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.     

How additives of graft copolymers affect the structural-mechanical properties of fibres from mixtures of incompatible homopolymers

Conclusions 1. The authors have studied the effect of the composition of a CA-PAN mixture and their graft copolymers on the physicomechanical properties of fibres formed from them. It is shown that the physicomechanical properties of the fibre deteriorate with increasing ratio of CA and PAN in the mixture. The presence of graft copolymer in a CA-PAN mixture improves the fibre's physicomechanical properties.2. The structural characteristics of CA-PAN fibres and their graft copolymers have been studied by physicomechanical and electron-microscopic methods. It is shown that addition of a graft copolymer of CA and PAN to a heterogeneous mixture of CA and PAN leads to homogenisation of the structure and an increase in the structural homogeneity of the fibres.Tashkent Institute of the Textile and Light Industries. Translated from Khimicheskie Volokna, No. 6, pp. 20–23, November–December, 1969.     

Mechanism of the thermal transformations of polyacrylonitrile fibres in oxidation

Conclusions 1. The mechanism of the physicochemical transformations of PAN fibres which take place in an atmospheric oxygen medium at 200°C has been studied, and the time intervals for their occurrence have been established.2. It has been found that on heat treatment of PAN fibres for 3–4 h, dehydration reactions mainly take place; and on increasing the time from 3 to 9 h, mainly cyclization reactions take place. Intermolecular condensation reactions, which lead to the formation of polynuclear planar aromatic structures, take place after 11–12 h of heat treatment.3. A new approach has been proposed for interpreting DTA data, based on analysis of the components of the DTA curve equation, and also DTA parameters for control of the process of thermooxidative treatment of PAN fibres.4. It has been found by the XSA method that the cross-linking process leads to the formation of two-dimensional structures. An x-ray analysis figure has been proposed which makes it possible to discern the time intervals for occurrence of cross-linking.Translated from Khimicheskie Volokna, No. 5, pp. 8–11, September–October, 1993.     

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.     

Production and properties of fibres from blends of polyacrylonitrile and cellulose acetate

Conclusions 1. The presence of CA/PAN graft copolymer increases the stability of mixtures of CA and PAN, and ternary polymerisation mixtures are more stable in solution than mechanical mixtures.2. Increasing the stability of mixtures of solutions of cellulose acetate and polyacrylonitrile improves the properties of the fibres spun from them, by enhancing their physicomechanical characteristics.All-Union Scientific Research Institute for Sugar Beet; Moscow Textile Institute. Translated from Khimicheskie Volokna, No. 2, pp. 16–18, March–April, 1969.     

Appearance and development of polyconjugated structures in heat treatment of polyacrylonitrile fibres

The changes in the electrophysical and paramagnetic characteristics of PAN fibres during their heat treatment are similar to the corresponding changes in heat treatment of other polymer [10]; the character of these changes allows tracking the appearance and development of a polyconjugated structure in heat treatment of PAN fibres with the characteristic mobility of the -electrons and ability to form paramagnetic centers.Avtor Scientific and Industrial Association, Mytishchi. Translated from Khimicheskie Volokna, No. 6, pp. 13–16, November–December, 1993.     

The suitable itaconic acid content in polyacrylonitrile copolymers used for PAN‐based carbon fibers

This article was to provide some new insights into the influences of itaconic acid (IA) content in polyacrylonitrile (PAN) copolymers on polymerization, structural evolution, thermal behaviors and carbon yield relatively comprehensively. High IA containing poly(acrylonitrile‐co‐itaconic acid) (PAI) oligomers were successfully extracted from PAI copolymers with 2.0 and 3.0 mol % IA. PAI copolymers with 0.5 mol % and 1.0 mol % IA possessed more cyclized structures, conjugated carbonyl group, conjugated nitrile group, and less β‐amino nitrile group as well as faster structural evolution rate than those of the other three PAI copolymers. Kinetic parameters indicated that excessive IA content in PAI copolymer did not have advantages in promoting cyclization reaction. The PAI copolymers with 0.5 wt % to 1.0 mol % IA possessed better crystalline parameters as well as higher carbon yield than those of the other two PAI copolymers after carbonization at 1350 ºC. In summary, PAI copolymers with 0.5 mol % to 1.0 mol % IA will be more suitable for fabricating of high performance PAN‐based carbon fibers. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43919.     

Carbochain ion-exchange fibres prepared by the graft polymerization method

Conclusions A comparative analysis has been made of the laws governing the process of graft polymerization of partially hydrolyzed PAN fibres with monomers of ionogenic and nonionogenic character.It has been shown that the activity of the investigated monomers in graft polymerization reactions and their effective conversion are reduced, as a rule, with increase in the charge of the monomer, and the homopolymer content is increased.In selecting optimum conditions for a graft polymerization as a method of preparing fibrous ion-exchangers, along with the yield of graft copolymer and the effective conversion, one should also take into account the proportion of active functional groups in the graft copolymer.Leningrad Institute of Textile and Light Industry. Translated from Khimicheskie Volokna, No. 1, pp. 19–22, January–February, 1987.     

Thermal properties of acrylonitrile/itaconic acid polymers in oxidative and nonoxidative atmospheres

Thermal stabilization of polyacrylonitrile (PAN) fibers is an indispensable process in the manufacture of carbon fibers. The effects of acidic comonomers on the thermal properties of PAN have attracted much attention because of their importance in the fibers spinning and heat treatment process. In this study, oxidative and nonoxidative atmospheres are adopted in differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) test to disclose the key effects of oxygen on the thermal properties of PAN/itaconic acid (IA) polymers. The DSC results under oxidative atmosphere are consistence to the reports by previous researchers: the exothermic curves of copolymers containing 0.6 wt % and 1.0 wt % IA exhibit lower initiation temperature and more broaden shapes than that of PAN homopolymer, indicating that IA facilitates both cyclization and oxidation reactions. However, copolymers containing the same content of IA shows no apparent improving effect on the thermal properties under inert atmosphere, which has not been mentioned in the published literature. TGA indicates that oxygen remarkably increases the thermal stability of AN/IA copolymers structure, and will bring high carbon yield in the eventual carbon fibers. The influential mechanisms of oxidative and nonoxidative atmospheres on thermal stabilization reactions of PAN were discussed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Morphological and structural features of polyacrylonitrile fibres spun by the dry-wet method

Conclusions -- A technological regime for the preparation of polyacrylonitrile fibres from binary and ternary copolymers has been chosen; these differ from known specimens in having a more uniform cross-sectional structure and a smoother elementary filament surface.-- A considerable difference in crystalline structure of fibres from binary and ternary copolymers which have been spun into a dimethyl sulfoxide—water bath has been shown.-- Fibres from the binary or ternary copolymer which have been spun into a precipitation bath having a large dimethyl sulfoxide content in water are characterized by a lower degree of swelling.-- Shrinkage of fibres from the binary copolymer in the temperature range 200–220°C is twice as small as the shrinkage of fibres from the ternary copolymer.Deceased.VNIIPV. Translated from Khimicheskie Volokna, No. 3, pp. 19–22, May–June, 1991.     

Studies on fibers spun from poly(vinyl alcohol‐b‐acrylonitrile) emulsions prepared by ultrasonic technique. II. Properties of the fibers

The moisture content of poly(vinyl alcohol‐b‐acrylonitrile) fibers decreases with an increasing hydrophobic AN content and crystallinity of the fibers; however, the copolymer fiber with 26.94% AN, drawn × 5, and heat‐treated at 200°C has a moisture content value slightly lower than that of commercial PVA fiber, but much higher than that of commercial PAN fiber. The block copolymer fibers have a water‐retention value higher than that of commercial PVA fiber, owing to the presence of voids in these fibers, and have a stronger wicking ability than that of commercial PVA, PAN fibers, and wool and cotton mainly due to the grooved surface and bulk porous morphology of the fibers. The tensile strength of the copolymer fibers with an appropriate AN content are lower than that of commercial PVA fiber, but higher than that of commercial PAN fiber and much higher than that of wool and cotton. The melting temperatures of the copolymer fibers increase with increasing heat‐treatment temperature. The copolymer fibers possess a lower peak cyclizing temperature than that of the PAN fiber and have a higher thermal stability than that of both PVA and PAN fibers. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 989–994, 2001     

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.     

Viscoelastic properties and structure of technical polyacrylonitrile tows

Conclusions The connection between supermolecular structure of PAN tows and the parameters of the creep process has been discovered, which makes it possible to carry out structural interpretation of viscoelastic properties and can be used in the analysis of technological processes for the preparation of PAN tows.It has been found that carbon fibres with a high knot strength are obtained from technical PAN tows which are characterized by a more homogeneous and oriented structure, and fibres with a low knot strength are obtained from PAN tows with a heterophase structure and less orientation.Leningrad Institute of the Textile and Light Industries. Translated from Khimicheskie Volokna, No. 2, pp. 34–37, March–April, 1992.     

Thermal transformations in fibre blends

The reciprocal effect of polycaproamide and polyacrylonitrile in the presence of phosphorus-containing compounds on thermooxidation and carbonization was determined. It was found that in blends of PCA and PAN fibres previously undergoing thermal oxidation, the thermoplasticity of the polycaproamide decreases and they decompose with a lower rate, retaining approximately 50% of their mass at 600°C.Translated from Khimicheskie Volokna, No. 5, pp. 48–51, September–October, 1995.     

Experimental study of the structure of polyacrylonitrile gel fibres

The structure of PAN gel fibres spun by the water-thiocyanate method is investigated. It is shown that in identical spinning conditions, the packing density of the structural elements in gel fibres based on poly(AN-co-MA-co-ItA)terpolymer is lower than in gel fibres based on poly(AN-co-MA-co-AMPS). A structural model of PAN gel fibre is composed and substantiated. It is shown that the lower packaging density of the structural elements in PAN gel fibres is responsible for the higher sorption power with respect to different inorganic and organic compounds and higher rate polymer-analog transformations.Translated from Khimicheskie Volokna, No. 5, pp. 40–45, September–October, 2004.     

Effect of γ-radiation on the structure and thermal properties of polyacrylonitrile fibres

-Radiation significantly affects both the initial structure and the thermal properties of PAN fibres. The following are probably the most important results of radiation exposure: the temperature of the beginning of cyclization decreases; the exothermic nature of cyclization decreases so that the weight losses in the region of the m.p. decrease, indicating destructive processes in the polymer chain; when irradiated samples are heated, intermolecular cross-links form with the participation of oxygen; the duration of oxidation of the fibres before a given density level is attained is reduced significantly.St. Petersburg University of Design and Technology. Translated from Khimicheskie Volokna, No. 3, pp. 18–21, May–June, 1995.     

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.     

Combustibility,smoke evolution,and thermal stability of modified oksalon fibres

Conclusions A connection has been found between the bromine content of a polymer and its thermal stability, combustibility, and smoke evolution of oksalon fibres. At a bromine content of 4–5% by wt., a sharp increase in heat stability and smoke evolution is observed, plus a decrease in combustibility, which is caused by the formation of network structures.The figures for combustibility, smoke evolution, heat resistance, and rate of flame propagation on burning from above down are not sensitive to the means of introducing bromine into the polymer.An increase in bromine content leads to a change in the mechanism of inhibition of the combustion process.Translated from Khimicheskie Volokna, No. 6, pp. 32–33, November–December, 1983.     

Copolymerization of acrylonitrile,methyl acrylate,and itaconic acid in thiocyanate solutions in the presence of hydrolyzed nitron fibre waste

Conclusions -- The kinetics of the copolymerization process of AN, MA, and IA in the presence of hydrolyzed Nitron fibre characterized by various degrees of hydrolysis has been studied. It has been found that introducing H-PAN into the reaction mixture leads to an increase in degree of conversion in the copolymerization process and to an increase in molecular weight of the copolymer synthesized.-- Fibre has been spun from the products of joint copolymerization of AN, MA, and IA in the presence of H-PAN with various concentrations of these in the solution and various SEC values. Introducing up to 5% by wt. of an H-PAN with an SEC not over 0.2 meq/g into the reaction mixture aids in obtaining fibres with satisfactory properties and opens up the possibility of still another way of solving the question of regenerating wet Nitron fibre wastes.Translated from Khimicheskie Volokna, No. 4, pp. 17–19, July–August, 1991.     

Thermal transformations of polyacrylonitrile fibres with deep degrees of conversion

It was shown that oxidative dehydrogenation with primary formation of C=C double bonds and then C=C conjugated bonds is the basic chemical reaction in the early stages of thermal stabilization of PAN fibres. A hypothesis was advanced concerning the nature of the appearance of oxygen-containing functional groups. A correlation was found between the amount of oxygen added to the fibre and its density.Translated from Khimicheskie Volokna, No. 1, pp. 10–13, January–February, 1995.