2Fiber Evidence Fiber Can be natural (plant or animal) or man-made The smallest unit of a textile material that has a length many times greater than its diameterCan be spun with other fibers to form a yarn (rope) that can be woven or knitted to form a fabricCan be natural (plant or animal) or man-madeMan-made fibers now account for over ½ of all textile production
3Forensic Value Are considered class evidence Are common trace evidence at a crime sceneCan be characterized based on comparison of both physical and chemical properties
4Fiber ClassificationNatural fibers are classified according to their originVegetable or celluloseAnimal or proteinMineralSome natural fibers can be altered into artificial onesCotton and rayonRayon is chemically-altered cellulose
5Chemical AlterationNote the differences between the cotton fiber (left) and rayon (right). Can you detect what happens in the chemical transformation process?
6Fiber Evidence Important characteristics Type and length of fiberSpinning methodFabric constructionAbove characteristics can greatly affect transfer of fibers and significance as evidenceCan originate from more than clothingFurniture, upholstery, etc.
7Fiber Evidence Significance Based upon clear relationships between objects associated with crimeRelative value of evidence can be based upon several factorsType of fiberNumber of fibersColor or variation of colorLocation of fibersNumber of different fibersLikelihood of transfer based on fiber construction
8Fiber Evidence Useful in similar crimes to hairs Since DNA is not found, often limited to class characteristics due to mass productionTransfer usually found through physical contactRoutinely found in vehicle accidents or on glass/screens
9Animal Fibers Silk Technically a protein secretion No longer found in natureAmong the most expensive fibersFibers are altered by changing diet of silkwormDoes not resemble typical non-human hairHighly light reflective
10Mineral Fibers Fiberglass Asbestos Artificially produced fiber Natural fiber from the mineral serpentine
11Plant Fibers Cotton Most common plant fiber Virtually worthless as evidence if whiteIf dyed, the dye is more valuable than the cottonDistinctive twisted, ribbon-like shape
12Plant Fibers Flax Used to make linen Distinctive lateral structures through fiberCan be expensive
13Plant FibersRamie fiber, common in SE AsiaHemp fiber, the strongest natural fiberPlant fibers are based on the polymer cellulose, the chemical that forms the cell wall of plant cellsJute fiber, also common in Asia
14Synthetic FibersFirst introduced in 1911 (rayon) followed by nylon in 1939Hundreds of names currently used for essentially the same artificial fibersGenerally grouped into generic namesExample: Polyester - Sold under 28 different names
15Synthetic Fiber Chemistry Based on polymersLong chain moleculesCome in natural and man-made varietiesSynthetic polymers were first produced in 1909Originally discovered by accidentWhen a glass rod was removed from contact with polymer, it stretched and stuck to the rod. It hardened when cooled and would stretch into long filaments
16Synthetic Fiber Chemistry PolymersWell known natural polymersStarchCellulose - nature of polymer provided structure to plantsProteins - form animal hairsWell known man-made polymersNylonTeflonSiliconeVulcanized rubber
17Synthetic Fiber Chemistry Man-made polymersBasic chemical substance of all artificial fibersAlso include most paints, plastics, adhesives, rubbersPolymers are routinely formed from thousands of individual atomsComposed of repeating units called monomers that link like chains
18Synthetic Fiber Chemistry “Classic” polymer structure of the synthetic fiber nylon. Note the long chain of repeating atoms.
19Synthetic FibersIn spite of common names, practically no two of the same type of fiber are manufactured the same way all the way through the production processPositive ID almost always involves microscopy and chemical analysisThree different scanning electron microscope images of nylon carpet fibers. Note clear structural differences at this magnification.
20Synthetic Fiber Analysis Identification and ComparisonColorBased on introduced combinations of dyesDifferent dyes may identify manufacturerDiameterTypically very little variation due to precise machineryCross section usually helpful as wellProduction characteristicsStriations - almost always lengthwise“Pitting” - occurs from particles added to fiber to reduce shineTypical cross section of synthetic carpet fibers.
21Synthetic Fiber Analysis Production method can be single largest identifierCross sections are exceptionally importantSynthetic fibers are forced out of a nozzle when they are hotHoles of the nozzle are not always round
22Synthetic Fiber Analysis BurningChemistry of fibers can cause fiber to burn in different waysOdor, color of flame, smoke and the appearance of the residue can also be an indicatorThermal decompositionGently heating can break down polymers to basic monomersChemical testingSolubility and decomposition
23Synthetic Fiber Analysis Chemical compositionMost companies have different “formulas” for productProduct “fingerprint” can be determined if chemicals are identifiedRequire spectroscopyFibers can also be melted down into crystals and then identifiedLight reflectance will be different for unique crystalsKnown as crystallographyCommon nylon (above) and rayon (below) fibers under polarized light
24Synthetic Fiber Analysis Spectroscopic analysis of two apparently identical red, cotton fibers. Note the clear chemical differences between the two dyes.