Forensic Analysis of Fibers

Types of Fibers Natural – fibers that come from plants or animals Man-made – fibers that come from natural or synthetic polymers animal – wool, cashmere, cotton Examples – rayon, polyester, nylon

Animal Fibers Of all the natural fibers, these are examined the most in a crime lab Examples: wool, mohair, cashmere, fur (rabbits, mink) Analysis of animal fibers is the same as analyzing hair from animals: Microscopic evaluation of color and morphology Make sure to obtain a good number of control samples to get a range of the fiber’s properties Varying thicknesses of individual hairs are evident in the photomicrograph, which also shows the different textures characteristic of this fur. Mink Fur micro.magnet.fsu.edu/.../ mink.html micro.magnet.fsu.edu/.../ mink.html Wool july2000/deedric3.htm

Plant Fibers Most abundant plant fiber is cotton (also linen) - Use as evidence can be meaningless since it is so widely used Cotton Distinguishing feature: ribbon shape, twisting at different spots

Man-made Fibers First man-made fiber created was rayon (1911) and then nylon (1939) – now are more common than natural fibers. Man-made fibers have generic names for consumers but there are several manufactures for each fiber type. Polymers- Basic chemical component of all synthetic fibers (also used to make plastics, paints, adhesives)

Man-made Fibers Polymers- Resemble a chain of repeating units (monomers) It is by changing chemical structure of one monomer that scientists have been able to create such a wide range of polymers and types of fibers Polymers are also produced naturally Ex: Proteins are made of repeating amino acids Starch and cellulose are made from repeating carbohydrate units DNA is made from repeating nucleic acids

Types of Man-made Fibers Regenerated fibers – fibers made from cellulose (component of plants and a natural polymer), which is chemically treated and placed through a machine to make the fiber. Examples: rayon and acetate Synthetic fibers – fibers that are made only from synthetic chemicals. Examples: nylon, polyester, acrylic

Identification and Comparison of Man-Made Fibers Fibers are class evidence (unless actual piece of ripped fabric can be fit back into it’s original place) Steps for Examination: -Microscopic comparison – look at color, diameter and surface characteristics of individual fibers -Additional morphological features examined are weave patterns and cross sectional shape.

Identification and Comparison of Man-Made Fibers Steps for Examination: -Look at dye composition by chromatography – separates dye molecules by size (just like electrophoresis) -Physical and chemical composition must be determined a. IR spectrophotometry – different fibers absorb radiation at specific wavelengths- provides a unique chemical “fingerprint” of fiber. b. Also perform chemical/acid tests, burn tests, strength tests, water absorbency tests. Try to narrow this down to certain class of fibers and ultimately to the manufacturer.