2FibersFiber: is the smallest unit of a textile material woven or twisted together to form a thread or yarn.Fibers (like hair) are among the most common items left at a crime scene.Class evidence- mass produced by textile difficult to trace backProbative value- can create connection btwn a victim and suspect.
3Activity 6.1 pg. 129Collection and observing fibers from your shirt and pants.
4Sources & Types of Fibers Fibers can occur naturally (plant and animal fibers)OrFibers can also be man-made (synthetic).
5Types of Fabric WeaveIn a weave, the lengthwise yarn is called the warp.The crosswise yarn is called the weft or woof.Types include:PlainTwillSatin
6Woven Fabric PLAIN Simplest and most common weave Warp and weft pass under each other alternatelyDesign resembles a checkerboard
7Woven FabricTWILLCreate by passing the warp yearn over one to three weft yearns before going under oneMakes a diagonal weaveDesign resembles a stair stepsDenim is the most obvious example
8Woven Fabric SATIN The yarn interlacing is not uniform Creates long floatsInterlacing weave passes over four or more yarnsSatin is the most obvious example
9Knitted FabricKnitted fabrics are made by interlocking loops into a specific arrangement. It may be one continuous thread or a combination.Diagram:
10Blends use of different fabrics & colors to create the warp and weft patterns.
12FibersAll fibers are made of polymers which are long chains of repeating units.The word polymer means many (poly) units (mer).The repeating units of a polymer are called monomers.
13Fiber MorphologyInvestigators use: 1. fiber cross section 2. chemical structure 3. synthetic polymers for forensic analysis
14Fiber Cross SectionThe cross section of a man-made fiber can be manufacturer-specificUnusual cross sections increase fiber association.Cross-sectional views of nylon carpet fibers as seen with a scanning electron microscope (SEM)
15Types of Fibers Natural Synthetic Silk Polyester Cotton Rayon Wool MohairCashmereSyntheticPolyesterRayonNylonAcetateAcrylicSpandex
16Natural FibersMany different natural fibers that come from plants and animals are used in the production of fabric.Cotton fibers are the plant fibers most commonly used in textile materialsThe animal fiber most frequently used in the production of textile materials is wool, and the most common wool fibers originate from sheep.
17Natural FibersWool--animal fiber from sheep, may also be goat (mohair), rabbit (angora), camel, mink, beaverwool: composed of polypeptide keratin chains of amino acid.main bond is sulfur which accounts for the smell of wool when burnedWool Fibers (400X)
18Chemical structure: Natural fibers Silk: composed of proteins, only 2 amino acidsSilk--animal fiber produced by silkworms (cocoon)
19Cotton#polymers is glucose# smell like burning leaves# 40% of all fabric is cotton# 60% of all clothes and furniture# low probative value because its too common
20Linen: made from flax plant # Contains cellulose (fibers are longer than cotton)# often blended with other fibers because it is brittle.
21Synthetic FibersMore than half of all fibers used in the production of textile materials are synthetic or man-made.Nylon, rayon, and polyester are all examples of synthetic fibers.*nylon and polyester are the most commonFibers under a microscopeCross-section of a man-made fiberImages:
22Synthetic Fibers Made from cellulose Rayon--first man-made fiber; Acetate:– made from a reaction with acetic acid.
23Synthetic Fibers (Made from derivatives of petroleum, coal and natural gas) Acrylic- used in carpetsSpandex--elastic properties
24Forensics of Fiber Analysis Cross transfers of fiber often occur in cases in which there is person-to-person contactMore contact= more fiber transferred
25Forensic AnalysisWhat can be used to identify and compare fibers as forensic evidence? See book pg. 1351. fiber cross sectionView through microscopeBurn testThermal decompositionRefractive indexChemical test
26Microscopic Examination A compound microscope: uses lightThe comparison microscope (two compound microscopes joined by an optical bridge) is used for more precise identification. phase-contrast microscope, reveals fiber structureScanning electron microscope converts the emitted electrons into a photographic image for display. This affords high resolution and depth of focus.
27Fiber Comparison Can you tell the difference(s) between the cotton on the left and the rayon on the right?
28SpectrometerThe spectrometer, which separates light into component wavelengths. By passing light through something to produce a spectrum, the analyst can read the resulting lines, called "absorption lines." specific wavelengths are specific to molecules of the substance.
29Fiber Evidence Collection Fibers are gathered at a crime scene with tweezers, tape, or a vacuum. They generally come from clothing, drapery, wigs, carpeting, furniture, and blankets. For analysis, they are first determined to be natural, manufactured, or a mix of both.
30Steps of Fiber Analysis The first step in fiber analysis is to compare color and diameter. Dyes can also be further analyzed with chromatography, which uses solvents to separate the dye's chemical constituents.
31Fiber ColorColor influences the value given to a particular fiber identification.Often several dyes are usedHow color is applied and absorbed along the length of the fiber are important comparison characteristics.Color-fading and discoloration can also lend increased value to a fiber association.
33Testing FibersBurn Test: how a fiber burns, its odor, and appearance of ash.Thermal decomposition: how a fiber breaks down when heated.*it returns to its monomer (initial buildingblock)* ex: Acetate acetic acidlitmus test will turn paper blue to red
353) Chemical test: test the solubility and decomposition of a fabric using a strong acids (Hydrochloric acid or sulfuric acid) or strong bases (NaOCl, acetone, NaOH) – this determines the fabrics polymers. 4) Density: m/v (pg. 148). Density of water is 1.00 g/ml. Olefin is the only fabric that will float in water.
365) Refractive index: bending of light as it passes from air into a solid or liquid -- investigators measure the refractive index of an unknown sample with liquids of a known refractive index.--place sample in different liquids until Becke line is no longer visibleliquid same index as fabric liquid w/w/ high index low refractiveindexA B C
376) Fluorescence: some fibers will fluoresce when exposed to UV light --- laundry soap and some bleach has whiting agents that cause blue light to be reflected making it appear whiter. 7)Dyes: investigators use a fabric to see if it accepts a particular dye to identify and compare it to an unknown sample
38Rf value = distance of pigment 8) Chromatography: separation of dyes by thin layer chromatography (TLC)Rf value = distance of pigmentdistance of solvent front
39Other test used in Fiber Analysis 9) FTIR: Fourier Transform Infraredbased on the absorption and wavelength of light in a fabrics polymer.can be used on a single fiberNon-destructive10) PGS-MS: Pyrolysis Gas Chamber-Mass SpectrometryBurns and separates each combustion product of sampleMatch results of chromatogram & products to knownCan be used in short length fibers but is destructive.
40Fiber Forensics FYI- do not copy analyst gets only a limited number of fibers to work with—sometimes only one.Fibers are sent to the lab for analysis.Fibers from scene are compared to victimCopy###Any inconsistency (one property does not match) is sufficient to cancel association
41Fiber Transfer and Persistence Fibers can be used as trace evidence due to fiber transfer.How easy the fiber is transferred is affected by:Area of contactthe amount of pressure usedAny friction due to side to side contactNumber of passes or contactsKind of clothing donor/recipient was wearingFiber type, length and textureHistory of the garment.
42How long transfer fibers remain on victim is fiber persistence. Time of wear and movementWhat is covering the fabricType of activityWeather condition** fiber persistence decreases exponentially with time of wear.