SUPA Forensics
Fiber Analysis
• Natural fibers: fibers derived entirely
from animal or plant sources
• Man-made fibers: fibers derived from
either natural or synthetic polymers; the
fibers are typically made by forcing the
polymeric material through the holes of a
spinneret
• Polymer: a substance composed of a
large number of atoms. These atoms are
usually arranged in repeating units or
monomers
• Molecules: two or more atoms held
together by chemical bonds
• Macromolecule: a molecule with a high
molecular mass
• Monomer: the basic unit of structure
from which a polymer is constructed
Natural Fibers
Natural Fibers Are ...
• Nonthermoplastic
– do not soften when heat is applied
• Particularly susceptible to microbial
decomposition (mildew & rot)
– cellulose based
• decomposed by aerobic bacteria & fungi
– protein based
• decomposed by bacteria and molds
• moths, carpet beetles, termites, silverfish
Natural Fibers
• Classified according to their origin
– vegetable or cellulose based
– animal or protein based
– mineral class
• asbestos
WOOL
Microscopic images of wool fibers
Wool
Cotton
Cotton
• Cotton fiber, once it has been processed to
remove seeds and traces of wax, protein, etc.,
consists of nearly pure cellulose, a natural
polymer.
• Cotton production is very efficient, in the sense
that ten percent or less of the weight is lost in
subsequent processing to convert the raw cotton
bolls (seed cases) into pure fiber.
• The cellulose is arranged in a way that gives
cotton fibers a high degree of strength, durability,
and absorbency.
Cotton Micrograph
Spider Silk Spinnerets
http://science.howstuffworks.com/spider2.htm
Spider Silk Spinnerets
• Scientists don't know exactly how spiders form
silk, but they do have a basic idea of the
spinning process. Spiders have special glands
that secrete silk proteins (made up of chains of
amino acids), which are dissolved in a waterbased solution. The spider pushes the liquid
solution through long ducts, leading to
microscopic spigots on the spider's spinnerets.
Spiders typically have two or three spinneret
pairs, located at the rear of the abdomen.
Artificial Fibers
and
Polymeric Fibers
Polymers
Long strings of repeating chemical units
– poly (many)
– mer (unit)
Fibers are Polymers
Cellulose Based Fibers
• Cotton
• Jute
– sacks & bags
• burlap
– backing for tufted carpets & hooked rugs
• Oriental rugs
– twines & ruff cordage
Protein Based Fibers
• More vulnerable to environmental degradation
than cellulose based fibers
• Wool (sheep)
• Mohair (goat)
– fiber structure similar to wool
• half the scales of wool
• scales lie flat (smooth surface)
• <1% of fibers have a medulla
• Silk
Helical Proteins
• Based on alpha-keratin
A Hair Fiber
Sheet Proteins
• Based on beta-keratin
Mineral Polymers
• Asbestos
– any of several minerals that readily separate
into long, flexible fibers
• Chrysotile (hydrous magnesium silicate)
– Mg3Si2O5(OH)4
– formerly used in
• shingles
• insulation
• cement pipes
Man/Woman-Made Fibers
Man-Made Fibers
• Regenerated Fibers
– derived from naturally occurring polymers
• rayon
• acetate
• Synthetic Fibers
– made of polymers that do not occur naturally
• polyesters
• polyamides
Polymers are fibers too!
• Polymers arranged in fibers like this can be spun into threads
and used as textiles. The clothes you're wearing are made out
of polymeric fibers. So is carpet. So is rope. Here are some of
the polymers which can be drawn into fibers:
Polyethylene
• Polypropylene
• Nylon
• Polyester
• Kevlar and Nomex
• Polyacrylonitrile
• Cellulose
• Polyurethanes
Polyesters
• Polyethylene terephthalate (PET)
– X=O
– can be melt-spun into very practical and cheap fibers
• Dacron
• Clothing, furnishings, carpets, tire cord
PET
Polyamides
• Polyhexamethylene adipamide (Nylon 6,6)
– X= NH
– synthesized from adipic acid and hexamethylenediamine
– each contain six carbon atoms
• Nylon 6 or Nylon 6,6
• Apparel, carpets, and tire cord
Nylon 6,6
Hx of Nylon
• Nylons are one of the most common polymers used
as a fiber.
• Nylon is found in clothing all the time, but also in
other places, in the form of a thermoplastic.
• Nylon's first real success came with it's use in
women's stockings, in about 1940. They were a big
hit, but they became hard to get, because the next
year the United States entered World War II, and
nylon was needed to make war materials, like
parachutes and ropes. But before stockings or
parachutes, the very first nylon product was a
toothbrush with nylon bristles.
http://www.pslc.ws/mactest/nylon.htm
NYLON examples
Fishing net
rope
backpack
Dog
harness
Nylon
Polarizing microscope image of a nylon fiber.
TEM Nylon 6
SEM Nylon 6 400 mcm
Nylon strength
• In that case I suppose I can tell you that fibers
have their drawbacks. While they have good
tensile strength, that is, they're strong when you
pull or stretch them, they usually have bad
compressional strength, that is, they're weak
when you try to squash or compress them. Also,
fibers tend to be strong only in one direction, the
direction in which they're oriented. If you pull in
them in the direction at right angles to their
orientation, they tend to be weak
• Nylons are also called polyamides, because of
the characteristic amide groups in the backbone
chain.
• Proteins, such as the silk nylon was made to
replace, are also polyamides. These amide
groups are very polar, and can hydrogen bond
with each other. Because of this, and because
the nylon backbone is so regular and
symmetrical, nylons are often crystalline, and
make very good fibers
Nylon 6,6
The nylon in the pictures on this page is called nylon 6,6,
because each repeat unit of the polymer chain has two
stretches of carbon atoms, each being six carbon atoms
long. Other nylons can have different numbers of carbon
atoms in these stretches.
Making Nylon 6,6
Polyesters
• Polyesters have hydrocarbon backbones
which contain ester linkages, hence the
name.
Polyester as a fiber
• The ester groups in the polyester chain
are polar, with the carbonyl oxygen atom
having a somewhat negative charge and
the carbonyl carbon atom having a
somewhat positive charge. The positive
and negative charges of different ester
groups are attracted to each other. This
allows the ester groups of nearby chains
to line up with each other in crystal form,
which is why they can form strong fibers
TEM Polyester
Woven
Aromatic Polyesters (Aramids)
• Flexible CH2 groups replaced by rigid aromatic rings
• High melting
• Flame retardant clothing, bullet-poof vests, tire cord
Nomex and Kevlar
• Aramids are a family of nylons,
including Nomex® and Kevlar®.
Kevlar® is used to make things like
bullet proof vests and puncture
resistant bicycle tires. I suppose one
could even make bullet proof bicycle
tires from Kevlar® if one felt the need.
Nomex and Kevlar
• Blends of Nomex® and Kevlar® are used
to make fireproof clothing. Nomex® is
what keeps the monster truck and tractor
drivers from burning to death should their
fire-breathing rigs breathe a little too much
fire. Thanks to Nomex®, an important part
of American culture can be practiced
safely.
• Firefighters turnout gear
Kevlar
• Kevlar® is a polyamide, in which all the
amide groups are separated by paraphenylene groups, that is, the amide
groups attach to the phenyl rings opposite
to each other, at carbons 1 and 4.
Kevlar
• Kevlar is the DuPont Company's brand name
for material made out of synthetic fiber of polyparaphenylene terephthalamide which is
constructed of para-aramid fibers that the
company claims is five times stronger than the
same weight of steel, while being lightweight,
flexible and comfortable.
• It is also very heat resistant and decomposes
above 400 °C without melting
Kevlar Hx and uses
• It was invented by Stephanie Kwolek of DuPont from
research into high performance polymers, and patented
by her in 1966 and first marketed in 1971. Kevlar is a
registered trademark of E.I. du Pont de Nemours and
Company.
• Originally intended to replace the steel belts in tires, it is
probably the most well known name in soft armor such
as bulletproof vests.
• It is also used in extreme sports equipment, high-tension
drumhead applications, animal handling protection,
composite aircraft construction, fire suits, yacht sails, as
an asbestos replacement, sometimes in loudspeaker
cones, and recently, even in R/C model helicopter
blades.
Kevlar
Nomex
Nomex
Cellulose
• Cellulose is one of many polymers found in
nature. Wood, paper, and cotton all contain
cellulose. Cellulose is an excellent fiber. Wood,
cotton, and hemp rope are all made of fibrous
cellulose.
• Cellulose is made of repeat units of the
monomer glucose. This is the same glucose
which your body metabolizes in order to live, but
you can't digest it in the form of cellulose.
Because cellulose is built out of a sugar
monomer, it is called a polysaccharide.
Cellulose
Regenerated Fibers
• Fibers consisting of both natural and
artificial components
Manufacture of Synthetic Fibers
• Melted or dissolved
polymer is forced
through fine holes of
a spinnerette
– Similar to a bathroom
showerhead
• A fine filament is
produced
Manufacture of Synthetic Fibers
• polymer molecules
are aligned parallel
to the length of the
filament
• crystallinity
• imparts stiffness &
strength
Wood Cellulose
Wet structure
Synthetic fibers are the result of extensive research by scientists to increase and
improve upon the supply of naturally occurring animal and plant fibers that have been
used in making cloth and rope.
In general, synthetic fibers, or man-made fibers, are created by forcing, usually through
extrusion, fiber forming materials through holes (called spinnerets) into the air, forming a
thread.
Common synthetic fibers include:
Rayon (1910) (an artificial fiber, but not truly synthetic)
Acetate (1924)
Nylon (1939)
Modacrylic (1949)
Olefin (1949)
Acrylic (1950)
http://en.wikipedia.org/wiki/Synthetic_fiber
Polyester (1953)
PLA (2002)
Specialty synthetic fibers include:
Vinyon (1939)
Saran (1941)
Spandex (1959)
Vinalon (1939)
Aramids (1961) - known as Nomex, Kevlar and Twaron
Modal (1960's)
PBI (Polybenzimidazole fiber) (1983)
Sulfar (1983)
Lyocell (1992)
Fibers comparison methods
Microscopic Comparison
•
•
•
•
Color
Diameter
Lengthwise striations on surface
Pitting with delustering particles
– TiO2
– reduces shine
Dye Composition
• Visible Light Microspectrophotometry
– non-destructive
– fiber mounted on a microscope slide
• Chromatographic separation of dye
components
– dye extracted from fiber with solvent
– TLC of questions extract vs. control extract
Manufacture of Synthetic Fibers
Fiber Composition
• Attempts to place fiber into both a broad
generic class & a subclass
• Many man-made fibers exhibit
birefringence
– light passing through fiber emerges as two
rays
• one parallel to fiber length
• one perpendicular to fiber length
• Table 8-2
Nylon 6
Nylon 6, 10
Collection of Fiber Evidence
Collection of Fiber Evidence
• Investigator must identify & preserve
potential fiber “carriers”
• Clothing items are packaged individually in
paper bags
– different items must not be placed on the
same surface before being bagged
• Tape lifts of exposed skin areas of bodies
& inanimate objects
Collection of Fiber Evidence
• If fibers must be removed from an object
– clean forceps
– fold fiber into a small sheet of paper
– store in paper bag
Collection of Fiber Evidence
• Fibers are gathered at a crime scene with
tweezers, tape, or a vacuum.
• They generally come from clothing,
drapery, wigs, carpeting, furniture, and
blankets.
• For analysis, they are first determined to
be natural, manufactured, or a mix of both.
Narrow it down
• Natural fibers come from plants (cotton) or
animals (wool).
• Manufactured fibers are synthetics like rayon,
acetate, and polyester, which are made from
long chains of molecules called polymers.
• To determine the shape and color of fibers from
any of these fabrics, a microscopic examination
is made.
Non-invasive first
• Generally, the analyst gets only a limited number
of fibers to work with—sometimes only one.
• Whatever has been gathered from the crime
scene is then compared against fibers from a
suspect source, such as a car or home, and the
fibers are laid side by side for visual inspection
through a microscope.
Microscopy
• A compound microscope uses light
reflected from the surface of a fiber and
magnified through a series of lenses, while
the comparison microscope (two
compound microscopes joined by an
optical bridge) is used for more precise
identification.
Spectrophotometry
• Another useful instrument is the spectrometer, which
separates light into component wavelengths.
• In 1859, two German scientists discovered that the
spectrum of every organic element has a uniqueness to
its constituent parts.
• By passing light through something to produce a
spectrum, the analyst can read the resulting lines, called
"absorption lines." That is, the specific wavelengths that
are selectively absorbed into the substance are
characteristic of its component molecules.
• Then a spectrophotometer measures the light intensities,
which yields a way to identify different types of
substances.
Microscope + Spectrophotometer =
Microspectrophotometer
• A combination of these instruments for the most effective
forensic analysis is the micro-spectrophotometer.
• The microscope locates minute traces or shows how
light interacts with the material under analysis.
• Linking this to a computerized spectrophotometer
increases the accuracy. The scientist can get both a
magnified visual and an infrared pattern at the same
time, which increases the number of identifying
characteristics of any given material
Step 1
• The first step in fiber analysis is to compare color and
diameter.
• If there is agreement, then the analysis can go into
another phase.
• Dyes can also be further analyzed with chromatography,
which uses solvents to separate the dye's chemical
constituents.
• Under a microscope, the analyst looks for lengthwise
striations or pits on a fiber's surface, or unusual shapes--as with the one short and two long arms of the trilobal
fibers in the Williams case.
CASE STUDY
Fibers and Probability Theory
Wayne Williams Case
• From 1979 to 1981, someone was killing
Atlanta's youth. More than twenty-five black
males, some as young as nine, had been
strangled, bludgeoned or asphyxiated. A few
females were killed and some children were just
missing, but all potential leads turned into dead
ends. The only real clue---which was valuable
only if a suspect surfaced---was the presence on
several of the bodies and their clothing of some
kind of fiber threads. A few also bore strands of
what was determined to be hair from a dog.
These specimens were all sent to the Georgia State Crime
Laboratory for analysis, and technicians there isolated two
distinct types: a violet-colored acetate fiber and a coarse
yellow-green nylon fiber with the type of tri-lobed (three
branch) qualities associated with carpets. They searched
unsuccessfully for the manufacturer.
Wayne Williams Case
• Since the unknown predator seemed to favor the Chatahoochee
River, the police set up a stakeout.
• On May 22, 1981, this strategy appeared to pay off. In the early
morning hours, the stakeout patrol heard a loud splash. Someone
had just thrown something rather large into the river.
• On the James Jackson Parkway Bridge, they saw a white Chevrolet
station wagon, and when they stopped it, they learned that the
driver's name was Wayne Williams. He was a 23 year-old black
photographer and music promoter. They questioned him, but when
he said he'd just dumped some garbage they let him go.
• (Later he would claim that he'd come there to see the stakeout,
having heard about it from friends in the police force.)
• Only two days later, the police found what
they believed had been the source of the
splash---the body of 27-year-old Nathaniel
Cater. He was dredged up about a mile
from the bridge, and despite his
murderer's carefulness, a single yellowgreen carpet fiber was found in his hair.
• The police got a search warrant for Wayne Williams'
home and car, and the search turned up a valuable piece
of evidence: The floors of Williams' home were covered
with yellow-green carpeting, and he also had a dog.
• Comparisons from the samples removed from the
victims showed good consistency with Williams' carpet.
• Although Williams claimed to have an alibi, the
description he gave of his movements the night they
found him on the bridge was partly false and partly
unsubstantiated. Three separate polygraph tests
indicated deception on Williams' part.
• Then FBI experts analyzed samples from his rugs. With
special equipment, and in consultation with Du Pont,
they managed to ascertain that the fibers came from a
Boston-based textile company.
• The fiber was called Wellman 181B and it had been sold
to numerous carpet companies. Each uses its own dye,
so that made it possible to narrow down the likely
source, which was the West Point Pepperell Corporation
in Georgia. Their "Luxaire English Olive" color matched
that found in Wayne William's home.
• There were also similarities between the hair from
Williams' dog and the dog hair found on several victims.
Too good to be true
• However, many other homes had this
carpeting installed, too.
• Thus, it had to be determined just how
likely it was that Williams' carpeting was
unique enough to persuade a jury of his
connection to the murders.
• The next step was calculating the odds.
• A look into company records turned up information that
they had only made that type of carpet during a one-year
span of time, with over 16,000 yards of carpet distributed
throughout the South.
• In comparison with the total amount of carpet distributed
across the country, this was a very small sample. That
made the statistical probability of the carpet being in any
one person's home to be slight, if it could be assumed
that Luxaire English Olive had been fairly evenly
distributed.
• Altogether they figured that around eighty-two homes in
Georgia were carpeted with Luxaire English Olive. That
meant the odds were stacked against finding many
homes in Atlanta: 1 in 7792.
• To make their case, the prosecution relied on only two of
the twenty-eight suspected murders---the one from the
river, Nathaniel Cater, and another recovered in the
same general area a month before, Jimmy Ray Payne
• A single rayon fiber had been found on his shorts, which
was consistent with the carpeting in Williams' station
wagon.
• In this second case, statistical probability was also
employed. With Chevrolet's help, the investigators
determined that there was a 1 in 3,828 chance that
Payne had acquired the fiber via random contact with a
car that had this carpeting installed.
Math is good
• When the odds in both cases were
multiplied, the law of probability that both
men could have picked up these fibers in
places other than Williams' home and car
came out to 1 in almost 30,000,000. That
seemed pretty staggering.
• The prosecution also introduced into evidence
the fibers found on the bodies of ten of the other
victims (allowed in Georgia courts), which also
matched those in Williams' car or home.
• These, they claimed, showed a pattern, and
taken altogether, it increased the odds in the
fiber evidence into numbers that no one could
even comprehend.
• In total, there were 28 fiber types linked to
Williams.
• In addition, several witnesses had come forward
to place Williams with some of the victims, and
others claimed to have seen suspicious
scratches on Williams' arms.
• After only twelve hours, the jury returned a
guilty verdict, with two life sentences. The
police announced that twenty-two of the
unsolved murder cases were now closed,
despite the fact that there was no real
proof for those victims.
• Subsequently the Williams conviction has
become controversial. To understand this,
let's look at how fiber analysis is done.
Fiber Analysis
• Cross transfers of fiber often occur in cases in
which there is person-to-person contact, and
investigators hope that fiber traceable back to
the offender can be found at the crime scene, as
well as vice versa.
• Success in solving the crime often hinges on the
ability to narrow the sources for the type of fiber
found, as the prosecution did with their
probability theory on the fibers in the Williams
case.
• The problem with fiber evidence is that
fibers are not unique.
• Unlike fingerprints or DNA, they cannot
pinpoint an offender in any definitive
manner. There must be other factors
involved, such as evidence that the fibers
can corroborate or something unique to
the fibers that set them apart. For
example, when fibers appeared to link two
Ohio murders in the 1980s, it was just the
start of building a case, but without the
fibers, there would have been no link in
the first place.
Kristen Lea Harrison
• In 1982, Kristen Lea Harrison was abducted from a ball
field in Ohio and her body was found six days later some
thirty miles away. She had been raped and strangled.
• Orange fibers in her hair looked suspiciously like those
that had been found on a twelve-year-old female murder
victim from eight months earlier in the same county.
• Since they were made of polyester and were oddly
shaped (trilobal), forensic scientists surmised that it was
carpet fiber. In addition, a box found near Kristin's body
and plastic wrap around her feet indicated that the killer
had once ordered a special kind of van seat, but then
leads dried up.
Kristen Lea Harrison
• Some time later, a 28 year-old woman was abducted and
held prisoner in a man's home. He tortured her and
appeared to be intent on killing her. When he left, she
escaped and reported him.
• Police noticed that he had a van similar to the one into
which Kristin had been forced. It proved to have orange
carpeting that matched the fibers in her hair. The color
was unique, which allowed scientists to trace it to a
manufacturer who supplied information about its limited
run.
• Apparently only 74 yards of it had been shipped to that
area of Ohio. That helped to narrow down
possibilities. Other evidence established a more solid
link and Robert Anthony Buell was eventually convicted.