Identification of Manufactured or Synthetic Fibers

Synthetic Fibers

Synthetic fibers, also known as Man-made fibers, can be made from either natural or synthetic polymers. A polymer is a substance composed of a large number of atoms that are usually arranged in repeating units. The individual basic units of structure from which a polymer is constructed are known as monomers. The first two synthetic fibers, nylon and rayon, were produced in the early 1900s. Rayon was created in 1910 in a laboratory from chopped up pieces of cellulose fiber from wood. The cellulose was then chemically treated to make it softer and forced through a special strainer known as a spinneret which produced long threads of fiber. Because Rayon is made from cellulose which is a natural product, it is not a true synthetic fiber, but rather a regenerated fiber. Regenerated fibers are man made from regenerated cellulose which comes from natural substances such as wood or cotton pulp. Examples of regenerated fibers include acetate and triacetate. True synthetic fibers are completely manufactured using polymers and includes fibers such as nylon, polyester, and acrylics. Nylon was first manufactured in 1939 by Dupont. It is the second most popular synthetic fiber, with polyester being the most common synthetic fiber. Synthetic fibers are manufactured by melting small pieces of the material and forcing them through spinnerets.

sample images of synthetic fibers

Synthetic fibers are generally more uniform and smooth along the edges compared to natural fibers.

Identification and Comparison of Man-Made Fibers

Fabrics that have been torn and can be pieced together like pieces of a puzzle are easy to match and classify as individual evidence. When that is not possible, microscopic comparison of color and diameter is necessary as well as comparison of lengthwise striations and pitting on the surface of a fiber. Viewing the cross sections of fibers is also generally helpful.

You may recall how the use of fiber evidence and probability was used in the Wayne Williams case; the combined factors of color, size, shape, microscopic appearance, chemical composition, and dye content make it very unlikely to find two different people wearing identical fabrics.

The physical characteristics of fibers may be examined by the following:

Counting the number of filaments
Calculating the density of the fiber
Evaluating the Refraction Index of the fiber
Checking the fiber for fluorescence

The chemical characteristics of fibers may be examined in the following ways:

Oxidation tests: This involves burning the fiber to evaluate the ash, behavior in the flame and any smells associated with the fiber.
pH Testing
Evaluating any residues or component parts within synthetic fibers
Chemical Decomposition tests: Treating fibers with strong acids, bases or solvents

These tests would be conducted with the evidence samples and compared with the results of standard samples from the lab or common materials. A unique fiber on a victim matched with the same type unique fiber on a suspect, or in the suspect's possession, can be compelling evidence if the fiber characteristics match in all of the above testing! Even though fiber evidence is generally considered class evidence as mentioned previously, fibers that still have matching characteristics after numerous sets of testing is very useful evidence in an investigation! This is why so much care is taken in the collection and analysis of hair and fiber evidence.

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