fibers

Fibers

Catalyst 1/7/13Take the next 5-7 minutes to put your presentation together.

1. Save each KeyNote file as LastName.FiberType” (For example, if your last name is Rodriguez, your file should be saved as Rodriguez.FiberType)

2. Email ALL KeyNote files as POWERPOINT FILES to [email protected]. (No dongle so you must email it to me.)

3. When time is called, you must be ready to go or points will be deducted.

mailto:[email protected]

Agenda 1/7/13• Catalyst• Announcements

– Extra Credit Opportunity: Create review poster of Hair chapter (more details to be posted on Edmodo)

– HW: Answer the first 10 questions of Chapter 6 checkpoint questions. DO NOT COPY FROM EACH OTHER. Answers must be unique or no credit will be given, DUE WEDNESDAY, 1/9/13/.

• Fiber Types Presentations

Fiber Types Presentations Evaluation Criteria

• Organization of presentation• Clarity of information• Ability to discuss questions• Met all criteria described in original instructions

(physical properties, chemical structure, special properties, etc.)

• Proper Citation of References

Written Response Expectations

• Be specific. – Avoid using the word “things” – what things are

you referring to? Hair? Fibers? Fingerprints?• Never start off with the phrase “in my opinion”• Write in complete sentences (with a subject and

predicate)• When asked how a piece of evidence can be useful,

describe in detail what exactly the investigator is going to do and what he/she is going to look for.

Class Points

P8: 7 (on task)

Your class can earn class points if:everyone in class:

Comes to class quietly and on time

Stays focused and on task during class

Leaves classroom neat and organized

Students are teaching other students

Majority of class participates Follows all classroom

expectations and procedures And more…

Fibers Case Study • Fibers -- Atlanta Murders (1979-1981)

Over a two-year period, 29 young African Americans were found strangled and smothered in Atlanta, Ga. Eventually, a police stakeout identified a suspect, Wayne Williams, who had a suspicious explanation for why he was on a bridge not far from where a body was found two days later. Lacking witnesses, forensic investigators built a case against Williams that was based almost entirely upon fiber and statistical evidence. Working with chemists from textile maker DuPont, they linked a fiber found in one victim’s hair to an unusual make of carpet in Williams' home, and calculated that the odds of the victim coming in contact with it in the Atlanta area were 1 in 7,792. A fragment of rayon found on another victim’s shorts was consistent with the carpeting in Williams’ station wagon, a match that had a 1-in-3,828 chance of occurring in Atlanta. Either piece of evidence left room for reasonable doubt, but the probability of both happening by coincidence was 1 in 29,827,776. Fiber evidence from other victims drove the odds up into the trillions. It took a jury less than 12 hours of deliberation to find Williams guilty, and he is now serving two life terms.

Overview of Fiber Analysis Unit• Chemical and physical structure and properties of

fibers✔– Polymers✔

• Classifying Fibers– Weave Patterns✔– Chemical structures of various fibers✔

• Identifying Fibers– Analysis of physical characteristics– Chemical tests

Objective(s) 12/18/12

• Explain why fibers are class evidence.• Distinguish and identify different types of

fibers.

Kendall/Hunt Publishing Company 10

• Considered as class evidence (WHY?)

• Have probative value (WHY?)

• Are common trace evidence at a crime scene

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

Fibers


FabricFabric is made of fibers. Fibers are made of twisted filaments.

Types of fibers and fabric:

Natural Artificial

• animal• vegetable• inorganic

• Synthesized • created from altered

natural sources (rayon)


Types of Fibers

SyntheticRayon

Nylon

Acetate

Acrylic

Spandex

Polyester

NaturalSilk

Cotton

Wool

Mohair

Cashmere


Polymers

• Synthetic 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.

Fiber Polymers• Amino acids – composed of a carboxyl group and

amino group• Amino acids chemically combine to form polypeptides

Polyester Synthesis – Polymerization Reaction

Polymer

Forensics Fiber Analysis

• 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.

Objective

We will be able to:• Analyze weave patterns• Compare and contrast the chemical structures of

different types of fibers• Explain how the chemical structure of a fiber affects

its properties

Basic Chemistry (Chemistry is EVERYWHERE. Stop the groaning and get over it.)

• Organic chemistry deals with carbon-containing compounds

• Carbon can form ______ bonds• Most atoms want ______ valence electrons• Chemical reactions occur because _________.• Electronegativity is how attractive an atom is to

electrons in a chemical bond.

COPY THIS.


Classification

Natural fibers are classified according to their origin:1. Vegetable or cellulose

2. Animal or protein

3. Mineral


Cellulose FibersCotton—vegetable fiber;

strong, tough, flexible, moisture-absorbent, not shape-retentive

Rayon—chemically altered cellulose; soft, lustrous, versatile

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


Fiber Comparison

Can you describe the difference(s) between the cotton onthe left and the rayon on the right?


Protein Fibers

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


Mineral Fibers

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

Rock wool—a manufactured mineral fiber

Fiberglass—a manufactured inorganic fiber


Synthetic FibersMade 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


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

Weave Pattern Notes

• Create a table in your notebook that looks like the one below.

Plain Twill Satin


Weave Patterns


Plain Weave

• Simplest and most common

• The warp and weft yarns pass under each other alternately

• Looks like a checkerboard


Twill Weave• The warp yarn is passed

over one to three weft yarns before going under one.

• Makes a diagonal weave pattern.

• Design resembles stair steps.

• Denim is one of the most common examples.


Satin Weave

• The yarn interlacing is not uniform

• Creates long floats

• Interlacing weave passes over four or more yarns

• Satin is the most obvious example


Knitted Fabric

• made by interlocking loops into a specific arrangement.

• formed into successive rows of loops and then drawn through another series of loops to make the fabric.

37

Filament Cross Sections

Synthetic fibers are forced out of a nozzle when they are hot, and then they are woven. The holes of the nozzle are not necessarily round; therefore, the fiber filament may have a unique shape in cross section.

Round] 4-lobed

Octalobal

Irregular

Multi-lobed

or Serrate

Trilobal

Dogbone orDumbbell

Fiber, fiber, fiber• You will be assigned a type of fiber. Research the following:

– The chemical structure of that fiber– The physical properties of that fiber– Other special properties of that fiber– How to differentiate that fiber from others

• You will take the information you have researched and create a KeyNote slide(s)– Include images/diagrams where appropriate– Use concise language and avoid using excessive text (DO

NOT JUST COPY AND PASTE)– Cite your reference(s) using MLA format

Fiber Types Presentations Evaluation Criteria

• Organization of presentation• Clarity of information• Ability to discuss questions• Met all criteria described in original instructions

(physical properties, chemical structure, special properties, etc.)

• Proper Citation of References

Group assignmentsType of Fiber Person 1 Person 2

Wool Amanda Allan

Nylon Sara Brian

Cotton Tania Lissette

Rayon Omar Rood

Acetate Jessica Stephanie

Silk Natalie Steven

Polyester Abigail Brandon

Acrylic Christopher

fibers

Documents

fiber evidence

taskyour class

class pointsp8

wayne williams

williams home

williams guilty

victims hair

piece of evidence