FibersChapter 6

• all, except 4, 11

• 12, 13: see the table in the book

• hint 18: think of the small, small amount available to you

• hint: see chart on page 138

Objectives

• You will understand:

• Why fibers are class evidence.

• How fibers can be used as circumstantial evidence to link the victim, suspect, and crime scene.

• You will be able to:

• Distinguish and identify different types of fibers.

• Understand polymerization.

• Judge the probative value of fiber evidence.

• first, though, let’s look at some...

• on graph paper

• in pen

• title, purpose (your words) &procedure (“Refer to page p129”)

• Make sure you have both samples, correctly labelled (including fabric type), and accurately sketched in detail! In color!

• Good thing? *fibers they are everywhere so can easily be transferred

• Bad thing? They are everywhere, & are considered just class evidence

• But have probative value

• And are common trace evidence at a crime scene

Fibers

• fibers are wound up together to make a thread or yarn

• How yarn is made

• can be characterized based on comparison of both physical and chemical properties

• the more properties that are similar, the more likely the connection

• but get one not to match and *poof* - game over

Sources and Types of Fibers

• *fabric (again) is made of fibers

• fibers made of twisted *filaments that are either natural of artificial

• fibers are everywhere...(here wool from creepy girl’s creepy sheep, creepy rope & the material of creepy kids’ clothes and bedding and wallpaper)

• cloth, carpeting, cordage (rope, string, nets), brushes, filling materials (furniture, mattresses, optical fibers, structural materials)

• Types of fibers and fabric:

• Natural—animal, vegetable, or *inorganic

• Artificial—synthesized or created from altered natural sources

• Synthetic

• Rayon

• Nylon

• Acetate

• Acrylic

• Spandex

• Polyester

• Natural

• Silk

• Cotton

• Wool

• Mohair

• Cashmere

• before we look closely at the different types of fibers, we will briefly look at fabric...

Fabric Production

• Fabrics are composed of individual threads or yarns that are made of fibers and are knitted, woven, bonded, crocheted, felted, knotted, or laminated.

• Most are either woven or knitted.

• The degree of stretch, absorbency, water repellence, softness, and durability are all individual qualities of the different fabrics.

Weave Terminology

• *yarn —a continuous strand of fibers or filaments that may be twisted together

• *warp —lengthwise yarn

• *weft —crosswise yarn

• *blend —a fabric made up of two or more different types of fibers

• Simple - very, very simple - look at weaving

• How fabric is made...

Plain Weave

• the simplest and most common weave pattern

• the warp and weft yarns pass under each other alternately

• design resembles a checkerboard

Twill Weave

• the weft yarn is passed over one or more warp yarns before going under two or more, with a step between rows.

• makes a diagonal weave pattern.

• design resembles stair steps.

• denim is one of the most common examples.

• a famous twill pattern

Satin Weave

• interlacing weave floats over four or more yarns

• Satin itself is the most obvious example

• light is not scattered as much so appears “silky”

Knitted Fabric

• Knitted fabrics are made by interlocking loops into a specific arrangement. It may be one continuous thread or a combination. Either way, the yarn is formed into successive rows of loops and then drawn through another series of loops to make the fabric.

• How to knit... (just get the idea)

• back to fibers....

Fiber Morphology

What are important characteristics that can be used to identify and compare fibers as forensic evidence???

The Chemical Structure of Fibers

• fibers are made of polymers, which are long chains of repeating chemical units.

• The word polymer means many (poly) units (mer).

• The repeating units of a polymer are called monomers.

• By varying the chemical structure of the monomers or by varying the way they are joined together, polymers are created that have different properties.

• As a result of these differences, they can be distinguished from one another forensically.

Classification

• Natural fibers are classified according to their origin:

• Vegetable or cellulose

• Animal or protein

• Mineral

natural

• Some are based on the plant polymer material, cellulose:

• Cotton — vegetable fiber; strong, tough, flexible, moisture-absorbent, not shape-retentive

• Rayon — chemically altered tree cellulose; soft, lustrous, versatile

• Cellulose acetate — cellulose that is chemically altered to create an entirely new compound not found in nature...

natural

• cotton burns and smells like burning leaves

• is made up of long chains of cellulose

• cotton is king in fiber land (60% of clothing and home furniture made of cotton)

• downside: too much makes it tough to prove anything (low probative value)natural

• How jeans are made...

natural

natural

• linen is made from cellulose, too

• made from flax plant

• jute, also of cellulose, much coarser

• used to make burlap, rope, carpets

natural

• rayon is cellulose that has been altered

• very pure cellulose

• burns like cotton

natural

• acetates = chemically treated cellulose

• its lustrous sheen and smooth, satiny texture make it a good synthetic alternative to silk

• an “acetate” dress and a cigarette filter are made of same stuff :)

• Some are based on protein:

• Wool—animal fiber coming most often from sheep, but may be goat (mohair), rabbit (angora), camel, alpaca, llama, or vicuña

• Silk—insect fiber that is spun by a silkworm to make its cocoon; the fiber reflects light and has insulating properties

natural

• source of mohair

• (he probably can’t hold any mohair)

• a silk-like fabric or yarn made from the hair of the Angora goat.

• source of cashmere

• fine in texture, strong, light, and soft, garments made from it provide excellent insulation.

• angora rabbit

• source of angora wool

• wool is composed of polypeptide chains, helix-shaped, called keratin

• one of the amino acids is cysteine

• cysteine contains sulfur, which means stinky when burned

natural

natural

• this structure allows it to be water-insoluble, but also it has room for a lot of water to get stuck up in there

• and makes a good insulator

natural

• silk also a protein

• most is made of just two amino acids

• How silk is made

natural

• Some are based on minerals:

• Asbestos—a natural fiber that has been used in fire-resistant substances

• Rock wool—a manufactured mineral fiber

• Fiberglass—a manufactured inorganic fiber

natural

• synthetics are made from derivatives of petroleum, coal, and natural gas

• Nylon—most durable of man-made fibers; extremely lightweight

• Polyester—most widely used man-made fiber

• Acrylic—provides warmth from a lightweight, soft, and resilient fiber

• Spandex—extreme elastic properties

synthetic

• nylon = completely synthetic

• used e v e r y w h e r e

synthetic

synthetic

• polyesters have this basic monomer structure

• they are everywhere

• (Dacron is an example of a polyester)

• acrylics are all over the place, too

• (there are also Spandex and olefins and a bunch of others)

• natural and synthetic fibers seem to be everywhere! ;)

synthetic

• Synthetic fibers are forced out of a nozzle when they are hot, and then they are woven.

Fiber Cross Sections

52

Round 4-lobed

Octalobal

Irregular

Multi-lobedor Serrate

Trilobal

Dogbone orDumbbell

• The holes of the nozzle are not necessarily round; therefore, the fiber filament may have a unique shape in cross section

• the cross sections can help ID a particular sample

•work as groups

•use descriptive words found here (@ #4)

•no #5! no blends, all 100% pure fabric

•just fill out handout; the handout is your lab

•don’t use all your sample! you’ll need some for the next lab!

•don’t forget unknown!

•the handout is your lab! •don’t worry about the questions within the text this time, we’ll talk about it instead •half a wet litmus paper on the inside top •leave some sort of space for smoke to escape (prevents popping off) •after burning, let it cool on the wire mesh, then chuck it •work like a team!!!

lead acetate = no change or grey/black red litmus = no change or turns blue blue litmus = no change or turns red residue = best description

Refractive Index

• when light travels through a medium it slows down

• bottom line: when a fiber is put in something of the same refractive index, the fiber “vanishes”

• the Becke line appears as a halo if your fiber’s r.i. does not match the standard...

Becke lines

• if liquid r.i. > fiber r.i. – Becke lines appear outside the fiber edges

• if liquid r.i. = fiber r.i. – fiber seems to vanish!!!

• if liquid r.i. < fiber r.i. – Becke lines appear inside

• Refractive index: Imagine the glass stirring rod is a fiber...

Fluorescence

• some fibers fluoresce when exposed to UV

• some naturally, some by dyes, some by *optical brighteners

• these “agents” absorb UV, but re-emit in the blue end of the vis spectrum

• hence, fabrics and paper can look “whiter than white”

Other Tests of Fiber Evidence

• Fourier Transform Infrared analysis (FTIR) can be done on single fibers to figure out what it is

• Pyrolysis gas chromatography-mass spectrophotometry (PGC-MS) burns a sample and analyses the waste products, but the sample is destroyed

Collection of Fiber Evidence

• Bag clothing items individually in paper bags. Make sure that different items are not placed on the same surface before being bagged.

• Make tape lifts of exposed skin areas and any inanimate objects.

• Removed fibers should be folded into a small sheet of paper and stored in a paper bag.

• We will watch a show on this, and it will be on the quiz. :)

EOCs

• all, except 4, 11

• hint 18: think of the small, small amount available to you

• hint 20: see chart on page 138