Thermal properties of polyacrylonitrile copolymers having various chemical compositions

Conclusions 1. The thermal oxidative degradation of PAN fibres having an IA content from 1.2 to 6.4% in the copolymer has been studied by the DTA method.2. Increasing the IA content of the copolymer leads to a shift of the exothermic effects of the cyclization reaction into the lower temperature region, and also to a decrease in the thermally effect from thermal oxidation, which affords a possibility of increasing the efficiency of processes of heat treatment of PAN in the preparation of carbon fibres and of reducing heat expenditures.NITs Uglekhimvolokno (Mytishchi). Translated from Khimicheskie Volokna, No. 5, pp. 25–27, September–October, 1993.     

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.     

Stability constants of amidoximated chitosan‐g‐poly(acrylonitrile) copolymer for heavy metal ions

Amidoximated chitosan‐g‐poly(acrylonitrile) (PAN) copolymer was prepared by a reaction between hydroxylamine and cyano group in chitosan‐g‐PAN copolymer prepared by grafting PAN onto crosslinked chitosan with epychlorohydrine. The adsorption and desorption capacities for heavy metal ions were measured under various conditions. The adsorption capacity of amidoximated chitosan‐g‐PAN copolymer increased with increasing pH values, and was increased for Cu²⁺ and Pb²⁺ but a little decreased for Zn²⁺ and Cd²⁺ with increasing PAN grafting percentage in amidoximated chitosan‐g‐PAN copolymer. In addition, desorption capacity for all metal ions was increased with increasing pH values in contrast to the adsorption results. Stability constants of amidoximated chitosan‐g‐PAN copolymer were higher for Cu²⁺ and Pb²⁺ but lower for Zn²⁺ and Cd²⁺ than those of crosslinked chitosan. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 469–476, 1999     

Chemical and electrochemical synthesis of conducting graft copolymer of acrylonitrile with aniline

A new conducting copolymer, polyacrylonitrile‐graft‐polyaniline (PAN‐g‐PANi), has been prepared by chemical and electrochemical methods from a precursor polymer. Poly[acrylonitrile‐co‐(acrylimine phenylenediamine)] (PAN‐co‐PAIPD) was synthesized chemically by reacting PAN with sodium 1,4‐phenylenediamine salt. PAN‐g‐PANi was synthesized chemically using ammonium peroxydisulfate as the oxidant and p‐toluenesulfonic acid in dimethylsulfoxide solution and adding aniline to oxidized PAN‐co‐PAIPD. Electrochemical polymerization was carried out by spin coating PAN‐co‐PAIPD on the surface of a Pt electrode, then the growth of the graft copolymer (PAN‐g‐PANi) in the presence of fresh aniline and acidic solution. The structures of the graft copolymer and PAN‐co‐PAIPD were characterized using UV‐visible, Fourier transform infrared, and ¹H and ¹³C NMR spectroscopies. The thermal properties of PAN‐g‐PANi were studied using thermogravimetric analysis and differential scanning calorimetry. Scanning electron microscopy (SEM) images showed that the morphology of PAN‐g‐PANi copolymer films was homogeneous. Electrical conductivity of the copolymer was studied using the four‐probe method, which gave a conductivity of 4.5 × 10^?3 S cm^?1 with 51.4% PANi. SEM and electrical conductivity measurements supported the formation of the graft copolymer. Copyright © 2006 Society of Chemical Industry     

The spinning of polyacrylonitrile fibres in clean room conditions for the production of carbon fibres

Carbon fibres have been prepared from PAN fibres spun under clean conditions to avoid contamination with impurity particles. This has enabled carbon fibres with significantly higher tensile strengths to be produced. Clean PAN fibres yielded carbon fibres with a strength of 2·75 GN/m² after heat-treatment to 2500°C whereas control fibres spun under normal laboratory conditions only gave a strength of 1·51 GN/m² after the same heat-treatment. The average strength of carbon fibres from the clean precursor increased with heat-treatment temperature and was constant for gauge lengths of 1–5 cm after heating to 2500°C. This was in marked contrast to the control fibres which decreased in strength after heat-treatment. The results indicate that by working in clean conditions the average separation of severe flaws operative below 2 GN/m² was about 20 cm. Examinations of fracture surfaces with the scanning electron microscope showed that failures were initiated at the surface in all cases.     

PAN/SAN/SWNT ternary composite: Pore size control and electrochemical supercapacitor behavior

Single wall carbon nanotubes (SWNT) act as a compatabilizer for polyacrylonitrile (PAN)/styrene-acrylonitrile (SAN) copolymer blends. Carbonization of PAN/SAN/SWNT blend films results in pore widths in the range of 1-200 nm, while carbonized PAN/SAN blend films resulted in pores with typical width of 1-10 μm. Electrochemical supercapacitor behavior of the carbonized PAN/SAN/SWNT films was characterized using 6 M KOH electrolyte. Surface area and pore size distribution were analyzed using nitrogen gas adsorption and the BET and DFT theories. Double layer capacity of the carbonized PAN/SAN/SWNT films was as high as 205 μF/cm² based on the BET surface area.     

Sorption Properties of Polyacrylonitrile Fibres

As-spun undrawn PAN fibre wet-spun from solutions of the polymer in DMF, DMA, and DMSO are porous with a developed specific surface (up to 80 m²/g for nitrogen), while fibres spun from aqueous solutions of sodium thiocyanate or zinc chloride are nonporous with a specific surface of under 1 m²/g. The finished PAN fibres spun from solutions in different solvents have a closely packed structure, equivalent to highly crystalline, according to the data from sorption of inert gases and water vapors, and according to the results on the kinetics of sorption of vapors of liquids with different molecule sizes, they can be considered ultramicroporous.     

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.     

混合溶剂法合成高分于量PAN树脂

优质PAN原丝是生产高性能碳纤维(CF)的前提,采用高分子量聚丙烯腈(PAN)共聚树脂进行干喷混纺是提高原丝性能的有效途径之一。本文采用混合溶剂法合成了分子量(Mw)为5.2×10~5～3.16×10~6的PAN共聚树脂,系统地讨论了实验条件对聚合结果的影响,并对反应机理进行了初步探讨。对合成的树脂进行热分析时发现树脂的热行为更适合预氧化反应。     

Studies of structure in carbonized composites from a phenolic resin and oxidized PAN fibres using chromic acid as an etchant

Composites have been prepared from a phenolic resin (49 vol%) and oxidized PAN fibres (51vol%) with heat treatment to 423, 573, 873, 973, 1073 and 1173 K. Optical and scanning microscopy of polished surfaces indicate a fusing of these two materials into a homogeneous matrix. However, SEM of samples etched with chromic acid shows that the identity of materials is preserved. Initially the resin is less reactive than the PAN fibres. Upon carbonization, the carbon from the resin and the PAN have approximately equal reactivities. Enhanced etching occurs at the curved interfaces of the two carbons. The transverse sections of PAN fibres, HTT>973 K exhibit selective etching suggesting the existence of skin/core components in the fibre. It is the more graphitic components of the skin region which are oxidized preferentially.     

Effect of comonomer on the viscoelastic behavior of co-poly (acrylonitrile) solutions

Three copolymers of acrylonitrile-methacrylic acid [P(AN-co-MAA)], acrylonitrile-ammonium salt of methacrylic acid [P(AN-co-AMA)], acrylonitrile-methacrylamide-itaconic acid [P(AN-MAM-IA)] and PAN homopolymer were synthesized by aqueous dispersion polymerization technique. The polymerization conditions were adjusted in such a way to produce polymers with similar composition and molecular weight. The influence of comonomer nature on the viscoelastic behavior and spinnability of copolymer/dimethylsulfoxide (DMSO) solutions were investigated. It was found that incorporation of these comonomers into PAN chains led to intense decrease in zero-shear viscosity to lower value as well as appearance of distinct plateau in comparison with PAN homopolymer. However, comparing the results of complex viscosity and shear viscosity of each PAN polymer showed different shear-thinning behavior, typical deviation from Cox-Merz rule at high deformation rates. Amongst these copolymer solutions, P(AN-co-AMA) exhibited the longest relaxation time (λ) at low and medium frequencies. The lower values of frequency dependence of G′ (n′) and cross over frequency (ω_c) of storage modulus (G′) and loss modulus (G″) indicated that P(AN-co-AMA) was more elastic than other PAN copolymer solutions. The log-log plots of tan δ versus ω demonstrated that the comonomer nature affects the sol-gel transition behavior and elastic character of copolymer solutions. On average, based upon the slope of logG? versus logG? data, the incorporation of comonomers inside PAN chains led to ~50 % increase in the homogeneity of solutions compared to PAN homopolymer.     

Preparation and characterization of amphiphilic block copolymer of polyacrylonitrile‐block‐poly(ethylene oxide)

The synthesis of polyacrylonitrile‐block‐poly(ethylene oxide) (PAN‐b‐PEO) diblock copolymers is conducted by sequential initiation and Ce(IV) redox polymerization using amino‐alcohol as the parent compound. In the first step, amino‐alcohol potassium with a protected amine group initiates the polymerization of ethylene oxide (EO) to yield poly(ethylene oxide) (PEO) with an amine end group (PEO‐NH₂), which is used to synthesize a PAN‐b‐PEO diblock copolymer with Ce(IV) that takes place in the redox initiation system. A PAN‐poly(ethylene glycol)‐PAN (PAN‐PEG‐PAN) triblock copolymer is prepared by the same redox system consisting of ceric ions and PEG in an aqueous medium. The structure of the copolymer is characterized in detail by GPC, IR, ¹H‐NMR, DSC, and X‐ray diffraction. The propagation of the PAN chain is dependent on the molecular weight and concentration of the PEO prepolymer. The crystallization of the PAN and PEO block is discussed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1753–1759, 2003     

Investigation of polyacrylonitrile solution inhomogeneity by dynamic light scattering

Dynamic light scattering (DLS) has been used to quantify nanoscale heterogeneity in the industrially significant polyacrylonitrile (PAN) polymer solution. The heterogeneity in polymer solution, traced by the ratio of amplitudes of the slow to fast mode, is observed to be related to various parameters, such as molecular weight of the polymer, the type of co‐monomer, processing time, concentration of the solution, and the choice of the solvents. It has been identified that low molecular weight PAN homopolymer have the least heterogeneity issues. Amongst the chosen co‐polymers for this study, similar degree of heterogeneity was observed at concentration slightly above the critical concentration at which the polymer chains begin to overlap. Whereas, at higher concentration, PAN‐methacrylic acid (4 wt%) copolymer showed the least heterogeneity issue. The aggregate diffusion coefficient of PAN‐methacrylic acid (4 wt%) copolymer solution in dimethylformamide (DMF) and N,N‐dimethylacetamide (DMAc) are respectively determined to be ～1.6 × 10^?12 cm²/s and ～1.6 × 10^?13 cm²/s, which results in an estimated aggregate size of 9 nm and 90 nm. POLYM. ENG. SCI., 55:1403–1407, 2015. © 2015 Society of Plastics Engineers     

Improving Carbon Fibre Production Technology

The quality of carbon fibres, their strength and modulus of elasticity in particular, can be increased by the following methods: decreasing the porosity of the initial PAN fibres by selecting the optimum conditions for spinning, plasticizing drawing, finishing, and drying; decreasing the inhomogeneity of the diameters of PAN fibres by suppressing deformation resonance during spinning by selecting conditions of jet formation and precipitation that do not allow formation of bulbs in the jets or prevent their deformation; decreasing fibril and crystallite size by reducing the precipitant and solvent concentration gradient in the precipitation zone (spinning in mild baths); creating optimum conditions for interphase self-ordering of the polymer at 450-550°C during precarbonization; increasing the cohesive energy by increasing the density to 1.75-2.10 g/cm³. Substitution of convective tempering of PAN twists in thermooxidative treatment by conductive (contact) treatment decreases the duration of the treatment by 3-4 times and improves the environmental conditions. Use of reflecting screens in high-temperature furnaces reduces heat losses by 4-5 times and decreases consumption of cooling water. The progress made in the technology and creation of high-capacity equipment suggests that the cost of high-strength carbon fibre will decrease to $10-15/kg in the future in the condition of large-scale production.     

Mechanisms of Transformation of Acrylic Fibres During Thermooxidative Stabilization

The shrinkage of polyacrylonitrile fibres comprising 93% acrylonitrile, 5.7% methyl acrylate, and 1.3% itaconic acid was investigated by a thermomechanical method in heating them from room temperature to 300°C. It was shown that the irreversible shrinkage of the fibres during their first heating is due to a decrease in the stresses accumulated during spinning. The shrinkage observed in repeated heating of the fibres is caused by two processes: 1) by unfolding of segments of PAN macromolecules in the amorphous constituent of the structure of the polymer with an increase in the temperature (thermoelastic effect); this part of the shrinkage is reversible in heating-cooling cycles; 2) by cyclization of the polymer units due to polymerization of CN groups; this is the irreversible part of the shrinkage. In the 200-300°C temperature region, relaxation processes caused by irreversible unfolding of the macromolecules of the melted ordered structure of the fibre also contribute to the shrinkage. Mechanisms of the shrinkage processes in a wide range of temperatures are proposed. Shrinkage caused by physical processes of transformation of the structure of the fibre and chemical processes of formation of heterocycles is distinguished. It was shown that the kinetics of cyclization of PAN fibres can be investigated during their thermooxidative stabilization as one of the stages of fabrication of carbon fibres from PAN based on thermomechanical data.     

Dielectric properties of lithium‐perchlorate‐filled acrylonitrile–hexyl methacrylate copolymer films

A series of poly(acrylonitrile‐co‐hexyl methacrylate), PAN‐co‐PHMA, copolymers with various hexyl methacrylate (HMA) contents were synthesized by emulsion technique. The incorporation of HMA units into the copolymers was confirmed by Fourier transform infrared and proton nuclear magnetic resonance (¹H‐NMR) spectroscopy. Glass transition temperatures (T _g) and thermal decomposition temperatures of copolymers were determined by differential scanning calorimetry and thermogravimetric analysis. The T _g of copolymers were lowered monotonically by increasing HMA content, while thermal stabilities of copolymers were enhanced. The frequency dependence of dielectric properties of three different amounts of LiClO₄ salt doped copolymer films was investigated. The influence of molar fraction of HMA on dielectric constant and ac‐conductivity of copolymer films was examined. Samples with higher HMA contents showed better stability and conductivity, as a result of increase in free volume and the mobility of the dipoles. The ac conductivity of copolymers was also improved by increasing LiClO₄ salt which was due to the existence of more charge carriers. PAN(88)‐co‐PHMA(12) copolymer with 1.5 mol% of lithium salt exhibited ionic conductivity of the 7.8 × 10⁻⁴ S/cm at 298 K. POLYM. COMPOS., 38:1792–1799, 2017. © 2015 Society of Plastics Engineers     

Development of electroconductive polyacrylonitrile fibers through chemical metallization and galvanisation

The paper describes the modification of PAN fibres with metallic nickel in order to give the fibre electroconductive properties. This is achieved by two consecutively executed processes. The first process is chemical metallization, involving the immersion of the PAN fibres in a bath containing 0.5 mol l⁻¹ NiCl₂ and 1.5 mol l⁻¹ Rongalite at pH = 5.5 and T=288–293 K. Ni(II) is absorbed in the structure of the fibre and adsorbed at the surface through a complex reaction with the cyanide and carboxylic acid groups present in the PAN chemical structure and the Rongalite reduces the adsorbed Ni(II) to metallic Ni. The second process is galvanisation of the Ni-containing PAN surface (the Ni particles present at the surface form a “seed” layer) in an electrolyte bath using an electrolyte with 150 g l⁻¹ of NiSO₄ at pH 5–6 and room temperature. The resulting fibre showed a specific electrical resistance of the order of 10⁻⁶ Ω m, which is a promising result.     

Studies on fibers spun from poly(vinyl alcohol‐b‐acrylonitrile) emulsions prepared by ultrasonic technique. I. Characterization of fiber structure

The structural characteristics of poly(vinyl alcohol‐b‐acrylonitrile) fibers with different AN contents were studied by comparison with that of PVA and PAN fibers. X‐ray diffraction analysis showed that both PVA and PAN blocks in the copolymer fibers formed crystals. Two glass transition temperatures corresponding to PVA and PAN components appeared on the dynamic mechanical spectrum of the copolymer fiber, indicative of their incompatibility in the fiber. SEM intuitively exhibited a longitudinal cracked and grooved surface morphology similar to that of PAN fiber and revealed an internal microdomain separation morphology for the block copolymer fibers. TEM showed a morphological structure intermediate between those of PVA and PAN fibers for the block copolymer fibers. It was also found that the copolymer fiber with the lower AN content has a sheath–core structure. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 979–988, 2001     

Preparation and ionic conductivity of solid polymer electrolyte based on polyacrylonitrile‐polyethylene oxide

The transparent and flexible solid polymer electrolytes (SPEs) were fabricated from polyacrylonitrile‐polyethylene oxide (PAN‐PEO) copolymer which was synthesized by methacrylate‐headed PEO macromonomer and acrylonitrile. The formation of copolymer is confirmed by Fourier‐transform infrared spectroscopy (FTIR) measurements. The ionic conductivity was measured by alternating current (AC) impedance spectroscopy. Ionic conductivity of PAN‐PEO‐LiClO₄ complexes was investigated with various salt concentration, temperatures and molecular weight of PEO (Mn). And the maximum ionic conductivity at room temperature was measured to be 3.54 × 10^?4 S/cm with an [Li⁺]/[EO] mole ratio of about 0.1. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 461–464, 2006     

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.