Fiber Analysis.

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Presentation transcript:

Fiber Analysis

Crimes involving fiber evidence Homicide Battery Sexual Battery Hit and Run Burglary

Types of Fibers Natural= Derived from animal (Hair/Fur) or plant

Cotton Ribbon-like with twists and hollow Video

Silk Fibers are smooth and naturally transparent

Wool Appear round with scale-like markings Video

Other Natural Fibers Goat Mohair, cashmere Camel Llamas Alpacas Mink

Other Natural Fibers Rabbit Beaver Muskrat

Types of Fibers Man-made= Fibers derived from natural or man-made polymers

What is a polymer? A substance composed of a large number of atoms (macromolecules) arranged in repeating units of monomers

What is a monomer? Basic unit of a polymer

Types of Man-made Fibers Regenerated Fibers: Man-made but from natural sources (cotton or wood pulp to get cellulose) Ex. Rayon (First Manufactured Fiber) Acetate Triacetate

Rayon Soft, absorbent and dries quickly

Acetate Luxurious appearance, soft feel, fast drying

Triacetate

Types of Man-made Fibers Regenerated Fibers: Ex. Fiber Optics

Types of Man-made Fibers Synthetic Fibers= Made solely of chemicals Ex. Nylons Polyesters Acrylics

Nylon Strong, nonabsorbent, lustrous

Polyester Strong, Quick drying, Wrinkle-free

Acrylics Soft, warm, wool-like, quick-drying

Fiber Analysis (Easy) Jig-saw puzzle method

Fiber Analysis (Hard) Single Fibers Microscopic Comparative Studies Microscopic comparisons of color Microscopic comparisons of diameter Examination for lengthwise striations Examination for pitting (use Titanium dioxide to deluster fiber) Look at cross-sectional shape

Color Cross-sectional shape striations

Color Analysis of Fibers Compare dyes of two different fibers Use Thin-layer Chromatography

Refractive Index of Fibers Look for absence of Becke Line

Infrared Spectrophotometry and Fibers Case Study: 1979 Dr. Jeff MacDonald convicted of the murder of wife and children Claimed intruders committed act 11 years pass

Infrared Spectrophotometry and Fibers Case Study Analyzed wig fibers that were on a household brush (Claimed intruders wore wigs) FBI used infrared spectrophotometry to show that the fiber in brush matched a product of his wife

Other Tests on Fiber Flame Test Solubility Test Stain Test

Fiber Collection Identify, and preserve potential carriers of fibers

Collection Package Cloths Weapons Rugs Bedding Take adhesive tape-lifts from body