Nylon, Kevlar, and the Science of Synthetics

Alexander Richard Pierson

Math 89S

Professor Hubert Bray

6 December 2016

Abstract

This paper will talk about the development of synthetic materials and the

history surrounding their creation. It will talk about they are made as well as the

pros and cons of synthetic materials versus natural materials. The paper will then go

into specifics about how certain materials, including Kevlar and Nylon are made and

for what they are used.

Synthetic fibers are any materials created artificially by humans in a lab

rather than in nature. They often take the form of long strands and are inspired by,

mimic, and improve upon the polymers created in nature. Unlike naturally created

fibers, though, which are formed by adding monomers together one at a time,

synthetics fibers are created by extruding, or essentially spinning, objects through

materials prone to connecting to each other. In the late 19th Century, British

Above: A machine used for spinning viscose rayon, an early synthetic fiber

physicist and chemist Joseph Swan became the first person to successfully create a

synthetic fiber through this process, using a liquid containing a molecule similar to

cellulose, an essential building block of plants. Swan used the fiber to create the first

filaments in incandescent light bulbs. Following soon after this, many other

scientists, including French engineer Hilaire de Chardonnet, created synthetic

fabrics mimicking the consistency of silk. After that, in the early 20th century, there

was a rush to create useful synthetic fibers and an urge to commercialize them for

monetary gain. Many products were created, but nothing really took off until the

1930s, in which an American researcher named Wallace Carothers created a

material that changed the world, nylon. It began as a replacement for silk, in time for

Above: Wallace Carothers

rationing time in World War II, where it was used in parachutes and ropes for the

military, as well as in women’s stockings. Nylon slowly became incorporated into

everyday life in innumerable ways, as it could be used in many ways. Nylons

originally only took the form of strands but were then able to be formed into films

or different shapes, rendering them used in purposes not practical before when

strands had to be woven or joined together. As nylon was taking off, more synthetics

were being developed. Materials that were stronger, more resilient, and lighter than

anything created before. Some of those created were called Aramids, incredibly

strong, heat resistant materials that include Nomex and Kevlar. These materials

have essentially become synonymous with body armor, and indeed they are often

used for this purpose, but they have been used in bicycle tires and as a substitute for

asbestos as well.

Nylon is not just one type of material but actually a family of materials that

take a similar shape and have similar properties. Nylons can be made in many

different ways but are all long chains of repeating monomers held together by

peptide bonds. The molecules consist of Hydrogen, Oxygen, Nitrogen and Carbon

atoms bonded together, and as the monomers bond together, water molecules are

given off. The chemical reaction is given below:

The properties and distinctions in the type of nylon come from the R and R’

groups in the monomers, as most nylon has the same form in the parts of monomers

that join together. Two of the most common forms of nylon are nylon 6,6 and nylon

6. These materials have the same ratio of each type of atom in its structure, but the

monomers that make it up are different so they have different properties. Nylon 6 is

called such because it is made up of one type of monomer, caprolactam, which has 6

carbon atoms and joins head-to-tail throughout the chain. Nylon 6,6 is made up of

two different monomers, hexamethylene diamine and adipic acid, which alternate

down the chain of the polyamide.

One of the main differences between nylon 6,6 and nylon 6 is in their ability

to form hydrogen bonds. This determines a lot of the properties of nylon so the fact

that nylon 6,6 forms stronger hydrogen bonds is significant. There are 2 ways to

orient a molecule to form a hydrogen bond with nylon 6, and in approximately half

of its bonds, it is oriented in such a way that the bond is weaker. The only way to

create a hydrogen bond in nylon 6,6 creates a strong bond. Nylon 6,6 is also more

crystalline than nylon 6. They are both semi-crystalline, meaning they have parts

that are amorphous and parts that have more of a rigid structure, but nylon 6,6 has

more parts that are ordered. This causes nylon 6,6 to exhibit properties such as

higher resilience to compression, and higher melting point. Nylon 6,6 also has a

lower permeability due to the fact that its more crystalline nature allows it to stack

and group together more tightly.

Aramids are produced slightly differently in that the polymer is prepared

first and then spun to form chains. The general chemical formula is as follows:

n NH2−Ar−COCl → −(NH−Ar−CO)n− + n HCl

The chains of these polymers that are formed by the spinning are highly ordered, so

they stack together in a very cohesive and strong way, so that the strength of the

chemical bonds can be utilized. For this reason, the permeability of aramids is much

Above: Kevlar, an aramid used extensively in body armor

lower than nylons and they as a result are stronger. This leads to their use in body

armor and materials like bicycle tires, which need to be airtight and maintain their

structure without breaking under stress. The close packing also means that heat

transfer is improved, so aramids are much less susceptible to heat damage than

nylons or other synthetics. For this reason aramids are used in fire-retardant

materials and clothing.

Polyesters are another type of synthetic that can often include naturally

occurring chemicals, and are often used in clothing. Polyester is formed in a similar

way to other synthetics, but when is complete is a lot more flexible and stretchy

than the other synthetics mentioned earlier in the paper. Some polyesters also have

the added benefit of benefit of being more biodegradable than other synthetics,

which makes them a popular material in things that will be thrown away. However,

polyesters are highly flammable, and prone not only to heat damage but also

ignition.

Synthetic materials are a very interesting topic, due to the fact that they all

look more or less the same-they are made up of long strands of monomers-but they

can have such different and fascinating properties. Synthetics have truly shaped our

world and everything we do in it. Nylon alone was a revolution in plastics that now

make up essentially everything we use, from gears inside most mechanical objects

to toothbrushes to even the bodies of cars. Since then we have progressed so far as

to be able to develop new synthetics with properties of flexibility, strength, heat

resistance and many more. It is truly remarkable that all of these materials have

more or less the same structure and same process for creation, and all of these

creations leads to inspiration that we will be able to develop even more useful

materials in the future that we can do things we never dreamed of. The journey in

materials technology that began with Joseph Swan is going incredible places.

Bibliography

American Chemical Society National Historic Chemical Landmarks. "Foundations of

Polymer Science: Wallace Carothers and the Development of Nylon". ACS Chemistry

for Life. Retrieved 27 January 2015.

Committee on High-Performance Structural Fibers for Advanced Polymer Matrix

Composites, National Research Council (2005). High-Performance Structural Fibers

for Advanced Polymer Matrix Composites. The National Academies Press.

p. 34. ISBN 0-309-09614-6.

Day, Lance; Ian McNeil (1998). Biographical Dictionary of the History of Technology.

Taylor & Francis. p. 113. ISBN 0415193990.

History of Nylon US Patent 2,130,523 'Linear polyamides suitable for spinning into

strong pliable fibers', U.S. Patent 2,130,947 'Diamine dicarboxylic acid salt' and U.S.

Patent 2,130,948 'Synthetic fibers', all issued September 20, 1938

 Kohan, Melvin (1995). Nylon Plastics Handbook. Munich: Carl Hanser Verlag.

p. 2. ISBN 1569901899.