Nylon 6 or polycaprolactam is a

polymer A polymer () is a chemical substance, substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeat unit, repeating subunits derived from one or more species of monomers. Due to their br ...

, in particular

semicrystalline Crystallinity refers to the degree of structural order in a solid. In a crystal, the atoms or molecules are arranged in a regular, periodic manner. The degree of crystallinity has a large influence on hardness, density, Transparency and transluc ...

polyamide A polyamide is a polymer with repeating units linked by amide bonds. Polyamides occur both naturally and artificially. Examples of naturally occurring polyamides are proteins, such as wool and silk. Artificially made polyamides can be made throug ...

. Unlike most other

nylon Nylon is a family of synthetic polymers characterised by amide linkages, typically connecting aliphatic or Polyamide#Classification, semi-aromatic groups. Nylons are generally brownish in color and can possess a soft texture, with some varieti ...

s, nylon 6 is not a

condensation polymer In polymer chemistry, condensation polymers are any kind of polymers whose process of polymerization involves a condensation reaction (i.e. a small molecule, such as water or methanol, is produced as a byproduct). Natural proteins as well as s ...

, but instead is formed by

ring-opening polymerization In polymer chemistry, ring-opening polymerization (ROP) is a form of chain-growth polymerization in which the terminus of a polymer chain attacks cyclic monomers to form a longer polymer (see figure). The reactive center can be radical, anion ...

; this makes it a special case in the comparison between condensation and

addition polymer In polymer chemistry, an addition polymer is a polymer that forms by simple linking of monomers ''without'' the co-generation of other products. Addition polymerization differs from condensation polymerization, which ''does'' co-generate a product ...

s. Its competition with nylon 66 and the example it set have also shaped the economics of the

synthetic fibre Synthetic fibers or synthetic fibres (in British English; see spelling differences) are fibers made by humans through chemical synthesis, as opposed to natural fibers that are directly derived from living organisms, such as plants like cotton or ...

industry. It is sold under numerous trade names including Perlon (Germany), Dederon (former East Germany), Nylatron, Capron, Ultramid, Akulon, Kapron (former Soviet Union and satellite states), Rugopa (Turkey) and Durethan.

History

Polycaprolactam was developed by

Paul Schlack Paul Schlack (22 December 1897 – 19 August 1987) was a German chemist. He completed his studies at the Technical University of Stuttgart in 1921 and worked as a research chemist in Copenhagen for a year, before returning to Stuttgart. He re ...

IG Farben I. G. Farbenindustrie AG, commonly known as IG Farben, was a German Chemical industry, chemical and Pharmaceutical industry, pharmaceutical conglomerate (company), conglomerate. It was formed on December 2, 1925 from a merger of six chemical co ...

in late 1930s (first synthesized in 1938) to reproduce the properties of

Nylon 66 Nylon 66 (loosely written nylon 6-6, nylon 6/6, nylon 6,6, or nylon 6:6) is a type of polyamide or nylon. It, and nylon 6, are the two most common for textile and plastic industries. Nylon 66 is made of two monomers each containing six carbon at ...

without violating the

patent A patent is a type of intellectual property that gives its owner the legal right to exclude others from making, using, or selling an invention for a limited period of time in exchange for publishing an sufficiency of disclosure, enabling discl ...

on its production. (Around the same time, Kohei Hoshino at Toray also succeeded in synthesizing nylon 6.) It was marketed as Perlon, and industrial production with a capacity of 3,500 tons per year was established in Nazi Germany in 1943, using phenol as a feedstock. At first, the polymer was used to produce coarse fiber for artificial bristle, then the fiber quality was improved, and Germans started making parachutes, cord for aircraft tires and towing cables for gliders. The Soviet Union began its development of an analog in the 1940s, while negotiating with Germany on building an IG Farben plant in Ukraine, basic scientific work was ongoing in 1942. The production only started in 1948 in Klin, Moscow Oblast, after USSR obtained the 2000 volumes of IG Farben, and 10,000 volumes of

AEG The initials AEG are used for or may refer to: Common meanings * AEG (German company) ; AEG) was a German producer of electrical equipment. It was established in 1883 by Emil Rathenau as the ''Deutsche Edison-Gesellschaft für angewandte El ...

technical documentation, as a result of victory in World War II.

Synthesis

Nylon 6 can be modified using comonomers or stabilizers during polymerization to introduce new chain end or functional groups, which changes the reactivity and chemical properties. It is often done to change its dyeability or flame retardance. Nylon 6 is synthesized by

caprolactam Caprolactam (CPL) is an organic compound with the chemical formula, formula (CH2)5C(O)NH. This colourless solid is a lactam (a cyclic amide) of caproic acid. Global demand for this compound is approximately five million tons per year, and the vast ...

. Caprolactam has 6 carbons, hence ''Nylon 6''. When caprolactam is heated at about 533 K in an inert

atmosphere An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosph ...

nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...

for about 4–5 hours, the ring breaks and undergoes

polymerization In polymer chemistry, polymerization (American English), or polymerisation (British English), is a process of reacting monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are many fo ...

. Then the molten mass is passed through

spinnerets A spinneret is a silk-spinning organ of a spider or the larva of an insect. Some adult insects also have spinnerets, such as those borne on the forelegs of Embioptera. Spinnerets are usually on the underside of a spider's opisthosoma, and ar ...

to form fibres of nylon 6. During

, the amide bond within each caprolactam

molecule A molecule is a group of two or more atoms that are held together by Force, attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemi ...

is broken, with the active groups on each side re-forming two new bonds as the

monomer A monomer ( ; ''mono-'', "one" + '' -mer'', "part") is a molecule that can react together with other monomer molecules to form a larger polymer chain or two- or three-dimensional network in a process called polymerization. Classification Chemis ...

becomes part of the polymer backbone. Unlike nylon 6,6, in which the direction of the

amide In organic chemistry, an amide, also known as an organic amide or a carboxamide, is a chemical compound, compound with the general formula , where R, R', and R″ represent any group, typically organyl functional group, groups or hydrogen at ...

bond reverses at each bond, all nylon 6 amide bonds lie in the same direction (see figure: note the N to C orientation of each amide bond).

Properties

Nylon 6 fibres are tough, possessing high tensile strength, elasticity and lustre. They are wrinkleproof and highly resistant to abrasion and chemicals such as acids and alkalis. The fibres can absorb up to 2.4% of water, although this lowers tensile strength. The glass transition temperature of Nylon 6 is 47 °C. As a synthetic fibre, Nylon 6 is generally white but can be dyed in a solution bath prior to production for different color results. Its tenacity is 6–8.5 gf/ D with a density of 1.14g/cm. Its melting point is at 215 °C and can protect heat up to 150 °C on average.

Biodegradation

''Flavobacterium'' sp. 5and ''Pseudomonas'' sp. (NK87) degrade

oligomer In chemistry and biochemistry, an oligomer () is a molecule that consists of a few repeating units which could be derived, actually or conceptually, from smaller molecules, monomers.Quote: ''Oligomer molecule: A molecule of intermediate relativ ...

s of Nylon 6, but not polymers. Certain

white rot A wood-decay or xylophagous fungus is any species of fungus that digests moist wood, causing it to rot. Some species of wood-decay fungi attack dead wood, such as ''Serpula lacrymans'', and some, such as '' Armillaria'' (honey fungus), are par ...

fungal strains can also degrade Nylon 6 through oxidation. Compared to aliphatic polyesters, Nylon 6 has been said to have poor

biodegradability Biodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. It is generally assumed to be a natural process, which differentiates it from composting. Composting is a human-driven process in which biodegrada ...

. Strong interchain interactions from hydrogen bonds between molecular nylon chains is said to be the cause by some sources. However, in 2023 a team of

Northwestern University Northwestern University (NU) is a Private university, private research university in Evanston, Illinois, United States. Established in 1851 to serve the historic Northwest Territory, it is the oldest University charter, chartered university in ...

chemists led by Linda Broadbelt and Tobin J. Marks developed rare earth

metallocene A metallocene is a compound typically consisting of two cyclopentadienyl anions (, abbreviated Cp) bound to a metallic element, metal center (M) in the oxidation state II, with the resulting general formula Closely related to the metallocenes are ...

catalysts that rapidly break Nylon 6 down back to caprolactam at 220°C, which is considered mild conditions.

Production in Europe

At present, polyamide 6 is a significant construction material used in many industries, for instance in the automotive industry, aircraft industry, electronic and electrotechnical industry, clothing industry and medicine. Annual demand for polyamides in

Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

amounts to a million

tonne The tonne ( or ; symbol: t) is a unit of mass equal to 1,000 kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton in the United States to distinguish it from the non-metric units of the s ...

s. They are produced by all leading chemical companies. The largest producers of polyamide 6 in Europe: # Fibrant, 260,000 tonnes per year #

BASF BASF SE (), an initialism of its original name , is a European Multinational corporation, multinational company and the List of largest chemical producers, largest chemical producer in the world. Its headquarters are located in Ludwigshafen, Ge ...

, 240,000 tonnes per year #

Lanxess Lanxess AG is a German specialty chemicals company based in Cologne, Germany. It was founded in 2004 after Bayer AG spun off its chemicals division and parts of its polymers business. History The company's roots trace back to 1863, with the fou ...

, 170,000 tonnes per year # Radici, 125,000 tonnes per year # DOMO, 100,000 tonnes per year #

Grupa Azoty Grupa Azoty S.A. (until 2013 ''Zakłady Azotowe in Tarnów-Mościce'') is a major Poland, Polish chemical industry company headquartered in the Mościce district of Tarnów, in the Lesser Poland Voivodeship of southeastern Poland. The company wa ...

, 100,000 tonnes per year

References

{{Reflist, 30em

External links

The Promise of Nylon 6: A Case Study in Intelligent Product Design by William McDonough & Michael Braungart
Polyamides Plastics Synthetic fibers German inventions of the Nazi period