Unit 6 - Fibers Flashcards
Can fiber evidence have probative value?
Yes
Characteristics of synthetic fibers
Uniform and regular shape of cross section
Stronger
More chemically inert
Can a piece of fabric be individualized to a particular garment?
Yes, but only if the piece fits a tear or rip in the garment.
Can a fiber be individualized to a particular garment?
No. Fibers are class evidence.
Difference between a fabric and a fiber
Fabric - made from fibers
Fibers - made of twisted elements that are either natural or artificial.
Is silk synthetic or natural?
Natural
Most common type of natural fiber
Cotton
Most common type of synthetic fiber
Nylon
Can an investigator use the way a fabric accepts a specific dye to identify and compare samples?
Yes
Optical microscopy
The most important method of fiber identification
Involves polarizing light and comparison microscopes
Electropherogram
Plot of results from an analysis done by electrophoresis
Natural fibers
Cotton Wool Linen Silk Cashmere Jute
Synthetic Fibers
Nylon Polyester Acrylic Plastic Rayon Acetate Dacron
Polymer
A molecule consisting of many repeating units. Can be naturally occurring or synthetic.
Are all fibers polymers?
Yes
What types of tests can be used to test the dye in a particular fiber?
Chemical tests or chromotography
Is linen natural or synthetic?
natural
For there to be an association between a questioned fiber and an unknown fiber, what percentage of tests you run on the two samples must have identical results?
100% One off means the two fibers cannot be associated.
What was the first truly synthetic fiber to be discovered and sold?
Nylon
What fiber will fluoresce under ultraviolet light?
Cotton
The Amanda Davies case showed the importance of what?
fiber transfer
First person convicted on the basis of fiber evidence
Wayne Williams
Tests that can be done in lab to analyze fibers (in addition to what we did in class)
refractive index,
any type of chromotography,
optical microscopy
any infrared study
Properties that should be examined when comparing two fibers
birefringence diameter color cross-section fluorescence
Fibers that come from plant sources
Linen
Cotton
Fibers that come from animal sources
Asbestos
Mineral wool
Difference between a synthetic fiber and a natural fiber
synthetic fibers - man made through chemical alteration of natural fibers
natural fibers - produced by plants or animals
What does wool smell like when it is burned?
burning hair
Becke line
a light colored halo that appears around an object when it is immersed in a liquid of a different refractive index
Blend
a fabric composed of two or more different types of fiber, usually as warp and weft
Chromatography
a method of separating components of mixtures based on preferential absorption or partitioning of components in a gas, liquid, or solution
Chromatogram
the record of chromatographic separation
Density
a physical property of matter
D = M/V
Elute
in chromatography, to extract one material from another, usually by means of a solvent
Filament
single strands of material, usually twisted or bonded together to form a thread or yarn
Fluorescence
the absorption of light at one wavelength and its remission at a longer wavelength
Plain
simplest and most common weave. The warp and weft yarns pass under each other alternating
Twill
the warp yarn is passed over one to three weft yarns before going under one.
Makes a diagonal weave pattern
Satin
yarn lacing is not uniform. Creates long floats
Interlacing weaves pass over four or more yarns.
Viscosity
the resistance of fluid to flow
Warp
the lengthwise yard or thread in a weave
Weft
the crosswise yarn or thread in a weave; also called the woof.
Yarn
a continuous strand of fibers or filaments, either twisted or not
