Cocarbonization of polyacrylonitrile with lignin

The boundary and parameters of the thermochemical reaction of lignin and polyacrylonitrile were determined by dynamic and isothermal thermal analysis. The time, temperature, and concentration effects of formation of composites, allowing preparation of new carbonizates with enhanced heat resistance and noticeably higher carbon residue, were studied.     

Modification of polyacrylonitrile with ethylenedicarboxylic acid esters for preparing carbon fiber precursors

Russian Journal of Applied Chemistry - Specific features of copolymerization of acrylonitrile with dimethyl maleate and dimethyl fumarate under the action of a catalytic system based on copper(I)...     

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.     

Sequestration and transport of lignin monomeric precursors

Lignin is the second most abundant terrestrial biopolymer after cellulose. It is essential for the viability of vascular plants. Lignin precursors, the monolignols, are synthesized within the cytosol of the cell. Thereafter, these monomeric precursors are exported into the cell wall, where they are polymerized and integrated into the wall matrix. Accordingly, transport of monolignols across cell membranes is a critical step affecting deposition of lignin in the secondarily thickened cell wall. While the biosynthesis of monolignols is relatively well understood, our knowledge of sequestration and transport of these monomers is sketchy. In this article, we review different hypotheses on monolignol transport and summarize the recent progresses toward the understanding of the molecular mechanisms underlying monolignol sequestration and transport across membranes. Deciphering molecular mechanisms for lignin precursor transport will support a better biotechnological solution to manipulate plant lignification for more efficient agricultural and industrial applications of cell wall biomass.     

Microstructure and properties of polyacrylonitrile based carbon fibers

The microstructure of polyacrylonitrile (PAN)-based carbon fibers with different mechanical properties was investigated. It was found that the tensile strength of the PAN-based carbon fibers generally decrease with the increase in the modulus. The properties of PAN-based carbon fiber are mainly controlled by the microstructure and microvoids. The increase in size and orientation of graphite crystallites follows the decrease in interlayer space of graphite sheets, which accompanies the increase in modulus and decrease in tensile strength of the carbon fibers. Simultaneously, the increase in the modulus of the carbon fibers accompanies the merging of the elliptical microvoids along the fiber axis and the turbostratic graphite in the carbon fibers transforms into 3D ordered graphite lamellar structure. This work provides useful information on tailoring the mechanical properties of carbon fibers by adjusting the microstructure.     

A study on the orientation structure and mechanical properties of polyacrylonitrile precursors

The polyacrylonitrile precursors were made through the two‐stage drawing process. The orientation structure was examined through wide‐angle X‐ray diffraction (WAXD). The orientation factors and the modulus were measured through the sound velocity method. The mechanical properties, such as the Young's modulus, the tensile strength and the breaking elongation ratio were obtained by the single fiber tensile test. The results showed that the Young's modulus and the strength of the precursors increased with draw ratio, which is accordant with the enhancement of the micromolecular orientation degree. Therefore the orientation factors obtained from the experiments were compared with the theoretical curves which were predicted through the Crawford and Kolsky's model. The physical meaning of the parameters m and n were analyzed. A good agreement of the orientation factor between the experimental data and the theoretical curve was achieved. Copyright © 2005 John Wiley & Sons, Ltd.     

Synthesis and characterization of chemically modified polystyrene as processable carbon fiber precursors

In this study, the chemically modified polystyrene was studied for improvement of polystyrene which had low carbon yield, as a carbon fiber precursor. The polystyrene was synthesized with divinylbenzene which was used as a cross-linking agent by the solution polymerization method. Then the synthesized polystyrene was nitrated with sulfuric and nitric acids solution (H₂SO₄/HNO₃) followed by reduction to form nitrogen-functional groups. The surface properties of the modified polystyrene were investigated by Fourier transfer infrared spectroscopy to confirm the introduction of functional groups on the modified polystyrene surfaces. The thermal properties of the modified polystyrene were measured by thermogravimetric analysis and differential scanning calorimetry. The morphologies of the electrospun polystyrene fibers by a chemical modification were observed by scanning electron microscopy. From the results, the nitrogen-functional groups were introduced on the modified polystyrene surfaces which affected the quantity of functional groups. Also, the chemical treatment affected the carbon yield of the polystyrene owing to the introduction of nitrogen-functional groups on polystyrene surfaces. Consequently, it was concluded that the chemical treatment of polystyrene fibers enables it to be used as a possible carbon fiber precursor.     

Nanodispersed metal and metal oxide particles in polymeric matrices from polyacrylonitrile precursors

Two ways of the colloid formation of metals and metal oxides in the polyacrylonitrile (PAN) and its copolymer (1.5 wt % of itaconic acid) (PAN-I) have been studied. The thermal decomposition of W, Mo and Cr carbonyl complexes with PAN, prepared by the interaction of PAN nitrile groups with VI B group metal hexacarbonyls has been investigated. The thermolysis under air leads to a formation of metal oxide particles. For the Cr-containing PAN, the presence of dispersed Cr₂O₃ with a size less than 3 nm was estimated by ESR. Co-containing polymers were prepared by mixing Co₂(CO)₈ with PAN-I in DMF. It was found that Co₂(CO)₈ interacts with DMF giving salt [Co(DMF)₆]²⁺[Co(CO)₄]-₂. By ferromagnetic resonance and SAXS, colloid size depends on thermolysis conditions and loading of the Co complex and varies from 1 to 10 nm.     

Synthesis of mesoporous carbons using ordered and disordered mesoporous silica templates and polyacrylonitrile as carbon precursor

Mesoporous carbons were synthesized from polyacrylonitrile (PAN) using ordered and disordered mesoporous silica templates and were characterized using transmission electron microscopy (TEM), powder X-ray diffraction, nitrogen adsorption, and thermogravimetry. The pores of the silica templates were infiltrated with carbon precursor (PAN) via polymerization of acrylonitrile from initiation sites chemically bonded to the silica surface. This polymerization method is expected to allow for a uniform filling of the template with PAN and to minimize the introduction of nontemplated PAN, thus mitigating the formation of nontemplated carbon. PAN was stabilized by heating to 573 K under air and carbonized under N2 at 1073 K. The resulting carbons exhibited high total pore volumes (1.5-1.8 cm3 g(-1)), with a primary contribution of the mesopore volume and with relatively low microporosity. The carbons synthesized using mesoporous templates with a 2-dimensional hexagonal structure (SBA-15 silica) and a face-centered cubic structure (FDU-1 silica) exhibited narrow pore size distributions (PSDs), whereas the carbon synthesized using disordered silica gel template had broader PSD. TEM showed that the SBA-15-templated carbon was composed of arrays of long, straight, or curved nanorods aligned in 2-D hexagonal arrays. The carbon replica of FDU-1 silica appeared to be composed of ordered arrays of spheres. XRD provided evidence of some degree of ordering of graphene sheets in the carbon frameworks. Elemental analysis showed that the carbons contain an appreciable amount of nitrogen. The use of our novel infiltration method and PAN as a carbon precursor allowed us to obtain ordered mesoporous carbons (OMCs) with (i) very high mesopore volume, (ii) low microporosity, (iii) low secondary mesoporosity, (iv) large pore diameter (8-12 nm), and (v) semi-graphitic framework, which represent a desirable combination of features that has not been realized before for OMCs.     

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.     

Effect of carbon nanostructures on the carbonization of polyacrylonitrile

Composite materials based on polyacrylonitrile with carbon nanofillers (technical-grade carbon, thermally expanded graphite, carbon nanotubes) were synthesized. A carbonization of film and fiber composite samples in the temperature range 20–1000°C provided a noticeable increase in the thermal stability of fibers and a rise in the electrical conductivity of the composite material. Dependences of the degree of carbonization on the concentration of nanostructures, type of material, and nature of modifier were determined. Differential-thermal and X-ray diffraction analyses revealed the formation of oriented nucleus structures of turbostratic carbon in the temperature range 450–550°C.     

Structure and thermodynamics of carbon and carbon/silicon precursors to nanostructures

The structures at the Hartree-Fock level, as well as the energetics, are reported for the unsaturated system C(36)H(16), its Si-doped analogue C(32)Si(4)H(16), and several smaller, unsaturated fragments. Structural effects on the electronic distribution are discussed in terms of a localized orbital energy decomposition. The standard heats of formation are calculated based on homodesmic and isodesmic reactions and the G2(MP2,SVP) method with a valence double-zeta plus polarization basis. The origin of the observed explosion of the all-carbon system (C(36)H(16)) to form carbon nanotubes was investigated by exploring a possible initial reactive channel (dimerization), which could lead to the formation of the observed onion-type nanostructures.     

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.     

Rheological properties of polyacrylonitrile solutions containing highly dispersed carbon nanotubes

Rheological properties of dispersions of carbon nanotubes in dimethylsulfoxide solutions of polyacrylonitrile are studied at different concentrations of the components. The viscosity values of all the studied dispersions are substantially dependent on shear rate. For a number of systems, the energies of activation of viscous flow are determined. The relationship of viscosity and the energy of activation of flow to the compositions and possible structural features of dispersions is discussed. The concentration regime where a thermally reversible mixed network exists with crosslinks formed by physical contacts of the polymer with nano-tubes is characterized.     

Functionalized carbon nanotube/polyacrylonitrile composite nanofibers: fabrication and properties

The functionalized multi‐walled carbon nanotubes (f‐MWCNTs) were obtained by Friedel–Crafts acylation, which introduced aromatic amine groups onto the sidewall. And the grafted yield was adjusted by controlling the concentration of the catalyst. The composite solutions containing f‐MWCNTs and polyacrylonitrile (PAN) were then prepared by in‐situ or ex‐situ solution polymerization. The resulting solutions were electrospun into composite nanofibers. In the in‐situ polymerization, morphological observation revealed that f‐MWCNTs was uniformly dispersed along the axes of the nanofibers and increased interfacial adhesion between f‐MWCNTs and PAN. Furthermore, two kinds of f‐MWCNTs/PAN composite nanofibers had a higher degree of crystallization and a larger crystal size than PAN nanofibers had, so the specific tensile strengths and modulus of the composite nanofibers were enhanced. And the thermal stability of f‐MWCNTs/PAN from in‐situ method was higher than that of ex‐situ system. When the f‐MWCNTs content was less than 1 wt%, the specific tensile strengths and modulus of nanofibers were enhanced with increase in the amounts of f‐MWCNTs, and f‐MWCNTs/PAN of in‐situ system provided better mechanical properties than that of ex‐situ system. Copyright © 2010 John Wiley & Sons, Ltd.     

The highly conducting carbon electrodes derived from spin-coated polyacrylonitrile films

Carbon films prepared from pyrolyzation of spin-casted polyacrylonitrile (PAN) thin films display high electrical conductivity (600 S/cm, at 1000 °C carbonization), low sheet resistance (about 100 Ω/square at the PAN film thickness of 70 nm) and partial transmittance. These pyrolyzed PAN (PPAN) films were patterned as bottom electrodes by photolithography, and utilized as drain and source electrodes to fabricate organic field-effect transistor (OFET) devices with a p-type semiconductor (P3HT) and an n-type semiconductor (DPP-containing quinoidal small molecule) through a spin-coating procedure. The results showed that the devices with the PAN electrodes exhibited almost the same excellent performance without any further modification compared to those devices with traditional Au electrodes. Since these PPAN films had the advantages of low-cost, high performance, easier for large-area fabrication, thermal and chemical stability, it should be a promising electrode material for organic electrodes.     

Graphitic mesostructured carbon prepared from aromatic precursors

Mesostructured carbons with graphitic framework walls are conveniently prepared at ambient pressures through the replication of a mesostructured silica template using an aromatic hydrocarbon as the carbon precursor and a catalyst.     

Reactivity of lanthanide carbon σ bonds: Alkyllanthanide complexes as synthetic precursors to lanthanide alkynides

A general, halide-free synthesis of σ-bonded organolanthanides is demonstrated by the reaction of terminal alkynes with LiLn(t-C₄H₉)₄(THF)₄ to form a new series of homoleptic lanthanide alkynide complexes, LiLn(CCR)₄(THF), and by the synthesis of [(C₅H₅)₂LnCCR]₂ from [(C₅H₅)₂LnCH₃]₂.     

Production of polyacrylonitrile particles by precipitation polymerization in supercritical carbon dioxide

Polyacrylonitrile particles were produced by precipitation polymerization of acrylonitrile (AN) without any colloidal stabilizer in supercritical carbon dioxide as a polymerization medium at about 30 MPa for 24 h at 65 °C at different initiator concentrations (0.8–45.2 mmol/l) and at different AN concentrations (10–40% w/v). An increase in the initiator concentration led to increases in the conversion and in the degree of coagulation and to a decrease in the molecular weight. At AN concentration of 20% w/v, micron-sized, relatively monodisperse polyacrylonitrile particles with clean and uneven surfaces were produced.