1. Chemical Composition of Fibers

2. Chemical Composition of Fibers
Fibers are polymers:
long chains made of simple molecules

3. Chapter 6
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.
By varying the chemical structure of the monomers or by varying the way they are joined together, polymers are created that have different properties.
As a result of these differences, forensically they can be distinguished from one another.
Kendall/Hunt

4. Natural Fibers
Wool
Polymer= Polypeptide chains (forming the protein keratin)
Monomer= amino acids (one of which is cysteine . . .cysteine contains Sulfur)

5. Natural Fibers Wool Silk
Polymer= Polypeptide chains (forming the protein keratin)
Monomer= amino acids (one of which is cysteine . . .cysteine contains Sulfur)
Silk
Polymer= protein
Monomer= amino acids (but less of a variety than wool)

6. Natural Fibers Wool Silk Cotton
Polymer= Polypeptide chains (forming the protein keratin)
Monomer= amino acids (one of which is cysteine . . .cysteine contains Sulfur)
Silk
Polymer= protein
Monomer= amino acids (but less of a variety than wool)
Cotton
Polymer= cellulose (plant)
Monomer= glucose

7. Natural Fibers Wool Silk Cotton Linen
Polymer= Polypeptide chains (forming the protein keratin)
Monomer= amino acids (one of which is cysteine . . .cysteine contains Sulfur)
Silk
Polymer= protein
Monomer= amino acids (but less of a variety than wool)
Cotton
Polymer= cellulose (plant)
Monomer= glucose
Linen
Polymer= cellulose (flax plant)
Longer chains than cotton which makes it brittle

8. Man-made Fibers Rayon Acetate
Cellulose fiber, then chemically altered, burns like cotton
Acetate
Made from a reaction between cellulose and acetic acid

9. Synthetic Fibers: Generic classification of synthetic fibers
Polyamides
—linked by amino group
Example: Nylon
Stronger and more chemically inert than natural fibers
Image from:

10. Synthetic Fibers: Generic classification of synthetic fibers
Polyamides—linked by amino group
Example: Nylon
Stronger and more chemically inert than natural fibers
Polyesters
—linked by ester group
Stronger linkage than polyamides
Linkage can be linear (flexible) or cross-linked (rigid)
Image from:

11. Synthetic Fibers: Generic classification of synthetic fibers
Polyamides—linked by amino group
Example: Nylon
Stronger and more chemically inert than natural fibers
Polyesters—lined by ester group
Stronger linkage than polyamides
Linkage can be linear (flexible) or cross-linked (rigid )
Spandex—structurally similar to polyamide
Made of segments of polyurethane connected to long segments of polyesters
Resulting spandex can stretch up to 600 times and recover original strength

12. Testing for Identification
Chapter 6
Testing for Identification
Microscopic observation
Burning—observation of how a fiber burns, the odor, color of flame, smoke and the appearance of the residue
Thermal decomposition—gently heating to break down the fiber to the basic monomers
Chemical tests—solubility and decomposition
Kendall/Hunt

13. Chapter 6
Dyes
Components that make up dyes can be separated and matched to an unknown.
There are more than 7000 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.
Kendall/Hunt

14. Collection of Fiber Evidence
Chapter 6
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 of bodies and any inanimate objects
Removed fibers should be folded into a small sheet of paper and stored in a paper bag.
Kendall/Hunt

15. Chapter 6
Fiber Evidence
Fiber evidence in court cases can be used to connect the suspect to the victim or to the crime scene. 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, car and on several murder victims.
Kendall/Hunt

16. Video clips on slide two —click on the two pictures within the chain
If link is broken, go to YouTube and search “Oil Absorbing Polymer”
Clip 2
If link is broken, go to YouTube and search “Spangler's Polymer Experiment on The Ellen Show”