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