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Aramid Based Fibers: Kevlar and Nomex

Güncelleme tarihi: 15 Ara 2021


Aramid is a polymer from the polyamide (Nylon) class. The name of Aramid comes from the combination of aromatic and polyamide words. The aromatic class of polyamides was given the name "Aramid" by the American Federal Trade Commission in 1974 because it has completely different properties from aliphatic polyamides. Commercially, the first Aramid fiber was introduced in 1965 by DuPont company in the USA. The name of this meta-aramid was Nomex.


High performance fibers are generally divided into two groups; The first group includes non-flammable fibers, the second group includes high-strength and modulus fibers. There are fibers in the aramids group that can fit both classes. There are currently two types of aramids that have found commercial success. Both of these technically fall under high performance fibers. The first group is again in the meta-aramid group, and although it has a medium modulus and strength, it has excellent heat resistance. No decomposition or melting is observed up to 600 –800 °C. It exhibits an excellent performance in uses where protection against heat and electricity is required. Dupont's Nomex is an example. The second class aramids are Kevlar, a para aramid fiber introduced by DuPont in the early 1970s. This fiber stood out as a fiber that could withstand high temperatures in the class of high modulus and strength fibers. In the market conditions of that day, producing a fiber that is “heat resistant like asbestos and hard as glass” meant filling a big gap in the market.


Kevlar

Created by Stephanie Kwolek, Kevlar is a heat-resistant para-aramid synthetic fiber with a molecular structure of many inter-chain bonds that make Kevlar incredibly strong. Best known for its use in ballistic body armor, Kevlar also has many other applications because of its high tensile strength-to-weight ratio


"Stronger than steel"

A pioneer in polymer research, Stephanie Kwolek accumulated several patents and awards throughout her career. Most notably, she is known for her groundbreaking work that led to the creation of Kevlar, an incredibly strong material that continues to push the limits of possible.



The chemical structure of Kevlar is comprised of several repeating inter-chain bonds. These chains are cross-linked with hydrogen bonds, providing a tensile strength 10x greater than steel on an equal weight basis.



Kevlar fibers are so tightly spun that it is nearly impossible to separate them. When a bullet or other high-velocity projectile hits Kevlar, the fibers essentially catch the projectile while absorbing and dissipating its energy.


Due to the fully extended and perfectly aligned molecular chains within Kevlar fiber, Kevlar provides a strong protective barrier against slashes, cuts and punctures.


Kevlar is inherently flame resistant—protecting against thermal hazards up to 800 degrees Fahrenheit. Additionally, Kevlar fibers won’t melt, drip or support combustion.


Nomex

Nomex fibers are heat and flame-resistant and are used in protective fabrics, clothing, electrical paper for insulation, and other high-performance applications to help provide protection for millions of people and applications around the world.


Nomex is essentially a flame resistant, high temperature resistant fiber; it does not melt, drip and does not catch fire in contact with air. Available in paper, felt, fabric and fiber formats. Nomex brand fiber is used in a wide range of applications but is perhaps best known for its role as a critical component of protective clothing. Today, more than three million firefighters around the world are protected by the unique flame protection, durability and comfort provided by Nomex to their firefighter clothing, other clothing and accessories. Nomex is also used in clothing worn by military and police forces, auto racing drivers, track crew members and officers, and workers in danger of flash fires and electric arcs.


Nomex fibers serve other purposes than the use of protective clothing. The stiffness and thermal stability of Nomex fibers ensures high reliability in the most demanding automotive applications such as turbocharger hoses. Many industries, from asphalt and concrete plants to chemical and steel mills, use filter bags made from Nomex fiber. Motor, generator, transformer and other electrical equipment manufacturers have been using Nomex paper, which has become the standard for electrical insulation for more than 40 years. The lightweight honeycomb texture developed with Nomex paper is used for structural support and helps to significantly improve the performance of commercial aircraft.


 

References

  • Çelikkanat, Aykut Burak. Teknik Tekstiller. Yüksek Lisans Tezi, İstanbul Teknik Üniversitesi, 2002.

  • Dupont. "Better, Stronger and Safer with Kevlar". 29 Kasım 2021. https://www.dupont.com/brands/kevlar.html

  • Dupont. "When the Heat is On, Nomex Delivers". 29 Kasım 2021. https://www.dupont.com/brands/nomex.html

  • Derstekstil. "Aramid Lifleri". 29 Kasım 2021. https://www.derstekstil.name.tr/component/k2/item/723-aramid-lifleri.html

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