fibers · synthetic (man-made) fibers regenerated fibers (modified natural fibers) – derived from...
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Fibers
Fibers
Used to create a link between a crime and a suspect
Form of trace evidence Direct transfer – fibers transferred
directly from victim to suspect or vice versa
Secondary transfer – fibers transferred from an original source to a suspect and then to a victim
Questions about Fibers
What type of fiber? Fiber color? Number of fibers found? Where fiber was found. Textile the fiber originated from Multiple fiber transfers? Type of crime committed. Time between crime and discovery of
fiber
Collection of Fibers
Fibers are collected with special vacuums, sticky tape and forceps
Analysis of Fibers
Nondestructive Polarizing light microscopy – can look at the
fiber using specific light wavelengths Infrared spectroscopy – emits a beam that
bounces off the material…how the beam changes reveals the chemical structure of the fiber, helpful for i.d.
Destructive Burn test Dissolving in solvents
Fiber Classification
Fibers are either natural or synthetic Natural fibers – come from animals,
plants and minerals that are mined from the ground
Synthetic fibers – man-made fibers include rayon, acetate, nylon, acrylics and polyesters
Animal Fibers
Used in clothing, carpets, decorative hangings and beddings
Consist of hair (wool from sheep, cashmere and mohair from goats, angora from rabbits), fur, and silk (collected from cocoons)
Plant Fibers
Used in a number of household products
All plant fibers contain cellulose which has different characteristics than animal fibers Cellulose is insoluble in water (won’t
dissolve), resistant to damage from harsh chemicals, and can only be dissolved by very strong acids, like sulfuric acid
Plant Fibers (continued)
Seed Fibers – cotton, found in seedpod of cotton plant. Used for clothing and household textiles
Fruit Fibers – coir, fiber from the covering of coconuts. When woven, it is very strong and waterproof. Used for doormats and baskets
Plant Fibers (continued)
Stem fibers – hemp, jute, flax. Flax is most common, found in linen (clothes, tablecloths). Jute is coarse, used to make rope, mats and handbags. Hemp is becoming a popular alternative to cotton.
Leaf fibers – used as the twine on hay bales (deteriorate quickly)
Mineral fibers – ex, fiberglass, asbestos, both used for insulation
Synthetic (man-made) Fibers
Regenerated fibers (modified natural fibers) – derived from cellulose and are mostly plant in origin. Rayon, Celanese (used in carpets) and Capron (used in high-performance clothing)
Synthetic polymer fiber – totally man-made. Polyester (found in polar fleece, wrinkle-resistant pants), nylon (easily brokne down by light and acid), acrylic(inexpensive…pills easily), olefins (quick drying) used in thermal socks and carpets
Yarns
Fibers that have been spun together
Any given yarn will have a direction of twist and the twist direction is helpful in identification.
Textiles
Any flexible, flat material made by interlacing yarns (or “threads”)
Weaving – consists of arranging lengthwise threads (the warp) side by side and close together, weaved with crosswise threads (the weft) in one of several different patterns
Weave Patterns
1. Plain or tabby weave – checkerboard Each weft passes over one warp before going under the
next one (1/1 weave)
2. Twill weave One weft passes over three warps, then under one, with
each row shifting over one (3/1 weave)
3. Satin weave One weft passes over three or more warps, then under
one (3/1, 4/1, 5/1 or 6/1)
Thread count – the number of threads packed together
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