Chapter 4 A Study of Fibers and Textiles

Chapter 4 A Study of Fibers and Textiles By the end of this chapter you will be able to: l identify and describe common weave patterns of textile samples l compare and contrast various types of fibers through physical and chemical analysis l describe principle characteristics used to identify common fibers l apply forensic science techniques to analyze fibers All Rights Reserved South-Western / Cengage Learning © 2009 1 Forensic Science: Fundamentals & Investigations, Chapter 4

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

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

Sampling and Testing l If a large quantity of fibers is found, some 4 can be subjected to destructive tests such as burning them in a flame (see analysis key above) or dissolving them in various liquids. l 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

Fiber Classification —Natural Fibers woven wool textile Animal fibers (made of proteins): l Wool from sheep, cashmere and mohair from goats, angora from rabbits, and hair from alpacas, llamas, and camels are commonly used in textiles. l Shimmering silk from caterpillar cocoons is longer and not as easily shed. 5 Forensic Science: Fundamentals & Investigations, Chapter 4

Fiber Classification —Natural Fibers Plant fibers (made of the polymer cellulose): l can absorb water. l are insoluble in water. l are very resistant to damage from harsh chemicals. l can only be dissolved by strong acids. l can be common at crime scenes because they become brittle over time. 6 Forensic Science: Fundamentals & Investigations, Chapter 4

Fiber Classification —Natural Fibers Plant fibers: l Cotton from seedpods is the plant fiber most commonly used in textiles (shown above). l Coir from coconuts is durable. l Hemp, jute, and flax from stems grow in bundles. l Manila and sisal from leaves deteriorate more quickly. Mineral Fibers: l Fiberglass is a fibrous form of glass. l Asbestos is a naturally occurring mineral with a crystalline structure. 7 Forensic Science: Fundamentals & Investigations, Chapter 4

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. 8 Forensic Science: Fundamentals & Investigations, Chapter 4

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. l Celenese® is cellulose chemically combined with acetate and is often found in carpets. l Polyamide nylon is cellulose combined with three acetate units, is breathable, lightweight, and used in performance clothing. l 9 Forensic Science: Fundamentals & Investigations, Chapter 4

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. 10 Forensic Science: Fundamentals & Investigations, Chapter 4

Fiber Classification— Synthetic (artificially produced) Fibers spandex nylon 11 Examples of synthetic polymer fibers: l Polyester—found in “polar fleece, ” wrinkle-resistant, and not easily broken down by light or concentrated acid; added to natural fibers for strength. l Nylon—easily broken down by light and concentrated acid; otherwise similar to polyester. l Acrylic—inexpensive, tends to “ball” easily, and used as an artificial wool or fur. l Olefins—high performance, quick drying, and resistant to wear. Forensic Science: Fundamentals & Investigations, Chapter 4

Comparison of Natural and Synthetic Fibers Visual Diagnostics of Some Common Textile Fibers under Magnification 12 Forensic Science: Fundamentals & Investigations, Chapter 4

Yarns, fabrics, and textiles l 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. l 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. 13 Forensic Science: Fundamentals & Investigations, Chapter 4

Yarns, fabrics, and textiles Weave Patterns 14 Forensic Science: Fundamentals & Investigations, Chapter 4

. . . . Summary l Fibers are spun into yarns having specific characteristics. l Yarns are woven, with different patterns, into clothing or textiles. l Fibers, trace evidence, are a form of class evidence used by crime scene investigators. l Fiber evidence may be gathered using different techniques. l Fibers may be analyzed using burn tests, tests for solubility in different solutions, polarized light microscopy, or infrared spectroscopy. 15 Forensic Science: Fundamentals & Investigations, Chapter 4