Polyacrylonitrile (PAN), also known as polyvinyl cyanide and Creslan 61, is a synthetic, semicrystalline organic
polymer
A polymer (; Greek '' poly-'', "many" + ''-mer'', "part")
is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...
resin, with the linear formula (C
3H
3N)
n. Though it is thermoplastic, it 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. Almost all PAN
resin
In polymer chemistry and materials science, resin is a solid or highly viscous substance of plant or synthetic origin that is typically convertible into polymers. Resins are usually mixtures of organic compounds. This article focuses on n ...
s are
copolymer
In polymer chemistry, a copolymer is a polymer derived from more than one species of monomer. The polymerization of monomers into copolymers is called copolymerization. Copolymers obtained from the copolymerization of two monomer species are some ...
s made from mixtures of
monomer
In chemistry, a monomer ( ; '' mono-'', "one" + ''-mer'', "part") is a molecule that can react together with other monomer molecules to form a larger polymer chain or three-dimensional network in a process called polymerization.
Classification
...
s with
acrylonitrile
Acrylonitrile is an organic compound with the formula and the structure . It is a colorless, volatile liquid although commercial samples can be yellow due to impurities. It has a pungent odor of garlic or onions. In terms of its molecula ...
as the main
monomer
In chemistry, a monomer ( ; '' mono-'', "one" + ''-mer'', "part") is a molecule that can react together with other monomer molecules to form a larger polymer chain or three-dimensional network in a process called polymerization.
Classification
...
. It is a versatile polymer used to produce large variety of products including ultra filtration membranes, hollow fibers for
reverse osmosis, 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 compo ...
. 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 racket
A racket, or racquet, is a sports implement used for striking a ball or shuttlecock in games such as squash, tennis, racquetball, badminton and padel. In the strictest sense a racket consists of a handled frame with an open hoop across which a ...
s and
bicycle frames. It is a component
repeat unit
In polymer chemistry, a repeat unit or repeating unit (or mer) is a part of a polymer whose repetition would produce the complete polymer chain (except for the end-groups) by linking the repeat units together successively along the chain, like the ...
in several important
copolymer
In polymer chemistry, a copolymer is a polymer derived from more than one species of monomer. The polymerization of monomers into copolymers is called copolymerization. Copolymers obtained from the copolymerization of two monomer species are some ...
s, such as
styrene-acrylonitrile Styrene acrylonitrile resin is a copolymer plastic consisting of styrene and acrylonitrile. It is also known as SAN. It is widely used in place of polystyrene owing to its greater thermal resistance. The chains of between 70 and 80% by weight styren ...
(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. However, as PAN is non-
fusible, and did not dissolve in any of the industrial
solvent
A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...
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 in the liquid state. 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 water and gasoline are predominantly made of ...
, 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. 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, cop ...
had been stolen in
Operation Paperclip
Operation Paperclip was a secret United States intelligence program in which more than 1,600 German scientists, engineers, and technicians were taken from the former Nazi Germany to the U.S. for government employment after the end of World War ...
. The product, branded as
Orlon
Acrylic fibers are synthetic fibers made from a polymer ( polyacrylonitrile) with an average molecular weight of ~100,000, about 1900 monomer units. For a fiber to be called "acrylic" in the US, the polymer must contain at least 85% acrylonitr ...
, was based on a patent filed exactly seven days after a nearly identical German claim. In the
German Democratic Republic
German(s) may refer to:
* Germany (of or related to)
** Germania (historical use)
* Germans, citizens of Germany, people of German ancestry, or native speakers of the German language
** For citizens of Germany, see also German nationality law
**G ...
(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
The Leuna works (german: Leunawerke) in Leuna, Saxony-Anhalt, is one of the biggest chemical industrial complexes in Germany. The site, now owned jointly by companies such as Total S.A., BASF, Linde AG, and DOMO Group, covers 13 km2 and produ ...
(
Dimethylformamide
Dimethylformamide is an organic compound with the formula ( CH3)2NC(O)H. Commonly abbreviated as DMF (although this initialism is sometimes used for dimethylfuran, or dimethyl fumarate), this colourless liquid is miscible with water and the maj ...
). In the same year, the collective was awarded the GDR's National Prize II Class for Science and Technology for its achievements.
Physical properties
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 is an organic compound with the formula ( CH3)2NC(O)H. Commonly abbreviated as DMF (although this initialism is sometimes used for dimethylfuran, or dimethyl fumarate), this colourless liquid is miscible with water and the maj ...
,
dimethylacetamide,
ethylene and
propylene
Propylene, also known as propene, is an unsaturated organic compound with the chemical formula CH3CH=CH2. 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 petro ...
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 synthes ...
,
zinc chloride
Zinc chloride is the name of inorganic chemical compounds with the formula ZnCl2 and its hydrates. Zinc chlorides, of which nine crystalline forms are known, are colorless or white, and are highly soluble in water. This salt is hygroscopic and e ...
or
nitric acid
Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available nitri ...
. 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
Acrylonitrile is an organic compound with the formula and the structure . It is a colorless, volatile liquid although commercial samples can be yellow due to impurities. It has a pungent odor of garlic or onions. In terms of its molecula ...
. In most of the cases, small amounts of other vinyl comonomers are also used (1–10%) along with AN depending on the final application. 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
Acrylic fibers are synthetic fibers made from a polymer ( polyacrylonitrile) with an average molecular weight of ~100,000, about 1900 monomer units. For a fiber to be called "acrylic" in the US, the polymer must contain at least 85% acrylonitr ...
. Acrylonitrile is commonly employed as a comonomer with
styrene
Styrene () is an organic compound with the chemical formula C6H5CH=CH2. This derivative of benzene is a colorless oily liquid, although aged samples can appear yellowish. The compound evaporates easily and has a sweet smell, although high concen ...
, e.g.
acrylonitrile
Acrylonitrile is an organic compound with the formula and the structure . It is a colorless, volatile liquid although commercial samples can be yellow due to impurities. It has a pungent odor of garlic or onions. In terms of its molecula ...
,
styrene
Styrene () is an organic compound with the chemical formula C6H5CH=CH2. This derivative of benzene is a colorless oily liquid, although aged samples can appear yellowish. The compound evaporates easily and has a sweet smell, although high concen ...
and
acrylate
Acrylates (IUPAC: prop-2-enoates) are the salts, esters, and conjugate bases of acrylic acid. The acrylate ion is the anion C H2=CHC OO−. Often, acrylate refers to esters of acrylic acid, the most common member being methyl acrylate. These acr ...
plastics. Labelling of items of clothing with acrylic (see
acrylic fiber
Acrylic fibers are synthetic fibers made from a polymer (polyacrylonitrile) with an average molecular weight of ~100,000, about 1900 monomer units. For a fiber to be called "acrylic" in the US, the polymer must contain at least 85% acrylonitri ...
) 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. 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.
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.
Oxidized polyacrylonitrile fiber (OPF)
Oxidized PAN Fiber is used to produce inherently flame resistant (FR) fabrics. Commonly when it is used in FR fabrics for protective apparel it is referred to as OPF (oxidized polyacrylonitrile fiber) and is a high-performance, cost-effective flame and heat resistance solution. OPF can be considered one of the most FR fabrics commercially produced since it has an LOI (Limiting Oxygen Index) in the range of 45–55% which is one of the highest LOI ranges available as compared with other common FR fabrics which have lower LOI values (e.g. Nomex @ 28–30%, Kevlar @ 28–30%, Modacrylic @ 32–34%, PBI @ 41%, and FR-Viscose @ 28%); and OPF also demonstrates the lowest toxic gas generation upon burning as compared with other common fabrics (e.g. Nomex, FR Polyester, and Cotton).
Support polymer
Polyacrylonitrile finds use as a porous supporting polymer for
adsorbents
Adsorption is the adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface. This process creates a film of the ''adsorbate'' on the surface of the ''adsorbent''. This process differs from absorption, in which a ...
for a variety of applications including ion exchange for cleaning up nuclear wastes. The PAN in this case is dissolved in a polar solvent such as
DMSO
Dimethyl sulfoxide (DMSO) is an organosulfur compound with the formula ( CH3)2. This colorless liquid is the sulfoxide most widely used commercially. It is an important polar aprotic solvent that dissolves both polar and nonpolar compounds ...
along with the desired adsorbent and a surfactant and then dropped into water where it is crashed out and forms beads suitable for column use.
Tholins
Polyacrylonitrile is used in experiments as a precursor to
tholin
Tholins (after the Greek (') "hazy" or "muddy"; from the ancient Greek word meaning "sepia ink") are a wide variety of organic compounds formed by solar ultraviolet or cosmic ray irradiation of simple carbon-containing compounds such as carbon ...
, a reddish-orange mixture of various organic compounds formed through radiolysis of carbon and nitrogen compounds. Naturally occurring tholins are expected to contain polyacrylonitrile and related
heteropolymer
In polymer chemistry, a copolymer is a polymer derived from more than one species of monomer. The polymerization of monomers into copolymers is called copolymerization. Copolymers obtained from the copolymerization of two monomer species are some ...
s containing some amino groups.
References
External links
Polyacrylonitrileat 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