Forensics Vocab

fibers

fibers

usually made up of many filaments twisted or bonded together to form a thread or yarn

textiles

fabrics woven in a distinctive pattern

class evidence

can only be associated with a group of items that share properties or characteristics

probative value

are able to create connections. the ability of evidence to prove something is relevant to the crime

generic

related to an entire group or class of products; not having a brand name

ligature

something used to knot or bind - can be important to forensic scientists

fabric

a cloth material made up of fibers woven or bonded together in a distinctive manner

filament

single strands of material, usually twisted with other filaments to make a thread or fiber

inorganic

refers to substances not composed primarily of hydrocarbons, that is carbon and hydrogen (ex. asbestos + fiberglass)

olefin

term used for hydrogen containing a carbon - carbon double bond (ex. ethylene, H2C = CH2)

yarn

a continuous strand of fibers or filaments, either twisted or not

warp

the lengthwise yarn or thread in a weave

weft or woof

the crosswise yarn or thread in a weave

blend

a fabric made up of two or more different types of fibers, usually as warp and weft

polymer

giant molecules created when simple molecules called monomers are chemically joined together (ex. mineral silicates, DNA + RNA, cellulose, starch, and keratin)

monomer

simple molecules

polypeptide

a biochemical polymer formed by linking amino acids; the longer chains are called proteins

helix

a spiral arrangement, like a corkscrew, of a long-chain molecule

keratin

the main protein in all animal hair, including human hair

amino acid

contain nitrogen - general compounds containing nitrogen can break down to form ammonia (NH3) - basic

sericulture

raising of silkworms - began in china in 2640 BC

cellulose

starch, makes up cotton, and polysaccharide consisting of chains of glucose monomers.

rayon

natural fibers that have been chemically altered - very pure cellulose fiber and burns like cotton, can be found in beds, blankets, curtains, etc.

acetate

natural fibers that have been chemically altered made from cellulose through reaction with acetic acid - used in making blouses, dresses, draperies, upholstery, cigarette filters, and more

plastics

substances that flow under heat and pressure and can, therefore, be molded into various shapes. All are polymers, but not all polymers are plastics

polyester

can be classified by generic names that describe their chemical type. Produced from a dialcohol and a diaacid (ex. wool and silk)

homopolymer

acrylic fibers often used in sweatshirts polymers made up of are type of repeating unit each is made from one monomer only

polyether

series of carbon atoms connected by oxygen atoms, such as: CO-CH2-CH2n, subscript n refers to number of ether units in polymer

density

physical property of matter - D=M/V, expressed in g/cc and can change with temperature and pressure in the case of gases

refractive index

measure of the bending of a ray of light as it passes from air into a solid or liquid

Becke Line

a halolike shadow appearing around an object immersed in a liquid of a different refractive index

fluorescence

exposed to UV radiation can be caused by the chemical and crystalline properties of fiber itself, by dyes, or optical brightness and other agents added to fabric

optical brightness

colorless dyes that cause blue light to be reflected, thereby making an object look whiter

chromatography

method of separating components of mixtures based on preferential adsorption or portioning of components in a gas, liquid, or solution - there is paper chromatography and TLC chromatography

chromatogram

record of chromatographic separation

elute

extract one material from another, usually by means of a solvent

retention factor (Rf)

a ratio used to characterize and compare components of samples in liquid chromatography

Fourier Transform Infrared analysis (FTIR)

very powerful way to identify fiber type of test is non destructive, and can be performed on single fibers - based on selective absorption of wave lengths of light by particular group in a polymer

optical microscopy

most important method of fiber identification and matching, using polarizing light and comparison microscopes

pyrolysis gas chromatography-mass spectrometry (PGC-MS)

burns a sample under controlled conditions and separates and analyzes each combustion product, can match the resulting chromatogram and product analysis to known standards can be used for short length fibers, but is destructive