Chapter11SilkFibersIntroductionThelarvaofcertaininsectsforuseintheirbuildingwebs,climbingropesandcocoonsSpidersCommercialsilkindustry:uselarvaofsilkwormApplication:Mostlyapparel,wasalsousedforparachutes.StructureMacrostructure:Length:1000-1300yds(915-1190m)/cocoonMax3000yds(2750m)/cocoon,1fiber/cocoon.Thickness:9-11mmor1.2-1.5denier.Varies:thickestinthemiddlethinnestinside(mayberunningoutofrawmaterial,ormaybejustmakeitselfcomfortable).StructureMicrostructurecross-section:2triangularfilamentsco-extrudedbyaworm.Thetwoarecalledbrinsheldtogetherbysericin(gumorsilkglue).Wildsilkwormsproduceribbon-likesilkfibersStructureSubmicrostructureSilkfromcultivatedworm:noidentifiablesubmicrostructure.WildsilkorTussahsilkhasinternalfibrillarstructure.StructureFibroinproteinpolymerAchainofaminoacidsformingaproteincalledfibroincomposedof15-18differentaminoacids.Glycine,alanineandserineoccupy86%ofthepolymerThesidegroupsoftheabove3aminoacidsaresmallcomparedwiththoseinwool:glycine:R=Halanine:R=-CH3Serine:R=-CH2OHCrystallizereadily:70-75%StructureFibroinproteinpolymerPackwell:lotsofH-bonds,smallnumberofionicbondsNocystine:noS-SbondsConfiguration:pleatedb-sheetDegreeofpolymerizationofsilkDPsilk

>DPwoolPropertiesForsilkproducers,i.e.silkworm,spideretc.,silkfibersareforprotection,transportandfoodcaptureMechanicalpropertiesMediumtenacitybuthigherthanwoolresultedfrommolecularstructure:zigzagb-sheetofsilkvs

a-helixofwoolhighercrystallinitythanwoolPropertiesMechanicalpropertiesMediumelongationatbreakHighelasticrecoveryatlowelongationWhenelongated2%,90%elasticrecoveryMediummodulusMediumabrasionresistanceMediumresilience:(cotton<silk<wool)pleatedsheetscanslideoverone-another.PropertiesComfortHighheatofwetting:lotsofpolargroupsavailableHighwaterabsorption:upto1/3ofitsweightSmoothandsoftHighluster:highcrystallinityandtriangularcross-sectionalshape.Scroop:rustlingsoundduetoanacidtreatmentthathardensfibersurface.PropertiesOtherpropertiesIgnitesandburnsbutsometimesselfextinguishingDry-cleaningpreferreddueto:lowertenacityandinitialmoduluswhenwetdegradedbyalkalinesolutionsmaybehand-washedusingmilddetergentsLowestUVlightresistance:avoidprolongedexposuretosunshineProductionMoth:BombyxfedonmulberrytreeleavesWorldproduction:145.5millionlbs/yrOriginallyfromChinaTypes:Rawsilk:silkwithgumTussah:wildsilkDuppioni:2silkwormspintheircocoonstogether:havingspecialappearancesimilartowildsilkbutbettercolorChapter12CottonFibersIntroductionCotton:seedhairobtainedfromthebollofthecottonplant~4000fibers/seed,max20,000fibers/seed250,000fibers/bollTypes:Commodity:UplandLongstaple:Pima-SuPimaSeaislandEgyptianOther:naturallycoloredIntroductionApplication:~55%ofapparelfibersarecotton~70%ofmen’sapparelsmadeofcotton~40%

ofwomen’sapparelsmadeofcotton65%ofallcottonfiberswereusedforapparelsin1990Additional27%ofcottonforsheetsandtowelsorothernon-apparelhouseholdapplications~7%forindustrialuseStructureCottonfiber:singleplantcellMacrostructureStaplelength:1/8”-2.5”(0.32-6.35cm)Cottonfibersusedintextileyarns:7/8”-1.25”Diameters:16-20mmbutvariesfromfibertofiber:longerfibersarefinerLengthtobreadthratio:6000:1to350:1RelativelyuniformalongitslengthColor:nevertrulywhitebutcreamywhitetograyStructureMicrostructureFlat,twistedribbon125twists/inch(convolutions)ThetwistsreverseindirectionalongthelengthCross-section:kidney-beanshapedwithalumenStructureSubmicrostructure5distinctiveregions:Cuticle:outlayerofwax,afewmoleculesthicktoprotectseedsbutcanberemovedbywetprocessingandlaundering.Primarywall:composedoffibrils:asheathofspiralingfibrils20-30degreetothefiberaxisMaturefibers-thickerprimarywalls;immaturefibersthinnerprimarywallsandentangles:formingclumpscalledneps:leadingtononuniformdyepropertiesandirregularsurfaceoffabricsStructureSubmicrostructure5distinctiveregions:Secondarywall:bulkofthefiberconcentriclayerofspiralingfibrilssimilartoringsoftrees~20ringsandeachcorrespondingto1day’sgrowth.outmostlayerofsecondarywall:windinglayerLumen:hollowcanalrunningthroughthelengthofthefiberStructurePolymersystemLinearcelluloseAverageDegreeofPolymerization6,000to10,000Functionalsidegroup:-OHCrystallinity:65-70%butdependsonhowtodefine.H-bondingsites:not-OHto-OHbutOHtotheOgroupbetweentheneighboringtworings:confersstrengthandadditionalrigiditytothefiber.-OH:reactingwithavarietyofchemicals:thusfinishcanbeappliedeasily,alsoattractandholdwater.StructurePolymersystem-C-O-C-bondsaremoresusceptibletooxidationthanC-C-Cbonds20~41%unoccupiedspace,1/3bylumenPropertiesMechanicalPropertiesTenacityandinitialmodulus:mediumElongationatbreak:low:spiralfibrils:makesitrelativelybrittleElasticrecovery:low,only75%at2%extension:duetoH-bondPropertiesComfortFiberendsandconvolutions:comfortabletotouchHydrophilic:maxwaterabsorption:25-27%regaindueto-OHgroupandfibrilsUponwaterabsorption,fibersbecomesofterandcollapsesontoskin,driesslowlyWhenitisdry:comfortablebecauseofwaterabsorption,watervaportransferandnostaticchargePropertiesComfortWaterresistantfabricpossible:swellingoffibersinwater:noliquidwaterpenetrationMaintenanceSoiling:easytobesoiledanddesoileddueto-OHgroupsLaunderability:dimensionallystableandtenacityincreaseswhenwet(10-20%)duetoimprovementoffibrilorientationandthusmolecularorientation.PropertiesMaintenanceNospecialprecautionsforlaundering,hightemperature,anydetergents,andbleachescanbeused.ShrinkagelikelyduetorelaxationofyarntensioninducedbyprocessingPropertiesOtherpropertiesacidscausedegradationofcottonorcellulose:acidfreepaperforlonglastingitemsnotaffectedbymostoforganicsolventsdamagedbyfungiandbacteriaprolongedexposuretosunlight:yellowheatresistantlowlusterhighcoverpowerPropertiesOtherpropertiesnopillbutlinthighlyflammableandcansmolderwithoutfireforhours:needflame-retardanttreatmentformanyendusesbiodegradablecanbeboiledandsterilized:goodforhospitaluseMercerizedcottonProcess:(appliedtoeitherfibersoryarns)coldbathof18-27%NaOHfor1minuteorlessrinsedandneutralizedbyacoldacidbathtensionappliedtobreakH-bondspolymerrearrangedandreoriented:untwistroundercross-sectionandtheconvolutionsarenearlygoneStronger,morelustrousandeasiertodyeChapter14RayonIntroductionRayon:rayoflightonInvented1884Definition:manufacturedfiberscomposedof100%regeneratedcellulose,aswellasmanufacturedfibersofregeneratedcelluloseinwhichsubstituentshavereplacednotmorethan15%ofthehydrogensofthe-OHgroups.IntroductionMadefrom4processes:Nitrocellulose:madeinU.S.during20’s-40’sandeasytoexplode.Viscose:95%todayspuninU.S.Cuprammonium:usecuprammoniumhydroxidesolventasspinningsolutionLyocell

Introduction<4%oftotalfiberconsumedintheU.S.Usage:52.4%apparels26.8%nonwovens20.8%householdsStructuresMacrostructureContinuousfilamentsorstaple:1.5-15denierMicrostructure:Surface:striatedCross-section:serratedSubmicrostructureSkin-corestructure:causedbyspinningprocessSkin:smallcrystal,imperfect,darkerCore:large,moreperfectcrystalStructuresMolecularRegularviscoserayon:DP~400(cotton6k-10k)35-40%amorphousPropertiesMechanicalMediumtenacityandelongationLowinitialmodulusLowelasticrecoveryLowbendingrigidityTenacityandmodulusdropsdrasticallyuponwaterabsorption:-50%.Elongationtofailure+20%.PropertiesComfortHydrophilicandhighmoistureregain:13%at70%RH:moreabsorbentthancottonduetomoreamorphousregion.HighheatofwettingHighcross-sectionalswellingIrregularsurfacenexttoskin:comfor