Forensics: Ch4 Fibers

Synthetic fiber

1/2 of fabrics purchased today are synthetic, they are categorized as regenerate fibers and polymers. These fibers are produced by first joining many monomers, or small combining molecules together to form polymers. (Rayon, acetate, nylon, acrylics, & polyester)

Mineral fibers

- Are neither proteins nor cellulose. They may not even be long, repeating polymers. - Fiberglass is a fiber form of glass. It's fibers are very short, very weak, and brittle. Rolls of fiberglass batting (layers or sheets) are used to insulate buildings. The fibers are very fine and easily stick to the skin, often causing an itchy skin rash. - Asbestos is a mineral naturally occurring in different types of rocks. It has a crystalline structure composed of long, thin fibers. Asbestos is very durable. It's many uses once included pipe covering, brake linings, ceiling tiles, floor titles, shingles, home siding, and insulation for building materials. Due to its health risks, it is no longer commonly used.

Natural fibers

- Come from animals, plants, and minerals that are mined from the ground. Fibers are composed of polymers, or long repeating molecules

Yarns

- Fibers too short in their natural state to be used to make textiles may be spun together to make yarn. (Thread) - Short cotton fibers only 2cm long can. Be twisted into very strong yarn of any length. Rope is simply a very thick yarn. Depending on their use, yarn may be spun thick or thin, loose or tight. - Some may blend fibers, such as wool and polyester, to give desired qualities such as strength or wrinkle resistance. - Any given yarn will have a direction of twist (forensic scientists analyze twist direction as part of their identification) said

Stem fibers

- Flax, jute, and hemp are all produced from the thick region of plant stems. They do not grow as single, unconnected fibers like cotton, but in bundles. These bundles extend the entire length of a plant. During processing, the bundles are separated from the stem and beaten, rolled, and washed until they separate into single fibers - Flax: is the most common stem fiber and is most commonly found in the textile linen. This material is not as popular as it once was because of its high cost. Linen is very smooth and often shiny fabric that resists wear and feels cool in hot weather. Linen is unique because it is highly crystalline, so it is a dense, strong fiber that resists rot and damage from light. - Jute: produce a textile that is too coarse for garments and is instead used to make rope, mats, and handbags. - Hemp: similar to flax and has been used for a long time in Asia for clothing. It has recently become a popular alternative to cotton in North America

Leaf fibers

- Manila: a fiber extracted from the leaves of abaca, a relative of the banana tree. The fiber bundles are taken from the surface of the leaves. A fiber bundle, composed of many fiber cells bound together can reach a length of 10ft. - Sisal: a desert plant with succulent leaves, also provides fibers, which are used for making ropes, twines, and netting. It is commonly seen as green garden twine or on farms as the twine on hay bales. These uses take advantage of the fiber's quick deterioration

Synthetic polymer fibers

- Originate with petroleum products and are non-cellulose-based fibers. The fibers are manufactured polymers that serve no other purpose except to be woven into textiles and ropes. They have no definite shape or size, and many, like polyester, may be easily dyed. Distinguishing among the synthetic fibers is easy using either a polarizing microscope or infrared spectroscopy. - Synthetic fibers may be very long or short. Their shape is determined by the shape of the spinneret and may be round, flat, clover-leaf, or even more complex. Polyester: represents a very large group of fibers with a common chemical makeup. It is found in polar fleece, wrinkle-resistant pants, and also added to many natural fibers to provide additional strength. Nylon: similar to polyester, although, easily broken down by light and concentrated acid. First introduced as an artificial silk, and synthetic pantyhose. Acrylic: often found as an artificial wool or imitation fur, acrylic has a light, fluffy feel. Acrylic clothing tends to ball or pill easily. This is inexpensive fiber. Olefins: are used in some clothing such as thermal socks and as fiberfill insulation and in carpeting, because they are quick drying and resistant to wear.

Animal Fibers

- Sources include fur, hair, and webbing. All animal fibers are made of proteins. They are used in clothing, carpets, decorative hangings such as curtains, and bedding - Fur: is not a textile but rather, an animal such as a fox or mink is trapped and the skin removed and treated. This results in a flexible skin that retinas the fur. - Hair fibers: animal hair is brushed out of the animal's coat, shred naturally and collected, or clipped. (Wool from sheep, cashmere & and mohair from goats, angora from rabbits, as well as hair from alpacas, llamas, and camels) - Hair fibers are used for articles of clothing bedding, heavy coats, carpets, bags, and furniture upholstery. When animal fibers are made into textiles, they are often loosely spun so they will feel comfortable - Silk: is collected from cocoons of the caterpillar Bombyx mori. The caterpillar are reared in captivity, and each cocoon must be carefully unwound by hand. The shimmering appearance of silk is caused by the triangular structure of fiber, which reflects some light back to your eye. (Commonly used in clothing and some bedding) Because silk fibers are very long, they tend not to shed as easily as hair fibers

Plant fibers

- Sources include seeds, fruits, stems, and leaves. - Plant fibers vary greatly in their physical characteristics; some are very thick and stiff, whereas others are very smooth, fine, and flexible. Plant fibers are often short, 2 to 5cm, and become brittle overtime. This means that small pieces of fibers are common as trace evidence at a crime scene. - Some fibers are amorphous, loosely arranged and soft, elastic, and absorbent. However, all plant fibers share the common polymer cellulose. - Cellulose is made up of simple glucose units. Proteins and cellulose have very different chemical and physical properties that allow a forensic scientist to tell animal and plant fibers apart - Plant based fibers because of the cellulose can absorb water but is insoluble (will not dissolve) in water. And are also very resistant to damage from harsh chemicals and can only be dissolved by very strong acids, such as sulfuric acid.

Textiles

- Weaving originated with basket-making. Stone Age humans used flax fibers to weave linen clothing. Wool fibers have been found dating to the Bronze Age. The oldest loom for weaving fabric was found in an Egyptian tomb dating to 4400 B.C. - Fibers are woven into textiles in their natural state, if they are long enough, or once they are spun into yarns. Weaving consists of arranging lengthwise threads (warp) side by side and close together. Crosswise threads (weft) are then pushed back and forth in a specific pattern.

Collecting fiber evidence & packaging

1. Fiber evidence is collected using tape, forceps, a vacuum, or a sticky line roller. 2. Fibers are individually removed, placed on a clean paper, and sealed inside evidence bags. The entire article of clothing or other textile from which the fiber was obtained is also rolled inside paper and sealed inside an evidence bag. Large objects such as screens or car fenders from which a fiber was removed are also boxed, sealed and sent to the crime lab for analysis. 3. Great care is take to avoid packaging evidence form different individuals together. It is important to be very accurate in recording where the fibers are found. Inaccurate or incomplete recording may cause evidence to be inadmissible in court

Sampling fiber evidence and analysis testing

1. Is identity the type of fiber and its characteristics (color, shape). The investigator compares the fiber to other fibers found at the crime scene and with fiber associated with the suspect. (When there is only one fiber as evidence, forensic scientists cannot preform tests that damage or alter the fiber in any way. 2. Sometime forensic scientists can complete a fiber analysis with a light microscope. 4 methods that can analyze fibers in more depth without damaging them are polarizing light microscopy, infrared spectroscopy, microspectrophotometry, and ultraviolet light analysis

Mineral fiber

A collection of mineral crystals formed into a recognizable pattern

Weft

A crosswise yarn or thread in a weave

Natural fiber

A fiber produced naturally and harvested from animal, plant, or mineral sources

Textile

A flexible, flat material Mae by interlacing yarns (for threads)

Warp

A lengthwise yarn or thread in a weave

Polymer

A substance composed of long chains of repeating molecules (monomers)

Fiber is...

Class evidence they are not specific to a single person. Small fibers shed from most textiles easily go unnoticed, and can therefore provide and important source of evidence

Fruit fibers

Coir is a coarse fiber obtained from the covering surrounding coconuts. The individual cells of the coir fibers are narrow, with thick walls made cellulose. When woven together, they are stronger than flax or cotton. Coir fiber is relatively waterproof, which makes it ideal for such things as doormats and baskets

Direct transfer

The passing of evidence, such as a fiber, from victim to suspect or vice versa

Seed fibers

Cotton is found in the seedpod of the cotton plant. Because of the ease with which cotton can be woven and dyed, it has been used extensively for clothing and household textiles.

Regenerated fibers

Derived from cellulose and are mostly plant in origin. The most common of this type is rayon. It is a fiber that can imitate natural fibers and generally is smooth and silky in appearance. Cellulose chemically combined with acetate produces the fiber Celanese that is used in carpets. When cellulose is combined with 3 acetate units, it forms polyamide nylon (such as Capron) a breathable, lightweight material, used in high-performance clothing

Crystalline

Geometrically shaped; fibers composed of polymers packed side by side, which makes them stiff and strong ( for example, flax)

Evaluating fiber evidence

Evidence of any kind must be evaluated, and this is especially important for fibers because they are so abundant. The value of fiber evidence in crime investigation depends on its potential uniqueness. 1. Type of fiber: composition, common or rare, what suspects or victims or part of the crime scene had this type of fiber? 2. Fiber color: do they match the suspect's clothing, or is it found in the victim's house, is the type of dye the same? 3. Number of fibers found: how many fibers were found? (More fibers suggest violence or a longer period of contact) 4. Where the fiber was found: how close can you place the suspect to the scene of the crime, or close to a victim's body? 5. Textile from which the fiber originated: carpet fibers, upholstery, or from a car? 6. Multiple fiber transfers: is there one type of fiber transferred at the crime scene? Or are there fibers from numerous sources from carpets, clothing, or bedding? 7. Type of crime committed: violence, a break-and-enter, or kidnapping? (Each type of crime has an expected pattern of contact among suspect, victim, and crime scene that will be reflected in the transfer of fibers) 8. Time between Crime and discovery of fiber: how long did the transfer take place? Unless the fiber location is undisturbed, the value of found fiber is greatly reduced with the passage of time because fibers not related to the crime can be picked up

Yarn (thread)

Fibers that have been spun together

Collection of fibers within 24 hours

Must be collected within 24 hours, an estimated 95% of all fibers may have fallen from a victim or been lost from the crime scene. Only fibers you would not expect to find in the area are investigated.

Fiber classification

Natural fibers & synthetic fibers. It is important for forensic scientists to be able to distinguish among different kinds of fibers because fibers can reveal critical information about suspects and victims and their environment

Monomer

Small, repeating molecules that can link to form polymers

Comparison of natural and synthetic fibers

Synthetic fibers are stronger than the strongest natural fibers. Unlike natural fibers, manufactured fibers are not damaged by micro organisms. A disadvantage of manufactured fibers is that they can deteriorate in bright sunlight and melt at a lower temperature then natural fibers.

Secondary transfer

The transfer of evidence such as fiber from a source (for example, a carpet) to a person (suspect), and then to another person (victim)

Amorphous

Without a defined shaper; fibers oomposed of a loose arrangment of polymers that are soft, elastic, and aborsbing (for example, cotton)

Synthetic fiber

a fiber made from a manufactured substance such as plastic

Fiber

the smallest indivisible unit of a textile, it must be at least 100 times longer than wide