Polyacrylonitrile mechanical properties

Another interesting type of novel carbons applicable for supercapacitors, consists of a carbon/carbon composite using nanotubes as a perfect backbone for carbonized polyacrylonitrile. Multiwalled carbon nanotubes (MWNTs), due to their entanglement form an interconnected network of open mesopores, which makes them optimal for assuring good mechanical properties of the electrodes while allowing an easy diffusion of ions. 

The first major application of microfiltration membranes was for biological testing of water. This remains an important laboratory application in microbiology and biotechnology. For these applications the early cellulose acetate/cellulose nitrate phase separation membranes made by vapor-phase precipitation with water are still widely used. In the early 1960s and 1970s, a number of other membrane materials with improved mechanical properties and chemical stability were developed. These include polyacrylonitrile-poly(vinyl chloride) copolymers, poly(vinylidene fluoride), polysulfone, cellulose triacetate, and various nylons. Most cartridge filters use these membranes. More recently poly(tetrafluo-roethylene) membranes have come into use. 

The first high-strength carbon fibres were produced in the 1950s (see Donnet and Bansal, 1984). The early carbonized products were rayon-based, but it was soon found that the mechanical properties and the carbon yield could be improved by the use of polyacrylonitrile (PAN) as the precursor. Also, less expensive fibres of somewhat lower strength and modulus could be made from various other precursors including petroleum pitch and lignin. However, cotton and other forms of natural cellulose fibres possess discontinuous filaments and the resulting mechanical properties were consequently found to be inferior to those of the rayon-based fibres. 

However, it seems likely that a conductivity value of 10 S cm at room temperature is a goal that can only be achieved with polymer networks including organic solvents as plasticizers [96] or with polymer matrixes like polyacrylonitrile [97] or poly(methyl methacrylate) [98] entrapping a large amount of organic electrolytic solution, i.e., with hybrid and/or gel electrolytes. These electrolytes combine the advantage of the polymer s mechanical properties with the electrochemical properties of the liquid electrolytes. 

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 ... 

Klein, E. Smith, J.K. Holland, F.F. "Rhone Poulenc Polyacrylonitrile Membrane - Laboratory Evaluation of Permeability, Physical and Mechanical Properties." Rept. No. PB 225066/OSET National Technical Information Service Springfield, VA, 1977. 

The unique molecular packing of rod-like chains in liquid crystalline polymers (LCP) closely resembles the extended chain structure of highly oriented flexible chain polymers, suggesting that these materials are good candidates for barrier applications. Thermotropic LCP s, first developed in the early 1970 s, have been the object of much interest because of their excellent mechanical properties and ease of product fabrication. Preliminary observations have shown that a commercially available wholly aromatic thermotropic copolyester has gas permeability coefficients that are lower than those of polyacrylonitrile (4.). These results raise some fundamental questions as to the nature of the mechanism for transport of small molecules through a matrix of ordered rigid rod-like chains. 

FIGURE 12.20 Dynamic-mechanical properties of undrawn polyacrylonitrile fiber measured with a Rheovibron at 110 Hz. (From Minami, S.J., Appl. Polym. Sci. Appl. Polym. Symp. 25, 145, 1974.)... 

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]. ... 

Zhou Z., Lai C., Zhang L., Qian Y, Hou H., Reneker D. H., and Fong H., Development of carbon nanofibers from aligned electrospun polyacrylonitrile nanofiber bundles and characterization of their microstructural, electrical, and mechanical properties. Polymer, 2009, 50,2999-3006. 

The improvement of mechanical properties of polymers with added CNTs has been previously observed in several studies. Cadek [39] found that Young s modulus increases by a factor of 1.8 with addition of 1 %(wAv) SWNTs to PVA and 2.8 and a 50% improvement in the elastic modulus of poly(p-phenylene enzobisoxazole) (PBO) was observed upon addition of Nes [40]. An increase in tensile strength and elastic modulus by a factor of 1.5 and 1.7 respectively was observed upon addition of 5 wt% SWNT to polyacrylonitrile (PAN)[41]. 

High barrier polymers, such as polyvinylidene chloride (PVDC), polyacrylonitrile (PAN), polyester, acid copolymers and ionomers have been proposed and are under evaluation as a replacement for PE. However, they present some drawbacks in terms of scalability and/or mechanical properties and/or outgassing rates. Cost of these polymers is also generally higher. 

Weisenberger, M. C., Grulke, E. A., Jacques, D., Rantell, T. Andrews, R. Enhanced mechanical properties of polyacrylonitrile/ multiwall caibtm nanotube composite fibers. J. Nanosci. Nanotech-nol. 3, 535 539 (2003). 

Moreton R, The removal of sodium from polyacrylonitrile precursor fibre and its effect on the mechanical properties of RAE carbon fibre, RAE Tech Memo MAT 78, Feb 1970. 

Most polymers are not miscible and those having closely similar solubility parameter values are likely to be compatible. Two incompatible polymers can be compatibihzed by the presence of a third component, which results in a good improvement in the physical and mechanical properties of the blend. The effect of the polyacrylonitrile compatibilizer, on the miscibility and properties of NBR/SBR blends, has been studied by Darwish et al. (2005). 

Most of the presently available carbon fibers are synthesized from polyacrylonitrile starting materials. Although several other precursors do exist such as rayon and pitch [18], PAN precursor fibers have the best mechanical properties for structural applications. The technology of carbon fiber synthesis is protected very strongly by carbon fiber producers. However, the basic chemistry of carbon fiber synthesis is known. A brief review is included here. 

Zhou, Z. et al. (2009). Development of Carbon Nanofibers from Ahgned Electrospun Polyacrylonitrile Nanofiber Bundles and Characterization of Their Microstructural, Electrical, and Mechanical Properties. Pot m 50, 2999—3006. 

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