Production of PAN-based carbon fibres (CF) is a rapidly developing sector. Production in 2006 was 28,000 tons. The production capacities in 2007 increased to 55,500 tons and will attain 66,000 tons in 2008. The Japanese companies Toray, Toho, and Mitsubishi are the leaders and are responsible for 77% of total production. Toray is the leader with respect to fibre quality. The CF manufactured by the company basically have a strength of 500-560 kgf/mm 2 . The properties of the PAN precursor are of decisive importance for the quality of the CF. Each company has its own PAN precursor plant for successfully competing. The fibre manufactured in the RF has a strength of 300-350 kgf/mm 2 . Uglekhimvolokno NITs has developed technology for production of CF with a strength of 450 kgf/mm 2 . Economy in production of CF is attained by creating units (flow production lines) with individual capacity of 150-200 and even 400 tons/year (the capacity of existing domestic units is 10-20 tons/year). This increase in capacity is attained by using primarily new technical solutions, including conductive tempering of oxidized tows, separate air-oxidant and air-heat carrier circulation, making the PAN tow compact by selecting an appropriate oiling agent, and vertically positioning the carbonization furnace stack. The maximum modulus of elasticity of PAN CF is 60,000 kgf/mm 2 . To attain high orientation and a high degree of crystallinity, boron, which decreases the temperature of transition of the fibre into the highly elastic state and thus facilitates the occurrence of orientation drawing and crystallite growth, should be used as a plasticizer. In semi-industrial conditions, when boron is added in the stage of oxidation in the form of boric acid, CF with a modulus of elasticity of 47,700 kgf/mm 2 are obtained. To prolong the lifetime of the graphite heaters, it is recommended that they be given a shape that allows focusing radiation on the processed fibre. Thin carbon fillers in the form of prepregs 0.04-0.17 mm thick and fabrics 0.11-0.15 mm thick are manufactured to increase the uniformity of the properties of multilayer composites. Prepregs made of thick PAN tow with a linear density of 3.2 ktex which are processed into CF with a strength of 500 kgf/mm 2 , elongation of 2%, and modulus of elasticity of 23,000 kgf/mm 2 , are the most economical. In the RF, unidirectional slivers of the Elur type 0.08 mm thick are manufactured for these purposes, but they have lower strength and due to the low processing speeds, high cost. These drawbacks have been eliminated in the semicontinuous method for manufacturing thin PAN fibres.Carbon fibres manufactured from a polyacrylonitrile (PAN) precursor have a set of properties (high strength and modulus of elasticity, thermal stability, low density) which has made them irreplaceable in high-tech sectors of technology. Modern wide-body airplanes from Boeing and Airbus consist of 20-25% carbon fibres. The nuclear industry is converting to a progressive centrifugal method of uranium enrichment which wou...

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The features of nanotechnologies and possibility of applying them in research and industrial practice in the chemical fibres sector are examined. Structural elements 1-100 nm in size are the objects of nanotechnologies. The cross sections of fibrils and their crystalline sections (large periods) whose structure determines the mechanical and physical properties of the fibres fall in this range. In the initial stage, the chemical fibres were improved, especially with respect to increasing the strength, by orientation drawing, which corresponded to the nanotechnology principle of topdown processing. The wide use of the more progressive bottom up processing principle by regulating the fibrillar structure by selecting the optimum conditions of spinning the fibre was recently supplemented by the method of self-ordering on the molecular level through the liquidcrystalline state. Fibre strength of 500-600 kgf/mm 2 was attained with this method. The energetic mechanism of transition of a substance into the liquid-crystalline state was substantiated. To attain a high degree of ordering of the fibrils before spinning, it is necessary to destroy the structural network of linkages in the spinning solutions and melts as completely as possible.Processes that take place in objects with characteristic linear dimensions of 1 to 100 nm, i.e., 0.001-0.100 μm are usually considered nanotechnologies. We note that the diameter of the hydrogen atom is equal to 0.22 nm, while the largest atom of the element rubidium has a diameter of 0.51 nm. The carbon most frequently used in nanotechnologies is 0.36 nm in size. This is beyond the limits of the resolution of ordinary optical microscopes, which does not exceed 0.2-0.5 μm. The minimum linear dimensions that process engineers specialists in production of chemical fibres are concerned with are close to these limits, but nevertheless still outside of them. Spinneret holes have a diameter of 40 μm in wet spinning to 500 μm in polymer melt spinning. The diameter of the spun fibre usually varies within 8-25 μm. The smallest objects are disperse particles of dyes and flatting agents added to the spinning solution or melt before spinning. They are 0.5-2.0 μm in size. As a consequence, the processes for production of chemical fibres cannot be formally considered nanotechnologies.This was the situation before the appearance of the electron microscope (1932). At the end of the 40s, its use showed [1] that almost all fibres have a complex fibrillar structure whose basic structural elements, microfibrils, fall in the nanoregion in almost all kinds of chemical fibres. They have cross sections of 5-15 nm and the length attains 0.5-1.5 μm. Alternation of ordered (crystalline) and amorphous segments 8-20 nm long, called major periods, is observed along the fibrils. With respect to the linear dimensions of the basic structural elements, it seems obvious that chemical fibres should be included in nanotechnologies. Since the fibrillar structure determines the physicomechanical properties of the fibres and is...

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Spinning baths are divided into three types as a function of the coagulating (desolvating) power: hard, soft, and ultrasoft. The concentration of precipitant c p in hard spinning baths is two times higher than the critical (threshold) precipitation concentration c cr , i.e., c p > 2c cr . Precipitation takes place with formation of a boundary line (precipitation front) which coincides with the critical supersaturation line spinodal. The fibre is characterized by large fibril size and high porosity. Soft baths are realized when the concentration of precipitant in the bath is less than two and more than one critical precipitation concentration, i.e., c cr < c p < 2c cr . Precipitation takes place according to a frontal mechanism with initial formation of a liquid segment in the spun fibre. In spinning into soft baths, the optimum conditions are created for formation of fibres with a small-fibril structure and elevated physicomechanical indexes. At a concentration of precipitant below c cr but above c e (equilibrium), the precipitant accumulates on the fibre and precipitation takes place over the entire volume, without formation of a precipitation front. The fibre obtained is characterized by high porosity.Coagulation, i.e., precipitation of the polymer from the spinning solution in wet spinning of fibres, is a phase transition and is subject to all of the rules of phase equilibria and kinetics [1, p. 153]. The difference between it and the well-studied phase transitions in spinning fibres from polymer melts is basically that the polymer in the spinning solution is in the form of a solvate compound with the solvent and precipitation takes place due to loss of solubility by partial decomposition of this compound. The coagulation temperature, in contrast to melt spinning, is of no determining importance in most cases.The solvate compound decomposes in the reaction of thin jets of spun filaments with the spinning bath containing a precipitant a substance capable of causing desolvation of the polymer molecules. The filaments lose solubility and are precipitated in the form of a solid polymer phase a gel. The mixture of solvent and precipitant (more precisely, solvate compound of the solvent with the precipitant) form a low-molecular-weight liquid phase. The polymer phase (gel) has a fibrillar-porous structure. Its composition is a function of the concentration and desolvating power of the precipitant. At low concentrations and weak desolvating power (soft bath), the polymer solvate does not completely decompose and the fibre is precipitated in the form of a strongly swollen gel. The polymer phase can probably totally or partially have a liquid aggregate state in some cases in very soft precipitation conditions where the change in the chemical potential is small. However, the polymer phase is usually in a solid aggregate state similar to hardening of fibres from a melt, i.e., it has a certain fibrillar structure, sufficiently high resistance to shear and longitudinal deformation, and a characteristic aggregate transition...