Transcript Fiber Analysis - WLWV Staff Blogs

Chapter 13: Fibers
Types, Fiber
Identification, and
Analysis
Notes 4.3
Fibers

Fibers are commonly found with burglary,
assault, breaking and entering, hit and run
accidents, etc.

Fibers can come from clothes, carpet,
curtains, wigs, furniture, paper, etc.

They are everywhere, and therefore are
very useful to forensic investigators.
What are Fibers?
The basic unit of raw material in textile
production (threads, yarns, fabrics)
 Fibers can occur naturally or can be produced
artificially.

Natural Fibers

produced entirely
from plants or
animals
– Animal fibers
 Sheep – wool
 Goats - mohair &
cashmere
 Camels – camelhair
 Llamas- wool
 Silkworm- silk
 Rabbit – fur
 Mink – fur…..
Natural Fibers (cont’d)

produced entirely
from plants or
animals
– Plant fibers
 Cotton - cotton
 Flax – linen
 Hemp - hemp

Man-Made Fibers
Regenerated Fibers (Regenerated
Cellulose)
– produced by taking natural raw materials like
wood pulp or cotton and chemically altering
them
 Rayon
 Cellulose Acetate (ping-pong balls)

Synthetic Fibers (Polymers)
– produced solely using synthetic chemicals
(often petroleum)
 nylon
 Polyester
 acrylics
CSI Using Fibers
(clothing, carpet, drapes, wigs, artificial turf,
paper)

Torn Fabric/Paper
– Fit together like puzzle pieces

Chemical Composition
– make sure fibers are from the same generic class with infrared
spectrophotometry (process of burning and detecting the colors
produced in the flame)

Dye Comparison
– Color comparison with microspectrophotometer or
chromatography

Microscopic comparison
– color, diameter, striations, thread count, weave pattern
Identifying Fibers

However, there are some simple tests
which help greatly in distinguishing
fabrics, the most common being the
chemical tests and burning test.
The Chemical Test

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Place a small swatch of each of the
fibers onto a divided well plate.
To each sample, add a drop of the test
chemical
Wait five to seven minutes. Remove the
fabric with a forceps and rinse well in a
beaker of warm water. Blot on paper
towels and allow to dry.
Examine & record results
Chemicals
1.
2.
3.
4.
5.
6.
7.
8.
distilled water
sulfuric acid
sodium hydroxide
chlorine bleach
Dupont fabric stain solution
Isopropanol (Rubbing Alcohol)
Acetone
Formic Acid
The Burn Test

Different materials burn in different ways
depending upon the materials from which they
are made.
–
–
–
–
–
the appearance of the burn
the odor given off
the size of the ash residue
the nature of the ash
The use of tongs to hold the sample is advised.
Crucibles and lids should be used to contain burning
samples and to collect ashes.
Cotton and Linen
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burns with a large flame
leaves almost no ash.
the odor, if any, is quite similar to that of
burning paper.
after the flame goes out, a glowing spark may
continue to travel through the unburnt material
the ash retains the shape of the original
material.
Wool
either smolder or burn with a very tiny
flame
 the odor of burnt hair or feathers is
unmistakable
 a gummy, beady, ash accumulates and
forms balls along the edge of the burning
portion
 leaves much more ash than cotton or
linen.

Silk
burns slowly and with a tiny flame
 characteristic odor is also of burnt hair or
feathers.
 The ash is black and shiny and, along the edge
of the fabric, forms into tiny brittle balls that
crush easily when pressed between thumb and
forefinger.

Synthetics

Rayon, made from cellulose will burn with
a large flame
– ash will vary, depending on the kind of rayon.

Nylon and other synthetic fibers do not
burn
– Usually Nylon fibers melt, leaving a brown
mass at the edge of the material.
Your Assignment

Conduct a series of chemical and burn tests on
these different fiber samples:
 Cotton
 Linen
 Acetate
 Nylon
 Polyester
 Wool
 Rayon
 Silk
Your Assignment

The 9 different tests will involve testing
fabric fibers with:
– Acids
– Bases
– Stains
– Organic solvants
– Dyes and indicators
– Water
– Flame