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

Forensic Science: Fundamentals & Investigations, Chapter 4 2 Introduction and How Forensic Scientists Use Fibers How are fibers used in Forensic Science? – To create a link between crime and suspect. Fibers are not specific to an individual, but… – often fall off and are picked up during activities and go unnoticed – may provide police with evidence even if a suspect wears gloves Fibers are a form of trace evidence – Where can fibers originate?

Forensic Science: Fundamentals & Investigations, Chapter 4 3 Introduction and How Forensic Scientists Use Fibers Through normal activities – We shed fibers – We picked up fibers Very small fibers are classified as trace evidence

Forensic Science: Fundamentals & Investigations, Chapter 4 4 Introduction and How Forensic Scientists Use Fibers Fiber Transfer Direct TransferSecondary Transfer Transfer occurs from victim to suspect or suspect to victim Transfer occurs from a source to the victim then to the suspect Give an example of this.

Forensic Science: Fundamentals & Investigations, Chapter 4 5 Introduction and How Forensic Scientists Use Fibers Why are dead bodies no longer shrouded (or covered) in cotton sheets? Why are plastic body bags used instead?

Forensic Science: Fundamentals & Investigations, Chapter 4 6 Introduction and How Forensic Scientists Use Fibers In an investigation, collection of fibers within 24 hours is critical. – Why? Fiber evaluation can show such things as the type of fiber, its color, the possibility of violence, location of suspects, and point of origin.

Forensic Science: Fundamentals & Investigations, Chapter 4 7 Introduction and How Forensic Scientists Use Fibers Questions a forensic scientist will consider when examining fiber evidence: – What type of fiber is it? – What is the fibers color? – Number of fibers found? – Where was the fiber found? – Textile the fiber originated from? – Are there multiple fibers transferred? – What type of crime was committed? – Time between crime and discovery of fibers?

Forensic Science: Fundamentals & Investigations, Chapter 4 8 How Forensic Scientists Use Fibers Fiber evaluation can show Type of fiber Color Possibility of violence Location of suspects Point of origin

Forensic Science: Fundamentals & Investigations, Chapter 4 9 Sampling and Testing How are fibers collected? – Special Vacuums – Sticky Tape – Forceps (tweezers) – Black Lights – Magnifying Glasses

Forensic Science: Fundamentals & Investigations, Chapter 4 10 Sampling and Testing Weaving spun fibers (yarns) together produces clothing and many textiles. Shedding from an article of clothing or a textile is the most common form of fiber transfer. Natural fibers require only an ordinary microscope to find characteristic shapes and markings.

Forensic Science: Fundamentals & Investigations, Chapter 4 11 Sampling and Testing Infrared spectroscopy can reveal something of the chemical structure of other fibers that, otherwise, may look very much alike. Destructive Testing Methods Burning fibers Dissolving fibers in various liquids

Forensic Science: Fundamentals & Investigations, Chapter 4 12 Sampling and Testing Compare fibers found on different suspects with those found at the crime scene

Forensic Science: Fundamentals & Investigations, Chapter 4 13 Fiber and Textile Evidence The most common fiber transfer is shedding of textiles (clothing, carpets, upholstery) Fibers can be classified as: – Natural Fibers (come from animals, plants, and minerals minded from the ground) – Synthetic Fibers (are man mad and are either regenerated or polymers)

Forensic Science: Fundamentals & Investigations, Chapter 4 14 Fiber Classification —Natural Fibers Animal fibers (made of proteins) : Wool and cashmere from sheep Mohair from goats Angora from rabbits Hair from alpacas, llamas, and camels Silk from caterpillar cocoons (longer fiber does not shed easily) woven wool textile

Forensic Science: Fundamentals & Investigations, Chapter 4 15 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.

Forensic Science: Fundamentals & Investigations, Chapter 4 16 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.

Forensic Science: Fundamentals & Investigations, Chapter 4 17 Fiber Classification —Natural Fibers Mineral Fibers: Fiberglass—a fibrous form of glass Asbestos—a crystalline structure

Forensic Science: Fundamentals & Investigations, Chapter 4 18 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. Examples: Rayon Acetate Nylon Acrylic Polyester

Forensic Science: Fundamentals & Investigations, Chapter 4 19 Fiber Classification —Synthetic Cellulose Fibers Regenerated Fibers (derived from cellulose) : Rayon – Most common in this group – Imitates natural fibers, but stronger Celenese ® – Cellulose chemically combined with acetate – Found in many carpets Polyamide nylon – Cellulose combined with three acetate units – Breathable and lightweight – Used in performance clothing

Forensic Science: Fundamentals & Investigations, Chapter 4 20 Fiber Classification —Synthetic Polymer Fibers Synthetic Polymer Fibers Petroleum base Very different from other fibers Monomers join to form polymers Fibers are spun together into yarns No internal structures Uniform diameters

Forensic Science: Fundamentals & Investigations, Chapter 4 21 Fiber Classification —Synthetic Polymer Fibers Polyester “Polar fleece” 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 spandex nylon

Forensic Science: Fundamentals & Investigations, Chapter 4 22 Fiber Classification —Synthetic Polymer Fibers Acrylic Inexpensive Tends to “ball” easily Substitute for artificial wool or fur Olefins High performance Quick drying Resistant to wear

Forensic Science: Fundamentals & Investigations, Chapter 4 23 Comparison of Natural and Synthetic Fibers Visual Diagnostics of Some Common Textile Fibers under Magnification

Forensic Science: Fundamentals & Investigations, Chapter 4 24 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.

Forensic Science: Fundamentals & Investigations, Chapter 4 25 Yarns, Fabrics, and Textiles Warp: lengthwise threads Weft: crosswise threads Weave Pattern: The pattern in which the weft passes over and under the warp.

Forensic Science: Fundamentals & Investigations, Chapter 4 26

Forensic Science: Fundamentals & Investigations, Chapter 4 27 Yarns, Fabrics, and Textiles Weave Patterns

Forensic Science: Fundamentals & Investigations, Chapter Summary Summary.... Fibers are a form of class evidence. Fibers are a form of trace evidence. Fibers are spun into yarns having specific characteristics. Yarns are woven, with different patterns, into clothing or textiles. Fiber evidence is gathered using different techniques.

Forensic Science: Fundamentals & Investigations, Chapter Summary Summary Fibers are analyzed using burn tests, tests for solubility in different solutions, polarized light microscopy, or infrared spectroscopy. Fibers are classified as natural or synthetic. Natural fiber sources include: Animal hair Plant seeds, fruit, stems, or leaves Minerals.

Forensic Science: Fundamentals & Investigations, Chapter 4 30 Scenario Discussions Working with a different group for each question discuss and then record your reasoning for each. – What if a woman’s roommate borrowed her coat and was then involved in a crime that left textile evidence behind? – How could investigators distinguish between the woman involved in the crime and the owner of the coat? – Would you ever be 100% sure of the conclusion you made? Explain