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Fabric & Fibers. Fabric. Common trace evidence Can be characterized based on comparison of both physical and chemical properties Made of fibers that are twisted filaments. Types of fibers. Natural- animal, vegetable, or inorganic Synthetic- created from altered natural sources.

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fabric
Fabric
  • Common trace evidence
  • Can be characterized based on comparison of both physical and chemical properties
  • Made of fibers that are twisted filaments
types of fibers
Types of fibers
  • Natural- animal, vegetable, or inorganic
  • Synthetic- created from altered natural sources
slide4
Synthetic Natural

Rayon Silk

Nylon Cotton

Acetate Wool

Acrylic Mohair

Spandex Cashmere

Polyester

slide5
Natural fibers are classified according to their origin:
  • Vegetable or cellulose
  • Animal or protein
  • Mineral
cellulose fibers
Cellulose Fibers

Cotton—vegetable fiber; strong, tough, flexible, moisture-absorbent, not shape-retentive

Rayon—chemically altered cellulose; soft, lustrous, versatile

Cellulose acetate—cellulose that is chemically altered to create an entirely new compound not found in nature

protein fibers
Protein Fibers

Wool—animal fiber coming most often from sheep, but may be goat (mohair), rabbit (angora), camel, alpaca, llama, or vicuña

Silk—insect fiber that is spun by a silkworm to make its cocoon; the fiber reflects light and has insulating properties

mineral fibers
Mineral Fibers

Asbestos—a natural fiber that has been used in fire-resistant substances

Rock wool—a manufactured mineral fiber

Fiberglass—a manufactured inorganic fiber

synthetic fibers
Synthetic Fibers

Nylon—most durable of man-made fibers; extremely lightweight

Polyester—most widely used man-made fiber

Acrylic—provides warmth from a lightweight, soft, and resilient fiber

Spandex—extreme elastic properties

fabric production
Fabric Production
  • Fabrics are composed of individual threads or yarns that are made of fibers and are knitted, woven, bonded, crocheted, felted, knotted, or laminated.
  • Most are either woven or knitted.
  • The degree of stretch, absorbency, water repellence, softness, and durability are all individual qualities of the different fabrics.
weave patterns
Weave Patterns

The simplest and most common weave pattern

Design resembles a checkerboard

twill weave
Twill Weave

Makes a diagonal weave pattern.

Design resembles stair steps.

Denim is one of the most common examples.

satin weave
Satin Weave

The yarn interlacing is not uniform

Creates long floats

Interlacing weave passes over four or more yarns

Satin is the most obvious example

knitted fabric
Knitted Fabric

Knitted fabrics are made by interlocking loops into a specific arrangement. It may be one continuous thread or a combination. Either way, the yarn is formed into successive rows of loops and then drawn through another series of loops to make the fabric.

polymers
Polymers

Synthetic fibers are made of polymers, which are long chains of repeating chemical units.

The word polymer means many (poly) units (mer).

The repeating units of a polymer are called monomers.

slide17

R

ound

4-lobed

Octalobal

T

rilobal

Irregular

Dogbone or

Multi-lobed

Dumbbell

or Serrate

Synthetic fibers are forced out of a nozzle when they are hot, and then they are woven. The holes of the nozzle are not necessarily round; therefore, the fiber filament may have a unique shape in cross section.

burn tests
Burn Tests
  • Observe the behavior of the flame and characteristics of the residue
  • Note:
    • How the fiber burns(quickly, curl)
    • Color of flame
    • Is it continuous burn or does it glow after removed from flame?
    • Is smoke produced? (what color)
slide20
Note Odor
    • Does it smell like hair, plastic, paper burning?

Note Residue characteristics

    • Does it form ash, melt in beads?
    • Color of ash
    • Consistency(fluffy, shiny, beaded, brittle, hard)
identification stain test
Identification Stain Test
  • Stain testing can be used and colors compared based on the chemical & physical properties of the fibers.
  • This is useful in environments where burn testing is not allowed, such as flammable chemicals present.
nitrogen testing
Nitrogen Testing
  • Nitrogen, in the form of NH3 is released as a product of the reaction.
  • It turns red litmus blue.
sulfur test
Sulfur Test
  • This is a test for wool.
  • Wool and hot NaOH causes the wool to dissolve
  • Lead from lead acetate and sulfur combine to form lead sulfide which is dark grey/black precipitate
cellulose test
Cellulose Test
  • Plants contain polysaccharide cellulose, which contains glucose molecules.
  • Sulfuric acid breaks the cellulose into glucose/
  • Use Benedict’s solution to test for the glucose.
  • You will get green, red, or yellow precipitate.
protein test
Protein Test
  • Animal fibers contain proteins.
  • Proteins contain specific bonds called a peptide bond.
  • Exposing a substance to copper sulfate and sodium hydroxide results in a purple color change if peptide bonds are present.
solubility test
Solubility Test
  • Fibers are soluble in different solvents.
  • Acetate dissolves in acetone
  • Nylon, silk, and acetate dissolve in formic acid.
absorbancy test
Absorbancy Test
  • Ability to take up water (moisture regain)
  • It is the measure of the weight of the moisture the fiber absorbs compared to the weight of the fiber alone
  • Hydrophilic- absorb water easily and swell
  • Hydrophobic –do not absorb water easily, tend not to wrinkle as much
  • Natural fibers tend to be hydrophilic
  • Synthetic tends to be hydrophobic
slide28
Dyes

Components that make up dyes can be separated and matched to an unknown.

There are more than 7,000 different dye formulations.

Chromatography is used to separate dyes for comparative analysis.

The way a fabric accepts a particular dye may also be used to identify and compare samples.

collection of fiber evidence
Collection of Fiber Evidence

Bag clothing items individually in paper bags. Make sure that different items are not placed on the same surface before being bagged.

Make tape lifts of exposed skin areas and any inanimate objects.

Removed fibers should be folded into a small sheet of paper and stored in a paper bag.