forensic analysis of fibres Flashcards
types of fibres
(1) natural
- animal
- plant
(2) man made
- synthetic polymer
- modified natural polymer
examples of natural fibres
animals- silk
- wool cashmere mohair
plant
-cotton
examples of synthetic fibres
synthetic polymer, modified natural polymer
sections of modified nautral polymer
rubber, regenerated cellulose - rayon, cellulose ester - acetate, triacetate
synthetic polymer classes
polyehtylene, polypropylene,
acrylic
nylon 6,
nylon 6,6
Cellulose Fibers
cellulose is an insoluble linear polymer of β-(1,4)-D-glucopyranose units (2000 - 14000 residues)
the conformation of beta linked glucopyranose residues stabilizes the chair structure, minimizing its felxibility
how is rayon made
made when wood pulp is treated with NaOH, and carbon disulfide
how is cellulose acetate made
made from wood pulp, treatment with acetic acid
nylon
6 is …
a polyamide from the sole monomer, caprolactam
when this molecule polymerized, the ring opens, and the molecules join up in a continuous chain
nylon 6,6 is …
both the di-amine and the di-acid monomers have 6 carbon atom backbones and join together
what is kevlar made from
the two monomers used to synthesis kevlar are benzene-1,4-dicarboxylic acid and 1,4 diaminobenzene
polyester (polyethylene terephthalate)
produced by condensation of ethylene glycol with terephthalic acid.
acrylic
produced from acrylonitrile, which polymerizes to give poly-acrolnitrile
types of forensic fiber samples
textile clothing, animal hair, carpets, insulations, home textiles, ropes and cordage
fiber identification
FT-IR and Ft-Raman spectroscopy
melting point determination, analysis of dyes and additives
melting point determination
distinguishes between some fiber classes based on the fiber contraction, softening and melting temperatures
melting points of nylon 6 and nylon 6,6
nylon 6 - 210 - 216
nylon 6,6 252-260
colorant
the term colorant is used to describe both dyes and pigments
dye is a soluble coloured substance that has an affinity to the fibre while
pigment is completely insoluble
acid dyes
can only be used on fibres that form a positive charge in the presence of an acid (nylon, silk, wood)
basic dyes
mainly applied to acrylic fibres, basic dyes are also used in the colouration of paper
direct dyes
predominantly used on cotton
also used a pH indications and biological stains
reactive dyes
particularly good for dyeing cotton and other cellulosic fibres
analysis of Dyes by TLC
dye components are separated by their differential migration affected by a mobile phase
for positive identification, the dye extracted from the fiber must match a standard dye in colour and Rf value
AFIS systems and what it does
is the automated fingerprint identification systems,
the afis computer system detects fingerprint characteristics and forms a algorithm to compare all fingerprints in the data base.
types of latent fingerprints
visible, invisible, moulded
chemicals used for staining latent fingerprints
sudan black - a hydrophobic dye for prints left in oil, grease or wax
chemical used for non porous surfaces
cyanoacrylate (superglue) fuming - uses cyanoacrylate polymerisation
chemical that reacts with amino acids in latent fingerprints
ninhydrin - it is indanedione + zinc chloride.
chemical that stains lipids such as cholesterol, fatty acids in latent fingerprints
Oil red O.
stain for biological samples, used on porous surfaces and can be used when surfaces is wet
