NOTES - FIBERS FIBER EVIDENCE FIBER ANALYSIS: natural man-made Class Individual A. Types of Fibers

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1 NOTES - FIBERS FIBER EVIDENCE Easier to see than pollen or dirt Cross transfers often occur in person-to-person contact Problem: fibers are usually not unique Fiber collection: tweezers, tape, vacuum Can collect from: clothing, drapes, carpets, furniture, blankets FIBER ANALYSIS: TWO types of fibers are natural and man-made. Microscopic examination should determine if natural or man-made (sometimes very little to work with) Comparison compare fibers found at the scene to a suspect source. Class or Individual? Class comparisons between a fiber and fabric Individual compare weave pattern, match torn sections, tears and cuts in ropes A. Types of Fibers Fibers may become important evidence in incidents that involve personal contact such as homicide, assault, or sexual offenses, in which cross-transfers may occur between the clothing of suspect and victim. Fibers may also become fixed in screens or glass or parts of a vehicle. The ultimate value of fabrics as forensic evidence will depend on the criminalist s ability to narrow their origin to a limited number of sources or even to a single source. The mass production of garments and fabrics has limited the use of fabrics. 1. Natural Fibers derived from plant or animal sources. Cellulose fibers (plants): cotton, hemp, linen(flax), ramie Protein fibers (animal and insects): wool, mohair, silk, and cashmere Mineral: asbestos, fiberglass, mylar Animal fibers comprise the majority of the natural fibers in crime labs: Wool (sheep), silk, mohair and cashmere

2 (goats), camels, llamas, alpacas, and furs (mink, rabbit, beaver and muskrat) Identification and comparison of such fibers will rely solely on a microscopic examination of color and morphological characteristics. A sufficient number of standard specimens must be examined to establish the range of fiber characteristics the make up the suspect fabric. Plant Material Cellulose Fibers: Most common plant fiber is cotton.(strong, tough, flexible, moisture absorbent, not shape retentive) Wide use of undyed white cotton fibers in clothing and other fabrics has made it almost useless as evidence, but dyed cotton in different colors can be useful. Cotton is a ribbon-like shape with twists at irregular intervals.(p.207) Ramie=vegetable fiber, less flexible than cotton so often blended with cotton. Rayon=first man-made fiber, soft, lustrous, versatile fiber. Flax=vegetable fiber, processed into linen, oldest known textile, thick, coarse and less uniform than cotton. Acetate = less expensive, cellulose chains treated with acetate anhydride Silk=excreted by a silkworm to make its cocoon. A single filament fiber may be over a mile in length, fibers reflect light, have insulating properties. 2. Man-made fibers comprise half of all fibers in textile materials. Most common: polyester, nylon, acrylic, rayon, and acetate. Readily distinguished from animal fibers in that they have NO medulla or scale pattern. Have replaced most natural fibers in clothing and fabrics. The U.S. Federal Trade Commission has approved generic or family names for grouping all man-made fibers. Many generic classes are produced by several manufacturers and are sold under different trademark names: In US, polyesters are Dacron, Fortrel, and Kodel. In England, polyesters are called Terylene. (Table 8-1, p )

3 Some man-made fibers are made from cotton or wood pulp. The cellulose is extracted from them and forced through small holes to produce the new fiber. (this is called regenerated fiber) = rayon, acetate, and triacetate. Most fibers currently being made are from synthetic chemicals (these are called synthetic fibers)= nylon, polyester, and acrylics. The creation of these became possible when scientists developed a method of synthesizing long-chained molecules called polymers. First manufactured fiber was rayon in 1911, then in 1920 s cellulose acetate, nylon in The Polymer=synthetic fibers made of long strings of repeating monomers. -the basic chemical substance of all synthetic fibers. (plastics, paints, adhesives, and synthetic rubber) Polymers are macromolecules. Polymers are chains of monomers. Identification and comparison of man-made fibers: If torn edges of fabric can be fitted together, it is a virtual certainty that the fabrics were of common origin. First and most important step in examination of fiber is a microscopic comparison for color and diameter using a comparison microscope. The visible light microspectrophotometer is a good way to compare colors of fibers through spectral patterns. Fiber as small as one millimeter or less in length can be examined by this type of microscope. 4 types of nylon differ in physical shape, appearance, and dyeability. According to criminalists, a very useful physical property of fibers comes from knowing that many man-made fibers show double refraction or birefringence. Light passing through a man-made fiber comes out polarized, perpendicular, and parallel to the length of the fiber. Each polarized plane of light will have a characteristic index of refraction.

4 Infrared spectrophotometry provides a quick and reliable method for identifying the generic class, and in some cases the subclasses of fibers. Collection and Preservation of Fiber Evidence Each article of clothing must be put into a separate paper bag. Car seats should be covered with polyethylene sheets to protect fiber evidence, and knife blades should be covered to protect adhering fibers. If a body was wrapped in fabric, adhesive tape will lift off fiber strands. Clean forceps should be used to remove small pieces of fiber. Then place sample in small sheet of paper, fold and label, and place into another container. Fiber Evidence Variables to look for include: Fiber type Shape Diameter Color and variation of color # of fibers/strand # of strands Thickness of fibers dye content Amount and direction of twists Type of weave Foreign matter trapped Cross-section Petroleum plastic fibers synthetic: Nylon most durable man-made fabric, extremely light, long-chain polymer of amide groups. Polyester most widely used man-made fiber, long-chain polymer made of primarily dihydric alcohol ester and terephthalic acid. Acrylic warm, light-wt., soft, resilient fabric; long chain polymer of mainly acrylonitrile units. Spandex elastic properties, long chain polymer of segmented polyurethane.

5 Fabric Production Fabrics are composed of individual threads that are either o knitted, o woven, o bonded, o crocheted, o felted, o knotted, or o laminated. Most fabrics are woven or knitted. Characteristics that are affected by how the fabric is made include: stretch, absorbency, water repellence, softness, and durability.