Fibers and Textiles Chapter 4

Objectives Identify and describe common patterns of textile samples Compare and contrast various types of fibers through physical and chemical analysis Describe principal characteristics of common fibers used in their identification Apply forensic science techniques to analyze fibers

Introduction Fibers are used in Forensic Science to create a link between crime and suspect. Fibers are a form of Trace Evidence. Direct transfer is when a fiber is transferred from victim to suspect or vice versa. Secondary transfer is a fiber that was picked up and then transferred to a suspect, or from original source to the suspect then to the victim.

How FS use Fibers Evidence of any kind should be evaluated, especially fibers because there are so many of them in each environment. Their value depends on their uniqueness White cotton fiber vs. angora fiber

Uses of Fibers Type of Fibers Fiber Color Number of Fibers Found Where Fiber was Found Textile the fiber originated from

Uses of Fibers Multiple Fiber Transfers Type of crime committed Time between crime and discovery of fiber

Sampling and Testing Fibers are gathered with special vacuums, sticky tape, and forceps. First task is to identify the fibers type and its characteristics Shape and color Polarized light microscopy Infrared Spectroscopy Large amounts of Fibers allow testing Polarized light microscopy- special filter in that allows scientist to look at the fiber using specific light wavelength. Infrared spectroscopy- emits a beam that bounces off the material an returns to the instrument - how the beam of light has changed reveals something of the chemical structure of the fiber - helping to identify the differences between fibers that look very much alike. When we have large amounts of fibers recovered, you can do a simple but destructive Burn test or dissolving them in various liquids.

Textiles The most common form of fiber transfer found at a crime scene: shredding of a textile Clothing, carpets, upholstery Constructed by weaving, or intertwining together Yarns – fibers that have been “spun” together

Fiber Classification Natural Fibers Synthetic Fibers (man-made) From animals, plants, and minerals that are minded from the ground Synthetic Fibers (man-made) Regenerated fibers and polymers. Produced by joining many monomers together to form polymers

Natural Fibers Animal Fibers Fur fibers Hair, fur, and webbing All are made of proteins Fur fibers Good donor of fibers, but not a textile Used primarily for coats and gloves

Natural Fibers Animal Fibers Cont’d Hair fibers Webbed Fibers Most popular animal fibers Brushed out, shed, collected and clipped naturally from animals Most common animal hair used in textile is Wool from sheep Webbed Fibers Silk, collected from cocoons of the caterpillar Bombyx mori Because silk fiber are very long, they tend not to shed as easily as hair fibers When animal fibers are made into textile, they are often loosely spun to feel more comfortable, making textiles that shed fibers easily. The shimming appearance of silk is caused by the triangular structure of the fiber, which scatters light as it passes through, just like a prism

Natural Fibers Plant Fibers Specialized plant cells Grouped by which part of the plant they come from Seeds, fruits, stems, and leaves Fibers differ greatly in physical characteristics Amorphous – loose arrangement of fibers that are soft, elastic, and absorbent. All plant fibers contain Cellulose Polymer the that is made up of simple glucose units Cotton is the most common plant fiber Easy way for FS to distinguish between animal and plant cells is the presence of cellulose. Cellulose can absorb water but is insoluble (will not dissolve in water), it is very resistant to damage from harsh chemicals and can only be dissolved by very strong acids, such as sulfuric acid.

Natural Fibers (plants) Seed fibers Cotton is found in the seedpod of the cotton plant. Fruit fibers Coir is a course fiber obtained fro the covering surrounding coconuts. Individual cells of coir fibers are narrow, with thick walls made of cellulose; woven together are stronger than flax or cotton. Relatively waterproof (doormats and baskets)

Natural Fibers (plants) Stem fibers Hemp, jute, and flax are all produced from the thick region of plant stems. Grow in bundles, can extend the entire length of a plant Flax is most common stem fiber and is most commonly found in the textile linen. Leaf fibers The fiber bundles are taken from the surface of the leaves, and when bound together can reach long lengths. Manila from abaca (relative of banana tree) Sisal desert plant used to make ropes, nettings and twines Linen is unique because of it is highly crystalline, high dense strong fiber that is resists rot and light damage. Jute is a textile that is too coarse for garments and is used to make ropes, mats and handbags. Hemp is similar to flax, used for a long time in Asia in clothing, becoming popular in US as an alternative to Cotton.

Natural Fibers (plants) Mineral fibers Neither protein or cellulose. Fiberglass fiber- form of glass where its fibers are very short, very weak, and brittle. Asbestos – mineral naturally occurring in rocks with a crystalline structure composed of long, thin fibers. Very durable.

Synthetic Fibers Regenerated fibers Derived from cellulose and are made mostly plant in origin. Rayon is most common. Cellulose chemically combined with acetate or 3 acetate units, form Celanese and polyamide nylon (Capron)

Synthetic Fibers Synthetic Polymer Fibers Originate with petroleum products and are non-cellulose based. 100% man-made No definite shape or size and can be easily dyed.

Synthetic Polymer Fibers Polyester Represents large group of fibers with a common chemical makeup Polar fleece, wrinkle-resistant pants, and added to many natural fibers to provide additional strength. Nylon Similar to polyester, except is easily broken down by light and concentrated acid. Acrylic Often found in artificial wool or imitation fur; light fluffy feel Olefins High-performance clothing (thermals, socks, carpets) Quick drying and resistant to wear