Fibers 1 Bertino Introduction o o Fibers are

  • Slides: 28
Download presentation
Fibers 1 Bertino

Fibers 1 Bertino

Introduction o o Fibers are used in forensic science to create a link between

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

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

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

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

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

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

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

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: •

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 – –

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

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

13 Forensic Science: Fundamentals & Investigations, Chapter 4

13 Forensic Science: Fundamentals & Investigations, Chapter 4

14 Forensic Science: Fundamentals & Investigations, Chapter 4

14 Forensic Science: Fundamentals & Investigations, Chapter 4

Fiber Classification —Synthetic Polymer Fibers o Polyester • • o “Polar fleece” spandex nylon

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

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

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,

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

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

Fibers as Evidence o 20 The quality of the fiber evidence depends on the

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:

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

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

Methods for Comparision o o 23 Infrared spectrophotometry is a rapid and reliable method

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

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

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

26 Forensic Science: Fundamentals & Investigations, Chapter 4

26 Forensic Science: Fundamentals & Investigations, Chapter 4

27 Forensic Science: Fundamentals & Investigations, Chapter 4

27 Forensic Science: Fundamentals & Investigations, Chapter 4

Collection and Preservation o 28 Need to identify what might be a carrier of

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