Development of electrospun metallic hybrid nanofibers via metallization

The metallized hybrid nanofiber webs were prepared by using a combined technology of electrostatic spinning and metallization. The electrospun polyurethane (PU) nanofibers were metallized with different thicknesses of copper layer via metal vapor deposition technique. The thickness of the copper layer, which ranges from 10 to 100 nm, was monitored and controlled. The resultant metallized hybrid nanofiber webs were characterized using field emission scanning electron microscopy (FE‐SEM), wide angle X‐ray diffraction (WAXD), and thermogravimetric analysis (TGA). FE‐SEM images demonstrated that the nanoscaled copper layers are well deposited on the surface of the PU nanofibers. TGA result indicated that the thermal stability of the metallized hybrid PU nanofibers was dramatically enhanced due to the barrier effects of thin metallic copper layer. WAXD data confirmed that the crystalline copper layers were well deposited onto the PU nanofibers. Moreover, the mechanical properties of the metallized hybrid PU nanofiber webs were increased with increase in the thickness of deposited copper layer. Unlike the organic PU nanofiber webs, it was observed that the metallized hybrid PU nanofiber webs showed higher conductive properties depending on the thickness of the deposited copper layer. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis and characterization of sol–gel alumina nanofibers

Abstract Alumina nanofibers of high aspect ratio with surface area of >300 m² g⁻¹ has been prepared successfully in bulk quantities by the sol–gel method. The synthesis parameters including the binary water–alcohol solvent system to aluminium isopropoxide ratio, pH, type of solvent and aging temperature affect the uniformity and formation of nanofibers. It is proposed that alumina nanofibers were formed by the curling of the nanosheets upon condensation after the hydrolysis. The phase evolution of alumina nanofibers from pseudoboehmite to α phase has been shown by XRD and FTIR. ²⁷Al NMR investigations show that the Al atoms are six and four coordinated. The morphology of the alumina nanofibers does not change much as the calcination temperature was increased. In addition, the average pore size increases and the BET surface area decreases as a function of calcination temperature. The thermal behavior of alumina nanofibers was investigated by TGA. Graphical Abstract      

Spectroscopic investigations on polypropylene‐carbon nanofiber composites. I. Raman and electron spin resonance spectroscopy

Isotactic polypropylene‐vapor grown carbon nanofiber composites containing various fractions of carbon nanofibers, ranging from 0 to 20 wt %, have been prepared. Raman spectroscopy was used to analyze the effect of the dispersion of carbon nanofibers within polypropylene and the interactions between carbon nanofibers and macromolecular chains. The as‐recorded Raman spectra have been successfully fitted by a linear convolution of Lorentzian lines. Changes of the Raman lines parameters (position, intensity, width, and area) of polypropylene and carbon nanofibers were analyzed in detail. The Raman spectra of the polymeric matrix—at low concentrations of nanofibers—show important modifications that indicate strong interactions between carbon nanofibers and the polymeric matrix reflecting by vibrational dephasing of macromolecular chains. The Raman spectrum of carbon nanofibers is sensitive to the loading with carbon nanofibers, showing changes of the resonance frequencies, amplitudes, and width for both D‐ and G‐bands. Raman data reveals the increase of the disorder, as the concentration of carbon nanofibers is increased. The presence of the typical ESR line assigned to conducting electrons delocalized over carbon nanofibers is confirmed and the presence of a spurious magnetic line due to catalyst's residues is reported. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1644–1652, 2009     

Flame retardant polypropylene through the joint action of sepiolite and polyamide 6

The influence of the incorporation of polyamide-6 (PA) and natural sepiolite nanoparticles on both the thermal degradation and fire behaviour of polypropylene (PP) matrix has been investigated by thermogravimetric analysis (TGA) and mass loss calorimetry. For that purpose, PP/PA blends and nanocomposites thereof were prepared by melt processing. TGA results evidenced that the use of maleic anhydride grafted-polypropylene (MA-g-PP) as compatibilizer led to a significant improvement in thermal stability under air. Such improvement was linked to the formation of a char layer preventing the thermo-oxidative degradation of PP. Interestingly, the thermal resistance of this char layer was further improved by adding 5 wt% of natural sepiolite leading to important increase of time to ignition and reduction of peak of heat release rate (pHRR) during mass loss calorimeter test.     

Morphology,thermal stability,and flammability of polymer matrix composites coated with hybrid nanopapers

In this study, a hybrid nanopaper consisting of carbon nanofiber (CNF) and polyhedral oligomeric silsequioxane (POSS) or cloisite Na⁺ clay, has been fabricated through the papermaking process. The hybrid nanopaper was then coated on the surface of glass fiber (GF) reinforced polymer matrix composites through resin transfer molding (RTM) process. The morphologies of the hybrid nanopaper and resulting nanocomposites were characterized with scanning electron microscopy (SEM). It can be seen that the nanopaper had a porous structure with highly entangled carbon nanofibers and the polyester resin completely penetrated the nanopaper throughout the thickness. The thermal decomposition behavior of the hybrid nanopapers and nanocomposites was studied with the real‐time thermogravimetric analysis/ flourier transform infrared spectrometry (TGA/FTIR). The test results indicate that the addition of pristine nanoclay increased the thermal stability of the nanopaper, whereas the POSS particles decreased the thermal stability of the nanopaper. The fire retardant performance of composite laminates coated with the hybrid nanopaper was evaluated with cone calorimeter tests using a radiated heat flux of 50 kW/m². The cone calorimeter test results indicate that the peak heat release rate (PHRR) decreased dramatically in composite laminates coated with the CNF‐clay nanopaper. However, the PHRRs of the CNF‐POSS nanopaper coated composite laminates increased. The formation of compact char materials was observed on the surface of the residues of the CNF‐clay nanopaper after cone calorimeter test. The flame retardant mechanisms of the hybrid nanopaper in the composite laminates are discussed. Copyright © 2009 John Wiley & Sons, Ltd.     

Flammability and Thermal Oxidative Degradation Kinetics of Magnesium Hydroxide and Expandable Graphite Flame Retarded Polypropylene Composites

The flammability and the thermal oxidative degradation kinetics of expandable graphite (EG) with magnesium hydroxide (MH) in flame‐retardant polypropylene (PP) composites were studied by limiting oxygen index (LOI), UL‐94 test, and thermogravimetric analysis (TGA). The results show that EG is a good synergist for improving the flame retardancy of PP/MH composite and the effect is enhanced with decreasing EG particle size. The Kissinger method and Flynn‐Wall‐Ozawa method were used to determine the apparent activation energy (E) for degradation of PP and flame retarded PP composites. The data obtained from the TGA curve indicate that EG markedly increases the thermal degradation temperature of PP/MH composites and improves the thermal stability of the composites. The kinetic results show that the values of E for degradation of flame retarded PP composites is much higher than that of neat PP, especially PP/MH composites with suitable amount of EG, which indicates that the flame retardants used in this work have a great effect on the mechanisms of pyrolysis and combustion of PP.     

Thermal Degradation Behavior and Kinetic Analysis of Ultra High Molecular Weight Polyethylene Based Multi-Walled Carbon Nanotube Nanocomposites Prepared Via in-situ Polymerization

Thermal degradation behavior of multi-wall carbon nanotubes (MWCNTs)/ultra high molecular weight polyethylene (UHMWPE) nanocomposites, with different nanotubes contents (0.5, 1.5 and 3.5 wt%) prepared via in-situ polymerization technique have been investigated using thermal gravimetric analysis (TGA). TGA spectra revealed that these nanocomposites had enhanced thermal stability and no significant mass loss (<0.4 wt%) occurred up to 350°C. Thermal degradation of these UHMWPE/MWCNT nanocomposites was investigated in terms of parameters such as the onset temperature of degradation (T₁₀), the decomposition temperature at 50% wt loss (T₅₀), the degradation temperature of maximum rate of the weight loss (T_m), and the residual yields (W_R) from TGA. The degradation activation energies (E) of virgin UHMWPE and its nanocomposites were estimated using the Friedman, the Ozawa, Flynn, and Wall (OFW), and the Kissinger's methods. Results indicated that the degradation activation energy for the virgin UHMWPE was 281.3 kJ/mol. The activation energy increased with increasing nanotube loading up to 1.5 wt% indicating that MWCNTs had a stabilizing effect on the degradation of the matrix. However, loadings of 3.5 wt% of nanotube or more could slightly decrease the activation energy. The decrease in the activation energy for degradation of nanocomposites with higher MWCNT concentrations might be attributed to the catalytic effects of nanotubes and polymerization catalyst residues. The “model fitting” method indicated a mechanism of n ^th-order auto-catalysis from the form of the conversion curves for UHMWPE/MWCNTs nanocomposites prepared via in-situ polymerization.     

A quantitative study of carbon monoxide and carbon dioxide evolution during thermal degradation of flame retarded epoxy resins

Thermogravimetric analysis (TGA) combined with infrared analysis of the evolved gases analysis (EGA) has been used to study the thermal degradation behaviour of epoxy resin both in air and nitrogen. The mass loss as a function of temperature has been correlated with the evolution of carbon monoxide (CO) and carbon dioxide (CO₂), and oxygen consumption as measured using an oxygen analyser. An analytical technique has been developed to quantitatively measure the carbon monoxide and dioxide gases evolved. The effect of a range of flame retardants containing phosphorus, nitrogen and halogen elements on CO and CO₂ evolution during thermal degradation of flame retarded epoxy resins has also been observed.     

Effect of reaction conditions on film morphology of polyaniline composite membranes for gas separation

Composite membranes combining polyaniline as an active layer with a polypropylene support have been prepared using an in situ deposition technique. The protonated polyaniline layer with a thickness in the range of 90–200 nm was prepared using precipitation, dispersion, or emulsion polymerization of aniline with simultaneous deposition on top of the porous polypropylene support, which was immersed in the reaction mixture. Variables such as temperature, concentration of reagents, presence of steric stabilizers, surfactants, and heteropolyacid were found to control both the formation and the quality of the polyaniline layers. Both morphology and thickness of the layers were characterized using scanning electron microscopy. Selective separation of carbon dioxide from its mixture with methane is used to illustrate potential application of these composite membranes. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Chemical catalysed recycling of polypropylene over a spent FCC catalyst and various commercial cracking catalysts using TGA

Thermogravimetric analysis (TGA) has been used as a tool to characterise the activity, regenerability and deactivation behaviour of spent FCC commercial catalyst (FCC-s1) in the degradation of polypropylene. The FCC-s1 catalysts and amorphous silica–alumina (SAHA) significantly reduced the activation energy as compared with thermal process, and zeolites (ZSM-5 and HUSY) further reduced the activation energy. However, silicalite catalysts gave very minimal effect on PP degradation at a temperature similar to that of thermal cracking. Analysis of the TGA results allowed a relationship between catalyst activity and coke content to be derived. The activity of FCC-s1 catalysts was found to fall exponentially with coke content, and it could be recover most its initial value. The results represent an interesting alternative to have significant impact on the economics of a catalytic polymer degradation process employing post-use FCC commercial catalysts of zero market value.     

Non-successive degradation in bulk-type all-solid-state lithium battery with rigid interfacial contact

Bulk-type all-solid-state lithium battery adopting garnet structured electrolyte has been successfully realized by improving the state of interface contact between cathode/electrolyte, as well as cathode particles in the composite layer. The cycle life of the battery has been examined at room temperature, and at elevated temperature of 80 ^°C and 150 ^°C. It exhibits that under high tested current density, the cell exhibits non-successive degradation during cycling, whereas successive degradation under low current density. Impedance spectroscopy measurements, as well as cross-sectional SEM images have been used to complement the electrochemical data in examining structural changes. The results indicate that the destructive damage of cracks originated from the volume change of LiCoO₂ particles in the composite layer is responsible for the non-successive degradation of cell during cycling.     

Study of the thermal properties of polyester composites loaded with oriented carbon nanofibers using the front-face flash method

In this work, we have prepared polyester resin based composites, loaded with carbon nanofibers decorated with magnetite nanoparticles (m-CNF) in several volumetric concentrations covering from 0 to 3.25% and oriented applying a constant magnetic field before polymerization. A study of the heat transfer along the direction of the alignment of the fibers was performed by measuring the in-depth thermal diffusivity and thermal effusivity using the laser flash method in the front-face configuration. For the maximum volumetric concentration of aligned nanofibers along the thickness of the sample, an improvement of 80% of the thermal conductivity above the thermal conductivity of the polyester resin was observed. In contrast, the increment of the thermal conductivity was only of 20% above the value of the matrix for samples with non-oriented carbon nanofibers. The effects of the m-CNF and their orientation on the effective thermal conductivity of the composites were analyzed using a simple theoretical model, which takes into account the thermal mismatch between the matrix and the fillers, as well as the aspect ratio of the embedded fibers.     

Design of aluminum trihydroxide and P‐N core‐shell structures and their synergistic effects on halogen‐free flame‐retardant polyethylene composites

In order to improve the performance of inorganic/organic composites, aluminum trihydroxide (ATH) core composites with a styrene‐ethylene‐butadiene‐styrene block copolymer grafted with maleic anhydride (MAH‐g‐SEBS) shell phase, and P‐N flame retardant as a synergistic agent, were prepared through an interface design. The effects of polyethylene glycol (PEG) content on the interfacial interaction, flame retardancy, thermal properties, and mechanical properties of high‐density polyethylene (HDPE)/ATH composites were investigated by small angle X‐ray diffraction, rotational rheometer, limiting oxygen index, thermogravimetric analysis (TGA), and tensile testing. The ATH synergistic effects of P‐N flame‐retardant improved the combustion performance of HDPE/ATH/PEG(3%)/MAH‐g‐SEBS/P‐N (abbreviated as HDPE/MH3/M‐g‐S/P‐N) composite by forming more carbon layer, increased the elongation at break from 21% to 558% compared to HDPE/ATH, and increased the interface thickness from 0.447 to 0.891 nm. SEM results support the compatibility of ATH with HDPE increased and the interfacial effect was enhanced. TGA showed the maximum decomposition temperature of the two stages and the yield of the residue at high temperature increased first and then decreased with the increase of PEG content. Rheological behavior showed the storage modulus, complex viscosity, and the relaxation time initially increased and then decreased with the increase of PEG content indicating PEG, M‐g‐S, and ATH powder gradually formed a partial coating, then a full coating, and finally an over‐coated core‐shell structured model.     

一步法溶剂热催化合成纳米碳纤维

利用四氢呋喃为溶剂和碳源,通过溶剂热催化方法在500 ℃一步合成了纳米碳纤维,X-射线衍射（XRD）分析显示此法合成的碳纤维晶型为碳的六方石墨相,场发射电镜(FESEM)和透射电镜(TEM)照片进一步表明碳纤维平均直径为100 nm,长度达几百纳米至几微米,高分辨电镜照片揭示产品中碳的晶间距为0.34 nm;产品纯度通过热重法（TGA）分析;同时,拉曼光谱图显示在1 347和1 584 cm^-1处有2个强峰,这与石墨相碳的典型拉曼光谱图是一致的。     

γ-Ray-induced grafting of DMAEMA and AAc onto PP by two step method

Binary graft copolymerization of thermosensitive 2-(dimethylamino) ethyl methacrylate (DMAEMA) and pH sensitive acrylic acid (AAc) monomers onto polypropylene (PP) films was carried out by a two step method using a ⁶⁰Co gamma radiation source. The PP film was initially modified by grafting of DMAEMA through a direct method. The DMAEMA-g-PP film obtained was then subjected to radiation grafting of AAc by the pre-irradiation method to give (DMAEMA-g-PP)-g-AAc. The optimal conditions, such as reaction time, reaction temperature, monomer concentration, and dose were studied. The grafted samples were verified by the FTIR-ATR spectroscopy and swelling; thermal properties were analyzed by DSC and TGA.     

Synthesis and characterisation of novel functional polyolefin containing sulfonic acid groups

The strong polar group, sulfonic acid, has successfully been introduced into ethylene/allylbenzene copolymers without degradation or crosslinking via chlorosulfonation reaction with chlorosulfonic acid as a chlorosulfonating agent in 1,1,2,2-tetrachloroethane followed by hydrolysis. The degree of sulfonation (DS) can be easily controlled by changing the ratio of chlorosulfonic acid to the pendant phenyls of the copolymer. The microstructure of sulfonated copolymers were unambiguously revealed by ¹H NMR and ¹H-¹H COSY spectral analyses, which indicates that all the sulfonation reactions exclusively took place at the para-position of the aromatic rings. The thermal behaviors were studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). DSC data exhibit a systematic trend of melting temperature increasing with DS. TGA data of sulfonated copolymers show an increase in degradation temperature from 444 to 460 °C compared to the received copolymer. Sulfonated copolymers also show an additional minor loss of mass at approximately 261 °C, which is not observed in the received copolymer. The wetting properties of the sulfonated copolymers were also evaluated by contact angle measurement, and a notable increase in surface hydrophilicity was identified.     

Thermal degradation behaviors of a novel nanocomposite based on polypropylene and Co-Al layered double hydroxide

The thermal degradation behaviors of a novel nanocomposite based on polypropylene and organic Co/Al layered double hydroxide (PP/CoAl-LDH) were studied via thermogravimetric analysis (TGA) in the present work. The thermal degradation activation energies of the PP/CoAl-LDH nanocomposite were determined via Friedman and Flynn-Wall-Ozawa methods, and were compared with those of neat PP. The relationship between the organic CoAl-LDH concentration and the activation energies in PP/CoAl-LDH nanocomposite also has been investigated. An internal reason and an outer reason leading to high fire retardancy of PP/CoAl-LDH nanocomposite were proposed. The presence of CoAl-LDH tended to increase significantly the decomposition activation energy of nanocomposite at full-scale temperature and had an important influence on both of internal and outer reasons.     

Effect of compatibilizer and Irganox MD 1024 on the thermo-oxidative stability of PP/PP-g-MA/OMMT nanocomposites

The thermo-oxidative stability of polymeric materials reinforced with mineral fillers, such as clays, may be lower than that of pristine polymers, due to the presence of metallic ions and compatibilizing agents. In this paper, an effort was made to understand the influence that a compatibilizing agent and a metal deactivator bonded to a primary stabilizer has on the thermal stability of polypropylene/polypropylene-grafted maleic anhydride/organic montmorillonite (PP/PP-g-MA/OMMT) nanocomposites. At the first stage of this work, the organically modified montmorillonite clay is chemically analyzed by Inductively Coupled Plasma Atomic Emission Spectrometry to quantify the metals present in the clay. TGA, DSC, OIT, and dynamic OIT were used to assess the degradation of the nanocomposites. The results showed that the use of compatibilizing agents has a positive effect on the stability of nanocomposites in the initial steps of degradation, but has a degradative effect at higher temperatures, as indicated by the decreasing T_max for compatibilized nanocomposites. In relation to Irganox MD 1024, an increase in all the parameters for assessing the stability of nanocomposites was observed; however, the most significant change was the delay in the temperature at which the occurrence of exothermal reactions begins. Use of this additive is responsible for delaying the beginning of the exothermic reaction until a higher temperature, as a function of its concentration, as well the differences between the beginning of volatile release and the exothermal reactions. Also was discussed the influence of Irganox MD1024 concentration on T_max, and the difference of temperature between the beginning of heat releasing and the initial weight loss, which decreases as the stabilizer concentration is increased. Thanks to the association of dynamic OIT and TGA results from experiments performed with identical conditions. This complementary use of these techniques is a powerful tool for assessing the stability in the polymeric system.     

Influence of MWCNT morphology on dispersion and thermal properties of polyethylene nanocomposites

In this study a series of multi-walled carbon nanotube (MWCNT)/Polyethylene (PE) composites with different kinds and several concentrations of carbon nanotubes (CNTs) were investigated. The morphology and degree of dispersion of the fillers in the polymer matrix at different length scales was investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Both individual and agglomerated MWCNTs were evident but a good dispersion was observed for some of them. TGA measurements were performed on nanocomposites in order to understand if CNTs affect the stabilization mechanism during thermal and oxidative degradation. The analysis demonstrates that MWCNTs presence slightly delays thermal volatilisation (15-20 °C) without modification of thermal degradation mechanism. In contrast, thermal oxidative degradation in air is delayed up to about 100 °C dependently from MWCNTs concentration, in the range used here (0.1-2.0 wt%), and degree of dispersion. The stabilization is due to the formation of a thin protective layer of entangled MWCNTs kept together by carbon char generated on the surface of the nanocomposites as shown by SEM images taken on degradation residues.     

Ultra-low platinum loading high-performance PEMFCs using buckypaper-supported electrodes

The microstructure of the catalyst layer in proton exchange membrane fuel cells (PEMFCs) greatly influences catalyst (Pt) utilization and cell performance. We demonstrated a functionally graded catalyst layer based on a double-layered carbon nanotube/nanofiber film- (buckypaper) supported Pt composite catalyst to approach an idealized microstructure. The gradient distribution of Pt, electrolyte and porosity along the thickness effectively depresses the transport resistance of proton and gas. A rated power of 0.88 W/cm² at 0.65 V was achieved at 80 °C with a low Pt loading of 0.11 mg/cm² resulting in a relatively high Pt utilization of 0.18g_Pt/kW. The accelerated degradation test of catalyst support showed a good durability of buckypaper support because of the high graphitization degree of carbon nanofibers.