Degradation, thermal polyacrylonitrile

No.14, Oct.l998,p.2503-12 SPECTROSCOPIC INVESTIGATIONS OF POLYACRYLONITRILE THERMAL DEGRADATION... 

There is much evidence that weak links are present in the chains of most polymer species. These weak points may be at a terminal position and arise from the specific mechanism of chain termination or may be non-terminal and arise from a momentary aberration in the modus operandi of the polymerisation reaction. Because of these weak points it is found that polyethylene, polytetrafluoroethylene and poly(vinyl chloride), to take just three well-known examples, have a much lower resistance to thermal degradation than low molecular weight analogues. For similar reasons polyacrylonitrile and natural rubber may degrade whilst being dissolved in suitable solvents. 

A series of papers have rqwrted FT-IR studies of the thermal degradation of polyacrylonitrile 22S-226,227 228, 229, 230>. These FT-IR measurements indicate that the nitrile groups play an important role in the degradation process even in the initial stages and show a steady decrease in nitrile with time both in air and under reduced pressure. These results are contrary to previous dispersive infrared measurements... 

Polyacrylonitrile has been the subject of investigations by Russian workers, particularly those aspects relating to its thermal degradation. Polyacrylonitrile itself is a semiconductor with an activation energy of 0.32 to 0.84 e. v. (69) or 1.5 to 4.6 e. v. (70) depending upon the method of polymerization, ambient atmosphere and sample history. 

Usami, T., Itih, T., Ohtani, H., Tsuge, S. (1990) Structural study of polyacrylonitrile libers during oxidative thermal degradation by pyrolysis-gas chromatography, solid state 13C Nuclear magnetic resonance and Fourier transform infrared spectroscopy, Macromolecules 23, 2460-2465. 

Composite conductive fibers based on poly(3,4-ethylene-diox)d hiophene]-polystyrene sulfonic acid (PEDOT-PSS) solution blended with polyacrylonitrile (PAN] were obtained via wet spinning. The influence of draw ratio on the morphology, structure, thermal degradation, electrical conductivity, and mechanical properties of the resulting fibers was investigated. The results revealed that the PEDOT-PSS/PAN composite conductive fibers crystallization, electrical conductivity and mechanical properties were improved with the increase of draw ratio. The thermal stability of the fibers was almost independent of draw ratio, and only decreased slightty with draw ratio. Besides, when the draw ratio was 6, the conductivity of the PEDOT-PSS/PAN fibers was 5.0 S cm, ten times the conductivity when the draw ratio was 2 (Fig 5.10]. ... 

Figure 5.3 Dependence of the rate of thermal degradation of polyacrylonitrile on its degree of decomposition at 1 250 °C, 2 260 °C and 3 270 °C. Source ...

Polyacrylonitrile is most commonly used in fiber form. Since it softens only slightly below its thermal degradation temperature, it must be processed by wet or dry spinning rather than melt spinning. Some typical properties are Glass Transition Temperature, Tg = 85 C Melting Temperature, Tm = 317 C Amorphous density at 25 C = 1.184 g/cc Molecular weight of repeat unit = 53.06 g/mole. 

Mathur RB, Bahl OP, Sivaram P, Thermal degradation of polyacrylonitrile fibres. Current Science, 62(10), 662-669, 1992. 

Figure 12.39 Series of transmission FTIR spectra for (a) Nikkoso precursor AN/MA/ITA, (b) Oxidized in air for 20 min 215°C/15 min 235°C, (c) Oxidized in air for 20 min 215°C/180 min 235°C, (d) Oxidized in air for 20 min 215°C/1800 min 235°C. Source Reprinted from UsamlT, ItohT, Ohtani H.Tsuge S, Structural study of polyacrylonitrile fibers during oxidative thermal degradation by Pyrolysis— Gas Chromatography, Solid State C Nuclear Magnetic Resonance and Fourier Transform Infrared Spectroscopy, Macromolecules, 23, 2460-2465, 1990.

Usami T, Itoh T, Ohtani H, Tsuge S, Structural study of polyacrylonitrile fibers during oxidative thermal degradation by Pyrolysis—Gas Chromatography, Sohd State C Nuclear Magnetic Resonance and Fourier Transform Infrared Spectroscopy, Macromolecules, 23, 2460 2465, 1990. 

Coleman, M., Petcavich, R. (1987). Fourier Transform Infrared Studies on the Thermal Degradation of Polyacrylonitrile. Journal of Polymer Science, Part A Polymer Chemistry, 16, 821-832. 

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