1. Trace Evidence- Fibers
Chapter 2
Trace Evidence- Fibers
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2. Wayne Williams- Fiber Evidence
16:50- 25:00

3. Chapter 2
Polymers
Fibers are made of polymers, which are long chains of repeating chemical units (monomers) The word polymer means many (poly) units (mer). 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, they can be distinguished from one another forensically.
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4. Chapter 2
Fibers
- Fibers are considered class evidence - Have probative value (evidence which is sufficiently useful to prove something important in trial) - Are common trace evidence found at a crime scene - Can be characterized based on comparison of both physical and chemical properties
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5. Chapter 2
Fabrics
Fabric is made of fibers composed of twisted filaments. Types of fibers and fabric: Natural—animal, vegetable, or inorganic Artificial—synthesized or created from altered natural sources
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6. Types of Fibers Silk Synthetic Natural Rayon Nylon Cotton Acetate Wool
Chapter 2
Types of Fibers
Synthetic
Rayon
Nylon
Acetate
Acrylic
Spandex
Polyester
Natural
Silk
Cotton
Wool
Mohair
Cashmere
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7. Chapter 2
Classification
Natural fibers are classified according to their origin:
- Vegetable or cellulose
- Animal or protein
- Mineral
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8. Chapter 2
Cellulose Fibers
Cotton—the most common plant (vegetable) fiber is simply a polymer of cellulose. Cotton is strong, tough, flexible, moisture-absorbent, not shape-retentive .
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9. Chapter 2
Cellulose Fibers
Rayon—(Regenerated Fiber) chemically altered cellulose; soft, lustrous, versatile
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10. Chapter 2
Cellulose Fibers
Cellulose acetate—(Regenerated Fiber) cellulose that is chemically altered to create an entirely new compound not found in nature.
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11. Chapter 2
Fiber Comparison
Can you describe the difference(s) between the cotton on
the left and the rayon on the right?
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12. Chapter 2
Protein Fibers
Wool—animal fiber coming most often from sheep, but may be goat (mohair), rabbit (angora), camel, alpaca, llama, or vicuña. Wool is primarily keratin.
What is keratin?
Wool tends to have a kinky appearance, itchy feel and is wrinkle resistant.
Both silk and wool consist of fibrous proteins made up of amino acid monomers.
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13. Chapter 2
Protein Fibers
Silk—insect fiber that is extruded by silkworms in long filaments- up to a mile long. Silk has insulating properties, is able to wick moisture away and is soft to the touch.
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14. Chapter 2
Protein Fibers
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15. Chapter 2
Mineral Fibers
Asbestos—a natural fiber that has been used in fire-resistant substances Rock wool—a manufactured mineral fiber Fiberglass—a manufactured inorganic fiber
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16. Chapter 2
Synthetic Fibers Made from derivatives of petroleum, coal, and natural gas
Nylon—most durable of man-made fibers; extremely lightweight Polyester—most widely used man-made fiber Acrylic—provides warmth from a lightweight, soft, and resilient fiber Spandex—extreme elastic properties
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17. Filament Cross Sections
Chapter 2
Filament Cross Sections R
ound
4-lobed
Octalobal
Irregular
Multi-lobed
or Serrate T
rilobal
Dogbone or
Dumbbell
Synthetic fibers are forced out of a nozzle when they are hot, and then they are woven. The holes of the nozzle are not necessarily round; therefore, the fiber filament may have a unique shape in cross section.
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18. Fabric Characteristics
All unique to type of fabric
Loop pattern
Knitted
Woven
Bonded
Crocheted
Felted
Knotted
Laminated
Types of fibers
Degree of stretch
Absorbency
Water repellence
Softness
Durability

19. Testing for Identification
Chapter 2
Testing for Identification
Microscopic observation Burning—observation of how a fiber burns, the odor, color of flame, color of smoke, and the appearance of the residue Thermal decomposition—gently heating to break down the fiber to the basic monomers Chemical tests—solubility and decomposition
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20. Testing for Identification
Chapter 2
Testing for Identification
Density—the mass of an object divided by the volume of the object Refractive index—measurement of the bending of light as it passes from air into a solid or liquid Fluorescence—absorption and reemission of light; used for comparing fibers as well as spotting fibers for collection
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21. Chapter 2
Burn Test
Record the number of the swatch next to the appropriate fiber type.
In Flame:
Burns and chars
Melts and burns
Out of Flame:
Stops burning
Keeps burning
Residue:
Crushable bead
Ash
Plastic bead
Odor:
Burning hair
Burning paper
Acrid chemical
FIBER
IDENTITY
Proteins:
Silk
Wool
Cotton
Rayon
Synthetic:
Nylon
Polyester
Regenerated synthetic:
Acetate
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22. Chapter 2
Dyes
Components that make up dyes can be separated and matched to an unknown. There are more than 7,000 different dye formulations. Chromatography is used to separate dyes to give a more detailed analysis of the dye composition
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23. Collection of Fiber Evidence
Chapter 2
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. Why is this important? Make tape lifts of exposed skin areas and any inanimate objects. Removed fibers should be folded into a small sheet of paper and stored in a paper bag.
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24. Chapter 2
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, in his car, and on several murder victims.
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