Chemical Composition of Fibers

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

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

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

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

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

Man-made Fibers Rayon Acetate 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 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 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 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 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

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

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

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

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