Fibers

1
Fibers
2
Forensic Examination of Fibers

• Important evidence in incidents involving
  personal contact- homicide, assault, sexual
• Cross-transfers may occur between the clothing of
  a suspect and victim
• Hit-and-run victims can leave fibers, threads, or
  whole pieces of clothing on a vehicle
• Fibers can also become fixed in screens or glass
  broken during a breaking-and-entering attempt

3
Natural Fibers

• Are derived from animal or plant sources
• Animal fibers comprise most natural fibers
  encountered in crime lab exams
• Can include hair coverings sheep (wool), goats
  (cashmere), camels, llamas
• Or fur fibers obtained from mink, rabbit,
  beaver, etc.
• Most common plant fiber is cotton

4
Manufactured Fibers

• Are derived from natural or synthetic polymers
• They have increasingly replaced natural fibers in
  clothing fabric
• They are made by
• Processing raw material from cotton/wood pulp and
  extracting cellulose
• The cellulose may be chemically treated and
  dissolved in a solvent
• It is then forced through small holes of a
  spinning jet (spinneret) to produce the fiber
• Fibers made from natural raw materials
  (regenerated cellulose) are called regenerated
  fibers rayon, acetate, triacetate
• Fibers made from synthetic chemicals are
  synthetic fibers nylon, polyester, acrylic

5
Microscopic Exam of Fibers

• The first and most important step is a comparison
  for color diameter by a comparison microscope
• Other features that may aid in the comparison are
  lengthwise striations (lined markings) on the
  surface of some fibers and pitting of the fibers
  surface with delustering particles (titanium
  dioxide particles added to reduce shine)
• Cross-sectional shape of a fiber may also help

6
Analytical Techniques Used

• Two fibers may seem to be the same color,
  differences may exist in the dyes applied to them
  when made
• Most fibers are dyed with a mixture of colors to
  obtain a desired shade
• Can use a visible light microspectrophotometer to
  compare the colors of fibers
• A fiber as small as 1 mm long or less can be
  examined

7
(No Transcript)
8
Analytical Techniques Used

• A more detailed analysis of the fibers dye
  composition can be obtained by a chromatographic
  separation of dye
• Small strands of fibers are compared for dye
  content by extracting the dye off each fiber with
  a solvent and then spotting the dye solution onto
  a thin-layer chromatography plate
• The dye of the questioned and standard fibers are
  separated on the plate and compared for
  similarity

9
Others

• When fibers are compared, they must be shown to
  have the same chemical composition (belong to the
  same class)
• For example, the standard and questioned fabric
  both being nylon instead of one being nylon while
  the other is cotton
• Many manufactured fibers exhibit double
  refraction or birefringence which will make it
  look crystalline
• Polarized white light will split into two rays
  that are perpendicular to each other and produce
  interference colors, polarization

10
Significance of Fiber Evidence

• Once a match has been determined, the
  significance is bound to be raised
• No technique can associate a fiber definitively
  to any single garment
• No database is available for determining the
  probability of a fibers origin
• Despite this, one should not discount the
  significance of a fiber match
• By observing what people wear, it is unlikely to
  find two different people wearing identically
  colored fabric ( exception jeans and cotton
  tees)
• There are thousands of different colored fibers
• Combine this with the fact that scientists not
  only compare color, but also size, shape,
  microscopic appearance, chemical composition and
  dye
• There will still be a good chance of linking a
  questioned fiber to a standard

11
Collection and Preservation

• Clothing should be packaged in paper bags
• Each article must be placed in separate bags to
  prevent contamination
• Must keep clothing from different people from
  coming into contact
• Carpets, rugs, and bedding should be folded to
  protect areas suspected of containing fibers
• Knife blades should be covered to protect
  adhering fiber
• If a body was wrapped in a carpet or blanket,
  tape lifts must be done on the body
• If individual fibers are found, they must be
  removed with clean forceps and placed in a small
  sheet of paper, must be folded and labeled and
  placed in another container

12
Types of Fiber
Cotton (ribbon-like)
Nylon
Polyester
Rayon fibers Silk
(fractures)
Wool