Aramid Fiber
Aramid fiber is a class of heat-resistant and strong synthetic fibers. They are used in aerospace and military applications, for ballistic rated body armor fabric, and as an asbestos substitute. The name is a shortened form of aromatic polyamide. They are fibers in which the chain molecules are highly oriented along the fiber axis, so the strength of the chemical bond can be exploited.
Aramid Fiber History
Aromatic polyamides were first introduced in commercial applications in the early 1960s, with a meta-aramid fiber produced by DuPont under the tradename Nomex. This fiber, which handles similarly to normal textile apparel fibers, is characterized by its excellent resistance to heat, as it neither melts nor ignites in normal levels of oxygen. Aramid Fiber is used extensively in the production of protective apparel, air filtration, thermal and electrical insulation as well as a substitute for asbestos. Meta-aramid is also produced in the Netherlands and Japan by Teijin under the tradename Teijinconex, in China by Yantai under the tradename New Star and a variant of meta-aramid in France by Kermel under the tradename Kermel.
Based on earlier research by Monsanto and Bayer, a fiber – para-aramid – with much higher tenacity and elastic modulus was also developed in the 1960s-1970s by DuPont and Akzo Nobel, both profiting from their knowledge of rayon, polyester and nylon processing.
Aramid Fiber Production
Aramid Fiber is generally prepared by the reaction between an amine group and a carboxylic acid halide group. Simple AB homopolymers may look like:
nNH2-Ar-COCl → -(NH-Ar-CO)n- + nHCl
The most well-known aramids (Nomex, Kevlar, Twaron and New Star) are AABB polymers. Nomex, New Star and Teijinconex contain predominantly the meta-linkage and are poly-metaphenylene isophtalamides (MPIA). Kevlar and Twaron are both p-phenylene terephtalamides (PPTA), the simplest form of the AABB para-polyaramide. PPTA is a product of p-phenylene diamine (PPD) and terephtaloyl dichloride (TDC or TCl). Production of PPTA relies on a co-solvent with an ionic component (calcium chloride (CaCl2)) to occupy the hydrogen bonds of the amide groups, and an organic component (N-methyl pyrrolidone (NMP)) to dissolve the aromatic polymer. Prior to the invention of this process by Leo Vollbracht, who worked at the Dutch chemical firm Akzo, no practical means of dissolving the polymer was known. The use of this system led to a patent war between Akzo and DuPont.
Aramid Fiber Spinning
After production of the polymer, the aramid fiber is produced by spinning the solved polymer to a solid fiber from a liquid chemical blend. Polymer solvent for spinning PPTA is generally 100% (water free) sulfuric acid (H2SO4).
Aramid Fiber Appearances
Fiber,Chopped fiber,Powder, Pulp
Aramid Fiber Properties
good resistance to abrasion
good resistance to organic solvents
nonconductive
no melting point, degradation starts from 500°C
low flammability
good fabric integrity at elevated temperatures
sensitive to acids and salts
sensitive to ultraviolet radiation
prone to static build-up unless finished
Aramid Fiber Uses
flame-resistant clothing
heat protective clothing and helmets
body armor, competing with PE based fiber products such as Dyneema and Spectra
composite materials
asbestos replacement (e.g. braking pads)
hot air filtration fabrics
tires, newly as Sulfron (sulfur modified Twaron) synthetic fibers, synthetic fibers list, synthetic fibers types, nylon fiber, spandex fiber, acrylic fiber
mechanical rubber goods reinforcement
ropes and cables
wicks for fire dancing
optical fiber cable systems
sail cloth (not necessarily racing boat sails)
sporting goods
drumheads
wind instrument reeds, such as the Fibracell synthetic fibers, synthetic fibers list, synthetic fibers types, nylon fiber, spandex fiber, acrylic fiber
brandspeaker woofers
boathull material
fiber reinforced concrete
reinforced thermoplastic pipes
tennis strings (e.g. by Ashaway and Prince tennis companies)
hockey sticks (normally in composition with such materials as wood and carbon)