FIBERS • Three viewpoints: • Individual strand • Thread • Fabric A fiber is the smallest unit of a textile material that has a length many times greater than its diameter. A fiber can be spun with other fibers to form a yarn that can be woven or knitted to form a fabric. The type and length of fiber used, the type of spinning method, and the type of fabric construction all affect the transfer of fibers and the significance of fiber associations. This becomes very important when there is a possibility of fiber transfer between a suspect and a victim during the commission of a crime.
FIBERS • Two types: • Natural • Synthetic • Matching unique fibers on the clothing of a victim to fibers on a suspect’s clothing can be very helpful to an investigation, whereas the matching of common fibers such as white cotton or blue denim fibers would be less helpful. • The discovery of crosstransfers and multiple fiber transfers between the suspect's clothing and the victim's clothing dramatically increases the likelihood that these two individuals had physical contact.
Natural Fibers • Animal: • Wool – sheep • Cashmere and Mohair – Goats • Silk - ???? • Plant • Cotton ** most prevalent – not very helpful • Linen- Flax • Hemp
Man-Made Fibers • Derived from polymers (natural or synthetic). • Made by forcing polymers (large molecules that are repeated) through a spinneret. • Rayon (1911) and Nylon(1939) first man-made fibers.
Man-Made Fibers Cont. • Regenerated Fibers • Made from regenerated cellulose (wood or cotton pulp) • Includes such fibers as rayon, acetate, and triacetate • Acetate – cellulose with an acetate molecule attached -celanese • Triacetate – cellulose with 3 acetate molecules - Arnel
Man-Made Fibers Cont. • Synthetic Fibers • Currently manufactured • Made from synthetic chemicals called polymers • Process of replicating the molecules is polymerization. • Include such fibers as nylons, polyesters, and acrylics • Amid and replicate it to get a polyamid – Nylon • Ester and replicate it to get a polyester • Olefin and replicate it to get polyolefin – carpets.
POLYMERS • Basic chemical substance of all synthetic fibers • Consist of long chains of repeating molecules. The repeating molecular units in the polymer are called monomers. • Often referred as macromolecules or “big” molecules • Countless varieties exist. Monomer Polymer
ID and Comparison of Man-Made Fibers • Fabrics that can be fitted together at their torn edge are easy to match • Microscopic comparison of color and diameter • The shape of the fiber—ex. Red fiber case, Wayne Williams case • Note: 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
Tools and Techniques to Aid in Comparing Fibers • Light infrared spectrophotometer—compares colors and chemical composition through spectral patterns • Chromatography—compares dye composition • Refraction—ID’s fiber by refractive index • Comparison microscope—reveals shape, coloring, pitting and striations
A B C Can you identify the types of fibers shown? D E F • Think About It … • Which samples are natural fibers? • (2) Which samples are synthetic fibers? • (3) What characteristics can be used to identify fiber samples?
A B C Acrylic Yarn Cotton Yarn Nylon Rope Types of Fibers - Key D E F Polyester Yarn Rayon Rope Wool Yarn