PAN fiber

Table 3. Gel Spun PAN Fibers Compared with Other High Performance Fibers...

Fig. 1. The stmcture of Dow EDF fiber. EDF = elongatable Dow fiber OPF = oxidized PAN fiber.

Process. Any standard precursor material can be used, but the preferred material is wet spun Courtaulds special acrylic fiber (SAF), oxidized by RK Carbon Fibers Co. to form 6K Panox B oxidized polyacrylonitrile (PAN) fiber (OPF). This OPF is treated ia a nitrogen atmosphere at 450—750°C, preferably 525—595°C, to give fibers having between 69—70% C, 19% N density less than 2.5 g/mL and a specific resistivity under 10 ° ohm-cm. If crimp is desired, the fibers are first knit iato a sock before heat treating and then de-knit. Controlled carbonization of precursor filaments results ia a linear Dow fiber (LDF), whereas controlled carbonization of knit precursor fibers results ia a curly carbonaceous fiber (EDF). At higher carbonizing temperatures of 1000—1400°C the fibers become electrically conductive (22). 

Data from the following technical data sheets PAN fibers Amoco Performance Products, Asahi Kasei, BASE Stmctural Materials, Courtaulds-Grafil, Hercules, Mitsubishi Rayon, Toho Beslon, Toray Pitch fibers Amoco Performance Products, Mitsubishi Kasei, Tonen Corp. 

The use of a wet-spinning process with inorganic solvents has also been attempted. Although the details of this process are proprietary, it is clear that these inorganic wet-spun PAN fibers make higher quality carbon fiber precursors than those produeed with traditional organic solvents [5]. 

The as-spun acrylic fibers must be thermally stabilized in order to preserve the molecular structure generated as the fibers are drawn. This is typically performed in air at temperatures between 200 and 400°C [8]. Control of the heating rate is essential, since the stabilization reactions are highly exothermic. Therefore, the time required to adequately stabilize PAN fibers can be several hours, but will depend on the size of the fibers, as well as on the composition of the oxidizing atmosphere. Their are numerous reactions that occur during this stabilization process, including oxidation, nitrile cyclization, and saturated carbon bond dehydration [7]. A summary of several fimctional groups which appear in stabilized PAN fiber can be seen in Fig. 3. 

Fig.3 Illustration of functional groups appearing in stabilized PAN fiber [9].

PAN fibers develop a structure with little point-to-point relationship between atoms in neighboring basal planes. This structure is labeled the turbostratic configuration and is characterized by interplanar spacing values greater than 0.344 nm. The crystallite size in the direction normal to the basal planes, or stack height (L, ), in turbostratic graphite is typically less than 5 nm. 

PAN fibers were purehased from AKZO Fortafil Fibers, Rockwood, Term., under the designation F3-0. Fibers with a mean length of 100,am and 200,am have been utilized. 

SEM examination of the steam activated PAN fiber monoliths showed the fiber diameter to be significantly reduced during the activation process, suggesting the fibers are consumed radially by a gasification process of the external surface [28]. 

FTIR is also an effective way to assess the orientation or alignment of CNTs since the absorption is much stronger when the electric field of the incident light wave is parallel to the axis of aligned CNTs. The anisotropic feature has been found in SWNT-PAN composite [164], The infrared spectra of PAN fibers for the two polarization directions (parallel and perpendicular) are comparable, while the composite fibers show significant differences in the two polarization directions. 

Kinetics of saponification of the PAN fibers treated by 5 - 40% solution of NH2NH2 H20 at 40-95 °C were studied in the range of NaOH solution concentration from 1 to 10% at 25 - 70 °C. For example, the kinetics of saponification by 5% NaOH solution of samples treated by 20% NH2NH2 H20 solution at 70 °C are given in Fig. 1. 

---