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FiberAnalysis
Fibers• IndividualorClassEvidence?
– Class– Eveniffibersfromtwoseparateplacescanbematchedvia
comparison,thatdoesnotmeantheyderivefromthesamesource
• DirectTransfer:fromvictimtosuspectorfromsuspecttovictim– Ex.fromsuspect’ssweatertovictim
• SecondaryTransfer:whenfibersaretransferredfromanoriginalsourcetoonepersonandthentoasecondperson.– Ex.Carpet(fibers)à Victim Victimà Suspect– Ex.Pet(fur)à SuspectSuspectà Victim
FibersareTime-Sensitive!
• Within24hours,95%ofallfibershavebeenlostfromacrimescene.
WhatQuestionsDoForensicScientistsAskaboutFibers?
1) Whatisitscomposition?2) Whatisitscolor?3) Isitcommonorrare?4) Howmanyfiberswerefound?5) Wherewerethefibersfound?6) Whattypeoftextiledidthefiberoriginatefrom?
(carpet,clothing,upholstery,etc.)7) Howmanydifferenttypesoffibersweretransferred?
Themoresourcesoffibers,thelongerormoreviolentthecontact.
8) Whattypeofcrimewascommittedanddoestheamountoffibertransferredmatchwithwhatwouldbeexpectedgiventhetypeanddurationofcontact?
9) Howmuchtimehaspassedbetweenthecrimeandthediscoveryoffiber?
Comeupwithatleast5Questions!
HowisFiberCollected?
• Vacuums• StickyTape• Forceps
• Withveryaccuraterecordofwherefiberswerefound.
HowisFiberAnalyzed?• Itdependsonifyouhavelargeorsmallquantitiesoffibers.
• SmallQuantities(methodsthatdonotdestroyfibers):1. Polarizinglightmicroscopy2. InfraredMicroscopy
• LargeQuantities(destructiveanalytictechniques):1. Burninginflame2. Dissolvinginvariousliquids
Textiles
• Textiles:clothing,carpet,upholstery.– Madebyweavingtogetheryarns.– Yarns:madeupoffibers thathavebeenspuntogether.
• 2TypesofFibers:1) Natural:comefromanimals,plants,
andminerals2) Synthetic(man-made):regenerated
fibers&polymers• 50%offabricsmadetodayaresynthetic(man-made)
Checkyourneighbor’slabels!
NaturalFibers
1) AnimalFibers–Madeofproteins.– Usedinclothing,carpets,curtains,bedding.– Obtainedfromhair,webbing,orfur:• Hair – wool(sheep),cashmereandmohair(goats),angora(rabbits)– Usuallylooselyspun,makingtextilesthatshedeasily.
• Webbing – Silk(caterpillarcocoons)– Triangularstructuregivessilkitsshinyappearance(workslikeaprism).– Silkfibersareverylong,tendnottoshedeasily
• Fur – notconsideredatextile,usedforcoatsandgloves
NaturalFibers
2) PlantFibers– Cancomefromtheseeds,fruits,stems,andleaves.– Madeofcellulose (apolymermadeofglucosemonomers)
• NOTmadeofproteinà easytodistinguishfromanimalfibers• Canabsorbwaterbutisinsoluble(willnotdissolve)inwater.• Canonlybedissolvedbyaverystrongacid(sulfuricacid).• Veryresistanttodamage.• Oftenshortfibers(2-5cm)thatbecomebrittleovertime.
– Characteristicsvaryfromthickandstifftosmooth,fineandflexible• Someareamorphous – havealoosearrangementoffibersthatmakesthemsoft,elastic,andabsorbent.
NaturalFibers
TypesofPlantFibers1) Seedfibers
• Cotton (foundinseedpod)2) Fruitfibers
• Coir – coarsefiberobtainedfromthecoveringofcoconuts.Strongerthanflaxorcotton.
3) StemFibers –notindividualfibers,foundinbundles• Flax –highlycrystalline,densestrongfibersthatresistrotanddamage,usedtomakelinen
• Jute – coarse;usedtomakerope,mats,handbags• Hemp – similartoflax,usedinAsiaforclothing
4) Leaffibers• Manila – extractedfromtheleavesofabaca(relativeofbananatree)• Sisal – desertplant;usedforrope,netting,greengardentwine,twineonhaybales;quickdeterioration
NaturalFibers
3) MineralFibers– neitherprotein,norcellulose– Fiberglass – short,weak,brittleglassfibers,used
asinsulation,easilystickstoskin(causingrash)– Asbestos – verydurable;usedinpipecoverings,
ceilingtiles,fire-resistantworkclothes,insulation
SyntheticFibers
• Synthetic =man-madeinalab– Monomersputtogethertoformpolymers
1) RegeneratedFibers– Derivedfromcellulose(plantorigin)– Examples:
• Rayon (smooth&silky)– mostcommonregeneratedfiber;madefromprocessedcellulose;oldest(1880s- France)
• Cellulose+Acetateà Celanese (usedincarpets)• 1Cellulose+3Acetateunitsà PolyamideNylon (abreathablelightweightmaterialusedinhigh-performanceclothing)
SyntheticFibers
2) SyntheticPolymerFibers– Originatefrompetroleumproducts(non-cellulosebased).
– Manycanbeeasilydyed.– Examples:
• Polyester – addedtonaturalfiberstoincreasestrength• Nylon – similartopolyester;buteasilybrokendownbylightandconcentratedacid(polyesterisresistanttothese);firstusedasartificialsilkinpantyhose
• Acrylic – artificialwool;clothingtendstopilleasily;inexpensive
• Olefins – highperformanceclothing(thermalsocks)andcarpet;quickdrying;resistanttowear
Syntheticvs.Natural• Syntheticfibers:– Arestrongerthannaturalfibers.
– Arenotdamagedbymicroorganisms.
– Areoftencheaperthannaturalfibers.
– Candeteriorateinbrightsunlight&meltatlowertemperatures.
– Haveveryregulardiametersundermagnification.
Polyester Cotton
Yarns
• Fibersthataretooshortintheirrawstatecanbespuntogethertomakeyarns. Ropeisjustaverybigyarn.
• Characteristicsthatcanbeusedtoidentifyatypeofyarn:– Specifictwistdirection.– Blendoffibers (ex.woolandpolyester)togiveaddedstrengthorwrinkleresistance.
– Color (DyeLot)
Textiles• Yarnsarewovenintotextilesorfabrics.• Weaving originatedwithbasket-making.– StoneAgemanusedflaxfiberstoweavelinen.
– BronzeAge– woolfabrics– OldestLoom– Egyptiantomb4400B.C.– Warp(lengthwise)andweft(over-under)
• ThreadCount– numberofthreadspackedtogether– Ex.Bedsheets– HighestCostTextiles - allnaturalfibersandhighthreadcount(ex.500threadsperinch)
WeavePatterns- patternofthewarpandweft(thelengthwiseandcrosswisethreads)
1) Tabby(plain)• Over1,under1
(1/1weave).• Simplest,mostcommon.
(cont’d)2) Twill(usedinjeans)• Over2,under1(2/1weave).• Createsdiagonaltextureonsurface.• Lesswrinkly,moredurable,showsdirtlessthanplain(tabby)
(cont’d)3) Satin• 3/1,4/1,5/1,6/1ormore.• Smoothandsilkyononeside,dullontheother.
(con’t)• 4.BasketWeave–Multiplehorizontalandmultipleverticalstrands
• 5.Knit– Coursesandwales
Lab- FiberBurnTest• Materials
– Obtainonefiberatatimefromthefrontoftheroom.
• Safety– Keepallpapersawayfromtheflame.– Holdfiberwithtweezers.– Usethealuminumfoiltoplacefiberremains.
• Disposal– Throwawayusedmatch,aluminumfoil,&fiberremains.– Placeeverythingelsebackintothebasket.
• WatchVideo(7min)– www.sciencenc.com/event-help/forensics.php
Lab– FiberBurnTest
• Analysis:Foreachtypeoffiber,identifythecharacteristic(s)thatwouldhelpyoudistinguishthattypeoffiberfromalltheothers.