'
Nylon' is a generic designation for a family of
synthetic polymers first produced on
February 28,
1935 by
Wallace Carothers at
DuPont.
Overview
Nylon is a
thermoplastic silky material, first used commercially in a nylon-
bristled
toothbrush (1938), followed more famously by women's “nylons”
stockings (1940). It is made of
repeating units linked by
peptide bonds (another name for
amide bonds) and is frequently referred to as ''
polyamide'' (PA). Nylon was the first
commercially successful polymer and the first
synthetic fiber to be made entirely from
coal, water and air. These are formed into
monomers of intermediate
molecular weight, which are then reacted to form long
polymer chains. It was intended to be a synthetic replacement for
silk and substituted for it in
parachutes and also making things like ropes, flak vests, vehicle tires, combat uniforms and many other military uses after the
United States entered
World War II in 1941, making stockings hard to find until the war's end. Nylon fibers are now used in
fabrics, bridal veils, carpets, guitar strings and
ropes, and solid nylon is used for
mechanical parts,
drumstick tips and as an
engineering material. Engineering grade Nylon is processed by extrusion, casting &
injection molding. Type 6/6 Nylon 101 is the most common commercial grade of Nylon, and Nylon 6 is the most common commercial grade of cast Nylon.
Chemistry
Nylons are
condensation copolymers formed by reacting equal parts of a
diamine and a
dicarboxylic acid, so that
peptide bonds form at both ends of each monomer in a process analogous to
polypeptide biopolymers. The numerical suffix specifies the numbers of
carbons donated by the monomers; the diamine first and the diacid second. The most common variant is
nylon 6-6 which refers to the fact that the diamine (
hexamethylene diamine) and the diacid (
adipic acid) each donate 6 carbons to the polymer chain. As with other regular
copolymers like
polyesters and
polyurethanes, the "repeating unit" consists of one of each monomer, so that they alternate in the chain. Since each monomer in this copolymer has the same
reactive group on both ends, the direction of the
amide bond reverses between each monomer, unlike natural polyamide
proteins which have overall directionality:
C terminal →
N terminal. In the laboratory, nylon 6,6 can also be made using
adipoyl chloride instead of adipic
It is difficult to get the proportions exactly correct, and deviations can lead to chain termination at molecular weights less than a desirable 10,000
daltons (
u). To overcome this problem, a
crystalline, solid "nylon
salt" can be formed at
room temperature, using an exact 1:1
ratio of the
acid and the
base to neutralize each other. Heated to 285 °C, the salt reacts to form nylon polymer. Above 20,000 daltons, it is impossible to spin the chains into
yarn, so to combat this, some
acetic acid is added to react with a free amine end group during polymer elongation to limit the molecular weight. In practice, and especially for 6,6, the monomers are often combined in a water solution. The water used to make the solution is evaporated under controlled conditions, and the increasing concentration of "salt" is polymerized to the final molecular weight.
DuPont patented
[1] nylon 6,6, so in order to compete, other companies (particularly the German
BASF) developed the
homopolymer nylon 6, or
polycaprolactam — not a condensation polymer, but formed by a
ring-opening polymerization (alternatively made by polymerizing
aminocaproic acid). The peptide bond within the caprolactam is broken with the exposed
active groups on each side being incorporated into two new bonds as the monomer becomes part of the polymer backbone. In this case, all amide bonds lie in the same direction, but the properties of nylon 6 are sometimes indistinguishable from those of nylon 6,6 — except for melt temperature (N6 is lower) and some fiber properties in products like carpets and textiles. There is also nylon 9.
Nylon 5,10, made from
pentamethylene diamine and
sebacic acid, was studied by Carothers even before nylon 6,6 and has superior properties, but is more expensive to make. In keeping with this naming convention, "nylon 6,12" (N-6,12) or "PA-6,12" is a copolymer of a 6C diamine and a 12C diacid. Similarly for N-5,10 N-6,11; N-10,12, etc. Other nylons include copolymerized dicarboxylic acid/diamine products that are ''not'' based upon the monomers listed above. For example, some
aromatic nylons are polymerized with the addition of diacids like
terephthalic acid (→
Kevlar) or
isophthalic acid (→
Nomex), more commonly associated with polyesters. There are copolymers of N-6,6/N6; copolymers of N-6,6/N-6/N-12; and others. Because of the way polyamides are formed, nylon would seem to be limited to unbranched, straight chains. But "star" branched nylon can be produced by the condensation of dicarboxylic acids with
polyamines having three or more
amino groups.
The general reaction is:
:
A molecule of
water is given off and the nylon is formed. Its properties are determined by the R and R' groups in the monomers. In nylon 6,6, R' = 6C and R = 4C
alkanes, but one also has to include the two carboxyl
carbons in the diacid to get the number it donates to the chain. In
Kevlar, both R and R' are
benzene
rings.
Nylon Fiber
The
Federal Trade Commissions' Definition for Nylon Fiber: A manufactured fiber in which the fiber forming substance is a long-chain synthetic polyamide in which less than 85% of the amide-linkages are attached directly (-CO-NH-) to two aliphatic groups.
★ A synthetic
thermoplastic fiber. (Nylon melts/glazes easily at relatively low temperatures).
★ Round, smooth, and shiny
filament fibers
★ cross sections can be either
★
★ trilobal to imitate silk
★
★ multilobal to increase staple like appearance and hand
★ It's most widely used structures are
multifilament,
monofilament,
staple or
tow and is available as partially drawn or as finished filaments.
★ Regular nylon has a round cross section and is perfectly uniform. The filaments are generally completely transparent unless they have been delustered or solution dyed. Thus, they are microscopically recognized as glass rods.
★ Molecular chains of nylon are long and straight variations but have no side chains or linkages.
★
★ Cold drawing (step 18 on the model) can align the chains so they are oriented with the lengthwise direction and are highly
crystalline.
★ Nylon is related chemically to the protein fibers silk and wool.
★
★ They both have similar dye sites but nylon has many fewer dye sites than wool.
Basic Concepts of Nylon Production
★ The first approach: combining molecules with an acid (COOH) group on each end are reacted with two chemicals that contain amine(NH2)groups on each end.
This process creates
nylon 6,6, made of hexamethylene diamine with six carbon atoms and acidipic acid, as well as six carbon atoms.
★ The second approach: a compound has an acid at one end and an amine at the other and is polymerized to for a chain with repeating units of(-NH-[CH2]n-CO-)x.
★
★ In other words, nylon 6 is made from a single six-carbon substance called caprolactam.
★
★ In this equation, if n=5, then
nylon 6 is the assigned name. (may also be referred to as polymer)
'Nylon 6,6'
★ Pleats and creases can be heat-set at higher temperatures
★ Difficult to dye
'Nylon 6'
★ Better dye Affinity
★ Softer Hand
★ Greater elasticity and elastic recovery
★ Better weathering properties; better sunlight resistance
'Full Nylon Production Model'
'Producers'
The producers of nylon include: Honeywell Nylon Inc., Invista, Wellman Inc. among many others. The Dupont Company, is the most famous pioneer of the nylon we know today. The companies above now produce the nylon used in our everyday lives.
Characteristics
★ Variation of luster: nylon has the ability to be very lusterous, semilusterous or dull.
★ Durability: it's high tenacity fibers are used for seatbelts, tire cords, ballistic cloth and other uses.
★ High elongation
★ Excellent abrasion resistance
★ Highly resilient (nylon fabrics are heat-set)
★ Nylon paved the way for 'easy-care garments'
★ High resistance:
★
★ insects and fungi
★
★ molds, mildew, rot
★
★ many chemicals
★ Single most important use of Nylon is in carpets
Bulk properties
Above their
melting temperatures, ''T''
m,
thermoplastics like nylon are
amorphous solids or viscous
fluids in which the chains approximate
random coils. Below ''T''
m, amorphous regions alternate with regions which are
lamellar crystals.
[1] The amorphous regions contribute elasticity and the crystalline regions contribute strength and rigidity. The
planar amide (-CO-NH-) groups are very
polar, so nylon forms multiple
hydrogen bonds among adjacent strands. Because the nylon backbone is so regular and symmetrical, especially if all the amide bonds are in the
''trans'' configuration, nylons often have high crystallinity and make excellent fibers. The amount of crystallinity depends on the details of formation, as well as on the kind of nylon. Apparently it can never be
quenched from a
melt as a completely amorphous solid.
Nylon 6,6 can have multiple parallel strands aligned with their neighboring peptide bonds at coordinated separations of exactly 6 and 4 carbons for considerable lengths, so the
carbonyl oxygens and amide
hydrogens can line up to form interchain
hydrogen bonds repeatedly, without interruption. Nylon 5,10 can have coordinated runs of 5 and 8 carbons. Thus parallel (but not antiparallel) strands can participate in extended, unbroken, multi-chain
β-pleated sheets, a strong and tough supermolecular structure similar to that found in natural
silk fibroin and the
β-keratins in
feathers. (Proteins have only an amino acid α-carbon separating sequential -CO-NH- groups.) Nylon 6 will form uninterrupted
H-bonded sheets with mixed directionalities, but the β-sheet wrinkling is somewhat different. The three-dimensional disposition of each
alkane hydrocarbon chain depends on
rotations about the 109.47°
tetrahedral bonds of singly-bonded carbon atoms.
When
extruded into fibers through pores in an
industrial spinneret, the individual polymer chains tend to align because of
viscous flow. If subjected to
cold drawing afterwards, the fibers align further, increasing their crystallinity, and the material acquires additional
tensile strength.
[2] In practice, nylon fibers are most often drawn using heated rolls at high speeds.
Block nylon tends to be less crystalline, except near the surfaces due to
shearing
stresses during formation. Nylon is
clear and
colorless, or milky, but is easily
dyed. Multistranded nylon cord and rope is slippery and tends to unravel. The ends can be
melted and fused with a heat source such as a
flame or
electrode to prevent this.
There are carbon fiber/nylon
composities with higher
density than pure nylon.
When dry, polyamide is a good electrical insulator. However, polyamide is
hygroscopic. The absorption of water will change some of the
material's properties such as its
electrical resistance. Nylon is less absorbant than wool or cotton.
Historical uses
Bill Pittendreigh,
DuPont, and other individuals and corporations worked diligently during the first few months of
World War II to find a way to replace Asian
silk with nylon in
parachutes. It was also used to make
tires,
tents,
ropes,
ponchos, and other
military supplies. It was even used in the production of a high-grade paper for
U.S. currency. At the outset of the war,
cotton accounted for more than 80% of all fibers used, and manufactured and
wool fibers accounted for the remaining 20%. By August 1945, manufactured fibers had taken a market share of 25% and cotton had dropped.
Some of the terpolymers based upon nylon are used every day in packaging. Nylon has been used for
meat wrappings and
sausage sheaths.
Etymology
In 1940 John W. Eckelberry of DuPont stated that the letters "nyl" were arbitrary and the "on" was copied from the suffixes of other fibers such as
cotton and
rayon. A later publication by DuPont (''Context'', vol. 7, no. 2,
1978) explained that the name was originally intended to be "No-Run" ("run" meaning "unravel"), but was modified to avoid making such an unjustified claim and to make the word sound better. The story goes that Carothers changed one letter at a time until DuPont's management was satisfied. But he was not involved in the nylon project during the last year of his life, and committed suicide before the name was coined.
Two theories about the origin of the name claim that it is an
acronym of "Now you've lost, Old
Nippon" (N.Y.L.O.N.), or that it stands for "
New York-
London". In the latter case, it is claimed that these were the two cities where the product was researched and developed, or that the inspiration came from a New York to London airplane ticket. There is no evidence for the 'airline ticket' theory, though some compelling evidence of the latter from contemporary researchers at
Oxford University who assisted in development...Oxford can be viewed as London from New York, but Nylox would have been more accurate.
Uses
★
carpet fiber
★
clothing
★
fishing lines
★
footwear
★ nylon
fiber
★
pantyhose
★
toothbrush bristles
★
velcro
★
airbag fiber
★
pants
★
auto parts: intake
manifolds,
gas (petrol) tanks
★
slings and
rope used in
climbing gear
★
machine parts, such as
gears and
bearings
★
parachutes
★ metallized nylon
balloons
★
classical and
flamenco guitar strings
★
paintball marker bolts
★
racquetball,
squash, and
tennis racquet strings
★
Strings for
String instruments
★
Drumstick heads
★ As filter media in sterlizing grade filters
★ Flexible tubing
★ Basketball netting
See also
★
Polymers
★
Plastic
★
Nylon riots
★
Cordura
★
Nylon 6
References
External links
★
A chemical demonstration of the synthesis of nylon in Carleton University's CHEM 1000 course. (Video)
★
Article on making Nylon at home
★
Typical physical characteristics of nylon
★
Polyamide material description
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