FIBERS Pgs Ch 16

I. Using Fibers as Evidence 1. Fibers are usually made up of many filaments twisted or bound together to form a thread or yarn. – They are everywhere. – Textiles (fabric with a distinctive pattern) are mass produced in huge quantities 2. Fibers are one of the most common items left at a crime scene. – Are considered class evidence – Creates a link among victim, suspect, and location

3. Investigators identify and compare fibers physically and chemically. – Compare questioned to a known – Statistics and probability are used to narrow the source

II. Sources for Fibers 4. Fabrics are made from fibers. – Fiber is made of natural or artificial filaments 5. Natural Fibers: – Animal, vegetable, or inorganic – Silk, wool, mohair, cashmere, cotton, linen, jute, asbestos, fiberglass 6. Artificial Fibers are synthesized or created from altered natural sources. – Acrylic, polyester, nylon, rayon, (Gore-Tex)

7. Fibers are used to make: – Textiles; cloth and carpeting – Cordage; rope, string, nets – Brushes; paint, cooking, make-up – Filling; mattresses, furniture, stuffed animals – Structural materials; used in cars, tires, airplanes

III. Types of Fibers 8. A weave consists of a lengthwise yarn and a crosswise yarn. – Lengthwise – called the warp – Crosswise – called the weft – Are usually different in type, size and color if the weave is “blend” 9. All fibers are polymers. – Long chains made of simple molecules

IV. Fiber Cross Sections 10. A cross-sectional shape of a fiber filament may be one of its characteristics. CottonSilk

V. The Chemical Structure of Fibers 11. The chemical structure of a fiber defines many of the properties that can be used to identify and further classify it. – Wool- composed of polypeptide chains that form a helical protein called keratin – Silk – is simpler in structure than wool

Cotton – is made of cellulose (like wood), but is the most commonly used Linen – (flax) composed of cellulose, but longer fibers Rayon – natural fiber that has been chemically altered, pure cellulose, burns like cotton Acetates – made from cellulose through a reaction with acetic acid. Nylon – synthetic fiber, stronger and more chemically inert (doesn’t react). Polyester – can be flexible or rigid, Acrylics – synthetic fibers, causes blue litmus paper to turn red when broken down by heat Spandex – structurally similar to polyesters, can stretch up to 600%, are usually blended Olefins – synthetic fiber, very resistant to weathering and chemicals, usually in carpets, auto interiors, and rope

Tests for Fabric/Fiber Identification Comparison of Unknown to a Known Burn Tests – How does it burn? Does it melt? Does it flame? What kind of residue? Stain Tests – What color does it turn when submerged in DuPont Solution? Chemical Tests – How do fibers react when exposed to Bleach? Sulfuric Acid? Hydrochloric acid? Acetone? Refractive Index