Analysis of Fiber Evidence

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Presentation transcript:

Analysis of Fiber Evidence

Types of Fibers Cotton Natural Fibers: fibers derived entirely form animal or plant sources. Majority of fiber evidence found at crime scene is animal fiber. Examples: sheep (wool), goat (mohair/cashmere), camel, llamas, alpacas, and vicunas. Uses same forensic procedures as determination of species hair analysis. Predominant plant fiber is cotton. Most distinguishing feature – ribbon-like shape with twists at irregular intervals. Has almost no evidential value. Why? Wool

Types of Fibers Manufactured: fibers derived from either natural or synthetic polymers. First man-made fibers: 1911 – Rayon 1939 - Nylon Hard to distinguish between fibers due to large number of sub names. Confusing system. Ex. Polyester is also known as Dacron Fortrel Kodel Classified as generic fibers

Natural vs. Man-made polymers Regenerated Fibers: derived from cotton or wood pulp. Process Cellulose is extracted and sometimes chemically altered. Forced through sinning jet/spinneret to create fiber. Synthetic Fibers: chemically created. Formed from long chain molecules called polymers.

Polymers Substance composed of a large number of atoms that are usually arranged in repeating units called monomers. Ex. Plastic, paint, adhesive, synthetic rubber Referred to as macromolecules. Ex. Linking blocks.

Polymers Polymerization: covalently bonded monomers that create long repeating subuntis. Nylon 6,6 is an example of a polymeric clothing material, involving one of each monomer, hexamethlene diamine and adipic acid, that react to form Nylon 66.

Identification and Comparison of Manufactured Fibers Microscopic Examination: 1st step – comparison of color and diameter. A cross sectional view of fiber may be helpful. Then need to look at mixture of dyes selected to create certain shade of fiber. Other Techniques (Analytical) Chemical Composition Nylon 6 vs. Nylon 6,6 Birefringence Difference in the two indices of refraction exhibited by most crystalline materials. Infrared Absorption Absorption of infrared light in a particular pattern.

NYLON 6 VS. Nylon 6,6

Collection and Preservation Articles of clothing should be placed in separate paper bags. Carpet, rugs, and bedding are to be folded carefully to protect areas suspected of containing fibers. Wrap knife blades that may contain fibers Remove fibers from body using adhesive tape. Loose fibers are to be removed with a clean forcep and placed in a small sheet of paper, which once folded and labeled can be placed inside another container.

Atlanta Child murders – Wayne Williams