forensic analysis of fibres

Question 1

types of fibres

Answer 1

(1) natural
- animal
- plant

(2) man made
- synthetic polymer
- modified natural polymer

Question 2

examples of natural fibres

Answer 2

animals- silk
- wool cashmere mohair

plant
-cotton

Question 3

examples of synthetic fibres

Answer 3

synthetic polymer, modified natural polymer

Question 4

sections of modified nautral polymer

Answer 4

rubber, regenerated cellulose - rayon, cellulose ester - acetate, triacetate

Question 5

synthetic polymer classes

Answer 5

polyehtylene, polypropylene,
acrylic
nylon 6,
nylon 6,6

Question 6

Cellulose Fibers

Answer 6

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

Question 7

how is rayon made

Answer 7

made when wood pulp is treated with NaOH, and carbon disulfide

Question 8

how is cellulose acetate made

Answer 8

made from wood pulp, treatment with acetic acid

Question 9

nylon

6 is …

Answer 9

a polyamide from the sole monomer, caprolactam

when this molecule polymerized, the ring opens, and the molecules join up in a continuous chain

Question 10

nylon 6,6 is …

Answer 10

both the di-amine and the di-acid monomers have 6 carbon atom backbones and join together

Question 11

what is kevlar made from

Answer 11

the two monomers used to synthesis kevlar are benzene-1,4-dicarboxylic acid and 1,4 diaminobenzene

Question 12

polyester (polyethylene terephthalate)

Answer 12

produced by condensation of ethylene glycol with terephthalic acid.

Question 13

acrylic

Answer 13

produced from acrylonitrile, which polymerizes to give poly-acrolnitrile

Question 14

types of forensic fiber samples

Answer 14

textile clothing, animal hair, carpets, insulations, home textiles, ropes and cordage

Question 15

fiber identification

Answer 15

FT-IR and Ft-Raman spectroscopy

melting point determination, analysis of dyes and additives

Question 16

melting point determination

Answer 16

distinguishes between some fiber classes based on the fiber contraction, softening and melting temperatures

Question 17

melting points of nylon 6 and nylon 6,6

Answer 17

nylon 6 - 210 - 216

nylon 6,6 252-260

Question 18

colorant

Answer 18

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

Question 19

acid dyes

Answer 19

can only be used on fibres that form a positive charge in the presence of an acid (nylon, silk, wood)

Question 20

basic dyes

Answer 20

mainly applied to acrylic fibres, basic dyes are also used in the colouration of paper

Question 21

direct dyes

Answer 21

predominantly used on cotton

also used a pH indications and biological stains

Question 22

reactive dyes

Answer 22

particularly good for dyeing cotton and other cellulosic fibres

Question 23

analysis of Dyes by TLC

Answer 23

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

Question 24

AFIS systems and what it does

Answer 24

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.

Question 25

types of latent fingerprints

Answer 25

visible, invisible, moulded

Question 26

chemicals used for staining latent fingerprints

Answer 26

sudan black - a hydrophobic dye for prints left in oil, grease or wax

Question 27

chemical used for non porous surfaces

Answer 27

cyanoacrylate (superglue) fuming - uses cyanoacrylate polymerisation

Question 28

chemical that reacts with amino acids in latent fingerprints

Answer 28

ninhydrin - it is indanedione + zinc chloride.

Question 29

chemical that stains lipids such as cholesterol, fatty acids in latent fingerprints

Answer 29

Oil red O.

stain for biological samples, used on porous surfaces and can be used when surfaces is wet