FIBERS

Pgs 330-333Ch 16

I. Using Fibers as Evidence1. Fibers are usually made up of many filaments twisted

or bound together to form a thread or yarn. – They are everywhere.– Textiles (fabric with a distinctive pattern) are mass

produced in huge quantities

2. Fibers are one of the most common items left at a crime scene.– Are considered class evidence– Creates a link among victim, suspect,

and location

3. Investigators identify and compare fibers physically and chemically.– Compare questioned to a known– Statistics and probability are used to narrow the

source

II. Sources for Fibers4. Fabrics are made from fibers.– Fiber is made of natural or artificial filaments

5. Natural Fibers:– Animal, vegetable, or inorganic– Silk, wool, mohair, cashmere, cotton, linen, jute, asbestos,

fiberglass 6. Artificial Fibers are synthesized or created from

altered natural sources.– Acrylic, polyester, nylon, rayon, (Gore-Tex)

7. Fibers are used to make:– Textiles; cloth and carpeting– Cordage; rope, string, nets– Brushes; paint, cooking, make-up– Filling; mattresses, furniture, stuffed animals– Structural materials; used in cars, tires, airplanes

III. Types of Fibers

8. A weave consists of a lengthwise yarn and a crosswise yarn.– Lengthwise – called the warp– Crosswise – called the weft– Are usually different in type, size and color if the

weave is “blend”

9. All fibers are polymers.– Long chains made of simple molecules

IV. Fiber Cross Sections

10. A cross-sectional shape of a fiber filament may be one of its characteristics.

Cotton Silk

V. The Chemical Structure of Fibers

11. The chemical structure of a fiber defines many of the properties that can be used to identify and further classify it.– Wool- composed of polypeptide chains

that form a helical protein called keratin

– Silk – is simpler in structure than wool

• Cotton – is made of cellulose (like wood), but is the most commonly used

• Linen – (flax) composed of cellulose, but longer fibers• Rayon – natural fiber that has been chemically altered, pure

cellulose, burns like cotton• Acetates – made from cellulose through a reaction with acetic acid. • Nylon – synthetic fiber, stronger and more chemically inert (doesn’t

react). • Polyester – can be flexible or rigid, • Acrylics – synthetic fibers, causes blue litmus paper to turn red

when broken down by heat• Spandex – structurally similar to polyesters, can stretch up to 600%,

are usually blended• Olefins – synthetic fiber, very resistant to weathering and

chemicals, usually in carpets, auto interiors, and rope

Tests for Fabric/Fiber Identification

• Comparison of Unknown to a Known• Burn Tests

– How does it burn? Does it melt? Does it flame? What kind of residue?

• Stain Tests– What color does it turn when submerged in DuPont Solution?

• Chemical Tests– How do fibers react when exposed to Bleach? Sulfuric Acid?

Hydrochloric acid? Acetone?

• Refractive Index