Fibers 1 Bertino Introduction o o Fibers are

Fibers 1 Bertino

Introduction o o Fibers are used in forensic science to create a link between crime and suspect Through normal activities – – o o 2 We shed fibers We picked up fibers Very small fibers are classified as trace evidence Collecting fibers within 24 hours is critical Forensic Science: Fundamentals & Investigations, Chapter 4

How Forensic Scientists Use Fibers Fiber evaluation can show • • • 3 Type of fiber Color Possibility of violence Location of suspects Point of origin Forensic Science: Fundamentals & Investigations, Chapter 4

Sampling and Testing o o Shedding—common form of fiber transfer Microscopes reveal characteristic shapes and markings Infrared spectroscopy reveals chemical structures to differentiate similar fibers Destructive Testing Methods • • 4 Burning fibers Dissolving fibers in various liquids Forensic Science: Fundamentals & Investigations, Chapter 4

Sampling and Testing Compare fibers found on different suspects with those found at the crime scene 5 Forensic Science: Fundamentals & Investigations, Chapter 4

Fiber Classification —Natural Fibers Animal fibers (made of proteins): o Wool and cashmere from sheep o Mohair from goats o Angora from rabbits o Hair from alpacas, llamas, and camels o Silk from caterpillar cocoons (longer fiber does not shed easily) 6 Forensic Science: Fundamentals & Investigations, Chapter 4 woven wool textile

Fiber Classification —Natural Fibers Plant fibers (made of the polymer cellulose): o Absorb water o Insoluble in water o Very resistant to damage from harsh chemicals o Dissolvable only by strong acids o Becomes brittle over time 7 Forensic Science: Fundamentals & Investigations, Chapter 4

Fiber Classification —Natural Fibers Plant fibers: o Cotton—most common textile plant fiber (picture) o Coir from coconuts is durable o Hemp, jute, and flax from stems grow in bundles o Manila and sisal from leaves deteriorate more quickly 8 Forensic Science: Fundamentals & Investigations, Chapter 4

Fiber Classification —Natural Fibers Mineral Fibers: o o 9 Fiberglass—a fibrous form of glass Asbestos—a crystalline structure Forensic Science: Fundamentals & Investigations, Chapter 4

Fiber Classification —Synthetic Fibers o o 50% of fabrics are artificially produced Examples: • • • 10 Rayon Acetate Nylon Acrylic Polyester Forensic Science: Fundamentals & Investigations, Chapter 4

Fiber Classification —Synthetic Cellulose Fibers Regenerated Fibers (derived from cellulose): o Rayon – – o Celenese® – – o Cellulose chemically combined with acetate Found in many carpets Polyamide nylon – – – 11 Most common in this group Imitates natural fibers, but stronger Cellulose combined with three acetate units Breathable and lightweight Used in performance clothing Forensic Science: Fundamentals & Investigations, Chapter 4

Fiber Classification —Synthetic Polymer Fibers o Petroleum base o Very different from other fibers o Monomers join to form polymers o Fibers are spun together into yarns o No internal structures o Uniform diameters 12 Forensic Science: Fundamentals & Investigations, Chapter 4

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Fiber Classification —Synthetic Polymer Fibers o Polyester • • o “Polar fleece” spandex nylon Wrinkle-resistant 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 15 Forensic Science: Fundamentals & Investigations, Chapter 4

Fiber Classification —Synthetic Polymer Fibers o Acrylic • Inexpensive • Tends to “ball” easily • Substitute for artificial wool or fur o Olefins • High performance • Quick drying • Resistant to wear 16 Forensic Science: Fundamentals & Investigations, Chapter 4

Comparison of Natural and Synthetic Fibers Visual Diagnostics of Some Common Textile Fibers under Magnification 17 Forensic Science: Fundamentals & Investigations, Chapter 4

Yarns, fabrics, and textiles o o o Yarns—fibers (of any length, thick or thin, loose or tight) twisted or spun together Blending fibers meets different needs (e. g. , resistance to wrinkling) Fibers are woven into fabrics or textiles • • 18 Threads are arranged side by side (the warp) More threads (the weft) are woven back and forth crosswise through the warp Forensic Science: Fundamentals & Investigations, Chapter 4

Weave Patterns 19 Forensic Science: Fundamentals & Investigations, Chapter 4

Fibers as Evidence o 20 The quality of the fiber evidence depends on the ability of the criminalist to identify the origin of the fiber or at least be able to narrow the possibilities to a limited number of sources. Forensic Science: Fundamentals & Investigations, Chapter 4

As Evidence o Other morphological features that could be important in comparing fibers are: – – – 21 Lengthwise striations on the surface of the fiber The presence of delustering particles that reduce shine The cross-sectional shape of the fiber Forensic Science: Fundamentals & Investigations, Chapter 4

Cross Section 22 Forensic Science: Fundamentals & Investigations, Chapter 4

Methods for Comparision o o 23 Infrared spectrophotometry is a rapid and reliable method for identifying the generic class of fibers. The molecules that compose a manufactured fiber selectively absorb infrared light to form a characteristic pattern. Forensic Science: Fundamentals & Investigations, Chapter 4

IR Spec o 24 Fiber found on a postcard compared to FBI database Forensic Science: Fundamentals & Investigations, Chapter 4

Under the Scope o 25 A most useful physical property of fibers is that many synthetic fibers exhibit double refraction or birefringence when viewed under a polorizing microscope. Depending on the class of fiber, each polarized plane of light will have a characteristic index of refraction. Forensic Science: Fundamentals & Investigations, Chapter 4

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Collection and Preservation o 28 Need to identify what might be a carrier of fiber evidence Forensic Science: Fundamentals & Investigations, Chapter 4