Chemical composition of fibers
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Chemical Composition of Fibers. Chemical Composition of Fibers. Fibers are polymers: long chains made of simple molecules. Polymers. Synthetic fibers are made of polymers which are long chains of repeating chemical units. The word polymer means many ( poly ), units ( mer ).

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Chemical Composition of Fibers

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Chemical composition of fibers

Chemical Composition of Fibers


Chemical composition of fibers1

Chemical Composition of Fibers

Fibers are polymers:

long chains made of simple molecules


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.

  • 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.


Natural fibers

Natural Fibers

  • Wool

    • Polymer= Polypeptide chains (forming the protein keratin)

    • Monomer= amino acids (one of which is cysteine . . .cysteine contains Sulfur)

http://www.leydenglenlamb.com/photos.htm


Natural fibers1

Natural Fibers

  • Wool

    • 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)

  • http://entomology.unl.edu/images/silkworm/silkworm1.jpg


    Natural fibers2

    Natural Fibers

    • Wool

      • 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

  • http://www.texaspolicecentral.com/Texas-Patriotism.php


    Natural fibers3

    Natural Fibers

    • Wool

      • 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

  • Monomer= glucose

  • http://www.flowers-cs.com/flax.html


    Man made fibers

    Man-made Fibers

    • Rayon

      • Cellulose fiber, then chemically altered, burns like cotton

    • Acetate

      • Made from a reaction between cellulose and acetic acid


    Synthetic fibers generic classification of synthetic fibers

    Synthetic Fibers:Generic classification of synthetic fibers

    • Polyamides

      —linked by amino group

      • Example: Nylon

      • Stronger and more chemically inert than natural fibers

    Image from: http://www.imageenvision.com/collection/fitness.html


    Synthetic fibers generic classification of synthetic fibers1

    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: http://www.imageenvision.com/collection/fitness.html


    Synthetic fibers generic classification of synthetic fibers2

    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

    http://www.fingerpainrelief.com/rubber-band-therapy-for-finger-pain/


    Testing for identification

    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


    Chemical composition of fibers

    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.


    Collection of fiber evidence

    Collection ofFiber 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.


    Fiber evidence

    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.


    Video clips on slide two click on the two pictures within the chain

    Video clips on slide two—click on the two pictures within the chain

    • Clip 1

      • http://www.youtube.com/watch?v=cmlunCbBV_o&feature=related

      • If link is broken, go to YouTube and search “Oil Absorbing Polymer”

    • Clip 2

      • http://www.youtube.com/watch?v=YWoQ3D6RMXs&feature=related

      • If link is broken, go to YouTube and search “Spangler's Polymer Experiment on The Ellen Show”


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