Carbon Fiber from PAN

In a similar approach, it is not the monomer, but a solution of the prefabricated polymer (polyacrylonibile in this case) in DMF that is being used. Herein the SWNTs are very finely dispersed. The product then also contains nano tubes aligned in the fiber s longitudinal direction. Another procedure resembles the method of producing carbon fibers from PAN (Section 1.2.3). Here the composite fibers are carbonized to yield a material of nanotube-reinforced carbon fibers. At a nanotube portion of as little as 3%, it already exhibits markedly improved mechanical properties. 

CARBON FIBERS FROM PAN AND PITCH 12 APPLICATIONS OF CARBON AND CERAMIC ... 

Figure 2. Main steps In the fabrication of a carbon fiber from PAN or pitch precursors.

Pitch as a precursor material is cheaper than PAN as a precursor fiber, but the conversion of pitch into mesophase pitch and subsequent fiber formation is complex and costly. When a pitch is not transformed into a mesophase and is spun as an isotropic liquid, the resulting carbon fibers have extremely poor mechanical properties. These considerations explain why more than 90% of today s carbon fibers are fabricated from PAN based precursors. Processes for fabricating carbon fibers from PAN or pitch based precursor fibers differ in important aspects, but also share important commonalties (Figure 2). Finally, the carbon yield from PAN based precursor fibers is 50%, that from mesophase pitch is 70-80%, and that from rayon is 25%. 

PG Rose, whilst with Rolls Royce, took his PhD at the University of Aston in Birmingham and his thesis [123] contains a wealth of information on the physics and chemistry of carbon fibers from PAN precursors and some of this data is highlighted in Chapters 4 and 6. 

Olive and Olive (1983) [202] present a review of the chemistry of formation of carbon fiber from PAN. 

Damodaran S, Desai P, Abhiraman AS, Chemical and physical aspects of the formation of carbon-fibers from PAN-based precursors, J Text Inst, 81(4), 384-420, 1990. 

Carbon fibers can be produced from a wide variety of precursors in the range from natural materials to various thermoplastic and thermosetting precursors Materials, such as Polyacrylonitrile (PAN), mesophase pitch, petroleum, coal pitches, phenolic resins, polyvinylidene chloride (PVDC), rayon (viscose), etc. [42-43], About 90% of world s total carbon fiber productions are polyacrylonitrile (PAN)-based. To make carbon fibers from PAN precursor, PAN-based fibers are generally subjected to four pyrolysis processes, namely oxidation stabilization, carbonization and graphitiza-tion or activation they will be explained in following sections later [43]. 

PAN carbon fiber research, "black Orion", U.S.A. (5) Probably first carbon fibers from PAN... 

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)... 

Recall from Section 1.4.5.1 that there are two primary types of carbon fibers polyacrylonitrile (PAN)-based and pitch-based. There are also different structural forms of these fibers, such as amorphous carbon and crystalline (graphite) fibers. Typically, PAN-based carbon fibers are 93-95% carbon, whereas graphite fibers are usually 99+%, although the terms carbon and graphite are often used interchangeably. We will not try to burden ourselves with too many distinctions here, since the point is to simply introduce the relative benefits of continuous-fiber composites over other types of composites, and not to investigate the minute differences between the various types of carbon-fiber-based composites. The interested reader is referred to the abundance of literature on carbon-fiber-reinforced composites to discern these differences. 

PAN fibers -carbon fiber from [CARBON AND GRAPHITE FIBERS] (Vol 5)... 

In order to produce carbon fibers from polyacrylonitrile) (PAN) and various pitches, stabilization is essential after the spinning, which consists of a chemical reaction using different oxidizing gases, such as air, oxygen, chlorine, hydrochloric acid vapor, etc. [91]. The stabilized fibers are then... 

One of the most significant steps in the preparation of carbon fibers from acrylic precursor fibers is the oligomerization of the nitrile groups. This reaction has originally been studied in context with the problem of thermal discoloration of PAN (e.g. McCarthney Grassie and McNeill Grassie and Hay It was supposed to lead to a so-called ladder structure ... 

Reinforcing carbon fibers from poly(acrylonitrile) (PAN)-fibers ... 

The overwhelming success of PAN-based carbon fibers over rayon and pitch can be attributed to several key aspects.f Structurally, PAN has a faster rate of pyrolysis without much disturbance to its basic structure and to the preferred orientation of the molecular chains along the fiber axis present in the original fiber. By contrast, carbon fibers from rayon suffer from extremely low carbon yield (20-25%) due to chain fragmentation, which eliminates the orientation of the precursor fiber. While improved properties can be achieved by stretch graphitization, this process is expensive and does not compensate for the low yields. 

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). 

In order to make high-modulus carbon fibers from pitch, petroleum- or coal-tar pitch is first filtered to remove solids which inhibit the growth of mesophase. This is followed by heat treatment, which results in a mesophase content of 70 to 95% then the mesophase pitch is spun into monofilaments with a fiber diameter of around 5 pm. Optimum viscosity and minor gas liberation of the pitch are of fundamental importance. The pitch monofilament is oxidized in the second stage to make it infusible. Oxygen is used as the oxidation agent. Unlike in the production of PAN fibers, it is not necessary to stretch the fibers before oxidation. 

In the early 1960s, polyacrylonitrile (PAN) fibers afforded a total carbon yield after pyrolysis that was higher, and high strength carbon fibers were obtained by stretching PAN fibers in steam and oxidizing them under stress before carbonization. Carbon fibers from pitch precursors are a more recent development. Pitches are low value residues of the petroleum industry. 

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