1. Chapter 6: Fibers

2. Fibers
Fiber: is the smallest unit of a textile material woven or twisted together to form a thread or yarn.
Fibers (like hair) are among the most common items left at a crime scene.
Class evidence- mass produced by textile difficult to trace back
Probative value- can create connection btwn a victim and suspect.

3. Activity 6.1 pg. 129
Collection and observing fibers from your shirt and pants.

4. Sources & Types of Fibers
Fibers can occur naturally (plant and animal fibers) Or
Fibers can also be man-made (synthetic).

5. Types of Fabric Weave
In a weave, the lengthwise yarn is called the warp.
The crosswise yarn is called the weft or woof.
Types include:
Plain
Twill
Satin

6. Woven Fabric PLAIN Simplest and most common weave
Warp and weft pass under each other alternately
Design resembles a checkerboard

7. Woven Fabric
TWILL
Create by passing the warp yearn over one to three weft yearns before going under one
Makes a diagonal weave
Design resembles a stair steps
Denim is the most obvious example

8. Woven Fabric SATIN The yarn interlacing is not uniform
Creates long floats
Interlacing weave passes over four or more yarns
Satin is the most obvious example

9. Knitted Fabric
Knitted fabrics are made by interlocking loops into a specific arrangement. It may be one continuous thread or a combination.
Diagram:

10. Blends use of different fabrics & colors to create the warp and weft patterns.

11. Fabric Observation
Laboratory Activity 6.1
Pg. 131

12. Fibers
All fibers are made of polymers which are long chains of repeating units.
The word polymer means many (poly) units (mer).
The repeating units of a polymer are called monomers.

13. Fiber Morphology
Investigators use: 1. fiber cross section 2. chemical structure 3. synthetic polymers for forensic analysis

14. Fiber Cross Section
The cross section of a man-made fiber can be manufacturer-specific
Unusual cross sections increase fiber association.
Cross-sectional views of nylon carpet fibers as seen with a scanning electron microscope (SEM)

15. Types of Fibers Natural Synthetic Silk Polyester Cotton Rayon Wool
Mohair
Cashmere
Synthetic
Polyester
Rayon
Nylon
Acetate
Acrylic
Spandex

16. Natural Fibers
Many different natural fibers that come from plants and animals are used in the production of fabric.
Cotton fibers are the plant fibers most commonly used in textile materials
The animal fiber most frequently used in the production of textile materials is wool, and the most common wool fibers originate from sheep.

17. Natural Fibers
Wool--animal fiber from sheep, may also be goat (mohair), rabbit (angora), camel, mink, beaver
wool: composed of polypeptide keratin chains of amino acid.
main bond is sulfur which accounts for the smell of wool when burned
Wool Fibers (400X)

18. Chemical structure: Natural fibers
Silk: composed of proteins, only 2 amino acids
Silk--animal fiber produced by silkworms (cocoon)

19. Cotton
#polymers is glucose
# smell like burning leaves
# 40% of all fabric is cotton
# 60% of all clothes and furniture
# low probative value because its too common

20. Linen: made from flax plant
# Contains cellulose (fibers are longer than cotton)
# often blended with other fibers because it is brittle.

21. Synthetic Fibers
More than half of all fibers used in the production of textile materials are synthetic or man-made.
Nylon, rayon, and polyester are all examples of synthetic fibers.
*nylon and polyester are the most common
Fibers under a microscope
Cross-section of a man-made fiber
Images:

22. Synthetic Fibers Made from cellulose Rayon--first man-made fiber;
Acetate:– made from a reaction with acetic acid.

23. Synthetic Fibers (Made from derivatives of petroleum, coal and natural gas)
Acrylic- used in carpets
Spandex--elastic properties

24. Forensics of Fiber Analysis
Cross transfers of fiber often occur in cases in which there is person-to-person contact
More contact= more fiber transferred

25. Forensic Analysis
What can be used to identify and compare fibers as forensic evidence? See book pg. 135
1. fiber cross section
View through microscope
Burn test
Thermal decomposition
Refractive index
Chemical test

26. Microscopic Examination
A compound microscope: uses light
The comparison microscope (two compound microscopes joined by an optical bridge) is used for more precise identification. 
phase-contrast microscope, reveals fiber structure
Scanning electron microscope converts the emitted electrons into a photographic image for display.  This affords high resolution and depth of focus.

27. Fiber Comparison Can you tell the difference(s) between the cotton on
the left and the rayon on the right?

28. Spectrometer
The spectrometer, which separates light into component wavelengths. 
By passing light through something to produce a spectrum, the analyst can read the resulting lines, called "absorption lines." 
specific wavelengths are specific to molecules of the substance. 

29. Fiber Evidence Collection
Fibers are gathered at a crime scene with tweezers, tape, or a vacuum. 
They generally come from clothing, drapery, wigs, carpeting, furniture, and blankets. 
For analysis, they are first determined to be natural, manufactured, or a mix of both.

30. Steps of Fiber Analysis
The first step in fiber analysis is to compare color and diameter. 
Dyes can also be further analyzed with chromatography, which uses solvents to separate the dye's chemical constituents. 

31. Fiber Color
Color influences the value given to a particular fiber identification.
Often several dyes are used
How color is applied and absorbed along the length of the fiber are important comparison characteristics.
Color-fading and discoloration can also lend increased value to a fiber association.

32. Fiber Analysis

33. Testing Fibers
Burn Test: how a fiber burns, its odor, and appearance of ash.
Thermal decomposition: how a fiber breaks down when heated.
*it returns to its monomer (initial building
block)
* ex: Acetate acetic acid
litmus test will turn paper blue to red

34. Thermal Decomposition of fiber activity

35. 3) Chemical test: test the solubility and decomposition of a fabric using a strong acids (Hydrochloric acid or sulfuric acid) or strong bases (NaOCl, acetone, NaOH) – this determines the fabrics polymers. 4) Density: m/v (pg. 148). Density of water is 1.00 g/ml. Olefin is the only fabric that will float in water.

36. 5) Refractive index: bending of light as it passes from air into a solid or liquid
-- investigators measure the refractive index of an unknown sample with liquids of a known refractive index.
--place sample in different liquids until Becke line is no longer visible
liquid same index as fabric liquid w/
w/ high index low refractive
index
A B C

37. 6) Fluorescence: some fibers will fluoresce when exposed to UV light --- laundry soap and some bleach has whiting agents that cause blue light to be reflected making it appear whiter. 7)Dyes: investigators use a fabric to see if it accepts a particular dye to identify and compare it to an unknown sample

38. Rf value = distance of pigment
8) Chromatography: separation of dyes by thin layer chromatography (TLC)
Rf value = distance of pigment
distance of solvent front

39. Other test used in Fiber Analysis
9) FTIR: Fourier Transform Infrared
based on the absorption and wavelength of light in a fabrics polymer.
can be used on a single fiber
Non-destructive
10) PGS-MS: Pyrolysis Gas Chamber-Mass Spectrometry
Burns and separates each combustion product of sample
Match results of chromatogram & products to known
Can be used in short length fibers but is destructive.

40. Fiber Forensics FYI- do not copy
analyst gets only a limited number of fibers to work with—sometimes only one.
Fibers are sent to the lab for analysis.
Fibers from scene are compared to victim
Copy###
Any inconsistency (one property does not match) is sufficient to cancel association

41. Fiber Transfer and Persistence
Fibers can be used as trace evidence due to fiber transfer.
How easy the fiber is transferred is affected by:
Area of contact
the amount of pressure used
Any friction due to side to side contact
Number of passes or contacts
Kind of clothing donor/recipient was wearing
Fiber type, length and texture
History of the garment.

42. How long transfer fibers remain on victim is fiber persistence.
Time of wear and movement
What is covering the fabric
Type of activity
Weather condition
** fiber persistence decreases exponentially with time of wear.

44. A B C D E F Types of Fibers - Key Acrylic Yarn Cotton Yarn Nylon Rope
Polyester Yarn
Rayon Rope
Wool Yarn