PAN based carbon fibers

Polymers mesophase pitch polyacrylonitrile carbons" mesocarbon microbeads, carbon fibers PAN-based carbon fibers ... 

Fig. 3. Schematic illustration of PAN-based carbon fiber microstmcture based on microscopic observations (3).

Pitch-based carbon fibers, on the other hand, provide properties not readily obtainable with PAN-based fibers. PAN-based fibers have excellent tensile strength at a modulus of 200 GPa, but the strength decreases as the modulus is increased. " Pitch-based fibers have lower tensile strengths, but are capable of modulus levels up to the theoretical modulus of graphite, 1000 GPa, and have much better thermal and electrical conductivity properties than PAN-based fibers. 

Using pitch-based ACFs, Mochida et al. [132] reported 87% conversion at room temperatnre in dry air. Lower conversions were obtained in the presence of water vapor. The anthors found that heat treatment at 1123 K enhanced the activity of the fibers. Such treatment removes oxygen functional groups from the surface of the ACFs the vacant sites created as a result of this treatment were thought to be the active sites for the reaction. On the other hand, the hydrophobic surface obtained after the heat treatment helps to decrease the amount of water adsorbed, which decreases NO conversion in humid air. An interesting point noted by Mochida et al. [131] is that PAN- and pitch-based ACFs exhibited the reverse order of activity for the oxidation of SO2 and NO. Thus, pitch fibers were best for NO oxidation, while PAN fibers were found to be more active for SO2 oxidation. No explanation was provided by the authors for this finding, which certainly reflects the different surface chemical properties of the two fiber types. A detailed kinetic study of this process was presented in a subsequent paper [133], while Guo et al. [134] compared the performances of different carbon fibers (PAN, pitch) and activated carbons. 

Electrochemical pretreatment of activated carbon fibers (ACEs) based on polyacrylonitrile (PAN-based) in a NaN03 solution resulted in an increase in the content of oxygen-containing functional groups in the fiber surface and therefore led to an increase in specific capacitance Cg. ACEs oxidized for 6h contained 1.3mmol/g of O and Co was formed on 76% of them under thermal treatment. Various carbon materials, including anthracite and different carbon fibers, were activated by KOH, NaOH, CO2, or water vapor at 650-750 C. The values of Cg measured for all carbon... 

The transverse radius of curvature of the graphene layers, n, increases from the core of a fiber to its surface, and graphene sheets near the fiber surface usually lie parallel to it. This structure is the cause of the notable skin/core effect and the low reactivity of the fiber surface. The reactivity of aromatic carbons is lower in-plane than at the layer edge. The turbostratic character of carbon in PAN based HM carbon fibers and the occurrence of elongated pores explain their low density (1.8-1.9 g/cm ). 

Figure 5.13 Gases evolved during the carbonization of PAN based carbon fiber from 200-1000°C. Source Reprinted with permission from Bromley J, Gas evolution processes during the formation of carbon fibres, Int Conf on Carbon Fibres, their Composites and Applications, The Plastics Institute London, 1971. Bromley J, Jackson EE, Robinson PS, United Kingdom Atomic Energy Authority Report, AERE R6297 Harwell, 1970. Copyright 1970, AEA Technology pic.

Deurbergue A, Oberlin A, Stabilization and carbonization of PAN-based carbon-fibers as related to mechanical properties. Carbon, 29(4 5), 621-628, 1991. 

The torsional modulus is shown in Figure 20.22 and appears to be governed by the structure of the microsection increasing in the order— mesophase pitch based carbon fiber < rayon based carbon fiber < isotropic pitch based carbof fiber < PAN based carbon fiber. 

Shimazaki K, Studies on the development of polyacrylonitrile based activated carbon fiber,6. Preparation of polyacrylonitrile based activated carbon fiber (PAN-ACF) having high mesopore volume, Nippon Kagaku Kaishi, 7, 807-812, 1993. 

Carbon fibers above are made from raw fibers through high-temperature carbonization, and PAN-based carbon fiber is now widely used as structural composites. 

Polyacrylonitrile (PAN) is the most favored precursor at this time for the production of high-performance fibers. PAN-based fibers are in the medium price range (- 40/ kg in 1992). They have the highest tensile strength of all carbon fibers and a wide range of moduli and are readily available in a variety of tows. 

Carbon-Fiber Network. Rayon-based carbon fibers were used in the early development of carbon-carbon and are still used as carbon felt. PAN-based fibers are now used extensively and pitch-based fibers are under investigation. jhe selection of the carbon-fiber architecture is determined by the application and include felt, short (chopped) fibers, continuous filament such as small-tow T-300 fiber, filament winding or tape-layup, and 3D structures (see Sec. 2.0 above). The effect of carbon-fiber type and architecture is reviewed in Refs. 22 and 23. The effect of carbon-fiber... 

Asymmetric, flexible hollow fiber carbon membrane with high mechanical strength was produced by thermooxidative stabilization and gradual carbonization of PAN based precursor membrane [11]. SEM showed that the itmer surface had the pores of 3-10 pm in diameter penetrating into the hollow fiber wall but not reaching the outer surface. Three membranes A, B, C were produced, the differ-... 

It has been more than 50 years that carbon fibers have been under development from rayon, polyacrylonitrile (PAN), isotropic and mesophase pitches. PAN-based technologies are most commercial production of carbon fibers and rayon-based carbon fibers are no longer in production. Pitch-based carbon fibers currently account for niche markets. Isotropic pitch-based carbon fibers have modest level of strength and modulus and are the least expensive carbon fibers. PAN and mesophase-based carbon fibers heat treated to improve modulus. Both PAN and mesophase pitch-based carbon fibers are not subject to creep or fatigue failure and set them apart from other material which is critical for application such as tension leg platforms for deep sea oil production [201]. The new generation of carbon based fibers is carbon nanotube (single and multi-walled). There are different synthesis methods for carbon... 

The property of mesophase that makes it suitable for carbon fiber and premium coke manufacture is that it forms ordered stmctures under stress which persist following carbonization. However, most carbon fiber production in the 1990s is based on polyacrylonitrile (PAN). 

Producers of PAN-based carbon fiber include Toray, Toho Beslon, Mitsubishi Rayon, and Asahi Kasai Carbon in Japan Hercules, Amoco Performance Products, BASE Stmctural Materials, Eortafil (Akzo), and Mitsubishi Rayon in the United States and Akzo, Sigri, and Soficar in Europe. Primary suppHers of high performance pitch-based carbon fibers include Amoco Performance Products, Mitsubishi Kasai, and Tonen Corp. 

More than 95% of current carbon fiber production for advanced composite appHcations is based on the thermal conversion of polyacrylonitrile (PAN) or pitch precursors to carbon or graphite fibers. Generally, the conversion of PAN or pitch precursor to carbon fiber involves similar process steps fiber formation, ie, spinning, stabilization to thermoset the fiber, carbonization—graphitization, surface treatment, and sizing. Schematic process flow diagrams are shown in Eigure 4. However, specific process details differ. 

Fig. 4. Process flow diagrams for (a) PAN-based and (b) pitch-based carbon fiber processes.

Fig. 6. Each of carbonization temperature on PAN-based carbon fiber strength and modulus (31). To convert GPa to psi, multiply by 145,000.

Fig. 8. Comparison of electrical and thermal conductivity of PAN- and pitch-based carbon fiber to metals, where P = pitch, T = Thornel, and...

There are two mechanisms of PAN-based carbon fiber oxidation dependent on oxidation temperature ((67,68). At temperatures below 400°C, oxygen diffuses into the fiber and attacks at pores resulting in significantly increased fiber surface area. At higher temperatures impurities catalyze the oxidation reaction. 

W. Johnson, "The Stmcture of PAN-Based Carbon Fibers and Relationship to Physical Properties," in W. Watt and B. V. Perov, eds., ELandbook of Composites, Vol. 1, Elsevier Science Pubhshers, New York, 1985. 

Fibers produced from pitch precursors can be manufactured by heat treating isotropic pitch at 400 to 450°C in an inert environment to transform it into a hquid crystalline state. The pitch is then spun into fibers and allowed to thermoset at 300°C for short periods of time. The fibers are subsequendy carbonized and graphitized at temperatures similar to those used in the manufacture of PAN-based fibers. The isotropic pitch precursor has not proved attractive to industry. However, a process based on anisotropic mesophase pitch (30), in which commercial pitch is spun and polymerized to form the mesophase, which is then melt spun, stabilized in air at about 300°C, carbonized at 1300°C, and graphitized at 3000°C, produces ultrahigh modulus (UHM) carbon fibers. In this process tension is not requited in the stabilization and graphitization stages. 

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