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Fiber Analysis

Fiber Analysis. Chapter 7. Objectives. Identify and describe common weave patterns of textile samples Compare and contrast various types of fibers through physical and chemical analysis Describe principle characteristics of common fibers used in their identification

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Fiber Analysis

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  1. Fiber Analysis Chapter 7

  2. Objectives • Identify and describe common weave patterns of textile samples • Compare and contrast various types of fibers through physical and chemical analysis • Describe principle characteristics of common fibers used in their identification • Apply forensic science techniques to analyze fibers

  3. Vocabulary • Amorphous: without a defined shape; fibers composed of a loose arrangement of polymers that are soft, elastic, and absorbing (for example, cotton) • Crystalline: regularly shaped; fibers composed of polymers packed side by side, which make it stiff and strong (for example, flax) • Direct transfer: the passing of evidence such as a fiber, from victim to suspect or vice versa

  4. Vocabulary • Fiber: the smallest possible indivisible unit of a textile, it must be at least 100 times longer than wide • Mineral fiber: a collection of mineral crystals formed into a recognizable pattern • Monomer: a small molecule that may bond to other monomers to become a polymer • Natural fiber: a fiber produced naturally and harvested from animal, plant, or mineral sources

  5. Vocabulary • Polymer: a substance composed of long chains of repeating units • Synthetic fiber: a fiber made from a man-made substance such as plastic • Secondary transfer: the transfer of evidence such as a fiber from a source (for example, a carpet) to a person (suspect), and then to another person (victim) • Textile: a flexible, flat material made by interlacing yarns (or “threads”)

  6. Vocabulary • Yarn: fibers that have been spun together

  7. Introduction • Fibers can link crime and suspect • We wear clothes, we shed fibers • Walk on carpet, sit on couch, pull on sweater • Fibers fall off or picked up • Fibers are not specific, but can be useful source of evidence

  8. Introduction • Trace evidence • Come from carpets, clothing, linens, furniture, insulation, rope • Direct transfer (suspectvictim or vic versa) • Secondary transfer (sourcesuspectvictim)

  9. Checkpoint • IF a carpet fiber were transferred from the clothing of a victim to his attacker…direct or secondary? • Secondary • Carpet went to the victim then to the attacker

  10. How Forensic Scientists Use Fibers • Early collection of fibers in an investigation is critical • In 24 hours, 95% of fibers on victim or crime scene may have been lost or fallen off • ONLY fibers that are not expected to find are investigated… • If pink fibers are found on victims clothes and suspects house has wall to wall pink carpet- the forensic scientist would NOT examine these • Value of fiber depends on uniqueness

  11. Questions for Fibers • Type of Fiber • Composition of fiber– how common or rare? What suspect of victims or part of crime scene had this type of fiber? • Fiber Color • To fibers on suspects clothing match the victims house? Is the type of dye the same? • Number of fibers found • More fibers suggest violence or longer period of contact • Where the fiber was found • Just in the house or right next to the victims body? How close can you place the suspect to the scene of the crime?

  12. Questions for Fibers • Textile the fiber originated from • Are they from a carpet? Or car upholstery? • Multiple fiber transfers • Is there one type of fiber? Or many from clothing, carpet, bedding, automobile…more types suggests longer contact or violence • Type of crime committed • Was it a kidnapping? A break and enter? A violent crime? Each type of crime has a typical pattern of fiber transfer • Time between crime and discovery of fiber • The value of fiber found is reduced with passage of time bc fibers will fall off or fibers not related can be picked up

  13. Sampling and Testing • Special vacuums, sticky tape, and forceps • WHERE the evidence is found is noted • Inaccurate and incomplete recording of evidence… inadmissible in court

  14. Sampling and Testing • 1st- FS collects small amounts, maybe one fiber from CS • Study type of fiber and characteristics of it • Shape, color • 2nd- FS match to suspect source • Car or home • Only one small tiny fiber may be recovered • Cannot do tests that damage or alter fiber

  15. Fiber and Textile Evidence • Textiles: clothing, carpets, and upholstery • Textiles are constructed by weaving, or intertwining together yarns. • Yarns are made up of fibers that have been “spun” together • NATURAL fibers • SYNTHETIC fibers

  16. You Think • What are the natural fibers you think of? • Animal fibers • Plant fibers • Seed fibers • Fruit fibers • Stem fibers • Leaf fibers • Mineral fibers • What are the synthetic fibers you think of? • Regenerated fibers • Synthetic polymer fibers • Acrylic • Olefins • Polyester • nylon

  17. Activity- Fiber Evidence Analysis • Analysis focuses on shape, size, composition, dye content, visual appearance • Color and Fiber diameter is first to be determined using a compound microscope • See striations that are not visible to the eye • Variation in color bands • Bundle of small threads, not a monofilament

  18. Natural Fibers • Animals, plants, and minerals that are mined from the ground • ANIMAL: • Hair, fur, and webbing • Made of proteins • In clothing, carpets, curtains, and bedding • Fur: fibers… though not a textile. Animal is trapped and skin is removed and treated (flexible skin that retains fur) • Used for coats and gloves

  19. Natural Fibers • Hair- brushed out of animal coat • Ex: wool from sheep • Cashmere & mohair from goats • Angora from rabbits • Hair from Camel, alpaca, and llamas • For bedding, clothing, heavy coats, carpets, bags, and furniture upholstery • Made into textiles- spun loosely- textiles shed fibers easily

  20. Natural Fibers • Silk- caterpillars are held captive, and each cocoon is unwound by hand • Shimmering appearance of silk is due to triangular structure of fiber, which scatters light like a prism • Used in clothing and bedding • Don’t shed as easily as hair fibers

  21. Plant Fibers- Natural • All contain cellulose • Become brittle over time • Seed fibers (ex cotton) • Fruit fibers (coir fiber on the outside of coconuts; used for door mats) • Stem fibers (from thick regions of stems, grows in bundles, ex: hemp, jute (too rough for clothing, used for rope, handbags, twine), flax (most common- linin)) • Leaf fibers (manilla- from banana relative abaca) • Mineral fibers (NOT protein or cellulose) fiberglass (short weak brittle fibers, insulates buildings, causes irritation); asbestos (crystalline structure, very durable, pipe coverings, break linings, ceiling tiles, floor tiles, fire resistant work clothes, shingles, siding, insulation- KNOWN Carcinogen!!!- inhalation causes cuts in throat.. leads to cancer)

  22. Synthetic (Man-made) Fibers

  23. DID YOU KNOW?? • Silk cocoons are 2.5cm long and are made from ONE fiber that may measure 1 to 2 km long! It takes 3,000 of these cocoons to make 1 square meter of fabric

  24. Sampling and Testing • FS then tries to match that fiber to the suspect source like car or home • Must perform tests that do not damage that ONE fiber • Polarizing light microscopy • Infrared spectroscopy

  25. Polarized light microscopy • Uses microscope that has special filter in it that allows the scientist to look at fiber using specific wave lenghts • Type of fiber can be determined (linen  ) • Natural fibers (wool/cotton) require only an ordinary microscope to view characteristic shape and markings • Birefringment: light property of synthetic fibers, refract light at different angles; can identify type of fiber

  26. Compound microscope • Natural fiber (cotton, wool) • See characteristic shapes and markings • Cotton looks like twisted ribbon • Wool is cylindrical and covered with scales • Linen looks like bamboo with joints • Silk looks like smooth glass rod with elliptical shapes sometimes (caused by marking with gum that is not removed)

  27. Infrared Spectroscopy • Infrared spectroscopy emits a beam that bounces off the material and returns to the instrument • How the beam of light changes reveals the chemical structure of the fiber • Fibers that LOOK alike will have a different chemical structure

  28. Burn Method • If many fibers are found, some of the fibers will be subject to destructive testing • Burn analysis • Dissolving in various liquids • Silk stops burning immediately when flame is removed (silk)

  29. QUIZ # 2 • T/F: A polymers are long chain molecules composed of smaller units called monomers • T/F: Sugar molecules form proteins • T/F: Amino acids form diamonds • T/F: ethylene forms polyethylene • T/F: catalysts cause a chemical reaction • Condensation is the loss of __________ to combine two molecules • Molecules with branching structures are very _____ (weak/strong) • Give ONE example of a natural polymer. _______________

  30. QUIZ # 2 • T/F: A polymers are long chain molecules composed of smaller units called monomers • T/F: Sugar molecules form proteins • T/F: Amino acids form diamonds • T/F: ethylene forms polyethylene • T/F: catalysts cause a chemical reaction • Condensation is the loss of WATER to combine two molecules • Molecules with branching structures are very _____ (weak/strong) • Give ONE example of a natural polymer: • Proteins • Polysaccharides • Nucleic acids • Asbestos • Graphite

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