The Plastic automotive engine
has its origins in the late 1970s with research and work done by
Matthew (Matti) Holtzberg of Polimotor Research and his associates. Since then Holtzberg and others have done steady work in the field.
Holtzberg's early work
Matti Holtzberg first attempted to make polymer pistons for an Austin Mini
engine in 1969. The pistons ran for only 20 minutes until failure.
Holtzberg remedied this by fitting the pistons with aluminium crowns and
he sold these pistons to racing builders during the early 1970s.
Polimotor research
Matti Holtzberg founded Polimotor Research Inc. in 1979. It was based in Fair Lawn, New Jersey.
The company, in cooperation with its suppliers and sponsors, created
and raced engines consisting of a large percentage of polymers in the
1980s.
Version One
Version one was based on Ford's 2.3-liter Pinto engine and weighed 152 pounds (69 kg) (vs. 415 pounds (188 kg) for its cast iron counterpart). It was designed to produce 318 horsepower (237 kW) at 9200 rpm. It was composed of metal cylinder sleeves, metal combustion chamber tops, metal piston crowns, bearings, valves and seats, and a stock 2.3L Pinto crankshaft. Nearly everything else in the engine, including the block, rods and piston skirts, were made of glass reinforced Polyamide-imidethermoplastic resins manufactured at the time by Amoco Chemicals Co. The engine was never installed in a vehicle.
Although sources claimed that Ford had been a partner in creating the engine, Holtzberg was later quoted as saying that "Ford was not involved at all".
Version Two
Another engine, supposedly based upon the Cosworth BDA and YB series engines, weighed 168 pounds (76 kg), half the weight of its metal counterpart.
Plastic parts included the engine block, cam cover, air intake
trumpets, intake valve stems, piston skirts and wrist pins, connecting
rods, oil scraper piston rings, tappets, valve spring retainers and
timing gears.
The engine was raced over two seasons. It was raced in a Lola T616 HU04 and competed in the International Motor Sports Association's (IMSA) Camel GT Championship
in the Camel Lights (Group C2) category in 1984 and 1985. The car
earned several top 5 finishes including its best finish of third in
class at the 1985 Lime Rock 2 hours.
Holtzberg patents
Throughout
the 1980s, Holtzberg was granted 10 patents for composite engine parts
and their methods of production. The patents were issued between 1983
and 1988 and are elaborated on in this section.
The first patent issued was for ignition cables, citing prior art
for other non-metallic conductive materials and their ability to reduce
RF interference related problems. These cables consisted of a graphite/resin composite conductor strands and a protective silicone
sheath. The strands were to be twisted together and drawn through the
liquid matrix material, finally being surrounded by the sheath. The two
parts would be extruded together to form the cable and ensure a well
bound structure of thousands of individual graphite composite filaments.
The majority of patents are for Polyamide-imide
engine components, with the potential for graphite, glass or titanium
reinforcement as a composite. The inventions are claimed to have a
superior stiffness-to-weight ratio, be up to 70% lighter than
traditional parts and reduce vibration and forces within the engine. The
composite parts are also claimed to reduce production requirements due
to being injection moulded with consequently reduced finishing work.
Although the temperature, time and other process variables differ
between parts, the general manufacturing process follows. The component
is first injection moulded
and allowed to cool past its plastic deformation temperature. It is
then post cured by solid state polymerisation at a series of temperature
steps. This is performed in an inert atmosphere which helps to expel
by-products of reactions until the polymer is chemically stable. During
this process the heat deflection temperature
of the material also increases. The part is now cooled and
post-processed. Post processing can take the form of machining,
insertion or adhesion of metal parts or a simple cleaning of the part.
Composite Castings LLC
In 1990 Matti Holtzberg founded Composite Castings LLC, based in West Palm Beach, Florida. By 2011 they had developed a V4carbon reinforced epoxy composite engine block with materials supplied by Toho Tenax.
The block is claimed by Holtzberg to be up to 50% lighter than an
equivalent aluminium model. The blocks are produced to net shape so
minimal finishing work is required to make them ready for use. Holtzberg
claims that this reduces tooling and production costs by 50% in
comparison to die casting.
Fraunhofer and Sumitomo research
In April 2015 the Fraunhofer group in collaboration with the high performance polymer division of Sumitomo Bakelite Co announced their development of a single cylinder research engine with a casing made of injection mouldedglass fibre reinforced phenolic resin (55/45 respective composition). The engine weighs about 20% less than an equivalent of aluminium. Their design uses metal inserts in places of high thermal and mechanical stress, for example in the cylinder liner.
In May 2015 it was reported that the Belgian chemical company Solvay had shown interest in reviving the concept with assistance from Matti Holtzberg.
The engine is planned to weigh less than 148 pounds (67 kg) and
generate over 420 horsepower (310 kW), it is also planned to be
turbocharged. Several components will be replaced with polymer counterparts, these can be seen in the table below.
The engine was planned to be installed in a Norma M-20 chassis and raced at Lime Rock in 2016 and a possible Le Mans entry in 2017. However this did not materialise.
Polyamide-imides are either thermosetting or thermoplastic, amorphous polymers
that have exceptional mechanical, thermal and chemical resistant
properties. Polyamide-imides are used extensively as wire coatings in
making magnet wire. They are prepared from isocyanates and TMA
(trimellic acid-anhydride) in N-methyl-2-pyrrolidone (NMP). A prominent distributor of polyamide-imides is Solvay Specialty Polymers, which uses the trademark Torlon.
Polyamide-imides display a combination of properties from both polyamides and polyimides, such as high strength, melt processibility,exceptional high heat capability, and broad chemical resistance.
Polyamide-imide polymers can be processed into a wide variety of forms,
from injection or compression molded parts and ingots, to coatings,
films, fibers and adhesives. Generally these articles reach their
maximum properties with a subsequent thermal cure process.
The currently popular commercial methods to synthesize polyamide-imides are the acid chloride route and the isocyanate route.
Acid chloride route
Trimellitic acid chlorideMethylene dianiline
The earliest route to polyamide-imides is the condensation of an aromatic diamine, such as methylene dianiline (MDA) and trimellitic acid chloride
(TMAC). Reaction of the anhydride with the diamine produces an
intermediate amic acid. The acid chloride functionality reacts with the
aromatic amine to give the amide bond and hydrochloric acid
(HCl) as a by-product. In the commercial preparation of
polyamideimides, the polymerization is carried out in a dipolar, aprotic
solvent such as N-methylpyrrolidone (NMP), dimethylacetamide (DMAC), dimethylformamide (DMF), or dimethylsulfoxide
(DMSO) at temperatures between 20–60 °C. The byproduct HCl must be
neutralized in situ or removed by washing it from the precipitated
polymer. Further thermal treatment of the polyamideimide polymer
increases molecular weight and causes the amic acid groups to form
imides with the evolution of water.
Diisocyanate route
This is the primary route to polyamide-imides which are used as wire enamels. A diisocyanate, often 4,4’-methylenediphenyldiisocyanate (MDI), is reacted with trimellitic anhydride
(TMA). The product achieved at the end of this process is a high
molecular weight, fully imidized polymer solution with no condensation
byproducts, since the carbon dioxide gas byproduct is easily removed.
This form is convenient for the manufacture of wire enamel or coatings.
The solution viscosity is controlled by stoichiometry, monofunctional
reagents, and polymer solids. The typical polymer solids level is 35-45%
and it may be diluted further by the supplier or user with diluents.
Fabrication
Polyamide-imides are commercially used for coatings and molded articles.
Coatings
The
product used mainly for coatings is sold in a powdered form and is
roughly 50% imidized. One of the major uses is as a magnet wire enamel.
The magnet wire enamel is made by dissolving the PAI powder in a strong,
aprotic solvent such as N-methyl pyrrolidone. Diluents and other
additives can be added to provide the correct viscosity for application
to the copper or aluminum conductor. Application is typically done by
drawing the conductor through a bath of enamel and then through a die to
control coating thickness. The wire is then passed through an oven to
drive off the solvent and cure the coating. The wire usually is passed
through the process several times to achieve the desired coating
thickness.
The PAI enamel is very thermally stable as well as abrasion and
chemical resistant. PAI is often used over polyester wire enamels to
achieve higher thermal ratings.
PAI is also used in decorative, corrosion resistant coatings for industrial uses, often in conjunction with fluoropolymers.
The PAI aids in adhering the fluoropolymer to the metal substrate. They
also find usage in non-stick cookware coatings. While solvents can be
used, some water-borne systems are used. These are possible because the
amide-imide contains acid functionality.
Molded or machined articles
The
polyamide-imides used for molded articles are also based on aromatic
diamines and trimellitic acid chloride, but the diamines are different
from those used in the products used for coatings and the polymer is
more fully imidized prior to compounding and pelletizing. Resins for
injection molding include unreinforced, glass-fiber reinforced, carbon
fiber reinforced, and wear resistant grades. These resins are sold at a
relatively low molecular weight so they can be melt processed by
extrusion or injection-molding. The molded articles are then thermally
treated for several days at temperatures up to 260 °C (500 °F). During
this treatment, commonly referred to a postcure, the molecular weight
increases through chain extension and the polymer gets much stronger and
more chemically resistant. Prior to postcure, parts can be reground and
reprocessed. After postcure, reprocessing is not practical.
Polyamide-imide
resin is hygroscopic, and picks up ambient moisture. Before processing
the resin, drying is required to avoid brittle parts, foaming, and other
molding problems. The resin must be dried to a moisture content of
500 ppm or less. A desiccant
dryer capable of maintaining a dew point of −40 °F (−40 °C) is
recommended. If drying is done in pans or trays, put the resin in layers
no more than 2 to 3 inches (5 to 8 cm) deep in drying trays. Dry for 24
hours at 250 °F, or 16 hours at 300 °F, or 8 hours at 350 °F. If drying
at 350 °F (177 °C), limit drying time to 16 hours. For the injection
molding press, a desiccant hopper dryer is recommended. The circulating
air suction pipe should be at the base of the hopper, as near the feed
throat as possible.
In general, modern reciprocating-screw injection molding presses
with microprocessor controls capable of closed-loop control are
recommended for molding PAI. The press should be fitted with a low
compression ratio, constant taper screw. The compression ratio should be
between 1.1 and 1.5 to 1, and no check device should be used. The
starting mold temperatures are specified as follows:
Zone
Temp, °F
Temp, °C
Feed zone
580
304
Middle zone
620
327
Front zone
650
343
Nozzle
700
371
The mold temperature should be in the range of 325 °F to 425 °F (163 °C to 218 °C).
Other applications
The
high temperature and chemical resistance of polyamide-imides make them
in principle suitable for membrane based gas separations. The separation
of contaminants such as CO2, H2S,
and other impurities from natural gas wells is an important industrial
process. Pressures exceeding 1000 psia demand materials with good
mechanical stability. The highly polar H2S and polarizable CO2 molecules can strongly interact with the polymer membranes causing swelling and plasticization
due to high levels of impurities. Polyamide-imides can resist
plasticization because of the strong intermolecular interactions arising
from the polyimide functions as well as the ability of the polymer
chains to hydrogen bond with one another as a result of the amide bond.
Although not currently used in any major industrial separation,
polyamide-imides could be used for these types of processes where
chemical and mechanical stability are required.
Nylons are white or colorless and soft; some are silk-like. They are thermoplastic, which means that they can be melt-processed into fibers, films, and diverse shapes. The properties of nylons are often modified by blending with a wide variety of additives.
Many kinds of nylon are known. One family, designated nylon-XY, is derived from diamines and dicarboxylic acids
of carbon chain lengths X and Y, respectively. An important example is
nylon-6,6. Another family, designated nylon-Z, is derived from
aminocarboxylic acids of with carbon chain length Z. An example is
nylon-[6].
Nylon polymers have significant commercial applications in fabric
and fibers (apparel, flooring and rubber reinforcement), in shapes
(molded parts for cars, electrical equipment, etc.), and in films
(mostly for food packaging).
Researchers at DuPont began developing cellulose-based fibers, culminating in the synthetic fiber rayon. DuPont's experience with rayon was an important precursor to its development and marketing of nylon.
DuPont's invention of nylon spanned an eleven-year period,
ranging from the initial research program in polymers in 1927 to its
announcement in 1938, shortly before the opening of the 1939 New York World's Fair. The project grew from a new organizational structure at DuPont, suggested by Charles Stine
in 1927, in which the chemical department would be composed of several
small research teams that would focus on "pioneering research" in
chemistry and would "lead to practical applications". Harvard instructor Wallace Hume Carothers
was hired to direct the polymer research group. Initially he was
allowed to focus on pure research, building on and testing the theories
of German chemist Hermann Staudinger. He was very successful, as research he undertook greatly improved the knowledge of polymers and contributed to the science.
Nylon was the first commercially successful synthetic thermoplastic polymer. DuPont began its research project in 1927.
The first nylon, nylon 66, was synthesized on February 28, 1935, by Wallace Hume Carothers at DuPont's research facility at the DuPont Experimental Station. In response to Carothers' work, Paul Schlack at IG Farben developed nylon 6, a different molecule based on caprolactam, on January 29, 1938.
In the spring of 1930, Carothers and his team had already synthesized two new polymers. One was neoprene, a synthetic rubber greatly used during World War II.
The other was a white elastic but strong paste that would later become
nylon. After these discoveries, Carothers' team was made to shift its
research from a more pure research approach investigating general
polymerization to a more practically focused goal of finding "one
chemical combination that would lend itself to industrial applications".
It was not until the beginning of 1935 that a polymer called "polymer 6-6" was finally produced. Carothers' coworker, Washington University alumnus Julian W. Hill had used a cold drawing method to produce a polyester in 1930. This cold drawing method was later used by Carothers in 1935 to fully develop nylon.
The first example of nylon (nylon 6.6) was produced on February 28,
1935, at DuPont's research facility at the DuPont Experimental Station.
It had all the desired properties of elasticity and strength. However,
it also required a complex manufacturing process that would become the
basis of industrial production in the future. DuPont obtained a patent
for the polymer in September 1938, and quickly achieved a monopoly of the fiber. Carothers died 16 months before the announcement of nylon, therefore he was never able to see his success.
Nylon was first used commercially in a nylon-bristledtoothbrush in 1938, followed more famously in women's stockings or "nylons" which were shown at the 1939 New York World's Fair and first sold commercially in 1940,
whereupon they became an instant commercial success with 64 million
pairs sold during their first year on the market. During World War II,
almost all nylon production was diverted to the military for use in parachutes and parachute cord. Wartime uses of nylon and other plastics greatly increased the market for the new materials.
The production of nylon required interdepartmental collaboration
between three departments at DuPont: the Department of Chemical
Research, the Ammonia Department, and the Department of Rayon. Some of the key ingredients of nylon had to be produced using high pressure chemistry, the main area of expertise of the Ammonia Department. Nylon was considered a "godsend to the Ammonia Department",
which had been in financial difficulties. The reactants of nylon soon
constituted half of the Ammonia Department's sales and helped them come
out of the period of the Great Depression by creating jobs and revenue at DuPont.
DuPont's nylon project demonstrated the importance of chemical engineering
in industry, helped create jobs, and furthered the advancement of
chemical engineering techniques. In fact, it developed a chemical plant
that provided 1800 jobs and used the latest technologies of the time,
which are still used as a model for chemical plants today.
The ability to acquire a large number of chemists and engineers quickly
was a huge contribution to the success of DuPont's nylon project.
The first nylon plant was located at Seaford, Delaware, beginning
commercial production on December 15, 1939. On October 26, 1995, the
Seaford plant was designated a National Historic Chemical Landmark by the American Chemical Society.
Early marketing strategies
An
important part of nylon's popularity stems from DuPont's marketing
strategy. DuPont promoted the fiber to increase demand before the
product was available to the general market. Nylon's commercial
announcement occurred on October 27, 1938, at the final session of the Herald Tribune's yearly "Forum on Current Problems", on the site of the approaching New York City world's fair.
The "first man-made organic textile fiber" which was derived from
"coal, water and air" and promised to be "as strong as steel, as fine as
the spider's web" was received enthusiastically by the audience, many
of them middle-class women, and made the headlines of most newspapers. Nylon was introduced as part of "The world of tomorrow" at the 1939 New York World's Fair and was featured at DuPont's "Wonder World of Chemistry" at the Golden Gate International Exposition in San Francisco in 1939. Actual nylon stockings
were not shipped to selected stores in the national market until May
15, 1940. However, a limited number were released for sale in Delaware
before that.
The first public sale of nylon stockings occurred on October 24, 1939,
in Wilmington, Delaware. 4,000 pairs of stockings were available, all of
which were sold within three hours.
Another added bonus to the campaign was that it meant reducing
silk imports from Japan, an argument that won over many wary customers.
Nylon was even mentioned by President Roosevelt's
cabinet, which addressed its "vast and interesting economic
possibilities" five days after the material was formally announced.
However, the early excitement over nylon also caused problems. It
fueled unreasonable expectations that nylon would be better than silk, a
miracle fabric as strong as steel that would last forever and never
run.
Realizing the danger of claims such as "New Hosiery Held Strong as
Steel" and "No More Runs", DuPont scaled back the terms of the original
announcement, especially those stating that nylon would possess the
strength of steel.
Also, DuPont executives marketing nylon as a revolutionary
man-made material did not at first realize that some consumers
experienced a sense of unease and distrust, even fear, towards synthetic
fabrics.
A particularly damaging news story, drawing on DuPont's 1938 patent for
the new polymer, suggested that one method of producing nylon might be
to use cadaverine (pentamethylenediamine),
a chemical extracted from corpses. Although scientists asserted that
cadaverine was also extracted by heating coal, the public often refused
to listen. A woman confronted one of the lead scientists at DuPont and
refused to accept that the rumour was not true.
DuPont changed its campaign strategy, emphasizing that nylon was
made from "coal, air and water", and started focusing on the personal
and aesthetic aspects of nylon, rather than its intrinsic qualities. Nylon was thus domesticated,
and attention shifted to the material and consumer aspect of the fiber
with slogans like "If it's nylon, it's prettier, and oh! How fast it
dries!".
Production of nylon fabric
Nylon stockings being inspected in Malmö, Sweden, in 1954
After nylon's nationwide release in 1940, production was increased. 1300 tons of the fabric were produced during 1940. During their first year on the market, 64 million pairs of nylon stockings were sold. In 1941, a second plant was opened in Martinsville, Virginia, due to the success of the fabric.
Close-up photograph of the knitted nylon fabric used in stockingsNylon fibers visualized using scanning electron microscopy
While nylon was marketed as the durable and indestructible material
of the people, it was sold at about one-and-a-half times the price of silk stockings ($4.27 per pound of nylon versus $2.79 per pound of silk).
Sales of nylon stockings were strong in part due to changes in women's
fashion. As Lauren Olds explains: "by 1939 [hemlines] had inched back up
to the knee, closing the decade just as it started off". The shorter
skirts were accompanied by a demand for stockings that offered fuller
coverage without the use of garters to hold them up.
However, as of February 11, 1942, nylon production was redirected from being a consumer material to one used by the military.
DuPont's production of nylon stockings and other lingerie stopped, and
most manufactured nylon was used to make parachutes and tents for World War II.
Although nylon stockings already made before the war could be
purchased, they were generally sold on the black market for as high as
$20.
Once the war ended, the return of nylon was awaited with great
anticipation. Although DuPont projected yearly production of 360 million
pairs of stockings, there were delays in converting back to consumer
rather than wartime production. In 1946, the demand for nylon stockings could not be satisfied, which led to the Nylon riots. In one instance, an estimated 40,000 people lined up in Pittsburgh to buy 13,000 pairs of nylons. In the meantime, women cut up nylon tents and parachutes left from the war in order to make blouses and wedding dresses.
Between the end of the war and 1952, production of stockings and
lingerie used 80% of the world's nylon. DuPont put focus on catering to
the civilian demand, and continually expanded its production.
Introduction of nylon blends
As
pure nylon hosiery was sold in a wider market, problems became
apparent. Nylon stockings were found to be fragile, in the sense that
the thread often tended to unravel lengthwise, creating 'runs'. People also reported that pure nylon textiles could be uncomfortable due to nylon's lack of absorbency. Moisture stayed inside the fabric near the skin under hot or moist conditions instead of being "wicked" away.
Nylon fabric could also be itchy and tended to cling and sometimes
spark as a result of static electrical charge built up by friction. Also, under some conditions, stockings could decompose
turning back into nylon's original components of air, coal, and water.
Scientists explained this as a result of air pollution, attributing it
to London smog in 1952, as well as poor air quality in New York and Los
Angeles.
The solution found to problems with pure nylon fabric was to blend nylon with other existing fibers or polymers such as cotton, polyester, and spandex.
This led to the development of a wide array of blended fabrics. The new
nylon blends retained the desirable properties of nylon (elasticity,
durability, ability to be dyed) and kept clothes prices low and
affordable. As of 1950, the New York Quartermaster Procurement Agency (NYQMPA), which developed and tested textiles for the Army and Navy,
had committed to developing a wool-nylon blend. They were not the only
ones to introduce blends of both natural and synthetic fibers. America's Textile Reporter referred to 1951 as the "Year of the blending of the fibers". Fabric blends included mixes like "Bunara" (wool-rabbit-nylon) and "Casmet" (wool-nylon-fur).
In Britain, in November 1951, the inaugural address of the 198th
session of the Royal Society for the Encouragement of Arts, Manufactures
and Commerce focused on the blending of textiles.
DuPont's Fabric Development Department cleverly targeted French
fashion designers, supplying them with fabric samples. In 1955,
designers such as Coco Chanel, Jean Patou, and Christian Dior showed gowns created with DuPont fibers, and fashion photographer Horst P. Horst was hired to document their use of DuPont fabrics. American Fabrics credited blends with providing "creative possibilities and new ideas for fashions which had been hitherto undreamed of."
Etymology
DuPont went through an extensive process to generate names for its new product.
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. Since the products were not really run-proof,
the vowels were swapped to produce "nuron", which was changed to
"nilon" "to make it sound less like a nerve tonic". For clarity in
pronunciation, the "i" was changed to "y".
A persistent urban legend
exists that the name is derived from "New York" and "London"; however,
no organisation in London was ever involved in the research and
production of nylon.
Longer-term popularity
Nylon’s
popularity soared in the 1940s and 1950s due to its durability and
sheerness. In the 1970s, it became more popular due to its flexibility
and price.
In spite of oil shortages in the 1970s, consumption of nylon
textiles continued to grow by 7.5% per year between the 1960s and 1980s.
Overall production of synthetic fibers, however, dropped from 63% of
the worlds textile production in 1965, to 45% of the world's textile
production in early 1970s. The appeal of "new" technologies wore off, and nylon fabric "was going out of style in the 1970s".
Also, consumers became concerned about environmental costs throughout
the production cycle: obtaining the raw materials (oil), energy use
during production, waste produced during creation of the fiber, and
eventual waste disposal of materials that were not biodegradable.
Synthetic fibers have not dominated the market since the 1950s and 1960s. As of 2020, the worldwide production of nylon is estimated at 8.9 million tons.
Although pure nylon has many flaws and is now rarely used, its
derivatives have greatly influenced and contributed to society. From
scientific discoveries relating to the production of plastics and
polymerization, to economic impact during the depression and the
changing of women's fashion, nylon was a revolutionary product. The Lunar Flag Assembly,
the first flag planted on the moon in a symbolic gesture of
celebration, was made of nylon. The flag itself cost $5.50 but had to
have a specially designed flagpole with a horizontal bar so that it
would appear to "fly".
One historian describes nylon as "an object of desire", comparing the
invention to Coca-Cola in the eyes of 20th century consumers.
Chemistry
In common usage, the prefix "PA" (polyamide) or the name "Nylon" are used interchangeably and are equivalent in meaning.
The nomenclature used for nylon polymers was devised during the
synthesis of the first simple aliphatic nylons and uses numbers to
describe the number of carbons in each monomer unit, including the
carbon(s) of the carboxylic acid(s).
Subsequent use of cyclic and aromatic monomers required the use of
letters or sets of letters. One number after "PA" or "Nylon" indicates a
homopolymer which is monadic or based on one amino acid (minus H2O) as monomer:
PA 6 or Nylon 6: [NH−(CH2)5−CO]n made from ε-caprolactam.
Two numbers or sets of letters indicate a dyadic homopolymer
formed from two monomers: one diamine and one dicarboxylic acid. The
first number indicates the number of carbons in the diamine. The two
numbers should be separated by a comma for clarity, but the comma is
often omitted.
For copolymers the comonomers or pairs of comonomers are separated by slashes:
PA 6/66: [NH−(CH2)6−NH−CO−(CH2)4−CO]n−[NH−(CH2)5−CO]m made from caprolactam, hexamethylenediamine and adipic acid;
PA 66/610: [NH−(CH2)6−NH−CO−(CH2)4−CO]n−[NH−(CH2)6−NH−CO−(CH2)8−CO]m made from hexamethylenediamine, adipic acid and sebacic acid.
The term polyphthalamide
(abbreviated to PPA) is used when 60% or more moles of the carboxylic
acid portion of the repeating unit in the polymer chain is composed of a
combination of terephthalic acid (TPA) and isophthalic acid (IPA).
Nylon 66 and related polyamides are condensation polymers forms from equal parts of diamine and dicarboxylic acids. In the first case, the "repeating unit" has the ABAB structure, as also seen in many polyesters and polyurethanes. 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 polyamideproteins, which have overall directionality: C terminal → N terminal. In the second case (so called AA), the repeating unit corresponds to the single monomer.
Wallace Carothers at DuPont patented nylon 66.
In the case of nylons that involve reaction of a diamine and a
dicarboxylic acid, 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. The salt is crystallized to purify it and
obtain the desired precise stoichiometry. Heated to 285 °C (545 °F), the
salt reacts to form nylon polymer with the production of water.
Nylon 510, made from pentamethylene diamine and sebacic acid, was included in the Carothers patent to nylon 66
Nylon 610 is produced similarly using hexamethylene diamine. These
materials are more expensive because of the relatively high cost of
sebacic acid. Owing to the high hydrocarbon content, nylon 610 is more hydrophobic and finds applications suited for this property, such as bristles.
These polymers are made from a lactam or amino acid. The synthetic route using lactams (cyclic amides) was developed by Paul Schlack at IG Farben, leading to nylon 6, or polycaprolactam—formed by a ring-opening polymerization. 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.
The 428 °F (220 °C) melting point of nylon 6 is lower than the 509 °F (265 °C) melting point of nylon 66. Homopolymer nylons are derived from one monomer.
Nylons can also be synthesized from dinitriles using acid catalysis. For example, this method is applicable for preparation of nylon 1,6 from adiponitrile, formaldehyde and water. Additionally, nylons can be synthesized from diols and dinitriles using this method as well.
Copolymers
It is easy to make mixtures of the monomers or sets of monomers used to make nylons to obtain copolymers. This lowers crystallinity and can therefore lower the melting point.
Some copolymers that have been or are commercially available are listed below:
PA6/66 DuPont Zytel
PA6/6T BASF Ultramid T (6/6T copolymer)
PA6I/6T DuPont Selar PA
PA66/6T DuPont Zytel HTN
PA12/MACMI EMS Grilamid TR
Blends
Most
nylon polymers are miscible with each other allowing a range of blends
to be made. The two polymers can react with one another by
transamidation to form random copolymers.
According to their crystallinity, polyamides can be:
low crystallinity: PAMXD6 made from m-xylylenediamine and adipic acid;
amorphous: PA6I made from hexamethylenediamine and isophthalic acid.
According to this classification, PA66, for example, is an aliphatic semi-crystalline homopolyamide.
Environmental impact
The general chemical reaction involving hydrolysis of an amide to form a carboxylic acid and an amine
All nylons are susceptible to hydrolysis, especially by strong acids, a reaction essentially the reverse of their synthesis. The molecular weight
of nylon products so attacked drops, and cracks form quickly at the
affected zones. Lower members of the nylons (such as nylon 6) are
affected more than higher members such as nylon 12. This means that
nylon parts cannot be used in contact with sulfuric acid for example, such as the electrolyte used in lead–acid batteries.
When being molded, nylon must be dried to prevent hydrolysis in
the molding machine barrel since water at high temperatures can also
degrade the polymer. The reaction is shown above.
The average greenhouse gas footprint of nylon in manufacturing carpets is estimated at 5.43 kg CO2 equivalent per kg, when produced in Europe. This gives it almost the same carbon footprint as wool, but with greater durability and therefore a lower overall carbon footprint.
Data published by PlasticsEurope indicates for nylon 66 a greenhouse gas footprint of 6.4 kg CO2 equivalent per kg, and an energy consumption of 138 kJ/kg. When considering the environmental impact of nylon, it is important to consider the use phase.
Various nylons break down in fire and form hazardous smoke, and toxic fumes or ash, typically containing hydrogen cyanide. Incinerating
nylons to recover the high energy used to create them is usually
expensive, so most nylons reach the garbage dumps, decaying slowly. Discarded nylon fabric takes 30–40 years to decompose. Nylon used in discarded fishing gear such as fishing nets is a contributor to debris in the ocean.
Nylon is a robust polymer and lends itself well to recycling. Much
nylon resin is recycled directly in a closed loop at the injection
molding machine, by grinding sprues and runners and mixing them with the virgin granules being consumed by the molding machine.
Because of the expense and difficulties of the nylon recycling
process, few companies utilize it while most favor using cheaper, newly
made plastics for their products instead. US clothing company Patagonia
has products containing recycled nylon and in the mid-2010s invested in
Bureo, a company that recycles nylon from used fishing nets to use in
sunglasses and skateboards. The Italian company Aquafil also has demonstrated recycling fishing nets lost in the ocean into apparel.
Vanden Recycling recycles nylon and other polyamides (PA) and has
operations in the UK, Australia, Hong Kong, the UAE, Turkey and Finland.
Nylon is the most popular fiber type in the residential carpet industry today. The US EPA estimates that 9.2% of carpet fiber, backing and padding was recycled in 2018, 17.8% was incinerated in waste-to-energy facilities, and 73% was discarded in landfills.
Some of the world's largest carpet and rug companies are promoting
"cradle to cradle"—the re-use of non-virgin materials including ones not
historically recycled—as the industry's pathway forward.
Properties
Above their melting temperatures, Tm, thermoplastics like nylon are amorphous solids or viscous fluids in which the chains approximate random coils. Below Tm, amorphous regions alternate with regions which are lamellarcrystals. 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.
Hydrogen bonding in Nylon 66 (in mauve)
Nylon 66 can have multiple parallel strands aligned with their
neighboring peptide bonds at coordinated separations of exactly six and
four carbons for considerable lengths, so the carbonyloxygens and amide hydrogens
can line up to form interchain hydrogen bonds repeatedly, without
interruption (see the figure opposite). Nylon 510 can have coordinated
runs of five and eight 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 alkanehydrocarbon chain depends on rotations about the 109.47° tetrahedral bonds of singly bonded carbon atoms.
When extruded into fibers through pores in an industry spinneret, the individual polymer chains tend to align because of viscousflow. If subjected to cold drawing afterwards, the fibers align further, increasing their crystallinity, and the material acquires additional tensile strength. 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 shearingstresses 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.
Nylons are hygroscopic and will absorb or desorb moisture as a
function of the ambient humidity. Variations in moisture content have
several effects on the polymer. Firstly, the dimensions will change, but
more importantly moisture acts as a plasticizer, lowering the glass transition temperature (Tg), and consequently the elastic modulus at temperatures below the Tg
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 absorbent than wool or cotton.
The characteristic features of nylon 66 include:
Pleats and creases can be heat-set at higher temperatures
On the other hand, nylon 6 is easy to dye, more readily fades; it has
a higher impact resistance, a more rapid moisture absorption, greater
elasticity, and elastic recovery.
Variation of luster: nylon has the ability to be very lustrous, semi-lustrous, or dull.
Durability: its 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)
Paved the way for easy-care garments
High resistance to insects, fungi, animals, as well as molds, mildew, rot, and many chemicals
Nylon clothing tends to be less flammable than cotton and rayon, but nylon fibers may melt and stick to skin.
Uses
Nylon was first used commercially in a nylon-bristledtoothbrush in 1938, followed more famously in women's stockings or "nylons" which were shown at the 1939 New York World's Fair and first sold commercially in 1940. Its use increased dramatically during World War II, when the need for fabrics increased dramatically.
Fibers
These worn out nylon stockings will be reprocessed and made into parachutes for army fliers c. 1942Blue Nylon fabric ball gown by Emma Domb, Science History Institute
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 and hemp 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 nearly all of the rest. By August 1945,
manufactured fibers had taken a market share of 25%, at the expense of
cotton. After the war, because of shortages of both silk and nylon,
nylon parachute material was sometimes repurposed to make dresses.
Nylon 6 and 66 fibers are used in carpet manufacture.
Nylon resins are widely used in the automobile industry especially in the engine compartment.
Molded nylon is used in hair combs and mechanical parts such as machine screws, gears, gaskets, and other low- to medium-stress components previously cast in metal.Engineering-grade nylon is processed by extrusion, casting, and 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 molded nylon. For use in tools such as spudgers, nylon is available in glass-filled variants which increase structural and impact strength and rigidity, and molybdenum disulfide-filled variants which increase lubricity. Nylon can be used as the matrix material in composite materials, with reinforcing fibers like glass or carbon fiber; such a composite has a higher density than pure nylon.
Such thermoplastic composites (25% to 30% glass fiber) are frequently
used in car components next to the engine, such as intake manifolds,
where the good heat resistance of such materials makes them feasible
competitors to metals.
Nylon was used to make the stock of the Remington Nylon 66 rifle. The frame of the modern Glock pistol is made of a nylon composite.
Food packaging
Nylon resins are used as a component of food packaging films where an oxygen barrier is needed. Some of the terpolymers based upon nylon are used every day in packaging. Nylon has been used for meat wrappings and sausage sheaths. The high temperature resistance of nylon makes it useful for oven bags.
Filaments
Nylon filaments are primarily used in brushes especially toothbrushes and string trimmers. They are also used as monofilaments in fishing line. Nylon 610 and 612 are the most used polymers for filaments.
Its various properties also make it very useful as a material in additive manufacturing; specifically, as a filament in consumer and professional grade fused deposition modeling 3D printers.
Other forms
Nylon resins can be extruded into rods, tubes, and sheets.
Nylon powders are used to powder coat metals. Nylon 11 and nylon 12 are the most widely used.
In the mid-1940s, classical guitarist Andrés Segovia mentioned the shortage of good guitar strings in the United States, particularly his favorite Pirastro catgut
strings, to a number of foreign diplomats at a party, including General
Lindeman of the British Embassy. A month later, the General presented
Segovia with some nylon strings which he had obtained via some members
of the DuPont family. Segovia found that although the strings produced a
clear sound, they had a faint metallic timbre which he hoped could be eliminated. Nylon strings were first tried on stage by Olga Coelho in New York in January 1944. In 1946, Segovia and string maker Albert Augustine
were introduced by their mutual friend Vladimir Bobri, editor of Guitar
Review. On the basis of Segovia's interest and Augustine's past
experiments, they decided to pursue the development of nylon strings.
DuPont, skeptical of the idea, agreed to supply the nylon if Augustine
would endeavor to develop and produce the actual strings. After three
years of development, Augustine demonstrated a nylon first string whose
quality impressed guitarists, including Segovia, in addition to DuPont.
Wound strings, however, were more problematic. Eventually, however,
after experimenting with various types of metal and smoothing and
polishing techniques, Augustine was also able to produce high quality
nylon wound strings.
The microscopic process of evaporation and condensation at the liquid surface.If vapor pressure exceeds the thermodynamic equilibrium value, condensation occurs in presence of nucleation sites. This principle is indigenous in cloud chambers, where ionizedparticles form condensation tracks when passing through.The pistol test tube experiment. The tube contains alcohol
and is closed with a piece of cork. By heating the alcohol, the vapors
fill in the space, increasing the pressure in the tube to the point of
the cork popping out.
Vapor pressure or equilibrium vapor pressure is the pressure exerted by a vapor in thermodynamic equilibrium with its condensedphases (solid or liquid) at a given temperature in a closed system.
The equilibrium vapor pressure is an indication of a liquid's
thermodynamic tendency to evaporate. It relates to the balance of
particles escaping from the liquid (or solid) in equilibrium with those
in a coexisting vapor phase. A substance with a high vapor pressure at
normal temperatures is often referred to as volatile.
The pressure exhibited by vapor present above a liquid surface is known
as vapor pressure. As the temperature of a liquid increases, the
attractive interactions between liquid molecules become less significant
in comparison to the entropy of those molecules in the gas phase,
increasing the vapor pressure. Thus, liquids with strong intermolecular
interactions are likely to have smaller vapor pressures, with the
reverse true for weaker interactions.
The vapor pressure of any substance increases non-linearly with temperature, often described by the Clausius–Clapeyron relation. The atmospheric pressureboiling point of a liquid (also known as the normal boiling point)
is the temperature at which the vapor pressure equals the ambient
atmospheric pressure. With any incremental increase in that temperature,
the vapor pressure becomes sufficient to overcome atmospheric pressure and cause the liquid to form vapor bubbles. Bubble
formation in high liquid depths requires a slightly higher temperature
due to the higher fluid pressure, due to hydrostatic pressure of the
fluid mass above. More important at shallow depths is the higher
temperature required to start bubble formation. The surface tension of
the bubble wall leads to an overpressure in the very small, initial
bubbles.
The vapor pressure that a single component in a mixture contributes to the total pressure in the system is called partial pressure.
For example, air at sea level, and saturated with water vapor at 20 °C,
has partial pressures of about 2.3 kPa of water, 78 kPa of nitrogen, 21 kPa of oxygen and 0.9 kPa of argon, totaling 102.2 kPa, making the basis for standard atmospheric pressure.
Measurement and units
Vapor pressure is measured in the standard units of pressure. The International System of Units (SI) recognizes pressure as a derived unit with the dimension of force per area and designates the pascal (Pa) as its standard unit. One pascal is one newton per square meter (N·m−2 or kg·m−1·s−2).
Experimental measurement of vapor pressure is a simple procedure for common pressures between 1 and 200 kPa.[1] Most accurate results are obtained near the boiling point of substances and large errors result for measurements smaller than 1kPa.
Procedures often consist of purifying the test substance, isolating it
in a container, evacuating any foreign gas, then measuring the
equilibrium pressure of the gaseous phase of the substance in the
container at different temperatures. Better accuracy is achieved when
care is taken to ensure that the entire substance and its vapor are at
the prescribed temperature. This is often done, as with the use of an isoteniscope, by submerging the containment area in a liquid bath.
Very low vapor pressures of solids can be measured using the Knudsen effusion cell method.
In a medical context, vapor pressure is sometimes expressed in other units, specifically millimeters of mercury (mmHg). This is important for volatile inhalational anesthetics, most of which are liquids at body temperature, but with a relatively high vapor pressure.
Estimating vapor pressures with Antoine equation
The Antoine equation
is a pragmatic mathematical expression of the relation between the
vapor pressure and the temperature of pure liquid or solid substances.
It is obtained by curve-fitting and is adapted to the fact that vapor
pressure is usually increasing and concave as a function of temperature.
The basic form of the equation is:
and it can be transformed into this temperature-explicit form:
where:
is the absolute vapor pressure of a substance
is the temperature of the substance
, and are substance-specific coefficients (i.e., constants or parameters)
is typically either or
A simpler form of the equation with only two coefficients is sometimes used:
which can be transformed to:
Sublimations and vaporizations of the same substance have separate sets of Antoine coefficients, as do components in mixtures.
Each parameter set for a specific compound is only applicable over a
specified temperature range. Generally, temperature ranges are chosen to
maintain the equation's accuracy of a few up to 8–10 percent. For many
volatile substances, several different sets of parameters are available
and used for different temperature ranges. The Antoine equation has poor
accuracy with any single parameter set when used from a compound's
melting point to its critical temperature. Accuracy is also usually poor
when vapor pressure is under 10 Torr because of the limitations of the
apparatus used to establish the Antoine parameter values.
The Wagner equation gives "one of the best" fits to experimental data but is quite complex. It expresses reduced vapor pressure as a function of reduced temperature.
A log-lin vapor pressure chart for various liquids
As a general trend, vapor pressures of liquids at ambient
temperatures increase with decreasing boiling points. This is
illustrated in the vapor pressure chart (see right) that shows graphs of
the vapor pressures versus temperatures for a variety of liquids.
At the normal boiling point of a liquid, the vapor pressure is equal to
the standard atmospheric pressure defined as 1 atmosphere, 760Torr, 101.325kPa, or 14.69595psi.
For example, at any given temperature, methyl chloride
has the highest vapor pressure of any of the liquids in the chart. It
also has the lowest normal boiling point at −24.2 °C (−11.6 °F), which
is where the vapor pressure curve of methyl chloride (the blue line)
intersects the horizontal pressure line of one atmosphere (atm) of absolute vapor pressure.
Although the relation between vapor pressure and temperature is
non-linear, the chart uses a logarithmic vertical axis to produce
slightly curved lines, so one chart can graph many liquids. A nearly
straight line is obtained when the logarithm of the vapor pressure is
plotted against 1/(T + 230)
where T is the temperature in degrees Celsius. The vapor pressure of a
liquid at its boiling point equals the pressure of its surrounding
environment.
Liquid mixtures: Raoult's law
Raoult's law gives an approximation to the vapor pressure of mixtures of liquids. It states that the activity (pressure or fugacity) of a single-phase mixture is equal to the mole-fraction-weighted sum of the components' vapor pressures:
where is the mixture's vapor pressure, is the mole fraction of component in the liquid phase and is the mole fraction of component in the vapor phase respectively. is the vapor pressure of component .
Raoult's law is applicable only to non-electrolytes (uncharged
species); it is most appropriate for non-polar molecules with only weak
intermolecular attractions (such as London forces).
Systems that have vapor pressures higher than indicated by the
above formula are said to have positive deviations. Such a deviation
suggests weaker intermolecular attraction than in the pure components,
so that the molecules can be thought of as being "held in" the liquid
phase less strongly than in the pure liquid. An example is the azeotrope
of approximately 95% ethanol and water. Because the azeotrope's vapor
pressure is higher than predicted by Raoult's law, it boils at a
temperature below that of either pure component.
There are also systems with negative deviations that have vapor
pressures that are lower than expected. Such a deviation is evidence for
stronger intermolecular attraction between the constituents of the
mixture than exists in the pure components. Thus, the molecules are
"held in" the liquid more strongly when a second molecule is present. An
example is a mixture of trichloromethane (chloroform) and 2-propanone
(acetone), which boils above the boiling point of either pure component.
The negative and positive deviations can be used to determine thermodynamic activity coefficients of the components of mixtures.
Solids
Vapor pressure of liquid and solid benzene
Equilibrium vapor pressure can be defined as the pressure reached
when a condensed phase is in equilibrium with its own vapor. In the case
of an equilibrium solid, such as a crystal, this can be defined as the pressure when the rate of sublimation
of a solid matches the rate of deposition of its vapor phase. For most
solids this pressure is very low, but some notable exceptions are naphthalene, dry ice
(the vapor pressure of dry ice is 5.73 MPa (831 psi, 56.5 atm) at
20 °C, which causes most sealed containers to rupture), and ice. All
solid materials have a vapor pressure. However, due to their often
extremely low values, measurement can be rather difficult. Typical
techniques include the use of thermogravimetry and gas transpiration.
There are a number of methods for calculating the sublimation
pressure (i.e., the vapor pressure) of a solid. One method is to
estimate the sublimation pressure from extrapolated liquid vapor
pressures (of the supercooled liquid), if the heat of fusion is known, by using this particular form of the Clausius–Clapeyron relation:
where:
is the sublimation pressure of the solid component at the temperature .
is the extrapolated vapor pressure of the liquid component at the temperature .
This method assumes that the heat of fusion is
temperature-independent, ignores additional transition temperatures
between different solid phases, and it gives a fair estimation for
temperatures not too far from the melting point. It also shows that the
sublimation pressure is lower than the extrapolated liquid vapor
pressure (ΔfusH > 0) and the difference grows with increased distance from the melting point.
Boiling point of water
Graph of water vapor pressure versus temperature. At the normal boiling point of 100°C, it equals the standard atmospheric pressure of 760torr or 101.325kPa.
Like all liquids, water boils when its vapor pressure reaches its
surrounding pressure. In nature, the atmospheric pressure is lower at
higher elevations and water boils at a lower temperature. The boiling
temperature of water for atmospheric pressures can be approximated by
the Antoine equation:
or transformed into this temperature-explicit form:
where the temperature is the boiling point in degrees Celsius and the pressure is in torr.
Estimating vapor pressure from molecular structure
Several
empirical methods exist to estimate the vapor pressure from molecular
structure for organic molecules. Some examples are SIMPOL.1 method, the method of Moller et al.,
and EVAPORATION (Estimation of VApour Pressure of ORganics, Accounting
for Temperature, Intramolecular, and Non-additivity effects).
Meaning in meteorology
In meteorology, the term vapor pressure means the partial pressure of water vapor in the atmosphere, even if it is not in equilibrium. This differs from its meaning in other sciences.
According to the American Meteorological SocietyGlossary of Meteorology, saturation vapor pressure
properly refers to the equilibrium vapor pressure of water above a flat
surface of liquid water or solid ice, and is a function only of
temperature and whether the condensed phase is liquid or solid.
Relative humidity is defined relative to saturation vapor pressure.
Equilibrium vapor pressure does not require the condensed phase
to be a flat surface; it might consist of tiny droplets possibly
containing solutes (impurities), such as a cloud.
Equilibrium vapor pressure may differ significantly from saturation
vapor pressure depending on the size of droplets and presence of other
particles which act as cloud condensation nuclei.
However, these terms are used inconsistently, and some authors use "saturation vapor pressure" outside the narrow meaning given by the AMS Glossary. For example, a text on atmospheric convection states, "The Kelvin effect causes the saturation vapor pressure over the curved surface of the droplet to be greater than that over a flat water surface" (emphasis added).
The still-current term saturation vapor pressure derives
from the obsolete theory that water vapor dissolves into air, and that
air at a given temperature can only hold a certain amount of water
before becoming "saturated". Actually, as stated by Dalton's law
(known since 1802), the partial pressure of water vapor or any
substance does not depend on air at all, and the relevant temperature is
that of the liquid. Nevertheless, the erroneous belief persists among the public and even meteorologists, aided by the misleading terms saturation pressure and supersaturation and the related definition of relative humidity.
