Short for aromatic polyamide fibers, aramid fibers are composed of high-strength, heat-resistant synthetic polymer fibers. Chemically, they are a combination of long chainlike molecules linked by strong hydrogen bonds. 

The first aromatic polyamides were produced in the early 1960s, with the first commercial product being a meta-aramid fiber from DuPont called Nomex®. Thanks to its strength and heat resistance combined with tactile characteristics that were close to normal textiles, Nomex® was quickly adopted for a number of uses including protective apparel, insulation, and more.

Types of Aramid Fibers and Fabrics

Today, tens of thousands of tons of meta-aramid and para-aramid fibers are manufactured each year by multiple manufacturers under several brand names.

By chemistry, there are numerous types of aramid fibers. The Federal Trade Commission defines an aramid fiber as any manufactured fiber with a long-chain synthetic polyamide that has a minimum of 85% of its amide linkages attached directly to two aromatic rings. Classifying aramid fibers by commercially branded products, their types include or have included:

• Kevlar®
• Nomex®
• Technora®
• Twaron®
• Conex®
• Arawin®
• New Star®
• Kermel® 

High-performance aramid fibers can transfer mechanical stress with high efficiency while maintaining a low molecular weight. The hydrogen bonds are aligned, for the most part, along the fiber axis, which gives them remarkable strength and flexibility.

Features

Aramid fibers are renowned for their high tensile strength. Aside from their resistance to abrasion and piercing, they also have high resistance to organic solvents and fire. They have no melting point, only begin to degrade at extremely high temperatures, and also have low flammability. Nomex® starts to decompose at around 350° C while Kevlar© and other para-aramids do not degrade until above 500° C. The fibers also operate well freezing temperatures and are nonconductive.

Aramid fibers have a strength per unit of weight several times that of steel, aluminum and E-glass, and are lighter than fiberglass. The fibers are not totally indestructible, however, as they are sensitive to UV rays, acids, and salts.

Applications

Their unique properties of high strength, low weight, and flame and solvent resistance have made them useful in an array of applications.

• Ballistic armor, in the form of vests and helmets
• fFame-resistant and heat PPE for firefighters, pilots, race car drivers, and others
• Asbestos replacement
• Mechanical reinforcement in rubber goods, such as tires
• Support ropes and cables
• Optical fiber cables
• Sporting goods (e.g. tennis strings, skis, snowboards, golf club shafts, hockey sticks)
• Musical equipment (e.g. drumheads, wood instrument reeds, loudspeaker diaphragms)
• Marine applications, such as boat hulls and sail cloth
• Helicopter rotors
• Solid rocket motors
• Compressed natural gas tanks
• Pipelines
• Aircraft panels
• Lightweight bicycles

• Filter bags and other filtration devices

• Automobile parts 

Materials

Aramid fibers are long chain-like molecules composed of oxygen, carbon, hydrogen, and nitrogen. For manufacturing, aramids are formed int oa polymer by the reaction between an amine group and a carboxylic acid halide group. These stiff polymer molecules have a strong crystal orientation and close interaction between polymer chains due to their strong hydrogen bonds.

Aramids are made into fiber form by spinning the dissolved polymer into a solid fiber form. During the production process they can be manufactured into a fiber, chopped fiber, powder, or pulp form. The manufacturing methods include hand lay-up, vacuum bagging, vacuum infusion, resin transfer molding (RTM), RTM light, press molding, filament winding, and pultrusion.

Selection

Kevlar® has outstanding strength-to-weight properties and an extremely high tolerance to heat that has made it one of the most popular aramid fibers for bulletproof vests. Nomex®, while not as strong as Kevlar® and para-aramid variants, has excellent thermal, chemical, and radiation resistance that makes it a popular fiber for protective firefighter apparel and hazardous material suits.  

Standards

A-A-50195—Aramid thread

FORD ESB-M9H112-A—Protective, nonwoven, aramid fabric

ISO TS 17920—Fibre ropes for offshore stationkeeping - Aramid

References

Image Credit: 

Mid-Mountain Materials, Inc.