A novel method for a high‐strength electrospun meta‐aramid nanofiber by microwave treatment

Electrospun nanofibers have attracted great attention as potential reinforcements in composite application due to their high specific surface area, high porosity, and versatility. Because the electrospun nanofibers exhibit relatively low mechanical strength due to low crystallinity and random alignment, many researchers have tried to enhance the mechanical strength through various approaches, such as heat treatment and fiber orientation control. These methods, however, are difficult to control and require the use of high temperatures and sophisticated apparatuses, and high costs. In this study, we investigate a novel microwave technique to fabricate high‐strength electrospun meta‐aramid nanofiber mats. To optimize the microwave irradiation conditions, the electrospun nanofiber was treated at varying levels of moisture and for different irradiation times. Field emission scanning electron microscopy was used to observe the surface morphology of the electrospun nanofiber mats at the different irradiation times. The changes in the crystallinity and thermal properties were investigated using X‐ray diffraction and thermogravimetric analysis measurements. Tensile tests were performed to measure the mechanical strength of the meta‐aramid nanofiber mats with respect to each parameter. As a result, any residual solvents and salts were removed, and the degree of crystallization was dramatically increased by microwave irradiation under wet conditions. These effects led to a 2.8‐fold increase in the tensile strength of the nanofiber mats compared with an untreated mat. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 807–814     

Calorimetric investigation of the interaction of carbon nanotubes with polystyrene

A simple, scalable procedure that does not require covalent modification of the filler or specialized high shear mixers is described for preparing well‐dispersed carbon nanotube composites. Excellent particle dispersions of multiple‐walled carbon nanotubes (NTs) and carbon black (CB) in polystyrene (PS) are obtained by coating the particles with a <2‐nm layer of PS adsorbed from dilute solution, prior to incorporation in the composite. Improved mechanical properties of composites containing coated particles, especially NT, are demonstrated by dynamic mechanical analysis at low frequency and low amplitude. Formation of a partially immobilized region of polymer surrounding the particles is quantified using flow microcalorimetry with ethyl acetate or methyl ethyl ketone vapor to measure the increase in solvation enthalpy in this region. This calorimetric method is applied to both composites and compacted powder mixtures of NT or CB with PS. The response of integral heat of vapor sorption as a function of particle loading in powder mixtures is similar to percolation curves reported for mechanical and electrical properties of composites. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1821–1834, 2006     

Carbonization of electrospun poly(acrylonitrile) nanofibers containing multiwalled carbon nanotubes observed by transmission electron microscope with in situ heating

Composite nanofibers with 5% w/w multiwalled carbon nanotubes (MWCNTs) in polyacrylonitrile (PAN) were fabricated using the electrospinning technique. Morphological development during the carbonization process was characterized by transmission electron microscopy (TEM) with in situ heating. It was found that the orientation of graphitic layers increases with temperature and does not change significantly with time during our TEM measurement, except the 750 °C. In the heating stage at 750 °C noticeable enhancement of orientation with time was observed. The presence of embedded CNTs enhances the order of the formed graphitic structures even when the CNTs are irregular or entangled. The results indicate that embedded MWCNTs in the PAN nanofibers nucleate the growth of carbon crystals during PAN carbonization. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Facile fabrication of novel polycaprolactone-based electrospun fibers using in-process water exposure

To overcome the problems related to the low surface enrichment of blended fibers from hydrophilic polymer, routine blend electrospinning setup was modified by exposing the polycaprolactone (PCL)–Pluronic P123 solution to water in order to attract the hydrophilic chains toward the fiber surface. Analysis of the modified fibers revealed a drastic surge of hydrophilic polymer surface enrichment value in comparison with that of the routine method which suggested homogenously positioned Pluronic on the surface and the subsequent reduction of its accumulations within fibers. The thermogram of the proposed method showed induced crystallization in the Pluronic section. Furthermore, the intensity of PCL characteristic peaks decreased for this method.     

Polypropylene/carbon nanotube magnetic composites obtained using carbon nanotubes from sawdust

Magnetic polypropylene (PP) nanocomposites with different loadings (from 0.5 to 20 wt %) of carbon nanotubes with iron (CNT‐Fe) were fabricated using the melt‐mixing method. The carbon nanotubes were synthesized by pyrolysis of sawdust from the furniture industry. The morphological characterization shows homogenous dispersion of the filler in the polymer matrix. The addition of only 0.5 wt % CNT‐Fe already results in ferromagnetic behavior in the diamagnetic polymer matrix. The thermal properties were investigated using thermogravimetric analysis and differential scanning calorimetry. The results show an increase in the maximum degradation, crystallization, and melting temperatures of the nanocomposites compared with neat PP. The nanocomposites showed improvement in terms of mechanical and oxygen permeability properties. A very significant result of the work is the high remnant magnetization and coercivity values of the nanocomposites at room temperature whereas most of the works on similar systems show magnetic properties only at very low temperatures.     

Singlewall carbon nanotubes covered with polystyrene nanoparticles by in‐situ miniemulsion polymerization

This work is to make carbon nanotubes dispersible in both water and organic solvents without oxidation and cutting nanotube threads. Polystyrene‐singlewall carbon nanotube (PS‐SWNT) composites were prepared with three different methods: miniemulsion polymerization, conventional emulsion polymerization, and mixing SWNT with PS latex. The two factors, crosslinking and surface coverage of PS are important factors for the mechanical and electrical properties, including dispersion states of SWNT in various solvents. The PS‐SWNT composite prepared via a conventional emulsion polymerization showed SWNT bundles entirely covered with PS, whereas the PS‐SWNT composite prepared via a miniemulsion polymerization showed SWNT partially covered with crosslinked PS nanoparticles. The method of mixing SWNTs with PS latex did not show the well dispersed state of carbon nanotubes because PS was not crosslinked and was dissolved in a solvent, and nanotubes separated from PS precipitated. So the PS nanoparticle‐SWNT composite had lower electrical resistance, and higher mechanical strength than the other composites made by the latter two methods. As the amount of SWNT increases, the bare surface area of SWNT increases and the electrical conductivity increases in the composite made by the miniemulsion polymerization. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 573–584, 2006     

Improved kinetics of ethanol oxidation on Pd catalysts supported on tungsten carbides/carbon nanotubes

Pd nanoparticles on tungsten carbides modified multiwalled carbon nanotubes (Pd-WC/MWCNT) catalysts have been prepared by an intermittent microwave heating (IMH) technique for the first time. The Pd-WC/MWCNT catalysts are evaluated and show an improved kinetics for the ethanol oxidation. It is recognized that the significant increase in the catalytic activity for ethanol oxidation on Pd-WC/MWCNT is attributed to both the synergistic effect between Pd nanoparticles and the WC support and the structure effect of the MWCNT. This type catalyst can be universally used as the oxygen reduction catalyst in fuel cells and sensors both in alkaline and acidic solutions.     

Studies on preparation of HDPE/CB composites including a novel oriented structure by the microwave heating and their characterization

Microwave heating has several advantages over traditional methods of heating, including rapid and uniform heating, greater penetration depth of heat into material, lower power costs and selective heating within the material and so on. In this paper, effects of microwave heating on the properties of high‐density polyethylene/carbon black (HDPE/CB) composites were studied. The results show that the HDPE/CB composites can be heated via microwave irradiation, and composites with different CB concentration exhibit different microwave heatability. The 20 wt% CB composites have the most rapid heating rate, and its temperature reaches 78°C after 10 sec, and 159°C after 150 sec, respectively. Meanwhile, microwave heating improves the mechanical properties of HDPE/CB composites. Scanning Electron Microscopy (SEM) analysis shows a better combination between CB particles and HDPE after microwave irradiation. Furthermore, selective heating of microwave was used to prepare a novel oriented structure, which the core layer has preferential orientation and the surface layer has little orientation. Characterization of the novel oriented structure was also studied. Wide angle X‐ray diffraction (WAXD) analysis of 25 wt% CB composites with the novel oriented structure shows that the diffraction peaks of the surface layer are obviously weaker than those of the core layer, which indicates that orientation in the core layer is more intensive than that in the surface layer. The novel oriented structure is different to the traditional skin‐core structure, in which the surface layer has preferential orientation and the core layer has little orientation. Copyright © 2009 John Wiley & Sons, Ltd.     

Structural responses of electrospun PVDF fibers induced by specific stretching and ensuing heating

Microstructure of electrospun fibers is often invoked to explain their properties but that is challenging to quantify properly. The electrospun PVDF fibers being rich in the β-phase crystal due to excellent piezoelectric properties are promising energy-harvesting materials for wearable and implantable applications. In this work, structural responses of electrospun PVDF fibers were investigated under the conditions of specific stretching at 25°C and ensuing heating from 25 to 170°C at strains of 5%, 10%, 20%, respectively, using the in situ WAXD with a thermos-mechanical coupled equipment. In this process, the fiber morphology, and the crystal orientation, the crystal structure, the β-phase content, as well as mechanical property of elctrospun PVDF fibers were studied. It is found that the specific stretching affects the β-phase crystal more than ensuing heating when the heating temperature is lower than the melting temperature of the fibers. Moreover, after 20% stretching and ensuing heating to 150°C, the tensile strength of electrospun PVDF fibers membrane can rise to 12.8 MPa, which is more than three times that of the pristine fibers, which is attributed to the higher crystal orientation and β-phase content, along with the alignment of the fibers. Therefore, structural responses of electrospun PVDF fibers induced by specific stretching and ensuing heating are propitious to explain and tailor their properties in practical applications, which also gives potential insights into other fibers.     

A novel method for the synthesis of polysubstituted diaminobenzonitrile derivatives using controlled microwave heating

A novel, simple and efficient method for the synthesis of polysubstituted diaminobenzonitriles has been developed that involves reaction of 1,1,3-tricyano-2-aminopropionitrile with nitroolefins under controlled microwave irradiation conditions.     

Removal of anionic and cationic dyes from wastewater by adsorption using multiwall carbon nanotubes

This paper evaluated the efficiency and reusability of multiwall carbon nanotubes (MWNTs) on removal of cationic and anionic dyes under effect of pH, dose of MWNTs and concentration of dyes. The characterization of MWNTs is characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), Raman spectra and BET (Brunauer, Emmett and Teller) surface area. SEM and TEM analyses showed that MWNTs had size within nano scale range of 10–50 nm. The experimental results indicated that the efficiency of removal of MWNTs increase under condition of normal pH, at contact time 60 min with agitation speed 240 rpm and initial concentration of dyes 10 mg/l. Under these optimal conditions, the removal reached 98.7% and 97.2% for anionic dyes and cationic dyes, respectively. For economic use, MWNTs can be used more than one time where the same experiments with the already used MWNTs was repeated and it was found that the percent removal is almost the same.     

In Situ polymerization functionalization of single‐walled carbon nanotubes with polystyrene

The in situ polymerization functionalization of single‐walled carbon nanotubes (SWNT) with polystyrene (PS) is demonstrated utilizing stabilized nanotubes reduced by dissolution of excess lithium in ammonia. Short PS chains are tethered to SWNT sidewalls to facilitate a robust compatibilization strategy for nanotube dispersion. To augment extents of functionalization, while maintaining in situ dispersion stability, the effects of multiple monomer addition steps and varied carbon to lithium ratio are studied. The developed functionalization scheme is also effective for the reductive alkylation of SWNT with dodecyl surface groups. By studying the dodecylated SWNT, the molecular weight of grafted PS chains is estimated. The discovery of a general experimental artifact has implications for all functionalization routes utilizing reduction with lithium in ammonia. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3716–3725     

Fundamental study of crystallization,orientation, and electrical conductivity of electrospun PET/carbon nanotube nanofibers

The morphology, structure, and properties of polyethylene terephthalate (PET)/Carbon Nanotubes (CNT) conductive nanoweb were studied in this article. Nanocomposite nanofibers were obtained through electrospinning of PET solutions in trifluoroacetic acid (TFA)/dichloromethane (DCM) containing different concentrations and types of CNTs. Electrical conductivity measurements on nanofiber mats showed an electrical percolation threshold around 2 wt % multi‐wall carbon nanotubes (MWCNT). The morphological analysis results showed smoother nanofibers with less bead structures development when using a rotating drum collector especially at high concentrations of CNTs. From crystallographic measurements, a higher degree of crystallinity was observed with increasing CNT concentrations above electrical percolation. Spectroscopy results showed that both PET and CNT orientation increased with the level of alignment of the nanofibers when the nanotube concentration was below the electrical percolation threshold; while the orientation factor was reduced for aligned nanofibers with higher content in CNT. Considerable enhancement in mechanical properties, especially tensile modulus, was found in aligned nanofibers; at least six times higher than the modulus of random nanofibers at concentrations below percolation. The effect of alignment on the mechanical properties was less important at higher concentrations of CNTs, above the percolation threshold. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2052–2064, 2010     

Electrochemistry of polystyrene intercalated vertically aligned single- and double-walled carbon nanotubes on gold electrodes

Electrochemical electrodes incorporating double- and single-walled carbon nanotubes (CNTs) were fabricated on cysteamine modified flat gold substrates. Through covalent coupling of the amine end groups with carboxyl functionalized CNTs, a dense forest of vertically aligned CNTs was produced. To these a 30 nm thick insulating polystyrene layer was spin coated, resulting in exposure of the uppermost carbon nanotube ends. The electrochemical performance of each electrode was then determined using the redox probe ruthenium hexaamine. Once surrounded by polymer, the double-walled CNTs (DWCNTs) showed an improved electron transfer rate, compared to the single-walled electrode. This improvement was attributed to the protection of the electronic properties of the inner wall of the DWCNT during the chemical modification and suggests that DWCNTs may offer a useful alternative to SWCNTs in future electrochemical sensors and biosensors.     

Electrically conducting electrospun silk membranes fabricated by adsorption of carbon nanotubes

We present a simple method of obtaining electrically conducting electrospun silk non-woven membranes consisting of nanofibers with multi-walled carbon nanotubes (MWCNTs) adsorbed on their surface. Nanofibrous membranes with fibroin diameters of 460 ± 40 nm were formed from aqueous Bombyx mori fibroin solution by electrospinning. The MWCNTs adhered well to the surface of the highly porous silk nanofibrous membranes when Triton X-100 was used as the surfactant for the dispersion of the MWCNTs in aqueous media. The electrical conductivity of the membranes was 2.4 × 10⁻⁴ S/cm due to the presence of the MWCNTs on their surface. In addition, the strong interaction between the MWCNTs and nanofibers keeps them from separating each other, even after ultrasonication. The combination of the high conductivity of the membranes and the simple process used to fabricate them could lead to significant advances in the development of new materials, such as electromagnetic interference shielding or electrostatic dissipation membranes.     

苯胺在碳纳米管上的吸附特征

苯胺是一种重要的有机化工原料,能通过皮肤和呼吸道进入人体而引起中毒,还会严重污染环境。目前,国内外处理含苯胺废水的方法主要有氧化法、萃取法、生化法、吸附法等。本文使用碳纳米管进行液相吸附除去苯胺。     

Selective adsorption of proteins on single-wall carbon nanotubes by using a protective surfactant

The dispersion of highly hydrophobic carbon materials such as carbon nanotubes in biological media is a challenging issue. Indeed, the nonspecific adsorption of proteins occurs readily when the nanotubes are introduced in biological media; therefore, a methodology to control adsorption is in high demand. To address this issue, we developed a bifunctional linker derived from pyrene that selectively enables or prevents the adsorption of proteins on single-wall carbon nanotubes (SWNTs). We demonstrated that it is possible to decrease or completely suppress the adsorption of proteins on the nanotube sidewall by using proper functionalization (either covalent or noncovalent). By subsequently activating the functional groups on the nanotube derivatives, protein adsorption can be recovered and, therefore, controlled. Our approach is simple, straightforward, and potentially suitable for other biomolecules that contain thio or amino groups available for coupling.     

Cytotoxicity of carbon nanotubes

With large-scale production and application at large scale, carbon nanotubes (CNTs) may cause ad-verse response to the environment and human health. Thus, study on bio-effects and safety of CNTs has attracted great attention from scientists and governments worldwide. This report briefly summa-rizes the main results from the in vitro toxicity study of CNTs. The emphasis is placed on the descrip-tion of a variety of factors affecting CNTs cytotoxicity, including species of CNTs, impurities contained, lengths of CNTs, aspect ratios, chemical modification, and assaying methods of cytotoxicity. However, experimental information obtained thus far on CNTs' cytotoxicity is lacking in comparability, and some-times there is controversy about it. In order to assess more accurately the potential risks of CNTs to human health, we suggest that care should be taken for issues such as chemical modification and quantitative characterization of CNTs in cytotoxicity assessment. More importantly, studies on physical and chemical mechanisms of CNTs' cytotoxicity should be strengthened; assaying methods and evaluating criteria characterized by nanotoxicology should be gradually established.     

Covalent surface functionalization of multiwalled carbon nanotubes through bergman cyclization of enediyne‐containing dendrimers

A method for covalent functionalization of multiwalled carbon nanotubes (MWCNTs) was developed using the free radicals generated through Bergman cyclization of enediyne‐containing compounds. Four enediyne‐bearing Frechet type dendrimers were synthesized in good quantities and characterized. Then, the enediyne‐containing molecules were reacted with MWCNTs in N‐methyl‐2‐pyrrolidinone at 206 °C under nitrogen. The structure and morphology of the resulting products were characterized by thermogravimetric analysis, ultraviolet–visible spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, and transmission electron microscopy. The dendrimer‐functionalized MWCNTs showed good solubility/dispersibility in common organic solvents and polymer solutions. They were used in the formation of polymer composites through electrospinning with polycaprolactone. The results confirmed the surface functionalization of MWCNTs. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011