Aspects on prestretching of PAN precursor: Shrinkage and thermal behavior

Polyacrylonitrile (PAN) fibers of a special grade have been modified by a method of prestretching with various stretching ratios from negative to positive before the onset of stabilization. The effect of such pretreatments on the thermorhelogical and thermal behaviors of PAN fibers was followed by free shrinkage experiments and differential scanning calorimetry (DSC) analyses. It was found that prestretching had a significant influence on the physical shrinkage of PAN fibers. DSC results of PAN fibers showed dependence not only on atmospheric conditions but also on the extent of prestretching. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1185–1190, 1998     

Micromorphological structure and its forming mechanisms of polyacrylonitrile‐based copper gradient composite film

In this article, the micromorphological structure of polyacrylonitrile‐copper gradient composite film obtained from the electrochemical reduction of a swelling cathode film was investigated with a scanning electronic microscope and a transmittance electronic microscope. It was found that the micromorphological structure in deposited phase is constructed with copper particles and sheaves of polyacrylonitrile chains. The diameters of both the copper particles and the sheaves of macromolecules are about 50 nm. Thus the idea of the interpenetration between polymeric matrix and deposited metal is suggested. Under the enhanced power voltage and the reactor temperature, the maximums of current in the loop of reaction system shift to lower electrochemical reaction time. That means the higher value of them makes the higher activity in the two aspects of ion move and ion reduction in swelling cathode film. The dissolving experiment of gradient composite film showed that it does not dissolve in N,N‐dimethylformamide, and this further confirmed the interpenetration between the polymer matrix and the deposited copper. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1927–1932, 1999     

Deposition of Gold Nanoparticles on Thin Polyaniline Films

Local and bulk deposition of gold particles was accomplished by the spontaneous reaction between chemically reduced polyaniline (PAN) thin films and AuCl. PAN layers were deposited on glass, indium tin oxide (ITO), and glassy carbon (GC) by the Langmuir–Blodgett method and spin-coating. Characterization of the PAN films was carried out by microscopy, UV–vis spectroscopy, and electrochemistry. We found that the nature of the gold deposit was greatly affected by the thickness of the PAN. Scanning electrochemical microscopy was used as a means of locally depositing gold nanoparticles on an unbiased PAN film by anodically dissolving a gold micro-electrode. This represents a generic approach whereby a variety of metal micro- and nanoparticles can be locally deposited on insulating supports.     

Regenerated and graft copolymer fibers from steam-exploded wheat straw: Characterization and properties

Steam explosion treatment has been proven to effectively induce such marked modifications to the chemical and supramolecular structure of wheat straw cellulose as to make this cellulose a suitable raw for dissolving processes. Regenerated and poly(acrylonitrile) (PAN) and poly(methyl methacrylate) (PMMA) grafted wheat straw fibers obtained on the laboratory scale were characterized by various techniques (X-ray diffraction, cross polarization-magic angle spinning (CP-MAS) ¹³C nuclear mag-netic resonance and vibrational spectroscopy, scanning electron microscopy, differential scanning calorimetry), and the relationships between the morphological–structural features and physicomechanical and end-use properties have been evidenced. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:961–974, 1998     

Synthesis and characterization of LiFePO4–carbon nanofiber–carbon nanotube composites prepared by electrospinning and thermal treatment as a cathode material for lithium‐ion batteries

Binder‐free LiFePO₄–carbon nanofiber (CNF)–multiwalled carbon nanotube (MWCNT) composites were prepared by electrospinning and thermal treatment to form a freestanding conductive web that could be used directly as a battery cathode without addition of a conductive material and polymer binder. The thermal decomposition behavior of the electrospun LiFePO₄ precursor–polyacrylonitrile (PAN) and LiFePO₄ precursor–PAN–MWCNT composites before and after stabilization were studied with thermogravimetric analysis (TGA)/differential scanning calorimetry and TGA/differential thermal analysis, respectively. The structure, morphology, and carbon content of the LiFePO₄–CNF and LiFePO₄–CNF–MWCNT composites were determined by X‐ray diffraction, high‐resolution transmission electron microscopy, Raman spectroscopy, scanning electron microscopy, and elemental analysis. The electrochemical properties of the LiFePO₄–CNF and LiFePO₄–CNF–MWCNT composite cathodes were measured by charge–discharge tests and electrochemical impedance spectroscopy. The synthesized composites with MWCNTs exhibited better rate performances and more stable cycle performances than the LiFePO₄–CNF composites; this was due to the increase in electron transfer and lithium‐ion diffusion within the composites loaded with MWCNTs. The composites containing 0.15 wt % MWCNTs delivered a proper initial discharge capacity of 156.7 mA h g^?1 at 0.5 C rate and a stable cycle ability on the basis of the weight of the active material, LiFePO₄. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43001.     

Structure evolution mechanism of polyacrylonitrile films incorporated with graphene oxide during oxidative stabilization

Oxidative stabilization is a key process for polyacrylonitrile (PAN)-based carbon materials. During this process, oxygen has a significant influence on the formation of cyclization structure and crosslinking structure of PAN matrix. Here, graphene oxide (GO) was used as filler in PAN matrix, the structure evolution of GO/PAN composite was studied during oxidative stabilization. Solubility measurement revealed that the crosslinking degree increased, while the cyclization degree of stabilized films decreased after GO incorporation. The effect of GO on the structure of PAN film was characterized by XRD, DSC, DMA, FTIR, and XPS. These results verified that GO could initiate the cyclization reaction of PAN at a lower temperature. The carboxylic groups on GO sheets might take part in the cyclization reactions during the heat treatment. Moreover, the oxygen-containing molecules released from GO decomposition during the heat treatment were beneficial to the formation of crosslinking structure. The possible mechanism of the structure evaluation was proposed in this article. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47701.     

Use of MWNTs‐COOH to improve thermal energy storage and release rates of capric–palmitic–stearic acid ternary eutectic/polyacrylonitrile form‐stable phase change composite fibrous membranes

A series of novel capric–palmitic–stearic acid ternary eutectic/polyacrylonitrile/carboxyl purified multi‐walled carbon nanotubes (CA–PA–SA/PAN/MWNTs‐COOH) form‐stable phase change composite fibrous membranes (PCCFMs) were fabricated by electrospinning and physical absorption methods. In these form‐stable PCCFMs, the CA–PA–SA ternary eutectic was served as phase change material for thermal energy storage, and the loaded MWNTs‐COOH was acted as thermal conductivity enhancement filler to improve heat transfer rates, as well as electrospun PAN/MWNTs‐COOH fibrous membranes with different weight fractions of MWNTs‐COOH (i.e., 5, 10, and 20 wt%) were used as supporting materials to provide structural strength and prevent liquid leakage of melted CA–PA–SA ternary eutectic. The morphological structure and thermal performances were investigated and analyzed. The images of scanning electron microscopy showed that the CA–PA–SA ternary eutectic was uniformly embedded and dispersed into the three‐dimensional porous network structure of electrospun PAN/MWNTs‐COOH fibrous membranes. Thermal performance tests suggested that the melting and freezing times of the CA–PA–SA/PAN/MWNTs‐COOH form‐stable PCCFMs with the addition of 10 wt% MWNTs‐COOH were significantly shorten by about 52% and 56% in comparison with those of the CA–PA–SA/PAN form‐stable PCCFMs. Their phase change temperatures and enthalpies were about 7°C–32°C and 130–138 kJ/kg, respectively. POLYM. ENG. SCI., 59:E403–E411, 2019. © 2018 Society of Plastics Engineers     

Physical and electrochemical studies of polyphenylsilane-derived porous carbon nanofibers produced via electrospinning

Polyacrylonitrile (PAN)/polyphenylsilane (PPS)-based composite carbon nanofibers (CCNFs) are prepared by one-step electrospinning and subsequent thermal treatment to produce organic-inorganic hybrid CCNFs. We investigate the electrochemical behavior and structural properties of these CCNF materials as a function the PAN/PPS ratio. The CCNFs show large specific surface area, high electrical conductivity and high thermal stability. In addition, the electrochemical performance of the organic–inorganic hybrid CCNF electrode is improved by the special porous structure and the silicon oxycarbide (Si–O–C)-related structure.     

Preparation and characterization of nanofiltration composite membranes using polyacrylonitrile (PAN). I. preparation and modification of PAN supports

Polyacrylonitrile (PAN) supports useful for the formation of nanofiltration (NF) composite membranes were prepared from PAN solutions in N‐methylpyrrolidone (NMP), using a phase‐inversion method. The compositions of the PAN/NMP solutions used were as follows: 10/90, 15/85, and 20/80 (in wt %). The PAN supports were treated with various concentrations of NaOH aqueous solutions (0.1, 0.5, 1, and 2 mol) for certain periods of times (0.5, 1, 2, and 3 h) in order to modify their surface chemically and morphologically. The characteristics of the supports, modified or unmodified, were carefully studied. The morphology of those were observed with field‐emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). The change of the chemical structure of those by the NaOH treatment was studied using FTIR–ATR spectroscopy and ESCA. The permeation properties of those were also determined at 1–5 bar of operation pressure using a PEG 35,000 aqueous feed solution. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1854–1862, 2001     

Crystallizable diluent-templated polyacrylonitrile foams for macroporous carbon monoliths

Polyacrylonitrile (PAN) foams with different pore structures were prepared for the fabrication of macroporous carbon monoliths. The foams were prepared through thermally induced phase separation (TIPS) method using dimethyl sulfone (DMSO2) as a crystallizable diluent. Honeycomb-like porous foam is obtained from PAN/DMSO2 mixture containing about 5 wt.% PAN, and those with channel-like pores are resulted from the mixtures with 10–40 wt.% PAN. However, they only have few mesopores and the porosity is as low as 30–47% for the foams prepared from those mixtures containing 50–60 wt.% PAN. Real-time observation with polarized optical microscopy reveals that the channel-like structure stems from the spherulitic orientation of DMSO2 crystals in the polymer matrix. Taking into account this morphology, DMSO2 crystals are capable of acting as in situ formed templates, which subsequently enable to shape the final pore structure of PAN foams. Macroporous carbon monoliths with honeycomb- or channel-like pores were constructed from PAN foams by oxidative stabilization and carbonization. Their graphitic structure and specific surface areas were analyzed by wide-angle X-ray diffraction and Brunauer–Emmett–Teller measurement. This TIPS method using crystallizable diluent provides a new route to control the porous structure of PAN foams for carbon materials.     

Conductive fibers based on poly(ethylene terephthalate)–polyaniline composites manufactured by electrochemical polymerization

A novel method of manufacturing composite conductive fibers was developed through electrochemical polymerization with an apparatus consisting of insulating fibers, cotton fabrics as electrolytic solution holders, an electrolytic solution, and planer electrodes. By this method, poly(ethylene terephthalate) (PET) fibers coated with polyaniline (PAN) were prepared readily and yielded PET–PAN composite conductive fibers (PPCFs). The content of PAN in PPCFs increased with an increase in both the aniline concentration in the electrolytic solution and the polymerization voltage, although it did not depend on the load applied to the electrodes. Observations of the PPCF surface by scanning electron microscopy confirmed that the formation processes of PPCFs could be divided into three steps: (1) fine (nanometer‐size) granular PAN was generated from the anode and adsorbed onto the PET fiber surface, (2) the size of the granular PAN increased up to about 90 nm in a short time, and (3) the granular PAN was linked together to form networks. The conductivity of PPCFs increased with an increasing content of PAN networks. The surface resistance of the PPCF fabric was about 3 × 10⁵ Ω/□ at a PAN content of approximately 2 wt %. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1073–1078, 2003     

Composite electrodes consisting of platinum particles and polyaniline nanowires as electrocatalysts for methanol oxidation

Polyaniline (PANI) with nanowire (PANI‐(NW)) network structure (mean diameter 10–20 nm) was successfully deposited on a stainless steel (SS) electrode by a galvanostatic process. Platinum particles were deposited into the PANI nanowire network structure to result the PANI(NW)‐Pt composite electrode. The PANI(NW)‐Pt electrode was used as electrocatalysts for the electrochemical oxidation of methanol. The PANI nanowires and PANI(NW)‐Pt nanocomposite were characterized by scanning electron microscopy (SEM), X‐ray photoelectron spectroscopy (XPS), and UV–vis absorption spectroscopy. Nanowire morphology with an average diameter of 10–20 nm could be seen from scanning electron micrograph. Small amount (70 mμm) of spherical Pt particles could be deposited into the PANI(NW). Catalytic activity for the oxidation of methanol was studied by using cyclic voltammetry (CV). For comparative purposes, bulk Pt (deposited Pt on SS) and PANI nanowires based electrodes were tested. The PANI(NW)‐Pt nanocomposite electrode exhibited excellent catalytic activity for the electrooxidation of methanol in comparison to bulk Pt electrodes, which reveals that the PANI(NW)‐Pt nanocomposite electrodeis more promising for application in electrocatalyst as a support material. POLYM. COMPOS., 28:650–656, 2007. © 2007 Society of Plastics Engineers     

Microwave pre‐oxidation for polyacrylonitrile precursor coated with nano‐carbon black

A surface coating was successfully applied through dipping the polyacrylonitrile (PAN) precursor fibers in a carbon black (CB) bath containing a hydrolyzed binder. The coated fibers were pre‐oxidized over the microwave furnace at temperatures ranging from 100°C to 170°C for different heating times. The changes in chemical structure were studied by Fourier transfer infrared spectroscopy combined with elemental analyzer. X‐ray diffraction was employed to study the crystalline structure and its related parameters. Differential scanning calorimeter and thermogravimetry were used for thermal analysis. In addition, the fiber morphology and the mechanical properties were also evaluated. Scanning electron microscopy results confirmed the presence of CB on the surface of PAN precursor. The analysis in the chemical structure showed an apparent response of coated PAN fibers to the microwave heating, since the microwave field induced the cyclization and crosslinking reactions. The crystallinity and the crystallite height decreased. Furthermore, the tensile strength and elongation of pre‐oxidized fibers decreased with the increase of heating time. The measured oxygen content revealed that the pre‐oxidized fibers can withstand the high temperatures on the following stage (carbonization). POLYM. ENG. SCI., 59:457–464, 2019. © 2018 Society of Plastics Engineers     

Novel,positively charged membrane from a blending,crosslinking, and coagulation procedure

A novel, positively charged membrane was prepared through a blending, crosslinking, and coagulation procedure in which poly(N,N‐dimethylaminoethyl methacrylate) (PDM) and polyacrylonitrile (PAN) were used as the functional and substrate component, respectively. Because 1,4‐dibromobutane (DBT) was used as the crosslinker and quaternizing agent, PDM was crosslinked and quaternized simultaneously. The effects of PDM content, polymer concentration, and additive dosage of the casting solution on the membrane performances are discussed in detail, and differences between the PAN membrane, PDM/PAN blend membrane, and crosslinked PDM/PAN blend membrane are also discussed. We also studied the adsorption behaviors of the membranes to a positively charged dye and a negatively charged dye. Environmental scanning electron microscopy observation showed that the resulting positively charged membrane from such a blending, crosslinking, and coagulation procedure possessed a unique and uniform structure. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1847–1854, 2005     

Localized electrodeposition of praseodymium oxide on boron-doped diamond

The deposition of praseodymium oxide (PrO₂) films on diamond electrodes is of interest for electrochemical applications, because of the catalytic and permselective properties of this material. In this work, PrO₂ was deposited on commercial boron-doped diamond (BDD) electrodes from solutions of praseodymium nitrate in hydrogen peroxide, where a local increase of pH at the electrode surface is used to precipitate hydrated praseodymium oxide at the solution-electrode interface. For particular deposition conditions, it is observed that pronounced lateral heterogeneities are seen in the observed deposition rate, arising from lateral fluctuations in the electrochemical activity of the diamond electrodes used. It is also observed that the use of scanning electrochemical techniques enables oxide deposition with good spatial control to be achieved.     

Influence of sputtering pressure on surface structure and oxygen reduction reaction catalytic activity of thin platinum films

The work presents a study on the influence of the sputtering pressure on the surface structure and morphology of low Pt loaded electrodes and their electrochemical behaviour toward oxygen reduction reaction (orr) in sulphuric acid solution and polymer electrolyte membrane (Nafion 117). Pt was deposited as thin film upon hydrophobic carbon paper substrates at sputtering pressure varied in the range 2-13 Pa. The test samples are analysed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The catalytic activity is assessed by applying the methods of linear sweep voltammetry (LSV) on rotating disc electrode (RDE) and cyclic voltammetry (CV). The results obtained show strong influence of the sputtering pressure on the surface structure and crystal orientation which in turn, affects the orr efficiency. The best electrode performance in both electrolytes used is obtained for the Pt film deposited at pressure of 9 Pa. The results obtained in Nafion 117 show that catalyst utilisation in this electrode exceeds significantly the one for a commercial ELAT electrode at the same operation conditions. The research demonstrated that by simple variations in the sputter regime it is possible to optimise the catalysts morphology in order to increase the catalytic activity toward the electrochemical reaction of interest at the same time controlling precisely the required precious metal loading.     

A study of spalling behaviour of PAN fibre-reinforced concrete by thermal analysis

Comparisons are made between polypropylene (PP) fibres and polyacrylonitrile (PAN) fibres in order to relate the thermal properties of fibres with the respective fibre mortar behaviour under thermal exposure. Thermogravimetry (TG), differential scanning calorimetry (DSC) and thermochromatography (ThGC) are utilized. When a cementitious fibre mortar is being heated, several physical phenomena occur in the temperature range between 100°C and 200°C. There is a significant difference in the thermal behaviour between PP and PAN fibres. PP fibres melt at 160–170°C. The non-melting behaviour of PAN fibre together with its rapid exothermic degradation reactions at around 300°C may add risk to the spalling of fibre mortar under rapid thermal exposure.     

Preparation of 0.4Li2MnO3·0.6LiNi1/3Co1/3Mn1/3O2 with tunable morphologies via polyacrylonitrile as a template and applications in lithium‐ion batteries

Samples of 0.4Li₂MnO₃·0.6LiNi_1/3Co_1/3Mn_1/3O₂ (LMO) with tunable morphologies were synthesized via polyacrylonitrile (PAN) as a template. The starting PAN/N,N‐dimethylformamide (DMF) ratios, including 1:9, 1:10, 1:12, and 1:14, were optimized for the fiber morphologies and electrochemical performance. Through electrospinning, metal salts were well dispersed in the PAN fibers. The crystal structure and morphologies of the PAN/LMO fibers were characterized by X‐ray diffraction, scanning electron microscopy, and thermal analysis. Along with the decrease in the concentration of PAN in the precursor, the diameters of the PAN/LMO fibers decreased. On the other hand, at the highest and lowest concentrations, 1:9 and 1:14, of PAN with DMF, micrometer PAN fibers were electrospun, whereas ratios of PAN to DMF of 1:10 and 1:12 resulted in the electrospinning of millimeter‐long fibers of PAN. In the interface of PAN and metal salts, LMOs were grown and accompanied the decomposition of PAN, and the crystal morphologies of LMO quite depended on the diameter and length of the PAN/LMO nanofibers. During heat treatment, the morphologies of the PAN fibers controlled the removal of small molecules and the crystal morphologies of LMOs. The charge/discharge results indicate that LMO with a tubular structure delivered a capacity of 262.3 mAh/g at a cutoff voltage of 2.5–4.8 V at a 0.1 C rate. Benefitting from a unique hollow and nanocrystalline architecture, it also exhibited good rate and cycling performances. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43022.     

Preparation of conducting polyacrylonitrile/polypyrrole composite films by electrochemical synthesis and their electrical properties

Electrically conducting polyacrylonitrile (PAN)/polypyrrole (PPy) composite films were prepared by electrochemical polymerization of pyrrole in an insulating PAN matrix under various polymerization conditions and their electrical properties were studied. The conductivities of PAN/PPy composite films peeled off from the platinum electrode he lie in the range of 10^?2–10^?3 s/cm, depending on the preparation conditions: The conductivity increased with the concentrations of the electrolyte and the monomer, but it decreased with the polymerization temperature of pyrrole and the applied potential.     

Gel-spun carbon nanotubes/polyacrylonitrile composite fibers. Part II: Stabilization reaction kinetics and effect of gas environment

Gel-spun polyacrylonitrile (PAN) and carbon nanotube (CNT) composite fibers have been stabilized using various processing conditions to study the kinetics of stabilization reactions. Differential scanning calorimetry, infrared spectroscopy, wide angle X-ray diffraction and thermo-gravimetric analysis studies suggest that individual stabilization reactions can be separated at different stabilization stages when inert and oxidative environments are used in sequence. Among various stabilization reactions, it was found that the cross-linking has the highest activation energy, followed by cyclization and oxidation. The oxidation preferentially occurs with the cyclized structure and the shrinkage during stabilization is affected by the gaseous environment. The addition of CNTs reduces both entropic and reaction shrinkages, and improves the maximum tension that a fiber can bear during stabilization in both inert and oxidative environments.