhaseDomain Insomecasesathreephaseregioncanbeobserved(Figure5).The coexistenceofthreephasesinequilibriuminanisothermalthreecomponent phasediagramisazerovariantsituation.Ofcourse,aninfinityofdifferent compo

Fig.5 AWinsorIIIternaryphasediagram.

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sitionsfallinsidethethreephasetriangle,butthecompositionsofthethree coexistingphasesdonotchangewiththeinitialcomposition.Theyare representedbythethreecornersofthethreephasetriangle.Allthatchange aretherelativeamountsofthethreephases. C.RecordingPhaseDiagrams Therearebasicallytwomethodsofrecordingphasediagrams:thetitration techniqueandtheconstantcompositionmethod.Bothhaveadvantagesand drawbacks. 1.TitrationMethod Inthetitrationmethod,amixtureistitratedbyanother.Typically,amixtureof twooftheingredientsistitratedbythethird.Theweightoftitranttoreacha phaseboundaryiscarefullyrecordedandplottedonthephasediagram.The processisthenrepeatedtocoverthewholedomaintobeinvestigated.Sucha methodisrelativelyquickandcangiveagoodideaofthephaseboundaries. Thereareneverthelesstwomajordrawbackstothismethod. First,thismethodgivesthephasediagramatonetemperatureonly.To determinethephasediagramatanothertemperature,theprocessmustbe repeated.Thetemperaturedomainpracticallyavailablewiththetitration methodislimited,becauseeverythingmustbekeptatthesametemperature. Theseconddrawbackofthetitrationmethodisthatitisusuallyusedinanout ofequilibriumcondition.Insomesystems,suchasthoseinvolvinglyotropic liquidcrystals,thetimeneededtoreachequilibriumcanbeverylong;besides, metastablephasescanalsobeencountered. Aphasediagramrecordedbythetitrationmethodshouldbeusedasaguide onlyandshouldneverbeappliedtolongtermstabilityprediction. 2.ConstantCompositionMethod Intheconstantcompositionmethod,aseriesofcompositions,coveringthe compositionrangetobestudied,arepreparedintesttubes,whichareclosed. Thetesttubesareshakenthoroughlyandallowedtostandinathermostatic bath.Thetesttubescontainingturbidsolutionsareallowedtostanduntilthey separateintotwoormorecompletelyclearphases.Thenumberofclear phasescanbereportedonthephasediagram,andthephasedomainscanbe mapped. Thismethodisverylong,butitallowsonetoapproachthetrueequilibrium conditions,andthetubescanbeusedatothertemperatures.Another advantageofthismethodisthat,whenasystemgivesmorethanonephase,it ispossibletoanalyzethephasesandtoknowexactlywherethephase boundariesare,aswellastheorientationofthetielines.

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III.PhaseDiagramsforIonicSurfactantContainingSystems A.IonicSurfactant:Water 1.KrafftPoint TheKrafftpointcanbedefinedasthetemperatureTkabovewhichthe amphiphilesolubilityinwatergreatlyincreases[3].Thereasonisthatthewater solubilityoftheamphiphile,whichincreaseswiththetemperature,reachesthe amphiphilecriticalmicelleconcentration(CMinFigure6).Whenthesolubility curveisaboveCM,thedissolvedamphiphileisformingmicellesandthe amphiphileactivityinwatersolutionnolongerincreases.Thereisaccordingly nolongeralimitationtosolubilization. TheKrafftpointisatriplepointbecauseatthistemperature,three“phases” coexist[4]:hydratedsolidamphiphile,individualamphiphilemoleculesin solution(monomers),andamphiphilemoleculesinvolvedinmicelles. Tkincreasesasthehydrophobicchainlengthincreases.TheKrafftpointsofthe sodiumsaltsoftheclassicamphiphiles(alkylsulfates,sulfonates,and benzenesulfonates)arebelowroomtemperature.TheKrafftpointisalsoa functionofthecounterion,thealkalineearthcationsgivinghigherKrafftpoints: sodiumlaurylsulfate,Tk=9°C;Casalt,50°C;Srsalt,64°C;andBasalt,105° C. BecausetheKrafftpointimposesalimitationinformulationprocesses,the followingrulestoreduceTkcanbeofessentialinterest: ChainbranchingandpolydispersityreduceTk. ComplexationofMgandCareducesTk.

Fig.6 TheKrafftpointisthetemperature atwhichthesolubilityofthe amphiphilebecomeshigherthanits criticalmicelleconcentration.

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ThepresenceofanunsaturationdecreasesTk. AveryefficientwaytoreduceTkistoincorporatetwoorthreeoxyethylene monomersbetweenthehydrophobicchainandthepolarheadgroup(alcohol ethoxysulfates). Ofcourse,ineachcase,otherpropertiesoftheamphiphile,suchasthesurface activity,canbeconsequentlybemodified. 2.PhaseDiagram Thephasediagramofsodiumdodecylsulfate/waterisrepresentativeofmany ionicsystems(Figure7)[5].Liquid(L1)istheaqueousmicellarphase;Hais thehexagonallyotropicliquidcrystal,sometimescalledthemiddlephase;and Laisthelamellarlyotopicliquidcrystal,sometimescalledtheneatphase.On thesurfactantrichside,severalhydratedsolidphasesarepresent. Asageneralrule,inany(real)phasediagram,atanypointrepresentativeofa regionandonitsboundaries,thenumberofphasesandtheirnaturearesimilar. Atielineisthelinejoiningthepointsrepresentativeoftwocoexistingphases.If thetotalcompositionofamixtureCfallsinatwophaseregion,itseparatesin thetwophaseslocatedatbothsidesofthetielinethatpassestheformulation point(AandB).Theweightdistributionofthetwophasesisgivenbythelever rule.

Fig.7 Typicalphasediagramofawateranionicsurfactantsystem.

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B.IonicSurfactant,WaterandOrganicMaterialTernarySystems 1.OrganicMaterial=Hydrocarbon Letusconsideranisothermofawaterionicamphiphilebinarymixtureabove theKrafftpoint(forexample,watersodiumoctanoate)[6].Atanamphiphile concentrationof7%(thecriticalmicellarconcentration),themicellarisotropic solutionL1appearsandlastsupto41%. Between41and46%isthemiscibilitygapbetweenL1andH1,thehexagonal phase,whichlastsupto52%.Above52%isthemiscibilitygapbetweenH1 andthehydratedcrystal. Ifanonpolarcomponent(aliphatichydrocarbonortetrachloromethane)is added,almostnothinghappens(Figure8a).Thesolubilityofdecaneineither themicellarsolutionortheliquidcrystalisverylimited.Thisistrueofany moleculeexhibitingonlydispersioncohesiveforces. 2.OrganicMaterial=PolarbutNotProtonDonatingMaterial ThesolubilityofamoleculeexhibitingdipoledipolecohesiveforcesandlowH bondingcohesiveforces,suchasmethyloctanoate,ishigherthanthatofa hydrocarbon,butnothingspecialhappensinthecenterofthephasediagram. 3.OrganicMaterial=ProtonDonatingMaterial Ifthethirdcomponentisanonwatersolublealcohol(fivecarbonsormore), amine,carboxylicacid,oramide,thephasetopographyisprofoundly modified. ThephasediagrampresentedinFigure8b[7]showsinadditiontoL1andH1a hugelamellarphase,anarrowreversehexagonalphaseH2,and,evenmore important,a“sectorlike”areaofreversemicellesL2.Thismeansthatthe solubilityinndecanolofasodiumoctanoatewatermixturecontaining between25and62%amphiphileisbyfarmoreimportant(30–36%)thanpure water(4%)andpuresodiumoctanoate(almostnil).Thisphaseisessentialto obtainwaterinoil(w/o)microemulsions. ThesolubilityofndecanolintheL1phaseisalsoimportant(upto12%atthe “end”oftheL1).TheL1phaseisresponsiblefortheobservationofoilinwater (o/w)microemulsions.TheLadomain,generallylocatedinthemiddleofthe diagram,pointstowardthewatersideforacriticalsurfactant/cosurfactant ratio.(A1:2sodiumoctanoatetondecanolratioleadstoalamellarphase withaslittleas17%surfactantcosurfactant.)Insomecases,suchasoctyl trimethylammoniumbromidehexanolwater,thelamellarphasealreadyexists for3%hexanol+3%OTAB! Thepracticalinterestofalamellarliquidcrystalliesinitssuspendingcapability. Alyotropicliquidcrystalexhibitsaviscoelasticbehaviorthatallows

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Fig.8 (a)Typicalternaryphasediagramofwater,anamphiphile (sodiumoctanoate),andahydrocarbon(octane).(b)Typical ternaryphasediagramofwater,anamphiphile (sodiumoctanoate),andacoamphiphile(decanol).This phasediagramwasestablishedbyEkwallin1975.

suspensionofsolidparticlesforaverylongtime.Thelamellarphaseis additionallycharacterizedbyanidealcriticalstraintoprovidethesuspension withgoodresistancetovibrationsandconvections,withoutimpairingits flowabilitybyaslimyaspect.

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C.IonicSurfactant,Water,ProtonDonatingMaterial,and HydrocarbonQuaternarySystems Thesolubilizationofanoil,suchasdecane,inthemicellarisotropicsolutionL1 orinthereversemicellarisotropicsolutionL2canbeveryimportant.L1leads towaterinoil(w/o)microemulsionsandL2tooilinwater(o/w) microemulsions. Notethatthe“cosurfactant”isanamphiphilewith(generally)alowermolecular weightthanthe“main”amphiphile,the“surfactant.” 1.WaterinOilSystems AsillustratedbyFigure9,theL2phaseisabletosolubilizeaverylargeamount ofanhydrocarbon,suchasdecaneorhexadecane.Infact,acomposition containingupto75%decaneandwater/surfactant/cosurfactantproportions correspondingtotheL2phaseisstillclear,fluid,andisotropic,forms spontaneously,andisthermodynamicallystable.Thestructureofthis microemulsioncanbe(tosomeextent)regardedasadispersionoftinywater droplets(reversemicelles)inacontinuousphaseofthehydrocarbon.The surfactantandcosurfactantareatthewater/oilinterphase.Thistypeofsystem isoftenreferredtoasawaterinoilmicroemulsion. Theterm“microemulsion”toqualifysuchsystemsisnotwellchosen:itconveys theideaofanactualemulsioncharacterizedbysubmicrometer(below0.1 m) droplets.Asiswellknown,anemulsionisnotthermodynamicallystableand cannotberepresentedbyasinglephasedomaininathermodynamicphase diagram.Ontheotherhand,thesocalledmicroemulsionsmustbeconsidered realmicellarsolutionscontainingoilinadditiontowaterandsurfactants.

Fig.9 A“waterinoil”microemulsion.

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Thesesolutions,althoughveryfarfrom“ideal”inthethermodynamicsense,are neverthelessalwaysrealinthethermodynamicsense. Anothergreatdifferencebetweenthemicroemulsionsandtheemulsionsisthat, intheverygeneralcase,amicroemulsionrequiressignificantlymoresurfactant thananemulsion. Thesewaterinoilmicroemulsionsexhibitotherimportantcharacteristics: Thedomainofexistenceislarge.Significantcompositionalchangescanoccur withoutcrossingaphaseboundary.Suchbehaviorisparticularlyimportantfor manufacturingprocesses,becauseittoleratessome“freedom”during formulation. Theyareverystableinalargetemperaturerange,usuallyfromtheKrafftpoint uptotheboilingpoint.Moreover,thephaseboundariesarealmostinsensitive totemperature. Thephasetopographyremainsalmostunchangedevenupto75%oftheionic amphiphileisreplacedbyanonionicamphiphile. Toobtainawidewaterinoilmicroemulsion,itisessentialtoadjustcarefully thecosurfactantstructure(usuallyitschainlength)anditsrelativeamount. Althoughtrialanderrorisstillthemostcommonlyusedmethodofobtaining microemulsions,atentativeruleistocombineaveryhydrophobiccosurfactant (ndecanol;C10OH)withaveryhydrophilicionicsurfactant(alcoholsulfates) andalesshydrophobiccosurfactant(C6OH)withalesshydrophilicionic surfactant(octyltrimetylammoniumbromide).Forveryhydrophobicionic surfactants,suchasdialkyldimethylammoniumchloride,evenawatersoluble cosurfactant,suchasbutanolorisopropanol,isadequate(thisrulederivesat leastpartiallyfromthefactthatanimportantfeatureofthecosurfactantconsists ofreadjustingthesurfactantpackingatthesolvent/oilinterface). 2.OilinWaterSystems WestatedearlierthatthesolubilityofdecaneintheL1phaseisalmostnil.For awelldefinedsurfactant/cosurfactantratio,hugequantitiesofdecane(orany hydrocarbon)canbesolubilizedfromtheL1.Athin,snakelikesinglephase domaindevelopstowardtheoilpole(Figure10).Thisphasecanberegarded asamphiphilemicellesswollenwithoil. Generally,theoilinwatermicroemulsionphasesareonlymetastablesystems. Aseverymetastablesystem,o/wmicroemulsionsneedanactivationenergyto separate,andsometimesthisactivationenergyissolargethattheseparation almostneveroccurs.Suchsystemsarenotthermodynamicallystableandcould accordinglynotbeconsideredinaphasediagram.Ontheotherhand,they formspontaneouslyandarestable(becauseofthehighactivationenergyfor separation)foraverylongtime.

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Fig.10 An“oilinwater”microemulsion.

Atypicalexampleofaverystablemetastablesystemisamixtureofone volumeofoxygenwithtwovolumesofhydrogen.Themixtureisspontaneous andstableforaverylongtime,withoutbeingthermodynamicallystable.The finalthermodynamicallystablestateisobtainedbyaddingacatalyst(platinum foam)oraflametothemixture. Althoughnotthermodynamicallystable,o/wmicroemulsionsform spontaneouslyandareaccordinglyuseful(easeofmanufacture). Nonthermodynamicstabilityimpliessomeconstraints: Thepositionofao/wmicroemulsioncandependontheorderofmixingofthe rawmaterialsandontheshearimposedonthesystem. Theirdomainofexistenceisgenerallynarrow. Thesystemcanbesensitivetofreezeandthawcycles. IV.PhaseDiagramsforNonionicSurfactantContainingSystems Thephasetopographyofaternarysysteminvolvingwater,ahydrocarbon,and apolyethoxylatedfattyalcoholdependsonthehydrocarbonchainlength, branching,degreeofinsaturation,aromaticity,andsoon,ontheamphiphile structure(hydrophobicandhydrophilicchainlength),andalsoontemperature, whichexertsaverystronginfluenceontheconfiguration(andaccordinglyon thesolubility)ofthepolyoxyethylenesegmentsinwatersolution.Areviewhas beenpresentedbyKalhweitetal.inaseriesofpapers[8–11].

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Thephasetopographyisstronglyinfluencedbythemoreelementarybehavior ofthebinaryamphiphileoilandamphiphilewatersystems. A.NonionicSurfactantandOil Polyethyleneoxideisnotsolubleinahydrocarbon,suchashexaneordecane. Ifafattychainisattachedtoashortsegmentofpolyethyleneoxide(4–8EO units),thenonionicamphiphileobtainedexhibitsasolubilityprofileinoil dependingontemperature. Atlowtemperatures,amiscibilitygapisobtained,translatingthenonsolubility ofthepolyethyleneoxidechainintheoil.Athightemperatures,theeffectofthe energyispreponderantandtheamphiphileissolubleinallproportionsinthe oil. AspredictedbytheFloryHugginstheory,suchasystemshowsalower miscibilitygapcharacterizedbyanuppercriticalpoint,thetemperatureTa whichdependsonboththeoilandtheamphiphilestructure(Figure11a).The criticalcompositionisusuallynotfarfromthepureoilside. Figure11bshowsthelowermiscibilitygapbetweensomenalkanesandC6E5 (nhexanolethoxylatedwith5ethyleneoxidemolecules).Theuppercritical temperatureTariseswithincreasingtheoilchainlength(itshydrophobicity). ThecriticaltemperatureTaisoftenreferredtoasthehazepointtemperature, andthemiscibilitygapbetweenoilandamphiphileplaysanessentialroleinthe ternaryphasediagram.

Fig.11 (a)Thehazepointtemperature.(b)Setofphasediagramsshowinghow thehazepointtemperatureisaffectedbythestructureoftheoil.

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B.NonionicSurfactantandWater 1.CloudPoint Thephasediagramofthebinarysystemnonionicamphiphilewaterismore complicated(seeFigure12).A“classic”uppercriticalpointexists,butusually below0°C.Athighertemperatures,mostnonionicamphiphilesshowanupper miscibilitygap,whichisactuallyaclosedloopwithanupperaswellaslower criticalpoint.ThelowercriticalpointTb isoftenreferredtoasthecloudpoint temperature.Theuppercriticalpointoftenliesabovetheboilingtemperatureof themixture(at0.1MPapressure). Thepositionandtheshapeoftheloopdependonthechemicalnatureofthe amphiphile.ThecloudpointtemperatureTb playsanessentialroleinthree componentphasediagramtopography. Theclosedloopcanberegardedasaverticalsectionthrougha“nose”inthe concentrationtemperaturepressurespace,atconstantpressure(seeFigure 13a).Whenthepressurerises,thesurfacecoveredinthetemperature concentrationphasebythephaseseparationloopdecreasesandvanishesata criticalpressureP*. TheshrinkingoftheloopofthesystemwaterC4E1withincreasingpressureis giveninFigure13b.ThecriticalconditionsforthelooptovanishareT*=95° C,P*=80MPa,andC*=28wt%. Toshowthemultidimensionalnatureofthesephenomena,notethatsimilar effects(shrinkingoftheloop,f.i.)canbeachievedbytheadditionof “hydrotropic”electrolytesatconstantpressureorbyincreasingthe hydrophilicityoftheamphiphile.Figure13cexhibitstheloopareasofbutanol (C4EO),ethyleneglycolbutylether(C4E1),anddiethyleneglycolbutylether (C4E2).Thelastdoesnotexhibitaloopat0.1MPa(±1atm),butthesystem behavesactuallyasifthenosewere“lurking.”Althoughnophaseseparation occursin

Fig.12 Thephasebehaviorofa waternonionicamphiphile system.

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Fig.13 (a)Theeffectofpressureonthesizeofthe“closedloop.”(b) Closedloopofthesystemwaterethyleneglycolbutyletherat differentpressures.(c)Effectofthehydrophilicgroupofthe amphiphileontheshapeoftheclosedloop.(FromRef.[16],with permission.)

water,thelurkingnoseexertssomeinfluenceonthethreecomponentphase diagram.Anotherwaytolookatthesamephenomenonistoconsiderthat,in conditionsclosetoT=90°CandC=30wt%,theC4E2watersystemissuch thatthemixingentropyisjusthighenoughtomaintainthemoleculesinasingle phase,theenthalpictermbeingpositive(endothermic).Assoonasathird incompatibleingredient(theoilf.i.)isincorporated,theentropyisnolonger abletomaintainthemoleculesinasinglephase,andphaseseparationoccurs.

Page52 TABLE1

Amphiphile

HLB

min (wt%)

C4E1

10.3

58.9

48.7

29.0

C6E3

12.7

47.4

45.4

13.5

C8E4

12.6

29.6

39.6

6.9

C10E5

12.5

19.7

40.3

3.5

C12E6

12.4

10.6

48.0

2.2

(°C)

Cb (wt%)

InTable1,theHLBiscalculatedaccordingtotheempiricalequation HLB=20MH/M whereMHisthemolarmassofthehydrophilicgroupandMthetotalmolar massoftheproduct.g ministheminimumamphiphileconcentrationrequiredfor thehom*ogenizationofa1:1mixtureofwaterandndecaneataround40°C (wt%).Tb andCb arethecoordinatesofthelowercriticalpoints(cloudpoint). AlthoughtheHLBseemstobecorrelatedwiththecloudpoint,itcannotgive anyinformationontheamphiphileefficacy(g min).EveniftheHLBremains constant,increasingboththepolarpartandthenonpolarpartofasurfactant moleculesignificantlyimprovesitsefficacy(atleastit*wateroilcompatibilizing efficacy). 2.LiquidCrystals Theclosedloopisnottheonlycharacteristicofthenonionicsurfactantwater binaryphasediagram.Liketheionicsurfactantwatermixture,thenonionic surfactants,atahigherconcentrationinwater,exhibitlyotropicmesophases. Figure14showsatypicalbinaryphasediagramexhibitingthefulllyotropic mesophasesequence: I1:cubic,isotropicphase H1:directhexagonalphase(middlephase) V1:specialcubic(viscousphase) La:lamellarphase(neatphase) Notethepresenceofthetwophasedomainssurroundingeachmesophase,the criticalpointontopofeach,andthezerovariantthreephasesituation. Althoughverydifficulttodeterminewithaccuracy,themiscibilitygapsalways exist,aswellasthethreephasesituations.Ofcourse,thecriticaltemperatures andconcentrationscorrespondingtoeachmesophasedependonthechemical natureoftheamphiphile,thepressure,andtheoptionalpresenceofan electrolyte.

criticalpointontopofeach,andthezerovariantthreephasesituation. Althoughverydifficulttodeterminewithaccuracy,themiscibilitygapsalways exist,aswellasthethreephasesituations.Ofcourse,thecriticaltemperatures andconcentrationscorrespondingtoeachmesophasedependonthechemical natureoftheamphiphile,thepressure,andtheoptionalpresenceofan electrolyte.

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Fig.14 Binaryphasediagramofa waterethoxylatednonionicamphiphile phasediagram,includinglyotropic liquidcrystaldomains.(FromRef. [11],withpermission.)

Figure15showssomeexamplesofnonionicamphiphilewaterbinaryphase diagrams[10,12].Asarule,amphiphileswithhydrocarbonchainlengthof8or fewercarbonatomsexhibitonlytheloop(inadomaindependingonthe ethoxylation)andnomesophase. Longerchainamphiphilesshowoneormoremesophases,onebeing preponderant.Thetypeofmainmesophase(theoneexhibitingthehighest criticaltemperature)dependsontherelativevolumesoftheEOand hydrocarbonchains.Ifthevolumesaresimilar,thelamellarphaseis preponderant.ThisisthecasewithC12E6.IfthevolumeoftheEOchainis significantlyhigherthanthevolumeofthehydrocarbonchain,thehexagonal phasewillmeltathighertemperature(C12E7);ifthevolumeoftheEOchainis muchhigherthanthevolumeofthehydrocarbonchain,thecubicphaseI1may appear. Insomecases,suchasC12E5,thelamellarphaseLa(ortheH1)interfereswith theloop(withthecloudpointcurve)andinducesthesocalledcriticalphase, L3.L3isanisotropic,oftenlactescentphase,exhibitingazerovariantthree phasecriticalpointatit*lowertemperatureofexistence.Thenatureofthe threephasesinpresenceatthecriticalconditionsareW(waterwithaminute amountofamphiphile),L3andLa.TheL3phaseseemstohaveabeneficial actiononcleaningperformance,maybebecauseofthepresenceofthecritical point. C.NonionicSurfactant,Water,andOil Fromthephasebehaviorofbothbinarymixtures(wateramphiphileandoil amphiphile),itisnowpossibletoaccount,atleastqualitatively,forthethree componentphasediagramasafunctionoftemperature.Thepresenceofa hazepointontheoilamphiphilephasediagram(criticalpointa)attemperature Tashowsthatthesurfactantismorecompatiblewiththeoilathightemperature

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Fig.15 Realexamplesofwaterethoxylated nonionicamphiphilebinaryphase diagrams.(FromRef.[10],with permission.)

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thanatlowtemperature.Thepresenceofacloudpointonthewater amphiphilephasediagram(thelowercriticalpoint )attemperatureTb shows that(atleastintheneighborhoodtemperaturedomain)theamphiphileisless compatiblewithwaterathighthanatlowtemperatures.Asaconsequence(the otherparametersbeingkeptconstant),theamphiphilebehaviordependson temperature. Atlowtemperature,thesemixturesaremorecompatiblewithwaterthanwith oil.ThephasediagramcorrespondingtothissituationisillustratedinFigure16, a1ora2.Thetielineorientationisdirectlydeducedfromthepartitioningofthe amphiphilebetweenwaterandoil:becauseunderthecurrentconditionsthe surfactantismorecompatiblewithwaterthanwithoil,themajorityofthe amphiphileisinthewaterphaseandonlyalimitedamountofamphiphileis presentintheoil.Accordingly,thetielinespointinthedirectionoftheoil corner.Diagramsa1anda2(Figure16)arereferredtoasWinsorI(WI).If thetemperatureatwhichthephasediagramisrecordedliesaboveTa(thehaze point),acriticalpointCPaispresentneartheoilcorner(althoughpure amphiphileandpureoilaremiscible,thepresenceofasmallamountofwater “recalls”thelackofcompatibilitybetweenamphiphileandoil).Ontheother hand,ifthetemperatureliesbelowTa,nocriticalpointappearsinthethree componentphasediagram(itseemstolieforanegativewaterconcentration). Athightemperatures,thesemixturesaremorecompatiblewithoilthanwith water.Thephasediagramcorrespondingtothissituationisc1orc2inFigure 16.Theamphiphilepartitioningnowfavorstheoil,andthetielinespointinthe directionofthewatercorner.c1andc2arereferredtoasWinsorII(WII).A criticalpointCPb isfoundifthetemperatureliesbelowthecloudpoint

Fig.16 Evolutionofwaterethoxylatednonionicamphiphileoilternaryphase diagramswithtemperature(risingfromatoc).

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Tb butmoreoften,thecriticalpointliesoutsidetheGibbstriangle(T>Tb ). InWIandWIIrepresentations,thecriticalpointCPb orCPaiscalledaplait point.IfthetemperaturedifferencebetweenthetemperatureTatwhichthe phasediagramisrecordedandthecriticalpointofthebinarymixture.Tb orTa, increases,thedistancefromtheplaitpointtotheoilamphiphileaxisforCPb andwateramphiphileforCPaincreases,too.Animportantcharacteristicofa ternarysystemisthelinethatlinkstheplaitpointsasafunctionoftemperature. Theplaitpointcurveisreallythetraceofthepartitioningoftheamphiphile betweenoilandwater.Theclosertotheoilistheplaitpoint,theamphiphileis moreinthewater,andviceversa. Atlowtemperatures,theamphiphileismorecompatiblewithwaterbecause waterinteractsstronglywiththehydrophilicheadgroup.Accordingly,the hydrodynamicvolumeoftheheadgroupisgreaterthanthehydrodynamic volumeofthehydrocarbontail.Athightemperatures,headgrouphydrationis reducedandsoishydrodynamicvolume,whichbecomessmallerthanthe hydrodynamicvolumeofthehydrocarbontail.Thereisnecessarilya temperatureatwhichthehydrodynamicvolumesofthetwoantagonisticparts oftheamphiphilemoleculeareequal.Thisparticulartemperature,represented by ,isthephaseinversiontemperature(alsocalledtheHLBtemperature). Thephaseinversiontemperatureisacharacteristic(andisaccordinglya function)ofthenatureoftheoil,theamphiphile,andthebrine(ifelectrolytes arepresent).Ifthepressurecanvary(asinoilrecovery),italsochanges .It isimportanttorealizethat canbehigherthanbothCPb andCPawhenthe amphiphilesolubilityisverysmallinwaterandtotalinoil. Thetopographyofthephasediagramatthephaseinversiontemperature dependsonthemutualincompatibilitiesbetweenoilamphiphile,water amphiphile,andwateroil.Evenwithapolaroilandwatercontaininga chaotropic(hydrotropic)electrolyte,thewateroilincompatibilityishigh enoughtoguaranteeamiscibilitygapfrom0to100°C. Withtheamphiphile,thesituationisnotassimple.Weshowedthat,at ,the amphiphileisequallycompatiblewithwaterandoil,butnoassumptionismade aboutthedegreeofcompatibility.Twolimitcasescanoccur: 1.Theamphiphileiseitherverycompatiblewithbothwaterandoilornotvery incompatible.ThephasediagramwilllooklikeFigure16b1,withaplaitpoint onlyforanequalamountofoilandwaterandwiththelinesparalleltothe wateroilside.(equalpartitioning).Thisplaitpointcorrespondstothemerger oftheCPaandCPb lines,andtheprojectionoftheplaitpointcurvesontheoil watertemperaturephasediagramshouldlooklikeFigure17aorb. 2.Theamphiphileisequally(andsignificantly)incompatiblewithbothwater andoil.ThephasediagramwillnowlooklikeFigure14b2.Athreephase triangle(3PT)appears.

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Fig.17 Transitionfromaninfratricriticalsituation(aandb)toasupertricritical situation(dande)throughatricriticalpoint(c).(FromRef.[11],withpermission.)

Threephasesarenowinequilibrium: 1.Awaterrichphase(W) 2.Anoilrichphase(O) 3.Anamphiphilerichphase(S) Theamphiphilerichphaseisalsocalledthesurfactantphaseorthemiddle phase.Thelastterms,duetoShinoda,resultsfromthephysicalappearanceof athreephasebody: 1.Adense,waterrichphaseatthebottom 2.Alight,oilrichphaseatthetop 3.Aphasecontainingmostoftheamphiphileinthemiddle Itisworthnotingthatwithhighermolarvolumeamphiphiles,suchasC12E4,a significantamountoftheamphiphilecanbepresentintheoilphase,evenat . Here,too,theplaitpointsCPaandCPb willbeorwillnotbeinsidetheGibbs triangledependingontherelativepositionsof ,Ta,andTb . Ifthephasediagramexhibitsathreephasetriangle,itiscalledaWinsorIII (WIII)system.Insuchasituation,theplaitpointcurvesdonotmergebut “cross”eachotherandstopattwoterminalcriticalpoints(seeFigure17dor e). Thesequenceoftheevolutionofathreecomponentsystemwhentemperature hasrisencanbesummarizedasfollows.Iftheamphiphileisstrongly incompatiblewithoilandwater, WI

WIII

WII

Iftheamphiphileiscompatibleorisweaklyincompatiblewithoilandwater, WI

WII

Awaytomodifyamphiphilecompatibilitywithoilandwateristochangeits molecularweight,keepingtheproperbalancebetweenoleophobicityand hydro

Page58

phobicity.AhighmolecularweightamphiphilelikeC12E6willshowaWIWII WIIsequence,althoughalowmolecularweightamphiphilelikeC4E2willshow (withdecanolacetateastheoil)aWIWIIsequence. Byvaryingtheamphiphile(in)compatibilitythroughitsmolecularweight,itis possibletopassfromaWIWIItoaWIWIIIWIIsequence.Atacertain point,asituationasillustratedinFigure15cwilloccur:theplaitpointcurves justmergecriticallyandthethreephasetriangle(3PT)collapses.Thissituation correspondstoatricriticalpoint,anessentialconceptintheoretical thermodynamics. Whenthesystemissuchthata3PTappears(byfarthemostcommoncase), the3PTexistsfromatemperatureT1lowerthan toatemperatureTuabove .Tosomeextent,thedifferencebetweenT1andTuisameasureofhowfar thesystemisfromthetricriticalconditions.(Notethat isnotnecessarilythe averageofTuandT1.) Thethermalevolutionofatypicalsystem,withbrokencriticallines(seeFig. 18),canbesummarizedasfollows: AtT400

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Fig.11 Wateruptakeasafunctionofsurfactantconcentrationusing thecollagenswellingtest.(Source:FromRef.84,reproduced bypermission.)

interfacialtensionsareusuallyanindicationofthesurfactant'seffectiveabilityto emulsifygreaseandoilysoils[18]. (b)DrainageTest.Fasterdryingandspotfreeutensilsmaybeother consumerdesiredbenefitsofLDLDs.Atestmethodtomeasurethedraining oflightdutyliquidswasdescribedinU.S.Patent5,154,850[66].Inthistest platesareimmersedinasolutionofproductforafixednumberoftimes, removed,anddriedunderambientconditions.Thiscycleisrepeated,withthe finaldippingfollowedbyrinsing.Theplateisallowedtodryandthewater spotsarecounted.Aproductthatprovidesgooddrainageleavesfeworno spotsontheutensils. Inanotherdrainagetest[87],variousregularkitchenutensils,suchasdrinking glasses,glassdinnerplates,andceramicdinnerplates,arewashedintest compositionsundercontrolledconditions.Theutensilsarethenrinsedand placedinaracktodry.Thetimeatwhichdrainagebeginsandthepercentage areadriedbythisdrainagearerecorded. (c)RinsingTest.Althoughcopiousandlonglastingfoamsaredesirablefor LDLDs,consumersalsowantthefoamtobeeasilyrinsedawayfromthe dishessoasnottoleaveresiduethatcouldappearasspots.Atestmethod wasdisclosedinU.S.Patent5,154,850fortheevaluationoftherinsabilityof foamgeneratedforanLDLD[66].Thisinvolvesmakingasolutionofproduct, chargingittoacontainerandstirring.Thesolutionisdischargedfrombot

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tomofthecontainer,leavingresidualfoaminthecontainer.Tapwaterisadded tothecontainerwithresidualfoamandstirredagain.Thestirringanddraining stepsarerepeateduntilnofoamremainsinthecontainer.Theproductthat needsfeweradditionsofwaterisconsideredtohavebetterrinsing characteristics. V.FormulationTechnology A.Formulation FormulatinganLDLDisbothascienceandanart.Itrequiresagoodbalance amongproductperformance,esthetics,safety,andcost.Fromtheconsumer pointofview,theimportantattributesforaliquidhanddishwashingdetergents arelistedinTable12.Consequently,liquiddishwashingdetergentsare formulatedtodeliveragainsttheseconsumerrelevantattributes. FormationofLDLDstypicallyinvolves(1)selectingappropriaterawmaterials forthedesiredperformance,(2)developingformulasandoptimizingfor performance,(3)optimizingproductesthetics,(4)testingproductsafety,(5) optimizingproductcost,and(6)agingforproductstability,and(7)validating withconsumers. Thefollowingsectionpresentsareviewonformulationagainstthese performanceattributeswiththeintentofprovidingsomeguidelines. B.GuidelinesandExamples 1.FormulatingforEffectiveCleaning ThemostimportantperformanceattributeofaLDLDiscleaning.Asdiscussed earlier,cleaningofdisheswithanLDLDreliesprimarilyontheinterfacial propertiesprovidedbythesurfactants.Varioussurfactantsexhibitdifferent interfacialpropertiesandthusvaryingabilityinremovingdifferentsoilsfrom TABLE12ImportantAttributesofaHand DishwashingLiquidDetergent

Effectivecleaning

Copiousandlonglastingfoam

Mildnesstohands

Pleasantfragrance

Convenienttouse

Safetohumans

Safetodishesandtableware

Storagestability

Economictouse

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varioussurfaces.Ingeneral,acombinationofsurfactantsisnecessaryforan LDLDtobeeffectiveagainstthewidespectrumofsoilsencounteredinthereal world. AsignificantnumberofpatentsonLDLDshavebeenissuedintheUnited States,Europe,andJapaninrecentyears.ListedinTable13arerecentU.S. patents[27,28,29,62,88–110]onLDLDformulatedforeffectivecleaning.The technologyutilizedinthesepatentsrangesfromspecialsurfactants,surfactant mixtures,salts,andmicroemulsionstotheuseofspecialadditives,suchas lemonjuiceandabrasives. 2.FormulatingforHighandLongLastingFoam Itiswellrecognizedthatfoamisthemostimportantvisualsignalconsumers usetojudgetheperformanceofanLDLD.Thisisdespitethelackofdirect correlationbetweenthefoamingandcleaningpropertiesofanLDLD,as discussedearlier.Therefore,itiscriticallyimportantthattheformulatorscreate anLDLDwithcopiousandlonglastingfoam. Copiousfoamusuallyrequirestheuseofhighfoamingsurfactants,typically anionicoramphotericsurfactants[10,21,111]oramixtureofsurfactants. Longlastingfoamoftenrequiresfoamstabilizers[22]inadditiontoaproper surfactantmixture.Table14isasummaryofrecentU.S.patents[26,72,112– 132]onLDLDsformulatingforgoodfoamingproperties.Thetechnologies involvedareeitherusingnovelsurfactantsorsurfactantblendsornovelfoam stabilizers. 3.FormulatingforMildness Forsomeconsumers,mildnesstoskinisanimportantattributeofaLDLD, especiallythosewhohavesensitiveskins. ThereareessentiallytwoapproachestoformulateanLDLDformildness:(1) usemildsurfactants,suchasnonionicsurfactants,zwitterionicsurfactants,ora combination;and(2)useadditivesthatareantiirritants,suchasmodified proteinsorpolymers.RecentU.S.patents[13,25,30,66,133–151]onLDLDs claimingamildnessbenefitaresummarizedinTable15. 4.FormulatingforDesirableEsthetics TheestheticattributesofLDLDsarejustasimportantastheirperformance. Thisincludescolor,fragrance,cloudandclearpoints,viscosity,andproduct stability.Color,fragrance,andviscosityareusuallychosenbasedonconsumer preference.Thecloudandclearpointsmustbeadequateforthetemperature towhichtheproductislikelytobeexposed. (a)CloudandClearPoints.Thecloudpointisthetemperatureatwhichthe productbeginstoturncloudyorhazyuponcooling.Theclearpointisthe temperatureatwhichthecloudyproductturnsclearagainuponwarming.In

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NorthAmericaandEurope,itisdesirablethatthecloudpointbebelow5°Cand theclearpointnotexceed10°C. ThecloudandclearpointsofanLDLDcanbeadjustedusinghydrotropes[6,15 suchassodiumxylenesulfonate,sodiumcumenesulfonate,alcohols,orurea.Fig 12showsthesignificanteffectofSXSontheclearpointofanLDLDformulation ishypothesizedthathydrotropesactbydestabilizingliquidcrystallinephasesthat mightformandseparatefromthebulkmixture[153]. (b)Viscosity.TheviscosityofanLDLDisveryimportantforitsconsumer acceptabilityanditsdispersibilityondilution[154].TheviscosityofanLDLDis typicallyintherangeof100–500CPS.Insomemarkets,suchasMalaysiaand HongKong,consumerslikemuchthickerproductwithviscosityintherangeof 2000–3000CPS.TheviscosityofanLDLDisastrongfunctionofitsactive ingredientlevel,theisomerdistributioninthesurfactant,therelativeamountof differentsurfactants,andthesaltlevels.Saltcanbebothaviscositybuilderanda viscosityreducer.AnexampleofasimplesystemissodiumAEOS(2.8EO)at 15%concentration.TheviscosityfirstincreaseswiththeadditionofNaClandth decreasesastheamountofNaClincreases[155].AEOSwithnarrowEO distributionthickensmuchmorethanAEOS

Pag

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withaconventional,broadEOdistribution.Otherfactorsthataffectsaltthickenin arecarbonchainlegnthandcarbonchaindistribution[155]. SaltalsohasasignificanteffectontheviscosityofLAS.Dependingonthecation oftheLAS,saltintherange0–2%canhaveamodestorgreateffectonthe viscosity[154].

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Fig.12 Effectofsodiumxylenesulfonateonclearpointofapremium LDLblend.(Source:FromRef.6,reproducedbypermission.)

Fattyalkanolamidesaremainlyusedasfoamstabilizers,buttheycanalsohave asignificanteffectontheviscosityofanLDLDformulation.Otherviscosity modifiersincludehydrotropes,suchasalcohol,SXS,SCS,urea,andwater solublepolymers. (c)PhysicalStability.Physicalstabilityisanotherimportantproductattribute thatcannotbeoverlooked.Consumersdonotwanttopurchaseaproductthat changesphysicallyovertime.Thismayincludeprecipitation,phaseseparation, ormicrobialcontamination. Agingstudiesaretypicallyconductedtoachievephysicalstabilityofproductat marketage.Variousagingconditionsarenecessarytosimulatetheconditions theproductmayencounterfromwarehousingandtransportationtostoragein storesandathome.Thisincludeselevatedtemperature,suchas50°C,andlow temperature—justabovethefreezingpoint. Theotherstandardagingstudynormallyconductedistoexposetheproductto sunlighttosimulatestorageofproductathomenearakitchenwindowfor colorandfragrancestability. Duringaging,periodicexaminationsofproductaremadetocheckforpH, color,fragrance,appearanceandcontainersforanychangesanddeviations fromroomtemperaturesamples.Anyunacceptablechangesanddeviations needtobeinvestigatedtoidentifythecauseandtodeterminecorrective measures.The

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entireseriesofa*gingstudiesmustberepeatedwhencorrectionsaremadeto theformula. Tobesurethattheproductcanwithstandmicrobialcontamination,adequacy ofpreservationstudiesmustbeconducted.Iftheproductisnotabletocontrol thegrowthofmicroorganism,incorporationofasuitablepreservativeis necessary. (d)ProductSafety.Inadditiontoperformanceandesthetics,already discussed,thesafetyofthefinalproductcannotbeoverlookedinformulatinga dishwashingdetergent.Thisincludessafetytohumans,safetytosurfacesit cleans,andsafetytotheenvironment.Typically,eyeandskinirritationtestsare required.Thesafetytestingandproductlabelingrequirementsmayvaryfrom countrytocountry.Itisimportanttoensurethatallsafetytestingisconducted inaccordancewithgovernmentregulatoryrequirements. 5.OtherFormulationTechnology OtherformulationtechnologymayincludewaystoconcentrateanLDLD productandformulatingforcosteffectivenessandimprovedodorstability. Table16listsrecentU.S.patents[31,156–165]ontheseformulation technologies. VI.NewProductsandFutureTrends Liquidhanddishwashingdetergentshavegonethroughcontinuedevolutionin recentyears.Manynewproductshavebeenintroducedtothemarketplace. Therearealsosomesignificantformulationchangesasaresultoftheadvances innewtechnologiesandthechangesinconsumerhabitsandpractices. A.LineExtensions Aperenniallypopularwayofexpandingthemarketforaproductistoproduce lineextensions.Inalineextension,thesamebrandnameisappliedtoa differentformoftheproduct.Sometimesthereisanalternativephysicalform, suchasaconcentrate,powder,orliquid.Sometimesthelineextensionhasnew esthetics,suchasnewcolor,degreeoftranslucency,oropacityorfragrance. Last,theremightbeothernewfeatures,suchasincreasedmildness, antibacterialefficacy,orpresenceofaspecialingredient.Thistrendcontinued tobestrongintheearly1990sbecauseoftheexpenseinintroducinganew brandnameandthedifficultiesofattractingcustomerattentioninacrowded market[166]. IntheUnitedStatescompetitionisparticularlykeenbecauseofatrendtoslow growthintheoverallLDLDvolume.Thecookingandeatinghabitsof consumersarechangingtolowerfat,easier,simplermealsandincreaseduse ofpreparedfood,allofwhichtranslatesintolessdishliquiduse[167].Line extensionsareawayofcombatingthistrend.

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B.Clear,ColorlessProducts Since1990therehasbeenabroadtrendintheconsumermarkettoclear,water whiteproducts.Colorlessproductspresenttheconsumerwithanewesthetic experience.Colorlessdetergentconnotesmildness,purity,andsafetytothe environment.Productsasdiverseasbeeranddeodoranthavebeenformulateda clearvariants[168,169]. Aspartofthistrend,atleastthreecleardishwashingliquidshaveappearedinthe UnitedStatesandspreadtoEurope(PalmoliveSensitiveSkinfrom

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ColgateandIvoryandDawnFreefromP&G).Ivorywasformerlyanopacified product.Onemethodwasdeveloped[31]toenhancethestabilityofcolorless detergentcompositions.Itinvolvestheadditionof0.05–0.5%oxygenbleach, preferablyH2O2,and0.01–2%chelatingagent,preferablycitricacid,asawayto keepthepercentagetransmittanceat97%after6monthsat140°F.Table17 showstwoLDLDcompositionsutilizingsuchtechnologyforastablecolorless LDLD.Also,therearerecentpatentsontheuseofpurerandlightercoloredraw materials[170,171]. C.IncreasedUseofNonionics Theappearanceofdishwashingliquidsusingmorenonionicsurfactantsisanother recenttrend.Smallamountsofnonionics,suchasamidesandamineoxides,have longbeenusedasfoamboosters.Asdiscussedearlier,nonionicshavenotbeen widelyusedtraditionallybecauseoftheirlowfoamingcharacteristics.Byproper formulation,itispossibletohaveasatisfactorilyfoamingdishliquidthatcontains atleast50%ethoxylatedfattyalcohol[13].Examplesofnonionicsurfactant basedcompositionshavingfoamingpropertiesequaltoorbetterthanthoseofa conventionalanionicsurfactantbaseddishwashingliquidarelistedinTable18. Newnonionicsarebecomingavailablethatarerelativelyhighsudsing. Alkylpolyglycosides(APGs)areaprimeexample[172].AlthoughAPGsarenot asfoamyasanionics,suchasethoxylatedalcoholsulfates,theyaremuchfoamier TABLE17ExamplesofStableColorlessLiquidDishwashingDetergentCompositions UsingH2O2

Ingredient

A(%)

B(%)

NH 4C12–13alkylEO1sulfate

15.5

28.5

NH 4C12–13alkylEO6.5sulfate

Tetronic704

0.1

Cocoamidopropylbetaine

0.9

C12dimethylamineoxide

2.6

NaCl

MgCl2

3.3

Ammoniumxylenesulfonate

3.0

Ethanol

5.5

Perfume

0.09

0.18

Citricacid

0.1

Disodiumdiethylenepentaacetate

0.1

H2O2

0.18

0.17

Pa TABLE18ExamplesofHighFoamingNonionicSurfactantBasedLiquidDishwashing DetergentCompositions Ingredient

A(%)

B(%)

C(%

Neodol918

Neodol916

Ammoniumlaurylsulfate

Cocoamidopropylbetaine

LMMEA

Ethanol

SXS

Water,fragrance,color

Balance

thannonionics.BytheRossMilesfoammethod(0.1%solution,49°C,after5 minutes),aC12alcoholsulfatewouldhave18.5cmfoam,aC12alkylpolyoxyethy (6.5EO)alcoholwouldhave2.5cmfoam,andaC12APGwouldhave15cmfo [173].APGsofvaryinghydrophobesanddegreesofpolymerizationareavailabl leastthreecommercialdishwashingdetergentscontainAPGs,oneinEurope,one theUnitedStates,andoneinJapan[174,175].Inadditiontobeingrelativelyhigh foamers,APGshavesomeotherusefulproperties.Theyarecompletely biodegradable,ecologicallysafe,andmildtotheskinandofferwettingproperties similartothoseofanionicsurfactants.Boththehydrophileandhydrophobecome fromoleochemicalresources[176].Table19showsexamplesofLDLDsformul withAPGs[116]. Polyoxyalkalenesandfattyacidglucamidesarealsopartofthetrendtotheincre useofnonionicsindishliquids.Fattyacidglucamidesinteractstronglywithanioni surfactantstogivesudsboosting,interfacialtensionlowering,andirritancyreducti [177].TheglucamidesarecompletelyandrapidlybiodegradableintheStermtes Theyarehighlyremovedinactivatedsludgesewagetreatment[178].Apartialp diagramhasbeenreported.Therearetwocrystalstructuresofpolymorphs,one extendedandonebent[179].ExamplesofLDLDsformulatedwithfattyacid glucamidesarelistedinTable20[18,20]. D.EnvironmentalandRegulatoryConcerns Productswithanenvironmentalpositioningareacontinuingtrend,especiallyin Europe[180].In1992,Pril,aleadingGermanbrand,wasreformulatedtohave mildnessandenvironmentalfriendlinessplatform.Onefeatureofboth

TABLE19ExamplesofLiquidDishwashingDetergentCompositionsUsingAlkylPolygly Ingredient

A(%)

B(%)

AmmoniumC11–12alkylbenzenesulfonate

17.5

—

MagnesiumC11.4alkylbenzenesulfonate

6.4

—

AmmoniumC12–13alkylpolyoxyethylene(EO0.8)sulfate

6.1

—

AmmoniumC12–13alkylsulfate

—

15.7

SodiumC12–16 olefinsulfonate

—

10.4

Cocomonoethanolamide

—

5.5

C12–13alkylpolyglycoside1.7

5.0

5.9

C12alkyldihydroxyethylamineoxide

—

MgCl2∙6H2

—

5.6

Ammoniumxylenesulfonate

3.0

—

Ethanol

3.7

Water,perfume,minors

Balance

APGandfattyacidglucamidesisthatbothhydrophobicandhydrophilicendsca “naturallyderived”orfrom“renewableresources.”Neitherisanaturalproduct. areintensivelyprocessed.Thereisconsiderabledebateoverwhetheroleochemic petrochemicalsourcingisbetterfortheenvironment[181]. Governmentregulationsareacontinuingsourceofchallengetothemakersofcon detergentproducts.Forexample,inEurope,theDirectiveontheClassification, LabelingofDangerousSubstancesoftheEuropeanEconomicCommunity(EEC published[182].Sincethen,thedirectivehasbeenamendedtorequiremanufact consumerproducts TABLE20ExamplesofLiquidDishwashingDetergent CompositionsUsingMethylEsterGlucamide Surfactant

A(%)

B(%)

C12–14alkylEO8

AEOS

Amineoxide

Glucamide

Betaine

C9–11EO8

0.025

0.25

Glucamide

Betaine

C9–11EO8

0.025

0.25

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accordingtothehazardsposedtotheconsumer(toxic,corrosive, carcinogenic,eyeorskinirritant,andsoon)andpackageandlabelthem accordingly[183,184].ThememberstatesoftheEEChadtoincorporatethe directiveintotheirlawsbyOctober1993.Themethodofclassificationis basicallyeitherdirectlytotestthefinalcompositionortoestimatethehazards byusingacalculation(calledtheconventionalmethod).Thecalculation dependsonthesumofthehazardsoftheindividualcomponentsandtheir percentageinthefinalcomposition.Theproductsmustbeclassifiedaccording totheirconcentrationwhentheyaresoldtothepublic.LDLDswith concentrationabove20%AImustbesoldinpackageswithirritantwarning labels,eventhoughthetheLDLDismildwhendilutedforuse.Labeling requirementsaffectthecompositionofdishliquidsbyacceleratingthe incorporationofmildersurfactants. E.DishLiquidswithAddedBenefits Anothertrendistheadditionofnewbenefits.Thisisinpartareflectionofthe overalltrendofmakingconsumerproductsmultipurpose[185].Anexample istheintroductionofacombinationdishwashingliquidandantibacterialhand soapbyColgatePalmolivein1994.Abouttwothirdsofthepeoplewhowash theirhandsinthekitchenusedishdetergent[186],possiblybecauseitis handy.Thisproducthasthebenefitthat,inadditiontowashingdishes,when usedundiluteditkillspossiblypathogenicgermsonhands.Colgate'sproduct wasquicklyfollowedbyDialdishwashingliquid,whichalsoclaimed antibacterialhandsoapproperties.Theinterestinantibacterialpropertiesfitsa growingconcernaboutgermsonthepartofthepublic[187]. F.Concentrates Dishdetergentsindevelopedmarketshavebecomemoreconcentratedaspart ofa*generaltrendthatcanalsobeseeninlaundrydetergentsandhardsurface cleaners[188–190].Thetrendtowarddishliquidconcentratesinformerly dilutemarketsstartedinEuropein1992.InGermany(previouslya20–25% AImarket),themarketwasevolvedintoconcentratedproductswiththe introductionofUnilever'sSunlightProgress,Colgate'sUltraPlus,Henkel'sPril Supra,andP&G'sFairyUltra.Itremainstobeseenwhetherproductswith evenhigheractivelevels(40–50%)willbeacceptedbyconsumersinthe UnitedStatesandEurope. References 1.H.AndreeandB.Middelhauve,inProceedingsofthe3rdWorld ConferenceonDetergents:GlobalPerspectives(A.Cahn,ed.),AOCS Press,Illinois,1994,pp.95–98.

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8 HeavyDutyLiquidDetergents AMITSACHDEVandSANTHANKRISHNAN ResearchandDevelopment,GlobalTechnology,ColgatePalmoliveCompany,P NewJersey I.Introduction II.PhysicalCharacteristicsofHDLDs A.Structuredliquids B.Unstructuredliquids C.Nonaqueousliquids III.ComponentsofHeavyDutyLiquidDetergentsandTheirProperties A.Surfactants B.Builders C.Enzymes D.Bleaches E.Opticalbrighteners F.Detergentpolymers G.Miscellaneousingredients IV.ProductEvaluationMethods A.Physicalproperties B.HDLDdetergencyevaluation V.FutureTrends Appendix References

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I.Introduction Heavydutyliquiddetergents(HDLDs)wereintroducedintothelaundry marketmuchlaterthanpowderdetergents.Thefirstcommercialheavyduty liquiddetergentappearedintheUnitedStatesin1956.Liquiddetergentswere introducedintheFarEast/PacificcountriesandEuropeonlyinthe1970sand 1980s,respectively(Fig.1). Heavydutyliquidshaveseveraladvantagesoverpowderdetergents.The liquiddetergentsreadilyandcompletelydissolveinwater,especiallycoolor coldwater.Theycanbeeasilydispensedfromthebottleorrefillpackagewith relativelylessmessinessthanpowderdetergents,andtheydonottendtocake

FIG.1 CommercialNorthAmerican(above)andEuropeanandAsian/Pacific HDLDs.

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instorageaspowdersoftendowhenexposedtomoisture.Furthermore,liquid detergentslendthemselvestopretreatmentatfullstrengthdirectlyonstainsand thusprovideaconvenientwaytoremovetoughstains. Atypicalheavydutyliquiddetergentconsistsofallorsomeofthefollowing components:surfactants,builders,opticalbrighteners,enzymes,polymers,and fragrance.Inaddition,itmaycontainotherspecialingredientsdesignedfor specificfunctions. Bothanionicandnonionicsurfactantsareusedintheformulationofliquid detergents.Surfactantsareprimarilyresponsibleforwettingthesurfacesof fabricsaswellasthesoil,helpingtoliftthestainsoffthefabricsurfaceandto stabilizedirtparticulatesoremulsifygreasedroplets[1–4].Themainanionic surfactantsaresodiumalkylbenzenesulfonate,alkylsulfate,andalkyl ethoxylatedsulfate.Nonionicsurfactantsusedareprimarilyethoxylatedfatty alcohols.OthersurfactantsarealsousedinHDLDsandarediscussedina subsequentsection. Buildersareformulatedintodetergentsmainlytosequesterthehardnessofthe wateraswellastodispersethedirtandsoilparticulatesinthewashwater. Commonbuildersusedaresodiumandpotassiumpolyphosphates,silicates, carbonates,aluminosilicates,andcitrates[5]. Opticalbrightenersarecolorlessdyesthatabsorbultravioletradiationandemit bluishlight,makingfabricslookwhiterandbrighter.Mostdetergentscontain brightenersintheircomposition,theircontentadjustedmoreorlesstoreflect regionalconsumerpreferencesandmarketingclaims. TheenzymesinHDLDsusuallyconsistofaproteaseandanamylase.In addition,thedetergentmayalsocontainlipaseandcellulaseenzymes.The functionoftheproteaseistodigestproteinstainssuchasbloodand proteinaceousfoodstains,whiletheamylaseactsonstarchystains.Lipase attacksfattychainsingreasystainsandisgoodatcleaningcertainoilysoils. Cellulaseisanenzymethatactsoncellulaseandisbeingusedindetergentsfor removingprillsincottonfabrics,therebyrestoringreflectanceofthefabric surfaceandmakingcolorslookbrighter[6]. Liquidlaundrydetergentsmaybeclassifiedintotwomaintypes:unstructured liquidsandstructuredliquids.Unstructuredliquiddetergentstypicallyare isotropic,havealargeandcontinuouswaterphase,andarethemost widespreadtypeofliquiddetergentsintheU.S.market.Structuredliquid detergentsarethoseconsistingofmultilamellarsurfactantdropletssuspendedin acontinuouswaterphase.Thesestructuredliquidsarecapableofsuspending insolubleparticlessuchasbuilders(phosphates,zeolites).Theseliquidsarein useinEuropeandinAsianandPacificcountries.Afurthertypeofliquidisone wherethecontinuousphaseisnonaqueous.Onlyonecommercialexampleof thistypeofliquiddetergentisknown.

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Thesectionsthatfollowdescribethephysicalcharacteristicsofheavyduty liquids,followedbydetaileddescriptionsoftypicalformulationcomponentsof liquiddetergentsandtheirfunctions.Abriefsectiononevaluation methodologiesfollows.Finally,emergingtrendsintheformulationand detergencyofheavydutyliquidsarediscussed.Acomprehensivetabulationof thepatentsrelevanttoHDLDsisgivenintheAppendixattheendofthis chapter. II.PhysicalCharacteristicsofHDLDs Thephysicalformandappearanceoflaundryliquidscanvarygreatlyamong variousregionsoftheworld.Thesedifferencesintypesofliquiddetergents fromregiontoregionislargelydictatedbythelaundryhabitsandpersonal choicesoftheconsumersinthatparticularmarket.HDLDscanbebroadly classifiedintotwomaintypes:structuredandunstructuredliquids.Athirdtype, nonaqueousliquids,havebeenactivelystudiedandarealsodiscussedinthis chapter. Structuredliquidsareopaqueandusuallythickandareformedwhensurfactant moleculesarrangethemselvesasliquidcrystals[7–9].Thisformofliquid detergentislargelymarketedinEuropeandtheAsian/Pacificregions. Unstructuredliquids,ontheotherhand,areusuallythin,clear,ortranslucent andareformedwhenallingredientsaresolubilizedinanaqueousmedium. Figure2givesexamplesofunstructuredandstructuredHDLDs.Nonaqueous liquids,inwhichthecontinuousmediumconsistsofanorganicsolvent,canbe eitherstructuredorunstructured. A.StructuredLiquids 1.Introduction Thegeneraltendencyofliquidscontaininghighlevelsofanionicsurfactantsand electrolyticbuildersistostructurethemselveswiththeformationofliquid crystallinesurfactantphases[7–12].Thistrendcanbeacceleratedwiththeuse oflongerorbranchedchainalkylgroupsandbyusingahigherelectrolytelevel [13].Theresultingliquidisopaque,extremelythick,unpourable,and frequentlyphysicallyunstable.Itmayalsosubsequentlyseparateintotwoor morelayersorphases:athick,opaquesurfactantrichphasecontainingthe flocculatedliquidcrystalsandathin,clearelectrolyterichphase.The challenge,therefore,indevelopingsuchaliquidistonotonlytopreventphase separationoftheproductbutalsotoreducetheviscositytoapourablelevel.A pourableleveldepends,ofcourse,onthepreferences,requirements,and convenienceoftheconsumer.Viscositiesofcommerciallyavailablestructured liquidsvaryfrom500to9000cps.

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FIG.2 Examplesofanunstructured(left)andastructured(right) HDLD.

2.LamellarStructures Theliquidcrystallinephaseinastructuredliquidisfrequentlyintheformof sphericallamellarbilayersordroplets[14–18].Theinternalstructureofthese dropletsisintheformofconcentricalternatinglayersofsurfactantandwater. Thisconfigurationisoftencomparedtothestructureofanonion,whichhasa similarconcentricshelllikestructure(Fig.3).Ithasbeendeterminedthatthe physicalstabilityofthesetypesofliquidsisachievedonlywhenthevolume fractionofthebilayerstructuresishighenoughtobespacefilling.This correspondstoavolumefractionofapproximately0.6[7,8,19].An excessivelyhighvalueofthisvolumefraction,however,willleadto flocculation,highviscosity,andanunstableproduct.Astabledispersionofthe lamellardropletsmakesitpossibletosuspendsolidsandundissolvedparticles betweenthelamellaeandinthecontinuouselectrolytephase.Thiscapability allowstheuseofrelativelyhighbuilder/electrolytelevels.Manypatentshave beenissuedforstructuredliquidsthathavethecapabilityofsuspending undissolvedsolids.Thesuspendedsolidsincludebleaches[20,21],builders suchaszeolites[22],andsofteners[23,24]. Thereareanumberoffactorsthatdeterminewhetherornotalamellardroplet canform.Asageneralrulethesebilayerstructureswilldevelopifthesurfactant headgroupissmallerthantwicethetranscrosssectionalareaofthealkyl chainsofthesurfactants[8,13].Thisratiooftheareasofthealkylchainand thesurfactantheadgroupisreferredtoasthepackingfactorofthesurfactant system.Amongtheelementsthatcanacceleratetheformationofthesestruc

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FIG.3 Schematicdiagramsofanonflocculatedlamellardispersion,alamellar droplet,andtheinternalstructureofalamellardroplet.(Reproducedwith permissionfromRef.10.)

turesistheuseoflongerchainalkylchains,branchedalkylgroups,dualalkyl groups,andhigherlevelsofelectrolytes.Conversely,byusingshort,straight chainalkylgroups,lowerelectrolytelevels,orhydrotropes,theonsetofthe liquidcrystallinephasecanbedelayed. Alamellardropletisheldtogetherbyanintricatebalanceofvariousinterand intradropletforces[10,11].Anyalterationorimbalanceintheseforcescan haveadirectimpactonthestabilityofthestructuredliquid.Electrostatic repulsionbetweenthechargedheadgroupsoftheanionicsurfactantsis compensatedbyattractivevanderWaalsforcesbetweenthehydrophobic alkylchainsoftheanionicandnonionicsurfactants.Inaddition,therearealso osmoticandstericforcesbetweenthehydratedheadgroupsofthenonionic surfactants.Theseparticularinteractionscanbeeitherattractiveorrepulsive dependingonthe“quality”ofthesolvent[8].Theresultantforcehasadirect influenceonthesizeofthewaterlayers,thesizeofthedroplet,andeventually thestabilityoftheliquid. 3.StabilityofStructuredLiquids Thebalanceofattractiveforcesbetweenthesurfactantlayersandthe compressive/repulsiveforcesduetostericand/orosmoticinteractionsmakes highlyconcentratedformulationspossible.Butasinglephasestructuredliquid, byits

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verynature,isneverinastateofcompleteequilibrium.However,forpractical purposesastablestructuredliquidisachievedwhentheinterandintralamellar forcesaremanipulatedinsuchawaythatphaseseparationisminimizedor avoided.Dependingontheextentofconcentrationoftheingredients,various methodscanbeemployedtostabilizethesestructuredliquids(Fig.4). Themostbasicmeansofachievingstabilizationandviscosityreductionisby theadditionofelectrolytes.Theadditionofcationsintheformofelectrolytes suchassodiumcitratehastheeffectofscreeningoutsomeoftherepulsive forcesbetweenthenegativelychargedanionicheadgroups.Also,the electrolytesinthecontinuouslayerprovideanelementofstabilitybygivingit ionicstrength.Thisscreeningoutprocessreducesthesizeoftheintralamellar waterlayerandconsequentlythesizeoftheentiredroplet.Thisreductionof thelamellarsizefreesupsomeextravolumeinthecontinuousphaseand thereforeprovidesanadditionalelementofstability.Increasingtheamountsof citrateworksonlyuptoacertainpointbeyondwhichthereisagreateramount ofundissolvedsaltthatwillbehavetobesuspendedbetweenthelamellar dropletsandcanleadtoexcessivethickening.Anotherconsequenceofadding large

FIG.4 Schematicdiagramsdepictingthestabilityof(a)unstableand(b)stable structuredHDLDs.

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amountsofelectrolyteisthefurthererosionoftheintralamellarwaterlayer. Thiswaterlayerhastobemaintainedatalevelthatissufficienttohydratethe headgroupsofthenonionicsurfactants.Saltingoutelectrolytes[25],ofwhich sodiumcitrateisanexample,alsohydrateandthereforecompetewiththe nonionicsandotheringredientsforthewater.Excessiveshrinkageofthewater layercanthereforeresultinproductinstability. (a)FreePolymers.Theadditionofelectrolytesassistsinloweringviscosities andinstabilizingthestructuredliquidonlyuptoacertaindegree[26–28]. Polyethyleneglycolandpolyacrylatesareexamplesoffreepolymers.These polymersarenonstructuring,andconsequentlytheydonothavethecapability ofadsorbingontothelamellardispersions.Insteadtheyfunctionbymeansof osmoticcompression,whichresultsinshrinkageofthelamellardroplet.The consequenceofthisreductioninthevolumeoftheindividualdropletsisa highervoidfractionintheliquid.Thispolymercanthereforebeusedonlyupto thepointatwhichtheoptimumvoidfractionisachieved.Furtherincreasesin thefreepolymeroftenleadtodepletionflocculation,whichisalso accompaniedbylargeincreasesinviscosityaswellasphaseseparation. Concentratingthestructuredliquidbymerelyformingthinnerlamellarlayers andincreasingthevolumefractionofthelamellaecanhaveimplicationsforthe rheologyandpourabilityoftheproduct.Thebestpourabilitycharacteristicsare obtainedwhenthevolumefractionofthelamellarphaseisaslowaspossible andthelamellaearerelativelylarge.Acompromisebetweenthesetwo pathwaysorstrategieshastobeachievedinordertoformulateastable, concentratedliquidwithacceptablerheologicaltraits.Thistaskbecomes increasinglydifficultatevenhigherconcentrations.Withonlyalimitedvoid fractionavailable,thelamellardroplets,eventhoughtheyarereducedinsize, beginflocculating. (b)DeflocculatingPolymers.Freepolymersareeffectiveinreducingthesize ofthelamellardispersionandtherebyimpartingstability.However,atever increasingconcentrationsofsurfactantsandbuilders,simplyreducingthe intralamellarwaterlayerisnotsufficienttopreventflocculation.Theproblem wassuccessfullyaddressedbyresearchersatUnilever,whowereableto preventflocculationbyalteringtheinterlamellarforces[13,19,29–31].This wasachievedbymeansofadeflocculatingpolymerthatcouldbeconsidered tobebifunctional.Thesepolymersconsistedofahydrophilicbackbone attachedtoahydrophobicsidechain.Thehydrophiliccomponentis fundamentallylikeafreepolymerorcopolymerinbothstructureandfunction. Thehydrophobesidechainistypicallyalongalkylchain.Figure5showsa schematicofanexampleofaUnileverdeflocculatingpolymer—anacrylate laurylmethacrylatecopolymer.Theuniqueaspectofthispolymerisitsability tonotonlyutilizeitshydrophiliccomponenttoinduceosmoticcompression withinthelamellarbilayers

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FIG.5 AnexampleofaUnileverdeflocculatingpolymer. (ReproducedwithpermissionfromRef.13.)

butalsotoemployitshydrophobicsidechaintoadsorbontothesurfactant layers.Thishydrophobicityalsopermitsthedeflocculatingpolymertoattach itselftotheoutersurfaceofthelamellardropletandconsequentlybeableto influencetheinterlamellarinteractions.Thistraitpreventsoratleastlessensthe likelihoodofflocculationoccurring. Thestabilityofthesestructuredliquids,therefore,isobtainedwhenthelamellae arenotonlysmaller,butalsowellseparated(Fig.4).Thisresultsinnotonlya singlephase,stableliquidbutalsoaproductwithgoodflowability characteristics.Table1showsthelistofingredientstypicallyfoundina structuredHDLD. B.UnstructuredLiquids 1.Introduction HeavydutyliquidsonthecurrentU.S.marketarepredominantlyinthethin, clear,andunstructuredform.Allmanufacturersmarketlaundryliquidsthatare

TABLE1ExampleofStructuredHDLDFormation Ingredient

Function

Sodiumlinearalkylbenzenesulfonate

Anionicsurfactant

Sodiumalkylethersulfate

Anionicsurfactant

Alcoholethoxylate

Nonionicsurfactant

Sodiumcarbonate

Builder

Zeolite

Builder

Sodiumperborate

Bleach

Polymer

Stabilizer

Protease

Enzyme

Fluorescentwhiteningagent

Brightener

Boricacid

Enzymestabilizer

Preservative

Fragrance

Colorant

unstructured,thin,andclear.Besidestheobviousdifferencesinthephysicalappe propertiesbetweenthestructuredandunstructuredliquids,thereareotherdissim theformulationoftheseliquidsthatcanhaveadirectimpactonthecleaningperfo theproduct.Unstructuredliquidsarecommonlyformulatedwithhigheramounts surfactantsinconjunctionwithlowerbuilderlevels(seeTable2).Thisisincontra structuredliquids,whichneedmorebuildersandelectrolytestosustainthestruct TABLE2ExampleofUnstructuredHDLDFormulation Ingredient

Function

Sodiumlinearalkylbenzenesulfonate

Anionicsurfactant

Sodiumalkylethersulfate

Anionicsurfactant

Alcoholethoxylate

Nonionicsurfactant

Sodiumcitrate

Builder

Monoethanolamine

Buffer

Soap

Defoamer

Protease

Enzyme

Fluorescentwhiteningagent

Brightener

Boricacid

Enzymestabilizer

Ethanol

Solvent

Sodiumxylenesulfonate

Hydrotrope

Preservative

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phase.Thephysicalappearanceandstabilityofstructuredliquidsarevery dependentonsurfactantratios,whereastheclear,unstructuredliquidsallowfar greaterflexibilityinchoosingsurfactantratiosaslongasasinglephaseis maintained.Themainadvantageinstructuredliquidsistheirabilitytosuspend undissolvedandinsolublesolids.Theunstructured,clearliquids,ontheother hand,bytheirverynaturedonotpermittheuseofinsolublematerials.This resultsintheuseofonlysolublebuilders,andatrelativelylowlevels,and precludestheuseofotherusefulbuilderingredientssuchaszeolites. Itcannotbesaidthatoneformofliquidhasad*stinctadvantageovertheother. Theformulationandmarketingofeitherformmaybedependentonsuch factorsasefficacytargets,consumerpreferencesandhabits,choiceand availabilityofrawmaterials,andcostconsiderations. 2.StabilityofUnstructuredLiquids Unlikestructuredliquids,unstructured,thin,clearliquidscanbedeveloped onlyiftheonsetoftheformationofliquidcrystalsisdelayedorbrokenup.This canbeaccomplishedbytwodifferentmethods:(1)byaddinghydrotropesand solventsthatcandisruptorpreventanyliquidcrystalformationandalsoaidin solubilizingtheothercomponentsintheformulationor(2)byincreasingthe watersolubilityoftheindividualcomponents.Morethanlikelyacombination ofthetwotechniquesisusedtodevelopastableliquid.Therespectivecostsof theseapproachesultimatelydeterminestheiruseinthefinalformulation.Some ofthemethodsusedtoformulatestable,singlephase,thin,clear,unstructured liquidsaresummarizedbelow. Compoundssuchassodiumxylenesulfonate(SXS),propyleneglycol,and ethanolareusefulindisruptingandpreventingtheformationoflamellar structuresthatcanopacifyandthickentheliquid.SXSisespeciallyusefulin solubilizingLAS.Propyleneglycolandethanolhavetheadditionalbenefitof contributingtoenzymestability.Themaindrawbackofusingthesecompounds isthattheydonotcontributetothedetergencyperformanceoftheproduct. Theirprincipalfunctionistoaidinachievingthethin,clearappearanceby solubilizingvariousingredientsandpreventingprecipitationandphase separation. Itispossibletoformconcentratedliquiddetergentsthatdonotrequire additionalingredientstoassistinthemaintenanceofaclearappearance.Thisis usuallyaccomplishedbyminimizingtheuseofLASandelectrolytesand maximizingtheuseofnonionics. Theuseofingredientswithincreasedwatersolubilityisprobablythemost effectivetoolforproducingasinglephasethin,clearliquid.Potassiumsalts generallytendtobemoresolublethantheirsodiumcationcounterparts.In theseformulations,ahigherlevelofpotassiumcitratethansodiumcitratecan besuccessfullyincorporated.Detergencyperformanceisnotaffectedby replacingtheNa+cationwithK+.

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Citratecompoundsaresaltingoutelectrolytes—theymaytieupwater moleculesintheliquidandasaresulthelpforcetheformationofliquidcrystals orlamellarstructures.Itissometimespossibletoreversethistrendbyadding saltinginelectrolytes,compoundswithhighlyotropicnumbers(>9.5)thatcan raisethecloudpointoftheliquidformulation[25].Thispermitsincreased concentrationwithouttheonsetofstructuring. Ethanolaminessuchasmonoethanolamine(MEA)andtriethanolamine(TEA) canalsobeinvaluableinenhancingthesolubilityoftheingredients.These compoundsarebifunctionalinthattheyhavecharacteristicscommontoboth alcoholsandamines.Asaresult,saltsofMEAandTEAaremoresolublethan thosepreparedwithNa+.NeutralizingsulfonicacidwithMEAisavery effectivewayoffreeingupadditionalwatertoallowforfurtherconcentration. Inaddition,anyfreealkanolaminethatisnottiedupasasaltbehaveslikean alcoholandcanaidinsolubilizingotheringredients.Thesecompoundsalso providedetergencybenefitsbybufferingthewashwater. C.NonaqueousLiquids Nonaqueousliquidsmaybeclassifiedasstructuredorunstructureddepending onthelevelofsurfactantsandothercomponentsintheirformulation[32]. Thesedetergentshaveseveraladvantagesoveraqueousformulations. Nonaqueousdetergentscancontainalltheprimaryformulationcomponents, includingthosethatarenotcompatiblewithoraredifficultinaqueoussystems. Theliquidmatrixisanonionicsurfactantoramixtureofnonionicsurfactants andapolarsolventsuchasglycolether[33–36].Builderssuchasphosphates, citrates,orsilicatescanbeincorporated,althoughzeolitescontainingabout 20%waterarenotgenerallyrecommended[37].Phosphatefreeformulations havealsobeenreported[38].Bleaches,suchastetraacetylethylenediamine (TAED)activatedsodiumperboratemonohydrate,canbeincludedinthese formulations.Sincetheseformulationsdonotcontainwater,enzymesmaybe addedwithminimalneedforstabilizers.Softeningingredientscanalsobe included[39,40].Furthermore,excellentflexibilityintheconcentrationofthe detergentcanbeattainedbecauseonlytheactivecleaningingredientscanbe includedintheformulation.Thedensityofthefinishedproductcanbeashigh as1.35g/mLforstructuredliquids,requiringlowdosagesforequivalent cleaning.However,thetwomajorchallengesfacingthistechnologyare physicalstabilityoftheproductanddispensabilityandsolubilizationinthe washingmachine. III.ComponentsofHeavyDutyLiquidDetergentsandTheir Properties Heavydutylaundryliquidformulationsvaryenormouslydependinguponthe washinghabitsandpracticesoftheconsumersinagivengeographicregion.

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Thedegreeofcomplexitycanrangefromformulationsthatcontainminimal amountsofcleaningingredientstohighlysophisticatedcompositionsconsisting ofsuperiorsurfactants,enzymes,builders,andpolymers.Thissection describestheingredientsfoundintypicalHDLDformulations. A.Surfactants SurfactantsarethemajorcleaningcomponentsofHDLDformulations throughouttheworld.Unlikepowderdetergents,physicalandphasestability considerationsgreatlylimittheuseofothercleaningingredients,chiefly builders.Surfactantscontributetothestainremovalprocessbyincreasingthe wettingabilityofthefabricsurfaceandstainsandbyassistinginthedispersion andsuspensionoftheremovedsoils. AnHDLDformulatorhasavastarrayofsurfactantsfromwhichtochoose [41].Acomprehensivelistinganddescriptionofthesesurfactantsarebeyond thescopeofthisarticle.Thechoiceandlevelsofsurfactantsusedin commercialHDLDproductsdependnotonlyontheirperformanceand physicalstabilitycharacteristicsbutalsoontheircosteffectiveness. Thissectionbrieflydescribestheanionicandnonionicsurfactantscommonly usedincommercialHDLDformulations.Cationicsurfactants,thoughalsoused onalargescale,aremostlyusedinfabricsoftenerproducts.Linear alkylbenzenesulfonates(LAS),alcoholethoxylates,andalkylethersulfactes arethreeofthemostwidelyusedtypesofsurfactantsinliquidlaundry detergents[42].Recently,variousexternalconsiderations,suchas environmentalpressures,havepromptedmanufacturerstochangetheir surfactantsmixtoincludenewernaturaltypesofsurfactants[43–45]. 1.LinearAlkylbenzeneSulfonate(LAS) Theexcellentcostperformancerelationshipoflinearalkylbenzenesulfonates (LAS)makesthemthedominantsurfactantsusedinlaundrydetergents[46]. RecenttrendsinEuropeandNorthAmericaindicateagradualreductionin theiruseinHDLDs.Nevertheless,theiruseinlaundryliquidsgloballyisstill substantial,especiallyinthedevelopingregionsoftheworld. DeAlmeidaetal.[47]andMatheson[48]provideacomprehensive examinationoftheprocessing,production,anduseoflinearalkylbenzeneinthe detergentindustry.Linearalkylbenzenesulfonatesareanionicsurfactantsand arepreparedbysulfonatingthealkylbenzenealkylateandsubsequently neutralizingitwithcausticsodaoranyothersuitablebase.Thealkylategroup istypicallyalinearcarbonchainoflengthrangingfromC10toC15,withaphenyl groupattachedtooneofthesecondarycarbonsonthealkylchain(Fig.6). Thealkylateportionofthemoleculeishydrophobic,whereasthesulfonate groupprovidesthewatersolubilityandthehydrophilicity.Mostcommercial alkylatesaremixturesofvariousphenylisomersandcarbonchainhom*ologs [49].The

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FIG.6 StructuresoftypicalHDLDsurfactants.

positionofthephenylgroupdependsonthemanufacturingmethod.Systems usingAlCl3orHFcatalystsarethemostcommon.Table3listsatypical isomericandhom*ologdistributioninlinearalkylbenzeneproducedusingthe HFprocess. Thelengthofthecarbonchainandtheisomericdistributionstronglyinfluence theformulatabilityandperformanceofthesurfactant.Ithasbeendetermined thatthesurfaceactivityofthissurfactantincreaseswithlongercarbonchain lengths[50].Alongeralkylchainincreasesthehydrophobicityofthemolecule, lowersitsCMC,andgenerallyprovidesbettersoilremovalcharac

TABLE3hom*ologandIsomericDistributionofLinearAlkylbenzenePreparedUsingthe Percent

Compound

C10

C11

C12

C13

5Phenyldecane

29.8

0.06

C10–13ØC11.5

4Phenyldecane

26.6

0.05

3Phenyldecane

22.7

0.09

2Phenyldecane

20.1

0.2

6/5Phenylundecane

0.4

43.1

4Phenylundecane

0.2

21.4

3Phenylundecane

0.2

17.6

2Phenylundecane

0.1

14.9

6Phenyldodecane

0.6

22.2

0.07

5Phenyldodecane

0.6

28.0

0.06

4Phenyldodecane

0.9

15.5

0.1

3Phenyldodecane

0.3

12.9

0.2

2Phenyldodecane

0.1

12.0

0.5

6/7Phenyltridecane

0.06

33.2

5Phenyltridecane

0.05

22.2

4Phenyltridecane

0.02

15.3

3Phenyltridecane

13.3

2Phenyltridecane

9.4

2Phenylisomer

20.2

15.2

12.0

9.9

Source:Ref.4.

14.8

2Phenyltridecane

9.4

2Phenylisomer

20.2

15.2

12.0

9.9

14.8

Source:Ref.4.

teristics[51–54].LASofferssuperiorandverycosteffectivedetergencyperfor especiallyonparticulatesoils.However,duetoitshighsensitivitytowaterhardn bestutilizedonlywithanaccompanyingbuilder[55].Figure7showstheincrease tohardnessionsforLASwithlongercarbonchainlengths.Withouttheassistanc builders,thesoilremovalefficacyofLASdropsrapidlywithincreasingwaterhar [4,56](Fig.8). TheamountandtypeofLASinHDLDsdependlargelyonthephysicalformoft liquid—unstructuredorstructured.Inunstructuredliquids,solubilityconsideration theuseofshortercarbonchainlengths( C11).Thechoiceofcationscanalsoen solubility.PotassiumandaminecationssuchasMEAandTEAcanbeusedinste sodiumionstoimprovestability[57].Anincreaseintheproportionofthe2phen theLAScanalsoincreasesolubility[58]andsometimesimprovethehardnesstol thesurfactant[59].Instructuredliquids,ontheotherhand,alongeralkylchainc desirablefortheformationofsurfactantlamellae.Thechoiceof

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FIG.7 Ca2+LASprecipitationboundarydiagrams.(Reproducedwith permissionfromRef.55.)

FIG.8 SoilremovaldataforLASasafunctionofwaterhardness. Resultsareshownforsurfactantwithbuilder(STPP)and electrolyte.(ReproducedwithpermissionfromRef.4.)

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thecounterioncanalsoaffectstabilitybecauseionssuchasNa+andK+have differentelectrolyticstrengths,whichcanalsoimpactphasestability. AdisadvantageofusingLASinHDLDsistheirdetrimentaleffectonenzymes. Withtheincreasinguseofenzymesitbecomesnecessarytodevoteasizable portionoftheformulationspaceandcosttoenzymestabilization.Alternative approachesusingsurfactantsmorecompatiblewithenzymescanbeemployed. 2.AlcoholEthoxylates Figure6showsthegeneralstructureofanonionicalcoholethoxylate surfactant.Itshydrophobicgroupislinearwiththecarbonchainlengthranging typicallyfromC10toC15.Thehydrophilicethoxylategroupcanvaryinsize fromanaverageof5to7molofethyleneoxide[60–62].Alcoholethoxylates aremarketedcommerciallyunderthetradenamesNeodol(ShellChemical Co.),Genapol(HoechstAG),Tergitol(UnionCarbideCo.),andAlfonic (VistaChemicalCo.).Thefeedstocksforthealcoholcanbederivedfrom naturalcoconutoilsourcesaswellasfrompetroleumfeedstocks.These surfactantsaresoldina100%concentrationandaretypicallyinliquidform. AlcoholethoxylateusageinHDLDsdependsonthetypeorthephysicalform oftheliquiddetergent.Itshighaqueoussolubilitymakesitausefulingredientin unstructuredliquids.Thissolubilitycanbefurtherenhancedbyincreasingthe degreeofethoxylationanddecreasingthecarbonchainlength.However,these modificationscansometimeshavenegativeramificationsforcleaning performance.Thechoiceofcarbonchainlengthandthedegreeofethoxylation dependonthephysicalstabilityandcleaningrequirementsofindividual formulations.Structuredliquids,ontheotherhand,cantolerateonlyalimited amountofthenonionicalcoholethoxylatesurfactant,asthestabilityofthese liquidsisdependentontheoptimumdistributionofthesizeandpacking configurationoflamellardroplets.Excessiveuseofnonionicsurfactantscan disturbthissomewhatdelicateequilibriumandcausephaseseparationofthe HDLD. Nonionicsurfactantslikealcoholethoxylatesdemonstratesuperiortoleranceto hardwaterions.ThischaracteristicisespeciallyusefulinunstructuredHDLD formulationsbecausesolubilityconstraintslimittheamountofbuilderthatcan beincorporated.Theyalsoprovideexcellentcleaningbenefitsandare commonlyusedinconjunctionwithLASinHDLDformulations[54,63]. StudieshaveshownthatinLAScontainingproducts,alcoholethoxylatescan lowerthecriticalmicelleconcentration(Fig.9)aswellasprovide improvementsinthedetergency[63].Superiorcleaningisobserved,especially onoilysoilssuchassebumonpolyesterfabrics[64].Thepresenceofalcohol ethoxylatesinanLAScontainingformulationwasfoundtoimprove detergency,especiallyathigher

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FIG.9 Criticalmicelleconcentration(CMC)asafunctionof nonionicsurfactantcontentinaLAS/NIsolution. (ReproducedwithpermissionfromRef.63.)

hardnesslevels(Fig.10).Improvementshavealsobeendetectedwhennarrow EOrangesurfactants(Fig.11)areused[65]. Thisinsensitivitytocalciumionsalsoprovidesaveryimportantbenefitinthe stabilizationofenzymes(seeSec.III.C).Ithasbeenshownthatthese surfactantsarenotasdetrimentaltothepreservationofenzymesinHDLDsas NaLAS.Withincreasingrelianceontheuseofenzymesinthelaundrycleaning process,nonionicsurfactantslikealcoholethoxylatesplayanimportantrolein enhancingenzymestability. 3.AlkylEtherSulfates(AEOS) Alkylethersulfatesarealsoanionicsurfactantsthataremanufacturedby sulfatingalcoholethoxylatesurfactants[66].Figure6showsthestructureofthe molecule,whichconsistsofthealcoholethoxylateconnectedtoasulfate group.TheEOgroupstypicallyrangeinsizefrom1to3moles. Thesesurfactantsprovidenumerousbenefitsthatmakethemanattractive optiontoHDLDformulators.Theyarecommonlyusedinbothstructuredand unstructuredliquids.Theirhighwatersolubilitymakesitpossibletouseawide rangeoflevelsinunstructuredliquids.Theycanalsobesuccessfully incorporatedinstructuredliquids. UnlikeNaLAS,alcoholethersulfatesaremoretoleranttohardnessionsand asaresultdonotrequireanaccompanyinghighlevelofbuilderinthe formulation.Figure12showstherelativeinsensitivityofalkylethersulfatesto hardnessions.TheadditionofsmallamountsofNaAEOStoLASwasfound toimproveinterfacialproperties.Theyaremorefriendlytoenzymes,whichcan alsoreducethecostofenzymestabilizersintheformulation.Theyarealso mildertotheskinandasaresultareusedinhanddishwashingformulations. The

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FIG.10 Detergencyperformanceat100°FofLASandLAS/AEblends. Formulationalsocontained25%STPP,10%silicate,and35% sodiumsulfate.(ReproducedwithpermissionfromRef.63.)

superiordetergencyperformanceofthissurfactantisdemonstratedbyits superiorefficacyinmoststaincategories. 4.AlkylSulfates Alkylsulfatesareanionicsurfactants(Fig.6)thatareusedprimarilyinEurope asasubstituteforLAS[43].Environmentalconsiderationshaveprompted manufacturerstousesurfactantsofthistype,whichcanbederivedfrom oleochemicalsources.ThecarbonchainlengthcanrangefromC10toC18. TallowalcoholsulfateisacommonformusedinHDLDs.Itprovidesexcellent detergencyandgoodfoamingandsolubilitycharacteristics.

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FIG.11 Typicalethoxylateadductdistributioninnarrowrange andbroadrangeC alcoholsurfactantswithsimilar 12–14

cloudpoints.(ReproducedwithpermissionfromRef.62.)

FIG.12 Datashowingthehardnesstoleranceofalkylether sulfatesurfactants.(ReproducedwithpermissionfromRef.4.)

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5.PolyhydroxyFattyAcidAmides(Glucamides) Polyhydroxyfattyacidamides(Fig.6)arecurrentlyusedinlightdutyand heavydutylaundryliquids.Recentadvancesinthetechnologyforthe manufactureofthesesurfactantshasmadetheiruseeconomicallyfeasible[67– 69].Theuseofnaturalorrenewablerawmaterialsimprovestheir biodegradationcharacteristics.Severalpatentshavebeenfiledfordetergent formulationscontainingglucamidesthatclaimsuperiorityincleaningefficacyfor oily/greasyandenzymesensitivestains[70–73].Synergieswithotheranionic andnonionicsurfactantshavebeenreported[72,73].Theirimprovedskin mildnessqualitiescanbeusefulinlightdutyliquidapplications[74].Enzyme stabilizationcharacteristicsinglucamideformulationsarealsoenhancedrelative toLAScontainingHDLDs. 6.MethylEsterSulfonates Methylestersulfonatesareanionicsurfactants(Fig.6)thatarealsoderived fromoleochemicalsourcesandhavegoodbiodegradabilitycharacteristics. Theyarecurrentlyusedinonlyalimitednumberofmarkets,primarilyinJapan [44].Theirgoodhardnesstolerancecharacteristics(Fig.13)andtheirabilityto alsofunctionasahydrotropemakesthesesurfactantsagoodcandidatefor liquiddetergents[74].Theyhavealsobeenfoundtobegoodcosurfactants forLAScontainingformulations.Theycanonlybeusedinproductswithlow alkalinityduetothelikelihoodofhydrolyticcleavageoftheesterlinkageunder highpHconditions. 7.OtherSurfactants Onceusedasamajorsurfactantindetergentformulations,soapisnowused onlyasaminoringredientinHDLDs.Itsfunctionisprimarilytoprovidefoam

FIG.13 Detergencyasafunctionofwaterhardnessin methylestersulfonate/LASformulations. Conditions:25°C,surfactant270ppm,Na2CO3 135ppm,silicate135ppm.(Reproducedwith permissionfromRef.44.)

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controlinthewashingmachine.Europeanliquidformulationscontainhigher soaplevelsthantheircounterpartsinNorthAmericabecauseofincreased foamingtendenciesinEuropeanmachines.Soapalsoaidsinthecleaning process.However,itcanleavebehindanencrustationofsoapscumonfabric surfaces.Avarietyofothersurfactantsarealsoused,primarilyforspecialty applications[76].Theyincludeamineoxides,amphoterics,andbetaines. B.Builders Theprimaryfunctionofbuildersinthedetergencyprocessistotieupthe hardnessionsCa2+andMg2+.Theyalsoprovideothervaluablebenefits includingmaintainingthealkalinityofthewashsolutionandfunctioningas antiredepositionandsoildispersingagentsand,insomecases,ascorrosion inhibitors[77–81]. Thelevelofbuildersusedinliquidformulationsdependslargelyonthreemain criteria:(1)theaqueoussolubilityofthebuilder,(2)thephysicalformofthe liquid,and(3)thecosteffectivenessoftheingredient.Duetoinherentsolubility constraintsinformulatingstableliquiddetergents,theusagelevelofbuildersin HDLDsissignificantlylowerthaningranulateddetergents.Thisisespecially trueinthecaseofunstructuredliquids,wherethesolubilitylimitationsofthe builderlargelydictateitslevelintheformulation.Instructuredliquids,however, acertainamountofelectrolyticbuilderisnecessarytoinducestructuring,which allowstheincorporationofsignificantlyhigheramountsofbuilder.Insoluble builderscanalsobeaddedbysuspendingthemintheliquid.Builderingredients suchaszeolites,phosphates,silicates,orcarbonatescanaccountfor20%or moreofthetotalformulation. 1.Mechanisms Buildercompoundsdecreasetheconcentrationofthewashwaterhardnessby formingeithersolubleorinsolublecomplexeswiththecalciumandmagnesium ions.Themechanismsbywhichtheseingredientsfunctioncanbebroadly groupedintothreeclasses:(1)sequestration,(2)precipitation,and(3)ion exchange.Allthreemethodshavetheultimateeffectofloweringthe concentrationofhardnessionsthatcouldinterferewiththecleaningprocessby renderingthesurfactantslesseffective. Insequestration(chelation),thehardnessionsCa2+andMg2+areboundtothe builderintheformofsolublecomplexes.Phosphates,citrates,andNTAare examplesofthisclassofbuildercompound.Table4liststhecalciumbinding capacitiesofvariousbuilders.Otherstronglychelatingcompoundsexist, phosphonatesandEDTAforexample,buttheyaregenerallynotextensively usedinHDLDs.Themostefficientbuilderissodiumtripolyphosphate. Unfortunately,tripolyphosphatehasbeenidentifiedasapossiblecauseof eutrophi

TABLE4SequestrationCapacityofSelectedBuilders

Structure

Ch Sodiumdiphosphate

Sodiumtriphosphate

1Hydroxyethane1,1dip

Aminotrismethyleneph

Nitrilotriaceticacid

TABLE4Continued

Structure

Chemicalname N(2Hydroxyethyl)im

Ethylenediaminetetra

1,2,3,4Cyclopentane

(tablecontinuedonnextpage)

(tablecontinuedfrompreviouspage)

Structure

Chemicalname Citricacid

OCarboxymethyltartr

Carboxymethyloxysuc

Source:Ref.82.

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cationoflakesandrivers.Itisseverelycontrolledandevenbannedinseveral countries.Asaresult,mostcountriesinNorthAmericaandEuropehave convertedtononphosphateformulations.Otherregionsarealsogradually imposingrestrictionsontheuseofphosphates. Carbonatesareexamplesofbuildersthatprecipitateoutthecalciumionsinthe formofcalciumcarbonate.Precipitationbuilders,however,canleavebehind insolubledepositsontheclothesandwashingmachineparts.Aluminosilicates suchaszeolitesareionexchangecompounds:theyremovecalciumand magnesiumionsandexchangethemwithsodiumions. Mostbuildersalsocontributesignificantlytodetergencybyprovidingalkalinity tothewashwater.AhighpH(>8)solutionaidsintheremovalofoilysoilssuch assebumstainsbysaponifyingthem.Insolublefattyacidsfoundinoilysoilsare convertedtosolublesoapinthepresenceofalkalinity. 2.BuilderClasses (a)Inorganic.Inregionswherephosphoruscompoundsarestillpermittedin detergentproducts,polyphosphatessuchastripolyphosphatesand pyrophosphatesareunsurpassedintheircosteffectivenessandcleaningability. Theseingredientsarenotonlyverygoodchelatingagentsbutalsoprovidea soilsuspendingbenefit.Stains,onceremovedfromthefabric,canbe suspendedinthewashwaterbyelectrostaticrepulsion,therebypreventingsoils fromredepositingontotheclothes.Toacertainextentphosphatesalsobuffer thewashwater.Thesolubilityoftripolyphosphatescanbeenhancedbyusing thepotassiumsalt.Thiswouldbethemoreappropriateforunstructured liquids.Instructuredliquids,thesodiumsaltcanbeincorporatedatmuch higherlevels. Carbonatecompoundsofferaneconomicalmeansofreducingthecalcium contentandalsoraisingthealkalinityofthewashwater.Theylowerthe concentrationofthecalciumbyprecipitatingitintheformofcalcium carbonate.Thiscouldleadtofabricdamageintheformofencrustation,which becomesespeciallyapparentafterrepeatedwashingcycles.Fortunately,thisis notamajorprobleminunstructuredHDLDs,becausetheamountofcarbonate usedintheformulationislimitedbysolubilityrestrictions.Compoundssuchas sesquicarbonatesandbicarbonatesthatarelesslikelytoleadtotheformation ofcalciumcarbonateprecipitateshavebettersolubilitycharacteristicsandcan beusedtoagreaterextentinunstructuredliquids.Ontheotherhand, structuredliquidsofferthepotentialofincorporatingmuchhigheramountsof thesecompounds.Carbonatesarealsogoodwashwaterbuffersandcan providethealkalinityneededforimprovedefficacy. Anotherclassofingredientsthatareeffectiveatprovidingalkalinityarethe sodiumsilicates[83].Althoughtheycanalsobegoodsequestrantsandare usedassuchinpowderformulations,theyprovidethisbenefitonlyathigher con

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centrations.Onceagain,thesolubilityrestrictionspreventtheincorporationof anysubstantialamountsinunstructuredliquids.Atthelowlevelsatwhichthey canbeused,theyarevaluableasalkalinebuffers.Theuseofsodiumsilicatesin HDLDsislimitedtotheliquidsilicates,whichhaveSiO2/Na2Oratiosfrom3.2 to1.8. Aluminosilicates[Mz(zAlO2:y SiO2)]areanothertypeofbuilders,ofwhich zeoliteAisacommonexample[84].ZeoliteAisasodiumaluminosilicatewith anAl/Siratioof1:1andaformulaofNa12(SiO2∙AO2)12∙27H2O.Itactsasa builderbyexchangingsodiumionsinsidethelatticewithcalciumionsfromthe washwater.Zeolitesarenoteffectiveinprovidingalkalinityandarenormally usedinconjunctionwithcarbonates.Theyareinsolubleinwaterandare thereforenotsuitableforformulatingunstructuredliquids.Instructuredliquids, zeolitesaresuspendedassolidparticles. (b)Organic.Therestrictionsplacedontheuseofphosphatecompoundsin detergentformulationshaveledtoavarietyoforganiccompoundsthatcould functionasbuildersbutmustalsobereadilybiodegradable.Althoughsomeof thesecompoundsdoapproachthesequestrationlevelofphosphates,theyare notascosteffective[85]. Variouspolycarboxylatecompounds,thosewithatleastthreecarboxylate groups,havenowbecomewidelyusedasreplacementsforphosphatesasthe buildercomponentofHDLDs.Inliquiddetergentformulations,citrate compoundshavebecomecommonplace.Thoughtheirchelatingabilityis relativelylow(Fig.14),citratecompoundsareusedinHDLDsforavarietyof reasons.Citrate'shighaqueoussolubilitymakesitusefulinunstructuredliquids, whereasinstructuredliquidsitshighelectrolyticstrengthcanaidinsaltingout andstabilizingtheformulation.Inaddition,itisusedinenzymecontaining formulationswheremaintenanceofthepHatlessthan 9.0iscrucialtothe stabilityoftheenzyme.Citricaciditselfhasalsobeenpatentedasaningredient inproteasestabilizationsystems[87]. Etherpolycarboxylateshavebeendeterminedtoprovideimprovementsover thecalciumandmagnesiumchelatingabilityofcitrates.Inaseriesofpatents assignedtoProcter&Gamble,ithasbeenclaimedthatacombinationof tartratemonosuccinatesandtartratedisuccinates(Fig.15)deliversexcellent chelatingperformance[88–90].DatashowninFig.16indicateahighlevelof calciumbindingcapacity. Saltsofpolyaceticacids,e.g.,ethylenediaminetetraaceticacid(EDTA)and nitrilotriaceticacid(NTA),havelongbeenknowntobeveryeffectivechelating agents[91].ThechelatingabilityofNTAhasbeenfoundtobecomparableto thatofTPP.Unfortunately,questionsregardingthetoxicityofthiscompound haveallbutpreventedanylargescaleuseinHDLDs.Currently,NTAusageis primarilylimitedtoafewpowderformulationsinCanada.Thehighchela

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FIG.14 Sequestrationofwaterhardnessionsbydetergent builders.( )SodiumpolyacrylateM w=170,000;( ) STPP;(

)NTA;(

)EDTA;(

)sodiumcitrate;(

)

CMOS;( )sodiumcarbonate;( )zeoliteA. (ReproducedwithpermissionfromRef.86.)

FIG.15 Etherpolycarboxylatebuilders.

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FIG.16 Effectofbuilderleveloncalciumionconcentration.(From Ref.89.)CMOS,sodiumcarboxymethoxysuccinate;ODS, sodiumoxydisuccinate;STP,sodiumtripolyphosphate; TMS,tartratemonosuccinate;TDS,tartratedisuccinate.

tionpowerofEDTAhasbeenusedincompositionswheremetalimpuritiesof ironandcoppercanbedetrimentaltotheproductstability,as,forexample,in peroxidebleachcontainingliquids. Polymericpolyelectrolyteshavealsofoundapplicationsasbuilderingredients [92,93].Highmolecularweightpolyacrylatesandacrylicmaleiccopolymers canbeveryeffectiveintyingupcalciumionsinthewash(Fig.17).However, concernsabouttheirbiodegradabilityandaqueoussolubilityhavesignificantly limitedtheiruseinliquidformulations.Thesepolymersystemscanalsoaidin soildispersionandinantiredeposition.Inproductscontainingcarbonates,these polymerscandisruptcalciumcarbonatecrystalliteformationandasaresult preventencrustationonclothes. Fattyacidssuchasoleicandcocofattyacid(saturationlevel)addedto HDLDscanserveamultifunctionalrole.Thoughtheyprimarilyprovideafoam suppressioncapability,theycanalsoprecipitateoutsomeofthecalciumionsin thewashbyformingcalciumsoap.Thiscould,however,poseaproblem becausesoapscumisinsolubleandmayimpacttheoverallcleaningresult. C.Enzymes Enzymeshavebecomeintegralcomponentsofmostliquiddetergent compositionsastheycontinuetoplayanincreasinglylargerroleinthestain removal

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FIG.17 Sequestrationofwaterhardnessionsbysodium polyacrylatepolymers.( ( (

)M w=2100;(

)M w=5100; )M w=20,000;( )M w=60,000;( )M w=170,000, )M =240,000.(Reproducedwithpermissionfrom w

Ref.86.)

process.Thishascomeaboutbecauseofmanyrecentadvancesinenzyme technologyandhasresultedinmoreefficientandeffectivestrains.Theabilityof theseenzymestotargetspecificclassesofstainscanprovidetheformulator withtheflexibilitytotailorthedevelopmentofproductsforconsumerswith differentrequirementsandpreferences.Inaddition,enzymesareespecially effectivewhentheliquiddetergentisusedasaprespotter. TherearefourtypesofenzymescurrentlybeingusedinHDLDs:protease, lipase,cellulase,andamylase[6,94].Theyareallproteinsandarederived fromvariouslivingorganisms.Theirroleistocatalyzethehydrolysisoflarge biologicalmoleculesintosmallerunitsthataremoresolubleandasaresultare washedawayrelativelyeasily.Theoptimumconditionsforthefunctioningof theseenzymesdependonindividualstrainsortypes.Generally,theratesof theseenzymaticreactionsrisewithincreasingtemperaturesandareusually optimumwithinanalkalinepHrangeof9–11.

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Proteasesarebyfarthemostwidelyusedofalldetergentenzymes.Introduced inthe1960s,theyhavesincebecomeoneofthemoreimportantcomponents ofthedetergentformulation[6].Proteasesaidintheremovalofmanysoils commonlyencounteredbytheconsumersuchasfoodstains,blood,andgrass. Theseenzymeshydrolyzeorbreakupthepeptidebondsfoundinproteins, resultingintheformationofsmallerandmoresolublepolypeptidesandamino acids.SincemostenzymeshavetofunctionathighpHconditions,subtilisin,a bacterialalkalineprotease,iscommonlyusedinlaundrydetergents.This particularproteasedoesnothydrolyzeanyspecificpeptidebondinthe proteinaceousstainbutcleavesbondsinasomewhatrandommanner. Amylaseenzymesworkonfoodstainsofthestarchyvariety,likerice, spaghettisauce,andgravy.Theseenzymeshydrolyzethe1–4glucosidic bondsinstarch,whichleadstotheformationofsmallerwatersoluble molecules. Amylaserandomlyhydrolyzesthebondsinthestarchpolymerto formdextrinmolecules. Amylase,ontheotherhand,cleavesthemaltose unitsthataresituatedattheendofthestarchpolymer. Theuseoflipasesindetergentsisarelativelyrecentoccurrence.Thefirst commercialdetergentlipasewasintroducedin1988[(6,94].Theseenzymes targettheoily/greasystainsthataresomeofthemostdifficultstainstoremove. Themajorcomponentsofmostoilystainsencounteredinhouseholdsare triglycerides.LipasescatalyzethehydrolysisofmostlytheC1andC3bondsin thetriglyceridemolecule,yieldingsolublefreefattyacidsanddiglyceride(Fig. 18).Inpractice,ithasbeendeterminedthatlipasesworkbestsubsequentto thefirstwash(Fig.19).Itisbelievedthatthetemperaturesencounteredina typicaldryingprocessareneededtoactivatetheenzyme.Thoughmostoily stainscanalsobecleanedusingtraditionalsurfactantmethods,themainbenefit oflipasesistheirabilitytoperformatrelativelylowconcentrationsandlow temperatures. Withgreateremphasisgiventothecareofthefabric,cellulaseenzymeshave becomeincreasinglyimportantindetergentproducts[94].Repeatedwashing oftenleadstocottonfabricslookingfadedandworn.Thisappearanceis attributedtothedamagedcellulosemicrofibrilsonthefabricsurface.Cellulase en

FIG.18 Lipasecatalyzedconversionofinsolubleoily(triglyceride)soils.

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FIG.19 Effectoflipaseenzyme(Lipolase)onlard/SudanRedstainsasa functionofthenumberofwashcycles.Conditions:Powder detergent,temp30°C,Tergotometer,pH9.7.(Reproducedwith permissionfromRef.6.)

zymesareabletohydrolyzethe (1–4)bondsalongthecellulosepolymer, resultinginsmallerunitsthatarecarriedawayinthewash(Fig.20).The removalofthesedamagedmicrofibrilsorpillinggivestheclothingalessfaded appearance(Fig.21).

FIG.20 Hydrolysisofcellulosefibersbycellulaseenzyme.

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FIG.21 Effectofcellulaseonthecolorclarityandpillingtendencyofa cottonfabric.Europeanmachineat40°Cusinganewblack cottonfabric.(ReproducedwithpermissionfromRef.6.)

1.EnzymeStabilization Enzymesarehighlysusceptibletodegradationinheavydutylaundryliquids. Withincreasingemphasisontheuseofenzymesascleaningagents,itbecomes allthemoreimportantthattheseenzymesbeprotectedagainstpremature degradationoratleastmaintaintheirperformancethroughouttheshelflifeof theproduct. ManyfactorscontributetothedenaturationoftheenzymesinHDLDs.They includefreewater,alkalinity,bleaches,andcalciumionconcentration.The presenceoffreewaterintheformulationisamajorcauseofenzyme degradation.Thisprocessisgreatlyacceleratedatincreasinglyalkaline conditions.Generally,enzymecontainingcommercialHDLDsaremaintained withinapHrangeof7–9(Fig.22).However,thisconstraintcanaffectthe detergency,asmostenzymesattaintheiroptimumefficacyatpHrangesof9– 11.Certainadditionalingredients,especiallybleaches,canalsohaveamajor detrimentaleffectonenzymestability. Itisbelievedthatingredientsthatarecapableofdeprivingtheenzyme'sactive siteofcalciumionsaredetrimentaltoenzymestability.Itishypothesizedthat calciumionsbindatthebendsofthepolypeptidechain,resultinginastifferand morecompactmolecule[96–98].Buildersandsurfactantsthathaveaffinities towardcalciumionsareexamplesofsuchingredients.Thedegreeofstability alsovariesgreatlywiththetypeofsurfactantorbuilderused.Linear alkylbenzenesulfonateandalkylsulfatesurfactantshavebeenfoundtobe moredetrimentaltoenzymesthanalcoholethoxylatesoralkylethersulfates [95].The

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FIG.22 EffectofproductpHonproteasestabilityinanHDLDcontaining alcoholethoxylateandalcoholethoxysulfates.(Reproducedwith permissionfromRef.95.)

degreeofethoxylationalsoaffectsthestatusoftheenzyme.Inethersulfates, improvedstabilityisobservedwithincreasingEOgroupsuptofivetoseven EOgroups[96].LASismorelikelytobindwiththecalciumionsinthe productthanothermorehardnesstolerantsurfactantssuchasalkylether sulfatesorthenonionicalcoholethoxylatesurfactants.Thishasbeen consideredapossiblecauseoffasterenzymedegradationinLAScontaining HDLDs(Fig.23).Similarly,informulationswithbuildersorchelants,additional calciumissometimesaddedtoshifttheequilibriumtofavortheenzyme'sactive sitesandpreventprematuredeactivation. Othermechanismsforenzymedenaturationinthepresenceofsurfactantshave alsobeenproposed.Onehypothesisisthatthehighchargedensitiesofthe ionicsurfactantsincreasetheprobabilityoftheirbindingstronglyontoprotein sites.Thiscausesconformationalchangesoftheenzyme,whichsubsequently leadtofurtherenzymedeactivation[95,99]. Thetaskofstabilizingenzymesisfurthercomplicatedbythefactthat increasinglyHDLDformulationscontainmorethanoneenzyme(e.g.,protease, lipase,andcellulase)system.Insuchsystems,notonlydotheenzymeshaveto beprotectedagainstdenaturation,butalsoenzymessuchaslipaseand cellulase,whicharethemselvesproteins,havetobeshieldedfromthe protease.

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FIG.23 Effectofsurfactanttypeonproteasestability.AE,Alcoholethoxylate; AE253S,Alcoholethoxysulfate;LAS,linearalkylbenzenesulfonate. (ReproducedwithpermissionfromRef.95.)

(a)ProteaseOnlyHDLDs.Allstabilizationsystemsfunctioneitherbybinding totheactivesiteoftheenzymeorbyalteringtheequilibriaoftheformulationto favorthestableactivesites.Thesystemiseffectiveinprotectingtheenzyme onlyifthestabilizingmoleculebindsstronglytotheenzymewhileina formulationbuteasilydissociatesfromtheenzyme'sactivesiteswhenit encountersthediluteconditionsinthewash. LettonandYunker[100]andKaminskyandChristy[101]describeprotease stabilizationsystemscomposedofacombinationofacalciumsaltandasaltof acarboxylicacid,preferablyaformate.Theseingredientsaremoderately effectiveinenzymestabilizationandarerelativelyinexpensive.Carehastobe taken,however,whenaddingdivalentionssuchascalciumtoHDLDsto preventthepossibilityofprecipitation. Animprovementoverthisearliersystemwasattainedwiththeadditionof boroncompoundssuchasboricacidorboratesalts[102–104].Ithasbeen hypothesizedthatboricacidandcalciumformintramolecularbondsthat effectivelycrosslinkorstapleanenzymemoleculetogether[103,104].The useofpolyolssuchaspropyleneglycol,glycerol,andsorbitolinconjunction withtheboricacidsaltshasfurtherenhancedthestabilityoftheseenzymes [105–107].

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Thepatentartcontainsnumerousexamplesofenzymestabilizationsystemsthat useborates,polyols,carboxylatesalts,calcium,andethanolaminesor combinationsthereof[87,108–111]. (b)MixedEnzymeHDLDs.InHDLDformulationswithadditionalenzymes besidesprotease,itbecomesincreasinglydifficulttostabilizealltheenzymes. Amylases,lipases,andcellulasesarethemselvesproteinsandhenceare susceptibletoattackfromtheprotease.Variousapproachestostabilizinga mixedenzymesystemhavebeendocumentedinthepatentliterature.One approachattemptstoextendthestabilizationtechniquesdevelopedtostabilize proteaseonlyformulationsandapplythemtomixedenzymeliquids[112– 114]. Compoundsthatbindevenmoretightlytotheproteaseactivesitesandasa resultinhibitthisenzyme'sactivityintheproductduringshelfstoragehavebeen identified.However,thismethodiseffectiveonlyiftheenzymeinhibitioncanbe reversedunderthediluteconditionsofthewashwater.Variousboronicacids [115–119](e.g.,arylboronicacidsand aminoboronicacids),peptide aldehyde[120],peptideketone[121],andaromaticborateester[122] compoundshavebeenfoundthatdeliverthistypeofperformance.Itis believedthatboronicacidsinhibitproteolyticenzymebyattachingthemselves attheactivesite.Aboronserinecovalentbondandahydrogenbondbetween histidineandahydroxylgroupontheboronicacidapparentlyareformed [118].Thepatentliteraturealsodescribesmethodsofstabilizingthecellulase enzymesinmixedenzymesystemswithhydrophobicaminecompoundssuch ascyclohexylamineandnhexylamine[123]. Recently,alternativemethodshavealsobeendevelopedtostabilizethese complexenzymesystems.Thetechniqueofmicroencapsulation[124]is designedtophysicallypreventtheproteaseenzymefrominteractingwiththe otherenzymes(Fig.24).Thisisaccomplishedbyacompositeemulsion polymer

FIG.24 Enzymemicroencapsulation.(Reproducedwithpermission fromRef.6.)

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systemthathasahydrophilicportionattachedtoahydrophobiccorepolymer. Theproteaseisstabilizedbytrappingitwithinanetworkformedbythe hydrophobicpolymer. D.Bleaches Bleachesplayasignificantroleindetergentformulationsbecausetheycan affectcleaningefficacy,whichiseasilyperceivedbyconsumers.Bleaching actioninvolvesthewhiteningorlighteningofstainsbythechemicalremovalof color.Bleachingagentschemicallydestroyormodifychromophobicsystems anddegradedyecompounds,resultinginsmallerandmorewatersoluble moleculesthatareeasilyremovedinthewash.Typicalbleachsensitivestains includefood,coffee,tea,fruits,andsomeparticulatesoils.Bleachescanalso aidinminimizing“dinginess,”whichgivesclothesagrayoryellowtintcaused byacombinationoffabricfiberdamageanddirtbuildup. Therearetwotypesofbleachesusedinthelaundryprocess:hypochloriteand peroxygenbleaches.Althoughhypochloritebleachesbythemselvesare effectivebleaches,theyleadtocolorfadingandfabricdamageandaredifficult toincorporateintodetergentformulations.Peroxygenbleaches,ontheother hand,thoughnotaseffective,canbeformulatedintodetergentsandcause minimalcolorfadingorfabricdamage.Theyalsobleachoutfoodstainsasthe chromophoresfoundinthesestainsaresusceptibletoperoxidebleaches. Fabricdyes,however,arenotasactiveasfooddyesandarethereforenot easilyaffectedbytheperoxygencompounds. Mostdetergentswithbleachformulationsareinthepowderform. Unfortunately,theaqueousnatureoftheHDLDsdoesnoteasilypermitthe formulationofbleachcomponents.Thisisespeciallytrueinunstructured liquids,wherethestabilityoftheperoxygencomponentsisseverely compromised.Nevertheless,attemptshavebeenmadetoproduceHDLDs thatalsocontainbleaches. 1.PeroxygenBleaches Detergentformulationscontainingperoxidebleachcontaineitherhydrogen peroxideorcompoundsthatreacttoformhydrogenperoxideinthewash.The mostdirectsourceforperoxidebleachingishydrogenperoxide.Numerous attemptshavebeenmadetodevelopstableHDLDscontaininghydrogen peroxide[125–127].Thestabilityofthisingredientinaqueousformulations, however,isofconcern.Hydrogenperoxideisverysusceptibleto decompositioninaqueousenvironments,largelybecausetraceimpuritiesof metalionssuchasiron,manganese,andcoppercancatalyzeitsdecomposition [128].Alkalinityalsoacceleratesthisprocess.ForthesereasonsHDLDs containinghydrogenperoxidearemaintainedatanacidicpHandusuallyalso containastrongchelatingagenttosequestermetalions.Afreeradical scavengerisalsosometimes

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addedtofurtherenhancestability.Polyphosphonatecompoundsandbutylated hydroxytoluene(BHT)areexamplesofchelatingagentsandfreeradical scavengers,respectively,thatareusedinhydrogenperoxidecontaining formulations[129].Still,thebleachingperformanceoftheseproductsis inadequate,especiallyatlowtemperatures.Theselimitationshaveprompted manufacturerstolooktoothermethodstodevelopbleachHDLDs. Inorganicperoxygencompoundssuchassodiumperboratetetrahydrateor monohydrateandsodiumpercarbonatecanalsobeusedassourcesof hydrogenperoxide.Theseinsolublecompoundsreleasehydrogenperoxideon contactwiththewashwater.ThechallengeistostabilizethemwithinanHDLD formulation.Theabilityofstructuredliquidstosuspendsolidsbetweenthe surfactantlamellaeorspherulitescanbemadeuseofintheseproducts[130– 133].Itispossibletosuspendsodiumperborateinhighlyconcentrated structuredliquids.Theminimizationofcontactwithwaterpreventsthe peroxygencompoundsfromdecomposingprematurely.Ithasalsobeenfound thattheuseofsolventsfurtherimprovestheirstability[134].Hydrophobic silicacanenhancestabilityinunstructuredliquids[135].Themosteffective methodofformulatingwithperboratesandpercarbonatesiswithnonaqueous liquids.Thecompleteabsenceofwaterandahighlevelofsolventssignificantly enhancethestabilityofbleachesintheproduct. 2.PeracidandActivatedPeroxygenBleaches Peroxycarboxylicacidsorperacidsarefarmoreeffectivebleaching compoundsthanperoxygenmolecules,especiallyatlowandambient temperatures.Thehighreactivityandlowstabilityofthesecompoundshaveso farpreventedthemfrombeingusedincommercialdetergentbleach formulations.PeracidsaresomewhatstableinaqueoussolutionsofneutralpH, andtheyequilibratewithwaterintheacidpHrangetoformhydrogenperoxide andcarboxylicacids.However,inalkalineconditionsthesecompounds undergoaccelerateddecomposition.Nevertheless,attemptshavebeenmade todevelopHDLDsthattakeadvantageofthe

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