Production of carbon fibers

Carbon fibers were first made by Thomas Alva Edison in 1879 from cellulose for lamp filaments. In Great Britain in 1961 the Royal Air Force produced a high-value carbon fiber from polyacrylonitrile (PAN). 

Production of pitch fibers was first investigated in Japan. In 1963, Sugio Otani obtained pitch fibers by the pyrolysis of lignin and later of PVC pitch. The first commercial product was the fiber from a pitch derived from crude oil pyrolysis, produced by Kureha, 

Industrial production of high-modulus carbon fibers based on pitch started in 1982, based on the fundamental work of Leonard Sidney Singer in the USA Union Carbide), 

Dependent on their carbon content, carbon fibers are divided into the following categories  

Whereas carbon fibers with a low carbon content are formed predominantly from aliphatic raw materials (rayon), carbon fibers with a high carbon content are produced from aromatic feedstocks or easy-to-aromatize base materials. The most important raw materials for the manufacture of high-carbon fibers are polyacrylonitrile and mesophase pitch. 

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Tibbetts, G.G., Gorkiewicz, D.W., and Alig, R.A. A new reactor for growing carbon fibers from liquid- and vapor-phase hydrocarbons, Carbon, 993, 31(5), 809 814. Tibbetts, G.G., Bernardo, C.A., Gorkiewicz, D.W. and Alig R.L. Role of sulfur in the production of carbon fibers in the vapor phase. Carbon, 1994, 32(4), 569 576. 

Current U.S. production of carbon fibers is approximately ten million pounds/year. 

Cyclization is a key reaction in the production of carbon fibers from polyacrylonitrile (PAN) (acrylic fiber see Sec. 3-14d-2). The acrylic fiber used for this purpose usually contains no more than 0.5-5% comonomer (usually methyl acrylate or methacrylate or methacrylic acid). Highly drawn (oriented) fibers are subjected to successive thermal treatments—initially 200-300°C in air followed by 1200-2000°C in nitrogen [Riggs, 1985]. PAN undergoes cyclization via polymerization through the nitrile groups to form a ladder structure (XXVII). Further reaction results in aromatization to the polyquinizarine structure (XXVIII)... 

The production of carbon fibers or filaments by decomposing a hydrocarbon gas over a transition metal catalyst has been the subject of extensive research. The product consists of filaments with diameters in the range of 1-100 pm and lengths up to 100 mm. In microstructure, it is different from traditional carbon fibers, resulting in a sword and sheath fracture mode without catastrophic failure. Since, in addition, these fibers are produced in a single step with no really expensive processing, they are attractive candidates for reinforcing composites. 

Materials. Several precursor materials exist for the production of carbon fibers (2). However, most of the presently available carbon fibers are synthesized from polyacrylonitrile (PAN) since these fibers have the best mechanical properties. Five PAN based carbon fibers were used in this study ... 

Around the same time, Mansmann and coworkers reported the production of carbon fibers from a variety of dry-spun materials, including lignin (lignosulfonates) by the simple addition of small amounts of PEO or acrylic acid-acrylamide copolymers. Although similar to the procedure of Ohtani, Mansmann employed acidic rather than neutral and/or alkaline spinning conditions. 

The total production of carbon fibers in 1987 was 4,5001, with polyacrylonitrile fibers currently by far the most important feedstock. 

Independent of the Japanese work, W. Watt, W. Johnson and L.N. Phillips (Figure 3.3) of the Royal Aircraft EstabUshment at Farnborough (RAE) started work in 1963 on the production of carbon fiber from a PAN precursor. Courtaulds were invited to submit a... 

Production of carbon fibers in the USA to the RAE patent was started in 1971 by two companies Hercules Inc. (who had an arrangement with Courtaulds Ltd.) and Morganite Modmor Inc. (a joint company formed by the Whittaker Corp. and Morgan Crucible). 

The rate controlling step in the production of carbon fiber from an acrylic precursor is the oxidation stage and G Gould and his research team looked at ways of speeding up this reaction. Various techniques could be used to catalyze the cyclization of PAN, but because the SAF already contained a catalyst comonomer (itaconic acid), the effects were much smaller than those reported in the literature for other acrylic fibers. One of the most promising was treatment with a Lewis acid, SnCU, which when applied as a solution in diphenyl ether, reduced the residual exotherm of SAF to less than 50 cal in only 6 min, which would normally have taken some 3 h of air oxidation at 220°C to have produced the... 

A detailed review of acryhc precursors for carbon fibers is given by Gupta et al [19], some precursor examples are discussed by Rajalingam and Radhakrishnan [20], whilst Bajaj and Roopanwal present an overview of the thermal stabilization of acrylic precursors for the production of carbon fibers [21]. 

The production of carbon fibers from kerosene has been investigated [285]. 

American Kynol Inc., Production of Carbon Fiber from Kynol Novaloid Precursor Fiber, New York, Jul 1997. 

Figure 5.3 Projected worldwide production of carbon fibers. Source Reprinted with permission from Katsumato M, Keynote Address at Carbon Fibers 98, San Antonio, Texas. Copyright 1998, Intertech.

In the oxidation stage, the PAN fiber will increase in density from 1.18 gcm to about 1.36-1.38 gcm for the oxidized PAN fiber (opf). The actual density will depend on whether the final product is to be used as opf or is required for onward processing to carbon fiber. The final density of an opf product will depend on the opf product specification, whereas for carbon fiber, the density must be at least 1.36 gcm , as otherwise, the fiber will tend to pull apart and break on entering the LT furnace. The upper opf density limit for the production of carbon fiber varies with the manufacturer and some manufacturers will use a value as high as 1.40 gcm , but others claim that this would produce inferior carbon fiber. The residual exothermicity of SAP heated in air at 230°C (Figure 5.8) after a 3 h treatment, has some 35% exothermic heat remaining in the oxidized fiber. 

Hiittinger KJ, Krekel G, Polydimethylsiloxane coated carbon fibers for the production of carbon-fiber reinforced carbon. Carbon, 29, 1065, 1991. 

Gibson JO, Gibson MG, Production of carbon fiber - tantalum carbide composites, U.S. Pat., 4196230, Apr 1 1980. 

Possible surface treatment mechanisms include anodization [32-34], plasma and flame treatment [35], solution oxidation [36,37], gas phase oxidation, and high temperature oxidation. Some of these treatments have been reviewed 1 Donnet and coworkers [18,38]. The most practical surface treatment for commercial production of carbon fibers is anodization. This is because anodization (electrolytic oxidation) can be performed continuously on carbon fibers. Typical anodizations have been performed in aqueous acidic or basic solutions. Electrolytes include sodium hydroxide, potassium hydroxide, sulfuric add, nitric add, and solutions of amine salts. Amine salts have an added advantage in that, after treatment, excess electrolyte can be removed simply by heating the fiber to high temperatures (250 C). 

PAN fibers are used in weaving (blanket, carpet and clothes) and in engineering-housing (instead of asbestos) and most importantly for producing carbon fibers [53]. In recent decade PAN fibers are considered as main material for production of carbon fibers. PAN fibers manufactured... 

Shimada, I., Takahagi, T. (1986). FT-IR Study of the Stabilization Reaction of Polyacrylonitrile in the Production of Carbon Fibers.. loumal of Polymer. Science. Part A Pohmer Chemistry. 24, 1989-1995. 

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