Fibers

Forensic Examination of Fibers Important evidence in incidents involving personal contact- homicide, assault, sexual Cross-transfers may occur between the clothing of a suspect and victim Hit-and-run victims can leave fibers, threads, or whole pieces of clothing on a vehicle Fibers can also become fixed in screens or glass broken during a breaking-and-entering attempt

Natural Fibers Are derived from animal or plant sources Animal fibers comprise most natural fibers encountered in crime lab exams Can include hair coverings: sheep (wool), goats (cashmere), camels, llamas Or fur fibers: obtained from mink, rabbit, beaver, etc. Most common plant fiber is cotton

Manufactured Fibers Are derived from natural or synthetic polymers They have increasingly replaced natural fibers in clothing & fabric They are made by: Processing raw material from cotton/wood pulp and extracting cellulose The cellulose may be chemically treated and dissolved in a solvent It is then forced through small holes of a spinning jet (spinneret) to produce the fiber Fibers made from natural raw materials (regenerated cellulose) are called regenerated fibers: rayon, acetate, triacetate Fibers made from synthetic chemicals are synthetic fibers: nylon, polyester, acrylic

Microscopic Exam of Fibers The first and most important step is a comparison for color & diameter by a comparison microscope Other features that may aid in the comparison are lengthwise striations (lined markings) on the surface of some fibers and pitting of the fiber’s surface with delustering particles (titanium dioxide particles added to reduce shine) Cross-sectional shape of a fiber may also help

Analytical Techniques Used Two fibers may seem to be the same color, differences may exist in the dyes applied to them when made Most fibers are dyed with a mixture of colors to obtain a desired shade Can use a visible light microspectrophotometer to compare the colors of fibers A fiber as small as 1 mm long or less can be examined

Analytical Techniques Used A more detailed analysis of the fiber’s dye composition can be obtained by a chromatographic separation of dye Small strands of fibers are compared for dye content by extracting the dye off each fiber with a solvent and then spotting the dye solution onto a thin-layer chromatography plate The dye of the questioned and standard fibers are separated on the plate and compared for similarity

Others When fibers are compared, they must be shown to have the same chemical composition (belong to the same class) For example, the standard and questioned fabric both being nylon instead of one being nylon while the other is cotton Many manufactured fibers exhibit double refraction or birefringence which will make it look crystalline Polarized white light will split into two rays that are perpendicular to each other and produce interference colors, polarization

Significance of Fiber Evidence Once a match has been determined, the significance is bound to be raised No technique can associate a fiber definitively to any single garment No database is available for determining the probability of a fiber’s origin Despite this, one should not discount the significance of a fiber match By observing what people wear, it is unlikely to find two different people wearing identically colored fabric ( exception: jeans and cotton tees) There are thousands of different colored fibers Combine this with the fact that scientists not only compare color, but also size, shape, microscopic appearance, chemical composition and dye There will still be a good chance of linking a questioned fiber to a standard

Collection and Preservation Clothing should be packaged in paper bags Each article must be placed in separate bags to prevent contamination Must keep clothing from different people from coming into contact Carpets, rugs, and bedding should be folded to protect areas suspected of containing fibers Knife blades should be covered to protect adhering fiber If a body was wrapped in a carpet or blanket, tape lifts must be done on the body If individual fibers are found, they must be removed with clean forceps and placed in a small sheet of paper, must be folded and labeled and placed in another container

Types of Fiber Cotton (ribbon-like) Nylon Polyester Rayon fibers Silk (fractures) Wool