1. Fiber Analysis

2. Fiber Evidence
Fiber
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

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
Plant
Animal
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

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

9. Animal Fibers Silk Technically a protein secretion
Among the most expensive fibers
Fibers are altered by changing diet of silkworm

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
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

13. 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

14. 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.

15. 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
Typical cross section of synthetic carpet fibers.

16. 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

17. Questions The most common type of plant fiber is…
cotton b) wool c) mohair d) hemp

18. What are the three main categories of natural fibers?

19. In plant-based fibers, the polymer _____________ is the major component of the fiber. This polymer is composed of the monomer ____________.

20. https://www. youtube. com/watch
While watching the video, write a paragraph on how investigators collect and analyze fibers as evidence. How has fiber evidence been useful in crime scene investigations? Give examples.