Module 2 - Law Enforcement Equipment and Police Canines
Lesson 1 - Bullet-resistant Vests and Conducted Energy Devices
The Invention of Kevlar
Kevlar was first invented in Wilmington, Delaware in 1964 by a chemist named Stephanie Kwolek. Born in Pennsylvania in 1923, she earned a Bachelor of Science degree in chemistry in 1946. In 1950, she began working at a new Dupont research laboratory where she conducted low-temperature experiments in the preparation of polymers for the creation of highly rigid and strong petroleum-based fibres. Kwolek created a solvent that caused unstable intermediates from these experiments to polymerize or bond into long chains or branched structures. When placed under these conditions, Kwolek’s polymers formed a cloudy fluid in contrast to the clear and viscous fluid of most polymers. She was able to spin this cloudy fluid into incredibly strong fibres that were eventually patented and marketed in 1971 under the brand name Kevlar.
|
Having been fired into a bullet-resistant vest, a bullet is deformed and leaves an impression in the Kevlar.
- Image Source: Sergeant A. Kowalyk, Edmonton Police Service Kevlar's structure consists of relatively rigid molecules, which tend to form sheet-like structures that have similarities to silk proteins. |
Molecular Traits of Kevlar
Bullet-resistant vests are made from a synthetic polymer known as Kevlar. A polymer is a natural or fabricated molecule formed by combining single units, called monomers, into long chains. Other common synthetic polymers include Lycra, nylon, polyester, and Teflon.
Kevlar is so strong because of five distinct molecular traits:
Molecular Trait 1:
Much like a long train consists of many individual train cars joined, the polymers that make up Kevlar consist of repeating single units called monomers.
A single Kevlar polymer chain contains approximately 5 million monomers bonded together. Each monomer in a Kevlar polymer is a chemical unit containing 14 carbon atoms, 2 nitrogen atoms, 2 oxygen atoms, and 10 hydrogen atoms.
Molecular Trait 2:
A single Kevlar fibre is an arrangement of molecules oriented parallel to each other like a bundle of sticks. This strong, untangled arrangement of molecules is known as a crystalline structure. A manufacturing process known as spinning is used to create the crystalline structure of Kevlar. This process involves extruding the molten polymer solution through small holes.
A single Kevlar fibre is an arrangement of molecules parallel to each other like a bundle of sticks.
Molecular Trait 3:
Kevlar is a polyaromatic amide; that is, it contains many aromatic and amide groups. The aromatic groups consist of an arrangement of atoms within one or more rings. The amide groups contain carbon (C), oxygen (O), nitrogen (N), and hydrogen (H) in the following arrangement: CONH2Molecular Trait 4:
The individual polymer strands of Kevlar are held together by hydrogen bonds that form between the polar amide groups. Hydrogen bonds are strong bonds also found in water. These bonds form when a negatively charged oxygen atom from one molecule is attracted to a positively charged hydrogen atom from a nearby molecule.
Four hydrogen bonds (shown as dotted lines) occur between two molecules.
- Image Source: Courtesy Wikipedia.com
Molecular Trait 5:
The aromatic components of Kevlar molecules have a radial composition like the spokes of a bicycle wheel. This spoke-like regularity gives a great deal of symmetry and strength to the internal structure of the Kevlar fibres.
Kevlar is used in underwater cables, boats, parachutes, and skis.
Viscous
- thick and resistant to flowing
Synthetic
- artificial; man-made; not natural
Polar
- carrying a partial positive charge on one side of a molecule and a partial negative charge on the other
Molten
- reduced to liquid form by heating
Monomer
- a simple molecule that can combine with other molecules to form a polymer
Aromatic
- in chemistry, a molecule in which the electrons are free to cycle around circular arrangements of atoms that are alternately singly and doubly bonded to one another
Amide
- a molecule containing the following functional group: (CO)NR2 where R = C or H
Radial
- arranged as rays from a central point