Polyacrylonitrile (PAN) is a synthetic, semicrystalline organic polymer resin, with the linear formula (C3H3N)n. Though it is thermoplastic, it does not melt under normal conditions. It degrades before melting. It melts above 300 0C if the heating rates are 50 degrees per minute or above. Almost all polyacrylonitrile resins are copolymers made from mixtures of monomers with acrylonitrile as the main component. It is a versatile polymer used to produce large variety of products including ultra filtration membranes, hollow fibers for reverse osmosis, fibers for textiles, oxidized PAN fibers. PAN fibers are the chemical precursor of high-quality carbon fiber. PAN is first thermally oxidized in air at 230 degrees to form an oxidized PAN fiber and then carbonized above 1000 degrees in inert atmosphere to make carbon fibers found in plenty 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, badminton rackets & high-tech bicycles. It is a component repeat unit in several important copolymers, such as styrene-acrylonitrile (SAN) and acrylonitrile butadiene styrene (ABS) plastic.
|Molar Mass||53.0626 ± 0.0028 g/mol
C 67.91%, H 5.7%, N 26.4%
|Glass Transition Temperature||~95 °C|
|Fusion Temperature||322 °C|
|Solubility Parameters||26.09 MPa1/2 (25 °C)
|Dielectric Constant||5.5 (1 kHz, 25°C)
4.2 (1 MHz, 25°C)
All commercial methods of production of PAN are based on free radical polymerization of Acrylonitrile (AN). Most of the cases, small amount 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.
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 spun fiber at DuPont in 1941 and marketed under the name of Orlon. Acrylonitrile is commonly employed as a comonomer with styrene, e.g. acrylonitrile, styrene and acrylate plastics.
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.
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.
In 2013, researches announced a structural PAN nanofiber that is both strong and tough. Strength refers to a material’s ability to carry a load, while toughness is the amount of energy needed to break it. The researchers used a technique called electrospinning (applying high voltage to a solution until a small jet of liquid ejects). Making the nanofiber thinner made it both stronger and tougher.
Electrospun PAN has different effects on the properties of the nanofibers. Depending on the ionic and nonionic surfactants added to the PAN during processing, the properties can be enhanced. With the presence of the anionic surfactant sodium dodecyl sulfate (SDS) during electro spinning, for example, the electron emission from PAN are enhanced.
High tacticity PAN has been made with the addition of AlCl3. Molecular weight and tacticity have been changed in PAN through atom transfer radical polymerization with the presence of AlCl3. This addition of AlCl3 improved the PAN’s isotacticity and narrowed its polydispersity.
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