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Analysis of Fiber Evidence

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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 ... – PowerPoint PPT presentation

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Title: Analysis of Fiber Evidence


1
Analysis of Fiber Evidence
2
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
3
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

4
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.

5
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.

6
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.

7
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.

8
NYLON 6 VS. Nylon 6,6
9
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.

10
Atlanta Child murders Wayne Williams
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