Fiber and Soil Analysis Flashcards
what is a textile?
- flexible material consisting of network of natural or artificial fibers (yarn or thread)
- formed by weaving, knitting, crocheting, knotting, or felting
what is a fiber?
threadlike strand used for spinning yarn (smallest unit)
what is yarn?
continuous length of interlocked fibers used for manufacturing textiles
what is a thread?
multiple yarns plied together producing a long, thin strand used in sewing or weaving
what are the warp and weft of weave patterns?
- warp = threads strung over loom, holding tension while weaving
- weft = threads woven between warp threads, creating pattern and structure
- weave patterns can create very different qualities of fabric (plain, basket, satin, twill, etc.)
what do fiber-plastic fusions indicate?
forceful contact in vehicle accidents and other impacts
what does reconstruction indicate?
contact with limited suspects
what is active transfer?
copious amounts of fibers link transfer to specific, uncommon event (EX: damaged textile from tearing fabric to bind victim)
what is the difference between dyes and pigments?
- dyes = soluble; permeate fiber
- pigments = insoluble; physically and chemically unaffected
what can fiber evidence reveal?
- identification and classification (natural vs manmade, generic type and sub-type)
- manufacturing info (source textile type, manufacturer)
- physical damage and surface characteristics (circumstances, fracture match)
- comparison (color, diameter, inclusions, cross-section)
what are the categories for natural and synthetic fibers?
- natural (animal, vegetable, mineral)
- synthetic (regenerated, totally synthetic)
what are most animal fibers derived from?
proteins - hair (besides silk)
what are notable natural fibers?
- cotton (seed fiber)
- hemp (bast fibers/plant stems)
- asbestos (mineral)
what are regenerated fibers?
- type of synthetic fiber
- natural polymers which are regenerated to form longer chains (most made from cellulose)
how is cellulose regenerated?
acetylated with acetic anhydride (remove OH to allow cellulose polymers to float free)
what can synthetic fibers be made into?
plastics (Nylon 6,6)
what is the only synthetic fiber that is less dense than water?
olefins (polyethylene)
what are some of the analytical strategies for fibers?
- morphology (for natural fibers and rayon)
- color comparison (dyed fibers)
- damage (FTIR tear, cut, melt)
- surface debris (microspectrophotometry)
- solubility testing
- size
- cross-section (round, trilobal, ribbon, bean)
- delusterants (small particles to make less shiny)
- indication of processing (crimp, weave)
- birefringence
- sign of elongation
what is important when doing color comparison of fibers?
- sufficient number and variety of known samples
- should be conducted under several different lighting conditions
what is metamerism?
when color perception is affected by background in which it appears
are dyes unique between manufacturers?
no
how are synthetic fibers manufactured?
- spinnerets have multiple holes so that numerous fibers can be produced simultaneously to form continuous filaments of semi-solid polymer
- at some point after spinning, drawing occurs (filaments are stretched, pulling the molecular chains together and orienting them along fiber axis - strengthens the fiber)
what is microspectrophotometry (MSP) used for?
differentiating colors from dyes, inks, and other substances
what is polarized light microscopy (PLM) used for?
determining sign of elongation and estimate birefringence
what is Fourier transform infrared (FTIR) spectrophotometry used for?
confirmatory identification
what is soil?
- layer(s) of generally loose mineral and/or organic material that are affected by physical, chemical, and/or biological processes at or near the planetary surface
- usually holds liquids, gases, biota, and supports plants
what is the difference between soil and dirt?
soil can support life while dirt has lost the ability to support life (EX: tracked in dirt inside)
what is the organic component of soil made of? what is soil that is only comprised of organic compounds?
- humus (decayed plant and animal remains)
- peat
what is the inorganic component of soil made of? what is soil that is only comprised of inorganic compounds?
- minerals
- sand
why is soil significant in investigations?
- violent crimes often occur/end up on ground
- criminals frequently bury bodies and other evidence
- crimes involving a vehicle (especially if used to dispose of evidence in a remote location) often involve driving in soil
- soil is everywhere and varies in composition within meters not miles
- soil evidence is commonly transferred to shoes, clothing, carpets, shovels, tools, tires, wheel wells, floormats, and vehicle trunks
- soil transfers often go unnoticed
- soil varies horizontally and vertically
- most transfers only involve topsoil but can interact with other layers
how is soil used as class evidence?
- not sufficient to individualize to single location
- can refute false alibi
- can profile unknown samples to provide leads (roadside, riverbank, industrial, etc.)
how is soil evidence analyzed and compared?
- color
- texture (particle and density distribution)
- stratification (layers)
- percent organic content
- pH
- mineral identification (PLM or X-Ray Diffraction)
what are the three components of soil color?
- hue = dominant wavelength (blue, green, red, etc.)
- value = brightness
- chroma = saturation
what are the size comparisons of soil texture components?
sand (largest) then silt then clay (smallest)
how is particle size analysis of soil done?
- after drying, soil is weighed and gently shaken through series of sieves (each with finer mesh)
- contents of each sieve are weighed
how is density distribution of soil done?
- density gradient column with two immiscible liquids of different densities
- high density layered on top of low density to form gradient
- soil added to column; sink until reach neutral buoyancy
how is percent organic of soil determined?
sample dried, ground up, weighed, and pyrolyzed to be weighed again
natural soil pH reflects the combined effects of what?
- climate
- organic and mineral content
- elevation and drainage
- time of year
what has lower pH and why? silt, sand, clay
sand because water is able to pass through it more quickly
what elements have the greatest effect on pH?
Calcium, Magnesium, and Potassium (raise pH)
are areas of forest or grass more acidic?
forest
