Stabilization and carbonization of gel spun polyacrylonitrile/single wall carbon nanotube composite fibers

Gel spun polyacrylonitrile (PAN) and PAN/single wall carbon nanotube (SWNT) composite fibers have been stabilized in air and subsequently carbonized in argon at 1100 °C. Differential scanning calorimetry (DSC) and infrared spectroscopy suggests that the presence of single wall carbon nanotube affects PAN stabilization. Carbonized PAN/SWNT fibers exhibited 10-30 nm diameter fibrils embedded in brittle carbon matrix, while the control PAN carbonized under the same conditions exhibited brittle fracture with no fibrils. High resolution transmission electron microscopy and Raman spectroscopy suggest the existence of well developed graphitic regions in carbonized PAN/SWNT and mostly disordered carbon in carbonized PAN. Tensile modulus and strength of the carbonized fibers were as high as 250 N/tex and 1.8 N/tex for the composite fibers and 168 N/tex and 1.1 N/tex for the control PAN based carbon fibers, respectively. The addition of 1 wt% carbon nanotubes enhanced the carbon fiber modulus by 49% and strength by 64%.     

Hydrogen peroxide modified polyacrylonitrile-based fibers and oxidative stabilization under microwave and conventional heating – The 1st comparative study

Polyacrylonitrile (PAN) precursor was modified with hydrogen peroxide, and oxidative stabilisation studies were carried out using conventional and microwave heating. Wetting property, bulk density, Fourier transform infrared spectroscopy (FT-IR), extent of reaction (EOR), X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy and mechanical properties were also investigated. Results show that PAN fibers have excellent wettability with hydrogen peroxide. Hydrogen peroxide modification can shorten the oxidation stabilisation time of PAN fibers. The FT-IR spectrum shows that the stabilised fibers modified by hydrogen peroxide have a conjugated structure, and the EOR value of hydrogen peroxide-modified PAN fibers stabilised by microwave heating is the largest. XRD analysis shows that hydrogen peroxide-modified fibers stabilised by microwave heating have low stack domains and height of the interlayer spacing. The SEM and Raman spectra indicate that hydrogen peroxide can improve the surface finish of the fibers and reduce defects. In addition, hydrogen peroxide-modified fibers stabilised by microwave heating exhibit excellent mechanical properties, with fineness of 0.78 dtex, strength of 1.60 dtex, and elongation at break of 3.49%.     

Fabrication and characterization of carbon nanofibers with a multiple tubular porous structure via electrospinning

Carbon nanofibers with a multiple tubular porous structure were prepared via electrospinning from a polymer blend solution of polyacrylonitrile (PAN) and polylactide (PLA) followed by carbonization. The electrospun composite nanofibers underwent pre-oxidization and carbonization, which selectively eliminated PLA phases and transformed the continuous PAN phase into carbon, thereby porous structure formed in the carbon nanofibers. The morphologies of as-spun, pre-oxidized and carbonized nanofibers were studied by scanning electron microscope (SEM) and transmission electron microscopy (TEM). It was found that carbon nanofibers with an average diameter about 250 nm and a multiple tubular porous structure were obtained. The chemical changes during thermal treatment were studied by Fourier transform infrared spectrometer (FTIR), Raman spectra, differential thermal analysis (DTA) and thermogravimetric analysis (TG). The results showed that PLA phases were effectively removed and the continuous PAN phase was completely carbonized. The obtained carbon nanofibers had more disordered non-graphitized structures than non-porous nanofibers.     

Carbon fibers derived from wet‐spinning of equi‐component lignin/polyacrylonitrile blends

Equi‐component blends of polyacrylonitrile (PAN) and lignin, i.e., with a lignin content as large as 50 wt %, were successfully used as precursors to produce carbon fibers. Rheological measurements demonstrated that increasing lignin content in spinning solution reduced shear viscosity and normal stress, indicating a decrease of viscoelastic behavior. This was confirmed by Fourier transform infrared results that show no discernable chemical reaction or crosslinking between PAN and lignin in the solution. However, the resulting carbon fibers display a large I_D/I_G ratio (by Raman spectroscopy) indicating a larger disordered as compared to that from pure PAN. The macro‐voids in the lignin/PAN blend fibers typically generated during wet‐spinning were eliminated by adding lignin in the coagulant bath to counter‐balance the out‐diffusion of lignin. Carbon fibers resulting from lignin/PAN blends with 50 wt % lignin content displayed a tensile strength and modulus of 1.2 ± 0.1 and 130 ± 3 GPa, respectively, establishing that the equi‐component wet‐spun L/P‐based carbon fibers possessed tensile strength and modulus higher than 1 and 100 GPa. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45903.     

Characterization on oxidative stabilization of polyacrylonitrile nanofibers prepared by electrospinning

Ultrafine polyacrylonitrile (PAN) fibers, as a precursor of carbon nanofibers, with diameters in the range of 220–760 nm were obtained by electrospinning of PAN solution using N,N-dimethyl formamide (DMF) as solvent. Morphology of the nanofibers for varying concentration and applied voltage was investigated by field emission scanning electron microscopy (FESEM). The thermal properties and structural changes during the oxidative stabilization process were primarily investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and Fourier transform infrared (FT-IR) and Raman spectroscopy. The nanofiber diameters increase as the applied voltage is increased and they also increase with an increase in the concentration of the polymer solution. It was also concluded that the electrospun fibers displayed a very sharp exothermic peak at 297.34 °C. A transition temperature observed by FT-IR and Raman was approximately 300 °C, which was closely consistent with the results of DSC and TGA studies. It was also found that oxidative stabilization in air was accompanied by a change in color of nanofibers webs.     

Low temperature graphitization of interphase polyacrylonitrile (PAN)

Ordered polyacrylonitrile (PAN) interphase structures were formed in solution-cast PAN/carbon nanotube (CNT) composite films by enhancing polymer crystallization conditions and processing parameters for five types of CNTs. All film samples were heat-treated using similar stabilization and carbonization (up to 1100 °C) processes. Both the precursor and carbonized materials were characterized by electron microscopy and X-ray spectroscopy. Highly ordered graphitic structure was formed predominantly in the carbonized materials at 1100 °C (i.e., ∼1500 °C lower than the temperature used in a commercial graphitization process). The ordering of the graphite structure formed at 1100 °C was further improved by heat treatment up to 2100 °C. Multiple characterization results indicate that the early onset of PAN conversion to graphite is directly related to the polymer interphase formation as well as the CNT type. Based on the stabilization and carbonization parameters used in this study, PAN/single-wall carbon nanotube (SWNT) samples showed more prevalent graphite formation at 1100 °C. This work demonstrates the influence of CNT type regarding interfacial confinement toward this low-temperature polymer-to-graphite conversion process.     

聚丙烯腈/水滑石插层共混体系的结构和性能研究

采用原位聚合法,以过氧化二苯甲酰为引发剂,在形成水滑石的同时单体丙烯腈进入其层间并发生聚合反应,制备出聚丙烯腈/水滑石插层复合材料.用红外光谱、扫描电镜和X射线衍射对这种插层复合材料的结构进行了分析和表征,并对其燃烧性能和热性能进行了初步研究.结果表明:在水滑石片层之间通过原位聚合的方法生成了聚丙烯腈大分子,使水滑石层间距有一定程度的增大.聚丙烯腈/水滑石共混复合物的阻燃性能有一定提高,其极限氧指数(LOI)从18%提高到了21%;耐热性能得到一定程度改善.     

Preparation and characterization of electrospun Ag/polyacrylonitrile composite nanofibers

Novel composite nanofibers consisting of Ag nanoparticles and polyacrylonitrile (PAN) were fabricated successfully. The Raman properties of these Ag/PAN nanofibers were studied at low temperatures, which showed good Raman characteristics. In the process, a PAN solution containing Ag ions was directly electrospun to obtain nanofiber films containing Ag ions, and the Ag ions of resulting composite nanofibers were reduced to Ag nanoparticles in N₂H₅OH aqueous solution. Then, we treated Ag/PAN composite nanofibers at 100 °C, 200 °C, 400 and 600 °C, respectively. The Ag/PAN nanocomposite film was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) patterns and surface-enhanced Raman scattering (SERS) spectroscopy.     

Microscopic,structural, and electrical characterization of the carbonaceous materials synthesized from various lignin feedstocks

Microscopic, structural and electrical characterization of the carbonaceous materials synthesized from different types of lignin precursors are investigated employing scanning electron microcopy (SEM), Raman spectroscopy, X‐ray diffraction, and AC conductivity techniques. Lignin precursors from various resources carbonized at 900°C for 6 h under nitrogen atmosphere are used for this study. SEM analysis indicates formation of various microstructures, which are highly influenced by the carbonization behavior of lignin feedstocks that varies with chemical composition as well as purity. Raman spectroscopy of the carbon materials shows significant variations of its features, which represents their unique carbonization behaviors and graphitization events. Clear understanding of peak intensity, shape, and area gave very different structural features influenced by their chemical environment of the chosen precursor lignins. Phase purity and the graphitization degree are investigated through their X‐ray diffraction patterns. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41786.     

Graphitic carbon nanofibers developed from bundles of aligned electrospun polyacrylonitrile nanofibers containing phosphoric acid

Graphitic carbon nanofibers (GCNFs) with diameters of approximately 300 nm were developed using bundles of aligned electrospun polyacrylonitrile (PAN) nanofibers containing phosphoric acid (PA) as the innovative precursors through thermal treatments of stabilization, carbonization, and graphitization. The morphological, structural, and mechanical properties of GCNFs were systematically characterized and/or evaluated. The GCNFs made from the electrospun PAN precursor nanofibers containing 1.5 wt.% of PA exhibited mechanical strength that was 62.3% higher than that of the GCNFs made from the precursor nanofibers without PA. The molecules of PA in the electrospun PAN precursor nanofibers initiated the cyclization and induced the aromatization during stabilization, as indicated by the FT-IR and TGA results. The stabilized PAN nanofibers possessed regularly oriented ladder structures, which facilitated the further formation of ordered graphitic structures in GCNFs during carbonization and graphitization, as indicated by the TEM, XRD, and Raman results.     

Mass production of carbon nanotube‐reinforced polyacrylonitrile fine composite fibers

A facile and large‐scale production method of polyacrylonitrile (PAN) fibers and carboxyl functionalized carbon nanotube reinforced PAN composite fibers was demonstrated by the use of Forcespinning® technology. The developed polymeric fibers and carbon nanotube‐reinforced composite fibers were subsequently carbonized to obtain carbon fiber systems. Analysis of the fiber diameter, homogeneity, alignment of carbon nanotube and bead formation was conducted with scanning electron microscopy. Thermogravimetric analysis, electrical, and mechanical characterization were also conducted. Raman and FTIR analyses of the developed fiber systems indicate interactions between carbon nanotubes and the carbonized PAN fibers through π–π stacking. The carbonized carbon nanotube‐reinforced PAN composite fibers possess promising applications in energy storage applications. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40302.     

Preparation of ultra-thin PAN-based activated carbon fibers with physical activation

This study elucidates the stabilization and activation in forming activated carbon fibers (ACFs) from ultra-thin polyacrylonitrile (PAN) fibers. The effect of stabilization time on the properties and structure of resultant stabilized fibers was investigated by thermal analysis, X-ray diffraction (XRD), elemental analysis, and scanning electron microscopy (SEM). Stabilization was optimized by the pyrolysis of ultra-thin PAN fibers in air atmosphere at 280°C for 15 min, and subsequent activation in steam at 1000°C for 0.75 to 15 min. Resultant ACFs were characterized by N₂ adsorption at 77 K to evaluate pore parameters, XRD to evaluate structure parameters, and field emission scanning electron microscopy (FESEM) to elucidate surface morphology. The produced ACFs had surface areas of 668–1408 m²/g and a micropore volume to total pore volume ratio from 78 to 88%. Experimental results demonstrate the surface area and micropore volume of 1408 m²/g and 0.687 cm³/g, respectively, following activation at 1000°C for 10 min. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Pyrolysis and structure of hyperbranched polyborate modified phenolic resins

Novel boron modified phenolic resins (PR) were prepared by blending PR with boric acid terminated hyperbranched polyborate (HBb). In order to reveal the effect of HBb on the structure of the carbonized PR, several experimental tools were employed such as X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Both the XRD and Raman spectroscopy analyses indicated that the boron incorporation resulted in an increase in the crystallite height and a decrease of interlayer spacing. Moreover, the C1s XPS of PR and HBb modified PR revealed that the graphite carbon decreased from 54.50% to 42.85% after incorporating boron atoms in that some of carbon atoms are substituted with boron atoms by forming B-C bonds. The presence of the B-C bonds indicated that part of boron atoms have been introduced into the structure of carbonized PR. These findings revealed that HBb exhibited obvious effects both in promoting the graphite crystallite and in improving the thermal stability.     

Effects of nitrogen-doped carbon nanotubes on the discharge performance of Li-air batteries

Carbon nanotubes (CNTs) and nitrogen-doped carbon nanotubes (N-CNTs) were synthesized using a floating catalyst chemical vapor deposition method and characterized by scanning electron microscopy (SEM), transmission electron microscopy, Raman and X-ray photoelectron spectroscopy. The study found that the as-prepared CNTs and N-CNTs showed different discharge capacity as cathode materials in Li-air battery. To further study the reason why N-doping improves the electrochemical performance exceptionally, the discharge products on the two kinds of nanotubes were detected by SEM, XRD and Raman. SEM study showed, for the first time, that more uniform distribution of discharge products on the surface of CNTs arising from N-doping affected the boost of discharge capacity, a result which was discussed in detail. In comparison to non-doped CNTs, nitrogen doping was considered to be a promising way to improve the performance of carbon based cathode material for Li-air batteries.     

A novel form of carbon micro-balls from coal

A novel form of ball-like carbon material with its size in micrometer range was prepared from coal with nickel as catalyst by arc plasma method. The carbon material has been systematically studied by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and ultraviolet laser Raman spectroscopy. The SEM observation shows that the novel carbon material exists in various forms such as individual balls, net-like and plate-like forms, all of which have a quite smooth surface. The diameters of these carbon spheres are quite uniform and in a narrow range of 10-20 μm. The EDS analysis reveals that the ball-like carbon material contains more than 99.5% of carbon and a little amount of other elements such as nickel, silicon and aluminum. The XRD and UV-Raman results reveal that the novel carbon material is a kind of highly graphitized carbon. The growth mechanism of the ball-like carbon material was proposed and discussed in terms of arc plasma parameters and the chemical structure of coal-based carbon.     

Mn-P共掺杂氮化碳的制备及其光催化性能研究

采用四水氯化锰、磷酸氢二铵和三聚氰胺为原料制备了Mn-P共掺杂的石墨相氮化碳(g-C3 N4).使用X射线衍射光谱(XRD)、扫描电子显微镜(SEM)、傅里叶变换红外光谱(FT-IR)、光致荧光光谱(PL)、紫外-可见漫反射光谱(UV-Vis DRS)、电化学阻抗谱(EIS)、瞬态光电流响应等分析测试手段对制备的催化剂...     

Non-catalytic CVD preparation of carbon spheres with a specific size

A simple chemical vapor deposition method was used to prepare carbon spheres (CPS) from toluene without any catalysts. The diameters of CPS are in a range of 60 nm to 1 μm and can be controlled by changing the composition and flow rate of a mixture gas that was used as the carrier gas. The carbon spheres have been systematically studied by scanning electron microscopy (SEM), element analysis, energy dispersive X-rays spectroscopy (EDX), X-ray diffraction (XRD) and ultra-violet laser Raman spectroscopy. The SEM examination shows that these carbon spheres have a ball-like and chain-like morphology, all of which have smooth surfaces and a quite uniform diameter. The element analysis reveals that the carbon content of the spheres is over 97.0% while the EDX analysis shows that more than 92.0% of the carbon spheres is carbon. The XRD and UV-Raman studies reveal that they are not highly graphitized carbons.     

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.     

Influence of char-forming lignin in combination with aluminium phosphinate on thermal stability and combustion properties of polyamide 11 blends

Polyamide 11 (PA) blends based on char-forming industrial lignin and aluminum phosphinate (AlP) were prepared to improve flame retardant (FR) properties using a green and eco-friendly approach. This study investigates the thermal degradation and combustion behavior of PA blends prepared by using AlP in combination with two different types of industrial lignins (i.e., kraft lignin (DL) and lignosulphonate lignin (LL). Thermogravimetric (TG) analysis showed that ternary blends containing LL and AlP developed higher char residue up to 10.7 wt% upon decomposition in inert atmospheres. The combination of lignin and AlP increases the thermal stability by shifting the initial decomposition temperature (T_5%) and temperature at maximum decomposition (T_max) to a higher temperature range, attributed to the stabilization of decomposition products. Furthermore, combustion behavior studied by cone calorimeter (forced combustion) and pyrolysis combustion flow calorimeter (PCFC) tests presented a significant reduction in the peak of heat release rate (PHRR) and total heat release (THR). It was found that LL and AlP-containing blends more effectively decreased fire parameters like PHRR and THR than that of DL and AlP-containing blends. The best interaction with reduced fire-retardant properties was obtained when 10 wt% loading of lignin (DL/LL) and AlP was used. The reduction in heat release parameters was mainly ascribed to the condensed phase mechanism by forming an efficient protective char layer, which acts as a barrier against heat and mass transfer between the condensed and the gas phases. Raman spectroscopy analysis also confirmed the formation of the protective graphitic layer in the condensed phase.     

Fabrication and microstructural characterization of the diamond@amorphous carbon nanocomposite core/shell structure via in-situ polymerization

A novel diamond@carbon core/shell structure, constituting diamond as a hard core and carbon as a soft shell, was synthesized from resole resin and nanodiamond as the starting materials via in-situ polymerization and subsequently high-temperature carbonization. The diamond@carbon nanocomposite was characterized using field emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectra, and Fourier transform infrared spectroscopy (FT-IR). The results indicated that the shell material are comprised of amorphous carbon. The thickness of carbon shell was controlled from 502.5 nm to 27 nm by adjusting the concentration of the nanodiamond. As confirmed by TEM, FT-IR and XPS, the diamond@carbon nanocomposite revealed a stable structure, due to the formation of the chemical bonding between diamond and carbon shell after calcination process. Overall, the diamond@carbon nanocomposite abrasives could lead to a reducted surface roughness and damage of SiC wafer comparing with the nanodiamond abrasives, due to the spring-like effect coming from the elastic component of the amorphous carbon shell. Moreover, the as-prepared nanoparticles exhibited better dispersion stability than the pure diamond in the pH range from 8 to 11.