Multi walled carbon nanotubes induced viscoelastic response of polypropylene copolymer nanocomposites: Effect of filler loading on rheological percolation

Polypropylene random copolymer nanocomposites having 0.2–7.0 vol% multi-walled carbon nanotubes (MWCNTs) were prepared via melt processing. Transmission electron microscopy (TEM) was employed to determine the nano scale dispersion of carbon nanotubes. Linear viscoelastic behavior of these nanocomposites was investigated using parallel plate rheometry. Incorporation of carbon nanotubes in the polymer matrix resulted in higher complex viscosity (η*), storage (G′) and loss modulus (G″) as compared to neat polymer, especially in the low-frequency region, suggesting a change from liquid to solid-like behavior in the nanocomposites. By plotting storage modulus vs. carbon nanotube loading and fitting with a power law function, the rheological percolation threshold in these nanocomposites was observed at a loading of ∼0.27 vol% of MWCNTs. However, electrical percolation threshold was reported at ∼0.19 vol% of MWCNTs loading. The difference in the percolation thresholds is understood in terms of nanotube connectivity with nanotubes and polymer chain required for electrical conductivity and rheological percolation.     

Effect of different nanoparticles on HDPE UV stability

In the present study different series of HDPE nanocomposites were prepared by melt mixing on a Haake-Buchler Reomixer, containing 2.5 wt% of multiwall carbon nanotubes, pristine and modified montmorillonite, and SiO₂ nanoparticles. Nanocomposites in the form of thin films were exposed to UV irradiation at 280 nm at constant temperature (25 °C) and constant relative humidity (50%) for several times. From tensile strength and Young’s Modulus measurements it was verified a high increase with initial UV irradiation times (till 100 h) and a slight reduction thereafter. The increase was higher in nanocomposites compared with neat HDPE, except these containing MWCNTs, and was attributed to the crystallinity increase in the particular samples. The mechanical properties reduction at higher UV irradiation times was attributed to the extensive macromolecular chain scission causing irregularities and holes in film surfaces. However, from FTIR study it was found that SiO₂ and organically modified montmorillonite cause a serious effect on HDPE during UV degradation. New chemical compounds containing carbonyl, vinyl and hydroxyl groups were formed. It seems that these nanoparticles have an accelerating effect acting as catalysts to HDPE photo-oxidation. This was also verified from micro-Raman analysis. Untreated montmorillonite has also a small influencing effect while neat HDPE and nanocomposites containing multiwall carbon nanotubes have the highest UV stability.     

Synthesis of Pt and Pt-Fe nanoparticles supported on MWCNTs used as electrocatalysts in the methanol oxidation reaction

This work reports a feasible synthesis of highly-dispersed Pt and Pt-Fe nanoparticles supported on multiwall carbon nanotubes （MWCNTs） without Fe and multiwall carbon nanotubes with iron （MWCNTs-Fe） which applied as electrocatalysts for methanol electrooxidation. A Pt coordination complex salt was synthesized in an aqueous solution and it was used as precursor to prepare Pt/MWCNTs, Pt/MWCNTs-Fe, and Pt-Fe/MWCNTs using FeC12.4H20 as iron source which were named S 1, S2 and S3, respectively. The coordination complex of platinum （TOA）2PtC16 was obtained by the chemical reaction between （NH4）2PtC16 with tetraoctylammonium bromide （TOAB） and it was characterized by FT-IR and TGA. The materials were characterized by Raman spectroscopy, SEM, EDS, XRD, TEM and TGA. The electrocatalytic activity of Pt-based supported on MWCNTs in the methanol oxidation was investigated by cyclic voltammetry （CV） and chronoamperometry （CA）. Pt-Fe/MWCNTs electrocatalysts showed the highest electrocatalytic activity and stability among the tested electrocatalysts due to that the addition of ＂Fe＂ promotes the OH species adsorption on the electrocatalyst surface at low potentials, thus, enhancing the activity toward the methanol oxidation reaction （MOR）.     

Properties of matrix-grafted multi-walled carbon nanotube/poly(methyl methacrylate) nanocomposites synthesized by in situ reversible addition-fragmentation chain transfer polymerization

Multi-walled carbon nanotubes (MWCNT)/poly(methyl methacrylate) (PMMA) nanocomposites were synthesized by the in situ reversible addition-fragmentation chain transfer (RAFT) polymerization of methyl methacrylate (MMA) in the presence of MWCNTs, at which the bulk polymer was grafted onto the surface of nanotubes through the ??grafting through?? strategy. For this purpose, MWCNTs were formerly functionalized with polymerizable MMA groups. MMA and PMMA-grafted MWCNTs were characterized by Fourier-transform infrared spectroscopy, Raman, X-ray photoelectron spectroscopy, transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). Dissolution of nanotubes was examined in chloroform solvent and studied by UV?Cvis spectroscopy. Thermogravimetric and degradation behavior of prepared nanocomposites was investigated by TGA. MWCNTs had a noticeable boosting effect on the thermal stability of nanocomposites. TGA thermograms showed a two-step weight loss pattern for the degradation of MWCNT-PMMA/PMMA nanocomposites which is contrast with neat PMMA. Introduction of MWCNTs also improved the dynamic mechanical behavior and electrical conductivity of nanocomposites. TEM micrograph of nanocomposite revealed that the applied methods for functionalization of nanotubes and in situ synthesis of nanocomposites were comparatively successful in dispersing the MWCNTs in PMMA matrix.     

Fluorescent probe for Fe(III) based on pyrene grafted multiwalled carbon nanotubes by click reaction

The attempt to decorate carbon nanotubes with organic molecules to form new functional materials has attracted broad attention in the scientific community. Here, we report the covalent functionalization of multiwalled carbon nanotubes (MWCNTs) with pyrene via Cu(I)-catalysed azide/alkyne click (CuAAC) reactions under mild conditions to afford the nanocomposites of pyrene-MWCNTs. Fourier transform infrared spectroscopy (FT-IR), ultraviolet and visible spectroscopy (UV-Vis), and fluorescence spectroscopy were used to characterize the nanocomposites of pyrene clicked MWCNTs. Experimental results indicate that the CuAAC reaction occurs in an efficient manner and the spacer linking MWCNTs and the photoactive molecule is well defined. In contrast to the noncovalent functionalization of π-π stacking, the nanocomposites of pyrene clicked MWCNTs show relatively strong fluorescence and have potential applicability in photoluminescent devices as a highly sensitive and selective fluorescence "turn-off" sensor for Fe(3+).     

Carbon Nanotubes: An Example of Multiscale Development—A Mechanistic View from the Subnanometer to the Meter Scale

We summarize the catalytic synthesis of multiwall carbon nanotubes (MWCNTs). The current understanding of the reaction mechanism is presented, in particular the catalyst design for the CCVD process is analyzed. To complement that, kinetics and reaction engineering aspects are discussed along with the impact of the reaction and reactor operation on the product properties. All these issues are analyzed from the perspective of the industrial synthesis and implications for the application of carbon nanotubes. Carbon‐nanotube technology is a perfect example of multi‐scale development and covers challenges from the nanometer to the meter scale. Problems, methods, and solutions characteristic for different scales will be highlighted. The Co/Mn catalyst is used as reference as one of the first commercially used technologies for the scalable production of multiwall carbon nanotubes.     

Preparation of multiwall carbon nanotubes (MWCNTs) stabilised by highly branched hydrocarbon surfactants and dispersed in natural rubber latex nanocomposites

The performance of single-, double- and triple-chain anionic sulphosuccinate surfactants for dispersing multiwall carbon nanotubes (MWNCTs) in natural rubber latex (NR-latex) was studied using a range of techniques, including field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and Raman spectroscopy. The conductivities of the nanocomposites were also investigated using four-point probe measurements. Here, MWCNTs were efficiently dispersed in NR-latex with the aid of hyperbranched tri-chain sulphosuccinate anionic surfactants, specifically sodium 1,4-bis(neopentyloxy)-3-(neopentyloxycarbonyl)-1,4-dioxobutane-2-sulphonate (TC14). This paper highlights that TC14 performs much better than that of the commercially available surfactant sodium dodecyl sulphate (SDS), demonstrating how careful consideration of surfactant architecture leads to improved dispersibility of MWCNTs in NR-latex. The results should be of significant interest for improving nanowiring applications suitable for aerospace-based technology.     

Removal of oxidation debris from multi-walled carbon nanotubes

Conventional liquid phase oxidation of multiwall carbon nanotubes (MWCNTs) using concentrated acids generates contaminating debris that should be removed using aqueous base before further reaction.     

Confinement crystallization of poly(l-lactide) induced by multiwalled carbon nanotubes and graphene nanosheets

Journal of Thermal Analysis and Calorimetry - Two sets of multiwalled carbon nanotubes (MWCNTs)/PLLA nanocomposites and graphene nanosheets (GNSs)/PLLA nanocomposites with various MWCNTs and GNSs...     

Influence of multiwall carbon nanotubes on morphological and structural changes during UV irradiation of syndiotactic polypropylene films

The effect of UV irradiation on the morphology and structure of syndiotactic polypropylene (sPP) is investigated both for pure films and those filled with multiwall carbon nanotubes (MWCNTs). UV treatment causes a structural reorganization of pure sPP films. It seems that the incorporation of MWCNTs has a strong stabilizing effect, with nanotubes acting as a limiter of the UV‐induced chain breakage, especially when a good dispersion of carbon nanotubes in the polymer is achieved. The incorporation of MWCNTs introduces a high concentration of defects in the crystal structure of sPP, which limits the UV‐induced growth of crystallites, and prevents the development and propagation of cracks caused by UV irradiation. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Bulk synthesis of linear carbon chains confined inside single-wall carbon nanotubes by vacuum discharge

Carbyne, an infinite carbon chain, has attracted much interest and induced significant controversy for many decades. Recently, the presence of linear carbon chains (LCCs), which were confined stably inside double-wall carbon nanotubes (DWCNTs) and multiwall carbon nanotubes (MWCNTs), has been reported. In this study, we present a novel method to produce LCCs in a film of carbon nanotubes (CNTs). Our transmission electron microscopy and Raman spectroscopy revealed the formation of a bulk amount of LCCs after electric discharge of CNT films, which were used as field emission cathodes. The LCCs were confined inside single-wall CNTs as well as DWCNTs. Furthermore, two or three LCCs in parallel with each other are encapsulated when the inner diameter of CNT is larger than approximately 1.1 nm.     

Thermal behavior of multiwall carbon nanotube/zeolite nanocomposites

Summary In this study we report the synthesis and thermal characterization of multiwall carbon nanotubes containing zeolite based nanocomposites. Three different zeolites (LTA, FAU and MFI) were used in this study and it was observed that the morphologies of the synthesized nanocomposites were significantly different. For FAU zeolite nanocrystals with a few nm in diameter were nucleated on the nanotubes covering their surface, however, for LTA and MFI zeolites bulky crystals with nanotubes crossing them were observed by transmission electron microscopy. One of the most important results of our study was the generation of secondary mesoporosity in the zeolites after removing the carbon nanotubes.     

Confirmation of a nanohybrid shish‐kebab (NHSK) structure in composites of PET and MWCNTs

Here, the confirmation of an oriented nanohybrid shish‐kebab (NHSK) crystalline structure in a series of composites of poly(ethylene terephthalate) (PET) and multiwall carbon nanotubes (MWCNTs) is reported. The combined use of small‐ and wide‐angle X‐ray scattering (SAXS/WAXS) and thermal analysis has been used to investigate the morphology development in PET‐MWCNT nanocomposites under hot isothermal crystallization conditions. The MWCNTs act as both heterogeneous nucleating agents and surfaces (oriented shish structures) for the epitaxial growth of PET crystallites (kebabs) giving an oriented crystalline morphology. In contrast, the PET homopolymer does not show any residual oriented crystalline morphology during isothermal crystallization but gave a sporadic nucleation of a classic unoriented lamellar structure with slower crystallization kinetics. The results provide a valuable insight into the role of MWCNTs as nanoparticulate fillers in the morphology development and subsequent modification of physical properties in engineering polymers. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 132–137     

Surfactants for CNTs dispersion in zirconia-based ceramic matrix by sol–gel method

Zirconium oxide is a ceramic material widely studied due to its mechanical and electrical properties that can be improved with the use of carbon nanotubes (CNTs) as reinforcement. The synthesis of CNT/zirconia composites by sol–gel method is still very scarce, due to the hydrophobic nature of the CNTs, being their dispersion in aqueous medium an intrinsic difficulty to the synthesis. In this work, we present a sol–gel synthesis for MWCNTs/zirconia composites, where two kinds of surfactants, sodium and ammonium stearates dissolved in water (1 g/100 mL), were used as dispersant agents for multiwall carbon nanotubes (MWCNTs). They are cheap and easy to prepare, and were very effective in dispersing the MWCNTs. Different quantities of MWCNTs (up to 5 wt%) were added in the solution of stearate/water and this solution with the highly dispersed MWCNTs was added to the zirconia sol–gel, producing composites of MWCNTs/zirconia with different concentrations of MWCNTs. All the powders were heat treated at 300 and 500 °C and the powder characterization was performed by transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and infrared spectroscopy (FTIR). The composite MWCNTs/zirconia remained amorphous at 300 °C and presented a tetragonal phase at 500 °C with an average grain size of about 20 ± 3 nm, determined by the Scherrer equation from the XRD patterns. For these crystalline samples, TEM images suggest a more effective interaction between MWCNTs with ZrO₂ matrix, where it can be observed that the carbon nanotubes are fully coated by the matrix.     

Spontaneous coating of carbon nanotubes with an ultrathin polypyrrole layer

A novel protocol for precisely coating individual multiwall carbon nanotubes (MWCNTs) with an ultrathin layer of polypyrrole was developed. The nanocoated MWCNTs were successfully prepared by in situ chemical deposition of polypyrrole in an aqueous suspension of MWCNTs. The coating layer was very uniform and the thickness of the layer was determined by controlling the monomer concentration used, which gave nanometer precision. The products were characterized by transmission electron microscopy, scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, electron energy loss spectroscopy, and conductivity and current-voltage measurements. The ultrathin polypyrrole layer could electrically insulate individual MWCNTs.     

Synthesis of Pt and Pt-Fe nanoparticles supported on MWCNTs used as electrocatalysts in the methanol oxidation reaction

This work reports a feasible synthesis of highly-dispersed Pt and Pt-Fe nanoparticles supported on multiwall carbon nanotubes (MWCNTs) without Fe and multiwall carbon nanotubes with iron (MWCNTs-Fe) which applied as electrocatalysts for methanol electrooxidation. A Pt coordination complex salt was synthesized in an aqueous solution and it was used as precursor to prepare Pt/MWCNTs, Pt/MWCNTs-Fe, and Pt-Fe/MWCNTs using FeCl₂·4NH₂O as iron source which were named S1, S2 and S3, respectively. The coordination complex of platinum (TOA)₂PtCl₆ was obtained by the chemical reaction between (NH₄)₂PtCl₆ with tetraoctylammonium bromide (TOAB) and it was characterized by FT-IR and TGA. The materials were characterized by Raman spectroscopy, SEM, EDS, XRD, TEM and TGA. The electrocatalytic activity of Pt-based supported on MWCNTs in the methanol oxidation was investigated by cyclic voltammetry (CV) and chronoamperometry (CA). Pt-Fe/MWCNTs electrocatalysts showed the highest electrocatalytic activity and stability among the tested electrocatalysts due to that the addition of ”Fe” promotes the OH species adsorption on the electrocatalyst surface at low potentials, thus, enhancing the activity toward the methanol oxidation reaction (MOR).     

Melt‐crystallization mechanism of poly(ethylene terephthalate)/multi‐walled carbon nanotubes prepared by in situ polymerization

A series of poly(ethylene terephthalate)/multi‐walled carbon nanotubes (PET/MWCNTs) nanocomposites were prepared by in situ polymerization using different amounts of multi‐walled carbon nanotubes (MWCNTs). The polymerization of poly(ethylene terephthalate) (PET) was carried out by the two‐stage melt polycondensation method. The intrinsic viscosity (IV) of the composites is ranged between 0.31 and 0.63 dL/g depending on the concentration of the MWCNTs. A decrease of IV was found by increasing MWCNTs content. This is due to the reactions taking place between the two components leading to branched and crosslinked macromolecules. These reactions are, mainly, responsible for thermal behavior of nanocomposites. The melting point of the nanocomposites was shifted to slightly higher temperatures by the addition till 0.55 wt % of MWCNTs while for higher concentration was reduced. The degree of crystallinity in all nanocomposites was, also, reduced by increasing MWCNTs amount. However, from crystallization temperature, it was found that MWCNTs till 1 wt % can enhance the crystallization rate of PET, whereas at higher content (2 wt %), the trend is the opposite due to the formation of crosslinked macromolecules. From the extended crystallization analysis, it was proved that MWCNTs act as nucleating agents for PET crystallization. Additionally, the crystallization mechanism due to the existence of MWCNT becomes more complicated because two mechanisms with different activation energies are taking place in the different degrees of crystallization, depending on the percentage of MWCNT. The effect of molecular weight also plays an important role. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1452–1466, 2009     

Surface complexation modeling of Sr(II) and Eu(III) adsorption onto oxidized multiwall carbon nanotubes

Acid-base titrations of oxidized multiwall carbon nanotubes (MWCNTs), Sr(II) and Eu(III) adsorptions onto oxidized MWCNTs were conducted to investigate the surface charge characteristics of oxidized MWCNTs and the surface complexation interactions between Sr(II)/Eu(III) and oxidized MWCNTs. The results suggested that Sr(II) and Eu(III) adsorptions onto oxidized MWCNTs increased with increasing pH, and decreased with increasing ionic strength, and the affinity of oxidized MWCNTs for Eu(III) was much higher than that for Sr(II). The diffuse layer model (DLM) fitted the experimental data of Sr(II) and Eu(III) adsorptions well with the aid of FITEQL 3.2.     

MODIFICATION OF MULTI-WALLED CARBON NANOTUBES WITH POLY(NITRILOETHYLENENITRILOVINYLENE) “GRAFTING TO” THE SURFACE

A mild and facile way was used to prepare poly(nitriloethylenenitrilovinylene)-grafted multi-walled carbon nanotubes(MWCNTs-g-PNENV)nanocomposites via the"grafting to"method.The MWCNTs-g-PNENV nanocomposites are well dispersible in polar solvents such as water,tetrahydrofuran and ethanol.Chemical structure of the resulting product was characterized by Fourier transform infrared(FTIR)spectroscopy,transmission electron microscopy(TEM)and thermal gravimetric analysis(TGA).FTIR showed that the"grafting to"pr...