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