3 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.
Slide 4
1. Wool Polymer= Polypeptide chains (forming the protein
keratin) Monomer= amino acids (one of which is cysteine...cysteine
contains Sulfur) http://www.leydenglenlamb.com/photos.htm
Slide 5
1. Wool Polymer= Polypeptide chains (forming the protein
keratin) Monomer= amino acids (one of which is cysteine...cysteine
contains Sulfur) 2. Silk Polymer= protein Monomer= amino acids (but
less of a variety than wool)
http://entomology.unl.edu/images/silkworm/silkworm1.jpg
Slide 6
1. Wool Polymer= Polypeptide chains (forming the protein
keratin) Monomer= amino acids (one of which is cysteine...cysteine
contains Sulfur) 2. Silk Polymer= protein Monomer= amino acids (but
less of a variety than wool) 3. Cotton Polymer= cellulose (plant)
Monomer= glucose
http://www.texaspolicecentral.com/Texas-Patriotism.php
Slide 7
1. Wool Polymer= Polypeptide chains (forming the protein
keratin) Monomer= amino acids (one of which is cysteine...cysteine
contains Sulfur) 2. Silk Polymer= protein Monomer= amino acids (but
less of a variety than wool) 3. Cotton Polymer= cellulose (plant)
Monomer= glucose 4. Linen Polymer= cellulose (flax plant) Longer
chains than cotton which makes it brittle Monomer= glucose
http://www.flowers-cs.com/flax.html
Slide 8
1. Rayon Cellulose fiber, then chemically altered, burns like
cotton 2. Acetate Made from a reaction between cellulose and acetic
acid
Slide 9
1. Polyamides linked by amino group Example: Nylon Stronger and
more chemically inert than natural fibers Image from:
http://www.imageenvision.com/collection/fitness.html
Slide 10
1. Polyamideslinked by amino group Example: Nylon Stronger and
more chemically inert than natural fibers 2. Polyesters linked by
ester group Stronger linkage than polyamides Linkage can be linear
(flexible) or cross- linked (rigid) Image from:
http://www.imageenvision.com/collection/fitness.html
Slide 11
1. Polyamideslinked by amino group Example: Nylon Stronger and
more chemically inert than natural fibers 2. Polyesterslined by
ester group Stronger linkage than polyamides Linkage can be linear
(flexible) or cross-linked (rigid ) 3. Spandexstructurally similar
to polyamide 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
/
Slide 12
12 Testing for Identification Microscopic observation
Burningobservation of how a fiber burns, the odor, color of flame,
smoke and the appearance of the residue Thermal decompositiongently
heating to break down the fiber to the basic monomers Chemical
testssolubility and decomposition
Slide 13
13 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.
Slide 14
14 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.
Slide 15
15 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.
Slide 16
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