aramid
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What is an aramid?
An aramid is a synthetic polymer with repeating units containing phenyl rings linked by amide groups. The strong amide bonds resist solvents and heat, while the phenyl rings prevent the polymer chains from twisting. Aramid fibers are high-melting, rigid, and insoluble, making them ideal for high-performance applications. Nomex and Kevlar are well-known aramids. Nomex is used in flame-resistant clothing, while Kevlar is known for its use in bulletproof vests and is five times stronger than steel by weight.
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What are aramids made of?
Aramids are synthetic polymers with phenyl rings linked by amide groups, known for their strength and resistance to heat and solvents. They are made by reacting acids containing carboxyl groups with compounds containing amino groups, with the process requiring dissolution of the acids and amines in solvents at low temperatures.
The most well-known aramids are Nomex, used in flame-resistant clothing, and Kevlar, used in bulletproof vests. Kevlar is five times stronger than steel by weight.
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How are aramids different from other fibers like nylon and polyester?
Aramids, nylons, and polyesters are all polymers, but they differ significantly in their chemical structures and properties. Aramids are synthetic polyamides containing aromatic rings, which provide them with high strength, rigidity, and heat resistance. The strong amide bonds (CO-NH) and rigid phenyl rings in aramids contribute to their high melting points and resistance to solvents.
Nylons are also polyamides, but they are generally aliphatic, lacking the aromatic rings that characterize aramids. Polyesters are polymers linked by ester (CO-O) groups, and they can be either aliphatic or aromatic. The presence of amide groups (CO\u2015NH) in aramids and nylons leads to higher melting points compared to polyesters because of hydrogen bonding between polymer chains.
Due to their exceptional properties, aramids are used in high-performance applications such as bulletproof vests and flame-resistant clothing, while nylons and polyesters are used in a broader range of applications, including clothing, home furnishings, and packaging.
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What special properties do aramids have?
Aramids are synthetic polymers with phenyl rings linked by amide groups, forming strong, solvent- and heat-resistant bonds. The rigid structure of aramids makes them ideal for spinning into high-performance fibers. Nomex fibers are known for high-melting and flame-proof qualities, while Kevlar fibers are known for high-strength. Kevlar is five times stronger per weight than steel. Aramids are used in items such as protective clothing, tires, cables, and sports equipment.
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Where are aramids commonly used in everyday life?
Aramids, known for their strength and heat resistance, have various everyday applications. Nomex-type fibers are found in ironing board covers, flame-resistant suits for firefighters, military pilots, and race-car drivers. Kevlar, renowned for its use in bulletproof vests, is also utilized in sports equipment like golf club shafts and lightweight bicycles. Additionally, aramids serve as a replacement for asbestos in automobile clutches and brakes and are present in belts for radial tires. Though not as common as nylon and polyester, their unique properties make them increasingly valuable in industrial applications.
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Why are aramids chosen for use in products like bulletproof vests and fire-resistant clothing?
Aramids are chosen for products like bulletproof vests and fire-resistant clothing due to their unique molecular structure. Amide groups in aramids create strong, heat-resistant bonds, while bulky phenyl rings prevent the polymer chains from twisting.
Kevlar, an aramid, has a high melting point and greater stiffness and tensile strength, making it ideal for bulletproof vests. Nomex, another aramid, is known for its flame-proof qualities and is used in protective clothing. These properties result from the close packing of aromatic polymer chains.
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aramid, any of a series of synthetic polymers (substances made of long chainlike multiple-unit molecules) in which repeating units containing large phenyl rings are linked together by amide groups. Amide groups (CO-NH) form strong bonds that are resistant to solvents and heat. Phenyl rings (or aromatic rings) are bulky six-sided groups of carbon and hydrogen atoms that prevent polymer chains from rotating and twisting around their chemical bonds. As a result, aramids are rigid, straight, high-melting, and largely insoluble molecules that are ideal for spinning into high-performance fibres. The best known aramids are Nomex, a high-melting fibre made into flame-proof protective clothing, and Kevlar, a high-strength fibre made into bulletproof vests.
The development of aramids followed that of nylon, a related class of polyamides produced by reacting acids containing carboxyl groups (CO2H) with compounds containing amino groups (NH2). During the 1950s and 1960s, methods for extending this class to compounds containing carbon rings were devised by researchers at E.I. du Pont de Nemours & Company (now DuPont Company) in the United States. Particularly as developed by Paul W. Morgan and Stephanie L. Kwolek, these methods involved dissolving the acids and amines in suitable solvents and reacting them at low temperatures. In 1961 DuPont introduced Nomex, or poly-m-phenylene isophthalamide, a product of isophthalic acid chloride and m-phenylenediamine, and in 1971 it introduced Kevlar, or poly-p-phenylene terephthalamide, produced from terephthalic acid chloride and p-phenylenediamine. These two polymers are distinguished by the structure of their molecules, Nomex being characterized by meta-oriented phenyl rings and Kevlar by para-oriented rings: 
Nomex melts and simultaneously decomposes at approximately 350 °C (660 °F); the melting point of Kevlar is above 500 °C (930 °F). The higher melting point of Kevlar, as well as its greater stiffness and tensile strength, partly results from the regular para-orientation of its molecules. In solution the polymer assumes a liquid-crystal arrangement, which orients the molecules so that they can be spun and drawn into highly ordered fibres of ultrahigh stiffness and strength. (Kevlar is five times stronger per weight than steel.) Other trademarked Kevlar-type fibres are Twaron (from the Dutch company Akso NV) and Technora (from the Japanese company Teijin, Ltd.). A Nomex-type fibre is also produced by Teijin under the Conex trademark.
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Aramids are not produced in as high a volume as commodity fibres such as nylon and polyester, but because of their high unit price they represent a lucrative market. End uses for aramids in the home are few (Nomex-type fibres have been made into ironing-board covers), but industrial uses are increasing (especially for aramids of the Kevlar class) as designers of products learn how to exploit the properties offered by these unusual materials. Aside from lightweight body armour, Kevlar and its competitors are employed in belts for radial tires, cables, reinforced composites for aircraft panels and boat hulls, flame-resistant garments (especially in blends with Nomex), and sports equipment such as golf club shafts and lightweight bicycles and as replacements for asbestos in automobile clutches and brakes. Nomex-type fibres are made into filter bags for hot-stack gases, clothes for presses that apply permanent-press finishes to fabrics, dryer belts for papermakers, insulation paper and braid for electric motors, flame-resistant suits for fire fighters, military pilots, and race-car drivers, and automobile v-belts and hoses.