1. Fiber Analysis
Hair and Fiber 3

2. Fiber Evidence Fiber Can be natural (plant or animal) or man-made
The smallest unit of a textile material that has a length many times greater than its diameter
Can be spun with other fibers to form a yarn (rope) that can be woven or knitted to form a fabric
Can be natural (plant or animal) or man-made
Man-made fibers now account for over ½ of all textile production

3. Forensic Value Are considered class evidence
Are common trace evidence at a crime scene
Can be characterized based on comparison of both physical and chemical properties

4. Fiber Classification
Natural fibers are classified according to their origin
Vegetable or cellulose
Animal or protein
Mineral
Some natural fibers can be altered into artificial ones
Cotton and rayon
Rayon is chemically-altered cellulose

5. Chemical Alteration
Note the differences between the cotton fiber (left) and rayon (right). Can you detect what happens in the chemical transformation process?

6. Fiber Evidence Important characteristics
Type and length of fiber
Spinning method
Fabric construction
Above characteristics can greatly affect transfer of fibers and significance as evidence
Can originate from more than clothing
Furniture, upholstery, etc.

7. Fiber Evidence Significance
Based upon clear relationships between objects associated with crime
Relative value of evidence can be based upon several factors
Type of fiber
Number of fibers
Color or variation of color
Location of fibers
Number of different fibers
Likelihood of transfer based on fiber construction

8. Fiber Evidence Useful in similar crimes to hairs
Since DNA is not found, often limited to class characteristics due to mass production
Transfer usually found through physical contact
Routinely found in vehicle accidents or on glass/screens

9. Animal Fibers Silk Technically a protein secretion
No longer found in nature
Among the most expensive fibers
Fibers are altered by changing diet of silkworm
Does not resemble typical non-human hair
Highly light reflective

10. Mineral Fibers Fiberglass Asbestos Artificially produced fiber
Natural fiber from the mineral serpentine

11. Plant Fibers Cotton Most common plant fiber
Virtually worthless as evidence if white
If dyed, the dye is more valuable than the cotton
Distinctive twisted, ribbon-like shape

12. Plant Fibers Flax Used to make linen
Distinctive lateral structures through fiber
Can be expensive

13. Plant Fibers
Ramie fiber, common in SE Asia
Hemp fiber, the strongest natural fiber
Plant fibers are based on the polymer cellulose, the chemical that forms the cell wall of plant cells
Jute fiber, also common in Asia

14. Synthetic Fibers
First introduced in 1911 (rayon) followed by nylon in 1939
Hundreds of names currently used for essentially the same artificial fibers
Generally grouped into generic names
Example: Polyester - Sold under 28 different names

15. Synthetic Fiber Chemistry
Based on polymers
Long chain molecules
Come in natural and man-made varieties
Synthetic polymers were first produced in 1909
Originally discovered by accident
When a glass rod was removed from contact with polymer, it stretched and stuck to the rod. It hardened when cooled and would stretch into long filaments

16. Synthetic Fiber Chemistry
Polymers
Well known natural polymers
Starch
Cellulose - nature of polymer provided structure to plants
Proteins - form animal hairs
Well known man-made polymers
Nylon
Teflon
Silicone
Vulcanized rubber

17. Synthetic Fiber Chemistry
Man-made polymers
Basic chemical substance of all artificial fibers
Also include most paints, plastics, adhesives, rubbers
Polymers are routinely formed from thousands of individual atoms
Composed of repeating units called monomers that link like chains

18. Synthetic Fiber Chemistry
“Classic” polymer structure of the synthetic fiber nylon. Note the long chain of repeating atoms.

19. Synthetic Fibers
In spite of common names, practically no two of the same type of fiber are manufactured the same way all the way through the production process
Positive ID almost always involves microscopy and chemical analysis
Three different scanning electron microscope images of nylon carpet fibers. Note clear structural differences at this magnification.

20. Synthetic Fiber Analysis
Identification and Comparison
Color
Based on introduced combinations of dyes
Different dyes may identify manufacturer
Diameter
Typically very little variation due to precise machinery
Cross section usually helpful as well
Production characteristics
Striations - almost always lengthwise
“Pitting” - occurs from particles added to fiber to reduce shine
Typical cross section of synthetic carpet fibers.

21. Synthetic Fiber Analysis
Production method can be single largest identifier
Cross sections are exceptionally important
Synthetic fibers are forced out of a nozzle when they are hot
Holes of the nozzle are not always round

22. Synthetic Fiber Analysis
Burning
Chemistry of fibers can cause fiber to burn in different ways
Odor, color of flame, smoke and the appearance of the residue can also be an indicator
Thermal decomposition
Gently heating can break down polymers to basic monomers
Chemical testing
Solubility and decomposition

23. Synthetic Fiber Analysis
Chemical composition
Most companies have different “formulas” for product
Product “fingerprint” can be determined if chemicals are identified
Require spectroscopy
Fibers can also be melted down into crystals and then identified
Light reflectance will be different for unique crystals
Known as crystallography
Common nylon (above) and rayon (below) fibers under polarized light

24. Synthetic Fiber Analysis
Spectroscopic analysis of two apparently identical red, cotton fibers. Note the clear chemical differences between the two dyes.