Transcript Slide 1

Chapter 4 A Study of
Fibers and Textiles
By the end of this chapter you will be able to:
 identify and describe common weave patterns
of textile samples
 compare and contrast various types of fibers
through physical and chemical analysis
 describe principle characteristics used to
identify common fibers
 apply forensic science techniques to analyze
fibers
All Rights Reserved South-Western / Cengage Learning © 2009
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Forensic Science: Fundamentals & Investigations, Chapter 4
Introduction and How Forensic
Scientists Use Fibers
 Fibers often fall off and are picked up during
normal activities.
 become trace evidence
 In an investigation, collection of fibers within
24 hours is critical.
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95% lost from victim and crime scene
Forensic Science: Fundamentals & Investigations, Chapter 4
How Forensic Scientists Use Fibers
 A forensic scientists will ask questions about
the following:
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Type of fiber
Fiber color
# fibers found and where
Textile fiber came from
Multiple fiber transfers
Type of crime committed
Time between crime and discovery of fiber
Forensic Science: Fundamentals & Investigations, Chapter 4
Sampling and Testing
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Evidence gathered by vacuums, sticky tape, and
forces
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Id type of fiber and characteristics
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Match to suspect
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Polarizing light microscopy – special filter to
observe with different wavelengths of light
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Infrared spectroscopy – tell difference between
fibers that look a lot alike
Forensic Science: Fundamentals & Investigations, Chapter 4
Sampling
and Testing
 If a large quantity of fibers is found, some
can be subjected to destructive tests such
as burning them in a flame (see analysis
key above) or dissolving them in various
liquids.
 Crimes can be solved in this way by
comparing fibers found on different
suspects with those found at the crime
scene.
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Forensic Science: Fundamentals & Investigations, Chapter 4
Fiber
Classification
—Natural
Fibers
woven wool textile
Animal fibers (made of proteins):
 come from hair, fur, webbing
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Fur – coats and gloves
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Hair - Wool from sheep, cashmere and mohair from
goats, angora from rabbits, and hair from alpacas,
llamas, and camels are commonly used in textiles.
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Shimmering silk from caterpillar cocoons is longer
and not as easily shed.
Forensic Science: Fundamentals & Investigations, Chapter 4
Fiber Classification
—Natural Fibers
Plant fibers (made of the polymer cellulose):
 can absorb water.
 are insoluble in water.
 are very resistant to damage from harsh
chemicals.
 can only be dissolved by strong acids.
 can be common at crime scenes because
they become brittle over time.
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Forensic Science: Fundamentals & Investigations, Chapter 4
Fiber
Classification
—Natural Fibers
Plant fibers:
 Seed - cotton
 Fruit - Coir from coconuts is durable.
 Stem - Hemp, jute, and flax (linen)
 Leaf - Manila and sisal from leaves deteriorate more
quickly.
Mineral Fibers:
 Fiberglass is a fibrous form of glass.
 Asbestos is a naturally occurring mineral with a
crystalline structure.
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Forensic Science: Fundamentals & Investigations, Chapter 4
Fiber Classification
—Synthetic (artificially produced)
Fibers
Until the nineteenth century only plant and
animal fibers were used to make clothes
and textiles.
Half the products produced today are
artificially produced.
Artificially produced fibers include rayon,
acetate, nylon, acrylics, and polyesters.
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Forensic Science: Fundamentals & Investigations, Chapter 4
Fiber Classification
—Synthetic (artificially produced)
Fibers
Regenerated Fibers (derived from cellulose):
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Rayon is the most common of this type of fiber.
It can imitate natural fibers, but it is stronger.
 Celenese® is cellulose chemically combined
with acetate and is often found in carpets.
 Polyamide nylon is cellulose combined with
three acetate units, is breathable, lightweight,
and used in performance clothing.
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Forensic Science: Fundamentals & Investigations, Chapter 4
Fiber Classification
—Synthetic (artificially produced)
Fibers
Synthetic Polymer Fibers:
Petroleum is the basis for these fibers, and they have
very different characteristics from other fibers.
Monomers in large vats are joined together to form
polymers. The fibers produced are spun together into
yarns.
They have no internal structures, and under
magnification they show regular diameters.
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Forensic Science: Fundamentals & Investigations, Chapter 4
Fiber Classification—
Synthetic
(artificially produced)
Fibers
nylon
spandex
Examples of synthetic polymer fibers:
 Polyester—found in “polar fleece,” wrinkle-resistant, and
not easily broken down by light or concentrated acid;
added to natural fibers for strength.
 Nylon—easily broken down by light and concentrated
acid; otherwise similar to polyester.
 Acrylic—inexpensive, tends to “ball” easily, and used as
an artificial wool or fur.
 Olefins—high performance, quick drying, and resistant to
wear.
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Forensic Science: Fundamentals & Investigations, Chapter 4
Comparison of
Natural and
Synthetic Fibers
Visual Diagnostics of Some Common Textile Fibers
under Magnification
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Forensic Science: Fundamentals & Investigations, Chapter 4
Yarns, fabrics, and textiles
 Fibers can be twisted (spun) into yarn of any
length, thick or thin, loose, or tight. A blend can
be made to meet different needs such as
resistance to wrinkling.
 Fibers can be woven into fabrics or textiles.
– Threads are arranged side by side (the warp).
– More threads (the weft) then are woven back
and forth crosswise in one of a number of
different patterns through the warp.
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Forensic Science: Fundamentals & Investigations, Chapter 4
Yarns, fabrics, and textiles
Weave Patterns
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Forensic Science: Fundamentals & Investigations, Chapter 4
. . . . . . . . . . . . . . . . . Summary
 Fibers are spun into yarns having specific characteristics.
 Yarns are woven, with different patterns, into clothing or
textiles.
 Fibers, trace evidence, are a form of class evidence used
by crime scene investigators.
 Fiber evidence may be gathered using different
techniques.
 Fibers may be analyzed using burn tests, tests for
solubility in different solutions, polarized light microscopy,
or infrared spectroscopy.
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Forensic Science: Fundamentals & Investigations, Chapter 4