Whiter

纺织类

doi:10.1111/j.1478-4408.2011.00312.x

Whiterwoolfrom?eecetofabric

KeithRMillington,*ALKing,SHatcherandCDrum

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a,abc

CSIROMaterialsScienceandEngineering,Belmont,Vic.3216,AustraliaEmail:keith.millington@csiro.au

IndustryandInvestmentNSW,OrangeAgriculturalInstitute,ForestRd,Orange,NSW2800,Australia

TheMerinoCompany,460CollinsStreet,Melbourne,Vic.3000,Australia

b

c

Received:5November2010;Accepted:11April2011

ThenaturalcreamcolourandlowphotostabilityofMerinowoolareimpedimentsthataffectthewool’scompetitivenessoverawiderangeofapparelandinteriortextileproducts.Inparticular,thesetwopropertiesneedimprovementifthewoolistomatchtheperformanceofcottonandsyntheticsintheexpandingmarketfortrans-seasonalknitwear.ThestrategyadoptedbytheCooperativeResearchCentre(CRC)forSheepIndustryInnovationistoimprovethewhitenessofcleanwoolbygeneticselectionandtomaintainwhitenessthroughprocessingbydevelopingaminimum-colour-impactroutefrom?eecetofabric.Recentstudiesonthe‘InformationNucleus’?ocksestablishedbytheCooperativeResearchCentrehavecon?rmedthehighheritabilityofcleanwoolcolourandshownforthe?rsttimethatphotostabilityismoderatelyheritableusingdatafromanewphotostabilitytestmethod.Apilot-scalecommercialprocessingtrialhasshownthatsigni?cantimprovementsinthewhitenessofknittedproducts(upto40CIEGanzunits)canbeachievedbyselectingwhite?eecewoolsandoptimisingtheprocessingroutetoavoidstagesthatmaycauseyellowing.

Introduction

Woolismoreprominentinformalapparelthanothermarketsandhasbeentraditionallyregardedasawinter?bre.ThecontinuingtrendtowardsmorecasualclothingandtheubiquitousclimatecontrolinbuildingsinWesterncountrieshavesigni?cantlyreducedthevolumesoftheformalandwinterclothingmarketsandhaveexpandedothers,inparticularthemarketforactivesportswearandtrans-seasonalknitwear.

Naturalcolourandcolourstabilityarekeypropertiesfortextile?bresaimedatthesenewmarkets.Brilliantwhitesandpastelshadesareessentialforthesemarkets;however,therangeofshadestowhichaparticular?brecanbedyeddependsuponitsinitialwhiteness.Dyed?bresshouldalsoberesistanttocolourchangesinducedbyexposuretosunlight,heatandotherconditionsencounteredduringproduction,processing,wearorlaundering.Whereaswoolhasmanyhighlydesirableattributesasatextile?bre,itscolourandcolourstabilityaretechnicallyinferiortothoseofcottonandsynthetics.Herein,wereviewcurrentresearchbeingcarriedoutbytheCooperativeResearchCentre(CRC)forSheepIndustryInnovation’sWhiterLightfastWoolsproject,theaimofwhichistoimprovethewhitenessandphotostabilityofscouredMerinowoolandtomaintainwhitenessthroughprocessingfrom?eecetofabric.Woolcolourresearchisfocusedonthreeareas.The?rstistheidenti?cationofgeneticandenvironmentalfactorsthatin?uencecleanwoolcolour,thelong-termaimofwhichistoimprovethewhitenessofMerinowoolthroughgeneticselection.Secondly,althoughitiswellknownthatwoolyellowsmorerapidlythancottonorsyntheticswhenexposedtotheultraviolet(UV)componentsofsunlight[1,2]andthatthethermalstabilityofwoolat150°Cisheritable[3],nostudieshaveestablishedtheheritabilityofwoolphotostability.Finally,ananalysisof

theimpactofdownstreamprocessingonwoolwhitenessandphotostabilityisimperativeifwhiterwoolsaretobegrownandwhiterwoolgarmentsaretobeproducedcommercially.Amethodforproducingwooltextilesinbrightwhiteandpastelshadesisrequiredforfurthermarketpenetration.

Geneticfactorsin?uencingwoolcolour

TheInternationalWoolTextileOrganisationhasapprovedastandardmethodformeasuringcleanwoolcolour[4].Inthismethod,acell?ttedwithglasswindowsateitherendispackedwithwooltoaconstantdensityorpressure.Thecolourofscouredwoolisexpressedintermsofthethreetristimulusvalues,X,YandZ,whicharederivedfromthere?ectancespectrumofwoolinthecell.Thesevaluesrepresenttheamountsofthered?orange(X),yellow?green(Y)andblue?indigo?violet(Z)componentsofthespectrumofwhitelightthatarere?ectedfromthesample.Scouredwoolcolourisnormallydescribedintermsoftwooftheseparameters,theYtristimulusvalue(brightness)andtheY–Zvalue(yellowness).Thecolourofscouredwoolrangesfrompalecreamtodeepyellowandthewhitestwoolscommandpremiumprices.Yellownessvalues(Y–Z)<8.5areconsideredgoodforMerinowool,whereasY–Zvalues>11indicatehighlyyellowedwoolandareundesirable[5].

StudiesonCollinsvilleMerinossuggestedthatcleanwoolcolourisheritable[6,7]andthishasbeencon?rmedbymorerecentstudiesonbothNewZealand[8]andAustralianMerinosusingNewSouthWales[9]andSouthAustralian?ocks[10].Theheritabilityestimatesfromthesestudieswereintherange0.25–0.54,showingthatscouredwoolcolourisamoderatelytohighlyheritabletraitandsuggestingthatcleancolourwouldrespondfairlyrapidlytoselection.However,fewMerinosheep

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producersinAustraliacurrentlyrequestscouredwoolcolourmeasurementsfortheirwoolsalelots,thecurrentadoptionrateforcolourtestingbeingjust0.6%[11].Neitherdotheyselecttheirramswiththeassistanceofobjectivelymeasuredscouredwoolcolourdata[12],relyingonsubjectivescoringofgreasywoolcolour.

Toassistwithdeterminationofgeneticparameters,theCRChasestablishedseveralgeneticallywell-characterised?ocks[theInformationNucleus(IN)]indifferentregionsofAustraliatotalling5000ewes[13].TheINanimalsaredistributedamongseveralregions,inwhichtheyareexposedtodifferentclimatesandconsumedifferentdiets,enablinggeneticeffectstobedistinguishedfromenvironmentaleffects.

Astrongcorrelationbetweenmean?brediameter(MFD)andcleancolourhasbeenreported[9,14],i.e.?nerwoolsappeartobewhiter.ThisisattributablemainlytochangesintheratioofopticalscatteringtolightabsorptionwithMFD.Synthetic?bresofvaryingMFDhavebeenusedtocreateamodeltocorrectfortheeffectsofMFDon?brecolourandthemodelhasbeensuccessfullyappliedtodatafromtheIN?ocks[15].PreliminaryanalysisofdatafromtheIN?ockshasshownthatcolourhasaheritabilityof0.70,whichissubstantiallyhigherthanthatreportedinapreviousstudy[16].

Environmentalfactorsin?uencingwoolcolour

Woolcolourisadverselyaffectedbyweatheringwhenexposedtosunlightonthesheep’sback.ColourmeasurementsoncleanwoolfromdifferentsitesonMerino?eecesgrowninAustraliashowadeteriorationofca.3brightness(Y)unitsandca.1yellowness(Y–Z)unitsforwoolgrownonthebackofthesheepcomparedwithmid-?anksamples[17].Incontrast,onruggedsheepthebackwoolisslightlybrighterandlessyellowthan?ankwool.Sheepcoatsareeffectiveinreducingtheexposureofwooltosunlightanddust,makingthewoolwhiterandcleanerandreducingtipdamage[18].

ACRCstudywascarriedoutusingsheepcoats?ttedwithUV-transparentandUV-opaquewindowstodistinguishtheeffectsofUVandvisibleradiationonwoolcolourfromtheeffectsofdirtanddustaccumulationonthesurfaceofthe?eece[19].TheUV-transparentpolyethylenewindowsresultedinanincreaseinyellownessof2–3unitsforrumpandshoulderwoolafter11weeksofgrowth,whereasUV-opaquepolyvinylchloride(PVC)windowsresultedinnosigni?cantchangeinwoolyellowness.AnotherCRCstudyonthepenetrationofsunlightintoasimulated?eece100mminlengthusinga?bre-opticprobeshowedthat<10%ofincidentlightpenetratesmorethan40mmintothe?eece[20].Lightintensityandstapleyellowing(Y–Z)werestronglycorrelatedwithdistancefromtheexposed?bretip,asexpected.

Itisknownthatfree-radicaloxidationofwoolproteinsisinvolvedinthephotoyellowingofwoolandthatfree-radicaloxidationisstronglycatalysedbycertaintracemetals[21].Merinowoolcontainstraceelements,manyofwhicharestronglyboundtokeratinproteinandare

notremovedduringwoolscouringorwetprocessing.Itiswellknownthattracemetalsin?uencewoolcolourinpigmentedsheep;forexample,copperde?ciencycauses‘white’bandsinpigmentedwool.AlthoughthegeneticandenvironmentalvariationinthetracemetalcontentofMerinowoolhasnotbeenmeasured,studiesonhumanhairhaveshownconcentrationsoftracemetalionssuchasironandcoppervarysigni?cantlywithinlocalisedpopulationsandtheircontentiscorrelatedwithhaircolourandsex[22].Itishighlylikelythat,inadditiontogeneticeffects,differencesinthemineralcontentofsoils,animalhusbandry,dietaryfactors,healthandageaffecttracemetalconcentrationsinwoolfromdifferentregions.AstudyusingexistingwoolcolourdataandtracemineraldataforSouthAustralianWoolStatisticalAreas(WSAs)wasconductedtoinvestigaterelationshipsbetweenwoolcolourandtraceelementstatus.MeansforwoolcolourmeasurementswithinWSAswereadjustedforyield,?brediameter,staplelengthandstaplestrengthandcomparedwithmeansforwoolfromWSAswithalowmineralstatus(copper,seleniumandcobalt).Woolyellownesswasstronglycorrelatedwithlowcopperstatus.Woolfromareaswithahighincidenceofcopperde?ciency,basedonaprevioussurveyofthecoppercontentofliversfromslaughteredcattle,waslessyellowthanwoolfromareaswithanadequatecopperstatus[23].Astudyontheeffectsofthecopperchelators,kojicacidandmethylgentisate,onwoolcolourduringgrowthshowedthat,althoughbothchelatorsreducedthecoppercontentofwool,theyalsocausedpronouncedyellowing[19].

Inbiologicalsystems,protein-boundironandcoppercauseoxidationofproteinswhenoxygenandanelectrondonorarepresent.Thesereactionsandthedamagetocellularproteinsassociatedwiththemhavebeenstudiedextensivelyinrelationtohumandiseases[24,25].HydrogenperoxideproducedbycellsreactswiththemetalcomplextoproducehydroxylradicalsviaFentonreactions:

Fe2þþH2O2!Fe3þþOH??þOHÀFe3þþH2O2!Fe2þþOOH??þHþ

ð1Þð2Þ

Thisprocessultimatelyoxidisesanddamagestheproteinadjacenttothemetalbindingsite.Tracemetalsmaybeincorporatedintothewool?breviathefollicleduringgrowth(endogenous)ormaybedepositedontoorabsorbedintothe?brefromair-orwater-bornematerialspresentintheenvironment(exogenous).SynchrotronX-ray?uorescencehasbeenusedforhigh-resolutionimagingoftracemetalsincross-sectionsofhumanhair?bres[26].Thisstudysuggestedthatonlycopperandzincareendogenousandthatothertraceelementssuchasironandcalciumareenvironmentalcontaminants.Copperandzincbothplayimportantrolesinthekeratinisationofwoolandhair.

AnextensiveanalyticalprogrammeisbeingcompiledtodeterminethetracemetalcontentofwoolfromtheIN?ocks,toestablishwhetherwooltracemetalcontentiscorrelatedwithwoolcolourandphotostabilityandtodetermineenvironmentalandgeneticeffectsontheseparameters.Previousworkhasshowntheimportanceof

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thoroughcleaningonthetracemetalcontentofhumanhair[27,28]andarecentstudyexaminedtheeffectsofseveralcleaningprotocolsonthetracemetalcontentofIcelandicwool[29].Arigorousstudy[30]ontheeffectivenessofvarioushaircleaningprocedureswasusedasthebasisfortheprotocolappliedtoIN?eecewoolsamplesbeforetraceelementalanalysisusinginductivelycoupledplasma–atomicemissionspectroscopy.

Figure1showsthevariationintraceelementcontentwithyellowness(Y–Z)forthecolourextremesintheIN?ocksin2009.Concentrationsofcalcium,magnesiumandmanganesehadaweakcorrelationwithyellowness,whereaszinc,copperandironwerenotcorrelatedwithyellowness.However,itisinterestingthatmostoftheyellowedsamplescontainedrelativelylowlevelsofcopperandiron.Ahypothesisforthis?ndingisthatsevereyellowingiscausedbybacterialattackandthatthemicrobesresponsiblemaysequestermetalionsfromwool?bre.Yellowandbrowndiscolorationofwoolhasbeenlinkedtomixedpopulationsofbacteria,includingPseudomonasmaltophilia[31].ItisknownthatPseudomonassynthesisesandsecretessiderophores,

whicharechelatingagentsthatscavengemetalsfrommineralsandformsolublemetalcomplexesthatarereadilytakenupbythemicrobes[32].

Woolphotostabilityandcomparisonwithother?bres

Thechemistryofwoolphotoyellowinghasbeencomprehensivelyreviewed[1,2].Photoyellowingdoesnotoccurintheabsenceofatmosphericoxygenandisaphoto-oxidationprocess.Itproceedsviaafreeradicalchainreaction,theBolland–Geeauto-oxidationmechanism,similartothatwhichoccursinsyntheticpolymers.Thereareseveralprimarylight-absorbingspeciesinwoolkeratin,includingtryptophan(Trp)andtyrosine(Tyr)residues,whichabsorblightintheUVregion,andnaturalcreamchromophoresandyellowoxidationproductsfromphoto-oxidationreactions,whichbothabsorbvisiblelight.

Surprisinglylittleisknownregardingtheidentityofthenaturalcreamchromophoresofwool.Incontrast,recentstudieshavecon?rmedthepresenceof13yellowchromophoresin25photomodi?edpeptidesequences

181614

Yellowness Y-Z

R2 = 0.2849

Yellowness Y-Z

181614121086420

R2 = 0.004

1210864200181614121086420

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8001000120014001600Calcium, mg/kg

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R2 = 0.0032

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Iron, mg/kg

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6810Manganese, mg/kg

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Magnesium, mg/kg

Yellowness Y-Z

R2 = 0.2712

121086420

R2 = 0.0949

507090110130150

Zinc, mg/kg

Figure1Relationshipbetweenyellowness(Y–Z)andtracemetalcontent(mg?kg)ofwoolsampledfromIN?ocksin2009ª2011TheAuthors.ColorationTechnologyª2011SocietyofDyersandColourists,Color.Technol.,127,297–303

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fromheavilyUV-irradiatedwoolfabrics.AllofthesechromophoresarederivedfromTrpandTyrresiduesinthekeratinintermediate?lamentsandproteinshighinglycineandtyrosineinthewool?brecortex[33,34].

BeforetheCRCprogrammebegan,itwasunknownwhetherthereisanyvarianceinthephotostabilityofscouredMerino?eecewoolswithsimilarcolourattributes.Atestmethodcapableofassessingthephotostabilityofthesmallsamplesof?eecewoolwasrecentlydevelopedforthispurpose[35].Thiswasacomplextask,astheprocessesofphotobleachingandphotoyellowingoccurconcurrentlywhenwoolisexposedtonaturalorsimulatedsunlight[36].SourcesthatproducebothUVandvisibleradiation,suchasnaturalsunlightorsimulatedsunlightfromanAtlasorXenotestsource,bleachtheyellowerwoolsduringtheearlystagesofexposure,whereaswhiterwoolsareyellowedfromtheoutset.Exposuretobluewavelengths(400–450nm)causesthephotobleachingofwool.However,whenexposedtoUVradiation(280–400nm)alone,woolsundergophotoyellowingregardlessoftheirinitialyellowness.YellowingoccursmorerapidlywhenwoolisexposedtohighenergyUVB(280–320nm)radiationthanwhenitisexposedtoUVA(320–400nm)radiation.Therefore,exposuretomeasureddosesofUVBirradiationappearedtobeapromisingbasisforaphotostabilitytest.

Preliminarystudiesusingthisapproachshowedthatatestprotocolinvolving4hofexposuretoUVBresultedinreproducibleyellowingofscoured?eecewool.Forthewhitestwools,theincreaseinY–Zafter4hofUVBexposurewasequivalentto5–9daysofexposuretosimulatedsunlight.Scouredwoolsamples(0.5g)werecompressedtoaconstantdensityindisposablepolymethylmethacrylate(PMMA)spectrophotometercells(transparentdownto300nm)andwoolcolourwasmeasuredbeforeandafterirradiationusingastandardtextilelaboratoryre?ectancespectrophotometer.Thedensityofscouredwoolinthecellisdesignedtoensurethattheirradiated

woolsurfaceheldagainstthecellwindowisquitestable,sothatindividual?bresareunabletomoverelativetooneanotherduringcolourmeasurementandirradiation.Theapparatusiscapableofirradiatingupto48scouredwoolsamplesinonebatch.TheprecisionofphotostabilitymeasurementswasassessedandtherelativeerrorinD(Y–Z)was<6%.TherelationshipbetweentheinitialyellownessandD(Y–Z)afterexposuretoUVBfor4hisbroadlylinear,inagreementwithpreviousworkthatshowedthatwhiterwoolsundergosigni?cantlymoreyellowingthanyellowerwoolsduringUVBexposure[36].Furtherdetailsofthetestmethodhavebeenpublishedelsewhere[35].

AplotofinitialyellownessagainstphotostabilityD(Y–Z)forsamplesobtainedin2008fromthreeIN?ocksisshowninFigure2.Samplesofagiveninitialyellownessvaryinphotostability,demonstratingthatvarianceinphotostabilityexists.Thisvariancemaybeattributabletoacombinationofphenotypic,geneticandenvironmentaleffects.AninitialstudybasedonthedatashowninFigure2foundthatphotostabilityhasmoderateheritabilityof0.18[16].

Anoptimisedprocessingmethodforwhitewool

ThereislittletobegainedbyimprovingthecolourofMerino?eecewoolonfarmifthebene?tthereofislostduringprocessing.Thecolourandphotostabilityofundyedwoolcanbeprofoundlyaffectedbycommercialprocessing.Oxidativebleachingwithhydrogenperoxideandapplicationofopticalbrighteningagentsreducephotostability[37].Severalotherprocessingfactorsaffectwoolcolourandphotostability,includingthermalyellowingduringdryinganddyeingathightemperature,alkaliyellowingduringscouringandchlorinationduringshrink-resisttreatment.

Twostagesofparticularimportancearewoolscouringandlowcolourimpactshrink-resisttreatment.Effective

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KirbyHamiltonTurretfied

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PhotostabilityΔ(Y-Z)

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Initial yellowness (Y-Z) by CSIRO method

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Figure2PlotofphotostabilityD(Y–Z)vsinitialyellownessforwoolsamplesobtainedin2008fromtheKirby,HamiltonandTurret?eldIN?ocks300

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scouringisimportanttoobtainthebrightestpossiblewoolcolour.Re-washingofcommerciallyscouredwoolimprovesbothbrightness(Y)andyellowness(Y–Z)[38].Theef?cacyofscouringdependsonadequaterefreshmentofthescouringliquor;failuretodosoaffectsthebrightnessofscouredwool[39].

AstudyontheprocessingofgreasyMerinowooltothesliverstageshowedthatthebrightnessandyellownessofwoolissimilaratthegreasystageandthetopstage[40].Ineightmillconsignments,thecolourofscouredwoolwassigni?cantlyinferiortothatofgreasywool,presumablybecauseofinef?cientscouring,http://wendang.chazidian.commercialwoolcleaningcanbeviewedasatwo-stageprocess,inwhichthemajorityofcontaminantsareremovedduringscouringandtheremainderareremovedduringcardingandcombing.AmorerecentstudyonAustralian,NewZealandandUSwoolscon?rmedthatcardingimprovesthecolourofscouredwool[41].

Commercialshrink-proo?ngofwoolsliverinvolveschlorinationofwoolfollowedbytheapplicationofHercosettresin.ThedegreeofwoolyellowingthatoccursduringchlorinationisdependentonpH,temperatureandtheconcentrationofthechlorinatingagent.WhenusedatalowpHandatroomtemperature,thechlorinatingagentdichloroisocyanuricacid(DCCA)causestheleastamountofyellowing[42].Themechanismbywhichwoolisyellowedbychlorineisunknown,butmayinvolveoxidationofaromaticaminoacidresidues,similartophoto-oxidation.Alternativechlorine-freeslivershrink-resistprocessesforwoolhaverecentlybeendevelopedforenvironmentalreasons,astheef?uentfromtheseprocessesisfreeofadsorbableorganohalogens.

Acommercialtrialusingalowcolourimpactprocessingmethodhasnowbeencompletedusingtwobalesofsuper?newool(MFD,18.1lm)sourcedfromMertonVale,Tasmania.ThewoolwasscouredattheCommonwealthScienti?candIndustrialResearchOrganisation(CSIRO)inGeelongandwasshippedtoChinaforcarding,combingandshrink-resisttreatmentusingachlorine-freeprocessinvolvinghydrogenperoxideasoxidant.ThetreatedtopwasthenshippedtoIndoramainThailandandspuninto40-texmetricsinglesyarnbeforebeingshippedtoLevanaTextilesinNewZealandforknittingand?nishing.TheCRCfabricwascircularknittedand?nishedusingthesametreatmentasthestandardcommercialundyedproduct,‘ToiToi’.Forthisshade,adouble-bleachingprocesswasappliedinwhichanopticalbrightenerUvitexNFW(0.5%owf;Ciba,Basel,Switzerland)wasincludedinthereductivebleachbath.Table1showsthattheCRCtrialfabricwassigni?cantlywhiterthanthreebatchesofthestandardcommercialproduct.Themagnitudeoftheimprovementwas30–40CIEGanzindexpointsforthetestfabricthatwas?nishedusingthestandarddouble-bleachingprocessand10–20pointsforthetestfabricthatwas?nishedwithareductivebleachonly.

A30–40CIEGanzindexpointimprovementincolouroverthestandardcommercialprocessforthisshadeisavaluableandpleasingresultfromthe?rsttrial.Itshowsthatlargeimprovementsinwoolwhitenessarepossible

Table1Colourmeasurementson?nishedToi-ToiknitfabricproducedviastandardcommercialorCRCprocessingroutes

WIGANZ82–80.689.782.3–101.1120.0

Fabric

Un?nishedstandardknitStandard?nishbatch1Standard?nishbatch2Standard?nishbatch3Un?nishedCRCknitCRCknitreductivebleachonly

CRCknitstandard?nish

X65.374.975.073.665.074.374.7

Y69.678.478.576.869.077.377.5

Z59.984.485.783.263.486.188.9

Y–Z9.7)6.1)7.2)6.45.6)8.8)11.4

whentheinitial?eecewooliscarefullyselectedandanoptimisedprocessingroutewithalowimpactoncolourateverystageisused.

Apreviousstudy[43]monitoredcolourchangesinsevenlotsofAustralianMerino?eecewoolfromthegreasywooltothetopstage.Theyfoundthat,althoughthebrightness(Y)improvedslightlyduringprocessing,yellowness(Y–Z)alsoincreasedslightly.Toourknowledge,therearenoreportsoncolourchangesfrom?eecetofabricfor?eecewoolfromoneorigin.Onereasonforthepaucityofdataisthatitisdif?culttocomparecolourmeasurementsobtainedfromloose?brewiththoseobtainedfromyarnorfabricbecauseofdifferencesin?brepackingdensity,theneedforawindowforloose?bremeasurementsanddifferencesin?brealignment.Fibrepackingdensityinparticularhasasigni?canteffectontheX,YandZtristimulusvalues[44].

Tofacilitatecomparativemeasurement,yarnandfabricwerebrokendowntoloose?bresusingasmall(0.5mwidth)samplecard.Squaresofknittedfabric(2·2cm)andca.15-cmlengthsofcutyarnwereused.Thecardwas?rstclearedusingundyedrawpolyester?breandthenthewoolfabricoryarnwasplacedonthefeedbeltofthecardandslowlyfedin.Averyloosemassofseparated?bremixedwithstartingmaterialwasobtainednearthedofferendofthecardandthiswasputthroughthemachineanumberoftimesuntilsuf?cientloose?brewasobtainedforcolourandphotostabilitytesting.Fibrelengthwassigni?cantlyreducedafterseveralpasses,butpreviousworkhasshownthat?brelengthhasverylittleeffectonthedeterminationofcolourtristimulusvalues[44].Colourmeasurementswerecarriedoutusingthephotostabilitytestmethodbecauseitrequiresonly0.5gof?bre.

Figure3showsthattherewasasmallincreaseinyellownessduringcardingandcombing,possiblybecauseoftheuseoflubricants,followedbyalargeimprovementinwhitenessaftershrink-resisttreatmentwithactivatedhydrogenperoxide.ThelargedecreaseinY–Zafter?nishingwascausedbytheapplicationoftheopticalbrightener(UvitexNFW0.5%owf).

Wealsoexaminedtheeffectsofeachprocessingstageonphotostability(Figure4).Applicationoftheopticalbrightenersigni?cantlydecreasedthephotostabilityoftheCRCtrialwoolasexpected,withD(Y–Z)increasing

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