FIBERS Pgs 330-333 Ch 16. I. Using Fibers as Evidence 1. Fibers are usually made up of many...
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Transcript of FIBERS Pgs 330-333 Ch 16. I. Using Fibers as Evidence 1. Fibers are usually made up of many...
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FIBERS
Pgs 330-333Ch 16
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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
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3. Investigators identify and compare fibers physically and chemically.– Compare questioned to a known– Statistics and probability are used to narrow the
source
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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)
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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
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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
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IV. Fiber Cross Sections
10. A cross-sectional shape of a fiber filament may be one of its characteristics.
Cotton Silk
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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
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• 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
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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