1. Fibers

2. Locard’s Exchange Principle
When a criminal comes in contact with an object or person, a cross-transfer of evidence occurs.
Suspect may transfer evidence to scene or pick up evidence from the scene

3. Cases involving fibers
Physical Contact (hugging, etc.)
Any physical struggle between two people
Carpet fibers adhering to shoes
Hit and run - pedestrian fibers on suspect vehicle
Primary and Secondary Transfer
Primary – direct transfer
Secondary – indirect…home: you: crime scene

4. Types of Fibers Natural Fibers Man-made Fibers (synthetic)
derived from animal, plant or mineral sources
Man-made Fibers (synthetic)
manufactured from raw materials or synthetic chemicals

5. Natural Fibers Broken into 3 classifications Animal fibers
Silk, sheep (wool), goats (mohair, cashmere), camels, horse, rabbits
Vegetable Fibers
Cotton, hemp, jute, ramie, flax, linen
Mineral Fibers
asbestos

6. Cotton Most prevalent natural fiber!!
White cotton fibers have no evidentiary value
Cotton jean fibers have little to no evidentiary value
Microscopic appearance: Ribbon-like shape with irregular twists

7. White Cotton Fibers

8. Polymers Basic chemical substance of all synthetic fibers
Assumes different chemical and physical properties
Macromolecules of thousands to millions of atoms
Huge chains of repeating monomers
Natural polymers also exist

9. Man-made Fibers
Regenerated Fibers – produced from the naturally occurring polymer, cellulose
Cellulose = repeating units of glucose
rayon
Acetate
Triacetate

10. More Man-made Fibers
Synthetic Fibers - produced from synthetic chemicals (polymers)
Nylon
Polyesters
Acrylics

11. Identification and Comparison
Microscopic Comparison
Color, diameter, lengthwise striations, delusterant particles, inclusions, fluorescence, refractive indices (parallel and perpendicular), birefringence
Polarized Light Microscopy (PLM)
Cross section shape
Microspectrophotometer (color)
Chemical composition (FT-IR)

12. Natural vs. Synthetic Thru the Microscope
Natural fibers
Usually have a “twisty” appearance
Variable diameter
NO delustrant particles
Scales and medulla (animal hairs)
Cross hatching
Synthetic fibers
Smooth edges, lengthwise striations
Consistent diameter (usually)
Very clear or has delustrant particles

13. Collection of Fiber Evidence
Post-It notes and paper packets (individual or small numbers of fibers
Tape Lifts cover large areas (i.e.. Care seats, victim’s clothing, etc.)
ALWAYS collect known samples (if several different carpets in the scene, collect a known from each one)
Package items separately to avoid cross-contamination

14. Single Fibers Collected onto a Post-It Note

16. Cross Sectioning Fibers – determine shape
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.

17. Cut square piece from edge of polypropylene heat seal bag

18. Polypropylene Piece
Fibers

19. Once the fibers are sandwiched between in the polypropylene, place another slide on top so fibers are trapped between

20. Place slides with fibers/polypropylene on hot plate and push down with micro spatula or other object until the polypropylene melts (will turn clear)
PLAY VIDEO

21. Use scalpel or razor blade to slice across to an area where good cross sections can be made (perpendicular to the fibers)

22. Hold the polypropylene with a forceps and carefully shave off thin layers from the edge (this is the most difficult step, you want to shave off layers like a deli would slice sandwich meat)

24. Good cross sections thru the microscope
20X
Good cross sections thru the microscope
40X

25. Burn Tests
Different fiber types will react differently when exposed to a flame
Some fibers fuse and shrink, some continue to burn after removal from the flame, so give off smoke, others have distinct smells when burned
The resulting ashes will also vary based on fiber type

26. Burn Tests
Silk and wool produce burning hair smell with a black crushable ash
Nylon burns slowly with melting and usually self-extinguishes to form a hard gray bead (supposedly has a celery-like odor)
Polyester burns/melts with black smoke, usually self-extinguishes to form a hard black bead (supposedly has a sweet odor)
Cotton and flax burns with an afterglow and produces a gray feathery smooth edged ash (produces a burning paper odor)

27. Solubility Tests
Acetate fibers are soluble in acetone (other fibers are not) and glacial acetic acid
Nylon fibers are soluble in hydrochloric acid

28. Class Exercises on Fibers
Mount different types/colors of fibers permanently and sketch them thru the microscope
Perform Burn tests on various fiber samples
Perform chemical tests on various chemical fibers
Make tape lifts and then compare to known fibers