Properties of polycaproamide fibres which have been modified by grafting polyacrylonitrile

Conclusions The properties of modified polycaproamide fibres containing various amounts of grafted polyacrylonitrile have been investigated.It has been shown that the attachment of polyacrylonitrile to polycaproamide fibres leads to an improvement in a number of properties (light resistance, heat resistance, wool-like appearance) which determine the customer acceptance of fibres and articles made from them.Translated from Khimicheskie Volokna, No. 3, pp. 32–33, May–June, 1984.     

Defect content and nonuniformity in mechanical properties of polyacrylonitrile fibres

Conclusions Defect content and nonuniformity in mechanical properties of polyacrylonitrile fibres have been investigated in the cross section of tow and over the length of individual elementary fibres.For a generalized evaluation of defectiveness and nonuniformity in mechanical properties we have used the scale dependence of strength and histograms for strength distribution. Scale coefficients for the strength of polyacrylonitrile fibres have been determined.For rapid characterization of defectivity and nonuniformity of mechanical properties of fibres one can use the ratio of the mean strengths at two clamped lengths which differ significantly (by an order of magnitude or so).Translated from Khimicheskie Volokna, No. 1, pp. 33–34, January–February, 1989.     

Surface topography and mechanical properties of carbon fibres

Surface topography of polyacrylonitrile based carbon fibres preoxidized under a variety of conditions has been studied in detail. Only those carbon fibres processed under optimum conditions are found to possess defect free surface topography. Changes in surface topography and the tensile strength of carbon fibres with processing conditions have been discussed.     

Effect of a constant electrical field on the shrinkage of polyacrylonitrile fibres

Conclusions The possibility of physically modifying polyacrylonitrile fibres by stretching them in a constant electrical field, with the objective of attaining a high degree of shrinkage, has been demonstrated.The mechanism of the effect of an electrical field on polyacrylonitrile fibres consists in breaking up part of the dipole-dipole bonds between nitrile groups and partial polarization of the polymer.Translated from Khimicheskie Volokna, No. 2, pp. 34–36, March–April, 1985.     

Dependence of the combustibility of fibres on their degree of pyrolysis and carbonization

Conclusions The combustibility characteristics of pyrolyzed and carbonized viscose and polyacrylonitrile fibres have been investigated: oxygen index, limiting oxygen concentration, autoignition temperature, and glow point.It has been shown that the combustibility of pyrolyzed and carbonized fibres prepared from polyacrylonitrile is somewhat lower than the combustibility of those made from viscose fibres: this is connected with a more perfect aromatic structure and with the presence of nitrogen atoms in the first and of oxygen atoms in the second.Translated from Khimicheskie Volokna, No. 2, pp. 47–49, March–April, 1984.     

Deformation properties of modified polyacrylonitrile fibres

Conclusions Deformation properties of polyacrylonitrile fibres modified with alkali metal salts have been studied.The introduction of alkali metals by treatment of freshly spun gel-fibre with solutions of the appropriate salts aids in loosening fibre structure.Both the form of cation and also of the anion in the salt introduced affect the deformability of the modified fibres.Translated from Khimicheskie Volokna, No. 4, pp. 40–41, July–August, 1989.     

Modification of polyacrylonitrile fibres to improve the properties of carbon fibres prepared from them

Conclusions -- It has been found that treatment of acrylonitrile fibres obtained by the wet dimethyl formamide method before thermal oxidation with inorganic salts considerably changes the properties of the thermally oxidized fibres.-- On treatment of the fibres with an aqueous solution containing copper ion in a reducing medium, their sorptive powers are considerably impaired, the fibre diameter is increased, and the electrical conductivity is increased, plus processes of cyclization and oxidation are accelerated.-- On treatment with a solution of aluminum chloride in the presence of orthophosphoric acid, the fibre structure is made denser and its strength is increased.-- Sodium thiosulfate as a modifier considerably changes the functional composition of polyacrylonitrile fibres; thereupon, a process of structural amorphization takes place.Translated from Khimicheskie Volokna, No. 5, pp. 48–50, September–October, 1991.     

Modification of polyacrylonitrile fibres with halogen-containing polymers

Conclusions The physicomechanical and relaxation properties of fibres based on mixtures of polyacrylonitrile with halogen-containing polymers — polyvinyl chloride, chlorinated polyvinyl chloride, and Ftorlon — have been studied.It has been found that on introducing small additions of HCP, the physicomechanical properties of the fibres rise in an extreme fashion.Translated from Khimicheskie Volokna, No. 2, pp. 44–45, March–April, 1984.     

Length changes in PAN fibres during their pyrolysis to carbon fibres

A systematic study of the shrinkage taking place during the carbonization of polyacrylonitrile (PAN) fibres is reported. Shrinkage occurs from 200°C to 1000°C, the extent of which has been found to depend on (a) the time of preoxidation, (b) the type of oxidizing gas and (c) the carbonization conditions. The carbonization shrinkage is found to be independent of length changes during the preoxidation but can decrease from the usual 23% to about 2% by applying tension during the carbonization. A reaction is proposed to explain the shrinkage between 600°C and 800°C. The strength as well as Young's modulus of carbon fibres of under-oxidized fibres can be improved by applying tension during the carbonization. It is further predicted that the mechanical properties of carbon fibres preoxidized to the optimal level would decrease if carbonized under excessive tension.     

Molecular mechanism of shrinkage of polyacrylonitrile fibres

Conclusions The shrinkage of polyacrylonitrile fibres in air at 130–170°C, and also in steam or boiling water is connected with the formation of ordered structures due to a redistribution of the interacting CN groups.Shrinkage of fibres in air at temperatures below 130°C is caused only by disorientation of the macromolecule chains.Translated from Khimicheskie Volokna, No. 4, pp. 26–27, July–August, 1988.     

Chemical fibres and thread in a crisis year

For the first time in recent years, the total consumption of all types of fibres dropped significantly in 2008 — by 6.7%, including natural fibres by 10.1% and chemical fibres by 4.5%. The economic crisis affected the large-tonnage synthetic fibre sector especially negatively: world consumption decreased by 4.1% in comparison to 2007: polyacrylonitrile by 20%, polypropylene by 11%, polyamide by 10%, and polyester by 2%. Chemical fibre production in 2008 was 42,156 tons, i.e., a 4.5% decrease, primarily in Europe, Japan, and the US. China alone enjoyed a 2.5% increase in comparison to 2007. In CIS countries, chemical fibre production decreased by 2.6%. Belarus leads on all indexes, although there was a decrease there, too, especially in the first half of 2009. In Russia, the crisis was deeper, with an unfortunate tendency for chemical fibre production to decrease from year to year: in 2008, it was 18% lower in comparison to the preceding year, with an extremely low (almost postwar) volume of 121,000 tons/year. Many enterprises in the sector almost disappeared, production of viscose fibres and polyester staple fibre for textile applications almost totally stopped, and production of polyacrylonitrile and polypropylene fibres, and PA-6 textile and cord fibres dropped sharply. The development of production of nonwovens in the country was comforting. The revival around construction of new enterprises is still only apparent.     

Characterization of surfaces of carbon fibres by scanning tunneling microscopy

Summary The experimental results obtained by scanning tunneling microscopy (STM) studies of different carbon fibres are presented and discussed. The comparative analysis of the STM images at scales from hundreds of nanometers down to atomic scale reveals the differences of surface features for carbon fibres processed from different precursors, polyacrylonitrile fibres and pitch. The high temperature treatment of carbon fibres — the so-called graphitization process — as used to improve the stress modulus induces drastically increased ordering phenomena at the atomic level. Structural information obtained by STM on the surface of the fibres as well as in their cross sectional areas is discussed in comparison with known results of diffraction studies. STM appears to be the new powerfull technique for the detailed structural studies of surfaces of carbon fibres. The perspectives of these studies are under discussion.     

Ion-exchange fibres based on polyacrylonitrile modified with heteroorganic compounds

Conclusions A method has been developed for the preparation of ion-exchange fibres based on polyacrylonitrile, using alkali metal alkylsiliconates as modifying agents.The role of the sodium alkylsiliconate in the process of modifying PAN fibres has been ascertained by physicochemical methods. It has been shown that silicon is introduced into the structure of the fibre as a result of the modification.The possibility of using tetraethoxysilane as a cross-linking agent for PAN fibres has been investigated.Leningrad Institute of Textile and Light Industry. Translated from Khimicheskie Volokna, No. 1, pp. 16–19, January–February, 1987.     

Manufacture of graft copolymers of polyvinyl alcohol fibres with vinyl polymers

Conclusions 1. Methods have been developed, and the conditions studied, for obtaining graft copolymers of PVA fibres with polyacrylic acid, poly-2-methyl-5-vinylpyridine and polyacrylonitrile, using for formation of macroradicals carboxyl, aldehyde, and titanium groups, introduced into the fibres when they are rendered hydrophobic.2. Certain properties of the graft copolymers thus obtained have been studied. It is shown that fibres with ionogenic graft copolymers have high exchange capacities, reaching 5.8 meq/g when poly-2-methyl-5-vinylpyridine is used.S. M. Kirov Leningrad Institute of Textile and Light Industries (LITLP). Translated from Khimicheskie Volokna, No. 5, pp. 14–16, September–October, 1969.     

Structural and chemical transformations in thermooxidative stabilization of copolymeric polyacrylonitrile fibres

The processes that take place during thermooxidative stabilization in copolymeric polyacrylonitrile (PAN) fibres of varying composition were examined. It was shown that the primary, or relaxation, shrinkage of PAN fibres is a function of the conditions of their fabrication and can be reduced by annealing the fibres above the glass transition temperature. The chemical transformations of PAN fibres are accompanied by structural transformations, manifested as shrinkage or elongation (flow) of the fibre. Mechanisms of deformation processes are proposed. The schemes of the chemical transformations of the structure of the fibres during their thermooxidative stabilization were examined. The direction and rate of chemical transformations of the structure of the fibres are a function of the composition of the copolymers; these parameters can be assigned and regulated by altering the conditions of spinning the fibres in the spinning bath. All-Russian Scientific-Research Institute of Polymer Fibres, Mytishchi. Translated fromKhimicheskie Volokna, No. 6, pp. 14–18, November–December, 1999.     

Preparation of fibres from graft copolymers of acrylonitrile and polyvinyl alcohol

Conclusions The possibility of spinning fibres from graft copolymers of polyvinyl alcohol and acryonitrile by the scheme for spinning polyacrylonitrile fibre has been established.It has been shown that spinning solutions can be prepared directly from latexes of the graft copolymers.The suggestion has been made that long side chains in the copolymers participate in formation of supermolecular structural elements and aid in obtaining fibres with adequately high mechanical strength and an increased thermal stability.Translated from Khimicheskie Volokna, No. 1, pp. 13–15, January–February, 1988.     

Study of the kinetics of oxidation of acrylic fibres

The kinetics of absorption of oxygen by polyacrylonitrile fibre and fibre from the copolymer of acrylonitrile and methacrylate was investigated during their thermooxidative stabilization at different temperatures and oxygen pressures. The dependence of the rate of oxidation of the fibres on the oxygen pressure in the region of low values and the absence of this dependence at high pressure was detected. Passage from one oxidation mechanism to the other for fibres of different compensation begins at a different oxygen pressure and is a function of the temperature. It was shown that the rate of oxidation of the fibres can be increased not by changing the oxygen pressure, but by increasing the total pressure in the system by addition of an inert gas whose molecules activate the oxygen molecules. A mechanism of oxidation of acrylic fibres based on concepts of the kinetics of monomolecular reactions was proposed. It was concluded that at atmospheric pressure, oxidation of acrylic fibres takes place in the kinetic region. All-Russian Scientific-Research Institute of Polymer Fibres, Mytishchi. Translated fromKhimicheskie Volokna, No. 1, pp. 28–31, January–February, 2000.     

Thermomechanical and chemical properties of cross-linked polyacrylonitrile fibres

Conclusions 1. We have studied the thermomechanical and chemical properties of PAN fibres, cross-linked by treating with hydrazine hydrate, semicarbazide, and thiosemicarbazide.2. Cross-linked PAN fibres have increased heat resistances and thermal stabilities.3. Cross-linked PAN fibres do not dissolve in any known organic solvents and are resistant to hot mineral acids and alkalies.Third communication on: Deformation and thermomechanical properties of cross-linked polyacrylonitrile fibres.All-Union Synthetic Fibre Research Institute (VNIIV). Translated from Khimicheskie Volokna, No. 2, pp. 49–50, March–April, 1969.     

Thermal behavior of bicomponent systems of polyacrylonitrile and hydrated cellulose fibres

Mixed bicomponent systems of polyacrylonitrile (PAN) and hydrated cellulose (HC) fibres are not mechanical mixtures with the additive properties of each component; their thermooxidative degradation takes place at lower temperatures than for each fibre individually, and takes place less actively and in a wider range of temperatures. When the degree of grinding of the fibres in the mixed systems is decreased, the temperature of the beginning and rate of thermooxidative degradation also increase. Increasing the concentration of HC fibre in the mixture from 15 to 50 wt. % decreases the heat effect of the first exothermic peak on the DTA curve, and this is of practical importance for conducting heat treatment of the fibres.All-Russian Scientific-Research Institute of Polymer Fibres, Mytishchi. Translated from Khimicheskie Volokna, No. 6, pp. 27–29, November–December, 1992.     

Microscopic study of modified polyacrylonitrile fibres

Conclusions Microscopic studies have been made on polyacrylonitrile fibres which have been modified with solutions of CdSO₄, ethylenediamine, and a mixture of these solutions.Treatment with an ethylenediamine solution aids in a significant change in structure of the fibre surface.Treatment with a mixture of CdSO₄ and ethylenediamine solutions leads to development of a structural nonuniformity in the fibre and the twisting of the fibre on drying in the free state.Translated from Khimicheskie Volokna, No. 2, pp. 33–34, March–April, 1989.