Forensic Science: Fundamentals & Investigations, Chapter 4 1 Introduction and How Forensic Scientists Use Fibers Fibers often fall off and are picked up during normal activities. small fibers easily shed from most textiles- trace evidence

Transfer of Fibers Direct Transfer-fibers from an article are left on a person after contact Secondary Transfer-fibers from an article are left on a person and they transfer those fibers to another person or place Forensic Science: Fundamentals & Investigations, Chapter 4 2

3 In an investigation, collection of fibers within 24 hours is critical. Fiber evaluation- type of fiber, color, number found, possibility of violence, location of suspects, & point of origin

Forensic Science: Fundamentals & Investigations, Chapter 4 4 Sampling and Testing Fibers collected using tape, forceps & special vacuums Observe macroscopic detail-color, length Weaving spun fibers (yarns) together produces clothing and many textiles. Natural fibers require a microscope - characteristic shapes and markings. Infrared spectroscopy-chemical structure of other fibers that may look alike.

Forensic Science: Fundamentals & Investigations, Chapter 4 5 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.

Forensic Science: Fundamentals & Investigations, Chapter 4 6 Fiber Classification —Natural Fibers woven wool textile Animal fibers (made of proteins): 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.

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8 Fiber Classification —Natural Fibers Plant fibers (made of the polymer cellulose): can absorb water. are insoluble in water. are very resistant to damage from harsh chemicals. can only be dissolved by strong acids. can be common at crime scenes-they become brittle over time.

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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. Mineral Fibers: Fiberglass is a fibrous form of glass. Asbestos is a naturally occurring mineral with a crystalline structure.

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Forensic Science: Fundamentals & Investigations, Chapter 4 12 Fiber Classification —Synthetic (artificially produced) Fibers Until the 19th century only plant and animal fibers were used ½ of products produced today-artificially produced. include rayon, acetate, nylon, acrylics, and polyesters.

Forensic Science: Fundamentals & Investigations, Chapter 4 13 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 14 Fiber Classification —Synthetic (artificially produced) Fibers Synthetic Polymer Fibers: Petroleum is the basis and they have very different characteristics from other fibers. Monomers in large vats are joined together to form polymers. The fibers produced are spun together into yarns-spinnerets They have no internal structures, and under magnification they show regular diameters.

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Forensic Science: Fundamentals & Investigations, Chapter 4 16 Fiber Classification— Synthetic (artificially produced) Fibers spandex nylon polyester 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 17 Comparison of Natural and Synthetic Fibers Visual Diagnostics of Some Common Textile Fibers under Magnification

Forensic Science: Fundamentals & Investigations, Chapter 4 18 Yarns, fabrics, and textiles Fibers can be twisted (spun) into yarn of any length, thick or thin, loose, or tight. A blend can be made to meet different needs such as resistance to wrinkling. Fibers can be woven into fabrics or textiles. – Threads are arranged side by side (the warp). – More threads (the weft) then are woven back and forth crosswise in one of a number of different patterns through the warp.

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Forensic Science: Fundamentals & Investigations, Chapter 4 20 Yarns, fabrics, and textiles Weave Patterns