Fibers Analysis

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Fibers Analysis

• Kelly, Jeff, Hieu
• Dr. Hornbuckle
• Clayton State University

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OBJECTIVES

• Be able to identify the types of fibers
• Be able to define fibers
• Be able to understand importance of Fiber
  Transfer
• Be able to differentiate between types of Fiber
  Transfer
• Be able to understand the evidential value of
  fibers.
• Be able to define the methods of examination.
• Be able to understand the Microscopy Technique
• Be able to understand the TLC Technique
• Be able to understand the Pyrolysis Gas
  Chromatography Technique
• Be able to recall how fiber evidence was useful
  in the case of Kristen Lea Harrison

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DEFINITION OF FIBER

• A fiber is the smallest unit of a textile
  material.
• Fibers can occur naturally as plant and animal
  fibers, but they can also be man-made.
• A fiber can be spun with other fibers to form a
  yarn that can be woven or knitted to form a
  fabric.
• Fibers are usually collected from clothing,
  carpeting, furniture, beds, and blankets.

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Types of Fibers

• Natural fibers are derived in whole from animal
  or plant sources.
• - Examples wool, mohair, cashmere, furs, and
  cotton.
• Man-made fibers are manufactured.
• - Regenerated fibers are manufactured from
  natural raw materials and include rayon, acetate,
  and triacetate
• - Synthetic fibers are produced solely from
  synthetic chemicals and include nylons,
  polyesters, and acrylics.
• Polymers, or macromolecules, are synthetic fibers
  composed of a large number of atoms arranged in
  repeating units known as monomers.

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Types of Fibers
Many different natural fibers originating from
plants and animals are used in the production of
fabric.
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Types of Fibers

• Man-made fibers can be defined as a fiber of a
  particular chemical composition that has been
  manufactured into a particular shape and size,
  contains a certain amount of various additives,
  and has been processed in a particular way

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FIBER TRANSFER

• The type and length of fiber, the type of
  spinning method, and the type of fabric
  construction all affect the transfer of fibers
  and the significance of fiber associations.
• This becomes very important when there is a
  possibility of fiber transfer between a suspect
  and a victim during the commission of a crime.
• The discovery of cross transfers and multiple
  fiber transfers between the suspect's clothing
  and the victim's clothing dramatically increases
  the probability that these two individuals had
  physical contact.

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FIBER TRANSFER

• When fibers are transferred from the fabric of an
  individual's clothing to the clothing of another
  individual, it is called a primary transfer.
• As these same fibers are transferred to other
  objects during subsequent contacts, secondary
  transfers are occurring.

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Fiber Evidence

• The quality of the fiber evidence depends on the
  ability of the analysts to identify the origin of
  the fiber or at least be able to narrow the
  possibilities to a limited number of sources.
• Obviously, if the examiner is presented with
  fabrics that can be exactly fitted together at
  their torn edges, it is a virtual certainty that
  the fabrics were of common source.
• Matching dyed synthetic fibers or dyed natural
  fibers on the clothing of a victim to fibers on a
  suspects clothing can be very helpful to an
  investigation, whereas the matching of common
  fibers such as white cotton or blue denim cotton
  would be less helpful.

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Fiber Evidence

• Microscopic comparisons between questioned and
  standard or reference fibers are initially
  undertaken for color and diameter
  characteristics, using a comparison microscope.
• Other morphological features that could be
  important in comparing fibers are
• - Lengthwise striations on the surface of the
  fiber
• - The presence of delustering particles that
  reduce shine
• - The cross-sectional shape of the fiber
• Compositional differences may exist in the dyes
  that were applied to the fibers during the
  manufacturing process.

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Methods For Fiber Comparison

• The visible light microspectrophotometer is a
  convenient way for analysts to compare the colors
  of fibers through spectral patterns.
• A more detailed analysis of the fibers dye
  composition can be obtained through a
  chromatography separation.
• Infrared spectrophotometry is a rapid and
  reliable method for identifying the generic class
  of fibers, as does the polarizing microscope.
• Depending on the class of fiber, each polarized
  plane of light will have a characteristic index
  of refraction.

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Microscopy

• Microscopic examination provides the quickest,
  most accurate, and least destructive means of
  determining the microscopic characteristics and
  polymer type of textile fibers.
• Microscopic View

Acetate
Dacron
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Stereomicroscope

• Should be used first to examine fibers.
• Physical features such as crimp, length, color,
  relative diameter, luster, apparent cross
  section, damage, and adhering debris should be
  noted.
• Fibers are then tentatively classified into broad
  groups such as synthetic, natural, or inorganic.

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Comparison Microscope

• If all of the characteristics are the same under
  the stereoscope, then the comparison microscope
  is used.
• A point-by-point and side-by-side comparison
  provides the most discriminating method of
  determining if two or more fibers are consistent
  with originating from the same source.
• Comparisons should be made
• under the same illumination
• conditions at the same magnifications.
• This requires color balancing
• the light sources.
• A balanced neutral background
• color is optimal.
• Side-by-side Comparison
• Bright Field Adjustment

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Polarized Light Microscope

• Perhaps the most versatile of all microscopes
  allows the analyst to actually see and manipulate
  the sample of interest.
• Refractive indices, birefringence, and dispersion
  can all be quantitatively determined.

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Microspectrophotometry

• Using a grating spectrometer, light absorbed by
  or reflected from a sample is separated into its
  component wavelengths, and intensity at each
  wavelength plotted.
• Microscope linked to a
• Spectrophotometer
• - IR Absorption spectrum
• - UV/VIS Absorption Spectrum

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Microspectrophotometry

• IR spectography identifies generic subtypes
  indistinguishable by microscopic exam .
• Use of IR microscopes coupled with Fourier
  transform infrared (FTIR) spectrometers has
  greatly simplified the IR analysis of single
  fibers.
• Advantages
• Nondestructive
• Not limited to sample size
• Disadvantages
• Reactive dyes
• Chemical composition
• Tentative identification

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Scanning Electron Microscopy

• SEM with energy dispersive spectroscopy(EDS) is
  used as an imaging and microanalytical tool in
  characterization of fibers.
• Surface morphology can be examined with great
  depth of field at continually variable
  magnifications.

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Thin-Layer Chromatography

• An inexpensive, simple, well-documented technique
  that can be used (under certain conditions) to
  complement the use of visible spectroscopy in
  comparisons of fiber colorants.
• Dye components are separated by their
  differential migration caused by a mobile phase
  flowing through a porous, adsorptive medium.
• Should be considered for single-fiber comparisons
  only when it is not possible to discriminate
  between the fibers of interest using other
  techniques, such as comparison microscopy and
  microspectrophotometry in the visible range

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Thin-Layer Chromatography

• Technique
• Extraction of dyes
• Solid stationary phase
• Liquid moving phase
• Capillary action
• Chromatogram
• Interpretation
• Rf (retention factor)
• Color
• Proportions
• Scanning densitometer
• Fluorescence
• Analysis of Chromatograms
• Positive association
• Exclusion
• Inconclusive

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Pyrolysis Gas Chromatography

• Pyrolysis is a destructive analytical method.
• When the heat energy applied to the polymer
  chains is greater than the energy of specific
  bonds in that polymer chain, these bonds will
  fragment.
• In PGC, the fragments generated by pyrolysis are
  introduced into a gas chromatograph for
  separation and characterization
• PGC can be used to ID the generic type of an
  unknown fiber, and in some cases it can ID
  subclasses within a generic class

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Analysis of Fibrous Materials

• The analyst should perform a combination of
  methods that extract the greatest potential for
  discrimination between samples.
• A minimum of 2 of the analytical techniques must
  be performed for each category.

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Case Study

• In 1982, Kristen Lea Harrison was abducted and
  found dead six days later in Ohio.
• She had been raped and strangled.
• They founded a orange pieces of fiber in her hair
  that was similar to a murder case 8 month
  earlier.
• By analyzing the fiber under a microscope the
  forensic scientists determine that it was carpet
  fibers based on the oddly shaped (trilobal) fiber.

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Case Study-Continued

• Sometime later there were another women that was
  kidnapped by Robert Anthony Buell, however she
  escape and reported him to the police.
• The police notice that the Mr. Buell has a van
  that contain a distinct orange carpet that
  matched the fiber in Kristen hair.

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Case Study-Continued

• In order to determine the structure of the fiber,
  the scientist must analyze the fiber under a
  microscope.
• The forensic scientist determined that the fiber
  have a trilobal shape and this is commonly found
  as carpet fiber.
• The next step is to determine the composition of
  the dye from both sources.
• Even though the colors of the fiber and the
  carpet are the same by observation, the scientist
  must run test to determine the chemical
  composition of the two dye are the same.

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Case Study-Continued

• In order to test the chemical composition of the
  dye, the forensic scientist may use TLC.
• When a scientist use thin layer chromatography
  (TLC) they can obtain a Rf, if these value are
  the same, then the chemical composition are the
  same.
• Once this fact is established, the scientist can
  contact the manufacturer to obtain more facts on
  these dyes.

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Case Study-Continued

• Apparently only 74 yards of it had been shipped
  to that area of Ohio.
• Other evidence established a more solid link and
  Robert Anthony Buell was eventually convicted.

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REFERENCES

• Ramsland, Katherine. "Fiber Analysis." Crime
  Library. 13 Mar 2008lthttp//www.crimelibrary.com/c
  riminal_mind/forensics/trace/1.htmlgt.
• "Masthead of Forensic Science Communications."
  Forensic Fiber Examination Guidelines. April 1999
  Volume 1 Number 1. Federal Bureau of
  Investigation. 13 Mar 2008lthttp//www.fbi.gov/hq/l
  ab/fsc/backissu/april1999/houcktoc.htgt.
• Lewin, Menachem, and Pearce. Handbook of Fiber
  Chemistry. New York Marcel Dekker.
• "The Thin Blue Line." Forensic Scientists, Hair
  and Fibers. 13 Mar 2008 lthttp//www.policensw.com/
  info/forensic/forensic7a.htmlgt.
• Carpet and Rug Fiber Chemistry. Bane-Clene
  Corporation 2007. 13 Mar 2008 lthttp//www.baneclen
  e.com/articles/fiber-chemistry.htmlgt.