Mechanism of low-temperature carbonization of polyacrylonitrile

Low-temperature carbonization of polyacrylonitrile was studied in relation to the synthesis procedure, heat treatment conditions, and presence of natural polymers as cocarbonization participants.     

Composite precursor of polyacrylonitrile with hydrolytic lignin

Composite precursor based on hydrolytic lignin and polyacrylonitrile was obtained and fibrous composite materials were formed at 80: 20 to 40: 60 ratios between the starting components. A probable mechanism is suggested by which products of cocarbonization of lignin and polyacrylonitrile are formed, with 80–90 wt % carbonized residue produced in an inert atmosphere.     

热处理及与KOH共炭化对深度脱除煤中无机矿物质的促进作用

研究了煤经热处理（炭化）以及煤与ＫＯＨ共炭化对酸洗脱灰的影响。结果表明，煤经炭化再用盐酸洗涤，可以在缓和的条件下大幅度提高酸洗脱灰率；煤与ＫＯＨ共炭化后再酸洗，不仅对煤中的粘土、黄铁矿等无机矿物质有很好的效果，还特别适于脱除在一般情况下都难以除去的石英矿物。     

Cocarbonization of polymers as a new concept for synthesis of carbon composites

Foundations of cocarbonization of a series of carbon-chain and heterochain polymers in the solid phase and in solution were considered; the concept of this process was formulated. The temperature and kinetic parameters of the maximal thermal activity were determined. The possibilities of intermolecular interactions of compatible macromolecular compounds depending on the chemical structure of the initial components of composites and concentration and temperature-time parameters were studied.     

Mechanism of flame retardant action of red phosphorus in polyacrylonitrile

The mechanism of flame retardant (FR) action of red phosphorus in polyacrylonitrile combustion was investigated by thermogravimetry, flash-pyrolysis GC-MS, and combustion methods. Red phosphorus was found to increase the thermal stability in air of polyacrylonitrile and to induce a char residue increment on this substrate. Both these effects disappeared when pyrolysis was carried out under nitrogen flow. Flash-pyrolysis GC-MS experiments showed that red phosphorus does not alter the pyrolysis product distribution of polyacrylonitrile, which implies that there is no specific interaction between polyacrylonitrile and red phosphorus. These data also showed that polymeric red phosphorus decomposes to volatile white phosphorus (P₄) during pyrolysis. These observations allow us to propose a simple model for the mechanism of FR action of red phosphorus on polyacry-lonitrile at the molecular level. Combustion data for polyacrylonitrile-red phosphorus mixtures are in agreement with the proposed mechanism of FR action.     

Thermomechanical properties of composite films of polyacrylonitrile with chitin and chitosan

Composite films were prepared from polyacrylonitrile synthesized by anionic and radical polymerization and combined with chitin or chitisan. The thermomechanical properties of the films were examined. The compatibility of polyacrylonitrile synthesized by radical polymerization with chitosan was studied by DSC over a wide temperature range 140–280°C.     

Composites of lignin and polyacrylonitrile as carbon precursors

Films of polyacrylonitrile and lignin cast from dimethylformamide were studied by dynamic thermal analysis in a self-generated atmosphere and in a vacuum. The occurrence of a thermochemical reaction of the components on heating was demonstrated. The optimal conditions of the reaction between polyacrylonitrile and lignin were determined.     

Nanostructured carbon arrays from block copolymers of polyacrylonitrile

Arrays of graphitic carbon nanoclusters were obtained by pyrolysis of nanoscale phase-separated block copolymers of polyacrylonitrile and poly(n-butyl acrylate). Upon heating in an inert atmosphere to temperatures ranging from approximately 400 to 1200 degrees C, polyacrylonitrile domains were converted into carbon nanoclusters, maintaining the overall shape and spacing, whereas the poly(n-butyl acrylate) phase was sacrificed. Preservation of the original nanoscale morphology of a block copolymer was possible only if pyrolysis was preceded by oxidation at temperatures of approximately 230 degrees C, in analogy with thermal stabilization of polyacrylonitrile precursor in the process used in the manufacturing of carbon fibers. Preorganization of the carbon precursor through self-assembly in block copolymers of polyacrylonitrile appears to be an attractive and robust strategy for templated synthesis of well-defined nanostructured carbon materials.     

Cyclization and carbonization of anionic polyacrylonitrile in the presence of carbon nanofibers

Composites based on anionic polyacrylonitrile and carbon nanofibers were studied by X-ray diffraction, differential scanning calorimetry, thermal gravimetric analysis, and electron microscopy. The effect of carbon nanofibers on the specific features of cyclization and carbonization of anionic polyacrylonitrile at temperatures of to 550°C was studied.     

Carbonization of Polyacrylonitrile Composites with Nitrogen-containing Cellulose Derivatives

Thermal carbonization of nitrogen-containing cellulose derivatives (chitin, chitosan, cyanoethyl chitosan, cyanoethyl cellulose, copolymers of allyl carboxymethyl cellulose with polyacrylonitrile) as models of probable products of thermal reaction of cellulose with polyacrylonitrile was studied. The quantitative characteristics of carbonization of the model compounds are influenced by the nitrile group.     

The degradation and stabilization of polyacrylonitrile—II. Degradation of 1,3,5,7-tetracyanoheptane

A pure model compound for polyacrylonitrile, 1,3,5,7-tetracyanoheptane, was shown to discolour thermally in a similar manner to the polymer. This and other evidence is presented to support the view that thermal degradation of polyacrylonitrile is a free radical reaction involving tertiary hydrogen atoms.     

Solvent effect in the formation of polyconjugated system during pyrolysis of polyacrylonitrile

IR spectroscopy and quantum chemistry were used in the studies of structural transformations taking place in polyacrylonitrile films, formed from dimethylformamide and dimethyl sulfoxide upon their IR pyrolysis and convection annealing. Residual solvent was found to affect conditions of the formation of polyconjugated bonds in polyacrylonitrile films.     

Influence of electron beam pre-irradiation on the thermal behaviors of polyacrylonitrile

Thermal treatment of polyacrylonitrile pre-irradiated by electron beam was performed to investigate the radiation effects on thermally activated reactions. Thermal properties were characterized by differential scanning calorimetry and thermogravimetric analyses. Pre-irradiation lowers the onset temperature of reactions and alleviated the heat evolution process. Char yields (800 °C) of polyacrylonitrile increase significantly with increasing irradiation dose. FTIR was used to monitor the thermal reaction. The results reveal that the thermal reactions can be regulated by pre-irradiation dose. FTIR and UV-visible absorption spectra of pre-irradiation polyacrylonitrile illustrate the formation of -HCN-NCH- conjugation across the polymeric chains as a function of dose, which could improve the thermal behaviors of polyacrylonitrile.     

新型含季铵基腈纶纤维的制备

以商品级腈纶为基体,二甲氨基丙胺(Ⅰ)为胺化剂,经胺化反应制得含叔胺基的腈纶纤维(1)。以溴辛烷(Ⅱ)为季铵化试剂对1进行季铵化改性,制得新型的含季铵基的腈纶纤维(2),其结构经IR和EDS表征。较佳的胺化反应条件为:以乙二醇为溶剂,Ⅰ的体积分数为30%,于118℃反应3 h。较佳的季铵化反应条件为:以乙醇为溶剂,Ⅱ.的体积分数为10%,于70℃反应6 h。     

The stereoregularity of polyacrylonitrile and its dependence on polymerization temperature

The stereoregularity of polyacrylonitrile was studied by NMR spectroscopy. The methylene protons in isotactic configuration are equivalent in dimethylformamide-d₇ solution and are nonequivalent in dimethylsulfoxide-d₆ solution. In the case of the latter solution the difference in chemical shift between the isotactic methylene protons is 6.6 cps. The stereoregularity of polyacrylonitrile-α-d instead of polyacrylonitrile was determined on the dimethylformamide-d₇ solution. In the radical polymerization all the polyacrylonitrile-α-d's that polymerized at temperatures between 80 and ?78°C. have a configuration consisting of about 50% of isotactic diads and, accordingly, the stereoregularity of polyacrylonitrile does not depend upon the polymerization temperature. Analysis of the NMR spectra of isotactic polyacrylonitrile prepared from acrylonitrile–urea canal complex was also carried out. The NMR spectra of meso- and dl-2,4-dicyanopentanes, dimer models of isotactic and syndiotactic polyacrylonitriles, respectively, were analyzed by a computer program proposed by Bothner-By.     

Bioelectrochemical Response and Kinetics of Choline Oxidase Entrapped in Polyaniline—Polyacrylonitrile Composite Film

A novel choline oxidase electrode was constructed by entrapping choline oxidase into polyaniline-polyacrylonitrile composite film,The enzyme film was prepared by in situ electropolyme-ritztion of aniline into porous polyacrylonitrile-coated platinum electrode in the presence of choline oxidase ,the enzyme electrode exhibited sensitive and stable electrochemical response to choline ,The kinetics analysis,showed that the mass transport is partially rate-liniting.The influences of pH,applied potential and temperature on the response of the enzyme electrode were also desribed.     

Influence of silver nano‐additive amount on the supramolecular structure,porosity, and properties of polyacrylonitrile precursor fibers

This work examines the influence of the amount of silver nanoparticles added to polyacrylonitrile spinning solutions on their rheological properties as well as the structure and properties of the fibers produced. The influence of the amount of silver nanoparticles on the supramolecular structure of nanocomposite polyacrylonitrile precursor fibers, their porosity, as well as thermal and tensile strength properties was determined. The distribution of the nano‐ additive in fiber cross‐sections and on the surface was estimated. It was found that the addition of silver nanoparticles to polyacrylonitrile precursor fibers in an amount of up to 1.5% does not cause a decrease in the susceptibility of the fiber matter to deformation at the drawing stage. The produced fibers were characterized by an increased total volume of pores of 0.35 cm³/g and tenacity of more than 34 cN/tex. Copyright © 2009 John Wiley & Sons, Ltd.     

Effects of synthesis conditions and the mechanism of homopolymerization of acrylonitrile on the thermal behavior of the resulting polymer

The effect of the conditions of polyacrylonitrile synthesis (nature of the solvent, homogeneity of the reaction medium, and type of initiation) on the conditions of formation of the polyconjugation system during the pyrolysis of polyacrylonitrile is studied. The controlled synthesis of polyacrylonitrile via radiation polymerization mediated by dibenzyl trithiocarbonate as a reversible addition-fragmentation chain-transfer agent at 25 and 80°C is performed for the first time. It is shown that the type of initiation in reversible addition-fragmentation chain-transfer polymerization (material initiation or radiolysis) strongly affects the structure of the formed polyconjugation system.     

Spinnability of Polyacrylonitrile Gel Dope in the Mixed Solvent of Dimethyl Sulfoxide/Dimethylacetamide and Characterization of the Nascent Fibers

In this work, acrylonitrile copolymers were prepared via precipitation polymerization. The copolymer solutions prepared at various ratio of dimethyl sulfoxide and dimethylacetamide were tested to prepare the nascent fibers by one-step wet-spun method. The effect of temperature, solvent ratio, molecular weight and the solid content on the rheological properties of polyacrylonitrile gel solution in different mixed solvent were studied. It was shown that the viscosity decreased with the increase of the temperature and fluctuated with the different solvent ratio reaching the minimal value at the ratio of dimethyl sulfoxide to dimethylacetamide equal to 1.25. The crystallinity of copolymers and the structure of the nascent fiber surface also depended from the solvent ratio in polymerization. The optimum conditions for spinnability of copolymers were determined. The high-quality polyacrylonitrile precursor was achieved with the controllable range of 0.5–0.8 dtex and the toughness of polyacrylonitrile precursor was greater than 6.0 cN/dtex after the wet spinning process, while the tensile strength of carbon fiber is up to 6.25 GPa after their pre-oxidation and carbonization process.     

Studies of reactions with polymers. V. The reaction mechanism and resultant structure of PVA with PAN in DMSO without any catalyst

The reaction of polyacrylonitrile with poly(vinyl alcohol) in dimethyl sulfoxide without any catalyst was studied, and it showed that the adjacent nitrile groups on polyacrylonitrile could be linked up to form conjugated carbon-nitrogen sequence by the presence of poly(vinyl alcohol). However, no such reaction occurred when poly(vinyl alcohol) was replaced by i-propanol or poly(vinyl alcohol) graft copolymers. The structure of the resulting polymers were proposed by means of IR, UV, ¹H, and ¹³C-NMR spectroscopies. On the basis of the results, the effect of polymer feed and polymerization condition on this reaction were discussed. The compositions were determined by elemental analysis. The viscosity and thermal analysis of the products were also determined. At feed weight ratios of poly(vinyl alcohol) to polyacrylonitrile above one-half, gels were obtained.