CHAPTER 6- FIBERS

Fibers

  1. ______
  2. ______
  3. ______
  4. Can be characterized based on comparison of both physical and chemical properties

Fabric

  1. ______
  2. ______
  3. Types of fibers and fabric:

-Natural—______

-Artificial—______

Types of Fibers

Synthetic

______

______

______

______

______

______

Natural

______

______

______

______

______

Classification

Natural fibers are classified according to their origin:

  1. ______
  2. ______
  3. ______

Cellulose Fibers

  1. Cotton—______
    ______
  2. Rayon—______
    ______
  3. Cellulose acetate—______
    ______

Fiber Comparison

Describe the difference(s) between the cotton on the left and the rayon on the right.

______

Protein Fibers

  1. Wool—______
    ______
  2. Silk—______
    ______

Mineral Fibers

  1. Asbestos—______
    ______
  2. Rock wool—______
  3. Fiberglass—______

Synthetic Fibers

Made from derivatives of ______

  1. Nylon—______
  2. Polyester—______
  3. Acrylic—______
  4. Spandex—______

Man-made Fibers

Fibers derived from ______

–

–

SUMMARY QUESTIONS:

Read p. 128-135 in the textbook

1)Why are fibers valuable at a crime scene?

______

2)How do fibers have probative value?

______

3)How are fabrics made?

______

4)What are the different characteristics of a fiber, a filament & a fabric?

______

5)Are inorganic fibers natural or synthetic? Name two.

______

Fabric Production

  1. ______
  2. Most are either ______or ______
  3. ______

Weave Terminology

  1. Yarn—______
    ______
  2. Warp—______
  3. Weft—______
  4. Blend—______
    ______

Weave Patterns

Plain Weave

  1. ______
  2. ______
  3. Design resembles a ______

Twill Weave

  1. ______
  2. ______
  3. Design resembles ______
  4. ______is one of the most common examples.

Satin Weave

  1. ______
  2. ______
  3. ______
  4. ______is the most obvious example

Knitted Fabric

  1. ______
  2. It may be one continuous thread or a combination.
  3. ______

Polymers

  1. Synthetic fibers are made of ______
    ______
  2. The word polymer means many (poly) units (mer).
  3. ______
  4. By varying the ______or by ______, polymers are created that have different properties.
  5. As a result of these differences, they can be distinguished from one another forensically.

Filament Cross Sections

  1. ______
  2. The holes of the nozzle are not necessarily round; therefore, the fiber filament may have a unique shape in cross section.

Summary Questions:

Read p. 136-143 in the textbook

  1. What is the monomer of a polymer?

______

  1. What is the monomer of wool? In silk? In cotton?

______

  1. List four synthetic fibers.

______

  1. What is the most common natural fiber used in textiles? The most common synthetic fiber?

______

  1. Why does wool have a distinctive smell when it is burned?

______

  1. How is silk produced?

______

  1. Why is silk a simpler structure than wool?

______

  1. What is rayon?

______

  1. How are acetate fibers made? What products are formed from acetate fibers?

______

  1. Why was the discovery of Nylon 66 important?

______

  1. Which of the fabrics found in Activity 6.3 would have the most probative value in an investigation? Which would have the least? Explain.

______

  1. How are the properties of a linear polymer different from a cross-linked polymer?

______

  1. Identify the two types of acrylic fibers and their uses.

______

  1. What is the structure of spandex (Lycra)

What is the significance of fiber evidence?

  1. Can prove ______
  2. Can prove ______
  3. Value is dependent on:

•______

•______

•______

•______

Fiber as trace evidence

Primary Transfer

______

Secondary Transfer

______

Using fibers to reconstruct crime scenes

  1. ______
  2. The ______& ______of the fabric.
  3. Mobility of victim

•______

  1. The length of time between actual physical contact.

•______

Testing for Identification

  1. Microscopic observation
  2. Burning — ______
    ______
  3. Thermal decomposition — ______
    ______
  4. Chemical tests — ______
  1. Density — the _____ of an object divided by the ______of the object
  2. Refractive index — ______
    ______
  3. Fluorescence — ______
    ______

Dyes

  1. Components that make up dyes can be separated and matched to an unknown.
  2. There are more than ______
  3. ______
  4. ______

Collection of Fiber Evidence

  1. ______
  2. ______
  3. ______

Fiber Evidence

  1. ______
  2. In the case of Wayne Williams, fibers weighed heavily on the outcome of the case. Williams was convicted in 1982 based on carpet fibers that were found in his home, in his car, and on several murder victims.

Problems with Fiber Evidence

  1. Class Characteristic

•______

  1. The less common the fiber the more useful it is to identify a suspect.

•______

Basic Comparison of Fiber Samples

  1. ______
  2. ______
  3. ______
  4. ______
  5. ______

Summary Questions:

Read p. 144-161 in the textbook

1)Can a fiber be individualized to a particular textile fabric? Why of how?

______

2)Can a piece of fabric be individualized to a particular garment? Why or how?

______

3)If an unknown fiber is suspended in a solution with a density of 1.30, what might the fiber be?

______

4)If the same fiber in question 3 is found to have a refractive index of 1.53, what might it be?

______

5)How is the Becke line used to determine Refractive Index?

______

6)Explain how an optical brightener may change how light reacts with fibers.

______

7)If a fiber disappears in castor oil, what might it be?

______

8)How is chromatography used in identifying the make up of dyes?

______

9)What is trace evidence? What is the common basis for analyzing trace evidence, that is, what are the goals?

______

10)During a trial, what are the primary concerns in analyzing and using extremely small bits of trace evidence?

______

11)How do forensic scientists use FTIR to analyze fibers?

______

12)How does the FBI use a crook’s jeans to catch them?

______

13)How did Fibers & their analysis play a major role in the Amanda Davis case?

______