Analysis of Fiber Evidence

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Analysis of Fiber Evidence
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Types of Fibers
Cotton

• Natural Fibers fibers derived entirely form
  animal or plant sources.
• Majority of fiber evidence found at crime scene
  is animal fiber.
• Examples sheep (wool), goat (mohair/cashmere),
  camel, llamas, alpacas, and vicunas.
• Uses same forensic procedures as determination of
  species hair analysis.
• Predominant plant fiber is cotton.
• Most distinguishing feature ribbon-like shape
  with twists at irregular intervals.
• Has almost no evidential value. Why?

Wool
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Types of Fibers

• Manufactured fibers derived from either natural
  or synthetic polymers.
• First man-made fibers
• 1911 Rayon
• 1939 - Nylon
• Hard to distinguish between fibers due to large
  number of sub names. Confusing system.
• Ex. Polyester is also known as
• Dacron
• Fortrel
• Kodel
• Classified as generic fibers

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Natural vs. Man-made polymers

• Regenerated Fibers derived from cotton or wood
  pulp.
• Process
• Cellulose is extracted and sometimes chemically
  altered.
• Forced through sinning jet/spinneret to create
  fiber.
• Synthetic Fibers chemically created.
• Formed from long chain molecules called polymers.

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Polymers

• Substance composed of a large number of atoms
  that are usually arranged in repeating units
  called monomers.
• Ex. Plastic, paint, adhesive, synthetic rubber
• Referred to as macromolecules.
• Ex. Linking blocks.

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Polymers

• Polymerization covalently bonded monomers that
  create long repeating subuntis.
• Nylon 6,6 is an example of a polymeric clothing
  material, involving one of each monomer,
  hexamethlene diamine and adipic acid, that react
  to form Nylon 66.

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Identification and Comparison of Manufactured
Fibers

• Microscopic Examination
• 1st step comparison of color and diameter.
• A cross sectional view of fiber may be helpful.
• Then need to look at mixture of dyes selected to
  create certain shade of fiber.
• Other Techniques (Analytical)
• Chemical Composition
• Nylon 6 vs. Nylon 6,6
• Birefringence
• Difference in the two indices of refraction
  exhibited by most crystalline materials.
• Infrared Absorption
• Absorption of infrared light in a particular
  pattern.

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NYLON 6 VS. Nylon 6,6
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Collection and Preservation

• Articles of clothing should be placed in separate
  paper bags.
• Carpet, rugs, and bedding are to be folded
  carefully to protect areas suspected of
  containing fibers.
• Wrap knife blades that may contain fibers
• Remove fibers from body using adhesive tape.
• Loose fibers are to be removed with a clean
  forcep and placed in a small sheet of paper,
  which once folded and labeled can be placed
  inside another container.

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Atlanta Child murders Wayne Williams