1. Chapter 4 A Study of Fibers and Textiles By the end of this chapter you will be able to:
identify and describe common weave patterns of textile samples
compare and contrast various types of fibers through physical and chemical analysis
describe principle characteristics used to identify common fibers
apply forensic science techniques to analyze fibers
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Forensic Science: Fundamentals & Investigations, Chapter 4

2. Introduction and How Forensic Scientists Use Fibers
Fibers often fall off and are picked up during normal activities.
Very small fibers easily shed from most textiles and can become trace evidence.
In an investigation, collection of fibers within 24 hours is critical.
Fiber evaluation can show such things as the type of fiber, its color, the possibility of violence, location of suspects, and point of origin.
Forensic Science: Fundamentals & Investigations, Chapter 4

3. Sampling and Testing
Weaving spun fibers (yarns) together produces clothing and many textiles.
Shedding from an article of clothing or a textile is the most common form of fiber transfer.
Natural fibers require only an ordinary microscope to find characteristic shapes and markings.
Infrared spectroscopy can reveal something of the chemical structure of other fibers that, otherwise, may look very much alike.
Forensic Science: Fundamentals & Investigations, Chapter 4

4. Sampling and Testing
If a large quantity of fibers is found, some can be subjected to destructive tests such as burning them in a flame (see analysis key above) or dissolving them in various liquids.
Crimes can be solved in this way by comparing fibers found on different suspects with those found at the crime scene.
Forensic Science: Fundamentals & Investigations, Chapter 4

5. Fibers Material composing fabric and garments Two types:
Natural and Synthetic (man-made)
Forensic Science: Fundamentals & Investigations, Chapter 4

6. Natural Fibers Come from three places: 1. Plants 2. Animals
3. Minerals
Forensic Science: Fundamentals & Investigations, Chapter 4

7. Animal Fibers
Identified by microscopic examination of color and diameter of fiber.
Most prevalent (common) natural fiber is cotton.
Forensic Science: Fundamentals & Investigations, Chapter 4

8. Natural Fibers Animal fibers (made of proteins):
Comes from three places:
1. Hair
2. Fur
woven wool textile
Wool from sheep, cashmere and mohair from goats, angora from rabbits, and hair from alpacas, llamas, and camels are commonly used in textiles.
Shimmering silk from caterpillar cocoons is longer and not as easily shed.
3. Webbing
Forensic Science: Fundamentals & Investigations, Chapter 4

9. Fiber Classification —Natural Fibers
Plant fibers (made of the polymer cellulose):
are very resistant to damage from harsh chemicals.
can only be dissolved by strong acids.
can be common at crime scenes because they become brittle over time.
Forensic Science: Fundamentals & Investigations, Chapter 4

10. Fiber Classification —Natural Fibers
Plant fibers:
Cotton from seedpods is the plant fiber most commonly used in textiles (shown above).
Coir from coconuts is durable.
Hemp, jute, and flax from stems grow in bundles.
Manila and sisal from leaves deteriorate more quickly.
Forensic Science: Fundamentals & Investigations, Chapter 4

11. Microscopic Examination of Cotton
Under microscope, the cotton looks like twisted ribbon or collapsed and twisted tubes. These twists are called convolutions.

12. Mineral Fibers: (neither plant nor animal)
Fiberglass is a fibrous form of glass.
Asbestos is a naturally occurring mineral with a crystalline structure.
Forensic Science: Fundamentals & Investigations, Chapter 4

13. Synthetic (man-made) Fibers
Until the nineteenth century only plant and animal fibers were used to make clothes and textiles.
Fibers created from or synthetic polymers.
Dates back to 1911 with rayon and 1939 with nylon.
Forensic Science: Fundamentals & Investigations, Chapter 4

14. Half the products produced today are artificially produced.
Artificially produced fibers include rayon, acetate, nylon, acrylics, and polyesters.
Polymers: chains of regular and repeating atoms.
Forensic Science: Fundamentals & Investigations, Chapter 4

15. Fiber Classification —Synthetic (artificially produced) Fibers
Regenerated Fibers (derived from cellulose):
Rayon is the most common of this type of fiber. It can imitate natural fibers, but it is stronger.
Celenese® is cellulose chemically combined with acetate and is often found in carpets.
Polyamide nylon is cellulose combined with three acetate units, is breathable, lightweight, and used in performance clothing.
Forensic Science: Fundamentals & Investigations, Chapter 4

16. Fiber Classification —Synthetic (artificially produced) Fibers
Synthetic Polymer Fibers:
Petroleum is the basis for these fibers, and they have very different characteristics from other fibers.
They have no internal structures, and under magnification they show regular diameters.
Forensic Science: Fundamentals & Investigations, Chapter 4

17. Fiber Classification—Synthetic (artificially produced) Fibers
Examples of synthetic polymer fibers:
Polyester—found in “polar fleece,” wrinkle-resistant, and not easily broken down by light or concentrated acid; added to natural fibers for strength.
Nylon—easily broken down by light and concentrated acid; otherwise similar to polyester.
Acrylic—inexpensive, tends to “ball” easily, and used as an artificial wool or fur.
Olefins—high performance, quick drying, and resistant to wear.
Forensic Science: Fundamentals & Investigations, Chapter 4

18. Microscopic View of Polyester
Smooth fibers with regular diameter. Diameter generally ranges from micrometers. The un-dyed fabric is usually off white and transparent.

19. Comparison of Natural and Synthetic Fibers
Visual Diagnostics of Some Common Textile Fibers
under Magnification
Forensic Science: Fundamentals & Investigations, Chapter 4

20. Comparison and Identification of Fibers
Most important is the ability to trace the origin of the fibers
Only if pieces completely fit together can a definite origin be determined
If cannot fit together, the fibers must be compared side-by-side with standard/reference samples

21. Comparison and Identification of Fibers (cont’d)
First microscopically compare fibers for diameter and color
Look for other morphological details like striations or pitting
Use visible light microspectrophotometer to analyze colors of fibers for comparison

22. Collection and Preservation of Fiber Evidence
Know potential carriers of fiber evidence
Collect and package evidence in separate paper bags
Fold blankets, carpets and rugs to prevent loss of evidence
Cover car seats with polyethylene sheets

23. Summary
Fibers are spun into yarns having specific characteristics.
Yarns are woven, with different patterns, into clothing or textiles.
Fibers, trace evidence, are a form of class evidence used by crime scene investigators.
Fiber evidence may be gathered using different techniques.
Fibers may be analyzed using burn tests, tests for solubility in different solutions, polarized light microscopy, or infrared spectroscopy.
Forensic Science: Fundamentals & Investigations, Chapter 4