FRS581 FORENSIC

CHEMISTRY
Forensic Fiber
by
Khairulmazidah Mohamed
Learning Outcomes:

1. Classify fibers.
2. List the properties of fibers that are most useful
for forensic comparisons.
3. Describe the proper collection of fiber evidence.
4. Describe the common forensic analysis of fiber
evidence
5. Explain cordage examination and its significance
 • DEFINITION: A fiber is the smallest unit of a textile
Fibers material that has a length many times greater than its
diameter.

• Fibers make up thousands of products, including

clothing, upholstery, carpet, rope, and building
components.

• A fiber can be spun with other fibers to form a

yarn that can be woven or knitted to form a fabric.

• The different origins of the materials that make

up a fiber, and the differing ways that a fiber can be
formed together to create the finished fabric, are
all important in identifying the fiber.
 Fiber

Thread

Fabric

Figure 1: Fiber, Thread and a fabric

 Types of fibers Man made fibers
Regenerated/ Natural-polymer fiber
Natural fibers
- made from natural materials by processing these
• occur in both materials to form a fiber structure.
plants and animals. - Rayon and acetate are two common regenerated
• More than half of fibers.
the fibers produced Synthetic-polymer fiber
are natural fibers. - made entirely from chemicals.
• Natural fibers - Synthetic fibers are usually stronger than either
include cotton, hair, natural or regenerated fibers.
fur, silk, and wool. - Synthetic fibers will melt if touched with too hot
iron.
- The most widely used kinds of synthetic fibers are
nylon (polyamide), polyester, acrylic, and olefin.
 Textile fiber

Natural Man-made

animal vegetable Synthetic- natural- Other (carbon, textile

mineral polymer polymer glass, metal etc.)
silk hair (asbestos)
wool regenarated
rubber
Seed cellulose/ rayon
leaf
(cotton, Cellulose
regenarated
etc ) Bast (jute, ester
protein
kenaf etc.)

polyolefin Polyvinyl polyamide aramid

polyester
derivatives
polyurethane
polyethylene polypropylene

Classification of textile fiber

 Natural Fibers : plant
• Many different natural fibers
originating from plants and animals
are used in the production of fabric.
• Cotton fibers are the plant fibers most
commonly used in textile materials
• the type of cotton, fiber length, and
degree of twist contributing to the
diversity of these fibers.

Cotton fibers

• Other plants fibers: Flax (linen), ramie, sisal,

jute, hemp, kapok, and coir.
• The identification of less common plant fibers
at a crime scene or on the clothing of a suspect
or victim would have increased significance.

Flax fiber
• Plant fibers are specialized plant cells. They are grouped
by the part of the plant from which they come. Seeds,
fruits, stems, and leaves all produce natural plant
fibers.
• Plant fibers vary greatly in their physical
characteristics; some are very thick and stiff, whereas
others are very smooth, fine, and flexible.
• Some are amorphous, a loose arrangement of fibers
that are soft, elastic, and absorbent.
• However, all plant fibers share the common polymer
cellulose. Cellulose is a polymer that is made up of
simple glucose units, and is not protein.
• Proteins and cellulose have very different chemical and
physical properties that allow a forensic scientist to tell
animal and plant fibers apart.
• For example, cellulose can absorb water
but is insoluble (will not dissolve) in
water. It is very resistant to damage from
harsh chemicals and can only be
dissolved by very strong acids, such as
sulfuric acid.
• Cotton is the most common plant fiber
used in textiles.
• Plant fibers are often short, two to five
centimeters, and become brittle over
time. This means that small pieces of
fibers are common as trace evidence at a
crime scene.
Seed fibers
• Cotton is found in the seedpod of the
cotton plant.
• Because of the ease with which cotton
can be woven and dyed, it has been
used extensively for clothing and
household textiles.
Fruit fibers
• Coir is a coarse fiber obtained from the covering surrounding
coconuts.
• The individual cells of the coir fibers are narrow, with thick walls
made of cellulose.
• When woven together, they are stronger than flax or cotton.
• Coir fiber is relatively waterproof, which makes it ideal for such
things as doormats and baskets.
Stem fibers
• Hemp, jute, and flax are all produced from the
thick region of plant stems/ bast.
• They do not grow as single, unconnected fibers
like cotton, but in bundles.
• These bundles may be six feet in length and
extend the entire length of a plant.
• During processing, the bundles are separated
from the stem and beaten, rolled, and washed
until they separate into single fibers.
• Flax is the most common stem fiber and is most commonly found in
the textile linen.
• Jute fibers produce a textile that is too coarse for garments and is
instead used to make rope, mats, and handbags.
• Hemp is similar to flax and has been used for a long time in Asia for
clothing.
• Kenaf fibers are widely used and find application in special fabrics for gardening, packaging materials,
specialty paper types as well as in the production of cords and bags.
• Kenaf fiber has emerged as an important plant cultivated in third-world countries and has been
regarded as an industrial crop. Third industrial crop in Malaysia after palm oil and rubber.
• It has a great potential for replacing synthetic fiber such as glass fiber.
 Animal fiber
• Animals provide fibers from three sources: hair, fur,
and webbing.
• All animal fibers are made of proteins. They are used
in clothing, carpets, decorative hangings such as
curtains, and bedding.
• Fur is a good donor of fibers, but it is not a textile.
Rather, an animal such as a beaver or fox is trapped,
and the skin removed and treated.
• This results in a flexible skin that retains the fur. Fur
is used almost exclusively for coats and gloves.
• Hair fibers are the most popular of animal fibers.
Animal hair is brushed out of the animal’s coat, shed
naturally and collected, or clipped.
• The most common animal hair used in textiles is wool from
sheep, but there is also cashmere and mohair from goats,
angora from rabbits, as well as hair from members of the
camel family—alpacas, llamas, and camels.
• Hair fibers are used for articles of clothing, bedding, heavy
coats, carpets, bags, and furniture upholstery.
• When animal hair fibers are made into textiles, they are
often loosely spun to feel more comfortable, making
textiles that shed fibers easily.

Wool fiber
(L) and
Angora fiber
(R)
• Silk, another natural fiber, is collected from the
cocoons of the caterpillar Bombyx mori.
• The caterpillars are reared in captivity, and each
cocoon must be carefully unwound by hand.
• The shimmering appearance of silk is caused by
the angular structure of the fiber, which scatters
light as it passes through, just like a prism.
• Fabrics made from silk are commonly used in
clothing and some bedding.
Silk cocoons are
• Because silk fibers are very long, they tend not
2.5cm long and
to shed as easily as hair fibers. are made from
one fiber that may
measure 1 to 2km
long! However, it
takes 3,000 of
these cocoons to
make 1 square
meter of fabric.
• Mineral fibers are neither proteins nor cellulose, and may not even
be repeating polymers.
• It is form of molten mineral that is spun to fiber.
• Example: Basalt wool, asbestos, rockwool, fiberglass
• Fiberglass is a fiber form of glass. Its fibers are very short, very weak, and brittle.
• Rolls of fiberglass batting (layers or sheets of fiberglass) are used to insulate buildings.
• The fibers are very fine and easily stick to the skin, causing an itchy skin rash.
• Asbestos is a mineral naturally occuring in different types of rocks with a crystalline
structure composed of long, thin fibers.
• Asbestos is very durable. Its many uses include pipe coverings, brake linings, ceiling tiles,
floor tiles, fire-resistant work clothes, shingles, home siding, and insulation for building
materials.
• Basalt wool used as fireproof textile in automotive
• Mineral fibers are resistant to temperatures above 1,000 °C thus most are served as
high-temperature insulation (but its not fire resistant)
Basalt wool fabric and under microscope
Rockwool formed by spinning molten mineral or rock materials to thin fiber
by air blowing technique. Good for insulation and soundproofing.
Asbestos was incorporated into a huge variety of products, especially building materials
such as concrete, pipes, cement, bricks, tiles, and insulation for buildings and ships. It was
also used in car parts, protective clothing, mattresses, and even cigarette filters.
The fibers are so small that most can only be seen under a microscope. Billions can be
inhaled in a single day with no immediate effect, but longer-term the consequences can
be deadly.
 Man-Made (Synthetic) Fibers
• More than half of all fibers used in the
production of textile materials are man-made.
• Some man-made fibers originate from natural
materials and synthetic materials.
• There are also many other less common man-
made fibers. Cross section of man-
• The amount of production of a particular man- made fibers
made fiber and its end use influence the
degree of rarity of a given fiber.
• The cross section of a man-made
fiber can be manufacturer-specific
• Unusual cross sections encountered
through examination can add
increased significance to a fiber
association.

Cross-sectional views of nylon

carpet fibers
• Regenerated fibers (or modified natural fibers) are derived
from cellulose and are mostly plant in origin.
• The most common of this type is rayon.
• It is a fiber that can imitate natural fibers and generally is
smooth and silky in appearance.
• Cellulose chemically combined with acetate produces the
fiber Celanese® that is used in carpets.
• When cellulose is combined with
three acetate units, it forms
polyamide nylon (such as Capron®)—a
breathable, lightweight material, used
in high-performance clothing.
 Synthetic fiber under
microscope

Polyester under 40 x

Nylon under 40x

Nylon under 100 x
Polyester under 400 x
• Synthetic polymer fibers originate with petroleum products and are
noncellulose-based fibers.
• The fibers are totally man-made polymers that serve no other purpose
except to be woven into textiles, ropes, and the like.
• These fibers can have very different characteristics. They have no definite
shape or size, and many, like polyester, may be easily dyed.
• Their shape is determined by the shape of the spinneret and may be round,
flat, cloverleaf, or even more complex.
• However, under magnification, all synthetic fibers have very regular
diameters.
• They do not have any internal structures, but may be solid or hollow,
twisted, and pitted on the surface.
• Depending on what is put into the mix, they may be clear or translucent.
How synthetic and semi synthetic fiber
have a uniform cross section?
Polymer resin
mixture

Spinerette. This is how synthetic fibers

gained its uniform shape

Diagram of fiber manufacturing

• The fiber cross shape is determined
by the shape of the spinneret filter
• It can be round, flat, cloverleaf, or
even more complex.
• The internal structures may be
solid or hollow, twisted, and pitted
on the surface.
• Depending on what is put into the
mix, they may be clear or
translucent.
Comparison of Natural and Synthetic Fibers

• The synthetic fibers are stronger than the strongest natural

fibers.
• Unlike natural fibers, man-made fibers are not damaged by
microorganisms.
• A disadvantage of man-made fibers is that they can
deteriorate in bright sunlight and melt at a lower
temperature than the natural fibers.
• The table shown below shows the different characteristics of
various textile fibers.
How fibers are made into
Textile/ Fabric
 YARNS
• Fibers too short in their raw state to be used to make textiles, may
be spun together to make yarns.
• Short cotton fibers only two centimeters long can be twisted into
very strong yarn of any length.
• Rope is simply a very big yarn.
• Depending on their use, yarns may be spun
thick or thin, loose or tight.
• Some may be a blend of fibers, such as
wool and polyester, to give desired qualities
such as strength or wrinkle resistance.
• Any given yarn will have a direction of twist.
• Forensic scientists identify the twist
direction as part of their identification.
 Weave Pattern
• Fibers are woven into textiles or fabrics.
• Weaving consists of arranging lengthwise threads (the warp)
• side by side and close together.
• Crosswise threads (the weft) are then woven back and forth in
one of several different patterns.
• The pattern in which the weft passes over and under the warp
fibers is called the weave pattern.
• Weave patterns have names like tabby, twill, and satin. Satin is
not a type of fiber, it is a type of weave.
• Some of the examples of weave patterns is in the next slide.
 Thread Count
• The number of threads that are packed together for any given
amount of fabric is another characteristic, which is known as
thread count.
• Every package of bed sheets includes information on thread
count, as well as the type of fiber used to make them.
• The price of sheets varies a great deal, and high prices tend to
come with all-natural fibers and high thread counts.
• A high thread count is more costly to manufacture and
provides a smoother finish.
• Thread count is often written as threads per inch. Typical
sheets will have a thread count between 180 and 300 threads
per inch, but high-quality sheets can have thread counts of
500 threads per inch.
Thread count
 Fiber Evidence
• Fibers are one of the several pieces of forensic
evidence known as trace evidence.
• Placing a suspect at the scene of crime is an
important element in criminal investigations.
The value relies on:
➢the location of textile fibers similar to those from the victim's clothing
➢the crime scene on the clothing of the suspect
➢through the discovery of fibers like those in the suspect's clothing at the crime
scene.

• When fibers are matched with a specific source (fabric from the victim, suspect,
and/or scene), a value is placed on that association.
• The amount of fibers that are transferred at a crime scene can be
influenced by the nature of the fabrics that are worn by the people involved
in the crime.
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An understanding of the mechanics of primary and secondary transfer

is important when reconstructing the events of a crime.
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The problem with fiber evidence is

that fibers are not unique.

• Unlike fingerprints or DNA, they cannot pinpoint an offender

in any definitive manner.
• 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

Factors such as standard samples may be old/ exposed to

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weathering/ have been washed or dry-cleaned etc. may

caused a much greater potential for variation in the
population of fibers which are available on any items for
transfer.
• In short, the fiber analyst compares shape, dye
content, size, chemical composition, and
microscopic appearances, yet all of this is still about
"class evidence.“

• Even if fibers from two separate places can be

matched via comparison, that does not mean they
derive from the same source, and there is no fiber
database that provides a probability of origin.
Fiber classifications method
Protocol used to examine will depends on:
i) Nature of the fibers
ii) Starting materials
iii) Physical and chemical component of fiber

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However, combined factors of color, size, shape,

microscopic appearance, chemical composition and
dye content make it very unlikely to find 2 different
people wearing identical fabrics.
Laboratory Examination of
Fibers
 Laboratory examination of fibers
• The examination of fiber evidence includes physical
examination and chemical analysis.

• Fiber-trained forensic scientist:

a) Identification of the generic fiber class (class, type, colour,
chemical composition)
b) Comparison of the questioned fiber to known fiber standards or
suspects/victim
 Laboratory examination of fibers
• A guideline for forensic fiber examination has been developed
by the Scientific Working Group on Materials Analysis
(SWGMAT) and American Society of Testing Material (ASTM)

✓ E2224-02 Standard Guide for Microscopic Examination of Textile Fibers

✓ E2224-02 Standard Guide for Forensic Analysis of Fibers by Infrared
Spectroscopy
✓ E2225-02 Standard Guide for Forensic Examination of Fabrics and Cordage
 Sample collection of fibers
1. A piece of clothing or garment exhibit
a) Package each garment separately
b) Fold the garment with a piece of paper
c) Package them in the evidence bag and label

2. Fiber shredded
a) Place the fiber in a small paper envelope using tweezer
b) If no envelope is available, place it in a plastic/glass
container or fold them in a piece of paper
c) Then package them in the evidence bag and label

3. A piece of fiber
• Similar to shredded fiber
 Laboratory examination of fibers
a) Retrieval of fibers
– Using tape/ tweezers/ vacuum
b) Low microscopic examination
c) Identification of fiber type/class using High Power/ Polarising microscope
d) Physical testing (burn test)
e) Analytical comparison
– Microspectrophotometry
– FTIR
– TLC
– Pyrolysis- GC
 a) Fiber retrieval

• Recover fibers from items in question

• Picking off the fiber individually using tweezers
• Or multiple fibers in a single area using taping
❖Do not overload the tape
• Vacuum

• Systematic approach must be employed ;location on

the garment is important
• Label each taping or sample evidence clearly
• Reference slide
Recovering fibers from items in question : The garment should be
• Extra care must be taken to keep each piece of garment exhibit of divided into parts before
each individual separated from other garments/objects. fiber sample are retrieved.
• In the lab, each garment should be-laid on a clean sheet of paper Using tweezers or tape.
on the lab desk
• Once the physical marking of the exhibit is done, separately
rolled up in the paper

Taping fiber
 b) Low microscopic examination
• The most crucial steps in examining fiber b) and c)
• Taping are examine using transmitted white light 40x-
400x
• Tapes examine and observed in methodological
manner and any fibers deemed to match control fibers
are marked
• Selection of marked fibers recovered for further
examination against control fibers
 Recovered fibers
are mounted
individually for further
Individual Fiber examination against control
fibers

You can mount one slide with

one fiber or divided as in the
figure.
Fiber taping
evidence.

Tape Lifting Fiber

Selection of marked fibers
recovered for further
examination need to be
mounted individually
 b) Low microscopic examination

Assessment:
• Colour transmitted in white light
• Synthetic or manmade
• Colour and intensity of fluorescence in UV
• Thickness (diameter)
• Cross sectional shape (round, bilobal, trilobal, irregular, hollow etc.)
• Presence / absence of delustrant
• Presence of any surface characteristics, damage or adhering debris
• Refractive index (Becke line method)
Fiber cross
sections
Becke line
• In order to determine whether the Refractive Index of fiber is greater or less than the
mounting material, Becke line method is used
• In order to see Becke line using a PLM , fiber is place on a slide with and mounting
media with known RI. (Immersion oil’s RI= 1.518)
• Focus is increase (stage line will move upward), the becke line moves into the
medium indicate FIBER HAS HIGHER RI than the mounting media and vice versa

RI Fiber > Mounting Media RI Fiber < Mounting Media

c) Identification using High Power/ Polarising microscope

• If all of the characteristics are the same under the stereoscope, the next step is to
examine the fibers with a comparison microscope to discriminate between fibers,
especially those that appear to be similar.

• Comparisons should be made under the same illumination conditions at the same
magnifications.

• Two fibers or fiber samples from the same source mounted on two microscope
slides, which are then compared.

• Eyes can recognized about 120 hues in the visible spectrum (400-750 nm)
 d) Other Fiber Physical Testing

• Burning the fiber

• Odor of burning hair – Animal source
• Odor of burning paper – Plant source
• Melts, but does not burn – Manufactured

• Chemically treating the fiber/ Solubility test

• Dissolves in strong acid – plant, silk, or manuf.
• Dissolves in strong base – wool
Common solvents Dimethylformamide (DMF), Cyclohexanone and
Nitromethane
 e) Analytical comparison :
Microspectrophotometry
• A microspectrophotometer integrates a
microscope and a spectrophotometer for broad
coverage in the ultraviolet-visible-infrared
region.
• Measure transmittance, absorbance, reflectance
, light polarization, fluorescence
• Examining colour/dye of a fiber through
electromagnetic spectrum
– Colour- hue (colour spectrum)
– Saturation
– Lightness
 e) Analytical comparison :
Microspectrophotometry

– Light absorbed by or reflected from a

sample is separated into its
component wavelengths, and
intensity at each wavelength plotted.

– Can be IR or UV/Vis
 e) Analytical comparison :
Fourier Transform Infra Red (FTIR)
• Exploits the most man made fibers are carbon based polymers
• Concerned with the energy changes involved in the stretching
and bending of the covalent bonds
• Bonds between specific atoms have particular frequencies of
vibrations, FTIR provides mean of identifying the of bonds in a
molecule
• A mathematical function called the FT allows us to convert an
intensity vs time spectrum into an intensity vs spectrum
• For synthetic fiber since dye cannot be extracted
 e) Analytical comparison :
Thin Layer Chromatography (TLC)
• Dye components are separated by their
differential migration caused by a mobile
phase flowing through a porous, adsorptive
medium.
• Known and questioned sample shall be run
on the same plate
• Observe under UV light.
• Results recorded: photograph
• Destructive method
 Other analytical instrumentations
• Pyrolysis chromatography (Py GC-MS or Py GC-FID)
• Indicate the monomers of the fiber, also for determining acrylic fibers,
destructive
• Raman spectroscopy
• For dye spectrum determination
• Raman is able to show set of polyester fibers from different
manufacturers- quantitation of the dye mixture
• SEM is useful to study damage on fibers
• Determining whether the fiber has been cut or torn
• HPLC has also been used for dye detection
• Not very helpful as it needed database/standard for comparison
• But it provide “fingerprint” chromatogram pf the dye which can be used
for comparison
 Fabrics and Cordage
• Because of their general availability, fabric and
cordage are often encountered by forensic
scientists, who must compare these types of
evidence in order to determine if the two
pieces could have originated from the same
source.
 Cordage; Its Examination and Significance
• Cordage is a term collectively used for ropes and cords.
• Pieces of string or rope are sometimes found at the crime
scenes, if used for tying the victim, gaining entry, knots may be
found.
 Cases where cordage evidence are found
• Suicidal hanging
• Strangulation
• Tying the victim for immobilizing
• Winding a package or booty
• As pieces left from items as gunny bags
• To climb up walls etc for gaining entry using rope
• Erotic asphyxiation - the intentional restriction
of oxygen to the brain for the purposes of sexual arousal
 Possible examinations using cordage
• Cut ends – in cordages made of nylon or other synthetic materials,
even physical matching is possible – recovery of exemplar sample
• Materials from which cordage is manufactured
• Number of strands in the cordage
• Direction of twist in the rope
• Color, diameter and weight per unit length
• Comparison of the marks left on the human body or other objects with
the twist pattern of the strands in the cordage
• Trace evidence on the cordage – these maybe dust of dirt on the
cordage or more importantly epithelial (skin cells) attached to the
cordage or occupational trace evidence
 Procedure for preserving the knots
• After photograph, cut the remaining part of the rope leaving the points of the knot
without altering or damaging the knot.
• Remove the ligature from the neck and immediately bound together the two cut
ends using a string.
• Never remove the ligature material in its loose state by dragging it along the head –
this would lead to transfer of scalp hairs while removal.
• In cases where hanging is suspected to be postmortem, the cord must be protected
more carefully by placing it stretched in a long box so that the length of the cord
hangs freely with its ends held fast to the side of the box.
• In cases in which life may be still suspected in the victim, the victim should be
brought down sidelining the above rules so that the victim can be saved without loss
of time.
Thank You