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Forensic Science: Fundamentals & Investigations, 2e
Chapter 4
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Chapter 4 A Study of Fibers and
Textiles
By the end of this chapter you will be able to:
4.1 Identify and describe common weave
patterns of textile samples.
4.2 Compare and contrast various types of
fibers through physical and chemical analysis.
4.3 Describe principal characteristics of
common fibers used in their identification.
4.4 Apply forensic science techniques to
analyze fibers.
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Forensic Science: Fundamentals & Investigations, 2e
Chapter 4
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Cengage/NGL/South-Western © 2016
Chapter 4
Vocabulary
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amorphous
crystalline
direct transfer
fiber
mineral fiber
monomer
natural fiber
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Forensic Science: Fundamentals & Investigations, 2e
Chapter 4
polymer
synthetic fiber
secondary transfer
textile
warp
weft
yard (thread)
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Introduction
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Fibers are used in forensic science to create
a link between crime and suspect.
Fibers are not specific to a single person.
Fibers are a form of trace evidence.
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Direct transfer
Secondary transfer
Collecting fibers within 24 hours is critical.
Forensic Science: Fundamentals & Investigations, 2e
Chapter 4
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Collecting, Sampling, and
Testing Fiber Evidence
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Fiber evidence
is collected
using tape,
forceps, a
vacuum, or a
sticky lint roller.
Forensic Science: Fundamentals & Investigations, 2e
Chapter 4
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Evaluating Fiber Evidence
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The value of fiber evidence in a crime
investigation depends on its potential
uniqueness.
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Type of fiber
Fiber color
Number of fibers found
Where the fiber was found
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Chapter 4
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Evaluating Fiber Evidence
(continued)
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Textile from which
the fiber originated
Multiple fiber
transfers
Type of crime
committed
Time between crime
and discovery of fiber
https://www.youtube.com/watch?v=BjLHW7qQEl0 4.5 min
Forensic Science: Fundamentals & Investigations, 2e
Chapter 4
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Fiber and Textile Evidence
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Fiber Classification
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Natural Fibers
Synthetic (Manufactured) Fibers
Forensic Science: Fundamentals & Investigations, 2e
Chapter 4
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Natural Fibers
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Natural fibers come from animals, plants,
and minerals that are mined from the
ground.
Fibers are composed of polymers, or
long, repeating molecules.
https://www.youtube.com/watch?v=-wbmEjTvszI 4.5 min story of silk Black and white
https://www.youtube.com/watch?v=1I5Fyf-YrVA 5.5 min Silk – Good
https://www.youtube.com/watch?v=BibC0CqZhPI 3.4 Silk Factory good
https://www.youtube.com/watch?v=YYWlevX7Kw0 4:30 – Make fabrics
Forensic Science: Fundamentals & Investigations, 2e
Chapter 4
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Animal Fibers
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Three sources of animal fibers are hair, fur,
and webbing.
All animal fibers are made of proteins.
Forensic Science: Fundamentals & Investigations, 2e
Chapter 4
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Plant Fibers
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All plant fibers share the column polymer
cellulose.
Cellulose is made up of simple glucose units.
Proteins and cellulose have very different
chemical and physical properties that allow a
forensic scientist to tell animal and plant
fibers apart.
Forensic Science: Fundamentals & Investigations, 2e
Chapter 4
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Natural Fibers (continued)
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Seed fibers
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https://www.youtube.com/watch?v=AAUQNMldp_Y (8.4 min story of cotton)
Leaf fibers
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Cotton is found in the seed pod of the cotton
plant.
It is used extensively for clothing and household
textiles.
Manila
Sisal
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Chapter 4
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Natural Fibers (continued)
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Fruit fibers
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Coir fiber is
obtained from
coconuts
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Stem fibers
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It is relatively
waterproof.
Forensic Science: Fundamentals & Investigations, 2e
Chapter 4
Flax, jute, and hemp
are all produced from
the thick region of
plant stems.
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Natural Fibers (continued)
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Mineral fibers
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Neither proteins nor
cellulose
May not even be
long, repeating
polymers
Although it is very
durable, because of
its health risks,
asbestos is no longer
commonly used.
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Chapter 4
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Synthetic (Manufactured) Fibers
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Half of the fabrics produced today are
synthetic fibers.
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The fibers are produced by joining many
monomers together to form polymers.
Rayon, acetate, nylon, acrylics, and polyesters
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Chapter 4
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Synthetic (Manufactured) Fibers
(continued)
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Regenerated fibers (or modified natural
fibers)
Synthetic polymer fibers
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Polyester
Nylon
Acrylic
Olefins
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Chapter 4
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Comparison of Natural and
Synthetic Fibers
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Synthetic fibers are stronger than the
strongest natural fibers.
Manufactured fibers are not damaged by
microorganisms.
Manufactured fibers can deteriorate in bright
sunlight and melt at a lower temperature than
natural fibers.
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Chapter 4
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Yarns
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Fibers too short in their raw state to be used
to make textiles may be spun together to
make yarns.
Very thin yarns are often called threads.
For identification purposes, forensic
scientists analyze twist direction of yarn.
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Chapter 4
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Chapter 4
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Textiles
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Weaving consists of arranging lengthwise
threads (the warp) side-by-side and close
together.
Cross wise threads (the weft) are then woven
back and forth in one of several different
patterns.
https://www.youtube.com/watch?v=YYWlevX7Kw0 (4.4min make fabrics)
Forensic Science: Fundamentals & Investigations, 2e
Chapter 4
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21
Forensic Science: Fundamentals & Investigations, 2e
Chapter 4
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Textiles (continued)
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The ways that fabrics differ include:
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Weave pattern
Thread count
Two ply
Fiber identification using various microscopes, gas
chromatography, and mass spectrometers is
possible.
Fiber identification provides class evidence only and
should not be used to convict someone.
Forensic Science: Fundamentals & Investigations, 2e
Chapter 4
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23
Forensic Science: Fundamentals & Investigations, 2e
Chapter 4
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Summary
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Fibers are a form of class evidence used by crime-scene
investigators; they are a form of trace evidence.
Fiber evidence may be gathered using tape, forceps, a
vacuum, or a sticky lint roller.
Forensic scientists will try to determine the type of a fiber,
its color, how many fibers of each kind were found, where
they were found, what textile the fiber came from, and
whether there were transfers of multiple types of fibers.
Fibers may be analyzed using polarized light microscopy,
infrared spectroscopy, burn tests, or tests for solubility in
different liquids.
Forensic Science: Fundamentals & Investigations, 2e
Chapter 4
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Summary (continued)
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Fibers may be classified as natural or synthetic.
Natural fibers include animal hair; plant fibers from
seeds, fruit, stems, or leaves; and mineral fibers.
Synthetic fibers include regenerated or modified
natural fibers as well as synthetic polymer fibers.
Fibers are spun into yarns that have specific
characteristics.
Yarns are woven, with different weave patterns, into
textiles.
Forensic Science: Fundamentals & Investigations, 2e
Chapter 4
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Cengage/NGL/South-Western © 2016