Textiles and Fibers Forensic Science: Fundamentals & Investigations, Chapter 4

A Study of Fibers and Textiles you will be able to: identify and describe common weave patterns of textile samples compare and contrast various types of fibers through physical and chemical analysis describe principle characteristics used to identify common fibers apply forensic science techniques to analyze fibers

Introduction and How Forensic Scientists Use Fibers How are fibers used in Forensic Science? To create a link between crime and suspect or to Fibers are not specific to an individual, but… often fall off and are picked up during activities and go unnoticed may provide police with evidence even if a suspect wears gloves Fibers are a form of trace evidence Where can fibers originate? Forensic Science: Fundamentals & Investigations, Chapter 4

Textile Fiber Defined Defined as the smallest part of a textile material Many objects in our environment (clothing, ropes, rugs, blankets, etc.) are composed of yarns made of textile fibers

Textile Fiber Categories Animal (hairs) Wool, cashmere, silk Vegetable Cotton, kapok, linen Mineral Asbestos Manmade Acetate, rayon, nylon, acrylic, polyester, and olefin

Fibers Vary widely in class characteristics Fibers are very useful as trace evidence: Vary widely in class characteristics color, shape, chemical composition, etc. Easily transferred from one source to another (carpets, clothes, etc.) Significant persistence (won’t degrade)

Importance of Fiber Evidence Perpetrators of crimes are not always aware or able to control the fibers they have left behind or picked up

How are fibers used as evidence? Trace > Fibers How are fibers used as evidence? As with other trace evidence, fibers can be transferred to/from a person or objects linking them to one another.

How long do fibers persist? Trace > Fibers How long do fibers persist? Most fiber evidence is lost (fall off) a short time after the transfer occurs. The fibers that do remain will be persistent.

Importance of Fiber Evidence In contrast to hair, fibers offer much greater evidential value because they incorporate numerous variables Number of fibers in each strand, diameter of strands and fibers, direction and number of twists, type of weave, and dye content, as well as foreign material embedded or adherent to the fiber

Introduction and How Forensic Scientists Use Fibers Fiber Transfer Direct Transfer Secondary Transfer Transfer occurs from victim to suspect or suspect to victim Transfer occurs from a source to the victim then to the suspect Give an example of this. Forensic Science: Fundamentals & Investigations, Chapter 4

MiniActivity: Fiber Transfer Procedures: Press the sleeves (or cuffs) or your clothing together. Examine your clothes for fiber transfer using masking tape and a hand lens. Questions: Can fibers from one sleeve be detected on the other? Do masking tape and hand lenses aid the investigation? How? Forensic Science: Fundamentals & Investigations, Chapter 4

Introduction and How Forensic Scientists Use Fibers THINK: Why are dead bodies no longer shrouded (or covered) in cotton sheets? Why are plastic body bags used instead? Forensic Science: Fundamentals & Investigations, Chapter 4

Introduction and How Forensic Scientists Use Fibers In an investigation, collection of fibers within 24 hours is critical. Why? Fiber evaluation can show such things as the type of fiber, its color, the possibility of violence, location of suspects, and point of origin. Forensic Science: Fundamentals & Investigations, Chapter 4

Introduction and How Forensic Scientists Use Fibers Questions a forensic scientist will consider when examining fiber evidence: What type of fiber is it? What is the fibers color? Number of fibers found? Where was the fiber found? Textile the fiber originated from? Are there multiple fibers transferred? What type of crime was committed? Time between crime and discovery of fibers? Forensic Science: Fundamentals & Investigations, Chapter 4

Sampling and Testing How are fibers collected? Special Vacuums Sticky Tape Forceps (tweezers) Black Lights Magnifying Glasses Forensic Science: Fundamentals & Investigations, Chapter 4

Trace > Fibers > Analysis Begin by identifying and comparing class characteristics for unknown sample (evidence) and known sample. Known Unknown

Fibers from rug in a van. Fibers found on victim. Trace > Fibers > Analysis Fibers from rug in a van. Fibers found on victim.

Sampling and Testing Weaving spun fibers (yarns) together produces clothing and many textiles. Shedding from an article of clothing or a textile is the most common form of fiber transfer. Natural fibers require only an ordinary microscope to find characteristic shapes and markings. Infrared spectroscopy can reveal something of the chemical structure of other fibers that, otherwise, may look very much alike. Forensic Science: Fundamentals & Investigations, Chapter 4

Sampling and Testing If a large quantity of fibers is found, some can be subjected to destructive tests such as burning them in a flame (see analysis key above) or dissolving them in various liquids. Crimes can be solved in this way by comparing fibers found on different suspects with those found at the crime scene. Forensic Science: Fundamentals & Investigations, Chapter 4

Fibers can be classified into three main categories: Trace > Fibers Fibers can be classified into three main categories: Natural (animal, plant, mineral) Manufactured Synthetic

Fiber Classification —Natural Fibers woven wool textile Animal fibers (made of proteins): Wool from sheep, cashmere and mohair from goats, angora from rabbits, and hair from alpacas, llamas, and camels are commonly used in textiles. Shimmering silk from caterpillar cocoons is longer and not as easily shed. Forensic Science: Fundamentals & Investigations, Chapter 4

Fiber Classification —Natural Fibers Plant fibers (made of the polymer cellulose): can absorb water. are insoluble in water. are very resistant to damage from harsh chemicals. can only be dissolved by strong acids. can be common at crime scenes because they become brittle over time. Forensic Science: Fundamentals & Investigations, Chapter 4

Fiber Classification —Natural Fibers Plant fibers: Cotton from seedpods is the plant fiber most commonly used in textiles (shown above). Coir from coconuts is durable. Hemp, jute, and flax from stems grow in bundles. Manila and sisal from leaves deteriorate more quickly. Mineral Fibers: Fiberglass is a fibrous form of glass. Asbestos is a naturally occurring mineral with a crystalline structure. Forensic Science: Fundamentals & Investigations, Chapter 4

Fiber Classification —Synthetic (artificially produced) Fibers Until the nineteenth century only plant and animal fibers were used to make clothes and textiles. Half the products produced today are artificially produced. Artificially produced fibers include rayon, acetate, nylon, acrylics, and polyesters. Forensic Science: Fundamentals & Investigations, Chapter 4

Natural Fibers: Found in nature Can be artificially colored or treated Trace > Fibers > Natural Natural Fibers: Found in nature Can be artificially colored or treated Cotton Wool Hemp

Animal Fibers Wool - Hairs from sheep Silk - comes from silkworm Most common of animal fibers Hairs are spun to form thread Silk - comes from silkworm Spun as double filament (separated before use) Because of length, doesn’t shed easily Other Hairs from Animals

Animal Fibers Woolen fibers occupy less than 1% of all fibers used in production of textile materials Wool has a microscopic structure that is characteristic of hair The cuticle (outer covering) is made of flattened cells, commonly called scales

Animal Fibers (continued) The scales resemble shingles of a roof and are one of the most useful features to ID an unknown textile fiber as wool Other animal hairs are not as frequently encountered so they can be quite valuable if they occur as evidence Include goat (cashmere, mohair), llama (alpaca, vicuna, guanaco), and camel hair

Animal Fibers Cattle and rabbit hair are found in the manufacture of certain kinds of felts Felts are made from water suspensions of randomly arranged fibers. When the fibers settle out, the water is removed and the mass of fibers is pressed to form the felt Some modern felts are no longer made exclusively from hairs but are mixtures with other fibers

Animal Fibers Silk places a distant second to wool in occurrence, and its use has decreased since development of artificial fibers Silk fibers are not very often encountered in crime investigations, probably because silk fabrics do not shed very easily

Fiber and Textile Evidence The most common fiber transfer is shedding of textiles (clothing, carpets, upholstery) Fibers can be classified as: Natural Fibers (come from animals, plants, and minerals minded from the ground) Synthetic Fibers (are man mad and are either regenerated or polymers) Forensic Science: Fundamentals & Investigations, Chapter 4

Plant Fibers Cotton - seed hairs of cotton plant Trace > Fibers > Natural Plant Fibers Cotton - seed hairs of cotton plant by far most common fiber (find almost everywhere) Under microscope, fibers resemble twisted ribbon

Vegetable Fibers Only cotton is found in any large extent in items of clothing Approximately 24% of total US textile fiber production was cotton in 1979 Other plant fibers, such as jute and sisal, are seen in various types of cordage and baggings

Vegetable Fibers Cotton fibers have a distinctive flattened, twisted microscopic appearance, which is quite characteristic The fibers resemble a twisted ribbon In mercerizing process, fibers are treated with alkali, making them swell up and become more rounded and less twisted in appearance. This process results in improved texture and feel, but the fibers are still recognizable as cotton under the microscope

Vegetable Fibers Undyed cotton fibers are so common they have little value as physical evidence Almost any surface or dust sample will be found to contain white cotton fibers Household Dust

Other Plant Fibers: Linen - stem fiber from flax plant Trace > Fibers > Natural Other Plant Fibers: Linen - stem fiber from flax plant Kapok - from seed hairs of kapok plant Other fibers - Manila, hemp, sisal, jute

Mineral Fibers Asbestos - crystalline material Used to be used for insulation Fractures into thin rods that can get into your lungs; can kill you Not used much anymore

Filament vs. Staple Filament: Long continuous fiber (like silk) Staple: Filament is cut into smaller pieces; staples are spun together to form thread (like cotton)

Manade Fibers Represent approximately 75% of total textile fiber production in US Can be defined as a fiber of a particular chemical composition that has been manufactured into a particular shape and size, contains a certain amount of various additives, and has been processed in a particular way

Manmade Fibers Within the 6 most seen of the 21 generic classifications established by the US Federal Trade Commission, there are well over a 1,000 different fiber types Therefore, numerous fiber types can be present in the composition of textile materials This is true before even considering differences in color

Fiber Classification —Synthetic (artificially produced) Fibers Regenerated Fibers (derived from cellulose): Rayon is the most common of this type of fiber. It can imitate natural fibers, but it is stronger. Celenese® is cellulose chemically combined with acetate and is often found in carpets. Polyamide nylon is cellulose combined with three acetate units, is breathable, lightweight, and used in performance clothing. Forensic Science: Fundamentals & Investigations, Chapter 4

Manufactured Fibers Regenerated Fibers Example: Rayon Cellulose is dissolved, then resolidified to form the polymer fiber Can occur in filament or staple form Example: Rayon

Synthetic Fibers Man made Can also be filament or staple Examples: Nylon and Polyester

Synthetic Fibers Acrylics More common as evidence Usually in staple form Staples spun together, similar to wool

Class characteristics Trace > Fibers > Analysis Class characteristics Color: microscopic examination Size: length and width can be measured Shape: cross section is viewed

Class characteristics Refractive Index – n. The ratio of the speed of light in air or in a vacuum to the speed of light in another medium. Other microscopic properties (PLM)

Class characteristics Chemical Composition: determined by advanced instrumentation

Fiber Classification —Synthetic (artificially produced) Fibers Synthetic Polymer Fibers: Petroleum is the basis for these fibers, and they have very different characteristics from other fibers. Monomers in large vats are joined together to form polymers. The fibers produced are spun together into yarns. They have no internal structures, and under magnification they show regular diameters. Forensic Science: Fundamentals & Investigations, Chapter 4

Fiber Classification—Synthetic (artificially produced) Fibers spandex nylon Examples of synthetic polymer fibers: Polyester—found in “polar fleece,” wrinkle-resistant, and not easily broken down by light or concentrated acid; added to natural fibers for strength. Nylon—easily broken down by light and concentrated acid; otherwise similar to polyester. Acrylic—inexpensive, tends to “ball” easily, and used as an artificial wool or fur. Olefins—high performance, quick drying, and resistant to wear. Forensic Science: Fundamentals & Investigations, Chapter 4

Comparison of Natural and Synthetic Fibers Visual Diagnostics of Some Common Textile Fibers under Magnification Forensic Science: Fundamentals & Investigations, Chapter 4

Yarns, Fabrics, and Textiles Fibers can be twisted (spun) into yarn of any length, thick or thin, loose, or tight. A blend can be made to meet different needs such as resistance to wrinkling. Fibers can be woven into fabrics or textiles. Threads are arranged side by side (the warp). More threads (the weft) then are woven back and forth crosswise in one of a number of different patterns through the warp. Forensic Science: Fundamentals & Investigations, Chapter 4

Threads, Yarn, Rope, Cordage Smallest component is fibers (staple) twisted together to form thread or is a filament. This thread can then be twisted with other threads to form a thicker thread (string, etc.) This thicker cord can then be twisted with other thicker cords, etc.

Threads, Yarn, Rope, Cordage Small cords or fibers twisted together to form larger cords At each step, the number of cords can be counted. At each step, the twist direction is either “S” or “Z”

Yarns, Fabrics, and Textiles Warp: lengthwise threads Weft: crosswise threads Weave Pattern: The pattern in which the weft passes over and under the warp. Forensic Science: Fundamentals & Investigations, Chapter 4

Forensic Science: Fundamentals & Investigations, Chapter 4

Yarns, Fabrics, and Textiles Weave Patterns Forensic Science: Fundamentals & Investigations, Chapter 4

Important to Remember: It is important to collect evidence from both complainants and suspects as soon as possible Studies show that some 80% of fibers can be expected to be lost in four hours, with just 5-10% remaining at the end of 24 hours

Methods of Examination In the recent past, the ID and comparison of fibers were at a relatively simple level which relied heavily on microscopy

From Less than 1 cm of a 20 mm Diameter Fiber It is Possible to Determine: Generic class Polymer composition Finish--bright/dull Cross-sectional shape Melting point Refractive Indices Birefringence Color Fluorescence Absorption spectrum Dye class Dye Components

Microscopy Microscopic examination provides the quickest, most accurate, and least destructive means of determining the microscopic characteristics and polymer type of textile fibers.

Microscopic View Acetate Dacron

Stereomicroscope Should be used first to examine fibers. Physical features such as crimp, length, color, relative diameter, luster, apparent cross section, damage, and adhering debris should be noted. Fibers are then tentatively classified into broad groups such as synthetic, natural, or inorganic.

Comparison Microscope If all of the characteristics are the same under the stereoscope, then the comparison microscope is used. A point-by-point and side-by-side comparison provides the most discriminating method of determining if two or more fibers are consistent with originating from the same source.

Scenario Discussions Working with a different group for each question discuss and then record your reasoning for each. What if a woman’s roommate borrowed her coat and was then involved in a crime that left textile evidence behind? How could investigators distinguish between the woman involved in the crime and the owner of the coat? Would you ever be 100% sure of the conclusion you made? Explain Forensic Science: Fundamentals & Investigations, Chapter 4