Nomex®

by Chris Woodford. Last updated: September 22, 2014.

It's a racing driver's worst nightmare. You come down the straight at over 200mph (300 kph),

a tire blows out, and you skid off into the crash barrier. You survive the crash but the energy of the impact generates enough heat to make your fuel tank explode. Suddenly, the car that

could have carried you to victory has turned into a fireball. You manage to escape, but now there's another terrifying threat: your overalls catch fire! Fortunately, you're wearing an inner body-suit made of an amazing flame-resistant material called Nomex®. So, as you pelt from

the car, the fire goes out all by itself. Shaken but unharmed, you owe your life to an piece of amazing chemical technology. Let's take a closer look at how Nomex works and some of the

other things it can be used for!

Photo: A soldier puts on a Nomex® hood and a flameproof suit. Photo by Ryan C. Matson courtesy of US Army.

What is Nomex?

Photo: A pair of Nomex® gloves like these could make nasty oven burns a thing of the past.

Nomex® is the brand name for a heat- and flame-resistant textile made by the DuPont™

chemical company. Technically, it's called a synthetic aromatic polyamide polymer—which sounds complex but starts to make more sense if you consider it one word at a time:

Synthetic textiles are made in a chemical laboratory (unlike natural textiles such as cotton, which grows on plants, and wool, which comes from animals).

Aromatic means its molecules have a strong, ring-like structure not unlike that of benzene.

Polyamide means the ring-like aromatic molecules connect together to form long chains. These run inside (and parallel to) the fibers of Nomex a bit like the steel bars

in reinforced concrete. Polymer means that Nomex is made from many identical molecules bonded together

(each one of which is called a monomer). Plastics are the most familiar polymers in our world. As we've seen, the monomers in Nomex are based on a modified, benzene-like ring structure.

In short, what we have in Nomex is a man-made textile whose ring-like monomers are

bonded together into tough, long chains to make immensely strong fibers. Break Nomex up and sort it into its atoms and you'd have four neat piles of carbon hydrogen, oxygen, and

nitrogen.

Photo: Left: Turn Nomex gloves inside out and you can see how very thickly woven they are.

Although they look much like ordinary woollen gloves, wool alone could never give such amazing heat protection. Right: Inspect the label carefully and you'll see this is actually

Nomex III, which is roughly 95 percent Nomex, 5 percent Kevlar, and a little carbon fiber to reduce static.

Aromatic polyamides such as Nomex are often called aramids for short. Kevlar® (another DuPont textile) is also an aramid, but with a slightly different chemical structure. If you're

interested, the full chemical name of Nomex is poly (m-phenylenediamine isophthalamide), while Kevlar is poly (p-phenylenediamine terephthalamide); Nomex is a meta-aramid

polymer while Kevlar is a para-aramid polymer.

Aramids are made in a two-stage process. First, the basic polymer is made by reacting together organic (carbon-based) substances to form a liquid. In the second stage, the liquid is spun out to make solid fibers, which can then be woven into textiles or converted into sheet

form.

Nomex generally comes in three kinds. It's either used by itself (as 100 percent Nomex), blended with up to 60 percent Kevlar, or blended with Kevlar and some anti-static fibers. In

this last form, it's known as Nomex III.

What makes Nomex fireproof?

Two superb properties of Nomex make it a perfect protective material for race-car drivers. Although Nomex burns when you hold a flame up to it, it stops burning as soon as the heat

source is removed. In other words, it is inherently flame resistant. Just as important, the thick

woven structure of synthetic fibers is a very poor conductor of heat. It takes time for heat to travel through Nomex; hopefully by that time, you're away from the flames and out of

danger.

The tough, woven structure of Nomex is extremely strong, has high heat resistance, is flame retardant (it doesn't melt or drip) and doesn't react with water.

What is Nomex used for?

Photo: Ready for battle: soldiers put on body armor made from Kevlar and Nomex and used

by explosives experts. Photo by courtesy of US Army and Defense Visual Information Center.

Nomex is best known as a barrier to fire and heat. Apart from race-car drivers, it's worn by

astronauts, fire-fighters, and military personnel. It's also widely used in more mundane ways, such as in my household oven gloves. In sheet form, heatproof Nomex finds many uses in automobiles, including high-temperature hoses and insulation for spark plugs.

But Nomex isn't just useful for protective clothing. The molecular structure that stops heat

passing through stops electricity flowing through it as well. That means Nomex is an extremely poor conductor—almost a perfect insulator, in fact. Nomex, made into the form of

a paper sheet or board, is a superb insulating material for all kinds of electrical equipment, from motors and generators to transformers and other electrical equipment. For these applications, Nomex is often laminated with Mylar® (polyester film) to make a stronger,

tougher insulating material that works at high temperatures without the individual layers coming apart. Two-ply Nomex-Mylar laminate is called NM; three-ply is known as NMN

(where the Nomex goes either side of the Mylar); and four ply is NMNM.

Like Kevlar, Nomex is both very strong and very light, so it's often used in aerospace applications. Nomex sheet is widely used to make the honeycomb reinforcement inside helicopter blades and airplane tail fins.

Photo: Nomex isn't the only fire-retardant fabric. Textiles used to cover chairs are often made from fire-resistant polyesters and other materials. This simple demonstration in Think Tank (the science museum in Birmingham, England) shows very clearly how fabrics like these can

save lives. On the left, we have a chair made from ordinary fabric. A cigarette or match burn sets the fabric alight very quickly and gives off toxic fumes. Had this fire been left to burn,

the whole chair (and the rest of the room) would have been completely destroyed. On the right, a chair made from fire-retardant fabric burns much slower. Often the fire goes out before too much damage is done.

Who invented Nomex?

The credit for this excellent invention goes to Dr Wilfred Sweeny, a Scottish-born scientist working at the world-famous DuPont laboratory in Wilmington, Delaware that also spawned

nylon and Kevlar. While researching polymers, he developed one with with particularly good thermal properties that could be woven into a very tough fiber. Since Nomex was introduced in 1967, it has saved the lives of countless firefighters, pilots, soldiers, industrial workers—

and, of course, racing drivers!

Velocidade, curvas perigosas e muita adrenalina. Para arriscar a vida a mais de 300 km/h os pilotos precisam ter certeza de que estão bem protegidos. Para ter confiança e ousar em

ultrapassagens que os motoristas comuns nem podem imaginar, os pilotos precisam, entre as muitas coisas que essa atividade exige, de uma roupa especial. Por isso, ao longo dos anos, os macacões para pilotos de corrida evoluíram muito e se transformaram em itens

tecnologicamente sofisticados, que combinam máxima proteção com um impecável conforto.

O macacão é produzido com um tecido importado à base de aramida e é resistente ao fogo.

Todo material é produzido para não pegar fogo: o forro, o zíper, a malha e até a linha de costura. Mas como você está acostumado, os macacões são também os responsáveis por marcar o estilo de cada piloto e sua equipe, além de ser uma grande vitrine para os patrocinadores.

Por isso, a produção final do macacão acontece quando o cliente leva o seu logotipo e escolhe

as cores que serão predominantes na peça. Em seguida é feito o molde e por ultimo é colocado o forro. Somente após sua confecção completa é que são bordados os patrocínios e o macacão

finalmente fica pronto para encarar as pistas. E isso tudo leva em aproximadamente quinze dias, além de garantir muito estilo, esses macacões são parte muito importante para que os

pilotos profissionais corram total tranquilidade e segurança

Aramids are a family of nylons, including Nomex® and Kevlar®. Kevlar® is used to

make things like bullet proof vests and puncture resistant bicycle tires. I suppose one

could even make bullet proof bicycle tires from Kevlar® if one felt the need.

Blends of Nomex® and Kevlar® are used to make fireproof clothing. Nomex® is what

keeps the monster truck and tractor drivers from burning to death should their fire -

breathing rigs breathe a little too much fire. Thanks to Nomex®, an important part of

American culture can be practiced safely. (Polymers play another part in the monster

truck show in the form of elastomers from which those giant tires are made.) Nomex®-

Kevlar® blends also protect fire fighters.

Kevlar® is a polyamide, in which all the amide groups are separated by para-phenylene

groups, that is, the amide groups attach to the phenyl rings opposite to each other, at

carbons 1 and 4. Kevlar is shown in the big picture at the top of the page.

Nomex®, on the other hand, has meta-phenylene groups, that is, the amide groups are

attached to the phenyl ring at the 1 and 3 positions.

Kevlar® is a very crystalline polymer. It took a long time to figure out how to make

anything useful out of Kevlar® because it wouldn't dissolve in anything. So processing it

as a solution was out. It wouldn't melt below a right toasty 500 oC, so melting it down

was out, too. Then a scientist named Stephanie Kwolek came up with a brilliant plan.

Click here to find out what it was.

Aramids are used in the form of fibers. They form into even better fibers than non-

aromatic polyamides, like nylon 6,6.

Why? Why?

Ok, since it seems everyone just has to know, I'll tell you. It has to do with a little quirky

thing that amides do. They have the ability to adopt two different shapes, or

conformations. You can see this in the picture of a low molecular weight amide. The two

pictures are the same compound, in two different conformations. The one on the left is

called the trans conformation, and the one on the right is the cis- conformation.

In Latin, trans means "on the other side". So when the hydrocarbon groups of the

amide are on opposite sides of the amide bond, the bond between the carbonyl oxygen

and the amide nitrogen, it's called a trans-amide. Likewise, cis in Latin means "on the

same side", and when both hydrocarbon groups are on the same side of the amide bond,

we call it a cis-amide.

The same amide molecule can twist back and forth between the cis- and trans-

conformations, given a little bit of energy.

The same cis- and trans-conformations exist in polyamides, too. When all the amide

groups in a polyamide, like nylon 6,6 for example, are in the trans conformation, the

polymer is fully stretched out in a straight line. This is exactly what we want for fibers,

because long, straight, fully extended chains pack more perfectly into the crystalline

form that makes up the fiber. But sadly, there's always at least some amide linkages in

the cis-conformation. So nylon 6,6 chains never become fully extended.

But Kevlar® is different. When it tries to twist into the cis-conformation, the hydrogens

on the big aromatic groups get in the way! The cis conformation puts the hydrogens just

a little closer to each other than they want to be. So Kevlar® stays nearly fully in the

trans- conformation. So Kevlar® can fully extend to form beautiful fibers.

Now it may help to look at a close-up picture of this. Look at the picture below and you

can see that when Kevlar® tries to form the cis-conformation, there's not enough room

for the phenyl hydrogens. So only the trans-conformation is usually found.

But there's another polymer that stretches out even better called ultra-high molecular

weight polyethylene. It even replaced Kevlar® for making bullet-proof vests!

But back to Kevlar®...

Also the phenyl rings of adjacent chains stack on top of each other very easily and

neatly, which makes the polymer even more crystalline, and the fibers even stronger.

Nomex

From Wikipedia, the free encyclopedia

A Canadian firefighter in Toronto affixes a Nomex hood in 2007.

Nomex is a registered trademark for flame-resistant meta-aramid material developed in the early 1960s by DuPont and first marketed in 1967.[1]

Contents

1 Properties 2 Production

3 Applications 4 History 5 See also

6 References 7 External links

Properties

Nomex and related aramid polymers are related to nylon, but have aromatic backbones, and hence are more rigid and more durable. Nomex is the premier example of a meta variant of the aramids (Kevlar is a para aramid). Unlike Kevlar, Nomex cannot align during filament

formation and has poorer strength. However, it has excellent thermal, chemical, and radiation resistance for a polymer material.

Production

The polymer is produced by condensation reaction from the monomers m-phenylenediamine

and isophthaloyl chloride.[1]

It is sold in both fiber and sheet forms and is used as a fabric wherever resistance from heat and flame is required. Nomex sheet is actually a calendered paper and made in a similar

fashion. Nomex Type 410 paper is the original and one of the larger grade types made, mostly for electrical insulation purposes. Nomex fiber is made in the USA and in Spain (Asturias).

Wilfred Sweeny (1926–2011), the DuPont scientist responsible for discoveries leading to Nomex, earned a DuPont Lavoisier Medal[2] partly for this work in 2002.

Applications

The paper is used in electrical laminates such as circuit boards and transformer cores as well as fireproof honeycomb structures where it is saturated with a phenolic resin. Honeycomb

structures such as these, as well as mylar-Nomex laminates are used extensively in aircraft construction. Both the firefighting and vehicle racing industries use Nomex to create clothing

and equipment that can withstand intense heat.

A Nomex hood is a common piece of racing and firefighting equipment. It is placed on the head on top of a firefighter's face mask. The hood protects the portions of the head not covered by the helmet and face mask from the intense heat of the fire.

Wildland firefighters wear Nomex shirts and trousers as part of their personal protective equipment during wildfire suppression activities.

Race car drivers wear driving suits constructed of Nomex and or other fire retardant materials, along with Nomex gloves, long underwear, balaclavas, socks, helmet lining and

shoes to protect them in the event of a fire. The FIA and the SFI Foundation provide specifications for flame-resistant drivers clothing to be used in racing. The standards range

from single layer suits that provide some protection against flash fires to much thicker multilayer SFI-15 suits required by the National Hot Rod Association that can protect a driver for up to 30 seconds against the intense heat and almost invisible flames generated by the

nitromethane, ethanol and methanol fuels that are used in championship drag racing.

Military pilots and aircrew wear flight suits made of over 92 percent Nomex to protect them from the possibility of cockpit fires and other mishaps. Recently, troops riding in ground

vehicles have also begun wearing Nomex. The remaining material is typically Kevlar thread used to hold the fabric together at the seams.

Military tank drivers also typically use Nomex hoods as protection against fire and extreme cold. [3]

In the U.S. space program, Nomex has been used for the Thermal Micrometeoroid Garment on the Extravehicular Mobility Unit (in conjunction with Kevlar and Gore-Tex) and ACES pressure suit, both for fire and extreme environment (water immersion to near vacuum)

protection, and as thermal blankets on the payload bay doors, fuselage, and upper wing surfaces of the Space Shuttle Orbiter. It has also been used for the airbags for the Mars

Pathfinder and Mars Exploration Rover missions, the Galileo atmospheric probe, the Cassini-Huygens Titan probe, as an external covering on the AERCam Sprint, and is planned to be incorporated into NASA's upcoming Crew Exploration Vehicle.

Nomex has also been used for its acoustic qualities, the first time being used in Troy, NY, at

Rensselaer Polytechnic Institute's Experimental Media and Performing Arts Center (EMPAC's) main concert hall. A ceiling canopy of Nomex reflects high and mid frequency

sound, providing reverberation, while letting lower frequency sound partially pass through the canopy.[4] According to RPI President Shirley Ann Jackson, EMPAC is the first venue in the world to use Nomex for acoustic reasons.

Nomex (like Kevlar) is also used in the production of loudspeaker drivers.

Honeycomb-structured Nomex paper is also used as a spacer between layers of lead in the ATLAS Liquid Argon Calorimeter.[5]

History

The death of race car drivers in fiery crashes, notably those of Fireball Roberts at Charlotte,

and Eddie Sachs and Dave MacDonald at Indianapolis, all in 1964, meant something had to be done.[6] In early 1966 Competition Press and Autoweek reported: "During the past season, experimental driving suits were worn by Walt Hansgen, Masten Gregory, Marvin Panch and

Group 44's Bob Tullius; these four representing a fairly good cross section in the sport. The goal was to get use-test information on the comfort and laundering characteristics of Nomex.

The Chrysler-Plymouth team at the recent Motor Trend 500 at Riverside also wore these suits."[7]

Propiedades del Kevlar y del Nomex

Las propiedades de estos dos materiales van ligadas intrínsecamente a las

aplicaciones que podemos encontrar tanto en la industria como en la vida

cotidiana, las cuales se ven en el siguiente punto.

No derriten ni se contraen en llama, y carbonizan solamente a temperaturas muy altas. Ofrecen una

resistencia excelente al agua y al petróleo, incluyendo

el aceite de motores y lubricantes, además tienen una buena resistencia química y son químicamente estables

bajo una gran variedad de condiciones de exposición. Son ambos extremadamente resistentes y con alta

resistencia a la abrasión, además se cortan y se rasgan.

NOMEX® es un polímero aromático sintético de poliamida que proporciona altos

niveles de la integridad eléctrica, química y mecánica.

Esto es lo que hace que NOMEX® no se contraiga, ni dilate, ni se ablande ni

derrita durante la exposición a corto plazo a temperaturas tan altas como

300°C. A largo plazo puede estar trabajando como aislante tanto térmico como

eléctrico o químico soportando continuamente temperaturas de hasta 220°C durante más de 10 años.

La fuerza y la resistencia de los papeles y de los cartones prensados de

NOMEX® ayudan a ampliar vida del equipo que rota en condiciones de

funcionamiento severas. Estas condiciones incluyen choque severo y vibraciones excesivas propiciadas por desequilibrios rotantes, como por

ejemplo las que pueden aparecer en molinos de acero, motores para tracción ferroviaria, o turbinas de gas. En todos ellos además tenemos grandes

temperaturas de funcionamiento.

Fuerza dieléctrica inherente

En tensiones eléctricas muy elevadas, como cortocircuitos, a corto plazo los productos de

NOMEX® de 18 a 40 V/mil de kV/mm (457 a 1015), dependiendo de tipo de producto y grueso,

proporcionan la protección necesaria y adecuada.

Dureza mecánica

Los productos de alta densidad de NOMEX® son

fuertes, resistentes y (en los grados más finos) flexibles, con buena resistencia al rasgado y a la

abrasión.

Estabilidad termal

Las temperaturas hasta 200°C tienen poco o nada de efecto en las

características eléctricas y mecánicas de los productos de NOMEX®, y los valores útiles se conservan en temperaturas considerablemente más altas.

Además, estas características útiles se mantienen por por lo menos 10 años de

exposición continua a 220°C de temperatura.

Compatibilidad química

NOMEX® es esencialmente inerte a la mayoría de

los disolventes, y es totalmente resistente a los ataques de ácidos y álcalis. Es compatible con

todas las clases de barnices y de pegamentos, de líquidos de transformadores, de aceites

lubricantes, y de refrigerantes. Puesto que los productos de NOMEX® no son digestibles, no son

atacados por insectos, hongos, etc.

Capacidades criogénicas

NOMEX® ha encontrado una gran aceptación en una variedad de usos criogénicos debido a su estructura polimérica única. En el punto que hierve el

nitrógeno (77°K), los cartones prensados de papel de NOMEX® resisten

plenamete las fuerzas de contracción/dilatación que aparecen.

Insensibilidad a la humedad

En equilibrio con un 95 por ciento de humedad relativa, los papeles de NOMEX®

y los cartones prensados mantienen un 90 por ciento de su fuerza dieléctrica, mientras que muchas características mecánicas además mejoran.

Resistencia de la radiación

NOMEX® es esencialmente inafectado por 800 megarads (8Mgy) de radiación de ionización y todavía conserva características mecánicas y eléctricas útiles

después de ocho veces esta exposición.

No toxicidad

Los productos de NOMEX® no producen ninguna

reacción tóxica conocida en seres humanos o animales. Los productos de NOMEX® no se derriten

y, con un índice limitador del oxígeno (LOI) en 220°C

sobre 20,8 (el valor crítico para la combustión en aire normal), no favorecen la combustión.

Estructura química del

Kevlar y del Nomex:

El Kevlar y el Nomex pertenecen a la familia de las aramidas, las cuales , a su

vez, pertenecen a una familia de nylons. Todos ellos son polímeros. Algunos otros

polímeros sintéticos comunesson el Teflon, la Lycra, y el poliéster. Un polímero es una

cadena hecha de muchos grupos moleculares similares, conocido como monómeros, que

se enlazan juntos. Para conseguir entender mejor todo esto, imagínese que está mirando

un tren de mercancías muy largo. Cada vagón idéntico podría representar un

monómero y el tren en su conjunto representaría la cadena del polímero.

Una sola cadena del polímero de Kevlar podría tener desde cinco hasta un millón de

monómeros enlazados juntos. Cada monómero de Kevlar es una unidad química que

contiene 14 átomos de carbono, 2 átomos de nitrógeno, 2 átomos de oxígeno y 10 átomos

de hidrógeno.

Químicamente se puede representar un monómero de Kevlar como esto:

El Kevlar es una poliamida, en la cual todos los grupos amida están separados por

grupos para-fenileno, es decir, los grupos amida se unen al anillo fenilo en posiciones

opuestas entre sí, en los carbonos 1 y 4. El Kevlar se muestra en la figura grande, en la

parte superior de esta página.

El Nomex, por otra parte, posee grupos meta-fenileno, es decir, los grupos amida se

unen al anillo fenilo en las posiciones 1 y 3.

Las aramidas se utilizan en forma de fibras. Forman fibras aún

mejores que las poliamidas no aromáticas, como el nylon 6,6.

Las cadenas del polímero se pueden juntar aleatoriamente o se pueden orientar cuidadosamente de lado a lado en una fila. Resulta que la

orientación de las cadenas del polímero es muy importante para ciertas características tales como flexibilidad, rigidez, y fuerza.

Una fibra de Kevlar es un arsenal de moléculas orientadas en paralelo como un paquete

de espaguetis crudos. Esta colocación espacial es lo que proporciona las moléculas con

estructura cristalina. La cristalinidad es obtenida por un proceso de fabricación que

implica sacar la solución fundida del polímero a través de agujeros pequeños de la

extrusora. La cristalinidad de los filamentos del polímero de Kevlar contribuye

perceptiblemente a su fuerza y rigidez únicas.

¿Cómo son realmente las moléculas de Kevlar?

Una resistencia excepcional.

IR

Las amidas tienen la capacidad de adoptar dos formas diferentes, o conformaciones.

Usted puede ver ésto en la figura de una amida de bajo peso molecular. Las dos figuras

son del mismo compuesto, en dos conformaciones diferentes. La que está a la izquierda

se denomina conformación trans, y la que está a la derecha conformación cis.

En latín, trans significa "del otro lado". Así, cuando las cadenas hidrocarbonadas de la

amida están en lados opuestos al enlace peptídico, el enlace entre el oxígeno del

carbonilo y el nitrógeno de la amida, ésta se denomina amida trans. Asimismo, cis en

latín significa "en el mismo lado", y cuando las cadenas hidrocarbonadas están del

mismo lado del enlace peptídico, la llamamos amida cis.

La misma molécula de la amida puede torcerse hacia adelante y hacia atrás entre las

conformaciones cis y trans, originando una pequeña energía.

En las poliamidas también existen las conformaciones cis y trans. Cuando en una

poliamida todos los grupos amida están en su conformación trans, como el nylon 6.6 por

ejemplo, el polímero se estira completamente en una línea recta. Esto es exactamente lo

que deseamos para las fibras, porque las cadenas largas y completamente extendidas se

empaquetan más adecuadamente, dando lugar a la forma cristalina que caracteriza a

las fibras. Pero lamentablemente, siempre existen unos pocos enlaces amida en la

conformación cis. Por ello las cadenas del nylon 6.6 nunca llegan a estar completamente

extendidas.

Sin embargo el Kevlar es diferente. Cuando intenta adoptar la conformación cis, los

hidrógenos de los voluminosos grupos aromáticos se interponen en el camino. La

conformación cis coloca a los hidrógenos un poco más cerca de lo que quisieran estar.

De este modo, el Kevlar permanece casi enteramente en su conformación trans. Y así,

puede extenderse completamente para formar unas hermosas fibras.

Veamos ésto en un primer plano. Observe la figura de abajo y podrá apreciar que

cuando el Kevlar intenta adoptar la conformación cis, no queda espacio suficiente para

los hidrógenos de los fenilos. De modo que la conformación trans es la que se encuentra

generalmente.