Chapter 6: Trace Evidence: FiberFiber EvidenceFiber Evidence
• Fabric is the type of material and fibers are the “threads” that make it up.
PolymersPolymers• Synthetic fibers are made of polymers which are a long string of repeating chemical units.• The word polymer means many (poly) units (mer).• The repeating units of a polymer are called monomers.• By varying the chemical structure of the monomers or by varying the way they are weaved together, polymers are created that have different properties.• As a result of these differences, forensically they can be distinguished from one another.
Types of FibersTypes of Fibers Natural: Animal, vegetable or inorganic Artificial: Synthesized or created from altered natural sources
Synthetic Rayon Nylon Acetate Acrylic Spandex Polyester
Fiber ClassificationFiber Classification There are two types of fibers and fabric
A. Natural B. Artificial
Classified according to their origin: Vegetable or cellulose Animal or protein Mineral (asbestos, fiberglass)
Cellulose FibersCellulose FibersCotton Vegetable fiber Strong, tough, flexible, moisture absorbent, not shape retentive
Rayon First man made fiber Soft, lustrous, versatile fiber
Cellulose Esters Chemically altered to create an entirely new compound not found
in nature.
Cellulose Acetate Less expensive, less polluting than rayon
Petroleum PlasticsPetroleum Plastics Made from derivates of petroleum, coal, and natural gas
Nylon Most durable man-made fabric Extremely light weight
Polyester Most widely used man-made fiber
Acrylic Provides warmth from a lightweight, soft, and resilient fabric
Spandex Extreme elastic propertiesProtein FibersProtein FibersWool Animal fiber coming most often from sheep but may be goat
(mohair), rabbit (angora), camel, mink, beaver
Silk Animal fiber that is spun by a silk worm to make its cocoon; fiber
reflects light and has insulting properties
Mineral FibersMineral FibersAsbestos A natural fiber that was used in fire-resistant substances A natural fiber that was used in fire-resistant substances
Fiberglass A manufactured mineral fiber
Rock wool A manufactured mineral fiber
Fabric ProductionFabric ProductionFabrics are composed of individual threads or yarns, made of fibers,
that are knitted, woven, bonded, crocheted, felted, knotted or laminated.
The degree of stretch, absorbency, water repellence, softness, and durability are all individual qualities of the different fabrics.
Weave TerminologyWeave TerminologyYarn: A continuous strand of fibers or filaments, either twisted or notWarp: Lengthwise yarnWeft: Crosswise yarnBlend: A fabric made up of two or more different types of fiber.
Woven FabricWoven Fabric Woven fabrics are made by interlacing warp (lengthwise) and weft
(filling) yarns. Warp run the length of the fabric and parallel to the selvage which
is the edge of the fabric. Weft crosses over and under the warp patterns. Types include: Plain Twill Satin Fabrics are composed of individual threads or yarns, made of fibers,
that are knitted, woven, bonded, crocheted, felted, knotted or laminated.
Most are woven or knotted.
Plain Simplest & most common weave Warp & weft pass under each other alternately Design resembles a checkerboard
Woven FabricWoven Fabric
Plain
Twill Create by passing the warp yearn over one to three weft yearns
before going under one Makes a diagonal weave Design resembles stair steps Denim is the most common example
Woven FabricWoven Fabric
Twill
Satin The yarn interlacing is not uniform Creates long floats
Interlacing weave passes over four or more yarns Satin is the most common
Woven FabricWoven Fabric
Satin
Knitted FabricKnitted Fabric Knitted fabrics are made by interlocking loops into a specific
arrangement. It may be one continuous thread or a combination. The yarn is formed into successive rows of loops & then drawn
through another series of loops to make the fabric.
Identification & Comparison of FibersIdentification & Comparison of Fibers
Microscopic Examination Color: compositional differences in the dyes Fibers surface: delustering particles that may be added by
manufacturers
Microspectrophotometer: Compares fiber colors through spectral patterns
ChromatographyUsed to separate dyes for comparative analysis.The way a fabric accepts a particular dye may also be used to
identify and compare samples.
Optical Microscopy:Uses polarizing light and comparison microscopes
Pyrolysis Gas Chromatography-Mass Spectrometry (PGC-MS):
Burns a sample under controlled conditions, separates and analyzes each combustion product
Collection of Fiber EvidenceCollection of Fiber Evidence
Bag clothing items individually in paper bags. Make sure that different items are not placed on the same surface before being bagged.
Make tape lifts of exposed skin areas of bodies and any inanimate objects
Make tape lifts of exposed skin areas of bodies and any inanimate objects