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Chemical Composition of Fibers

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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  1. Chemical Composition of Fibers

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

  3. 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.

  4. 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

  5. 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

  6. 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

  7. 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

  8. Man-made Fibers • Rayon • 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: http://www.imageenvision.com/collection/fitness.html

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

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

  12. 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

  13. 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.

  14. 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.

  15. 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.

  16. 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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