Polyacrylonitrile (PAN) is a synthetic, semicrystalline organic
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 ...
resin, with the linear formula (CH
2CHCN)
n.
Almost all PAN
resin
A resin is a solid or highly viscous liquid that can be converted into a polymer. Resins may be biological or synthetic in origin, but are typically harvested from plants. Resins are mixtures of organic compounds, predominantly terpenes. Commo ...
s are
copolymers with
acrylonitrile as the main
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 ...
. PAN is used to produce large variety of products including ultra filtration membranes, hollow fibers for
reverse osmosis
Reverse osmosis (RO) is a water purification process that uses a partially permeable membrane, semi-permeable membrane to separate water molecules from other substances. RO applies pressure to overcome osmotic pressure that favors even distribu ...
, fibers for textiles, and oxidized PAN fibers. PAN fibers are the chemical precursor of very high-quality
carbon fiber
Carbon fiber-reinforced polymers (American English), carbon-fibre-reinforced polymers ( Commonwealth English), carbon-fiber-reinforced plastics, carbon-fiber reinforced-thermoplastic (CFRP, CRP, CFRTP), also known as carbon fiber, carbon comp ...
. PAN is first thermally oxidized in air at 230 °C to form an oxidized PAN fiber and then carbonized above 1000 °C in inert atmosphere to make carbon fibers found in a variety of both high-tech and common daily applications such as civil and military aircraft primary and secondary structures, missiles, solid propellant rocket motors, pressure vessels, fishing rods,
tennis rackets and
bicycle
A bicycle, also called a pedal cycle, bike, push-bike or cycle, is a human-powered transport, human-powered or motorized bicycle, motor-assisted, bicycle pedal, pedal-driven, single-track vehicle, with two bicycle wheel, wheels attached to a ...
frames. It is a component
repeat unit in several important
copolymers, such as
styrene-acrylonitrile (SAN) and
acrylonitrile butadiene styrene (ABS) plastic.
History
Polyacrylonitrile (PAN) was first synthesized in 1930 by Hans Fikentscher and Claus Heuck in the Ludwigshafen works of the German chemical conglomerate
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 ...
. However, as PAN is non-
fusible, and did not dissolve in any of the industrial
solvent
A solvent (from the Latin language, Latin ''wikt:solvo#Latin, solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a Solution (chemistry), solution. A solvent is usually a liquid but can also be a solid, a gas ...
s being used at the time, further research into the material was halted.
In 1931, Herbert Rein, head of polymer fiber chemistry at the Bitterfeld plant of IG Farben, obtained a sample of PAN while visiting the Ludwigshafen works. He found that
pyridinium benzylchloride, an
ionic liquid
An ionic liquid (IL) is a salt (chemistry), salt in the liquid state at ambient conditions. In some contexts, the term has been restricted to salts whose melting point is below a specific temperature, such as . While ordinary liquids such as wate ...
, would dissolve PAN. He spun the first fibers based on PAN in 1938, using aqueous solutions of
quaternary ammonium sodium thiocyanate and aluminum perchlorate for the production process and considered other solvents including DMF. However, commercial introduction was delayed due to the wartime stresses on infrastructure, inability to melt the polymer without degradation, and solvents to allow solution processing were not known yet.
The first mass production run of PAN fiber was in 1946 by American chemical conglomerate
DuPont
Dupont, DuPont, Du Pont, duPont, or du Pont may refer to:
People
* Dupont (surname) Dupont, also spelled as DuPont, duPont, Du Pont, or du Pont is a French surname meaning "of the bridge", historically indicating that the holder of the surname re ...
. The German
intellectual property
Intellectual property (IP) is a category of property that includes intangible creations of the human intellect. There are many types of intellectual property, and some countries recognize more than others. The best-known types are patents, co ...
had been stolen in
Operation Paperclip. The product, branded as
Orlon, was based on a patent filed exactly seven days after a nearly identical German claim.
In the
German Democratic Republic
East Germany, officially known as the German Democratic Republic (GDR), was a country in Central Europe from Foundation of East Germany, its formation on 7 October 1949 until German reunification, its reunification with West Germany (FRG) on ...
(GDR), industrial polyacrylonitrile fibre production was started in 1956 at the
VEB Film- und Chemiefaserwerk Agfa Wolfen due to the preliminary work of the "Wolcrylon" collective (''
:de:Max Duch'', Herbert Lehnert et al.). Prior to this, the preconditions for the production of the raw materials had been created at the
Buna Werke Schkopau (Polyacrylonitrile) and
Leuna works (
Dimethylformamide
Dimethylformamide, DMF is an organic compound with the chemical formula . Its structure is . Commonly abbreviated as DMF (although this initialism is sometimes used for 2,5-dimethylfuran, dimethylfuran, or dimethyl fumarate), this colourless liqui ...
). In the same year, the collective was awarded the GDR's National Prize II Class for Science and Technology for its achievements.
Physical properties
Although it is thermoplastic, polyacrylonitrile does not melt under normal conditions. It degrades before melting. It melts above 300 °C if the heating rates are 50 degrees per minute or above.
Glass transition temperature
The glass–liquid transition, or glass transition, is the gradual and reversible transition in amorphous materials (or in amorphous regions within semicrystalline materials) from a hard and relatively brittle "glassy" state into a viscous or rub ...
is around 95 °C and
fusion temperature is at 322 °C. PAN is soluble in
polar solvents, such as
dimethylformamide
Dimethylformamide, DMF is an organic compound with the chemical formula . Its structure is . Commonly abbreviated as DMF (although this initialism is sometimes used for 2,5-dimethylfuran, dimethylfuran, or dimethyl fumarate), this colourless liqui ...
,
dimethylacetamide,
ethylene
Ethylene (IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon–carbon bond, carbon–carbon doub ...
and
propylene
Propylene, also known as propene, is an unsaturated organic compound with the chemical formula . It has one double bond, and is the second simplest member of the alkene class of hydrocarbons. It is a colorless gas with a faint petroleum-like o ...
carbonates, and in aqueous solutions of
sodium thiocyanate
Sodium thiocyanate (sometimes called sodium sulphocyanide) is the chemical compound with the formula NaSCN. This colorless deliquescent salt is one of the main sources of the thiocyanate anion. As such, it is used as a precursor for the synth ...
,
zinc chloride
Zinc chloride is an Inorganic chemistry, inorganic chemical compound with the chemical formula, formula ZnCl2·''n''H2O, with ''n'' ranging from 0 to 4.5, forming water of hydration, hydrates. Zinc chloride, anhydrous and its hydrates, are colo ...
or
nitric acid
Nitric acid is an inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but samples tend to acquire a yellow cast over time due to decomposition into nitrogen oxide, oxides of nitrogen. Most com ...
. Solubility parameters: 26.09 MPa
1/2 (25 °C) are 25.6 to 31.5 J
1/2 cm
−3/2. Dielectric constants: 5.5 (1 kHz, 25 °C), 4.2 (1 MHz, 25 °C).Can behave as branched as well as linear polymer.
Synthesis
Most commercial methods for the synthesis of PAN are based on
free radical polymerization of
acrylonitrile. In most of the cases, 10% amounts of other vinyl comonomers are also used (1–10%) along with AN depending on the final application. Comonomers include
acrylic acid,
acrylamide, allyl compounds, and sulfonated
styrene.
[ Anionic polymerization also can be used for synthesizing PAN. For textile applications, molecular weight in the range of 40,000 to 70,000 is used. For producing carbon fiber higher molecular weight is desired.
In the production of carbon fibers containing 600 tex (6k) PAN tow, the linear density of filaments is 0.12 tex and the filament diameter is 11.6 μm which produces a carbon fiber that has the filament strength of 417 kgf/mm2 and binder content of 38.6%. This data is demonstrated in the Indexes for Experimental Batches of PAN Precursor and Carbon Fibers Made from It table.
]
Applications
Homopolymers of polyacrylonitrile have been used as fibers in hot gas filtration systems, outdoor awnings, sails for yachts, and fiber-reinforced concrete. Copolymers containing polyacrylonitrile are often used as fibers to make knitted clothing like socks and sweaters, as well as outdoor products like tents and similar items. If the label of a piece of clothing says "acrylic", then it is made out of some copolymer of polyacrylonitrile. It was made into the spun fiber at DuPont in 1942 and marketed under the name of Orlon. Acrylonitrile is commonly employed as a comonomer with styrene, e.g. acrylonitrile, styrene and acrylate plastics. Labelling of items of clothing with acrylic (see acrylic fiber) means the polymer consists of at least 85% acrylonitrile as the monomer. A typical comonomer is vinyl acetate, which can be solution-spun readily to obtain fibers that soften enough to allow penetration by dyes. The advantages of the use of these acrylics are that they are low-cost compared to natural fiber, they offer better sunlight resistance and have superior resistance to attack by moths.
Acrylics modified with halogen-containing comonomers are classified as modacrylics, which by definition contain more than PAN percentages between 35-85%. Incorporation of halogen groups increases the flame resistance of the fiber, which makes modacrylics suitable for the use in sleepwear, tents and blankets. Some mattresses also use them to meet the flame resistance requirements in North America. However, the disadvantage of these products is that they are costly and can shrink after drying.
PAN absorbs many metal ions and aids the application of absorption materials. Polymers containing amidoxime groups can be used for the treatment of metals because of the polymers’ complex-forming capabilities with metal ions.
PAN has properties involving low density, thermal stability, high strength and modulus of elasticity. These unique properties have made PAN an essential polymer in high tech.
Its high tensile strength and tensile modulus are established by fiber sizing, coatings, production processes, and PAN's fiber chemistry. Its mechanical properties derived are important in composite structures for military and commercial aircraft.
Carbon fiber
Polyacrylonitrile is used as the precursor for 90% of carbon fiber production. Approximately 20–25% of Boeing and Airbus wide-body airframes are carbon fibers. However, applications are limited by PAN's high price of around $15/lb.
A carbon fiber was created using resonant acoustic mixing with boron nitride nanotubes that has an increased tensile strength and storage modulus.
Glassy carbon
Glassy carbon, a common electrode material in electrochemistry, is created by heat-treating blocks of polyacrylonitrile under pressure at 1000 to 3000 °C over a period of several days. The process removes non-carbon atoms and creates a conjugated double bond structure with excellent conductivity.
Support polymer
Divinylbenzene-crosslinked polyacrylonitrile is a precursor to ion exchange resin
An ion-exchange resin or ion-exchange polymer is a resin or polymer that acts as a medium for ion exchange, that is also known as an ionex. It is an solubility, insoluble matrix (or support structure) normally in the form of small (0.25–1.43&nbs ...
s. Hydrolysis converts the nitrile groups to carboxylic acids. Amberlite IRC86 is one commercial product. These weakly acidic resins have high affinities for divalent metal ions like Ca2+ and Mg2+.
References
External links
Polyacrylonitrile
at Polymer Science Learning Center
Stanford engineers develop new air filter that could help Beijing residents breathe easily
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Acrylate polymers
Copolymers
Synthetic resins
Synthetic fibers
Thermoplastics