8.3 Notes8.3 Notes

FibersFibers

ObjectivesObjectives

Understand the differences between Understand the differences between natural and manufactured fibersnatural and manufactured fibers

List the properties of fibers that are more List the properties of fibers that are more useful for forensic comparisonsuseful for forensic comparisons

Describe proper collection of fiber Describe proper collection of fiber evidenceevidence

Types of FibersTypes of Fibers

Fibers important evidence in incidents that Fibers important evidence in incidents that involve personal contact involve personal contact

May be fixed on vehicle of hit and run May be fixed on vehicle of hit and run

May be fixed in screens, broken glass May be fixed in screens, broken glass

Must be able to narrow their origin to a Must be able to narrow their origin to a limited number of sources limited number of sources

May be natural or synthetic May be natural or synthetic

Natural FibersNatural Fibers

Derived from animal or plant sources Derived from animal or plant sources

Hair coverings Hair coverings

Most common fiber is cotton Most common fiber is cotton

Has a ribbon-like shape with irregular Has a ribbon-like shape with irregular interval twists interval twists

Man Made Fibers Man Made Fibers

First was rayonFirst was rayon

Grouped into major generic fibers with Grouped into major generic fibers with common trade names and characteristics common trade names and characteristics

1.1. Regenerated fibersRegenerated fibers Manufactured from natural raw materials and Manufactured from natural raw materials and

include rayon, acetate, triacetate include rayon, acetate, triacetate Produced from regenerated celluloseProduced from regenerated cellulose

Man Made Fibers cont.Man Made Fibers cont.

2.2. Synthetic fibers Synthetic fibers Include nylons, polyesters, acrylicsInclude nylons, polyesters, acrylics Composed of synthesized polymers Composed of synthesized polymers

(pages 208-209) (pages 208-209) 13 major generic fiber groups with 13 major generic fiber groups with

characteristics and domestic and industrial characteristics and domestic and industrial uses uses

PolymerPolymer

basic chemical substance of all synthetic basic chemical substance of all synthetic fibers fibers –– plastics, paints, adhesives, plastics, paints, adhesives, synthetic rubbersynthetic rubber Often referred to a macromolecules Often referred to a macromolecules ––

thousands or millions of atoms linked as large thousands or millions of atoms linked as large molecules molecules

Monomers are repeating units that make up a Monomers are repeating units that make up a polymer polymer

Identification and Comparison Identification and Comparison of Man Made Fibersof Man Made Fibers

1.1. most cases have limited number of fibers most cases have limited number of fibers for identification and comparison and for identification and comparison and therefore the criminalist must use therefore the criminalist must use comparison of standard and crime scene comparison of standard and crime scene fibers fibers

2.2. microscopic comparison for color and microscopic comparison for color and diameter using a comparison microscope diameter using a comparison microscope

3.3. lengthwise striations on the surface of lengthwise striations on the surface of some fibers and the pitting of the surface some fibers and the pitting of the surface

Identification cont.Identification cont.

4.4. dye composition is essential using a dye composition is essential using a microspectrophotometer to show the microspectrophotometer to show the same chemical composition same chemical composition

5.5. may use analysis of fiber dye through may use analysis of fiber dye through chromatographic separation and then a chromatographic separation and then a TLC TLC

6.6. both fibers (victim/suspect) must have both fibers (victim/suspect) must have same chemical composition down to the same chemical composition down to the types of fibers within each group types of fibers within each group

Identification cont.Identification cont.

7.7. most useful physical property of fibers is their most useful physical property of fibers is their double refraction due to the crystallinity of the double refraction due to the crystallinity of the finished fiber after processing finished fiber after processing

8.8. light that passes through a synthetic fiber light that passes through a synthetic fiber emerges polarized, perpendicular and parallel emerges polarized, perpendicular and parallel to the length of the fiber. This can be used to to the length of the fiber. This can be used to compare it to a refractive index of known fibers. compare it to a refractive index of known fibers.

9.9. Using a microspectrophotometer the infrared Using a microspectrophotometer the infrared analysis can also be used to determine generic analysis can also be used to determine generic class class

Collection and Preservation Collection and Preservation of Fiber Evidenceof Fiber Evidence

Must identify and preserve potential Must identify and preserve potential carriers of fiber evidence carriers of fiber evidence

Relevant articles of clothing are packaged Relevant articles of clothing are packaged carefully in paper bags separately carefully in paper bags separately

No contact between articles of clothing No contact between articles of clothing (included the surface) (included the surface)

Some fibers removed at the scene must Some fibers removed at the scene must be laid on paper be laid on paper