Transcript Chemical Composition of Fibers

Polymers
 Synthetic fibers are made of polymers which are
long chains of repeating chemical units.
 The word polymer means many (poly), units (mer).
 The repeating units of a polymer are called
monomers.
 By varying the chemical structure of the monomers
or by varying the way they are joined together,
polymers are created that have different properties.
 As a result of these differences, forensically they
can be distinguished from one another.
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1.
Wool
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Polymer= Polypeptide chains (forming the
protein keratin)
Monomer= amino acids (one of which is
cysteine . . .cysteine contains Sulfur)
http://www.leydenglenlamb.com/photos.htm
1.
Wool


2.
Polymer= Polypeptide chains (forming the
protein keratin)
Monomer= amino acids (one of which is
cysteine . . .cysteine contains Sulfur)
Silk


Polymer= protein
Monomer= amino acids (but less of a variety
than wool)
http://entomology.unl.edu/images/silkworm/silkworm1.jpg
1.
Wool


2.
Silk


3.
Polymer= Polypeptide chains (forming the protein
keratin)
Monomer= amino acids (one of which is cysteine .
. .cysteine contains Sulfur)
Polymer= protein
Monomer= amino acids (but less of a variety than
wool)
Cotton


Polymer= cellulose (plant)
Monomer= glucose
http://www.texaspolicecentral.com/Texas-Patriotism.php
1.
Wool


2.
Silk

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3.
4.
Polymer= Polypeptide chains (forming the protein
keratin)
Monomer= amino acids (one of which is cysteine .
. .cysteine contains Sulfur)
Polymer= protein
Monomer= amino acids (but less of a variety than
wool)
Cotton


Polymer= cellulose (plant)
Monomer= glucose

Polymer= cellulose (flax plant)
Linen

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Longer chains than cotton which makes it brittle
Monomer= glucose
http://www.flowers-cs.com/flax.html
Rayon
1.
•
Cellulose fiber, then chemically altered,
burns like cotton
Acetate
2.
•
Made from a reaction between cellulose
and acetic acid
Polyamides
—linked by amino group
1.
•
•
Example: Nylon
Stronger and more chemically inert than
natural fibers
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Polyamides—linked by amino group
1.
•
•
Example: Nylon
Stronger and more chemically inert than
natural fibers
Polyesters
—linked by ester group
2.
•
•
Stronger linkage than polyamides
Linkage can be linear (flexible) or crosslinked (rigid)
Image from: http://www.imageenvision.com/collection/fitness.html
Polyamides—linked by amino group
•
Example: Nylon
•
Stronger and more chemically inert than natural fibers
2.
Polyesters—lined by ester group
•
Stronger linkage than polyamides
•
Linkage can be linear (flexible) or cross-linked (rigid )
1.
Spandex—structurally similar to polyamide
3.
•
•
Made of segments of polyurethane connected
to long segments of polyesters
Resulting spandex can stretch up to 600 times
and recover original strength
http://www.fingerpainrelief.com/rubber-band-therapy-for-finger-pain/
Testing for Identification
 Microscopic observation
 Burning—observation of how a fiber burns,
the odor, color of flame, smoke and the
appearance of the residue
 Thermal decomposition—gently heating to
break down the fiber to the basic monomers
 Chemical tests—solubility and
decomposition
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Dyes
 Components that make up dyes can be
separated and matched to an unknown.
 There are more than 7000 different dye
formulations.
 Chromatography is used to separate dyes for
comparative analysis.
 The way a fabric accepts a particular dye
may also be used to identify and compare
samples.
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Collection of
Fiber Evidence
 Bag clothing items individually in paper
bags. Make sure that different items are
not placed on the same surface before
being bagged.
 Make tape lifts of exposed skin areas of
bodies and any inanimate objects
 Removed fibers should be folded into a
small sheet of paper and stored in a
paper bag.
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Fiber Evidence
Fiber evidence in court cases can be
used to connect the suspect to the
victim or to the crime scene. In the
case of Wayne Williams, fibers
weighed heavily on the outcome of the
case. Williams was convicted in 1982
based on carpet fibers that were found
in his home, car and on several
murder victims.
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Clip 1
› http://www.youtube.com/watch?v=cmlunCbBV_o&f
eature=related
› If link is broken, go to YouTube and search “Oil
Absorbing Polymer”
 Clip 2
› http://www.youtube.com/watch?v=YWoQ3D6RMXs
&feature=related
› If link is broken, go to YouTube and search
“Spangler's Polymer Experiment on The Ellen Show”
