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.