What Are Aramid Fibers?
Aramid Fiber is a general term for high-performance fibers made of aromatic polyamides. They were developed by DuPont in 1965. In 1974, it was given the generic name Aramid Fiber to distinguish it from nylon.
They are synthesized by polycondensation of para- or meta-phenyldiamine with diamine phthalate.
Aramid Fiber can be classified into two groups, para- and meta-aramid, based on differences in molecular structure. The former has superior mechanical strength, cut resistance, and vibration damping properties, while the latter has superior heat resistance, flame resistance, and chemical resistance.
Uses of Aramid Fiber
Para- and meta-aramid fibers have different characteristics, and are used in applications that take advantage of these characteristics.
1. Para-Aramid Fiber
Para-aramid fibers are used in an extremely wide range of fields, from industrial applications to the aerospace industry. Examples of industrial applications include tension members and ropes for optical fiber. These applications take advantage of the material’s resistance to elongation, while being about five times stronger than steel of the same weight.
In addition, its high resistance to friction is used in applications such as tires and brake pads, which need to withstand long-term wear. Furthermore, because of its cut resistance, it is also used as a fiber for safety and protective goods such as work gloves and bulletproof vests.
In the aerospace field, its heat resistance is also used as a parachute component.
2. Meta-Aramid Fiber
Unlike para-aramid fibers, meta-aramid fibers do not excel in strength. While possessing the same strength, specific gravity and texture as general-purpose polyester, meta-aramid fibers have a high oxygen index, which indicates flame-retardant performance, and do not melt or decompose at temperatures up to 400°C.
Aramid is used in applications requiring heat resistance and flame retardancy, such as firefighting uniforms and aircraft seats.
Properties of Aramid Fiber
1. Para-Aramid Fiber
The strength and high modulus of para-aramid fibers are derived from the strength of the bonds within the polymer. Para-aramid fibers are all-trans, resulting in a molecular backbone with high linearity and flatness.
When para-aramid fiber is dissolved in concentrated sulfuric acid and stretched, molecular chains are first hydrogen bonded to each other, which then chain together to form flat plates. The plates then aggregate with each other by intermolecular forces to form a cylindrical fiber material. The special arrangement of molecular chains and the formation of a higher-order structure result in a variety of properties, including high strength and high elastic modulus.
2. Meta-Aramid Fiber
Because the molecules of meta-aramid fibers are arranged in a zigzag pattern, hydrogen bonds and intermolecular forces are weaker than those of para-aramid fibers, and the strength is comparable to that of polyester and nylon fibers.
On the other hand, they have a relatively flexible structure, and since the benzene rings form a dense structure at high temperatures, they are resistant to decomposition and ignition, and exhibit excellent heat resistance.
They also have excellent chemical resistance to acids and alkalis.
Other Information on Aramid Fibers
Differences Between Aramid Fiber and Carbon Fiber
Carbon fiber is also known as an organic fiber with high strength. Carbon fiber is a material with applications ranging from sporting goods to the aerospace field due to its overwhelming light weight and strength.
However, its conductivity makes it impermeable to electromagnetic waves, and it has the disadvantage of low abrasion resistance. In addition, it is very time-consuming to process, making its cost high. For this reason, plastics with insulating and abrasion-resistant aramid fiber composites are often used for the back panels of smartphones.