1. Physical Aspects of Forensic Science
Fiber Analysis
Physical Aspects of Forensic Science .

2. Fiber Evidence
A fiber is the smallest unit of a textile material that has a length many times greater than its diameter. A fiber can be spun with other fibers to form a yarn that can be woven or knitted to form a fabric.
The type and length of fiber used, the type of spinning method, and the type of fabric construction all affect the transfer of fibers and the significance of fiber associations. This becomes very important when there is a possibility of fiber transfer between a suspect and a victim during the commission of a crime.
Matching unique fibers on the clothing of a victim to fibers on a suspect’s clothing can be very helpful to an investigation, whereas the matching of common fibers such as white cotton or blue denim fibers would be less helpful.
The discovery of cross transfers and multiple fiber transfers between the suspect's clothing and the victim's clothing dramatically increases the likelihood that these two individuals had physical contact.

3. 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.

4. 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.
Fibers under a microscope
Cross-section of a man-made fiber
Images:

5. Fibers 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)

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

7. 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

8. 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.

9. 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.

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

11. 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

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

13. 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

14. 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

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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

21. 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

22. 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

23. 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

24. 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

25. 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)

26. 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

27. 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

28. 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

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

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

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

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

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

34. 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)

35. Class characteristics
Chemical Composition: determined by advanced instrumentation

36. 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.

37. 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”

38. Fiber
niso
nll n
Biref
MP (ºC) K1
1.518 to 1.528
1.544 to 1.551
1.505 to 1.516
0.035 to 0.039
Does not melt K2
1.777 to 1.877
2.050 to 2.350
1.641 to 1.646
0.200 to 0.710 K3
1.512 to 1.521
1.510 to 1.520
1.512 to 1.525 to
-0.005 K4
1.538 to 1.539
1.530 to 1.539 to
-0.002
192 – 210 K5
1.533 to 1.545
1.568 to 1.583
1.515 to 1.526
0.049 to 0.061
210 – 230 K6
1.540 to 1.541
1.577 to 1.582
0.056 to 0.063
250 – 264 K7
1.522
1.553
1.507
0.046
182 – 186 K8
1.535 to 1.539
1.568 to 1.574
1.518 to 1.522
0.050 to 0.052
133 – 138 K9
1.567 to 1.575
1.632 to 1.642
1.534 to 1.542
0.098 to 0.102
282 – 290
K10
1.474 to 1.478
1.474 to 1.479
1.473 to 1.477
0.002 to 0.005
245 – 260 Q
1.520
1.515
1.513
-0.003

39. 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

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

41. 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

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

43. Microscopic View
Acetate Dacron

44. 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.

45. 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.

46. Comparison Microscopy
Side-by-side Comparison
Bright Field Adjustment

47. Comparison Microscopy
Characterization
Fluorescence
Chemical factors
Environmental factors

48. Comparison Microscope
Comparisons should be made under the same illumination conditions at the same magnifications.
This requires color balancing the light sources.
A balanced neutral background color is optimal.

49. Fluorescence Microscopy
The sample is illuminated by ultraviolet light, causing some phases to fluoresce so they can be observed, counted, sized and mapped.
Kevlar fibers in complex composite material strongly fluoresce.

50. Polarized Light Microscope
Perhaps the most versatile of all microscopes; allows the analyst to actually see and manipulate the sample of interest.
Refractive indices, birefringence, and dispersion can all be quantitatively determined.

51. Microspectrophotometry
To the unaided eye, 2 dyes may be identical.
Using a grating spectrometer, light absorbed by or reflected from a sample is separated into its component wavelengths, and intensity at each wavelength plotted.

52. Microspectrophotometry
Microscope linked to a Spectrophotometer
IR Absorption spectrum
UV/VIS Absorption Spectrum

53. Microspectrophotometry
IR spectography identifies generic subtypes indistinguishable by microscopic exam
Use of IR microscopes coupled with Fourier transform infrared (FT-IR) spectrometers has greatly simplified the IR analysis of single fibers

54. Microspectrophotometry
Advantages
Nondestructive
Not limited to sample size
Disadvantages
Reactive dyes
Chemical composition
Tentative identification

55. Scanning Electron Microscopy
SEM with energy dispersive spectroscopy(EDS) is used as an imaging and microanalytical tool in characterization of fibers.
Surface morphology can be examined with great depth of field at continually variable magnifications.

56. Thin-Layer Chromatography
An inexpensive, simple, well-documented technique that can be used (under certain conditions) to complement the use of visible spectroscopy in comparisons of fiber colorants.
Dye components are separated by their differential migration caused by a mobile phase flowing through a porous, adsorptive medium.

57. TLC (continued)
Should be considered for single-fiber comparisons only when it is not possible to discriminate between the fibers of interest using other techniques, such as comparison microscopy (brightfield and fluorescence) and microspectrophotometry in the visible range

58. TLC (continued) Technique Extraction of dyes Solid stationary phase
Liquid moving phase
Capillary action
Chromatogram

59. TLC (continued) Interpretation Rf (retention factor) Color Proportions
Scanning densitometer
peak height ratios
Fluorescence

60. TLC (continued) Analysis of Chromatograms Positive association
Exclusion
Inconclusive