User:Mbvanleeuwen/MB-Aramid
Introduction
Aromatic Polyamides were first introduced in a commercial application in the early 1960s, with the meta-aramid fibre Nomex, by DuPont. This fiber is still used as heat resistant material for thermal and electrical insulation.
A fiber with much higher tenacity and modulus was also developed in the early 1960s by Monsanto, Dupont and Akzo Nobel. Much work was done by Stephanie Kwolek in 1961 while working at DuPont and they introduced a para-aramid called Kevlar in 1973.
A similar fiber called Twaron with roughly the same chemical structure was introduced by Akzo Nobel in 1987. Due to earlier patents on the production process, Akzo Nobel and Dupont had a patent-war in the 1980s. Twaron is currently owned by the Teijin company.
Aramids are used in many high-tech applications, such as aerospace and military applications, for "bullet-proof" body armor fabric, and as an asbestos substitute.
The Federal Trade Commission definition for aramid fiber is
"A manufactured fiber in which the fiber-forming substance is a long-chain synthetic polyamide in which at least 85% of the amide linkages, (-CO-NH-) are attached directly to two aromatic rings."
An especially fire proof variant is meta-Aramid, like Nomex, created by DuPont or Teijinconex by Teijin.
Production
Polymer preparation
Aramids are generally prepared by the reaction between an amine group and a carboxylic acid halide group. Simple AB or AABB homopolymers may be look like:
nNH2-Ar-COCl -> -(NH-Ar-CO)n- + nHCl
Spinning
Aramid fiber is produced by spinning a solid fiber from a liquid chemical blend. This relies on a co-solvent with an ionic component (calcium chloride) to occupy the hydrogen bonds of the amide groups, and an organic solvent (N-methyl pyrrolidone) to dissolve the aromatic polymer; prior to the invention of this process by Leo Vollbracht, working at the Dutch chemical firm Akzo Nobel, no practical means of dissolving the polymer was known. The use of this system led to a patent war between Akzo Nobel and Dupont.
Other types of Aramids
Beside meta aramids like Nomex, other variations which belong to the aramid fiber range. These are mainly of the copolyamide type, most wellknown under the brandname Technora, as developed by Teijin and introduced in 1976.
Aramid fiber characteristics
- sensitive to degradation from ultraviolet radiation
- good resistance to abrasion, organic solvents, and thermal degradation
- sensitive to moisture and salts
- nonconductive
- no melting point
- low flammability
- good fabric integrity at elevated temperatures
- para-aramid fibers such as Kevlar and Twaron, provide outstanding strength-to-weight properties, and have high tenacity, and high Young's modulus.
- difficult to dye - usually solution dyed [1]
- prone to static build-up unless finished[1]
Major industrial uses
- flame-resistant clothing
- protective clothing and helmets
- body armor, competing with PE based fiber products such as Dyneema and Spectra.
- composite materials
- asbestos replacement
- hot air filtration fabrics
- tire and mechanical rubber goods reinforcement
- ropes and cables
- sail cloth (not necessarily racing boat sails)
- sporting goods
- drumheads
- speaker woofers
- Boathull material
- Fiber reinforced concrete
- Pipes
- Recently in tennis strings, because of its extreme durability. Popular aramid kevlar strings are made by Ashaway and Prince tennis companies.