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.     

Correlation of chemical shrinkage of polyacrylonitrile fibres with kinetics of cyclization

It has been established that the most important step in the production of carbon fibres from polyacrylonitrile (PAN) precursor fibres is the oxidative thermal treatment applied. During this treatment, physical phenomena and chemical reactions take place accompanied by the shrinkage of the fibres, which has a physical or chemical origin, depending on the nitrile cyclization reactions. The aim of the present study is to establish a correlation between the chemical shrinkage of PAN fibres and the kinetics of cyclization reactions. Based on the isothermal treatment of PAN fibres, we developed a method in order to distinguish between physical and chemical shrinkages. The onset time for the chemical shrinkage follows a relationship with temperature. Chemical shrinkage versus cyclization time data were fitted with the exponential rise to the maximum of the curves. Furthermore, the cyclization kinetics was studied using differential scanning calorimetry and the kinetic parameters determined were identical to those calculated from the chemical shrinkage, demonstrating that the latter is directly related to the kinetics of the cyclization reactions. It was therefore concluded that according to the method developed to distinguish the physical from the chemical shrinkages: (1) there exists a certain onset time for a given treatment temperature to trigger the chemical shrinkage; (2) cyclization reactions do not start below a limiting temperature of 168 °C; (3) at 340 °C, the temperature where the cyclization reactions are completed, the maximum shrinkage is 24%; and (4) the oxidized PAN fibres contain mainly ladder polymer structures with approximately symmetrical sequences connected in angled positions. Copyright © 2007 Society of Chemical Industry     

Effect of calcium salts on the thermal properties of polyacrylonitrile fibres

Conclusions -- On interaction of CaCl₂ with polyacrylonitrile fibres, strong chemical bonds are formed between the polymer macromolecules.-- The introduction of Ca(II) into the fibre helps reduce polymer deformation up to a temperature of 200°C and helps increase its thermal resistance.Translated from Khimicheskie Volokna, No. 6, pp. 51–52, November–December, 1990.     

聚丙烯腈纤维热物理收缩行为的研究

利用动态力学分析、热机械分析以及X射线衍射分析等方法对聚丙烯腈(PAN)纤维在不同拉伸条件下的热物理收缩行为进行了研究。结果表明:拉伸有利于PAN纤维非晶区的取向,在热环境条件下,随着分子链运动活性的提高而生产解取向;拉伸倍数越大,PAN纤维解取向越容易发生,物理收缩量越大;沸水处理后,PAN纤维的物理收缩量随拉伸倍数的增加而减小,纤维晶态结构完善,非晶区相对含量减少。     

Preparation of crimped polyacrylonitrile fibres

Conclusions The effect of the concentration of the components of the modifying solution and of its temperature on the degree of crimp of polyacrylonitrile fibre has been described.It has been found that the modifying solutions are rather stable in storage for several days at 4–5°C; at room temperature a decomposition of a complex compound formed by the organic components apparently takes place.Translated from Khimicheskie Volokna, No. 2, pp. 39–40, March–April, 1984.     

Effect of the aggregation structure on the thermal shrinkage of polyacrylonitrile fibers during the heat-treatment process

Secondary thermal shrinkage or chemical shrinkage involved in the thermal shrinkage of polyacrylonitrile (PAN) fibers was not only associated with the cyclization degree but also the thermal mobility of molecular chains in the aggregation structures during crosslinking. In this study, the cyclization process was monitored with differential scanning calorimetry and IR spectroscopy. The evolution of aggregation structures throughout cyclization and variations in the secondary shrinkage for the PAN fibers were characterized with wide-angle X-ray diffraction and thermal mechanical analysis, respectively. The results show that with increasing temperature, the cyclization degree increased; the cyclization occurred first in amorphous regions and then extended to the crystalline regions. Correspondingly, the secondary shrinkage also increased and could be separated into two stages: those of the amorphous and crystalline phases. The shrinkage of the crystalline regions was much bigger than that of the amorphous regions. For fibers with different aggregation structures, the crystallinity affected the cyclization degree in the amorphous and crystalline regions and resulted in the difference in total shrinkage. Furthermore, because the unoriented molecular chains in both the amorphous and crystalline regions shrank more after cyclization, the shrinkage of both regions was primarily decided by the level of orientated molecular chains participating in the cyclization. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

New complexing sorbents based on polyacrylonitrile fibres

Modified sorbents with bis-amide groups active in the pH 4–5 range were fabricated from PAN fibres. The characteristics of extraction of copper, nickel, and cobalt ions were investigated, the sorption capacity for these metals was determined, and the possibility of using the new sorbents for fine afterpurification of electroplating wastes and purification of wastewaters from dye plants was investigated. A sorbent which is highly selective for (trivalent) iron ions was fabricated from PAN fibre modified with salicylaldehyde, and the indexes and areas of application were determined, in particular, for purification of sulfate-nickel electroplating solutions in nonferrous metallurgy enterprises.St. Petersburg State University of Technology and Design. Translated from Khimicheskie Volokna, No. 6, pp. 22–27, November–December, 1996.     

Fabrication of carbon fibres from wet-spun commercial polyacrylonitrile fibres

The possibility of fabricating carbon fibre from commercial PAN fibres for textile applications was demonstrated. It is necessary to make some changes in the temperature—time conditions for total completion of the thermal stabilization process. Better strength of the carbon fibres, equal to 1401 MPa, was attained in conducting thermal stabilization cycle B. __________ Translated from Khimicheskie Volokna, No. 5, pp. 31–33, September–October, 2006.     

Intensification of thermooxidation of polyacrylonitrile fibres

It was found that in thermooxidation of PAN fibres in air by the conductive (contact) method, the density of 1.38–1.40 g/cm³, required for subsequent high-temperature treatment, is attained in 30–60 min. The chemical composition and equilibrium sorption of the PAN fibre oxidized by convective tempering do not differ significantly from the fibre fabricated in industrial conditions in convective tempering. All-Russian Scientific-Research Institute of Polymer Fibres, Mytishchi. Translated fromKhimicheskie Volokna. No. 6, pp. 22–24, November–December, 1999.     

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.     

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.     

Some properties of modified polyacrylonitrile fibres

Fibre-forming copolymers of acrylonitrile and a monomeric quaternary ammonium salt, β-methacryloylhydroxyethyl-(N-dimethyl,methylene)ammonium iodide, were obtained by wet spinning and their physicomechanical and structural properties were investigated. It was found that the modified fibres have a set of valuable properties in comparison to the industrial fibre Nitron.     

Effect of the conditions of laser treatment on the thermal and strength indexes of polyacrylonitrile fibres

The results of laser treatment of fibres are not only determined by the average laser energy flux density on the sample during treatment but also the irradiation regimen. In going from a continuous irradiation mode to a pulsed mode, the probability of accumulation of energy in chemical bonds increases, and this increases the probability of their breaking and is the cause of a decrease in the strength indexes of the fibres. The probability of destructive processes increases with a decrease in the duration of the pulse and correspondingly with an increase in the peak laser energy flux values and with an induced decrease in molecular mobility due to removal of heat from the processed fibres. Changing the conditions of laser treatment of fibres allows varying the thermal indexes of PAN fibres during pyrolysis.St. Petersburg State University of Design and Technology. Translated from Khimicheskie Volokna, No. 3, pp. 20–23, May–June, 1996.