1. Forensic Science: Fundamentals & Investigations, Chapter 4 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 All Rights Reserved South-Western / Cengage Learning © 2009

2. 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. become trace evidence In an investigation, collection of fibers within 24 hours is critical. – 95% lost from victim and crime scene

3. Forensic Science: Fundamentals & Investigations, Chapter 4 3 How Forensic Scientists Use Fibers A forensic scientists will ask questions about the following: – Type of fiber – Fiber color – # fibers found and where – Textile fiber came from – Multiple fiber transfers – Type of crime committed – Time between crime and discovery of fiber

4. Forensic Science: Fundamentals & Investigations, Chapter 4 4 Sampling and Testing Evidence gathered by vacuums, sticky tape, and forces Id type of fiber and characteristics Match to suspect Polarizing light microscopy – special filter to observe with different wavelengths of light Infrared spectroscopy – tell difference between fibers that look a lot alike

5. 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. Crimes can be solved in this way by comparing fibers found on different suspects with those found at the crime scene.

6. Forensic Science: Fundamentals & Investigations, Chapter 4 6 Fiber Classification —Natural Fibers woven wool textile Animal fibers (made of proteins): come from hair, fur, webbing Fur – coats and gloves Hair - 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.

7. Forensic Science: Fundamentals & Investigations, Chapter 4 7 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 because they become brittle over time.

8. Forensic Science: Fundamentals & Investigations, Chapter 4 8 Fiber Classification —Natural Fibers Plant fibers: Seed - cotton Fruit - Coir from coconuts is durable. Stem - Hemp, jute, and flax (linen) Leaf - 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.

9. Forensic Science: Fundamentals & Investigations, Chapter 4 9 Fiber Classification —Synthetic (artificially produced) Fibers Until the nineteenth century only plant and animal fibers were used to make clothes and textiles. Half the products produced today are artificially produced. Artificially produced fibers include rayon, acetate, nylon, acrylics, and polyesters.

10. Forensic Science: Fundamentals & Investigations, Chapter 4 10 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.

11. Forensic Science: Fundamentals & Investigations, Chapter 4 11 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. Monomers in large vats are joined together to form polymers. The fibers produced are spun together into yarns. They have no internal structures, and under magnification they show regular diameters.

12. Forensic Science: Fundamentals & Investigations, Chapter 4 12 Fiber Classification— Synthetic (artificially produced) Fibers spandex nylon 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.

13. Forensic Science: Fundamentals & Investigations, Chapter 4 13 Comparison of Natural and Synthetic Fibers Visual Diagnostics of Some Common Textile Fibers under Magnification

14. Forensic Science: Fundamentals & Investigations, Chapter 4 14 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.

15. Forensic Science: Fundamentals & Investigations, Chapter 4 15 Yarns, fabrics, and textiles Weave Patterns

16. Forensic Science: Fundamentals & Investigations, Chapter 4 16................. Summary................. 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.